SrTaO₂N Nanowire Photoanode Modified with a Ferrihydrite Hole-Storage Layer for Photoelectrochemical Water Oxidation

Abstract

The perovskite-related oxynitride SrTaO 2 N is a prospective photoanode candidate with favorable band-edge positions. We have synthesized SrTaO 2 N nanowires with roughened surfaces by a hydrothermal process on a tantalum substrate and nitridation at 1273 K under flowing ammonia and hydrogen. The nanowires were coated with a ferrihydrite hole-storage layer for photoelectrochemical water oxidation under AM 1.5G illumination in 0.1 M NaOH electrolyte (pH 13). The nanowires exhibit an electronic band gap of 2.32 eV, and the photocorrosion can be decreased with ferrihydrite coating. In the presence of Na 2 SO 3 as a hole scavenger, the nanowires do not yield higher photocurrent. This indicates that the limiting factors for hole extraction are processes occurring in the bulk instead of at the semiconductor–electrolyte interface. Our work is the first trial of a SrTaO 2 N photoanode based on nanowires and may also be promising for other quaternary oxynitride semiconductors to achieve a one-dimensional morphology.