Electrochemical and capacitance properties of rod-shaped MnO2 for supercapacitor

A novel kind of electrode material, rod-shaped MnO2, was synthesized under high viscosity for the first time. The MnO2 was proved to be the multicrystal with the mixture of alpha- and gamma-MnO2 by X-ray diffraction. From transmission electron micoscopy, it could be seen that the sample has a length of 250 similar to 350 nm and a diameter of 10, 15 nm. The ratio of length to diameter could reach more than 20:1. The electrochemical properties were examined by cyclic voltammograms (CV), galvanostatic charge/ discharge, and electrochemical impedance spectroscopy (EIS) in three electrode cell. According to CV results, 2 mol L-1 (NH4)(2)SO4 aqueous solution was a proper electrolyte for MnO2 supercapacitors. A maximum specific capacitance (SC) of 398 F g(-1) was obtained from galvanostatic charge/ discharge curve in 2 mol L-1 (NH4)(2)SO4 solution at constant current of 10 mA. The SC value was 328 F g(-1) at a high current of 50 mA which exhibit high power characteristics of the rod-shaped MnO2. The electrolyte resistance was 0.21 ohm cm(2) by researching on EIS. Long cycle-life and high coulombic efficiency of rod-shaped MnO2 were also demonstrated by charging and discharging 1000 cycles. (c) 2005 The Electrochemical Society. All rights reserved.