Control Synthesis And Electrochemical Properties Of Hierarchical Vanadium Oxides

Batteries,electrocatalysis and supercapacitor are three hottest research inerests in electrochemical field.Supercapacitor have attracted much attention for its high power density,good cycling stability and high rate capability,but the low energy density always limits the practical use od supercapacitor.Vanadium oxides generally possess layered structure,that unique layered structure may improve the utilization of active materials,and increases the ion mobility during the charge/discharge process.Meanwhile,the layered structure can also reduce the stress from ions intercalation and deintercalation;the multiple valence provide vanadium oxides a high theoretical energy density.All these factors make vanadium oxides promising electrode materials.To date,various vanadium oxides nanostructures were prepared and exhibited improved utilization,but the developement is always puzzled by the complicated synthetic method and severe reaction condition.In this work,three different kinds of hierarchical porous vanadium oxides were synthesized by a facile and template-free method,and the component,structure and morphology were analysized by XRD?SEM?TEM?IR,Raman,etc.Electrochemical properties of the as-obtained hierarchical porous vanadium oxides and kinds of flexible supercapacitor devices fabricated using the as-obtained hierarchical porous vanadium oxides were investigated.The results are as follows:?1?Hierarchical porous VOOH hollow spheres possessing the macropores from the hollow interior and mesopores derived from the shell were successfully synthesized using ammonium metavanadate as the starting vanadium source materials by a facile and template-free hydrothermal method.The diameter of the as-obtained VOOH hollow microspheres ranges from 300 to 500 nm,the surface of VOOH spheres is very rough and consists of lots of nanoparticles.The BET specific surface area of hierarchical VOOH hollow spheres is 32 m²·g^-1.VOOH hollow spheres had the capacitive behavior based on the pseudocapacitance.Hierarchical VOOH hollow spheres exhibited typical pseudocapacitance and the specific capacitance of 93 F·g^-1 in organic electrolyte.The cycling stability of hierarchical VOOH hollow spheres in the aqueous and organic electrolytes were discussed in detail and showed that their cycle performance was greatly improved using organic electrolyte.Then we discussed the different between symmetrical supercapacitor and a symmetrical supercapacitor fabricated using the as-obtained VOOH hollow spheres.?2?Three-dimensional porous V₂O₅ hierarchical spheres composed of stacked platelets were fabricated by a facile,low-cost and template-free method.the diameter of as-prepared V₂O₅ spheres ranged from 250 nm to 400 nm.the as-prepared V₂O₅ spheres had rough surface and numerous of line fringes appeared.Most probable distribution pore size ranged 10 nm to30 nm.The V₂O₅ spheres exhibits an excellent capacity up to 473 C·g^-1 as a battery-typed electrode The layered structure effectively enhanced the rate capability,it retain 70%capacitance with the current density has a tenfold increase,and prolong its using life nearly sixfold by using it as a battery-typed electrode material for HSC device.?3?A facile and template-free hydrothermal route combined with subsequent annealing treatment are developed to controllably synthesize of V₂O₅ hollow spheres with hollow core and V₂O₅ mesoporous shell.Diameter of V₂O₅ hollow spheres ranged from 400 nm to 600 nm,and thickness of V₂O₅ shells was about 40 nm in average.Most probable distribution pore size ranged 17 nm to 30 nm.The surface of V2O5 nanospheres was rough and consisted of numerous nanoparticles.Specific capacity of as-prepared V₂O₅ hollow spheres reached as high as 512 C·g^-1,the hierarchical porous and the layered structure effectually improve the rate capability,it retain 76%capacitance with the current density has a tenfold increase.The as-prepared V₂O₅ hollow spheres were assembled into symmetrical supercapacitor and hybrid supercapacitor devices,and the different between two kinds of devices were discussed as follow.