Fe-N-C catalysts offer excellent performance for the oxygen reduction reaction (ORR) in alkaline media. With a view toward boosting the intrinsic ORR activity of Fe single-atom sites in Fe-N-C catalysts, fine-tuning the local coordination of the Fe sites to optimize the binding energies of ORR intermediates is imperative. Herein, a porous FeN4 -O-NCR electrocatalyst rich in catalytically accessible FeN4 -O sites (wherein the Fe single atoms are coordinated to four in-plane nitrogen atoms and one subsurface axial oxygen atom) supported on N-doped carbon nanorods (NCR) is reported. Fe K-edge X-ray absorption spectroscopy (XAS) verifies the presence of FeN4 -O active sites in FeN4 -O-NCR, while density functional theory calculations reveal that the FeN4 -O coordination offers a lower energy and more selective 4-electron/4-proton ORR pathway compared to traditional FeN4 sites. Electrochemical tests validate the outstanding intrinsic activity of FeN4 -O-NCR for alkaline ORR, outperforming Pt/C and almost all other M-N-C catalysts reported to date. A primary zinc-air battery constructed using FeN4 -O-NCR delivers a peak power density of 214.2 mW cm-2 at a current density of 334.1 mA cm-2 , highlighting the benefits of optimizing the local coordination of iron single atoms.
Keywords: Fe single-atom catalysts; axial charge redistribution; d-band center; electrocatalysis; oxygen reduction reaction.
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