Proton exchange membrane fuel cell ammonia

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). 

The water-gas-shift reaction (Eqn. 1) has been studied extensively as a basis for improving the yield of hydrogen production. In many applications, including ammonia synthesis or fuel reforming for proton exchange membrane (PEM) fuel cells, the maximum acceptable level of CO in hydrogen is in the parts per million range, therefore the water-gas shift reaction is needed. 

As ammonia is alkaline, it is absorbed by a PEM fuel cell s acidic membrane (e.g., Nafion membrane), where it forms ammonium. Partial or full exchange of H+ by NHJ or other cations in the membrane will reduce membrane conductivity and thereby decrease fuel cell performance. As shown in Table 2.1 [84], the conductivity of a fully exchanged NH4+-form Nafion 105 membrane is only about one-quarter that of the protonic-form membrane. 

Cationic contaminants may emanate from many sources. Metals, such as iron and copper, in system components may ionize due to corrosion exchange with protons in the membrane. Metallic salts, such as sodium and calcium, may enter the fuel cell from coastal water or from deicing agents. The most likely source of cationic contaminants is from the fuel line. Hydrogen from reformed hydrocarbons usually contain parts per million (ppm) of ammonia. This ammonia can be oxidized to ammonium ions and enter the polymer electrolyte. 

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