Fe–N–C electrocatalysts derived from a 1,10-phenanthroline–iron complex: kinetic insights into the acidic oxygen reduction reaction

Abstract

Iron–nitrogen–carbon (Fe–N–C) electrocatalysts have emerged as promising alternatives to platinum for the oxygen reduction reaction (ORR) in acidic media. Herein, we report the synthesis of an Fe–N–C catalyst via impregnation and complexation of iron(III) nitrate and 1,10-phenanthroline onto carbon black, followed by pyrolysis at high temperature. Transmission electron microscopy and X-ray energy-dispersive spectroscopy revealed a uniform distribution of Fe within the porous carbon matrix. The ORR performance was investigated using rotating ring-disk electrode experiments in oxygen-saturated 0.5 mol L⁻¹ H₂SO₄. The material exhibited an onset potential of approximately 0.83 V vs. RHE, with a maximum turnover frequency of 5.4 O₂ s⁻¹ per active site at 10 mA cm⁻². A Tafel slope of approximately 118 mV dec⁻¹ identified the first electron transfer as the rate-determining step. A comprehensive kinetic model was developed in the frequency domain, accounting for both interfacial electron transfer and mass transport in the porous electrode, enabling the extraction of intrinsic rate constants and surface coverage parameters. The findings demonstrate the mechanistic and kinetic advantages of Fe–N–C catalysts synthesized using 1,10-phenanthroline, offering valuable insights for the design of advanced ORR electrocatalysts for fuel cells and metal–air batteries.