Preparation Of Graphene-nickel Based Compounds And Its Application Of Supercapacitors

With the development of modern technology,fossil fuels play an important role,and its attendant consequences have led to dramatic reductions in fossil fuels,environmental pollution,and global warming.Therefore,in order to solve the above problems,we must find a new and efficient energy storage device to efficiently transfer the recyclable resources.As a new type of energy storage device,supercapacitors are widely used in various fields due to their high charge and discharge rate,good cycle stability,high power density,and good environmental friendliness.Among them,transition metal oxide electrode materials typified by nickel-based compounds have attracted wide attention due to their large specific capacitance,good cycle stability,long cycle life,and good environmental compatibility.However,due to the serious agglomeration of simple transition metal compounds,the poor conductivity and the small contact area between the electrode material and the electrolyte seriously restrict its development.Graphene,as a material composed of two-dimensional planar structure sp² hybridized,has been widely used in the field of energy storage due to its advantages of high electrical conductivity,high mechanical strength,good thermal stability,and large specific surface area.The modification of graphene into three-dimensional nitrogen-doped graphene can not only increase the conductivity of the material,but also greatly increase the specific surface area of??the material,and can provide more active sites for the loading of the nickel-based compound and increase the composite material.Electrochemical properties.This dissertation starts our discussion mainly from the following three aspects:?1?Ni?OH?₂/NG was prepared by a one-step hydrothermal synthesis method using N,N-dimethylformamide as a surfactant,hexamethylenetetramine as an alkali source and a nitrogen source.NiO/NG was also successfully obtained through tube furnace calcination method.The morphologies of the materials were tested by XRD,Raman,SEM,TEM,FTIR,XPS and other characterization methods.The electrochemical activity of the materials was tested by an electrochemical workstation.The results show that the Ni O/NG material can reach 1314.1 F g^-11 at a current density of 2 A g^-1.Its specific capacitance is slightly lower than Ni?OH?₂/NG,but its cycle stability is much higher than that of Ni?OH?₂/NG.NiO/NG composite electrode exhibited better electrochemical performance.?2?Three-dimensional nitrogen-doped graphene?3DNG?was prepared by a template method,and then NiO/NiFe₂O₄/3DNG was directly synthesized by microwave synthesis.Using XRD,Raman,SEM,TEM,BET,XPS and other means to test the morphology and structure of the material,and then electrochemical performance of the material under different electrolyte conditions by electrochemical workstation.The results show that NiO/NiFe₂O₄/3DNG exhibited the smallest impedance,the largest specific capacitance and the best cycle stability in 6 mol/L KOH electrolyte.By testing the material at a current density of 1 A g^-1,its specific capacitance can reach 1556.5 F g^-1,and 92.5%of the maximum value of the capacitance retention after 2000 cycles.This is due to the fact that the 3D nitrogen-doped graphene has a larger specific surface than the nanoparticle load provides more active sites,so that the nanoparticles can be more uniformly distributed on the surface of the material and the synergistic effect of NiO and Ni Fe₂O₄.?3?Three-dimensional nitrogen-doped graphene and nickel-iron sulfide were synthesized by different methods and compounded.The composite condition was determined by XRD,SEM and TEM.The three-dimensional porous nitrogen-doped graphene prepared by the template method and the Ni FeS₂ composite synthesized by microwave were obtained.The obtained NiFeS₂/3DNG has the advantages of good dispersibility,smaller nano-particle size and good electrochemical performance.