Carbon Sphere-Infused PET CS/PET: Enhancing Energy Storage Efficiency of Vanadium Flow Batteries and Supercapacitors

The recycling of widely available polyethylene terephthalate (PET) into activated carbon–carbon sphere composites represents a sustainable approach for developing advanced energy storage materials. In this study, a novel carbon sphere@polyethylene terephthalate (CS/PET) active material was synthesized using a cost-effective hydrothermal process, integrating dextrose-derived oxygen-rich carbon spheres and PET-derived activated carbon. This eco-friendly composite was utilized to modify 132 cm² graphite felt electrodes for vanadium redox flow batteries (VRFBs) and served as an active material in supercapacitors. As a positive electrode electrocatalyst in VRFBs, the CS/PET-modified electrode achieved a coulombic efficiency (CE) of 88.43%, a voltage efficiency (VE) of 59.79%, and an energy efficiency (EE) of 51.92%, with excellent stability over 100 cycles. For supercapacitor applications, the CS/PET composite exhibited an impressive specific capacitance of 193 F/g at 2 A/g, delivering 100% coulombic efficiency and 92% retention over 2500 cycles. These results highlight the potential of CS/PET composites as cost-effective, clean, and high-performance materials for sustainable energy storage systems, demonstrating significant promise for meeting future energy demands while addressing global environmental challenges.