Stabilizing Single-Atom Iron Electrocatalysts for Oxygen Reduction via Ceria Confining and Trapping

Atomically dispersed Fe-N-C materials recently hold great interest in costly Pt substitution for the cathodic oxygen reduction reaction of fuel cells. However, the heat treatment involved in the material preparation excites Fe aggregating into nanosized species with low activity rather than single-atom Fe sites. Herein, we propose a ceria-assisted strategy to preferentially generate active single-atom Fe sites in Fe-N-C materials, which involves oxidative polymerization of pyrrole, Ce3+ and Fe3+ adsorption, and subsequent heat treatment. Because of its spatial confinement and strong trapping for Fe atoms, ceria can effectively suppress agglomeration of isolated Fe atoms and stabilize the Fe atoms by bonding to O in the lattice during the heat treatment, leading to a high content of atomically dispersed Fe (4.6 wt %). Accordingly, the final catalyst showed ultrahigh ORR activity with a half-wave potential of 0.915 V and kinetic current density of 7.15 mA cm(-2) at 0.9 V. When used at the cathode in anion exchange membrane fuel cell, a maximum power density of 496 mW cm(-2) was achieved, which is one of the best performance reported in the literature for Fe-N-C-type electrocatalysts.