<p>In this study, cobalt oxide (Co₃O₄) nanoparticles were synthesized using the co-precipitation method. The calcination temperatures significantly influenced the morphology and size of the Co₃O₄ nanoparticles. The structural analysis was studied by X-ray diffraction pattern and confirmed the Co₃O₄ nanoparticles had a cubic phase. The presence of metal oxides were confirmed from the detected peaks below 1000&#xa0;cm^− 1 in FTIR spectra. FESEM images showed the changes of spherical structure to hexagonal structure, with increasing calcination temperatures. EDS mapping proved the presence of elements of Co and O. The optical investigations found potential electronic transitions that could explain the two absorption bands of Co₃O₄ nanoparticles. As the calcination temperatures increased, it was found that the optical bandgap values decreased. The calculated specific surface area from BET analysis is 155.88 m²/g. The hysteresis loops of synthesized samples revealed weak ferromagnetic behaviour at lower temperatures, whereas increasing crystallite size with calcination leads to better ferromagnetic nature. The Co₃O₄ electrode had the highest capacitance value of 535 Fg^− 1 at a scan rate of 5 mV/s. These findings suggested that the Co₃O₄ electrode was an better electrode material for supercapacitor applications.</p>