Rational Design of Atomically Immobilized Fe-N₄ Sites via Acid-Amine Chemistry: Leveraging Metal Ionic Assistance for Precise Morphology Control

Abstract

Tailoring atomically dispersed single-atom catalyst (Fe-SAC) holding well-defined coordination structure (Fe-N₄) along with precise control over morphology is a critical challenge. Herein, we propose a novel acid-amine coupling reaction between metal-chelated ionic liquid ([1-(3-aminopropyl) 3-methylimidazolium tetrachloroferrate(III)] [APIM]⁺[FeCl₄]^–) and carboxylic groups of carbon allotropes (C = GO, CNT, CNF, and vX-72) to precisely immobilize Fe-N_x sites. Out of designed single-atom catalyst (IL-Fe-SAC-C), Fe-N₄ on graphene (IL-Fe-SAC-Gr) delivered superior oxygen reduction reaction (ORR) activity by holding higher halfwave potential of 0.882 V versus RHE in 1.0 M KOH akin to Pt/C (0.878 V vs. RHE) and surpassing recently reported M–N–C catalysts with superior ethanol tolerance. Thanks to higher graphitization degree, enhanced surface characteristics, and richness in high-density Fe-N₄ sites of IL-Fe-SAC-Gr confirmed by XPS, X-ray absorption spectroscopy (XAS), and HAADF analysis. The IL-Fe-SAC-Gr catalyst-coated cathode on testing in flexible direct ethanol fuel cells (f-DEFC) delivered higher peak power density of 18 m W cm^–2 by outperforming Pt/C-based cathode by 3.5 times as a result of excellent ethanol tolerance. Further, the developed f-DEFC successfully powered the Internet of Things (IoT)-based health monitoring system. This method demonstrates novel strategy to tailor high-performance single-atom (Fe-SAC-C) sites on desired morphologies to meet specific application requirements with feasibility and versatility.

Keywords

carbon allotropes / flexible direct ethanol fuel cells / IoT-based health monitoring systems / oxygen reduction reaction (ORR) / single-atom catalyst

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2024 The Author(s). SusMat published by John Wiley & Sons Ltd. on behalf of Sichuan University.