Quantitative Structure of an Acetate Dye Molecule Analogue at the TiO₂–Acetic Acid Interface

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

Water Dissociates at the Aqueous Interface with Reduced Anatase TiO₂ (101)

Elucidating the structure of the interface between natural (reduced) anatase TiO₂ (101) and water is an essential step toward understanding the associated photoassisted water splitting mechanism. Here we present surface X-ray diffraction results for the room temperature interface with ultrathin and bulk water, which we explain by reference to density functional theory calculations. We find that both interfaces contain a 25:75 mixture of molecular H₂O and terminal OH bound to titanium atoms along with bridging OH species in the contact layer. This is in complete contrast to the inert character of room temperature anatase TiO₂ (101) in ultrahigh vacuum. A key difference between the ultrathin and bulk water interfaces is that in the latter water in the second layer is also ordered. These molecules are hydrogen bonded to the contact layer, modifying the bond angles