Origin of hydroxyl pair formation on reduced anatase TiO 2 (101).

The interaction of water with metal oxide surfaces is of key importance to several research fields and applications. Because of its ability to photo-catalyze water splitting, reducible anatase TiO 2 (a-TiO 2 ) is of particular interest. Here, we combine experiments and theory to study the dissociation of water on bulk-reduced a-TiO 2 (101). Following large water exposures at room temperature, point-like protrusions appear on the a-TiO 2 (101) surface, as shown by scanning tunneling microscopy (STM). These protrusions originate from hydroxyl pairs, consisting of terminal and bridging OH groups, OH t /OH b , as revealed by infrared reflection absorption spectroscopy (IRRAS) and valence band experiments. Utilizing density functional theory (DFT) calculations, we offer a comprehensive model of the water/a-TiO 2 (101) interaction. This model also explains why the hydroxyl pairs are thermally stable up to ∼480 K.