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 (Cvd) 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.