Photocatalytic water oxidation over LaWO0.6N2.4 mesoporous single crystals under visible and near-infrared light illumination

Abstract

Narrow-bandgap perovskite oxynitrides emerge as a promising class of inorganic photocatalysts to store solar energy in chemical fuels. However, conventional synthetic routes generally introduce a high defect concentration in these compounds, particularly at grain boundaries (GBs), which also intercept charge transportation, thus severely undermining the photocatalytic performance. Herein, we demonstrate that GB-free porous single crystals (PSCs) of narrow bandgap semiconductor LaWO_0.6N_2.4 can be prepared by the topotactic conversion of BiLaWO₆. Due to a high structural homogeneity and porosity, LaWO_0.6N_2.4 PSCs deliver a good photocatalytic activity for oxidizing water into O₂ even under near-infrared light illuminations. Under optimal conditions, an apparent quantum efficiency (AQE) value as high as 0.13% at 800 ± 20 nm were achieved, being the first near-infrared-light active oxynitride for photocatalytic water oxidation thus far. Steady overall water splitting into stoichiometric H₂ and O₂ has also been realized in a Z-scheme system employing LaWO_0.6N_2.4 PSCs as the O₂-evolution moiety under visible light insolation. These results not only justify that PSCs serve as an ideal platform to trigger the photocatalytic performance of oxynitrides with high defects content but also attract great attention upon W-based perovskite oxynitrides for solar energy conversions.