Noble-Metal-Free\nFe–N/C Catalyst for Highly\nEfficient Oxygen Reduction Reaction under Both Alkaline and Acidic\nConditions

Abstract

In this work, we\nreport the synthesis and assessment of a new non-precious-metal\noxygen reduction reaction (ORR) catalyst from pyrolysis of an iron-coordinated\ncomplex which manifests superior activity in both alkaline and acidic\nmedia. 11,11′-bis­(dipyrido­[3,2-<i>a</i>:2′,3′-<i>c</i>]­phenazinyl) (bidppz) was selected as a ligand for the\nformation of a nitrogen-rich iron-coordinated coordination polymer\n(Fe–bidppz) which forms a self-supporting catalyst containing\nhigh densities of nitrogen and iron doping by pyrolysis. The catalyst\npyrolyzed at 800 °C (Fe–N/C-800) shows the highest ORR\nactivity with onset and half-wave potentials of 923 and 809 mV in\n0.1 M KOH, respectively, which are comparable to those of Pt/C (half-wave\npotential 818 mV vs RHE) at the same catalyst loading. Besides, the\nFe–N/C-800 catalyst has an excellent ORR activity with onset\nand half-wave potentials only 38 and 59 mV less than those of the\nPt/C catalyst in 0.1 M HClO₄. The optimal Fe–N/C-800\ncatalyst displays much greater durability and tolerance of methanol\nthan Pt/C. We propose that the Fe–N/C-800 catalyst has a considerably\nhigh density of surface active sites because Fe–N/C-800 possesses\nexcellent ORR activity while its specific surface area is not so high.\nElectrochemical measurements show that the Fe–N/C-800 catalyst\nin KOH and HClO₄ follows the effective four-electron-transfer\npathway.