Active hydrogen species on TiO2 for photocatalytic H2 production

Abstract

Photocatalytic H₂ production over TiO₂ has attracted tremendous attention and achieved great progress, but the active hydrogen species is still unknown. Employing a rutile TiO₂(110) surface as a model catalyst we report here for the first time the direct observation of photocatalytic H₂ production under ultrahigh vacuum conditions during UV-light irradiation at 115 K and the identification of negatively-charged hydride-type H-Ti species as the corresponding photoactive surface species by means of thermal desorption spectroscopy, photon-stimulated desorption spectroscopy, X-ray photoelectron spectroscopy and DFT calculations. The formation and stability of H-Ti species are closely related to available surplus electrons on the rutile TiO₂(110) surface that can be created by the formation of surface BBO vacancies or by the formation of surface hydroxyls via the adsorption of atomic H or molecular H₂ on O sites. The photocatalytic H₂ production from H-Ti species is hole-mediated and co-existing water exerts a negative effect on this process.