Scientists at the London Centre for Nanotechnology and Liverpool University have used a combination of nanoscale techniques to understand the role of oxygen atoms in making the surface titanium dioxide chemically reactive. Titanium dioxide is a candidate catalyst for producing hydrogen cheaply from water – a key step in a future hydrogen economy.
Every day, you probably stare at a wall covered in it. Titanium dioxide is a ubiquitous material, and the key to what makes most white paint so white. It also has many other useful applications, including in catalysis where it can help transform water into its hydrogen and oxygen constituents, by simply exposing the material to light.
Understanding what makes the surface of titanium dioxide so usefully reactive is a challenge. Scientists have proposed rival and quite different explanations, some backing the role of missing oxygen atoms at the catalyst surface, others arguing that extra titanium atoms just below the surface are responsible for electrons that help to drive the catalytic process.
Geoff Thornton and his colleagues at the London Centre for Nanotechnology, a joint venture between University College London and Imperial College, has used a combination of scanning tunnelling microscopy – a technique that images individual surface atoms – and photoemission spectroscopy, which probes the energies of electrons in a material, to decide the debate in favour of the oxygen defects.
Speaking about the results, Professor Thornton said “getting to grips with this sort of atomic scale issue is vital, as in the long term, it will help industrial manufacturers of photocatalysts optimize their production techniques”
The research, published in the Proceedings of the US National Academy of Sciences and Physical Review Letters, is just part of an ongoing effort at LCN to tackle what Director Gabriel Aeppli calls the challenge of Planet Care. “New technologies for clean energy require new materials, and an atomic-scale understanding of how they work”, says Aeppli, “and these latest results from LCN are an important step towards optimizing a promising new material for hydrogen fuel production.”
This research was supported by a Grant from the EPSRC.
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References: C. M. Yim, C.L. Pang, G. Thornton, Phys. Rev. Lett. 104, 036806 (2010)
A.C. Papageorgiou, N.S. Beglitis, C.L. Pang, G. Teobaldi, G. Cabailh, Q. Chen, A.J. Fisher,
W.A. Hofer, G. Thornton, Proc. Nat. Acad. Sci. USA 107 2391 (2010)
Fig. 1: Spectroscopic signature of a charge trapping site at an oxygen vacancy on TiO2