Regulating the N-Coordination Structure of Fe-Fe Dual Sites as the Electrocatalyst for the O 2 Reduction Reaction in Metal-Air Batteries.

Iron-nitrogen coordinated catalysts are regarded as efficient catalysts for the oxygen (O 2 ) 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 Fe 2 sites (i.e., Fe 2 -N 6 -C and Fe 2 -N 4 -C) on the performance of the ORR. The half-wave potential ( E 1/2 ) of Fe 2 -N 6 -C is 0.880 V vs RHE, outperforming that of the tetracoordinate Fe 2 -N 4 -C (0.851 V) and commercial Pt/C (0.850 V) in alkaline electrolytes. The Fe 2 -N 6 -C-based zinc-air battery delivers a maximum power density of (258.6 mW/cm 2 ) and superior durability under 10 mA/cm 2 . Theoretical calculations unveil that the moieties of Fe 2 -N 6 profits the d-electron rearrangement of the Fe 2 sites. The electronic and geometrical structure of Fe 2 -N 6 promotes the O 2 molecules adsorbed on the Fe 2 site and reduces the dissociation energy barrier of O 2 , benefiting fracture of O-O bonds and acceleration of the transformation of O 2 to *OOH (the first step of the ORR process). Such exploration of modulating the local N-coordination environment of Fe 2 dimers paves an in-depth insight to design and optimize dual-atomic catalysts.