Understanding Competitive Photo-Induced Molecular Oxygen Dissociation and Desorption Dynamics atop a Reduced Rutile TiO<sub>2</sub>(110) Surface: A Time-Domain Ab Initio Study
Cheng Cheng, Niall J. English, Wei‐Hai Fang, Run Long
Abstract
Photochemical O2 activation is the key to many photo-oxidation chemical reactions where the efficiency and chemical processes are significantly affected by the substrate–adsorbate interactions. However, the underlying mechanisms of the reactions are still unclear. Focusing on the reduced rutile TiO2(110) surface with an adsorbed O2, we perform time-domain density functional theory and nonadiabatic molecular dynamics simulations to investigate photo-induced O2 dissociation and desorption processes. The simulations demonstrate that O2 exhibits three distinct adsorption positions atop a reduced TiO2(110) surface where it prefers to adsorb at a bridge oxygen vacancy (OV) site, followed by two metastable fivefold-coordinated Ti (Ti5c) sites, leading to the formation of peroxide O22– by accepting two excess electrons of Ti3+ ions induced by the OV. The adsorbed O2 at an OV site creates no midgap states for capturing photo-excited holes and favors facile O2 dissociation instead of desorption due to a small dissociation energy barrier, leaving the charge carrier lifetime up to over half a nanosecond. In contrast, midgap states composed of O2 π* antibonding orbitals present in the two Ti5c adsorption configurations are able to rapidly trap photoexcitation holes in the range of several to tens of picoseconds, which cause the elongation of the interfacial O–Ti bond length and drive O2 desorption. The two Ti5c adsorption configurations are switchable between each other and occur at Ti5c sites due to the minute energy barriers, consolidating the experimental results. A good choice of a transition metal can enhance p–d polarization to manipulate the positions of O2 antibonding orbitals and control O2 chemical reactions. The reported results provide a fundamental understanding of the influence of the interplay between photoexcitation holes and the adsorbate–substrate interaction on O2 dissociation and desorption. The study shows how electronic and charge properties can be controlled by dopants, allowing one to design high-performance transition metal oxide catalysts.