Investigation of electrochemical behavior of Mn–Co doped oxide electrodes for electrochemical capacitors

Abstract

The electrochemical properties of nanocrystalline Co-doped Mn oxide electrodes were investigated to determine the relationship between physicochemical feature evolution and the corresponding electrochemical behavior of synthesized electrodes. Co-doped Mn oxide electrodes with a rod-like morphology and antifluorite-type structure were synthesized by anodic electrodeposition on Au coated Si substrates from a dilute solution of 0.01 M Mn acetate (Mn(CH 3COO) 2) and 0.001 M Co sulphate (CoSO 4). Electrochemical characterization of synthesized electrodes, with and without a conducting polymer (PEDOT) coating, was performed with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) at different scan rates. In addition, structural characterization of as-deposited and cycled electrodes was conducted using SEM, TEM and XPS. Capacitance values for all deposits increased with increasing scan rate to 100 mV s −1, and then decreased after 100 mV s −1. The Mn–Co oxide/PEDOT electrodes showed improved specific capacity and electrochemical cyclability relative to uncoated Mn–Co oxides. Mn–Co oxide/PEDOT electrodes with rod-like structures had high capacitances (up to 310 F g −1) at a scan rate of 100 mV s −1 and maintained their capacitance after 500 cycles in 0.5 M Na 2SO 4 (91% retention). Capacitance reduction for the deposits was mainly due to the loss of Mn ions by dissolution in the electrolyte solution.