Effect of pre-carbonization temperature on the porous structure and electrochemical properties of activated carbon fibers derived from kapok for supercapacitor applications

Activated carbon fibers (ACFs) were successfully synthesized from kapok via a two-step process: (i) pre-carbonization and (ii) chemical activation. The pre-carbonization temperature was varied at 300℃, 400℃, and 500℃. The mixing ratio of the pre-carbonized product and potassium hydroxide (KOH) was 3:1, while the activation temperature was 800℃. The effect of pre-carbonization temperature on the morphology, surface area and porosity, chemical functional group, and phase structure of ACFs was investigated and discussed. The characterization results showed that ACFs exhibited an amorphous carbon structure with a hollow fiber shape resembling the kapok. The specific surface area decreased from 487 m2×g-1 to 326 m2×g-1 as the pre-carbonization increased. The pore structure of ACFs possessed a major contribution of micropores, and mesopores became more dominant at a high pre-carbonization temperature. The potential use of ACFs as electrode materials in supercapacitors was electrochemically tested by cyclic voltammetry and galvanostatic charge-discharge measurements. The ACFs obtained from pre-carbonization at 500℃ had the highest specific capacitance of 31.9 F×g-1 at a current density of 1 A×g-1. The results in this work will be a helpful guideline for the further design and development of ACFs from kapok for supercapacitor applications.