Controllable morphologies of Co3O4@MnO2 core-shell structure grown on nickel foam and their supercapacitor behavior

The supercapacitor performances of MnO2, Co3O4 nanowire and Co3O4@MnO2 core-shell structure are compared, and optimized Co3O4@MnO2 core-shell nanowire arrays present the highest specific capacitance of 1646 Fg(-1) at a current density of 1 Ag-1 and lowest interfacial charge transfer resistance. The impedance spectroscopy clearly shows the MnO2 nanosheets surrounding Co3O4 nanowire play an important role in reducing the resistance. During the hydrothermal process, the concentration of KMnO4 solution has a significant effect on the final morphology of Co3O4@MnO2 core-shell structure which is controllable and shows quite different electrochemical property. The relationship between morphology and supercapacitor behavior is studied, and the optimal concentration of KMnO4 solution is approximately 0.015 M. The pore size distribution shows that the sample synthesized in 0.015 M KMnO4 solution has the highest percentage of relatively larger poles, which facilitate the electrolyte ion transfer.