TiO2 is a prototypical material used in photocatalytic reactions, e.g. in water remediation, photocatalytic water splitting or in the oxidation of organic molecules [1, 2]. Two polymorphs of TiO2 are used industrially - rutile and anatase, where the anatase is typically preferred in applications. Surface chemistry of water and oxygen is the base of many important processes such as photocatalytic water splitting or oxygen reduction reaction, which are essentially inverse mechanisms mediated by holes and electrons, respectively. Here we study adsorption and reactions of oxygen and water on a reduced anatase TiO2(101) using Scanning Tunneling Microscopy (STM), Temperature Programmed Desorption (TPD), Photoemission Spectroscopy (PES) and Density Functional Theory (DFT). While water exhibits molecular adsorption on the Anatase (101) surface [3] and desorbs below room temperature, reaction with oxygen results in the dissociation and formation of terminal OH groups. The terminal OH groups are the final product of the reaction and are stable at room temperature. We identify OOH as an important metastable intermediate of the reaction. Based on DFT calculations, we discuss the energy balance of the single reaction steps in dependence on the number of excess electrons available in the slab. The reactions mentioned above are energetically favorable as long as the substrate provides enough excess electrons. We compare the results on anatase (101) surface to equivalent reactions reported on the rutile (110), and point out key differences between these two TiO2 polymorphs. Work supported by the Advanced ERC grant “OxideSurfaces”. [1] M. A. Henderson, Surf. Sci. Rep. 66, 185 (2011). [2] A. L. Linsebigler et al., Chem. Rev. 95, 735 (1995) [3] Y. He et al., Nat. Materials 8, 585 (2009)

Surface chemistry of oxygen and water on anatase TiO2 (101)

251st National Meeting (2016)

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