An asymmetric supercapacitor (ASC) was fabricated using reduced graphene oxide (RGO) sheets modified with ruthenium oxide (RGO–RuO2) or polyaniline (RGO–PANi) as the anode and cathode, respectively. The ASC exhibited a significantly improved capacitive performance in comparison with that of the symmetric supercapacitors fabricated with RGO–RuO2 or RGO–PANi as the electrodes. The improvement was attributed to the broadened potential window in an aqueous electrolyte, leading to an energy density of 26.3 W h kg−1, about two-times higher than that of the symmetrical supercapacitors based on RGO–RuO2 (12.4 W h kg−1) and RGO–PANi (13.9 W h kg−1) electrodes. In addition, a power density of 49.8 kW kg−1 was obtained at an energy density of 6.8 W h kg−1.
