<p>In this study, cobalt oxide nanoparticles were synthesized using a green extraction method, with <i>Aloe vera</i> serving as a bio-reducing agent. The synthesized nanoparticles were characterized using Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Energy-Dispersive X-ray Spectroscopy (EDX) to confirm the presence of functional groups, analyze surface morphology, and identify elemental composition. Following successful synthesis, the biological activity of the nanoparticles was evaluated. Initially, the minimum inhibitory concentration (MIC) and antimicrobial activity were assessed against <i>Bacillus cereus</i>, <i>Escherichia coli</i>, and <i>Pseudomonas aeruginosa</i>, with the zones of inhibition measured in millimeters after incubation. Subsequently, the electrochemical performance was examined by coating Co₃O₄ nanoparticles onto an aluminum plate (1 × 1 × 0.1&#xa0;cm) and assembling a symmetric two-electrode supercapacitor cell. Sodium sulfate was used as the electrolyte, and Whatman 41 filter paper served as the separator. The results of the antibacterial and antifungal assays indicated that cobalt oxide nanoparticles exhibited stronger resistance against bacterial strains compared to fungal strains. In electrochemical evaluations, the nanoparticles demonstrated superior performance in Galvanostatic Charge–Discharge (GCD) studies compared to Cyclic Voltammetry (CV). The specific capacitance ranged ~ 183 to 468&#xa0;F/g, with an energy density of 4.27 mWh/kg and a power density of 2923 mW/kg. These findings suggest that the fabricated supercapacitor is well-suited for high-power, short-duration applications, such as regenerative braking in electric vehicles, pulse energy delivery in sensors, and portable electronic devices.</p> Graphical Abstract <p></p>