Preparation And Electrochemical Properties Of Ni₃S₂/Graphene Composites

Supercapacitor(SC)is a kind of electric energy storage device with high power density,whose performance is mainly determined by the quality of its internal electrode material.Ni₃S₂ is one of the electrode materials commonly used in SC,but its structure often changes in the process of charge and discharge,which makes it difficult to keep the performance of electrode materials in a stable state.In this work,Ni₃S₂/reduced graphene oxide(r GO)/nickel foam(NF)and Ni₃S₂/chemical vapor deposition graphene(CVD G)/NF composite electrode materials were prepared by the improved Hummers method+electrodeposition method and the chemical vapor deposition(CVD)method+electrodeposition method on the NF substrate,respectively.Through the morphology and structure characterization,electrochemical performance test and optimizing preparation process of the two composite electrode materials,the Ni₃S₂-based composite electrode materials with excellent performance were obtained,which provided a new idea for its application in SC.The main research contents and achievements are as follows:1.The optimum electrodeposition parameters of preparing Ni₃S₂ were investigated by adjusting the concentration ratio of the precursor in the electrodeposition precursor solution.It was found that when the molar concentration ratio of Ni Cl₂·6H₂O to thiourea in the precursor solution is 1:20,the specific capacitance of the prepared Ni₃S₂/NF was the highest of 796 Fg^-1 at the current density of 1 Ag^-1.2.The improved Hummers method was used to prepare graphene oxide(GO)solution.Then,r GO was prepared by hydrothermal reduction method and loaded on NF to obtain r GO/NF.Finally,heazlewoodite phase Ni₃S₂ was grown on the surface of r GO/NF by electrodeposition method to obtain Ni₃S₂/r GO/NF composite electrode material.The specific capacitance of the composite is 1241 Fg^-1 at the current density of 1 Ag^-1.It was found that the recombination of r GO could improve the electrochemical properties of the electrode materials to some extent,but the improvement was not significant,which may be due to the decrease of the electrical conductivity caused by the defects on the surface of r GO.3.CVD G was prepared on the surface of NF by the CVD method,and network-like heazlewoodite phase Ni₃S₂ was prepared on the surface of CVD G/NF by the electrochemical deposition method,finally,binder-free Ni₃S₂/CVD G/NF composite electrode material was obtained.The specific capacitance of Ni₃S₂/CVD G/NF is as high as 2585 Fg^-1 at the current density of 1 Ag^-1,the capacitance retention rate is 70.68%as the current density increased to 30 Ag^-1,the capacitance can be retained 88.9%after5000 cycles of charge and discharge at the current density of 20 Ag^-1.The excellent electrochemical performance of Ni₃S₂/CVD G/NF composite electrode material is mainly attributed to the preparation of perfect heazlewoodite phase Ni₃S₂ by simple electrochemical deposition method and the good electrochemical contact between Ni₃S₂and substrate.In addition,the composite of CVD G can effectively improve the electrical conductivity and specific surface area of the electrode material.The research results provide an effective way to improve the capacitance characteristics of Ni₃S₂.