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

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(CH3COO)2) and 0.001 M Co sulphate (CoSO4).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 Na2SO4 (91% retention). Capacitance reduction for the deposits was mainly due to the loss of Mn ions by dissolution in the electrolyte solution.

► Rod-like, Co-doped Mn oxide films were obtained without templates by electrodeposition from simple acetate solutions.
► Higher capacitances (213 F g−1) and better cyclability were obtained compared with undoped Mn oxide electrodes.
► PEDOT coated structures had improved capacitances (310 F g−1) and cyclability (91%) compared with uncoated structures.
► An anomalous effect was obtained with scan rate. Capacitances for all deposits increased with increasing scan rate, up to 100 mV s−1, and then decreased at higher scan rates.