Unraveling the atomic structure and dissociation of interfacial water on anatase TiO2 (101) under ambient conditions with solid-state NMR spectroscopy

Abstract

Anatase TiO₂ is a widely used component in photo- and electro-catalysts for water splitting, and the (101) facet of anatase TiO₂ is the most commonly exposed surface. A detailed understanding of the behavior of H₂O on this surface could provide fundamental insights into the catalytic mechanism. This, however, is challenging due to the complexity of the interfacial environments, the high mobility of interfacial H₂O, and the interference from outer-layer H₂O. Herein, we investigate the H₂O/TiO₂ interface using advanced solid-state NMR techniques. The atomic-level structures of surface O sites, OH groups, and adsorbed H₂O have been revealed and the detailed interactions among them are identified on the (101) facet of anatase TiO₂. By following the quantitative evolution of surface O and OH sites along with H₂O loading, it is found that more than 40% of the adsorbed water spontaneously dissociated under ambient conditions on the TiO₂ surface at a loading of 0.3 mmol H₂O/g, due to the delicate interplay between water–surface and water–water interactions. Our study highlights the importance of understanding the atomic-level structures of H₂O on the surface of TiO₂ in catalytic reactions. Such knowledge can promote the design of more efficient catalytic systems for renewable energy production involving activation of water molecules.