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

Abstract

ABSTRACTTailoring 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‐Nx 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 mW 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.