PNNL

Abstract

The reactions of molecular oxygen with bridging hydroxyl groups, OHb, formed by H2O dissociation on bridging oxygen vacancies of TiO2 (110) are studied at low and high OHb coverages as a function of the O2 exposure, using scanning tunneling microscopy (STM), temperature programmed desorption (TPD), and electron simulated desorption (ESD) techniques. On partially hydroxylated surfaces, the sudden simultaneous disappearance of oxygen vacancies and oxygen adatoms formed by O2 dissociation is observed at high O2 exposures. On fully hydroxylated TiO2 surfaces, which enable us to compare results of STM, TPD and ESD studies, most of OHb’s are removed via reacting with O2. Hence, fully hydroxylated TiO2 surfaces can be converted to nearly stoichiometric surfaces, albeit with some amount of adsorbed molecular water. Formation of mobile H2O molecules and water-assisted diffusion of the reactants plays an important role in the kinetics of the processes on both partially and fully hydroxylated surfaces.