A self-supporting graphene/MnO2 composite for high-performance supercapacitors

A self-supporting graphene (SSG) was prepared by electrochemical re-intercalation of a flexible graphite sheet (FGS) in the (NH4)2S2O8 electrolyte. The in-situ grown SSG rooted in the unexpanded FGS substrate which acted as a current collector. A thin, homogeneous and conformal MnO2 layer was coated on the surface of SSG by microwave-assisted deposition. The obtained FGS-SSG/MnO2 electrode displayed the areal and specific capacitances as high as 2.8 F cm−2 and 465 F g−1 at 2 mV s−1. An asymmetric supercapacitor of FGS-SSG/MnO2//FGS-SSG was assembled, which exhibited a maximum energy density of 25.6 Wh kg−1 at a power density of 1000 W kg−1. In addition, the capacitance retention ratio of FGS-SSG/MnO2//FGS-SSG reached 87% at the current density of 1 A g−1 after 5000 charge-discharge cycles. High electrochemical properties indicate that the FGS-SSG/MnO2 is a promising electrode for supercapacitors.