Iron resonant photoemission spectroscopy on anodized hematite points to electron hole doping during anodization

Artur Braun, Qianli Chen, Dorota Flak, Giuseppino Fortunato, Krisztina Gajda-Schrantz, Michael Grätzel, Thomas Graule, Jinghua Guo, Tzu Wen Huang, Zhi Liu, Anastasiya V. Popelo, Kevin Sivula, Hiroki Wadati, Pradeep P. Wyss, Liang Zhang, Junfa Zhu

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

Anodization of α-Fe2O3 (hematite) electrodes in alkaline electrolyte under constant potential conditions the electrode surface in a way that an additional current wave occurs in the cyclic voltammogram. The energy position of this current wave is closely below the potential of the anodization treatment. Continued cycling or exchanging of the electrolyte causes depletion of this new feature. The O 1s and Fe 2p core-level X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine structure (NEXAFS) spectra of such conditioned hematite exhibit a chemical shift towards higher binding energies, in line with the general perception that anodization generates oxide species with dielectric properties. The valence band XPS and particularly the iron resonant valence band photoemission spectra, however, are shifted towards the opposite direction, that is, towards the Fermi energy, suggesting that hole doping on hematite has taken place during anodization. Quantitative analysis of the Fe 2p resonant valence band photoemission spectra shows that the spectra obtained at the Fe 2p absorption threshold are shifted by virtually the same energy as the anodization potential towards the Fermi energy. The tentative interpretation of this observation is that anodization forms a surface film on the hematite that is specific to the anodization potential.

Original languageEnglish
Pages (from-to)2937-2944
Number of pages8
JournalChemPhysChem
Volume13
Issue number12
DOIs
Publication statusPublished - Aug 27 2012

    Fingerprint

Keywords

  • X-ray absorption spectroscopy
  • anodization
  • hematite
  • photoelectrochemistry
  • water splitting

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Physical and Theoretical Chemistry

Cite this

Braun, A., Chen, Q., Flak, D., Fortunato, G., Gajda-Schrantz, K., Grätzel, M., Graule, T., Guo, J., Huang, T. W., Liu, Z., Popelo, A. V., Sivula, K., Wadati, H., Wyss, P. P., Zhang, L., & Zhu, J. (2012). Iron resonant photoemission spectroscopy on anodized hematite points to electron hole doping during anodization. ChemPhysChem, 13(12), 2937-2944. https://doi.org/10.1002/cphc.201200074