Exploring oxygen migration and capacitive mechanisms: Crafting oxygen-enriched activated carbon fiber from low softening point pitch

A green pitch fiber from coal tar distillation residue, with a softening point of 190 °C, was used to make activated carbon fiber through an in-situ oxygen-doped method. Oxygen-rich pitch-based activated carbon fibers (OPACFs) were successfully created with a three-stage stabilization process using this low softening point pitch fiber. The OPACFs exhibit a moderate pore size distribution and high surface oxygen content (20.83 at%). The migration and transformation of oxygen during this process were studied. Due to the formation of stable oxygen-containing functional groups (CO), the resulting material shows excellent electrochemical performance. It achieved a specific capacitance of 334 F/g at 0.5 A/g and maintained good rate capacity (73.7 %, 0.5–50 A/g) in a 6 M KOH electrolyte. The assembled supercapacitor displayed exceptional cycle stability, retaining 91.4 % capacitance at 1 A/g after 10,000 cycles. Further investigation revealed that the specific capacitance includes both surface-controlled and diffusion-controlled capacitance, with oxygen doping significantly enhancing the latter. [Display omitted]