Hydrogen crossover membrane resistance

Figure 11.30. Hydrogen crossover rates through a Hyflon extraded membrane under OCV tested with different reactants. Electrode area = 25 cm Pt = 0.25 mg cm at either anode or cathode T = 70 °C RH = 50% for both anode and cathode membrane thickness = 50 pm ionomer equivalent weight = 870 g equiv [26]. (Reprinted from Journal of Power Sources, 171(1), Merlo L, Ghielmi A, Cirillo L, Gebert M, Arcella V, Resistance to peroxide degradation of H3rflon Ion membranes, 140-7, 2007, with permission from Elsevier.)...

As shown in Fig. 1.4 of Chapter 1, under a load, PEM fuel cell performance is determined by four voltage losses the voltage loss caused by mixed potential and hydrogen crossover, which is related to the Pt catalyst status and the membrane properties the activation loss, which is related to the electrode kinetics the ohmic loss, which is determined by ohmic resistance and the voltage loss caused by mass transfer, which is affected by the characteristics of the gas diffusion layer and catalyst layer. The voltage loss caused by mixed potential and hydrogen crossover will be discussed in detail in Chapter 7. The activation loss, ohmic loss, and mass transfer loss can be calculated from the charge transfer resistance, ohmic resistance, and mass transfer resistance, which can be determined by EIS measurement and simulation. 

Temperature = 80°C, Pressure = 300 kPa, both gases fully saturated. Calculate cell ionic resistance and hydrogen crossover for two different membranes, namely Nafion 112 and 117. 

Thicker electrolytes than what is normal for PEMFCs are used. Clearly this will reduce fuel crossover, though it will also increase the cell resistance. There is a compromise to be found, and in the DMFC that optimum is with a somewhat thicker electrolyte than for hydrogen fuel cells. The thickness membrane normally used by DMFC developer is between 0.15 and 0.20 mm, whereas for a hydrogen PEMFC it would be between 0.05 and 0.10mm. ... 

This result may be due to the protons inside the connected 3D channels of analcime, obtained after H-form transformation. Therefore, these protons act as bridges for the proton transport, thus increasing the proton conductivity. Furthermore, the incorporation of solid particles in the hybrid membrane increases the resistance to hydrogen diffusion through the membrane, lowering its fuel crossover in PEMFC applications. Nevertheless, at 7 >90°C, the sPEEK/Analcime membrane loses water fast with a consequent depletion of proton conductivity [151]. 

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