Electrochemical Formation of C2+ Products Steered by Bridge-Bonded *CO Confined by *OH Domains

During the electrochemical CO₂ reduction reaction (eCO₂RR) on copper catalysts, linear-bonded CO (*CO_L) is commonly regarded as the key intermediate for the CO-CO coupling step, which leads to the formation of multicarbon products. In this work, we unveil the significant role of bridge-bonded *CO (*CO_B) as an active species. By combining in situ Raman spectroscopy, gas and liquid chromatography, and density functional theory (DFT) simulations, we show that adsorbed *OH domains displace *CO_L to *CO_B. The electroreduction of a ¹²CO+¹³CO₂ cofeed demonstrates that *CO_B distinctly favors the production of acetate and 1-propanol, while *CO_L favors ethylene and ethanol formation. This work enhances our understanding of the mechanistic intricacies of eCO₍₂₎RR and suggests new directions for designing operational conditions by modifying the competitive adsorption of surface species, thereby steering the reaction toward specific multicarbon products.