Coordination polymer derived Fe–N–C electrocatalysts with high performance for the oxygen reduction reaction in Zn–air batteries

Abstract

Developing high performance noble-metal-free electrocatalysts as an alternative to Pt-based catalysts for the oxygen reduction reaction (ORR) in energy conversion devices is highly desirable. We report herein the preparation of a coordination-polymer (CP)-derived Fe/CP/C composite as an electrocatalyst for the ORR with excellent activity and stability both in solution and in Zn–air batteries. The Fe/CP/C catalyst was obtained from the pyrolysis of an iron porphyrin Fe(TPP)Cl (5,10,15,20-tetraphenyl-21H,23H-porphyrin iron(III) chloride) grafted Zn-coordination polymer with dangling functional groups 4,4′-oxybisbenzoic acid and 4,4′-bipyridine ligands. The Fe/CP/C catalyst showed much higher ORR activity with a half-wave potential (E_1/2) of 0.90 V (vs. RHE) than the Fe/C catalyst (E_1/2 = 0.85 V) derived from the carbon-black-supported Fe porphyrins in 0.1 M KOH solution. When Fe/CP/C was used as the cathode electrocatalyst in Zn–air batteries (ZABs), the ZABs achieved a significantly higher open circuit voltage (OCV = 1.43 V) and maximum power density (P_max = 142.8 mW cm⁻²) compared with Fe/C (OCV = 1.38 V, P_max = 104.5 mW cm⁻²) and commercial 20 wt% Pt/C (OCV = 1.41 V, P_max = 117.6 mW cm⁻²). Using dangling functional groups in CP to increase the loading efficiency of iron porphyrins offered a facile method to prepare high-performance noble-metal-free electrocatalysts for the ORR, which may provide promising applications to energy conversion devices.