Theoretical study of the interaction of molecular oxygen with a reduced TiO2 surface

We investigate the re-oxidation of the reduced TiO2 (1 1 0) surface by adsorption of molecular oxygen using quantum-chemical, ab-initio periodic Hartree–Fock calculations. The absorption sites considered are anion defects and cation Ti(5f) positions. The results show evidence of strong charge transfer from the defect surface to the O2 molecule. In agreement with experiment, we find that the most stable species is one in which molecular oxygen adsorbs at the defect sites as O2−. Adsorption of three O2 molecules per vacancy site is thermodynamically favored compared to one or two adsorbed molecules.