We invite you to the 58th NARECOM, which will be delivered by Prof. Krýsa from the Faculty of Chemical Technology of the University of Chemistry and Technology in Prague, on Wednesday, October 21st, 2026, at 2:30 p.m. The title of the presentation is Fe2O3 and WO3 Photoanodes: Photocorrosion protection, Applications. The abstract is below. ZOOM link upon request !!! on nanoenvicz@jh-inst.cas.cz

Fe2O3 and WO3 Photoanodes: Photocorrosion protection, Applications

Prof. Dr. Ing. Josef Krýsa

Department of Inorganic Technology, Faculty of Chemical Technology, University of Chemistry and Technology, Prague

Abstract:

Iron oxide in the form of hematite is an n-type semiconductor that is photoactive in the visible region [1]. The favourable value of the band gap (Eg = 2.1 eV) allows the absorption of a significant part of sunlight, resulting in a theoretical maximum energy conversion efficiency of 27 % (under AM 1.5G illumination). Another widely used n-type semiconductor metal oxide for photoelectrochemical applications is tungsten trioxide. Due to its higher bandgap  (~2.7 eV [2]), the theoretical maximum energy conversion efficiency is lower (~12 %) but still significantly higher than that of TiO2 (~4%). Hematite has low stability in acidic media (pH ≤ 2) where it undergoes dissolution, while WO3 has poor stability in alkaline media (pH > 7). The present paper describes the fabrication of hematite and tungsten oxide photoanodes by aerosol pyrolysis and coverage by ALD TiO2 overlayers of different thicknesses.

Coverage of hematite by a very thin 2 nm ALD TiO2 film resulted only in a small decrease in photocurrent (in 0.1 M NaOH) (about 40 %), while the increase of the thickness to 8 nm led to almost complete suppression of photocurrent. (about 95 %). Exposure of uncovered hematite films to 0.01 M sulfuric acid led to a nominal dissolution rate of 7 pm/h. In addition to dissolution, a pH dependent alteration of the surface and photoelectrochemical corrosion took place. The Faradaic efficiency of this process was reduced from 0.026 % to 0.014 % when a 2 nm TiO2 layer was applied [3]. In the case of stratified tungsten trioxide electrodes, the negative influence of an ALD overlayer on the photocurrent was not as strong as in the case of hematite. Coverage of tungsten oxide films by an 8 nm ALD TiO2 film resulted in a decrease in photocurrent (in 0.1 M HClO4) by about 25 %, and an increase of the thickness to 20 and 50 nm led to a further decrease of photocurrent of about 50 % and 95 %, respectively. Exposure of uncovered tungsten trioxide films to 0.1 M phosphate buffer (pH 8) results in a nominal dissolution rate of 550 nm/h. In addition to dissolution, photoelectrochemical corrosion took place during anodic polarization under irradiation resulting in a nominal dissolution rate of 1200 nm/h. The nominal dissolution rate during anodic polarization and illumination was significantly decreased by the coverage of TiO2 overlayers of 8, 20 and 50 nm, to 500, 30 and 10 nm/h, respectively.

 

References

1. J.H. Kennedy, K.W. Frese, Journal of the Electrochemical Society, 125 (1978) 709-714.

2. N. S. Gaikwad, G. Waldner, A. Brüger, A. Belaidi, S. M. Chaqour and M. Neumann-Spallart, Journal of the Electrochemical Society, 2005. 152(5): p. G411.

3. T. Imrich, H. Krýsová, M. Neumann-Spallart, J. Krýsa, Journal of Electroanalytical Chemistry 892 (2021) 115282.