Exploring ionomer distribution strategies within catalyst layers for high-performance proton exchange membrane fuel cells

Proton exchange membrane fuel cell (PEMFC) performance is strongly affected by ionomer distribution within catalyst layers (CLs). In this study, five catalyst-coated membrane (CCM) configurations, with additional ionomer layers, uniform ionomer distribution, and gradient ionomer distribution, are investigated to assess the impact of these structural modifications on electrochemical behavior. The results show that introducing a single ionomer layer between the membrane and CL improves interfacial contact and proton transport, whereas excessive ionomer layers increase transport resistance. For uniformly distributed ionomer, ionomer-to-carbon support (I/C) mass ratios from 0.75 to 1.25 reveal a balance between proton conduction and transport resistance, with the optimum performance at I/C = 1.00. Based on this, a gradient structure with I/C = 1.25 near the membrane and I/C = 1.00 toward the gas diffusion layer achieves the best performance, reaching 1.44 W/cm 2 at 2.5 A/cm 2 , with increasing trend maintained toward higher current densities.