Nitrogen-Doped Carbon-Encapsulated FeCo Alloy Nanostructures with Surface-Dangling Fe(Co)-N _xActive 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-N_xactive sites were fabricated, and the corresponding electrocatalytic performance was carefully investigated toward ORR in both alkaline and acid media. The coexistence of M-N_xactive species (Co_5.47N or FeN_0.0324) and FeCo alloy makes the ORR reactivity strongly enhanced compared to the counterparts with only M-N_xor FeCo species. Density functional theory calculations clearly reveal that the synergistic effect between FeCo, Fe-N_x, 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 FeN_0.0324-FeCo@NC nanocatalyst with abundant mesopores and macropores shows enhanced electrocatalytic performance in both media (E_1/2are 0.86 and 0.74 V, respectively).