Potential oscillations in a proton exchange membrane fuel cell with a Pd-Pt/C anode

We report in this paper the occurrence of potential oscillations in a proton exchange membrane fuel cell (PEMFC) with a Pd-Pt/C anode, fed with H(2)/100 ppm CO, and operated at 30 degrees C. We demonstrate that the use of Pd-Pt/C anode enables the emergence of dynamic instabilities in a PEMFC. Oscillations are characterized by the presence of very high oscillation amplitude, ca. 0.8 V. which is almost twice that observed in a PEMFC with a Pt-Ru/C anode under similar conditions. The effects of the H(2)/CO flow rate and cell current density on the oscillatory dynamics were investigated and the mechanism rationalized in terms of the CO oxidation and adsorption processes. We also discuss the fundamental aspects concerning the operation of a PEMFC under oscillatory regime in terms of the benefit resulting from the higher average power output. (c) 2010 Elsevier B.V. All rights reserved.

Trade effects of exchange rate fluctuations: Evidence from Sweden

An overview of the theoretical literature for the last two decades suggests that there is no clear-cut relationship one can pin down between exchange rate volatility and trade flows. Analytical results are based on specific assumptions and only hold in certain cases. Especially, the impact of exchange rate volatility on export and import activity investigated separately leads also to dissimilar conclusions among countries studied. The general presumption is that an increase in exchange rate volatility will have an adverse effect on trade flows and consequently, the overall heath of the world economy. However, neither theoretical models nor empirical studies provide us with a definitive answer, leaving obtained results highly ambiguous and inconsistent (Baum and Caglayan, 2006). We purposed to empirically investigate trade effects of exchange rate fluctuations in Sweden from the perspective of export and import in this research. The data comprises period from January 1993 to December 2006, where export and import volumes are considered from the point of their determinants, including exchange rate volatility, which has been measured through EGARCH model. The results for the case of Sweden show that short run dynamics of volatility negatively associated with both export and import, whereas considered from the case of previous period volatility it exhibits positive relationship. These results are consistent with the most findings of prior studies, where the relationship remained ambiguous.

Investigation of Iron (III) desferrioxamine B oxalate ligand exchange by UV-vis spectroscopy: the next step in developing a quantitative analytical method for measuring bioavailable iron in marine ecosystems

To date there are no analytical techniques designed to exclusively measure bioavailable iron in marine environments. The goal of this research is to develop such a technique by isolating the bioavailable iron using the terrestrial siderophore desferrioxamine B (DFB). This project contained many challenging aspects, but the specific goal of this study was to develop a robust analytical technique for quantification of Fe(III)-DFB complexes at nanomolar concentrations. Past work showed that oxalate (Ox) promotes photodissociation of Fe(III)-DFB to Fe(Il), and we are specifically interested in the mechanism of this process. A model was developed using known thermodynamic constants for Fe(III)-DFB and Fe(III) oxalato complexes and adjusting for ionic strength. The model was confirmed by monitoring the UV-VIS absorbance of the system at a variety of oxalate concentrations and pH. The model did not include ternary complexes. Next., the rate of Fe(1I) production during UV irradiation was examined. The results showed that the rate of Fe(II) production was based entirely on the [Fe(Ox)?]3- speciation, and that reoxidation of Fe(II) occurred via reactive oxygen intermediates. This reoxidation could be avoided by either decreasing the oxygen concentration or by adding a Fe(II) stabilizing reagent, such as ferrozine. Further studies need to be done to confirm that these results apply at sub nanomolar concentrations, and the issue of Fe(II) reoxidation at lower Fe concentrations needs to be addressed.