N, S Codoped Carbon Matrix‐Encapsulated Co9S8 Nanoparticles as a Highly Efficient and Durable Bifunctional Oxygen Redox Electrocatalyst for Rechargeable Zn–Air Batteries

Abstract Herein, a N, S co‐doped carbon encapsulating Co 9 S 8 nanoparticles (Co 9 S 8 @N, S–C) catalyst is successfully synthesized by a new precursor of Co‐pyridine coordinated‐polymer consisting of 2,6‐diacetylpyridine and 4,4′‐dithiodianiline. Benefiting from the abundant pore‐structure (average pore‐size ≈25nm) and unique electronic‐properties of the Co 9 S 8 and N, S–C layer, the as‐prepared Co 9 S 8 @N, S‐C exhibits rapid oxygen reduction reaction (ORR) kinetics with high electron transfer number of ≈3.998 and demonstrates a low overpotential of 304 mV for the oxygen evolution reaction (OER). It exhibits a small potential difference of 0.647V for overall ORR/OER activity, outperforming most of the non‐precious metal‐catalysts previously reported. The rechargeable Zn–Air battery test further demonstrates its excellent activity and stability, in which the battery delivers a maximum power density output of 259 mW cm −2 , a specific capacity of 862 mAh g Zn −1 , and after continuous 110 h operation the charge‐discharge round‐trip efficiency only reduces by 4.83%. Theoretical calculation studies show that the surface N, S–C layers and Co 9 S 8 can adjust each other's Fermi levels, so that the adsorption energy of Co 9 S 8 @N, S–C on O intermediate is more favorable than using Co 9 S 8 and N, S–C alone. This study reveals the structure‐function relationship of coated‐nanostructures with multifunctional electrocatalytic properties, and provides a feasible strategy for the design of non‐noble metal‐catalysts.