**4. Conclusions**

**4. Conclusions** In summary, vacuum residue directly acquired from the extraction facilities of the local industry was used to prepare activated carbons using various activating agents, such as KOH, Ca(OH)2, and MgO. Characterizations of the final activated carbons derived from the vacuum residue resulted in the highest porosity for VR-KOH. Ca(OH)<sup>2</sup> and MgO as activating agents might require higher temperatures. However, the electrochemical supercapacitor performances of VR-Ca(OH)<sup>2</sup> and VR-MgO reveal being comparable with carbon black, which is typically made at >900 °C of the activation temperature. When the powder capacitance values are normalized with their corresponding BET surface area values, VR-KOH ranks the lowest, while VR-MgO and VR-Ca(OH)<sup>2</sup> exhibit higher numbers similar to the nonporous carbon black. This comparison highlights the discrepancies of surfaces in micropores for the capacitive current generation. This indicates that the In summary, vacuum residue directly acquired from the extraction facilities of the local industry was used to prepare activated carbons using various activating agents, such as KOH, Ca(OH)2, and MgO. Characterizations of the final activated carbons derived from the vacuum residue resulted in the highest porosity for VR-KOH. Ca(OH)<sup>2</sup> and MgO as activating agents might require higher temperatures. However, the electrochemical supercapacitor performances of VR-Ca(OH)<sup>2</sup> and VR-MgO reveal being comparable with carbon black, which is typically made at >900 ◦C of the activation temperature. When the powder capacitance values are normalized with their corresponding BET surface area values, VR-KOH ranks the lowest, while VR-MgO and VR-Ca(OH)<sup>2</sup> exhibit higher numbers similar to the nonporous carbon black. This comparison highlights the discrepancies of surfaces in micropores for the capacitive current generation. This indicates that the micropores in VR-KOH are too narrow for the hydrated K<sup>+</sup> and NO<sup>3</sup> − species. Future work to optimize the activation step to shift the porosity distribution in VR-KOH to larger diameters is expected to enhance the specific capacity of the activated carbon sample.

**Author Contributions:** Conceptualization, A.R. and A.S.J.; methodology, A.R. and A.S.J.; validation, A.A. (Abdualilah Albaiz), M.A., A.A. (Abdullah Alzahrani), A.R. and A.S.J.; formal analysis, A.A. (Abdualilah Albaiz), M.A. and A.A. (Abdullah Alzahrani); investigation, A.A. (Abdualilah Albaiz), M.A. and A.A. (Abdullah Alzahrani); resources, A.R. and A.S.J.; data curation, A.A. (Abdualilah Albaiz), M.A., A.A. (Abdullah Alzahrani), H.A., A.R. and A.S.J.; writing—original draft preparation, A.A. (Abdualilah Albaiz), M.A., A.A. (Abdullah Alzahrani), A.R. and A.S.J.; writing—review and editing, A.R. and A.S.J.; visualization, A.R. and A.S.J.; supervision, A.R. and A.S.J.; project administration, A.R. and A.S.J.; funding acquisition, A.S.J. All authors have read and agreed to the published version of the manuscript.

**Funding:** King Fahd University of Petroleum and Minerals (KFUPM), the Deanship of Research Oversight, and Coordination funding project DF191019.

**Data Availability Statement:** The data is available upon request from the corresponding authors.

**Acknowledgments:** The authors thank the financial support of King Fahd University of Petroleum and Minerals (KFUPM), the Deanship of Research Oversight, and Coordination for funding this work through project DF191019.

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