Research Of Graphene/Metal Oxide Composite As Elelctrode Material For Supercapacitor

Graphene, a new type of carbon allotropes followed by carbon nanotubes and fullerenes, is considered to be an ideal electrode material, due to its large surface area and high electrical conductivity. However, the serious aggregation and re-staking of graphene, resulting in low capacitance, and largely hinders its application in supercapacitors. Transition metal oxides have aroused wide interest because of its high capacity and low cost. However, the low electrical conductivity, poor compatibility with electrolyte and poor cycle stability of graphene, lower its electrochemical performance in surpercapacitor. In this paper, by using the unique structure characteristics of graphene, we prepare a variety of graphene/metal oxide composites, which combine advantage of both graphene and metal oxide, obtain electrode materials with the outstanding electrochemical capacitance for supercapacitor.By using microwave expansion nanographite sheet replace the natural flack graphite as raw material, the traditional Hummers method is further modified and effectively improve the preparation efficiency. The test results show that the electrochemical performance of graphene is different in KOH and Na2SO4 electrolyte. The specific capacitance of graphene at a current density of 1 A/g is 146 F/g in KOH electrolyte, which is higher than in Na2SO4 electrolyte. The electrochemical impendence analysis show that the series resistance and the charge transfer resistance values of graphene are more small in KOH electrolyte,indicating that graphene exhibit better hydrophilicity. Meanwhile, there is still 92 % of the initial capacitance is retained for graphene over 1000 cycles in KOH electrolyte, exhibits a higher electrochemical stability.Synthesize a variety of composite: G/MnO2、G/ Fe2O3、G/Co3O4、G/NiO, by a simple method without any additives. The characterization results show that the metal oxide generate on the surface graphene successfully, and the G/MnO2 composite shows a better structural characteristic, the MnO2 nanoparticles with well-defined size are dispersed on graphene sheets. The capacitances of above composites are 242 F/g, 169 F/g, 181.5 F/g and 178 F/g, respectively. The improvement of graphene material is due to the contributions of metal oxide. The G/MnO2 composite exhibits most superior capacity performance, owe to its unique structure.To further investigate the properties of G/MnO2 composite, by varying the feeding ratio between graphene and Mn source, we prepared a variety of G/MnO2 Composites: GMn1:1, GMn1: 4, GMn1:7 and GMn1:10. The average size of particles increased hen raising the composite proportion, reunion happen eventually. The study found that the optimize ratio of graphene and Mn source is 1:7, the size and distribution of MnO2 nanoparticles are more uniform, prevent the graphene from agglomeration effectively. A specific capacitance of 450 F/g for GMn1:7 composite was achieved at a current density of 1 A/g. Meanwhile, the composite shows excellent cycle stability without decline over 5000 cycles. We assembled supercapacitor using GMn1:7 composite as the electrode material, and obtained a specific capacitance of 123 F/g at a current density of 1 A/g.