Facile synthesis of metal organic framework-derived cobalt sulfide on Ni foam as binder-free electrode of battery supercapacitor hybrid

Metal organic framework derivatives are intensively applied as the active material of battery supercapacitor hybrids (BSH) as clean energy technology because of their high surface area and tunable pore sizes. Cobalt and nickel sulfides are promising battery-type materials with multiple redox states for conducting abundant redox reactions and with conductive sulfur for transferring electricity efficiently for energy development. Binder-free electrodes fabricated without insulated binders in the facile synthesis are widely investigated for reducing time and money costs. In this work, it is the first time to fabricate binder-free electrodes with sulfurized zeolitic imidazolate framework 67 (ZIF67) on nickel foam (S-ZIF67/NF) as the battery-type electrode of BSH. The temperature and duration of the hydrothermal process for synthesizing S-ZIF67/NF electrodes are investigated. Based on 100 °C and 4 h, the S-ZIF67/NF electrode shows the largest specific capacitance (C_F) of 2744.6 F/g along with the capacity of 533.7 mAh/g at 10 A/g, due to the formation of cobalt and nickel sulfides respectively from the cobalt precursor and the NF as well as the favorable sheet-assembled flower-like structures with large surface area and regular assembly. A BSH composed of the reduced graphene oxide negative electrode and the S-ZIF67/NF positive electrode shows a maximum energy density of 38.5 Wh/kg at 750 W/kg, and C_F retention of 71% and Coulombic efficiency higher than 85% after 8000 cycles.