Synthesis And Electrochemical Properties Of Vanadium Oxyhydroxide And Their Carbonous Composites

Energy crisis has been a serious problem owing to rapid growth rate of population,environmental pollution and waste of resources as rapid development of the globalization.Therefore,the demands for inexpensive,natural abundance and renewable resources and energies are vital and extremely urgent.Supercapacitors?SCs?have gained increasing and considerable attention in recent years compared with batteries.In the past decades,vanadium based materials have been widely applied to energy storage,not only due to their various oxidation states and structures,but also the high energy density and wide potential window.Comparing with vanadium oxides,vanadium oxyhydroxide has been paid rare attention as the energy storage materials.Hence,this study focus on the synthesis and electrochemical performance of vanadium oxyhydroxide compound with CNT and GO composite.The specific results are as follows:?1?To explore the synthesis conditions of vanadium oxyhydroxide.With the assistance of polyvinyl pyrrolidone?PVP?and by adjusting pH about 4.7,VO?OH?₂ was successfully synthesized by a facile hydrothermal method for the first time.VO?OH?2nanorods showed capacitive behavior based on pseudocapacitance and superior rate capability.Specific capacitance of 198 F·g^-11 was achieved at 0.5 A·g^-1.Due to the poor durability,it is easy to dissolve in electrolyte after many cycles.Therefore,vanadium oxyhydroxide needs to combine with carbon materials to improve its electrochemical properties?2?A novel intercalation pseudocapacitance material,VO?OH?₂/CNT binary composite with cross-linked structure is first successfully synthesized by a facile one-step hydrothermal method.VO?OH?₂/CNT composite electrode exhibit a capacitance of 256 F·g^-11 at 0.5 A·g^-1within the wide potential range of-0.8¹.2 V.The VO?OH?₂/CNT SSC delivers an high energy density of 32.08 Wh·kg^-11 at a power density of 63.65 W·kg^-11 in a large operating voltage of 2.2 V.As well as a well it performs a well cycling stability that the capacitance retention is about 90%after 3000 cycles.?3?We develop a novel 3D VO?OH?₂/rGO which VO?OH?₂ nanoflakes wrapped with reduced graphene oxide nanosheets,and a small amount of V⁴⁺is oxidized to V⁵⁺.VO?OH?₂/rGO composite electrode yields a high specific capacitance of 512 F·g^-1(1024C·g^-1)at 0.5 A·g^-11 within the large potential window of-1.2⁰.8 V.And the VO?OH?₂/rGO SSC exhibits the integration of desirable flexibility,2.4 V high voltage and high energy density,which reaches an energy density of 56.26 Wh·kg^-1at a power density of 104.16W·kg^-1.After charging for 100 s,two devices in series can light red and blue LED for 12 min and 5 min,respectively.?4?3D hierarchical VO_x?OH?_y/CNT/rGO composite is synthesized by a facile and self-assembly method through a low temperature one-step hydrothermal treatment.VO_x?OH?_y anchoring densely on the surface is a novel vanadium oxyhydroxide with a mixed-valence V^+4/+5.VO_x?OH?_y/CNT/rGO composite electrode exhibits a high specific capacitance of 414F·g^-1at 0.5 A·g^-1within the potential range of-1.2⁰.6 V in 1 mol·L^-1LiClO₄/PC.The symmetrical supercapacitor can deliver a high energy density of60.90 Wh·kg^-1at a power density of 81.85 W·kg^-11 with a large voltage window of 2.2 V.In conclude,this paper enriches the study of the vanadium oxyhydroxides,not only the guiding significance for its synthesis and composites,but also the enlightenment for the research of electrochemical properties,which is of great significance to their further research.