Rutile TiO2(110) has for many years been regarded as the benchmark surface for fundamental studies of metal oxide surface chemistry. Since water is an integral part of the environment, the H2O/TiO2(110) system has received more attention than any other comparable system [1,2]. While the dissociation of water on the oxygen deficient TiO2(110) surface has been characterized in detail, there is as of yet no consensus reached between experimentalists and theorists regarding a very fundamental question: Does water dissociate upon adsorption on the defect-free TiO2(110) surface?

 

We have studied the interaction of water with the rutile TiO2(110) surface using synchrotron radiation photoemission at beamline D1011 at the MAX-lab synchrotron radiation source, and in this contribution we demonstrate that O 1s spectra recorded at grazing emission angle at optimized photon energy in conjunction with valence spectra allow for the observation of OH on the surface even when substrate oxygen is present. The surface was prepared free from oxygen vacancies following the recipe in ref. [3].

 Here we find evidence for mixed molecular and dissociative water adsorption at monolayer coverage on the rutile TiO2(110) surface free from oxygen vacancies. At monolayer coverage the OH:H2O ratio is close to 0.5 and reducing the coverage by heating yields an increased OH:H2O ratio. At room temperature neither species originating from the monolayer on the defect free surface can be detected. The OH species of the monolayer hence recombines and leaves the surface at much lower temperatures than OH formed by water dissociation on oxygen vacancies.

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