Saptarsi Mondal Ultrafast & multidimensional IR spectroscopy
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RESEARCH / ■ THEME I · CURRENT WORK

Interfacial and electrochemical dynamics

How does the hydrogen-bond network of water rearrange in the few nanometres next to an electrode, and how does applied potential — or an added cosolvent — change it?

Surface-enhanced 2D IR isolates hydrogen-bond rearrangement within a few nanometres of the electrode, where confinement and the interfacial electric field both act on the probe.

The interface is not a thin slice of the bulk. Confinement, the electrode’s field and the broken symmetry at the surface each change how water finds and loses hydrogen-bonding partners — and not always in the same direction. So I measure interface and bulk with the same molecular reporter and compare the two numbers directly, with no model in between.

That comparison produced the result I use most. DMSO slows bulk water down; the two liquids form long-lived microdomains. At a gold surface the same addition speeds hydrogen-bond exchange up about fivefold, without touching the applied potential. Structure from operando SEIRAS, dynamics from voltage-dependent surface-enhanced 2D IR, both under working conditions — that pairing is the methodological centre of the programme I am building.

Methods

  • Operando ATR-SEIRAS spectro-electrochemistry
  • Surface-enhanced 2D IR spectroscopy
  • Constant-potential molecular dynamics
  • Isotopic dilution for interfacial O–H assignment

Publications in this theme

4 records → publications

Projects in this theme

  • 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. Current work
Why it matters
Electrocatalysis happens in a layer a few nanometres thick, where interfacial water is both reactant and proton shuttle. Its structure sets the barrier for proton-coupled electron transfer in reactions such as hydrogen evolution and CO₂ reduction, yet bulk measurements average over exactly the motions that matter.
My contribution
With SEIRAS and constant-potential MD I mapped potential-dependent DMSO–water structure at gold electrodes, then built the surface-enhanced 2D IR measurement that resolves the corresponding dynamics. The interface turned out to move in the opposite direction to the bulk.
What we found
Negative potential enriches DMSO at the surface and reorients interfacial water. Small DMSO fractions speed interfacial hydrogen-bond exchange from about 10 ps in pure water to about 2 ps at 20 mol% — while the same mixtures slow the bulk. A neutral cosolvent is, in effect, a second handle on interfacial structure, orthogonal to applied potential.
Where it goes next
Map interfacial water structure and dynamics across cosolvent identity and applied potential, then correlate those observables with hydrogen-evolution and CO₂-reduction kinetics on gold, copper and silver. The hypothesis: a more fluxional interfacial water layer eases proton transfer and reshapes selectivity.

Where this work was done

Presented at

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