Enhanced Hydrogen Adsorption on In₂O₃(111) via Oxygen Vacancy Engineering

The emergence of In₂O₃ as an efficient catalyst for selective hydrogenation has attracted significant attention. However, the mechanism of hydrogen (H₂) dissociation on In₂O₃ remains experimentally elusive. In this work, we show that the interaction of H₂ with In₂O₃ is strongly influenced by the presence of oxygen vacancies. Using a combination of <i>in situ</i> near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS), ultraviolet photoelectron spectroscopy (UPS), infrared reflection absorption spectroscopy (IRRAS), and density functional theory (DFT) calculations, we systematically investigated the interaction of H₂ on well-defined oxidized In₂O₃(111) and partially reduced In₂O_3-<i>x</i> (111) surfaces. Our results reveal that H₂ dissociates and adsorbs as hydroxyl groups (OH), which are exclusively stabilized on the In₂O_3-<i>x</i> (111) surface. The adsorbed hydrogen species act as electron donors, contributing to interfacial electron accumulation near the surface and inducing downward band bending. DFT calculations further indicate that oxygen vacancies in In₂O_3-<i>x</i> (111) are critical for facilitating the heterolytic dissociation of H₂, leading to the stabilization of In-H and OH species. These findings provide valuable implications for the catalytic behavior of indium oxide in hydrogenation and hydrogen-involved redox reactions.