Self-Polymerized Perfluorinated Iron Phthalocyanine/Carbon Nanotube Catalyst with Integrated Mass-Transport Channels for Efficient Oxygen Reduction

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Abstract Fe–N–C single-atom catalysts are among the leading nonprecious-metal candidates for the oxygen reduction reaction (ORR) in fuel cells, but their performance in membrane electrode assemblies is constrained by poor active-site utilization and sluggish mass transport within the catalyst layer. These limitations arise, in part, because the high-temperature pyrolysis used to prepare Fe–N–C materials introduces structural heterogeneity, making it difficult to engineer porosity and surface chemistry without perturbing the active site. Here, we synthesized a perfluorinated iron phthalocyanine polymer catalyst (FePPCF16/CNT) by self-polymerizing FePcF16 monomers directly on carbon nanotube surfaces. The resulting macrocyclic polymer retains a well-defined Fe–N4 coordination environment, as verified by X-ray absorption and photoelectron spectroscopy, while the CNT support withdraws electron density from the Fe center through π–π conjugation, shifting the iron oxidation state upward and decreasing the high-overpotential Tafel slope from >160 to ∼91 mV dec−1. The perfluorinated backbone renders the catalyst strongly hydrophobic (water contact angle: 128.2°), preventing liquid water from blocking gas pores while maintaining the water accessibility required for cathodic ORR. Concurrently, the interstitial voids and mesopores generated by CNT templating and polymerization create dedicated O2 diffusion pathways, as confirmed by rapid bubble-uptake tests, while the interconnected pore network sustains OH– conduction through the ionomer-filled interstices. In an operating anion exchange membrane fuel cell, FePPCF16/CNT-0.75 delivers a half-wave potential of 0.90 V and a peak power density of 386 mW cm−2, with negligible voltage loss in the mass-transport-limited regime above 200 mA cm−2. These results demonstrate that self-polymerized macrocyclic catalysts can integrate electronic activation, ionic connectivity, and gas-transport pathways within a single material, without the structural heterogeneity introduced by pyrolysis.

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