Tuning Charge Distribution of FeN4 via External N for Enhanced Oxygen Reduction Reaction

Atomically dispersed FeN4 catalysts have been considered as potential materials to replace Pt-based catalysts for the oxygen reduction reaction (ORR), but they often suffer from sluggish O2 activation kinetics due to the symmetrical charge distribution. Herein, we introduce external N, including pyrrolic-N (PN) and graphitic-N (GN), as an electron acceptor near FeN4 to regulate its charge distribution and improve its ORR activity. Theoretical calculations reveal that introduction of PN evokes much enhanced electron redistribution and local electrical field on the Fe site compared with those observed with GN introduction and the pristine one. Synchrotron X-ray absorption spectroscopy and X-ray photoelectron spectroscopy validate the positive charge accumulation of Fe in the FeN4 site induced by introducing PN. Thus, the obtained FeN4-PN exhibits a great performance for ORR in 0.1 M KOH with a remarkable half-wave potential of 0.91 V versus reversible hydrogen electrode, as well as a Tafel slope of 58 mV decade–1. This work provides a guide to improve the catalytic performances of single-atom catalysts by introducing charge-redistribution sites.