Precise Axial Coordination Tailors the Spin State of Single‐Atom Iron for Boosted Oxygen Reduction Electrocatalysis

ABSTRACT Modulating the electronic spin state of metal centers is a powerful strategy for optimizing single‐atom catalysts (SACs), yet achieving this through precise synthesis remains a grand challenge. Here, we develop a controlled one‐step pyrolysis that enables the direct and uniform grafting of axial Fe‐X (X = F, Cl, Br, I) moieties onto a nitrogen‐doped carbon (NC) support, thereby establishing a definitive link between the spin state of iron and the oxygen reduction reaction (ORR) activity in Fe‐N‐C catalysts. This synthetic control allows us to experimentally validate theoretical predictions: axial chlorine coordination induces a high‐spin Fe(III) state, which is critical for optimizing oxygen intermediate adsorption and lowering the rate‐determining energy barrier. This spin‐state engineering translates directly to top‐tier performance. The FeN 4 Cl catalyst exhibits an outstanding half‐wave potential of 0.910 V, surpassing commercial Pt/C. Furthermore, when employs in a zinc‐air battery, it delivers a high specific capacity of 794 mAh g Zn −1 and exceptional long‐term stability for over 700 h. This study demonstrates that rational catalyst design through atomic‐level spin‐state control is a clear and precise pathway to next‐generation electrocatalysts.