Electrochemical CO Reduction Builds Solvent Water into Oxygenate Products.

Numerous studies have examined the electrochemical reduction of CO (COR) to oxygenates (e.g., ethanol). None have considered the possibility that oxygen in the product might arise from water rather than from CO. To test this assumption, C16O reduction was performed in H218O electrolyte. Surprisingly, we found that 60-70% of the ethanol contained 18O, which must have originated from the solvent. We extended our previous all-solvent density functional theory metadynamics calculations to consider the possibility of incorporating water, and indeed, we found a new mechanism involving a Grotthuss chain of six water molecules in a concerted reaction with the *C-CH intermediate to form *CH-CH(18OH), subsequently leading to (18O)ethanol. This competes with the formation of ethylene that also arises from *C-CH. These unforeseen results suggest that all previous studies of COR under aqueous conditions must be reexamined.