Imaging Water Dissociation on TiO₂(110):  Evidence for Inequivalent Geminate OH Groups

Abstract

Identical regions of partially reduced TiO2(110) surfaces with bridge-bonded oxygen vacancy (BBO(V)) concentrations of approximately 10% ML (1 ML = 5.2 x 10(14) cm(-2)) were imaged using scanning tunneling microscopy (STM) before and after dosing H2O at ambient temperature (approximately 300 K). Atomically resolved images confirm that H2O adsorbs dissociatively on the BBO(V) sites, producing two hydroxyl species, one positioned at BBO(V) and denoted OH(V) and the other, denoted OH(B), formed by protonation at either of the two nearest-neighbor bridge-bonded oxygen atoms. Hydrogen hopping along the [001] direction is observed at ambient temperature, with a strong preference for OH(B) (approximately 10x) hydrogen motion. This powerful imbalance demonstrates the inequality of OH(V) and OH(B) and suggests differences in their charge and/or binding configuration.

Imaging of the Hydrogen Subsurface Site in RutileTiO2

“…2(b) and 2(d) before and after downwards diffusion of the H reveals that the OH sub seems to have moved one lattice constant along the [001] row direction. Row diffusion has many similarities with surface diffusion of sOH, which has been found theoretically to have a high diffusion barrier of 1.5 eV [25,26]. We therefore attribute this jump to be a result of the manipulation process.…”

Influence of alkali metals on Pd/TiO2catalysts for catalytic oxidation of formaldehyde at room temperature

“…There was little difference observed in the concentration of the surface OH groups and the mobility of chemisorbed O 2 for the Na-, K-and Cs-doped catalysts; however, the K-Pd/TiO 2 catalyst exhibited much higher TOFs (see Table 1) than the Naand Cs-Pd/TiO 2 catalysts, which may be attributed to the smaller Pd particle size over K-Pd/TiO 2 catalyst with more metal-support interface. On the one hand, the adsorbed H 2 O can easily dissociate into a surface OH group on oxygen vacancies, 57 especially in the proximity of the Pd particles at View Article Online the metal-support interface. 60 On the other hand, the dissociation of the molecularly adsorbed mobile oxygen may also take place at the metal-support interface.…”

Properties of oxide thin films and their adsorption behavior studied by scanning tunneling microscopy and conductance spectroscopy

“…4.5). 351 From their diffusion behavior at room temperature, the inequivalence of the two surface OH-groups was demonstrated. Whereas the hydroxyl group that includes an intrinsic lattice O-atom performs a diffusive motion with an activation energy of approximately 1.0 eV (theoretical value is 1.5 eV), 350 the defect-bound hydroxyl group is essentially immobile at room temperature.…”