Phase Equilibria of the SiO2–V2O5 system

The SiO₂–V₂O₅ system is one of the key systems for vanadium extraction and applications of vanadium oxides in the ceramic industries. However, only limited data in this system and contradictive results were reported from preceding studies. In the present study, high-temperature phase equilibrium experiments were conducted to construct the phase diagram of SiO₂–V₂O₅ system at temperature range of 660–1100 °C. Electron probe X-ray micro-analyzer (EPMA) was used to analyze the microstructure and composition of the phases presented in quenched samples. The liquidus temperatures in both SiO₂ and V₂O₅ primary phase field were determined. The eutectic temperature is confirmed to be within 670–680 °C and the eutectic composition comprises 1.9 wt% SiO₂. SiO₂ phase contains up to 1.4 wt% V₂O₅ in the temperature range investigated.     

Intercalation of conducting poly(N‐propane sulfonic acid aniline) in V2O5 xerogel

Poly(N‐propane sulfonic acid aniline) (PSPAN) can be formed between the lamellas of V₂O₅ xerogel by in situ oxidative polymerization/intercalation of N‐propane sulfonic acid aniline in the presence of air (V₂O₅ being the oxidation agent). The PSPAN/V₂O₅ nanocomposites were characterized by XRD, TEM, TGA, FTIR, UV–vis‐NIR, and conductivity measurement. The results show that the V₂O₅ maintains lamellar structure, but its interlayer spacing has increased from 1.18 to 1.31 nm. The FTIR spectra indicate that there is interaction between negatively charged oxygen of the sulfonic group of PASPN and the vanadium ion in V₂O₅ matrix. The electrical conductivity of PSPAN/V₂O₅ nanocomposite reached the value of 1.2 × 10^?2 S/cm, which is 10⁴ times higher than that of the V₂O₅ xerogel, and is 10² times more than that of the PSPAN. It was found that the aging in air facilitated the chain growth of PSPAN between the V₂O₅ lamellas, resulting in the increase of the electrical conductivity. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2569–2574, 2007     

Improved cycling stability of V2O5 modified spinel LiMn2O4 cathode at high cut-off voltage for lithium-ion batteries

Spinel lithium manganese oxide, LiMn₂O₄ coated with V₂O₅ layer (labeled as LMO-VO) has been developed and its electrochemical performances as cathode material for lithium-ion batteries has been evaluated at high cut-off voltage (>4.5 V vs. Li/Li⁺) and compared with pristine LiMn₂O₄ (labeled as LMO). The crystal structure investigations show that LMO-VO has longer Li–O bond length for fast Li-ion diffusion kinetic process. The scanning electron microscopy results indicate that LMO-VO has finer particles and the V₂O₅ layer has been successfully coated on the LMO surface uniformly. The highly conductive V₂O₅ coating layer enhances the ionic conductivity of the LMO cathode, as evidenced by the significant drop of R_ct value from the Nyquist plot. Under high operating voltage, the cell employed with coated LMO shows exceptional cycling performance in capacity retention and potential difference. After 300 cycles, the capacity retention per cycle has been boosted from 99.90% to 99.94% by adopting the V₂O₅ coating layer. In addition, surface coating with V₂O₅ stabilizes the potential difference at very minimal change for a longer period. This convincingly proves that the V₂O₅ coating layer not only protects against hydrofluoric acid (HF) attack and greatly restrains the increase of cell polarization at high voltage.     

Synthesis and characterization of poly(o‐anisidine)/V2O5 and poly(o‐anthranilic acid)/V2O5 nanocomposites

Poly(o‐anisidine)/V₂O₅ and poly(o‐anthranilic acid)/V₂O₅ nanocomposites were prepared by in situ intercalative polymerization, and the structure and electrical properties of these nanocomposites were investigated using GPC, TGA, XRD, TEM, FTIR, UV‐vis as well as conductivity measurement. The results show that the steric effect and nature of the substituting groups in the aromatic ring has an influence on the structure and electrical properties of the nanocomposites. Poly(o‐anisidine) or poly(o‐anthranilic acid) exists as a monolayer of outstretched chains in the gallery of the V₂O₅ xerogel owing to the confined environment in the nanometer‐size gallery. And intercalation of poly(o‐anisidine) or poly(o‐anthranilic acid) can improve the conductivity of V₂O₅ xerogel. Copyright © 2005 Society of Chemical Industry     

Investigations on performance of PEDOT:PSS/V2O5 hybrid symmetric supercapacitor with redox electrolyte

Nanocomposites of PEDOT:PSS with V₂O₅ nanoparticles are synthesized by simple physical mixing of the two with different weight percentages of the latter and their performance as supercapacitor electrode materials is verified. Best performance is obtained for an optimum weight percent of 16.8% of V₂O₅. The specific capacitance and specific energy of the composite with 16.8% V₂O₅ increases by more than two fold, with increase in specific power, as compared to that of pristine PEDOT:PSS device. This is attributed to increase in conductivity brought about by the presence of V₂O₅ nanoparticles, easier transportation and intimate contact of electrolyte ions with the nanolayers of V₂O₅ due to the intercalation of PEDOT:PSS between the layers, and additional redox reactions due to various oxidation states of vanadium element, besides redox electrolyte effects. This is further confirmed by the reduced ESR of the composite device as compared to that of pristine PEDOT:PSS device.     

Thermal Decomposition of Divanadium Pentoxide V2O5: Towards a Nanocrystalline V2O3 Phase

Thermal decomposition of V₂O₅ was studied by means of transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). Samples were heated in a specimen chamber of an electron microscope up to 600 °C in vacuum at 10^-7 Torr. TEM and EELS reveal a sequence of transformations from V₂O₅ via VO₂ to V₂O₃, which differs from the electron-beam-induced reduction of V₂O₅. The phase transformation does not proceed topotactically. Our observation reveals that the initial thermal decomposition of V₂O₅ to V₂O₃ is followed by a combination of diffusion, coalescence, and stabilization processes. Our experiments open a new way for the preparation of single-crystalline V₂O₃ nano-particles.     

Vacancy-engineered V2O5-x films for ultrastable electrochromic applications

In the present study, we prepared vacancy-engineered V₂O_5-x films for electrochromic (EC) applications. To investigate the vacancy effect of V₂O_5-x films with high EC performance capabilities, precursor concentrations of V-based sol solutions were varied at 1 wt%, 5 wt%, and 10 wt%. Among them, V₂O_5-x films with a precursor concentration of 5 wt% (V₂O₅-5wt%) showed superior EC performance outcomes due to the (001)-plane-oriented crystal structure, which provides high electrical conductivity with the oxygen vacancy (V_o). In addition, the gravel-like uniform surface morphology with the optimized film thickness provides a stable electrochemical reaction during the EC measurement. As a result, V₂O₅-5wt% exhibited fast switching speeds (2.1 s for coloration and 3.6 s for bleaching), high transmittance modulation (ΔT) (51.32%), high coloration efficiency (CE) (52.3 cm²/C), and excellent cycle stability (85.85% ΔT retention after 500 cycles). In addition, V₂O₅-5wt% showed energy storage capability of 443.7 F/g at a current density of 2 A/g, thus proving its potential for use in multi-functional applications. Therefore, these results provide valuable insight related to the engineering of vacancies in EC films to achieve high-performance EC devices and additional multi-functional applications.     

Reactivity of V2O5/MgF2 Catalysts for the Selective Ammoxidation of 3-Picoline

V₂O₅/MgF₂ catalysts with V₂O₅ contents ranging from 2.1 to 15.7 wt% were prepared, and the influence of the V₂O₅ content of the V₂O₅/MgF₂ catalyst on the structure and activity for the ammoxidation of 3-picoline was investigated. XRD data indicate that V₂O₅ is in a highly dispersed state though segregation of V₂O₅ into tiny crystallites occurs at and above 8 wt% V₂O₅. The 3-picoline ammoxidation activity increased with an increase in V₂O₅ content due not only to the species arising out of interaction of V₂O₅ and MgF₂, but also to the presence of V₂O₅ microcrystals in the catalysts.     

Kinetic studies and Mechanism Evolution of the Ammoxidation of 3‐picoline Over V2O5/ZrO2 Catalyst

A kinetic investigation of the ammoxidation of 3‐picoline to 3‐cyanopyrdine has been studied over V₂O₅/ZRO₂ Catalyst in a differential flow reactor in the temperature range 573‐683 K. The partial pressures of 3‐picoline, oxygen and ammonia were varied and rates were measured for the formation of 3‐cyanopyridine. Kinetics studies reveal that the mechanism of the reaction is of the “Redox” type. The rate equation deduced, assuming a study state involving a three stage oxidation‐reduction process, represented the data most satisfactorily for conversion of 3‐picoline to nicotinonitrile. Catalysts have been characterized using IR, XRD, ESR, Surface area and ammonia desorption methods with a view to understanding the structure and nature of bonding over the surface of the catalyst. A tentative mechanism of the process has been suggested.     

SO2 oxidation over the V2O5/TiO2 SCR catalyst

The effects of V₂O₅ loading of the V₂O₅/TiO₂ SCR catalyst on SO₂ oxidation activity were examined by infrared spectroscopy (DRIFT) and SO₂ oxidation measurement. Vanadium oxide added to the catalyst was found to be well dispersed over the TiO₂ carrier until covered with monolayer V₂O₅. The rate of SO₂ oxidation increased almost linearly with V₂O₅ loading below the monolayer capacity and attained saturation with further increase. The hydroxyl groups bonded to vanadium atoms, V–OH, might be altered by SO₂ oxidation. Both V=O and V–OH groups are likely involved in the adsorption and desorption of SO₂ and SO₃.     

Molten V2O5/Cs0.9K0.9Na0.2S2O7 and V2O5/K2S2O7 catalysts as electrolytesin an electrocatalytic membrane separation device for SO2 removal

Bench scale fuel cell tests have been carried out on the SO₂ oxidation catalyst systems V₂O₅/M₂S₂O₇ (M = alkali) used as electrolytes in a standard molten carbonate fuel cell (MCFC) fuel cell setup for removal of SO₂ from power plant flue gases. Porous Li _x Ni_(1–x)O electrodes were used both as anode and cathode. The cleaning cell removes SO₂ when a potential is applied across the membrane, potentially providing cheap and ecological viable means for regeneration of SO₂ from off-gases into high quality H₂SO₄. Results show that successful removal of up to 80% SO₂ at 450 °C can be achieved at approximately 5 mAcm^–2. However, the data obtained during the experiments explain the current limitations of the process, especially in terms of electrolyte wetting capability and acid/base chemistry of the electrolyte.     

The phase structure,thermodynamic properties,and dissolution behavior of Ca5Mg4V6O24

A Ca₅Mg₄V₆O₂₄ compound was synthesized through solid-state roasting routes under an air atmosphere, and its crystal structure and thermodynamic properties were determined using various methods. The cell parameters of Ca₅Mg₄V₆O₂₄ indicate that it crystallizes in cubic space group Ia3d with the unit cell parameters a = 12.442 ± 0.001 Å. X-ray photoelectron spectroscopy also confirmed that the vanadium element in the Ca₅Mg₄V₆O₂₄ sample is present in the +5 state. The melting of Ca₅Mg₄V₆O₂₄ was detected at 1442 K. The molar heat capacity (374 J mol K⁻¹) and entropy (688.2 J mol K⁻¹) of Ca₅Mg₄V₆O₂₄ at 298.15 K were determined using physical properties measurement system, and simultaneous thermal analyzer for the first time. The solubility of Ca₅Mg₄V₆O₂₄ in water at different temperatures was measured and its dissolution behavior in sulfuric acid and kinetics was experimentally established.     

Adjacent relations of primary phase fields and invariant reactions of the system CaO-SiO2-Nb2O5-La2O3

The adjacent relation of primary phase fields and corresponding invariant reactions of the system CaO-SiO₂-Nb₂O₅-La₂O₃ are of great importance for the study on its phase diagram. In the present work, the phase equilibrium in the high w(La₂O₃) region of CaO-SiO₂-Nb₂O₅-La₂O₃ system was studied by thermodynamic equilibrium experiment. The adjacent relation of primary phase fields was determined and represented in the form of adjacent tetrahedrons. The Alkemade Rule applicable to quaternary phase diagram was deduced, which can be used to infer the liquidus temperature trend on univariant curves. The rule was then used to determine the possible temperature range of invariant reactions corresponding to the adjacent tetrahedron in CaO-SiO₂-Nb₂O₅-La₂O₃ system, and the result was shown in the form of Schairer diagram. Finally, the reaction types of five invariant points were determined according to the Lever Rule for quaternary phase diagram, including: ① L₁+CaO·3SiO₂·2La₂O₃→CaO·SiO₂+SiO₂+La₂O₃·Nb₂O₅, ② L₂→CaO·SiO₂+La₂O₃·Nb₂O₅+SiO₂+CaO·Nb₂O₅, ③ L₃+CaO·3SiO₂·2La₂O₃+2CaO·Nb₂O₅→10CaO·6SiO₂·Nb₂O₅+La₂O₃·Nb₂O₅, ④ L₄+10CaO·6SiO₂·Nb₂O₅→CaO·SiO₂+2CaO·Nb₂O₅+La₂O₃·Nb₂O₅, ⑤ L₅+2CaO·Nb₂O₅→CaO·Nb₂O₅+La₂O₃·Nb₂O₅+CaO·SiO₂.     

Understanding the structure,thermal, and optical properties in Al2O3-incorporated La2O3-TiO2-Nb2O5 glasses

Glasses in the 30La₂O₃-40TiO₂-30Nb₂O₅ system are known to have excellent optical properties such as refractive indices over 2.25 and wide transmittance within the visible to mid-infrared (MIR) region. However, titanoniobate glasses also tend to crystallize easily, significantly limiting their applications in optical glasses due to processing challenges. Therefore, the 30La₂O₃-40TiO₂-(30−x) Nb₂O₅-xAl₂O₃ (LTNA) glass system was successfully synthesized using a aerodynamic containerless technique, which improves glass thermal stability and expands the glass-forming region. The effects of Al₂O₃ on the structure, thermal, and optical properties of base composition glasses were investigated by XRD, DSC, NMR, Raman spectroscopy, and optical measurements. DSC results indicated that as the content of Al₂O₃ increased, the thermal stability of the glasses and glass-forming ability increased, as the 30La₂O₃-40TiO₂-25Nb₂O₅-5Al₂O₃ (Nb-Al-5) glass obtained the highest ΔT value (103.5°C). Structural analysis indicates that the proportion of [AlO₄] units increases gradually and participates in the glass network structure to increase connectivity, promoting more oxygen to become bridging oxygen and form [AlO₄] tetrahedral linkages to [TiO₅] and [NbO₆] groups. The refractive index values of amorphous glasses remained above 2.1 upon Al₂O₃ substitution, and a transmittance exceeding 65% in the visible and mid-infrared range. The crystallization activation energies of 30La₂O₃-40TiO₂-30Nb₂O₅ (Nb-Al-0) and Nb-Al-5 glasses were calculated to be 611.7 and 561.4 kJ/mol, and the Avrami parameters are 5.28 and 4.96, respectively. These results are useful to design new optical glass with good thermal stability, high refractive index and low wavelength dispersion for optical applications such as lenses, endoscopes, mini size lasers, and optical couplers.     

Electron Beam Induced Reduction of V2O5 Studied by Analytical Electron Microscopy

The reduction of V₂O₅ under electron irradiation was studied by means of electron energy-loss spectroscopy, electron diffraction, and high-resolution imaging. The decrease of spectral intensity of O 1s excitations indicates a preferential removal of oxygen. The observed chemical shifts of the V 2p_3/2 and V 2p_1/2 peaks reveal that V⁵⁺ is reduced to V²⁺. Electron diffraction and high-resolution imaging show a structural change from the orthorhombic V₂O₅ to cubic VO. The beam induced reduction is compared with thermal decomposition of V₂O₅.     

A review on the optical characterization of V2O5 micro-nanostructures

Bulk V₂O₅ is a diamagnetic semiconductor with a band gap (E_g) of about 2.3 eV, which is based on the ionic configuration with filled O2p and unoccupied V3d orbitals. However, the band edge absorption and photoluminescence (PL) peak positions of low-dimensional V₂O₅ materials do not coincide and are distributed over wide ranges of 0.75–3.49 eV and 0.73–3.3 eV, respectively. This review summarizes the fabrication processes, structure, and optical characterization of V₂O₅ micro-nanostructures, including 0D, 1D, 2D, and 3D morphologies. The wide ranges of band edge absorption and broad PL of V₂O₅ micro-nanostructures are clarified in terms of factors such as the morphology, synthesis method, growth conditions, crystal size, micro-nano size, phase transition, and measurement conditions. The relations among the separation, diffusion, recombination, and degradation of the electron-hole pairs in V₂O₅ micro-nanostructures are also discussed. Fundamental understanding of the optical characteristics plays a key role in V₂O₅ micro-nano device applications. The review also demonstrates the role of V₂O₅ micro-nanostructures and other materials (MOs) in V₂O₅/OMs heterostructures for slowing down recombination, prolonging lifetime, improving electron-hole separation, and increasing photocurrent to enhance the photocatalytic activity.     

The influence of vanadium pentoxide on the structure and dielectric properties of poly(vinyl alcohol)

Polymers containing metal oxides of nanoscale dimensions have attracted attention because of their unique properties and new findings concerning technological applications. Polymers containing vanadium pentoxide (V₂O₅) have attracted our interest in respect of their potential applications in memory and switching devices. Poly(vinyl alcohol) (PVA) containing different concentrations of V₂O₅ ranging from 0 to 0.5 wt% were prepared. The synthesized PVA/V₂O₅ composites were cast as self‐standing flexible films. The composites were characterized using X‐ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. An attempt was made to study the relaxation characteristics of PVA/V₂O₅ samples. The permittivity and dielectric loss were determined as a function of V₂O₅ concentration. The results show that the optimum concentration is 0.3 wt%. The electrical conductivity and dielectric modulus in the temperature range 303–433 K at various frequencies (10–100 kHz) for the optimum concentration were investigated. XRD and FTIR results show that the addition of V₂O₅ reduces the crystallinity of PVA due to the interaction of vanadium ions with the OH groups of PVA. The application of the dielectric modulus formulism gives a simple method for evaluating the activation energy of the dielectric relaxation. The frequency dependence of the electrical conductivity follows the Jonscher universal dynamic law. The conductivity in the direct regime is described by the small polaron model. The electrical conductivity and dielectric properties show that Hunt's model is well adapted to PVA/V₂O₅ films. Copyright © 2010 Society of Chemical Industry     

High cyclic performance of V2O5@PPy composite as cathode of recharged lithium batteries

Micro–nanosized vanadium pentoxide (V₂O₅) was synthesized by hydrothermal reduction of amorphous V₂O₅, followed by thermal treatment in air atmosphere. Pyrrole was in-situ polymerization on the surface of V₂O₅ to obtain V₂O₅@PPy hybrid material.The as-synthesized V₂O₅ with about 100 nm in diameter and several hundreds nanometers in length were obtained and PPy layer with about 100 nm in thickness coated on the surface of V₂O₅. Electrochemical measurement showed that V₂O₅@PPy hybrid material had improved lithium storage ability and cycling performance compared with pure V₂O₅. PPy modification supplied a new route to obtain V₂O₅ hybrid cathode with significantly improved cyclic performance and showed promising applications in recharged lithium batteries.     

High-temperature ultrafast welding creating favorable V2O5 and conductive agents interface for high specific energy thermal batteries

The high interfacial resistance between V₂O₅ cathode materials and conductive agents (molten salt and super carbon) is one of the biggest issues that hinder the development of high specific energy thermal batteries. Designing fast Li⁺ and e^– transport channels in cathode electrodes is considered as an effect method to improve electrochemical performance. Hence, a high-temperature ultrafast welding is proposed to reduce V₂O₅/conductive agents interfacial resistance by reconstructing the transmission channels of Li⁺ and e^– in this paper. The experimental studies reveal the optimum ultrafast welding of 700 °C for 10 s, eliminating gap resistance of cathode electrodes induced by the melt of solid molten salt and rebuilding the more plentiful Li⁺ and e^– transport channels, further reducing the contact resistance and gap resistance. Therefore, the electrodes deliver a high specific capacity of 270.69 mAh g^?1 and a high specific energy of 610.60 Wh kg^?1 at 0.1 A cm^?2 and 500 °C with a cut-off voltage of 1.6 V. The high-temperature ultrafast welding provides guidance to build Li⁺ and e^– transport channels of other cathode materials in thermal batteries.     

Hot corrosion behavior of NdYbZr2O7 exposed to V2O5 and Na2SO4 + V2O5 molten salts

In order to evaluate the application prospects of NdYbZr₂O₇ as a novel TBC material, NdYbZr₂O₇ ceramic was synthesized via a solid-state reaction sintering method, and its hot corrosion behavior exposed to V₂O₅ and Na₂SO₄ + V₂O₅ molten salts at 900 °C, 1000 °C, and 1100 °C was comparatively investigated. For the V₂O₅ salt, the primary corrosion products were granular (Nd,Yb)VO₄ as well as cube-like m-ZrO₂. The corrosion layer consisted of two distinct layers, one of which was Zr-rich layer and another was V-rich layer. In the case of Na₂SO₄ + V₂O₅, NaVO₃, as an intermediate product, played an important role in dissolving the NdYbZr₂O₇ ceramic. Herein, the (Nd,Yb)VO₄ exhibited a rod/plate-like morphology, which could be attributed to the synergistic effect of low driving force and low nucleation rate. Since the molten salt infiltration rate was superior to the pore filling rate throughout the hot corrosion, the thickness of corrosion layer increased with the rise of temperature. The hot corrosion mechanisms of NdYbZr₂O₇ ceramic in various molten salts were discussed based on the phase diagram, Lewis acid-base rule and chemical thermodynamics. On this basis, the NdYbZr₂O₇ coating was prepared by atmospheric plasma spray (APS) and it exhibits a higher corrosion resistance compared to YSZ coating.