New pentlandite-like oxide semiconductors IrIn6XYO8 (X = Ga, In; Y = Ge, Sn, Ti) as potential candidates for photocatalytic water splitting under visible-light irradiation

Abstract

Narrow-band gap metal oxide semiconductors, such as those based on Pb²⁺, Bi³⁺, and Sn²⁺ ions, have achieved significant success in the field of photocatalysis due to their effective utilization of visible light. The key is the presence of antibonding states derived from the lone-pair ns orbitals at the valence band maximum. In contrast, the feature of a narrow band gap in In-based metal oxides with the empty 5s orbital of the In³⁺ cation is actually rather uncommon. In this study, we present a mechanistic investigation of IrIn₆XYO₈ (X = Ga, In; Y = Ge, Sn, Ti), a class of narrow-band gap semiconductors, using first-principles calculations. Based on bond theory analysis, we determine the band edge electronic feature by elucidating the role of orbital interactions within In–O/In bonds. Leveraging the advantages of their narrow band gap and efficient carrier separation capability, IrIn₆XYO₈ (X = Ga, In; Y = Ge, Sn, Ti) demonstrate significant potential for photocatalytic water splitting. Moreover, by integrating band edge positions and Gibbs free energy calculations, we identify that IrIn₆XTiO₈ (X = Ga, In) are effective catalysts for overall water splitting under visible light irradiation, while IrIn₆GaGeO₈ presents as a highly promising photocatalyst for H₂ evolution.