Synthesis of Co- and V-doped Ta1.1O1.05 electrode material using tryptophan- and aspartic-acid-functionalized boron-doped graphene quantum dots with excellent supercapacitor performance†

Abstract

Tantalum oxide has emerged as an important electrode material for supercapacitors due to its multiple redox capabilities, high capacitance and structural stability, but the low electrical conductivity prevents its practical applications. This study reports the synthesis of Co- and V-doped Ta_1.1O_1.05 using tryptophan- and aspartic-acid-functionalized boron-doped graphene quantum dots (DWB-GQD). Ta⁵⁺, V⁵⁺ and Co³⁺ were combined with DWB-GQD to form water-soluble complexes. The complex was then soaked in cotton, dried and annealed at 850 °C in an N₂ atmosphere. The resulting Ta_1.1O_1.05 nanocrystals showed a cube-like nanostructure. The self-doping of low-valent Ta, V and Co species induced the production of oxygen vacancies. The presence of oxygen vacancies narrowed the bandgap and created new electron transfer pathways. The graphene surface modification accelerated the electron transfer from Ta_1.1O_1.05 to graphene and improved the structural stability. The unique structure significantly improved the conductivity and led to a wide safe voltage window of 1.9 V. The symmetrical supercapacitor with Co/V–Ta_1.1O_1.05@DWB-GQD electrodes and a 1 M Li₂SO₄/PVA gel electrolyte exhibited high specific capacitance (560.9 F g⁻¹ at a current density of 1 A g⁻¹), high-rate capacitance (365.55 F g⁻¹ at a current density of 10 A g⁻¹), cycling stability (99.5% capacitance retention over 10 000 cycles), and energy density (140.63 W h kg⁻¹ at a power density of 475 W kg⁻¹). Based on these results, the soft supercapacitor shows a wide application prospect in wearable electronic devices.