Enhancement of Specific Capacitance Using a Mixture of Sweet Potato Ash and Zinc Oxide Nanoparticles on Reduced Graphene Oxide Sheets

A straightforward approach for synthesizing graphene-metal oxide hybrid materials suitable for coating stainless steel sheets in supercapacitors is presented. Zinc oxide (ZnO) nanoparticles with an average particle size of 84.45 ± 15.83 nm were deposited onto reduced graphene oxide (rGO) sheets to impart pseudocapacitance. Carbon source from sweet potato ash (CSP), carbonized using concentrated sulfuric acid treatment, exhibited remarkable electric double-layer capacitance. Coating stainless steel electrodes with 60% CSP and 40% ZnO/rGO mixture with a thickness of approximately 500 µm yielded an excellent specific capacitance of 323.12 F g–1 at a current density of 2 A g–1 and cyclic stability with a retention rate of 91.84% after 3000 charging-discharging cycles. This approach offers a new cost-effective means of enhancing supercapacitor capacitance.