Abstract
In this work, three dimensional graphene was synthesized by the chemical vapor deposition method using nickel foam as a template. Activated carbon was dip-coated with graphene to combine carbon materials of different dimensions. Subsequently, MnO2/activated carbon/graphene composite electrodes with hierarchical pore structure and controllable MnO2 loading were synthesized using a self-limiting growth method; this was achieved by redox reactions of KMnO4 on sacrificial carbon materials. Furthermore, the capacitances between the carbon-only electrodes and the MnO2/carbon composite electrodes were compared. The former one are normally electrochemical double-layer capacitors, nevertheless, the latter one also show pseudocapacitive properties. The optimum MnO2/activated carbon/graphene composite electrode exhibited a specific capacitance of 813.0 F/g at a current density of 1 A/g, as well as good stability of 98.4% capacitance retention after 1000 cycles. When the symmetric solid-state supercapacitor was built from MnO2/activated carbon/graphene composite electrodes, it showed an energy density of 33.9 Wh/kg and a power density of 319.3 W/kg. Results of the feasibility tests indicate that the composite electrodes can be promising for supercapacitor applications.