γ-Fe2O3/graphene nanocomposites as a stable high performance anode material for neutral aqueous supercapacitors

gamma-Fe2O3/graphene nanocomposites were developed as a high performance anode material for environmentally friendly neutral aqueous supercapacitors. This composite electrode, in addition to its good capacitive characteristics, exhibited outstanding rate capability and cycling stability. gamma-Fe2O3 nanocrystals of 5 nm in size were potentiostatically deposited onto a hosting 'porous graphene film to form the gamma-Fe2O3/graphene nanocomposite. The porous graphene film provided a highly conductive network to enhance the charge transport/transfer involved in the capacitance generation process and helped disperse the gamma-Fe2O3 nanocrystals within the graphene network to promote better utilization of the gamma-Fe2O3 nanocrystals for capacitance generation. The capacitive performances of the gamma-Fe2O3/graphene composite electrode were investigated by cyclic voltammetry and galvanostatic charging/discharging analyses in 1 M Na2SO3 over a potential window of 0 to -0.8 V (vs. Ag/AgCl). A high specific capacitance of 224 F gFe(2)o(3)(-1) was achieved for the gamma-Fe2O3/graphene composite electrode at 25 mV s(-1) fold that of the plain gamma-Fe2O3 electrode. The outstanding rate capability of the composite electrode was demonstrated with a high capacitance retention rate of 91% when the charging/discharging current density increased from 1 to 20 A g(-1). At the high charging/discharging current density of 20 A g(-1), the Coulombic efficiency remained high at 95%. The composite electrode experienced an electrochemical activation and its specific capacitance remained high above the starting specific capacitance after 40 000 cycles at 500 mV s(-1), exhibiting outstanding cycling stability.