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

Abstract

AbstractElectrochemical CO2 reduction (ECR) to value‐added products such as formate/formic acid is a promising approach for CO2 mitigation. Practical ECR requires long‐term stability at industrially relevant reduction rates, which is challenging due to the rapid degradation of most catalysts at high current densities. Herein, we report the development of a bismuth (Bi) gas diffusion electrode 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, Ag@Bi maintains formate FE above 90 % for at least 500 hours at the current density of 100 mA cm−2. We found that the Ag@Bi catalyst degrades 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.