## 3 Results and Discussion  
### Fabrication of Multiporous Activated Carbon Nanofibers  
Figure 1 shows the method of fabricating activated multiporous carbon nanofibers (a-MPCNFs) and the structural changes in the nanofibers at each step. First, to produce a template structure for forming a multiporous carbon nanofiber, different polymer mixed solutions (polyacrylamideonitrile (PAN) and polystyrene (PS)) were electrospun using a single nozzle. In the above step, PAN forms a continuous phase and PS forms a discontinuous phase in the mixed solution due to phase separation resulting from the different physical properties (i.e., surface tension) of the two polymers [42]. Then, under the influence of the pressure from the syringe pump applied to the mixed solution and the electric field force between the nozzle and the ground, a multi-core nanofiber is formed that surrounds the PS cylinder through the PAN. The multi-core nanofibers are exposed to high-energy gas molecules using a vacuum plasma device, and functional groups related to exposed gas molecules are introduced onto the surface. Three types of plasma gases (O\({}_{2}\), NH\({}_{3}\) and C\({}_{4}\)F\({}_{8}\)) are used for the activation of the multi-core nanofibers to introduce different types  
of functional groups. Thereafter, the multi-core polymer nanofibers form multiporous carbon nanofibers, to which a functional group is introduced in the process of stabilization and carbonization. During the heat treatment process, the PAN in the polymer nanofibers forms functional groups by interacting with plasma gases introduced during the process of transformation into sp\({}^{2}\) carbon whereas the PS undergoes pyrolysis, creating channels and micropores in the fiber structure [43].  
The composition of the electrospinning polymer solution and the type of plasma gas were adjusted to confirm the conditions affecting the formation of the carbon nanostructure. First, carbon nanofibers produced using only PAN and without plasma processing form a nonporous smooth surface structure with a uniform diameter of ca. 400 nm (Figure S1). On the other hand, the multi-core polymer nanofiber-based carbon nanostructures formed by electrospinning of the PAN and PS mixed polymer solution show a different structure. The electrospun polymer nanofibers, which are not subjected to plasma treatment, have a diameter of ca. 420 nm and a smooth surface (Figure 2a,b). Under the influence of gas plasma, the polymer surface is etched by high-energy molecules, reducing the fiber diameter to ca. 400 nm and making the surface rough (Figure 2c,d). The morphology of carbon nanofibers formed after the carbonization process also shows different aspects  
Figure 1: (**a**) Schematic diagram of the fabrication stage of activated multiporous carbon nanofibers. (**b**) Structural changes in and chemical structures of nanofibers according to each fabrication step.  
depending on the exposure to plasma gas. When not subjected to plasma treatment, carbon fibers with a relatively smooth surface and an average diameter of ca. 360 nm are formed in the channel structure (Figure 3a,b). However, in the case of carbon fibers treated with oxygen plasma, the channel is formed evenly in the structure, but the diameter is reduced to ca. 320 nm and the surface roughness is significantly increased (Figure 3c,d). This structure change occurs in the same way when other plasma gases (NH\({}_{3}\) and C\({}_{4}\)F\({}_{8}\)) are used (Figure S2). In other words, the etching phenomenon caused by the high-energy plasma gas also affects the structure of the final carbon structure, resulting in an uneven surface formation.