High-performance symmetric electrochemical capacitor based on graphene foam and nanostructured manganese oxide

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 (MnO(sub2)) deposited by hydrothermal synthesis. Raman spectroscopy and X-ray diffractionmeasurements showed the presence of nanocrystallineMnO(sub2) 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(sup-1) at a current density of 0.1 Ag(sup-1) for symmetric supercapacitors using a two-electrode configuration. A maximum energy density of 8.3 Whkg(sup-1) was obtained, with power density of 20 kWkg(sup-1) and no capacitance loss after 1000 cycles. GF is an excellent support for pseudo-capacitive oxide materials such as MnO(sub2), and the composite electrode provided a high energy density due to a combination of double-layer and redox capacitance mechanisms.