Regulating the N-Coordination Structure of Fe–Fe Dual Sites as the Electrocatalyst for the O₂ Reduction Reaction in Metal–Air Batteries

Abstract

Iron-nitrogen coordinated catalysts are regarded as efficient catalysts for the oxygen (O₂) reduction reaction (ORR), wherein the coordination environment of Fe sites is critical to the catalytic activity. Herein, we explored the effect of the nitrogen-coordination structure of dual-atomic Fe₂ sites (i.e., Fe₂-N₆-C and Fe₂-N₄-C) on the performance of the ORR. The half-wave potential (<i>E</i>_1/2) of Fe₂-N₆-C is 0.880 V vs RHE, outperforming that of the tetracoordinate Fe₂-N₄-C (0.851 V) and commercial Pt/C (0.850 V) in alkaline electrolytes. The Fe₂-N₆-C-based zinc-air battery delivers a maximum power density of (258.6 mW/cm²) and superior durability under 10 mA/cm². Theoretical calculations unveil that the moieties of Fe₂-N₆ profits the d-electron rearrangement of the Fe₂ sites. The electronic and geometrical structure of Fe₂-N₆ promotes the O₂ molecules adsorbed on the Fe₂ site and reduces the dissociation energy barrier of O₂, benefiting fracture of O-O bonds and acceleration of the transformation of O₂ to *OOH (the first step of the ORR process). Such exploration of modulating the local N-coordination environment of Fe₂ dimers paves an in-depth insight to design and optimize dual-atomic catalysts.