Altering the Symmetry of Fe-N-C by Axial Cl-Mediation for High-Performance Zinc–Air Batteries

Abstract

Fe-N-C catalyst is acknowledged as a promising alternative for the state-of-the-art Pt/C in oxygen reduction reaction (ORR) towards cutting-edge electrochemical energy conversion/storage applications. Herein, a "Cl-mediation" strategy is proposed on Fe-N-C for modulating the catalyst's electronic structure towards achieving remarkable ORR activity. By coordinating axial-Cl atoms to iron phthalocyanine (FePc) molecules on carbon nanotubes (CNTs) matrix, a Cl-modulated Fe-N-C (FePc-Cl-CNTs) catalyst is synthesized. The as-prepared FePc-Cl-CNTs exhibit an improved ORR activity with a half-wave potential of 0.91 V vs. RHE in alkaline solution, significantly outperforming the parent FePc–CNTs (0.88 V vs. RHE). The advanced nature of the as-prepared FePc-Cl-CNTs is evidenced by a configured high-performance rechargeable Zn-air battery, which operates stably for over 150 h. The experiments and density functional theory calculations unveil that axial-Cl atoms induce the transformation of FePc from its original D4h to C4v symmetry, effectively altering the electrons distribution around the Fe-center, by which it optimizes *OH desorption and subsequently boosts the reaction kinetics. This work paves ways for resolving the dilemma of Fe-N-C catalysts’ exploration via engineering Fe-N-C configuration.