Multi-scale structure/function modeling of fuel cell electrolytes September 19, 2011, SC 5326
S. J. Paddison
Department of Chemical and Biomolecular Engineering University of Tennessee, Knoxville, TN 37996 U.S.A.
Proton exchange membranes (PEMs) are the electrolyte in current state-of-the-art fuel cells and function as not only the separator of the electrodes and reactant gases (H2 and O2) but importantly as the internal ion conductor [1]. Efficient operation of these energy conversion devices in diverse applications (vehicular, portable, and stationary) places demands on the PEM which include: longtime thermal and chemical stability (including resistance to oxidation and degradation by reactive species) at temperatures as high as 120°C, and high proton conductivity (≈ 10-1 Scm-1) under low humidity conditions (25-50% relative humidity). Although a large number of strategies have been devised in the pursuit of membranes that meet these requirements [2], current PEM fuel cells still utilize perfluorosulfonic acid (PFSA) ionomers such as Nafion®. Recently, proton conduction in these polymeric materials has been developed within a framework consisting of: complexity, connectivity, and cooperativity [3]. Experiments and modeling have shown that the transport of water and hydrated protons within PFSAs is dependent upon: the characteristic dimensions of the phase-separated hydrated polymer morphology (typically on the order of only a few nanometers); acidity, density, and distribution of the sulfonic acid groups; and the external conditions including humidity, temperature, and pressure. A complete understanding of how all these factors may be used in a synergetic fashion in the engineering of novel high performance materials remains forthcoming [4]. This talk will describe our multi-scale modeling effort in securing a fundamental molecular-level understanding of how structure determines function and properties [5-10].
References
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[2] M. A. Hickner, Mater. Today 2010, 13, 34.
[3] Device and Materials Modeling in PEM Fuel Cells; Paddison, S. J., Promislow, K. S., Eds.;
Springer-Verlag Berlin: Berlin, 2008, 113, pp. 1-588.
[4] J. A. Elliott and S. J. Paddison, Phys. Chem. Chem. Phys. 2007, 9, 2602.
[5] D.-S. Wu, S. J. Paddison, and J. A. Elliott, Energy Environ. Sci. 2008, 1, 284.
[6] D.-S. Wu, S. J. Paddison, and J. A. Elliott, Macromolecules 2009, 42, 3358.
[7] R. L. Hayes, S. J. Paddison, and M. E. Tuckerman, J. Phys. Chem. B 2009, 113, 16574.
[8] C. Wang and S. J. Paddison, Phys. Chem. Chem. Phys. 2010, 12, 970.
[9] B. F. Habenicht, S. J. Paddison, and M. E. Tuckerman, J. Mater. Chem. 2010, 20, 6342.
[10] J. A. Elliott, D. Wu, S. J. Paddison, and R. B. Moore, Soft Matter 2011, 7, 6820.