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

A facile self-template solvothermal method was developed to fabricate amicrosphere precursor, which was followed by annealing in air to give ZnCo2O4 microspheres. The ZnCo2O4 microspheres possess irregular diameters from 600 nm to 1.2 mm and a high specific surface area of 34.60 m(2) 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.