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

Abstract

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.