Structural and Morphological Characterization of Bifunctional ZnCoS/NF Catalysts Synthesized Under Varying Conditions for Potential Electrocatalytic Applications

Growing concerns over global air pollution have intensified interest in hydrogen as a clean and sustainable energy carrier capable of generating both heat and electricity. Developing efficient and cost-effective electrocatalysts is essential for improving the sluggish hydrogen and oxygen evolution reactions in alkaline water electrolysis. In this study, CoS and Zn-doped CoS (ZnCoS) catalysts were synthesized on nickel foam (NF) using a two-step hydrothermal method, with systematic variations in Zn:Co molar ratios and synthesis temperatures. Structural and morphological characterisation revealed that incorporating Zn²⁺ into CoS significantly modified the catalyst architecture, transforming the moss-like CoS morphology into well-defined flower-like nanostructures composed of interconnected nanoflakes. These nanostructures enhanced surface roughness and porosity, providing greater accessibility to electrochemically active sites. XRD and HRTEM analyses further confirmed the successful incorporation of Zn into the CoS lattice through observable lattice distortion and the coexistence of CoS₂ and Zn₀.₇₆Co₀.₂₄S phases. Among the synthesized samples, ZnCoS prepared at a 1:3 Zn:Co ratio and 100 °C exhibited the smallest crystallite size, lowest cell volume, and the most favourable nanoflake assembly. In contrast, higher synthesis temperatures led to increased crystallite growth and reduced porosity. Overall, this study establishes a clear structure–morphology relationship and identifies ZnCoS/NF prepared at low synthesis temperatures as a promising candidate for further electrochemical evaluation toward alkaline water electrolysis applications.