Electrochemical fabrication of porous manganese–cobalt oxide films for electrochemical capacitors

Abstract

A manganese–cobalt coating was electrodeposited from an aqueous solution and then converted to a manganese–cobalt oxide by anodic oxidation. The composition, morphology, structure, and pseudocapacitive performance of the obtained oxide were evaluated by X-ray fluorescence, X-ray photoelectron spectroscopy, scanning electron microscope, cyclic voltammetry, and electrochemical impedance spectroscope. The results show that after anodic oxidation, the manganese in the obtained binary oxide exists as Mn⁴⁺ oxide and the cobalt as Co₃O₄. The as-prepared manganese-cobalt oxide with a cobalt content of 4.87 % is amorphous and porous, which exhibits a symmetrical and rectangular cyclic voltammetry curve in the scan-rate range from 5 to 100 mV s⁻¹ and a specific capacitance of 231.6 F g⁻¹ at 5 mV s⁻¹. The capacitance loss of the symmetric supercapacitor assembled with these electrodes is just about 2 % after 500 charge–discharge cycles. Compared to the pure porous manganese oxide obtained by the same method, the electrochemical impedance spectroscopy and galvanostatic charge–discharge tests reveal that the binary oxide has a lower charge-transfer resistance, higher doubly layer capacitance, and pseudocapacitance.