Sustainable development of vanadium pentoxide carbon composites derived from Hibiscus sabdariffa family for application in supercapacitors

Abstract

For the future development of environmentally friendly and sustainable electrode materials, herein, novel orthorhombic vanadium pentoxide@carbon composites (V₂O₅@C–WHS, V₂O₅@C–R₁HS and V₂O₅@C–R₂HS) were synthesized via a green solvothermal process. According to the SEM and TEM analysis, the vanadium pentoxide@carbon (V₂O₅@C) composites exhibited a flower-like morphology with a few agglomerated nanoflakes located on their surface. The incorporation of carbon in the V₂O₅ matrix was established based on the element distribution mapping images, Raman spectroscopy, FTIR spectroscopy and XPS. The V₂O₅@C–R₂HS composite presented the smallest thickness (40 nm) of the flower-like morphology and the highest content of carbon and V⁵⁺ ions. The electrochemical performance of all the electrode materials was studied in a three-electrode configuration using 6 M KOH aqueous electrolyte. The V₂O₅@C–R₂HS composite electrode displayed the best electrochemical performance compared to that of the V₂O₅@C–WHS and V₂O₅@C–R₁HS composites. The two-electrode configuration was evaluated using the V₂O₅@C–R₂HS composite as the positive electrode and activated carbon as the negative electrode to fabricate an asymmetric device (V₂O₅@C–R₂HS‖AC). The V₂O₅@C–R₂HS‖AC device presented a specific energy and associated specific power of 33.4 W h kg⁻¹ and 670 W kg⁻¹, respectively, at 1 A g⁻¹ and voltage of 1.6 V. The asymmetric cell showed excellent cycling stability of 98.9% coulombic efficiency and 88% capacity retention during a large number of cycles (25 000). Thus, the present study confirms that this novel green V₂O₅@C–R₂HS composite exhibits a superior performance as a positive electrode for future sustainable supercapacitors.