Dirk Gerhard

Surface Studies on the Ionic Liquid 1-Ethyl-3-Methylimidazolium Ethylsulfate Using X-Ray Photoelectron Spectroscopy (XPS)

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.

Temperature Dependent Impedance Analysis of Binary Ionic Liquid Electrolytes for Dye-Sensitized Solar Cells

At platinum electrodes kinetics of the I - /I - 3 electrode reaction were studied at two potential electrolyte systems for dye-sensitized solar cells (DSSCs) based on binary ionic liquid (IL) blends, i.e., 1-ethyl-3-methylimidazolium dicyanamide ([EMIM] [N(CN) 2 ])/1-methyl-3-propylimidazolium iodide ([PMIM]I) and l-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM] [BF 4 ])/[PMIM]I, respectively. The charge transfer resistances of the electrode reaction were determined via impedance spectroscopy for electrolyte blends at a mixing ratio of ILs of 9 mol % [PMIM]I (for [EMIM][N(CN)2]/[PMIM]I) and 10 mol % [PMIM]I (for [EMIM][BF 4 ]/[PMIM]I) up to 100 mol % [PMIM]I. In addition, the influence of iodine concentration on the electrode reaction was investigated for both electrolyte systems. The measurements were taken in a temperature range of 25 to 60°C to analyze the electrolyte properties in view of thermal stress of the DSSC for later practical application. Furthermore, exchange current densities were determined: the expected Arrhenius behavior was observed. Activation energies were obtained by fitting linearized Arrhenius plots.

Trialkylsulfonium dicyanamides - a new family of ionic liquids with very low viscosities

Trialkylsulfonium dicyanamides show surprisingly low viscosities down to -20 degrees C and are therefore highly interesting liquid materials for separation processes and electrolyte applications at low temperatures.

Aggregation Models of Potential Cyclical Trimethylsulfonium Dicyanamide Ionic Liquid Clusters

Raman and infrared spectra of trimethylsulfonium dicyanamide [(CH(3))(3)SN(CN)(2)] are reported and accurately reproduced by DFT methods (B3LYP and B3PW91), MP2, and MP3, and to a lesser extent by the RHF method. The (CH(3))(3)SN(CN)(2) ionic liquid forms two isomeric dimers that are of cyclic structure, one of which is 13 kcal/mol lower in energy than the other. Both isomeric cyclic pairs (versions 1 and 2), [(CH(3))(3)SN(CN)(2)](2), have the potential to further combine and form a common structure containing four pairs of (CH(3))(3)SN(CN)(2). This structure can then conceivably undergo a stacking procedure to form extended ionic liquid nanotubes of eight ionic liquids, [(CH(3))(3)SN(CN)(2)](8). The possible formation of gas phase ionic liquid clusters of two, four, and eight trimethylsulfonium dicyanamide ionic liquids is supported by highly exergonic free energy changes obtained from B3LYP/(6-311+G(d,p)) density functional calculations.