Composition, structure, and stability of the rutileTiO2(110)surface: Oxygen depletion, hydroxylation, hydrogen migration, and water adsorption

Abstract

A comprehensive phase diagram of lowest-energy structures and compositions of the rutile TiO2(110) surface in equilibrium with a surrounding gas phase at finite temperatures and pressures has been determined using density functional theory in combination with a thermodynamic formalism. The exchange of oxygen, hydrogen, and water molecules with the gas phase is considered. Particular attention is given to the convergence of all calculations with respect to lateral system size and slab thickness. In addition, the reliability of semilocal density functionals to describing the energetics of the reduced surfaces is critically evaluated. For ambient conditions the surface is found to be fully covered by molecularly adsorbed water. At low coverages, in the limit of single, isolated water molecules, molecular and dissociative adsorption become energetically degenerate. Oxygen vacancies form in strongly reducing, oxygen-poor environments. However, already at slightly more moderate conditions it is shown that removing full TiO2 units from the surface is thermodynamically preferred. In agreement with recent experimental observations it is furthermore confirmed that even under extremely hydrogen-rich environments the surface cannot be fully hydroxylated, but only a maximum coverage with hydrogen of about 0.6-0.7 monolayer can be reached. Finally, calculations of migration paths strongly suggest that hydrogen prefers to diffuse into the bulk over desorbing from the surface into the gas phase.

Electric-dipole effect of defects on the energy band alignment of rutile and anatase TiO2

“…When sputtered and annealed in ultra-high vacuum or bombarded with electrons, TiO2 samples will lose some bridging oxygen atoms forming oxygen vacancies (Ovac's) 32 . When treated in the hydrogen containing atmosphere, they are ready to combine with hydrogen atoms forming hydroxyl groups (O-H's) 42,43 . The energy band alignment between the anatase (101) and rutile (110) surfaces with the O-H and O-vac coverage of 1/6 monolayer is shown in the third and fourth columns of Fig.…”

On the Impact of Solvation on a Au/TiO2Nanocatalyst in Contact with Water

“…In line with our previous work [21,22,30], the value of U = 4.2 eV was adopted. We have carefully checked the charge distribution dependence on U by recomputing the Löwdin charges of the top and middle Au atoms of the supported gold nanocluster in liquid water for selected snapshots along the trajectory shown in Fig.…”

A Molecular Mechanism for the Water–Hydroxyl Balance during Wetting of TiO2

“…22 The appropriate theoretical modeling of the system has in the meantime remained the subject of an intense debate. 19,23 The most recent DFT calculations, however, all shows dissociative adsorption at low coverages (≤0.25 ML) while a molecular or a partially dissociated water layer are favored at high coverages (≥0.5 ML). 20,24,25 .…”

“…17 In contrast, theoretical studies based on density function theory (DFT) predicted facile dissociation on the stoichiometric surface at coverages below 0.25 ML. [18][19][20] A few years ago a recipe for the preparation of defect free TiO 2 (110) terraces was presented. 21 We exploited this method in a core level photoemission study to demonstrate that the first layer of water on stoichiometric TiO 2 (110) is partially dissociated.…”