## 3 Results and Discussion
### Physical Properties and Surface Characteristics of CP and CDPC
On the other hand, at the 2D-band (2945 cm\({}^{-1}\)), this small and obtuse peak for CDPC is due to the disruption of the stacking order layers by the oxidation reaction [32]. Thus, it can be seen that the activation of CP to form CDPC dissociated the planes of graphite to form graphene and then oxidized it to form graphene oxide. The 2D-band peak CP (2945 cm\({}^{-1}\)) has a sharp peak and a high base, which are typical for defects. It is most likely that coal has many defects and CP has a highly disordered crystalline structure similar to that of the CDPC material. Based on the BET (Brunauer-Emmett-Teller) method, the specific surface area of CP was calculated to be 4.1704 m\({}^{2}\)/g, while the specific surface area of CDPC is determined to be 33.9601 m\({}^{2}\)/g. The nitrogen isotherm adsorption curves of CP and CDPC are shown in Figure 4a. The isotherm of adsorption for CP is a Type III isotherm according to the IUPAC classification. Type III isotherms are commonly associated with materials with a large pore size (d > 50 nm). In contrast, the adsorption and desorption isotherms of CDPC are Type IV isotherms, featuring a hysteresis loop of type H4 according to the IUPAC classification. The presence of the H4 hysteresis loop is often encountered in adsorbents exhibiting particle sizes spanning from microcapillary to medium pore dimensions. This observation is attributed to the nitrogen isotherm adsorption curves manifested within the relative pressure (P/P\({}^{0}\)) range of 0.40 to 0.90, which are associated with the adsorption process of particles possessing medium dimensions. Conversely, the curves discerned at P/P\({}^{0}\) > 0.90 correspond to the adsorption behavior of particles characterized by microcapillary sizes. The BJH adsorption cumulative volume of pores between 1.7 nm and 300.0 nm is 0.3143 cm\({}^{3}\) g\({}^{-1}\) for CDPC and 0.0148 cm\({}^{3}\) g\({}^{-1}\) for CP. From the BET measurement results and SEM analysis of CP and CDPC materials, it is evident that there is a coexistence of mesopores and macropores within the CDPC. The surface area and the porous volume of CDPC are higher than those of CP, indicating that the acid activation process of CP \begin{table}
\begin{tabular}{c c c} \hline
**Element** & **\% Mass** & **\% Atom** \\ \hline C & 80.88 & 85.53 \\ O & 17.18 & 13.64 \\ Al & 0.41 & 0.19 \\ Si & 0.87 & 0.39 \\ S & 0.51 & 0.20 \\ Mn & 0.15 & 003 \\ Total & 100.00 & 100.00 \\ \hline \end{tabular}
\end{table} 
Table 1: EDX analysis results of CDPC. has increased its ability to form a double-layer electric charge, thus enhancing the specific capacitance of CDPC. Pore size is also a critical factor that determines the energy storage capacity of a material. The calculated pore diameter from the BET method for CDPC is 2.5 nm, which is suitable for the formation of a double-layer electric charge because it is larger than the size of ions in the KOH electrolyte. This result is consistent with those reported for other carbon materials in previous studies [31]. The above results show that CDPC has been successfully fabricated from CP using the modified Hummers method.