Phytosynthesis of Co 3 O 4 Nanoparticles as the High Energy Storage Material of an Activated Carbon/Co 3 O 4 Symmetric Supercapacitor Device with Excellent Cyclic Stability Based on a Na 2 SO 4 Aqueous Electrolyte.

The benign preparation of cobalt oxide nanoparticles (Co 3 O 4 -NPs) was performed using marine red algae extract ( Grateloupia sparsa ) as a simple, cost-effective, scalable, and one-pot hydrothermal technique. The nominated extract was employed as an environmental reductant and stabilizing agent. The resultant product showed the typical peak of Co 3 O 4 -NPs around 400 nm wavelength as ascertained by UV-vis spectroscopy. Size and morphological techniques combined with X-ray diffraction (XRD) showed the small size of Co 3 O 4 -NPs deformed in a spherical shape. The activated carbon (AC) electrode and Co 3 O 4 -NP electrode delivered a specific capacitance ( C sp ) of 125 and 182 F g -1 at 1 A g -1 , respectively. The energy density of the AC and AC/Co 3 O 4 electrodes with a power density of 543.44 and 585 W kg -1 was equal to 17.36 and 25.27 Wh kg -1 , respectively. The capacitance retention of designed electrodes was 99.2 and 99.5% after 3000 cycles. Additionally, a symmetric AC/Co 3 O 4 //AC/Co 3 O 4 supercapacitor device had a specific capacitance ( C sp ) of 125 F g -1 and a high energy density of 55 Wh kg -1 at a power density of 650 W kg -1 . Meanwhile, the symmetric device exhibited superior cyclic stability after 8000 cycles, with a capacitance retention of 93.75%. Overall, the adopted circular criteria, employed to use green technology to avoid noxious chemicals, make the AC/Co 3 O 4 nanocomposite an easily accessible electrode for energy storage applications.