\(\:{\text{Z}\text{n}}_{1-x}{{\text{N}\text{i}}_{x}\text{C}\text{o}}_{2}{\text{O}}_{4}\) nanocomposites (0 ≤ x ≤ 1) were synthesized via the hydrothermal method and characterized through XRD, EDX mapping, FE-SEM, HR-TEM, and XPS. Furthermore, their supercapacitive performance was systematically characterized to assess their potential for energy storage applications. XRD analysis revealed the coexistence of polycrystalline and nanocrystalline features in the spinel structure. XPS confirmed the expected oxide composition, with binding energies and oxygen variations indicating surface oxidation states and vacancies. The direct optical bandgap was determined using the Tauc equation, with values ranging from 2.8 eV for Zn0.8Ni0.2Co2O4 to 4.0 eV for ZnCo2O4. The electrochemical performance of \(\:{\text{Z}\text{n}}_{1-x}{{\text{N}\text{i}}_{x}\text{C}\text{o}}_{2}{\text{O}}_{4}\) electrodes, demonstrating that NiCo₂O₄ demonstrated a superior capacitance retention of ~ 65% at 100 mV/s and cycling stability of 60.75 F/g after 200 cycles compared to Zn-rich compositions (~ 45% retention). The specific capacitance decreases at higher scan rates (20–100 mV/s), reflecting diffusion-controlled kinetics, exacerbated in Zn-rich phases due to Zn2+ having a larger ionic radius. Ni-rich compositions exhibit higher specific energy (3.36 Wh/kg) and structural integrity, while intermediate stoichiometries (e.g., Zn0.8Ni0.2Co2O4) balance capacitance and stability, highlighting the importance of optimized Ni/Zn ratios for enhanced charge storage. Superior performance arises from optimal structural design, facilitating efficient charge storage, rapid ion transport, and robust diffusion kinetics. The study suggests doping, hybrid composite formation, and surface engineering to enhance supercapacitance performance for energy storage applications.
