Water DMSO Cosolvent Mixtures Modulate Hydrogen Bonding at a Gold Electrode Interface

Water often serves as both the reactant and solvent in electrocatalytic reactions. The interfacial water network can affect the transport and kinetics of these reactions, e.g., hydrogen evolution reaction and CO2 reduction reaction. Adding cosolvents that influence the hydrogen bonding environment, such as DMSO, has potential to tune the reactivity of these important electrocatalytic reactions through the regulation of the interfacial local environment and water network. We investigate interfacial hydrogen bonding networks in water DMSO cosolvent mixtures on gold surfaces using a combination of surface enhanced infrared absorption spectroscopy and molecular dynamics simulations. Experiments and simulations show that the gold surface is enriched with partially dehydrated DMSO molecules and the mixture phase separates to form water clusters. Simulations also show a “buckled” conformation for water at the surface that further constrains interfacial hydrogen bonding. The small size of these water clusters (<40 water molecules) combined with the energetically unfavorable hydrogen bond conformations might inhibit hydrogen bonding of interfacial water molecules with the bulk and suppress the proton diffusion required for efficient HER processes.