Fast and reversible surface redox reaction of graphene–MnO 2 composites as supercapacitor electrodes

Abstract

We present a quick and easy method to synthesize graphene–MnO 2 composites through the self-limiting deposition of nanoscale MnO 2 on the surface of graphene under microwave irradiation. These nanostructured graphene–MnO 2 hybrid materials are used for investigation of electrochemical behaviors. Graphene–MnO 2 composite (78 wt.% MnO 2) displays the specific capacitance as high as 310 F g −1 at 2 mV s −1 (even 228 F g −1 at 500 mV s −1), which is almost three times higher than that of pure graphene (104 F g −1) and birnessite-type MnO 2 (103 F g −1). Interestingly, the capacitance retention ratio is highly kept over a wide range of scan rates (88% at 100 mV s −1 and 74% at 500 mV s −1). The improved high-rate electrochemical performance may be attributed to the increased electrode conductivity in the presence of graphene network, the increased effective interfacial area between MnO 2 and the electrolyte, as well as the contact area between MnO 2 and graphene.