Upcycling plastic waste into electrode materials for energy storage applications

The accumulation of plastics in the environment poses a major threat to ecosystems, as discarded plastics release toxic chemicals or degrade into microplastics that enter food chains. Since 1950, over 6.3 billion tonnes of plastic waste have been produced, with about 80% ending up in landfills or the environment. Conventional waste management methods are ineffective for plastics with crosslinked structures and complex compositions, while incineration generates significant pollution. This research presents a sustainable route for upcycling non-recyclable plastic waste into electrode materials for energy storage applications. A plastic foam waste containing vulcanized rubber (60%), polyvinyl chloride (35%), and additives was selected due to its non-recyclable nature. The waste was pyrolyzed into carbon and chemically activated with potassium hydroxide at 500–800 °C to develop porous carbon materials (PWC). Increasing activation temperature enhanced porosity, producing larger pores, a more disordered graphitic structure, and higher charge transfer resistance. The prepared PWC was employed to fabricate cathodes for two types of energy storage devices. First, PWC samples were used to confine selenium (Se) and prepare Se-based cathode composites for lithium-selenium (Li-Se) batteries. The sample activated at 600 °C (PWC600) delivered the best performance, achieving a stable reversible capacity of 655 mAh g⁻¹ at 0.1 C (97% of Se’s theoretical capacity) with excellent cycling stability over 150 cycles. Its superior performance was attributed to low charge transfer resistance and effective Se confinement, which mitigated side reactions. Next, PWC samples were used as active cathode materials in Zn-ion hybrid supercapacitors (ZHSCs). The sample activated at 800 °C (PWC800) exhibited the highest surface area (2300 m² g⁻¹) and the best electrochemical performance, achieving a capacitance of 248.5 F g⁻¹ at 0.5 A g⁻¹, an energy density of 97 Wh kg⁻¹, and a power density of 1600 W kg⁻¹. Overall, this research demonstrates the potential of converting complex, non-recyclable plastic waste into valuable carbon materials for efficient energy storage systems. It highlights how activation parameters influence carbon morphology and performance, providing insights for the rational design of sustainable carbon-based electrodes.