Bridging the gap between material design and device performance for non-PGM cathode electrocatalysts

Integrating Platinum Group Metal-free (PGM-free) catalysts into High-Temperature Proton Exchange Membrane Fuel Cells (HT-PEMFCs) is hindered by phosphoric acid flooding and poor durability. This study optimizes the electrode-electrolyte interface for a binder-free electrode using a Fe-N-C catalyst. While commercial high-doping-level polybenzimidazole (PBI) membranes revealed mass-transport bottlenecks, an undoping/redoping strategy combined with thermal-mechanical stabilization resolved the limitations. Results demonstrate that the triple phase boundary is optimized through spontaneous capillary acid transfer from the calibrated membrane rather than supplemental addition. Furthermore, there is a critical volumetric utilization limit, beyond which non-linear oxygen diffusion resistance outweighs benefits of additional active sites. The optimized MEA demonstrated operational range up to 0.6 A/cm 2 , maintaining stable performance at 180 °C for over 12 days (approx. 300 h) under continuous operation. This work establishes a design rule for PGM-free HT-PEMFCs, where a controlled, self-regulating acid inventory is a prerequisite for translating high intrinsic catalyst activity into stable, high-current-density cell performance.