Crucial Role of Donor Density in the Performance of Oxynitride Perovskite LaTiO<inf>2</inf>N for Photocatalytic Water Oxidation

LaTiO2N photocatalysts were prepared by thermal ammonolysis of flux-synthesized La2Ti2O7 and La2TiO5, and were investigated for water oxidation. Though LaTiO2N derived from La2TiO5 appears defect-free by UV/Vis/near-IR and electron paramagnetic resonance (EPR) spectroscopy, its performance is much lower than that of conventional La2Ti2O7-derived LaTiO2N with defects. It is shown by Mott–Schottky analysis that La2TiO5-derived LaTiO2N has significantly lower donor density; this can result in insufficient built-in electric field for the separation of photogenerated electrons and holes. The lower donor density is also consistent with the smaller difference between the Fermi level and the valence-band maximum, which accounts for a lower oxidative power of the holes. In light of this discovery, the donor density was increased substantially by introducing anion vacancies through annealing in Ar. This resulted in improved performance. The CoOx-assisted La2TiO5-derived LaTiO2N annealed at 713 °C has a higher quantum efficiency (25 %) at 450 nm than high-performance conventional CoOx/LaTiO2N (21 %).