PEMFC fuel cell tests membranes

Ammonia (NH3) or ammonium (NH4+) can exist in both the fuel and air streams. The diffusion of ammonium is fast, therefore, the ammonium entering the fuel cell from either side can quickly diffuse to the other side causing the contamination effect on both sides. For instance, for a typical membrane with a thickness of 10 to 100 jim, the estimated characteristic time constant for diffusion is 1 to 100 sec [149]. Ammonia may affect the PEMFC performance in different ways (1) by the reduction of the ionic conductivity of the membrane, which in its ammonium form is a factor of 4 lower than in the protonated form [149-151] (2) by poisoning the cathode catalyst [151] and (3) by poisoning the anode catalyst [149]. Recently, fuel cell tests have shown that the reduced membrane conductivity is not the major reason for performance losses induced by ammonia [149,150]. The effect of ammonia on the HOR was found to be minor at current densities below 0.5 A cm", but would increase with increasing current densities. The current density did not exceed 1 A cm in the presence of ammonia [149]. 

It can be concluded from this chapter that membranes have an essential role in electrochemical devices such as fuel cells and water electrolysis. Moreover, considering the variety of systems and their specific electrolytic membranes, a huge field emerges, embracing research, from testing to fundamentals, demonstration programmes and, in some cases, a real market entry. Commercialisation of electrical fuel cell vehicles in a couple of years, as announced by Daimler, should favour the development of PEMFCs. Whereas, the use of MCFCs and SOFC for co-generation and varied... 

Mocoteguy P, Ludwig B, Scholia J, Nedellec Y, Jones DJ, Roziere J (2010) Long-term testing in dynamic mode of HT-PEMFC H3PO4/PBI Celtec-P based membrane electrode assemblies for micro-CHP applications. Fuel Cells 10(2) 299-311... 

Loss of catalyst electrochemical surface area (ECSA), as discussed above, could be caused by Pt dissolution and migration into the membrane. In addition, increase in Pt particle size during fuel cell operation is another cause of ECSA loss in the catalyst layer. Loss of Pt surface area vs. time during fuel cell operation has been observed in both the phosphoric acid fuel cell [87-89] and PEMFC operations [9, 33, 90]. An increase in Pt particle size from 2-3 mn up to more than 10 mn during durability testing in the catalyst layer has been reported, determined by X-ray diffraction [46] or TEM image analysis [9, 33-38, 90]. 

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