Reserach On The Capacitive Performance Of Three Dimensional Graphene/Ni₃S₂ Composite For Supercapacitor

Due to the worsening environmental pollution and energy shortage of resources, energy storage devices such as batteries, supercapacitors, fuel cells, have been widely studied.In addition, the increasing demand of portable and wearable devices, accelerate the development of the energy storage device to replace long cable connection of external power supply.In existing energy storage devices, supercapacitors due to its characteristics of long service life, high power density is considered to have great potential applications.Electrochemical performance can be achieved by using the super capacitor electrode materials with high specific surface area and high conductivity to improve.Up to now, carbon materials, such as carbon nanotubes（CNTs）,graphene and graphene form（GF） has been used in the field of supercapacitor. graphene supercapacitor due to its superior electric double layer capacitance characteristic, high electrical conductivity, the theory of capacity showed the good performance has been widely studied. However, graphene films due to its twodimensional structure has a low specific surface area. Thus, self-assembled threedimensional（3 d） porous structure of the carbon is used to improve the specific surface area. However, due to the weak connection between graphene films leads to low electrical conductivity and mechanical strength, make it difficult to applied to flexible energy storage device. As a possible solution, by chemical vapor deposition（CVD） growth on nickel foam of three dimensional graphene（3DG） have attracted great interest. 3DG growed by CVD method showed high conductivity and high and the electrolyte contact area due to its large number of microsize pore. In addition, it can make the electrolyte ion spread quickly, and provide a multi-dimensional electron transport pathways. The metal sulfides, such as NiSx, CuSx and CoSx, can significantly improve the capacitive performance. In particular, NiSx due to its high natural abundance, low cost, the characteristics of environmental protection and high theoretical capacity which has been widely used. As one of sulfur nickel compounds（such as the NiS, Ni₃S₂, NiS2, Ni3S4, Ni7S6, Ni9S8）, Ni₃S₂ not only has high sulfur nickel compound common conductivity, low cost, easy preparation but also the theory of the advantages of low toxicity and high specific capacitance, good rate and good electrical conductivity, and so on characteristics is widely applied in the field of supercapacitor. Ni₃S₂ widely exists in natural environment in the form of the sixparty sulfur nickel, it has a lot and cheap source of material.Three-dimensional graphene/Ni₃S₂（3DG/Ni₃S₂） composite electrodes were produced by a facile two-step synthesis route involving CVD growth of graphene foam and in situ hydrothermal synthesis of Ni₃S₂. The structure, morphology, and composition of the prepared 3DG and composite electrode were characterized by X-ray power diffraction（XRD）, Raman spectroscopy, transmission electron microscopy（TEM）, field emission scanning electronic microscopy（FESEM）, and X-ray photoelectron spectroscopy（XPS）. Cyclic voltammetry（CV） and galvanostatic charge-discharge（GCD） analysis, and electrochemical impedance spectroscopy（EIS） were carried out to test the electrochemical performance of the composite electrode.Results show that the 3DG is made of high quality with open less structure/networking carrier materials, and the methane content is 7 SCCM quality is better.At the same time, through the base of scanning image contrast before and after corrosion can be found that have an impact on the quality of the 3DG transfer process, can improve the defect of 3DG. In composite materials with the increase of the water thermal response time, the relative content of Ni₃S₂ increases with increasing time and covered the entire basal surface after 6 h, at the same time Ni₃S₂ micro globular grains grow along with the time and also increases gradually.Through electrochemical test and analysis, composite electrode showed high specific capacitance（5 mV/s 1509 F/g, 2 mA/cm2 11.529 F/cm2） and better performance of long cycle（88.97% capacity after 1000 cycles）.Analysis is due to the covered 100 nm size small basal condition provides enough Ni₃S₂ crystal as the electrode electrochemical active specific surface area and facilitate the electron transfer, ion diffusion.In addition, by comparing the two sets of samples of different base data can be found that 3DG excellent electrical conductivity, electron transfer rate and depth of open frame structure makes the ratio of composite electrode showed excellent properties.