Oxygen Transport Loss in the Gas Diffusion Layer

The equations in the section CCL Polarization Curves of Chapter 4 contain the oxygen concentration ci at the CCL/GDL interface. This concentration is, itself, related 

Dividing both sides of this relation by c9, finally results in 

The polarization curve, which takes into account the oxygen transport loss in the GDL, results from the substitution of Equation 5.41 into the CL polarization curves obtained in the previous sections. Consider first the simplest Tafel equation. Equation 

FIGURE 5.5 A schematic of the oxygen concentration profile through the GDL and CCL thicknesses. 

the second logarithm describes the potential loss due to oxygen transport in the GDL. In the dimensional form, this equation reads 

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Equation 4.189 can be used for the fitting at experimental polarization curves, provided that (i) the oxygen stoichiometry is large and (ii) the potential loss caused by oxygen transport in the GDL is minimal. The validity of the second condition is usually not known a priori. However, it can be easily relaxed by incorporating the respective transport loss into the polarization equation, as discussed in the section Oxygen Transport Loss in the Gas-Diffusion Layer in Chapter 5. 

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