Study On Properties Of Graphene-coated Nickel Sulfide Composite For Supercapacitor

In recent years,energy crisis and environmental pollution caused by fossil energy have forced countries around the world to gradually turn to new green energy sources such as solar energy,wind power and tidal power.However,the original energy storage equipment can no longer meet the application of new green energy.In addition,with the economic development,the increasing demand for intelligent portable devices has also promoted the development of new energy storage devices.The supercapacitor as a new type of energy storage devices,not only inherited the traditional capacitor original high power,long life and other advantages,also has the very high energy density,so the super capacitor highly potential applications in energy storage area.As one of the supercapacitors,the pseudocapacitor is used to store electrical energy through a rapidly reversible chemical reaction,which has a higher energy density than the conventional capacitor.In recent years,nano-structured metal sulfide MS_X?such as M=Ni,Cu,Mo...?has been used in numerous pseudocapacitance materials.Due to its excellent physical and chemical properties and good electrochemical properties,it has become a promising electrode material.As the pseudocapacitor electrode material of Ni₃S₂ has high theoretical specific capacitance,long cycle life,abundant raw materials and environmentally friendly,but due to the high internal resistance and easy to reunite Ni₃S₂ factors such as limit its wide application in the field of energy storage.Usually in order to alleviate the problem,in addition to the reasonable design of Ni₃S₂ electrode materials nanostructures,will also be its graphene composite with good electrical conductivity,to reduce the internal resistance of electrode material and improve its electrochemical properties.In this paper,firstly,nickel hydroxide with two-dimensional nanosheet array structure was prepared on different substrates.High-quality graphene oxide was prepared by modified Hummers method,and graphene was loaded onto nickel hydroxide by physical coating.Finally,The graphene-coated nickel sulfide composites were prepared by ion exchange method.In this paper,scanning electron microscopy,X-ray diffractometry,X-ray photoelectron spectroscopy and energy dispersive spectroscopy were used to characterize the graphene and the composite electrode materials.The cyclic voltammetry,galvanostatic charge-discharge and alternating current impedance were used to characterize the graphene.The electrochemical properties of the composite electrode materials were tested and the electrochemical properties of graphene-coated nickel sulfide electrode materials were studied.The results of structural test show that the nickel sulfide is synthesized on the surface of different substrates,and the surface of graphene is coated with nickel sulfide.The structure has good electrochemical stability first,secondly has good ionic and electronic transmission,furthermore,two-dimensional slices array structure has high specific surface area,is advantageous to the electrochemical reaction.At the same time,the involvement of graphene can provide a faster electron transport channel for active substances.Electrochemical tests show that the graphene sulfide composite electrode has considerable electrochemical properties.In this case,the composite electrode with carbon fabric as the base is at the current density of 2 mA cm^-2,compared with the capacitance of 1910 mF cm^-2,and the ratio is still 100%after 1000cycles.In graphene nickel sulfide in composite materials,although there are few than capacitance graphene itself,but due to the intervention of graphene,the composites compared with the pure nickel sulfide electrode has better electrochemical performance.