A new asymmetric aqueous supercapacitor: Co3O4//Co3O4@polypyrrole

A new asymmetric supercapacitor (ASC) with high energy density based on Co3O4 and Co3O4@polypyrrole (PPy) nanowires arrays (NWAs) on Ni foams as electrodes and aqueous KOH solution as electrolyte has been developed. The Co3O4@PPy NWAs were used as negative electrodes for the first time and were obtained by a simple electrochemical deposition method, using Co3O4 NWAs as the templates. Electrochemical tests show a high specific capacitance and relatively good cycling stability of the Co3O4@PPy NWAs in the potential window from −0.8 to 0 V. The excellent electrochemical performance is mainly due to the special unique structure of the Co3O4 core, which can improve the specific capacitance by an order of magnitude, in compare with the PPy depositing directly on bare Ni foam. Additionally, the Co3O4//Co3O4@PPy ASC exhibits a high energy density of 26.25 Wh/kg at a power density of 350 W/kg, and even when the power density increased to 2100 W/kg, the energy density still remains 22.17 Wh/kg.