The realizing of high‐performance rechargeable aqueous zinc‐ion batteries (ZIBs) with high energy density and long cycling life is promising but still challenging due to the lack of suitable layered cathode materials. The work reports the excellent zinc‐ion storage performance as‐observed in few‐layered ultrathin VSe2 nanosheets with a two‐step Zn2+ intercalation/de‐intercalation mechanism verified by ex situ X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy (XPS) characterizations. The VSe2 nanosheets exhibit a discharge plateau at 1.0–0.7 V, a specific capacity of 131.8 mAh g−1 (at 0.1 A g−1), and a high energy density of 107.3 Wh kg−1 (at a power density of 81.2 W kg−1). More importantly, outstanding cycle stability (capacity retention of 80.8% after 500 cycles) without any activation process is achieved. Such a prominent cyclic stability should be attributed to its fast Zn2+ diffusion kinetics (DZn2+ ≈ 10−8 cm−2 s−1) and robust structural/crystalline stability. Density functional theory (DFT) calculation further reveals a strong metallic characteristic and optimal zinc‐ion diffusion pathway with a hopping energy barrier of 0.91 eV. The present finding implies that 2D ultrathin VSe2 is a very promising cathode material in ZIBs with remarkable battery performance superior to other layered transitional metal dichalcogenides.

Graphene, having a perfect two-dimensional crystal structure, has many excellent features such as a high specific surface area, and extraordinary electrical, thermal and mechanical properties. However, during the production process, lattice defects will inevitably be produced. Therefore, the performance of graphene with various defects is much lower than its theoretical value. We summarize the major advances of research into graphene defects in engineering in this paper. Firstly, the main types and causes of defects in graphene are introduced. Secondly, the influence of different defects in graphene on the chemical, electronic, magnetic and mechanical properties is discussed. Also, the control methods of graphene defects are reviewed. Finally, we propose the future challenges and prospects for the study of the defects of graphene and other nano-carbon materials.

Featured Application: gas sensors based on graphene and its derivatives have brilliant development prospects on innovating composite material and designing appropriate structure.Abstract: Gas sensors are devices that convert a gas volume fraction into electrical signals, and they are widely used in many fields such as environmental monitoring. Graphene is a new type of two-dimensional crystal material that has many excellent properties including large specific surface area, high conductivity, and high Young's modulus. These features make it ideally suitable for application for gas sensors. In this paper, the main characteristics of gas sensor are firstly introduced, followed by the preparation methods and properties of graphene. In addition, the development process and the state of graphene gas sensors are introduced emphatically in terms of structure and performance of the sensor. The emergence of new candidates including graphene, polymer and metal/metal oxide composite enhances the performance of gas detection significantly. Finally, the clear direction of graphene gas sensors for the future is provided according to the latest research results and trends. It provides direction and ideas for future research.2 of 21 excellent conductivity, and easy adsorption of gas molecules, and the surface can easily be modified by functional groups, so it has good gas sensing properties.Graphene, a monolayer of graphite sheet consisting of sp 2 hybridized carbon atoms covalently bonded to three other atoms which was first isolated by Geim and Novoselov using micro-mechanical peeling of graphite in 2004, so they won the 2010 Nobel Prize in Physics [8]. Graphene is the thinnest and highest strength material in nature at present and has the advantages of strong electric conductivity and heat conductivity, and is almost transparent and dense, thus attracts people's attention [9].Nowadays, there are many studies about graphene gas sensors focused on the performance improvement in the field of composite materials, computational chemistry and Micro-Electro-Mechanical System (MEMS). Considering the practical application of graphene gas sensor, we need to find the most potential direction. In this article, the development process and the state of art of graphene gas sensors are introduced. The direction of graphene gas sensors for the future is also provided. The review provides important reference for follow-up research work. Gas Sensor Key Parameters of Gas SensorGas sensors are the crucial components to detect the type and concentration of gas. The components can transform gas composition, gas concentration and other information from non-electricity to electricity to achieve the measurement of gas [10].The key parameters of gas sensor measuring performance include the following aspects [11]:

Two-dimensional (2D) hydroxide nanosheets can exhibit exceptional electrochemical performance owing to their shortened ion diffusion distances, abundant active sites, and various valence states. Herein, we report ZnCo(OH)Cl·0.45HO nanosheets (thickness ∼30 nm) which crystallize in a layered structure and exhibit a high specific capacitance of 3946.5 F g at 3 A g for an electrochemical pseudocapacitor. ZnCo(OH)Cl·0.45HO was synthesized by a homogeneous precipitation method and spontaneously crystallized into 2D nanosheets in well-defined hexagonal morphology with crystal structure revealed by synchrotron X-ray powder diffraction data analysis. In situ growth of ZnCo(OH)Cl·0.45HO nanosheet arrays on conductive Ni foam substrate was successfully realized. Asymmetric supercapacitors based on ZnCo(OH)Cl·0.45HO nanosheets @Ni foam// PVA, KOH//reduced graphene oxide exhibits a high energy density of 114.8 Wh kg at an average power density of 643.8 W kg, which surpasses most of the reported all-solid-state supercapacitors based on carbonaceous materials, transition metal oxides/hydroxides, and MXenes. Furthermore, a supercapacitor constructed from ZnCo(OH)Cl·0.45HO nanosheets@PET substrate shows excellent flexibility and mechanical stability. This study provides layered bimetallic hydroxide nanosheets as promising electroactive materials for flexible, solid-state energy storage devices, presenting the best reported performance to date.

Hierarchical nanostructures with highly exposed active surfaces for high‐performance pseudocapacitors have attracted considerable attention. Herein, a one‐step growth of (Ni xCo1−x)9Se8 solid solution series in various conductive substrates as advanced electrodes for flexible, foldable supercapacitors is developed. The formation of (NixCo1−x)9Se8 solid solution is confirmed by Vegard's law. Interestingly, the as‐grown (NixCo1−x)9Se8 solid solution series spontaneously crystallized into nanodendrite arrays with hierarchical morphology and fractal feature. The optimized (Ni0.1Co0.9)9Se8 nanodendrites deliver a specific capacitance of 3762 F g−1 at a current density of 5 A g−1 and remains 94.8% of the initial capacitance after 5000 cycles, owing to the advantage from fractal feature with numerous exposed () surface as well as fast ion diffusion. The as‐assembled flexible (Ni0.1Co0.9)9Se8@carbon fiber cloth (CFC)//PVA/KOH//reduced graphene oxide@CFC device exhibits an ultrahigh energy density of 17.0 Wh kg−1@ 3.1 kW kg−1, outperforming recently reported pseudocapacitors based on nickel‐cobalt sulfide and selenide counterparts. This study provides rational guidance toward the design of fractal feature with superior electrochemical performances due to the significantly increased electrochemical active sites. The resulting device can be easily folded, pulled, and twisted, enabling potential applications in high‐performance wearable and gadget devices.