MnO2 nanoflakes/hierarchical porous carbon nanocomposites for high-performance supercapacitor electrodes

Abstract A facile strategy is developed for the synthesis of MnO 2 nanoflakes/hierarchical porous carbon spheres (HPCs) nanocomposites via a two-step redox process. The external MnO 2 nanoflakes with thickness of ∼10 nm deposited on the surface of the HPCs result in the formation of hierarchical architecture of the composites, while the internal MnO 2 layer stabilizes the interaction between MnO 2 nanoflakes and HPCs. The resultant composites still retain porous structure after removal of mesoporous SiO 2 template and exhibit relatively high specific surface area. The morphology control of the composites can be easily achieved by varying the initial content of Mn(NO 3 ) 2 and KMnO 4 . Electrochemical performance of the composites as supercapacitor electrode materials was evaluated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy techniques. The MnO 2 nanoflakes/HPCs composite with 75 wt% MnO 2 possesses the highest specific capacitance at a high scan rate or current density (417.2 F g −1 at 20 mV s −1 and 326.9 F g −1 at 1 A g −1 , respectively) and extraordinary cycling stability (slightly over 100% capacitance retention after 10000 cycles at a scan rate of 100 mV s −1 ), which are superior to other reported MnO 2 /carbon composites. The results suggest that rational design and synthesis of MnO 2 /porous carbon composite electrode materials with maximum electrochemical active sites is important to further improve their electrochemical performance.