Fluorine-decorated high loading Fe–N–C electrocatalysts for proton exchange membrane fuel cells

Abstract

Fe–N–C electrocatalysts bear the high promise to eventually substitute platinum for acidic oxygen reduction reaction (ORR). However, the loading of atomically dispersed Fe in Fe–N–C is frequently less than 3 wt% and has a relatively low ORR activity. Herein, we report the synthesis of F-decorated Fe–N–C (F–Fe–N–C) by pyrolysis of trifluoromethyl imidazole decorated zeolitic imidazolate framework-8 with hemin as Fe precursor. Interestingly, F–Fe–N–C exhibits an exceptional half-wave potential of 0.858 V (vs. RHE) primarily because of atomically dispersed 7.1 wt% Fe in the form of Fe^IIIN₄C₁₂ and Fe^IIN₄C₁₀. Moreover, F–Fe–N–C catalyst layers (CLs) enable a high single cell power density that is 2.4 times that of house-made Fe–N–C. According to theoretical studies together with mercury intrusion porosimetry, the enhancement of single cell performance appears to originate from the high activity of F–Fe–N–C, abundant pore volume including nanopores where Knudsen diffusion dominates, and F-induced scattered distribution of ionomer for proton transfer.