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Preparation of Nanostructured Ta3N5 Electrodes by Alkaline Hydrothermal Treatment Followed by NH3 Annealing and Their Improved Water Oxidation Performance

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journal contribution
posted on 30.04.2019, 08:13 by Ashraf Abdel Haleem, Nagaraju Perumandla, Yoshinori Naruta
Solar water splitting is a clean and sustainable process for green hydrogen production. It can reduce the fossil fuel consumption. Tantalum nitride (Ta3N5) is one of the limited candidates of semiconductors, which absorb a broad range of visible light and are thermodynamically able to split water without external bias potential. In the present work, we introduce a facile method to prepare a nanostructured Ta3N5 photoanode in a two-step process: hydrothermal deposition of perovskite-type NaTaO3 in a hydrofluoric acid-free NaOH aqueous solution followed by heat treatment in NH3 atmosphere. The resulted bare Ta3N5 electrode was subsequently modified with a Ni-doped CoFeOx (Ni:CoFeOx) as a water oxidation catalyst. After the cocatalyst loading, the electrode shows a photocurrent of about 5.3 mA cm–2 at 1.23 V vs reversible hydrogen electrode. The electrode maintained about 82% of its initial photocurrent after 7 h irradiation. In addition, a continuous oxygen evolution occurred for 3 h at Faraday efficiency of 96%. This performance is superior to that of the single-layer-modified Ta3N5 photoanodes reported so far. This remarkable improvement on the photochemical performance could be due to the uniform nanostructured surface morphology of the present Ta3N5 photoanode. Other alkaline salt treatments, such as LiOH and KOH, do not give such nanostructured morphology and accordingly exhibit lower performance than the one treated in NaOH.