Soft X-ray spectroscopic studies of the electronic structure of M:BiVO4 (M = Mo, W) single crystals

V. Jovic*, J. Laverock, A. J E Rettie, J. S. Zhou, C. B. Mullins, V. R. Singh, B. Lamoureux, D. Wilson, T. Y. Su, B. Jovic, H. Bluhm, T. Söhnel, K. E. Smith

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

19 Citations (Scopus)

Abstract

Bismuth vanadate, BiVO4, is a promising material for use as an anode in photoelectrochemical water splitting. However, its conversion efficiency is limited by poor bulk charge transport, which is via small-polarons. We report here the use of a suite of X-ray spectroscopic probes to determine the electronic structure of 0.3-0.6 at% M:BiVO4 (M = Mo or W). The results are interpreted in the context of current theories regarding the influence of doping on the existence of inter-band gap small-polaron states and their effect on the conversion efficiency of BiVO4. Preliminary X-ray absorption and emission measurements reveal that doping widens the band gap from 2.50 to 2.75 eV, whereas the indirect nature of the band gap remains unaffected. X-ray absorption spectroscopy verified that the doping levels did not affect the distorted tetrahedral environment of V5+ in BiVO4. For BiVO4 and W:BiVO4, V L3 resonant inelastic X-ray scattering showed energy loss features related to charge transfer from low lying valence metal/oxygen states to unoccupied V eg conduction band states. A 3.8 eV energy loss feature, coupled with small polaron-like peaks measured in valence band resonant photoelectron spectroscopy of M:BiVO4, point to the population of inter-band gap V 3d states of eg symmetry. The data reveals the existence of a band gap state in the absence of an applied bias in M:BiVO4, linked to small-polaron formation. We tentatively assign it as a deep trap state, which suggests that the improved conversion efficiency of M:BiVO4 relative to the undoped material is largely due to the increased carrier concentration in spite of increased carrier recombination rates.

Original languageEnglish
Pages (from-to)23743-23753
Number of pages11
JournalJournal of Materials Chemistry A
Volume3
Issue number47
DOIs
Publication statusPublished - 2015

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