Highly active Fe–N4 sites confined in ordered carbon nanotube arrays as a self-supporting cathode catalyst for oxygen conversion

Abstract

To develop low-cost and efficient oxygen reduction reaction (ORR) electrocatalysts, single-atom catalysts (SACs) have attracted great attention to become vital to the applications of zinc–air batteries (ZABs) because of their high catalytic activity. The development of integrated SACs as self-supporting electrodes is crucial for ZABs to overcome the drawback of powder catalysts requiring a binder. Herein, an integrated atomically dispersed Fe_SA/NC catalyst was obtained by pyrolysis of Fe-containing ZIF-8 on fir wood-derived carbon. Atomically dispersed Fe–N₄ is an efficient catalytically active site for the ORR. The self-supported ordered porous structure and continuous conductive network of the catalyst provide favorable conditions for rapid mass/electron transfer. The Fe_SA/NC catalyst demonstrates a positive half-wave potential of 0.90 V in 0.1 M KOH electrolyte and 0.80 V in an acidic solution. The outstanding ORR activity outperforms those of commercial Pt/C and most reported M–N–C (M = Fe, Co, Ni, etc.) catalysts. A quasi-solid-state ZAB using Fe_SA/NC in the cathode shows an excellent peak power density of 77 mW cm⁻² at 121 mA cm⁻². The performance in quasi-solid-state batteries exceeds that of most other catalysts. This work provides a new path to catalytically active carbon via design of self-supporting SACs, and a clear demonstration of prospects in quasi-solid-state energy devices.