Nanolayered structures present significantly enhanced electrochemical performance by facilitating the surface-dependent electrochemical reaction processes for supercapacitors, which, however, causes capacitance fade upon cycling due to their poor chemical stability. In this work, we report a simple and effective approach to develop a stable, high performance electrode material by integrating 2D transition metal hydroxide and reduced graphene oxide sheets at nanometer scale. Specifically, a hybrid nanolayer of Ni-Co hydroxide @reduced graphene oxide (Ni,Co-OH/rGO) with an average thickness of 1.37 nm is synthesized through an easy one-pot hydrothermal method. Benefiting from the face to face contact model between Ni-Co hydroxide and rGO sheets, such unique structure presents superior specific capacitance and cycling performance as compared to the pure Ni-Co hydroxide nanolayers. An asymmetric supercapacitor based on Ni,Co-OH/rGO and three-dimensional (3D) hierarchical porous carbon is developed, exhibiting a high energy density of 56.1 Wh kg(-1) along with remarkable cycling stability (80% retention after 17 000 cycles), which holds great promise for practical applications in energy storage devices.

The emergence of atomically thick nanolayer materials, which feature a short ion diffusion channel and provide more exposed atoms in the electrochemical reactions, offers a promising occasion to optimize the performance of supercapacitors on the atomic level. In this work, a novel monolayer Ni-Co hydroxyl carbonate with an average thickness of 1.07 nm is synthesized via an ordinary one-pot hydrothermal route for the first time. This unique monolayer structure can efficiently rise up the exposed electroactive sites and facilitate the surface dependent electrochemical reaction processes, and thus results in outstanding specific capacitance of 2266 F g(-1). Based on this material, an all-solid-state asymmetric supercapacitor is developed adopting alkaline PVA (poly(vinyl alcohol)) gel (PVA/KOH) as electrolyte, which performs remarkable cycling stability (no capacitance fade after 19 000 cycles) together with promising energy density of 50 Wh kg(-1) (202 μWh cm(-2)) and high power density of 8.69 kW kg(-1) (35.1 mW cm(-2)). This as-assembled all-solid-state asymmetric supercapacitor (AASC) holds great potential in the field of portable energy storage devices.

PM2.5 concentrations have decreased remarkably in China in recent years, coinciding with a more rapid decrease in SO2 concentrations and a slower decrease in NO2 concentrations, while O3 concentrations increased. Correlations between PM2.5 and key gaseous pollutants were studied to identify linked trends as a means of understanding the impacts of air pollution control in China. In most cities, the PM2.5–NO2 correlation coefficients were higher than the PM2.5–SO2 correlation coefficients, and the gap tended to expand as air quality improved. Multiple linear regression also indicated that PM2.5 concentrations were more sensitive to changes in NO2 than in SO2. The rate of decrease in the PM2.5 concentration with a decreasing NO2 concentration is nearly 3 times higher than that with SO2. These results support the priority of controlling NO x to further reduce PM2.5 pollution in China. The chemistry behind this was twofold: (1) NO x can be converted into nitrate, and (2) NO x contributes to atmospheric oxidation capacity. The decrease in PM2.5 concentration always coincided with an increase in O3 concentration when the PM2.5 concentration was higher than 50 μg m–3. However, the correlation between PM2.5 and O3 tended to change from negative to positive as air quality improved, indicating O3 and PM2.5 control could both benefit from reducing the concentrations of gas precursors.

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Aqueous hybrid capacitors (HCs) suffer from sacrificed power density and long cycle life due to the insufficient electric conductivity and poor chemical stability of the battery-type electrode material. Herein, we report a novel NH4-Co-Ni phosphate with a stable hierarchical structure combining ultrathin nanopieces and single crystal microplatelets in one system, which allows for a synergistic integration of two microstructures with different length scales and different energy storage mechanisms. The microplatelets with a stable single crystal structure store charge through the intercalation of hydroxyl ions, while the ultrathin nanopieces store charge through surface redox reaction providing enhanced specific capacitance. Furthermore, the large single crystal can bridge the small nanopieces forming continuous electronic conduction paths as well as ionic conduction channels, and facilitate both electron and ion transportation in the hierarchical structure. The HC cell based on the as prepared material and a 3D hierarchical porous carbon delivers a high energy density of 29.6 Wh kg(-1) at a high power density of 11 kW kg(-1). Particularly, an ultralong cycle life along with 93.5% capacitance retention after 10,000 charge-discharge cycles is achieved, which is outstanding among the state-of-the-art aqueous HC cells.

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Since shaft parts operate under harsh environments for a long time, many critical parts suffer from corrosion, wear and other problems, leading to part failure and inability to continue in service. It is imperative to repair failed parts and increase their service life. An orthogonal experimental scheme is designed to numerically simulate the process of laser cladding of Inconel 718 alloy powder on 4140 alloy structural steel based on the ANSYS simulation platform, derive the relationship equation of cladding layer thickness according to the heat balance principle, establish a finite element model, couple three modules of temperature field, stress field and fluid field, and analyze different modules to realize the monitoring of different processes of laser cladding. The optimal cladding parameters were laser power 1000 W, scanning speed 15 rad/s, spot radius 1.5 mm, thermal stress maximum value of 696 Mpa, residual stress minimum value of 281 Mpa, and the degree of influence of three factors on thermal stress maximum value: laser power > spot radius > scanning speed. The pool in the melting process appears to melt the “sharp corner” phenomenon, the internal shows a double vortex effect, with a maximum flow rate of 0.02 m/s. The solidification process shows a different shape at each stage due to the different driving forces. In this paper, multi-field-coupled numerical simulations of the laser cladding process were performed to obtain optimal cladding parameters with low residual stresses in the clad layer. The melt pool grows and expands gradually during melting, but the laser loading time is limited, and the size and shape of the melt pool are eventually fixed, and there is a vortex flowing from the center to both sides of the cross-section inside the melt pool, forming a double vortex effect. The solidification is divided into four stages to complete the transformation of the liquid phase of the melt pool to the solid phase, and the cladding layer is formed. The multi-field-coupled numerical simulation technique is used to analyze the temperature, stress and fluid fields to provide a theoretical basis for the residual stress and surface quality of the clad layer for subsequent laser cladding experiments.

This paper provides an overview of the commonly used processes and equipment for laser cladding, including pre-set powder feeding, simultaneous powder feeding, wire feeding cladding, and coaxial cladding nozzles. By comparing the above processes and related nozzles, the coating characteristics are summarized for the selection of appropriate methods and equipment in different working environments. Meanwhile, the morphology and properties of the clad layers of shaft parts processed with different process parameters (e.g. laser power, scanning speed, lap rate, powder feed rate) and the influence of the combined parameters are overviewed. The changes and mechanisms of metals, ceramics, and metalceramic composites in terms of hardness, wear resistance, metallurgical bonding, and microstructure are analyzed. In addition, the application of numerical simulation techniques to simulate the temperature and stress fields and to plan the melting trajectory when laser cladding processing is performed on the surface of shaft parts are reviewed. Finally, the problems in the current research on laser cladding of shaft parts are summarized and the development directions are discussed.