Journal
CHEMSUSCHEM
Volume 7, Issue 3, Pages 934-940Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/cssc.201300603
Keywords
anodization; hematite; iron; purity; water splitting
Funding
- DFG
- DFG cluster of excellence Engineering of Advanced Materials (EAM)
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Anodization of iron substrates is one of the most simple and effective ways to fabricate nanotubular (and porous) structures that could be directly used as a photoanode for solar water splitting. Up to now, all studies in this field focused on achieving a better geometry of the hematite nanostructures for a higher efficiency. The present study, however, highlights that the purity of the iron substrate used for any anodic-hematite-formation approach is extremely important in view of the water-splitting performance. Herein, anodic self-organized oxide morphologies (nanotubular and nanoporous) are grown on different iron substrates under a range of anodization conditions, including elevated temperatures and anodization supported by ultrasonication. Substrate purity has not only a significant effect on oxide-layer growth rate and tube morphology, but also gives rise to a ninefold increase in the photoelectrochemical water-splitting performance (0.250 vs. 0.028mAcm(-2) at 1.40V vs. reversible hydrogen electrode under AM1.5 100mWcm(-2) illumination) for 99.99% versus 99.5% purity iron substrates of similar oxide geometry. Elemental analysis and model alloys show that particularly manganese impurities have a strong detrimental effect on the water-splitting performance.
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