Facile and ecofriendly green synthesis of Co₃O₄/MgO-SiO₂ composites towards efficient asymmetric supercapacitor and oxygen evolution reaction applications

The development of low-cost, eco-friendly, and earth-friendly electrode materials for energy storage and conversion applications is a highly desirable but challenging task for strengthening the existing renewable energy systems. As part of this study, orange peel extract was utilized to synthesize a magnesium oxide-silicon dioxide hybrid substrate system (MgO-SiO₂) for coating cobalt oxide nanostructures (Co₃O₄) via hydrothermal methods. A variety of MgO-SiO₂ compositions were used to produce Co₃O₄ nanostructures. The purpose of using MgO-SiO₂ substrates was to increase the porosity of the final hybrid material and enhance its compatibility with the electrode material. This study investigated the morphology, chemical composition, optical properties, and functional group properties. In hybrid materials, the shape structure is inherited from nanoparticles with uniform size distributions that are well compacted. A relative decrease in the optical band was observed for Co₃O₄ when deposited onto an MgO-SiO₂ substrate. An improvement in the electrochemical properties of Co₃O₄/MgO-SiO₂ composites was observed during the measurements of supercapacitors and oxygen evolution reaction (OER) in alkaline solutions. The Co₃O₄/MgO-SiO₂ composite prepared on 0.4 g of the MgO-SiO₂ substrate (sample 2) demonstrated excellent specific capacitance, high energy density, and recycling stability for 40 000 galvanic charge-discharge cycles. The assembled asymmetric supercapacitor (ASC) device demonstrated a specific capacitance of 243.94 F g⁻¹ at a current density of 2 A g⁻¹. Co₃O₄/MgO-SiO₂ composites were found to be highly active towards the OER in 1 M KOH aqueous solution with an overpotential of 340 mV at 10 mA cm⁻² and a Tafel slope of 88 mV dc⁻¹. It was found that the stability and durability were highly satisfactory. Based on the use of orange peel extract, a roadmap was developed for the synthesis of porous hybrid substrates for the development of efficient electrode materials for energy storage and conversion.