Direct growth of mesoporous MnO2 nanosheet arrays on nickel foam current collectors for high-performance pseudocapacitors

Well-defined mesoporous MnO2 nanosheet arrays have been directly grown on Ni foam current collectors using one-step electrodeposition, followed by a low-temperature thermal annealing process. The as-deposited MnO2 nanosheets are 20-25 nm thick on average and are mesoporous with a pore size ranging from 2 to 8 nm. The potential for using these MnO2 nanosheet arrays as supercapacitor electrodes has been explored by cyclic voltammetry and galvanostatic charge/discharge tests within a potential window of 0-1.0 V versus saturated calomel electrode. The cyclic voltammograms of the Mn02 nanosheet electrode show a typical pseudocapacitive behavior. The nanosheets exhibit specific capacitance of 201, 150, 122, 105 and 96 F g-1 at current densities of 1, 5, 10, 15 and 20 A g(-1), respectively. Furthermore, it is found that upon cycling at 5 A g(-1), the specific capacitance loses 35% of its initial value in the beginning 1800 cycles and then remains constant up to 3000 cycles, showing reasonably good cycling performance. The electrochemical impedance spectroscopy demonstrates that the equivalent series resistance and charge transfer resistance of the electrode are very low, suggesting that the nickel foam supported MnO2 nanosheet array is a promising binder-free electrode for use in pseudocapacitors. (C) 2013 Elsevier B.V. All rights reserved.