Ionic Liquid Ordering at an Oxide Surface

The interaction of the ionic liquid [C(4)C(1)Im][BF(4)] with anatase TiO(2), a model photoanode material, has been studied using a combination of synchrotron radiation photoelectron spectroscopy and near‐edge X‐ray absorption fine structure spectroscopy. The system is of interest as a model for fundamental electrolyte–electrode and dye‐sensitized solar cells. The initial interaction involves degradation of the [BF(4)](−) anion, resulting in incorporation of F into O vacancies in the anatase surface. At low coverages, [C(4)C(1)Im][BF(4)] is found to order at the anatase(101) surface via electrostatic attraction, with the imidazolium ring oriented 32±4° from the anatase TiO(2) surface. As the coverage of ionic liquid increases, the influence of the oxide surface on the topmost layers is reduced and the ordering is lost.