High-performance supercapacitors based on a graphene–activated carbon composite prepared by chemical activation

Abstract

Graphene has been widely applied as a promising supercapacitor material based on the electric double-layer mechanism. In order to solve the dispersed problem of graphene, noncovalent functionalized graphene is prepared. However, not all of these functionalized graphene materials can be employed in supercapacitors due to non-electrochemically activated molecules absorbed on graphene. Here we find a route of chemical activation with KOH to transfer noncovalent functionalized graphene to a graphene–activated carbon composite with a high specific surface area. Stable graphene colloids absorbed by oligomers of p-phenylene diamine was produced during the reduction of graphite oxide. KOH can homogeneously contact the solid graphene nanosheets after drying the colloid. Chemical activation by annealing the graphene based hybrid with KOH leads to a greatly increased specific surface area of 798 m² g⁻¹. The resulting graphene–activated carbon composite has a good capacitance of 122 F g⁻¹ and energy density of 6.1 Wh kg⁻¹ in aqueous electrolyte. The supercapacitor exhibits maximum energy densities of 52.2 and 99.2 Wh kg⁻¹ in an ionic liquid electrolyte at room temperature and 80 °C, respectively.