Pulse electrodeposited manganese oxide on carbon fibers as electrodes for high capacity supercapacitors

Arrays of manganese dioxide (MnO₂), a pseudocapacitive material, have been deposited on the carbon fibers (CF) of a carbon woven fabric by electrodeposition from a solution containing manganese sulfate and sulfuric acid using galvanostatic square waves. The thickness of the MnO₂ was varied by increasing/decreasing the time of deposition, and the electrochemical performance of the MnO₂ has been analyzed. The CF serves as a substrate material with high surface area, good electrical conductivity and excellent mechanical strength. The electrochemical properties of the resultant electrode were examined by cyclic voltammogram (CV), galvanostatic charge/discharge, and electrochemical impedance spectroscopy in a three-electrode system. From the specific capacitance calculations obtained from CV and charge-discharge, a high specific capacitance of 769 F g^-1 @ 5 mV s^-1 (low weight electrode) has been achieved. The maximum area capacitance, estimated from the charge-discharge curves, was 790 mF cm^-2 @ 5 mV s^-1. The high-performance is attributed to the double layer capacitance of the CFs combined with the pseudocapacitive nature of MnO_2, the large surface area, and high degree of ordering of the ultrathin MnO₂.