Facile fabrication and supercapacitive properties of mesoporous zinc cobaltite microspheres

Mesoporous zinc cobaltite (ZnCo2O4) microspheres have been successfully prepared by a facile solvothermal method followed by an annealing process. The as-prepared ZnCo2O4 displays uniform sphere-like morphology composed of interconnected ZnCo2O4 nanoparticles. The Brunauer-Emmett-Teller (BET) surface area of mesoporous ZnCo2O4 microspheres is about 51.4 m2 g−1 with dominant pore diameter of 7.5 nm. The novel ZnCo2O4 material exhibits high specific capacitance of 953.2 F g−1 and 768.5 F g−1 at discharge current densities of 4 A g−1 and 30 A g−1, respectively. The energy density can be estimated to be 26.68 Wh kg−1 at a power density of 8 kW kg−1. The specific capacitance retention is 97.8% after 3000 cycles, suggesting its excellent cycling stability. The superior electrochemical performance is mainly attributed to the uniformity of the surface structure and the porosity of the microspheres, which benefit electrons and ions transportation, provide large electrode-electrolyte contact area, and meanwhile reduce volume change during the charge-discharge process. This method of constructing porous microspheres is very effective, yet simple, and it could be applied in other high-performance metal oxide electrode materials for electrochemical capacitors, as well as in Li-ion batteries.