Catalyst Layer Pore Design Based on Oxygen Mean Free Path for Low-Pt HT-PEMFCs

Mass transport limitations critically restrict the performance of high-temperature proton exchange membrane fuel cells (HT-PEMFCs), primarily due to the mismatch between the oxygen mean free path and the pore size of conventional catalyst layers (CLs). This mismatch leads to severe Knudsen diffusion, particularly under low platinum (Pt) loadings. In this work, the mean free path of oxygen in the 100°C-200°C range is calculated to determine an optimal pore size of approximately 200 nm. Correspondingly, cumulative macropores are introduced into the CL using a sacrificial templating strategy, thereby enabling efficient gas diffusion. This mean-free-path-informed design promotes molecular diffusion over restricted Knudsen diffusion, reducing oxygen transport resistance by 61.2% at a low Pt loading of 0.14 mg_Pt cm^-2. As a result, peak power densities of 634 and 920 mW cm^-2 are achieved at Pt loadings of 0.14 and 0.43 mg_Pt cm^-2, respectively. The optimized electrode delivers an outstanding rated power density of 4.53 W mg_Pt ^-1, representing a 5.8-fold enhancement compared with conventional commercial CLs. These findings demonstrate that a mean-free-path-guided pore architecture offers an effective strategy for reducing Pt loading and advancing the commercialization of HT-PEMFCs.