Hydride Accessibility and Reactivity in the Configurational and Stoichiometric Space of β-Ga₂O₃ for CO₂ Hydrogenation

Understanding how surface species evolve under reaction conditions is essential for improving catalyst design for efficient CO₂ hydrogenation. This work combines systematic DFT calculations with grand canonical sampling to investigate the stability and reactivity of Ga-H species on β-Ga₂O₃ across a range of reaction conditions. Initial DFT studies reveal that when Ga-H species are present, they facilitate formate formation via a low-barrier pathway, largely independent of the surface termination or hydrogen site. However, grand canonical sampling shows that under a broad range of reaction conditions─especially at high oxygen chemical potentials associated with high water content─Ga-H species are thermodynamically inaccessible. Furthermore, adsorbed water molecules can block reactive sites, inhibiting CO₂ activation even when hydrides are present. These findings suggest that the lack of accessible hydride species, rather than their intrinsic reactivity, could contribute to reduced catalytic performance of β-Ga₂O₃ under more oxidizing, high-conversion conditions.