Dissociative adsorption of H₂O onto a Pt thin film in direct contact with GaN (0001): Effect of electronic communications between catalyst and a semiconducting support

Heterogeneous catalysts that contain metal/semiconductor heterojunctions have been applied in numerous chemical transformations. While the involvement of these heterojunctions in catalytic processes has been recognized widely, limited information about their local chemical, geometrical, and electronic structures is available, particularly under catalytic operating conditions. Here, using Pt/GaN (0001) and Pt (111) as model systems, we investigated the interfacial chemistry of H₂O/Pt under operando conditions using ambient pressure X-ray photoelectron spectroscopy (APXPS). We found that H₂O remains intact in its molecular form on pristine Pt (111) at room temperature; however, when a thin Pt film was brought into direct contact with a semiconductor, i.e., GaN (0001), electronic communications at the heterojunction were established and were observed spectroscopically. The build-up of hot carriers under steady-state X-ray photoexcitation drives the dissociative adsorption of H₂O onto Pt at room temperature that otherwise does not proceed on bare Pt (111). H₂O and its dissociation products, hydroxyls (OH) and surface oxides, were observed binding to surface Pt atoms under elevated pressures and/or temperatures, which in return altered the hot carrier transfer and therefore, the band alignment at the Pt/GaN interface, leading to the observed evolutions in Pt, O, and Ga core-level photoemission spectra. Our findings demonstrate that the selection of semiconducting supports can govern the outcome of a chemical transformation event directly; the catalytic performance and reaction pathway of metal (or oxides)-based catalysts can be modulated by electronic modifications at the catalyst/support interface and drive reactions that are kinetically sluggish or non-spontaneous.