Mesoporous carbon promoting the efficiency and stability of single atomic electrocatalysts for oxygen reduction reaction

Abstract

Single-atom Fe–N–C electrocatalysts are attracting more attentions as one most promising transition metal based single-atom catalyst towards the oxygen reduction reaction (ORR). However, the inaccessibility of internal Fe-Nx active sites and insufficient stability hinder their large-scale application. Herein, a facile benzoate-assisted self-template strategy which could dramatically enhance the oxygen reduction reaction catalytic performance and stability of ZIF-8 derived atomically dispersed Fe–N–C catalysts (Fe-SA/Meso-C) is developed. The sodium benzoate used in the present work is effective for promoting the formation of Fe–N–C catalysts with denser accessible active sites as well as mesopores with diameters ranging from 2.5 to 5 nm. These structural advantages make the synthesized Fe-SA/Meso-C catalysts afford excellent electrocatalytic performance for the ORR in 0.1 M KOH with a positive half-wave potential (E1/2) of 0.926 V vs. RHE and exceptionally high kinetic current density (Jk) of 92.5 mA cm−2 at 0.85 V. Beyond that, Fe-SA/Meso-C shows outstanding long-term stability with over 90% activity retain after 90 h chronoamperometry i-t test as well as superior tolerance to methanol crossover. More importantly, the assembled zinc-air battery with Fe-SA/Meso-C as the cathode material achieves a high peak power density of 166.2 mW cm−2 and a high specific capacity of 776.1 mA h g−1. Our results reveal that small mesopores in atomically dispersed Fe–N–C electrocatalysts could facilitate mass transport, increase the accessibility of active sites and optimize the interface between electrolyte and carbon matrix, thus optimizing their electrocatalytic performance for the ORR. This work paves a way to the design and synthesis of stable single-atom electrocatalysts with optimized structure, electrochemical performance and promising applications.