Enhanced electrochemical energy storage performance of CTAB-assisted hydrothermal Ni₂CoS₄ spinel nanostructures

Nickel–cobalt sulfide (Ni₂CoS₄) nanoparticles were successfully synthesized via a facile hydrothermal approach and systematically investigated as potential electrode materials for high-performance supercapacitor applications. Structural characterization using X-ray diffraction confirmed the formation of a well-crystallized cubic spinel phase, while Fourier transform infrared (FTIR) spectroscopy verified the presence of characteristic surface functional groups. Optical studies revealed strong absorption across the visible region, with a narrow optical band gap of 1.07 eV, highlighting the semiconducting nature of the synthesized material. The electrochemical performance of pristine and cetyltrimethylammonium bromide (CTAB)-modified Ni₂CoS₄ electrodes was comprehensively evaluated in a 1 M KOH electrolyte using cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. Surface functionalization with CTAB significantly enhanced the electrochemical response by improving the electrode morphology and facilitating electrolyte ion transport. Furthermore, impedance analysis revealed a low charge-transfer resistance of 0.8 Ω for the pristine electrode, and CTAB modification effectively reduced the Warburg diffusion impedance, indicating enhanced electrolyte ion diffusion. The enhanced electrochemical performance is primarily attributed to the CTAB-assisted morphology engineering during hydrothermal synthesis, which produced smaller crystallites, reduced particle agglomeration, and a more porous interconnected structure that facilitates electrolyte penetration and ion diffusion. These findings demonstrate that CTAB-functionalized Ni₂CoS₄ nanostructures are promising electrode materials for next-generation high-performance supercapacitors, offering improved energy storage and superior ion transport.