Atomic layer deposited nickel sulfide for bifunctional oxygen evolution/reduction electrocatalysis and zinc–air batteries

Rechargeable Zn−air batteries are a promising type of metal-air batteries for high-density energy storage. However, their practical use is limited by the use of costly noble-metal electrocatalysts for the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occurred at the air electrode of the Zn−air batteries. This work reports a new non-precious bifunctional OER/ORR electrocatalyst of NiS_x/carbon nanotubes (CNTs), which is made by atomic layer deposition (ALD) of nickel sulfide (NiS_x) on CNTs, for the applications for the air electrode of the Zn−air batteries. The NiS_x/CNT electrocatalyst on a carbon cloth electrode exhibits a low OER overpotential of 288 mV to reach 10 mA cm⁻² in current density, and the electrocatalyst on a rotating disk electrode exhibits a half-wave ORR potential of 0.81 V in alkaline electrolyte. With the use of the NiS_x/CNT electrocatalyst for the air electrode, the fabricated aqueous rechargeable Zn−air batteries show a fairly good maximum output power density of 110 mW cm⁻², which highlights the great promise of the ALD NiS_x/CNT electrocatalyst for Zn−air batteries. (paper)