Surface gallium hydride on Ga2O3 polymorphs: A comparative solid-state NMR study

Abstract

As a highly reactive reaction intermediate, surface gallium hydride (Ga–H) has garnered significant attention due to its critical role in various catalytic reactions. However, the detailed experimental characterization of this unique species remains challenging. Recently, we have demonstrated that solid-state NMR can be an effective tool for studying surface Ga–H. In this work, we report a comparative solid-state NMR study on H₂ activation over different Ga₂O₃ polymorphs, specifically α-, β- and γ-Ga₂O₃. ¹H solid-state NMR enabled the identification of Ga–H species formed on all the three samples following high-temperature H₂ treatment. The characteristic ¹H NMR signals of Ga–H species are resolved using J-coupling-based double-resonance NMR methods, revealing highly similar lineshapes of Ga–H for all the Ga₂O₃ samples. This suggests potentially similar surface Ga–H configurations among different Ga₂O₃ polymorphs. In addition, the local hydrogen environments on the oxide surfaces are further explored using two-dimensional (2D) ¹H–¹H homonuclear correlation spectra, revealing multiple spatially proximate Ga–H and Ga–H/–OH pairs on different Ga₂O₃ polymorphs. These findings provide insights into the potential mechanism of H₂ dissociation. Overall, this work offers new perspectives on the local structure of surface Ga–H on Ga₂O₃, and the analytical approach presented here can be further extended to the study of other Ga-based catalysts and other metal hydride species.