Abstract
The positions of atoms in and around acetate molecules at the rutile TiO2(110) interface with 0.1 M acetic acid have been determined with a precision of ±0.05 Å. Acetate is used as a surrogate for the carboxylate groups typically employed to anchor monocarboxylate dye molecules to TiO2 in dye-sensitized solar cells (DSSC). Structural analysis reveals small domains of ordered (2 × 1) acetate molecules, with substrate atoms closer to their bulk terminated positions compared to the clean UHV surface. Acetate is found in a bidentate bridge position, binding through both oxygen atoms to two 5-fold titanium atoms such that the molecular plane is along the [001] azimuth. Density functional theory calculations provide adsorption geometries in excellent agreement with experiment. The availability of these structural data will improve the accuracy of charge transport models for DSSC.
Highlights
The interaction of carboxylic acids with TiO2 is important in a number of applications
We used ultra high vacuum (UHV) scanning tunneling microscopy (STM) to study the adsorption sites of carboxylates formed at aqueous interfaces, finding that the same sites are occupied as those identified in UHV adsorption.[3]
We move even closer to measurements in a technologically relevant environment, examining in a quantitative fashion the in situ structure of the TiO2(110) interface formed upon immersion in 0.1 M acetic acid using surface X-ray diffraction (SXRD)
Summary
The interaction of carboxylic acids with TiO2 is important in a number of applications. We used UHV scanning tunneling microscopy (STM) to study the adsorption sites of carboxylates formed at aqueous interfaces, finding that the same sites are occupied as those identified in UHV adsorption.[3] Here we move even closer to measurements in a technologically relevant environment, examining in a quantitative fashion the in situ structure of the TiO2(110) interface formed upon immersion in 0.1 M acetic acid using surface X-ray diffraction (SXRD). This concentration is chosen to match that used in an infrared spectroscopy study of the TiO2 acetic acid interface, the results of which point to bidentate bonding of acetate.[3]. A discussion about the adequacy of this model to simulate the adsorption of molecules at this surface can be seen in ref 19
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