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Formation of an electron hole doped film in the alpha-Fe2O3 photoanode upon electrochemical oxidation

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Publication date 2013
Author Gajda-Schrantz Krisztina, Tymen Simon, Boudoire Florent, Toth Rita, Bora Debajeet K., Calvet Wolfram, Graetzel Michael, Constable Edwin C., Braun Artur,
Project Defects in the bulk and on surfaces and interfaces of metal oxides with photoelectrochemical properties: In-situ photoelectrochemical and resonant x-ray and electron spectroscopy studies
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Original article (peer-reviewed)

Volume (Issue) 15(5)
Page(s) 1443 - 1451
DOI 10.1039/c2cp42597a


Solar hydrogen generation by water splitting in photoelectrochemical cells (PEC) is an appealing technology for a future hydrogen economy. Hematite is a prospective photoanode material in this respect because of its visible light conjugated band gap, its corrosion stability, its environmentally benign nature and its low cost. Its bulk and surface electronic structure has been under scrutiny for many decades and is considered critical for improvement of efficiency. In the present study, hematite films of nominally 500 nm thickness were obtained by dip-coating on fluorine doped tin oxide (FTO) glass slides and then anodised in 1 molar KOH at 500, 600, and 700 mV for 1, 10, 120 and 1440 minutes under dark conditions. X-ray photoelectron spectra recorded at the Fe 3p resonant absorption threshold show that the eg transition before the Fermi energy, which is well developed in the pristine hematite film, becomes depleted upon anodisation. The spectral weight of the eg peak decreases with the square-root of the anodisation time, pointing to a diffusion controlled process. The speed of this process increases with the anodisation potential, pointing to Arrhenius behaviour. Concomitantly, the weakly developed t2g peak intensity becomes enhanced in the same manner. This suggests that the surface of the photoanode contains Fe2+ species which become oxidized toward Fe3+ during anodisation. The kinetic behaviour derived from the experimental data suggests that the anodisation forms an electron hole doped filmon and below the hematite surface.