▎ 摘　　要

Graphene/MnO2 composites were prepared by hydrazine hydrate-mediated reduction of graphene oxide (GO)/MnO2 at various reduction times to determine the optimal conditions for obtaining materials with excellent electrochemical performance. Variations in the oxygen-containing surface functional groups were observe.d as the reduction time was varied. These changes were found to affect the electrical conductivity and density of nanoneedle MnO2, which influence the surface area and significantly affect the supercapacitive performance of the composites. Morphological and microstructural characterizations of the as-prepared composites demonstrated that MnO2 was successfully formed on the GO surface and indicated the efficacy of hydrazine hydrate as a reducing agent for GO. The capacitive properties of the graphene/MnO2 electrodes prepared at a reduction time of 28 h (rGO(28)/MnO2) exhibited a low sheet-resistance value as well as a high surface area, resulting in a GO/MnO2 composite with excellent electrochemical performance (371.74 F g(-1) at a scan rate of 10 mV s(-1)). It is anticipated that the formation of MnO2-based nanoneedles on GO surfaces by the demonstrated 28-h hydrazine-reduction protocol is a promising method for supercapacitor electrode fabrication. (C) 2013 Elsevier Ltd. All rights reserved.