Fuel cell contaminants other contamination sources

Similar to SO, NO, are also important fuel cell contaminants. NO, derive from several sources [104-106]. The primary sources are motor vehicles, electrical utilities, and other industrial, commercial, and residential sources that burn fuels. Other NO, arise from human activities that include biomass burning, waste disposal, solvent use, and fertilizer use. NO, are formed when fuel is burned at high temperatures, as in a combustion process. Fossil... 

The main contaminants for the membrane are cationic species, such as metal ions, which may come from contaminated air and fuel streams when moisture is present, metal fuel cell components, balance-of-plant components, or nonmetal contaminated component materials. Other organic and inorganic materials can also contaminate the membrane, but the effects of these are less well documented. Component materials supplying contaminants may include the platinum catalyst or alloying metals, such as ruthenium or cobalt, which may leach out into the membrane the raw material source for the carbon materials (in the catalyst support, microporous layer, gas diffusion layer, or plate materials) may also have inherent metal or other chemical impurities and seal and gasketing materials, such as silicone, can decompose and contaminate the membrane. All of the membrane contaminants can also impact the ionomer materials present in the catalyst layers. 

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. 

Other than the contaminant sources mentioned above, some contaminants can also come from coolants and deionized water (e.g.. Si, Al, S, K, Fe, Cu, Cl, V, Cr), compressors (e.g., oils), and sealing gaskets (e.g.. Si), as summarized by Cheng et al. [150]. In recent studies [151-153], silicon was detected in a fuel cell catalyst layer after long-term operation. Silicon released due to gasket failure will get into the fuel cell catalyst layer, adsorb on the Pt catalyst surface or the interface of the Pt and ionomer, and thereby cause degradation in fuel cell performance. 

In addition to the fuel source, contamination can come from the environment or from other fuel cell components. The major somces of the contaminants in the air stream fed to fuel cells are determined by the general air quality standards. Thus, these feed streams will contain contaminants from vehicle emissions, such as NO, SO , CO , and specific chemical species. The impact of SO is particularly critical since its presence can cause fuel cell death depending on its concentration or dosage [33]. Contamination sources can also be from fuel cell components, such as the seals, lines, or fittings. 

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