Scalable slot-die coated flexible supercapacitors from upcycled PET face shields

Upcycling Covid19 plastic waste into valuable carbonaceous materials for energy storage applications is a sustainable and green approach to minimize the burden of waste plastic on the environment. Herein, we developed a facile single step activation technique for producing activated carbon consisting of spherical flower like carbon nanosheets and amorphous porous flakes from used PET [poly(ethylene terephthalate)] face shields for supercapacitor applications. The as-obtained activated carbon exhibited a high specific surface area of 1571 m² g^-1 and pore volume of 1.64 cm³ g^-1. The specific capacitance of these carbon nanostructure-coated stainless steel electrodes reached 228.2 F g^-1 at 1 A g^-1 current density with excellent charge transport features and good rate capability in 1 M Na₂SO₄ aqueous electrolyte. We explored the slot-die coating technique for large-area coatings of flexible high-performance activated carbon electrodes with special emphasis on optimizing binder concentration. Significant improvement in electrochemical performance was achieved for the electrodes with 15 wt% Nafion concentration. The flexible supercapacitors fabricated using these electrodes showed high energy and power density of 21.8 W h kg^-1 and 20 600 W kg^-1 respectively, and retained 96.2% of the initial capacitance after 10 000 cycles at 2 A g^-1 current density. The present study provides a promising sustainable approach for upcycling PET plastic waste for large area printable supercapacitors.