Developing zeolitic imidazolate frameworks 67-derived fluorides using 2-methylimidazole and ammonia fluoride for energy storage and electrocatalysis

Zeolitic imidazolate framework 67 (ZIF67) with large surface area and tunable structure is one of the promising electroactive materials of electrochemical devices. In this study, NH4F and nickel salt are applied to synthesize bimetallic ZIF67-derived fluoride for supercapacitor (SC) and electrocatalytic water splitting at the first time. Nickel with multiple redox states enhances energy storage and catalytic ability. NH4F can confine crystalline growth and induce fluoride formation. Ratio of 2-methylimidazole to NH4F for synthesis is optimized regarding to surface area and electrical conductivity. The highest specific capacitance (CF) of 735.7 F/g at 20 mV/s is obtained for ZIF67-derived fluoride prepared using 2methylimidazole to NH4F ratio of 2 to 1, due to smaller particle size and high electrical conductivity. The symmetric SC shows the maximum energy density of 24.6 Wh/kg at 0.6 kW/kg. The CF retention of 100 % and Coulombic efficiency higher than 96 % are obtained in 6000 times charge/discharge process. The ZIF67-derived fluoride and IrO2 composite is fabricated as electrocatalyst for water splitting. This composite shows a high current density of 0.11 A/cm(2) at 1.6 VRHE and a small overpotential of 1.58 VRHE at 0.10 A/cm(2). Current density retention of 100 % after continuous illumination for 600 min is also achieved. (c) 2021 Elsevier Ltd. All rights reserved.