*2.3. Synthesis of N-Doped Activated Carbon*

As obtained eucalyptus leaves powder (ELP), 10 g was weighed and carbonized at 300 ◦C @ 5 ◦C min−<sup>1</sup> under inert atmosphere. As obtained sample from the previous step was mixed with ZnCl<sup>2</sup> and urea in the proportion of 1:4:2 (ZnCl2: sample: urea). Next, the product was then carbonized to 700 ◦C @ 5 ◦C min−<sup>1</sup> for 1 h. The resultant product was washed with 1 M HCl followed by DI water until the pH attained to 7 and finally the product was dried and collected. The Eucalyptus leaves N-doped carbon materials (ELNAC) so the resultant was labelled as NAC-x, where x (x = 700 ◦C) represents the carbonization temperature.
