Controlled reverse pulse electrosynthesized spike-piece-structured Ni/Ni(OH)2 interlayer nanoplates for electrochemical pseudocapacitor applications

Controllable Pulse Reverse Electrodeposition of Mesoporous Li xMnO2 Nano/Microstructures with Enhanced Electrochemical Performance for Li-Ion Storage

Given the ever-growing demand of electric vehicles and renewable energies, addressing the poor cyclic stability of lithium manganese dioxide is an urgent challenge. In this study, pulse reverse current as the driving force of a one-pot anodic electrodeposition was exploited to design the physicochemical and electrochemical characteristics of lithium manganese dioxides as cathode materials of Li-ion battery. The pulse reverse parameters, including the span of anodic and cathodic current application ( t_a and t_c) and frequency ( f'), were systematically modulated to determine the optimized values through monitoring the physicochemical properties using X-ray diffraction, thermogravimetric analysis/differential scanning calorimetry, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive spectrometry, Raman spectroscopy, N₂ adsorption-desorption isotherms, and inductively coupled plasma-optical emission spectroscopy, as well as the electrochemical properties using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge-discharge at different currents. Based on the results, Li_0.65MnO₂ synthesized using t_a = 95 ms, t_c = 5 ms, and f' = 8.33 Hz at the constant magnitude of anodic peak current density of 1 mA dm^-2 was determined as the optimized sample. The optimized lithium manganese dioxide rendered superior electrochemical performance with the initial discharge capacity of 283 mAh g^-1, which accounts for 96.4% of the theoretical discharge capacity, preserving 88.3% of this capacity after 300 cycles at 0.1 C and, in the meantime, was able to release a discharge capacity of 115 mAh g^-1 even after cycling at a higher current of 10 C. The superior electrochemical behavior of Li_0.65MnO₂ was attributed to the exclusive hierarchical urchin-like morphology as well as mesoporous nano/microstructures having a notably high Brunauer-Emmett-Teller surface area of 320.12 m² g^-1 alongside mixed-phase α/γ structure owing to the larger 2 × 2 tunnels, which offer more facile Li⁺ diffusion.

Ni(OH)2 nanosheets grown on porous hybrid g-C3N4/RGO network as high performance supercapacitor electrode

A porous hybrid g-C₃N₄/RGO (CNRG) material has been fabricated through a facile hydrothermal process with the help of glucose molecules, and serves as an efficient immobilization substrate to support ultrathin Ni(OH)₂ nanosheets under an easy precipitation process. It was found that the g-C₃N₄ flakes can uniformly coat on both sides of the RGO, forming sandwich-type composites with a hierarchical structure. It is worth noting that the introduction of the g-C₃N₄ can effectively achieve the high dispersion and avoid the agglomeration of the nickel hydroxide, and significantly enhance the synthetically capacitive performance. Owning to this unique combination and structure, the CNRG/Ni(OH)₂ composite possesses large surface area with suitable pore size distribution, which can effectively accommodate the electrolyte ions migration and accelerate efficient electron transport. When used as electrode for supercapacitor, the hybrid material exhibits high supercapacitive performance, such as an admirable specific capacitance (1785 F/g at a current density of 2 A/g), desirable rate stability (retain 910 F/g at 20 A/g) and favorable cycling durability (maintaining 71.3% capacity after 5000 cycles at 3 A/g). Such desirable properties signify that the CNRG/Ni(OH)₂ composites can be a promising electrode material in the application of the supercapacitor.