Bimetallic Nickel Cobalt Sulfide as Efficient Electrocatalyst for Zn-Air Battery and Water Splitting

The development of efficient earth-abundant electrocatalysts for oxygen reduction, oxygen evolution, and hydrogen evolution reactions (ORR, OER, and HER) is important for future energy conversion and energy storage devices, for which both rechargeable Zn-air batteries and water splitting have raised great expectations. Herein, we report a single-phase bimetallic nickel cobalt sulfide ((Ni,Co)S₂) as an efficient electrocatalyst for both OER and ORR. Owing to the synergistic combination of Ni and Co, the (Ni,Co)S₂ exhibits superior electrocatalytic performance for ORR, OER, and HER in an alkaline electrolyte, and the first principle calculation results indicate that the reaction of an adsorbed O atom with a H₂O molecule to form a *OOH is the potential limiting step in the OER. Importantly, it could be utilized as an advanced air electrode material in Zn-air batteries, which shows an enhanced charge-discharge performance (charging voltage of 1.71 V and discharge voltage of 1.26 V at 2 mA cm^-2), large specific capacity (842 mAh g_Zn^-1 at 5 mA cm^-2), and excellent cycling stability (480 h). Interestingly, the (Ni,Co)S₂-based Zn-air battery can efficiently power an electrochemical water-splitting unit with (Ni,Co)S₂ serving as both the electrodes. This reveals that the prepared (Ni,Co)S₂ has promising applications in future energy conversion and energy storage devices.