## 3 Results and Discussion
### Characterization of Multiporous Activated Carbon Nanofibers  
X-ray photoelectron spectroscopy (XPS) was used to confirm the change in the composition of surface elements and functional groups of the carbon structure depending on the plasma gas exposure. Figure 4a shows a carbon structure that is not exposed to plasma treatment (MPCNFs), which is decomposed into four peaks as viewed from the C1 peak of the material. Specifically, the four peaks represent the following functional groups: 284.4 eV for a C-C or C=C aromatic ring; 285.6 eV for a C and N sp\({}^{2}\) single bond; 286.7 eV for a C and O single bond (e.g., epoxy and hydroxyl groups); 288.3 eV for a C and O double bond (e.g., carbonyl and carboxyl groups); [44; 45; 46]. When exposed to plasma, not only does the ratio of the four peaks change, but peaks associated with the elements of the exposed gas are also generated. For the carbon structure generated via exposure to oxygen plasma (O-MPCNFs), the intensities of the 286.7 eV and 288.3 eV peaks increase, which indicates the bond between carbon and oxygen atoms (Figure 4b). Among the two peaks, 288.3 eV is more clearly increased, indicating that the carbonyl group is superior to the other functional groups (i.e., hydroxyl and quinone) generated via oxygen plasma exposure. In the case of carbon fibers treated with ammonia gas plasma (N-MPCNFs), the 285.6 eV peak, which indicates the bonding of sp\({}^{2}\) carbon and nitrogen, was clearly increased (Figure 4c). This is because the high-energy ammonia plasma provides positively excited nitrogen  
Figure 2: Field emission scanning electron microscopy (FE-SEM) images of electrospun polymer nanofibers (**a,b**) before and (**c,d**) after the plasma process. components (nitrogen-containing molecules or atoms) that introduce nitrogen into the polymer chain structure. After that, going through the carbonization process, nitrogen is directly doped into the sp\({}^{2}\) carbon chain. Carbon nanofibers exposed to C4F8 plasma (F-MPCNFs) show new peaks at 290.2 eV and 292.8 eV in addition to the existing four peaks (Figure 4d). The 290.2 eV and 292.8 eV peaks show the C-F-C bond and the F-C-F bond, respectively, indicating that the F element is doped into the sp\({}^{2}\) carbon structure. To gain insight into the changes that occurred in nanofibers after exposure to plasma gas, Fourier-transform infrared (FTIR) spectra were investigated (Figure S3a). In the case of O2 plasma (O-MPCNFs), an increase in the intensity of the peaks at 3433 cm\({}^{-1}\) and 1220 cm\({}^{-1}\) was observed, which corresponded to the -OH and -C-O, respectively. When NH3 was exposed, the intensity of the peaks at 2356 cm\({}^{-1}\) and 1606 cm\({}^{-1}\) characterizing -C-N and =C-N, respectively, increased. The small C-F bonds at 2921 cm\({}^{-1}\) and 816 cm\({}^{-1}\) were also detected in the case of C4F8 plasma (F-MPCNFs). Furthermore, a difference in the D band intensity of a-MPCNF samples compared with MPCNFs was observed, which meant that functional groups derived after the plasma process contributed to the formation of defects in the carbon structure, leading to the increases in the intensity of the D band (Figure S3b). Functional groups introduced into the polymer chain after plasma treatment increase the surface roughness and create various structural defects after the carbonization step and change the surface area of the carbon structure. The method of adsorption and desorption using nitrogen gas was used to confirm the difference in surface area and micropore distribution of carbon nanofibers depending on plasma exposure and gas type (Figure 5). The active surface area and pore distribution of the material were illustrated using the Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods, respectively. First, when comparing the BET curve of each material, the adsorption in the low-pressure range (0-0.2 P/P\({}_{0}\)) of the micropores is clearly visible when plasma treatment is performed, and is greatest when oxygen gas is used.