Transformation of postsynthesized F-MOF to Fe/N/F-tridoped carbon nanotubes as oxygen reduction catalysts for high power density Zn-air batteries

Abstract

The oxygen reduction reaction (ORR), an important process in Zn-air batteries (ZABs), shows sluggish reaction kinetics, which significantly impairs the further improvement of battery performance. Thus, rationally designing cathodic catalysts for ZABs has drawn sufficient attention. We herein synthesize and characterize Fe/N/F-tridoped CNTs (FeNFCs) by annealing the postsynthesized trifluoroacetic anhydride-modified Fe-MIL-88B-NH 2 nanocrystals with melamine at high temperature in a N 2 atmosphere. Benefiting from the Fe/N/F element doping, high specific surface area, and CNT structure, the FeNFC800 catalyst prepared at 800°C exhibits a preferable half-wave potential of 0.829 V vs . RHE. The Zn-air battery equipped with FeNFC800 shows a high open-circuit voltage of 1.47 V, a gratifying peak power density of 196 mW/cm 2 , and extraordinary long-term stability, outperforming the benchmark 20% Pt/C. Fe/N/F-tridoped carbon nanotubes were grown from the postsynthesized F-Fe-MIL-88B-NH 2 microcrystals through a self-catalyzed process. The synergistic effect of Fe, N, F doping and the carbon nanotube structure enhanced the ORR catalytic performance. A Zn-air battery assembled with FeNFC800 shows a high peak power density of 196 mW/cm 2 , outperforming the benchmark 20% Pt/C.