Synthesis of Nanostructured BaTaO₂N Thin Films as Photoanodes for Solar Water Splitting

Synthesis of nanostructured BaTaO 2 N thin films on metallic Ta substrates, and their application as photoanodes for solar-driven photoelectrochemical water oxidation were studied. Ba 5 Ta 4 O 15 nanosheets vertically grown on Ta substrates by a hydrothermal process were converted into perovskite BaTaO 2 N with a branching nanostructure by thermal nitridation under an ammonia gas flow. The crystal quality and photoelectrochemical properties of the BaTaO 2 N thin films were found to improve with increasing nitridation temperature up to 1000 °C. A Ta 4 N 5 interfacial layer was formed between the BaTaO 2 N thin film and the Ta substrate. Under simulated AM 1.5G light, the BaTaO 2 N electrode generated a photoanodic current, although it rapidly decreased due to photo-oxidative corrosion. The degradation of the BaTaO 2 N electrode could be alleviated by the deposition of a cobalt phosphate layer on its surface. The modified electrode maintained a photoanodic current of 0.75 mA cm –2 at 1.23 V versus the reversible hydrogen electrode with a Faradaic efficiency of almost unity.