Optimizing the Mass Transport and Atomic Fe Intrinsic Activity to Achieve High-Performing Fuel Cells

Due to the insufficient three-phase interfaces and high oxygen transport resistance, the high intrinsic activity cannot be sufficiently utilized in practical proton-exchange membrane fuel cells (PEMFCs). The efficient transport of protons and reactants within the catalyst layers (CL) is largely influenced by the pore structure of the carbon support, hosting both metal sites and ionomers. Herein, we constructed a porous nanosheet Pt-free catalyst (Fe_AC-N-SC) by selecting a highly nitrogen-rich GT-18 MOF via salt template to realize the improvement of PEMFC performance. The simulation and experimental results illustrate that the microstructure can benefit the homogeneous dispersion of ionomers and facilitate oxygen mass transport in the cathode CL, ultimately achieving efficient utilization of catalytic activities. The PEMFC assembled from the Fe_AC-N-SC catalyst exhibited an outstanding peak power density of 1.1 W cm^–2 and durability (61% power density retention after AST-30k cycles and 92% voltage retention after 100 h OCV test). DFT results demonstrated that the introduction of Fe atomic clusters can boost the intrinsic activity of ORR by regulating the electron distribution of single-atomic Fe–N₄ sites. This study reveals the relationship between CL design, mass transport, and electrode microstructure, which successfully exploits the intrinsic activity of cathode catalysts and enhances the power generation capacity.