A self-template synthesis of porous ZnCo2O4 microspheres for high-performance quasi-solid-state asymmetric supercapacitors

Abstract

A facile self-template solvothermal method was developed to fabricate a microsphere precursor, which was followed by annealing in air to give ZnCo₂O₄ microspheres. The ZnCo₂O₄ microspheres possess irregular diameters from 600 nm to 1.2 μm and a high specific surface area of 34.60 m² g⁻¹ with an average pore diameter of 6.96 nm. Each ZnCo₂O₄ microsphere was found to be constructed by many intertwined nanoparticles. When investigated as electrode materials for supercapacitors, the ZnCo₂O₄ microspheres exhibited a high specific capacitance of 542.5 F g⁻¹ at 1 A g⁻¹, excellent rate capability of 55.3% retention at 10 A g⁻¹, and good cycling stability with 95.5% retention of the maximum capacitance (440 F g⁻¹) after 2000 cycles at 2 A g⁻¹. Additionally, a quasi-solid-state asymmetric supercapacitor fabricated with the as-prepared ZnCo₂O₄ microspheres was used as the positive electrode and activated carbon as the negative electrode. The asymmetric device exhibited a remarkable cycling stability with 76.68% retention of the maximum capacitance (68.93 F g⁻¹) after 1000 cycles at 0.5 A g⁻¹. Moreover, two asymmetric devices connected in a series can successfully light up a red light-emitting-diode (LED) and last for more than 15 min. Therefore, this fascinating electrochemical performance demonstrates that the ZnCo₂O₄ microspheres have potential applications in supercapacitors.