Facile synthesis of V4+-doped and graphene-decorated V2O5/biomass carbon nanocomposite using graphene quantum dots for supercapacitors with wide voltage window and high energy density

Abstract

Vanadium oxide has become a promising electrode material for supercapacitors because of its multiple states, but the low electrical conductivity and poor cycling stability restrict its wide application in high-performance supercapacitors. This study reports the synthesis of a V₂O₅/biomass carbon nanocomposite using serine- and histidine-functionalized and boron-doped graphene quantum dots (S/H-GQD-B). NH₄VO₃ reacted with S/H-GQD-B to form a stable V-S/H-GQD-B complex, which was absorbed into cotton, vacuum-dried and annealed to produce V₂O₅-S/H-GQD-B/BC. The introduction of S/H-GQD-B and cotton to aid the construction of small V₂O₅ nanocrystals (25 ± 1.2 nm), oxygen vacancies and graphene electron traps. The integration of these structural engineering features significantly improved the inherent electronic conductivity, expanded the safe voltage window (1.7 V) and enhanced the discharge capacity. The specific capacitance of the V₂O₅-S/H-GQD-B/BC electrode reached 552.94 F g⁻¹ at 1 A g⁻¹ and 291.48 F g⁻¹ at 50 A g⁻¹. The symmetrical supercapacitor exhibited high capacitance (435.53 F g⁻¹ at 1 A g⁻¹), high rate behavior (205.88 F g⁻¹ at 50 A g⁻¹), energy density (43.7 W h Kg⁻¹ at 425 W Kg⁻¹), and cycling stability (98.9% capacitance retention after 10 000 cycles at 10 A g⁻¹). The study also paves an avenue for the synthesis of metal nanomaterials with outstanding electrochemical behavior for energy storage, catalysis and sensing applications.