*3.6. Galvano-Static Charge and Discharge (GCD)*

The GCD curves have been performed for each sample (AC-400 ◦C to 800 ◦C and NAC-700 ◦C). Figure 6c,d shows the GCD curves for AC-700 ◦C and NAC-700 ◦C of supercapacitor devices with potential windows from −1.0 to 0 V at different current densities. The AC-700 ◦C and NAC-700 ◦C show the best electrochemical measurements compared to all other carbonization temperatures. Figure 6a shows GCD of AC and NAC at a current density of 0.25 A g−<sup>1</sup> , It is note worthy that NAC shows a good dicscharge time. Figure 6d shows the specific capacitance of AC's is increased as with the carbonization temperature reaches up to 700 ◦C then start decreasing further due to the temperature rise leading to dissociation of the pore already existing [37]. Form Figure 6b,c AC-700 ◦C exhibits the specific capacitance of 183 F/g among all other carbonization temperature from the GCD curve and at this optimum carbonization temperature as prepared N-doped activated carbon (NAC-700 ◦C) shows a better specific capacitance of 258 F/g. After N-doping the improvement of specific capacitance is approximately 32%. The charge and discharge time decreases as the current densities increases because at low current density the charge transfer between the electron and electrolyte on the electrode surfaces is more [37]. The specific capacitance of all samples decreases as the current density increases. But at the same time, increase in current density didn't result in a change in the profile of the GCD graphs, revealing that both electrode material has high-rate capability. Thus, the two samples resulted in symmetric triangular shape. This quasi-symmetric triangular curve indicates the ideal properties of EDLC, high efficiency, and good reversibility in the charge-discharge process [23,38]. For comparative studies, the NAC performance as electrode materials was analyzed with other N-doped activated carbon as listed in Table 2.

**Figure 6.** GCD graph of AC an NAC at various temperature (**a**) GCD of AC and NAC at a current density of 0.25 A g−<sup>1</sup> , (**b**) GCD curve of AC-700 ◦C, (**c**) GCD curve of NAC-700 ◦C, (**d**) effect of temperature on specific capacitance from GCD.


