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  • Open Access

Stability of Polarons and Oxygen Vacancies in BiVO4 Revealed by Machine-Learning-Driven Simulations

Ethan Berger*, Tobias Hainer, Tobias Möslinger, Paul Erhart, and Julia Wiktor†

  • *Contact author: ethan.berger@chalmers.se
  • †Contact author: julia.wiktor@chalmers.se
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PRX Energy 5, 033004 – Published 9 July, 2026

DOI: https://doi.org/10.1103/xwxv-6s55

Abstract

Bismuth vanadate is a promising photoanode material for photoelectrocatalytic water splitting. Localized charges play a crucial role in the water-splitting mechanism by introducing charge-transition levels within the band gap and thereby modifying the band alignment. Additionally, the introduction of oxygen vacancies, which can interact with electron polarons, has been reported to improve the photoelectrocatalytic efficiency. However, charge-transition levels are typically evaluated at 0 K, whereas operating conditions involve finite temperatures and, in thin films, epitaxial strain. Capturing these effects requires free energies and extensive sampling that are generally prohibitive for ab initio methods. In this work, we train a machine-learned interatomic potential for BiVO4, including electron polarons and oxygen vacancies in various charge states, to resolve how free energies, transition levels, and charge trapping evolve under operando temperature and strain conditions. For oxygen vacancies, the use of a machine-learned potential enables efficient sampling of charge-localization sites in the vicinity of the vacancy, revealing favored configurations. The energies of the localized polaron and oxygen-vacancy states remain essentially unchanged with temperature, while their transition levels relative to the band edges vary due to temperature-dependent band-edge shifts. In contrast, strain more strongly modifies both the localized states and the band edges. These results provide new insights into the stability of localized charges and their role in photoelectrocatalytic water splitting at finite temperature.

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Bismuth vanadate is a promising photoanode for photoelectrochemical water splitting, a technology that could help produce hydrogen fuel using sunlight instead of fossil energy. The efficiency of this process is strongly influenced by localized charges, which are challenging to detect experimentally and expensive to simulate under operating conditions. In this work, the authors present a machine-learned interatomic potential capable of modeling localized charges in electron polarons and around oxygen vacancies and simulate their energy levels at finite temperatures and under strain. The results provide new insights into the stability of localized charges under operando conditions and their role in the photoelectrochemical efficiency of bismuth vanadate.

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PRX Energy 5, 033004– Published 9 July, 2026
  • Received 2 April 2026
  • Revised 20 May 2026
  • Accepted 17 June 2026
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