Enhanced Ni–Co redox dynamics in dual-SDA engineered ZIF-67 derivatives for high-performance supercapacitors: Insights from operando X-ray spectroscopy

The development of high-performance supercapacitor electrodes demands novel synthesis methods to precisely control the properties of the active material. Here, we report an advanced one-step approach that employs ammonium hydrogen fluoride (NH₄HF₂) and ammonium tetrafluoroborate (NH₄BF₄) as dual-structure directing agents (SDAs) to develop novel zeolitic imidazolate framework-67 (ZIF-67) derivatives (ZIF-HB), with cobalt and nickel hydroxides as the main components. Modulation of the NH₄HF₂/NH₄BF₄ molar ratio results in significant changes to the morphology, surface and electronic configurations, and electrochemical behavior. The optimized ZIF-HB (ZIF-HB12) electrode delivers impressive electrochemical performance, achieving a high specific capacitance (C_F) of 1933.3 F/g at 20 mV/s. It is revealed from advanced structural analyses, including operando X-ray absorption spectroscopy that the redox reactivity and charge transfer dynamics are considerably boosted as a result of synergistic interactions between Co and Ni sites. An asymmetric supercapacitor (SC) assembled using ZIF-HB12 shows maximum energy density of 19 Wh/kg at 1143 W/kg, with a C_F retention of 81.3% and a Coulombic efficiency of 97.2% after 10,000 cycles. This study highlights the effectiveness of dual-function SDAs in designing structurally robust, electrochemically active, and electronically optimized electrode materials for cutting-edge energy storage solutions.