Transition Metal Ion Doping on ZIF-8 Enhances the Electrochemical CO₂ Reduction Reaction

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Electrochemical reduction of carbon dioxide (CO2) is crucial for mitigating greenhouse gas emissions and producing valuable chemicals.
• Existing electrocatalysts often suffer from poor activity and low Faradaic efficiency (FE).
• Metal-organic frameworks (MOFs) show promise as CO2 reduction reaction (CO2 RR) catalysts but require optimization.

Purpose of the Study:

• To fabricate and investigate doped ZIF-8 materials for efficient electrocatalytic CO2 reduction to carbon monoxide (CO).
• To understand the role of transition metal doping (Ni, Fe, Cu) on ZIF-8's catalytic performance and reaction mechanism.
• To explore the potential of MOF-based catalysts as alternatives to conventional CO2 RR systems.

Main Methods:

• Synthesis of ZIF-8 doped with various transition metal ions (Ni, Fe, Cu) at different concentrations.
• Electrochemical CO2 reduction reaction (CO2 RR) testing to evaluate catalytic activity, partial current density, and Faradaic efficiency (FE).
• X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations to analyze atom coordination and theoretical performance.

Main Results:

• Optimized copper doping in ZIF-8 (Cu0.5Zn0.5/ZIF-8) demonstrated high partial current density (11.57 mA cm-2) and maximum FE for CO (88.5%) at -1.0 V (vs RHE).
• The doped catalyst exhibited stable catalytic activity for over 6 hours.
• Cu doping facilitated the COOH* intermediate formation via a local electronic effect between Zn-N4 and Cu-N4 sites, enhancing the CO2 RR pathway.

Conclusions:

• Cu-doped ZIF-8 is a highly efficient and stable electrocatalyst for CO2 reduction to CO.
• The study elucidates the mechanism of enhanced CO2 RR activity in MOFs through specific metal doping and coordination environments.
• These findings support the development of advanced MOF-based catalysts for sustainable CO2 utilization.