Modulation of Spin States in the Second Coordination Shell of Single‐Atom Electrocatalysts for Efficient Water Oxidation

ABSTRACT The catalytic performance of single‐atom catalysts (SACs) is critically shaped by their local chemical environment, yet the role of structural features beyond the first coordination shell remains poorly understood. Here, we employ Ir single‐atom‐loaded ZnCo 2 O 4 spinel oxides with calcination‐tuned Co spin‐state distributions to elucidate their impact on the oxygen evolution reaction (OER). We find that the OER activity shows a quasi‐linear correlation with the fraction of high‐spin (HS) Co 3+ ions in the second coordination shell. Among the series, Ir–ZCO–600, dominated by HS Co 3+ , delivers outstanding OER performance, requiring overpotentials of only 256 mV (alkaline) and 302 mV (acidic) to achieve 10 mA cm −2 current density. Density functional theory calculations show that the Ir‐Co‐HS model exhibits a lower Ir d‐band center and weaker *OOH binding than the corresponding IS and LS models, consistent with the experimentally observed activity trend. These results suggest that the spin state of Co in the second coordination shell may serve as a relevant descriptor for tuning the catalytic behavior of oxide‐supported SACs.