Composition, structure, and stability of the rutile TiO_2(110) surface: oxygen depletion, hydroxylation, hydrogen migration and water adsorption

Abstract

A comprehensive phase diagram of lowest-energy structures and compositions of the rutile TiO_2(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 TiO_2 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.

17 pages, 11 figures, to appear in PRB

References in corpus (6)

• Composition, structure and stability of RuO_2(110) as a function of oxygen pressure
• Density-functional study of the structure and stability of ZnO surfaces
• First-principles study of the polar O-terminated ZnO surface in thermodynamic equilibrium with oxygen and hydrogen
• The Adsorption of H2O on TiO2 and SnO2(110) Studied by First-Principles Calculations
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Cited by in corpus (15)

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• On the Impact of Solvation on a Au/TiO2 Nanocatalyst in Contact with Water
• A theoretical analysis of small Pt particles on rutile TiO${}_2$(110) surfaces
• Structure, stability, and mobility of small Pd clusters on the stoichiometric and defective TiO${}_2$ (110) surfaces
• Electric-Dipole Effect of Defects on Energy Band Alignment of Rutile and Anatase TiO2
• Quasiparticle interfacial level alignment of highly hybridized frontier levels: H${}_2$O on TiO${}_2$(110)
• Improving photocatalytic activity of TiO${}_2$ through reduction
• Interdependence of electroformation and hydrogen incorporation in titanium dioxide
• Re-assigning (1x2) reconstruction of rutile TiO_2(110) from DFT+U calculations
• DFT study of noble metal impurities on TiO_2(110)
• Speeding-up Hybrid Functional based Ab Initio Molecular Dynamics using Multiple Time-stepping and Resonance Free Thermostat
• Analysis of Photocatalytic Nitrogen Fixation on Rutile TiO${}_2$(110)