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Co-published with the Waterloo Centre for German Studies For centuries, large numbers of German-speaking people have emigrated from settlements in Europe to other countries and continents. In German Diasporic Experiences: Identity, Migration, and Loss, more than forty international contributors describe and discuss aspects of the history, language, and culture of these migrant groups, individuals, and their descendants. Part I focuses on identity, with essays exploring the connections among language, politics, and the construction of histories--national, familial, and personal--in German-spea

Our presentation focuses on durability testing and degradation of fuel cells. A major motivation of our work is the lack of common description procedures and determination approaches of voltage losses in durability tests of fuel cell for both stationary and automotive applications; this issue leads to severe difficulties in the comparison of results obtained by different institutions or within different projects, especially if only a single value for the degradation rate is reported. In this context, special attention is devoted to the discrimination between so called reversible and irreversible voltage losses. The first are permanent and determine the maximum lifetime of a fuel cell. The latter strongly depend on the chosen operation conditions and can be recovered by specific procedures. In order so systematically address voltage losses we have performed single cell durability measurements of several hundreds of hours in 25 cm2 lab-scale cells using different test protocols containing regular refresh procedures (soak time) allowing to distinguish between reversible and irreversible losses. Furthermore, operation strategies to minimize reversible degradation without using the time consuming refresh procedures are provided. To test the refresh procedures and analyze their effect on cell performance, parameters such as duration of the soak time steps have been varied. Between these refresh steps the cells were typically operated for 50 to 150 h. As samples conventional 5-layer membrane electrode assemblies were used with PFSA membranes, Pt-based catalysts and hydrophobized carbon fiber substrates with micro porous layers as GDLs. For in-situ diagnosis of the operated cells polarization curves, electrochemical impedance spectra, and cyclic voltammograms were recorded in order to determine the impact of the operation conditions and the refresh procedures on degradation. The interpretation of the degradation of the measured membrane electrode assemblies is supported by post-mortem analysis using physical characterization techniques. Additionally, we provide possible approaches to quantitatively determine irreversible voltage decay rates. For instance, voltage values before or after voltage recovery steps can be used to calculate the irreversible loss rate. The advantages and drawbacks of different approaches are discussed. One clear conclusion is that short time tests in the range of 100 hour are not conclusive since this time is too short to make a reliable discrimination between reversible and irreversible losses; also, the decay rate of reversible loss observed after each refresh step increases substantially upon long time operation independent on the type of the refresh procedure. In summary, in our presentation strategies for determination of fuel cell voltages loss rates are compared, evaluated and assessed according to their suitability to distinguish between reversible and irreversible degradation rates; a description of voltage loss rates is proposed. Moreover, operation strategies to minimize reversible degradation are provided. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant No. 621216 (SecondAct) and No. 303452 (Impact).

1. Introduction Polymer electrolyte fuel cells with their high gravimetric energy density face a water balance problem especially under variable loads, in particular under automotive conditions: The excess product water needs to be removed from the fuel cell while maintaining a humidified membrane. The gas diffusion layer (GDL), which also provides contact to the electrochemically active components, has to achieve the passive management of the water balance. The adjustment of the hydrophobicity of the GDL is crucial for stable operation, and non-uniform hydrophobicity has already been proven shown to be advantageous. 2. Experiment Typically, gas diffusion electrodes for polymer electrolyte fuel cells (PEFC) consist of conductive medium, either a carbon based powder in the microporous layer (MPL) or carbon felt/fibres/cloth in the macroporous backing, and a hydrophobicity impregnation agent like polytetrafluoroethylene (PTFE). The ratio determines the hydrophobicity and thus the performance. The surface hydrophobicity of GDL components were characterized by x-ray photoemission spectroscopy and infrared absorption spectroscopy. Modifications applied by irradiation with laser, x-ray, and ion-beam were assessed and correlated to the alterations of hydrophobicity. In particular, non-uniform hydrophobicity was applied and tested for improvements. 3. Summary It was observed, that while a direct improvement in output power could not be achieved with pure hydrophobicity modifications, the current density distribution in a running fuel cell was more homogeneous. Both the areas of extremely high and low current densities were reduced. Due to the close correlation of these extreme conditions and the degradation of PEFCs, it can be expected, that the durability is increased with the applied non-uniform surface modifications. 4. References [1] M. Schulze, C. Christenn, XPS investigation of the PTFE induced hydrophobic properties of electrodes for low temperature fuel cells, App. Surf. Sci. 252 5. Acknowledgements The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant No. 303446 (IMPALA).

Polymer electrolyte fuel cells with their high gravimetric energy density face a water balance problem especially under variable loads, e.g. in automotive conditions: The excess product water needs to be removed from the fuel cell while maintaining a humidifed membrane. The gas diffusion layer, which also provides contact to the electro- chemically active components, has to achieve the passive management of the water balance. Heterogeneously hydrophobic gas diffusion media have already shown to be more capable of balancing these opposing requirements than conventional materials. Various methods of pattern- ing gradients of hydrophobicity are applied, like microperforation and laser, focused X-Ray and ion beam irradiation. The modifcations are analysed with photoemission and infrared spectroscopy and compared for their performance, applicability and scalability. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant No. 303446 (Impala).

A particular challenge related to low temperature polymer electrolyte fuel cells (PEMFC) is to maintain high performance and long-term durability concurrently with the further reduction of Pt loading. These are conflicting goals because of a direct correlation of Pt surface with activity and Pt amount with durability. Moreover the lack of common procedures to reliably determine voltage loss rates leads to severe difficulties in the comparison of results obtained by different institutions or projects. Accordingly, special attention is devoted to the discrimination between irreversible and reversible voltage losses. Regarding the influence of Pt loading on PEMFC performance and durability our recent rainbow stack study performed in dynamic operation shows that for Pt/C based cathodes a sudden drop of performance is observed for loadings 1 Acm-2. A similar threshold value is found for the increase of irreversible voltage losses which lead to a reduction of PEMFC durability for cathodes with <=0.2-0.3 mgPt/cm2. Another durability issue at cathodic loadings <0.4 mgPt/cm2 is the acceleration of reversible degradation leading to a significant voltage drop at continuous fuel cell operation. The results show that the Pt loading of Pt/C based electrodes cannot be reduced below 0.2-0.3 mgPtcm-2 by just varying the thickness of the catalyst layers without suffering durability issue. To go below 0.2 mgPtcm-2 new electrode designs are needed. A special combination of coating techniques is also considered as promising approach to solve this issue. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant No. 303452 (Impact).