Vanadium Hydride Research Articles

Effects of alloying elements (Al, Mn, Ru) on desorption plateau pressures of vanadium hydrides: An experimental and first-principles study

Vanadium-based alloys are promising for the reversible and compact storage of renewable hydrogen. To improve the hydrogen desorption plateau pressure of vanadium hydrides, V–3A binary alloys of V97Al3, V97Mn3, and V97Ru3 were prepared by vacuum arc melting. Hydrogen absorption and desorption properties of the newly prepared V–3A alloys were studied, and compared to vanadium hydrides, by pressure-composition-temperature measurements and first-principles calculations. Among the studied materials, V–3Ru showed the highest hydrogen desorption plateau pressures between T = 373 and 433 K. During hydrogen loading, V–3Ru also reached the highest hydrogen to metal ratio between the alloys. Meanwhile, V–3Ru was also the alloy with the highest hardness. Findings of hydrogen absorption and desorption measurements were supported with DFT calculations of hydride formation energies. The calculated DOS, ELF and atomic charges were used to study the effects of alloying on the electronic properties of hydrides. The bonding interactions in vanadium dihydrides were influenced the most through Al alloying, whereas V–3Mn and V–3Ru hydrides showed comparable electronic properties.

Superconductivity of Pressure-Stabilized Vanadium Hydrides.

The study of the high-temperature superconductive property in compressed hydrogen (H)-rich hydrides has been motivated by hydrides, which become superconducting at low pressure due to chemical precompression. In the present study, we report the first-principles structure searches for stable vanadium(V) hydrides over a pressure scope 0-200 GPa, where stable unexpected stoichiometries of H-rich V hydrides (e.g., VH3, VH5, and VH8) emerge. These dense H-rich V hydrides are metallic with a strong ionic feature, and the coordination number of metal V gradually increases with H content. In particular, C2/m-VH8, which consists of infinite zigzag chains of sole H2 molecules, has the highest coordination number of 16. From our electron-phonon calculations, one can see that P63/mmm-VH5 and C2/m-VH8 are superconductors with estimated superconducting temperatures (Tc) of 18.5 and 71.4 K at 200 GPa, respectively. Our simulations not only uncovered the crystal structures of V hydrides, but also established the high-temperature superconductive nature of them.

Alloying effects of Fe and Al on formation and decomposition temperatures of vanadium hydride, V2H

The alloying effects of iron and aluminum on the formation and decomposition temperatures of vanadium hydride, β phase, have been investigated by a series of in-situ X-ray diffraction measurements in hydrogen atmosphere. It is found that the addition of iron increases the formation temperature of β phase, while the addition of aluminum decreases the formation temperature drastically.According to the first principal calculations, the addition of iron, chromium or nickel increases the hydrogen dissolution energy when hydrogen atom is inserted to the nearest neighbor site of alloying element. These results is considered to correspond to the increase in the plateau pressure of α–β phase transition by the addition of these alloying elements. The alloying effect on the change in the total energy upon hydrogen insertion into T-site is larger than O-site. As a result, the energy difference between T-site model and O-site model becomes small by the addition of these alloying elements, which will lead to increase the formation temperature of β phase. Aluminum in vanadium shows strong repulsive interaction with hydrogen so that hydrogen cannot occupy the nearest neighbor sites of aluminum energetically. Owing to this blocking effects, the formation temperature of β phase may decreases drastically by the addition of aluminum into vanadium.

Shock compression of vanadium hydrides and deuterides with different concentrations of gas atoms

This paper presents the results of experimental studies of the shock compression of samples of vanadium deuterides and hydrides of the following compositions: VX0.51, VX0.7–0.9, and VX≥1.6, where X is H or D. The experiments were carried out in the pressure range 20–140 GPa. The technology of synthesizing samples using electrolytic vanadium of not less than 99.7% purity. The Hugoniots of vanadium deuterides and hydrides were determined using the well-known reflection method. The samples were compressed using shock-wave generators based on the use of explosive charges of different power. The obtained experimental data are described by an equation of state developed using a model in which the specific heats and Gr¨uneisen ratios of ions and electrons are functions of density and temperature. At low temperature, the specific heat changes in accordance with the Debye theory. The removal of the degeneracy of the electron gas at higher temperatures is considered. The influence of ionization processes on the thermodynamic functions is effectively taken into account.

Investigation of superconductivity in compressed vanadium hydrides.

Aiming at finding new superconducting materials, we performed systematical simulations on phase diagrams, crystal structures, and electronic properties of vanadium hydrides under high pressures. The VH, VH2, VH3, and VH5 species were found to be stable under high pressures; among these, VH2 had previously been investigated. Moreover, all three novel stoichiometries showed a strong ionic character as a result of the charge transfer from V to H. The electron-phonon coupling calculations revealed the potentially superconductive nature of these vanadium hydrides, with estimated superconducting critical temperature (Tc) values of 6.5-10.7 K for R3[combining overline]m (VH), 8.0-1.6 K for Fm3[combining overline]m (VH3), and 30.6-22.2 K for P6/mmm (VH5) within the pressure range from 150 GPa to 250 GPa.

High‐Pressure Raman and Calorimetry Studies of Vanadium(III) Alkyl Hydrides for Kubas‐Type Hydrogen Storage

AbstractThe front cover artwork is provided by David Antonelli′s materials chemistry group at the University of South Wales. The image shows the binding of H2 via the Kubas interaction on amorphous vanadium hydride frameworks. The material stores 5.4 wt % H2 reversibly, and surprisingly the calorimetry measurements shown below the central image demonstrate that the overall process is thermodynamically neutral. Read the full text of the Full Paper at 10.1002/cphc.201501093

Atomistic simulation of hydrogen dynamics near dislocations in vanadium hydrides

Kinetics of interstitial hydrogen atoms near dislocation cores were analyzed by atomistic simulation. Classical molecular dynamics method was applied to model structures of edge and screw dislocations in α-phase vanadium hydride. Simulation showed that hydrogen atoms aggregate near dislocation cores. The spatial distribution of hydrogen has a planner shape at edge dislocation due to dislocation partialization, and a cylindrical shape at screw dislocation. Simulated self-diffusion coefficients of hydrogen atoms in dislocation models were a half- to one-order lower than that of dislocation-free model. Arrhenius plot of self-diffusivity showed slightly different activation energies for edge and screw dislocations. Directional dependency of hydrogen diffusion near dislocation showed high and low diffusivity along edge and screw dislocation lines, respectively, hence so called ‘pipe diffusion’ possibly occur at edge dislocation but does not at screw dislocation.

Tailoring the hydrogen desorption thermodynamics of V2H by alloying additives

Vanadium could be a potential candidate for on board hydrogen storage application because of its high gravimetric hydrogen storage capacity (∼3.8mass%) which is even better then the most widely explored AB5, AB2 & AB intermetallic compounds. Hydrogen absorption of vanadium takes place at ambient temperature and pressure with fast kinetics. The vanadium hydride (VH2) releases hydrogen in two steps: (1) VH2(γ)(s)↔½ V2H(β)(s) and (2) V2H(β)(s)↔2V(s)+½ H2(g). First step is achievable at the ambient temperature and pressure conditions while, the second step requires high temperature (590K). Thus only half of the total hydrogen storage capacity is available for use on subsequent absorption–desorption cycles at the ambient temperature. The usable hydrogen storage capacity of VH2 at ambient conditions could be enhanced by tailoring the thermodynamics and kinetics of second step of hydrogen desorption reaction. This could be possible by selecting suitable alloy additives. The present study deals with the selection criteria of alloy additives based on the electronic consideration to tailor the hydrogen desorption thermodynamics and kinetics of V2H.

Energy and diffusion of hydrogen atoms in titanium substituted vanadium hydrides from ab initio calculations

The equilibrium lattice parameters, formation energy, and diffusion behavior of hydrogen atoms in vanadium hydrides with and without Ti substitution were calculated by ab initio calculations and quantum correction by zero point energy was achieved using phonon vibration calculations. The calculated formation energies indicated that Ti substitution induces instability in the vanadium hydrides and electron density calculations showed that hydrogen has strong electrochemical affinity with Ti. The diffusion behavior was examined by the nudged elastic band (NEB) method to investigate the transition states of the hydrides. It revealed that Ti substitution is shown to reduce the diffusion coefficient and this effect was decreased with increasing temperature. The results of this study are expected to provide useful guidelines for understanding hydrogen absorption and desorption properties of hydrogen storage materials.

Suppression of the critical temperature in binary vanadium hydrides

Abstract The tendency of vanadium-based alloy membranes to embrittle is the biggest commercialisation barrier for this hydrogen separation technology. Excessive hydrogen absorption and the α → β hydride transition both contribute to brittle failure of these membranes. Alloying is known to reduce absorption, but the influence of alloying on hydride phase formation under conditions relevant to membrane operation has not been studied in great detail previously. Here, the effect of Cr, Ni, and Al alloying additions on V–H phase equilibrium has been studied using hydrogen absorption measurements and in situ X-ray diffraction studies. The addition of 10 mol% Ni increases the critical temperature for α + β hydride formation to greater than 400 °C, compared to 170 °C for V. Cr also increases the critical temperature, to between 200 and 300 °C. The addition of 10 mol% Al, however, suppresses the critical temperature to less than 30 °C, thereby enabling this material to be cycled thermally and hydrostatically while precluding formation of the β-hydride phase. This is despite Al also decreasing hydrogen absorption. The implication of this finding is that one of the mechanisms of brittle failure in vanadium-based hydrogen-selective membranes has been eliminated, thereby increasing the robustness of this material relative to V.

Improvement of hydrogen sorption properties of compounds based on Vanadium “bcc” alloys by mean of intergranular phase development

Body centered cubic structure (bcc) type alloys based on Vanadium [1] reveal promising characteristics for mobile applications. These disordered solid solutions have particular metal/hydride equilibrium and some regulation aspects have leaded us to pay special attention to this type of material [2]. Compounds based on Vanadium-rich solid solution have been elaborated in order to destabilize γ hydride phase (corresponding to the face centered cubic (fcc) structure of VH2). Addition of Ni and Zr-rich Laves phase as a secondary phase results in the development of a particular microstructure composed of a principal bcc matrix rounded by intergranular activating phase. This results in a facilitated and faster activation of these compounds. The present study shows that some constituting species of the secondary phase have diffused in the main matrix and therefore have modified the thermodynamic of hydride. In fact, chromium diffusion into the bcc matrix destabilizes hydride. It is correlated to the lower stability of chromium hydride compared to Vanadium hydride. The enthalpic terms of each sample have been measured (assuming standard entropy of 130 J mol−1 K−1). The equilibrium metal/hydride can be easily switched in order to adapt it to a mobile hydride tank and obtain low working temperature in regard to the potential use.

Computational study of lattice defects in metal–hydrogen systems

Abstract Effects of lattice defects in vanadium hydrides on hydrogen storage property were analyzed by computer simulation. Element substitution, dislocation, and polyhedral surface were modeled as for point, line and plane lattice defects. DFT calculation revealed that Mo-substitution in β-phase vanadium hydride enhanced the shift of hydrogen occupancy from O Z1 site to neighboring T sites. Classical MD calculation on edge dislocation in a-phase vanadium hydride showed that interaction between edge dislocations was reduced by hydrogen aggregation at the vicinity of dislocation core. The MD simulation on polyhedral vanadium nanoparticle showed that polycrystal structure with fivefold symmetry can be generated by hydrogenation as a result of multi-twin-boundaries associated with bcc to bct transformation. Structure models of lattice defects were also briefly discussed.

A modified embedded-atom method interatomic potential for the V–H system

An interatomic potential for the vanadium–hydrogen binary system has been developed based on the second nearest-neighbor modified embedded-atom method (2NN MEAM) potential formalism, in combination with the previously developed potentials for V and H. Also, first-principles calculation has been carried out to provide data on the physical properties of this system, which are necessary for the optimization of the potential parameters. The developed potential reasonably reproduces the fundamental physical properties (thermodynamic, diffusion, elastic and volumetric properties) of V-rich bcc solid solution and some of the vanadium hydride phases. The applicability of this potential to the development of V-based alloys for hydrogen applications is discussed.

Kubas-Type Hydrogen Storage in V(III) Polymers Using Tri- and Tetradentate Bridging Ligands

Oxalic acid, oxamide, glycolic acid, and glycolamide were employed as 2-carbon linkers to synthesize a series of one-dimensional V(III) polymers from trismesityl vanadium(III)·THF containing a high concentration of low-valent metal sites that can be exploited for Kubas binding in hydrogen storage. Synthesized materials were characterized by powder X-ray diffraction (PXRD), nitrogen adsorption (BET), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), Raman spectroscopy, thermogravimetric analysis, and elemental analysis. Because each of these organic linkers possesses a different number of protons and coordinating atoms, the products in each case were expected to have different stoichiometries with respect to the number of mesityl groups eliminated and also a different geometry about the V(III) centers. For example, the oxalate and glycolate polymers contained residual mesityl groups; however, these could be exchanged with hydride via hydrogenolysis. The highest adsorption capacity was recorded on the product of trismesityl vanadium(III)·THF with oxamide (3.49 wt % at 77 K and 85 bar). As suggested by the high enthalpy of adsorption (17.9 kJ/mol H(2)), a substantial degree of performance of the vanadium metal centers was retained at room temperature (25%), corresponding to a gravimetric adsorption of 0.87 wt % at 85 bar, close to the performance of MOF-177 at this temperature and pressure. This is remarkable given the BET surface area of this material is only 9 m(2)/g. A calculation on the basis of thermogravimetric results provides 0.88 hydrogen molecule per vanadium center under these conditions. Raman studies with H(2) and D(2) showed the first unequivocal evidence for Kubas binding on a framework metal in an extended solid, and IR studies demonstrated H(D) exchange of the vanadium hydride with coordinated D(2). These spectroscopic observations are sufficient to assign the rising trends in isosteric heats of hydrogen adsorption observed previously by our group in several classes of materials containing low-valent transition metals to the Kubas interaction.

Preparation, characterization and stability of vanadium/Y 2O 3-stabilized ZrO 2 composite membranes under different atmospheres

In this experimental work vanadium/Y 2O 3-stabilized ZrO 2 composite membrane was successfully fabricated by a two-step sintering process. The formation of a well-defined ceramic metal composite membrane was confirmed under high vacuum sintering conditions. Their surface morphology, stability and structural properties were studied as a function of temperature up to 1100 °C by thermogravimetry, differential thermal analysis, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction analysis. Significant differences were observed in the crystalline structure of the vanadium/Y 2O 3-stabilized ZrO 2 composite membranes when they were treated at high temperature in different atmospheres (vacuum, air, hydrogen, nitrogen, and helium). The first hydrogen permeation investigation of vanadium/Y 2O 3-stabilized ZrO 2 composite membrane is reported. Preliminary hydrogen permeation experiments have been confirmed that hydrogen flux was 1.08 ml min −1 cm 2 for a dense vanadium/Y 2O 3-stabilized ZrO 2 composite membrane (thick: 380 μm) at 300 °C using 100% H 2 as the feed gas. Both high temperature XRD and ex situ study showed deterioration of membranes and the formation of a small amount of vanadium nitride (VN x ) and vanadium hydride (VH x ) solid solutions under nitrogen and hydrogen gas conditions, respectively.

A Density Functional Theory Study of the Charge State of Hydrogen in Metal Hydrides

Density functional theory and Bader charge analyses were used to investigate the charge state of hydrogen in vanadium, niobium, tantalum, palladium, and niobium−palladium alloys. Over a range of concentrations and hydrogen-site configurations, it is found that hydrogen consistently acquires a net charge of between approximately −0.51e and −0.64e in the pure group 5 metals compared with a significantly smaller value of 0.3e in palladium. Although there is indirect evidence that the electronic charge plays a role in the solubility and diffusivity of hydrogen in the group 5 metals, this is the first work to quantify the value of the charge. Hydrogen tends to migrate to regions of the metal lattice that minimize its overall charge density, which generally corresponds to the T-site in the bcc metals. It is found that the charge of hydrogen at the O-site of vanadium can be slightly lower due to lattice deformation and may explain the occupation of both T- and O-sites in vanadium hydrides.

Low and high-pressure hydriding of V–0.5at.%C

The low-pressure hydriding characteristics of V–0.5at.%C alloy were determined in this study. There are several prior reports on the pressure-composition-temperature (p-c-T) isotherms and stability of the low-pressure vanadium hydride phases (V 2H or β 1), and of vanadium alloyed with transition elements, but there are no reports on the hydrides of V–C alloys. The thermodynamic properties of the vanadium did not change significantly with the addition of carbon. In addition to low-pressure studies on V–0.5at.%C, we also performed high-pressure studies on V 2H ↔ VH ↔ VH 2 (β 1 ↔ β 2 ↔ γ) hydrides, including thermal cycling (778 cycles) between the β and γ phases. Thermal cycling between VH ↔ VH 2 increased the pressure hysteresis. The effects of thermal cycling (4000 cycles) on the absorption and desorption isotherms of V–0.5at.%C and on the H/M ratios for the β 1-, β 2- and γ-phase hydrides are also presented. There was minimal decrepitation (pulverization) of the alloy; decrepitation of the V–0.5at.%C alloy was dramatically less than that of pure vanadium.

Ethene Insertion into Vanadium Hydride Intermediates Formed via Vanadium Atom Reaction with Water or Ethene: A Matrix Isolation Infrared Spectroscopic Study

The reaction of V atoms with H2O and various concentrations of C2D4 in argon has been investigated by matrix isolation infrared (IR) spectroscopy. Both C2D6 and CD2H-CD2H are observed as the major products of a set of parallel processes involving hydrogenation of ethene where the formal source of hydrogen is either C2D4 or H2O. Portions of the IR spectrum of CD2H-CD2H isolated in an argon matrix are observed for the first time. For experiments involving low concentrations of C2D4, irradiation of the matrix with light of wavelengths >455 nm results in VH2 formation, with limited observation of ethene hydrogenation. The source of H2 is believed to be due to photoelimination of molecular hydrogen from HO-V-H species, during matrix deposition, with OV as an additional product. Recombination of OV with available H2 in the matrix is proposed as the source of OVH2 under low ethene conditions. No evidence for VD2 formation is observed under our conditions. At higher C2D4 concentrations, VH2 formation is suppressed, while products of ethene hydrogenation are maximized. A second process competing with H2 elimination in which HO-V-H reacts with C2D4 is proposed. Parallel reaction schemes involving V atom insertion into the O-H bonds of water or the photoinduced insertion of V atoms into the C-D bonds of C2D4 are proposed to account for the observed hydrogenation products. In each mechanism, insertion of C2D4 into the V-H or V-D bonds of transient intermediates is followed by photoinduced elimination of the associated ethane isotopomer.

First-principles calculation of dehydrogenating properties of MgH2-V systems

Based on experimental results in which VH0.81/MgH2 interface was found during the process of mechanically milling MgH2+5at%V nanocomposite, a VH/MgH2 interface is designed and constituted in this work. A first-principles plane-wave pseudopotential method based on Density Functional Theory (DFT) has been used to investigate the vanadium alloying effects on the dehydrogenating properties of magnesium hydride, i.e., MgH2. A low absolute value of the negative heat of formation of VH/MgH2 interface compared with that of MgH2 indicates that vanadium hydrides befit to improve the dehydrogenating properties of MgH2. Based on the analysis of the density of states (DOS) and the total valence electron density distribution of MgH2 before and after V alloying, it was found that the improvement of the dehydrogenating properties of MgH2 caused by V alloying originates from the increasing of the valence electrons at Fermi level (EF) and the decreasing of the HOMO-LUMO gap (ΔEH-L) after V alloying. The catalysis effect of V on dehydrogenating kinetics of MgH2 may attribute to a stronger bonding between V and H atoms than that between Mg and H atoms, which leads to nucleation of the α-Mg at the VH/MgH2 interface in the MgH2-V systems easier than that in pure MgH2 phase.

Synthesis of the dihydride phase of vanadium

There are two constituents that determine success in synthesizing vanadium hydride: activation and supply of hydrogen to vanadium at an appropriate pressure. The most efficient activation has been found to occur, depending on the vacuum produced in a facility, in temperature ranges between 550 and 750 K or above 850 K. Dependencies of equilibrium sorption pressures of protium and deuterium over respective dihydride phases of vanadium are provided. At an atomic ratio of 0.85 ≤ X/V ≤ 1.5 (X is protium or deuterium), they take the following form, respectively, log P ( Pa ) = − 2160 / T + 12.8 and log P ( Pa ) = − 2480 / T + 13.6 . At higher hydrogen concentrations, coefficients in the Van’t Hoff equation are observed to depend on the hydrogen content. Based on the obtained experimental data on equilibrium sorption pressures and available literature data on isotopic effects, the same dependence of sorption pressure has been calculated for vanadium ditritide. For T/V = 0.85 , it is expressed as: log P ( Pa ) = − 2490 / T + 13.4 . Dependencies of equilibrium sorption pressures for all the three hydrogen isotopes at temperatures between 273 and 323 K and ratios of 0.85 ≤ ( H, D or X ) / V ≤ 1.9 are presented in the form of diagrams.