Preparation of Nanostructured Ta(3)N(5) Electrodes by Alkaline Hydrothermal Treatment Followed by NH(3) Annealing and Their Improved Water Oxidation Performance

[Image: see text] Solar water splitting is a clean and sustainable process for green hydrogen production. It can reduce the fossil fuel consumption. Tantalum nitride (Ta(3)N(5)) 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 Ta(3)N(5) photoanode in a two-step process: hydrothermal deposition of perovskite-type NaTaO(3) in a hydrofluoric acid-free NaOH aqueous solution followed by heat treatment in NH(3) atmosphere. The resulted bare Ta(3)N(5) electrode was subsequently modified with a Ni-doped CoFeO(x) (Ni:CoFeO(x)) 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 Ta(3)N(5) photoanodes reported so far. This remarkable improvement on the photochemical performance could be due to the uniform nanostructured surface morphology of the present Ta(3)N(5) 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.