Reaction Intermediates in the Photoreduction of Oxygen Molecules at the (101) TiO₂ (Anatase) Surface

The structural, electronic, and vibrational properties of intermediates of the O2 photoreduction at the (101) TiO2 (anatase) surface have been investigated by performing ab initio density functional calculations. In detail, a recently proposed approach has been used where molecules on the surface are treated like surface defects. Thus, by applying theoretical methods generally used in the physics of semiconductors, we successfully estimate the location and donor/acceptor character of the electronic levels induced by an adsorbed molecule in the TiO2 energy gap, both crucial for the surface−molecule charge-transfer processes, and investigate the formation and the properties of charged intermediates. The present approach permits a view of the O2 photoreduction process through several facets, which elucidates the molecule−surface charge-transfer conditions and reveals the key role played by charged intermediates. A comparison of present results with those of a highly sensitive IR (infrared) spectroscopy study of intermediates of the O2 photoreduction leads to a deeper understanding of this process and to revised vibrational-line assignments and reaction paths.