Design, hydrothermal synthesis and electrochemical properties of porous birnessite-type manganese dioxide nanosheets on graphene as a hybrid material for supercapacitors

摘要

MnO_2-graphene hybrid with a unique structure of porous birnessite-type manganese dioxide (MnO_2) 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 MnO_2-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 Fg~(-1) at 6 Ag~(-1)) compared with both the graphene and MnO_2 electrodes. Moreover, the capacitance of MnO_2-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 MnO_2.