Axial O‐Bridge Bond Induced Electron High‐Spin and Destroyed d–π Conjugation of Fe Single‐Atom Sites for Enhanced CO ₂ Electroreduction

ABSTRACT Fine‐tuning the electronic structure of single‐atom sites (SAS) in catalysts is crucial yet challenging for improving electrocatalytic CO 2 reduction (CO 2 RR). Herein, we construct axial O‐bridge bond coordinated Fe single‐atoms in a nitrogen‐doped carbon‐skeleton catalyst (O─Fe─N 4 SACs) derived from ZIF‐8, achieving Fe 3d‐orbital spin regulation and destroyed d–π conjugation. Experimental and theoretical results reveal that the axial O‐bridge bond breaks the D 4h symmetry of the Fe─N 4 active center, resulting in the rearrangement of the spinning electron in the Fe 3d orbital to disrupt surface d–π conjugation of the Fe─N─C structure. Meanwhile, the Jahn‐Teller effect of the adjacent axial O‐bridge bond can effectively induce the Fe spin‐state transition from medium‐spin ( ↓↑ , ↓↑ , ↑ , ↑ , _) to high‐spin ( ↑ , ↑ , ↑ , ↑ , ↑ ). Therefore, the decreased population of paired electrons on d orbitals is pivotal for activating *COOH intermediates, thus greatly enhancing the electrocatalytic CO 2 RR reaction activity. The optimized catalyst presents a superior faraday efficiency (FE, 98.67% at ‐0.7 V) during CO 2 RR process, which is 5.6‐fold higher than that of non‐axial coordinated Fe─N 4 SACs. This work presents a new insight into electronic spin state regulation through the destroyed d–π conjugation strategy of D 4h symmetry SACs for enhancing electrocatalytic CO 2 RR performance.