Preparation And Electrochemical Properties Of Cobalt-based Bimetallic Compounds

Due to ongoing energy price and environmental issues stemming from the consumption of fossil fuels,supercapacitors have gained considerable attention as a new type of energy storage device due to their superior rate performance and power density.However,their low energy density limits their usage to peak power demands in hybrid energy storage systems,rather than standalone energy storage systems.This low energy density is primarily due to the electrostatic storage being restricted by the surface area of the electrodes.Consequently,research into electrode materials,aimed at increasing specific surface area and introducing pseudocapacitance,has been essential for improving supercapacitor performance.Considering the cost and performance,this thesis will focus on cobalt-based sulfide with high theoretical specific capacitance.In this thesis,we synthesized a series of cobaltbased sulfide nanomaterial electrodes through various preparation processes,mainly by hydrothermal method,and comprehensively explored the improvement in chemical composition and expansion in morphology of cobalt-based sulfide through morphology and structure characterization and electrochemical performance test.The specific research contents are as follows:（1）A series of cobalt sulfide electrodes and cobalt oxide electrodes were synthesized by controlling the addition of surfactants,the number of hydrothermal synthesis steps,and the electrode preparation process,and the differences between these electrodes were compared.Furthermore,the morphology and electrochemical performance differences between cobalt sulfide nanowire arrays grown at different hydrothermal concentrations were studied.Cobalt sulfide nanowire array electrodes prepared at moderate concentrations had a specific capacitance of 656.3 F g^-1 at a current density of 1 A g^-1.（2）The differences in morphology and structure of ternary cobalt-based sulfide nanowire arrays combined with different transition metal materials（iron,nickel,copper）were explored,and their electrochemical performance was compared.Based on this,a nickel-cobalt-sulfur nanowire array with better comprehensive performance was selected,and the effects of hydrothermal growth concentration on its morphology and electrochemical performance were further explored.The nickel-cobalt-sulfur nanowire array electrode prepared at moderate hydrothermal concentration had a specific capacitance of 876.8 F g^-1 at a current density of 1 A g^-1,and better rate performance and cycle stability than the cobalt sulfide nanowire array.（3）A new nano-sheet structure of nickel-cobalt-sulfur material was introduced into the nickel-cobalt-sulfur nanowire array by two different processes,electro-deposition and hydrothermal methods,to form a core-shell structure,thereby increasing the material’s spatial utilization and specific surface area.Furthermore,by controlling the number of electro-deposition cycles and hydrothermal growth concentration,a core-shell nickel-cobalt-sulfur nanowire array with better comprehensive performance was found.The core-shell nickel-cobalt-sulfur nanowire array electrode prepared at moderate hydrothermal concentration had a specific capacitance of 1136.5 F g^-1 at a current density of 1 A g^-1,with minimal loss of rate performance and cycle stability.