Determination of the Intrinsic Defect at the Origin of Poor H₂ Evolution Performance of the Monoclinic BiVO₄ Photocatalyst Using Density Functional Theory

The effects of intrinsic defects in monoclinic bismuth vanadate (BiVO₄) on its stability and optoelectronic properties for photochemical water splitting application were examined using density functional theory. Among the most favorable structures, only that associated with V-antisites on Bi with additional Bivacancies (Bi_(1-5x)V_(1+3x)O₄ with x = 0.0625) revealed narrower band gap energy by 0.5 eV compared to pristine material (calculated value is 2.8 eV) giving a value of 2.3 eV, which is very close to the experimentally reported ones (in the 2.4-2.5 eV range). The low electron mobility reported experimentally for this material was also confirmed by the relatively large electron effective masses obtained for the intrinsic defective Bi_(1-5x)V_(1+3x)O₄ (x = 0.0625) structure along the three principal crystallographic directions. The strongly localized nature of the accommodated electrons on the d-orbitals of the newly substituted V at Bi sites was also predicted to be at the origin of the poor H₂ evolution performance of this material.