Interfacial & electrochemical dynamics
Cosolvent and potential control of interfacial water
Establishing cosolvent composition as a second, orthogonal handle — alongside applied potential — on the structure and dynamics of water at an electrode surface, and measuring both with surface-specific vibrational spectroscopy.
The premise of this project is that the interface has to be measured, not inferred from bulk behaviour. That sounds obvious, but it is not how most cosolvent electrochemistry is done — the composition of the bulk electrolyte is known, the interfacial composition is assumed to follow, and the dynamics are not measured at all.
SEIRAS solves the first half. A nanostructured gold film on an attenuated-total-reflection element enhances infrared absorption of molecules within roughly 5–20 nm of the surface by orders of magnitude, and in the Kretschmann geometry that same film serves as the working electrode. The result is chemically specific, potential-resolved structural information from the interface alone, with a clean surface selection rule and unobstructed mass transport.
What SEIRAS cannot give is a timescale. That is what surface-enhanced 2D IR adds: by correlating initial and final frequencies of a vibrational mode, it measures spectral diffusion and hydrogen-bond rearrangement directly, and the plasmonic enhancement brings the third-order signal up to monolayer sensitivity. Running both on the same electrode, with the same probe, under the same conditions is the methodological point of the project.
- Scientific motivation
- Interfacial water is both reactant and proton shuttle at an electrified interface, and its hydrogen-bond connectivity sets the barrier for proton-coupled electron transfer. Traditionally the applied potential has been the only control variable available. If an electrically neutral cosolvent can reshape the interfacial network as effectively, it offers a way to steer electrocatalysis without resorting to large — and often damaging — applied potentials.
- The research question
- How do cosolvent identity and applied potential jointly determine the population, orientation and hydrogen-bond exchange dynamics of water in the first few nanometres above a metal electrode?
- My contribution
- I designed and ran both halves of the measurement. Using operando ATR-SEIRAS with a gold film as the working electrode, I mapped potential-dependent interfacial composition and water orientation in DMSO–water mixtures. I then built the surface-enhanced 2D IR measurement on tethered nitrile probes to extract interfacial hydrogen-bond lifetimes, and ran the bulk 2D IR reference that makes the interface-versus-bulk comparison meaningful.
- Results and current status
- Negative bias enriches DMSO at the gold surface and reorients interfacial water, modestly increasing hydrogen-bond populations at low DMSO content. Surface-enhanced 2D IR then showed that even small DMSO fractions dramatically accelerate interfacial hydrogen-bond exchange — from roughly 10 ps in pure water to about 2 ps at 20 mol% DMSO — while the same mixtures slow bulk water dynamics. The interface and the bulk respond to the same additive in opposite directions.
- Future direction
- Build the full two-dimensional map across cosolvent identity (DMSO, dimethylformamide, acetonitrile and others spanning donor and acceptor character) and applied potential, then correlate the spectroscopic observables with measured hydrogen evolution and CO₂ reduction kinetics and product distributions on gold, copper and silver. Isotopic dilution with HOD will give clean assignment of interfacial O–H and O–D modes.
Publications from this project
PublishedACS Electrochem. · 2025 · 1 (5), 709–717
Tuning Hydrogen Bond Networks at Gold Electrodes: A Study of Potential-Dependent DMSO−Water Interfaces
Under reviewChemRxiv · 2025