Hydrothermal synthesis of nickel selenides on Ni foam for electrocatalytic oxygen evolution

다국어 초록 (Multilingual Abstract)

Nickel selenides have emerged as promising electrocatalysts for the oxygen evolution reaction (OER) due to their high conductivity, tunable electronic structure, and ability to transform into catalytically active oxyhydroxides under alkaline conditions. In this study, nickel selenides were directly synthesized on Ni foam via a simple hydrothermal process using elemental selenium powder and hydrazine as precursors. The synthesis temperature was systematically varied from 120 to 200 ºC to investigate its influence on phase formation, morphology, and electrocatalytic activity. Structural analysis by X-ray diffraction (XRD) revealed a gradual evolution from poorly crystallized products at low temperature to highly crystalline NiSe₂/Ni₃Se₂ phases at elevated temperature, with the NS-160 sample (160 ºC) exhibiting the most balanced crystalline structure. FE-SEM and EDS analyses confirmed that NS-160 possessed a uniform nanosheet-like morphology and a homogeneous Ni-Se distribution. Electrochemical evaluation demonstrated that NS-160 delivered the best OERperformance, requiring the lowest overpotential (η-100) to achieve 100 mA·cm-2, the smallest Tafel slope, and the lowest charge-transfer resistance, along with the highest double-layer capacitance (Cdl) and electrochemically active surface area (ECSA). These results highlight that optimized crystallinity and morphology at 160 ºC yield superior electrocatalytic activity by maximizing accessible active sites and facilitating rapid charge transport. This work provides a cost-effective and scalable route for fabricating efficient nickel selenide-based electrodes for alkaline water electrolysis.