*3.3. Scanning Electronic Microscopy (SEM)*

The morphological structures and characteristics of untreated, AC (at different carbonization temperatures), and NAC were analyzed by using the SEM technique, and Figure 3b–f shows the microstructure of AC samples of temperature from 400 ◦C to 800 ◦C at different magnification. The observation of micrographs (SEM Image) having good porosity with macro pores in nature has resulted from the synthesized AC. As can be seen from Figure 3a, there are some vacant sites after pre-carbonization (untreated). Once it is

activated with chemical activating agent guides to activate the inactive sites and as increasing the carbonization temperature leads to more active site formation so that the porosity of AC has been increased which corresponds to increasing the specific surface area of AC [26]. As observed from Figure 3e,g, most of the inactive site are active as carbonization temperature reaches to 700 ◦C. From Figure 3f, as the temperature increase further lead to damaging pores as well as non-uniform porous material. Further, the chemical composition of AC at different carbonization temperatures and NAC was determined using energy dispersive spectroscopy (EDS). A summary of the chemical composition of the different samples is presented in Figure S1 and Table S1. According to Table S1, the weight and atomic percentage of carbon increase as the carbonization temperature increases. Low to high heating rates increased the carbon content of the AC from 80.2 to 97.5 wt.%, whereas low to high heating rates decreased the oxygen content from 15.0 to 0%. Therefore, the formation of porosities in AC facilitates the mobility of ions between both the electrode and electrolyte during the charge and discharge cycle [28].

**Figure 3.** SEM images of (**a**) untreated, (**b**) AC-400 ◦C, (**c**) AC-500 ◦C, (**d**) AC-600 ◦C, (**e**) AC-700 ◦C, (**f**) AC-800 ◦C, and (**g**) NAC-700 ◦C.
