Adsorption of formic acid on ZnO (10-10) – An Infrared Reflection Absorption Spectroscopy study

Maria Buchholz¹, Qiang Li², Karin Fink², Alexei Nefedov¹, Christof Wöll¹

¹ Institute of Functional Interfaces, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany

² Institute of Nanotechnology, Karlsruhe Institute of Technology, 76344 Eggenstein-Leopoldshafen, Germany

One of the most important oxides is ZnO, as a result of its semiconducting and optical properties, this material is used in many applications such as gas sensors, thin film solar cells, as well as in photocatalysis and photooxidation^[1]. The different surfaces of ZnO single crystals are used for investigations, both polar Zn- or O-terminated ZnO {0001} and mixed-terminated ZnO(10-10) surface. The later is the dominating surface for ZnO powder particles and energetically most favorable. In this study we investigated adsorption of formic acid molecules on the mixed-terminated ZnO(10-10) surface with UHV- Infrared Reflection Absorption Spectroscopy (IRRAS) and DFT-calculation. Formic acid is a good model for dye-sensitized solar cells, where carboxylic acids are forming the dye-surface contact.

In last decades numerous IR investigations of oxide powders have been reported, however, an unambiguous assignment of the features in the complex IR spectra recorded for molecules bound to the oxide powder particle is only possible on the basis of data recorded for well-defined reference systems, e.g. surfaces of single crystals.

M. Buchholz gratefully acknowledges the financial support from the Helmholtz Research School “Energy-Related Catalysis”.

[1] C. Wöll, Progress in Surface Science 2007, 82, 55-120.