Effect of ionomer content on fuel cell performance and mass transport under different Pt loadings: Experimental and molecular simulation study

The ionomer within the catalyst layer of proton exchange membrane fuel cells plays a crucial, yet ambivalent, role in facilitating proton conduction while impeding oxygen transport. Its judicious optimization is pivotal for balancing performance and cost. Herein, we systematically investigate the impact of the ionomer content on the output performance and mass transport properties under two representative cathode Pt loadings (0.48 and 0.12 mg cm−2), employing a strategy that couples experimental characterization with molecular dynamics simulations. A key contribution is the discovery that the optimal I/C ratio is not a fixed value but is distinctly Pt-loading dependent, shifting from 0.6 for conventional Pt loading to 0.4 for low Pt loading. Insufficient ionomer leads to an incomplete proton-conduction network, limiting catalyst utilization, whereas excessive ionomer results in the drastic (>170%) increase in oxygen transport resistance, inducing severe concentration polarization at high current densities. Crucially, the optimized low Pt electrode achieves the peak power density (0.82 W cm−2) nearly identical to conventional Pt counterpart (0.84 W cm−2), demonstrating a viable path toward significant cost reduction without the performance penalty. Microscopic simulations further reveal that increasing ionomer content thickens the ionomer film, thereby hindering bulk diffusion, and exacerbates sulfonate poisoning