Surfaces of ionic liquids: Angle‐dependent X‐ray photoelectron spectroscopy (XPS) shows that the surface composition of a solution of [Pt(NH3)4]Cl2 in the ionic liquid 1‐ethyl‐3‐methylimidazolium ethyl sulfate ([EMIM][EtOSO3]) deviates considerably from the bulk composition. The [Pt(NH3)4]2+ cation is enriched on the surface at the expense of the [EMIM] cation (see picture), while the Cl− anion is depleted to below the XPS detection limit.

Surface studies of ionic liquids are particularly important for all kinds of multiphasic operations employing ionic liquids, e.g. biphasic homogeneous catalysis or supported ionic liquid phase catalysis. Using X-ray photoelectron spectroscopy (XPS), the surface composition of the model system 1-ethyl-3-methylimidazolium ethylsulfate [EMIM][EtOSO3] was investigated. By comparing two different samples of this ionic liquid from two different origins, we observed a decisive influence of silicon containing impurities on composition and structure of the surface. For the case of the impurities containing ionic liquid, our angle-dependent XPS data are in agreement with a model of a surface layer consisting of highly oriented ionic liquid molecules. From a fundamental point of view, our study may be of general relevance for the understanding of the chemistry of liquid surfaces in general.

Oberflächen ionischer Flüssigkeiten: Laut winkelabhängiger Röntgenphotoelektronenspektroskopie (XPS) weicht die Zusammensetzung einer Lösung von [Pt(NH3)4]Cl2 in der ionischen Flüssigkeit 1‐Ethyl‐3‐methylimidazolium(EMIM)ethylsulfat an der Oberfläche deutlich von der im Volumen ab. [Pt(NH3)4]2+ wird an der Oberfläche auf Kosten des EMIM‐Kations angereichert, während die Cl−‐Konzentration bis auf Werte unterhalb der XPS‐Detektionsgrenze abnimmt.

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