Mechanical Strain Tunes Proton Chemistry at Oxide–Water Interfaces

ABSTRACT Proton transfer at oxide–water interfaces controls surface hydroxylation, interfacial charge, and elementary photocatalytic steps, and is usually tuned electrostatically, through pH or applied potential. Whether mechanical strain provides an independent handle, and by what molecular mechanism, has remained unclear. Using Deep Potential molecular dynamics with density‐functional‐theory accuracy, we study the anatase (101)–water interface under biaxial strain from to . Tension switches the contact layer from molecular to dissociative adsorption, raising the dissociated fraction from 8% to 67%; free‐energy surfaces show the proton is released through an intermediate solvent water rather than transferred directly, with tension lowering the barrier and inverting the molecular‐dissociated stability. The Wannier centers of the electronic distribution trace this to a rearrangement of valence electron density at both surface reactive sites, which results in ‐bound water becoming a stronger acid and becoming a stronger base. Analysis of the strain dependence of the dissociation free energy also indicates a reciprocal mechanical effect: water dissociation contributes a compressive interfacial stress that reduces the tensile stress at fixed imposed strain. Strain thus tunes both halves of an interfacial acid–base pair at once, providing a mechanical handle on proton chemistry at oxide–water interfaces.