Reaction of O2 with subsurface oxygen vacancies on TiO2 anatase (101)

M. Setvin, U. Aschauer, P. Scheiber, Y.-F. Li, W. Hou, M. Schmid, A. Selloni, U. Diebold

Institut für Angewandte Physik, Technische Universität Wien, 1040 Wien, Austria
Department of Chemistry, Princeton University, Frick Laboratory, Princeton NJ 08544, U.S.A.
ETH Zurich, Materials Theory, Wolfgang-Pauli-Strasse 27, 8093 Zürich, Switzerland.

Science 341 (2013) 988-991

Oxygen (O2) adsorbed on metal oxides is important in catalytic oxidation reactions, chemical sensing, and photocatalysis. Strong adsorption requires transfer of negative charge from oxygen vacancies (VOs) or dopants, for example. With scanning tunneling microscopy, we observed, transformed, and, in conjunction with theory, identified the nature of O2 molecules on the (101) surface of anatase (titanium oxide, TiO2) doped with niobium. VOs reside exclusively in the bulk, but we pull them to the surface with a strongly negatively charged scanning tunneling microscope tip. O2 adsorbed as superoxo (O2-) at fivefold-coordinated Ti sites was transformed to peroxo (O22-) and, via reaction with a VO, placed into an anion surface lattice site as an (O2)O species. This so-called bridging dimer also formed when O2 directly reacted with VOs at or below the surface.

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Corresponding author: Ulrike Diebold (diebold< encoded email address >).

This article was also featured in Chemical & Engineering News Vol. 91, Issue 35, p. 11