| AVS 64th International Symposium & Exhibition | |
| Surface Science Division | Thursday Sessions |
| Session SS+EM+HC+MI-ThM |
| Session: | Oxides: Structures and Reactions |
| Presenter: | Igor Beinik, Aarhus University, Denmark |
| Authors: | I. Beinik, Aarhus University, Denmark K.C. Adamsen, Aarhus University, Denmark S. Koust, Aarhus University, Denmark J.V. Lauritsen, Aarhus University, Denmark S. Wendt, Aarhus University, Denmark |
| Correspondent: | Click to Email |
The interaction of water with titanium dioxide (TiO2) is pivotal for many practical applications of this material in heterogeneous catalysis because water is almost always present either as a reactant or a product in many catalytic reactions. In our model study, we focus on the anatase polymorph of TiO2 that has demonstrated a higher catalytic activity in water splitting than rutile and is generally considered as a more technologically relevant polymorph. The nanocrystals of anatase that are present in powder catalysts normally expose a high fraction of low surface energy (101) facets and a significantly smaller fraction of high energy, but supposedly more reactive (001) facets. The (001) facet is intrinsically unstable and reconstructs upon annealing in vacuum forming 1x4 reconstructed terraces, where rows of bridging oxygen atoms in [100] and [010] directions are replaced by TiO3 units [1]. This kind of reconstruction has been found both on the (001) facets of anatase single crystals and nanoparticles [2], however the interaction of water with this surface has been significantly less investigated.
In the present work, we study the adsorption and dissociation of water on the anatase (001) 1x4 reconstructed surface by means of STM, TPD, and synchrotron core-level and valence band PES under UHV conditions. Our results show that water dissociates to some extent even at 120 K and that low water exposures (up to 3 L) at this temperature results in a mixture of molecularly and dissociatively adsorbed molecules. A systematic analysis of the data obtained using all three techniques leads us to a conclusion that the A-TiO2(001)-1x4 surface is rather reactive - in agreement with an earlier study [3] we find that water dissociates at the ridges of the 1x4 reconstruction. Moreover, the 1x4 reconstruction remains stable upon water exposures at least up to ~45 L (at 120 K). However, after desorption of a multilayer ice film, the ridges themselves contain a high number of defects, which remain stable up to 800 K. The nature of these defects will be discussed.
References:
1. Lazzeri, M. & Selloni, A. Phys. Rev. Lett. 87, 266105 (2001).
2. Yuan, W. et al. Nano Letters 16, 132–137 (2016).
3. Blomquist, J., et al. J Phys Chem C 112, 16616–16621 (2008).