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

We report the development of bismuth (Bi) gas diffusion electrodes on a polytetrafluoroethylene-based electrically conductive silver (Ag) substrate (Ag@Bi), which exhibits high Faradaic efficiency (FE) for formate of over 90% in 1 M KOH and 1 M KHCO3 electrolytes. The catalyst also shows high selectivity of formic acid above 85% in 1 M NaCl catholyte, which has a bulk pH of 2-3 during ECR, at current densities up to 300 mA cm-2. In 1 M KHCO3 condition, the Ag@Bi maintains a formate FE above 90% for at least 500 hours at the current density of 100 mA cm-2. We found that Ag@Bi catalysts degrade over time due to the leaching of Bi in the NaCl catholyte. To overcome this challenge, we deposited a layer of Ag nanoparticles on the surface of Ag@Bi to form a multi-layer Ag@Bi/Ag catalyst. This designed catalyst exhibits 300 hours of stability with FE for formic acid ≥ 70% at 100 mA cm-2. Our work establishes a new strategy for achieving the operational longevity of ECR under wide pH conditions, which is critical for practical applications.