Engineering Cobalt-Based Bimetallic Compounds via NH₄F‑Directed ZIF67 Transformation for Battery-Supercapacitor...

Area of Science:

• Materials Science
• Electrochemistry
• Nanotechnology

Background:

• Cobalt-based compounds are promising electroactive materials for energy storage due to high theoretical capacitance and cost-effectiveness.
• Zeolitic imidazolate framework-67 (ZIF67) offers high surface area and tunable porosity but suffers from low conductivity, limiting its electrochemical performance.
• Structure-directing agents (SDAs) are crucial for enhancing ZIF67 derivatives' surface characteristics and energy storage capabilities.

Purpose of the Study:

• To synthesize and investigate cobalt-based bimetallic compounds using NH4F as an SDA.
• To explore the influence of secondary metal species (Ni, Cu, Al, Zn, Mn) on material morphology, composition, and electrochemical properties.
• To evaluate the energy storage performance of the synthesized materials, particularly the cobalt-nickel (CoNi) electrode.

Main Methods:

• Synthesis of bimetallic cobalt compounds using NH4F as an SDA in a 2-methylimidazole medium.
• Characterization of material morphology and composition.
• Electrochemical testing to determine specific capacitance (CF), energy density, and cycling stability.
• Assembly of a battery supercapacitor hybrid (BSH) device.

Main Results:

• Material morphology and composition were significantly influenced by the secondary metal species.
• The cobalt-nickel (CoNi) electrode exhibited the highest specific capacitance (CF) of 997.3 F/g at 20 mV/s.
• Quantitative assessment of diffusion-controlled and surface-capacitive processes was performed.
• A BSH device using CoNi electrodes achieved a maximum energy density of 9.2 Wh/kg at 375 W/kg, with 83.1% CF retention and 94.2% Coulombic efficiency after 10,000 cycles.

Conclusions:

• The synergistic redox behavior of cobalt and nickel in the CoNi electrode significantly enhances electrochemical performance.
• NH4F as an SDA effectively facilitates the development of high-performance cobalt-based bimetallic materials for energy storage.
• The synthesized CoNi material demonstrates excellent potential for applications in advanced energy storage devices like battery supercapacitor hybrids.