The Influence of Molar Ratio of Reactants on the Crystal Structure and Electrochemical Property of NiO Nanocrystals

Transition metal oxides such as nickel oxide (NiO) have garnered significant attention for supercapacitor applications due to their high surface area and excellent chemical stability. In this study, NiO nanocrystals were successfully synthesized using four different concentrations of NaOH (0.5, 1.0, 1.5, and 2.0 M), yielding samples designated as NiO-A, NiO-B, NiO-C, and NiO-D, respectively. The structural and morphological characteristics of the synthesized samples were thoroughly investigated. Among them, NiO-A exhibited superior crystallinity, as confirmed by X-ray diffraction (XRD) analysis. Field emission scanning electron microscopy (FESEM) revealed that NaOH concentration significantly influenced the morphology of the nanocrystals. X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of Ni in the + 2-oxidation state in NiO-A. Electrochemical performance was evaluated through cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). NiO-A demonstrated the highest specific capacitance of 165 F/g at a scan rate of 5 mV/s, attributed to its large Brunauer–Emmett–Teller (BET) surface area of 462 m²/g, pore volume of 0.49 cc/g, and low charge transfer resistance of 65.13 Ω. Additionally, GCD analysis revealed an energy density of 3.2 Wh/kg at a power density of 1870 W/kg, highlighting NiO-A's potential as a promising electrode material for high-performance supercapacitors.