Anode contamination modeling

Chapter 7 provides a comprehensive literature review and discussion on fuel cell anode confamination modeling. An introduction to fuel contamination is provided, including a hydrogen fuel quality specification for transportation hydrogen. 

Carbon monoxide is the most understood poisoning phenomena due to extensive studies. The goal of this chapter (7) is to provide a full understanding of the CO poisoning phenomenon, sufficient to enable the reader to numerically simulate CO poisoning as well as its mitigation methods. Empirical models are usually developed and an example of fhis is described. Mathematical models, which include the fundamental physical and chemical properties of the system under study, are more useful for parametric studies, such as, for example, the effects of fhe catalyst layer structure. Several approaches to the mathematical models are briefly described. 

The adsorption, desorption, and electro-oxidation reactions of hydrogen and carbon monoxide are discussed. The hydrogen oxidation reaction requires the dissociation of the hydrogen molecule onto bare platinum sites. The CO molecules will also adsorb on the Ft sites, and require oxidation at higher electrode potentials in the range of 0.6 to 0.9 V for removal. Since this potential does not readily occur on the anode, the hydrogen oxidation occurs on a reduced number of Ff sites, resulting in increased anode overpotential. 

A complete model of CO poisoning is presented, including the catalyst layer as well as transport in the GDL and flow channel. An example of validation of fhe models based on the polarization curve is presented. 

The comprehensive overview of fhe modeling approaches includes a discussion of fhe model approaches used to invesfigafe the actual kinetics including the use of either Langmuir or Tempkin kinetics. The CO poisoning effect also depends on the concentration of H2, wifh a greater effect for more 

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A general anode contamination model was developed by Zhang et al. (2005) and is capable of describing the effect of various contaminant species. St.-Pierre s generalized contamination model that is applicable to both the cathode and anode (St.-Pierre, 2009) has already been discussed briefly in the Section 8.3.1.2. All of the above models use similar reactions to describe tbe kinetics of HOR and the contamination reactions, along with Butler-Volmer expression to determine the PC s overpotential or current density. The reaction network and rate constants for a contamination process involving a general contaminant P is shown below ... 

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