Dipoles Effect in Fe-N-C Catalyst by High-Energy p Orbitals for Enhanced Acidic Oxygen Reduction Reaction

Tailoring the coordination sphere of the metal atoms represents a highly promising strategy to modulate Fe single-atom catalysts. However, modifications in the first coordination shell often led to reduced catalyst stability, while those in the second shell exhibit limited efficacy in enhancing catalytic activity. In this work, we introduce N-group elements to engineer N-X_VA dipoles, leveraging their characteristic "high density near the source but sparse at a distance" electric field to modulate the 3d orbitals of Fe. The introduction of N-X_VA dipoles enhances the polarization of Fe single atoms, especially, with the increase of the periods, Fe 3d orbitals rearrangement occurs, resulting in an optimized binding energy for OH* intermediates that approaches the peak of the volcano plot. The resulting FeN4-Sb/C catalyst exhibits a high half-wave potential of 0.833 V and a degradation of only 18 mV after 30,000 cycles accelerated durability testing, superior to commercial Pt/C. Furthermore, PEMFCs assembled with the FeN4-Sb/C catalyst deliver impressive performance (H₂-O₂: 1.1 W cm^-2; H₂-air: 0.6 W cm^-2), outperforming nearly all recently reported single-atom and dual-atom catalysts. This work not only reveals the periodic trend of dipole-modulated ORR activity in Fe single atom catalysts, but also demonstrates its potential for application in PEMFCs.