Solid-state stepwise temperature-programmable synthesis of bioinspired Fe-N-C oxygen reduction electrocatalyst featuring Fe-N<inf>5</inf> configuration

Abstract

The bioinspired Fe-N-C features an asymmetric Fe-N5 configuration to produce active metal-oxygen intermediates by introducing axial N ligand into a symmetric Fe-N4 structure, enabling highly active oxygen reduction reaction (ORR). However, the artificial creation of active Fe-N5 configuration with a direct, facile and green method has been rarely developed yet, as current techniques involve complex processes and costly precursors. Herein, we advance a novel solid-state stepwise temperature-programmable (SST) route to directly produce bioinspired Fe-N5-C. We then demonstrate that such a Fe-N5-C exhibits a quite higher half-wave potential (0.92 V) with 22-fold faster ORR kinetics (15.6 mA·cm−2 @ 0.85 V) over that of the commercial Pt/C counterpart. Indeed, we perform density functional theory (DFT) to find that the Fe is discharged with an extra 0.1 e− through the axially coordinate N ligand, which significantly enhances the ability to activate O2 and enables an easier desorption of the crucial intermediate *OH on the Fe-N5 configuration over the conventional Fe-N4 structure.