Engineering a Nanoflower-like Fe-N-C Cathode with Hierarchical Porosity to Mitigate Oxygen Transport Resistance in PEMFCs

Fe-N-C oxygen reduction catalysts, while promising as alternatives to costly platinum in proton exchange membrane fuel cells (PEMFCs), suffer from significant oxygen transport resistance. This resistance stems from the predominant microporosity of conventional catalysts, which restricts oxygen access to active sites and exacerbates electrode flooding. To overcome this bottleneck, we report a morphology-engineering strategy by constructing a nanoflower-like Fe-N-C catalyst composed of stacked ultrathin nanosheets with a hierarchically porous architecture. Electron microscopy and mercury intrusion porosimetry confirm that this unique structure features interconnected ultrathin nanosheets and abundant macropores, which collectively establish efficient gas-transport pathways. As a result, the oxygen transport resistance is dramatically reduced from 56 to 9.08 s m –1, while enhanced hydrophobicity improves water management within the electrode. When integrated into a practical PEMFC, the nanoflower-like structured catalyst achieves a peak power density of 1.15 W cm – 2, significantly outperforming the conventional catalyst (0.725 W cm – 2 ). This work demonstrates that rational structural regulation can effectively address mass-transport limitations, providing a feasible route toward high-performance, non-precious metal cathode catalysts for PEMFCs.