Synthesis of hollow ZnCo2O4 microspheres with enhanced electrochemical performance for asymmetric supercapacitor

To construct high energy density asymmetric supercapacitors, a new class of electrodes with high ion transport performance and high electrical conductivity is needed. The hollow ternary metal oxides are considered as promising materials for supercapacitors. Herein, hollow ZnCo2O4 microspheres are successfully obtained using a solvothermal and coordinating etching route. Particularly, the transformation process from core-shell ZnCo2O4/ZnO structure to pure hollow ZnCo2O4 structure is explored in detail for the first time. The hollow ZnCo2O4 microspheres have a uniform morphology of 1-2 μm and a high surface area of 24.7 m2 g−1. The ZnCo2O4 exhibits a high specific capacitance of 78.89 mAh⋅g−1 at current density of 1 A g−1 with a high loading of 6 mg cm−2 and superior cycling stability after 2000 cycles. Furthermore, the ZnCo2O4//activated carbon asymmetric supercapacitor device achieves a high specific capacitance of 34.7 mAh⋅g−1 at 0.2 A g−1 and an energy density of 27.78 Wh⋅kg−1 at a power density of 158.5 W kg−1. Moreover, three asymmetric devices in series can efficiently power 3 mm diameter red and green LED indicators for more than 30 and 15 min, respectively. These excellent capacitive performances indicate the as-fabricated hollow structures ZnCo2O4 is a promising electrode material for supercapacitors.