Activated graphene-based carbons as supercapacitor electrodes with macro- and mesopores

Electric double layer capacitors (or supercapacitors) store charges through the physisorption of electrolyte ions onto porous carbon electrodes. The control over structure and morphology of carbon electrode materials is therefore an effective strategy to render them high surface area and efficient paths for ion diffusion. Here we demonstrate the fabrication of highly porous graphene-derived carbons with hierarchical pore structures in which mesopores are integrated into macroporous scaffolds. The macropores were introduced by assembling graphene-based hollow spheres, and the mesopores were derived from the chemical activation with potassium hydroxide. The unique three-dimensional pore structures in the produced graphene-derived carbons give rise to a Brunauer-Emmett-Teller surface area value of up to 3290 m(2) g(-1) and provide an efficient pathway for electrolyte ions to diffuse into the interior surfaces of bulk electrode particles. These carbons exhibit both high gravimetric (174 F g(-1)) and volumetric (~100 F cm(-3)) specific capacitance in an ionic liquid electrolyte in acetonitrile. The energy density and power density of the cell assembled with this carbon electrode are also high, with gravimetric values of 74 Wh kg(-1) and 338 kW kg(-1) and volumetric values of 44 Wh L(-1) and 199 kW L(-1), respectively. The supercapacitor performance achieved with these graphene-derived carbons is attributed to their unique pore structure and makes them potentially promising for diverse energy storage devices.