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) toward 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 toward 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 versus RHE in alkaline solution, significantly outperforming the parent FePc-CNTs (0.88 V versus 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 D_4h to C_4v 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.