Abstract
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 (NiCo(2)S(4) NS/CC) over the commercial benchmarking catalyst under both pH conditions. In particular, the NiCo(2)S(4) 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 NiCo(2)S(4) 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 NiCo(2)S(4) and the conducting carbon cloth, and the active layer formed of nickel-cobalt (oxy)hydroxides during water splitting. These results suggest that NiCo(2)S(4) NS/CC could be a promising candidate as an efficient electrode for high-performance water electrolyzers and rechargeable zinc-air batteries.