A facile route to high nitrogen-containing porous carbon fiber sheets from biomass-flax for high-performance flexible supercapacitors

Abstract A facile and cost-effective approach to flexible high nitrogen-containing porous carbon fiber sheets (PNCFs) was disclosed. The PNCFs were fabricated through a facile strategy of activation/doping of flax fabrics in ammonia (NH3). The procedure parameters of NH3 modification, such as the timing of NH3 switching, activation temperature and duration time were systematically investigated. PNCFs with the highest specific surface area (SSA) of 1152 m2 g-1, largest pore volume of 0.502 cm3 g-1 and maximal nitrogen content of 5.56 at.% were obtained by activation via NH3 at 900°C for 45 minutes after pre-carbonization. The optimized sample PNCF-IV-900-45 with the highest SSA, developed hierarchical micro-mesoporous structure and maximal nitrogen content exhibits a large energy density of 16.4 Wh Kg-1 at 100 W Kg-1. The NH3-activated flax-derived carbon fiber sheets assembled into a flexible supercapacitor also shows preeminent electrochemical performance and the flexibility. The symmetric flexible capacitor by PNCF-IV-900-45 electrodes displays a remarkable specific energy density of 174.7 μWh cm-2 at 500 μW cm-2, which results from the hierarchical porous structure and N functionalities. The synergistic combination of the hierarchical micro-mesoporous textures, high specific surface area, N-doping and flexibility of flax-based PNCFs to the enhanced electrochemical performance in flexible supercapacitor.