Green-Mediated Synthesis of Co₃O₄ Nanostructures for Efficient Oxygen Evolution Reaction and Supercapacitor Applications

A simple, scalable, and environmentally friendly process was demonstrated for the synthesis of Co₃O₄ nanostructures using lemon juice and hydrothermal chemistry. The reducing, capping, and stabilizing agents in lemon juice result in improved performance in oxygen evolution reactions and supercapacitors due to their positive effects on morphology, crystal size, and surface defects. Several techniques were used to characterize Co₃O₄ nanostructures grown with different quantities of lemon juice, including field emission scanning electron microscopy, energy-dispersive spectroscopy, and x-ray diffraction. The results show that lemon juice alters the size and homogeneity of Co₃O₄ nanostructures as well as surface defects like oxygen vacancies and interstitial Co. A sample prepared with 4 mL of lemon juice (sample 1) performed best, demonstrating an overpotential of 260 mV at 10 mA cm⁻² and good stability at 20 mA cm⁻² for 40 h. With the prepared nanomaterial, supercapacitors were developed with a specific capacitance of 398 F g⁻¹ at 0.8 A g⁻¹, a specific capacity retention percentage of 97%, a high energy density of 9.5 Wh kg⁻¹, and excellent stability during 880 galvanic charge and discharge cycles. Co₃O₄ nanostructures have experienced dramatic improvements in electrochemical performance as a result of morphological changes and oxygen vacancy concentrations on their surfaces. By reducing, capping, and stabilizing lemon juice, a new generation of electroactive electrodes have been developed for storage and conversion of energy.