Controlled Synthesis Of Vanadium Oxides And Their Optical And Electrochemical Performance

Vanadium oxide nanomaterials with unique physical and chemical properties have potential application in the fields of intelligent energy saving and energy storage due to their rich valence states and diversified structures.Vanadium dioxide(VO2(M)),as a representative of inorganic thermochromic materials,has a reversible metal-insulator phase transition,and its optical and electrical properties and other physical properties show great changes before and after the phase transition,and thus VO2(M)can be used in many fields such as infrared camouflage materials,thermochromic smart windows and laser protection.There are many studies on the improvement of VO2(M)performance,but there are still some bottleneck problems in practical applications.The solution of these bottlenecks has become the only way to promote the industrialization of VO2(M)films.As the representatives of transition metal oxide materials,vanadyl hydroxide(VOOH)and vanadium pentoxide(V2O5)have shown excellent performance in energy storage devices such as supercapacitors due to their rich valence states and special layered structure.How to obtain high-performance electrode materials is the key for practical applications.In this thesis,based on the application in the smart windows and supercapacitors,the controllable synthesis,thermochromics and electrochemical performance of vanadium oxide nanomaterials are systematically studied.A mild low-temperature thermal decomposition method was designed.Vanadyl ethylene glycol(VEG)nanorod precursor with uniform particle size and good dispersion were obtained by using amorphous vanadium oxide as vanadium source.And VO2(M)nanoparticles were successfully prepared by thermal decomposition of VEG nanorod precursors.It was found the thermal decomposition atmosphere and temperature have obvious influences on the phase,morphology,size and phase transition temperature of the products.As a nanothermochromic film,the composite of VO2(M)with ITO glass substrate can improve the difference of visible light transmittance of VO2(M)nanoparticles before and after phase transition,and thus enhance the thermochromic performance of the composite film.The best optical performance of the VO2(M)/ITO composite film is of the visible light transmittance(Tlum)of 48%,infrared modulation(?TIR)of 25%,solar light transmittance modulation(?Tsol)of 11%.Under the action of external electric field,the VO2(M)/ITO composite film shows a programmable infrared switch behaviors.VOOH nanosheets were successfully prepared by hydrothermal reaction using amorphous vanadium oxide as vanadium source,and VO2(M)nanosheets films were obtained by further vacuum annealing treatment of the VOOH nanosheets.It was found the annealing temperature and vacuum degree obvious affect the structure and thermochromic performance of VO2(M)nanosheets films.The VO2(M)nanosheets can significantly improve the difference of visible light transmittance and thermochromic properties of the VO2(M)nanosheets films before and after phase transition due to their special two-dimensional morphology.The optimal Tlum,?TIR and ?Tsol of the VO2(M)nanosheets films are of 47%?24.7%and 11%,respectively.Using commercial V2O5 powder as vanadium source,VOOH nanosheets with high specific surface area were successfully prepared.The electrochemical performance of VOOH nanosheets as electrode material for supercapacitors in lmol/L lithium perchlorate/propylene carbonate(LiClO4/PC)organic electrolyte was investigated.It was found that the capacitance performance of VOOH nanosheets can be obviously enhanced due to their higher specific surface area and lower charge transfer resistance and diffusion resistance.The highest specific capacitance of VOOH nanosheets is 3 times that of VOOH nanoparticles and the hollow spheres reported in literature,and the capacitance retention rate can reach 70%after 2000 cycles,showing a good cycling stability.Using VOOH nanosheets as raw material,porous V2O5 nanosheets with mixed valence state and high specific surface area(56.9 ml/g)were successfully fabricated by simple annealing treatment in air.The annealing temperature influences the electrochemical properties of porous V2O5 nanosheets and it was found that the low V5+/V4+valence ratio is beneficial in improving the electrochemical performance of porous V2O5 nanosheets as electrode materials for supercapacitors.The highest specific capacitance of porous V2O5 nanosheets can reach 549 F/g.