Breaking the ORR Trade-Off via Mg-Steered Fe-N₄ Pyridinic Conversion

Single-atom Fe sites coordinated by pyrrolic nitrogen (Fe-N_pyrr-C) are highly active for the oxygen reduction reaction (ORR) but suffer from rapid demetalization-induced deactivation. Here, we overcome this limitation via a Mg-assisted sacrificial templating strategy that precisely reconstructs Fe-N₄ coordination, driving partial conversion of unstable pyrrolic-N to robust pyridinic-N ligands. The resulting Fe(Mg)-N-C(1) catalyst exhibits exceptional ORR performance (half-wave potential E_1/2 = 0.91 V) and outstanding durability, retaining 95.2% of its initial current after 55 h, surpassing both Fe-N-C and Pt/C. In Zn-air batteries, it enables stable operation for > 530 h (peak power density: 271 mW cm^{- 2}). This work demonstrates that enriching pyridinic-N-coordinated Fe-N₄ sites simultaneously enhances activity and suppresses demetalization, offering a general coordination-engineering strategy to unify activity and stability in Fe-N-C electrocatalysts.