Decorating unsaturated iron–nitrogen coordination sites with small-sized iron selenide nanoparticles for highly efficient oxygen reduction catalysis

Abstract

Given the growing concerns about energy and environmental issues, it is imperative to develop cost-effective and highly efficient catalysts towards the oxygen reduction reaction (ORR) for clean and advanced metal–air battery systems, such as Zn–air and Mg–air batteries. Herein, a hybrid catalyst, consisting of small-sized iron selenide nanoparticles and unsaturated iron–nitrogen coordination sites (Fe–N₂) dispersed on a nitrogen and sulfur co-doped mesoporous carbon matrix, is synthesized via a facile pyrolysis and acid leaching method. The resulting catalyst exhibits superior ORR catalytic activity, with notable half-wave potentials of 0.91 V in 0.1 M KOH and 0.61 V in 3.5 wt% NaCl. It also demonstrates excellent durability and achieves remarkable performance when evaluated in assembled Zn–air and Mg–air batteries, outperforming the benchmark Pt/C catalyst. Density functional theory calculations indicate that iron selenide nanoparticle decreases the d-band center of an Fe–N₂ active site and modulates the binding strength to oxygen-containing intermediates, thereby substantially reducing the energy barrier in the catalytic reaction. Furthermore, the spatial distance between FeSe nanoparticles and Fe single-atom sites needs to be precisely controlled within the optimal range to maximize synergistic electronic effects. This work offers insightful perspectives on developing non-precious metal ORR catalysts.