In-situ carbonization of zeolitic imidazolate framework-67 on Ni foam as binder-free electrode for energy storage

Zeolitic imidazolate framework-67 (ZIF67) derivatives are intensively applied as the active material of battery supercapacitor hybrids (BSH) as clean renewable energy. Binder-free electrodes without insulated binders possessing high electrical conductivity can be fabricated with less time and money. In this work, carbonized ZIF67 (C-ZIF67) is fabricated on Ni foam using in-situ binder-free technique. The C-ZIF67 electrode is applied as battery-type electrode of BSH for the first time. Using Ni foam as a conductive substrate of binder-free electrodes is beneficial for generating nickel compounds with multiple redox states. The electrocapacitive nitrogen-doped carbon can be generated from ZIF67 after thermal treatments. Carbonization temperature for synthesizing C-ZIF67 electrodes is optimized regarding morphology and defect to graphitic intensity ratios of C-ZIF67. The C-ZIF67 electrode prepared using 600 °C presents the highest specific capacitance (C_F) of 914.0 F/g along with capacity of 126.9 mAh/g at 20 mV/s, due to tightly attached active material with favorable vertical grown sheet array on Ni form and suitable defect to graphitic intensity ratio. A BSH composed of reduce graphene oxide negative electrode and carbonized ZIF67 positive electrode presents a maximum energy density of 15.15 Wh/kg at 600 W/kg, and the C_F retention of 71% and Coulombic efficiency higher than 85% after 6000 charge/discharge cycles.