2D Nanoporous Fe−N/C Nanosheets as Highly Efficient Non-Platinum Electrocatalysts for Oxygen Reduction Reaction in Zn-Air Battery

Abstract

It is an ongoing challenge to fabricate nonprecious oxygen reduction reaction (ORR) catalysts that can be comparable to or exceed the efficiency of platinum. A highly active non-platinum self-supporting Fe-N/C catalyst has been developed through the pyrolysis of a new type of precursor of iron coordination complex, in which 1,4-bis(1H-1,3,7,8-tetraazacyclopenta(1)phenanthren-2-yl)benzene (btcpb) functions as a ligand complexing Fe(II) ions. The optimal catalyst pyrolyzed at 700 °C (Fe-N/C-700) shows the best ORR activity with a half-wave potential (E_1/2 ) of 840 mV versus reversible hydrogen electrode (RHE) in 0.1 m KOH, which is more positive than that of commercial Pt/C (E_1/2 : 835 mV vs RHE). Additionally, the Fe-N/C-700 catalyst also exhibits high ORR activity in 0.1 m HClO₄ with the onset potential and E_1/2 comparable to those of the Pt/C catalyst. Notably, the Fe-N/C-700 catalyst displays superior durability (9.8 mV loss in 0.1 m KOH and 23.6 mV loss in 0.1 m HClO₄ for E_1/2 after 8000 cycles) and better tolerance to methanol than Pt/C. Furthermore, the Fe-N/C-700 catalyst can be used for fabricating the air electrode in Zn-air battery with a specific capacity of 727 mA hg^-1 at 5 mA cm^-2 and a negligible voltage loss after continuous operation for 110 h.