Surface modification strategy for constructing Fe-Nx species and FeF2/Fe3C nanoparticles co-anchored N, F co-doped carbon nanotubes for efficient oxygen reduction

Abstract

Fe-N-C catalysts have served as ideal catalysts for oxygen reduction reaction (ORR), but the strong adsorption to ORR-relevant intermediates and less utilization of Fe-Nx sites endow those catalysts with inferior performance. Here, an efficient catalyst consisted of Fe-Nx species and FeF2/Fe3C nanoparticles co-anchored on N, F co-doped carbon nanotubes (Fe-NF-CNTs) has been constructed through a surface modification strategy. Sodium trifluoroacetate as functional linker modified on metal-organic framework surface promotes to form abundant and accessible active sites. FeF2/Fe3C nanoparticles and hydrogen fluoride generated in pyrolysis process facilitate to construct N, F co-doped CNTs with defects and holes. N, F co-doping modifies the adsorption characteristic of Fe-Nx sites, while CNTs improve the accessibility of active sites and the capability of material transport. Therefore, Fe-NF-CNTs exhibits outstanding activity (E1/2 = 0.85 V) and stabilization (ΔE = 6 mV, 10k cycles). Impressively, Fe-NF-CNTs delivers high power density (144 and 68 mW cm–2) and cycle stability (300 and 60 h) in liquid and flexible Zn-air batteries, respectively. This work provides a surface modification strategy to guide the tuning of electronic structure of efficient ORR catalysts designed for renewable green energy.