Manipulating the\nAdjacent Microenvironment of Atomically\nDispersed FeN<sub>4</sub> Sites via Cross-Link-Induced 3D Carbon Nest\nfor Efficient Oxygen Reduction

Electronic\nperturbation induced by the microenvironment regulation\nadjacent to the FeN<sub>4</sub> sites anchored on metal–N–C\nmaterials will accelerate its oxygen reduction reaction (ORR) kinetics.\nHerein, we report a fine-tuning in the charge configuration of FeN<sub>4</sub> sites through a defect-rich N/S-doped carbon nest derived\nfrom the chemically cross-linked pyrrole/thiophene copolymer (CCPPT)\nwith a sp<sup>3</sup>-hybridized cross-linker. Compared with the pyrrole/thiophene\ncopolymer (PPT) without the cross-linker, CCPPT with a knitted three-dimensional\n(3D) network delivers higher defect density and ∼2-fold sulfur\nretention after pyrolysis. The structural characterizations combined\nwith theoretical calculations suggest that adjacent vacancy defects\n(<i>C</i><sub>vd</sub>) and FeN<sub>4</sub>/S<sub>2</sub> moiety together induce the charge redistribution of the FeN<sub>4</sub> sites on the resultant CC-Fe<sub>1</sub>/NSC from CCPPT,\nreducing the adsorption strength of the oxygen-containing intermediates\nand the energy barrier of ORR. As expected, CC-Fe<sub>1</sub>/NSC\nshows an impressive half-wave potential of ∼0.91 V vs reversible\nhydrogen electrode (RHE), surpassing both the PPT-derived Fe<sub>1</sub>/NSC (0.88 V) and the commercial Pt/C (0.86 V). This work provides\na distinctive path to manipulate the adjacent microenvironment of\nthe single-atom catalysts toward ORR or even beyond.