Iron nanoparticles with a square pyramidal structure in mesoporous carbons as an effective catalyst toward oxygen reduction

Abstract

Mesoporous carbons supported well-dispersed square pyramidal structures of Fe–N_x (FeAMC-T) have been fabricated by pyrolyzing amino-functionalized ionic liquids and iron precursors in a mesoporous silica. The fabricated FeAMC-T is heat-treated in a nitrogen environment at various temperatures (873–1273 K) to obtain optimized catalysts for the oxygen reduction reaction (ORR). The electrochemical activities of the catalysts are investigated by rotating disk electrode tests in 0.5 M H₂SO₄ saturated with oxygen. A series of different spectroscopic (X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS)) and analytical techniques (N₂ adsorption–desorption isotherms and elemental analysis (EA)) are used to characterize the mesoporous structure, morphology and chemical environment of the catalysts. The FeAMC-1273 catalysts, which are most likely to possess a high specific surface area (1002 m² g⁻¹) with moderate nitrogen doping (∼2.8 wt%) on mesoporous carbons and more pyridinic-N (34.9%) as well as pyridinic-N–Fe (52.3%) species for the creation of a square pyramidal planar geometry around iron (confirmed by XAS), exhibit a four-electron transfer process, the best ORR activity (onset potential = 0.69 V vs. Ag/AgCl) and methanol-resistant durability in acid solution while compared to the commercially available catalysts (20 wt% of Pt on activated carbon).