(104c) Engineering Water Microenvironments in Aprotic Solvent for Enhanced CO2 Electrochemical Reduction

Electrochemical carbon dioxide reduction (CO2R) presents a promising avenue for sustainable production of fuels and chemicals. Water molecules play a crucial role in this process by stabilizing key reaction intermediates and acting as a proton donor. However, the CO2R selectivity is often hindered by the competing hydrogen evolution reaction (HER), even at low water concentrations. In this study, we tune the water microenvironment and electrochemical activity within a series of organic aprotic solvents featuring different functional groups and physicochemical properties.

Through spectroscopic analyses, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations, we establish a direct correlation between solvent donor number and the water hydrogen bonding strength and dynamics. By confining water within a strong hydrogen bond network, we could extend the HER onset potential by nearly 1 V. Using a gold electrode, we could then achieve CO Faradaic efficiency (FE) values of 100% for water concentrations as high as 3 M. Our results showcase the effectiveness of modulating the water microenvironment in enhancing CO2R selectivity. We further extend this approach to mildly acidic conditions, achieving sustained 98% FE towards CO over an earth-abundant zinc catalyst, with virtually no carbonate losses.

By elucidating the interplay between water solvation and electrochemical activity, we offer valuable descriptors to guide efficient electrolyte design across various chemical transformations.