Mitigating Mass Transport Capacity in Ultralow Pt PEMFCs via Optimization of Ionomer Coverage and Pt Utilization

The development of high-performance, low-platinum proton exchange membrane fuel cells (PEMFCs) is crucial for sustainable energy conversion. However, this goal is hindered by mass transport limitations and inefficient Pt utilization at ultralow loadings. This work addresses these challenges by engineering a nitrogen-functionalized carbon support (N-HSC-0.1) with an optimized pore structure to adjust the ionomer distribution and Pt utilization in the catalyst layer. The optimized support features abundant pyridinic-N species and a tailored pore structure, with a 38.7% reduction in micropore volume while preserving mesoporous networks. These characteristics promote the uniform dispersion of ultrafine Pt nanoparticles (2.3 nm) and enhance the ionomer distribution on the catalyst surface. In situ ATR-FTIR spectroscopy suggested enhanced reaction kinetics via a bridge-assisted pathway. When implemented in a membrane electrode assembly with an ultralow cathode Pt loading, MEA-Pt/N-HSC-0.1 delivered a peak power density of 0.971 W cm^-2 at the total Pt loading of 0.05 mg_Pt/cm², with a 33.7% increase over the commercial benchmark. Quantitative analysis of double-layer capacitance further confirmed a more favorable ionomer coverage on the optimized support, minimizing the ionomer poisoning of Pt sites. This study demonstrates the collaborative benefit of carbon support modification in simultaneously enhancing oxygen reduction reaction kinetics and mass transport, providing a practical strategy for advanced ultralow Pt PEMFCs.