▎ 摘　　要

MnO2-graphene hybrid with a unique structure of porous birnessite-type manganese dioxide (MnO2) nanosheets on graphene has been designed and synthesized by a simple hydrothermal method. The formation mechanism of the hybrid is discussed based on a series of time-dependent experiments. Electrochemical measurements reveal that the MnO2-graphene electrode exhibits much higher specific capacitance (315 F g(-1) at a current density of 0.2 A g(-1)) and better rate capability (even 193 F g(-1) at 6 A g(-1)) compared with both the graphene and MnO2 electrodes. Moreover, the capacitance of MnO2-graphene electrode is still 87% retained after 2000 cycles at a charging rate of 3 A g(-1). The superior capacitive performance of the hybrid is attributed to its unique structure, which provides good electronic conductivity, fast electron and ion transport, and high utilization of MnO2. (C) 2013 Elsevier B.V. All rights reserved.