Nitrogen-doped asphaltene-based porous carbon fibers as supercapacitor electrode material with high specific capacitance

Porous carbon fibers with developed micro-mesopore structure, oxygen and nitrogen co-doping were synthesized from asphaltene, and were selected as electrode material for high performance supercapacitor. In three-electrode system, the original porous carbon fiber exhibited high specific capacitance of 301 and 482 F/g at 1 A/g in 6 M KOH and 1 M H2SO4, respectively. While the ammoniated porous carbon fiber showed good rate capability retention in KOH electrolyte (76.9%, 0.5–50 A/g) and H2SO4 electrolyte (66%, 1–50 A/g). Based on the relationship between the capacity and square-root of discharge time, the diffusion control capacitance of porous carbon fibers in H2SO4 electrolyte were significantly higher than that in KOH electrolyte. In two-electrode system (1 M KOH), the samples showed the specific capacitance of 201, 209 and 225 F/g for original, ammoniated and in-situ nitrogen-doped porous carbon fiber at 1 A/g and excellent cycling stability with 96.3%, 95.8% and 94.3% capacity retention after 10,000 cycles. The superior capacitance performance of porous carbon fibers was resulted from the synergistic effects of high specific surface area with abundant narrow micropores for charge storage, the unique open-framework structure on fibers providing short diffusion path for electrolyte ion and heteroatoms incorporation improving its wettability.