Working Paper: Cosolvents Disrupt Water H-bond Networks at Electrode Interfaces: a Surface-enhanced 2D IR Study

In electrochemical reactions, interfacial water restructuring can drive electrocatalytic activity. Characterizing interfacial water’s H-bond network structure and dynamics is one of the first steps towards obtaining a mechanistic understanding of electrochemical processes in aqueous environments. Here we use surface-enhanced two-dimensional infrared (SE 2D IR) spectroscopy to quantify the effect of dimethyl sulfoxide (DMSO) on water dynamics by measuring the picosecond frequency fluctuation of nitrile-based vibrational probes at a functionalized gold electrode. Pure water, biexponential dynamics show a fast component of ~1.0 ps corresponding to local spectral diffusion and a slower component of 9.9 ps attributed to H-bond exchange. DMSO considerably accelerates interfacial H-bond rearrangements. For example, at 20 mol% DMSO the slow component shortens to 1.8 ps, indicating a more labile H-bond networks. In stark contrast, DMSO slows dynamics in the bulk, consistent with long-lived water–DMSO microdomains. The interface vs bulk comparison shows that DMSO disrupts cooperative H-bonding of water by inducing disorder at the metal-liquid interface, speeding up H-bond rearrangements. Whereas in 3D bulk environment, long-lived microheterogeneity exhibits slower dynamics. The study demonstrates how cosolvents can be used to modulate interfacial water dynamics but also highlights the complexities of predicting solvent behavior at electrochemical interfaces