Manipulating the Adjacent Microenvironment of Atomically Dispersed FeN4 Sites via Cross-Link-Induced 3D Carbon Nest for Efficient Oxygen Reduction

Electronic perturbation induced by the microenvironment regulation adjacent to the FeN₄ sites anchored on metal–N–C materials will accelerate its oxygen reduction reaction (ORR) kinetics. Herein, we report a fine-tuning in the charge configuration of FeN₄ sites through a defect-rich N/S-doped carbon nest derived from the chemically cross-linked pyrrole/thiophene copolymer (CCPPT) with a sp³-hybridized cross-linker. Compared with the pyrrole/thiophene copolymer (PPT) without the cross-linker, CCPPT with a knitted three-dimensional (3D) network delivers higher defect density and ∼2-fold sulfur retention after pyrolysis. The structural characterizations combined with theoretical calculations suggest that adjacent vacancy defects (C_vd) and FeN₄/S₂ moiety together induce the charge redistribution of the FeN₄ sites on the resultant CC-Fe₁/NSC from CCPPT, reducing the adsorption strength of the oxygen-containing intermediates and the energy barrier of ORR. As expected, CC-Fe₁/NSC shows an impressive half-wave potential of ∼0.91 V vs reversible hydrogen electrode (RHE), surpassing both the PPT-derived Fe₁/NSC (0.88 V) and the commercial Pt/C (0.86 V). This work provides a distinctive path to manipulate the adjacent microenvironment of the single-atom catalysts toward ORR or even beyond.