Remarks to the Sections

If the cell current is high, the polarization curves of CLs are similar, when either feed or ion transport is insufficient. In both the cases, the curve exhibits doubling of the Tafel slope (Equations 4.88 and 4.134). This makes it difficult to distinguish the physical origin of this doubling, by measuring the polarization curve only. 

Further, in the CCL with poor oxygen transport, the thickness of the conversion domain Id is proportional to D, Equation 4.91, and this domain is located at the 

FIGURE 4.22 A Tafel plot for the electrode and the characteristic current densityy.  

CCL/GDL interface. In the CCL with poor ionic transport, la is proportional to the ionic conductivity op. Equation 4.154, and the conversion domain resides at the membrane interface. It is expected that the long-term degradation processes run faster in the conversion domain. Thus, post mortem pictures of the CCL may give a hint on the prevailing regime of CCL operation. 

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