title: Anodic nanotubular/porous hematite photoanode for solar water splitting: substantial effect of iron substrate purity.
abstract: 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. 0.028 mA cm−2 at 1.40 V vs. reversible hydrogen electrode under AM 1.5 100 mW cm−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.
authors.forename: Chong-Yong
authors.initials: CY
authors.lastname: Lee
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.forename: Yuya
authors.initials: Y
authors.lastname: Kado
authors.forename: Manuela S
authors.initials: MS
authors.lastname: Killian
authors.forename: Patrik
authors.initials: P
authors.lastname: Schmuki
mesh_terms: D004566:Electrodes; D005290:Ferric Compounds / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D043942:Nanotubes / Q000737:chemistry*; D055668:Photochemical Processes; D016062:Porosity; D013472:Sunlight; D014867:Water / Q000737:chemistry*
chemical_list: D005290:Ferric Compounds; D014867:Water; C000499:ferric oxide; D007501:Iron