Increasing the density of Fe–N₄ sites in Fe–N–C materials is pivotal for enhancing the kinetics of the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). Fe utilization is a vital parameter for the Fe–N–C catalyst evaluation, but it shows a tendency to decrease with increasing density of the Fe–N₄ sites. Herein, dense edge Fe–N₂₊₂ sites are deposited in the outermost and subsurface layers of a surface-rich pyridinic-N carbon substrate (Fe_g–NC/Phen). We have demonstrated that the surface-rich pyridinic-N carbon substrate is more favorable to form surface Fe–N₂₊₂ sites with superior intrinsic activity. The surface Fe–N₄ sites can improve both the site density and Fe utilization, while shortening the transport pathways of protons and O₂ effectively. By means of these structural advantages, Fe_g–NC/Phen can exhibit a high current density of 0.046 A cm⁻²@0.9 V_iR-free and a high peak power density (P_max) of 1.53 W cm⁻² in 2 bar H₂–O₂ PEMFCs, and outperform almost all the reported M–N–C catalysts. This outstanding performance will inspire relevant research in the distribution of active sites. Moreover, it requires particular attention to obtain a viable solution to performance durability in fuel cells.

中文翻译：

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抓住气态 Fe2+ 以致密化 O2 可接近的 Fe-N4 位点，用于高性能质子交换膜燃料电池

_{增加 Fe-N-C 材料中 Fe-N 4}位点的密度对于提高质子交换膜燃料电池 (PEMFC) 中氧还原反应 (ORR) 的动力学至关重要。Fe利用率是Fe-N-C催化剂评估的一个重要参数，但它显示出随着Fe-N ₄位点密度的增加而降低的趋势。在此，密集的边缘 Fe-N _{2+2位点沉积在富含表面的吡啶-N 碳基底 (Fe g} -NC/Phen)的最外层和次表层中。我们已经证明，富含表面的吡啶-N碳底物更有利于形成具有优异本征活性的表面Fe-N _2+2位点。表面 Fe-N ₄位点可以提高位点密度和Fe利用率，同时有效缩短质子和O ₂的传输路径。借助这些结构优势，Fe _g -NC/Phen 可以表现出 0.046 A cm ^-2 @0.9 V _iR-free的高电流密度和1.53 W cm ^-2 in 2 bar的高峰值功率密度 ( P _max ) H ₂ -O ₂ PEMFCs，并且优于几乎所有报道的 M-N-C 催化剂。这种出色的表现将激发对活跃站点分布的相关研究。此外，需要特别注意获得燃料电池性能耐久性的可行解决方案。