Structure of a model TiO2 photocatalytic interface
Journal: Nature Materials
Publication Date: 14 September, 2016
Department of: Materials
New insights into water splitting
The interaction of water with titania (TiO2) is crucial to many of its practical applications, including photocatalytic water splitting. Following the first demonstration of this phenomenon 40 years ago there have been numerous studies of the model single crystal TiO2(110) surface and water. This work has provided an atomic level understanding of the water/TiO2 interaction. However, nearly all the previous studies of water/TiO2 interfaces involve water in the vapour phase.
Now, an international collaboration of scientists, including surface scientists from the University of Manchester have explored the interfacial structure between liquid water and a TiO2(110) surface pre-characterised at the atomic level. Interface-sensitive microscopy and diffraction are used to determine the structure, which is comprised of an ordered array of hydroxyl molecules with molecular water in the second layer. Complementary theoretical modelling suggests that a possible mechanism for the formation of this hydroxyl overlayer involves the mixed adsorption of oxygen and water on a partially defected surface – not what was expected from the earlier vapour-phase work. The quantitative structural properties derived here provide a basis with which to explore the atomistic properties and hence mechanisms involved in TiO2 photocatalysis.
- TiO2 is one of the most abundant oxides on earth. It is non-toxic, and has myriad applications, including as a basis for water splitting – a method for obtaining hydrogen fuel cleanly from the Sun’s energy.
- TiO2(110) is a prototypical metal oxide surface. Use of such a single crystal substrate is key to understanding what’s happening atom by atom.
- Various techniques that can measure atomic scale structure and electron distribution such as scanning tunnelling microscopy, surface x-ray diffraction, and photoelectron spectroscopy have been used, and teamed with density functional calculations to understand the TiO2(110)/H2O interfacial structure.
- The interface structure, created in the aqueous aerobic environment considered here, had not been anticipated and differs from what has been found previously in an ultra high vacuum environment.
- Point defects, such as interstitial titanium atoms, appear to be key to the interfacial structure.