Preparation And Capacitance Properties Of Graphene/Metal Oxide Composite Electrode Materials

With the vigorous development of electric vehicles and portable electronics,supercapacitors highlight its important position due to fast charging rate and long cycle life.Graphene,as an alternative to activated carbon,carbon nanotube,one of the most promising electrode material for supercapacitors in the future.Graphene is extremely popular with many countries because of high specific surface area and excellent electrical conductivity,etc.However,graphene can easily produce aggregation after drying,reducing the actual specific surface area and decreasing the specific capacitance and energy density of graphene supercapacitors,which makes the seperation between scientific research and practical application.To solve the above problems,we try to optimize the structure and electrochemical performance of graphene-based supercapacitor from the reduction method of graphene,assembly technology of supercapacitors and doping and modification of graphene,to obtain the graphene-based supercapacitor electrode materials with high specific capacitance and high energy density.Firstly,GO is synthesized by a modified Hummers method.And we studied the effects of impurity ions and the electrical conductivity on GO purity.The results show that the pure GO is finally obtained when the dialysis proccess maintain the temperature about 50? and keep the time 900 min.The impacts of hydrazine hydrate reduction method,hydrothermal reduction method and vacuum thermal reduction method on the morphology and electrochemical properties of graphene supercapacitor are investigated by FTIR,BET,SEM and electrochemical characterization.The results show that the graphene prepared by hydrazine hydrate reduction method can effectively avoid the irreversible agglomeration of graphene,assemble into supercapacitors with the higher specific capacitance?173.75F/g?and the lower resistance?0.21??,and exhibiting 109.09% of the initial capacity after 1000 cycles.The influence of these process parameters such as coating amount of the active material,membrane and electrolyte on the electrochemical performance of graphene supercapacitor which using the graphene prepared above as electrode material is discussed.The results demonstrate that the best electrochemical performance of graphene supercapacitor can be obtained by coating amount of electrode materials in 5.3mg/cm2,using PTFE as the diaphragm and 1M?NH4?2SO4,1MLiOH,or 6M KOH as electrolyte.The C/NiO/MnO₂/RGO composites are obtained by ultrasonically assembling into two metal oxides of C/NiO/MnO₂ on the surface of graphene sheet by using carbon sphere as template.The effects of single material and the composite on the structure,surface morphology and electrochemical properties are analyzed by XRD,FTIR,SEM and electrochemical tests.The results show that the C/NiO/MnO₂ with core-shell structure can prevent the restacking of graphene.The addition of a certain amount of graphene?170F/g?has effectively increased the specific capacitance of the C/NiO/MnO₂/RGO50% composites?237.91F/g?.To obtain C/NiO/MnO₂/RGO composites with higher performance,the effects of C/NiO/MnO₂/RGO on electrochemical properties are investigated by converting the mass ratio of RGO and C/NiO/MnO₂.The study suggests that the C/NiO/MnO₂/RGO₃0% composites exhibit the maximum specific capacitance?304.85F/g?and energy density?27.11Wh/kg?when the composite's mass ratio of RGO and C/NiO/MnO₂ is 30%:70%.C/NiO/MnO₂/RGO composites have the potential application in the field of highperformance graphene supercapacitors.A novel MoO₃/PANI/RGO composite is prepared by doping the surface of graphene with MoO₃ metal oxide and PANI conductive polymer.The study shows that the specific capacitance?437.87F/g?of MoO₃/PANI/RGO₃0% can be greatly improved by the addition of graphene?19.2F/g?.The electrochemical behavior of MoO₃/PANI/RGO composites are further investigated by changing mass ratio of RGO from 10% to 50%.The results indicate that the MoO₃/PANI/RGO₂0% material have excellent specific capacitance?496.7F/g?and energy density?24.8Wh/kg?with the best mass ratio of MoO₃/PANI:RGO 80%: 20%.MoO₃/PANI/RGO composites can be expected to promote the development of a new generation of graphene-based supercapacitors.