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

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).