Halogen Atom (Cl, Br, and I) Doping Effects on the Electronic Character and OER Performance of BiVO₄ as a Photoanode Nanomaterial for Solar Water Splitting: A Theoretical Study

Halogen elements, as common nonmetal dopants, have attracted significant attention for their potential in creating highly active photocatalysts. To improve the electronic property of BiVO₄, a highly promising photoanode nanomaterial for solar water splitting, the halogen atom (Cl, Br, and I) doping strategy and underlying modification mechanisms were explored in detail by the first-principles calculations here. Formation energies confirmed that halogen doping at the O sites of BiVO₄ is energetically favorable and can be realized experimentally. The conduction band minimum (CBM) energy level is stabilized and even shifted into the occupied electron states, while the valence band maximum (VBM) energy level is increased for BiVO₄ upon halogen atom doping with a trend: I > Br > Cl. Furthermore, the n-type electron-donating behavior becomes increasingly significant with higher dopant mass concentrations, which is attributed to the lower electronegativity of introduced halogen atoms compared to that of the substituted O atoms. Moreover, doping with Cl, Br, or I atoms induces strong spin polarization and effectively suppresses the recombination of photogenerated electron-hole pairs in BiVO₄. Furthermore, H₂O adsorption energy and Gibbs free energy change (Δ<i>G</i>) results for each fundamental stage confirmed that the oxygen evolution reaction (OER) process is favored by such an n-type doping method. All of these results proved that halogen atom (Cl, Br, and I) doping is a reliable strategy to improve photoelectrical properties, consequently boosting the photocatalytic performance of BiVO₄ through modifications to its electronic structure.