Active-Sites-Integrated Hierarchical Porous Nanofibers for Improved Oxygen Reduction in Fuel Cells

M-N-C catalysts have emerged as a promising class of non-precious electrocatalysts for accelerating the kinetically sluggish oxygen reduction reaction (ORR). Nevertheless, their practical application in proton exchange membrane fuel cells (PEMFCs) faces significant challenges due to the complex reaction environment and stringent mass transport requirements, which place stringent demands on the structural design of electrocatalysts. Here, a strategy is proposed to construct a self-supporting membrane of zeolitic imidazolate framework-connected nanofibers, serving as an integrated substrate to cooperatively optimize active sites and mass transfer channels. The nanofiber-shaped electrocatalysts (Fe_SA/AC-N-PCNFs) with hierarchical porous structure can achieve the anchor of well-dispersion atomically Fe-N₄ and Fe cluster. The Fe_SA/AC-N-PCNFs, as a catalyst layer of cathode, to assemble PEMFC and realized 43% enhanced maximum power density compared with traditional spraying. The finite element simulation proved that the self-supported porous fiber structure effectively reduced the oxygen diffusion resistance in the electrode. This work established an effective enhancement strategy for the M-N-C electrocatalysts from the structure engineering, which opens new avenues for the design and manufacture of high-performance fuel cell electrocatalysts.