Alleviating the Misalignment of Fe Single Sites Relative to Triple-Phase Interfaces to Achieve High Performance Fuel...

Single-atom catalysts (SACs), represented by Fe─N─C, are promising alternatives to Pt in proton exchange membrane fuel cells (PEMFCs). However, the molecular-scale misalignment of the SACs at the triple-phase interfaces (TPIs) has led to extremely low atomic efficiency, making it difficult to translate the high activity of SACs into the actual cell performance. Therefore, the design of the catalyst layer structure to increase the density of reactant-accessible single sites is crucial for the application of SACs in PEMFCs. Here, we report tailored catalyst layer structure induced by hierarchical porous Fe─N─C_pot catalysts with tuned surface hydrophilicity. Coarse-grained molecular dynamic (MD) reveals macropores and tuned surface hydrophilicity act as molecular-level "on-switches" that pull Nafion/water domains deep inside, collapsing the classic transport bottlenecks for both O₂ and H₃O⁺. Combinatory spectroscopic evidence confirms the superiority of the structure in forming continuous mass transfer channels, thereby increasing site utilization of Fe by 80%. Exceptional P_max at 1581 mW cm^-2 is achieved, and capable of sustaining 60k AST with 63% performance retained. This study establishes the first design rule that links pore hierarchy and surface chemistry to TPI activation.