Biomimetic Square Pyramidal N₁-Fe-N₄ Single Sites with Optimized Electron Distribution for the Efficient Oxygen...

Single atom iron-nitrogen-carbon (Fe-N-C) catalysts with a planar Fe─N₄ structure are widely investigated as potential alternatives to platinum-based materials for oxygen reduction reaction (ORR), while they still suffer from the imperfect adsorption and activation of reaction intermediates, limiting their reduction efficiency. Herein, a Fe single-atom catalyst with a biomimetic square pyramidal N₁-Fe-N₄ site supported by honeycomb-like porous carbon (SA-FeN₅/HPC) is successfully prepared by a supramolecular confinement-pyrolysis strategy. Theoretical calculations unveil that the introduction of spatially axial N ligands effectively regulates the charge redistribution around the planar Fe─N₄ active centers and confers Fe active moieties with appropriate adsorption strength for intermediates, thereby resulting in accelerated ORR kinetics. Consequently, the oversaturated SA-FeN₅/HPC catalyst showed excellent electrocatalytic ORR activity, achieving a half-wave potential of 0.93 V versus RHE and superior durability. Moreover, Zn-air batteries with SA-FeN₅/HPC as the cathode electrocatalyst displayed excellent performance, demonstrating great potential for practical application. This work paves the way for the design and development of high-coordination single-atom electrocatalysts.