Durable Multimetal Oxychloride Intergrowths for Visible Light-Driven Water Splitting

Metal heteroanionic compounds such as oxynitrides, oxysulfides, and oxyhalides have emerged as promising photocatalysts for water splitting, owing to their reduced band gaps compared to conventional oxides. Nonetheless, many of these compounds undergo self-oxidation of the non-oxide anions by photogenerated holes. Herein, we present new metal oxychloride intergrowths based on Bi4TaO8Cl–Bi2GdO4Cl as stable visible light photocatalysts. These intergrowths were prepared using a halide flux method, with their crystal structures analyzed by Rietveld refinement of powder X-ray diffraction data and high-resolution scanning transmission electron microscopy. These analyses support intergrowth formation. The Ta/Gd molar ratio was systematically varied in the intergrowths to rationalize the effect of charge separation and changes in band structure toward photocatalytic water-splitting activity. Furthermore, these intergrowths are capable of sustained overall water splitting in a Z-scheme with Ru/SrTiO3/Rh as a hydrogen evolution catalyst. The high stability of these intergrowth materials is attributed to O 2p orbitals at the valance band edge rather than Cl 3p orbitals, as discerned from electronic structure calculations. These results provide new strategies for designing durable artificial photosynthetic systems by rational modulation of crystal and electronic structure.