V2O5 Sol Research Articles

Evaluation of Flexible Electrochromic Device Based on V2 O5 Film Prepared by Electrophoresis

The red V2O5 sol was prepared by facile alternating stirring and ultrasonic dispersion route. A V2O5 film fabricated on ITO-PET by electrophoresis method was used to demonstrate a flexible electrochromic device. The effects of applied voltage and electrophoresis time for V2O5films were investigated in detail. When the electrophoresis time was kept 30 s, the applied voltage was above 3 V to deposit uniform V2O5-PET film. The electrophoresis time could more significantly regulate the deposition of V2O5 on ITO-PET film. A flexible electrochromic device with “sandwich” structure was fabricated using V2O5 film, and its electrochromic performance of the device was evaluated. The flexible V2O5 electrochromic devices show the multicolor electrochromic performance of yellow, yellow-green, green and orange-red. The coloration efficiency values of V2O5 devices were 21.6 cm2C[Formula: see text] (from initial yellow to green) and 26.9 cm2C[Formula: see text] (from green to orange-red), respectively, and the highest transmittance modulation range was 51% at 741 nm. The work provided a facile and green method for fabrication of flexible V2O5 electrochromic device.

High-performance self-doped V4+-V2O5 ion storage films grown in situ using a novel hydrothermal-assisted sol-gel composite method

• V 2 O 5 ion storage nanofilm was prepared on ITO substrate by a novel sol-gel method. • There was no seed layer and additives in situ hydrothermal-assisted sol-gel method. • The annealing affects oxygen vacancy concentration, and in turn affects on ion storage capacity. • The electrochromic device assembled with V 2 O 5 film showed excellent performance. The advancement of efficient ion storage film is a formidable challenge. A kind of self-doped V 4+ -V 2 O 5 ion storage nanofilm on ITO-coating glass substrate is prepared in situ by a novel hydrothermal-assisted sol-gel composite method, which is without seed layers of hydrothermal process and additives of traditional sol-gel method. There are two important factors for the growth of V 2 O 5 nanofilm, that is, heterogeneous nucleation during hydrothermal method and the electrostatic attraction between V 2 O 5 sol and ITO substrate. A small amount of oxygen vacancies are introduced into V 2 O 5 lattice during the hydrothermal process, and the oxygen vacancy concentration is controlled by annealing treatment (200∼400 °C), which significantly improve the storage capacity and Li + diffusion. The excellent cycling performance of 300 °C-V 2 O 5 nanofilm is attributed to the synergistic effect of the gradient oxygen vacancies and the good bonding force between the film and the substrate. Comparing with the ion storage capacity of V 2 O 5 film prepared by traditional sol-gel method with the same annealing treatment (17.88 mC cm −2 ) and V 2 O 5 film without annealing treatment (17.79 mC cm −2 ), 300 °C-V 2 O 5 film has the highest ion storage performance, whose initial value of ion storage is up to 112.25 mC cm −2 and cycling stability is excellent with only a 2.4% decrease after 2000 cycles. The electrochromic device (ECD) with 300 °C-V 2 O 5 nanofilm as ion storage layer and WO 3 as the electrochromic layer has been successfully assembled, which shows fascinating performance.

Dramatically improved mechanical properties of diamond composites via tuning the wettability between diamond abrasive and vitrified bond using V2O5 film

ABSTRACT In this paper, the V2O5 film was coated on the diamond surface by adopting sol–gel method to improve the wettability of the vitrified bond to diamond and the mechanical properties of the vitrified diamond composites. The results show that a uniform and compact V2O5 film formed on the diamond surface at a temperature of 600°C by heat treatment when V2O5 sol had a viscosity of 2 mPa·s. During the process of heat treatment, the unsaturated carbon atoms on the diamond surface combined with V2O5 film to form O–V–C and V–O–C bonds. During the sintering process of vitrified diamond composites, V2O5 film on the diamond surface dissolved in the vitrified bond, which would reduce the surface tension and refractoriness of vitrified bond at the interface and improve the wettability of vitrified bond to diamond. When the sintering temperature was at 650°C, the flexural strength and Rockwell hardness of the diamond composites coated with V2O5 film were 92.8 MPa and 99.4 HRB, which are about 8.4% and 13.5% higher than those of the uncoated composites at 85.6 MPa and 87.6 HRB, respectively.

Facile Synthesis, Characterization of Flower-Like Vanadium Pentoxide Powders and Their Photocatalytic Behavior

In this paper, V2O5 sol was firstly prepared using vanadyl sulfate as a vanadium source by modified sol–gel method at room temperature. Then flower-like V2O5 powders were prepared by coagulating as-prepared sol with anhydrous ethanol and subsequent annealing crystallization. The X-ray diffraction analysis indicated that V2O5 powders exhibited orthorhombic crystal structure after annealing at 450 °C. The experimental data obtained from both field emission scanning electron microscopy and high-resolution transmission electron microscopy identified that V2O5 powders were approximately flower-like in shape and about 5 μm in size. Besides, the Brunauer–Emmett–Teller specific surface area of flower-like V2O5 powders was 24.25 m2/g. According to Uv–Vis spectroscopy, the degradation rate of toluidine blue O (TBO) on as-prepared flower-like V2O5 powders during 10 h of visible light irradiation with an intensity of 15.4 mW/m2 was 88%, which was faster than those over P25 (46%) as a comparison. In addition, the mineralization process of TBO was investigated, which primarily consisted of demethylation and ring-opening oxidation processes, and confirmed by liquid chromatograph-mass spectrometry. The precipitation–oxidation–peptization, coagulation, and crystallization processes were proposed as the formation mechanism for the preparation of flower-like V2O5.

Effect of aging of V2O5 sol on properties of nanoscale films

Abstract Nanoscale films having thicknesses in the range of 92 nm–137 nm were obtained by spin coating V 2 O 5 sol at different stages of aging. The observed structural and morphological changes with time can be attributed to the reactions occurring in the sol. The film morphology changed from an indistinctive featureless film to a homogenous film having ribbon-like nanostructures with aging of sols. TGA and FTIR analysis confirmed loss in the amount of intercalated water content with aging giving rise to structural changes (decrease in interlayer spacing) which were observed using XRD. Variations in mechanical, electrical, and optical properties of the thin films were observed with aging of the sol. Strain in the films were found to decrease with aging. The electrical conductivity increased with aging and this can be correlated to the improved crystallinity of the films with aging. The optical bandgap (calculated from UV–Vis data) decreased and the transmittance increased with aging.

Electrochemical properties of V2O5/carbon composite electrodes in aqueous solutions

The reaction mechanism of V2O5 xerogel and the electrode properties of V2O5/carbon composites in an aqueous electrolyte solution were examined to obtain high-performance electrodes for rechargeable proton batteries. Based on the results of the chemical analysis of the electrode, proton intercalation is suggested to be the dominant reaction mechanism. By using the relationship between the capacity and current density of a thin-film electrode consisting of V2O5 xerogel, the diffusion coefficient in the V2O5 xerogel was determined to be 8 ± 1 × 10−11 cm2 s−1. The V2O5/carbon composite electrode was prepared by drying a homogeneous dispersion of carbon particles in the V2O5 sol. The composite electrodes showed a large capacity of 460 mAh g−1 at a current density of 1 A g−1 and maintained a relatively large capacity of 160 mAh g−1 at 100 A g−1. These properties were attributed to the homogeneous microstructure of the V2O5/carbon composites. The V2O5/carbon composite electrodes were thus revealed as high-performance electrodes with large capacities and excellent high-rate capabilities.

Sn-Doped V2O5 Film with Enhanced Lithium-Ion Storage Performance

Homogeneous Sn-doped V2O5 sol was prepared by the sol–gel method with H2O2, V2O5, and SnCl4·5H2O as precursors, and the films were fabricated by drop-casting, drying at ambient, and then annealing at 450 °C in air for 2 h. X-ray photoelectron spectroscopy (XPS) reveals that the Sn-doped V2O5 film contains 10% V4+ likely compensates with the accommodation of Sn4+ ions. Electrochemical and lithium-ion intercalation properties of both the pure and Sn-doped V2O5 films are systematically studied by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry (CP) tests. The Sn-doped V2O5 film shows much enhanced lithium-ion storage capacity, faster kinetics, and improved cyclic stability in comparison with pure V2O5 film. For example, after 50 cycles, the specific capacity of the Sn-doped V2O5 film retains 334 mAh g–1 with a current density of 500 mA g–1, much higher than 157 mAh g–1 of the pure V2O5 film. Sn-doping is found to reduce the electrochemical reaction resistance, increase the electrochemical reaction reversibility, and enhance the lithium-ion diffusivity. The possible explanation for such significant enhancement in lithium-ion intercalation capacity and cyclic stability of the Sn-doped V2O5 film is discussed.

Effects of TiO2 Interlayers on the Optical Switching of VO2 Thin Films Grown by Sol-Gel Process

Thermochromic VO2 and VxW1-xO2 films were deposited on TiO2/mica substrates. The TiO2/mica substrates were fabricated via Sol-Gel process, and the hydrophilicity of the TiO2/mica substrate was improved under UV light irradiated. The V2O5 sol was deposited on the TiO2/mica substrate by the spin coating method, and then it was annealed. SEM and XRD analysis were applied to analyze the morphology, phases and microstructure of the films. FTIR was used to study the thermochromic properties. The results suggest that VO2/TiO2 grow preferentially along single orientation. VxW1-xO2/TiO2 composite film is impossible to fabricate single orientation films. TiO2 interlayers are favorable to compact the VO2 thin films and reduce the transition temperature. It will make the hysteresis width of VxW1-xO2/TiO2 composite film reduce to about 4℃ particularly.

Synthesis and Electrochromic Characterization of Vanadium Pentoxide/Graphene Nanocomposite Films

The vanadium pentoxide (V2O5)/graphene nanocomposite films have been synthesized by direct intercalation method using V2O5 sol and graphene. The structure of the films was investigated with X-Ray Diffraction (XRD). The electrochemical properties of the nanocomposite films were studied by cyclic voltammetry and chronoamperometry with the standard three-electrode configuration. The optical properties were characterized by UV–Visible spectrophotometer. The intercalation of graphene improves the stability and reversibility of the V2O5 xerogel films. The response rate of the V2O5/graphene nanocomposite films is enhanced. The optical modulatory range of the V2O5/graphene nanocomposite films is 1.5 times larger than that of V2O5 xerogel films. These results demonstrate that the nanocomposite films can be used potentially in fast switching electrochromic devices.

Selective Synthesis of Vanadium Oxides and Investigation of the Thermochromic Properties of VO2 by Infrared Spectroscopy

AbstractThis paper reports a facile and low‐cost routine for the selective synthesis of vanadium oxides by hydrothermal treatment of V2O5 sol. Our experiments found a defined phase evolution sequence [V2O5 → V3O7·H2O → VO2 (B) → VO2 (A) → VO2 (M)] that is strongly dependent on the hydrothermal temperature, pressure, and reaction time. A mechanism for the formation of the vanadium oxides based on the oriented attachment (OA) growth model is proposed and discussed. The VO2 (A + M) phase and the pure VO2 (M) phase each show an abrupt change in infrared transmittance with temperature, which demonstrates their potential for applications in the field of energy conservation, and the modulation in the infrared properties of the VO2 (M) phase, thanks to its high purity, is far more prominent than that of the mixture phase VO2 (A + M).

Atomic layer deposition of Al2O3 on V2O5 xerogel film for enhanced lithium-ion intercalation stability

V2O5 xerogel films were fabricated by casting V2O5 sols onto fluorine-doped tin oxide glass substrates at room temperature. Five, ten and twenty atomic layers of Al2O3 were grown onto as-fabricated films respectively. The bare film and Al2O3-deposited films all exhibited hydrous V2O5 phase only. Electrochemical impedance spectroscopy study revealed increased surface charge-transfer resistance of V2O5 films as more Al2O3 atomic layers were deposited. Lithium-ion intercalation tests at 600 mAg−1 showed that bare V2O5 xerogel film possessed high initial discharge capacity of 219 mAhg−1 but suffered from severe capacity degradation, i.e., having only 136 mAhg−1 after 50 cycles. After deposition of ten atomic layers of Al2O3, the initial discharge capacity was 195 mAhg−1 but increased over cycles before stabilizing; after 50 cycles, the discharge capacity was as high as 225 mAhg−1. The noticeably improved cyclic stability of Al2O3-deposited V2O5 xerogel film could be attributed to the improved surface chemistry and enhanced mechanical strength. During repeated lithium-ion intercalation/de-intercalation, atomic layers of Al2O3 which were coated onto V2O5 surface could prevent V2O5 electrode dissolution into electrolyte by reducing direct contact between active electrode and electrolyte while at the same time acting as binder to maintain good mechanical contact between nanoparticles inside the film.

Enhanced Lithium-Ion Intercalation Properties of V2O5 Xerogel Electrodes with Surface Defects

V2O5 xerogel films were fabricated by casting V2O5 sols onto fluorine-doped tin oxide (FTO) glass substrates and annealing at 300 °C for 3 h in different annealing atmospheres of air and nitrogen. Films prepared in different annealing conditions possess different grain sizes and crystallinity, while the vanadium ion oxidation state also varies, as identified by X-ray absorption spectroscopy. A nitrogen annealing atmosphere induces the presence of defects, such as V4+ ions, and associated oxygen vacancies. Thus, the presence of defects, whether on the film surface or in the bulk, can be controlled by using air and nitrogen annealing atmospheres in the proper order. Electrochemical impedance analyses reveal enhanced charge-transfer conductivity in films with more V4+ and oxygen vacancies on the film surface, that is, a film annealed, first, for 0.5 h in air and then for 2.5 h in nitrogen. Lithium-ion intercalation measurements show that, at a charge/discharge current density of 600 mA g−1, this film possesses a noticeably better lithium-ion storage capability than films without surface defects. This sample starts with an initial discharge capacity of 139 mA h g−1, and the capacity increases slowly to a maximum value of 156 mA h g−1 in the 15th cycle, followed by a mild capacity degradation in later cycles. After 50 cycles, the discharge capacity is still as high as 136 mA h g−1. A much improved lithium-ion intercalation capacity and cyclic stability are attributed to V4+ surface defects and associated oxygen vacancies introduced by N2 annealing.

Hydrothermal synthesis of VO2 (B) nanorings with inorganic V2O5 sol

Metastable phase VO2 (B) nanorings were synthesized by hydrothermal treatment of inorganic V2O5 sol. It was found that oriented attachment growth and a subsequent rolling mechanism are essential for the formation of VO2 (B) nanorings under hydrothermal conditions.

Synthesis of vanadium pentoxide (V2O5) ultralong nanobelts via an oriented attachment growth mechanism

A cost-saving and easy-handling sol-gel process coupled with a hydrothermal approach was proposed to synthesize V2O5 ultralong nanobelts by merely using inorganic V2O5 sol as the precursor without any organic or inorganic templates. An Oriented Attachment growth mechanism was suggested to explain the growth process of V2O5 ultralong nanobelts.

Synthesis, field-emission and electric properties of metastable phase VO2 (A) ultra-long nanobelts

High quality single crystalline metastable phase VO(2) (A) ultra-long nanobelts were synthesized by hydrothermal method using inorganic V(2)O(5) sol as precursor and polyethylene glycol (PEG) as both surfactant and reducing agent. It was found that the oriented attach growth mechanism is responsible for the formation of VO(2) (A) nanobelts. In addition to an endothermic peak, an unusual exothermic peak was detected in DSC curve of the nanobelts. The temperature dependence of the lattice parameters have been studied, and it was found that the a-axis expands while the c-axis contracts in the high-temperature XRD test. The VO(2) (A) nanobelt has a low turn-on field of 3.8 V μm(-1) and a high field enhancement factor of 1739 in the field emission measurement. Electrical transport measurement of a single VO(2) (A) nanobelt gives a relative low hoping activation energy of 0.28 eV.

High Li<sup>+</sup>-Ion Storage Capacity and Multi-Electrochromism Behavior of Electrodeposited Molybdenum Doped Vanadium Oxide Films

Molybdenum doped vanadium oxide (Mo doped V2O5) xerogel films were prepared by cathodic electrodeposition on indium tin oxide (ITO) substrate from Mo doped V2O5 sol synthesized by sol-gel combined with hydrothermal reaction. Mo doped V2O5 xerogel films were deposited at different potentials between -0.01 V and -0.7 V vs saturated calomel electrode (SCE) with the potentiostatic mode. The structure was characterized for using X-ray diffraction (XRD), atomic force microscopy (AFM). These studies reveal that films consist of layered V2O5 host structure with various surface morphologies depending upon the deposition potentials. As shown by the cyclic voltammograms results, the films electrodeposited at -0.3 V exhibited Li+-ion storage capacity as high as ca. 70 mC/cm2 for the 50th cycle and showed multi-electrochromic behavior (orangered-green-blue) depending on the extent of intercalation during the electrochemical lithium insertion/extraction processes. It is proposed that the particles forming the films arrange directionally and crystallize partly, which lead to the enhanced electroactivity of vanadium oxide films by shortening the diffusion distance or quickening the transference rate of Li+ ions in the films.

Vanadium pentoxide gels: From “chimie douce” to “matière molle”

This article presents a review of the colloidal and liquid-crystalline properties of vanadium pentoxide suspensions from a physicist's perspective. The processes occurring during the synthesis of these suspensions are first discussed. Then, the liquid-crystalline properties of V2O5 sols and gels are described. These nematic phases are easily aligned by weak magnetic fields or by alternative electric fields. The delicate interplay between repulsive hardcore and electrostatic interactions and van der Waals attractions defines the (concentration, ionic strength) phase diagram that includes an isotropic phase, a uniaxial nematic phase, a biaxial nematic gel state and a flocculated state. Deuterium NMR spectroscopy of D2O molecules gives information on the rotational dynamics of the nematic phase. Finally, various applications of these colloidal suspensions in the fields of hybrid organic/inorganic materials, mesoporous solids, and of the structures of biomolecules, are reviewed. Cet article présente une revue des propriétés colloïdales et cristal-liquides des suspensions de pentoxyde de vanadium selon une perspective de physicien. Les processus qui ont lieu durant la synthèse sont tout d’abord discutés. Puis, les propriétés cristal-liquides des sols et des gels de V2O5 sont décrites. Ces phases nématiques sont facilement alignées par de faibles champs magnétiques ou par des champs électriques alternatifs. Le jeu subtil des interactions répulsives de type volume exclu et électrostatiques et des attractions de van der Waals définit le diagramme de phases (concentration, force ionique) qui inclut une phase isotrope, une phase nématique uniaxe, un état gel nématique biaxe et un état flocculé. La spectroscopie RMN du deutérium de molécules D2O renseigne sur la dynamique rotationnelle de la phase nématique. Enfin, différentes applications de ces suspensions colloïdales, dans les domaines des matériaux hybrides organique/inorganique, des solides mésoporeux et des structures de biomolécules, sont décrites.

V2O5 xerogel electrodes with much enhanced lithium-ion intercalation properties with N2 annealing

V2O5 xerogel films were fabricated by casting V2O5 sols onto FTO glass substrates and annealing at 300 °C for 3 hours in nitrogen and air. The films annealed in nitrogen and air possessed different grain size and crystallinity. Optical absorption measurements and electrochemical impedance analyses revealed a reduced optical bandgap and enhanced electrical conductivity of N2 annealed V2O5 film. Lithium ion intercalation measurements showed that at a charge/discharge current density of 600 mAg−1, the N2 annealed sample possessed noticeably better lithium ion storage capability. In contrast to the air annealed sample, which started with a discharge capacity of 152 mAhg−1 but after 50 cycles the capacity had decreased to a low value of only 44 mAhg−1, the N2 annealed sample started with a low value of 68 mAhg−1 but the capacity increased sharply to a high value of 158 mAhg−1 at the 24th cycle, followed by little capacity degradation in later cycles and after 50 cycles, the discharge capacity was still as high as 148 mAhg−1. Much improved lithium ion intercalation capacity and cyclic stability could be attributed to surface defects V4+ and/or V3+ and associated oxygen vacancies introduced by N2annealing as well as much less crystallized vanadium oxide.

Field Emission from V2O5·nH2O Nanorod Arrays

Hydrated vanadium pentoxide (V2O5·nH2O) nanorod arrays with diameters of ∼200 nm and lengths of more than 5 μm have been synthesized via template-based physical wetting of V2O5 sols. The V2O5·nH2O ...

High Power Battery Electrodes Using Nanoporous V2O5/Carbon Composites

Nanoporous composite electrodes for lithium ion batteries were successfully fabricated by coating porous carbon with V2O5 gel, and their high rate capability was demonstrated. The porous carbons prepared by using SiO2 colloidal crystals as templates exhibited ordered three dimensionally interconnected pores. The porous carbons were immersed in V2O5 sol under reduced pressure repeatedly to obtain V2O5/carbon composites. The nanoporous V2O5/carbon composites thus obtained exhibited large capacity of more than 100 mAh (g-composite)-1 and good rate capability of 80% at 5.0 A (g-composite)-1. The good performance is explained by electric double layer capacitance of large surface area and high rate lithium insertion to V2O5 gel. According to a calculation, very high-power energy sources with 177 mAh (g-composite)-1 at 100 A (g-composite)-1 are expected by using the nanoporous composite electrodes.