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

Picosecond electric field fluctuations mediate local environments that govern electrocatalysis at the electrode-water interface. Consequently, cosolvents modulate hydrogen-bond networks and interfacial dynamics. Here, we use surface-enhanced two-dimensional infrared (SE 2D IR) spectroscopy to quantify the effect of the cosolvent dimethyl sulfoxide (DMSO) on water dynamics by measuring the picosecond frequency fluctuation timescales of nitrile-based vibrational probes at a functionalized gold surface to extract H-bond lifetimes. We find that DMSO considerably accelerates interfacial H-bond rearrangements. In 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 interface, speeding up H-bond rearrangements, whereas in a bulk environment, long-lived microheterogeneity exhibits slower dynamics. The study demonstrates that bulk properties rarely reflect the interface highlighting the complexities of predicting solvent behavior at electrochemical interfaces. The results indicate that cosolvents can modulate local dynamics and offer extra control over interfacial properties.