Carboxylated cotton fiber-integrated PPy/PANI composites for high-performance flexible supercapacitor electrodes via TEMPO oxidation

Improving the interfacial interaction between conductive polymers and fiber substrates is essential for developing high-performance flexible supercapacitor electrodes. Herein, a simple and scalable approach is reported to modify cotton fibers via TEMPO-mediated oxidation, introducing carboxyl groups onto the fiber surface to produce carboxylated cotton fibers (C-CF). These functional groups significantly enhance the affinity between the fiber substrate and conducting polymers. Sequential in situ polymerization of polyaniline (PANI) and polypyrrole (PPy) on C-CF results in a well-integrated composite structure with improved active material loading and optimized multi-scale pore architecture (mesoporous channels together with a preserved open macroporous fiber network). Compared with unmodified fibers, the PPy/PANI/C-CF electrodes exhibit higher porosity, stronger interfacial bonding, and enhanced electrochemical activity. The symmetric flexible supercapacitor exhibits an areal capacitance of 102 μF cm−2 and a mass-specific capacitance of 85 mF g−1 at an operating voltage of 1.0 V, with an active material loading of 1.2 mg cm−2. The optimized electrode achieves a specific capacitance of 911 F g−1 at a current density of 2 mA cm−2 and maintains 79.08% capacitance after 1000 cycles, demonstrating cycling stability. This work highlights the effectiveness of fiber surface functionalization via TEMPO oxidation in improving electrode structure and performance, offering a promising strategy for flexible energy storage applications.