VO Cluster-Stabilized H 2 O Adsorption on a TiO 2 (110) Surface at Room Temperature.

We probe the adsorption of molecular H 2 O on a TiO 2 (110)-(1 × 1) surface decorated with isolated VO clusters using ultrahigh-vacuum scanning tunneling microscopy (UHV-STM) and temperature-programmed desorption (TPD). Our STM images show that preadsorbed VO clusters on the TiO 2 (110)-(1 × 1) surface induce the adsorption of H 2 O molecules at room temperature (RT). The adsorbed H 2 O molecules form strings of beads of H 2 O dimers bound to the 5-fold coordinated Ti atom (5c-Ti) rows and are anchored by VO. This RT adsorption is completely reversible and is unique to the VO-decorated TiO 2 surface. TPD spectra reveal two new desorption states for VO stabilized H 2 O at 395 and 445 K, which is in sharp contrast to the desorption of water due to recombination of hydroxyl groups at 490 K from clean TiO 2 (110)-(1 × 1) surfaces. Density functional theory (DFT) calculations show that the binding energy of molecular H 2 O to the VO clusters on the TiO 2 (110)-(1 × 1) surface is higher than binding to the bare surface by 0.42 eV, and the resulting H 2 O-VO-TiO 2 (110) complex provides the anchor point for adsorption of the string of beads of H 2 O dimers.