Abstract:
We have fabricated a symmetric electrochemical capacitor with high energy and power
densities based on a composite of graphene foam (GF) with ~80 wt% of manganese oxide
(MnO2) deposited by hydrothermal synthesis. Raman spectroscopy and X-ray diffraction
measurements showed the presence of nanocrystalline MnO2 on the GF, while scanning and
transmission electron microscopies showed needle-like manganese oxide coated and
anchored onto the surface of graphene. Electrochemical measurements of the composite
electrode gave a specific capacitance of 240 Fg-1 at a current density of 0.1 Ag-1 for symmetric supercapacitors using a two-electrode configuration. A maximum energy density
of 8.3 Whkg-1 was obtained, with power density of 20 kWkg-1 and no capacitance loss after
1000 cycles. GF is an excellent support for pseudo-capacitive oxide materials such as MnO2,
and the composite electrode provided a high energy density due to a combination of doublelayer
and redox capacitance mechanisms.