Construction of advanced Nb9VO25 electrode material by introducing graphene quantum dot for high energy supercapacitors with exceptionally high diffusive capacitance

Unreasonable tunnel structure and low intrinsic conductivity limit practical applications of niobium oxide in high-performance supercapacitors. The study reports the construction of Nb 9 VO 25 electrode material via coordination of Nb(V) and V(V) with histidine and serine-functionalized and boron-doped graphene quantum dot (HSBGQD) and subsequent annealing. The introduction of HSBGQD and rambutan peel leads to formation of small Nb 9 VO 25 nanocrystal and low valent Nb and V species. The combination of small size and more reasonable tunnel structure accelerates the ion diffusion. The Nb(IV) and V(IV) double doping optimizes the tunnel structure, narrows the bandgap and creates new pathways for high-speed electron transfer. The integration of defect engineering with graphene surface modification enhance the intrinsic conductivity. The Nb 9 VO 25 electrode shows exceptionally high specific capacitance of 2925.3 F/g, which is more than 142 times that of Nb 2 O 5 . The symmetrical supercapacitor with Nb 9 VO 25 electrodes and PVA/Li 2 SO 4 gel electrolyte offers high specific capacitance (263 F/g at 1 A/g), high-rage capacity (138 F/g at 50 A/g), cycling stability (capacitance retention of 95.2 % after 10,000-cycle), energy density (146 W h Kg −1 at 996 W Kg −1 and 77 W h Kg −1 at 50181 W kg −1 ) and broad application prospect in wearable electronic devices.