ABSTRACT
The membrane electrode assembly (MEA) in a proton exchange membrane (PEM) fuel cell has been identied as the key component that is probably most affected by the contamination process [1]. An MEA consists of anode and cathode catalyst layers (CLs), gas diffusion layers (GDLs), as well as a proton exchange membrane, among which the CLs present the most important challenges due to their complexity and heterogeneity. The CL is several micrometers thick and either covers the surface of the carbon base layer of the GDL or is coated on the surface of the membrane. The CL consists of: (1) an ionic conductor (ionomer) to provide a passage for proton transport;
CONTENTS
3.1 Introduction ..................................................................................................85 3.2 Impacts of SOx .............................................................................................. 87 3.3 Impacts of NOx ............................................................................................. 91 3.4 Impacts of NH3 and H2S ............................................................................. 93 3.5 Impacts of VOCs .......................................................................................... 95 3.6 Impacts of Multiple Contaminants ........................................................... 98 3.7 Mitigation Strategies for Airside Contamination .................................. 100 3.8 Example Analysis: Development of Cell Performance Predictor
under the Inuence of Toluene in the Air Stream ................................ 101 3.8.1 Experimental .................................................................................. 102
3.8.1.1 Description of Semiempirical Models .......................... 102 3.8.2 Results and Discussion ................................................................. 106
3.8.2.1 Simulation of KCK and Kt ................................................ 106 3.8.2.2 Model Prediction ............................................................. 106
3.8.3 Conclusions ..................................................................................... 110 3.9 Summary ..................................................................................................... 110 Acknowledgments .............................................................................................. 111 References ............................................................................................................. 111
(2) Pt (platinum) catalysts supported on a conductive matrix, such as carbon, to provide electron conduction; and (3) a hydrophilic agent, such as polytetrauoroethylene (PTFE) to provide sufcient porosity and adjust the hydrophobicity/hydrophilicity of the CL for gaseous reactants to be transferred to active sites [2,3]. With each of those elements optimized to provide the best overall performance, the CL functions as a place for electrochemical reactions. The processes occurring in a CL include mass transport of the gaseous reactants, interfacial reactions of the reactants (e.g., H2 at anode and O2 at cathode) at the electrochemically active sites, proton transport in the electrolyte phase, and electron conduction in the electronic phase. When contaminants are present in the reactant streams, one or more of the above processes can be adversely affected, causing degradation in fuel cell performance or even fuel cell failure.
