Vanadium Hydride Research Articles

Mxene-supported NbVH nanoparticles as efficient catalysts for reversible hydrogen storage in magnesium borohydride

Bimetallic niobium vanadium hydride nanoparticles (NbVH NPs) anchored on Ti3C2 were synthesized using a facile ball milling method as an effective catalyst for the dehydrogenation kinetics and reversibility of Mg(BH4)2. It was found that the onset dehydrogenation temperature of the Mg(BH4)2 + 30NbVH NPs@Ti3C2 composite was 105.7 °C and released 9.07 wt% of hydrogen at 330 °C, while undoped Mg(BH4)2 only released 4.2 wt% of H2 from 248 °C to 330 °C. Additionally, the Mg(BH4)2 + 30NbVH NPs@Ti3C2 composite achieved remarkable hydrogen release of over 9.44 wt% at a temperature as low as 230 °C, indicating unexpected dehydrogenation kinetics. In the reversible hydrogen desorption tests, Mg(BH4)2 + 30NbVH NPs@Ti3C2 released 5.98 wt% of H2 in the 2nd cycle at 250 °C and maintained a reversible capacity of 4.35 wt% after 10 cycles, demonstrating a remarkable enhancement in reversibility. The enhancement in the dehydrogenation kinetics of Mg(BH4)2 could be attributed to the greatly reduced activation energies from 343 kJ·mol−1 and 138.3 kJ·mol−1 to 103.7 kJ·mol−1 and 124 kJ·mol−1. Investigations on the evaluation of catalyst and Mg(BH4)2 during reversible hydrogen storage have revealed that NbVH NPs actually acted as a “bidirectional hydrogen pump”, facilitating both the hydrogen release and uptake from Mg(BH4)2. This strategy of multi-component hydrides may show a new way to design effective catalysts for solid-state hydrogen storage materials.

Compact fusion blanket using plasma facing liquid Li-LiH walls and Pb pebbles

Liquid plasma facing walls allow for increased neutron-wall loading expanding the design space of fusion power-plants and experimental devices towards compact high-field reactors. This study presents the design of a compact radial build blanket for fusion devices composed of variable quantities of Lead (Pb) and Lithium-Lithium Hydride (Li-LiH). A tank-like cylindrical neutronic model of the early design of the stellarator reactor proposed by Renaissance Fusion is implemented in OpenMC (neutron transport and dose rate analyses). The reactor's radial build composition and blanket layer thicknesses are varied to fulfill the requirements on tritium breeding ratio (TBR), nuclear heat extraction, radiation shielding (for the coils, internal structures and external environment) for a stellarator-based power-plant. The analyses suggest that a radial build lower than a meter thick between the plasma and coils would be sufficient to allow for a TBR ∼ 1.60, an energy multiplication factor of ∼ 1.07, to capture ≥ 90% of the nuclear heat, limit the neutron fluence at the coils below 1019 n/cm2, and limit the structural damage on the liquid metal vessel and magnet structure. In particular, a blanket composed of 32 cm of Pb and Li-LiH, 54 cm of a heavy metal hydride such as vanadium hydride (VH2), along with a 1.3 m of concrete bioshield, would minimize the radial build of the stellarator reactor while fulfilling tritium breeding, shielding and heat extraction requirements.

Kinetics of H· Transfer from CpCr(CO)3H to Various Enamides: Application to Construction of Pyrrolidines.

The rate constants kH (kD) have been determined at 27 °C for H· (D·) transfer from CpCr(CO)3H(D) to the C=C bonds of various enamides. This process leads to the formation of α-amino radicals. Vinyl enamides with N-alkyl and N-phenyl substituents have proven to be good H· acceptors, with rate constants close to those of styrene and methyl methacrylate. A methyl substituent on the incipient radical site decreases kH by a factor of 4; a methyl substituent on the carbon that will receive the H· decreases kH by a factor of 380. The measured kH values indicate that these α-amino radicals can be used for the cyclization of enamides to pyrrolidines. A vanadium hydride, HV(CO)4(dppe), has proven more effective at the cyclization of enamides than Cr or Co hydrides-presumably because the weakness of the V-H bond leads to faster H· transfer. The use of the vanadium hydride is operationally simple, employs mild reaction conditions, and has a broad substrate scope. Calculations have confirmed that H· transfer is the slowest step in these cyclization reactions.

Low temperature hydrogen superpermeation in vanadium composite metal foil pumps

Palladium-based foil membranes are an effective option for hydrogen isotope recovery from the plasma exhaust of future fusion plants, but cost and availability are concerns. Vanadium (V) is a relatively low cost, neutron tolerant material with high hydrogen permeability. It has been well-studied as a superpermeable membrane at high temperature (>500 °C), but V displays negligible superpermeation at low temperature (75–200 °C) due to catalytic limitations. Composite membranes were fabricated by depositing thin layers (∼100 nm) of either Pd or BCC PdCu on sputter-cleaned vanadium foils (100 μm). Symmetric membranes elevated superpermeation to levels approaching bulk Pd or PdCu foils, with ∼5X higher flux in the latter reflecting the superior properties of PdCu. Asymmetric membranes revealed that the Pd-based catalyst layer was critical for both efficient absorption of superthermal hydrogen upstream as well as catalyzing re-combinative desorption downstream. At T ≥ 150 °C composite membrane superpermeation was equivalent to the Pd-based foils, but the flux was attenuated by a factor of 2-3X as the temperature was reduced. This deviation from pure foil performance coincided with the formation of vanadium hydride (β-V2H), which also impacted the transient response. Nevertheless, no embrittlement was observed under the conditions examined and elevating the temperature >150 °C removed the hydride and restored full performance. The achievement of palladium-level performance with a >99% reduction in Pd inventory makes these V composite metal foils pumps an attractive option for low temperature hydrogen isotope recovery in future fusion plants.

Influence of Gas for Thermal Treatment on Hydrogen Permeation in V-Ni Alloy Membranes.

Hydrogen separation is an important step for the utilization of hydrogen energy. Metallic alloys, such as vanadium-nickel, are potential hydrogen separation materials. Due to the strong propensity of vanadium to form oxides and hydrides, vanadium alloy has a lower hydrogen permeability, and it is difficult to maintain the permeability over time. Therefore, special preparation processes such as Pd coating have been suggested for hydrogen separation vanadium-based membranes. However, aside from the prohibitive price of palladium, the interdiffusion of palladium and vanadium makes the coated membrane inviable to be used at a high temperature. Thermal treatment with inert gas was investigated in this study to assess the applicability of the vanadium alloy without palladium coating for hydrogen separation and clarify the mechanism behind the thermal treatment. Argon is inert with vanadium and displayed permeability recovery after 43 h thermal treatment, but the permeability declined under certain conditions. In contrast, nitrogen is known to interact with vanadium and the hydrogen permeability was maintained at a level lower than the test with argon. Given that nitrogen can compete with hydrogen for the active sites on vanadium, nitrogen might hinder hydrogen adsorption and hydride formation, whereas argon reduced the partial pressure of hydrogen during the thermal treatment, enhancing the driving force of hydrogen desorption. In the X-ray diffraction spectrum, vanadium hydrides and oxides were confirmed after hydrogen permeation and thermal treatment. In the X-ray photoelectron spectroscopy data, oxygen was a dominant element due to vanadium oxides and adsorbed nitrogen was also observed. According to binding energy shifts of nitrogen, nitrogen used for thermal treatment might substitute or compete for active sites with adsorbed nitrogen and hydrogen, existing in vanadium lattice. Although thermal treatment can be used to recover hydrogen permeability, the alloy cannot be recovered as hydrogen-free. However, results demonstrate the potential of thermal treatment to complement an uncoated vanadium alloy for a hydrogen separation membrane.

High-pressure stability and superconductivity of vanadium hydrides*

Using variable-composition crystal structure prediction algorithm USPEX combined with first-principles calculations, we systematically explore stable vanadium hydrides (VxHy) in the pressure range from 0 to 300 GPa. Besides reproducing all previously reported VxHy compounds, we discover three new V-rich (C222–V2H, I4/mmm-V3H2 and C222–V6H5) and three new H-rich (R-3m-V3H7, I-42m-V4H11 and Cmmm-VH11) stable phases. All stable VxHy compounds are metallic, as indicated by their electronic structures. Electron-phonon coupling calculations reveal the potential superconductive nature of VH3 (Fm-3m), VH5 (P6/mmm) and VH11 (Cmmm), with estimated critical temperature of 2.4–2.5 K for VH3, 14.5–15.5 K for VH5 and 90.9–122.6 K for VH11 at 200 GPa, respectively. Superconductivity of VH3 comes largely from coupling of the electrons with V vibrations, while in VH5 and VH11 coupling with H vibrations becomes more important as hydrogen content increases.

First detection and analysis of an electronic spectrum of vanadium hydride: The D5Π-X5Δ (0,0) band.

The D5Π-X5Δ (0,0) band of vanadium hydride at 654nm has been recorded by laser excitation spectroscopy and represents the first analyzed spectrum of VH in the gas phase. The molecules were generated using a hollow cathode discharge source, with laser-induced fluorescence detected via the D5Π-A5Π (0,0) transition. All five main (ΔΩ = ΔΛ) subbands were observed as well as several satellite ones, which together create a rather complex and overlapped spectrum covering the region 15 180-15 500 cm-1. The D5Π state displays the effects of three strong local perturbations, which are likely caused by interactions with high vibrational levels of the B5Σ- and c3Σ- states, identified in a previous multiconfigurational self-consistent field study by Koseki et al. [J. Phys. Chem. A 108, 4707 (2004)]. Molecular constants describing the X5Δ, A5Π, and D5Π states were determined in three separate least-squares fits using effective Hamiltonians written in a Hund's case (a) basis. The fine structure of the ground state is found to be consistent with its assignment as a σπ2δ, 5Δ electronic state. The fitted values of its first-order spin-orbit and rotational constants in the ground state are A=36.537815cm-1 and B = 5.7579(13)cm-1, the latter of which yields a bond length of R0=1.72122 Å. This experimental value is in good agreement with previous computational studies of the molecule and fits well within the overall trend of decreasing bond length across the series of 3d transition metal monohydrides.

Theoretical prediction of structure, electronic and optical properties of VH2 hydrogen storage material

The vanadium hydrides have better hydrogen storage capacity in comparison to the other metal hydrides. Although the structure of VH2 hydride has been reported, the structural stability, electronic and optical properties of VH2 hydride are unclear. To solve these problems, we apply the first-principles method to study the structural stability, electronic and optical properties of VH2 hydrides. Similar to the metal dihydrides, four possible VH2 hydrides such as the cubic (Fm-3m), tetragonal (I4/mmm), tetragonal (P42/mnm) and orthorhombic (Pnma) are designed. The result shows that the cubic VH2 hydride is a thermodynamic and dynamical stability. In particular, the tetragonal (I4/mmm) and the orthorhombic (Pnma) VH2 hydrides are firstly predicted. It is found that these VH2 hydrides show metallic behavior. The electronic interaction of V (d-state)-H (s-state) is beneficial to improve the hydrogen storage in VH2 hydride. In addition, the formation of V–H bond can improve the structural stability of VH2 hydride. Based on the analysis of optical properties, it is found that all VH2 hydrides show the ultraviolet response. Compared to the tetragonal and orthorhombic VH2 hydrides, the cubic VH2 hydride has better storage optical properties. Therefore, we believe that the VH2 hydride is a promising hydrogen storage material.

Neutron irradiation of tungsten in hydrogen environment at HFIR

Neutron irradiation of tungsten with and without the presence of hydrogen is needed to understand the influence of hydrogen on microstructure development under fusion reactor conditions. However, there is a risk of ignition if air ingress occurs during seal welding of irradiation capsules in a pressurized hydrogen environment. Therefore, an irradiation capsule was designed that contains several disks of vanadium hydrides at a 30% hydrogen-to-metal atomic ratio. During irradiation, the hydrogen is released from the hydrides as the capsule temperature increases, so the irradiation capsule environment is mostly hydrogen when the capsule reaches its 400 °C design temperature. This paper describes the design and operating characteristics of this first-of-a-kind irradiation capsule.

High-Pressure Stability and Superconductivity of Vanadium Hydrides

High-Pressure Stability and Superconductivity of Vanadium Hydrides

Resonant enhancement of grazing incidence neutron scattering for the characterization of thin films

We use signal enhancement in a quantum resonator for the characterization of a thin layer of vanadium hydride using neutron reflectometry and demonstrate that pressure-concentration isotherms and expansion coefficients can be extracted from the measurement of totally externally reflected neutrons only. Moreover, a consistent data analysis of the attenuation cross section allows us to detect and quantify off-specular and small angle scattering. As our experiments are effective direct beam measurements, combined with resonant signal enhancement, counting times become considerably reduced. This allows us to overcome the challenges resulting from the comparatively low brilliance of neutron beams for grazing incidence scattering experiments. Further, we discuss the potential of resonant enhancement to increase any scattering, which is of particular interest for grazing incidence small angle neutron scattering and spectroscopy.

Unveiling structural, electronic properties and chemical bonding of (VH2)n (n=10–30) nanoclusters: DFT investigation

The geometries, electronic properties, and chemical bonding of (VH2)n (n=10–30) nanoclusters are systematically investigated by a combination of artificial bee colony optimization with density functional theory calculations. Structure analysis indicates that the structures of (VH2)n nanoclusters tend to be a disorder, where the hydrogen atoms prefer to occupy the hollow sites among different V atoms, binding three V atoms to form the HV3 moieties. The bond length suggests that the average V–V bond lengths are about 2.60 Å, and the average V–H bond lengths are near 1.86 Å, which close to the experimental values of 2.77 Å and 1.79 Å for the V–V and V–H of bulk vanadium hydride, respectively. Interestingly, the coordination numbers of V–H fluctuate around 5.50 in the nanoclusters, and the corresponding value of H–V is estimated at 3.00. Moreover, the electronic properties and chemical bonding analyses indicate that d orbitals of V atoms and s orbitals of H atoms have a relatively large overlap to form sigma bonds. Specifically, the σ molecular orbital of H2 can donate electronic density to the d orbital of V atom, exhibiting the Kubas interaction in V24H48 and V29H58 nanoclusters. Kubas interaction results in a longer bond between the hydrogen molecule and the V atom.

Theoretical calculation for the phonon spectrum and thermodynamic functions of vanadium and its hydride

Based on density functional theory(DFT), using virtual crystal approximation and generalized gradient approximation(GGA)with pseudopotential method, the lattices and energies for five crystallines of vanadium hydrides are optimized and calculated. The phonon densities of states are calculated based on density functional perturbation theory(DFPT). The standard Heat capacities, Entropies, Helmholtz free energies and Gibbs functions of vanadium and its hydride are deduced at 298.15K. The calculated results are discussed and compared with experimental data.

Vanadium Hydride as an Ammonia Synthesis Catalyst

AbstractEarly 3d transition metals, such as Ti, V, or Nb are known to be inactive for the Haber‐Bosch process, due to their strong M−N bonds. However, recently some hydride compounds have been found to effectively counteract this effect, imparting catalytic activity on a wide range of elements. With these hydride catalysts, hydride (and nitride) bulk diffusion mechanisms have been proposed; if so, more open structures should enhance their activity. Here, we expand the study to hydrides of other early transition metals, V and Nb. These metals benefit from body‐centered cubic (bcc) related structures which enhance hydride diffusion, in addition to having relatively lower M−N bond strengths. The activity of vanadium hydride, most likely with an active composition of VH0.44N0.16, is superior to the previously reported BaTiO2.5H0.5, and comparable to TiH2 and Cs−Ru/MgO at 400 °C under 5 MPa. These results show that there is more potential for developing new single‐phase hydride catalysts of previously overlooked elements without sacrificing activity.

What is the Bond Dissociation Energy of the Vanadium Hydride Cation?

Recent electronic state-selected measurements of the reactions of atomic vanadium cations with D2 and CO2 are reanalyzed to properly account for the kinetic energy distribution of the reactant neutrals. The need for this is demonstrated in the present work by comparing the D2 data to that obtained previously in earlier experiments but unpublished. It is shown that the earlier data, which utilized a surface ionization source of V+, and the state-selected data for V+(a5D2) are essentially identical in the threshold regions where they overlap. Differences in the electronic state energies and kinetic energy distributions of V+ in the two experiments are very small and much smaller than the kinetic energy distribution of the neutral reactant, which is identical in both experiments. It is shown that properly accounting for the latter distribution alters the conclusions regarding the threshold energy for the endothermic formation of VD+ such that recent conclusions regarding the bond energy of VD+ are substantially altered and found to reproduce the original bond energy determination. Accounting for all experiments, a revised best value for D0(VH+) is 2.07 ± 0.09 eV [or D0(VD+) = 2.10 ± 0.09 eV]. This conclusion is validated by high-level ab initio calculations. Differences in the new and older data sets for the V+ + D2 reaction at higher energies (above the onset for dissociation of the product ion) are also discussed. The same methodology is then applied to recent studies on the state-selected V+ + CO2 reaction.

Vanadium Hydride as Conversion Type Negative Electrode for All-Solid-State Lithium-Ion-Battery

Vanadium Hydride as Conversion Type Negative Electrode for All-Solid-State Lithium-Ion-Battery

Hydrogen site location in ultrathin vanadium layers by N-15 nuclear reaction analysis

We present a method using resonant nuclear reaction analysis combined with optical transmission and heavy-ion Rutherford backscattering spectrometry to study the absorption of hydrogen in single crystalline thin vanadium films. Probing with the resonant 1H(15N,αγ)12C reaction allows for highly resolved hydrogen depth profiling, while measurements along the crystal axes render possible the direct identification of the interstitial site occupancy. First experiments were performed on thin vanadium hydrides in Fe(Cr)/V superlattices revealing differences in site occupancy.

Theoretical study of M–H (M=Ti, V, Zr or Nb) structure phase diagram at high pressures

Abstract We have performed structure searches for titanium (Ti) hydrides, vanadium (V) hydrides, zirconium (Zr) hydrides and niobium (Nb) hydrides under ambient and high pressure up to high hydrogen content using CALYPSO method combined with first-principles calculations. Ten novel stable phases, R 3 ¯ -TiH3, P42/mnm-TiH3, Ibam-TiH2.5, Cccm-VH, Pna21-ZrH4, R 3 ¯ -ZrH3, Pm 3 ¯ n_1-ZrH3, R 3 ¯ m-ZrH2.5, P2/c-NbH2.5 and P42/mcm-NbH2.5 were discovered under various pressures. In particular, the high hydrogen content Pna21-ZrH4 can be stabilized at 4–12 GPa. The detailed crystal structure, dynamical stability and electronic structure are also investigated for those novel stable phases. Combined with earlier predicted structures, comprehensive pressure–chemical potential (P- Δ μ H ) phase diagrams are constructed for these M−H systems.

Effects of substitutional Mo and Cr on site occupation and diffusion of hydrogen in the β-phase vanadium hydride by first principles calculations

The effects of substitutional Mo and Cr in β-phase VH0.5 and V1−xMxH0.5625 (M = Mo, Cr; x = 0, 0.0625, 0.125) on the site occupation and diffusion paths of hydrogen are investigated by quantum mechanical calculations based on density functional theory. Fundamental processes of the interstitial-assisted mechanisms are systematically figured out, and specific values of the site energies are obtained with zero-point energy (ZPE) corrections. Hydrogen atoms are found to occupy the octahedral (O) interstitial sites in β-phase (V + M)H0.5 in the ground state. Upon increasing the hydrogen concentration H/(V + M) higher than 0.5, the additional H atom prefers to reside at the tetrahedral (T) interstitial sites. The minimum energy paths of hydrogen diffusion are analyzed by the Nudged Elastic Band method with ZPE corrections. The site occupation energy and activation energy for each hydrogen diffusion path are found to be strongly influenced by the substitution of Mo or Cr into vanadium hydride. The results presented in this work indicate that the additional H prefers to migrate directly from T site to the nearest neighboring T site without crossing O site. The energy barriers in the order of 0.253–0.276 eV of hydrogen migration in the V1−xMxH0.5625 hydrides obtained from ab initio simulations are in good agreement with the experimental data by means of 1H NMR measurement.

Shock Compression of Vanadium Hydrides and Deuterides with Different Concentrations of Gas Atoms

Shock Compression of Vanadium Hydrides and Deuterides with Different Concentrations of Gas Atoms