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Unformatted text preview: 2334 J. Electrochem. Soc., Vol. 138, No. 8, August 1991 The Electrochemical Society, Inc. 5. U n io n C arbide Corporation, C arbon P roducts Division (now A M O CO P e r f o r m a n c e Products), Technical In- form ation Bulletins 465-223,465-225, 465-246. 6. P. Wagner, J. Am. Ceramic Soc., 55, 214 (1971). 7. O. M. Baycura, IEEE Trans. Indust., 5, 208 (1968). 8. K. K inoshita and S. C. Leach, This Journal, 129, 1993 (1982). 9. "C h em ical E ngineers H a n d b o o k ," 5th ed., R. H. P erry and C. H. Chilton, McGraw-Hill, N e w Y ork (1973). 10. W. L. I n g m a n s o n et aI., TAPPI, 42, 840 (1959). Polymer Electrolyte Fuel Cell Model T. E. Springer,* T. A. Zawodzinski,* and S. Gottesfeld* Los Alamos National Laboratory, Los Alamos, New Mexico 87545 A B S T R A C T We present here an isotherm al, one-dim ensional, steady-state m o d el for a co m p lete p o ly m e r electrolyte fuel cell (PEFC) w ith a 117 Nation | m e m b ra n e . In this m o d e l w e e m p lo y w ater diffusion coefficients electro-osm otic drag coeffi- cients, w ater sorption isotherm s, and m e m b r a n e conductivities, all m easured in our laboratory as functions of m e m b r a n e w ater content. T he m o d e l pre.dicts a net-w ater-per-proton flux ratio of 0.2 H20/H § u n d er typical operating conditions, w h ich is m u c h less than the m e a s u re d electro-osm otic drag coefficient for a fully hydrated m em b ran e. It also predicts an increase in m e m b r a n e resistance w ith increased current density and dem onstrates the great advantage of a th in n e r m em - brane in alleviating this resistance problem . B oth of these predictions w ere verified ex p erim en tally u n d e r certain condi- tions. F u el cells e m p lo y in g hydrated Nation or other hydrated perfluorinated io n o m eric m aterials as the electrolyte are prom ising candidates for electric vehicle applications (1). T he p o ly m e r electrolyte provides r o o m te m p e ra tu re start- up, elim ination o f m a n y corrosion problem s, and the po- tential for low resistance losses. Resistive losses w ithin the fuel cell result, in part, from the decrease of m e m b r a n e protonic c o n d u c tiv ity follow ing partial dehydration of the m em b ran e. On the other hand, cathode flooding problem s are caused w h e n too m u c h w ater is in the system. Clearly, w ater m a n a g e m e n t w ithin the fuel cell involves w alking a tightrope b e tw e e n the two extrem es. Spatial variations of w ater content w ithin the polym eric electrolyte of a current~carrying fuel cell result from the electro-osm otic dragging of w ater w ith proton transport from anode to cathode, the p ro d u ctio n of w ater by the oxy- gen red u ctio n reaction at the cathode, hum idification con- ditions of the inlet gas streams, and "back-diffusion" of w ater from cathode to anode, w h ic h lessens the concentra- tion gradient....
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This note was uploaded on 10/28/2010 for the course EE 89 taught by Professor Asgarian during the Fall '10 term at Amirkabir University of Technology.
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