Symmetry-Broken FeN3-O on a Negatively Charged Carbon Host: Dual Modulation of Electronic Structure and Interfacial Field for Robust Oxygen Reduction

Abstract

Fe-N-C catalysts, especially Fe-N4 moieties, attract great promise for boosting the oxygen reduction reaction (ORR). However, they still suffer from sluggish reaction kinetics due to the unsatisfactory adsorption energy of intermediates resulting from the symmetrical distribution of electrons in Fe-N4 active sites. Strategies of single-atom catalysis have primarily focused on tailoring the local coordination of metal centers.Here, we advance this approach by demonstrating that the intrinsic properties of the support can be harnessed as active, cooperative components. We report a symmetrybroken O-Fe-N3 moiety anchored on a hierarchical porous carbon sphere with a negatively charged surface. This "smart" carrier establishes an interfacial electric field that facilitates O2 activation and electrostatically repels harmful intermediates (e.g., H 2 O 2 ), concurrently enhancing activity and stability. Theoretical calculations also reveal that the resultant structure can trigger energy level splitting of Fe 3d orbital, thereby regulating the hybridization of center Fe 3d orbital. Combined with the optimized electronic structure of the Fe site, the catalyst achieves an exceptional halfwave potential of 0.90 V vs. RHE and remarkable durability. A flexible Zn-air battery using this catalyst delivers a high power density of 249 mW cm⁻². This work establishes a new "active site-smart carrier" synergistic design principle, opening a distinct avenue for next-generation electrocatalysts.