Fast and reversible surface redox reaction of graphene–MnO2 composites as supercapacitor electrodes

We present a quick and easy method to synthesize graphene–MnO2 composites through the self-limiting deposition of nanoscale MnO2 on the surface of graphene under microwave irradiation. These nanostructured graphene–MnO2 hybrid materials are used for investigation of electrochemical behaviors. Graphene–MnO2 composite (78 wt.% MnO2) 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 MnO2 (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 MnO2 and the electrolyte, as well as the contact area between MnO2 and graphene.