Electrochemical and Capacitance Properties of Rod-Shaped MnO[sub 2] for Supercapacitor

Abstract

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 α- and γ-MnO2 by X-ray diffraction. From transmission electron micoscopy, it could be seen that the sample has a length of 250∼350nm and a diameter of 10∼15nm. 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, 2molL−1 (NH4)2SO4 aqueous solution was a proper electrolyte for MnO2 supercapacitors. A maximum specific capacitance (SC) of 398Fg−1 was obtained from galvanostatic charge/discharge curve in 2molL−1 (NH4)2SO4 solution at constant current of 10 mA. The SC value was 328Fg−1 at a high current of 50 mA which exhibit high power characteristics of the rod-shaped MnO2. The electrolyte resistance was 0.21Ωcm2 by researching on EIS. Long cycle-life and high coulombic efficiency of rod-shaped MnO2 were also demonstrated by charging and discharging 1000 cycles.