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 (E1/2) 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.