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O: Fachverband Oberflächenphysik
O 42: Solid-Liquid Interfaces: Reactions and Electrochemistry - Theory II
O 42.6: Vortrag
Dienstag, 21. März 2017, 15:15–15:30, WIL B321
Driving Forces for Aggregation and Dissociation of Water on Zinc Oxide — •P. Ulrich Biedermann1 and Stephane Kenmoe1,2 — 1Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany — 2current address Department of Theoretical Chemistry, University of Duisburg-Essen, Essen, Germany
The interactions of water with zinc oxide play an important role in the fields of catalysis, corrosion protection and biomedical applications. The properties of water adsorbed at the interface of oxides are significantly different from bulk water. In particular, the high degree of water dissociation observed in the contact layer indicates O-H bond activation. This facilitates proton transfers, an important step in many catalytic processes. We present a comprehensive DFT study of water adsorbed on the non-polar ZnO (1010) and (1120) surfaces using PBE. In view of the band-gap problem of GGA-DFT, the results are benchmarked against hybrid DFT results. Several new interface structures have been discovered in the coverage regime of 0-3 ML. Water aggregation on ZnO is controlled by a subtle interplay of direct water-water interactions including H-bonds and dipole-dipole interactions versus surface- or adsorption-mediated interactions including enhanced water-surface interactions and reduced relaxation energies required to optimize the geometry of the water molecules and ZnO surface for adsorption. While water dissociation also depends on aggregation and the geometrical arrangement of the molecules on the surface, direct water-water interactions do not contribute to this process. Water dissociation is driven by enhanced water-surface interactions.