Upcycling waste PET to oxygen-rich carbon nanotubes for high-performance supercapacitor with ultra-high cycling stability†

The upcycling of post-consumer polyethylene terephthalate (PET) waste to value-added carbon materials, particularly carbon nanotubes (CNTs), has emerged as a promising chemical recycling approach. However, it remains a great challenge to convert PET waste to high-quality CNTs. Here, we report a facile one-step pyrolysis method to chemically convert discarded PET bottles to oxygen-rich CNTs by using a homemade nickel-based catalyst. As-prepared CNTs exhibit a high degree of graphitization, a well-developed porous structure, and abundant oxygen-containing functional groups. The as-obtained CNTs (CNT-700, prepared at 700 °C) exhibited superior electrochemical properties, including a high specific capacitance of 240.5 F g⁻¹ at a current density of 0.5 A g⁻¹, low resistance (R_s = 0.42 Ω, R_ct = 0.20 Ω), and excellent cycling stability, retaining 92.31% of its initial capacitance after 9000 charge–discharge cycles. Moreover, the symmetric two-electrode system assembled with CNT-700 demonstrated a remarkable cycling stability, maintaining 103.57% of its initial capacitance after 10 000 cycles. This work offers a sustainable upcycling strategy to convert PET waste to value-added CNTs which show great potential for high-performance ultra-stable supercapacitor applications.