Mesopore-Rich Fe–N–C Catalyst with FeN4–O–NC Single-Atom Sites Delivers Remarkable Oxygen Reduction Reaction Performance in Alkaline Media

Abstract

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.