layers are quite thin and dense which can hinder species
transport, particularly, air diffusion in the cathode and can
severely deteriorate the cell performance [24,28]. This problem
can partially be alleviated by carefully controlling the
amount of ionomer in the cathode catalyst layer. Here, the
performance of the MEAs with ionomer contents of 5, 7, 10
and 12 wt.% in the cathodes was compared, and the results are
shown in Fig. 13(a). When the ionomer content is very low
such as 5 wt.% or very high such as 12 wt.%, the single-cell
performance is quite poor and peak power density is lowered
to 90e100mW cm2. A percentage of ionomer that is too