Proton exchange membrane fuel cell impurities

Fuel cells can be broadly classified into two types high temperature fuel cells such as molten carbonate fuel cells (MCFCs) and solid oxide polymer fuel cells (SOFCs), which operate at temperatures above 923 K and low temperature fuel cells such as proton exchange membrane fuel cells (PEMs), alkaline fuel cells (AFCs) and phosphoric acid fuel cells (PAFCs), which operate at temperatures lower than 523 K. Because of their higher operating temperatures, MCFCs and SOFCs have a high tolerance for commonly encountered impurities such as CO and CO2 (CO c)- However, the high temperatures also impose problems in their maintenance and operation and thus, increase the difficulty in their effective utilization in vehicular and small-scale applications. Hence, a major part of the research has been directed towards low temperature fuel cells. The low temperature fuel cells unfortunately, have a very low tolerance for impurities such as CO , PAFCs can tolerate up to 2% CO, PEMs only a few ppm, whereas the AFCs have a stringent (ppm level) CO2 tolerance. 

Figure 5.36. Effects that long-term NH3 exposure has on H2-air fuel cell high-frequency resistance at 80°C. 30 ppm NH3 (g) was injected into the anode feed stream [39], (Reproduced by permission of ECS—The Electrochemical Society, from Uribe FA, Gottesfeld S, Zawodzinski Jr. TA. Effect of ammonia as potential fuel impurity on proton exchange membrane fuel cell performance.)...

Uribe FA, Gottesfeld S, Zawodzinski Jr TA (2002) Effect of ammonia as potential fuel impurity on proton exchange membrane fuel cell performance. J Electrochem Soc 149 A293-6... 

F. Uribe, S. Gottesfeld and T. Zawodzinski, "The Effect of Ammonia as Potential Fuel Impurity on Proton Exchange Membrane Fuel Cell Performance", J. Electrochem. Soc., 149, A293 (2002). 

Narusawa K, Myong K, MurookaK, Kamiya Y (2007) A study regarding effects of proton exchange membrane fuel cell poisoning due to impurities on fuel eell performanee, SAE technical paper series, pp 2007-01-0698... 

Typical low-temperature proton exchange membrane fuel cells (LT-PEMFCs), operated at temperatures lower than 90 °C, use H2 as fuel. H2 is not a naturally occurring resource, and is mainly produced by reforming organic fuels such as natural gas and methanol or by coal gasification. The reforming process produces H2 with traces of impurities, mainly CO, H2S, and SO2, among which CO is the... 

FIGURE8.20 Cell voltage response to exposure to 1 ppm CO in Hj at the anode at 60 C and 1 A cm . (Reprinted from Journal of Power Sources, 193, Bender, G. et al.. Method using gas chromatography to determine the molar flow balance for proton exchange membrane fuel cells exposed to impurities, 713-722, Copyright (2009), with permission from Elsevier.)... 

Other technical hurdles must be overcome to make fuel cells more appealing to automakers and consumers. Durability is a key issue and performance degradation is usually traceable to the proton exchange membrane component of the device. Depending on the application, 5,000 40,000 h of fuel cell lifetime is needed. Chemical attack of the membrane and electrocatalyst deactivation (due to gradual poisoning by impurities such as CO in the feed gases) are critical roadblocks that must be over come. 

Abstract The durability of fuel cell components constitutes a major barrier towards their financial viabihty. Lifetime requirements include 5000 and 40 000 h for automotive and stationary applications respectively, and thus it is impractical to evaluate fuel cell components lifetime using prolonged time periods. Accelerated durability testing protocols for fuel cell components (proton exchange membrane, electrocatalyst and supports) have been developed to obtain cell component lifetimes in shorter e q)erimental time and are discussed in detail, along with fiiel/air impurities testing protocols. 

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