Revealing of Active Sites and Catalytic Mechanism in N-Coordinated Fe, Ni Dual-Doped Carbon with Superior Acidic Oxygen Reduction than Single-Atom Catalyst.

Abstract

Herein, we synthesized a Fe, Ni dual-metal embedded in porous nitrogen-doped carbon material to endow higher turnover frequency (TOF), lower H2O2 yield, and thus superior durability than for the single-atom catalyst for oxygen reduction in acid media. Quantitative X-ray absorption near edge structure (XANES) fitting and density functional theory (DFT) calculation were implemented to explore the active sites in the catalysts. The results suggest FeNi-N6 with type I (each metal atom coordinated with four nitrogen atoms) instead of type II configuration (each metal atom coordinated with three nitrogen atoms) dominates the catalytic activity of the noble-metal free catalyst (NMFC). Further, theoretical calculation reveals that the oxygen reduction reaction (ORR) activity trend of different moieties was FeNi-N6 (type I) > FeNi-N6 (type II) > Fe-N4 > Fe2-N6. Our research represents an important step for developing dual-metal doping NMFC for proton exchange membrane fuel cells (PEMFCs) by revealing its new structural configuration and correlation with catalytic activity.