Vanadium Valence Research Articles

Revealing the Multi-Electron Reaction Mechanism of Na3 V2 O2 (PO4 )2 F Towards Improved Lithium Storage.

Na3 V2 O2 (PO4 )2 F (NVOPF) as an attractive electrode material has received much attention based on the one-electron reaction of V4+ /V5+ . However, the electrochemical reactions involving lower vanadium valences were not investigated till now. Herein, a composite of graphene decorated nanosheet-assembled NVOPF microflowers (NVOPF/G) was synthesized and the multi-electron reaction of NVOPF/G was conducted by controlling the operation voltage windows. The reaction mechanism, structural changes, and vanadium valences during the insertion/extraction of Li ions (from 2 to 6) were elucidated clearly by in-situ X-ray diffraction and ex-situ X-ray photoelectron spectroscopy. Theoretical computations also revealed the Li-ion locations in the structure of NaV2 O2 (PO4 )2 F. Due to the additional redox couple of V3+ /V4+ , NVOPF/G displayed a much higher initial capacity of 183.3 mAh g-1 in the wider voltage window of 1.0-4.8 V than that of 2.5-4.8 V (129.3 mAh g-1 ). Moreover, excellent Li-storage performance of NVOPF/G at a lower voltage (≤2.5 V) with the active reaction of V2+ /V3+ /V4+ was obtained for the first time, demonstrating the high potential of NVOPF/G as an anode material for Li ion storage.

Radiation-induced changes in vanadium speciation in basaltic glasses: Implications for oxybarometry measurements using vanadium K-edge X-ray absorption spectroscopy

Abstract Magmatic oxygen fugacity (fO2) exerts a primary control on the discrete vanadium (V) valence states that will exist in quenched melts. Vanadium valence proxies for fO2, measured using X-ray absorption near-edge spectroscopy (XANES), can provide highly sensitive determinations of the redox conditions in basaltic melts. However, X-ray beam-induced changes in V speciation will introduce uncertainty in the calculated average V valence (V*) that must be properly evaluated to make meaningful interpretations of the igneous evolution of the system. The study presented here showed that beam-induced modifications in V speciation are observed in silicate glasses that are dependent on the radiation dose rate used during analysis. Changes in V speciation are observed to be most pronounced at the highest flux density tested, 9.25 × 1011 ph/s/µm2 (photons per second per square micrometer), with rapid changes occurring in the first 200 s of analysis. The high-dose rate conditions result in changes in calculated V* ~0.3 valence unit for the most oxidized glass analyzed (V* = 4.94), which can correspond to ~0.5 log unit reduction in calculated fO2. However, at flux densities ≤1.13 × 109 ph/s/μm2, measured changes in V* were found to be <0.03 for all standard glasses analyzed. The degree of reduction observed during analysis is also found to be progressively smaller as the initial V* of the glass decreases, such that magmatic glasses with V* values ≤3.7 show no statistically significant change in calculated valence during analysis at any flux density tested. For most terrestrial magmatic glasses, where V* is found to be <4, beam-induced changes in V* can be effectively minimized (<0.04), within analytical uncertainty of the XAFS analysis, by limiting flux densities to be ≤1 × 109 ph/s/μm2.

Enhancement of metal-insulator transition performance of VO2 thin films by conventional furnace annealing

The vanadium dioxide (VO2) thin films fabricated by rapid thermal annealing (RTA) of vanadium thin films have high defect density and low phase transition magnitude. In this manuscript, VO2 thin films were fabricated by sputtering deposition and RTA process, then the VO2 thin films were annealed by the conventional furnace to improve metal-insulator transition performance. The effect of conventional furnace annealing (CFA) on content, grain size and phase transition property of VO2 thin films were studied. From the calculations of the VO2 grain size, the CFA method effectively increases the VO2 grain size. The valence and chemical composition of vanadium before and after annealing were studied by X-ray photoelectron spectroscopy. The results show that the content of V4+ in the film is significantly increased by CFA. After CFA on the basis of RTA, the transition magnitude of VO2 film increased from 90 to about 1600. It is feasible to prepare high-quality VO2 films with enhanced metal-insulator transition performance by CFA of VO2 films after RTA, which is beneficial to the application of VO2 thin films in optoelectronic devices.

N and O multi-coordinated vanadium single atom with enhanced oxygen reduction activity

Recently, atomically dispersed transition-metal single atom in nitrogen-doped carbon matrix as electrocatalysts has aroused general interest. However, there is no report about vanadium single atom for ORR in the literature. According to d-band center theory for transition-metals, the performance of catalysts is regulated by the electronic structure of the catalytic center which determines the intermediate adsorption kinetics. Indeed, the valence of vanadium is variable, its electron structure could be modulated by an appropriate coordination structure. Here, a novel method is developed to prepare the N and O co-coordinated vanadium single atom (V-N1O4) embedded in the carbon matrix. The catalyst displays a half-wave potential of 865 mV in base solution which surpasses 20% Pt/C, and also shows a high power density of 180 mW/cm2 in Zn-air batteries. DFT calculations reveal that the N and O coordination configuration could regulate the electron structure and geometry of vanadium to boost the electrocatalytic activity.

Synthesis and characterization of (68-x) CuO – xV2O5 – 32TeO2 (x = 0–68 mol%) and (35-x) CuO – xV2O5 – 65TeO2 (x = 0–35 mol%) glasses: Conduction mechanism, structure and EPR study

In this work, two series of glasses, i.e. (68-x) CuO – xV2O5 – 32TeO2 (x = 0–68 mol%, Te32 series) and (35-x) CuO – xV2O5 – 65TeO2 (x = 0–35 mol%, Te65 series), were synthesized by the melt-quenching method and subjected to physical, thermal and electrical characterization. Their vitreous nature was confirmed by X-Ray diffraction and differential scanning calorimetry, while their structural units were determined by Raman spectroscopy. CuO substitution by V2O5 led to a decrease in density and glass-transition temperature, together with a conductivity increase. Conduction mechanism was interpreted as mainly due to small polaron hopping from the lower (V4+) to the higher (V5+) vanadium valence states.Te32 glasses, possessing the highest electronic conductivities (ranging from 2 E−4 to 5 E−7 Ω−1 cm−1), were investigated by the Electron Paramagnetic Resonance technique, in order to more deeply analyze their structure-conductivity correlation. Particularly, the observed signals were determined to consist in a superposition of a first line due to paramagnetic Cu2+ ions and a second line due to exchange-coupled CuO clusters. Differences in the spectra were determined between samples with higher (i.e. 20-30 mol%) Cu2+ concentrations and samples with lower Cu2+ concentrations, suggesting they are located in different local environments. Finally, it was found that the Cu2+ ions are not involved in the process of electron transfer.

In‐Situ Electrochemically Activated Surface Vanadium Valence in V2C MXene to Achieve High Capacity and Superior Rate Performance for Zn‐Ion Batteries

AbstractVanadium‐based materials are fascinating potential cathodes for high energy density Zn‐ion batteries (ZIBs), due to their high capacity arising from multi‐electron redox chemistry. Most vanadium‐based materials suffer from poor rate capability, however, owing to their low conductivity and large dimension. Here, we propose the application of V2C MXene (V2CTx), a conductive 2D nanomaterial, for achieving high energy density ZIBs with superior rate capability. Through an initial charging activation, the valence of surface vanadium in V2CTx cathode is raised significantly from V2+/V3+ to V4+/V5+, forming a nanoscale vanadium oxide (VOx) coating that effectively undergoes multi‐electron reactions, whereas the inner V‐C‐V 2D multi‐layers of V2CTx are intentionally preserved, providing abundant nanochannels with intrinsic high conductivity. Owing to the synergistic effects between the outer high‐valence VOx and inner conductive V‐C‐V, the activated V2CTx presents an ultrahigh rate performance, reaching 358 mAh g−1 at 30 A g−1, together with remarkable energy and power density (318 Wh kg−1/22.5 kW kg−1). The structural advantages of activated V2CTx are maintained after 2000 cycles, offering excellent stability with nearly 100% Coulombic efficiency. This work provides key insights into the design of high‐performance cathode materials for advanced ZIBs.

The Role of Niobium Substitution in Lithium Vanadyl Phosphate for Lithium-Ion Batteries

Li-ion intercalation compound enlisting multi-electron redox is a promising strategy to maximize the storage capacity of LIBs. Lithium vanadyl phosphate, LiVOPO4, is one such material that can intercalate up to two Li+ ions per vanadium ion through the change in vanadium valence from V5+ to V3+, which translates to a theoretical capacity of 305 mAh/g and an energy density above 900 Wh/kg. However, Li-ion intercalation in the high voltage region (V5+/V4+) is kinetically limited by the sluggish Li-ion diffusion, and thus impedes the use of LiVOPO4 in practical applications. The goal of this work is to explore experimentally if niobium substitution can enhance the electrochemical performance of LiVOPO4. Lab X-ray diffraction, electron microscopy-energy-dispersive X-ray analysis, and inductively coupled plasma atomic emission spectroscopy indicate niobium is substituted into the LiVOPO4 crystal structure. A qualitative difference in the charge-discharge voltage profile is observed between the pristine and the niobium-substituted samples, suggesting a more complex substitution mechanism than the direct V substitution with Nb. The effects of niobium substitution on the crystal structure and the electrochemical performance of LiVOPO4 will be discussed.

Influence of technological parameters on the vanadium valence form in slags

The multivalence of vanadium in oxide melts is considered. It is shown that the vanadium oxidation state in the slags is determined by the slag and metal compositions as well as the oxidation potential of the gas phase. Using a polymer model, vanadium valence form fractions were calculated depending on technological parameters. Calculations show that in an air atmosphere, vanadium in the slag should be predominantly in the tetravalent and trivalent state, and in contact with the molten iron, mainly in the trivalent and partly divalent state. Upon contact with pig iron, VO oxide becomes the main form of vanadium in the slag. Slag basicity and temperature have a significant effect on the relationship of vanadium forms. The suggested design-basis using the polymer model can be useful in accomplishment of the thermodynamic calculations for the vanadium equilibrium distribution between metal and slag in the iron and steel production. It allows us to describe the dependence of the vanadium oxidation state on the free oxygen activity in the slag and the gas phase oxidation potential.

Theoretical insight into the interaction mechanism between V2O5/TiO2 (0 0 1) surface and arsenic oxides in flue gas

The arsenic oxides in flue gas can cause severe poisoning and deactivation of the vanadium-titanium-based denitrification catalyst. Investigation of the interaction mechanism between arsenic oxides and denitrification catalyst can provide theoretical guidance for the development of anti-arsenic poisoning catalyst. To this end, the periodic V2O5-TiO2 (001) models were constructed to represent the actual vanadium-titanium-based catalyst in this study. Density functional theory (DFT) calculations were applied to explore the interaction mechanism between the catalyst surface and typical arsenic oxide (As2O3) in flue gas. Stable adsorption configurations and adsorption energies for As2O3 and NH3 adsorption were calculated, the detailed interaction pathways and reaction barriers were also obtained. The results indicate that As2O3 is chemisorbed on the catalyst surface, strong interaction and electron transfer occur after As2O3 adsorption. The adsorption strength of NH3 on Lewis and Brønsted sites are decreased after As2O3 adsorption and the inhibition effect on the Lewis acid sites is much stronger. As2O3 is oxidized to As2O5 on catalyst surface, the Lewis acid sites (V = O) are destroyed and the valence of vanadium is decreased, which should be responsible for the catalyst deactivation. The analysis of the interaction pathway shows that As2O3 inclines to react with two adjacent V2O5 clusters to produce V2O4 because of the lowest energy barrier. Therefore, when the catalyst is poisoned by As2O3 in flue gas, the active component V2O5 inclines to generate V2O4, which is consistent with previous experimental researches.

Effect of source temperature on phase and metal–insulator transition temperature of vanadium oxide films grown by atomic layer deposition**Project supported by the National Natural Science Foundation of China (Grant Nos. 11674038, 61674021, 61704011, and 61904017), the Developing Project of Science and Technology of Jilin Province, China (Grant Nos. 20170520118JH and 20160520027JH), and the Youth Foundation of Changchun University of Science

Vanadium oxide films were grown by atomic layer deposition using the tetrakis[ethylmethylamino] vanadium as the vanadium precursor and H2O as the oxide source. The effect of the source temperature on the quality of vanadium oxide films and valence state was investigated. The crystallinity, surface morphology, film thickness, and photoelectric properties of the films were characterized by x-ray diffraction, atomic force microscope, scanning electron microscope, I–V characteristics curves, and UV–visible spectrophotometer. By varying the source temperature, the content of V6O11, VO2, and V6O13 in the vanadium oxide film increased, that is, as the temperature increased, the average oxidation state generally decreased to a lower value, which is attributed to the rising of the vapor pressure and the change of the ionization degree for organometallics. Meanwhile, the root-mean-square roughness decreased and the metal–insulator transition temperature reduced. Our study is great significance for the fabrication of vanadium oxide films by atomic layer deposition.

Synergistic effects in V3O7/V2O5 composite material for high capacity and long cycling life aqueous rechargeable zinc ion batteries

Zinc ion batteries (ZIBs) have great competitiveness in large-scale energy storage because of their low price, environmental friendliness, safety and efficiency. In this work, we study a composite material of V3O7/V2O5 as the cathode in ZIBs. Owing to the synergistic effects of V3O7 and V2O5, it presents an excellent zinc ion storage performance including high cyclic stability with capacity retention of 96.2% after 1120 cycles (1000 cycles after activation) at 2 A g−1, excellent rate capability with specific discharge capacity of 176 mA h g−1 at 5 A g−1 and long circle life with 17.4% capacity fading after 6500 cycle. In addition, the battery offers a high energy density of 271 W h kg−1 at 0.2 A g−1 and a high power density of 3220 W kg−1 at 5 A g−1 (based on the cathode and the theoretically required of Zn anode). The synergistic effect is confirmed by a series structural and electrochemical characterization that the interaction of V2O5 and V3O7 can promote the vanadium valence change from Ⅴ (or Ⅳ) to Ⅲ. This work provides a promising cathode material with high capacity and long cycling stability, which will have a great advantage and prospect in the large-scale energy storage.

V2O5-montmorillonite nanocomposites of peroxidase-like activity and their application in the detection of H2O2 and glutathione

In this work, montmorillonite, a traditional layered mineral, the surface of which was modified was further applied in biological detection. Specifically, a novel composite (V2O5-Mt) composed of V2O5 nanoparticles anchored on montmorillonite was synthesized by a simple method. The V2O5-Mt possessed the enhanced peroxidase-like activity, proved by evaluating the catalysis of 3′,3′,5′,5′-tetramethylbenzidine (TMB) oxidized by H2O2, accompanied by a visual change of color. Furthermore, the more the H2O2 content, the deeper the color changed. On the basis of this, a novel colorimetric platform for detecting H2O2 was established with the linear range and the limit of detection was found to be 30 to 400 μM and 4.0 μM, respectively. The peroxidase-like activity of V2O5-Mt is in accord with Michaelis-Menten kinetics. The fluorescent probe experiments verified that the catalytic activity of V2O5-Mt was attributed to the acceleration of electrons transfer among V2O5-Mt, TMB, and H2O2, which was promoted by the vanadium valence state changes between V and IV. The sensing platform was also successfully applied to detect H2O2 in real samples. Furthermore, a colorimetric sensing platform was established to detect glutathione with the linear range and limit of detection to be 0.1–30 μM and LOD = 0.069 μM, respectively.

Fast and stable Mg2+ intercalation in a high voltage NaV2O2(PO4)2F/rGO cathode material for magnesium-ion batteries

Sluggish kinetics of Mg2+ intercalation and low working potential seriously hinder the development of high-energy-density magnesium-ion batteries (MIBs). Hence developing cathode materials with fast Mg2+ diffusion and high working voltage is a key to overcome the obstacles in MIBs. Herein, a tetragonal NaV2O2(PO4)2F/reduced graphene oxide (rGO) is proposed as an effective Mg2+ host for the first time. It exhibits the highest average discharge voltage (3.3 V vs. Mg2+/Mg), fast diffusion kinetics of Mg2+ with the average diffusivity of 2.99×10−10 cm2 s−1, and ultralong cycling stability (up to 9500 cycles). The Mg2+ storage mechanism ofNaV2O2(PO4)2F/rGO is demonstrated as a single-phase (de)intercalation reaction by in situ X-ray diffraction (XRD) technology. Density functional theory (DFT) computations further reveal that Mg2+ ions tend to migrate along the a direction. X-ray absorption near edge structure (XANES) demonstrates a decrease in the average valence of vanadium, and the local coordination environment around vanadium site is highly conserved after magnesiation. Moreover, the assembled NaV2O2(PO4)2F//Mg0.79NaTi2(PO4)3 Mg-ion full cell exhibits high power and energy densities, which indicates thatNaV2O2(PO4)2F/rGO owns potential for practical applications. This work achieves a breakthrough in the working voltage of cathode materials for MIBs and provides a new opportunity for high-energy-density MIBs.

Competition between V2O3 phases deposited by one-step reactive sputtering process on polycrystalline conducting electrode

This comprehensive work investigates a technologically appealing synthesis of V2O3 oxide thin films for electronic applications by the use of direct reactive sputtering with a heavily diluted gas mixture on a conducting platinum electrode. Morphological characterization was performed by Scanning Electron Microscopy, Atomic Force Microscopy, X-Ray Diffraction and X-Ray Reflectometry. Vanadium valence states were investigated by X-Ray Photoelectron Spectroscopy and crystalline phases were checked by X-Ray Grazing Incidence measurements. Low temperature electrical transport characteristics were determined by 2-point probe measurements. Only amorphous V2O3 was found to exist in a mixed-valence phase in the investigated parameter range. Deposition temperatures between 400 °C and 550 °C enable formation of mixtures between crystallographic phases of corundum- and bixbyite-type V2O3 polymorphs. Depending on temperature and sputtering power, morphology and stoichiometry can be tuned to generate four distinct type of electrical transport characteristics. Most promising electrical properties of corundum V2O3 with a resistance ratio of up to four orders of magnitude (during the low temperature insulator-to-metal transition) have been obtained for a moderate sputtering power of 50 W (on a 1″ target) at a deposition temperature of 600 °C. Reactive sputtering thus enables direct control of structural and electrical parameters for polycrystalline V2O3 thin film phases on a conducting substrate.

Atomic-scale structural and chemical evolution of Li3V2(PO4)3 cathode cycled at high voltage window

Here, by using atomically resolved scanning transmission electron microscopy and electron energy loss spectroscopy, we investigate the structural and chemical evolution of Li3V2(PO4)3 (LVP) upon the high-voltage window (3.0–4.8 V). We find that the valence of vanadium gradually increases towards the core corresponding to the formation of electrochemically inactive Li3-xV2(PO4)3 (L3-xVP) phases. These Li-deficient phases exhibit structure distortion with superstructure stripes, likely caused by the migration of the vanadium, which can slow down the lithium ion diffusion or even block the diffusion channels. Such kinetic limitations lead to the formation of Li-deficient phase along with capacity loss. Thus, the LVP continuously losses of electrochemical activity and Li-deficient phases gradually grow from the particle core towards the surface during cycling. After 500 cycles, the thickness of active LVP layer decreases to be ∼ 5–20 nm. Moreover, the micromorphology and chemical composition of solid electrolyte interphase (SEI) have been investigated, indicating the thick SEI film also contributes to the capacity loss. The present work reveals the structural and chemical evolution in the cycled electrode materials at an atomic scale, which is essential to understand the voltage fading and capacity decaying of LVP cathode.

Controlled Hydrothermal Growth and Li+ Storage Performance of 1D VOx Nanobelts with Variable Vanadium Valence.

One-dimensional (1D) vanadium oxide nanobelts (VOx NBs) with variable V valence, which include V3O7·H2O NBs, VO2 (B) NBs and V2O5 NBs, were prepared by a simple hydrothermal treatment under a controllable reductive environment and a following calcination process. Electrochemical measurements showed that all these VOx NBs can be adopted as promising cathode active materials for lithium ion batteries (LIBs). The Li+ storage mechanism, charge transfer property at the solid/electrolyte interface and Li+ diffusion characteristics for these as-synthesized 1D VOx NBs were systematically analyzed and compared with each other. The results indicated that V2O5 NBs could deliver a relatively higher specific discharge capacity (213.3 mAh/g after 50 cycles at 100 mA/g) and median discharge voltage (~2.68–2.71 V vs. Li/Li+) during their working potential range when compared to other VOx NBs. This is mainly due to the high V valence state and good crystallinity of V2O5 NBs, which are beneficial to the large Li+ insertion capacity and long-term cyclic stability. In addition, the as-prepared VO2 (B) NBs had only one predominant discharge plateau at the working potential window so that it can easily output a stable voltage and power in practical LIB applications. This work can provide useful references for the selection and easy synthesis of nanoscaled 1D vanadium-based cathode materials.

Structure and thermochromic properties of Mo-doped VO2 thin films deposited by sol–gel method

Thermochromic VO2 thin films were prepared on quartz substrates with sol–gel method. After the Vanadium oxide films were annealed at 550 °C for 4 h in a tube furnace within a nitrogen atmosphere, Mo6+-doped VO2 films were obtained. As the concentration of Mo6+ increased, the primary diffraction peaks shifted slightly toward the small angle, and the VO2 grains became larger and larger. The XPS demonstrated that the valence of vanadium was mainly +4 and molybdenum was mainly +6. Finally, it is found that the effect of Mo6+ doping decreases Tc by approximately 5 °C per 1 at. % on average.

V2O5 Nanospheres with Mixed Vanadium Valences as High Electrochemically Active Aqueous Zinc-Ion Battery Cathode

HighlightsHollow V4+-V2O5 nanospheres are prepared by a novel and simple method using VOOH as the precursor.V4+-V2O5 with mixed vanadium valences is firstly constructed as an electrochemically active cathode for aqueous zinc-ion batteries.The V4+-V2O5 cathode exhibits a prominent cycling performance up to 1000 cycles and an excellent rate capability.

MnO promoted phase-pure M1 MoVNbTe oxide for ethane oxidative dehydrogenation

Abstract M1 phase of MoVNbTe oxide catalyst is a promising catalyst for oxidative dehydrogenation of ethane (ODHE) process. Raising V5+ concentration in the catalyst is an effective way to improve the catalytic performance while thermal oxidation in air has limited effect on the increase of vanadium valence state. In this work, manganese is introduced into the catalyst system, acting as oxygen facilitator, making M1 oxidized by gas phase oxygen at lower temperature during the preparation process. The influence of manganese addition amount and combination method on catalyst activity is studied. BET, XPS, SEM, TEM, ICP, TPR, and TPD characterizations are performed to study the correlation between catalyst properties and catalytic performance. Corresponding to the valence state increment, the catalyst promoted by MnOx gives an improved catalytic performance, e.g., over 20% improvement in ODHE process at 400 °C based on the ethane conversion.

Boosting operating voltage of vanadium oxide-based symmetric aqueous supercapacitor to 2 V

Vanadium oxides have great potentials in high voltage symmetric supercapacitors, benefiting from the available multiple oxidation states of vanadium. In this work, charge storage in a wide potential window of −1.1 to 0.9 V vs. SCE is achieve for vanadium oxide through vanadium valence tuning and incorporation in functionalized carbon nanowire array. The functionalized carbon nanowire array provides a good three dimensional conductive scaffold for the oxide nanowires, leading to high electron and ion transportation for the pseudo-capacitive materials. A high areal capacitance of 1.31 F cm−2 is achieved for the obtained vanadium oxide electrode (at 1 mA cm−2 in 5 M LiCl aqueous solution). It also displays good rate capability, demonstrating a quite high areal capacitance of 687 mF cm−2 at 100 mA cm−2. The assembled symmetric supercapacitor can be operate with a large voltage of 2 V and so can deliver a high volumetric energy density of 3.61 mWh cm−3 at 0.01 W cm−3. The supercapacitor also shows good stability, it can retain 91% of its capacitance after 10 000 galvanostatic charge-discharge cycles.