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

Synthesis of nanostructured BaTaO2N thin films on metallic Ta substrates, and their application as photoanodes for solar driven photoelectrochemical water oxidation were studied. Ba5Ta4O15 nanosheets vertically grown on Ta substrates by a hydrothermal process were converted into perovskite BaTaO2N with a branching nano structure by thermal nitridation under an ammonia gas flow. The crystal quality and photoelectrochemical properties of the BaTaO2N thin films were found to improve with increasing nitridation temperature up to 1000 degrees C. A Ta4N5 interfacial layer was formed between the BaTaO2N thin film and the Ta substrate. Under simulated AM 1.5G light, the BaTaO2N electrode generated a photoanodic current, although it rapidly decreased due to photo oxidative corrosion. The degradation of the BaTaO2N 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.