**4. Conclusions**

In summary, activated carbon (AC) and N-Doped activated carbon (NAC) were synthesized from eucalyptus leaves using chemical activation techniques at various temperature with ZnCl<sup>2</sup> as activator, and the source of nitrogen was loaded using urea. The synthesized AC at 700 ◦C showed a better performance with a surface area of 1027 m<sup>2</sup> g <sup>−</sup><sup>1</sup> and the enhanced performance was observed in NAC at 700 ◦C with a surface area of have a surface area 1042 m<sup>2</sup> g −1 . The impact of activator and nitrogen doped showed different morphology such as porous, graphitic sheet, honeycomb structure. The specific capacitance of AC and NAC were obtained 194 F g−<sup>1</sup> and 258 F g−<sup>1</sup> , respectively, at a scan rate of 5 mV s−<sup>1</sup> . The energy densities of AC and NAC were obtained 22 Wh Kg−<sup>1</sup> and 28.76 Wh

Kg−<sup>1</sup> , respectively, at a current density of 0.25 A g−<sup>1</sup> , for the carbon electrode. This carbon electrode shows good performance with alkaline electrolyte. The electrochemical performance suggest that AC and NAC were potentially excellent electrode for supercapacitor cell application. Finally, the findings of this study highlight the need of defining abundant residue as a necessary step in determining prospective usage for a subsequent valorization.

**Supplementary Materials:** The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/c9010024/s1, Figure S1: EDS spectra; Table S1: EDS summary.

**Author Contributions:** D.B.: Experimental, results, investigation, writing original draft, review, and revisions. P.B.: Experimental, results analysis, revision, and editing. V.B.K.: conceptualization review and editing. P.S.K.: Supervision; conceptualization, review, suggestions, and editing. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
