Cu Doped Zinc Cobalt Oxide Based Solid-State Symmetric Supercapacitors: A Promising Key for High Energy Density

Abstract

Improvement in the capacitance and energy density of zinc cobalt oxide based materials is vital for creating supercapacitors with excellent electrochemical performance. We synthesized Cu doped zinc cobalt oxide (Zn1–xCuxCo2O4) nanostructures via a facile hydrothermal method to accomplish excellent supercapacitive performance. Significantly, the incorporation of Cu into ZnCo2O4 brings a 2 times increase in specific surface area (52 m2 g–1) and decrease in charge transfer resistance for the Zn0.7Cu0.3Co2O4 (x = 0.3) sample. Consequently, the Cu doped Zn0.7Cu0.3Co2O4 electrode displays a high specific capacitance of 1425 F g–1, which is 1.55-fold increased as compared to 917 F g–1 of the pristine ZnCo2O4 electrode. About 96% of capacitance is retained by the Zn0.7Cu0.3Co2O4 after 2000 charge–discharge cycles. Later, a Zn0.7Cu0.3Co2O4 based solid-state symmetric supercapacitor has been fabricated, which displays a potential window of 1.5 V with enlarged cycling stability. The assembled device shows a high energy density of 55 W h kg–1 at a power density of 2621 W K g–1 and successfully lightens the yellow LED of 1.5 V. The immense improvement in electrochemical performance is credited to the increased surface area and electronic conductivity of the electrode. The obtained results clearly evidenced that the fabricated solid-state symmetric supercapacitor has the potential to be used in flexible energy storage devices.