The Importance of Bulk Ti3+ Defects in the Oxygen Chemistry on Titania Surfaces

The role of bulk defects in the oxygen chemistry on reduced ruffle TiO2(110)-(1 x 1) has been studied by means of temperature-programmed desorption spectroscopy and scanning tunneling microscopy measurements. Following O-2 adsorption at 130 K, the amount of O-2 desorbing at similar to 410 K initially increased with increasing density of surface oxygen vacancies but decreased after further reduction of the TiO2(110) crystal. We explain these results by withdrawal of excess charge (Ti3+) from the TiO2(110) lattice to oxygen species on the surface and by a reaction of Ti interstitials with O adatoms upon heating. Important consequences for the understanding of the O-2-TiO2 interaction are discussed.