Multi-metallic Layered Catalysts for Stable Electrochemical CO₂ Reduction to Formate and Formic Acid

Area of Science:

• Electrochemistry
• Materials Science
• Environmental Science

Background:

• Electrochemical CO2 reduction (ECR) offers a promising route for CO2 mitigation by converting CO2 into valuable products like formate.
• Achieving long-term catalyst stability at industrially relevant rates is a significant challenge in practical ECR due to catalyst degradation at high current densities.
• Bismuth (Bi)-based catalysts are explored for ECR, but their stability, especially under varying pH conditions, needs improvement for widespread application.

Purpose of the Study:

• To develop a robust and stable bismuth (Bi) gas diffusion electrode for efficient electrochemical CO2 reduction (ECR).
• To investigate the performance and durability of the developed catalyst under industrially relevant conditions, including high current densities and varying pH.
• To establish a new strategy for enhancing the operational longevity of ECR catalysts for practical CO2 mitigation.

Main Methods:

• Fabrication of a bismuth (Bi) gas diffusion electrode on a silver (Ag) substrate (Ag@Bi).
• Electrochemical testing of the Ag@Bi catalyst in various electrolytes (1 M KOH, 1 M KHCO3, 1 M NaCl) to assess Faradaic efficiency (FE) and selectivity for formate/formic acid.
• Stability testing at high current densities (up to 300 mA cm-2) and development of a modified Ag@Bi/Ag catalyst to address degradation issues.

Main Results:

• The Ag@Bi catalyst achieved high FE (>90%) for formate in 1 M KOH and 1 M KHCO3 electrolytes.
• High selectivity (>85%) for formic acid was observed in 1 M NaCl catholyte (pH 2-3) at current densities up to 300 mA cm-2.
• The Ag@Bi catalyst demonstrated over 500 hours of stability in 1 M KHCO3 at 100 mA cm-2, while the modified Ag@Bi/Ag catalyst showed 300 hours stability with ≥70% FE for formic acid at 100 mA cm-2, overcoming Bi leaching issues.

Conclusions:

• The developed Ag@Bi gas diffusion electrode shows excellent performance and stability for electrochemical CO2 reduction to formate/formic acid.
• A multi-layer Ag@Bi/Ag catalyst design effectively addresses catalyst degradation, enabling prolonged operational stability under challenging conditions.
• This work presents a viable strategy for achieving the operational longevity of ECR catalysts, critical for advancing CO2 mitigation technologies.