Ammonia fuel cell performance

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). 

Impurities that adsorb mito the electrocatalysts surface inhibit the charge-transfer processes, resulting in performance loss. Common fuel impurities include carbon monoxide, ammonia, hydrogen sulfide, hydrogen cyanide, hydrocarbons, formaldehyde, and formic acid [93]. On the cathode side, ambient air may contain impurities such as sulfur dioxide, nitrogen oxides, and particulate matter (including salts) that can affect fuel cell performance [93]. 

Szymanski ST, Gruver GA, Katz M, Kunz HR. The effect of ammonia on hydrogen-air phosphoric acid fuel cell performance. J Electrochem Soc 1980 127 1440-4. 

The major air contaminants are carbon oxides (CO and CO2), sulfur oxides (SO2 and SO3), nitrogen oxides (NO2 and NO), volatile organic carbons (VOCs), and ammonia (NH3). In the absence of a filfrafion sysfem, fhese contaminants can impact the fuel cell performance. 

Ammonia in the hydrogen fuel originates from the hydrogen production process. The impact on fuel cell performance is as described for the cathode contamination, and is similar whether it is introduced in the cathode or anode. 

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. 

Hydrogen is produced via reformation of hydrocarbons (Dicks, 1996 Hohlein et al., 1996 Schmidt et al., 1994), partial oxidation of small organics (Parsons, and VanderNoot, 1988), hydrolysis of sodium borohydride (Wee et al., 2006)) arrd water electrolysis (Onda et al., 2004 Smolinka, 2009). However, reformation techniques do not produce pitre hydrogen since low concentrations of impurities such as sitlfur (H2S), carbon oxides (CO2 and CO) and ammonia (NHj) exist in the reformate gas, resulting in fuel cell performance losses. 

Other possible by-products in the reformate may have a detrimental effect on PEM fuel cell performance. Figure 9-35 shows what happens when a small quantity (13 to 130ppm) of ammonia is injected in the anode fuel stream [22]. The cell current at given cell potential steadily declines. It seems that this poisoning is reversible, that is, after the flow of ammonia is discoimected, the cell performance slowly improves. Note that the performance did not return to its original value even after several hours. Ammonia may be generated in the autothermal reformer under certain... 

Rajalakshmi N, Jayanth T T and Dhathathreyan K S (2003) Effect of carbon dioxide and ammonia on polymer electrolyte membrane fuel cell performance, FUEL CELLS, 3, pp. 177-180. 

Ammonia, produced due to the coexistence of H2 and N2 at high temperatures in the presence of catalyst, was estimated to be in the concentration range of 30 to 90 ppm [37, 38], Uribe et al. [39] examined the effects of ammonia trace on PEM fuel cell anode performance and reported that a trace in the order of tens of parts per million could lead to considerable performance loss. They also used EIS in their work. By measuring the high-frequency resistance (HFR, mainly contributed by membrane resistance) with an operation mode of H2 + NH3/air (feeding the anode with hydrogen and ammonia), they obtained some information related to membrane conductivity, and found that conductivity reduction due to ammonia contamination is the major cause of fuel cell degradation. 

Fournier G G M, Gumming 1W, HeUgardt K (2006), High performance direct ammonia solid oxide fuel cell , J. Power Sources, 162(1), 198-206. 

Halsied R, Vie P J S, Tunold R (2006), Effect of ammonia on the performance of polymer electrolyte membrane fuel cells , J. Power Sources, 154, 343-350. 

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