PNNL

Abstract

Atomic-level investigation of the interaction of H2O with a partially re-oxidized TiO2(110) has been performed at 300 K by combining scanning tunneling microscopy and density functional theory. In particular, we demonstrate that oxygen adatoms (Oa), produced during O2 exposure of reduced TiO2(110) surfaces, alter water dissociation/ recombination chemistry through two different pathways. When H2O diffuses to Oa on the same Ti row, it becomes trapped near the Oa, exchanges a proton easily to dissociate and form a pair of terminal hydroxyls (OHt) along the row, which can then readily recombine and re-dissociate many times or overcome the barrier to move away. When H2O passes along the Oa on an adjacent row, an across-row proton transfer facilitated by the bridging O atom results in spontaneous dissociation of H2O on a Ti trough leading to the formation of a stable across-row OHt pair, which after awhile can recombine and H2O diffuses away. The across-row process has not been reported previously, and it starts from a ‘‘pseudo-dissociated’’ state of water. We also show how the H2O dissociation and OHt pair statistical reformation induce an apparent along- or across-row shift of Oa as a result of the oxygen scrambling process between H2O and Oa.