Professor Hui-Ming Cheng

Advanced electrochemical energy storage devices (EESDs) that can store electrical energy efficiently while being miniature/flexible/wearable/load-bearing are much needed for various applications ranging from flexible/wearable/portable electronics to lightweight electric vehicles/aerospace equipment. Carbon-based fibers hold great promise in the development of these advanced EESDs (e.g., supercapacitors and batteries) due to their being lightweight, high electrical conductivity, excellent mechanical strength, flexibility, and tunable electrochemical performance. This review summarizes the fabrication techniques of carbon-based fibers, especially carbon nanofibers, carbon-nanotube-based fibers, and graphene-based fibers, and various strategies for improving their mechanical, electrical, and electrochemical performance. The design, assembly, and potential applications of advanced EESDs from these carbon-based fibers are highlighted. Finally, the challenges and future opportunities of carbon-based fibers for advanced EESDs are discussed.

The use of highly-active and robust catalysts is crucial for producing green hydrogen by water electrolysis as we strive to achieve global carbon neutrality. Noble metals like platinum are currently used catalysts in industry for the hydrogen evolution, but suffer from scarcity, high price and unsatisfied performance and stability at large current density, restrict their large-scale implementations. Here we report the synthesis of a type of monolith catalyst consisting of a metal disulfide (e.g., tantalum sulfides) vertically bonded to a conductive substrate of the same metal tantalum by strong covalent bonds. These features give the monolith catalyst a mechanically-robust and electrically near-zero-resistance interface, leading to an excellent hydrogen evolution performance including rapid charge transfer and excellent durability, together with a low overpotential of 398 mV to achieve a current density of 2,000 mA cm(-2) as required by industry. The monolith catalyst has a negligible performance decay after 200 h operation at large current densities. In light of its robust and metallic interface and the various choices of metals giving the same structure, such monolith materials would have broad uses besides catalysis. Water electrolysis is a promising hydrogen production technique but is restricted from large-scale application due to poor performance and high cost. Here, the authors report a mechanically stable monolith electrocatalyst that achieves superior hydrogen evolution at large current densities.

The unprecedented advancement in power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) has rendered them a promising game-changer in photovoltaics. However, unsatisfactory environmental stability and high manufacturing cost of window electrodes are bottlenecks impeding their commercialization. Here, a strategy is introduced to address these bottlenecks by replacing the costly indium tin oxide (ITO) window electrodes via a simple transfer technique with single-walled carbon nanotubes (SWCNTs) films, which are made of earth-abundant elements with superior chemical and environmental stability. The resultant devices exhibit PCEs of ≈19% on rigid substrates, which is the highest value reported to date for ITO-free PSCs. The facile approach for SWCNTs also enables application in flexible PSCs (f-PSCs), delivering a PCE of ≈18% with superior mechanical robustness over their ITO-based counterparts due to the excellent mechanical properties of SWCNTs. The SWCNT-based PSCs also deliver satisfactory performances on large-area (1 cm2 active area in this work). Furthermore, these SWCNT-based PSCs can retain over 80% of original PCEs after exposure to air over 700 h while ITO-based devices only sustain ≈60% of initial PCEs. This work paves a promising way to accelerate the commercialization of ITO-free PSCs with reduced material cost and prolonged lifetimes.

Van der Waals organic/inorganic heterostructures in the two-dimensional (2D) limit with extensive structural tunability will advance the development of artificial solids with tailored functionalities. Recent breakthroughs in several types of 2D organic materials, including molecular monolayer films, 2D polymers, covalent-organic frameworks, and metal oxide frameworks, have greatly enriched the design possibilities of heterostructures with inorganic 2D materials. This review provides a timely summary of the latest advances in synthesis approaches toward advanced organic/inorganic heterostructures, answers the fundamental questions regarding the interfacial interactions in the 2D limit, and further highlights the uses of such organic/inorganic heterostructures in advanced transistors, optoelectronics, neuromorphic, and other multifunctional devices with unique capabilities.

A conventional two-electrode rechargeable zinc-air battery (RZAB) has two major problems: 1) opposing requirements for the oxygen reduction (ORR) and oxygen evolution (OER) reactions from the catalyst at the air cathode; and 2) zinc-dendrite formation, hydrogen generation, and zinc corrosion at the zinc anode. To tackle these problems, a three-electrode RZAB (T-RZAB) including a hydrophobic discharge cathode, a hydrophilic charge cathode, and a zinc-free anode is developed. The decoupled cathodes enable fast ORR and OER kinetics, and avoid oxidization of the ORR catalyst. The zinc-free anode using tin-coated copper foam that induces the growth of (002)(Zn) planes, suppresses hydrogen evolution, and prevents Zn corrosion. As a result, the T-RZABs have a high discharge capacity per cycle of 800 mAh cm(-2), a low voltage gap between the discharge/charge platforms of 0.66 V, and an ultralong cycle life of 5220 h at a current density of 10 mA cm(-2). A large T-RZAB with a discharge capacity of 10 Ah per cycle with no obvious degradation after cycling for 1000 h is developed. Finally, a T-RZAB pack that has an energy density of 151.8 Wh kg(-1) and a low cost of 46.7 US dollars kWh(-1) is assembled.

[Display omitted] Common solar-driven photoelectrochemical (PEC) cells for water splitting were designed by using semiconducting photoactive materials as working photoelectrodes to capture sunlight. Due to the thermodynamic requirement of 1.23 eV and kinetic energy loss of about 0.6 eV, a photo-voltage of 1.8 V produced by PEC cells is generally required for spontaneous water splitting. Therefore, the minimum bandgap of 1.8 eV is demanded for photoactive materials in single-photoelectrode PEC cells, and the bandgap of about 1 eV for back photoactive materials is appropriate in tandem PEC cells. All these PEC cells cannot effectively utilize the infrared light from 1250 to 2500 nm. In order to realize the full spectrum utilization of solar light, here, we develop a solar-driven PEC water splitting system integrated with a thermoelectric device. The key feature of this system is that the thermoelectric device produces a voltage as an additional bias for the PEC system by using the temperature difference between the incident infrared-light heated aqueous electrolyte in the PEC cell as the hot source and unirradiated external water as the cold source. Compared to a reference PEC system without the thermoelectric device, this system has a significantly improved overall water splitting activity of 1.6 times and may provide a strategy for accelerating the application of full spectrum solar light-driven PEC cells for hydrogen production.

Perovskite solar cells (PSCs) have emerged as a ‘rising star’ in recent years due to their high-power conversion efficiency (PCE), extremely low cost and facile fabrication techniques. To date, PSCs have achieved a certified PCE of 25.2% on rigid conductive substrates, and 19.5% on flexible substrates. The significant advancement of PSCs has been realized through various routes, including perovskite composition engineering, interface modification, surface passivation, fabrication process optimization, and exploitation of new charge transport materials. However, compared with rigid counterparts, the efficiency record of flexible perovskite solar cells (FPSCs) is advancing slowly, and therefore it is of great significance to scrutinize recent work and expedite the innovation in this field. In this article, we comprehensively review the recent progress of FPSCs. After a brief introduction, the major features of FPSCs are compared with other types of flexible solar cells in a broad context including silicon, CdTe, dye-sensitized, organic, quantum dot and hybrid solar cells. In particular, we highlight the major breakthroughs of FPSCs made in 2019/2020 for both laboratory and large-scale devices. The constituents of making a FPSC including flexible substrates, perovskite absorbers, charge transport materials, as well as device fabrication and encapsulation methods have been critically assessed. The existing challenges of making high performance and long-term stable FPSCs are discussed. Finally, we offer our perspectives on the future opportunities of FPSCs in the field of photovoltaics.

Liquid crystal devices using organic molecules are nowadays widely used to modulate transmitted light, but this technology still suffers from relatively weak response, high cost, toxicity and environmental concerns, and cannot fully meet the demand of future sustainable society. Here, an alternative approach to color-tunable optical devices, which is based on sustainable inorganic liquid crystals derived from 2D mineral materials abundant in nature, is described. The prototypical 2D mineral of vermiculite is massively produced by a green method, possessing size-to-thickness aspect ratios of >10(3), in-plane magnetization of >10 emu g(-1), and an optical bandgap of >3 eV. These characteristics endow 2D vermiculite with sensitive magneto-birefringence response, been several orders of magnitude larger than organic counterparts, as well as capability of broad-spectrum modulation. The finding consequently permits the fabrication of various magnetochromic or mechanochromic devices with low or even zero-energy consumption during operation. This work creates opportunities for the application of sustainable materials in advanced optics.

Mixed-cation perovskite quantum dot solar cells possess decent phase stability but considerably low efficiency. Here Hao et al. show that ligands are key to the formation of quantum dots with lower defect density and demonstrate devices that are more stable and efficient than their bulk counterparts. The mixed caesium and formamidinium lead triiodide perovskite system (Cs(1-x)FA(x)PbI(3)) in the form of quantum dots (QDs) offers a pathway towards stable perovskite-based photovoltaics and optoelectronics. However, it remains challenging to synthesize such multinary QDs with desirable properties for high-performance QD solar cells (QDSCs). Here we report an effective oleic acid (OA) ligand-assisted cation-exchange strategy that allows controllable synthesis of Cs(1-x)FA(x)PbI(3) QDs across the whole composition range (x = 0-1), which is inaccessible in large-grain polycrystalline thin films. In an OA-rich environment, the cross-exchange of cations is facilitated, enabling rapid formation of Cs(1-x)FA(x)PbI(3) QDs with reduced defect density. The hero Cs(0.5)FA(0.5)PbI(3) QDSC achieves a certified record power conversion efficiency (PCE) of 16.6% with negligible hysteresis. We further demonstrate that the QD devices exhibit substantially enhanced photostability compared with their thin-film counterparts because of suppressed phase segregation, and they retain 94% of the original PCE under continuous 1-sun illumination for 600 h.

Monolithic integrated micro-supercapacitors (MIMSCs) with high systemic performance and cell-number density are important for miniaturized electronics to empower the Internet of Things. However, fabrication of customizable MIMSCs in an extremely small space remains a huge challenge considering key factors such as materials selection, electrolyte confinement, microfabrication and device-performance uniformity. Here, we develop a universal and large-throughput microfabrication strategy to address all these issues by combining multistep lithographic patterning, spray printing of MXene microelectrodes and controllable 3D printing of gel electrolytes. We achieve the monolithic integration of electrochemically isolated micro-supercapacitors in close proximity by leveraging high-resolution micropatterning techniques for microelectrode deposition and 3D printing for precise electrolyte deposition. Notably, the MIMSCs obtained demonstrate a high areal-number density of 28 cells cm (340 cells on 3.5 × 3.5 cm ), a record areal output voltage of 75.6 V cm , an acceptable systemic volumetric energy density of 9.8 mWh cm and an unprecedentedly high capacitance retention of 92% after 4000 cycles at an extremely high output voltage of 162 V. This work paves the way for monolithic integrated and microscopic energy-storage assemblies for powering future microelectronics.

Water electrolysis in alkaline electrolyte is a promising technology for large-scale hydrogen production. However, the hydrogen evolution reaction (HER) is quite sluggish in alkaline electrolyte. Developing highly active and stable non-noble metal electrocatalysts is highly desired to solve this issue but of great challenge. Here, we report a catalyst constructed by Ni–Mo–N nanoparticles decorated on nitrogen-doped reduced graphene oxide (Ni–Mo–N/NG). Due to the high intrinsic electrocatalytic activity of heterostructured Ni–Mo–N nanoparticles and synergistic effects between the nanoparticles and graphene, the catalyst exhibits excellent HER electrocatalytic activity with zero onset potential and 46.6 and 159.8 mV overpotentials for 10 and 100 mA cm−2, respectively, in alkaline electrolyte at low mass loading. Such electrocatalytic performances exceed those of many reported non-noble metal catalysts even with much higher mass loading, demonstrating the great potential of our Ni–Mo–N/NG catalysts for hydrogen production by water electrolysis. [Display omitted]

The great attention of rechargeable Zn-air battery has motivated extensive research on the development of inexpensive, highly efficient, and robust noble-metal-free bifunctional catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Herein, a supramolecular complex derived strategy was used to prepare bamboo-like carbon nanotubes with abundant Fe single atoms and sub-nanometer clusters anchored on tube walls. When served as a bifunctional ORR/OER electrocatalyst, this hybrid showed a small overpotential gap of 0.713 V and excellent stability. More importantly, a large power density of 213 mW cm−2 and stable long-time round-trip charge-discharge performance were achieved for the assembled rechargeable Zn-air batteries. Density functional theory calculations revealed that atomic Fe–N4 moiety in the catalyst could be the essence of high ORR activity, while atomic Fe–N4 moiety coupled sub-nanometer cluster significantly reduces the OER energy barrier. This work provides an effective strategy for the preparation of high-performance and robust oxygen electrode catalysts as well as a significant new insight on the catalytic mechanisms, helping to realize significant advances in energy devices. A supramolecular complex derived strategy was used to synthesize a tubular Fe–N/C material enriched with atomically dispersed Fe–N4 moiety to boost the oxygen reduction activity and atomic Fe–N4 moiety coupled sub-nanometer cluster to improve the oxygen evolution activity. [Display omitted]

High-performance flexible electrodes can be realized by nested wrinkle texturing of graphene, which serves as stress-release scaffold to achieve high stretchability as well as excellent electrochemical performances. [Display omitted] Flexible lithium-ion batteries (LIBs) are critical for the development of next-generation smart electronics. Conversion reaction-based electrodes have been considered promising to construct high energy–density flexible LIBs, which satisfy the ever-increasing demand for practical use. However, these electrodes suffer from inferior lithium-storage performance and structural instability during deformation and long-term lithiation/delithiation. These are caused by the sluggish reaction kinetics of active-materials and the superposition of responsive strains originating from the large lithiation-induced stress and applied stress. Here, we propose a stress-release strategy through elastic responses of nested wrinkle texturing of graphene, to achieve high deformability while maintaining structural integrity upon prolonged cycles within high-capacity electrodes. The wrinkles endow the electrode with a robust and flexible network for effective stress release. The resulting electrode shows large reversible stretchability, along with excellent electrochemical performance including high specific capacity, high-rate capability and long-term cycling stability. This strategy offers a new way to obtain high-performance flexible electrodes and can be extended to other energy-storage devices.

The development of ultrahigh-voltage lithium metal batteries is one of the most promising ways to increase the energy density. However, commercial ethylene carbonate (EC)-based electrolytes have poor compatibility with both lithium metal anodes and cathodes at ultrahigh voltages. We report a high-voltage resistant electrolyte (HV electrolyte) produced by the fluorination of commercial solvents with the guidance of theoretical calculations. These designed solvents, with low energy levels of the lowest unoccupied molecular orbital (LUMO), can be preferably reduced at the lithium metal anode, suppressing lithium dendrite growth because of the formation of a LiF-rich solid–electrolyte interphase (SEI). Fluorination also decreases the energy levels of the highest occupied molecular orbital (HOMO), resulting in improved anodic stability at ultrahigh voltages. The low binding energies between fluorinated solvents in the HV electrolyte and Li + accelerate the desolvation of Li + , leading to excellent electrochemical kinetics. As a result, Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) cells, which can work in a wide operating temperature range from −30 to 70 °C, have capacity retentions of 95.1% after 160 cycles and 85.7% after 100 cycles at ultrahigh cut-off voltages of 4.7 and 4.8 V, respectively. Li||NCM811 cells with a thin (50 μm) lithium metal anode and a lean electrolyte were constructed, and had a capacity retention of 89.2% after 150 cycles, demonstrating high potential in practical use as high energy density batteries.

Significance In recent years, lithium-ion batteries (LIBs) have been widely applied in electric vehicles as energy storage devices. However, it is a great challenge to deal with the large number of spent LIBs. In this work, we employ a rapid thermal radiation method to convert the spent LIBs into highly efficient bifunctional NiMnCo-activated carbon (NiMnCo-AC) catalysts for zinc-air batteries (ZABs). The obtained NiMnCo-AC catalyst shows excellent electrochemical performance in ZABs due to the unique core-shell structure, with face-centered cubic Ni in the core and spinel NiMnCoO 4 in the shell. This work provides an economical and environment-friendly approach to recycling the spent LIBs and converting them into novel energy storage devices. The skyrocketing production of lithium-ion batteries (LIBs) for electric vehicles portends that tremendous numbers of used LIBs will be generated. However, the recycling of used LIBs is limited by the complicated separation processes of traditional pyrometallurgy and hydrometallurgy methods. Here, we applied a rapid thermal radiation method to convert spent LiNi 1-x-y Mn x Co y O 2 (NMC) cathodes from used LIBs into highly efficient NiMnCo-based catalysts for zinc-air batteries (ZABs) through acid leaching and radiative heating processes, which avoids sophisticated separation of different metals and can synthesize the catalysts rapidly. The prepared NiMnCo-activated carbon (NiMnCo-AC) catalyst presents a unique core-shell structure, with face-centered cubic Ni in the core and spinel NiMnCoO 4 in the shell, which redistributes the electronic structure of the NiMnCoO 4 shell to decrease the energy barrier for oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) processes and ensures high electrocatalytic activities. The NiMnCo-AC catalyst in ZABs as cathode materials exhibits a high power density of 187.7 mW cm −2 , low voltage gap of 0.72 V at the initial three cycles, and long cycling duration of 200 h at the current density of 10 mA cm −2 . This work provides a promising strategy to recycle spent LIBs to highly efficient catalysts for ZABs.

Carbon aerogels (CAs) are attractive candidates for the thermal protection of aerospace vehicles due to their excellent thermostability and thermal insulation. However, the brittleness and low mechanical strength severely limits their practical applications, and no significant breakthroughs in large CAs with a high strength have been made. We report a high-pressure-assisted polymerization method combined with ambient pressure drying to fabricate large, strong, crack-free carbon/carbon (C/C) composites with an excellent load-bearing capacity, thermal stability, and thermal insulation. The composites are comprised of an aerogel-like carbon matrix and a low carbon crystallinity fiber reinforcement, featuring overlapping nanoparticles, macro-mesopores, large particle contact necks, and strong fiber/matrix interfacial bonding. The resulting C/C composites with a medium density of 0.6 g cm have a very high compressive strength (80 MPa), in-plane shear strength (20 MPa), and specific strength (133 MPa g cm ). Moreover, the C/C composites of 7.5-12.0 mm in thickness exposed to an oxyacetylene flame at 1800 °C for 900 s display very low back-side temperatures of 778-685 °C and even better mechanical properties after the heating. This performance makes the composites ideal for the ultrahigh temperature thermal protection of aerospace vehicles where both excellent thermal-insulating and load-bearing capacities are required.

Lithium sulfur batteries (LSBs) have attracted tremendous attention owing to their high theoretical specific capacity and specific energy. However, their practical applications are hindered by poor cyclic life, mainly caused by polysulfide shuttling. The development of advanced materials to mitigate the polysulfide shuttling effect is urgently demanded. Metal-organic frameworks (MOFs) have been exploited as multifunctional materials for the decoration of separators owing to their high surface area, structural diversity, tunable pore size, and easy tailor ability. In this review, we aim to present the state-of-the-art MOF-based separators for LSBs. Particular attention is paid to the rational design (pore aperture, metal node, functionality, and dimension) of MOFs with enhanced ability for anchoring polysulfides and facilitating Li+ transportation. Finally, the challenges and perspectives are provided regarding to the future design MOF-based separators for high-performance LSBs.

On‐skin electronics that offer revolutionary capabilities in personalized diagnosis, therapeutics, and human–machine interfaces require seamless integration between the skin and electronics. A common question remains whether an ideal interface can be introduced to directly bridge thin‐film electronics with the soft skin, allowing the skin to breathe freely and the skin‐integrated electronics to function stably. Here, an ever‐thinnest hydrogel is reported that is compliant to the glyphic lines and subtle minutiae on the skin without forming air gaps, produced by a facile cold‐lamination method. The hydrogels exhibit high water‐vapor permeability, allowing nearly unimpeded transepidermal water loss and free breathing of the skin underneath. Hydrogel‐interfaced flexible (opto)electronics without causing skin irritation or accelerated device performance deterioration are demonstrated. The long‐term applicability is recorded for over one week. With combined features of extreme mechanical compliance, high permeability, and biocompatibility, the ultrathin hydrogel interface promotes the general applicability of skin‐integrated electronics. Ultrathin hydrogel films are fabricated by a facile cold‐lamination method and demonstrated as the skin–electronics interface. The hydrogels comply with glyphic lines and subtle minutiae on the skin surface, allowing unimpeded transepidermal water loss and breathing of the skin underneath. Multitype organic thin‐film (opto)electronics can attach to the skin interfaced with the ultrathin hydrogel, realizing seamless integration and long‐term applications.

Rational design of pre-catalysts to in situ form active structures is vital for efficient catalysis, especially when surface reconstruction occurs. Here we report a surface engineering strategy to form highly active surfaces on Ni-based catalysts (NiMo in this work) under oxygen evolution reaction (OER) conditions. The NiMo catalyst is decorated with mononuclear Fe-O-5 species on its surface. During the OER reconstruction process, the Fe-O-5 species will further bond to the surface of Ni oxyhydroxide reconstructed from NiMo. In situ X-ray absorption spectroscopy and theoretical calculations reveal that the Fe-O-5 species anchored on Ni oxyhydroxide are easily oxidized under OER conditions, which compensates for the charges of Ni and increases the reducibility of Ni active sites. As a result, such a catalyst shows a 33-fold increase in intrinsic activity compared with the NiMo catalyst, which also decreases the full cell voltage by 0.72 V at 500 mA cm(-2) in an anion exchange membrane electrolyzer compared with the IrO2 catalyst.

Resource‐abundant metal (e.g., zinc) batteries feature intrinsic advantages of safety and sustainability. Their practical feasibility, however, is impeded by the poor reversibility of metal anodes, typically caused by the uncontrollable dendrite enlargement. Significant effort is exerted to completely prevent dendrites from forming, but this seems less effective at high current densities. Herein, this work presents an alternative dendrite regulation strategy of forming tiny, homogeneously distributed, and identical zinc dendrites by facet matching, which effectively avoids undesirable dendrite enlargement. Confirmed by multiscale theoretical screening and characterization, the regularly exposed Cu(111) facets at the ridges of a copper nanowire are capable of such dendrite regulation by forming a low‐mismatched Zn(002)/Cu(111) interface. Consequently, reversible zinc electroplating/stripping is achieved at an unprecedentedly high rate of 100 mA cm−2 for over 30 000 cycles, corresponding to an accumulative areal capacity up to 30 Ah cm−2. A full cell using this anode shows a high capacity of 308.3 mAh g−1 and a high capacity retention of 91.4% after 800 cycles. This strategy is also viable for magnesium and aluminum anodes, thus opening up a promising and universal avenue toward long‐life and high‐rate metal anodes. The strategy of dendrite regulation, growing tiny, identical, and homogeneously distributed Zn dendrites by facet matching of Cu(111)/Zn(002), can achieve reversible Zn plating/stripping and long‐life Zn anode at ultrahigh current densities.

Different kinds of transition metal disulfides (TMDCs) were prepared via solvothermal method. The morphologic structure of TMDCs were controlled by tuning the injecting rates of the reaction precursor. The crystallization of the products could be improved by annealing treatment at high-temperature, and thus improving the electrocatalytic activity of TMDC catalyst. The results of electmcatalytic hydrogen evolution in acidic electrolyte show that the metallic "flower-like" niobium disulfide (NbS2) exhibits excellent catalytic activity and stability. It possess a small overpotential of only 146 mV to achieve a current density of 10 mA/cm(2). The current density almost shows no decays after 24 h continuous working at 10 mA/cm(2). The excellent performance of NbS2 catalyst is attributed to the "flower-like" structure that can expose abundant active sites, and to the improvement of electrical conductivity and material quality after annealing treatment.

Ball milling is a widely used method to produce graphene and other two-dimensional (2D) materials for both industry and research. Conventional ball milling generates strong impact forces, producing small and thick nanosheets that limit their applications. In this study, a viscous solvent-assisted planetary ball milling method has been developed to produce large thin 2D nanosheets. The viscous solvent simultaneously increases the exfoliation energy ( ) and lowers the impact energy ( ). Simulations show a giant ratio of η = / , for the viscous solvent, 2 orders of magnitude larger than that of water. The method provides both a high exfoliation yield of 74%, a high aspect ratio of the generated nanosheets of 571, and a high quality for a representative 2D material of boron nitride nanosheets (BNNSs). The large thin BNNSs can be assembled into high-performance functional films, such as separation membranes and thermally conductive flexible films with some performance parameters better than those 2D nanosheets produced by chemical exfoliation methods.

Electrocatalytically reducing the energy barrier for Li2S deposition/dissociation is a promising strategy for high -rate Li-S batteries. However, the catalytic sites would be covered by the insulating Li2S product during discharge, which deteriorates the catalytic activity. Here, suggested by first-principles calculations, single-atom copper (SA -Cu) was screened out to endow the insulator-to-metal transition of adsorbed Li2S in view of the electronic structure. In addition to the thermodynamically reduced redox energy barrier, metallic Li2S nuclei deposited on SA-Cu decorated nitrogen-doped carbon fiber foam (SA-Cu@NCNF) with favorable electronic transport present 3D spherical clusters rather than conventional 2D lateral morphology by continuous 3D nucleation and growth. The Li2S deposition capacity and the catalytic efficiency of Li2S-covered catalytic sites are thus greatly improved. As a result, SA-Cu@NCNF based Li-S cells with a sulfur loading of 4 mg cm- 2 retained an areal capacity of 1.60 mAh cm-2 at 5 C after 500 cycles (0.038% decay per cycle). A competitive areal capacity of 8.44 mAh cm-2 was obtained at 0.2 C with a sulfur loading of 10 mg cm-2. The demonstration of the distinctive design of catalysts to adjust the electronic structure of adsorbed Li2S paves the way for developing high-rate and long-life Li-S batteries.

Lithium-sulfur batteries (Li-S batteries) are promising next-generation energy storage devices due to their high theoretical energy density, low cost, and environmental compatibility. When trying to convert experiment into practice, one finds that sulfur cathodes, especially a cyclic octasulfur cathode, and lithium metal anodes present several problems, including sulfur shuttling, the fact that S is an insulator, complex 16-electron reactions, and the formation of lithium dendrites. In recent years, organosulfur compounds have been extensively investigated for Li-S batteries in order to solve these problems and understand the electrochemical process during their redox reactions. This review aims to summarize the different functions of organosulfur compounds, and figure out a guideline for understanding and using them in Li-S batteries. The organosulfur compounds currently used as active materials are classified into three types based on their electrochemical behavior, and design principles of the molecular and polymer structures of organosulfur compounds are concluded. Based on these design principles, we summarize how to control their electrochemical performance, and suggest possible electrochemical mechanisms and other characteristics. Finally, we propose guidelines for the development of promising organosulfur compounds using emerging technologies, including advanced characterization techniques, innovative methods of synthesis of such compounds, and machine-learning techniques.

The spatial distribution and transport characteristics of lithium ions (Li+) in the electrochemical interface region of a lithium anode in a lithium ion battery directly determine Li+ deposition behavior. The regulation of the Li+ solvation sheath on the solid electrolyte interphase (SEI) by electrolyte chemistry is key but challenging. Here, 1 m lithium trifluoroacetate (LiTFA) is induced to the electrolyte to regulate the Li+ solvation sheath, which significantly suppresses Li dendrite formation and enables a high Coulombic efficiency of 98.8% over 500 cycles. With its strong coordination between the carbonyl groups (C(sic)O) and Li+, TFA(-) modulates the environment of the Li+ solvation sheath and facilitates fast desolvation kinetics. In addition, due to relatively smaller lowest unoccupied molecular orbital energy than solvents, TFA(-) has a preferential reduction to produce a stable SEI with uniform distribution of LiF and Li2O. Such stable SEI effectively reduces the energy barrier for Li+ diffusion, contributing to low nucleation overpotential, fast ion transfer kinetics, and uniform Li+ deposition with high cycling stability. This work provides an alternative insight into the design of interface chemistry in terms of regulating anions in the Li+ solvation sheath. It is anticipated that this anion-tuned strategy will pave the way to construct stable SEIs for other battery systems.

It has been a great challenge to optimize the growth conditions toward structure-controlled growth of single-wall carbon nanotubes (SWCNTs). Here, a high-throughput method combined with machine learning is reported that efficiently screens the growth conditions for the synthesis of high-quality SWCNTs. Patterned cobalt (Co) nanoparticles were deposited on a numerically marked silicon wafer as catalysts, and parameters of temperature, reduction time and carbon precursor were optimized. The crystallinity of the SWCNTs was characterized by Raman spectroscopy where the featured G/D peak intensity (IG/ID) was extracted automatically and mapped to the growth parameters to build a database. 1,280 data were collected to train machine learning models. Random forest regression (RFR) showed high precision in predicting the growth conditions for high-quality SWCNTs, as validated by further chemical vapor deposition (CVD) growth. This method shows great potential in structure-controlled growth of SWCNTs. [Figure not available: see fulltext.].

Semiconducting single-walled carbon nanotubes (s-SWCNTs) with large diameters are highly desired in the construction of high performance optoelectronic devices. However, it is difficult to selectively prepare large-diameter s-SWCNTs since their structure and chemical stability are quite similar with their metallic counterparts. In this work, we use SWCNTs with large diameter as a raw material, conjugated polymer of regioregular poly-(3-dodecylthiophene) (rr-P3DDT) with long side chain as a wrapping agent to selectively separate large-diameter s-SWCNTs. It is found that s-SWCNTs with a diameter of similar to 1.9 nm are effectively enriched, which shows a clean surface. By using the sorted s-SWCNTs as a channel material, we constructed thin-film transistors showing charge-carrier mobilities higher than 10 cm(2) V-1 s(-1) and on/off ratios higher than 10(3).

Nitrogen (N) doping has been widely adopted to improve the light absorption of TiO 2 . However, the newly introduced N-2 p states are largely localized thus barely overlap with O-2 p states in the valence band of TiO 2 , resulting in a shoulder-like absorption edge. To realize an apparent overlap between N-2 p and O-2 p states, charge compensation between N 3 - and O 2 - via electron transfer from oxygen vacancies (V O ) to N dopants is one possible strategy. To verify this, in numerous doping configurations of N/V O -codoped anatase TiO 2 , we identified two types of V O position independent N-dopant spatial orderings by efficient screening enabled with a newly designed structural descriptor. Compared with others, these two types of the N-dopant spatial orderings are highly beneficial for charge compensation to produce an apparent overlap between N-2 p and O-2 p states, therefore achieving a large bandgap narrowing. Furthermore, the two types of the N-dopant spatial orderings can also be generalized to N/V O -codoped rutile TiO 2 for bandgap narrowing. (c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Abstract The scalable and high-efficiency production of 2D materials is a prerequisite to their commercial use. Currently, only graphene and graphene oxide can be produced on a ton scale, and the inability to produce other 2D materials on such a large scale hinders their technological applications. Here we report a grinding exfoliation method that uses micro-particles as force intermediates to resolve applied compressive forces into a multitude of small shear forces, inducing the highly efficient exfoliation of layer materials. The method, referred to as intermediate-assisted grinding exfoliation (iMAGE), can be used for the large-scale production of many 2D materials. As an example, we have exfoliated bulk h-BN into 2D h-BN with large flake sizes, high quality and structural integrity, with a high exfoliation yield of 67%, a high production rate of 0.3 g h−1 and a low energy consumption of 3.01 × 106 J g−1. The production rate and energy consumption are one to two orders of magnitude better than previous results. Besides h-BN, this iMAGE technology has been used to exfoliate various layer materials such as graphite, black phosphorus, transition metal dichalcogenides, and metal oxides, proving its universality. Molybdenite concentrate, a natural low-cost and abundant mineral, was used as a demo for the large-scale exfoliation production of 2D MoS2 flakes. Our work indicates the huge potential of the iMAGE method to produce large amounts of various 2D materials, which paves the way for their commercial application.

The six-membered ring (SMR) is a common structure unit for numerous material systems. These materials include, but are not limited to, the typical two-dimensional materials such as graphene, h-BN, and transition metal dichalcogenides, as well as three-dimensional materials such as beryllium, magnesium, MgB2 and Bi2Se3. Although many of these materials have already become 'stars' in materials science and condensed-matter physics, little attention has been paid to the roles of the SMR unit across a wide range of compositions and structures. In this article, we systematically analyze these materials with respect to their very basic SMR structural unit, which has been found to play a deterministic role in the occurrence of many intriguing properties and phenomena, such as Dirac electronic and phononic spectra, superconductivity and topology. As a result, we have defined this group of materials as SMR inorganic materials, opening up a new perspective on materials research and development. With their unique properties, SMR materials deserve wide attention and in-depth investigation from materials design, new physical discoveries to target-wizard applications. It is expected that SMR materials will find niche applications in next-generation information technology, renewable energy, space, etc.

Graphene shows great potential for flexible optoelectronic devices owing to its unique 2D structure and excellent electronic, optical, and mechanical properties. Chemical vapor deposition (CVD) is the most promising method for fabricating large-area and high-quality graphene films at an acceptable cost; therefore enormous efforts have been attempted to investigate the flexible optoelectronic devices based on CVD-grown graphene. Here, recent advances and significant development of CVD-grown graphene towards flexible optoelectronics including photodetectors, organic solar cells, and light-emitting diodes are reviewed. Insight into the challenges of improvement of optoelectronic properties, work function tuning, as well as interfacial control of CVD-grown graphene for high-performance devices is provided. In particular, the availability to fabricate large-area devices on the flexible substrates is discussed, which is crucial to drive the practical use of CVD-grown graphene for future wearable optoelectronics.

The inefficient production of structurally uniform single-wall carbon nanotubes (SWCNTs) is an obstacle to their practical use in high-performance electronic devices. We have synthesized SWCNTs with a narrow diameter distribution (1.35 +/- 0.25 nm) using a CoRu catalyst. Monodispersed nanoparticles with a narrow size dis-tribution (2.4 +/- 0.6 nm) and different compositions were prepared and used as catalysts for SWCNT growth. A furnace with an 80 cm-long uniform temperature zone (+/- 10 degrees C) was designed and used to study the effect of catalyst composition on the growth of SWCNTs under the same conditions. By optimizing the composition of the bimetallic CoRu catalyst, SWCNTs with a uniform structure were efficiently synthesized. In addition, the effect of the growth conditions of temperature and carbon feed rate was investigated, and it was found that with an increase in yield, the structural uniformity of SWCNTs usually became worse. Both catalysts with elements in the suitable proportions and appropriate growth conditions are critical to achieving the high-efficiency structure-controlled growth of SWCNTs.

The dissolution of more LiNO3 in an ester electrolyte is a promising way to stabilize the lithium metal anode in a lithium metal battery. Considering that the maximum solubility of LiNO3 is determined by the dynamic equilibrium between the dissociation (dissolution) of LiNO3 and the recombination (precipitation) of solvated Li+ and NO3 –, we report a solvation structure that prevents the recombination of anions and cations by ethylene glycol diacetate with low permittivity mixed with ethylene carbonate as cosolvent. The uncoordinated carbonyl of ethylene glycol diacetate in the solvation structure prevents the recombination of cations and anions. The new dissociation–recombination equilibrium establishes, and the solubility of LiNO3 increases. Therefore, the designed ester electrolyte with high LiNO3 solubility achieves lithium metal batteries with high Coulombic efficiency and long cycling life. Our findings show that the solvents with low permittivity can change the solvation structures of cations and increase the solubility of salts as well by preventing the recombination of anions and cations.

This work aims to obtain a fundamental understanding of active sites near stone-wales (SW) defects rich nitrogen-doped graphene (DG) with specific coordination of carbon atom rings. It reveals that the SW rich defects (e.g., pentagon (5), pentagon-octagon-pentagon (i.e. 585), or pentagon-heptagon-heptagon-pentagon (5775) rings, appears correspondingly with carbon rings that brought active sites during catalytic reactions. Moreover, we anchored dual isolated metallic atoms (Ni/Fe) on DG support via linkers (O/N) called NiFe-DG. X-ray absorption spectroscopy indicates Ni/Fe metal single atoms are embedded via Fe-N-4 and Ni-N-4 coordination on DG surfaces. It exhibits high catalytic activity for oxygen reduction reaction (ORR) with an onset potential of 0.97 V, a half-wave potential of 0.86 V, and diffusion current density of 5.7 mA cm(-2), which is at par with commercial Pt/C. The catalyst shows superior stability, retained 82% of the initial current density even after 12 h under an applied potential of 0.86 V. Similarly, the oxygen evolution reaction (OER) overpotential of 358 mV was achieved at 10 mA cm(-2) with a lower Tafel slope value (76 mV/dec) than commercial Pt/C. It maintains 85% stability for 12 h at a constant potential of 1.588 V, shows better stability than commercial Pt/C.

Potassium ion batteries (PIBs) have shown great potential as a next-generation electrochemical energy storage system, due to the natural abundance of potassium and the relatively low redox potential of K ions. To accommodate the large ionic radius of K ions, conversion-type electrode materials are regarded as suitable candidates for K ion storage. However, the triggering mechanism of a conversion reaction in most anode materials of PIBs is unclear, which limits their further development. To reveal the mechanism, in this work, MoSe2, MoS2, and MoO2 were selected as model materials, guided by theoretical calculations, to investigate the K ion storage process. Through ex situ characterization, it was found that intercalation reactions preferentially occur in MoSe2 and MoS2, while an adsorption reaction preferentially occurs in MoO2. This is because of the larger interlayer spacing and lower K ion intercalation barrier in MoSe2 and MoS2 than in MoO2. The preferential intercalation reactions are able to induce a further conversion reaction by reducing the reaction barrier, thereby realizing high K ion storage capacities. As a result, the MoSe2-rGO and MoS2-rGO hybrids showed higher reversible capacities than the MoO2-rGO hybrid. By demonstrating a relationship between intercalation and the conversion reaction and understanding the mechanism, guidance is provided for selecting the electrode materials to obtain PIBs with high performance.

Organic electrode materials have been developed for decades because of their tunable structures, environmental compatibility and low carbon footprint. Limited by the contradiction between the functions of organic groups and the low specific capacity of organic cathodes, organic lithium batteries hardly simultaneously achieve high specific capacity, stable cycling and high rate performance in Ampere-hour-scale pouch cells. Herein, we developed a general strategy to construct a series of random terpolymer cathode materials by tuning their components related to electrochemical performance. In terpolymers, sulfur chains, propyl groups and benzoquinone/pyridine groups are chosen as active components, carbon backbones and functional groups, respectively. Benzoquinone/pyridine groups with a low content in terpolymers not only promote ionic conductivity and reaction kinetics, but also ensure a high sulfur content. An Ampere-hour-scale pouch cell retains 85% capacity after 80 cycles, and the energy density of the cathode materials is over 870 W h kg −1 . The strategy provides new insight into the construction of organic lithium batteries with a high energy density promising for practical applications.

Fabricating conductive graphene films by assembling graphene oxide (GO) sheets is highly desired for many applications, however a very high temperature around 3000 K is usually required to repair the sp(2) structure for traditional thermal annealing. Here, an electric field assisted Joule heating method was developed to repair the sp(2) structure in GO at a temperature lower than 1500 degrees C. The resulting free-standing graphene film shows a high electrical conductivity (similar to 1840 S/cm) and high C/O ratio (132), both of which are much higher than those of thermally reduced GO films under the same temperature. These findings provide new possibilities for fabricating high-quality graphene films in an energy-efficient and low-cost manner.

Carbon nanotube (CNT)/Cu core-shell fibers are a promising material for lightweight conductors due to their higher conductivity than pure CNT fibers and lower density than traditional Cu wires. However, the electrical properties of the hybrid fiber have been unsatisfactory, mainly because of the weak CNT-Cu interfacial interaction. Here we report the fabrication of a single-walled CNT (SWCNT)/Cu core-shell fiber that outperforms commercial Cu wires in terms of specific electrical conductivity and current carrying capacity. A dense and uniform Cu shell was coated on the surface of wet-spun SWCNT fibers using a combination of magnetron sputtering and electrochemical deposition. Our SWCNT/Cu core-shell fibers had an ultrahigh specific electrical conductivity of (1.01 +/- 0.04) x 104 S m2 kg-1, 56% higher than Cu. Experimental and simulation results show that oxygen-containing functional groups on the surface of a wet spun SWCNT fiber interact with the sputtered Cu atoms to produce strong bonding. Our hybrid fiber preserved its integrity and conductivity well after more than 5000 bending cycles. Furthermore, the current carrying capacity of the coaxial fiber reached 3.14 x 105 A cm-2, three times that of commercial Cu wires.

Single-wall carbon nanotube/silicon (SWCNT/Si) heterojunction solar cells are no longer a laboratory curiosity, but the commercial manufacture of devices with a high and stable conversion efficiency remains a big challenge. Here we report the fabrication of a FeCl3-functionalized GO/SWCNT/Si heterojunction solar cell by using a simple drop-casting method. It was found that the GO layer not only serves as an antireflection layer, leading to reduced incident light loss and a similar to 20% increase in photocurrent, but also acts as a carrier transport bridge and physical barrier that traps more metal chloride. The FeCl3 acts as a solid-state redox functional material doping both the GO and the SWCNT film, resulting in a higher-conductivity composite film, which increases the work function and the charge carrier transport, contributing to a significant increase of the photovoltage and fill factor. As a result, the FeCl3-GO/SWCNT/Si heterojunction solar cell achieved a high conversion efficiency of 17.5% and good stability, where more than 90% of original efficiency was retained after exposure to air for 15 days.

We discovered superconducting homologous compounds of 2D MoSi2N4, MoSi2N4(MoN)(4n), which provides a new strategy to tailor the structure and properties of 2D materials by phase homology. The number and stacking order of layers are two important degrees of freedom that can modulate the properties of 2D van der Waals (vdW) materials. However, the layers' structures are essentially limited to the known layered 3D vdW materials. Recently, a new 2D vdW material, MoSi2N4, without known 3D counterparts, was synthesized by passivating the surface dangling bonds of non-layered 2D molybdenum nitride with elemental silicon, whose monolayer can be viewed as a monolayer MoN (-N-Mo-N-) sandwiched between two Si-N layers. This unique sandwich structure endows the MoSi2N4 monolayer with many fascinating properties and intriguing applications, and the surface-passivating growth method creates the possibility of tuning the layer's structure of 2D vdW materials. Here we synthesized a series of MoSi2N4(MoN)(4n) structures confined in the matrix of multilayer MoSi2N4. These super-thick monolayers are the homologous compounds of MoSi2N4, which can be viewed as multilayer MoN (Mo4n+1N4n+2) sandwiched between two Si-N layers. First-principles calculations show that MoSi2N4(MoN)(4) monolayers have much higher Young's modulus than MoN, which is attributed to the strong Si-N bonds on the surface. Importantly, different from the semiconducting nature of the MoSi2N4 monolayer, the MoSi2N4(MoN)(4) monolayer is identified as a superconductor with a transition temperature of 9.02 K. The discovery of MoSi2N4(MoN)(4n) structures not only expands the family of 2D materials but also brings a new degree of freedom to tailor the structure of 2D vdW materials, which may lead to unexpected novel properties and applications.

Calcium ion batteries (CIBs) are considered as an important candidate for post-lithium energy storage devices due to their abundance of resources and low cost. However, CIBs still suffer from slow kinetics due to the large solvation structure and high desolvation energy of Ca2+ ions. Here, a solvation regulation strategy based on donor number (DN) is reported to achieve easy-desolvation and rapid storage of Ca2+ in sodium vanadate (Na2V6O16 center dot 2H(2)O, NVO). Specially, the solvent with a low DN, represented by propylene carbonate (PC), forms the first solvation shell of calcium ions with weak binding energy and small shell structure, which facilitates the migration of Ca2+ in the electrolyte. More importantly, the low DN solvent is preferentially desolvated at the cathode/electrolyte interface, promoting the insertion of Ca2+ into the NVO electrode. Mechanism studies further confirm the highly reversible uptake/release of Ca2+ in the NVO cathode, along with the V-O distance change in the coordination structure. Therefore, the NVO cathode achieves high capacity (376 mAh g(-1) at 0.3 A g(-1)) and high-rate performance (151 mAh g(-1) at 5 A g(-1)). The weak solvation effect strategy further improves the electrochemical performance and provides great importance for the design of the long-term development of CIBs.

Integrating a graphene transparent electrode (TE) matrix with driving circuits is essential for the practical use of graphene in optoelectronics such as active-matrix organic light-emitting diode (OLED) display, however it is disabled by the transport of carriers between graphene pixels after deposition of a semiconductor functional layer caused by the atomic thickness of graphene. Here, the carrier transport regulation of a graphene TE matrix by using an insulating polyethyleneimine (PEIE) layer is reported. The PEIE forms an ultrathin uniform film (≤10 nm) to fill the gap of the graphene matrix, blocking horizontal electron transport between graphene pixels. Meanwhile, it can reduce the work function of graphene, improving the vertical electron injection through electron tunneling. This enables the fabrication of inverted OLED pixels with record high current and power efficiencies of 90.7 cd A and 89.1 lm W , respectively. By integrating these inverted OLED pixels with a carbon nanotube-based thin-film transistor (CNT-TFT)-driven circuit, an inch-size flexible active-matrix OLED display is demonstrated, in which all OLED pixels are independently controlled by CNT-TFTs. This research paves a way for the application of graphene-like atomically thin TE pixels in flexible optoelectronics such as displays, smart wearables, and free-form surface lighting.

The domains and domain boundaries in 2D materials are known to play essential roles in investigating intriguing physical properties and have potential applications in nanoscale devices. Understanding the influence of individual domains on the superconducting properties of ultrathin 2D superconductors is of crucial importance for fundamental studies on mesoscopic superconductivity as well as applications in superconducting nanoelectronics. Here, low-temperature electronic transport measurements of high quality ultrathin Mo2C crystals are presented that show clear evidence for the presence of multiple superconducting phase induced by the nanoscale domain structures. In particular, the observation of an anomalous resistance peak in the vicinity of the onset of the superconducting transition is reported. This resistive anomaly is interpreted as a consequence of nonequilibrium charge imbalance near the domain boundaries, which could induce effective normal-superconducting interfaces in 2D Mo2C crystals. Moreover, the magnetic field-tuned superconductor-metal transition for ultrathin Mo2C crystals is examined. The observed scaling behavior is consistent with the appearance of quantum Griffiths singularity in 2D superconducting systems. This study sheds light on the understanding of the domain boundaries and their role on the transport properties of highly crystalline 2D superconductors, which may open potential application of domain structure in functional superconducting nanodevices.

Lithium (Li) is the lightest and most electronegative metallic element and has been considered the ultimate anode choice for energy storage systems with high energy density. However, uncontrollable dendrite formation caused by high ion transfer resistance and low Li atom diffusion, and dendrite growth with large volume expansion and high electronegative activity, result in severe safety concerns and poor coulombic efficiency. In this review, the latest progress is presented from the viewpoint of dendrite evolution (from dendrite formation to growth) as the main line to understand the factors that influence the deposition chemistry. For the dendrite formation, specific attention is focused on the four distinct but interdependent factors: (a) how the dielectric constant, donor number, viscosity and salt concentration affect the movement of solvated Li+ in nonaqueous electrolyte. (b) The effect of non-polar solvents and anions with polar groups or high concentration on the Li+ desolvation step. (c) The effect of the formation of solid electrolyte interphase (SEI), along with its specific adsorption and solvated structure, and its physical structure, chemical composition and growth thickness on Li+ diffusion. (d) The effect of the diffusion coefficient of the host material on Li atom migration. After dendrite formation, the attention is focused on two detrimental factors together with dendrite growth: (e) low coulombic efficiency; (f) large volume expansion. Correspondingly, the emphasis is placed on reducing the side reactions and minimizing the volume expansion. Conclusions and perspectives on the current limitations and future research directions are recommended. It is anticipated that the dynamic dendrite evolution can provide fresh insight into similar electrochemical reaction processes of other anode chemistries in nonaqueous electrolytes, ranging from a conversion-reaction metal anode (Li, Na, Al) and an alloying anode (LiAlx, NaAlx) to an intercalation-based anode (graphite, TiS2), as well as aqueous, ionic liquid and flow redox battery systems.

Ambient-stable solution-processed conductive materials with a low work function are essential to facilitate electron injection. Here, the authors design and synthesise polymer electrolyte with work function down to 2.2 eV for applications in high-performance light-emitting diodes and solar cells. Ambient solution-processed conductive materials with a sufficient low work function are essential to facilitate electron injection in electronic and optoelectronic devices but are challenging. Here, we design an electrically conducting and ambient-stable polymer electrolyte with an ultralow work function down to 2.2 eV, which arises from heavy n-doping of dissolved salts to polymer matrix. Such materials can be solution processed into uniform and smooth films on various conductors including graphene, conductive metal oxides, conducting polymers and metals to substantially improve their electron injection, enabling high-performance blue light-emitting diodes and transparent light-emitting diodes. This work provides a universal strategy to design a wide range of stable charge injection materials with tunable work function. As an example, we also synthesize a high-work-function polymer electrolyte material for high-performance solar cells.

A joint chemical vapor infiltration-precursor infiltration and pyrolysis (CVI-PIP) process was used to fabricate C/C-SiC-ZrC composites with different volume ratio of CVI-derived C-SiC. The composite with a C-SiC volume ratio of 0.91 has a higher tensile and flexural strength of 181.7 MPa and 352.8 MPa, respectively, and also exhibits a better anti-oxidation property at 800 similar to 1400 degrees C for 30 h. After an oxyacetylene ablation for 600 s at similar to 2100 degrees C, the composite with a C-SiC volume ratio of 0.12 possesses a better anti-ablation performance with a linear and mass ablation rates of 0.94 um x s(-1) and 0.13 mg x cm(-2)x s(-1), respectively.

1D materials have attracted significant research interest due to their unique quantum confinement effects and edge-related properties. Atomically thin 1D nanoribbons are particularly interesting because it is a valuable platform with the physical limits of both thickness and width. Here, a catalyst-free growth method is developed and the growth of Bi2O2Se nanostructures with tunable dimensionality is achieved. Significantly, Bi2O2Se nanoribbons with a thickness down to 0.65 nm, corresponding to a monolayer, are successfully grown for the first time. Electrical and optoelectronic measurements show that Bi2O2Se nanoribbons possess decent performance in terms of mobility, on/off ratio, and photoresponsivity, suggesting their promise for devices. This work not only reports a new method for the growth of atomically thin nanoribbons but also provides a platform to study properties and applications of such nanoribbon materials at a thickness limit.

Fabricating highly crystalline macroscopic films with extraordinary electrical and thermal conductivities from graphene sheets is essential for applications in electronics, telecommunications and thermal management. High-temperature graphitization is the only method known to date for the crystallization of all types of carbon materials, where defects are gradually removed with increasing temperature. However, when using graphene materials as precursors, including graphene oxide, reduced graphene oxide and pristine graphene, even lengthy graphitization at 3000 & DEG;C can only produce graphene films with small grain sizes and abundant structural disorders, which limit their conductivities. Here, we show that high-temperature defects substantially accelerate the grain growth and ordering of graphene films during graphitization, enabling ideal AB stacking as well as a 100-fold, 64-fold and 28-fold improvement in grain size, electrical conductivity and thermal conductivity, respectively, between 2000 & DEG;C and 3000 & DEG;C. This process is realized by nitrogen doping, which retards the lattice restoration of defective graphene, retaining abundant defects such as vacancies, dislocations and grain boundaries in graphene films at a high temperature. With this approach, a highly ordered crystalline graphene film similar to highly oriented pyrolytic graphite is fabricated, with electrical and thermal conductivities (& SIM;2.0 x 10(4) S cm(-1); & SIM;1.7 x 10(3) W m(-1) K-1) that are improved by about 6- and 2-fold, respectively, compared to those of the graphene films fabricated by graphene oxide. Such graphene film also exhibits a superhigh electromagnetic interference shielding effectiveness of & SIM;90 dB at a thickness of 10 & mu;m, outperforming all the synthetic materials of comparable thickness including MXene films. This work not only paves the way for the technological application of highly conductive graphene films but also provides a general strategy to efficiently improve the synthesis and properties of other carbon materials such as graphene fibers, carbon nanotube fibers, carbon fibers, polymer-derived graphite and highly oriented pyrolytic graphite. The high-temperature defects induced by nitrogen doping significantly accelerate the grain growth and ordering of graphene films during graphitization, enabling highly-oriented-pyrolytic-graphite-like highly conductive films.

The challenges of developing neuromorphic vision systems inspired by the human eye come not only from how to recreate the flexibility, sophistication, and adaptability of animal systems, but also how to do so with computational efficiency and elegance. Similar to biological systems, these neuromorphic circuits integrate functions of image sensing, memory and processing into the device, and process continuous analog brightness signal in real-time. High-integration, flexibility and ultra-sensitivity are essential for practical artificial vision systems that attempt to emulate biological processing. Here, we present a flexible optoelectronic sensor array of 1024 pixels using a combination of carbon nanotubes and perovskite quantum dots as active materials for an efficient neuromorphic vision system. The device has an extraordinary sensitivity to light with a responsivity of 5.1x10(7)A/W and a specific detectivity of 2x10(16) Jones, and demonstrates neuromorphic reinforcement learning by training the sensor array with a weak light pulse of 1 mu W/cm(2). To emulate nature biological processing, highly-integrated ultra-sensitive artificial neuromorphic system is highly desirable. Here, the authors report flexible sensor array of 1024 pixels using combination of carbon nanotubes and perovskite QDs as active matetials, achieving highly responsive device for reinforcement learning.

This review summarizes the current progress on single-atom catalysts (SACs) for high-energy metal-sulfur batteries from aspects of synthesis, characterization, and electrochemical performance. Challenges and future perspectives are discussed for designing high-performance SACs. [Display omitted] Metal-sulfur batteries are recognized as a promising candidate for next generation electrochemical energy storage systems owing to their high theoretical energy density, low cost and environmental friendliness. However, sluggish redox kinetics of sulfur species and the shuttle effect lead to large polarization and severe capacity decay. Numerous approaches from physical barrier, chemical adsorption strategies to electrocatalysts have been tried to solve these issues and pushed the rate and cycle performance of sulfur electrodes to higher levels. Most recently, single-atom catalysts (SACs) with high catalytic efficiency have been introduced into metal-sulfur systems to achieve fast redox kinetics of sulfur conversion. In this review, we systematically summarize the current progress on SACs for sulfur electrodes from aspects of synthesis, characterization and electrochemical performance. Challenges and potential solutions for designing SACs for high-performance sulfur electrodes are discussed.

The controlled growth of metallic single-wall carbon nanotubes (m-SWCNTs) is very important for the fabrication of high-performance interconnecting wires, transparent conductive electrodes, light and conductive fibers, etc. However, it has been extremely difficult to synthesize m-SWCNTs due to their lower abundance and higher chemical reactivity than semiconducting SWCNTs (s-SWCNTs). Here, we report the kinetically controlled growth of m-SWCNTs by manipulating their binding energy with the catalyst and promoting their growth rate. We prepared CoRe4, nanoparticles with a hexagonal close-packed structure and an average size of similar to 2.3 nm, which have a lower binding energy with m-SWCNTs than with s-SWCNTs. The selective growth of m-SWCNTs from the CoRe4 catalyst was achieved by using a low concentration of carbon source feed at a relative low temperature of 760 degrees C. The m-SWCNTs had a narrow diameter distribution of 1.1 +/- 0.3 nm, and their content was over 80%.

Collective behavior widely exists in nature, ranging from the macroscopic cloud of swallows to the microscopic cloud of colloidal particles. The behavior of an individual inside the collective is distinctive from its behavior alone, as it follows its neighbors. The introduction of such collective behavior in two-dimensional (2D) materials may offer new degrees of freedom to achieve desired but unattained properties. Here, we report a highly sensitive magneto-optic effect and transmissive magneto-coloration via introduction of collective behavior into magnetic 2D material dispersions. The increase of ionic strength in the dispersion enhances the collective behavior of colloidal particles, giving rise to a magneto-optic Cotton-Mouton coefficient up to 2700 T-2 m(-1) which is the highest value obtained so far, being 3 orders of magnitude larger than other known transparent media. We also reveal linear dependence of magneto-coloration on the concentration and hydration ratios of ions. Such linear dependence and the extremely large Cotton-Mouton coefficient cooperatively allow fabrication of giant magneto-birefringent devices for color-centered visual sensing.

Lithium (Li) metal, a typical alkaline metal, has been hailed as the "holy grail" anode material for next generation batteries owing to its high theoretical capacity and low redox reaction potential. However, the uncontrolled Li plating/stripping issue of Li metal anodes, associated with polymorphous Li formation, "dead Li" accumulation, poor Coulombic efficiency, inferior cyclic stability, and hazardous safety risks (such as explosion), remains as one major roadblock for their practical applications. In principle, polymorphous Li deposits on Li metal anodes includes smooth Li (film-like Li) and a group of irregularly patterned Li (e.g., whisker-like Li (Li whiskers), moss-like Li (Li mosses), tree-like Li (Li dendrites), and their combinations). The nucleation and growth of these Li polymorphs are dominantly dependent on multiphysical fields, involving the ionic concentration field, electric field, stress field, and temperature field, etc. This review provides a clear picture and in-depth discussion on the classification and initiation/growth mechanisms of polymorphous Li from the new perspective of multiphysical fields, particularly for irregular Li patterns. Specifically, we discuss the impact of multiphysical fields' distribution and intensity on Li plating behavior as well as their connection with the electrochemical and metallurgical properties of Li metal and some other factors (e.g., electrolyte composition, solid electrolyte interphase (SEI) layer, and initial nuclei states). Accordingly, the studies on the progress for delaying/suppressing/ redirecting irregular Li evolution to enhance the stability and safety performance of Li metal batteries are reviewed, which are also categorized based on the multiphysical fields. Finally, an overview of the existing challenges and the future development directions of metal anodes are summarized and prospected.

It is crucial to control the ion transport in membranes for various technological applications such as energy storage and conversion. The emerging functional two-dimensional (2D) nanosheets such as graphene oxide and MXenes show great potential for constructing ordered nanochannels, but the assembled membranes suffer from low ion selectivity and stability. Here a class of robust charge-selective membranes with superhigh cation/anion selectivity, which are assembled with monolayer nanosheets of cationic/anionic clays that inherently have permanent and uniform charges on each layer is reported. The transport number of cations/anions of cationic vermiculite nanosheet membranes (VNMs)/anionic Co-Al layered double hydroxide (CoAl-LDH) nanosheet membranes is over 0.90 in different NaCl concentration gradients, outperforming all the reported ion-selective membranes. Importantly, this excellent ion selectivity can persist at high-concentration salt solutions, under acidic and alkaline conditions, and for a wide range of ions of different sizes and charges. By coupling a pair of cation-selective vermiculite membrane and anion-selective CoAl-LDH membrane, a reverse electrodialysis device which shows an output power density of 0.7 W m(-2) and energy conversion efficiency of 45.5% is constructed. This work provides a new strategy to rationally design high-performance ion-selective membranes by using 2D nanosheets with inherent surface charges for controllable ion-transport applications.

Carbon nanotubes (CNTs) are considered a promising candidate for the detection of toxic gases because of their high specific surface area and excellent electrical and mechanical properties. However, the detecting performance of CNT-based detectors needs to be improved because covalently bonded CNTs are usually chemically inert. We prepared a nitrogen-doped single-wall CNT (SWCNT) film by means of gas-phase fluorination followed by thermal annealing in NH 3 . The doped nitrogen content could be changed in the range of 2.9–9.9 at%. The N-doped SWCNT films were directly used to construct flexible and transparent gas sensors, which can work at a low voltage of 0.01 V. It was found that their NO 2 detection performance was closely related to their nitrogen content. With an optimum nitrogen content of 9.8 at%, a flexible sensor had a detection limit of 500 ppb at room temperature with good cycling ability and stability during bending.

Artificial synapses are promising for dealing with large amounts of data computing. Great progress has been made recently in terms of improving the on/off current ratio, the number of states, and the energy efficiency of synapse devices. However, the nonlinear weight update behavior of a synapse caused by the uncertain direction of the conductive filament leads to complex weight modulation, which degrades the delivery accuracy of information. Here we propose a strategy to improve the weight update behavior of synapses using chemical-vapor-deposition -grown transition metal dichalcogenides (TMDCs) with a vertical composition gradient, where the sulfur concentration decreases gradually along the thickness direction of TMDCs and thus forms a certain direction of the conduction filament for synapse devices. It is worth noting that the devices show an excellent linear conductance of potentiation and depression with a high linearity of 0.994 (surpassing most state-of-the-art synapses), have a large number of states, and are able to fabricate synapse arrays with wafer-scale. Furthermore, the devices based on the TMDCs with the vertical composition gradient exhibit an asymmetric feature of potentiation and depression behaviors with high linearity and follow the simulated linear Leaky ReLU function, resulting in a high recognition accuracy of 94.73%, which overcomes the unreliability issue in the Sigmoid function due to the vanishing gradient phenomenon. This study not only provides a universal method to grow TMDCs with a vertical composition gradient but also contributes to exploring highly linear synapses toward neuromorphic computing.

High-voltage aqueous MXene symmetric planar micro-supercapacitors based on water-in-LiCl electrolyte were developed, which presented a record operating voltage of 1.6 V and a wide temperature range of -40 degrees C to 60 degrees C. MXenes are one of the key materials for micro-supercapacitors (MSCs), integrating miniaturized energy-storage components with microelectronics. However, the energy densities of MSCs are greatly hampered by MXenes' narrow working potential window (typically

Lithium-ion batteries (LIBs) play a vital role in portable electronic products, transportation and large-scale energy storage. However, the electrochemical performance of LIBs deteriorates severely at low temperatures, exhibiting significant energy and power loss, charging difficulty, lifetime degradation, and safety issue, which has become one of the biggest challenges for LIBs. This article aims to review challenges and limitations of the battery chemistry in low-temperature environments, as well as the development of low-temperature LIBs from cell level to system level. This review introduces feasible solutions to accelarate low-temperature kinetics by increasing the inherent reactivity from cell design and improving the external reaction temperature from heating techniques. In addition, real-time and accurate monitoring of the battery temperature for the battery thermal management, as well as the optimization of charging protocols and the online lithium-plating monitoring in battery management systems are outlined. In general, a systematic review of low-temperature LIBs is conducted in order to provide references for future research. •Challenges and limitations of lithium-ion batteries at low temperatures are introduced.•Feasible solutions for low-temperature kinetics have been introduced.•Battery management of low-temperature lithium-ion batteries is discussed.

Recycling spent lithium-ion batteries (LIBs) has become an urgent task to address the issues of resource shortage and potential environmental pollution. However, direct recycling of the spent LiNi0.5Co0.2Mn0.3O2 (NCM523) cathode is challenging because the strong electrostatic repulsion from a transition metal octahedron in the lithium layer provided by the rock salt/spinel phase that is formed on the surface of the cycled cathode severely disrupts Li+ transport, which restrains lithium replenishment during regeneration, resulting in the regenerated cathode with inferior capacity and cycling performance. Here, we propose the topotactic transformation of the stable rock salt/spinel phase into Ni0.5Co0.2Mn0.3(OH)2 and then back to the NCM523 cathode. As a result, a topotactic relithiation reaction with low migration barriers occurs with facile Li+ transport in a channel (from one octahedral site to another, passing through a tetrahedral intermediate) with weakened electrostatic repulsion, which greatly improves lithium replenishment during regeneration. In addition, the proposed method can be extended to repair spent NCM523 black mass, spent LiNi0.6Co0.2Mn0.2O2, and spent LiCoO2 cathodes, whose electrochemical performance after regeneration is comparable to that of the commercial pristine cathodes. This work demonstrates a fast topotactic relithiation process during regeneration by modifying Li+ transport channels, providing a unique perspective on the regeneration of spent LIB cathodes.

2D semiconductors are promising for fabricating miniaturized and flexible electronic devices. The manipulation of polarities in 2D semiconductors is key to fabricate functional devices and circuits. However, the switchable and reversible control of polarity in 2D semiconductors is challenging due to their ultrathin body. Herein, a reversible and non‐destructive method is developed to dope 2D semiconductors by using ionic 2D minerals as the electrostatic gating. The 2D semiconductor channel can be reversibly transformed between n+ and p+ types with carrier concentrations of 1.59 × 1013 and 6.82 × 1012 cm−2, respectively. With the ability to in situ control carrier type and concentration in 2D semiconductors by ionic gating, a reversible PN/NP junction and programmable logic gate are demonstrated in such devices. This 2D mineral materials‐based ionic doping approach provides an alternative method for achieving multi‐functional and complex circuits in an all‐2D material flatform. Accurately modulating carrier concentration and type is essential for developing logic devices. Ionic 2D mineral‐based electrostatic doping serves as a reversible method to achieve a wide range of carrier concentrations in 2D materials, enabling realization of programmable PN/NP junctions and Boolean logics in a single all‐2D material device.

Efficient electrochemical bubbling delamination is highly promising for realizing the scalable transfer of high-quality chemical vapor deposition (CVD) graphene film. However, it remains a challenge to significantly improve the low delamination rate of large-area graphene without causing structural damage. Here, a strain-engineering strategy is reported to break this rate-integrity dilemma by introducing appreciable compressive strain into graphene to dramatically accelerate the delamination of CVD graphene from Cu foil in a non-destructive manner. An astonishing 25-fold improvement in the delamination rate is achieved by hot bubbling graphene coated with a post-cured UV-epoxy adhesive. Meanwhile, the inherent structural integrity of delaminated graphene films is well preserved. The strategy is superior to the prevalent methods by simultaneously realizing the unprecedented high-rate delamination and intact transfer. It is further demonstrated that it allows the highly efficient roll-to-roll bubbling transfer of meter-scale high-quality graphene films.

Gradient heterostructure is one of fundamental interfaces and provides an effective platform to achieve gradually changed properties in mechanics, optics, and electronics. Among different types of heterostructures, the gradient one may provide multiple resistive states and immobilized conductive filaments, offering great prospect for fabricating memristors with both high neuromorphic computation capability and repeatability. Here, we invent a memristor based on a homologous gradient heterostructure (HGHS), comprising a conductive transition metal dichalcogenide and an insulating homologous metal oxide. Memristor made of Ta–TaSxOy–TaS2 HGHS exhibits continuous potentiation/depression behavior and repeatable forward/backward scanning in the read‐voltage range, which are dominated by multiple resistive states and immobilized conductive filaments in HGHS, respectively. Moreover, the continuous potentiation/depression behavior makes the memristor serve as a synapse, featuring broad‐frequency response (10−1–105 Hz, covering 106 frequency range) and multiple‐mode learning (enhanced, depressed, and random‐level modes) based on its natural and motivated forgetting behaviors. Such HGHS‐based memristor also shows good uniformity for 5 × 7 device arrays. Our work paves a way to achieve high‐performance integrated memristors for future artificial neuromorphic computation. We invent a memristor based on a homologous gradient heterostructure (HGHS), comprising a conductive transition metal dichalcogenide and an insulating homologous metal oxide. Memristor made of Ta–TaSxOy–TaS2 HGHS exhibits continuous potentiation/depression behavior and repeatable forward/backward scanning in the read‐voltage range, which are dominated by multiple resistive states and immobilized conductive filaments in HGHS, respectively.

As a rapidly growing family of 2D transition metal carbides and nitrides, MXenes are recognized as promising materials for the development of future electronics and optoelectronics. So far, the reported patterning methods for MXene films lack efficiency, resolution, and compatibility, resulting in limited device integration and performance. Here, a high-performance MXene image sensor array fabricated by a wafer-scale combination patterning method of an MXene film is reported. This method combines MXene centrifugation, spin-coating, photolithography, and dry-etching and is highly compatible with mainstream semiconductor processing, with a resolution up to 2 mu m, which is at least 100 times higher than other large-area patterning methods reported previously. As a result, a high-density integrated array of 1024-pixel Ti3C2Tx/Si photodetectors with a detectivity of 7.73 x 10(14) Jones and a light-dark current ratio (I-light/I-dark) of 6.22 x 10(6), which is the ultrahigh value among all reported MXene-based photodetectors, is fabricated. This patterning technique paves a way for large-scale high-performance MXetronics compatible with mainstream semiconductor processes.

Lithium metal is considered a promising anode material because of its high specific capacity and low redox potential. However, there are two factors that prevent a lithium metal anode from being used, a safety issue caused by dendrite formation and a low Coulombic efficiency caused by the formation of a solid electrolyte interface. Solving these problems by designing reliable liquid electrolytes is an appropriate strategy for two reasons. First, it is the only method that has good compatibility with the current industrial fabrication techniques for lithium ion pouch cells, compared with other strategies such as the use of 3D current collectors or solid-state electrolytes. Second, liquid electrolytes can achieve good kinetics and avoid an energy density loss caused by non-active materials in 3D current collectors. To better understand the benefits which can be realized by designing reliable liquid electrolytes, this review discusses state-of-art electrolyte modification strategies and the mechanisms for improving the performance of a lithium metal anode by the proper selection, design and combination of solvents, solutes, and additives. Furthermore, the problems related to electrolyte modification, and advanced characterization techniques for the anode/electrolyte interface and for solvent-ion interactions are introduced. It is expected that this review will stimulate scientists and engineers to design promising electrolyte components for developing reliable lithium metal batteries.

Proton transport in nanochannels under humid conditions is crucial for the application in energy storage and conversion. However, existing materials, including Nafion, suffer from limited conductivity of up to 0.2 siemens per centimeter. We report a class of membranes assembled with two-dimensional transition-metal phosphorus trichalcogenide nanosheets, in which the transition-metal vacancies enable exceptionally high ion conductivity. A Cd0.85PS3Li0.15H0.15 membrane exhibits a proton conduction dominant conductivity of similar to 0.95 siemens per centimeter at 90 degrees Celsius and 98% relative humidity. This performance mainly originates from the abundant proton donor centers, easy proton desorption, and excellent hydration of the membranes induced by cadmium vacancies. We also observed superhigh lithium ion conductivity in Cd0.5PS3Li0.3 and Mn0.77PS3Li0.46 membranes.

Designed alloy catalysts have shown promise in structure-controlled growth of single-wall carbon nanotubes (SWCNTs). However, due to the high-dimensional growth parameter space and low efficiency of the conventional trial-and-error optimizing approach, it is still challenging to explore and to establish the relations between catalyst compositions and the structure of SWCNTs. Here, we present a high-throughput strategy to investigate the statistical patterns in catalyst activity and selective growth of SWCNTs using Co/Pt/Mo ternary catalysts. Statistical analysis reveals that in the Co/Pt/Mo ternary diagram, there is an active region in the Co-rich Co–Mo corner to grow SWCNTs with high yield (≥25 tubes/μm2) and high quality (IG/ID ≥ 40). Enriched semiconducting (s-) SWCNTs with a purity higher than 90% were obtained along the boundary of the high yield region, near the Co–Pt axis. The statistical patterns of the yield, quality and selectivity are associated with the alloy composition, revealing a negative correlation between the yield and enrichment of s-SWCNTs. High-resolution transmission electron microscope characterization shows that a Co–Pt alloy catalyst with a uniform size distribution facilitates the s-SWCNT enrichment. And the separate phases of a Co–Mo/Co catalyst stabilize the active Co phase, leading to long catalyst lifetime and high yield of SWCNTs. A high-throughput strategy is developed to investigate the statistical patterns of the catalyst activity and the selective growth of single-wall carbon nanotubes (SWCNTs) grown from Co/Pt/Mo ternary catalysts. The structure of Co/Pt and Co/Mo catalysts linked with SWCNTs are further identified by using high-resolution transmission electron microscope. [Display omitted]

Reactive melt infiltration (RMI) has been proved to be one of the most promising technologies for fabrication of C/SiC composites because of its low cost and short processing cycle. However, the poor mechanical and anti-ablation properties of the RMI-C/SiC composites severely limit their practical use due to an imperfect siliconization of carbon matrixes with thick walls and micron-sized pores. Here, we report a high-performance RMI-C/SiC composite fabricated using a carbon fiber reinforced nanoporous carbon (NC) matrix preform composed of overlapping nanoparticles and abundant nanopores. For comparison, the C/C performs with conventional pyrocarbon (PyC) or resin carbon (ReC) matrixes were also used to explore the effect of carbon matrix on the composition and property of the obtained C/SiC composites. The C/SiC derived from C/NC with a high density of 2.50 g cm−3 has dense and pure SiC matrix and intact carbon fibers due to the complete ceramization of original carbon matrix and the almost full consumption of inspersed silicon. In contrast, the counterparts based on C/PyC or C/ReC with a low density have a little SiC, much residual silicon and carbon, and many corroded fibers. As a result, the C/SiC from C/NC shows the highest flexural strength of 218.1 MPa and the lowest ablation rate of 0.168 µm s−1 in an oxyacetylene flame of ∼ 2200 °C with a duration time of 500 s. This work opens up a new way for the development of high-performance ceramic matrix composites by siliconizing the C/C preforms with nanoporous carbon matrix.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted great attention due to their physical and chemical properties that make them promising in electronics and optoelectronics. Because of the difficulties in controlling concentrations of solid precursors and spatially nonuniform growth dynamics, it is challenging to grow 2D TMDCs over large areas with good uniformity and reproducibility so far, which significantly hinders their practical use. Here we report a vertical chemical vapor deposition (VCVD) design with gaseous precursors to grow monolayer TMDCs with a uniform density and high quality over the whole substrate and with excellent reproducibility. Such a gaseous VCVD design can well control the three key parameters in TMDC growth, including precursor concentration, gas flow, and temperature, which cannot be done in a currently widely used horizontal CVD system with solid precursors. Statistical results show that VCVD-grown monolayer TMDCs including MoS2 and WS2 are of high uniformity and quality on substrates over centimeter size. We also fabricated multiple van der Waals heterostructures by one-step transfer of VCVD-grown TMDCs, owning to their good uniformity. This work sheds light on the growth of 2D materials with high uniformity on a large-area substrate, which can be used for the wafer-scale fabrication of 2D materials and their heterostructures.

[Display omitted] Metal foams with hierarchically porous structures are highly desirable in energy applications as active materials or their host substrates. However, conventional preparation methods usually have a quite limited flexibility of adjusting pore size of metal foams. Herein, an alternative new method based on gaseous thermal oxidation-nitridation-denitridation processes was developed to prepare metal (copper and nickel) foams with adjustable pore size by controlling the thermal nitridation temperature. Moreover, this environment-friendly method is independent of the shape of starting pure metal substrates and can be repeatedly applied to the metal substrates to create hierarchical porous structures containing different size pores. As a demonstration of the advantages of the resultant foams with abundant pores by this method, compared with its starting material (commercial Ni foam with the pore size of several millimeters), the resultant hierarchical porous Ni foam gives the remarkably enhanced performance of electrochemical water splitting as HER/OER electrodes and electrochemical energy storage as the host substrate of capacitive material MnO2. The metal foams with adjustable pore size prepared by the developed method will find a wide range of important applications in energy storage and conversion areas.

Aggregation of two-dimensional (2D) nanosheet fillers in a polymer matrix is a prevalent problem when the filler loading is high, leading to degradation of physical and mechanical properties of the composite. To avoid aggregation, a low-weight fraction of the 2D material (

Water electrolysis is promising for industrial hydrogen production to achieve a sustainable and green hydrogen economy, but the high cost of the technology limits its market share. Developing efficient yet economic electrocatalysts is crucial to decrease the cost of electricity and electrolytic cell. Meanwhile, electrolysis in seawater electrolyte can further reduce feedstock cost. Here, a type of electrocatalyst is synthesized, where trace precious metals are strongly anchored on a corrosion-resistive matrix. As an example, the produced Pt/Ni-Mo electrocatalyst only needs an overpotential of 113 mV to reach an ultrahigh current density of 2000 mA cm(-2) in the saline-alkaline electrolyte, demonstrating the best performance reported thus far. It shows high activity and long durability in various electrolytes and under harsh conditions, including strong alkaline and simulated seawater electrolytes, and under elevated temperatures up to 80 degrees C. This electrocatalyst is produced on a large scale at a low cost and shows good performance in a commercial membrane electrode assembly stack, demonstrating its feasibility for practical water electrolysis.

Unlike single‐step reactions, multi‐step reactions can be greatly facilitated only if all the intermediate reactions can be catalyzed simultaneously and progressively. Herein, the theoretical analysis and experiments to illustrate the superiority of the cascade oxygen evolution reaction (OER) are conducted. As different OER intermediate reactions demand FexNi1‐xOOH with altered Fe/Ni ratios, gradient Fe‐doped NiOOH can be an ideal electrocatalyst for the efficient cascade OER in line. Fine controlling of the nucleation sequence of iron and nickel sulfides leads to a FeS2@NiS2 core–shell structure. The activated outward diffusion of Fe dopants results in the gradient Fe/Ni ratios in the FexNi1‐xOOH shell, where a cascade OER can happen. Electrochemical tests suggest that the FeS2@NiS2 only needs an overpotential of 237 mV to reach the current density of 10 mA cm−2, with fast reaction kinetics and good stability. In ideal conditions, the continuous intermediate reactions in oxygen evolution reaction (OER) require active sites with high, moderate, and low Fe/Ni ratios, as well as gradient spatial distribution of them. Here, activating FeS2@NiS2 core–shell structure results in a shell of FexNi1‐xOOH with gradient Fe/Ni ratios, thus realizing cascade OER with superior performance.

Graphene and graphene oxide (GO), as wonder materials, have penetrated nearly every field of research. One of their most attractive features is the functionality and assembly of graphene or GO, in which they can be considered to be chemically functionalized building blocks for creating unconventional porous graphene materials (PGMs) that not only combine the merits of both porous materials and graphene, but also have major advantages over other porous carbons for specific applications. The chemistry and approaches for functionalizing graphene and GO are first introduced, and typical procedures for pore creation (e.g., in-plane pores, 2D laminar pores, and 3D interconnected pore assemblies), self-assembly, and tailoring mechanisms for PGMs to highlight the significance of precise control over the pore morphology and pore size are summarized. Because of their unique pore structures, with different morphologies and intriguing properties, PGMs serve as key components in a variety of applications such as energy storage, electrocatalysis, and molecular separation. Finally, the challenges relating to PGMs from the understanding of chemical self-assembly to specific applications are discussed, and promising solutions on how to tackle them are presented. This provides an insightful outlook for the future development of the chemistry and applications of PGMs.

Magnetically influenced light-matter interaction provides a contactless, noninvasive and power-free way for material characterization and light modulation. Shape anisotropy of active materials mainly determines the sensitivity of magneto-optic response, thereby making magnetic two-dimensional (2D) materials suitable in achieving the giant magneto-birefringence effect as discovered recently. Consequently, relationship between magneto-birefringence response and shape anisotropy of 2D materials is critical but has remained elusive, restricting its widespread applications. Here, we report the highly sensitive and largely tunable magneto-coloration via manipulating the shape-anisotropy of magnetic 2D materials. We reveal a quadratic increasing relationship between the magneto-optic Cotton-Mouton coefficient and the lateral size of 2D materials and achieve a more than one order of magnitude tunable response. This feature enables the engineerable transmissive magneto-coloration of 2D materials by tailoring their shape anisotropy. Our work deepens the understanding of the tunability of magneto-optic response by size effect of active materials, offering various opportunities for their applications in vast areas where color is concerned.

Sluggish evolution of lithium ions' solvation sheath induces large charge-transfer barriers and high ion diffusion barriers through the passivation layer, resulting in undesirable lithium dendrite formation and capacity loss of lithium batteries, especially at low temperatures. Here, an ion-dipole strategy by regulating the fluorination degree of solvating agents is proposed to accelerate the evolution of the Li+ solvation sheath. Ethylene carbonate (EC)-based fluorinated derivatives, fluoroethylene carbonate (FEC) and di-fluoro ethylene carbonate (DFEC) are used as the solvating agents for a high dielectric constant. As the increase of the fluorination degree from EC to FEC and DFEC, the Li+-dipole interaction strength gradually decreases from 1.90 to 1.66 and 1.44 eV, respectively. Consequently, the DFEC-based electrolyte displays six times faster ion desolvation rate than that of a non-fluorinated EC-based electrolyte at -20 degrees C. Furthermore, LiNi0.8Co0.1Mn0.1O2||lithium cells in a DFEC-based electrolyte retain 91% original capacity after 300 cycles at 25 degrees C, and 51% room-temperature capacity at -30 degrees C. By bridging the gap between the ion-dipole interactions and the evolution of Li+ solvation sheath, this work provides a new technique toward rational design of electrolyte engineering for low-temperature lithium batteries.

With Fe3+ as both the morphology-controlling agent and dopant, Fe-doped NiS2 microcrystals with the exposed chemically stable {001} facets were synthesized hydrothermally for electrocatalytic OER. After the electrocatalytic activation, the iron-rich surface transformed into active Fe-doped nickel oxyhydroxide, while the inner {001}-oriented NiS2 retained, endowing the catalysts with high OER activity and long-term stability. [Display omitted] Developing high-performance electrocatalysts with favorable phase, surface structure and electronic structure for oxygen evolution reaction (OER) is crucial for efficient electrocatalytic water splitting. With Fe3+ ions as both dopant and morphology-controlling agent, Fe-doped NiS2 microcrystals with the exposed chemically stable {001} facets were synthesized hydrothermally for electrocatalytic OER. The initial electrocatalytic OER activation processes led to the conversion of iron-rich surface layers of the NiS2 microcrystals into Fe-doped Ni (oxy)hydroxide as the shell and the residual inner of the NiS2 microcrystals as the core. Such Fe-doped NiS2 microcrystals with the derived core/shell structure only required a small OER overpotential of 277 mV to reach an electrochemical current density of 10 mA/cm2, and showed a good stability in a more than 20 h duration test almost without overpotential increase.

Abstract The use and storage of renewable and clean energy has become an important trend due to resource depletion, environmental pollution, and the rising price of refined fossil fuels. Confined by the limited resource and uneven distribution of lithium, non‐lithium‐ion batteries have become a new focus for energy storage. The six‐membered‐ring (SMR) is a common structural unit for numerous material systems. 2D SMR inorganic materials have unique advantages in the field of non‐lithium energy storage, such as fast electrochemical reactions, abundant active sites and adjustable band gap. First‐principles calculations based on density functional theory (DFT) can provide a basic understanding of materials at the atomic‐level and establish the relationship between SMR structural units and electrochemical energy storage. In this review, the theoretical progress of 2D SMR inorganic materials in the field of non‐lithium‐ion batteries in recent years is discussed to summarize the common relationship among 2D SMR non‐lithium energy storage anodes. Finally, the existing challenges are analyzed and potential solutions are proposed.

As an important energy carrier in terms of carbon neutrality, green hydrogen produced by water electrolysis using renewable electricity has attracted worldwide attention. The polymer electrolyte water electrolyzer (PEWE) has the potential to be a mainstay in the green hydrogen market in the future because of its superior performance. However, the development of PEWE is constrained by the slow progress of the membrane electrode assembly (MEA), which is an essential component of PEWE and largely determines the cost and performance of the system. Therefore, the MEA must be optimized from the aspects of reducing cost and improving performance to promote the development of PEWEs. In this review, we first discuss the recent progress of the materials and design strategies of MEA, including the cost, activity, and stability of catalysts, distribution and thickness of ionomers, and ion transport efficiency of ion exchange membranes (IEMs). Then, the effects of all components and interlayer interfaces on the ions, electrons, and mass transfer in MEA and, consequently, the performance of PEWE are analyzed. Finally, we propose perspectives on developing MEA by optimizing the catalyst activity and stability of IEM, interface contact between adjacent components, and evaluation methods of performance.

Electrochemical deposition has emerged as an efficient technique for preparing conjugated polymer films on electrodes. However, this method encounters difficulties in synthesizing crystalline products and controlling their orientation on electrodes. Here we report electrochemical film deposition of a large polycyclic aromatic hydrocarbon. The film is composed of single-crystalline nanorods, in which the molecules adopt a cofacial stacking arrangement along the pi-pi direction. Film thickness and crystal size can be controlled by electrochemical conditions such as scan rate and electrolyte species, while the choice of anode material determines crystal orientation. The film supports exceptionally efficient migration of both free carriers and excitons: the free carrier mobility reaches over 30 cm(2) V-1 s(-1), whereas the excitons are delocalized with a low binding energy of 118.5 meV and a remarkable exciton diffusion length of 45 nm.

Graphene has emerged as an attractive candidate for flexible transparent electrode (FTE) for a new generation of flexible optoelectronics. Despite tremendous potential and broad earlier interest, the promise of graphene FTE has been plagued by the intrinsic trade-off between electrical conductance and transparency with a figure of merit (sigma(DC)/sigma(Op)) considerably lower than that of the state-of-the-art ITO electrodes (sigma(DC)/sigma(Op)

High extraction capacity with precise selectivity to trace amounts of gold over a wide range of co-existing elements remains a challenge for effective e-waste recycling. Here, authors demonstrate the excellent performance of rGO for gold extraction from e-waste leachate, even at minute concentrations. Materials capable of extracting gold from complex sources, especially electronic waste (e-waste), are needed for gold resource sustainability and effective e-waste recycling. However, it remains challenging to achieve high extraction capacity and precise selectivity if only a trace amount of gold is present along with other metallic elements . Here we report an approach based on reduced graphene oxide (rGO) which provides an ultrahigh capacity and selective extraction of gold ions present in ppm concentrations (>1000 mg of gold per gram of rGO at 1 ppm). The excellent gold extraction performance is accounted to the graphene areas and oxidized regions of rGO. The graphene areas spontaneously reduce gold ions to metallic gold, and the oxidized regions allow good dispersibility of the rGO material so that efficient adsorption and reduction of gold ions at the graphene areas can be realized. By controlling the protonation of the oxidized regions of rGO, gold can be extracted exclusively, without contamination by the other 14 co-existing elements typically present in e-waste. These findings are further exploited to demonstrate recycling gold from real-world e-waste with good scalability and economic viability, as exemplified by using rGO membranes in a continuous flow-through process.

A simple, fast and cost-effective method for monolithic carbon aerogels (CAs) preparation was proposed through sol-gel polycondensation of resorcinol with formaldehyde in a basic aqueous solution followed by ambient pressure drying without solvent exchange, and carbonization. The microstructure and network strength of CAs were tailored by adjusting the catalyst concentration ([resorcinol]/[sodium carbonate] in the range of 300–2000), water content ([deionized water]/[resorcinol] equals to 17 and 24, respectively), and gelation temperature (Tgel in the range of 30−90 °C). Resultantly, the CAs with a wide range of density (0.30–1.13 g/cm3), high specific surface area (465−616 m2/g), high compressive strength (6.5–147.4 MPa) and low thermal conductivity (0.065-0.120 Wm−1 K−1) were obtained in this work. Moreover, the large-sized CAs (100 × 100 × 20 mm3) can also be prepared by this method since the formed robust skeleton network can resist shrinkage/collapse of pore structure and prevent cracking during drying. The improved mechanical strength and monolithic forming abilities could be mainly attributed to the uniform arrangement of carbon particles and pores, fine particle size, abundant network structure and enhanced particle neck.

Fast ion conduction and stable interfaces are predicted to be important in the development of new electrolytes. However, many unconventional solvents for electrolytes remain challenging, although they are fast ion carriers, because of the narrow voltage window of solvent oxidation and reduction. Here, we report a general solidified localized high-concentration electrolyte (S-LHCE) strategy with the decoupling of ion pairing and ion conduction to achieve the application of unstable solvents (dimethyl sulfoxide, DMSO) in high-voltage lithium-metal batteries. By decoupling electrolytes with a non-solvating solid framework, the interfacial compatibility was further improved with lithium anodes and high-voltage cathodes. The anion migration was limited with a high Li+ transference number of 0.72, and the lithium-ion conduction was enhanced (0.27 mS cm(-1) at 20 degrees C) by the regulated solvation structure in an ultrahigh salt concentration regime. The S-LHCE strategy enabled solid-state lithium-metal batteries with excellent electrochemical performance over a wide temperature range from -10 to 100 degrees C and with 83.3% and 60.1% capacity retention of the theoretical capacity when cycled at a 30C rate and a 50C rate at an evaluated temperature. The results in this work provide new insight for the application of potential but unconventional active components to high-performance electrolytes.

N-doped monolayer carbon encapsulated Mo-doped ultrafine Ni nanoparticles anchored on a freestanding film of single-wall carbon nanotubes attains a current density of 20 mA cm−2 at 1.6 V for total water splitting in alkaline media. [Display omitted] •A freestanding and binder-free NMoNi/SWCNT hybrid electrocatalyzing film is constructed.•Ni nanoparticles with ultrafine size of ∼2.8 nm are encapsulated by N-doped monolayer carbon.•Limited content of Mo is doped into Ni nanoparticles.•This unique structure enables efficient and stable electrocatalyzing properties for total water splitting. Electrochemical water splitting is regarded as a sustainable and cost-effective route for the production of hydrogen. However, the high-cost and poor stability of traditional rare-earth metal-based electrocatalysts make it difficult to yield hydrogen economically. Here, we report an efficient and durable film electrocatalyst of N-doped monolayer carbon encapsulated Mo-doped ultrafine Ni nanoparticles anchored on single-wall carbon nanotube network (NMoNi/SWCNT) for total water splitting in an alkaline solution. The single layer carbon prevents oxidation of encapsulated Ni and Mo species and facilitates desired electronic structure modulation to achieve a high catalytic activity. Hence, the freestanding NMoNi/SWCNT film catalyst shows low overpotentials of 255 mV and 130 mV to attain a current density of 10 mA cm−2 for oxygen evolution reaction and hydrogen evolution reaction, respectively, with a good stability. More importantly, the NMoNi/SWCNT film only requires a potential of 1.6 V to reach a current density of 20 mA cm−2 when employed as both anode and cathode for a total water splitting.

Highly active, robust and low-cost oxygen evolution reaction (OER) electrodes are urgently required to satisfy the industrial hydrogen production via water electrolysis. However, numerous earth-abundant materials have severely suffered from the low stability over thousands of hours at large current densities. Herein, ultrathin NiFeOOH nanosheets with abundant undercoordinated Fe active sites on a Ni foam electrode for OER were obtained via an electrochemically topologic transition process. They deliver a low overpotentials of 210 mV at 10 mA cm-2 and a small Tafel slope of 32 mV dec-1 owing to the abundant Fe active sites and exhibit high stability at high current densities of 400–600 mA cm-2 over 2000 h due to their strong adhesion to Ni foam. Moreover, only a 370 mV overpotentials is required to produce a high current density of 400 mA cm-2 in a two-electrode water electrolysis system, demonstrating an energy efficiency as high as ∼77%. [Display omitted] •An electrochemically topologic transition process was applied to generate the NiFeOOH nanosheets with abundant undercoordinated Fe active sites.•The nanosheets based electrode delivers a low overpotential of 210 mV at 10 mA cm-2 and a small Tafel slope of 32 mV dec-1 for water oxidation.•An unprecedentedly good stability was achieved at high current densities of 400–600 mA cm-2 over 2000 h.•Only a 370 mV overpotential is required to produce a high current density of 400 mA cm-2 in a two-electrode water electrolysis system.

In this work, we report a universal dual-metal precursors method with the use of a mixture of a metal and its chloride as the source to grow various non-layered 2D TMCs. Using this method, we can control the evaporation rate to provide a constant metal supply and facilitate the growth of non-layered 2D TMCs. Taking Fe1−xS as an example, flakes as thin as 3 nm with a lateral size over 100 μm are grown. [Display omitted] Two-dimensional (2D) transition metal chalcogenides (TMCs) are promising for nanoelectronics and energy applications. Among them, the emerging non-layered TMCs are unique due to their unsaturated dangling bonds on the surface and strong intralayer and interlayer bonding. However, the synthesis of non-layered 2D TMCs is challenging and this has made it difficult to study their structures and properties at thin thickness limit. Here, we develop a universal dual-metal precursors method to grow non-layered TMCs in which a mixture of a metal and its chloride serves as the metal source. Taking hexagonal Fe1–xS as an example, the thickness of the Fe1–xS flakes is down to 3 nm with a lateral size of over 100 μm. Importantly, we find ordered cation Fe vacancies in Fe1–xS, which is distinct from layered TMCs like MoS2 where anion vacancies are commonly observed. Low-temperature transport measurements and theoretical calculations show that 2D Fe1–xS is a stable semiconductor with a narrow bandgap of ∼60 meV. In addition to Fe1–xS, the method is universal in growing various non-layered 2D TMCs containing ordered cation vacancies, including Fe1–xSe, Co1–xS, Cr1–xS, and V1–xS. This work paves the way to grow and exploit properties of non-layered materials at 2D thickness limit.

Layered materials with unique structures and symmetries have attracted tremendous interest for constructing two-dimensional (2D) structure. The weak interlayer interaction renders them to be readily isolated into various ultrathin nanosheets with exotic properties and diverse applications. In order to enrich the library of 2D materials, extensive progress has been made in the field of ternary layered materials. Consequently, many brand-new materials are derived, which greatly extends the members of 2D realm. In this review, we emphasize the recent progress made in synthesis and exploration of ternary layered materials. We first classify them in terms of stoichiometric ratio, and summarize their difference in interlayer interaction, which is of great importance to produce corresponding 2D materials. The compositional and structural characteristics of resultant 2D ternary materials are then discussed so as to realize desired structures and properties. As a new family of 2D materials, we overview the layer-dependent properties and related applications in the fields of electronics, optoelectronics, and energy storage and conversion. The Review finally provides a perspective for this rapidly developing field.

Although the artificial Z-scheme system, mimicking natural photosynthesis, has shown promising applications in photocatalytic water splitting, it often suffers from the side reaction of redox mediator, which considerably undermines the efficacy of photocarrier utilizations. Herein, we propose to suppress the side reaction by using ferroelectric polarization, which not only provides a strong driving force to spatially separate photocarriers to the oppositely poled surface but also induces spatially selective adsorption of redox ions. Single-domain ferroelectric PbTiO3 nanoplates have been adopted as a model ferroelectric to construct the Z-scheme system with BiVO4 particles and a cationic redox mediator. In contrast to the inactive multi-domain ferroelectric PbTiO3-based system, the so-formed Z-scheme system delivers stable high activity for photocatalytic overall water splitting under both visible light and simulated solar insolation. This work offers a proof of concept to realize efficient solar photocatalytic water splitting based on single-domain ferroelectric Z-scheme system. [Display omitted] •Ferroelectric polarization induced the spatial separation of carriers and redox mediators•Single-domain ferroelectric PbTiO3-based Z-scheme system for overall water splitting•Greatly suppressed side reaction The Z-scheme system involving two isolated photocatalysts and a redox mediator has been actively used for photocatalytic water splitting. However, this system always suffers from the redox mediators’ side reaction largely due to random distributions of both the redox mediators and photogenerated electrons/holes on the photocatalyst surfaces. The side reaction could be suppressed by making use of ferroelectric polarization to enable the selective adsorption of the cationic redox mediator on the negatively poled surface of ferroelectric photocatalyst, which simultaneously has the ability to induce the spatial separation of photogenerated electrons and holes on the positively and negatively poled surfaces. This strategy was validated by constructing a Z-scheme system with single-domain ferroelectric PbTiO3 as water reduction photocatalyst, faceted BiVO4 as water oxidation photocatalyst, and cationic redox mediator for enhanced photocatalytic overall water splitting. The single-domain PbTiO3 has a built-in electric field to enable the spatial separation of the photocarriers and the selective adsorption of redox mediators on oppositely poled surfaces, i.e., electrons on the positively poled surface and cationic redox mediators on the negatively poled surface. This feature endows PbTiO3 as a promising water reduction photocatalyst in the Z-scheme system due to the suppression of mediator side reactions. This strategy could be applicable for designing much more efficient Z-scheme systems.

A unique mixed-dimensional van der Waals heterostructure can be formed by integrating one-dimensional (1D) and two-dimensional (2D) materials. Such a 1D/2D mixed-dimensional heterostructure will not only inherit the unique properties of 2D/2D heterostructures, but also has a variety of stacking configurations, offering a new platform to adjust its structure and properties. The combination of p-type 1D single-walled carbon nanotubes (SWCNTs) and n-type 2D molybdenum disulfide (MoS2) is one such example, possessing tunable properties. In situ chemical vapor deposition (CVD) is one of the most effective methods to construct 1D SWCNT/2D MoS2 mixed-dimensional heterostructures. There are several reports of successfully grown SWCNT/MoS2 heterostructures. The reports indicate that these heterostructures exhibit strong electrical and mechanical couplings between the SWCNTs and MoS2, making it suitable for the construction of high-performance electronic and optoelectronic devices. However, there are still several prob

Doping of bulk silicon and III-V materials has paved the foundation of the current semiconductor industry. Controlled doping of 2D semiconductors, which can also be used to tune their bandgap and type of carrier thus changing their electronic, optical, and catalytic properties, remains challenging. Here the substitutional doping of nonlike element dopant (Mn) at the Mo sites of 2D MoS2 is reported to tune its electronic and catalytic properties. The key for the successful incorporation of Mn into the MoS2 lattice stems from the development of a new growth technology called dual-additive chemical vapor deposition. First, the addition of a MnO2 additive to the MoS2 growth process reshapes the morphology and increases lateral size of Mn-doped MoS2. Second, a NaCl additive helps in promoting the substitutional doping and increases the concentration of Mn dopant to 1.7 at%. Because Mn has more valance electrons than Mo, its doping into MoS2 shifts the Fermi level toward the conduction band, resulting in improved electrical contact in field effect transistors. Mn doping also increases the hydrogen evolution activity of MoS2 electrocatalysts. This work provides a growth method for doping nonlike elements into 2D MoS2 and potentially many other 2D materials to modify their properties.

H-2 is considered an indispensable component of the atmosphere for the growth of high-quality single-wall carbon nanotubes (SWCNTs) by chemical vapor deposition. However, details of the roles H-2 playing are still unclear due to the complex conditions of SWCNT growth. In this study, we elucidate the functions of H-2 in the selective growth of semiconducting SWCNTs (s-SWCNTs) by using monodispersed uniform Fe nanoparticles as a catalyst. High-quality s-SWCNTs were synthesized by finely tuning the concentration of H-2 and the other growth parameters. Experimental data combined with atomistic simulations indicate that H-2 not only adjusts the concentration of the carbon source, but also serves as a mild etchant that selectively removes small carbon caps grown by a perpendicular mode from the Fe nanoparticles. These results provide useful hints for the controlled growth of SWCNTs with a semiconducting or metallic conductivity, and even a specific chirality. (C) 2020 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Abstract The great interest in rechargeable Zn–air batteries (ZABs) arouses extensive research on low‐cost, high‐active, and durable bifunctional electrocatalysts to boost the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). It remains a great challenge to simultaneously host high‐active and independent ORR and OER sites in a single catalyst. Herein a dual‐phasic carbon nanoarchitecture consisting of a single‐atom phase for the ORR and nanosized phase for the OER is proposed. Specifically, single Co atoms supported on carbon nanotubes (single‐atom phase) and nanosized Co encapsulated in zeolitic‐imidazole‐framework‐derived carbon polyhedron (nanosized phase) are integrated together via carbon nanotube bridges. The obtained dual‐phasic carbon catalyst shows a small overpotential difference of 0.74 V between OER potential at 10 mA cm −2 and ORR half‐wave potential. The ZAB based on the bifunctional catalyst demonstrates a large power density of 172 mW cm −2 . Furthermore, it shows a small charge‐discharge potential gap of 0.51 V at 5 mA cm −2 and outstanding discharge‐charge cycling durability. This study provides a feasible design concept to achieve multifunctional catalysts and promotes the development of rechargeable ZABs.

[Display omitted] Currently, the demand for clean energy to replace fossil energy is increasing dramatically, which is driving the fast development of lithium batteries and other advanced battery systems with high energy density, high power density, good safety and low price. On the way from laboratory to market, the problems of different materials and battery systems should be overcome first. Therefore, qualitative and quantitative techniques that can operate under real battery working conditions are urgently needed to determine the reasons for these limits and reveal the kinetics and mechanisms of electrochemical reactions. In this review, such in-situ imaging techniques are introduced in detail with the aim of obtaining a better understanding of their functions and limitations, and to promote their wide use to solve the existing problems in advanced batteries. The limitations of these techniques are also discussed.

High-quality single-wall carbon nanotube (SWCNT) films were lightly fluorinated by treatment with xenon difluoride at room temperature, which led to the formation of ionic C–F bonds on tube walls and controllable p-type doping of the nanotubes. The fluorinated SWCNT films showed improved electronic conductivity and a higher work function. In addition, the fluorination process increased the areal density of SWCNT films and decreased their surface roughness, leading to better interface contact between them and silicon. As a result, a heterojunction solar cell constructed using the lightly fluorinated SWCNT film has a high power conversion efficiency of 13.6% and excellent stability. [Display omitted] •Lightly fluorinated SWCNT (F-SWCNT) film was prepared by simply exposing the free-standing SWCNT film to XeF2 gas at room temperature.•Stable C–F ionic bonds in F-SWCNT film enhanced film conductivity and caused p-type doping effect.•Fluorination improved the areal density of the SWCNT film and decreased its surface roughness.•Owing to excellent photovoltaic properties, the PCE of the F-SWCNT/Si solar cell with an active area of 9 mm2 reached 13.6%.

The photodetector is a key component in optoelectronic integrated circuits. Although there are various device structures and mechanisms, the output current changes either from rectified to fully-on or from fully-off to fully-on after illumination. A device that changes the output current from fully-off to rectified should be possible. We report the first photon-controlled diode based on a n/n(-) molybdenum disulfide junction. Schottky junctions formed at the cathode and anode either prevent or allow the device to be rectifying, so that the output current of the device changes from fully-off to rectified. By increasing the thickness of the photogating layer, the behavior of the device changes from a photodetector to a multifunctional photomemory with the highest non-volatile responsivity of 4.8 x 10(7) A/W and the longest retention time of 6.5 x 10(6) s reported so far. Furthermore, a 3 x 3 photomemory array without selectors shows no crosstalk between adjacent devices and has optical signal-processing functions including wavelength and power-density selectivity. Photon-controlled diodes, as a new circuit element proposed for the first time, change the output current from a fully-off state to a rectified state after illumination, which paves the way for future highly integrated, low-power, intelligent optoelectronic systems.

High-purity and well-graphitized single-walled carbon nanotubes (SWCNTs) with excellent physiochemical properties are ideal building blocks for the assembly of various CNT macrostructures for a wide range of applications. We report the preparation of high-quality SWCNTs on a large scale using a floating catalyst chemical vapor deposition (FCCVD) method. Under the optimum conditions, the conversion rate of the carbon source to SWCNTs reached 28.8%, and 20.4% of the metal nanoparticles were active for SWCNT growth, which are 15% and similar to 400 times higher than those previously reported for FCCVD synthesis, respectively. As a result, the prepared SWCNTs have a very low residual catalyst content of similar to 1.9 wt % and a high rapid oxidation temperature of 717 degrees C. Using these high-quality SWCNTs, we spun macroscopic SWCNT fibers by a wet-spinning process. The resulting fibers had a high electrical conductivity of 6.67 MS/m, which is 32% higher than the best value previously reported for SWCNT fibers.

Sustainable recycle of spent Li ion batteries is an effective strategy to alleviate environmental concerns and support resource conservation. Here, authors report the direct regeneration of LiFePO4 cathode using multifunctional organic lithium salts, leading to high environmental and economic benefits. The recycling of spent lithium-ion batteries is an effective approach to alleviating environmental concerns and promoting resource conservation. LiFePO4 batteries have been widely used in electric vehicles and energy storage stations. Currently, lithium loss, resulting in formation of Fe(III) phase, is mainly responsible for the capacity fade of LiFePO4 cathode. Another factor is poor electrical conductivity that limits its rate capability. Here, we report the use of a multifunctional organic lithium salt (3,4-dihydroxybenzonitrile dilithium) to restore spent LiFePO4 cathode by direct regeneration. The degraded LiFePO4 particles are well coupled with the functional groups of the organic lithium salt, so that lithium fills vacancies and cyano groups create a reductive atmosphere to inhibit Fe(III) phase. At the same time, pyrolysis of the salt produces an amorphous conductive carbon layer that coats the LiFePO4 particles, which improves Li-ion and electron transfer kinetics. The restored LiFePO4 cathode shows good cycling stability and rate performance (a high capacity retention of 88% after 400 cycles at 5 C). This lithium salt can also be used to recover degraded transition metal oxide-based cathodes. A techno-economic analysis suggests that this strategy has higher environmental and economic benefits, compared with the traditional recycling methods.

Sodium-ion batteries (SIBs) based on conversion-type metal sulfide (MS) anodes have attracted extraordinary attention due to relatively high capacity and intrinsic safety. The highly reversible conversion of M/Na2S to pristine MS in charge plays a vital role with regard to the electrochemical performance. Here, taking conventional MoS2 as an example, guided by theoretical simulations, a catalyst of iron single atoms on nitrogen-doped graphene (SAFe@NG) is selected and first used as a substrate to facilitate the reaction kinetics of MoS2 in the discharging process. In the following charging process, using a combination of spectroscopy and microscopy, it is demonstrated that the SAFe@NG catalyst enables an efficient reversible conversion reaction of Mo/Na2S -> NaMoS2 -> MoS2. Moreover, theoretical simulations reveal that the reversible conversion mechanism shows favorable formation energy barrier and reaction kinetics, in which SAFe@NG with the Fe-N-4 coordination center facilitates the uniform dispersion of Na2S/Mo and the decomposition of Na2S and NaMoS2. Therefore, efficient reversible conversion reaction MoS2 NaMoS2 Mo/Na2S is enabled by the SAFe@NG catalyst. This work contributes new avenues for designing conversion-type materials with an efficient reversible mechanism.

Substitutional doping provides an effective strategy to tailor the properties of 2D materials, but it remains an open challenge to achieve tunable uniform doping, especially at high doping level. Here, uniform lattice substitution of a 2D Mo2C superconductor by magnetic Cr atoms with controlled concentration up to ≈46.9 at% by chemical vapor deposition and a specifically designed Cu/Cr/Mo trilayer growth substrate is reported. The concentration of Cr atoms can be easily tuned by simply changing the thickness of the Cr layer, and the samples retain the original structure of 2D Mo2C even at a very high Cr concentration. The controlled uniform Cr doping enables the tuning of the competition of the 2D superconductor and the Kondo effect across the whole sample. Transport measurements show that with increasing Cr concentration, the superconductivity of the 2D Cr‐doped Mo2C crystals disappears along with the emergence of the Kondo effect, and the Kondo temperature increases monotonously. Using scanning tunneling microscopy/spectroscopy, the mechanism of the doping level effect on the interplay and evolution between superconductivity and the Kondo effect is revealed. This work paves a new way for the synthesis of 2D materials with widely tunable doping levels, and provides new understandings on the interplay between superconductivity and magnetism in the 2D limit. Controlled uniform lattice substitution of a 2D Mo2C superconductor by magnetic Cr atoms is performed through chemical vapor deposition, with the Cr concentration up to ≈46.9 at%. The controlled substitutional doping enables the tuning of the competition of the 2D superconductor and the Kondo effect across the whole sample, and the Kondo effect with a high Kondo temperature is achieved at high Cr concentration.

We demonstrate the first 2D mica RRAM device, which exhibit unique non-Markov chain characteristic. The migration of inner K+ in mica under electrical field is responsible for this unique transport behavior. Our work shows great potential of 2D mineral materials for electronics. [Display omitted] The non-Markov process exists widely in thermodymanic process, while it usually requires the packing of many transistors and memories with great system complexity in a traditional device structure to minic such functions. Two-dimensional (2D) material-based resistive random access memory (RRAM) devices have the potential for next-generation computing systems with much-reduced complexity. Here, we achieve a non-Markov chain in an individual RRAM device based on 2D mineral material mica with a vertical metal/mica/metal structure. We find that the potassium ions (K+) in 2D mica gradually move in the direction of the applied electric field, making the initially insulating mica conductive. The accumulation of K+ is changed by an electric field, and the 2D-mica RRAM has both single and double memory windows, a high on/off ratio, decent stability, and repeatability. This is the first time a non-Markov chain process has been established in a single RRAM, in which the movement of K+ is dependent on the stimulated voltage as well as their past states. This work not only uncovers an intrinsic inner ionic conductivity of 2D mica, but also opens the door for the production of such RRAM devices with numerous functions and applications.

Ferroelectric materials hold great promise in the field of photocatalytic water splitting due to their spontaneous polarization that sets up an inherent internal field for the spatial separation of photogenerated charges. The ferroelectric polarization, however, is generally accompanied by some intrinsic defects, particularly oxygen vacancies, whose impact upon photocatalysis is far from being fully understood and modulated. Here, we have studied the role of oxygen vacancies over the photocatalytic behavior of single-domain PbTiO3 through a combination of theoretical and experimental viewpoints. Our results indicate that the oxygen vacancies in the negatively polarized facet (001) are active sites for water oxidation into O-2, while the defect-free sites prefer H2O2 as the oxidation product. The apparent quantum yield at 435 nm for photocatalytic overall water splitting with PbTiO3/Rh/Cr2O3 is determined to be 0.025%, which is remarkable for single undoped metal oxide-based photocatalysts. Furthermore, the strong correlation among oxygen vacancies, polarization strength, and photocatalytic activity is properly reflected by charge separation conditions in the single-domain PbTiO3 . This work clarifies the crucial role of oxygen vacancies during photocatalytic reactions of PbTiO3, which provides a useful guide to the design of efficient ferroelectric photocatalysts and their water redox reaction pathways.

Electrochemical capacitors (ECs), including electrical-double-layer capacitors and pseudocapacitors, feature high power densities but low energy densities. To improve the energy densities of ECs, redox electrolyte-enhanced ECs (R-ECs) or supercapbatteries are designed through employing confined soluble redox electrolytes and porous electrodes. In R-ECs the energy storage is based on diffusion-controlled faradaic processes of confined redox electrolytes at the surface of a porous electrode, which thus take the merits of high power densities of ECs and high energy densities of batteries. In the past few years, there has been great progress in the development of this energy storage technology, particularly in the design and synthesis of novel redox electrolytes and porous electrodes, as well as the configurations of new devices. Herein, a full-screen picture of the fundamentals and the state-of-art progress of R-ECs are given together with a discussion and outlines about the challenges and future perspectives of R-ECs. The strategies to improve the performance of R-ECs are highlighted from the aspects of their capacitances and capacitance retention, power densities, and energy densities. The insight into the philosophies behind these strategies will be favorable to promote the R-EC technology toward practical applications of supercapacitors in different fields.

Atomically thin two-dimensional (2D) semiconductors are promising for next-generation memory to meet the scaling down of semiconductor industry. However, the controllability of carrier trapping status, which is the key figure of merit for memory devices, still halts the application of 2D semiconductor-based memory. Here, we introduce a scheme for 2D material based memory using wrinkles in monolayer 2D semiconductors as controllable carrier trapping centers. Memory devices based on wrinkled monolayer MoS2 show multilevel storage capability, an on/off ratio of 106, and a retention time of >104 s, as well as tunable linear and exponential behaviors at the stimulation of different gate voltages. We also reveal an interesting wrinkle-based carrier trapping mechanism by using conductive atomic force microscopy. This work offers a configuration to control carriers in ultrathin memory devices and for in-memory calculations.

As one of the CO2 capture and utilization technologies, Li-CO2 batteries have attracted special interest in the application of carbon neutral. However, the design and fabrication of a low-cost high-efficiency cathode catalyst for reversible Li2CO3 formation and decomposition remains challenging. Here, guided by theoretical calculations, CO2 was utilized to activate the catalytic activity of conventional nitrogen-doped graphene, in which pyridinic-N and pyrrolic-N have a high total content (72.65%) and have a high catalytic activity in both CO2 reduction and evolution reactions, thus activating the reversible conversion of Li2CO3 formation and decomposition. As a result, the designed cathode has a low voltage gap of 2.13 V at 1200 mA g–1 and long-life cycling stability with a small increase in the voltage gap of 0.12 V after 170 cycles at 500 mA g–1. Our work suggests a way to design metal-free catalysts with high activity that can be used to activate the performance of Li-CO2 batteries.

[Display omitted] Memristor-based neuromorphic computing is promising for artificial intelligence. However, most of the reported memristors have limited linear computing states and consume large operation energy which hinder their applications. Herein, we report a memristor based on ionic two-dimensional CuInP2S6 (2D CIPS), in which up to 1350 linear conductance states are achieved by controlling the migration of internal Cu ions in CIPS. In addition, the device shows a low operation current of ∼100 pA. Cu ions are proven to move along the electric field by in-situ scanning electron microscopy and energy dispersive spectroscopy measurements. Furthermore, complex signal transport among multiple neurons in the brain is imitated by 2D CIPS-based memristor arrays. Our results offer a new platform to fabricate high-performance memristors based on ion transport in 2D materials for neuromorphic computing.

Single-wall carbon nanotubes (SWCNTs) with ultra-thin channels are considered promising nanoreactors for confined catalysis, chemical reactions, and drug delivery. The fabrication of SWCNT nanoreactors by cutting usually suffers from low efficiency and poor controllability. Here we develop a defect-induced gas etching method to efficiently cut SWCNTs and to obtain nanoreactors with ultrasmall confined space. H plasma treatment was performed to generate defects in the walls of SWCNTs, then H O vapor was used as a "knife" to cut SWCNTs at the defect sites, and short cut-SWCNTs with an average length of 175 nm were controllably obtained with a high yield of 75% under optimized conditions. WO @SWCNT derivatives with different morphologies were synthesized using short cut-SWCNTs as nanoreactors. The radiation resistance of WO @SWCNT hybrids improved obviously, thus providing a platform for the synthesis of novel SWCNT-based derivatives with fascinating properties.

Six-membered-ring (SMR) inorganic materials have many common features. They can be exfoliated to 2D nanostructures, or grown into 2D nanostructures with appropriate base materials, then assembled to unique microstructures/macrostructures; most of them can achieve both fast electron mobility and high density of state with unique topological state; and their microstructures and electronic structures can be controlled to realize a variety of functions. Aiming to better understand the functions and develop the potential applications for electrochemical reactions, we summarize three main application scenarios of SMR inorganic materials: charge storage, reaction confinement, and reaction acceleration. The functions and mechanisms of SMR inorganic materials to modifying the electrochemical reactions are well discussed. Finally, further developments of SMR inorganic materials for electrochemical reactions are reviewed. SMR inorganic materials have a common six-membered-ring basic unit, which endows them with unique nanostructures and electronic structures.The atom types and combinations of the units of SMR inorganic materials vary substantially, leading to unique properties and electrochemical applications.Based on universality and individuality, various SMR inorganic materials are suitable for electrochemical applications, such as charge storage, reaction confinement, and reaction acceleration.

A large amount of spent LiFePO4 (LFP) has been produced in recent years because it is one of the most widely used cathode materials for electric vehicles. The traditional hydrometallurgical and pyrometallurgical recycling methods are doubted because of the economic and environmental benefits; the direct regeneration method is considered a promising way to recycle spent LFP. However, the performance of regenerated LFP by direct recycling is not ideal due to the migration of Fe ions during cycling and irreversible phase transition caused by sluggish Li+ diffusion. The key to addressing the challenge is to immobilize Fe atoms in the lattice and improve the Li+ migration capability during cycling. In this work, spent LFP is regenerated by using environmentally friendly ethanol, and its cycling stability is promoted by elevating the d-band center of Fe atoms via construction of a heterogeneous interface between LFP and nitrogen-doped carbon. The Fe-O bonding is strengthened and the migration of Fe ions during cycling is suppressed due to the elevated d-band center. The Li+ diffusion kinetics in the regenerated LFP are improved, leading to an excellent reversibility of the phase transition. Therefore, the regenerated LFP exhibits an ultrastable cycling performance at a high rate of 10 C with approximate to 80% capacity retention after 1000 cycles.

Table of contents: This review focuses on the development of devices combining three-dimensional structures and low-dimensional materials. With the deep explore of nano-devices, the improvement of device performance may not only depend on innovation at a certain level. By combining these two key design strategies, it is expected to achieve the highest gate control ability and device density in the post-Moore’s law era. [Display omitted] Since the 1960s, the feature size of metal oxide semiconductor field-effect transistors has been scaled down to sub-micrometer and even nanometer to increase the transistor density on a chip according to the Moore’s law, leading to smaller device, faster speed and lower power consumption. In this process, various new materials and technologies have been introduced including SiGe strained silicon and high-k metal gate. Today, tremendous efforts are being made for the use of three-dimensional (3D) technologies such as fin-structured field-effect transistors, gate-all-around field-effect transistors and 3D integration. At the same time, low-dimensional materials such as carbon nanotubes, graphene and transition metal dichalcogenides are being extensively studied for nano-device fabrication. Here, the development of devices using both 3D structures and low-dimensional materials is reviewed. By combining these two key strategies, 3D transistors and integration based on low-dimensional materials are expected to achieve the highest gate control ability and device density, which is promising to continue the Moore’s law even further.

Monolayer transition metal dichalcogenides are 2D materials with many potential applications. Chemical vapor deposition (CVD) is a promising method to synthesize these materials. However, CVD-grown materials generally have poorer quality than mechanically exfoliated ones and contain more defects due to the difficulties in controlling precursors' distribution and concentration during growth where solid precursors are used. Here, thiol is proposed to be used as a liquid precursor for CVD growth of high quality and uniform 2D MoS2. Atomic-resolved structure characterizations indicate that the concentration of sulfur vacancies in the MoS(2)grown from thiol is the lowest among all reported CVD samples. Low temperature spectroscopic characterization further reveals the ultrahigh optical quality of the grown MoS2. Density functional theory simulations indicate that thiol molecules could interact with sulfur vacancies in MoS(2)and repair these defects during the growth of MoS2, resulting in high-quality MoS2. This work provides a facile and controllable method for the growth of high-quality 2D materials with ultralow sulfur vacancies and high optical quality, which will benefit their optoelectronic applications.

The recycling of spent lithium-ion batteries (LIBs) has become a necessity for recovering valuable resources and protecting the environment to support sustainable development. We report the design of a highly efficient CoFe/C catalyst by combining the Co and Fe wastes from spent LIBs with sawdust-derived carbon, which were cathode materials in zinc- air batteries (ZABs). As a result of the electrostatic attraction between the Co3+/Fe3+ cations and the hydroxyl groups in sawdust, CoFe nanoparticles are uniformly dispersed in the CoFe/C catalyst after annealing. The Fe atoms in the CoFe nanoparticles are all isolated into single sites by the Co atoms, which redistribute the electrons in the CoFe/C catalyst. The catalyst produced a Pt-like dissociative mechanism, contribu ting to an excellent oxygen reduction reaction performance. After assembly in ZABs, the CoFe/C catalyst cathode exhibits a long cycling stability of 350 h and an impressive power density of 199.2 mW cm(-2). The CoFe/C catalyst cathode has also been used in flexible ZABs to power LEDs or charge a mobile phone. The work combines spent LIBs with sawdust to fabricate high-performance catalysts, which could reduce environmental pollution and realize high economic value.

High-melting point alloy catalysts have been reported to be effective for the structure-controlled growth of single-wall carbon nanotubes (SWCNTs). However, some fundamental issues remain unclear because of the complex catalytic growth environment. Here, we directly investigated the active catalytic phase of Co-W-C alloy catalyst, the growth kinetics of CNTs, and their interfacial dynamics using closed-cell environmental trans-mission electron microscopy at atmospheric pressure. The alloy catalyst was precisely identified as a cubic eta- carbide phase that remained unchanged during the whole CNT growth process. Rotations of the catalyst nano -particles during CNT growth were observed, implying a weak interfacial interaction and undefined orientation dependence for the solid catalyst. Theoretical calculations suggested that the growth kinetics are determined by the diffusion of carbon atoms on the surface of the eta-carbide catalyst and through the interface of the catalyst-CNT wall.

Moire superlattices of van der Waals heterostructures provide a powerful way to engineer electronic structures of two-dimensional materials. Many novel quantum phenomena have emerged in graphene and transition metal dichalcogenide moire systems. Twisted phosphorene offers another attractive system to explore moire physics because phosphorene features an anisotropic rectangular lattice, different from isotropic hexagonal lattices previously reported. Here we report emerging anisotropic moire optical transitions in twisted monolayer/bilayer phosphorenes. The optical resonances in phosphorene moire superlattice depend sensitively on twist angle and are completely different from those in the constitute monolayer and bilayer phosphorene even for a twist angle as large as 19 degrees. Our calculations reveal that the Gamma -point direct bandgap and the rectangular lattice of phosphorene give rise to the remarkably strong moire physics in large-twist-angle phosphorene heterostructures. This work highlights fresh opportunities to explore moire physics in phosphorene and other van der Waals heterostructures with different lattice configurations. Twisted phosphorene offers another attractive system to explore moire physics. Here, the authors report emerging anisotropic moire optical resonances in twisted monolayer/bilayer phosphorene, exhibiting strong twist dependence for angles as large as 19 degrees.

[Display omitted] •Trap concentration is important for trap-controlled RRAM with SCLC conduction.•A flexible multi-level NiPc RRAM is explored due to its high trap-concentration.•NiPc film provides numerous traps, enabling effective resistance switching.•NiPc RRAM shows the flexibility, reliability, uniformity and multi-level capability.•A fast operation speed is also primary for NiPc RRAM. Metal phthalocyanine is considered one of the most promising candidates for the design and fabrication of flexible resistive random access memory (RRAM) devices due to its intrinsic flexibility and excellent functionality. However, performance degradation and the lack of multi-level capability, which can directly expand the storage capacity in one memory cell without sacrificing additional layout area, are the primary obstacles to the use of metal phthalocyanine RRAMs in information storage. Here, a flexible RRAM with pristine nickel phthalocyanine (NiPc) as the resistive layer is reported for multi-level data storage. Due to its high trap-concentration, the charge transport behavior of the device agrees well with classical space charge limited conduction controlled by traps, leading to an excellent performance, including a high on-off current ratio of 107, a long-term retention of 106 s, a reproducible endurance over 6000 cycles, long-term flexibility at a bending strain of 0.6 %, a write speed of 50 ns under sequential bias pulses and the capability of multi-level data storage with reliable retention and uniformity.

Rechargeable zinc–air batteries (ZABs) have stimulated extensive interests, but the slow reaction kinetics of oxygen reactions hinder their further development. Here a bifunctional oxygen electrocatalyst enriched with both single Fe atoms and NiFe2O4 nanoparticles is designed to mitigate this issue. Specifically, iron phthalocyanine with single–atom Fe–N4 moiety is coupled with graphene by π−π stacking interaction to accelerate the oxygen reduction reaction (ORR) during discharging, while NiFe–based Prussian blue analogue derived NiFe2O4 nanoparticles are anchored on graphene to promote the oxygen evolution reaction (OER) during charging. The catalyst shows a small overpotential difference of 0.72 V between OER potential at 10 mA cm–2 and ORR half–wave potential. When used as an oxygen electrode catalyst, the corresponding ZAB exhibits a large power density of 185 mW cm–2, a small charge–discharge voltage gap of 0.717 V at 5 mA cm–2, and outstanding discharge–charge durability without any decay after 1035 cycles. This work offers a new concept to design multifunctional catalysts and stimulates the development of ZABs. [Display omitted] An ingenious strategy is developed to synthesize a graphene–based hybrid consisting of single–atom Fe–N4 moieties for oxygen reduction during discharging and nanosized NiFe2O4 species from for oxygen evolution during charging, showing a large power density of 185 mW cm–2 and outstanding discharge–charge durability without any decay after 1035 cycles for rechargeable Zn-air battery.

Recent progresses in the growth and fabrication techniques for preparing crystalline two-dimensional (2D) superconductors have stimulated intense interest in the studies of the electronic properties of these systems. Here we investigate the superconducting transport properties based on chemical vapor deposition-grown thin NbC crystals consisting of network structures. The 2D character of the superconductivity in individual NbC crystals is revealed by examining the angular dependence of magnetotransport measurements. At low temperatures, the samples show nonmonotonic double-step superconducting transitions as a function of temperature and magnetic field. We demonstrate that the observed transport characteristics can be understood in terms of coupled Josephson junctions forming between isolated NbC crystals, including the effects of Josephson and quasiparticle tunneling. In particular, detailed analysis of the magnetic field-driven transition suggests the existence of quantum flux-creep regime at low temperatures and small magnetic fields in such thin NbC superconducting crystals. Our work underlines the importance of the morphology on the transport properties of 2D superconducting crystals, providing a comprehensive understanding of crystalline 2D superconductors.

Two dimensional transition metal dichalcogenides (TMDCs) have attracted much interest and shown promise in many applications. However, it is challenging to obtain uniform TMDCs with clean surfaces, because of the difficulties in controlling the way the reactants are supplied to the reaction in the current chemical vapor deposition growth process. Here, we report a new growth approach called ‘dissolution-precipitation’ (DP) growth, where the metal sources are sealed inside glass substrates to control their feeding to the reaction. Noteworthy, the diffusion of metal source inside glass to its surface provides a uniform metal source on the glass surface, and restricts the TMDC growth to only a surface reaction while eliminating unwanted gas-phase reaction. This feature gives rise to highly uniform monolayer TMDCs with a clean surface on centimeter-scale substrates. The DP growth works well for a large variety of TMDCs and their alloys, providing a solid foundation for the controlled growth of clean TMDCs by the fine control of the metal source. 2D materials with good quality and ultraclean surface were obtained by a universal dissolution-precipitation growth method that precisely controls the metal source and restricts the growth of materials to surface reaction.

Development of high-performance lithium metal batteries with a wide operating temperature range is highly challenging, especially in carbonate electrolyte. Herein, a multifunctional high-donor-number solvent, tris(pyrrolidinophosphine) oxide (TPPO), is introduced into carbonate electrolyte to regulate both electrode-electrolyte interfaces. On the one hand, lithium nitrate can be easily dissolved in carbonate electrolyte because of the strong interaction between TPPO and Li+, resulting in the formation of a robust and ionic conductive Li3N-rich solid electrolyte interphase, which efficiently inhibits the formation of lithium dendrites. On the other hand, TPPO can be preferentially oxidized into an ultrathin and robust cathode electrolyte interphase, significantly suppressing electrolyte decomposition. As a result, the TPPO-containing electrolyte enables stable lithium stripping/plating cycling performance (1000 h at 3 mA cm(-2) and 3 mAh cm(-2)). Furthermore, Li/LiFePO4 cells exhibit stable cycling performance even at temperatures as high as 70 degrees C and as low as -15 degrees C, demonstrating their potential in temperature tolerance.

Two-dimensional transition metal dichalcogenides (TMDCs) show great potential as efficient catalysts for Li-CO2 batteries. However, the basal plane engineering on TMDCs toward bifunctional catalysts for Li-CO2 batteries is still poorly understood. In this work, density functional theory calculations reveal that nucleophilic N dopants and electrophilic S vacancies in the ReS2 plane tailor the interactions with Li atoms and C/O atoms in intermediates, respectively. The electrophilic and nucleophilic dual centers show suitable adsorption with all intermediates during discharge and charge, resulting in a small energy barrier for the rate-determining step. Thus, an efficient bifunctional catalyst is produced toward Li-CO2 batteries. As a result, the optimal catalyst achieves an ultrasmall voltage gap of 0.66 V and an ultrahigh energy efficiency of 81.1% at 20 μA cm–2, which is superior to those of previous catalysts under similar conditions. The introduction of electrophilic and nucleophilic dual centers provides new avenues for designing excellent bifunctional catalysts for Li-CO2 batteries.

High-purity (∼96%) isolated s-SWCNT film with narrow diameter distribution were prepared on large scale by oxygen-assisted FCCVD method. [Display omitted] •Bulk isolated s-SWCNT films with a high content of 96% were selectively prepared.•O2 was found to play function on catalyst particle size and s-SWCNT diameter.•FET devices show good performance verifying the enrichment of s-SWCNTs. Semiconducting single-wall carbon nanotubes (s-SWCNTs) are promising for use in flexible electronics as a channel material. However, it remains a big challenge to directly grow high purity, high-quality s-SWCNTs in large scale. Here we report the synthesis of isolated s-SWCNTs by an oxygen-assisted floating catalyst chemical vapor deposition method. By controlling the density of nucleated SWCNTs, isolated or small-bundled, rather than large-bundled SWCNTs were generated in a floating state, so that the oxygen introduced could more efficiently selectively etch the metallic-SWCNTs formed. In addition, it was found that the oxygen also functions in limiting the size of Fe catalyst nanoparticles in a narrow range of 5–8 nm. As a result, isolated s-SWCNTs with a narrow diameter distribution were synthesized. The content of s-SWCNTs reached ∼96%, and the percentage of isolated tubes was estimated to be ∼83%. Thin-film transistors (TFTs) constructed using the s-SWCNT film showed high on/off ratios ranging from 2.1 × 104 to 1.2 × 106, verifying the effective enrichment of s-SWCNTs.

In the vicinity of a competing electronic order, superconductivity emerges within a superconducting dome in the phase diagram, which has been demonstrated in unconventional superconductors and transition-metal dichalcogenides (TMDs), suggesting a scenario where fluctuations or a partial melting of a parent order are essential for inducing superconductivity. Here, we present a contrary example, the two-dimensional (2D) superconductivity in transition-metal carbide can be readily turned into charge density wave (CDW) phases via dilute magnetic doping. Low temperature scanning tunneling microscopy/spectroscopy (STM/STS), transport measurements, and density functional theory (DFT) calculations were employed to investigate Cr-doped superconducting Mo2C crystals in the 2D limit. With ultralow Cr doping (2.7 atom %), the superconductivity of Mo2C is heavily suppressed. Strikingly, an incommensurate density wave (IDW) and a related partially opened gap are observed at a temperature above the superconducting regime. The wave vector of IDW agrees well with the calculated Fermi surface nesting vectors. By further increasing the Cr doping level to 9.4 atom %, a stronger IDW with a smaller periodicity and a larger partial gap appear concurrently. The resistance anomaly implies the onset of the CDW phase. Spatial-resolved and temperature-dependent spectroscopy reveals that such CDW phases exist only in a nonsuperconducting regime and could form long-range orders uniformly. The results provide the understanding for the interplay between charge ordered states and superconductivity in 2D transition-metal carbide.

Chemical vapor deposition (CVD) graphene film is a promising electrode-modifying material for fabricating high-performance glucose sensor due to its high electrical conductivity and two-dimensional structure over large area. However, the use of typical metal-based CVD graphene suffers from the residue contamination of polymer transfer-support and heavy metal ions. In this work, we directly grew few-layer graphene on the SiO2/Si substrate without transfer process and then fabricated graphene-based glucose sensors by sequentially immobilizing glucose oxidase and depositing Nafion layer on its surface that was functionalized by oxygen-plasma treatment. Our transfer- and metal-free process shows distinct advantage over the common metal-CVD method in improving the electrochemical performance by eliminating the contamination of transfer-residue. Thus-obtained glucose sensor shows a high sensitivity (16.16 μA mM−1 cm-2) with a detection limit of 124.19 μM. This method is simple and promising for the development of highly sensitive glucose sensors.

Revealing the nucleation and growth mechanism of single-wall carbon nanotubes (SWCNTs) from faceted solid catalysts is crucial to the control of their structure and properties. However, due to the small size and complex growth environment, the early stages and dynamic process of SWCNT nucleation have rarely been directly revealed, especially under atmospheric conditions. Here, we report the atomic-resolved nucleation of SWCNTs from the faces of truncated octahedral Pt catalysts under atmospheric pressure using a transmission electron microscope equipped with a gas-cell. It was found that the graphene layers were initially formed preferentially on (111) surfaces, which then joined together to form an annular belt and a hemispherical cap, followed by the elongation of the SWCNT. Based on the observations, an annular belt assembly nucleation model and a possible chirality control mechanism are proposed for SWCNTs grown from well-faceted Pt catalysts, which provides useful guidance for the controlled synthesis of SWCNTs by catalyst design.

Single-atom metal catalysts (SACs) are used as sulfur cathode additives to promote battery performance, although the material selection and mechanism that govern the catalytic activity remain unclear. It is shown that d-p orbital hybridization between the single-atom metal and the sulfur species can be used as a descriptor for understanding the catalytic activity of SACs in Li-S batteries. Transition metals with a lower atomic number are found, like Ti, to have fewer filled anti-bonding states, which effectively bind lithium polysulfides (LiPSs) and catalyze their electrochemical reaction. A series of single-atom metal catalysts (Me = Mn, Cu, Cr, Ti) embedded in three-dimensional (3D) electrodes are prepared by a controllable nitrogen coordination approach. Among them, the single-atom Ti-embedded electrode has the lowest electrochemical barrier to LiPSs reduction/Li2S oxidation and the highest catalytic activity, matching well with the theoretical calculations. By virtue of the highly active catalytic center of single-atom Ti on the conductive transport network, high sulfur utilization is achieved with a low catalyst loading (1 wt.%) and a high area-sulfur loading (8 mg cm(-2)). With good mechanical stability for bending, these 3D electrodes are suitable for fabricating bendable/foldable Li-S batteries for wearable electronics.

Birefringent optical elements that work in deep ultraviolet (DUV) region become increasingly important these years. However, most of the DUV optical elements have fixed birefringence which is hard to be tuned. Here, we invent a birefringence-tunable optical hydrogel with mechano-birefringence effect in the DUV region, based on two-dimensional (2D) low-cobalt-doped titanate. This 2D oxide material has an optical anisotropy factor of 1.5 x 10(-11) C-2 J(-1) m(-1), larger than maximum value obtained previously, leading to an extremely large specific magneto-optical Cotton-Mouton coefficient of 3.9 x 10(6) T-2 m(-1). The extremely large coefficient enables the fabrication of birefringent hydrogel in a small magnetic field with an ultra-low concentration of 2D oxide material. The hydrogel can stably and continuously modulate 303 nm DUV light with large phase tunability by varying the strain (compression or stretching) from 0 to 50%. Our work opens the door to design and fabricate new proof-of-concept DUV birefringence-tunable element, as demonstrated by optical hydrogels capable of DUV modulation by mechanical stimuli.

Monolithic carbon aerogel composites with low density have been prepared from phenolic resin as a reactive precursor and ultralight and hyper-elastic carbon fiber felt as a soft reinforcement by a low-cost ambient pressure drying approach. During carbonization, the felt shrinks collaboratively with the phenolic aerogel so that the typical shrinkage mismatch between fibers and matrix can be overcome. Therefore, a robust, crack-free and large-size carbon fiber reinforced carbon aerogel composite was obtained, which has a low density (0.16 g cm−3), high compressive strength (0.93 MPa), extremely low thermal conductivity (0.03 Wm−1K−1) and outstanding ultrahigh temperature thermal insulation performance. [Display omitted]

Ultrathin, lightweight, high-strength, and thermally conductive electromagnetic interference (EMI) shielding materials with high shielding effectiveness (SE) are highly desired for next-generation portable and wearable electronics. Pristine graphene (PG) has a great potential to meet all the above requirements, but the poor processability of PG nanosheets hinders its applications. Here, efficient synthesis of highly aligned laminated PG films and nacre-like PG/polymer composites with a superhigh PG loading up to 90 wt% by a scanning centrifugal casting method is reported. Due to the PG-nanosheets-alignment-induced high electrical conductivity and multiple internal reflections, such films show superhigh EMI SE comparable to the reported best synthetic material, MXene films, at an ultralow thickness. An EMI SE of 93 dB is obtained for the PG film at a thickness of approximate to 100 mu m, and 63 dB is achieved for the PG/polyimide composite film at a thickness of approximate to 60 mu m. Furthermore, such PG-nanosheets-based films show much higher mechanical strength (up to 145 MPa) and thermal conductivity (up to 190 W m(-1) K-1) than those of their MXene counterparts. These excellent comprehensive properties, along with ease of mass production, pave the way for practical applications of PG nanosheets in EMI shielding.

The development of low-cost, high-activity, and durable integrated bifunctional flexible air electrodes for use in Zn-air batteries is both challenging and important. We report a simple and scalable electropolymerization method used to prepare an electrode material comprising heavily N-doped carbon covering single-walled carbon nanotube (N/CSWCNT) networks. The resulting core/shell structure of the hybrid electrode enabled the flexibility, mechanics, and three-dimensional interconnected porous structure of SWCNT films while containing abundant pyridinic N, which provided excellent catalytic activity for both the oxygen reduction and evolution reactions (overpotential gap = 0.76 V). A binder-free Zn-air battery using the N/C-SWCNT film as an oxygen electrode was assembled and showed a high peak power density of 181 mW/cm(2), a high specific capacity of 810 mAh/g and stable discharge? charge cycling performance. We also constructed a flexible solid-state Zn-air battery featuring not only a high power density of 22 mW/cm(2) but also good flexibility and stability.

Abundant active sites and their easy accessibility in a stable and conductive structure are of great importance for efficient electrocatalysts. In principle, activated mesoporous single-crystal microparticles can meet these desired requirements. Here, the Fe-doped NiS2 mesoporous single crystal microparticles decorated with FeS clusters on the pore walls (FeS@MSC-NiS2:Fe) are constructed via a pre-decorated and sequentially seeded mesoporous silica template. Throughout the external and internal surfaces, the Fe-doped NiS2 modulated by the adjacent FeS clusters induces favorable charge distributions and promotes the crucial formation of the active Fe/Ni (oxy)hydroxide. Combined with the spatial enrichment effect of the intermediates in the holey space and the boosted charge transfer within the continuous single-crystalline framework, the dually regulated FeS@MSC-NiS2:Fe as ideal integral microreactors show efficient performances in oxygen evolution reaction. In electrochemical tests, the particulate FeS@MSC-NiS2:Fe requires an overpotential of only 236 mV to reach a current density of 10 mA cm-2 and displays fast reaction kinetics with a Tafel slope of 32.4 mV dec(-1). This study provides an important strategy to construct electrocatalysts with highly active sites and good accessibility.

[Display omitted] Semiconductor heterostructures mediated by electrical conductors are very promising for Z-scheme photocatalytic water splitting. In contrast to conventional particulate heterostructures, alternate TiO2 and Cu2O film stripes patterned parallel on a fluorine-doped tin oxide (FTO) conductive substrate was fabricated as a model film photocatalyst to study the characteristics of the photogenerated charge transfer process. The Z-scheme transfer process with an effective transport distance of up to 5 μm occurs only in regions distant from the TiO2/Cu2O strip edges through the FTO substrate from the bottom. In contrast, the transfer of charge around their contact regions follows the conventional transfer process through the TiO2/Cu2O strip interface. These results indicate that the Z-scheme transfer process occurring in such a large region dominates the charge transfer processes in the TiO2/FTO/Cu2O pattern film heterostructure. Importantly, unlike the single component film, which is inactive for photocatalytic overall water splitting, the modified TiO2/Cu2O pattern film can induce photocatalytic overall water splitting at a stoichiometric H2/O2 ratio close to 2:1. These findings have significant implications in designing efficient heterostructures by employing a Z-scheme charge transfer process.

One of the long-sought-after goals in light manipulation is tuning of transmitted interference colours. Previous approaches toward this goal include material chirality, strain and electric-field controls. Alternatively, colour control by magnetic field offers contactless, non-invasive and energy-free advantages but has remained elusive due to feeble magneto-birefringence in conventional transparent media. Here we demonstrate an anomalously large magneto-birefringence effect in transparent suspensions of magnetic two-dimensional crystals, which arises from a combination of a large Cotton-Mouton coefficient and relatively high magnetic saturation birefringence. The effect is orders of magnitude stronger than those previously demonstrated for transparent materials. The transmitted colours of the suspension can be continuously tuned over two-wavelength cycles by moderate magnetic fields below 0.8 T. The work opens a new avenue to tune transmitted colours, and can be further extended to other systems with artificially engineered magnetic birefringence. Materials with tunable transmitted colours are sought after for a range of applications. The authors here present magnetic-field-controlled color tuning in a transparent suspension of 2D crystals with unusually large magneto-birefringence.

Deteriorating interfacial contact under mechanical deformation induces large cracks and high charge transfer resistance, resulting in a severe capacity fading of flexible lithium-ion batteries (LIBs). Herein, an oxygen plasma treatment on a polymer separator combined with high-speed centrifugal spraying to construct ultrastable interfacial contacts is reported. With the treatment, abundant hydrophilic oxygen-containing functional groups are produced and ensure strong chemical adhesion between the separator and the active materials. With single walled carbon nanotubes (SWCNTs) sprayed onto the active materials, a dense thin film is formed as the current collector. Meanwhile, the centrifugal force caused by high-speed rotation together with van der Waals forces under fast evaporation produces a much closer interface between the current collector and the active materials. As a result of this ultrastable interfacial interaction, the integrated electrode shows no structural failure after 5000 bending cycles with the charge-transfer resistance as low as 35.8% and a Li-ion diffusion coefficient nearly 19 times of the untreated electrode. Flexible LIBs assembled with these integrated electrodes show excellent structural and electrochemical stability, and can work steadily under various deformed states and repeated bending. This work provides a new technique toward rational design of electrode configuration for flexible LIBs.

Superconducting wire-networks are paradigms to study Cooper pairing issues, vortex dynamics and arrangements. Recently, emergent low-dimensional crystalline superconductors were reported in the minimal-disorder limit, providing novel platforms to reveal vortices-related physics. Study on superconducting loops with high-crystallinity is thus currently demanded. Here, we report fabrication and transport measurement of finite square-network based on two-dimensional crystalline superconductor Mo2C. We observe oscillations in the resistance as a function of the magnetic flux through the loops. Resistance dips at both matching field and fractional fillings are revealed. Temperature and current evolutions are carried out in magnetoresistance to study vortex dynamics. The amplitude of oscillation is enhanced due to the interaction between thermally activated vortices and the currents induced in the loops. The driving current reduces the effective activation energy for vortex, giving rise to stronger vortex interaction. Moreover, by the thermally activated vortex creep model, we derive the effective potential barrier for vortex dissipation, which shows well-defined correspondence with structures in magnetoresistance. Our work shows that low-dimensional crystalline superconducting network based on Mo2C possesses pronounced potential in studying the modulation of vortex arrangements and dynamics, paving the way for further investigations on crystalline superconducting network with various configurations.

Solid polymer electrolytes (SPEs) are being intensively pursued as a means to develop safe, stable and long-life Li-ion batteries. However, the low Li+ conductivity and transference number in SPEs still impede all-solid-state polymer batteries from practical commercialization. Here, lithium polysulfides that cause a shuttle effect problem in Li–S batteries are reduced on a Poly(ethylene oxide) (PEO) chain as an effective way to stimulate Li+ transport. It is shown that the product of the reduction (main –S4Li) dramatically increases Li+ transport while forming a strong interaction with the PEO matrix through intermolecular interactions. In contrast to PEO electrolytes, the –S4Li grafted electrolyte membranes have a lithium transfer number almost 3 times higher, and the LiFePO4|ScPEO|Li cell shows an ultra-long cycle life exceeding 1200 cycles with a capacity decay of 0.024% per cycle at 1 C. The results reveal lithium polysulfides tremendous potential in a solid-state electrolyte system for improving the ion transport and cycling stability. Lithium polysulfides grafted on a polyethylene oxide (PEO) chain is obtained through in situ reduction of polysulfide-bridged copolymer in solid polymer electrolyte. The -S4Li dramatically increases Li+ transport while forming a strong interaction with the PEO matrix through intermolecular interactions, which also achieves the stable and intimate electrode-electrolyte interface in the cell. [Display omitted] •Lithium polysulfides are reduced on a PEO chain as an effective way to stimulate Li+ transport.•The RS4Li grafted on PEO electrolytes have a high ionic conductivity of 2.13*10−4 S/cm at 50 °C.•The RS4Li can form strong interaction with PEO matrix and loosen O–Li+ coordination.•The organic lithium polysulfide is a very attractive material for solid-state electrolytes.

Solid-state lithium-metal batteries (SLMBs) have been regarded as one of the most promising next-generation devices because of their potential high safety, high energy density, and simple packing procedure. However, the practical applications of SLMBs are restricted by a series of static and dynamic interfacial issues, including poor interfacial contact, (electro-)chemical incompatibility, dynamic Li dendrite penetration, etc. In recent years, considerable attempts have been made to obtain mechanistic insight into interfacial failures and to develop possible strategies towards excellent interfacial properties for SLMBs. The static and dynamic failure mechanisms at interfaces between solid electrolytes (SEs) and electrodes are comprehensively summarized, and design strategies involving interfacial modification, electrode/SE engineering, and the monolithic construction of SLMBs are discussed in detail. Finally, possible research methodologies such as theoretical calculations, advanced characterization techniques, and versatile design strategies are provided to tackle these interfacial problems.

Flexible organic photodetectors that are lightweight, conformable, cost-effective, and compatible with large-scale processing techniques will meet the demands of next-generation wearable devices in the era of Internet of Things (IoT). Recent advances in various flexible organic photodetectors and their accompanied signal processing circuits have greatly enriched the application scenarios of wearable devices. This review provides a comprehensive summary of general design principles for organic photodetectors, addresses the device architecture and signal processing relations, reveals the challenges in improving the performance of flexible device units and their integrated systems, and highlights methodologies in concrete scenarios for precision design and optimization.

Floating catalyst chemical vapor deposition (FCCVD) has been one of the most important techniques for the synthesis of high-quality single-, double-, and multi-wall carbon nanotubes (CNTs). The method is characterized of simple processing, good controllability, and desirable scalability. The bulk morphologies of the synthesized CNTs can be sponge-like, an array, a thin film, or fiber by simply changing the growth parameters and the way they are collected, which facilitates a wide range of applications. The authors comprehensively review the state-of-the-art progress on the controlled growth of CNTs by FCCVD which have a defined number of walls, and controlled diameter, bundle size, and type of conductivity. The properties and possible applications for the CNTs and their hybrids are summarized. Finally, insights into the key challenges and prospects for CNTs synthesized by FCCVD are discussed.

Tattoo electronics, flexible patches that mount directly onto the skin with the ease and flexibility of a temporary tattoo, have foreseen remarkable application potentials in personalized healthcare monitoring and human-machine interfaces. Documented tattoo electronics mostly have an on-skin form factor to date. Using dermal tattoos for in vivo diagnostics presents an unexplored paradigm. Here, we extend the application scenario of “tattoo electrodes” from an on-skin fashion to an actual under-skin configuration, enabled by a highly soft, conductive, and biocompatible polymer matrix. With printed ultrathin electrodes, we achieve a record-high conductivity and record-low skin contact impedance, allowing the design of a single-lead electrocardiogram system for seamless wearing and precise detection of intervals and rhythms in dynamic conditions. Furthermore, the biocompatible ink enables the development of dermal electrodes by virtue of tattoo artistry. It shows enormous potential for electrical communication between bioelectronics and biological tissues at a deep-tissue level. [Display omitted] •Extending “tattoo electrodes” from on-skin to an actual under-skin configuration•High-quality in vitro and in vivo electrophysiology using conductive polymer•PEDOT:PSS-based electrodes exhibiting record-high electrical conductivity•Dermal electrodes eliminate unfavorable contact impedance from the stratum corneum Wei et al. report “tattoo electrodes” extended from an on-skin to an actual under-skin configuration, enabled by highly soft, conductive, and biocompatible polymer blends. An ultraflexible and wearable system for electrophysiological recording is demonstrated. Dermal electrodes further eliminate unfavorable contact impedance from the stratum corneum, showing high precision in signal acquisition.

Precursor infiltration and pyrolysis (PIP) has been widely used to fabricate C/C-SiC-ZrC composites. However, the use of organic polymeric precursor of zirconium carbide (PZC) can usually cause the degradation of their mechanical property due to the reaction of ZrO2 intermediate with pyrocarbon (PyC) and carbon fibers (Cf) during pyrolysis. In this study, pitch resin was directly added into the mixture solution of PZC and polycarbosilane (PCS) to supply extra carbon. The composition, microstructure and mechanical property of the as-prepared composites were investigated systematically. The pure ZrC-SiC with a high ZrC content is obtained at 1500 °C when the PZC/PCS/resin mass ratio is 20:1:5. The resulting C/C-SiC-ZrC composites have the highest flexural strength of 247.4 MPa since the degradation of PyC and Cf is greatly alleviated by the addition of resin. The damage mechanism of PyC and Cf during pyrolysis was revealed under the different fabrication conditions. •The C/C-SiC-ZrC composites with a high ZrC/SiC volume ratio were prepared by adding pitch resin to precursors.•The resultant composites have an improved mechanical property due to the reduced damage of PyC and Cf.•The damage mechanism of PyC and Cf during pyrolysis was revealed based on the reactivity and diffusion of carbon.

Developing highly efficient oxygen evolution reaction (OER) catalysts for electrolytic water splitting is urgently desirable but remains a challenge due to sluggish kinetic process of water oxidation. Herein, we report a one-step electrodeposition strategy to prepare Ni(OH)(2) modified with Ir single-atom catalysts (SACs) (Ir SACs/Ni(OH)(2)) on an electrically conductive substrate of three dimensional (3D) hierarchical porous nickel foam (HP-NF) as efficient OER electrocatalyst. The HP-NF with abundant open pores can not only enable the full exposure of catalytically active sites but also facilitate the diffusion of electrolyte and release of gaseous oxygen produced. The optimal Ir SACs/Ni(OH)(2)@HP-NF exhibits a remarkable catalytic performance and outstanding stability for the OER activity in 1.0 M KOH alkaline media, delivering a low overpotential of similar to 223 mV at a current density of 10 mA.cm(-2) and a low Tafel plot of 58 mV-dec(-1). Various characterizations together with control electrochemical experiments demonstrated that the superior activity and robust stability of Ir SACs/Ni(OH)(2)@HP-NF for OER are originated from the highly distributed and exposed Ir SACs and 3D interconnected pores of HP-NF with high electric conductivity.

Fast-charging batteries have attracted great attention, and are anticipated to charge electrical vehicles and consumer electronics to full-capacity in several minutes. However, commercial electrode materials in batteries generally have a limited rate performance and are difficult to be used in fast-charging batteries. Designing electrodes with an aligned structure is an effective way to shorten the ion transport path and improve the rate performance of a battery. The excellent electronic conductivity of carbon-based electrodes is another key factor for increasing the rate capability of rechargeable batteries. Therefore, aligned carbon-based electrodes (ACBEs) can significantly improve the power density by combining the advantages of an aligned structure and carbon-based materials. In this review, the mechanism, advantages, and challenges of ACBEs for fast-charging batteries are evaluated, and then the design and preparation methods of ACBEs based on their different dimensions are summarized, and their applications in different batteries are illustrated. Finally, the future development of ACBEs for fast-charging batteries is considered.

Two-dimensional (2D) materials possess unique thickness- and lateral-size-dependent properties. Many efforts have been devoted to obtaining 2D materials with narrow structure heterogeneity while it is still challenging to independently control their thickness and lateral size, limiting their widespread applications. Here, we develop a three-step method which achieves independent thickness and lateral size sorting of 2D materials. Taking 2D h-BN flakes as an example, their thickness and lateral size are independently sorted to different fractions with thicknesses smaller than 6 nm. In addition, the 2D h-BN flakes possess narrow distributions of both thickness and lateral size. We further develop a force field extraction method and achieve scalable size sorting of 2D h-BN, which is universal for sorting other 2D materials including MoS2 and graphene oxide. This work reports an effective method to produce structure homogenous 2D materials and will help fundamental studies and applications of 2D materials where thickness and lateral size are of concern.

Two-dimensional (2D) black arsenic phosphorus (b-AsP), as an alloy of black phosphorus (b-P) with arsenic, has attracted great attention because of its outstanding electronic and optical properties, including high carrier mobility, tunable bandgap and in-plane anisotropy. B-AsP has a smaller bandgap (0.15-0.3 eV) than the b-P bandgap (0.3-2.0 eV), and thus can be used for mid-infrared photodetectors. In addition, both of them can form various van der Waals (vdW) heterojunctions with other 2D materials to realize novel functional optoelectronic devices. Here, we compare the basic characteristics of b-AsP and b-P, including crystal structure, optical properties, band structure, electrical properties and stability, and we summarize the update progress of b-AsP in photo detection, including representatives of phototransistor and photodiode devices. In the last part, the future research directions are discussed.

Hydrogen production coupled with biomass upgrading is vital for future sustainable energy developments. However, most biomass electrooxidation reactions suffer from high working voltage and low current density, which substantially hinder large-scale industrial applications. Herein, we report an acidic hydrogen production system that combined anodic ascorbic acid electrooxidation with cathodic hydrogen evolution. Unlike C-H and O-H bonds cleavage with slow kinetics in conventional organic oxidation, the highly active enol structure in ascorbic acid allows for an ultralow overpotential of only 12 mV@10 mA/cm using Fe single-atom catalysts, and reaches 1 A/cm at only 0.75 V (versus reversible hydrogen electrode) with approximately 100% Faraday efficiency for hydrogen production. Furthermore, the fabricated two-electrode membrane-free electrolyser delivers an industrial current density of 2 A/cm @1.1 V at 60 °C (2.63 kWh/Nm  H ), which requires half of the electricity consumption in conventional water electrolysis (~5 kWh/Nm  H ). This work provides a new avenue for achieving industrial-scale hydrogen production from biomass.

Lithium cobalt oxide (LCO) is widely used in Li-ion batteries due to its high volumetric energy density, which is generally charged to 4.3 V. Lifting the cut-off voltage of LCO from 4.3 V to 4.7 V will increase the specific capacity from 150 to 230 mAh g(-1) with a significant improvement of 53%. However, LCO suffers serious problems of H1-3/O1 phase transformation, unstable interface between cathode and electrolyte, and irreversible oxygen redox reaction at 4.7 V. Herein, interface stabilization and band structure modification are proposed to strengthen the crystal structure of LCO for stable cycling of LCO at an ultrahigh voltage of 4.7 V. Gradient distribution of magnesium and uniform doping of nickel in Li layers inhibit the harmful phase transitions of LCO, while uniform LiMgxNi1-xPO4 coating stabilizes the LCO-electrolyte interface during cycles. Moreover, the modified band structure improves the oxygen redox reaction reversibility and electrochemical performance of the modified LCO. As a result, the modified LCO has a high capacity retention of 78% after 200 cycles at 4.7 V in the half cell and 63% after 500 cycles at 4.6 V in the full cell. This work makes the capacity of LCO one step closer to its theoretical specific capacity.

Graphene oxide (GO) has received considerable attention for glucose detection because of high surface area, abundant functional groups, and good biocompatibility. Defects and functional groups of the GO are beneficial to immobilization of glucose oxidase (GOD), but sacrificing electron-transfer capability for highly-sensitive detection. In order to obtain high GOD loading and highly-sensitive detection of biosensors, we first designed and fabricated a graphene-laminated electrode by combining GO and edge-functionalized graphene (FG) layers together onto glassy-carbon electrode. The graphene-laminated electrodes exhibited faster electron transfer rate, higher GOD loading of 3.80 × 10−9 mol∙cm-2, and higher detection sensitivity of 46.71 μA∙mM-1∙cm-2 than other graphene-based biosensors reported in literature. Such high performance is mainly attributed to the abundant functional groups of GO, high electrical conductivity of FG, and strong interactions between components in the graphene-laminated electrodes. By virtue of their high enzyme loading and highly-sensitive detection, the graphene-laminated electrodes show great potential to be widely used as high-performance biosensors in the field of medical diagnosis.

Intercalation chemistry/engineering has been widely investigated in the development of electrochemical energy storage. Graphite, as an old intercalation host, is receiving vigorous attention again via a new halogen intercalation. Whereas, exploiting new intercalation hosts and optimizing the intercalation effect still remains a great challenge. This study fabricates a Cu2Se intercalation compound showing expanded interlayer space and nanosheet array features by using a green growth approach, in which cetyltrimethyl ammonium bromide (CTAB) is inserted into Cu2Se at an ambient temperature. When acting as an electrode material for sodium‐ion batteries, the Cu2Se–CTAB nanosheet arrays exhibit excellent discharge capacity and rate capability (426.0 mAh g−1 at 0.1 A g−1 and 238.1 mAh g−1 at 30 A g−1), as well as high capacity retention of ≈90% at 20 A g−1 after 6500 cycles. Benefiting from the porous array architecture, the transport of electrolytes is facilitated on the surface of Cu2Se nanosheets. In particular, the CTAB intercalated in the interlayer space of Cu2Se can increase its buffer space, stabilize the polyselenide shuttle, and prevent the fast growth of Cu nanoparticles during its electrochemical process. A nanosheet array of Cu2Se intercalation compounds with expanded interlayer space is directly grown on Cu foil by the insertion of cetyltrimethyl ammonium bromide (CTAB) at room temperature. The CTAB inserted in the interlayer space provides buffer space for electrochemical volume expansion, confines the fast growth of Cu metal particles and restricts the shuttling of polyselenide intermediates.

A 2D material based liquid-crystal shows an extremely large optical anisotropy factor in the deep ultraviolet region, showing magnetically tunable birefringence. Birefringence is a fundamental optical property that can induce phase retardation of polarized light. Tuning the birefringence of liquid crystals is a core technology for light manipulation in current applications in the visible and infrared spectral regions. Due to the strong absorption or instability of conventional liquid crystals in deep-ultraviolet light, tunable birefringence remains elusive in this region, notwithstanding its significance in diverse applications. Here we show a stable and birefringence-tunable deep-ultraviolet modulator based on two-dimensional hexagonal boron nitride. It has an extremely large optical anisotropy factor of 6.5 x 10(-12) C-2 J(-1) m(-1) that gives rise to a specific magneto-optical Cotton-Mouton coefficient of 8.0 x 10(6) T-2 m(-1), which is about five orders of magnitude higher than other potential deep-ultraviolet-transparent media. The large coefficient, high stability (retention rate of 99.7% after 270 cycles) and wide bandgap of boron nitride collectively enable the fabrication of stable deep-ultraviolet modulators with magnetically tunable birefringence.

Single-wall carbon nanotube (SWCNT)/n-type silicon (n-Si) heterojunctions with a high photoresponsivity are considered promising for use in photodetectors. However, the performance of large-area SWCNT film/n-Si heterojunction-based photodetectors has been much lower than that fabricated using isolated SWCNTs, where the efficient assembly of SWCNT networks with the desired structure is a key issue. In this study, we prepared a small-bundled SWCNT (SB-SWCNT) film with a carbon-welding structure at tube-tube junctions, which greatly decreased the contact resistance and improved the work function. The fabricated SB-SWCNT film/n-Si heterojunction-based photodetectors showed a very high detectability of 4.2 x 10(13) Jones for an 890 nm laser with 0 bias, much higher than that of commercial photodetectors. The detectors also demonstrated good stability with a 97% R value retained after being exposed in air for 30 days, and a broad spectral response (540-1090 nm).

Freestanding membrane electrodes with a high electrocatalytic activity and stability are desirable for use in highperformance metal-air batteries. Here, we report a gas-phase fluorination-assisted method to anchor single atom Fe-Nx moieties on a freestanding single-wall carbon nanotube (SWCNT) film that involves fluorination and defluorination/ammoniation processes. It is shown that the fluorination followed by defluorination/ammoniation harvests Fe atoms from the residual Fe nanoparticles used for SWCNT growth to form high density of Fe-Nx active sites, while retaining the flexibility, integrity and high quality of the films so that they can be directly used as a bifunctional oxygen electrode for rechargeable Zn-Air batteries. The single-atom Fe-Nx loaded SWCNT film shows an even better catalytic activity than commercial Pt/C-Ir/C catalysts, and an assembled Zn-Air battery using it exhibits a low charge-discharge voltage gap of 0.84 V under 20 mA/cm2, a high peak power density of 210 mW/cm2, and excellent long-time cycling stability. In addition, a flexible all-solid-state Zn-Air battery was assembled which has a stable open circuit voltage when bent to different angles.

Graphene has shown tremendous potential as a transparent conductive electrode (TCE) for flexible organic solar cells (OSCs). However, the trade-off between electrical conductance and transparency as well as surface roughness of the graphene TCE with increasing layer number limits power conversion efficiency (PCE) enhancement and its use for large-area OSCs. Here, we use a 300 nm-thick poly[(2,5-bis(2-hexyldecyloxy) phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]thiadiazole)]:[6,6]-phenyl-C-71-butyric acid methyl ester blend as the photoactive layer and a benzimidazole (BI)-doped graphene as the transparent anode to demonstrate efficient OSCs with good flexibility. It is found that 3 layer (L) graphene had the best balance between sheet resistance, optical transmittance and surface roughness for optimized cell design. A 0.2 cm2 cell with a 3L BI-doped graphene anode had a PCE of 6.85%, which is one of the highest PCE values reported so far for flexible graphene anode-based OSCs. The flexible cells were mechanically robust, showing only a small performance degradation during up to 250 flexing cycles. Moreover, the combination of the thick photoactive layer with the optimized 3L BI-doped graphene TCE enabled production of 1.6 cm(2) flexible OSCs with a PCE of 1.8%. Our work illustrates the importance of graphene TCE development for flexible OSCs as well as other wearable optoelectronic devices. (C) 2020 Elsevier Ltd. All rights reserved.

Single-wall carbon nanotubes (SWCNTs) have a high aspect ratio, large surface area, good stability and unique metallic or semiconducting electrical conductivity, they are therefore considered a promising candidate for the fabrication of flexible gas sensors that are expected to be used in the Internet of Things and various portable and wearable electronics. In this review, we first introduce the sensing mechanism of SWCNTs and the typical structure and key parameters of SWCNT-based gas sensors. We then summarize research progress on the design, fabrication, and performance of SWCNT-based gas sensors. Finally, the principles and possible approaches to further improving the performance of SWCNT-based gas sensors are discussed.

Rechargeable aqueous zinc-ion batteries (ZIBs) are receiving increased attention because of their high safety and low cost. However, their practical application is plagued by their low energy density as a result of low output voltage and a narrow voltage window of aqueous electrolytes. Here, we explored a ZIB with a wider potential window using bication (1 M Al(CF3SO3)(3)/1 M Zn(CF3SO3)(2)) as the electrolyte and alpha-MnO2 as the cathode, obtaining a discharge voltage of 1.7 V, similar to 0.3 V higher than the value reported earlier. The resultant cell delivers a record high energy density of 448 W h kg(-1) (based on MnO2 mass) and retains 100% capacity over 1000 cycles. The ion-storage mechanism and the role of Al3+ in enlarging the output voltage were elucidated. This research indicates the important role of using bications in improving the electrochemical performance of aqueous ZIBs, opening a new way to increase the energy density of aqueous energy storage devices.

Recently, 2D Mo2C, a new member of the MXene family, has attracted much attention due to the exotic superconducting properties discovered in 2D alpha-Mo2C. Here, not only 2D alpha-Mo2C but also 2D beta-Mo2C crystal sheets with distinct disordered carbon distributions were successfully grown. 2D beta-Mo2C shows a much stronger superconductivity than 2D alpha-Mo2C, and their superconductivities have different hydrostatic pressure responses. The superconducting transition temperatureT(c)of 2D alpha-Mo2C shows a dome-shaped profile under pressure, implying the existence of two competing effects arising from phononic and electronic properties, while for 2D beta-Mo2C,T(c)decreases monotonically with increasing pressure, possibly due to phonon stiffening. These results indicate that the electronic properties have a more important influence on the superconductivity in 2D alpha-Mo2C compared to 2D beta-Mo2C. The ordered and disordered carbon distributions in 2D alpha-Mo2C and beta-Mo2C, respectively, may be the underlying origin for their different electronic and superconducting properties.

Lithium-metal batteries (LMBs) are considered as promising next-generation batteries due to their high energy density. However, commercial carbonate electrolytes cannot be used in LMBs due to their poor compatibility with the lithium-metal anode and detrimental hydrogen fluoride (HF) generation by lithium hexafluorophosphate decomposition. By introducing lithium nitrate additive and a small amount of tetramethylurea as a multifunctional cosolvent to a commercial carbonate electrolyte, NO3-, which is usually insoluble, can be introduced into the solvation structure of Li+ to form a conductive and stable solid electrolyte interface. At the same time, HF generation is suppressed by manipulating the solvation structure and a scavenging effect. As a result, the Coulombic efficiency (CE) of Li||Cu half cells using the designed carbonate electrolyte can reach 98.19% at room temperature and 96.14% at low temperature (-15 degrees C), and Li||LiFePO4 cells deliver a high capacity retention of 94.9% with a high CE of 99.6% after 550 cycles. This work provides a simple and effective way to extend the use of commercial carbonate electrolytes for next-generation battery systems.

Severe shuttle effect of sulfur cathodes hinders commercial application of lithium-sulfur batteries. Current technologies for sulfur cathodes by physical confinement and chemical absorptions are not enough to solve the issues of the sulfur cathodes. Organosulfur cathodes with solid-solid conversions were proposed to fundamentally avoid shuttle effect. However, in previous reports, low sulfur content and complicated electrochemical process prevent application of organosulfur cathodes in lithium-sulfur batteries. Herein, we report new solid-solid conversion based on the organosulfur cathodes in ether-based electrolytes by developing sulfur-chain controlling strategy to obtain trisulfide polymers with high sulfur content over 76 wt%. Furthermore, reaction mechanism of sulfur based cathodes is analyzed by constructing different sulfur chains based on the strategy. Theoretical calculations suggest polymers with disulfide bonds might exhibit new lithiation behavior, which is consistent with electrochemical results. This work demonstrates new electrochemical behavior of organosulfur cathode with solid-solid conversion and show promising application prospect of these polymers.

The keen interest in fuel cells and metal-air batteries stimulates a great deal of research on the development of a cost-efficient and high-performance catalyst as an alternative to traditional Pt to boost the sluggish oxygen reduction reaction (ORR) at the cathode. Herein, we report a facile and scalable strategy for the large-scale preparation of a free-standing and flexible porous atomically dispersed Fe-N-doped carbon microtube (FeSAC/PCMT) sponge. Benefiting from its unique structure that greatly facilitates the catalytic kinetics, mass transport, and electron transfer, our FeSAC/PCMT electrode exhibits excellent performance with an ORR potential of 0.942 V at -3 mA cm(-2). When the FeSAC/PCMT sponge was directly used as an oxygen electrode for liquid-state and flexible solid-state zinc-air batteries, high peak power densities of 183.1 and 58.0 mW cm(-2) were respectively achieved, better than its powdery counterpart and commercial Pt/C catalyst. Experimental and theoretical investigation results demonstrate that such ultrahigh ORR performance can be attributed to atomically dispersed Fe-N-5 species in FeSAC/PCMT. This study presents a cost-effective and scalable strategy for the fabrication of highly efficient and flexible oxygen electrodes, provides a significant new insight into the catalytic mechanisms, and helps to realize significant advances in energy devices.

Large-area fabrication and stacking of various nanometer-thick functional layers from solutions is essentially important for the construction of flexible thin-film optoelectronic devices, but very challenging. The existing fabrication methods suffer from either non-uniformity caused by the coffee-ring effect or serious solution waste (excess of 90% for spin coating), and are hard to scale up and create stacks. Here, it is shown that centrifugal casting is a universal, scalable, and efficient method to fabricate uniform nanometer-thick films and their stacks of various materials. The coffee-ring effect is effectively suppressed, the solution utilization ratio is higher than ≈61%, and the films/stacks show a smooth surface/high-quality interface. Using this method, flexible quantum dot light-emitting diode displays with uniform luminance in a large lighting area of ≈115 cm that have not been achieved even on rigid substrates by the existing methods, are realized. This efficient and low-cost solution processing method paves a way for large-area fabrication of various flexible thin-film optoelectronic devices.

Modulating electronic structure of monolayer transition metal dichalcogenides (TMDCs) is important for many applications, and doping is an effective way toward this goal, yet is challenging to control. Here, the in situ substitutional doping of niobium (Nb) into TMDCs with tunable concentrations during chemical vapor deposition is reported. Taking monolayer WS2 as an example, doping Nb into its lattice leads to bandgap changes in the range of 1.98-1.65 eV. Noteworthy, electrical transport measurements and density functional theory calculations show that the 4d electron orbitals of the Nb dopants contribute to the density of states of Nb-doped WS2 around the Fermi level, resulting in an n- to p-type conversion. Nb-doping also reduces the energy barrier of hydrogen absorption in WS2, leading to an improved electrocatalytic hydrogen evolution performance. These results highlight the effectiveness of controlled doping in modulating the electronic structure of TMDCs and their use in electronic related applications.

Developing materials that do not ablate, which are thermally insulating and strong at temperatures above 1650 degrees C, is of prime importance for the thermal protection of aerospace vehicles, but remains a great challenge. Carbon aerogels (CAs) are attractive candidates for thermal protection due to their excellent thermostability and thermal insulation. However, their poor anti-oxidative performance and difficulty in producing an anti-oxidative refractory coating, as well as brittleness and low mechanical strength severely limit their practical use, especially in oxidizing environments. Here, an unusual carbon fiber-reinforced carbon-ceramic composite with gradual changes in composition and pore size is reported. On the top is a carbon fiber-reinforced SiC-C modified by mullite-Al2O3 and at the bottom is a carbon fiber-reinforced analogous CA. The resulting material shows excellent ablation resistance, outstanding thermal insulation, extremely high thermostability, and strong load-carrying capacity. Compared with conventional porous non-ablative and thermal insulating materials with a working temperature of 1600 degrees C and a specific strength of 10 MPa g(-1) cm(-3), its respective values are increased to 1900 degrees C and 119 MPa g(-1) cm(-3). This work provides a new way to improve the ablation resistance property of nano-porous carbon monoliths, and the carbon-ceramic composite developed has great promise for ultra-high temperature thermal protection in aerospace.

Poly(ethylene oxide) (PEO)-based electrolytes are promising for all-solid-state batteries but can only be used above room temperature due to the high-degree crystallization of PEO and the intimate affinity between ethylene oxide (EO) chains and lithium ions. Here, a homogeneous-inspired design of PEO-based solid-state electrolytes with fast ion conduction is proposed. The homogeneous PEO-based solid-state electrolyte with an adjusted succinonitrile (SN) and PEO molar ratio simultaneously suppresses the PEO crystallization and mitigates the affinity between EO and Li+. By adjusting the molar ratio of SN to PEO (SN:EO approximate to 1:4), channels providing fast Li(+)transport are formed within the homogeneous solid-state polymer electrolyte, which increases the ionic conductivity by 100 times and enables their application at a low temperature (0-25 degrees C), together with the uniform lithium deposition. This modified PEO-based electrolyte also enables a LiFePO(4)cathode to achieve a superior Coulombic efficiency (>99%) and have a long life (>750 cycles) at room temperature. Moreover, even at a low temperature of 0 degrees C, 82% of its room-temperature capacity remains, demonstrating the great potential of this electrolyte for practical solid-state lithium battery applications.

Flexible Zn-air batteries (FZABs) have significant potentials as efficient energy storage devices for wearable electronics because of their safeties and high energy-to-cost ratios. However, their application is limited by their short cycle lives, low discharge capacities per cycle, and high charge/discharge polarizations. Accordingly, herein, a poly(sodium acrylate)-polyvinyl alcohol (PANa-PVA)-ionic liquid (IL) hydrogel (PANa-PVA-IL) is prepared using a hygroscopic IL, 1-ethyl-3-methylimidazolium chloride, as an additive for twin-chain PANa-PVA. PANa-PVA-IL exhibits a high conductivity of 306.9 mS cm(-1) and a water uptake of 2515 wt% at room temperature. Moreover, a low-cost bifunctional catalyst, namely, Co9S8 nanoparticles anchored on N- and S-co-doped activated carbon black pearls 2000 (Co9S8-NSABP), is synthesized, which demonstrates a low O-2 reversibility potential gap of 0.629 V. FZABs based on PANa-PVA-IL and Co9S8-NSABP demonstrate high discharge capacities of 1.67 mAh cm(-2) per cycle and long cycle lives of 330 h. Large-scale flexible rechargeable Zn-air pouch cells exhibit total capacities of 1.03 Ah and energy densities of 246 Wh kg(cell)(-1). This study provides new information about hydrogels with high ionic conductivities and water uptakes and should facilitate the application of FZABs in wearable electronics.

Two-dimensional (2D) materials have attracted significant attention for their ability to support novel magneto-electrical transport and their optical and magnetic properties, of which their superconductivity is particularly of interest. Here we report on the behavior of superconductivity in 2D Mo2C crystals when hydrostatic pressure is applied, which has not yet been described in the literature. We found that the localization of boundary atoms disorder-induced Cooper pairs can suppress the superconducting transition temperature (T c) as effectively as a magnetic field and current. We observed that the T c initially decreased as the pressure increased to 1.75 GPa but then began to increase as the pressure increased further to 2.5 GPa. Our density functional theory calculations revealed that this behavior was linked to the modulation of the strength of the electron–phonon coupling and the electron property, which was triggered by compression of the lattice under high pressure. We attributed the inflection point in the hydrostatic pressure-dependent T c curve to the structural phase transition of Mo2C from a hexagonal to an orthorhombic structure. This work presents a new avenue for the study of the superconductivity of Mo2C, which can be extended to apply to other 2D superconductors to modulate their electronic states.

Transparent hydrogels are key materials for many applications, such as contact lens, imperceptible soft robotics and invisible wearable devices. Introducing large and engineerable optical anisotropy offers great prospect for endowing them with extra birefringence-based functions and exploiting their applications in see-through flexible polarization optics. However, existing transparent hydrogels suffer from limitation of low and/or non-fine engineerable birefringence. Here, we invent a transparent magneto-birefringence hydrogel with large and finely engineerable optical anisotropy. The large optical anisotropy factor of the embedded magnetic two-dimensional material gives rise to the large magneto-birefringence of the hydrogel in the transparent condition of ultra-low concentration, which is several orders of magnitude larger than usual transparent magnetic hydrogels. High transparency, large and tunable optical anisotropy cooperatively permit the magnetic patterning of interference colours in the hydrogel. The hydrogel also shows mechanochromic and thermochromic property. Our finding provides an entry point for applying hydrogel in optical anisotropy and colour centred fields, with several proof-of-concept applications been demonstrated. Though transparent hydrogels with tunable optical anisotropy are attractive for soft robotics, wearable devices and optical applications, achieving large birefringence has been a challenge. Here, the authors report a transparent hydrogel with large, uniform and magnetically tunable birefringence.

Next-generation batteries based on conversion reactions, including aqueous metal-air batteries, nonaqueous alkali metal-O-2 and -CO2 batteries, alkali metal-chalcogen batteries, and alkali metal-ion batteries have attracted great interest. However, their use is restricted by inefficient reversible conversion of active agents. Developing bifunctional catalysts to accelerate the conversion reaction kinetics in both discharge and charge processes is urgently needed. Graphene-, or graphene-like carbon-supported atomically dispersed metal catalysts (G-ADMCs) have been demonstrated to show excellent activity in various electrocatalytic reactions, making them promising candidates. Different from G-ADMCs for catalysis, which only require high activity in one direction, G-ADMCs for rechargeable batteries should provide high activity in both discharging and charging. This review provides guidance for the design and fabrication of bifunctional G-ADMCs for next-generation rechargeable batteries based on conversion reactions. The key challenges that prevent their reversible conversion, the origin of the activity of bifunctional G-ADMCs, and the current design principles of bifunctional G-ADMCs for highly reversible conversion, have been analyzed and highlighted for each conversion-type battery. Finally, a summary and outlook on the development of bifunctional G-ADMC materials for next-generation batteries with a high energy density and excellent energy efficiency are given.

This review focuses on the study of reversible Li-CO2 batteries, including the understanding of the conversion reaction mechanism and the development of bidirectional catalysts. The design strategies at the atomic level in terms of the single active component and multiple active components are highlighted. [Display omitted] With the increasing demand for carbon neutrality, Li-CO2 batteries are a promising technology for using CO2 as an energy storage medium and have attracted extensive attention. However, the sluggish kinetics and complex reaction mechanism significantly affect the reversibility of Li-CO2 batteries, which has stimulated the study of reaction pathways, product regulations, and bidirectional catalysts. Modulating the structure of catalysts at the atomic level has attracted increasing attention recently for improving their selectivity and activity, thus accelerating reaction kinetics and regulating the reaction pathways. In this review, we systematically discuss the conversion reaction mechanisms and analyze the key factors that affect the reaction pathways during discharge and charge in Li-CO2 batteries. Then the strategies at the atomic level for developing efficient bidirectional catalysts are highlighted, including their features, advantages, and limitations. Finally, a summary and outlook on fundamental investigation and advanced catalysts development for high-performance Li-CO2 batteries are presented.

Graphene has shown great promise in the development of next-generation electronic and optoelectronic devices owing to its atomic thickness and extraordinary electrical/optical/thermal/mechanical properties. Surface charge transfer doping is an important strategy to modulate graphene's electrical and optical properties. Compared with other doping methods, surface charge transfer doping shows distinct advantages in several aspects such as the minimized negative impact on the carrier mobility without disrupting the graphene lattice, wide range and precise control over the doping concentration, and highly efficient treatment processes without using high-temperature or ion implantation. Therefore, it is necessary to develop strong and stable surface charge transfer dopants to improve the electrical and optical performances of graphene, advancing its potential application in electronics and optoelectronics. For more than a decade, efforts has been devoted to developing diverse surface charge transfer p- and n-type dopants, including acids, gases, transition metals, alkali metals, metal chlorides, metal oxides, organics containing electron-donating/withdrawing groups, ferroelectric organics, and carbon-based materials, which serve as a wide range of ways to modulate the properties of graphene. Recently, remarkable progress has been made in realizing heavy and stable doping by surface charge transfer. In this review, we summarize the research status of surface charge transfer doping for graphene and its application in electronic and optoelectronic devices by focusing on the doping strength and stability. Initially, we survey the typical surface charge transfer doping mechanisms and widely used characterization measures, discussing their advantages and limitations. We then review the recent progress in the development of strong p- and n-type surface charge transfer dopants for graphene. For example, heavy p- and n-doping in graphene has been achieved by intercalation doping with metal chlorides and alkali metals, respectively. A large-area graphene film with stable p-doping was also realized. Of particular interest, organics are promising materials for developing emerging dopants with high structural tunability and diverse functions. We also introduce novel stable dopants and effective strategies for improving the ambient/thermal/solvent stability of typical dopants. Then, we devote a manuscript section to advances in high-performance optoelectronic devices using doped graphene electrodes with superior performances, focusing on graphene-based touch screens, organic light-emitting diodes, and organic photovoltaics. In this area, graphene-based flexible light-emitting devices have demonstrated advantages over typical tin-doped indium oxide (ITO) devices in terms of overall efficiencies. Finally, we discuss the challenges faced in developing state-of-the-art surface charge transfer dopants with future perspectives.

The development of flexible zinc-air batteries (FZABs) has attracted broad attention in the field of wearable electronic devices. Gel electrolyte is one of the most important components in FZABs, which is urgent to be optimized to match with Zn anode and adapt to severe climates. In this work, a polarized gel electrolyte of polyacrylamide-sodium citric (PAM-SC) is designed for FZABs, in which the SC molecules contain large amount of polarized -COO- functional groups. The polarized -COO- groups can form an electrical field between gel electrolyte and Zn anode to suppress Zn dendrite growth. Besides, the -COO- groups in PAM-SC can fix H2O molecules, which prevents water from freezing and evaporating. The polarized PAM-SC hydrogel delivers a high ionic conductivity of 324.68 mS cm(-1) and water retention of 96.85 % after being exposed for 96 h. FZABs with the PAM-SC gel electrolyte exhibit long cycling life of 700 cycles at -40 degrees C, showing the application prospect under extreme conditions.

Straining to make a transistor The use of carbon nanotubes (CNTs) as short-channel-length transistors will require control of their chirality, which determines whether they are semiconducting or metallic and if they form strong, low-resistance contacts. Tang et al . fabricated CNT intramolecular transistors by progressive heating and straining of individual CNTs within a transmission electron microscope. Changes to chirality along sections of the nanotube created metallic-to-semiconducting transitions. A semiconducting nanotube channel was covalently bonded to the metallic nanotube source and drain regions. The resulting CNT intramolecular transistors had channel lengths as short as 2.8 nanometers. —PDS Strain and heating of carbon nanotubes in a transmission electron microscope created internal metal-semiconductor junctions. Carbon nanotubes have a helical structure wherein the chirality determines whether they are metallic or semiconducting. Using in situ transmission electron microscopy, we applied heating and mechanical strain to alter the local chirality and thereby control the electronic properties of individual single-wall carbon nanotubes. A transition trend toward a larger chiral angle region was observed and explained in terms of orientation-dependent dislocation formation energy. A controlled metal-to-semiconductor transition was realized to create nanotube transistors with a semiconducting nanotube channel covalently bonded between a metallic nanotube source and drain. Additionally, quantum transport at room temperature was demonstrated for the fabricated nanotube transistors with a channel length as short as 2.8 nanometers.

The conventional strategy of fabricating resistive random access memory (RRAM) based on graphene oxide is limited to a resistive layer with homogeneous oxidation, and the switching behavior relies on its redox reaction with an active metal electrode, so the obtained RRAMs are typically plagued by inferior performance and reliability. Here, we report a strategy to develop high-performance flexible RRAMs by using graphene oxidized with a perpendicular oxidation gradient as the resistive layer. In contrast to a homogeneous oxide, this graphene together with its distinctive inter-layer oxygen diffusion path enables excellent oxygen ion/vacancy diffusion. Without an interfacial redox reaction, oxygen ions can diffuse to form conductive filaments with two inert metal electrodes by applying a bias voltage. Compared with state-of-the-art graphene oxide RRAMs, these graphene RRAMs have shown superior performance including a high on-off current ratio of ∼105, long-term retention of ∼106 s, reproducibility over 104 cycles and long-term flexibility at a bending strain of 0.6%, indicating that the material has great potential in wearable smart data-storage devices.

Abstract 2D materials have a range of unique properties and are promising building blocks for the fabrication of macroscopic materials for many applications ranging from flexible electronics to energy storage devices. The development of effective methods to fabricate 2D material‐based macroscopic materials with designed structures is the key to enabling high performance. Lately, 3D printing has emerged as a new technique to assemble such materials. Compared to conventional fabrication methods, 3D printing techniques have a high degree of customization of the structure with a broad range of domain sizes from nanometers to centimeters, and thereby give the resulting products additional structure‐related functionalities. Recent advances in the fabrication of 2D material‐based macrostructures using 3D printing techniques and their uses in different fields are reviewed. Challenges and opportunities for the future development of the topic are also discussed.

Abstract The assembly of different levels of structure from the nano‐ to the macroscale has produced materials with outstanding performance. Here, using graphene as a model building block, the fabrication of multiscale structures is reported, with tailorable features spanning seven orders of magnitude in size by a 3D printed template‐directed assembly method which combines the ability to customize structures from the meso‐ to macroscale using digital light processing and from the nano‐ to microscale using self‐assembly. It is shown that by a careful design of the structures, a number of extraordinary properties can be produced including ultralow density (≥0.08 mg cm –3 ), and ultrahigh stiffness, and compressibility (full recovery from 95% strain). The approach not only provides diversified structure control over wide length scales for nanomaterial assembly but also shows the possibility of changing the properties of the structure for different applications.

Lithium–sulfur (Li–S) batteries are one of the most promising next generation battery systems owing to their high energy density and low cost, but they suffer from the low conductivity of sulfur, polysulfide shuttling and lithium dendrite growth, which limit their practical applications. Porous graphene networks (PGNs) not only have the advantages of graphene as a multifunctional host, but also exhibit unique properties derived from their porous structures, which enable PGNs to have a variety of positive effects in Li–S batteries. Here, we provide an overview of the roles and functions of PGNs in Li–S batteries, including increasing sulfur utilization, confining sulfur species, accommodating the volume change of sulfur, improving the conversion kinetics of polysulfides, reducing the consumption of lithium, preventing the dendrite growth, and acting as flexible hosts. The systematic summary of the recent progress in the use of PGNs in different components of Li–S batteries provides guidance for designing materials with diversity that meet different requirements. By mechanism analysis and a recent achievement summary of PGNs in Li–S batteries, we hope to inspire further developments of PGNs in Li–S batteries one step closer to industrialization.

Lithium-sulfur (Li-S) batteries have recently emerged as a promising candidate for next-generation energy storage systems. Yet the polysulfide dissolution and shuttle issues cause severe performance degradation, hindering their practical use. Here, we report an in-situ solidification strategy for efficient polysulfide blocking via nucleophilic substitution reactions triggered by 2, 5-dichloro-1, 4-benzoquinone (DCBQ) in the electrolyte. Polysulfides could be covalently fixed by DCBQ in the form of solid organosulfur to enable effective immobilization of polysulfides within the cathode, contributing to high capacity-retention. Moreover, the benzoquinonyl groups of DCBQ were found able to accelerate the lithium-ion transport and promote the sulfur redox reaction kinetics. Consequently, the Li-S cell with DCBQ exhibited good electrochemical performances. This approach demonstrates a novel avenue for polysulfide blocking to boost Li-S battery performance.

Recycling forms an essential dimension of batteries' sustainability. Here the authors show a straightforward process that directly upgrades spent LiCoO2 to a Mg and Al co-substituted LiCoO2 cathode with a high voltage of 4.6 V and excellent cycling stability. The continued market growth for electric vehicles globally is accelerating the transformational shift to a low-carbon transportation future. However, the sustainability of this transition hinges to a large extent on the management of waste, including end-of-life batteries where strategic elements such as lithium (Li) and cobalt (Co) are present. Different from the existing pyrometallurgical and hydrometallurgical recycling methods that involve heavy energy inputs and the use of hazardous chemicals, here we show a feasible single-step process that not only reclaims lithium cobalt oxide (LiCoO2) from waste Li-ion batteries but also upgrades it to a cathode with enhanced electrochemical properties. Our recycling process is based on a direct reaction between spent LiCoO2 and added mixture of Al2O3, MgO and Li2CO3, during which the Li vacancies aid the diffusion of Al and Mg to yield dual-doped LiCoO2. The upgraded LiCoO2 cathode possesses even better structural stability and sustains 300 cycles retaining 79.7% of its initial capacity at a voltage of 4.6 V. As evidenced by the technoeconomic analysis, the current circularity approach exhibits cost benefits and could catalyse further progress in the upcycling of different materials for batteries.

•A closed-loop recycling strategy was proposed starting from spent Li-ion battery cathode materials to high-performance cathodes with less energy consumption and little pollution.•Low temperature annealing (< 400 °C) was used to decompose LiCoO2 by the aid of (NH4)2SO4.•Water was used as leaching reagent for rapid extraction of Co and Li.•The re-generated LiCoO2 cathode shows superior cyclability than commercial LiCoO2 at 4.5 V.•The recycling process exhibits excellent economic and environmental benefits. Lithium cobalt oxide (LiCoO2) is the most widely used cathode materials for smart phones and laptop batteries. With the rapid development of portable electronics, more than 100,000 tons of spent lithium-ion batteries (LIBs) are produced every year. Conventional battery recycling processes including pyrometallurgical and hydrometallurgical processes mainly aim at extracting valuable metallic components from spent LIB cathodes, which requires high temperature reduction and/or acid/alkali chemicals to destroy covalent bond in cathodes and convert them into atoms for further extraction. The former leads to high energy consumption and the latter produces a lot of wastewater, which not only increases cost, but also damages our environment. Moreover, traditional recycling starts from spent battery cathodes and ends up with lithium/cobalt salts, which is unsustainable. Herein, a different recycling strategy to directly convert degraded LiCoO2 into high-voltage LiCoO2 cathode materials was proposed, featuring a closed-loop and green procedure. The directly-converted LiCoO2 from spent cathodes exhibits excellent cyclability at 4.5 V with a high capacity retention of 97.4% after 100 cycles, even superior than pristine LiCoO2. The recovery efficiencies of lithium and cobalt reach 91.3% and 93.5%, respectively, and the energy consumption could be greatly reduced since the roasting temperature was dropped below 400 °C with the assistance of ammonium sulfate. Due to the utilization of low-cost reagents and water as the leaching agent, the potential benefit of the recovery process was estimated to reach 6.94 $/kg cell. [Display omitted]

Cationic doping is mainly used to improve the performance of rocksalt-structured GeTe thermoelectric materials. However, its counterpart anionic doping is scarcely facilitated. Here, a comprehensive discussion is provided on doping at the anion site of rocksalt-structured thermoelectric materials, surrounding its influence on bonding mechanisms, carrier and phonon transport characteristics, and thermoelectric figure-of-merit. To verify the viewpoint, a modified flux-assist method is adopted to synthesize anionic Iodine (I) doped GeTe samples, which show comparably optimized electrical and thermal properties with that of cationic Antimony (Sb) or Bismuth (Bi) doped GeTe samples. Further combining cationic Bi and anionic I co-doping, an enhanced figure-of-merit from 0.8 in pristine GeTe to 2.5 at 675 K can be realized in 8% (Bi and I) co-doped GeTe, which corresponds to a maximum heat-to-electricity conversion efficiency of 14.6% under a temperature difference of 430 K. This work rationalizes the influence of anionic doping on the electrical and thermal properties of the rocksalt-structured materials, which serves as an effective yet previously neglected strategy toward high-performance GeTe thermoelectrics.

The microstructure evolution of carbon fiber reinforced carbon aerogel-like matrix (C/CA) composites with carbonization temperature and its influence on their properties were investigated. The removal of residual organo-functional groups of the C/CA precursors is dominant when carbonized at 600–750 °C with a large volume shrinkage difference by 17–22% as compared to that at 1200 °C, while the rearrangement of novolac structures is dominant at 900–1200 °C with a slight volume shrinkage fluctuation of 6%. Resultantly, the amount of micropore first increases and then decreases, while the particle size experiences an opposite change. The microstructure correspondingly transforms from a completely amorphous state to a partially amorphous state with graphite crystallites in low-angle misorientation, and then with graphite-like entangling ribbons. Due to the reduced residual tensile stress and increased interfacial bonding, the resulting composites with a variable bulk density of 0.58–0.64 g cm−3 have much higher compressive strengths of 45.8–96.9 MPa than other reported carbon foams or aerogels with similar bulk densities. The increase of strength and modulus with carbonization temperature is mainly due to the smaller tensile stress, higher particle packing compactness, larger microcrystallite size and less residual organo-functional groups. The composites also present a relatively low thermal conductivity of 0.12–0.59 W m−1 K−1. The increase of thermal conductivity with temperature is related to the synergistic effect of reduced phonon scattering associated with smaller specific surface area, larger microcrystallite size and less organo-functional groups and improved phonon transfer associated with increased inter-particle contact area. [Display omitted]

Two-dimensional (2D) nanosheets with a high electrochemical capacitance, density, and electrical conductivity are promising for assembling thick and dense films for supercapacitors with a high volumetric energy density. However, 2D nanosheet-based films with cascading nanochannel networks are not ideal for efficient ion transport due to the tortuous pathways. We used a micro-stamping method to create a perpendicular micro-hole array in a thick, dense MoS2-based electrode without lowering its density. Our nuclear magnetic resonance measurement and computational simulations reveal that the micro-hole array can serve as ion reservoirs and provide shortcuts in the cascading nanochannel network, greatly improving the ion accessibility to MoS2-based electrodes in both the adsorption and charging processes. A MoS2-based film electrode with 2-3 times the density of a conventional carbon electrode, shows almost thickness independent capacitance performance with a mass loading up to 18.6 mg cm−2. The electrode has a volumetric capacitance of 469.5 F cm−3 and the assembled device a volumetric energy density of 80.5 Wh L−1 in an ionic liquid electrolyte. This micro-stamping strategy is easy to scale up and may pave the way for the development of 2D materials-based compact energy storage systems.

LiCoO2 has suffered from poor stability under high voltage as a result of insufficient Co-O bonding that causes lattice oxygen release and lattice distortions. Herein, we fabricated a high-voltage LiCoO2 at 4.6 V by doping with Ni/Mn atoms, which are obtained from spent LiNi0.5Mn0.3Co0.2O2 cathode materials. The as-prepared high-voltage LiCoO2 with Ni/Mn substitutional dopants in the Co layer enhances Co-O bonding that suppresses oxygen release and harmful phase transformation during delithiation, thus stabilizing the layered structure and leading to a superior electrochemical performance at 4.6 V. The pouch cell of modified LiCoO2 exhibits a capacity retention of 85.1% over 100 cycles at 4.5 V (vs graphite). We found that our strategy is applicable for degraded LiCoO2, and the regenerated LiCoO2 using this strategy exhibits excellent capacity retention (84.1%, 100 cycles) at 4.6 V. Our strategy paves the way for the direct conversion of spent batteries into high-energy-density batteries.

Thermoelectric (TE) materials and devices have attracted great attention due to their ability to convert waste heat to electrical power and active cooling. However, the conventional bulk TE materials are inorganic semiconductors with inherent brittleness and rigidity. They cannot closely contact curved heat sources and sinks, which limits their application in modern electronics. It remains a big challenge to fabricate high-performance TE materials and devices with good flexibility. Here, we report a flexible TE device comprised of a single wall carbon nanotube (SWCNT) network and (000l)-textured Bi2Te3 nanocrystals prepared by a magnetron sputtering technique. The unique Bi2Te3-SWCNT hybrid structure has a TE figure of merit (ZT) value of ∼0.23 at ∼330 K. A prototype TE device made of this hybrid gives a maximum output power density of ∼0.93 mW cm−2 under a temperature difference of 25 K at ambient temperature and shows good flexibility under bending. Our results open up a new way to the development of flexible TEs and their application in self-powered portable devices.

Flexible self-powered sensors are attracting increasing research interest with the emergence and rapid development of the Internet of Things. However, inefficient power supplies and difficulties in device assembly have largely limited their applications. Here, we report an integrated gas-sensing system using a single-walled carbon nanotube film with good flexibility and large surface area to detect a target gas. A single-walled carbon nanotube/silicon heterojunction solar cell capable of stably providing a voltage of ∼0.5 V under the illumination of a standard solar intensity powers the sensor. Our self-powered sensing system shows an ideal rectangle-shaped nitrogen dioxide detection curve and demonstrates higher sensitivity and faster response time than one driven by external power at room temperature. We attribute this better activity to the increased carrier concentration originating from single-walled carbon nanotubes in both sensing and powering components. Finally, wireless communication between the system and a phone is demonstrated with a Bluetooth Low Energy module. [Display omitted] •A gas sensor based on single-walled carbon nanotube films is developed•The sensor shows its best performance when powered by light•Combining a sensing unit and self-powering unit leads to good performance•The sensor holds potential for wireless human-machine interaction Guo and Hu et al. report a flexible and self-powered nitrogen dioxide sensor based on single-walled carbon nanotube films. The sensor works without an external power supply while under illumination and demonstrates the potential for quick wireless alarm notifications to users’ mobile phones.

Potassium-ion batteries are a compelling technology for large scale energy storage due to their low-cost and good rate performance. However, the development of potassium-ion batteries remains in its infancy, mainly hindered by the lack of suitable cathode materials. Here we show that a previously known frustrated magnet, KFeC2O4F, could serve as a stable cathode for potassium ion storage, delivering a discharge capacity of similar to 112 mAh g(-1) at 0.2 A g(-1) and 94% capacity retention after 2000 cycles. The unprecedented cycling stability is attributed to the rigid framework and the presence of three channels that allow for minimized volume fluctuation when Fe2+/Fe3+ redox reaction occurs. Further, pairing this KFeC2O4F cathode with a soft carbon anode yields a potassium-ion full cell with an energy density of similar to 235Wh kg(-1), impressive rate performance and negligible capacity decay within 200 cycles. This work sheds light on the development of low-cost and high-performance K-based energy storage devices.

Doping is an effective way to modify the electronic property of two-dimensional (2D) materials and endow them with additional functionalities. However, wide-range control of the doping concentrations in monolayer 2D materials with large-scale uniformity remains challenging. Here, we report in situ chemical vapor deposition growth of vanadium-doped monolayer molybdenum disulfide (MoS2) with widely tunable doping concentrations ranging from 0.3 to 13.1 atom %. The key to regulate the doping concentration lies in the use of appropriate vanadium precursors with different doping abilities, which also generate large-scale uniform doping to MoS2. Artificial synaptic transistors were fabricated using the heavily doped MoS2 as the channel material. Synaptic potentiation, depression, and repetitive learning processes were mimicked by the gate-tunable changes of channel conductance in such transistors with abundant vanadium atoms to trap/detrap electrons. This work develops a feasible method to dope monolayer 2D semiconductors and demonstrates their applications in artificial synaptic transistors.

Developing efficient noble-metal-free surface-enhanced Raman scattering (SERS) substrates and unveiling the underlying mechanism is crucial for ultrasensitive molecular sensing. Herein, we report a facile synthesis of mixed-dimensional heterostructures via oxygen plasma treatments of two-dimensional (2D) materials. As a proof-of-concept, 1D/2D WO3-x/WSe2 heterostructures with good controllability and reproducibility are synthesized, in which 1D WO3-x nanowire patterns are laterally arranged along the three-fold symmetric directions of 2D WSe2. The WO3-x/WSe2 heterostructures exhibited high molecular sensitivity, with a limit of detection of 5 x 10(-18) M and an enhancement factor of 5.0 x 10(11) for methylene blue molecules, even in mixed solutions. We associate the ultrasensitive performance to the efficient charge transfer induced by the unique structures of 1D WO3-x nanowires and the effective interlayer coupling of the heterostructures. We observed a charge transfer timescale of around 1.0 picosecond via ultrafast transient spectroscopy. Our work provides an alternative strategy for the synthesis of 1D nanostructures from 2D materials and offers insights on the role of ultrafast charge transfer mechanisms in plasmon-free SERS-based molecular sensing.

Surface plasmons, merging photonics and electronics in nanoscale dimensions, have been the cornerstones in integrated informatics, precision detection, high-resolution imaging, and energy conversion. Arising from the exceptional Fermi-Dirac tunability, ultrafast carrier mobility, and high-field confinement, graphene offers excellent advantages for plasmon technologies and enables a variety of state-of-the-art optoelectronic applications ranging from tight-field-enhanced light sources, modulators, and photodetectors to biochemical sensors. However, it is challenging to co-excite multiple graphene plasmons on one single graphene sheet with high density, a key step toward plasmonic wavelength-division multiplexing and next-generation dynamical optoelectronics. Here, we report the heteroepitaxial growth of a polycrystalline graphene monolayer with patterned gradient grain boundary density, which is synthesized by creating diverse nanosized local growth environments on a centimeter-scale substrate with a polycrystalline graphene ring seed in chemical vapor deposition. Such geometry enables plasmonic co-excitation with varied wavelength diversification in the nanoscale. using high-resolution scanning near-field optical microscopy, we demonstrate rich plasmon standing waves, even bright plasmonic hotspots with a size up to 3 μm. Moreover, by changing the grain boundary density and annealing, we find the local plasmonic wavelengths are widely tunable, from 70 to 300 nm. Theoretical modeling supports that such plasmonic versatility is due to the grain boundary-induced plasmon-phonon interactions through random phase approximation. The seed-induced heteroepitaxial growth provides a promising way for the grain boundary engineering of two-dimensional materials, and the controllable grain boundary-based plasmon co-generation and manipulation in one single graphene monolayer will facilitate the applications of graphene for plasmonics and nanophotonics.

Recently, two-dimensional (2D) materials have exhibited many exotic properties, such as topological bands, superconductivity, etc. Among these intriguing systems, interface engineering plays a critical role in inducing, manipulating and even enhancing the properties. Our scanning tunneling microscopic/spectroscopic (STM/S) analysis of 2D superconducting thin α-Mo2C crystal has previously revealed the enhanced TC = 8.02 K originating from the lattice defects. With the same TC, here we demonstrate that the scattering mechanism leads to a more consistent picture to understand the superconductivity in a defected crystal, which can be tuned by interlayer coupling. Using a low-temperature STM, dI/dV spectra were fitted with the Dynes formula to extract the quasiparticle scattering rates at various temperatures. Moreover, the STS analysis of defective sample surfaces and terraces reveals that both quasiparticle scattering rates and zero-bias conductance oscillate as a result of interlayer coupling variation. A temperature-dependent model considering elastic, electron-electron, and electron-phonon inelastic scattering rates was used to fit excellently the quasiparticle scattering rates measured along defects and terraces. The electron-electron scattering rate exhibits a negative fitting parameter, indicating the loss of inelastic electron-electron scattering rate. Additionally, the elastic scattering rate is much higher than the total inelastic scattering rate, which is an indication of the retarded quasiparticle interactions with impurities.

In a modern electronics system, charge-coupled devices and data storage devices are the two most indispensable components. Although there has been rapid and independent progress in their development during the last three decades, a cofunctionality of both sensing and memory at single-unit level is yet premature for flexible electronics. For wearable electronics that work in ultralow power conditions and involve strains, conventional sensing-and-memory systems suffer from low sensitivity and are not able to directly transform sensed information into sufficient memory. Here, a new transformative device is demonstrated, which is called "sen-memory", that exhibits the dual functionality of sensing and memory in a monolithic integrated circuit. The active channel of the device is formed by a carbon nanotube thin film and the floating gate is formed by a controllably oxidized aluminum nanoparticle array for electrical- and optical-programming. The device exhibits a high on-off current ratio of approximate to 10(6), a long-term retention of approximate to 10(8) s, and durable flexibility at a bending strain of 0.4%. It is shown that the device senses a photogenerated pattern in seconds at zero bias and memorizes an image for a couple of years.

The lack of low-cost catalysts with high activity leads to the unsatisfactory electrochemical performance of Li-CO2 batteries. Single-atom catalysts (SACs) with metal-N-x moieties have great potential to improve battery reaction kinetics and cycling ability. However, how to rationally select and develop highly efficient electrocatalysts remains unclear. Herein, we used density functional theory (DFT) calculations to screen SACs on N-doped graphene (SAMe@NG, Me = Cr, Mn, Fe, Co, Ni, Cu) for CO2 reduction and evolution reaction. Among them, SACr@NG shows the promising potential as an effective electrocatalyst for the reversible Li-CO2 batteries. To verify the validity of the DFT calculations, a two-step method has been developed to fabricate SAMe@NG on a porous carbon foam (SAMe@NG/PCF) with similar loading of similar to 8 wt %. Consistent with the theoretical calculations, batteries with the SACr@NG/PCF cathodes exhibit a superior rate performance and cycling ability, with a long cycle life and a narrow voltage gap of 1.39 V over 350 cycles at a rate of 100 mu A cm(-2). This work not only demonstrates a principle for catalysts selection for the reversible Li-CO2 batteries but also a controllable synthesis method for single atom catalysts.

As a promising charge storage method, hybrid charge storage has a high energy density, high power density, and long cycle life due to its combination of the mechanisms of secondary batteries and electrochemical capacitors. However, the difference in the charge storage mechanisms of the cathode and anode and thus the strong coupling makes it impossible to match cathode and anode in all situations. Research has investigated cell configuration, material design, electrolyte composition, etc., for matching the cathode and anode of hybrid charge storage devices, but there is no complete understanding and analysis from an electrochemical perspective. To better guide and promote the development of hybrid charge storage, this study discusses the matching and coupling of the anode and cathode from the following aspects, using hybrid capacitors as a typical example and combining the analysis of mainstream electrochemical systems, strategies, and materials. First, the charge storage mechanism and the major problems involved in matching the cathode and anode, as well as the “self-matching” of potential and zero-voltage potential, are considered as the basis of coupling. Second, from the perspective of electrochemical behavior and potential range of electrodes, we analyze the conflicts and correlations in coupling between each match and discuss the problems and solutions faced in specific matching processes. Third, the problem of matching a practical but complex electrochemical system is analyzed from the perspective of the coupling relationship. Fourth, the design and development of hybrid charge storage, ideas for future research, and the use of machine learning for electrode matching and coupling are proposed. [Display omitted] In this review, we propose a transformative discussion idea to analyze to maximize the performance of hybrid charge storage devices from an electrochemical point of view. Hybrid charge storage requires simultaneous optimal performance of the anode and cathode. However, various properties of electrodes will affect and restrict each other (which was defined as “coupling”), making it difficult for them to achieve optimum performance simultaneously. For in-depth discussion, zero-voltage potential and “self-matching” were defined as the basis of coupling to analyze the interrelationship and influence among the matchings of capacity, kinetics, and cycle life in detail. What is more, the influence of non-ideal electrochemical behavior and other possible factors on matching was also thoroughly discussed. The idea of matching and coupling does not apply only to hybrid charge storage. Considering the difference in the charge storage process of electrodes, matching and coupling are unavoidable to any charge storage system. What is more, the theoretical research on matching and coupling means that the electrochemical behavior can be modeled and analyzed through machine learning so as to predict the overall performance of the device and optimize the design based on the data collection in future. Our analysis, discussion, and insight could provide a deeper understanding of the design concepts for hybrid charge storage and other charge storage systems from an electrochemical perspective. Despite being proposed as an ideal charge storage method, the performance of hybrid charge storage devices is constrained by the matching problem between cathode and anode. To this end, the research ideas of coupling and matching are proposed. Combined with well-defined self-matching and zero-voltage potential, the problems faced in the construction of various electrochemical systems are discussed in depth, and the design, development, and future research of hybrid charge storage are comprehensively prospected.

Bolometric photodetectors based on single-wall carbon nanotubes (SWCNTs) have shown advantages of an ultrawide absorption spectrum, high charge carrier mobility, good processability, and high mechanical flexibility. However, their detection performance needs to be improved to meet the requirements of real applications. A flexible infrared photodetector was fabricated based on high quality SWCNT films. The device showed an ultrahigh detectivity up to 1.35 × 108 Jones under a bias voltage of 0.2 V, and a short response time of 70 ms in air. In addition, we found that the photocurrent response of the detector was closely related to the structure of the SWCNT network. A negative photocurrent was measured using photodetectors constructed from highly-crystalline SWCNTs owing to dominant phonon scattering transfer, while a positive photocurrent was detected from those fabricated using defect-rich SWCNTs due to dominant electron hopping transfer. Our results shed light on the construction of high-performance SWCNT film-based infrared photodetectors. A high negative photocurrent was measured using photodetectors constructed from highly-crystalline SWCNTs (IG/ID∼177) owing to dominant phonon scattering transfer, while a positive photocurrent was detected from those fabricated using defect-rich SWCNTs (IG/ID∼31) due to dominant electron hopping transfer. [Display omitted]

The realization of high-quality heterostructures or hybrids of graphene and superconductor is crucial for exploring various novel quantum phenomena and devices engineering. Here, the electronic transport on directly grown high-quality graphene/Mo2C vertical heterostructures with clean and sharp interface is comprehensively investigated. Owing to the strong interface coupling, the graphene layer feels an effective confinement potential well imposed by two-dimensional (2D) Mo2C crystal. Employing cross junction device geometry, a series of resonance-like magnetoresistance peaks are observed at low temperatures. The temperature and gate voltage dependences of the observed resonance peaks give evidence for geometric resonance of electron cyclotron orbits with the formed potential well. Moreover, it is found that both the amplitude of resonance peaks and conductance fluctuation exhibit different temperature-dependent behaviors below the superconducting transition temperature of 2D Mo2C, indicating the correlation of quantum fluctuations and superconductivity. This study offers a promising route toward integrating graphene with 2D superconducting materials, and establishes a new way to investigate the interplay of massless Dirac fermion and superconductivity based on graphene/2D superconductor vertical heterostructures.

Carbon nanotube-based derivatives have attracted considerable research interest due to their unique structure and fascinating physicochemical properties. However, the controlled growth mechanism of these derivatives remains unclear, and the synthesis efficiency is low. Herein, we proposed a defect-induced strategy for the efficient heteroepitaxial growth of single-wall carbon nanotubes (SWCNTs)@hexagonal boron nitride (h-BN) films. Air plasma treatment was first performed to generate defects on the wall of SWCNTs. Then, atmospheric pressure chemical vapor deposition was conducted to grow h-BN on the surface of SWCNTs. Controlled experiments combined with first-principles calculations revealed that the induced defects on the wall of SWCNTs function as nucleation sites for the efficient heteroepitaxial growth of h-BN.

Electroactive organic materials with tailored functional groups are of great importance for aqueous Zn-organic batteries due to their green and renewable nature. Herein, a completely new N-heteroaromatic material, hexaazatrinaphthalene-phenazine (HATN-PNZ) is designed and synthesized, by an acid-catalyzed condensation reaction, and its use as an ultrahigh performance cathode for Zn-ion batteries demonstrated. Compared with phenazine monomer, it is revealed that the pi-conjugated structure of N-heteroaromatics can effectively increase electron delocalization, thereby improving its electrical conductivity. Furthermore, the enlarged aromatic structure noticeably suppresses its dissolution in aqueous electrolytes, thus enabling high structural stability. As expected, the HATN-PNZ cathode delivers a large reversible capacity of 257 mAh g(-1) at 5 A g(-1), ultrahigh rate capability of 144 mAh g(-1) at 100 A g(-1), and an extremely long cycle life of 45 000 cycles at 50 A g(-1). Investigation of the charge-storage mechanism demonstrates the synergistic coordination of both Zn2+ and H+ cations with the phenanthroline groups, with Zn2+ first followed by H+, accompanying the reversible formation of zinc hydroxide sulfate hydrate. This work provides a molecular-engineering strategy for superior organic materials and adds new insights to understand the charge-storage behavior of aqueous Zn-organic batteries.

Lithium metal batteries (LMBs) are considered promising candidates for next-generation battery systems due to their high energy density. However, commercialized carbonate electrolytes cannot be used in LMBs due to their poor compatibility with lithium metal anodes. While increasing cut-off voltage is an effective way to boost the energy density of LMBs, conventional ethylene carbonate-based electrolytes undergo a number of side reactions at high voltages. It is therefore critical to upgrade conventional carbonate electrolytes, the performance of which is highly influenced by the solvation structure of lithium ions (Li+). This review provides a comprehensive overview of the strategies to regulate the solvation structure of Li+ in carbonate electrolytes for LMBs by better understanding the science behind the Li+ solvation structure and Li+ behavior. Different strategies are systematically compared to help select better electrolytes for specific applications. The remaining scientific and technical problems are pointed out, and directions for future research on carbonate electrolytes for LMBs are proposed.

Doped 2D transition metal dichalcogenides have attracted much attention as room-temperature ferromagnetism can be realized in such semiconductors. For example, the magnetism of vanadium-doped WS2 (V-WS2) has been revealed, but there is still confusion about how the substituted vanadium atoms affect the carrier scattering of V-WS2. Here, we study the electron-phonon coupling and carrier scattering of V-WS2 by temperature-dependent Raman spectroscopy and electrical transport measurements. We identify a characteristic Raman peak at similar to 212 cm(-1), a fingerprint for V-WS2. We also reveal that the electron-phonon coupling is strengthened in V-WS2 and becomes more sensitive to temperature, which suppresses the carrier mobility and improves the sensitivity of its electronic performance to temperature. Moreover, the substituted vanadium not only causes an n- to p-type transition of the carrier transport behavior but also serves as charged impurities, making ionization scattering dominate the carrier transport process in V-WS2. Such modulation of carrier transport behavior in V-WS2 will facilitate its application in electronic and spintronic devices.

Revealing the active phase and structure of catalyst nanoparticles (NPs) is crucial for understanding the growth mechanism and realizing the controlled synthesis of carbon nanotubes (CNTs). However, due to the high temperature and complex environment during CNT growth, precise identification of the active catalytic phase remains a great challenge. We investigated the phase evolution of cobalt (Co) catalyst NPs during the incubation, nucleation, and growth stages of CNTs under near-atmospheric pressure using an in situ close-cell environmental transmission electron microscope (ETEM). Strict statistical analysis of the electron diffractograms was performed to accurately identify the phases of the catalyst NPs. It was found that the NPs belong to an orthorhombic Co3C phase that remained unchanged during CNT growth, with errors in lattice spacing

Long and dense MoS2/Ni3S2 co-axial heterostructure nanowires were prepared on nickel foam by simple hydrothermal and annealing treatments. Such material shows extraordinary HER performance in alkaline solution at large current density with excellent stability. This study highlights that besides suitable component design, favorable structure design is also essentially important for improving the performance of electrocatalysts. [Display omitted] Splitting water under large current density is essential for efficient large-scale production and commercial utilization of hydrogen. However, the performance of the available electrocatalysts for hydrogen evolution reaction (HER) is far from satisfactory under large current density in alkaline electrolyte. Here we report a remarkably active and durable electrocatalyst, long and dense MoS2/Ni3S2 co-axial heterostructure nanowires on nickel foam (NF). Notably, it requires only 182 and 200 mV overpotential to achieve large current density of 500 and 1000 mA cm−2, respectively, in alkaline solution, which are far superior to those of Pt/C-NF (281 and 444 mV) and the reported best non-noble metal catalysts (191 and 220 mV). The physical origin for this extraordinary HER performance is analyzed, which provides a useful guide for structure design of electrocatalysts to further improve their performance.

Four kinds of sandwich-structured C/C-SiC and C/C-SiC-ZrC composites with or without a SiC interphase deposited by isothermal chemical vapor infiltration (ICVI), were designed and fabricated by a joint process of electromagnetic coupling chemical vapor infiltration (ECVI) and precursor infiltration and pyrolysis (PIP). The fabricated composites are macroscopically nonhomogeneous materials with low density, high strength and low ablation rate. The interphase and matrix constituents had remarkable effects on the mechanical and ablation properties of these composites. The C/C-SiC composites with an ICVI-SiC interphase exhibited the highest flexural strength of 306.5 MPa. While the C/C-SiC-ZrC composites with the interphase showed the best antiablation performance with low linear and mass ablation rates of 0.37 mu m/s and 0.04 mg/cm2.s, respectively, after the ablation for 500 s under an oxyacetylene flame test at around 2000 degrees C.

Lithium metal is an ideal electrode material for future rechargeable batteries. However, dendrite formation and unstable solid electrolyte interphase film lead to safety concerns and poor Coulombic efficiency (CE). LiNO3 significantly improves the performance of the lithium metal anode in ester electrolytes but its use is restricted by low solubility. To increase the content of LiNO3 in the cell, a poly-(vinyl carbonate) organogel interlayer containing dissociated LiNO3 (LNO-PVC) is placed between the cathode and anode. The dissociated LiNO3 effectively increases the LiNO3-release rate and compensates for the LiNO3 consumed in ester electrolytes during cycling. Via this interlayer, the performance of the lithium metal anode is significantly improved. The average CE of a Li-Cu cell reaches 98.6% at 0.5 mA cm(-2)-1 h and 98.5% at 1 mA cm(-2)-1 h for 300 cycles. Also, a Li||NCM811 pouch cell with LNO-PVC interlayer can also reach a 400 Wh kg(-1) energy density with a cycling life of 65 cycles. This strategy sheds light on the effect of the state of this salt on its release/dissolution kinetics, which is determined by the interactions between the salt and host material.

Rocking‐chair based lithium‐ion batteries (LIBs) have extensively applied to consumer electronics and electric vehicles (EVs) for solving the present worldwide issues of fossil fuel exhaustion and environmental pollution. However, due to the growing unprecedented demand of LIBs for commercialization in EVs and grid‐scale energy storage stations, and a shortage of lithium and cobalt, the increasing cost gives impetus to exploit low‐cost rechargeable battery systems. Dual‐ion batteries (DIBs), in which both cations and anions are involved in the electrochemical redox reaction, are one of the most promising candidates to meet the low‐cost requirements of commercial applications, because of their high working voltage, excellent safety, and environmental friendliness compared to conventional rocking‐chair based LIBs. However, DIB technologies are only at the stage of fundamental research and considerable effort is required to improve the energy density and cycle life further. We review the development history and current situation, and discuss the reaction kinetics involved in DIBs, including various anionic intercalation mechanism of cathodes, and the reactions at the anodes including intercalation and alloying to explore promising strategies towards low‐cost DIBs with high performance. Beyond conventional batteries: This Review presents the development history and state of the art of DIBs and presents the reaction kinetics and corresponding critical issues including the various anionic intercalation mechanisms of cathodes, and the reactions at the anodes, including intercalation and alloying, to explore promising strategies towards low‐cost DIBs with high performance.

The efficient recovery of gold from industrial sewage is important for saving precious metals and remains a big challenge. We report the extraction of gold ions from a trace-level aqueous solution using a tannic acid (TA) coated single-wall carbon nanotube (SWCNT) film. The TA has many redox ligands that efficiently adsorb Au(III) from the solution and reduce them to Au particles. The interwoven SWCNTs not only act as a framework to improve the mechanical stability of the hybrid membrane, but also provide abundant paths for H 2 O transport, and facilitate the full exposure of the TA. As a result, the hybrid membrane has an excellent ability to capture gold ions from solution with a high flux of 157 L/(m 2 ·h·bar), and an ultra-high adsorption capacity of 2095 mg/g from solutions with an extremely low gold concentration of 20 ppm. The adsorbed gold ions are reduced to Au particles, which can be easily collected by oxidation. The recovered Au nanoparticles on the TA–SWCNT hybrid film had a remarkable surface-enhanced Raman scattering effect that enabled the sensitive detection of rhodamine 6G.

Graphite film has many remarkable properties and intriguing applications from energy storage, electromagnetic interference (EMI) shielding, and thermal management to ultraviolet lithography. However, the existing synthesis methods require an extremely high processing temperature of ∼3000 °C and/or long processing time of typically hours. Here, we report an ultrafast synthesis of tens of nanometer-thick high-quality graphite films within a few seconds by quenching a hot Ni foil in ethanol. The vertical growth rate can reach over 64 nm s–1, which is more than 2 orders of magnitude higher than those of the existing methods. Moreover, the films show excellent electrical conductivity (∼2.6 × 105 S/m) and mechanical strength (∼110 MPa) comparable to or even better than those synthesized by chemical vapor deposition. As an example, we demonstrate the potential of these graphite films for effective EMI shielding, which show a record absolute shielding effectiveness of 481,000 dB cm2 g–1, outperforming all the reported synthetic materials.

Lithium-sulfur (Li-S) batteries are considered to have great potential due to their high theoretical specific energy and natural abundance of sulfur. However, the practical specific energy and cycle life of Li-S pouch cells are significantly hindered by thin sulfur cathodes, flooded electrolytes and excess Li metal anodes. Here, an ultrathin and highly efficient boron nitride/single-wall carbon nanotube (BN/SWCNT) interlayer (UHEI) achieves excellent Li-S pouch cell performance with high sulfur loading and a lean electrolyte. Compared with the reported interlayer materials, the UHEI can not only hinder the diffusion of polysulfides, but also promote further redox reactions and allow Li+ to pass through easily. Meanwhile, this UHEI can significantly improve lean electrolyte performance (E/S ratio of 8 mu L mg(-1)) and both high and low plateau capacities of Li-S batteries with a high sulfur loading (10 mg cm(-2)). Moreover, a normalized "ratio of the areal loading interlayer to sulfur (I/S)" was proposed and two "interlayer efficiency index (IEI)" were obtained by using I/S to quantify the efficiency of interlayers at a certain current density and guide the design of high-efficiency interlayers. The IEI of our UHEI@PP is dozens of times higher than previously reported results. Li-S cells with UHEI@PP delivered a remarkable discharge capacity of 6.6 mA h cm(-2) after 100 cycles at 0.2C for pouch cells (4.1 mg cm(-2) per side, E/S ratio of 10 mu L mg(-1)). The work provides new insights into separator modification for the practical application of lithium-sulfur batteries in the future.

Solid-state lithium–sulfur (Li–S) batteries have been recognized as a competitive candidate for next-generation energy storage systems due to their high energy density and safety. However, the slow redox kinetics between S and Li 2 S and the large volume change of sulfur during charge/discharge have hindered the development of solid-state Li–S batteries. We report a solid-state Li–S battery using a polymer-in-salt solid-state electrolyte, in which the sulfur is anchored in a polyacrylonitrile (PAN) substrate during cycling, avoiding the formation of Li 2 S and thus resulting in much faster redox kinetics and a smaller volume change than the conventional solid-state Li–S batteries. The quasi-intercalation reaction in the system is achieved with the assistance of the residual N , N -dimethylformamide (DMF), which helps strengthen the C–S bond. As a result, the solid-state Li-sulfurized PAN (SPAN) batteries have a superb rate capability at room temperature, even higher than those of liquid-state Li–S batteries, due to the faster redox kinetics and smaller volume change without solid–solid S to Li 2 S conversion which is present in liquid-state Li–SPAN batteries. This is the first report of the redox kinetics of solid-state Li–SPAN batteries being increased by changing the bond-strength of the C–S bond instead of using catalysts. This technique opens up new opportunities for designing high-performance solid-state Li–S batteries.

Two-dimensional (2D) materials are promising for next-generation photo detection because of their exceptional properties such as a strong interaction with light, electronic and optical properties that depend on the number of layers, and the ability to form hybrid structures. However, the intrinsic detection ability of 2D material-based photodetectors is low due to their atomic thickness. Photogating is widely used to improve the responsivity of devices, which usually generates large noise current, resulting in limited detectivity. Here, we report a molybdenum-based phototransistor with MoS2 channel and alpha -MoO3-x contact electrodes. The device works in a photo-induced barrier-lowering (PIBL) mechanism and its double heterojunctions between the channel and the electrodes can provide positive feedback to each other. As a result, a detectivity of 9.8x10(16)cm Hz(1/2) W-1 has been achieved. The proposed double heterojunction PIBL mechanism adds to the techniques available for the fabrication of 2D material-based phototransistors with an ultrahigh photosensitivity. Here, the authors exploit a photo-induced barrier-lowering mechanism in MoS2/ alpha -MoO3-x heterojunctions to realize two-dimensional phototransistors with enhanced performance and fast response at low bias voltage.

The search for new two-dimensional monolayers with diverse electronic properties has attracted growing interest in recent years. Here, we present an approach to construct MA(2)Z(4) monolayers with a septuple-atomic-layer structure, that is, intercalating a MoS2-type monolayer MZ(2) into an InSe-type monolayer A(2)Z(2). We illustrate this unique strategy by means of first-principles calculations, which not only reproduce the structures of MoSi2N4 and MnBi2Te4 that were already experimentally synthesized, but also predict 72 compounds that are thermodynamically and dynamically stable. Such an intercalated architecture significantly reconstructs the band structures of the constituents MZ(2) and A(2)Z(2), leading to diverse electronic properties for MA(2)Z(4), which can be classified according to the total number of valence electrons. The systems with 32 and 34 valence electrons are mostly semiconductors. Whereas, those with 33 valence electrons can be nonmagnetic metals or ferromagnetic semiconductors. In particular, we find that, among the predicted compounds, (Ca,Sr)Ga2Te4 are topologically nontrivial by both the standard density functional theory and hybrid functional calculations. While VSi2P4 is a ferromagnetic semiconductor and TaSi2N4 is a type-I Ising superconductor. Moreover, WSi2P4 is a direct gap semiconductor with peculiar spin-valley properties, which are robust against interlayer interactions. Our study thus provides an effective way of designing septuple-atomic-layer MA(2)Z(4) with unusual electronic properties to draw immediate experimental interest. The discovery of a new two-dimensional van der Waals layered MoSi2N4 material inspires many attentions. Here, the authors report intercalation strategies to explore a much wider range of MA(2)Z(4) family and predict amount of materials accessible to experimental verifications with emergent topological, magnetic or Ising superconductivity properties.

The high-throughput scalable production of cheap, efficient and durable electrocatalysts that work well at high current densities demanded by industry is a great challenge for the large-scale implementation of electrochemical technologies. Here we report the production of a two-dimensional molybdenum disulfide-based ink-type electrocatalyst by a scalable exfoliation technique followed by a thermal treatment. The catalyst delivers a high current density of 1000mAcm(-2) at an overpotential of 412mV for the hydrogen evolution. Using the same method, we produce a cheap mineral-based catalyst possessing excellent performance for high-current-density hydrogen evolution. Noteworthy, production rate of this catalyst is one to two orders of magnitude higher than those previously reported, and price of the mineral is five orders of magnitude lower than commercial Pt electrocatalysts. These advantages indicate the huge potentials of this method and of mineral-based cheap and abundant natural resources as catalysts in the electrochemical industry. The large-scale implementation of electrochemical technologies will require the high-throughput production of high-performance, inexpensive catalysts. Here, authors demonstrate earth abundant molybdenite as raw materials to produce efficient MoS2 catalysts for high current density H-2 evolution.

Recycling spent lithium-ion batteries (LIBs) is promising for resource reuse and environmental conservation but suffers from complex processing and loss of embedded value of spent LIBs in conventional metallurgy-based recycling routes. Herein, we selected a eutectic LiI-LiOH salt with the lowest eutectic point among binary eutectic lithium salt systems to provide a Li-rich molten environment, not only offering excess lithium but benefiting ion diffusion compared with that in the solid environment. Hence, the highly degraded LiNi0.5Co0.2Mn0.3O2 in spent LIBs which suffers high Li-deficiency and serious structural defects with harmful phase transitions is directly regenerated. A facile one-step heating strategy in the presence of a combination of the eutectic lithium salt and Co2O3 and MnO2 additives not only simplifies the recycling process but also endows the cathode materials with lithium supplementation and structural ordering, which contributes to a restoration of the capacity and stable cycling performance. In particular, this eutectic salt with a low eutectic point helps decrease the temperature and time of the direct recycling process and shows good adaptability for other layer oxide cathode materials (LiCoO2 and LiNi0.6Co0.2Mn0.2O2) in spent LIBs with varying cathode chemistry. As such, the feasibility of the direct recycling route is improved and broadened with simple and efficient processing, providing an idea for energy-saving cathode regeneration in future LIB recycling.

C/SiC volume ratios in carbon fiber-reinforced carbon-silicon carbide (C-f/C-SiC) composites may influence greatly mechanical and oxidation properties of the composites, but have not been well investigated yet. Herein, C-f/C-SiC composites with different C/SiC volume ratios were fabricated by chemical vapor infiltration (CVI) technique through alternating the thickness of a pyrocarbon (PyC) interlayer. The composites with C/SiC volume ratios of 0.37 and 0.84 exhibited the better comprehensive mechanical properties. The CS0.37 showed the highest flexural strength of 340.6 MPa, and CS0.84 had the maximum tensile strength of 139.1 MPa. The excellent mechanical properties were closely related to the relatively low C/SiC volume ratios and porosities, optimum interfacial bonding and reduced matrix micro-cracks. The composite with a low C/SiC volume ratio of 0.10 showed the best anti-oxidation performance due to its high SiC content. The oxidation mechanisms at 1100 degrees C and 1400 degrees C were discussed by considering the effect of the C/SiC volume ratios, pores and matrix micro-cracks, oxidation of carbon phase and SiC.