Manganese oxide/graphene oxide composites for high-energy aqueous asymmetric electrochemical capacitors

A high-energy aqueous asymmetric electrochemical capacitor was developed using manganese dioxide (α-MnO2)/graphene oxide (GO) nanocomposites. The nanostructured α-MnO2 was prepared from micron-sized commercial electrolytic manganese dioxide (EMD) via a hydrothermal reaction in the presence and absence of sodium dodecylsulphate (SDS), α-MnO2(SDS) and α-MnO2, respectively. Unlike the as-prepared α-MnO2, the presence of SDS during the hydrothermal reaction conferred different morphologies on the intermediate precursors for the α-MnO2(SDS). Also, the XRD patterns showed that the α-MnO2(SDS) are more crystalline than the as-prepared α-MnO2. The superior electrochemical performance of the α-MnO2(SDS)/GO composite (280 F g−1, 35 Wh kg−1, and 7.5 kW kg−1 at 0.5 A g−1) coupled with excellent long cycle life clearly indicates that this electrode system has the potential of being developed as an efficient aqueous asymmetric electrochemical capacitor. The high performance of the α-MnO2(SDS)/GO composite was interpreted in terms of the enhanced crystallinity of the α-MnO2(SDS). Interestingly, the electrochemical performance is comparable to or even better than those reported for the more conductive graphene/MnO2 composites.