Axial N Disrupt d-π Conjugation of Asymmetric Fe─Cu Dual-Atom Enhances CO₂ Electroreduction

Precise spin-polarization modulation of electronic structures in dual single-atomic sites (DSAS) is critical yet challenging for boosting electrocatalytic CO₂ reduction reaction (CO₂RR). Here, we report a Fe 3d-orbital spin-polarization regulation strategy through constructing an axial N-bridge bond and adjacent Cu-N₄ on hollow bilayer Fe-Cu dual single-atom catalysts (HFeCu-N-C DSACs). Experimental and theoretical evidence demonstrate that the axial N-bridge bond disrupts the D_4h symmetry of the Fe-N₄ active center, resulting in the rearrangement of Fe 3d electrons and thereby breaking the surface d-π conjugate structure (Fe-N-C). Meanwhile, the Jahn-Teller effect of the adjacent Cu-N₄ sites is inferred to potentially regulate the spin state of Fe sites, which facilitates the transition from low-spin (↓↑, ↓↑, ↑, _, _) to high-spin (↑, ↑, ↑, ↑, ↑). Therefore, the increased population of unpaired electrons on $d_{z^2}$ d_xz, and d_yz orbitals is pivotal for stabilizing the π^* orbitals of CO₂ and activating CO₂, thus enhancing the intrinsic reaction activity of HFeCu-N-C DSACs. The as-made HFeCu-N-C DSACs present a superior faraday efficiency (FE) of a highly selective CO product, 99.32% @ -0.5 V (vs. RHE), and long-term durability. This work provides a new strategy for tuning the electronic spin state of DSACs to boost CO₂RR electrocatalytic performance.