Synergistic enhancement in the capacitance of nickel and cobalt based mixed oxide supercapacitor prepared by electrodeposition

Abstract

A simple and versatile electrodeposition method was adopted to prepare nickel oxide (NiO) and cobalt oxide (Co2O3) based mixed oxide supercapacitor material. The mixed electrode was fabricated by electrodeposition of Co2O3 on to NiO substrate at various potentials of 0.8, 1.0 and 1.2V vs Ag/AgCl reference electrode. The NiO substrate was prepared by simple air oxidation of Ni foil at two temperatures of 500 and 700°C for 2 and 6h. Ni-foil/Co2O3 electrode materials were also synthesized by electrodeposition of Co2O3 on to Ni foil under similar deposition conditions for comparative study. The morphology, phase and oxidation states of the composite electrodes were studied using SEM, EDAX and XPS methods. The overall emphasis of this work is to demonstrate the effect of mixed transition oxides in their bulk forms on the supercapacitance behavior of the electrode material. It was indeed observed that NiO/Co2O3 composite electrode showed significant improvement in supercapacitance behavior in their mixed oxide architecture. Cyclic voltammetric (CV) studies revealed that the NiO/Co2O3 composite electrode could attain a very high level of specific capacitance (>400Fg−1) at a scan rate of 20mVs−1, together with excellent rate capabilities. More than 50% retention in capacitance was also observed after 200 continuous CV cycles demonstrating promising stability of the electrode material. On the other hand, specific capacitance observed in the case of Ni-foil/Co2O3 electrodes was drastically reduced compared to the NiO/Co2O3 electrodes. It has been emphasized that the synergistic effect, due to the presence of multiple transition oxides, enhanced the overall capacitance behavior of the electrode material. Further, it was also observed that higher the oxidation temperature of the Ni substrates, lower was the specific capacitance for the NiO/Co2O3 electrode. The oxidation time, however, did not alter the capacitance significantly for the electrode material.