Nature of the Localized V 3d Electrons in Mo- and W‑Doped BiVO4 Revealed by Soft X‑ray Photoemission and Absorption Spectroscopy.

We have investigated the effects of Mo and W doping on BiVO4 by means of X-ray photoemission spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The V 2p XPS spectra indicate that the substitution of W6+ and Mo6+ for V5+ induces the formation of V4+ species. In addition, the Bi 4f XPS spectra exhibit a minor Bi5+ component, which further contributes to an increase in the V4+ concentration. A V 3d-derived feature emerges at approximately 1.5 eV below the Fermi level and is associated with the enhanced catalytic activity of Mo- and W-doped BiVO4. The center of mass of the V 3d spectral distribution is shifted toward the Fermi level with increasing dopant concentration, suggesting the importance of the long-range d-d Coulomb interaction in determining the electronic structure of the localized V 3d states.