Electrochemically synthesized MnO2-based mixed oxides for high performance redox supercapacitors

Nanostructured and microporous nickel-manganese oxide (NMO) and cobalt-manganese oxide (CMO) were deposited by potentiodynamic method onto inexpensive stainless steel substrate. A scan rate of 200 mV s(-1) was used for the deposition. The binary oxide deposited electrodes were characterized by cyclic voltammetry (CV) and charge/discharge cycling in 1 M Na(2)SO(4) electrolyte for redox supercapacitor applications. Maximum specific capacitance (SC) values of 621 and 498 F g(-1) were obtained with NMO and CMO electrodes, respectively, at a CV scan rate of 10 mV s(-1). SC values of 377 and 307 F g(-1) were obtained with NMO and CMO electrodes, respectively, at a high CV scan rate of 200 mV s(-1), indicating high power characteristics of the binary oxides. The results were more interesting from charge/discharge cycling, where SC values of 685 and 560 F g(-1) were obtained with NMO and CMO electrodes, respectively, at a current density of 2 mA cm(-2). These values of electrical parameters are much higher than those obtained with just MnO(2). Long cycle-life and excellent stability of the materials were also demonstrated. (C) 2004 Elsevier B.V. All rights reserved.