Flexible carbon fiber membrane derived from polypropylene for symmetric quasi-solid-state supercapacitors

The high-value recycling of disposable masks (DMMs) for energy storage applications is an effective way to deal with the overcapacity of waste plastics. In this work, we focus on developing a novel approach for flexible carbon fiber membrane electrodes that utilizes polypropylene nonwoven derived from DDMs. Herein, polypropylene nonwoven is transformed into flexible carbon fiber membrane (CPPK) via sulfuric acid sulfonation, potassium hydroxide (KOH) solution impregnation, and high-temperature carbonization. The KOH solution impregnation activation method offers distinct advantages over the traditional blending process by enhancing the uniformity of the pore structure, thereby improving the flexibility of CPPK. As a result, the as prepared CPPK shows no structural failure even after undergoing approximately one hundred times folds with nearly 180°. Furthermore, CPPK electrodes demonstrate a high specific capacitance of 194 F g−1 at 0.5 A g−1. Besides, symmetric quasi-solid-state supercapacitors (SSCs) comprised with CPPK deliver a great energy density of 10.50 Wh·kg−1 at a power density of 200 W kg−1, as well as excellent bending stability. This study provides a new perspective on developing flexible carbon materials derived from polypropylene nonwoven whether from the point of view of recycling waste plastics or mass production of industry.