Hierarchical Nickel–Cobalt Dichalcogenide Nanostructure as an Efficient Electrocatalyst for Oxygen Evolution Reaction and a Zn–Air Battery

A unique three-dimensional (3D) structure consisting of a hierarchical nickel–cobalt dichalcogenide spinel nanostructure is investigated for its electrocatalytic properties at benign neutral and alkaline pH and applied as an air cathode for practical zinc–air batteries. The results show a high oxygen evolution reaction catalytic activity of nickel–cobalt sulfide nanosheet arrays grown on carbon cloth (NiCo2S4 NS/CC) over the commercial benchmarking catalyst under both pH conditions. In particular, the NiCo2S4 NS/CC air cathode shows high discharge capacity, a narrow potential gap between discharge and charge, and superior cycle durability with reversibility, which exceeds that of commercial precious metal-based electrodes. The excellent performance of NiCo2S4 NS/CC in water electrolyzers and zinc–air batteries is mainly due to highly exposed electroactive sites with a rough surface, morphology-based advantages of nanosheet arrays, good adhesion between NiCo2S4 and the conducting carbon cloth, and the active layer formed of nickel–cobalt (oxy)­hydroxides during water splitting. These results suggest that NiCo2S4 NS/CC could be a promising candidate as an efficient electrode for high-performance water electrolyzers and rechargeable zinc–air batteries.