## 4 Conclusions  
In summary, the activated multiporous carbon nanofibers with functional groups were fabricated using a simple plasma process of multi-core nanofibers that resulted from single-nozzle co-electrospinning. The activated multiporous carbon nanofibers formed using this process can not only control the functional groups introduced according to the type of plasma gas (O\({}_{2}\), NH\({}_{3}\) and C\({}_{4}\)F\({}_{8}\)), but can also form micropores to maximize the active surface area. In particular, oxygen plasma-introduced multiporous carbon nanofibers (O-MPCNFs) exhibit high energy storage performance due to their large surface area and a large number of micropores. The symmetrical supercapacitor device manufactured using O-MPCNFs has a high specific capacitance (173.28 F g\({}^{-1}\) at 1 A g\({}^{-1}\)) and promotes the rapid movement of charges due to micropores into which oxygen functional groups are introduced, thereby exhibiting an excellent rate capability. In addition, due to the unique physical adsorption/desorption operation principle of the carbon material, it has a high cycle stability of 94.57% even after 5000 repetitions of charging/discharging. Therefore, the results of this study suggest an effective method for easily producing porous carbon nanofibers with a stable structure.  
**Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app131910840/s1](https://www.mdpi.com/article/10.3390/app131910840/s1)]([https://www.mdpi.com/article/10.3390/app131910840/s1](https://www.mdpi.com/article/10.3390/app131910840/s1)), Figure S1: Structure of carbon nanofibers using only PAN. Figure S2: Multiporous carbon nanofiber structures using different plasma gases. Figure S3:  
Figure 7: (**a**) Cyclic voltammetry curves at various scan rates (5 to 100 mV s\({}^{-1}\)) and (**b**) galvanostatic charge/discharge curves for different current densities (1 to 5 A g\({}^{-1}\)) of O-MPCNFs. (**c**) Electrochemical impedance spectroscopy (EIS) plots for different MPCNFs in the frequency range from 100 kHz to 10 mHz. (**d**) Long-term cycling performance and coulombic efficiency of different MPCNFs with charge/discharge numbers at 1 A g\({}^{-1}\) current density.  
FTIR and Raman spectra of the different MPCNFs. Figure S4: Rate capability of other multiporous carbon nanofibers. Figure S5: Capacitance maintenance of different multiporous carbon nanofibers. Figure S6: Structure of symmetric supercapacitor. Figure S7: CV curves of other multiporous carbon nanofibers in the two-electrode system. Figure S8: Galvanostatic charge/discharge curves of other multiporous carbon nanofibers in the two-electrode system. Figure S9: Specific capacitance change of symmetric supercapacitors.  
**Author Contributions:** The manuscript was written with contributions from all authors. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This work was supported by the Gachon University research fund of 2023 (GCU-202304440001).  
**Institutional Review Board Statement:** Not applicable.  
**Data Availability Statement:** Not applicable.  
**Conflicts of Interest:** The authors declare no conflict of interest.