Biomass-Derived Carbon Fiber Aerogel as a Binder-Free Electrode for High-Rate Supercapacitors

A flexible carbon fiber aerogel with a very high surface area for supercapacitor application is reported by carbonization and chemical activation of low-cost natural cotton with KOH. The carbon fibers in the aerogel present as a twisted and tubular structure. Depending on the amount of KOH used in the activation process, the specific surface area of aerogels ranges from 1536 to 2436 m g−1, while their electrical conductivity remains ∼860 S m−1. In spite of pore size in the range of 1.0−4.0 nm and pore volume mainly contributed by micropores, the carbon aerogel exhibits a high specific capacitance of 283 F g−1 (1 A g−1) in 6 M KOH aqueous electrolyte and retains a high capacitance retention of 224 F g−1 at current density up to 100 A g−1. Importantly, a symmetric capacitor built with the aerogel electrodes exhibits a rather small time constant (0.56 s). The superior capacitive performance of a CF electrode is closely related to its distinct structural advantage. The tubular carbon fibers that are several millimeters in length offer ultralong electronic and ionic pathways, while plenty of nanopores on the fiber walls created by KOH activation enable fast ion transport across the walls. Our results demonstrate that capacitive performance of the traditional microporous carbon, which is characterized by poor ion kinetics, can be significantly enhanced by properly engineering the electrode architecture.