Two Pathways for Water Interaction with Oxygen Adatoms on TiO2(110)

Scanning tunneling microscopy and density functional theory studies show that oxygen adatoms (O-a), produced during O-2 exposure of reduced TiO2(110) surfaces, alter the water dissociation and recombination chemistry through two distinctive pathways. Depending on whether H2O and O-a are on the same or adjacent Ti4+ rows, O-a facilitates H2O dissociation and proton transfer to form a terminal hydroxyl pair, positioned along or across the Ti4+ row, respectively. The latter process has not been reported previously, and it starts from a "pseudodissociated" state of water. In both pathways, the reverse H transfer results in H2O reformation and O scrambling, as manifested by an apparent along- or across-row motion of O-a's.