Metal mixed anion compounds such as oxynitrides, oxysulphides, and oxyhalides are promising photocatalysts for water splitting, owing to their higher valence band maximum (VBM) compared to conventional oxides. Substantial mixing of the p-orbitals from the non-oxide anions (e.g., N-2p, Cl-3p) with the O-2p orbitals causes an upward shift in the VBM. Unfortunately, most mixed-anion compounds undergo self-oxidation of non-oxide anions by photogenerated holes. In this presentation, new intergrowth oxyhalide photocatalysts composed of tantalum and gadolinium will be shown to be stable materials under visible light for photocatalysis. 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 towards photocatalytic water splitting activity. Furthermore, these intergrowths are capable of sustained overall water splitting in a Z-scheme with Ru/SrTiO<sub>3</sub>: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.

Toward durable multimetal oxyhalide intergrowths for solar water splitting

ACS Spring Meeting 2021

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