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.