Evolution of Excited States in Bismuth Vanadate: Trapping and Kinetic Pathways

Photoelectrocatalytic water splitting using bismuth vanadate (BiVO₄) is a promising approach for sustainable hydrogen production, but its efficiency is limited by charge carrier dynamics. Though charge trapping in the form of polarons is well-studied, the behavior of self-trapped excitons (STEs), particularly whether they remain stable or dissociate under operating conditions, remains far less understood. Using hybrid density functional theory with the nudged elastic band method, we quantify activation barriers for STE hopping, dissociation and transformation in BiVO₄, revealing distinct behaviors and kinetic time scales for two STE types: a separated, more mobile state and a compact, more stable one with higher barriers. Additionally, we study an alternative charge trapping mechanism via O-O dimers, providing an alternative multipolaron binding pathway with distinct kinetics. These findings provide fundamental insights into the kinetic stability and mobility of trapped charges in BiVO₄, aiding the interpretation of charge trapping dynamics under operating conditions.