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Strong intermolecular interactions in 2D organic molecular crystals arising from π-π stacking have been widely explored to achieve high thermal stability, high carrier mobility, and novel physical properties, which have already produced phenomenal progress. However, strong intermolecular interactions in 2D inorganic molecular crystals (2DIMCs) have rarely been investigated, severely limiting both the fundamental research in molecular physics and the potential applications of 2DIMCs for optoelectronics. Here, the effect of strong intermolecular interactions induced by unique short intermolecular Se-Se and P-Se contacts in 2D α-P4Se3 nanoflakes is reported. On the basis of theoretical calculations of the charge density distribution and an analysis of the thermal expansion and plastic-crystal transition, the physical picture of strong intermolecular interactions can be elucidated as a higher charge density between adjacent P4Se3 molecules, arising from an orderly and close packing of P4Se3 molecules. More importantly, encouraged by the strong intermolecular coupling, the in-plane mobility of α-P4Se3 nanoflakes is first calculated with a quantum nuclear tunneling model, and a competitive hole mobility of 0.4 cm2 V-1 s-1 is obtained. Our work sheds new light on the intermolecular interactions in 2D inorganic molecular crystals and is highly significant for promoting the development of molecular physics and optoelectronics.

Atomically thin two‐dimensional (2D) bismuth oxychalcogenides (Bi2O2X, X = S, Se, Te) have recently attracted extensive attention in the material research community due to their unique structure, outstanding long‐term ambient stability, and high carrier mobility, which enable them as promising candidates for high‐performance electronic and optoelectronic applications. Herein, we present a comprehensive review on the recent advances of 2D bismuth oxychalcogenides research. We start with an introduction of their fundamental properties including crystal structure and electronic band structure. Next, we summarize the common techniques for synthesizing these 2D structures with high crystallinity and large lateral size. Furthermore, we elaborate on their device applications including transistors, artificial synapses, optical switch and photodetectors. The last but not the least, we summarize the existing challenges and prospects for this emerging 2D bismuth oxychalcogenides field.

Bimetallic sulfides are expected to realize efficient CO2 electroreduction into formate over a wide potential window, however, will undergo in situ structural evolution under the reaction conditions. Therefore, clarifying the structural evolution process, the real active site and the catalytic mechanism appear significance. Here, taking Cu2SnS3 as an example, we unveiled that Cu2SnS3 occurred self-adapted phase separation toward forming the stable SnO2@CuS and SnO2@Cu2O heterojunction during the electrochemical process. Theoretical calculations illustrated that the strongly coupled interfaces as real active sites driven the electron self-flow from Sn4+ to Cu+, thereby promoting the delocalized Sn sites to combine HCOO* with H*. Cu2SnS3 nanosheets achieve over 83.4% formate selectivity in a wide potential range from -0.6 V to -1.1 V. Our findings provide insight into the structural evolution process and performance-enhanced origin of ternary sulfides under the CO2 electroreduction.

Thin (≤20 μm) and free-standing Li metal foils would enable precise prelithiation of anode materials and high-energy-density Li batteries. Existing Li metal foils are too thick (typically 50 to 750 μm) or too mechanically fragile for these applications. Here, we developed a facile and scalable process for the synthesis of an ultrathin (0.5 to 20 μm), free-standing and mechanically robust Li metal foil within a graphene oxide host. In addition to low areal capacities of ~0.1 to 3.7 mAh cm−2, this Li foil also has a much-improved mechanical strength over conventional pure Li metal foil. Our Li foil can improve the initial Coulombic efficiency of graphite (93%) and silicon (79.4%) anodes to around 100% without generating excessive Li residue, and increases the capacity of Li-ion full cells by 8%. The cycle life of Li metal full cells is prolonged by nine times using this thin Li composite anode. Thin Li foils are desirable for high-energy Li battery applications. Here, Cui and team devise a fabrication route for ultrathin (less than 20 μm) Li foils that show promise for improving existing anodes including silicon, graphite and metallic Li.

Low-symmetry 2D materials are reviving recently owing to their azimuth-angle-dependent physical properties, which can be applied in polarization-sensitive optical and photoelectric devices. In this work, layered V2P4S13 with a novel low-symmetry porous structure was introduced as a promising highly anisotropic 2D material. We systematically investigated the structural, phonon-vibrational, and optical properties of 2D V2P4S13 by transmission electron microscopy, angle-resolved polarized Raman spectroscopy, angle-resolved reflection, and absorption spectroscopy. We discovered that 2D V2P4S13 shows strong crystallographic anisotropy, highly porous structure, and unique bi-vanadium atom coupling in the 2D plane. Polarized Raman spectroscopy indicated the strong phonon vibration anisotropy of 2D V2P4S13. Additionally, angle-resolved difference reflection and absorption spectra demonstrated optical anisotropy with a high anisotropic absorption ratio of 1.55 at 468 nm. Remarkably, we discovered unusual linear dichroism conversion of V2P4S13 from 468 nm to 600 nm. Such unique structural features of 2D V2P4S13, in combination with high optical anisotropy, make it an ideal platform for novel polarization-sensitive devices.

Structural materials with excellent mechanical properties are vitally important for architectural application. However, the traditional structural materials with complex manufacturing processes cannot effectively regulate heat flow, causing a large impact on global energy consumption. Here, we processed a high-performance and inexpensive cooling structural material by bottom-up assembling delignified biomass cellulose fiber and inorganic microspheres into a 3D network bulk followed by a hot-pressing process; we constructed a cooling lignocellulosic bulk that exhibits strong mechanical strength more than eight times that of the pure wood fiber bulk and greater specific strength than the majority of structural materials. The cellulose acts as a photonic solar reflector and thermal emitter, enabling a material that can accomplish 24-h continuous cooling with an average dT of 6 and 8 °C during day and night, respectively. Combined with excellent fire-retardant and outdoor antibacterial performance, it will pave the way for the design of high-performance cooling structural materials.

Electrochemical synthesis based on electrons as reagents provides a broad prospect for commodity chemical manufacturing. A direct one-step route for the electrooxidation of amino C-N bonds to nitrile C≡N bonds offers an alternative pathway for nitrile production. However, this route has not been fully explored with respect to either the chemical bond reforming process or the performance optimization. Proposed here is a model of vacancy-rich Ni(OH)2 atomic layers for studying the performance relationship with respect to structure. Theoretical calculations show the vacancy-induced local electropositive sites chemisorb the N atom with a lone pair of electrons and then attack the corresponding N(sp3 )-H, thus accelerating amino C-N bond activation for dehydrogenation directly into the C≡N bond. Vacancy-rich nanosheets exhibit up to 96.5 % propionitrile selectivity at a moderate potential of 1.38 V. These findings can lead to a new pathway for facilitating catalytic reactions in the chemicals industry.

Highlights The 2D CoOOH sheet-encapsulated Ni2P into tubular arrays electrocatalytic system with expediting mass transport, structural stability, and tuned electron was conceptually proposed.The designed electrocatalysts realize expectant 1000 mA cm−2-level-current-density hydrogen evolution in neutral water for over 100 h. Electronic supplementary material The online version of this article (10.1007/s40820-020-00476-4) contains supplementary material, which is available to authorized users., Water electrolysis at high current density (1000 mA cm−2 level) with excellent durability especially in neutral electrolyte is the pivotal issue for green hydrogen from experiment to industrialization. In addition to the high intrinsic activity determined by the electronic structure, electrocatalysts are also required to be capable of fast mass transfer (electrolyte recharge and bubble overflow) and high mechanical stability. Herein, the 2D CoOOH sheet-encapsulated Ni2P into tubular arrays electrocatalytic system was proposed and realized 1000 mA cm−2-level-current-density hydrogen evolution over 100 h in neutral water. In designed catalysts, 2D stack structure as an adaptive material can buffer the shock of electrolyte convection, hydrogen bubble rupture, and evolution through the release of stress, which insure the long cycle stability. Meanwhile, the rich porosity between stacked units contributed the good infiltration of electrolyte and slippage of hydrogen bubbles, guaranteeing electrolyte fast recharge and bubble evolution at the high-current catalysis. Beyond that, the electron structure modulation induced by interfacial charge transfer is also beneficial to enhance the intrinsic activity. Profoundly, the multiscale coordinated regulation will provide a guide to design high-efficiency industrial electrocatalysts. Electronic supplementary material The online version of this article (10.1007/s40820-020-00476-4) contains supplementary material, which is available to authorized users.

Piezoresistive sensors, as an indispensable part of electronic and intelligent wearable devices, are often hindered by nonrenewable resources (graphene, conventional metal, or silicon). Biomass‐derived carbonaceous materials boast many advantages such as their light weight, renewability, and excellent chemical stabilization. However, a major challenge is that the strength and resilience of carbon‐based piezoresistive materials still falls short of requirements due to their random microarchitectures which cannot provide sufficiently good stress distribution. Encouraged by the excellent compressible properties and extraordinary strength of the Thalia dealbata stem, we propose a wood biomass‐derived carbon piezoresistive sensor with an artificial interconnected lamellar structure like the stem itself. By introducing a freezing‐induced assembly process, a wood‐based, completely delignified, nano‐lignocellulose material can be built into a “bridges supported lamellar” type architecture, where subsequent freeze‐drying and pyrolysis results in carbon aerogel monoliths. The resultant bioinspired carbon sponge has high compressibility and strength, of the order of two to five times higher than that of conventional metal, carbon, and organic materials. Combined with excellent biocompatible properties and chemical durability, these are useful properties for intelligent wearable devices and human‐motion detection.

Despite the high theoretical capacity of Si anodes, their huge volume change and poor electrical connectivity must be overcome by decreasing the feature sizes of the Si particles to the nanoscale and compositing them with highly conductive carbon materials. To ensure the mechanical integrity of the electrodes with uniform dispersion and good electrical contact of the nano-silicon, the industry has to use a relatively low amount of Si ( 2000 mA h g−1 after 300 cycles) and a commercial-level areal capacity (5.58 mA h cm−2). This strategy offers a new way to design electrodes with a high active material content for high performance batteries.

Hydrogen economy is imagined where excess electric energy from renewable sources stored directly by electrochemical water splitting into hydrogen is later used as clean hydrogen fuel. Electrocatalysts with the superhigh current density (1000 mA cm-2 -level) and long-term durability (over 1000 h), especially at low overpotentials (

Power sources with strong mechanical properties and high‐energy density are highly desirable for the next‐generation flexible electronics. However, the challenge arises from the current electrode structure design, which is unable to bring both satisfactory mechanical and electrochemical properties with high active materials content and mass. Herein, we reported novel flexible, high‐strength, and mechanically stable TiO2‐based film electrodes for advanced sodium‐ion batteries, achieving an ultrahigh strength (up to ≈60 MPa) and commercial‐level areal capacity (4.5 mAh cm−2). Highly‐dispersed TiO2 and interlaced carbon nanotube (CNT) networks are embedded in the sheet‐liked cellulose to form porous, high‐conductive, and high‐active TiO2‐C nanosheets that is basic building subunits of TiO2‐C films, allowing the films with structural robustness and origami‐level flexibility. This strategy reconciles the contradiction between mechanical properties and active material content in flexible electrodes, and the fabricated electrode with a high TiO2 content of >65% can be bent more than 11 000 times without breaking. Meanwhile, good capacity and excellent cycle stability (0.02‰ capacity‐decay rate over 9000 cycles) of TiO2‐C film under a higher active content (75%) has well satisfied the demands of flexible energy storage devices for electrochemical performances. This TiO2‐C subunit assembly methodology demonstrates enormous potential in high‐strength/toughness flexible electrode construction for flexible electronics.

Two-dimensional (2D) materials with atomic thickness are promising candidates for the applications in future semiconductor devices, owing to their fascinating physical properties and superlative optoelectronic performance. Chemical vapor deposition (CVD) is considered to be an efficient method for large-scale preparation of 2D materials toward practical applications. However, the high melting points of metal precursors and the thermodynamics instabilities of metastable phases limit the direct CVD synthesis of plenty of 2D materials. The salt has recently been introduced into the CVD process, which proved to be effective to address these issues. In this review, we highlighted the latest progress in the salt-assisted CVD growth of 2D materials, including layered and non-layered crystals. Firstly, strategies of adding salts are summarized. Then, the salt-assisted growth of various layered materials is presented, emphasizing on the transition metal chalcogenides of stable and metastable phases. Furthermore, strategies to grow ultrathin non-layered materials are discussed. We provide viewpoints into the techniques of using salt, the effects of salt, and the growth mechanisms of 2D crystals. Finally, we offer the challenges to be overcome and further research directions of this emerging salt-assisted CVD technique.

We develop a pre-sodiation method by simply immersing the electrode in a liquid sodium source to reduce irreversible capacity loss for titanium-based materials. This liquid is more safe in operation and penetrates through the electrode more homogeneously than sodium metal. This method is easily extended to other titanium-based materials, and provides a possibility for large industrial applications.

Wood is gaining increasing attention in applications related to solar steam generation because of its porous structure with microchannels, low heat conduction properties, highly hydrophilic properties and renewability. Wood surface modification is required to improve steam generation performance because of its low optical absorptivity. Unfortunately, the high energy consumption fabrication process and high cost of current photothermal conversion coatings on wood impede its large-scale application. This study develops a facile pyrrole polymerization method to acquire polypyrrole decorated wood (PPy–wood) for solar evaporation enhancement. The black PPy decoration considerably improves the wood light absorption, resulting in a high absorbance (>90%) of PPy–wood within a broad wavelength range, from the ultraviolet region to the near infrared region (300–2500 nm). The combination of advantages related to wood (microchanneled porous structure, high hydrophilicity and thermal insulation) and PPy (broadband and high solar absorption capacity) for easy and fast steam generation makes PPy–wood an ideal solar steam generator, which shows rapid evaporation abilities (1.014 kg m−2 h−1) and high evaporation efficiency (72.5%) under simulated one sun irradiation. Moreover, the obtained clean water using PPy–wood as the steam generator shows low ion concentrations and high transmittance, demonstrating that PPy–wood possesses excellent potential for seawater desalination and sewage treatment. Thus, such PPy–wood is a potential candidate for water desalination and purification to address water scarcity issues through the effective utilization of clean energy.

Uncontrolled dendrite growth, continuous dead Li formation together with host-less volume changes associated with lithium metal greatly hamper the commercialization of high-energy-density lithium metal batteries (LMBs). Manipulating the deposition behavior of lithium ions is generally believed effective to root out undesired sharp protrusions over the anode surface and various kinds of 3D conductive inert substrates/hosts are introduced to mitigate volume changes and dead Li formation. However, the introduction of alien host would inevitably sacrifice partial energy density of cells. Herein, we successfully achieved in-situ deposition of a 3D continuous dendrite-free lithium deposition with blunt surface at the absence of inert host by simply adding an electrochemical active polymer-PMMA into the electrolyte to manipulate the deposition behavior of lithium ions. The function mechanism of PMMA upon Li deposition is investigated in detail. Upon discharging, lithium ions could react with PMMA and become immobilized. These pre-trapped lithium ions are then in-situ reduced into initial lithium seeds to guide sequential lithium deposition at the vicinity, ending up with a morphology modeled after the 3D PMMA molecular chains. Such morphology provides 3D continuous pathways for fast electron transport to eliminate dead Li formation without the help of foreign host. Li-LCO full cells equipped with such a 3D anode present greatly enhanced rate and cycle performance and highly preserved morphology upon rate testing and cycling.

Specific surface area (SSA) and graphitization degree are the most critical factors for carbon used for supercapacitors. However, synthesizing carbon materials with high SSA and graphitization degree in one material is still a challenge. Herein, we successfully get a carbon material with 3D graphitic belt skeleton and high SSA (>2600 m2 g−1) by using alkali metal as a catalyst to boost the graphitization of amorphous carbon at a relatively low temperature. The alkali metal with high activity can induce rearrangement of carbon atoms by firstly generating and then recoupling carbon dangling bonds to form graphene layers and followed self-stack into crystalline graphitic skeleton, which results in the high graphitization degree and elimination of non-carbon atoms in O-containing groups. Besides, the alkali derivatives can further produce rich porosity thus can maintain a high SSA. When used as an electrode material for supercapacitors, this carbon can deliver a large capacitance in a wide voltage window of 3.2 V in organic electrolyte and 1.0 V in aqueous electrolyte with excellent rate performance even up to 100 A g−1 and superior cycling stability over 13,000 cycles at the same time. A high energy density of 44.7 W h kg−1 can be obtained at a high power density of 12.8 kW kg−1. The excellent electrochemical performance can be attributed to its high surface area with rich mesopores for rapid ion transport, high conductivity from 3D intercrossed graphitic skeleton, and good chemical stability from low content of surface functional groups and carbon dangling bonds.

As a novel layered indium selenide (InSe) semiconductor has been attracting considerable interest in the field of modern (opto)-electronics. Despite current progress, the synthesis of ultrathin InSe nanoflakes still poses quite a challenge, due to its universal co-existing varied stoichiometric compounds. In this work, a novel phase-engineered route is proposed for synthesizing ultrathin single-crystalline InSe nanoflakes with the assistance of a stable mass-transfer process in a space-confined chemical vapor deposition (CVD) system. By finely tuning the growth parameters, InSe can be obtained through engineering a phase-transition thereby eliminating the undesirable In2 Se3 phase, revealed by the synergistic effect of high-content H2 and deficient Se. Furthermore, owing to the non-centrosymmetric structure, the CVD-grown InSe nanoflakes exhibit a high-performance second harmonic generation (SHG), making it very promising for future SHG applications in 2D configurations. This approach paves the way for the synthesis of other similar ultrathin materials with multiphase homologous compounds.

Graphitic carbon nitride (GCN) is a rising star in photocatalysis due to its chemical stability, economic suitability, and variable modulation of structures. However, the inefficient charge carrier transfer to reactants as well as the restricted visible light absorption greatly hinders the activities of GCN. Promoting better structure organization and decreasing domain sizes are efficient strategies to boost charge carrier transfer of GCN. However, these modifications usually lead to decreased light harvesting properties. In this paper, we modified small domain-sized graphitic carbon nitride (polymerized by urea) with extended visible light absorption (by nitrogen deficiencies) as well as improved charge carrier transport behaviors (by better structure organization) through implementing post-thermal treatment for 2 min. Inspiringly, the modified graphitic carbon nitride shows improved photocatalytic hydrogen evolution activities with 78.6% that of benchmark material P25 under irradiation of λ > 300 nm as ...

The rational design of concentration-gradient (CG) structure is demonstrated as an available approach to improve the electrochemical performances of high-energy nickel-rich cathodes for lithium-ion batteries (LIBs). However, the complicated preparing processes, especially the CG-precursors, generally result in the less-than-ideal repeatability and consistency that is regarded as an extreme challenge for the widespread commercialization. Thus, the innovative strategy with facile steps and the feasibility of large-scale preparation for commercialized applications should be urgently developed. Herein, through the temperature-tunable cation diffusion, the feasibility of controllable preparation of nickel-rich CG-LiNi0.7Co0.15Mn0.15O2 (NCM) from multishell precursors is first demonstrated. As expected, the Li/CG-NCM half cells show much enhanced cycle-life, rate property, and safety because of the mitigated side-reactions and fast Li+ kinetics. Besides, the Li4Ti5O12/CG-NCM full cells also exhibit long-term li...

Two dimensional (2D) nanomaterials are promising fundamental building blocks for use in the next-generation semiconductor industry due to their unique geometry and excellent (opto)-electronic properties. However, large scale high quality fabrication of 2D nanomaterials remains challenging. Thus, the development of controllable fabrication methods for 2D materials is essential for their future practical application. In this review, we will discuss the importance of the space-confined vapor deposition strategy in the controllable fabrication of 2D materials and summarize recent progress in the utilization of this strategy for the synthesis of novel materials or structures. Using this method, various high quality ultrathin 2D materials, including large-area graphene and boron nitride, ReS2/ReSe2, HfS2, pyramid-structured multilayer MoS2, and the topological insulators Bi2Se3 and Bi2Te3, have been successfully obtained. Additionally, by utilizing van der Waals epitaxy growth substrates such as mica or other 2D materials, patterned growth of 2D nanomaterials can be easily achieved via a surface-induced growth mechanism. Finally, we provide a short prospect for future development of this strategy.

Fiber supercapacitors have attracted tremendous attention as promising power source candidates for the next generation of wearable electronics, which are flexible, stretchable, and washable. Although asymmetric fiber supercapacitors with a high energy density have been achieved, their stretchability is no more than 200%, and they still face mechanical instability and an unreliable waterproof structure. This work develops a highly integrated structure for a waterproof, highly stretchable, and asymmetric fiber-shaped supercapacitor, which is assembled by integrating a helix-shaped asymmetric fiber supercapacitor into a bifunctional polymer. The asymmetric fiber supercapacitor demonstrates a working voltage of 1.6 V, a high energy density of 2.86 mW h/cm3, has unchanged capacitance after being immersed in water for 50 h, and retains 95% of its initial capacitance after 3000 cycles of stretching-releasing at a maximum strain of 400%. The extraordinary waterproof capability, the large stretching strain, and excellent stretching stability are attributed to the highly integrated structure design, which can also simplify the assembly process of stretchable, waterproof fiber supercapacitors.

Layered materials with weak van der Waals interactions between interlayers are able to provide adequate spaces for sodium ion intercalation and expressways for ion diffusion. Ether solvents are proved capable to facilitate the transport of ions and electrons transport in electrodes in virtue of their flexible one-dimensional chain structure. The combination of layered graphite and ether-based electrolytes even contributes to the revival of graphite as a promising anode material for sodium ion batteries via solvent co-intercalation. Lighted by these findings, in this work, we choose a quasi-layered vanadium sulfide (VS 4 ) as the electrode material and diglyme (DGM) as a multifunctional electrolyte solvent, to investigate the synergetic effects of solid material structure and electrolyte solvent on the electrochemical performances. Contrast to a drastically decay of capacity in electrolytes with ethylene carbonate/dimethyl carbonate, the capacity of VS 4 /RGO composites in DGM could maintain a value of near 400 mAh·g − 1 at a current density of 100 mA·g − 1 over 30 cycles and a capacity about 300 mAh·g − 1 at a quite high current density of 800 mA·g − 1 . The performance enhancement could be ascribed to the solvent co-intercalation into the van der Waals gaps and the resulting facilitated ion diffusion in electrode, which was later proved by TEM characterization and EIS measurements. To further prove the role of DGM, the electrochemical performances of another typical layered material WS 2 in these two electrolytes were measured and DGM solvent was found to contribute to greatly promoted performances as well.

Current electrode materials for commercial lithium ion batteries (LIBs) suffer from poor low temperature electrochemical performance, which seriously limits their application in winter and cold climate areas. Herein, pure phase LISICON structured Li3V2(PO4)3 (r-LVP) was successfully prepared and investigated for the first time as a low temperature cathode for LIBs. Benefiting from a fast ionic conductive structure and high structural stability, the r-LVP exhibits an outstanding high rate performance in a wide temperature range from 25 °C to −20 °C. Even at −30 °C, a discharge capacity of 90 mA h g−1 at 0.2C can be achieved, corresponding to 80% of the room temperature capacity. After 5000 cycles at a high rate of 10C, 84% of the initial capacity can be retained at −10 °C. Such a high rate capability and long cycle stability promise r-LVP could be a competitive candidate for low temperature LIBs.

Antimony (Sb) shows high conductivity and reactivity not only with lithium ions, but also with sodium ions due to its unique puckered layer structure; also, it can deliver a high theoretical capacity of 660 mA h g−1 by forming Li3Sb or Na3Sb. Compared with graphite, Sb has much higher theoretical capacity and safer reaction potential; moreover, it has a simpler reaction process and smaller volume changes than Si, Ge and Sn. In this study, the recent progress of Sb-based materials including elemental Sb nano-structures, intermetallic Sb alloys and Sb chalcogenides for lithium-ion and sodium-ion batteries are introduced in detail along with their electrode mechanisms, synthesis, design strategies and electrochemical performance. This review aims to present a full scope of the structures and properties of Sb-based materials and highlight effective strategies to design high performance Sb-based anode materials in the field of rechargeable Li/Na ion batteries.

h-BN is a widely used ultrathin insulator that can be synthesized in a controllable manner by chemical vapor deposition, similar to the growth of graphene. However, it is challenging to grow large-size single crystalline h-BN because of the ambiguous understanding of its growth mechanism. In this study, we propose a novel in situ formed nanoparticle-assisted growth strategy for large-size single crystalline h-BN growth on conventional polycrystalline copper. We found that the areal nucleation density of h-BN can be suppressed from ∼105 nuclei per mm2 to ∼102 nuclei per mm2 by the in situ formed nanoparticles that were introduced by pre-oxidation. Thus, single crystalline h-BN with lateral length of up to ∼102 μm was readily synthesized. Furthermore, for first time we discovered that the areal nucleation density of h-BN initially decreases and then increases under extreme annealing conditions, indicating that there is a competition-induced limit for suppressing the nucleation of h-BN on copper. This mechanism is universal for h-BN and graphene synthesis, which probably paves the way for large-size graphene/h-BN heterostructures synthesis in the future.

Solid-state electrolytes have a lot of advantages, including the inhibition of alkali metal dendrite growth, the elimination of liquid electrolyte leakage, the improvement of safety, the enhancement of energy density and power density, and the potential application in flexible electronics. Therefore, solid-state electrolytes have become one of the hottest topics in energy-storage research area. An up-to-date review on solid-state electrolytes is of not only scientific significance but also technological imperative. Here, recent progress in solid-state electrolytes for alkali ion batteries is summarized. Through this comprehensive review and the comparison of different solid-state electrolytes, we hope it can give a clear figure of the state-of-art status and the development trend of the future solid-state electrolytes.

Two-dimensional (2D) materials have attracted increasingly great interest in recent years due to their unique structures and novel physical and chemical properties. 2D semiconductors, the brightest member of the family of 2D materials, allow for realizing versatile electronic and optoelectronic devices. Their layered structure and atomic thickness render them have promising applications in monolithic integration, flexible devices and wearables electronics. Moreover, their bandgaps are usually related to the thickness and external strain, which mean the electronic optoelectronic properties can be tuned by changing the number of layers or strain engineering. Interestingly, some 2D semiconductors such as black phosphorus, GeS, and ReS2 have low symmetry crystal structures, their electronic and optical properties are highly anisotropic, such characteristics give us another degree of freedom to photodetections using polarized light. This feature article reviews the recent research activities that focus on applications of 2D semiconductors as photodetectors. It begins with survey of photocurrent generation mechanisms, which include photoconductive effect, photogating effect, photovoltaic effect, photo-thermoelectric effect and bolometric effect. These mechanisms are systematically introduced and discussed. Then, the general meaning of figure of merit that evaluates the performance of photodetectors is introduced, including responsivity, external quantum efficiency, time response, signal to noise ratio, noise equivalent power, detectivity. Furthermore, the recent photodetectors based on 2D semiconductors including transition metal dichalcogenides (TMDs), black phosphorus, ternary chalcogenides and their hybrid structures such as 2D-0D, 2D-1D, 2D-2D and 2D-3D structures are presented. MoS2 is the most studied TMD semiconductor, photodetectors based on monolayer and multilayers MoS2 are widely studied, some strategies including doping, encapsulation, and device design for improving photoelectronic performance are presented. Another interesting TMD is ReS2, due to its direct bandgap nature regardless of thickness and the low symmetry structure, it is supposed to have promising optoelectronic properties including in plane anisotropy. Black phosphorus, a p-type direct bandgap semiconductor with ultrahigh room temperature mobility beyond 1000 cm2/V s, have also received much attentions in recent years. Unlike most 2D semiconductor have bandgap range from 1–2 eV, black phosphorus have a much wide tunable bandgap from 0.3–1.5 eV, depending on the thickness, which means it can be used for infrared detection. Besides, like ReS2, black phosphorus also have in plane anisotropy in optic and electronic properties, proving us another additional opportunity by using polarization techniques to control the photoelectronic properties. The no dangling bonds nature at surface of 2D materials make the mixing of 2D materials with each other and other materials possible without the constraints of crystal lattice matching possible. These 2D based hybrid structures are also used in photodetectors to broaden the response range, increase response speed, and even investigate new physics. The most challenges of 2D semiconducting photodetectors are the low absorptions, slow response and narrow detect range. We also summarize some strategies to improve the above mentioned problems. Plasmon antenna, optical waveguides and optical microcavities can help to improve light absorption of 2D semiconductors. p-n Diode devices not only have fast response, but also wide detect range, other strategies such as encapsulation, surface modification, electrode design and so on might also help. Finally, the article ends with a summary and outlook on the future developments in this growing field.

Recently, copper species have been extensively investigated to replace Pt as efficient co-catalysts for the evolution of H 2 due to their low cost and relatively high activity. Cu nanoparticles less than 5 nm are successfully decorated on TiO 2 surface in this work by an easy and mild milling process. These Cu nanoparticles are highly dispersed on TiO 2 when the loading amount of Cu is no more than 10 wt%. The sizes of Cu nanoparticles can be controlled by changing the milling environment and decrease in the order of Cu-ethanol > Cu-water > Cu nanoparticles obtained through drying milling. The highest and stable hydrogen generation can be realized on Cu/TiO 2 with 2.0 wt% Cu and sizes of Cu nanoparticles ranging from 2 to 4 nm, in which high and stable photocurrent confirms promoted photogenerated charge separation. Smaller Cu clusters are demonstrated to be detrimental to hydrogen evolution at same Cu content. High loading of Cu nanoparticles of 2–4 nm will benefit photogenerated electron-hole recombination and thus decrease the activity of Cu/TiO 2 . The results here demonstrate the key roles of Cu cluster size in addition to Cu coverage on photocatalytic activity of Cu/TiO 2 composite photocatalysts.

Fast progresses have been made for Li 3 VO 4 since it is firstly reported as an anode material in 2013. However, most of current works focus on its performance improvement in capacity, rate and cycle capability, little study has been done to address its charge/discharge mechanism. Herein, we try to give a comprehensive understanding of its charge/discharge behaviours and capacity loss mechanism. By controlling the depth of discharge, it is found that the first irreversible capacity loss is related to the formation of SEI film as well as the structure distortion initiated by first lithiation. And the cycle performance of Li 3 VO 4 can also be influenced by the discharge depth. First principle calculation is also performed to predict the structure changes of Li 3 VO 4 upon different Li insertion amounts, and the results prove that the volume expansion and crystal distortion becomes more irreversibly at deep discharge. Along with cycle number, the accumulated structure deterioration results in the decline of material crystallization and structure orders, leading to capacity loss upon cycles. Based on the systematically analysis, future optimization of Li 3 VO 4 are also proposed, for instance, the interface modification by surface coating or optimization of electrolyte components, and structure stabilization by ion doping.

With a large capacity and low, safe voltage, Li 3 VO 4 is considered to be a promising new insertion type anode for lithium-ion batteries. However, its poor electrical conductivity limits its practical application. Many works have been made to improve the electrochemical performance such as reducing the particle size via different synthesis methods, enhancing the conductivity by carbon coating or compositing. Within three years, the reversible capacity of Li 3 VO 4 increased from 320 to 590 mA h g −1 , its capacity can be remained at 230 mA h g − 1 even at a high current density of 125 C (50 A g − 1 ), long cycle life of 5000 cycles at 50 C (20 A g −1 ) with little capacity decay is also achieved. Simultaneously, the in-depth study by in-situ and ex-situ XRD push forward for the better understanding of Li 3 VO 4 on its insertion mechanism and structure evolution processes. In this article, we review the current research development of Li 3 VO 4 , discuss its merits/demerits for practical use, and analyze the challenges and perspectives of Li 3 VO 4 as an insertion anode for lithium-ion batteries.

The low electronic conductivity and the sluggish sodium-ion diffusion in the compact crystal structure of Ti-based anodes seriously restrict their development in sodium-ion batteries. In this study, a new hollandite KxTiO2 with large (2 × 2) tunnels is synthesized by a facile carbothermal reduction method, and its sodium storage performance is investigated. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses illustrate the formation mechanism of the hollandite KxTiO2 upon the carbothermal reduction process. Compared to the traditional layered or small (1 × 1) tunnel-type Ti-based materials, the hollandite KxTiO2 with large (2 × 2) tunnels may accommodate more sodium ions and facilitate the Na+ diffusion in the structure; thus, it is expected to get a large capacity and realize high rate capability. The synthesized KxTiO2 with large (2 × 2) tunnels shows a stable reversible capacity of 131 mAh g–1 (nearly 3 times of (1 × 1) tunnel-structured Na2Ti6O13) and superior cycling stability...

Recent reports demonstrate that a two-dimensional (2D) structural characteristic can endow perovskites with both remarkable photoelectric conversion efficiency and high stability, but the synthesis of ultrathin 2D perovskites with large sizes by facile solution methods is still a challenge. Reported herein is the controlled growth of 2D (C4 H9 NH3 )2 PbBr4 perovskites by a chlorobenzene-dimethylformide-acetonitrile ternary solvent method. The critical factors, including solvent volume ratio, crystallization temperature, and solvent polarity on the growth dynamics were systematically studied. Under optimum reaction condition, 2D (C4 H9 NH3 )2 PbBr4 perovskites, with the largest lateral dimension of up to 40 μm and smallest thickness down to a few nanometers, were fabricated. Furthermore, various iodine doped 2D (C4 H9 NH3 )2 PbBrx I4-x perovskites were accessed to tune the optical properties rationally.

Sodium ion batteries (SIBs) are considered to be a promising alternative to lithium ion batteries because of the high abundance of sodium. However, the scarcities of suitable anode materials severely hamper the development of SIBs. Here, we synthesized a GeP5/C composite with binary sodium-reactive components on a large scale. Theoretically, it can promise a capacity of 1888 mA h g−1 or 6891 mA h cm−3, which is the best record in anodes for SIBs reported so far. In practice, the GeP5/C showed a low potential of ≈0.4 V vs. Na+/Na with a smooth charge/discharge profile. It delivered a large reversible capacity of 1250 mA h g−1 with a first coulombic efficiency of 93%. Electrochemical-mechanism studies suggested that the formation of a GeP5 phase endowed a high first coulombic efficiency and synergetic effect between the sodiation of Ge and P. This effect smoothly leveled the multistep plateaus and effectively reduced the polarization between charge/discharge. When applied to a full cell by coupling a Na3V2(PO4)3/C cathode, the assembled Na3V2(PO4)3//GeP5 full cell showed a large capacity of 800 mA h g−1 with a high average output voltage of 2.65 V. The excellent sodium-storage performances of GeP5/C will ensure commercial utilization in future SIBs.

GeS with a layered structure is expected to be a promising anode material for lithium ion batteries by the theoretical prediction of its excellent ion intercalation response. However, its experimental investigation is limited because of its low yield and complicated synthesis procedure. In this work, we successfully synthesize pure GeS and its carbon composite on a large scale by a simple and facile ball milling method. When serving as a novel anode material, GeS/C delivers a high reversible capacity of 1768 mA h g−1 with a high initial coulombic efficiency of 94% for lithium-ion batteries. The ex situ XRD patterns and CV tests confirm that GeS undergoes firstly a conversion reaction followed by an alloying type of lithium storage mechanism, in which the electrochemical performance controlled within the alloying reaction region is very stable and highly reversible, with a low and safe potential of 0.35 V vs. Li+/Li. When further applied in a full cell by coupling commercial LiCoO2 as the cathode, the assembled LiCoO2//GeS full cell can offer a high capacity of 736 mA h g−1, with a high flat discharge plateau of 3.4 V, showing a high utilization efficiency of the GeS anode. These results demonstrate that the layered GeS is a potential anode for high-energy lithium-ion batteries.

Nanostructures have been proved to be a promising strategy to realize fast Na-ion diffusion and high electrochemical activity for sodium titanate anodes. However, most researchers pay their attention to the controllable synthesis of nano-morphology for sodium titanate; there are few reports on the existence of water molecules and their influence on the structure and electrochemical performance of these solution-synthesized sodium titanate electrodes. Herein, urchin-like layered sodium titanate ultrafine nanowires are synthesized and the existence of structural water in them is confirmed. Their structural evolution upon the removal of water is investigated by SEM, XRD, TEM, IR and Raman measurements. The departure of interlayer water not only leads to a morphology change from ultrafine nanowires to highly crystalline nanorods but also induces a structure transformation from layered NaTi3O6(OH)·2H2O into tunnel structured Na2Ti6O13. The electrochemical analysis confirms that the dehydrated sample exhibits a better rate capability and enhanced cycling performance, suggesting that the existence of interlayer water in sodium titanate is unfavourable for the sodium ion diffusion in TiO6 octahedral layers. Our findings give a new understanding of the design and synthesis of the sodium titanate nanostructure with high rate capability.

The dendritic lithium formation and sustained lithium consumption caused by the uncontrollable side reactions between lithium and electrolytes seriously restrict the applications of lithium anodes in high-energy density batteries, especially in carbonate electrolytes. Ameliorating the surface status of lithium anodes is critical for modulating lithium deposition behavior and improving the cycling stability of lithium metal batteries. Herein, magnesium chloride salt is first reported as a carbonate electrolyte additive for lithium surface modification by in situ reaction. It is proved that both Cl– and Mg2+ play important roles in building a stable electrode/electrolyte interface with a fast Li+ diffusion property. The coexistence of inorganic LiCl and metallic Mg species in the interface can effectively decrease the surface side reactions, lower interphase resistance, promote Li ions diffusion, and result in uniform lithium deposition. The electrochemical tests show that the reversible utilization rate of...

Integrating thermodynamically favorable ethanol reforming reactions with hybrid water electrolysis will allow room-temperature production of high-value organic products and decoupled hydrogen evolution. However, electrochemical reforming of ethanol has not received adequate attention due to its low catalytic efficiency and poor selectivity, which are caused by the multiple groups and chemical bonds of ethanol. In addition to the thermodynamic properties affected by the electronic structure of the catalyst, the dynamics of molecule/ion dynamics in electrolytes also play a significant role in the efficiency of a catalyst. The relatively large size and viscosity of the ethanol molecule necessitates large channels for molecule/ion transport through catalysts. Perforated CoNi hydroxide nanosheets are proposed as a model catalyst to synergistically regulate the dynamics of molecules and electronic structures. Molecular dynamics simulations directly reveal that these nanosheets can act as a "dam" to enrich ethanol molecules and facilitate permeation through the nanopores. Additionally, the charge transfer behavior of heteroatoms modifies the local charge density to promote molecular chemisorption. As expected, the perforated nanosheets exhibit a small potential (1.39 V) and high Faradaic efficiency for the conversion of ethanol into acetic acid. Moreover, the concept in this work provides new perspectives for exploring other molecular catalysts.

2D ternary systems provide another degree of freedom of tuning physical properties through stoichiometry variation. However, the controllable growth of 2D ternary materials remains a huge challenge that hinders their practical applications. Here, for the first time, by using a gallium/indium liquid alloy as the precursor, the synthesis of high-quality 2D ternary Ga2In4S9 flakes of only a few atomic layers thick (approximate to 2.4 nm for the thinnest samples) through chemical vapor deposition is realized. Their UV-light-sensing applications are explored systematically. Photodetectors based on the Ga2In4S9 flakes display outstanding UV detection ability (R-lambda = 111.9 A W-1, external quantum efficiency = 3.85 x 10(4)%, and D* = 2.25 x 10(11) Jones@360 nm) with a fast response speed (tau(ring) approximate to 40 ms and tau(decay) approximate to 50 ms). In addition, Ga2In4S9-based phototransistors exhibit a responsivity of approximate to 10(4) A W-1@360 nm above the critical back-gate bias of approximate to 0 V. The use of the liquid alloy for synthesizing ultrathin 2D Ga2In4S9 nanostructures may offer great opportunities for designing novel 2D optoelectronic materials to achieve optimal device performance.

Aqueous zinc-metal batteries have gained widespread attention because of their high safety, large capacity, cost effectiveness, and environmental friendliness . However, zinc anodes have long encountered with dendrite formation, inferior cycle life and low coulombic efficiency, which severely hinder the practical application. Here, the latest advances of zinc metal anodes for aqueous zinc-metal batteries are reviewed. The merits of zinc metal anodes, the reaction mechanisms in different media, and the issues faced are firstly summarized. Then the prominent progresses of zinc anodes in aqueous media are highlighted, including electrolyte optimization, host construction, interface modification, anode structure design, and working model regulation. Finally, the remaining challenges of zinc anodes are fully discussed, and the future perspectives of pursing stable zinc metal anodes by integrating multi-strategies, conducting in situ study of zinc plating/stripping behavior, exploring advanced cathode materials , and developing smart devices are also provided.

Here we employ cyclic atmospheric chemical vapor deposition method to readily achieve strictly monolayer graphene continuous sheet with size as large as several square centimeters on copper foil. The uniformity and quality of as-synthesized graphene sheet have been verified by optical microscope, Raman, and electronic measurement, etc. The mechanism of this method is also revealed by carbon isotope growth and following Raman mapping analysis. This simple but effective strategy is promising to be extended into mass production in future.

The existing asymmetric behavior of positive and negative electrodes has been early observed experimentally in carbon/carbon supercapacitors, however, the understanding of its working mechanism is still lacking. In this paper, experiment and molecular dynamics (MD) simulation were integrated to investigate this phenomenon and its underlying origins. Two different electrolytes, tetraethylammonium tetrafluoroborate (TEABF4)/propylene carbonate (PC) and lithium hexafluorophosphate (LiPF6)/PC, were employed in the electrochemical measurements. Regardless of whether anions are smaller than cations or not, the positive electrode where anions adsorbed possesses a larger capacitance than the negative electrode. This asymmetric behavior in electrolyte LiPF6/PC is more distinct than in TEABF4/PC. MD simulations were carried out to render a full-length understanding that the ion motion and desolvation as well as the size of solvated ions are the main factors accounting for the asymmetric behavior. As unbalanced capa...

Rhenium disulfide (ReS2) is attracting more and more attention for its thickness-depended direct band gap. As a new appearing 2D transition metal dichalcogenide, the studies on synthesis method via chemical vapor deposition (CVD) is still rare. Here a systematically study on the CVD growth of continuous bilayer ReS2 film and single crystalline hexagonal ReS2 flake, as well as their corresponding optoelectronic properties is reported. Moreover, the growth mechanism has been proposed, accompanied with simulation study. High-performance photodetector based on ReS2 flake shows a high responsivity of 604 A·W−1, high external quantum efficiency of 1.50 × 105 %, and fast response time of 2 ms. ReS2 film-based photodetector exhibits weaker performance than the flake one; however, it still demonstrates a much faster response time (≈103 ms) than other reported CVD-grown ReS2-based photodetector (≈104–105 ms). Such good properties of ReS2 render it a promising future in 2D optoelectronics.

In this work, a new aqueous rechargeable Na-ion battery is developed based on all NASICON structured electrodes in which NaTi 2 (PO 4 ) 3 serves as the anode, Na 3 V 2 (PO 4 ) 3 serves as the cathode, and aqueous Na 2 SO 4 solution serves as the electrolyte. Such a combination of cathode-anode can fulfil the theoretical working window of aqueous electrolyte, thus give rise to a high cell voltage surpassing most of the previous aqueous Na-ion batteries. The developed NaTi 2 (PO 4 ) 3 /Na 3 V 2 (PO 4 ) 3 aqueous full cell demonstrates a flat discharge plateau at 1.2 V and can well maintain its performance at high current rates. Even at a current density of 10 A g −1 , the battery discharge capacity can still reach 58 mAh g −1 . Together with a high voltage, this cell configuration enables a high energy density of 29 Wh kg −1 at a power density of 5145 W kg −1 . The NaTi 2 (PO 4 ) 3 /Na 3 V 2 (PO 4 ) 3 system can be a promising low cost alternative for the current aqueous secondary batteries especially in terms of the high voltage and high power application. By controlling the cut-off voltage and adjusting the mass ratio of cathode to anode, we explored the different electrochemical performances of the aqueous full cell and identify which side of the electrode dominantly affects the cell decay at the case of full utilizing one electrode material. This investigation may present useful insight to researchers working on both aqueous batteries and NASICON-based materials.

WS2/carbon nanofibers (WS2/CNFs) are obtained by a simple electrospinning method in which few-/single-layer WS2 is uniformly embedded in carbon fibers. When used as the active anode material for Li-ion cells, these nanofibers exhibit a first-cycle discharge/charge capacity of 941/756 mAh/g at 100 mA/g and maintain a capacity of 458 mAh/g after 100 cycles at 1 A/g. The evolution of size and crystallinity of WS2 with heating treatment are systematically studied, which are found to strongly influence the final electrochemical performance. Interestingly, the WS2 samples of lowest crystallinity show the highest performance among all studied samples, which could result from the large interfacial capacity for Li ions due to their large specific surface area. More interestingly, the inherent flexible attribute of electrospun nanofibers renders them a great potential in the utilization of binder-free anodes. Similar high discharge/charge capacity of 761/604 mAh/g with a first coulombic efficiency of 79.4 % has been achieved in these binder-free anodes. Considering the universal of such simple and scalable preparation strategy, it is very likely to extend this method to other similar two-dimensional layered materials besides WS2 and provides a promising candidate electrode for developing flexible battery devices.

Multi-heteroatom self-doped porous carbon was synthesized via carbonization and activation of amino-acid-rich swim bladders and used for high-performance supercapacitors. The effects of different activation temperatures on the pore structure and composition of the carbon were investigated by TEM, Raman, XPS and nitrogen sorption analyses. With increasing temperature, the pore size broadens and the amount of doped heteroatoms decreases. The obtained materials have a high surface area of up to 3068 m2 g−1 with nitrogen, oxygen and sulfur multi-heteroatom doping. Carbon activated at 550 °C shows the highest capacitance of 410 F g−1 and excellent cyclic stability during 10 000 cycles due to the high surface area and multi-heteroatom doping. The outstanding performance makes this material promising for supercapacitors.

Vanadium nitrides (VN) have drawn much attention due to their large negative potential window, high electronic conductivity and fast reversible redox reaction. The electrochemical performances of VN are affected by their morphology and specific surface area, which depend deeply on the synthesis method. Herein, a large-sized nanoflake V2O5 xerogel is synthesized by a hydrothermal method followed by freeze drying, and then the nanoflake V2O5 xerogel is thermally treated for various times under NH3 atmosphere to study the nitriding process. The results show that the nanoflake V2O5 xerogel is reduced to nanoflake V2O3 before being completely transformed into nanoflake VN. The nanoflake VN demonstrate superior capacitive performance than the nanoflake V2O5 xerogel and intermediate V2O3, which arises from higher intrinsic conductivity.

We, for the first time, successfully grafted well-aligned binary lithium-reactive zinc phosphide (Zn3P2) nanowire arrays on carbon fabric cloth by a facile CVD method. When applied as a novel self-supported binder-free anode for lithium ion batteries (LIBs), the hierarchical three-dimensional (3D) integrated anode shows excellent electrochemical performances: a highly reversible initial lithium storage capacity of ca. 1200 mA h g(-1) with a coulombic efficiency of up to 88%, a long lifespan of over 200 cycles without obvious decay, and a high rate capability of ca. 400 mA h g(-1) capacity retention at an ultrahigh rate of 15 A g(-1). More interestingly, a flexible LIB full cell is assembled based on the as-synthesized integrated anode and the commercial LiFePO4 cathode, and shows striking lithium storage performances very close to the half cells: a large reversible capacity over 1000 mA h g(-1), a long cycle life of over 200 cycles without obvious decay, and an ultrahigh rate performance of ca. 300 mA h g(-1) even at 20 A g(-1). Considering the excellent lithium storage performances of coin-type half cells as well as flexible full cells, the as-prepared carbon cloth grafted well-aligned Zn3P2 nanowire arrays would be a promising integrated anode for flexible LIB full cell devices.

Organic single-crystalline semiconductors show great potential in high-performance photodetectors. However, they suffer from persistent photoconductivity (PPC) due to the charge trapping, which has severely hindered high-speed imaging applications. Here, a universal strategy of solving the PPC by integrating with topological insulator Bi2 Se3 is provided. The rubrene/Bi2 Se3 heterojunctions are selected as an example for general demonstration due to the reproducibly high mobility and broad optoelectronic applications of rubrene crystals. By virtue of high carrier concentration on Bi2 Se3 surface and the strong built-in electrical field, the photoresponse of the heterotransistor is significantly reduced for more than two orders (from over 10 s to 54 ms), meanwhile the photoresponsivity can reach 124 A W-1 . To the best of knowledge, this operating speed is among the fastest responses in organic-inorganic heterojunctions. The heterotransistor also shows unique negative differential resistance under positive gate bias, which can be explained by photoinduced de-trapping of electron trap states in the bulk rubrene crystals. Besides, the rubrene/Bi2 Se3 heterojunction behaves as a gate-tunable backward-like diode due to the inhomogenous carrier distribution in the thick rubrene crystal and inversion of relative Fermi level positions. The findings demonstrate versatile functionalities of the rubrene/Bi2 Se3 heterojunctions for various emerging optoelectronic applications.