Ultra-fine Fe3C nanoparticles decorated in the Fe–N co-doped carbon networks with hierarchical nanoarchitectonics towards efficient oxygen reduction electrocatalysis

The iron-nitrogen co-doped carbon (Fe–N–C) materials have considered one of the oxygen reduction reaction catalysts with the best potential. Unfortunately, their insufficient intrinsic activity and low active sites result in thick cathode catalytic layers of fuel cell, which has limited discharge performance of the Fe–N–C catalysts in the fuel cells. Herein, a supramolecular assembly strategy is designed to prepare accessible Fe-Nx sites and ultra-fine Fe3C nanoparticles in porous carbon nanosheet with optimized pore structure toward oxygen reduction electrocatalysis. It is found that supramolecular assembly strategy has significantly increased the specific surface area and Fe-Nx site content, and induced the formation of highly dispersed Fe3C nanoparticles, which contributes to the high electrochemical active surface area and catalytic activity. The obtained FeNC-900-S catalyst exhibits a high half-wave potential of 0.860 V and a current density of up to 8.28 mA/cm2 (Jk at 0.85 V) in 0.1 M KOH, outperforming the those of commercial Pt/C. More importantly, when the FeNC-900-S is employed as an air cathode catalyst towards zinc-air batteries, it obtains an open-circuit voltage of 1.548 V, a power density of 188.8 mW/cm2 and a specific capacity of 790.5 mAh/g.