Local Coordination and Electronic Coupling Governs Charge Dynamics in BiVO₄ Photoanodes

Transition-metal incorporation is widely employed to enhance the photoelectrochemical performance of BiVO₄ photoanodes, yet how the local incorporation environment governs charge-carrier dynamics remains poorly understood. Here, we establish a structure-function relationship between the local environments of Fe, Co, and Ni and the resulting charge-dynamics in BiVO₄. Combining synchrotron-based x-ray spectroscopies with femtosecond-to-microsecond photophysical measurements, we show that all transition metals improve water oxidation activity relative to pristine BiVO₄, following the trend (Ni > Fe > Co) > BiVO₄. Fe and Co predominantly adopt heterogeneous, oxide-like local environments associated with weaker and more spatially heterogeneous coupling to the BiVO₄ framework, resulting in moderate improvements in charge separation. In contrast, Ni forms highly oxidized, locally octahedrally coordinated Ni-O units that exhibit stronger electronic coupling with the BiVO₄ framework, modifying the V-O electronic structure, suppressing charge localization and recombination, and extending carrier lifetimes across multiple timescales. Operando x-ray absorption further reveals that incorporated Ni species remain electronically responsive under working conditions, linking their local electronic structure to photogenerated charge accumulation. These findings demonstrate that the photoelectrochemical behavior of transition-metal-modified BiVO₄ is governed by the nature of metal-host electronic coupling rather than metal identity alone, providing a general design principle for oxide photoanodes.