Regulating Spin Polarization via Axial Nitrogen Traction at Fe-N Sites Enhanced Electrocatalytic CO Reduction for Zn-CO Batteries.

Single Fe sites have been explored as promising catalysts for the CO reduction reaction to value-added CO. Herein, we introduce a novel molten salt synthesis strategy for developing axial nitrogen-coordinated Fe-N sites on ultrathin defect-rich carbon nanosheets, aiming to modulate the reaction pathway precisely. This distinctive architecture weakens the spin polarization at the Fe sites, promoting a dynamic equilibrium of activated intermediates and facilitating the balance between *COOH formation and *CO desorption at the active Fe site. Notably, the synthesized FeN, supported on defect-rich in nitrogen-doped carbon (FeN@DNC), exhibits superior performance in CORR, achieving a Faraday efficiency of 99 % for CO production (-0.4 V vs. RHE) in an H-cell, and maintaining a Faraday efficiency of 98 % at a current density of 270 mA cm (-1.0 V vs. RHE) in the flow cell. Furthermore, the FeN@DNC catalyst is assembled as a reversible Zn-CO battery with a cycle durability of 24 hours. In situ IR spectroscopy and density functional theory (DFT) calculations reveal that the axial N coordination traction induces a transformation in the crystal field and local symmetry, therefore weakening the spin polarization of the central Fe atom and lowering the energy barrier for *CO desorption.