Bifunctionally active nanosized spinel cobalt nickel sulfides for sustainable secondary zinc-air batteries: Examining the effects of compositional tuning on OER and ORR activity

Abstract

A range of compositionally-tuned nanosized cobalt nickel sulfides (<15 nm) were prepared via a sustainable continuous hydrothermal flow synthesis (CHFS) method and evaluated as electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) as well as air cathodes in rechargeable zinc-air batteries. The electrochemical study results showed that with the nominal composition of Ni1.5Co1.5S4, the cobalt nickel sulfide powder possesses an OER activity on a par with that of RuO2, while displaying superior cycling stability (>125 cycles) and a decent power density of 87 mW cm-2 at 150 mA cm-2 in zinc-air batteries. The electrochemical study of the series of cobalt nickel sulfides made herein suggests that a high electronic conductivity is responsible for the high bifunctional performance, with Ni(iii) being identified as a contributor to the OER, while Co(ii) and Ni(ii) are identified as contributors to the ORR activity. These cathode materials would be highly suitable for safe, sustainable, and long-life zinc-air secondary batteries.