Understanding and engineering electrochemical environments often come secondary to electrocatalyst design when optimizing the activity and selectivity of electrocatalytic molecular transformations. In this study, we employ electrocatalytic CO 2 reduction in acetonitrile on nanoscale-roughened Ag catalysts as a model system and operando surfaceenhanced Raman scattering spectroscopy to demonstrate that the local environment of H 2 O affects proton-coupled electrochemical reactions. We show that an electrolyte that has absorbed ca. 4.3 wt % H 2 O from air provides a unique environment for H 2 O which alters the electrochemical activity and enhances the production of CO surface intermediates at potentials as low as −1.0 V vs Ag/Ag + . We also provide evidence that electrolytes can act as a carrier for H 2 O molecules, enhancing the mass transport of H 2 O to the electrode surface in this unique environment. Our results highlight that the local environment of H 2 O can be used to improve the activity and selectivity of proton-coupled electrochemical reactions.

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