Engineering Cobalt-Based Bimetallic Compounds via NH₄F-Directed ZIF67 Transformation for Battery–Supercapacitor Hybrids with Enhanced Energy Storage Performance

Cobalt-based compounds have attracted considerable attention as electroactive materials for energy storage owing to their high theoretical capacitance and cost-effectiveness. Zeolitic imidazolate framework-67 (ZIF67) is a cobalt-containing metal-organic framework that features a high surface area and a tunable porous architecture, but inherently low conductivity limits its electrochemical performance. To address this issue, structure-directing agents (SDAs) have been employed to enhance the surface characteristics and energy storage behavior of ZIF67 derivatives. In particular, the redox activity of battery-type electrodes is largely governed by the nature of the metal species involved. In this study, a series of cobalt-based bimetallic compounds incorporating Ni, Cu, Al, Zn, and Mn are synthesized using NH₄F as the SDA in 2-methylimidazole medium. Morphology and composition of the resulting materials are strongly dependent on the secondary metal species. The cobalt-nickel (CoNi) electrode achieves the highest specific capacitance (<i>C</i> _F) of 997.3 F/g at 20 mV/s, attributed to the synergistic redox behavior of cobalt and nickel. The contributions from both diffusion-controlled and surface-capacitive processes are also quantitatively assessed. A BSH assembled using the CoNi and carbon electrodes achieves a maximum energy density of 9.2 Wh/kg at 375 W/kg, along with a <i>C</i> _F retention of 83.1% and a Coulombic efficiency of 94.2% after 10,000 cycles.