Nitrogen-Doped Carbon-Encapsulated FeCo Alloy Nanostructures with Surface-Dangling Fe(Co)‑N<i>_x</i> Active Sites for Oxygen Reduction in Alkaline and Acid Media

Simultaneously increasing the activity and stability of the transition metal-based catalysts is critical for nonprecious metal catalysts toward oxygen reduction reaction (ORR). Herein, FeCo alloy nanoparticles encapsulated in nitrogen-doped carbon (NC) materials with surface-dangling M-Nx active sites were fabricated, and the corresponding electrocatalytic performance was carefully investigated toward ORR in both alkaline and acid media. The coexistence of M-Nx active species (Co5.47N or FeN0.0324) and FeCo alloy makes the ORR reactivity strongly enhanced compared to the counterparts with only M-Nx or FeCo species. Density functional theory calculations clearly reveal that the synergistic effect between FeCo, Fe-Nx, and NC can induce the hybridization effect between d orbitals of Fe/Co and p orbitals of N/C atoms, and thus favor the desorption of *OH intermediates. Therefore, the FeN0.0324-FeCo@NC nanocatalyst with abundant mesopores and macropores shows enhanced electrocatalytic performance in both media (E1/2 are 0.86 and 0.74 V, respectively)