The dynamic regulation effect in X@Fe-N4/C electrocatalyst for the sequential oxygen reduction reaction

Abstract

Metal-nitrogen-carbon based single atom catalysts (SACs) have been the subject of oxygen reduction reaction (ORR) electrocatalysts for electrochemical devices. Nevertheless, the scaling relationship of ΔG_*OOH, ΔG_*OH and ΔG_*O represents a significant obstacle to further enhancement of ORR efficiency for SACs. Accordingly, a confinement model X@M-N₄/C electrocatalyst was constructed. The density functional theory calculations demonstrate that the overpotential of Br@Fe-N₄/C54 (0.47 V vs. RHE) for ORR is significantly lower than that of Fe-N₄/C54 (0.67 V vs. RHE). The variation in distance between the Br and Fe atoms during the ORR process provides evidence that supports the hypothesis that the Br atom regulates the Fe-N₄ active center, through in-situ dynamic non-bonding coordination (d_Fe-Br>3 Å). The confined Br atom results in an increase in ΔG_*OH and a decrease in ΔG_*O. This results in a disruption of the linear relationship and a reduction in the overpotential associated with the rate-determining elementary reaction (*O+H⁺+e^-→*OH). The Fe-N₄ active center facilitates the sequential ORR catalytic process through in-situ dynamic regulation of the trapped Br atom. This conclusion is also applicable to Br@Fe-N₄/graphene and Br@Fe-N₄/CNT. The findings of our research represent a significant advancement in the field of enhancing the performance of SACs for multi-electron electrocatalytic reactions.