VO Cluster-Stabilized H₂O Adsorption on a TiO₂ (110) Surface at Room Temperature

We probe the adsorption of molecular H₂O on a TiO₂ (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 TiO₂ (110)-(1 × 1) surface induce the adsorption of H₂O molecules at room temperature (RT). The adsorbed H₂O molecules form strings of beads of H₂O 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 TiO₂ surface. TPD spectra reveal two new desorption states for VO stabilized H₂O 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 TiO₂(110)-(1 × 1) surfaces. Density functional theory (DFT) calculations show that the binding energy of molecular H₂O to the VO clusters on the TiO₂ (110)-(1 × 1) surface is higher than binding to the bare surface by 0.42 eV, and the resulting H₂O-VO-TiO₂ (110) complex provides the anchor point for adsorption of the string of beads of H₂O dimers.