Protection of hematite photoelectrodes by ALD-TiO2 capping

0539266 - ÚFCH JH 2022 RIV CH eng J - Journal Article
Imrich, T. - Zazpe, R. - Krýsová, Hana - Paušová, Š. - Dvořák, F. - Rodriguez-Pereira, J. - Michalička, J. - Man, O. - Macák, J. M. - Neumann-Spallart, M. - Krýsa, J.
Protection of hematite photoelectrodes by ALD-TiO2 capping.
Journal of Photochemistry and Photobiology A-Chemistry. Roč. 409, MAR 2021 (2021), č. článku 113126. ISSN 1010-6030. E-ISSN 1873-2666
R&D Projects: GA ČR(CZ) GA20-11635S
Institutional support: RVO:61388955
Keywords : ald * Chemical dissolution * Hematite * TiO capping layer 2 * xps
OECD category: Electrochemistry (dry cells, batteries, fuel cells, corrosion metals, electrolysis)
Impact factor: 5.141, year: 2021
Method of publishing: Limited access

Iron (III) oxide, in the form of hematite (α-Fe2O3), is a n-type semiconductor which is photoactive in the visible spectral region. Therefore, use in photoelectrocatalysis and photoassisted water electrolysis may be suggested. For such implementations, stability of contacts with liquid phases is mandatory. Hematite is stable in alkaline media but less stable in acidic media. For the first time the coverage of porous photoactive Sn doped hematite by thin capping layers of TiO2, deposited by Atomic Layer Deposition (ALD) and its impact on photocurrent and chemical stability of hematite is shown. The nominal thicknesses of the TiO2 ALD coatings were 0.5, 2 and 7.5 nm. The presence of the TiO2 coatings was evidenced by X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy (HR-TEM) and scanning TEM coupled with energy dispersive X-ray (EDX) spectroscopy. HR-TEM analyses revealed that the TiO2 capping layers were amorphous and conformal. Exposure of uncovered hematite layers to 1 M sulfuric acid led to a nominal dissolution rate of 0.23 nm/h which was halved when a TiO2 ALD coating (7.5 nm thin) was applied. Due to mismatch of the valence band positions of the two semiconductors, photocurrents were strongly diminished as the capping layer thickness was increased. Post-calcination of as deposited ALD films on hematite resulted in an increase of photocurrent, which only exceeded photocurrents of pristine hematite when the ALD thickness was not more than 0.5 nm.
Permanent Link: http://hdl.handle.net/11104/0316942