Preparation And Properties Of Graphene-based Supercapacitor Composite Electrode Materials

With the rapid development of the global economy,the demand of people for fossil fuels and other energy is growing.It is urgent to seek efficient and reliable renewable energy.It is urgent to seek efficient and reliable renewable energy sources.As a way to solve this problem,efficient energy conversion and storage devices are increasingly applied in all walks of life.Among electrochemical energy storage devices,supercapacitors(SCs)have attracted wide attention due to high power density,good cycle stability and high charge-discharge efficiency.However,the low energy density of SCs in practical applications limits its development.Since the energy density of SCs is directly proportional to its electrode specific capacitance,reasonable adjustment of material composition and design of nano-structured materials to improve the electrode specific capacitance may be the most effective strategy to solve the low energy density of SCs at present.Graphene is a kind of material where carbon atoms are closely connected with sp~2 hybridization to form a single two-dimensional honeycomb lattice structure.It has the advantages of high specific surface area,high conductivity,stable mechanical properties and fast electron transmission ability,etc.In this paper,graphene is used as a substrate to prepare graphene-based supercapacitor composite electrode materials with high specific capacitance by combining graphene with other materials or growing nanostructured materials on its surface through different strategies.The main research contents are as follows:(1)Graphene oxide(GO)containing a large number of hydroxyl and carboxyl groups was prepared by chemical oxidative stripping of graphite by Hummer’s method.In order to explore the electrochemical effects of graphene concentration on graphene aerogel electrode materials,the four concentrations(4 mg/m L-10 mg/m L)of GO used to prepare high specific surface area graphene aerogel with three-dimensional network structure by hydrothermal method and green reduction method.It can be used as electrode material directly,which simplifies the preparation process of electrode material effectively.The results showed that when the concentration of GO was 4 mg/m L,the prepared graphene aerogel had the largest specific surface area(112.55 m~2/g)and the best electrochemical performance.The specific capacitance is 87.65 F/g at 1 A/g current density,and has excellent cycle stability,capacity retention rate is 88%after 5000 constant-current charge and discharge.(2)In order to improve the specific capacitance of the graphene aerogel electrode,GO was intercalated with carbon nanotubes first to avoid the accumulation of the resulting graphene nanosheets caused by the action of interlayer van der Waals forces;then it was combined with the conductive polymer poly Pyrrole(PPy)to increase the loading capacity of PPy on the graphene nanosheets,thus introducing more active reaction sites and effectively improving the specific capacitance of the graphene/PPy/carbon nanotube composite electrode.P-benzoquinone(BQ)can oxidize pyrrole(Py)to PPy,while being reduced to hydroquinone,and GO can be reduced to graphene at high temperatures.The results showed that when the content of BQ was 8 mmol/L,the electrochemical performance of the prepared composite electrode was the best.The mass specific capacitance at 1 A/g current density is 244.67 F/g.After 6000times of constant current charge and discharge,the capacitance retention rate is 84.01%.(3)A simple one-step electrochemical co-deposition method was used to prepare the graphene based ternary nickel-co sulfide composite electrode material with controllable load on the basis of 3D structure graphene aerogel intercalated with carbon nanotubes.Because the transition metal oxides can provide more active sites for redox reaction,the composite electrode material has better electrochemical performance.The results showed that the electrochemical performance of the composite electrode material is the best when the deposition cycle number is 3.With a mass specific capacitance of 716.8 F/g at a current density of 1 A/g,the capacitance retention rate is 74.71%after 1000 constant-current charge and discharge.