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Contamination of proton exchange membrane fuel cells is coming to the forefront as commercialization activities multiply and fuel cell systems are confronted to field conditions away from the controlled laboratory environment. The recent progress achieved in understanding the disruptive effects of contaminants is reviewed. The analysis is focused on contaminant effects, contaminant sources, mechanisms, mitigation strategies and knowledge gaps in all these areas. IntroductionAs the commercialization of proton exchange membrane fuel cells (PEMFCs) comes closer to reality, systems are taken out of the controlled laboratory environment with purified air and hydrogen reagents. The impact of foreign species is coming to the forefront because air quality is currently beyond our ability to control (1) and the cost of hydrogen is partly tied to its composition (2). A multitude of contaminants, impurities, poisons and inhibitors have already been characterized (3,4). However, many species remain to be identified including their deactivation mechanisms, preventive mitigation approaches and recovery procedures. Foreign species have the capability to harmfully disrupt the functions of the oxygen reduction reaction (ORR) and the hydrogen oxidation reaction (HOR) catalysts, and the ion exchange polymer. Both of these membrane/electrode assembly materials are essential for PEMFC operation. The incumbent Pt ORR and HOR catalyst is poorly selective and thus has multiple uses (5) rendering it susceptible to deactivation (6,7). The present Nafion ion exchange polymer composed of perfluorovinyl ether groups terminated with sulfonate groups attached to a tetrafluoroethylene backbone, is also poorly selective and permeable to almost any species including gases, solvents and cations (813). The ionic conductivity and reactant permeability of the ionomer is smaller in the presence of foreign species (1417). The risk associated with many contaminant species left to be characterized is further compounded by the few organizations involved in such activities. Thus, many opportunities still remain to expand the knowledge base and enhance the commercialization potential of PEMFCs.Fundamentals aspects of PEMFC contamination are discussed with particular attention given to recent developments and existing knowledge gaps. This information is expected to facilitate the development of research and development programs focusing on the most urgent needs for a successful introduction of fuel cells into the market. The effects resulting from contamination are first described. The contaminants origins are 10.1149/06123.0001ecst ©The Electrochemical Society ECS Transactions, 61 (23) 1-14 (2014) 1 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 131.215.225.9 Downloaded on 2015-06-19 to IPsubsequently discussed. The contamination mechanisms section which includes characterization methods provides a background for the last section about mitigation. PEMFC Contamination Contaminan...

A PEMFC stack was contaminated with 50 ppm propene in air. The average performance decreased by 243 mV until a steady state was reached. After the propene injection was interrupted, the average performance increased until a new steady state was attained that exceeded the initial value by ~6 mV. Propene contamination amplified the uneven cell performance distribution along the stack length. End cells showed a larger performance change than the other cells with respect to the pre-contamination phase of respectively 24 and 15 mV. The effect was ascribed to interactions between propene and the uneven temperature distribution. Propene contamination affects both oxygen reduction kinetics and mass transfer as revealed by impedance spectroscopy measurements.

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