Interfacial Hydrogen-Bonding Dynamics in Surface-Facilitated Dehydrogenation of Water on TiO2(110)

Molecular-level understanding of the dehydrogenation of interfacial water molecules on metal oxides and their interactive nature relies on the ability to track the motion of light and small hydrogen atoms, which is known to be difficult. Here, we report precise measurements of the surface-facilitated water dehydrogenation process at terminal Ti sites of TiO2(110) using scanning tunneling microscopy. Our measured hydrogen-bond dynamics of H2O and D2O reveal that the vibrational and electronic excitations dominate the sequential transfer of two H (D) atoms from a H2O (D2O) molecule to adjacent surface oxygen sites, manifesting the active participation of the oxide surface in the dehydrogenation processes. Our results show that, at the stoichiometric Ti-5c, sites, individual H2O molecules are energetically less stable than the dissociative form, where a barrier is expected to be as small as approximately 70-120 meV on the basis of our experimental and theoretical results. Moreover, our results reveal that interfacial hydrogen bonds can effectively assist H atom transfer and exchange across the surface. The revealed quantitative hydrogen-bond dynamics provide a new atomistic mechanism for water interactions on metal oxides in general.