Nitrogen-Doped Carbon-Encapsulated FeCo Alloy Nanostructures with Surface-Dangling Fe(Co)-N_x Active Sites for Oxygen Reduction in Alkaline and Acid Media

Abstract

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 x active sites were fabricated, and the corresponding electrocatalytic performance was carefully investigated toward ORR in both alkaline and acid media. The coexistence of M-N x active species (Co 5.47 N or FeN 0.0324 ) and FeCo alloy makes the ORR reactivity strongly enhanced compared to the counterparts with only M-N x or 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 1/2 are 0.86 and 0.74 V, respectively).

Transition-Metal and Nitrogen-Doped Carbon Nanotube/Graphene Composites as Cathode Catalysts for Anion-Exchange Membrane Fuel Cells

“…The AEMFC results further proved the advantage of bimetallic CoFe-N-Gra/CNT over similar monometallic catalyst materials, suggesting that there are synergistic effects in play. The superiority of CoFe-based catalyst materials toward ORR has also been reported before. ,,, As a possible reason, a higher ORR activity of neighboring Co–N x /Fe–N x sites has been proposed; however, another and herein more applicable is the synergy of metal nanoparticles and the nitrogen-doped carbon shell surrounding them. , The latter has been shown to be especially beneficial with CoFe alloy nanoparticles. It has been shown by density functional theory calculations that the complex interplay of M–N x sites, CoFe alloy nanoparticles, and a nitrogen-doped carbon shell lowers the overpotential of ORR .…”

“…30,34,62,63 As a possible reason, a higher ORR activity of neighboring Co−N x /Fe−N x sites has been proposed; 33 however, another and herein more applicable is the synergy of metal nanoparticles and the nitrogen-doped carbon shell surrounding them. 64,65 The latter has been shown to be especially beneficial with CoFe alloy nanoparticles. It has been shown by density functional theory calculations that the complex interplay of M−N x sites, CoFe alloy nanoparticles, and a nitrogen-doped carbon shell lowers the overpotential of ORR.…”

“…It has been shown by density functional theory calculations that the complex interplay of M−N x sites, CoFe alloy nanoparticles, and a nitrogen-doped carbon shell lowers the overpotential of ORR. 65 This could be the reason for the improved ORR performance of bimetallic CoFe-N-Gra/CNT in comparison with single-metal counterparts.…”

Understanding the mechanism and synergistic interaction of cobalt-based electrocatalysts containing nitrogen-doped carbon for 4 e− ORR

“…This facilitates the adsorption of O 2 molecules and movement of electrons from the active sites to the reaction intermediates. 129 Guiwu Liu and co-workers synthesized dual-metalincorporated (Fe/Co) nitrogen-doped carbon hollow spheres (NCHSs). The catalyst (FeCoNCHSs) displayed E 1/2 = 0.82 V, which is signicantly comparable to Pt/C.…”

“…This facilitates the adsorption of O 2 molecules and movement of electrons from the active sites to the reaction intermediates. 129…”