We focus on charge hopping processes occurring at transition-metal oxide/water interfaces, such as they might be relevant in describing the water splitting mechanism. In the first part of the presentation, we focus on charge migration across the bulk of the transition-metal oxide. In these materials, the charge is often found in localized polaronic states, which are particularly challenging to describe computationally because of the necessity of properly accounting for self-interaction effects. Focusing on hole migration in TiO2 polymorphs (anatase and rutile), we turn to piecewise linear functionals to determine binding energies and hopping barriers [1]. In anatase, the charge is found to hop from one localized polaron state to a neighboring state of the same kind. At variance, in rutile, the charge diffusion occurs through intermediate states which are fully delocalized. In the second part of the presentation, we specifically focus on electron transfer across the semiconductor-water interface. One specific interest of our investigation is to determine to what extent the thermal motion of the water component affects the electron transfer mechanism and the involved kinetic barriers. In this case, we focus on the first proton coupled electron transfer across the BiVO4(010)-water interface [2], which appears to be the rate-determinant step of the oxygen evolution reaction (OER) at this interface. To determine the free-energy surface while keeping a hybrid-functional level of accuracy, we utilize machine learning potentials and enhanced sampling methods. In this way, we are able not only to determine the kinetic barrier of the OER process but also to provide insight into the underlying atomistic mechanism. One of the issues addressed is the effect of static [3] vs dynamic water [2] on the hopping barrier of the electron transfer across the interface. It is found that the impact of the water dynamics is essential, leading not only to a significantly lowering of the barrier, but also to a qualitatively different reaction path [2]. The role of nuclear quantum effects are also briefly discussed.
[1] G. Palermo, S. Falletta, and A. Pasquarello, Migration of hole polarons in anatase and rutile TiO2 through piecewise-linear functionals, Phys. Rev. B 110, 235205 (2024).
[2] Y. Zhuang and A. Pasquarello, Mechanism of first proton-coupled electron transfer of water oxidation at the BiVO4–water interface, Angew. Chem. Int. Ed. 64, e202507071 (2025).
[3] S. Liu, J. Wiktor, and A. Pasquarello, Oxygen evolution at the BiVO4-water interface: Mechanism of the water dehydrogenation reaction, ACS Catalysis 12, 11734-11742 (2022).
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