Reversible faradaic reactions involving redox mediators and oxygen-containing groups on carbon fiber electrode for high-performance flexible fibrous supercapacitors

Flexible fibrous supercapacitors (FFS) are taking account of as the energy storage devices for wearable electronics owing to their high power density, high safety, long cycle life, and simple manufacturing process. Nevertheless, FFSs have the disadvantage of low specific capacitance that results from the electrochemical characteristics of the electrical double layer on the carbon fiber electrode. In this study, for the first time, an FFS comprising surface-activated carbon fibers as an electrode/current collector and a redox additive gel polymer electrolyte (FFS-SARE) was fabricated for use as a wearable energy storage device. The FFS-SARE showed outstanding electrochemical performance, namely, high specific capacitances of 891 and 399 mF cm⁻² at current densities of 70.0 and 400 μA cm⁻², respectively, and remarkable ultrafast cycling stability over 5000 cycles with 92% capacitance retention at a current density of 400.0 μA cm⁻². Moreover, they exhibited mechanical flexibility and had high feasibility, and they showed good energy storage performance that renders them suitable for use in wearable electronic textiles.