Unraveling the atomic structure and dissociation of interfacial water on anatase TiO 2 (101) under ambient conditions with solid-state NMR spectroscopy.

Anatase TiO 2 is a widely used component in photo- and electro-catalysts for water splitting, and the (101) facet of anatase TiO 2 is the most commonly exposed surface. A detailed understanding of the behavior of H 2 O 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 H 2 O, and the interference from outer-layer H 2 O. Herein, we investigate the H 2 O/TiO 2 interface using advanced solid-state NMR techniques. The atomic-level structures of surface O sites, OH groups, and adsorbed H 2 O have been revealed and the detailed interactions among them are identified on the (101) facet of anatase TiO 2 . By following the quantitative evolution of surface O and OH sites along with H 2 O loading, it is found that more than 40% of the adsorbed water spontaneously dissociated under ambient conditions on the TiO 2 surface at a loading of 0.3 mmol H 2 O/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 H 2 O on the surface of TiO 2 in catalytic reactions. Such knowledge can promote the design of more efficient catalytic systems for renewable energy production involving activation of water molecules.