Preparation Of Nickel-Cobalt Phosphide Electrode Materials And Study On Its Supercapacitive Properties

Supercapacitors have some unique advantages over batteries and fuel cells,such as fast charge/discharge,long life（>10000 cycles）,high power density,have attracted considerable interest in academia and industry,and are supercapacitors.The research and development of electrode materials for capacitors has become a hot spot for researchers.The core component of supercapacitor is electrode material,which directly determines capacitance,energy density and power density.However,supercapacitor has the disadvantage of low energy density,so the design of electrode material with high specific capacitance is the key to solve this shortcoming.For transition metal phosphides,not only catalytic properties but also energy storage properties,when it is used as an energy storage device,the open framework structure with large channels and cavities endows the electrode material with good ion conductivity and charge storage capacity.However,the existing problems of transition metal phosphide are complex synthesis process,poor rate performance and cycle stability when tested in alkaline dielectric,so the development of practical application of transition metal phosphide is limited.In this thesis,nickel-cobalt bimetallic phosphide as the research object,by improving the synthesis method and improving the microstructure,improved the specific capacitance and enhanced the structural stability in the process of charging and discharging.The specific contents are as follows:1.A stepwise electrochemical deposition method was designed to prepare phosphide electrode materials on nickel foam.The effects of different electrochemical deposition times on the morphology and the synergistic effect of nickel-cobalt bimetal on the properties were investigated.After comparing the microscopic morphology,composition and electrochemical performance,it was observed that the Ni₂P@CoP composite prepared under the electrochemical deposition time of 30 min had a specific capacity of 654 F g^-1at a current density of 1 A g^-1.After10,000 cycles,the specific capacity remained at 73.8%of the original.2.The needle-like structure prepared on the nickel foam by electrochemical deposition-dealloying and hydrothermal reaction,and then interconnected to form a Ni@NCP electrode material with a nano-sheet structure.The synergistic effect of the hollow Ni nanotubes prepared by electrochemical deposition-dealloying and nickel-cobalt bimetallic phosphide not only optimized the morphology but also made full use of their respective advantages.Hollow Ni nanotubes played a supporting role,and the nanosheet synthesized by hydrothermal reaction exposed abundant active sites in the electrolyte,which improved the problem of poor electrical conductivity and provided a large number of paths for ion transmission,thus improving the electrochemical performance.Among them,Ni@NCP electrode material had a specific capacity of 980 F g^-1at 1A g^-1,and a specific capacitance of 640 F g^-1at 20 A g^-1,which was 65.3%of the initial specific capacitance.After 10,000 cycles,it could still maintain 81%of the original specific capacity.3.Porous ultrathin Cu@NCP electrode materials were prepared by one-step electrodeposition on the multi-active-site dendrite substrate.Because the nickel-cobalt-phosphorus nanosheets were interlaced on the dendritic copper substrate to form a nanosheet array structure,the"effective specific surface area"of the electrode material during ion transport was improved.Moreover,the Cu@NCP with multiple active sites in the electrolyte increased the high-speed channel of ion transmission and shorted the transmission distance of electrons in the reaction process,so that the volume change of electrode materials in the charge and discharge process could be controlled.Experimental results showed that Cu@NCP electrode had considerable specific capacitance(3212 F g^-1)at 1 A g^-1,excellent magnification performance(2960 F g^-1at 20 A g^-1,93%of the initial specific capacitance)and excellent cyclic stability（after 10,000cycles,the specific capacity could still maintain 90.6%of the initial specific capacity）.