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

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 LaWO0.6N2.4 can be prepared by the topotactic conversion of BiLaWO6. Due to a high structural homogeneity and porosity, LaWO0.6N2.4 PSCs deliver a good photocatalytic activity for oxidizing water into O-2 even under near-infrared light illuminations. Under optimal conditions, an apparent quantum efficiency (AQE) value as high as 0.13% at 800 & PLUSMN; 20 nm were achieved, being the first near-infrared-light active oxynitride for photocatalytic water oxidation thus far. Steady overall water splitting into stoichiometric H-2 and O-2 has also been realized in a Z-scheme system employing LaWO0.6N2.4 PSCs as the O-2-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.

Automated summary

Narrow-bandgap perovskite oxynitrides show promise as inorganic photocatalysts for solar energy conversion. However, conventional synthetic methods lead to high defect concentrations, particularly at grain boundaries, which negatively impact photocatalytic performance. This study demonstrates that defect-free LaWO0.6N2.4 single crystals can be produced by the topotactic conversion of BiLaWO6, and these crystals exhibit good photocatalytic activity for water oxidation. They achieved an apparent quantum efficiency of 0.13% at 800 ± 20 nm, the highest reported for near-infrared-light active oxynitrides. The crystals also enabled steady overall water splitting under visible light illumination. These findings highlight the potential of porous single crystals as a platform for enhancing the performance of oxynitride photocatalysts and the importance of W-based perovskite oxynitrides for solar energy conversion.