Geminal Cl-Bridged Dual-Fe-Atom Catalyst for Efficient and Stable Oxygen Reduction Reaction

Atomically dispersed iron-nitrogen-carbon (Fe-N-C) catalysts hold great promise for the oxygen reduction reaction (ORR), yet their structural instability under operational conditions restricts their practical application. In this study, we identify that electrochemical degradation of the Fe-N-C catalyst stems from a dynamic disparity between the Fe-N and Fe-O bonds during ORR, leading to pronounced Fe demetallization. Guided by this mechanistic insight, we synthesize a dual-Fe-atom catalyst featuring a well-defined N₃-Fe-Cl-Fe-N₃ structure. Combined theoretical and experimental results reveal that the bridging Cl atom induces charge redistribution and downshifts the Fe d-band center, thereby regulating the adsorption and activation of oxygenated intermediates. The electronic energy gained by Fe-O bonding during ORR triggers a dynamic reconfiguration of the N₃-Fe-Cl-Fe-N₃ moieties, which in turn reinforces structural Fe-N and Fe-Cl bonds while attenuating hyperergic Fe-O interactions. Such a dynamic process enables adaptable coordination and accelerates protonation kinetics, underscoring the cooperativity of metal coordination at dual-Fe centers and thereby ensuring electrochemical robustness. The resulting dual-Fe-atom catalyst demonstrates exceptional ORR stability with minimal Fe leaching (16.4 μg L^-1 after 20000 accelerated durability cycles) and retains 88% current over 160 h of operation. This catalyst delivers over 1000 h of stable performance in a zinc-air battery with a negligible overpotential increase. These findings deepen the mechanistic understanding of Fe demetallization in the Fe-N-C catalyst under operando ORR conditions, paving the way for the rational design of robust noble-metal-free ORR electrocatalysts.