The role of the isolated 6s states in BiVO₄ on the electronic and atomic structures

BiVO₄ is one of the most promising photoanodes for water-splitting applications. Similar to many d¹⁰ materials, where the full-shell d electrons are not directly involved in the bonding, the Bi 6s electrons form isolated low-energy bands in BiVO₄. By systematically altering the energy of the Bi 6s states, we find direct evidences that the isolated s states, through the s-p coupling, affect the BiVO₄ properties, including valence band maximum position, charge density, and atomic structural distortion. We find that many good properties of BiVO₄ for water splitting are related to the s-p coupling due to the existence of Bi 6s states. Based on this understanding, we propose that alloying Bi with Sb can enhance these properties, and hence improve the water-splitting efficiency.