Selloni group validated theoretical predictions featured in Science
August 30, 2013. Princeton, NJ. Oxygen adsorption and incorporation into an oxide surface are key steps in a range of important technological processes. At the molecular level, however, many of the details of precisely how oxygen is adsorbed and ultimately incorporated into a surface have long remained unknown. Now, using a combination of theoretical and experimental techniques, researchers in the laboratories of Annabella Selloni at Princeton and Ulrike Diebold at Vienna University of Technology have taken a close-up look at the way in which single oxygen molecules react with anatase, a metastable, highly active form of titanium dioxide and a widely used photocatalyst for water splitting.
The project began with a (quantum mechanics-based) numerical simulation in the Selloni laboratory. The simulation suggested that an adsorbed oxygen molecule could "heal" an oxygen vacancy (a very common defect in oxides) beneath the anatase surface through a multi-step process leading to the incorporation of the adsorbed O2 into the anatase surface lattice as a bridging dimer. Interestingly, this bridging oxygen species had been proposed to be a possible reactive intermediate in the photooxidation of water on the anatase surface.
The Diebold group then took up the charge of validating these theoretical predictions in the laboratory. In an important experimental achievement, the Vienna researchers showed that the strongly charged tip of a scanning tunneling microscope could be used to coax oxygen vacancies from deep within the anatase bulk to the surface of the material. Remarkably, molecular O2 was found to react with these sub-surface vacancies in precisely the manner predicted by the Selloni group. As shown in the accompanying movie, the oxygen molecule fills the vacancy through a cascade of microscopic events that culminates in its incorporation into the anatase lattice as the predicted bridged dimer species.
These groundbreaking results, reported in Science this week, showcase the scientific advances that can arise from collaborative interactions between researchers in the theoretical and experimental realms. Importantly, the authors believe that further study of this bridged O2 species could ultimately hold the key to the development of more efficient anatase–based photo-catalysts for water oxidation.