Facile preparation of cobalt-oxide nanostructures with enriched cobalt(<scp>ii</scp>) ion surface using <i>Solanum melongena</i> for energy application

The increasing demand for efficient energy conversion and storage systems necessitates the development of high-performance, cost-effective electrode materials. To address this challenge, we employed rotten <i>Solanum melongena</i> (eggplant) juice as a precursor for the fabrication of low-cost, earth-abundant, and active electrode materials based on cobalt oxide (Co₃O₄) nanostructures. Different volumes of rotten <i>Solanum melongena</i> juice (5 mL, 10 mL, 15 mL, and 20 mL) were utilized during the precipitation process to synthesize Co₃O₄ nanostructures. These nanostructures were characterized in terms of crystal quality, surface morphology, surface chemical composition, and electrochemical properties. Notably, the synthesis using 15 mL of rotten <i>Solanum melongena</i> juice resulted in a highly efficient electrode material for oxygen evolution reaction (OER) in 1 M KOH electrolytic solution, with an overpotential of 276 mV at 10 mA cm^-2. In addition to its electrocatalytic properties, the Co₃O₄ electrode material was evaluated for supercapacitor applications, demonstrating a specific capacitance of 1303.13 F g^-1, an energy density of 28.96 W h kg^-1 at 1.25 A g^-1, and a 97% specific capacitance retention over 30 000 galvanic charge-discharge cycles.