On the Enhanced Reducibility and Charge Transport Properties of Phosphorus-Doped BiVO₄ as Photocatalysts: A Computational Study

Phosphorus (P)-doped BiVO₄ has been proposed as a promising photoanode for water splitting as it exhibits significant improvement of photocurrent density and photocatalytic O₂ evolution rate. Previous findings suggest that substitution of V with P induces lattice polarization, which facilitates electron-hole separation. However, little attention has been paid to the mechanism underlying the observed changes in electronic conductivity due to oxygen vacancies. In this work, we carry out first-principles calculations to study the effect of P doping on the stability of oxygen vacancies and charge transport properties of BiVO₄ photocatalysts. Our computations reveal improved reducibility of P-doped BiVO₄ as reflected in the lower energies of oxygen vacancy formation. The generated oxygen vacancy yields two electron polarons localized at the two nearest V centers, where one polaron is always trapped at the defect site. The calculated polaron hopping barriers and their mobilities obtained from kinetic Monte Carlo simulations indicate that the P impurity by itself does not significantly alter the behavior of polaron transport. Hence, P doping improves reducibility of the material, which, in turn, increases the number of charge carriers and improves the electronic conductivity, which could lead to superior photocatalytic activity. These results can explain the experimentally observed higher concentration of oxygen vacancies and the enhancement of photocurrent density of P-doped BiVO₄. This study provides valuable insights for designing doping strategies to improve the photocurrent density of photocatalysts.