Facile synthesis of graphene-wrapped CNT-MnO2 nanocomposites for asymmetric electrochemical capacitors

CNT-MnO2 composites prepared by chemical redox deposition with various deposition times (0.5-2.0 h) were wrapped in functionalized graphene nanosheets (fGNSs) to improve their electrochemical pseudocapacitor properties. This treatment effectively improved the electrical conductivity and limited MnO2 loss during the charge-discharge process. The resulting fGNS-CNT-MnO2 (1 h) electrode exhibited the best pseudocapacitance of 202 F g(-1) and a cycling stability of 95%. In a two-electrode system with an activated carbon//fGNS-CNT-MnO2 asymmetric capacitor, the initial capacitance decreased by only 5% after 1000 cycles, and the corresponding power and energy densities were calculated to be 720W kg(-1) and 46 W h kg(-1), respectively, at 8 mA cm(-2). (C) 2017 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.