Hierarchical Porous Carbon Spheres from Low-Density Polyethylene for High-Performance Supercapacitors

Plastics are used extensively and provide great convenience in daily life. However, their stable and nonbiodegradable nature incurs challenging threats to the environment and ecosystems. It is essential that a sustainable method for plastic treatment and utilization be developed. We used low-density polyethylene (LDPE) as a precursor to synthesize a hierarchical porous carbon (HPC) through autogenic pressure carbonization followed by potassium hydroxide (KOH) activation. The noncatalytic carbonization in a closed system obtained 45% carbon residues from LDPE, which would not yield any carbon residues under normal pressure. The following KOH activation developed hierarchical porous structures in the carbon materials, which can be controlled by KOH dosage. The mechanism of carbonization and activation was proposed considering the nanostructure of carbon materials. The obtained HPC exhibited a micrometer-scale carbon sphere morphology with hierarchical pores, a large specific surface area of 3059 m2 g–1, and abundant surface functional groups. By acting as an electrode material for supercapacitors, the HPC displayed excellent electrochemical performance with a specific capacitance of 355 F g–1 at a current density of 0.2 A g–1 in 6 M KOH electrolyte, a high energy density of 9.81 W h kg–1 at a power density of 450 W kg–1, and an outstanding cycling stability. This research develops a sustainable way for plastic waste utilization and a green approach for HPC synthesis.