Hydrogen crossover fuel cell voltage

Figure 1.5 The slope of E ath versus log /orr through the fuel-cell-relevant potential range has an apparently constant value near RT/F (measured current density, here designated i, is corrected for hydrogen crossover current, designated i and the measured cell voltage is ir-corrected to provide the cathode potential E) [Neyerlin et al., 2006].

Vilekar, S. A., Datta, R. (2010,). The effect of hydrogen crossover on open-circuit voltage in polymer electrolyte membrane fuel cells. Journal of Power Sources, 795(8), 2241—2247. 

Figure 17.17 presents selected points of polarization curves as function of contact pressure for MEAs from three HT-PEM MEA suppliers operating with H2 and air. From Fig. 17.17a, b, the fuel cells behavior of Celtec P2100 MEAs exhibit a strong voltage drop at OCV and low current densities with increasing contact pressure. This is caused by an increase in hydrogen crossover and electrical short-circuit as shown in Fig. 17.16b, d. From Fig. 17.17c can be deduced that the Dapozol -G55 MEA fuel cell performance is nearly immune against contact pressure increase. The OCV is nearly constant in the whole range of contact pressure as hydrogen crossover has also been (Fig. 17.16c). At higher...

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. 

The fuels crossover and internal currents are equivalent that is, they both contribute voltage loss owing to a small equivalent cell current. However, fuel crossover and the internal cmrents have a different physical effect on fuel cell. In the internal current, the oxidation reaction has already taken place and the electrons are short-circuited through electrolyte. In case of fuel crossover such as hydrogen permeation from the anode to the cathode, first the fuel crosses over from the anode to the cathode and then oxidation and reduction reactions occur near the cathode. With reactant crossover and internal currents, a small amount of current is lost. In both cases, the current losses are similar to activation losses, and hence as an approximation, the current and potential behavior can be represented by the Tafel law. 

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