Noble-Metal-Free Fe–N/C Catalyst for Highly Efficient Oxygen Reduction Reaction under Both Alkaline and Acidic Conditions

Abstract

In this work, we report the synthesis and assessment of a new non-precious-metal oxygen reduction reaction (ORR) catalyst from pyrolysis of an iron-coordinated complex which manifests superior activity in both alkaline and acidic media. 11,11'-bis(dipyrido[3,2-a:2',3'-c]phenazinyl) (bidppz) was selected as a ligand for the formation of a nitrogen-rich iron-coordinated coordination polymer (Fe-bidppz) which forms a self-supporting catalyst containing high densities of nitrogen and iron doping by pyrolysis. The catalyst pyrolyzed at 800 °C (Fe-N/C-800) shows the highest ORR activity with onset and half-wave potentials of 923 and 809 mV in 0.1 M KOH, respectively, which are comparable to those of Pt/C (half-wave potential 818 mV vs RHE) at the same catalyst loading. Besides, the Fe-N/C-800 catalyst has an excellent ORR activity with onset and half-wave potentials only 38 and 59 mV less than those of the Pt/C catalyst in 0.1 M HClO4. The optimal Fe-N/C-800 catalyst displays much greater durability and tolerance of methanol than Pt/C. We propose that the Fe-N/C-800 catalyst has a considerably high density of surface active sites because Fe-N/C-800 possesses excellent ORR activity while its specific surface area is not so high. Electrochemical measurements show that the Fe-N/C-800 catalyst in KOH and HClO4 follows the effective four-electron-transfer pathway.