Surface Water as an Initial Proton Source for the Electrochemical CO Reduction Reaction on Copper Surfaces

We have employed in situ electrochemical shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) and density functional theory (DFT) calculations to study the CO reduction reaction (CORR) on Cu single‐crystal surfaces under various conditions. Coadsorbed and structure‐/potential‐dependent surface species, including *CO, Cu−O ad , and Cu−OH ad , were identified using electrochemical spectroscopy and isotope labeling. The relative abundance of *OH follows a “volcano” trend with applied potentials in aqueous solutions, which is yet absent in absolute alcoholic solutions. Combined with DFT calculations, we propose that the surface H 2 O can serve as a strong proton donor for the first protonation step in both the C 1 and C 2 pathways of CORR at various applied potentials in alkaline electrolytes, leaving adsorbed *OH on the surface. This work provides fresh insights into the initial protonation steps and identity of key interfacial intermediates formed during CORR on Cu surfaces.