Construction of an advanced Co-doped V2O3 electrode material with significantly enhanced conductivity and structural stability for supercapacitors using asparagic acid-functionalized graphene quantum dots

Abstract

Vanadium oxide has become a promising electrode material for supercapacitors because of its high capacitance and multiple redox states. However, low intrinsic conductivity, narrow interlayer spacing and poor structural stability limit its practical application. The study reports the construction of Co-doped V₂O₃ using asparagic acid-functionalized graphene quantum dots (GQD) and biomass carbon (BC). V⁵⁺ and Co²⁺ were combined with GQD to form the Co/V-GQD complex. Then, it was adsorbed on cotton, dried and annealed. The resulting Co–V₂O₃-GQD@BC shows the three-dimensional carbon framework. The formed V₂O₃ nanocrystals with rich edges and corners are dispersed on the carbon sheets. V⁵⁺ was partly reduced to form low-valent V²⁺ species. V²⁺ and Co²⁺ self-doping narrows the bandgap and creates new electron transfer pathways. Graphene modification accelerates the electron transfer from V₂O₃ to graphene and improves structural stability. The integration of double doping with graphene modification realizes a significant improvement in electrical conductivity and a safe voltage window (1.8 V). The specific capacitance of V₂O₃ in Co–V₂O₃-GQD@BC reaches 2182.89 F g⁻¹, which is more than that of the other vanadium oxide electrodes. The symmetrical supercapacitor with Co–V₂O₃-GQD@BC electrodes provides a high capacitance (664.89 F g⁻¹ at current density of 1 A g⁻¹), rate capacity (366.67 F g⁻¹ at 50 A g⁻¹), cycling stability (97.65% capacitance retention after 10 000 cycles) and energy density (74.8 W h kg⁻¹ at a power density of 425 W kg⁻¹).