Proton exchange membrane fuel cell contamination

Proton Exchange Membrane Fuel Cells Contamination and Mitigation Strategies... 

In Proton Exchange Membrane Fuel Cells Contamination and Mitigation Strategies, the nature, sources, and electrochemistry of contaminants, their... 

Knights S (2010), PEM Fuel Cell Principles and Introduction to Contamination Issues , in Li H, Knights S, Shi Z VanZee J and Zhang J, Proton Exchange Membrane Fuel Cells Contamination and Mitigation Strategies, Taylor and Francis Group, 1-52. 

Shi, Z., Song, D. T., Li, H. et al. 2009. A general model for air-side proton exchange membrane fuel cell contamination. Journal of Power Sources 186 435-445. 

St-Pierre, J. and Jia, N. (2002) Successful demonstration of Ballard PEMFCs for space shuttle applications. J. New Mater. Electrochem. Syst. 5, 263-271 St-Pierre, J., Jia, N. and Rahmani, R. (2008) Proton exchange membrane fuel cell contamination model - Competitive adsorption demonstrated with NO J. Electrochem. Soc. 155, B315-B320 St-Pierre, J., WrUdnson, D. P., Knights, S. and Bos, M. (2(XX)) Relationships between water management, contamination and Ufetime degradation in PEFC. J. New Mater. Electrochem. Syst. 3,99-106... 

Obviously, in practical situations one can hardly imagine a vacuum pump installed onboard of a fuel cell-powered vehicle. Even if so, the membrane of a Proton Exchange Membrane Fuel Cell (PEMFC) will be soon contaminated by the oil vapors released from the pump (dry pumps are possible but this would enormously complicate the entire design). 

Parry V, BerthomS G, Joud J-C, Lemaire O, Franco AA. XPS investigations of the proton exchange membrane fuel cell active layers aging characterization of the mitigating role of an anodic CO contamination on cathode degradation. J Power Sources 2011 196(5) 2530—8. 

Figure 23.8. Effect of CO contamination time on fuel cell performance in H2/IOO ppm CO during the poisoning period anode and cathode Pt on Vulcan XC72 T = 80 °C P(h2) = 0.22 MPa, P(02) = 0.24 MPa [51]. (Reprinted by permission of ECS— The Electrochemical Society, from Oetjen H-F, Schmidt VM, Stimming U, Trila F. Performance data of a proton exchange membrane fuel cell using H2/CO as fuel gas.)...

Gould, B. D., Bender, G., Bethune, K. et al. 2010. Operational performance recovery of SOj-contaminated proton exchange membrane fuel cells. Journal of the Electrochemical Society 157 B1569-B1577. 

High-temperature proton exchange membrane fuel cells (HT-PEM fuel cells), which use modified perfluorosulfonic acid (PFSA) polymers [1—3] or acid-base polymers as membranes [4—8], usually operate at temperatures from 90 to 200 °C with low or no humidity. The development of HT-PEM fuel cells has been pursued worldwide to solve some of the problems associated with current low-temperature PEM fuel cells (LT-PEM fuel cells, usually operated at <90 °C) these include sluggish electrode kinetics, low tolerance for contaminants (e.g. carbon monoxide (CO)), and complicated water and heat management [4,5]. However, operating a PEM fuel cell at >90 °C also accelerates degradation of the fuel cell components, especially the membranes and electrocatalysts [8]. 

Contaminant ingress within the cathode compartment of proton exchange membrane fuel cells fueled by hydrogen, the preferred system for automotive applications and the most technically challenging, represented the focus of this analysis. Therefore, proton exchange manhrane fuel cells based on other fuels, such as methanol and reformate, were excluded from the present analysis to focus the discussion. For these other fuels, additional contamination routes (contaminant leaching in the liquid methanol solution fuel followed by dissolution in the ionomer and transport to the cathode, etc.) and contaminants (CO, CO, CH, etc.) exist. 

For use in proton exchange membrane (PEM) fuel cells (see section 3.6), the CO contamination in the hydrogen produced must be below 50 ppm (parts per million). This is due to the poisoning limit of typical platinum catalysts used in PEM cells. The implication is the need for a final CO cleaning treatment, unless the main reaction steps (2.1) and (2.2) can be controlled so accurately that all reactants are accounted for. This CO cleaning stage may involve one of the following three techniques preferential oxidation. 

Adapt catalytic gate field effect transistor (FET) sensors to resolve and detect carbon monoxide (CO) contamination levels from 1-100 ppm in reformer produced hydrogen (H2) fuel for (proton exchange membrane (PEM) fuel cells... 

The proton exchange membrane can be a source of fluoride ions as well [143]. Hydroxyl radicals, formed via crossover gases or reactions of hydrogen peroxide with Fenton-active contaminants (e.g., Fe +), could attack the backbone of Nafion, causing the release of fluoride anions these anions in turn promote corrosion of the fuel cell plates and catalyst, and release transition metals into the fuel cell [143]. Transition metal ions, such as Fe, then catalyze the formation of radicals within the Nafion membrane, resulting in a further release of fluoride anions. On the other hand, transition metal ions also can cause decreased membrane and ionomer conductivity in catalyst layers, as discussed in section 2.4 of this chapter. 

The membrane electrode assembly (MEA) in a proton exchange membrane (PEM) fuel cell has been identified 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 ... 

Finally, the most important concerns regarding alloys as substitutes for Pt in fuel cell electrodes include the potential leach and contamination of the electrolyte membrane with cations coming from the dissolution of the base-metal therefore, the design of new catalysts requires not only optimizing the catalytic activity but also analyzing the stabihty of the Pt and non-Pt elements under proton exchange fuel cell conditions. 

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