Significantly Enhanced Supercapacitor Performance of W3Nb14O44 by Introducing Serine and Histidine-Functionalized and Boron-Doped Graphene Quantum Dots

Niobium tungsten oxide has become one the promising electrode materials for supercapacitors due to its high ion diffusion coefficient, multiple redox pairs and structural stability, however, extremely low inherent electrical conductivity limits its rate capability. The study reports the synthesis of a W3Nb14O44/biomass carbon (BC) composite by introducing serine and histidine-functionalized and boron-doped graphene quantum dots (SHB-GQDs). Here, ammonium tungstate and niobium oxalate combined with SHB-GQDs to form a water-soluble SHB-GQD-Nb/W complex, sucked into rambutan peel, freeze-dried and annealed. The introduction of SHB-GQD realizes the construction of the W3Nb14O44 nanocrystals with a (4 x 4)-sheer structure, more exposed high-index crystal faces and small size (22 +/- 0.18nm), oxygen vacancies and graphene electron trap. The integration of these multiple structure engineering improves the inherent electronic conductivity and expands the safe voltage window (2.1 V) and leads to outstanding supercapacitor performance. The W3Nb14O44-SHB-GQD/BC electrode offers a high capacitance of 535 F g(-1) at 1 A g(-1) (312 mA h g(-1)), which is more than the theoretical capacity of W3Nb14O44 in lithium ion batteries (293.56 mA h g(-1)). The symmetrical supercapacitor exhibits a high capacitance of 457 F g(-1) at 1 A g(-1), an energy density of 70 W h Kg(-1) at 525 W Kg(-1) and 95.6% capacitance retention after 10 000-cycle at 10 A g(-1). It shows a broad prospect for applications in wearable electronics.