Photoelectrochemical Water Splitting on Particulate ANbO2N (A = Ba, Sr) Photoanodes Prepared from Perovskite-Type ANbO3

Perovskite-type Nb-based oxynitrides (ANbO2N, A = Ba, Sr) exhibiting absorption of long light wavelengths up to (A = Sr) or even above 700 nm (A = Ba) were synthesized from stoichiometric perovskite-type oxides (ANbO3) by a typical thermal ammonolysis method. The preparation of BaNbO2N using BaNbO3 having an identical cubic-perovskite-type structure was demonstrated to effectively improve the surface and bulk crystallinity of the oxynitride because of the absence of a structural transition during nitridation and the stoichiometric 1:1 Ba/Nb ratio between the oxides and oxynitrides. The resulting BaNbO2N photoanode exhibited photoelectrochemical water oxidation activity with a current density of 0.85 mA cm–2 at 1.23 VRHE and a faradaic efficiency close to unity under simulated solar illumination (AM 1.5G). The associated incident photon-to-current efficiency in the range of 740–480 nm showed that BaNbO2N produces a photoanodic current at 740 nm, the longest response wavelength ever reported for a photoanode based on an (oxy)nitride.