Preparation And Electrochemical Properties Of Vanadium-Based Nanomaterials

As a kind of transition metals, vanadium owns variousoxidation states when generating vanadium oxides, can form VN combined with nitrogen which is good electric conductor, and have been widely investigated in electrochemical applications. In this thesis, we have demonstrated an efficient approach to fabricate two kinds of vanadium-based nanomaterials (V2O3-RGO and G-VNQD) via hydrothermal treatment of graphene oxide with NH4VO3 and subsequently annealing under hydrogen or ammonia gas, investigated the characteristics of the morphology and structure, and explored the electrochemical properties of lithium storage and catalytic activity for ORR.The distinctive and splendid features of V2O3-RGO and G-VNQD inclusive of homogeneous dispersionof nanocrystals onto graphene, multi-porous structureand continuous graphene backbone not only could accommodatethe volume changes effectively, prevent their aggregation during cycle process, but also allow for the fast diffusion of lithium and electron through the electrode, rendering significantly improved electrochemical activities for lithium storage. As a consequence, vanadium-based nanomaterials displayed prominent electrochemical performances in respect of the high reversible capacity, good high-rate capability, and long cyclability when it was used for lithium storage.V2O3-RGO 3D gels delivered the reversible capacities of 796 mAh g-1,201 mAh g-1 and 192 mAh g-1 at a current rate of 0.2C,50C and 100C, respectively. No capacity attenuation occured after 1000 cycles at a rate of 5 C and excellent electrochemical performances were exhibitedat at both high and low temperatures (0-75?). Remarkably, a high reversible capacity of 715 mAh g-1 was achieved at a current rate of 0.2 C for G-VNQD. The reversible capacities of 317 and 201 mAh g-1 were retained at 5 C and 20 C even after 50 cycles, respectively, and the Coulombic efficiencies exhibited almost 100%. Thus, even at a current rate of 5 C, a high capacity of 280 mAh g-1 could still be stably delivered after 800 cycles.As a nonprecious metal-based electrocatalysts for ORR, VNQD-NG prossess the unique structural features including plentiful VN quantum dots, high surface area and multi-level pores afford considerable structural edges and defects as active sites, maximizing the exposed active sites and providing sufficient electron transport pathways for ORR. Hence, the optimized VNQD-NG exhibits high electrocatalytic activity, long durability and high selectivity for ORR, superior to commercially available Pt-C.These achievements could provide an extension of developing various other 3D porous metal nitride quantum dots onto graphene for broad applications in batteries, sensors, catalysis, and other electronic devices.