A bimetallic CuBi catalyst for enhanced electrochemical CO reduction to acetate

Catalyst design principles for generating multicarbon (C₂₊) products from electrochemical carbon dioxide (CO₂) reduction (CO₂R) and carbon monoxide (CO) reduction (COR) are often similar and used interchangeably. However, here we demonstrate how a copper bismuth (CuBi) catalyst generates a drastically different product output for CO₂R versus COR, offering a valuable case study. During CO₂R, we observe predominant formate production, due to selective adsorption of the CO₂ reactant onto Bi sites rather than Cu sites. On the other hand, acetate is observed as the primary product for COR because formate production on Bi sites is shut down. Specifically, with the optimal CuBi catalyst, we achieve a high acetate Faradaic efficiency of 68.2% at 100 milliamperes per square centimeter under COR conditions. Experiments involving the coreduction of ¹³CO₂/¹²CO feeds of varying mixing ratios show that acetate has the highest carbon-12 content among the products. This suggests that CO-selective sites (Cu_CO) could play a role in facilitating selective acetate production. Notably, analysis of the acetate isotopologues also reveals a preference for the formation of ¹²CH₃¹³COO^- over ¹³CH₃¹²COO^-. We propose this to be due to an acetate-selective pathway involving asymmetric hydrogenation of *¹²CO¹³CO to *¹²CH₂¹³CO (ketene). This pathway is promoted at high pH and is postulated to occur at the interfaces between Cu_CO and CO₂-selective sites (Cu_CO2). Together, our results provide mechanistic insights into acetate formation under COR conditions.