## 3 Results and Discussion
### Characterization of Pd/CB Embedded in Carbon Nanofibers with Different Carbon Black Contents  
Heat treatment, carbonization, and steam activation were conducted using CBs embedded in polymer fibers prepared by electrospinning (since this is required to carbonize them). Figure 2 shows the morphology of Pd/CNF, Pd/VECNFs, and Pd/KECNFs at different ratios of CB/PAN. The Pd particles were homogenously dispersed along the CB-embedded CNF with the loading of Pd between 18-22 wt.%. The increasing ratio of CB/PAN distinctly showed changes in the decorated fibers with the existence of an increased coarse structure. There is an insignificant difference in the morphologies for both Pd/KECNF and Pd/VECNF at a low ratio: 0.125 for CB/PAN compared to the Pd embedded only in CNF. The roughness of the fiber surface increased in the case of Pd/KECNF [0.25] and Pd/VECNF [0.25], suggesting that CB was exposed on the surface of the fiber. The presence of CB \begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Catalyst**} & **Mass Activity at E\({}_{\mathrm{p}}\)**,** & **Peak Potential, Ep (V vs. normal** & **Electrochemical Active** \\  & **ip-FAOR (mA mg\({}_{\mathrm{d}}\)\({}^{-1}\))** & **hydrogen electrode, NHE)** & **Surface Area (m\({}^{2}\) g\({}_{\mathrm{d}}\)\({}^{-1}\))** \\ \hline Pd Cv-carb & 1397 & 0.76 & 22.9 \\ Pd Cv-act & 1667 & 0.84 & 26.1 \\ Pd Cv-all & 810 & 0.66 & 11.1 \\ Pd Cv-no & 250 & 0.44 & 7.1 \\ Pd Ck-carb & 1083 & 0.70 & 10.3 \\ Pd Ck-act & 845 & 0.64 & 8.8 \\ Pd Ck-all & 653 & 0.50 & 6.7 \\ Pd Ck-no & 1212 & 0.64 & 17.0 \\ \hline \end{tabular}
\end{table} 
Table 2: Summary of catalytic activity and electrochemical active surface area of Pd/C\({}_{\mathrm{v}}\) and Pd/C\({}_{\mathrm{k}}\) with various heat treatments. in the CNF increased the electrical conductivity of the ink solution during electrospinning due to the properties of the carbon material; this affected the end product of the fiber which was observed to have a thinner CNF diameter with the added CB [28]. However, at the CB/PAN ratio of 0.5, the fiber structures were significantly affected by the CB contents for both Pd/KECNF and Pd/VECNF. Table 3 summarizes the BET surface area, pore volume, and Pd crystallite size of Pd/VECNF and Pd/KECNF for the different weight ratios of CB. As Table 3 shows, the crystallite sizes of Pd were larger than those of Pd/Cs. The influence of the crystallite size in this study was negligible, ranging  
Figure 2: Field emission scanning electron microscope (FESEM) images of (**a**) Pd/Vulcan-embedded carbon nanofiber (VECNF) [0.125], (**b**) Pd/VECNF [0.25], (**c**) Pd/VECNF [0.50], (**d**) Pd/carbon nanofiber (CNF), (**e**) Pd/ Ketjen-embedded carbon nanofiber (KECNF) [0.125], (**f**) Pd/KECNF [0.25], (**g**) Pd/KECNF [0.50]. between 13.4 and 17.0 nm, because the effect of particles larger than 10 nm is not significant on the FAOR activity [29]. The BET surface area of Pd/KECNF was higher than that of Pd/VECNF. This is due to the Vulcan having a lower BET surface area than Ketjen. It was found that the BET surface areas of the VECNFs were lower than those of Pd/CNF, which contains no CB in the CNF, because the BET surface area of Vulcan (226 m\({}^{2}\) g\({}^{-1}\)) was lower than that of the CNF (650 m\({}^{2}\) g\({}^{-1}\)). Considering this fact, the BET surface area should decrease with the increasing Vulcan content; however, Pd/VECNF [0.25] showed a slightly higher BET surface area than Pd/VECNF [0.125]. On the other hand, Pd/KECNF [0.25] and Pd/KECNF [0.50] exhibited higher BET surface areas than Pd/CNF, whereas Pd/KECNF [0.125] exhibited a lower BET surface area. This is because the BET surface area of Ketjen (849 m\({}^{2}\) g\({}^{-1}\)) is higher than that of CNF. However, there is a slight difference in the BET surface area between Pd/KECNF [0.25] and Pd/KECNF [0.50]. This is because only a small amount of Ketjen was exposed on the surface due to the existence of numerous beads.