Electrocatalytic CO₂ Reduction in Acetonitrile Enhanced by the Local Environment and Mass Transport of H₂O

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 CO2 reduction in acetonitrile on nanoscale-roughened Ag catalysts as a model system and operando surface-enhanced Raman scattering spectroscopy to demonstrate that the local environment of H2O affects proton-coupled electrochemical reactions. We show that an electrolyte that has absorbed ca. 4.3 wt % H2O from air provides a unique environment for H2O 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 H2O molecules, enhancing the mass transport of H2O to the electrode surface in this unique environment. Our results highlight that the local environment of H2O can be used to improve the activity and selectivity of proton-coupled electrochemical reactions.