Oxygen-Mediated Fe-N3O Single-Atom Sites Enabled by Lignin-Derived Hierarchical Carbon for Efficient Oxygen Reduction.

Abstract

Iron single-atom catalysts (Fe SACs) offer excellent performance for the oxygen reduction reaction (ORR). However, their catalytic activity remains limited by the coordination structure and the accessibility of the active sites. Optimizing the local coordination and pore structure of the catalyst is imperative. Herein, we report a dual-template strategy using oxygen-rich lignin to synthesize Fe single-atom catalysts with asymmetric Fe-N3O coordination embedded in hierarchical porous carbon (HPC). Lignin serves both as the carbon precursor and a coordination modulator, while Zn/MgO dual templates facilitate the creation of a tri-modal (micro/meso/macro) pore architecture. Operando spectroscopy and DFT calculations reveal that the asymmetric Fe-N3O configuration downshifts the d-band center of Fe, which weakens *OOH adsorption and accelerates charge transfer, leading to enhanced intrinsic activity. The optimized Fe-N3O@HPC catalyst exhibits exceptional ORR activity in 0.1 M KOH, with a half-wave potential of 0.87 V vs. RHE, surpassing Pt/C by 40 mV. Moreover, it exhibits significantly smaller decay over 30 h than commercial Pt/C. In zinc-air batteries, the catalyst delivers a peak power density of 174.2 mW cm-2 and a specific capacity of 807 mAh gZn -1. This research offers a cost-effective methodology to design and fabricate high-performance catalysts for ORR.

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