Influence of nitrogen and iron precursors on the synthesis of FeN _x/carbons electrocatalysts toward oxygen reduction reaction in acid solution

A variety of non-noble electrocatalysts (Fe(III)N_x/C and Fe(II)N₆/C) have been fabricated by pyrolyzing nitrogen-rich compounds (ethylenediamine, tetraethylenepetamine and pentaethylenehexamine) and iron precursors (iron(III) chloride and iron(II) ammonium sulphate) on carbon blacks (Vulcan XC-72) in a nitrogen atmosphere. The catalytic performance (activity and durability) toward oxygen reduction reaction (ORR) is comparatively examined by rotating disk electrode and chronoamperometric techniques. The results show that nitrogen precursors play a crucial role on the chemical microstructure and performance of electrocatalysts. The influence of various nitrogen and iron precursors on the properties of electrocatalysts has been analyzed by X-ray based spectroscopies including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). Among all the Fe(III)N_x/C and Fe(II)N₆/C catalysts, Fe(III)N₆/C catalysts which pentaethylenehexamine and iron(III) chloride are used as starting precursors possess the superior electrocatalytic ORR activity and durability probably due to their higher surface Fe/C and N/C atomic ratios with the pyridinic-N and quaternary-N active sites for the formation of the FeN₄ species, as verified by XPS and XAS analyses.