Facile synthesis of perovskite ZIF67 derivative using ammonia fluoride and comparison with post-treated ZIF67 derivatives on energy storage ability

Oxidation, carbonization, sulfurization and selenization are commonly used to enhance electrical conductivity and electroactivity of metal–organic frameworks. However, extra costs on time and money are required for post treatments. In this work, ammonium fluoride (NH₄F) is incorporated in precursor solution for synthesizing perovskite ZIF67 derivatives as electroactive material. Novel particle-aggregated particle is obtained with largely reduced sizes and less grain boundaries. A highest specific capacitance (C_F) of 490.4 F/g is attained at 20 mV/s for the optimized ZIF67 derivative electrode prepared using NH₄F and Co:Ni ratio of 2:1 (CoNi21-NH₄F), while the untreated, oxidized, carbonized, sulfurized and selenized bimetallic ZIF67 electrodes synthesized without NH₄F only show the smaller C_F values of 3.5, 363.9, 28.7, 85.9 and 103.2 F/g at 20 mV/s, respectively. Replacing 2-methylimidazole with F⁻ in ZIF67 can improve electrical conductivity due to smaller size and higher electronegativity of F⁻ than 2-methylimidazole. Largely enhanced C_F value for CoNi21-NH₄F electrode strongly indicates success of improving energy storage via simply adding NH₄F in precursor solution without post treatments. Maximum energy density of 22.7 Wh/kg at power density of 0.6 W/kg, C_F retention of 94% and Coulombic efficiency of 99% in 10.000 cycles charge/discharged process are obtained for supercapacitor with CoNi21-NH₄F electrodes.