Coupling Nonstoichiometric Zn0.76Co0.24S with NiCo2S4 Composite Nanoflowers for Efficient Synergistic Electrocatalytic Oxygen and Hydrogen Evolution Reactions

Transition-metal sulfide-based composite nanomaterials have garnered extensive interest not only for their unique morphological architectures but also for exploring as a noble-metal-free cost-effective, durable, and highly stable catalyst for electrochemical water splitting. In this work, we synthesized in situ nonstoichiometric Zn0.76Co0.24S with NiCo2S4 binary composite flowers (Zn0.76Co0.24S/NiCo2S4) in one step by thermal decomposition of Zn2[PDTC]4 and Ni[PDTC]2 complexes by a solvothermal process in a nonaqueous medium from their molecular precursor, and their potential application in electrochemical oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) was investigated. Field-emission scanning electron microscopy and transmission electron microscopy analyses revealed the flower-shaped morphology of as-synthesized Zn0.76Co0.24S/NiCo2S4. Again, the structural and chemical compositions were confirmed through powder X-ray diffraction and X-ray photoelectron spectroscopy studies, respectively. The as-obtained 3D flower-type Zn0.76Co0.24S/NiCo2S4 nanostructure was further subject to electrochemical OER and HER in alkaline and acidic media, respectively. Zn0.76Co0.24S/NiCo2S4 showed low overpotential values of 248 mV (Tafel slope, 85 mV dec–1) and 141 mV (Tafel slope, 79 mV dec–1) for OER and HER activities, respectively, due to the synergistic effects of Zn0.76Co0.24S and NiCo2S4. Several long-term stability tests also affirmed that the Zn0.76Co0.24S/NiCo2S4 composite nanostructure is a highly stable and efficient electrocatalyst toward OER and HER activities as compared to the recently reported superior bifunctional electrocatalysts as well as state-of-the-art materials.