Electronic Structure of Tantalum Oxynitride Perovskite Photocatalysts

The tantalum oxynitride perovskites ATaO2N (A = Ca, Sr, and Ba) and PrTaON2 are promising candidates for the photocatalytic splitting of water under illumination with visible light. A combination of X-ray photoemission spectroscopy (XPS), Kelvin probe force microscopy (KPFM), UV–vis spectroscopy, and depth-resolved cathodoluminescence spectroscopy (DRCLS) has been used to determine the absolute conduction and valence band energy levels of these four compounds. All have conduction band edges that lie above the reduction potential for water and therefore are suitable for the photocatalytic production of hydrogen, whereas the valence band edges lie near the oxidation potential of water. The position of the conduction band edge is closely linked to the Ta–O/N–Ta bond angles and hence tilting of the octahedra, whereas the position of the valence band edge is more sensitive to the oxygen-to-nitrogen ratio.