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

Abstract

Atomically dispersed FeN 4 catalysts have been considered as potential materials to replace Pt-based catalysts for the oxygen reduction reaction (ORR), but they often suffer from sluggish O 2 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 FeN 4 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 FeN 4 site induced by introducing PN. Thus, the obtained FeN 4 -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 chargeredistribution sites.

Insights into the activity of single-atom Fe-N-C catalysts for oxygen reduction reaction

“…Advanced Fe-N-C materials show comparable ORR performance to that of benchmark Pt/C 3 , 5 – 7 . Both theoretical and experimental studies indicate that the Fe-N 4 site is the active species of Fe-N-C catalysts 3 , 4 , 6 , 8 – 10 . However, the ORR activity of Fe-N 4 site on different carbon supports varies greatly, and Fe-N 4 ORR activity on curved carbon supports is usually orientation-dependence 11 – 15 .…”

“…The intrinsic ORR activity of the Fe-N 4 site relates to the electronic structure of carbon supports 7 , 16 . Controlling the electronic structure of carbon supports alters the interaction between the supports and the Fe-N 4 site, resulting in the activity change of the Fe-N 4 site 6 , 7 , 13 , 16 – 18 . However, the essential of the change in Fe-N 4 ORR activity is still puzzling due to the complex factors affecting it.…”

Facile fabrication of single-atom catalysts by a plasma-etching strategy for oxygen reduction reaction

“…The rate-determining step of the four-coordination models is the formation of OOH*, while that of three-and two-coordination models is the desorption of OH*. 8,45,46 In contrast to the four-coordination models, the binding of intermediates on Cu-pd-N 3 and Cu-pd-N 2 is strong, leading to poor ORR activity with an overpotential of 1.44 and 1.86 V, respectively. Interestingly, the type of nitrogen atoms binding to Cu atoms has a signicant impact on the ORR activity of the Cu single-atom catalyst, which has been illustrated in an Fe-based single-atom catalyst.…”

“…[4][5][6] In such catalysts, the metal atom utilization is nearly 100%, which is very favorable for cost-sensitive catalysts that are used for industrial energy conversion and other applications. [7][8][9] Since the pioneering discovery of SACs by Zhang et al in 2011, strategies for fabricating SACs have rapidly developed. 10 In recent years, the rational design and preparation of SACs have been widely studied, and some novel strategies and inspiring results have been reported.…”

Surface Diels–Alder adducts on multilayer graphene for the generation of edge-enriched single-atom FeN4 sites for ORR and OER electrocatalysis

“…[22][23][24][25] In this sense, nitrogen-containing functional groups on a graphitic matrix also play a fundamental role in the performance and electronic conductivity of electrocatalytic processes. [26][27][28] Indeed, pyridinic-N enhances the potential onset while graphitic-N greatly improves the limiting current density for the ORR in N-doped graphene and N-doped carbon materials. 29,30 Furthermore, the pyridinic-N species are responsible for coordinating Fe atoms to generate an FeN 4 bridging structure which, together with the synergistic effect of the graphitic-N active sites, contributes to improve the ORR electrocatalytic activity.…”