Preparation of CoV-LDH@NiCo-LDH materials and energy storage performance of pseudocapacitors
Cobalt-vanadium layered bimetallic hydroxide(CoV-LDH)is rich in electrochemically active sites,but still suffers from the problems of expensive low-priced vanadium sources,difficult preparation,and vanadi-um dissolution.In this study,three-dimensional porous CoV-LDH electrode materials were prepared by electro-chemical cathodic reduction,and in order to improve the stability of CoV-LDH in alkaline electrolyte,the core-shell structure CoV-LDH@NiCo-LDH composites were constructed by secondary electrodeposition,which have the microscopic morphology of nanosphere-coated nanosheets and the uniform distribution of the three elements of Ni,Co,and V.This increased the contact area of the material's active sites and the electrolyte,and reduced the contact area of vanadium.With the uniform distribution of Ni,Co and V elements,the contact area between the active sites and the electrolyte is increased,the interfacial impedance of the material is reduced,and the pseudocapacitive energy storage performance is greatly improved.Under the current density of 1 A/g,the spe-cific capacitance of CoV-LDH@NiCo-LDH reaches 995.8 F/g,which is much better than that of CoV-LDH(575.2 F/g),with a significant increase of 73.1％in the specific capacitance,and it has excellent multiplicative performance,and the pseudocapacitance accounts for 85％of the total capacitance under the sweeping speed of 50 mV/s.The cycling stability reaches 85％after 2 000 cycles.Analyzing the reaction kinetics and energy stor-age mechanism of the NiCo-LDH@CoV-LDH electrode material,it exhibits not only the battery-type Faraday behavior but also the capacitive properties.The anode material was assembled with an activated carbon(AC)negative electrode to form a CoV-LDH@NiCo-LDH//AC asymmetric supercapacitor,with a specific capaci-tance of up to 222.2 F/g at a current density of 1 A/g,and an energy density of 30.86 Wh/kg at a power density of 222.2 W/kg.This work lays the foundation for the vanadium-based bimetallic hydroxide material,prepara-tion of vanadium-based bimetallic hydroxide materials and energy storage applications.
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