One-pot synthesis of CoO–ZnO/rGO supported on Ni foam for high-performance hybrid supercapacitor with greatly enhanced cycling stability

A series of interconnected CoO–ZnO/rGO supported on Ni foam samples were prepared by in-situ growth via hydrothermal synthesis and subsequent annealing treatment. The optimized sample exhibits excellent electrochemical performances with a higher specific capacitance of 1951.8 F/g (216.9 mAh/g) at a current density of 1 A/g with a good rate capability. The CoO–ZnO/rGO based hybrid supercacitor delivers a high energy density up to 45.9 Wh/kg at a power density of 800 W/kg with a decent cycling stability (90.1% capacitance retention after 5000 cycles). The high specific capacitance along with good cycling stability are crucial for practical applications of supercapacitors, which always demands high-performance and stable electrode materials. In this work, we report a series of ternary composites of CoO-ZnO with different fractions of reduced graphene oxide (rGO) synthesized by in-situ growth on nickel foam, named as CZG-1, 2 and 3, respectively. This sort of binder-free electrodes presents excellent electrochemical properties as well as large capacitance due to their low electrical resistance and high oxygen vacancies. Particularly, the sample of CZG-2 (CoO-ZnO/rGO 20 mg) in a nanoreticular structure shows the best electrochemical performance with a maximum specific capacitance of 1951.8 F/g (216.9 mAh/g) at a current intensity of 1 A/g. The CZG-2-based hybrid supercapacitor delivers a high energy density up to 45.9 Wh/kg at a high power density of 800 W/kg, and kept the capacitance retention of 90.1% over 5000 charge-discharge cycles.