Synergistic Catalysts with Fe Single Atoms and Fe3C Clusters for Accelerated Oxygen Adsorption Kinetics in Oxygen Reduction Reaction.

The design of cost-effective and efficient catalysts based on transition metal-based electrocatalysts for the oxygen reduction reaction (ORR) is crucial yet challenging for energy-conversion devices like metal-air batteries. In this work, we present a cost-effective strategy for preparing catalysts consisting of single-atomic Fe sites and Fe3C clusters encapsulated in nitrogen-doped carbon layers (FeSA-Fe3C/NC). The FeSA-Fe3C/NC electrocatalyst demonstrates outstanding ORR performance in alkaline electrolytes, achieving a high half-wave potential (E1/2 = 0.902 V), 4e- ORR selectivity, and robust methanol tolerance. The exceptional ORR catalytic performance is credited to the relatively substantial specific surface area and the optimal arrangement of active sites, including atomically dispersed Fe-N sites and synergistic Fe3C clusters. In situ spectroelectrochemical characterization and theoretical calculations verify that Fe3C clusters disrupt the symmetric electronic structure of Fe-N4, optimizing 3d orbitals of Fe centers, thereby accelerating O-O bond cleavage in *OOH to boost ORR activity. Furthermore, a zinc-air battery constructed with FeSA-Fe3C/NC demonstrates excellent potential in energy storage application, yielding a maximum power density of 151.3 mW cm-2 and robust cycling durability surpassing that of commercial Pt/C catalysts. This study establishes a cost-effective route for producing metal-based carbon electrocatalysts with exceptional performance using environmentally friendly raw materials.