Incorporation of manganese dioxide within ultraporous activated graphene for high-performance electrochemical capacitors.

Manganese dioxide (MnO(2)) particles 2-3 nm in size were deposited onto a porous "activated microwave expanded graphite oxide" (aMEGO) carbon scaffold via a self-controlled redox process. Symmetric electrochemical capacitors were fabricated that yielded a specific capacitance of 256 F/g (volumetric: 640 F/cm(3)) and a capacitance retention of 87.7% after 1000 cycles in 1 M H(2)SO(4); when normalized to MnO(2), the specific capacitance was 850 F/g. Asymmetric electrochemical capacitors were also fabricated with aMEGO/MnO(2) as the positive electrode and aMEGO as the negative electrode and had a power density of 32.3 kW/kg (for an energy density of 20.8 Wh/kg), an energy density of 24.3 Wh/kg (for a power density of 24.5 kW/kg), and a capacitance retention of 80.5% over 5000 cycles.