2.2. Preparation of PVA/PAN Bi-Component Fiber and Porous PAN Fiber (PPF)

The preparation of carbon fibers is summarized into four steps: (i) production of bicomponent polymeric solutions with different solubility in water; (ii) formation of PVA/PAN bi-component polymeric fibers via wet spinning (Dissol, Korea); (iii) removal of on polymeric component to create pores within the fibers; and (iv) calcination of porous polymeric fibers. Polymeric solutions of PVA_H (or PVA_L, 15 wt%) and PAN (15 wt%) were prepared by dissolving them in DMSO at 50 °C. Then, dope solutions (thermodynamically stable polymer solution formed by a polymer and solvent mixture) [22] were prepared for wet spinning by mixing the PAN and PVA_H (or PVA_L) bi-component solutions at a weight ratio of 5:5, 7:3, 9:1 and 1:0 (for preparing a non-porous PAN fiber as a reference sample). The dope solutions were then extruded through a spinneret with 32 orifices (diameter; 0.1 mm) and immersed in a MeOH coagulant at 25 °C. Subsequently, the resultants were drawn out through three continuous rollers at drawing speeds of 1, 3, and 3.4 m min⁻¹ to form PVA/PAN bi-component fibers Figure 1a, which were then dried at 90 °C and wound onto bobbins. To fabricate the porous PAN fiber (PPF) Figure 1b, the prepared bi-component fibers were immersed in distilled water at 100 °C for 5 h to selectively remove PVA_H (or PVA_L) from the fibers and were finally dried in an oven at 50 °C for 24 h.