An electrochemical route to quantitative oxidation of graphene frameworks with controllable C/O ratios and added pseudocapacitances.

We report an electrochemical oxidation route to tunable C/O ratios in the graphene framework, creating enhanced pseudocapacitance with increasing oxygen content. Controlled surface functionalities on graphene enable a high specific capacitance and negligible electric conductivity loss. A specific capacitance of up to 279 F g(-1) was achieved for the functionalized graphene at a discharge current of 1 A g(-1) in 1 M H2SO4 electrolyte; this capacitance remained as high as 152 F g(-1) at 100 A g(-1). These values are much higher than those of non-oxidized graphene. These excellent performances of the functionalized graphene signify the importance of precise control of the surface chemistry of graphene-based materials.