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 Co9S8 nanoparticles (Co9S8@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 Co9S8 and N, S–C layer, the as-prepared Co9S8@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 gZn−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 Co9S8 can adjust each other's Fermi levels, so that the adsorption energy of Co9S8@N, S–C on O intermediate is more favorable than using Co9S8 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. © 2021 Wiley-VCH GmbH