Fabrication Of Hierarchical Electrodes Based On Nickel Cobalt Compounds And Study On Their Electrochemical Energy Storage Performance

Nanoscale,hierarchically structured,well-ordered and open porous electrodes can not only shorten the transport distance of ions and improve the transport and transfer of electrons and ions,but also release stress during charging and discharging processes,showing g reat promise for achieving energy storage devices with high mass loadings,high specific capacitances,high rates as well as excellent cycle stabilities.Nonetheless,up to present,researchers have paid much more attention on the study of the intrinsic properties of electrode materials rather than the structure of electrode materials.Thus,in this study,by controlling the morphologies of nickel cobalt compounds deposited on nickel nanowire arrays,we managed to construct electrodes with unique structures and with enhanced electrochemical performances.We also tried to discover the inner mechanism of the electrochemical enhancement in this study.This thesis consists of two parts.Firstly,Cobalt hydroxide nanosheets were grown on nickel nanowires via hydrothermal reaction at mild temperature to form a lavender-like-structured electrode.The nickel nanowires acted as robust scaffold to support cobalt hydroxides and provide numerous fast channels for electrons;the ultrathin cobalt hydroxide sheets were evenly distributed on nickel nanowires,forming a three dimensional interconnected porous structure.Electrochemical measurements show that this electrode has greatly enhanced electrochemical performances.Secondly,we successfully grew nanoneedle-like nickel cobalt sulfides on nickel nanowires through a two-step hydrothermal method and obtained a test-tube-brush-like structured electrode.The nickel nanowires can improve the efficiency of the collection and transport of electrons,and the nanoneedle-like nickel cobalt sulfides can provide rich active sites for electrochemical redox reactions.We also used nickel foam and carbon clothes as substrates to grow nickel cobalt sulfides under the same condition,and the test-tube-brush-like structured electrode showed the best electrochemical performance.By controlling the concentration of the solutions in the first hydrothemal reaction,we successfully synthesized the test-tube-brush-like structured electrode with different mass loadings and investigated the effect of mass loading on the electrochemical performance.Furthermore,we fabricated an asymmtric supercapacitor consisting this electrode and activated carbon,and the supercapacitor exhibited enhanced electrochemical performance.Based on the results of the our studies,it was found that the as-fabricated electrodes could facilitate the exertion of the synergic effect of the nickel nanowires and the active materials and improve the efficiency of the transport of both electrons and ions,which could drastically enhance the electrochemical performances of the electrodes.