Chemical growth of Niobium-doped vanadium pentoxide on aminated graphene for all-solid-state asymmetric supercapacitors

In this investigation, niobium-doped vanadium pentoxide (Nb–V₂O₅) was grown on the surface of amine-functionalized graphene nanosheets (NH₂-Gr) using an in-situ hydrothermal method and explored the hybrid material as a positive electrode for the fabrication of an all-solid-state asymmetric supercapacitor (ASC). We have used KOH-loaded poly(acrylonitrile-co-1-vinylimidazole) (KOH/P(AN-Co-VIM)) gel as a solid electrolyte-cum-separator and exfoliated graphene (XGnP) as a negative electrode in the ASC. The morphological analysis of the Nb–V₂O₅/NH₂-Gr hybrid revealed homogeneous growth of Nb–V₂O₅ on NH₂-Gr nanosheets, while surface analysis confirmed a large fraction of mesopores with large surface areas in the hybrid. The hybrid electrode achieved a high specific capacitance of 1141.1 F/g at 1 A/g with 80.3% capacitance retention even after a 10-fold increase in current density, a significantly higher performance than a pure Nb–V₂O₅ electrode. As-assembled solid-state ASC device delivered a high energy density of 79.39 Wh kg⁻¹ at a power density of 280.3 W kg⁻¹, even though it retained high energy density at a higher power density of 12 kW kg⁻¹. The ASC exhibited slow a self-discharge rate owing to the suppression of Ohmic leakage by the use of KOH/P(AN-co-VIM) gel electrolyte. Thus, the as-synthesized Nb–V₂O₅/NH₂-Gr hybrid is an ideal alternative candidate for future supercapacitors.