Controllable synthesis of nanohorn-like architectured cobalt oxide for hybrid supercapacitor application

We demonstrate a facile and controllable synthesis of horn-like Co₃O₄ nanostructures through a solvothermal process followed by calcination at different temperatures. The particle sizes and defects of the as-obtained Co₃O₄ nanohorns are controlled with respect to calcining temperatures, while preserving the horn-like morphology. In particular, the Co₃O₄ nanohorn electrodes prepared at 300 °C reveal the specific capacitance of ∼2751 F g⁻¹ and the rate capability of 46.8%, which is greater than those of materials obtained at 350, 400, and 450 °C. In order to enlarge the potential window, a hybrid supercapacitor is configured with the Co₃O₄ nanohorn and activated carbon used as positive and negative electrodes, respectively. The as-fabricated hybrid supercapacitor shows high specific capacitance of ∼101 F g⁻¹ and the rate capability of 80.5%. The energy and power densities of hybrid supercapacitor are ∼31.70 W h kg⁻¹ and 16.71 kW kg⁻¹, respectively, along with 91.37% of capacitance retention over 350,000 cycles. These energy and power densities of the hybrid supercapacitors are approximately 8.5 and 3.5 times greater than values of Co₃O₄ symmetric supercapacitor.