Electrochemical investigation of MnO2 electrode material for supercapacitors

MnO2 electrode material is synthesized by low temperature solid state reaction between KMnO4 and MnCl2. Effects of the KMnO4:MnCl2 molar ratio on the structure, morphology and electrochemical properties of the as-prepared sample were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical tests. Results showed that the obtained MnO2 is alpha-MnO2, the average diameter is about 0.5-1.5 mu m, which are constituted of nanoparticles of 20 nm. Under 100 mA g(-1), the specific capacitances of the prepared sample is 258.7, 219.6, 215.3, 198.5 and 209.5 F g(-1) at the KMnO4/MnCl2 molar ratio of 3:2, 2:1, 1:1, 1:2 and 2:3, respectively. And the MnO2 sample with a KMnO4/MnCl2 molar ratio of 3:2 exhibits the best discharge capacitance and cycle performance. When the charge/discharge rate increases to 300 mA g(-1), the sample still remains initial discharge capacitance of 165.3 F g(-1), and the discharge capacitance is 145.9 F g(-1) after 200 cycles, the capacitance retention rate is 102.4% during the 20-200th cycles. Therefore, the MnO2 sample is an excellent material for use in supercapacitors because of its large specific capacitance and good cycle performance. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.