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Articles you may be interested inDielectric spectra broadening as a signature for dipole-matrix interaction. IV. Water in amino acids solutionsWe use terahertz ͑THz͒ transmission spectroscopy to obtain the frequency dependent complex dielectric constants of water, methanol, and propylene carbonate, and solutions of lithium salts in these solvents. The behavior of the pure solvents is modeled with either two ͑water͒ or three ͑methanol and propylene carbonate͒ Debye relaxations. We discuss the effects of ionic solvation on the relaxation behavior of the solvents in terms of modifications to the values of the Debye parameters of the pure solvents. In this way we obtain estimates for numbers of irrotationally bound solvent molecules, the numbers of bonds broken or formed, and the effects of ions on the higher-frequency relaxations.

There are significant impacts to fuel cell performance when contaminant cations replace protons in the ionomer. The purpose of this paper is to directly correlate extent of cationic contamination with fuel cell performance and also to elucidate main mechanisms responsible for this performance degradation. A series of standard membrane electrode assemblies (MEAs) were contaminated by varying the ratio of protons to cesium cations in the ionomer phase. The amount of contamination was determined using X-ray Fluorescence (XRF) Spectroscopy. These MEAs were then run in fuel cell mode to determine fuel cell performance as a function of cationic contamination level. A strip cell configuration was also utilized to distinguish between ohmic, thermodynamic, and kinetic effects. Additionally, the distribution of contaminants was measured using XRF.The decrease in fuel cell limiting current, power density, and membrane conductivity as a function of contamination level were quantified. Performance decreased monotonically with increased contamination. The cationic contaminant was preferentially located near the cathode of the strip cell under load. This distribution led to increases in thermodynamic and kinetic polarizations that were more important than changes in membrane conductivity.

We use terahertz (THz) transmission spectroscopy to obtain the frequency dependent complex dielectric functions for pure acetonitrile, pure 1-ethyl-3-methylimidazolium triflate (emim triflate, a room temperature molten salt), and mixtures of the two liquids. The behavior of the pure liquids is modeled with either two (acetonitrile) or three (emim triflate) Debye relaxations. We then discuss the interactions of the molten salt and solvent based on the modified Debye relaxations evident in the mixtures. We determine that at low molten salt concentrations, the mixtures behave like electrolyte solutions of a crystalline salt dissolved in a solvent. At higher molten salt concentrations, the behavior is that of a mixture of two liquids.