## 3 Results and Discussion
### Electrochemical Measurement Results of CDPC Electrode  
Electrochemical impedance spectroscopy (EIS) was conducted using the Autolab PSGTAT100 instrument with an oscillation frequency ranging from 100 kHz to 100 mHz. The impedance characteristics of the CDPC electrode are illustrated in Figure 4b. The point of intersection with the real axis indicates the resistance between the electrode and the electrolyte. The semicircle present in the high-frequency region is attributed to the charge-transfer resistance, while the low-frequency line corresponds to the diffusion impedance of ions penetrating the electrode, commonly referred to as the Warburg impedance. The absence of a semicircle is notable. This discrepancy arises from the fact that the diameter of the semicircle in the high-frequency region of the impedance measurement is typically associated with the charge-transfer resistance. This shows that the CDPC electrode conducts electricity well with small charge-transfer resistance and an obvious irreversible semicircle [33]. The results of the measurements of the electrochemical properties of the material show that the energy storage capacity of the CDPC material is good and stable. To rapidly evaluate the electrochemical properties of the CDPC electrode, the CV multi-cycle loop potential scanning method was used. The electrode after fabrication was CV-activated with a potential scanning speed of 20, 50, 70, and 100 mV/s and a potential scanning range from \(-\)0.7 to 1.1 V/SCE in a 6M KOH solution and then activated for 50 cycles until the CDPC electrode was stable, followed by activation for up to 1000 cycles with a scanning speed of 100 mV/S and potential scanning range from \(-\)0.7 to 1.1 V/SCE in a 6M KOH solution. The results of CV spectroscopy at different scanning speeds for the CDPC electrode are shown in Figure 5a. Figure 4: (**a**) Nitrogen adsorption–desorption isotherms of CP and CDPC; (**b**) CDPC electrode impedance. Figure 5a shows that as the scan rate of the CV increases from 20 to 100 mV/s, the CV curves still maintain a symmetrical leaf-like shape, with no appearance of oxidation-reduction peak positions. This indicates that the CDPC electrode operates well and remains stable. As the potential scanning speed increases, the charge current density (positive value) and discharge density (negative value) gradually increase. This shows that the CDPC electrode is highly reversible. This also suggests that the reaction mechanism of the CDPC electrode follows the double-layer capacitance mechanism, similar to carbon-based materials from previous studies [22]. Similarly, after 10, 30, and 50 CV activation cycles, the charge current density (positive value) and discharge density (negative value) also gradually increase (Figure 5b). This shows that the CDPC electrode performs stably. This issue can be explained as, at the beginning of the reaction, the CDPC electrode needs some wetting time for the electrolyte solution to penetrate the CDPC structure and activate the reaction sites, as well as to remove any remaining impurities. However, after 50 cycles of stable electrode activation with a CV, the charge current density and discharge current density at 500 and 1000 cycles both decreased. This shows that the electrode potential of the CDPC electrode decreases with the number of charge-discharge cycles (Figure 5c). With the CV of the CDPC electrode at cycles 1, 500, and 1000 with a scan rate of 100 mV/s (Figure 5c), software was used to help calculate the specific capacitance of the electrode. After the initial cycle, the specific capacitance registers at 6083 F/g. Subsequently, after 500 cycles, it decreases to 4736 F/g, and following 1000 cycles, it further reduces to 4548 F/g. The results show that the specific capacitance after 500 and 1000 CV was 77.85% and 74.7%, respectively, compared to the original electrode's specific capacitance. However, from 500 to 1000 CV cycles, the specific capacitance of the electrode was reduced by only 2%. This shows that the CDPC electrode works stably and efficiently.