## 3 Results and Discussions
In addition, the flexibility of the nanofiber mats is also improved by the addition of \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Quantity of** & **Mass Fraction of** & **Sheet Resistance** & **Average Diameter** \\  & **MWCNTs (g)** & **MWCNTs (\%)** & **(f)/sq)** & **(nm)** \\ \hline
**PMC-1** & 0.05 & 0.7 & 66 & 140 \\
**PMC-2** & 0.10 & 1.5 & 59 & 230 \\
**PMC-3** & 0.15 & 2.4 & 60 & 240 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Sheet resistance and average diameter of the carbon nanofiber mats fabricated with 12 wt% PAN with the addition of various amounts of mult-walled cabon nanotubes (MWCNTs). Figure 5: Electrochemical performance of the sample C-5: (**a**) cyclic voltammetry (CV) curves at a scan rate of 5-600 mV/s in potential window of \(-\)0.8–0 V; (**b**) galvanostatic charge-discharge (GCD) curve at the current density of 0.1 mA/cm\({}^{2}\); (**c**) Nyquist impedance spectrum. MWCNTs. The photographs of the co-spun carbon nanofiber mats, which can be easily bended and folded, demonstrating excellent flexibility, are shown in the insets of Figure 6c. Figure 6d-f shows electrochemical performance comparisons of samples C-5 and PMC-3. By comparing with the CV curves of two samples, it can be seen that sample PMC-3 has a similar potential window as sample C-5 at a low scanning rate, as depicted in Figure 6d. The specific capacitance of sample PMC-3 is calculated to be 18.8 F/g from Figure 6e, which is smaller than that of sample C-5. However, the electrical conductivity of the carbon nanofibers is improved by adding the MWCNTs. The impedance spectrum of the sample PMC-3 shows that the internal resistance value is about 56 \(\Omega\), which also exhibits the semicircle with a smaller radius than that of sample C-5. Although the MWCNT addition can improve the mechanical flexibility and conductivity of the PAN-derived carbon nanofiber mat, the specific capacitance is reduced. Therefore, it is necessary to further increase the electrochemical performances using another activation treatment. The activation methods and treatment conditions are listed in Table 3.  
Figure 7a-c illustrate SEM images of sample PMC-3 activated by 20 wt% HNO\({}_{3}\), 1:3 HNO\({}_{3}\):H\({}_{2}\)SO\({}_{4}\) and 1:1 HNO\({}_{3}\):H\({}_{2}\)SO\({}_{4}\), respectively. Figure 7a shows that sample PMC-3 activated by 20 wt% HNO\({}_{3}\) possesses a rough surface in several areas. After treating with 1:3 HNO\({}_{3}\):H\({}_{2}\)SO\({}_{4}\), the nanofibers reveal a rougher surface, as displayed in Figure 7b. Figure 7c shows that there are obvious cracks appearing on the nanofiber surfaces after the activation of 1:1 HNO\({}_{3}\):H\({}_{2}\)SO\({}_{4}\). Figure 7d,e depict the  
Figure 6: SEM images of the carbon nanofibers with an MWCNT mass fraction of 0.7 wt% (**a**), 1.5 wt% (**b**) and 2.4 wt% (**c**), respectively; electrochemical performance comparison of the sample C-5 and PMC-3: (**d**) CV curves at a scan rate of 5 mV/s in potential window of \(-\)0.8–0 V; (**e**) GCD curves at the current density of 0.1 mA/cm\({}^{2}\); (**f**) Nyquist impedance spectra. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Activating Agent** & **Activation Method** & **Treatment Time** \\ \hline
20 wt\% HNO\({}_{3}\) & Immersion with ultrasonic processing & 6 h \\
1:3 HNO\({}_{3}\):H\({}_{2}\)SO\({}_{4}\) & Immersion with ultrasonic processing & 6 h \\
1:1 HNO\({}_{3}\):H\({}_{2}\)SO\({}_{4}\) & Immersion with ultrasonic processing & 6 h \\ Ozone & Ozone treatment & 1 h \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Activation methods and treatment conditions of the PAN-derived carbon nanofiber mats. CV curves at a scan rate of 5 mV/s and GCD curves at a current density of 0.1 mA/cm\({}^{2}\) of sample PMC-3 activated using various methods.