Electronic Structure Modulation of Fe-N₄ Sites by Heteroatom Doping in Hollow N-Doped Carbon Spheres for Enhanced...

Covalent organic polymers (COP) have emerged as promising oxygen reduction reaction (ORR) catalysts due to their well-defined and tunable structures. However, the influence of carbon substrates doped with heteroatoms of varying electronegativities on the electronic structure of active sites remains poorly understood. In this study, core-shell structured COP_FePc@XNC catalysts (X = F, Cl, or Br) were constructed by supporting FePc-based covalent organic polymers (COP_FePc) on hollow N-doped carbon spheres that were doped with heteroatom X. Experimental results reveal that the electron-withdrawing capability of highly electronegative heteroatoms reduces the electron density at the Fe sites in COP_FePc, thereby weakening the adsorption of oxygenated intermediates and accelerating the ORR kinetics. COP_FePc@FNC exhibits outstanding ORR performance under alkaline conditions, with an onset potential (E₀) of 1.03 V and a half-wave potential (E_1/2) of 0.912 V, surpassing the commercial Pt/C catalyst (E₀ = 1.01 V, E_1/2 = 0.85 V). The insights gained into heteroatom doping strategies in this study guide the rational design of carbon-based electrocatalysts for enhanced performance.