Anodic Nanotubular/porous Hematite Photoanode for Solar Water Splitting: Substantial Effect of Iron Substrate Purity

Authors

  • Dr. Chong-Yong Lee,

    1. Department of Materials Science and Engineering, University of Erlangen-Nuremberg, Martensstr. 7, 91058 Erlangen (Germany)
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  • Dr. Lei Wang,

    1. Department of Materials Science and Engineering, University of Erlangen-Nuremberg, Martensstr. 7, 91058 Erlangen (Germany)
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  • Dr. Yuya Kado,

    1. Department of Materials Science and Engineering, University of Erlangen-Nuremberg, Martensstr. 7, 91058 Erlangen (Germany)
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  • Dr. Manuela S. Killian,

    1. Department of Materials Science and Engineering, University of Erlangen-Nuremberg, Martensstr. 7, 91058 Erlangen (Germany)
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  • Prof. Dr. Patrik Schmuki

    Corresponding author
    1. Department of Materials Science and Engineering, University of Erlangen-Nuremberg, Martensstr. 7, 91058 Erlangen (Germany)
    • Department of Materials Science and Engineering, University of Erlangen-Nuremberg, Martensstr. 7, 91058 Erlangen (Germany)

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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.

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