low will have insufficient proton conductivity and decreased
ionomerecatalyst interfacial contact. On the other hand, a too
high ionomer content will cause the blockage of small pores
and will decrease the total porosity of the catalyst layer [18].
The diameters of the semi-circle arcs are substantially larger
for the MEAs containing 5 and 12 wt.% cathode ionomer
compared with the other two, as shown in the full-cell EIS
spectra in Fig. 13(b). This suggests a high charge transfer
resistance arising from the either poor ionomerecatalyst
interface or limited availability of reactants due to the inadequate
cathode structure.