Restructuring-Regulated Bismuth Catalyst Promotes Electrochemical CO₂ Reduction to Formic Acid in Acidic Electrolyte.

Area of Science:

• Electrochemistry
• Materials Science
• Catalysis

Background:

• Electrochemical CO2 reduction (eCO2R) in acidic electrolytes offers high CO2 utilization efficiency.
• Bismuth (Bi)-based catalysts are explored for formate/formic acid production but often restructure during electrocatalysis.
• Understanding Bi-based catalyst restructuring mechanisms in acidic media is crucial for performance optimization.

Purpose of the Study:

• To elucidate distinct restructuring mechanisms in structurally different Bi-based compounds (Bi9O7.5S6 and Bi2O2S) during eCO2R in acidic electrolytes.
• To correlate catalyst structure with electrochemical performance for formic acid production.
• To identify strategies for enhancing catalyst stability and activity.

Main Methods:

• Synthesis and characterization of Bi-based compounds (Bi9O7.5S6 and Bi2O2S).
• Electrochemical evaluation of catalysts for CO2 reduction, including activity, selectivity, and stability.
• Quasi-in situ X-ray diffraction and in situ Raman spectroscopy to investigate catalyst restructuring mechanisms.

Main Results:

• Bi9O7.5S6 exhibits high selectivity and activity for formic acid production due to its unique layered structure.
• Bi2O2S shows inferior eCO2R performance compared to Bi9O7.5S6.
• Restructuring mechanisms were revealed, showing that metal elements between [Bi2O2]2+ layers resist decomposition, leading to stable Bi/Bi2O2CO3 interfaces.
• Bi9O7.5S6 achieved >95% Faraday efficiency at 100 mA cm-2 and 117 h stability in a flow cell.

Conclusions:

• Distinct restructuring mechanisms influence the performance of Bi-based catalysts in acidic eCO2R.
• The layered structure of Bi9O7.5S6 facilitates high formic acid production efficiency and stability.
• Stabilizing the catalyst structure through interfacial engineering is key for developing efficient and durable eCO2R catalysts.