Saturated Hydrides Research Articles

Crystal structure and hydrogen sorption properties of Nd0.5Y0.5MgNi4-xCox alloys (x = 0–3)

The gas-phase and electrochemical hydrogenation properties of Nd0.5Y0.5MgNi4-xCox (where x varies from 0 to 3) were studied. Samples were prepared using sintering and annealing procedures. X-ray diffraction analysis indicated that all the alloys were single-phase. The alloys readily absorbed hydrogen, and the crystal structures of the resulting saturated hydrides were refined. Nd0.5Y0.5MgNi4H4.2 and Nd0.5Y0.5MgNi3CoH4.4 belong to the NdMgNi4H3.6 structural type, while Nd0.5Y0.5MgNi2Co2H5.5 and Nd0.5Y0.5MgNiCo3H6.0 belong to the LaMgNi4H4.85 structural type. Electrochemical studies revealed that the maximum discharge capacity of Nd0.5Y0.5MgNi4-xCox electrodes increased from 236 mAh/g to 328 mAh/g as the cobalt content increased. The high-rate dischargeability (HRD1000) initially decreased from 48 % to 7 % with increasing cobalt content, but then increased to 32 % at the highest cobalt concentration. Additionally, the electrochemical kinetic properties were determined and compared for these electrodes, including the charge-transfer resistance (Rct), polarization resistance (Rp), exchange current density (I0), limiting current density (IL), and hydrogen diffusion coefficient (DH).

Quantification of Hydride Coverage on Cu(111) by Electrochemical Mass Spectrometry.

Electrochemical mass spectrometry (EC-MS) is combined with chronoamperometry to quantify H coverage associated with the surface hydride phase on Cu(111) in 0.1 mol/L H2SO4. A two-step potential pulse program is used to examine anion desorption and hydride formation, and the inverse, by tracking the 2 atomic mass unit (amu) signal for H2 production in comparison to the charge passed. On the negative potential step, the reduction current is partitioned between anion desorption, hydride formation, and the hydrogen evolution reaction (HER). For modest overpotentials, variations in partial processes are evident as inflections in the chronoamperometry and EC-MS signal. On the return step to positive potentials, hydride decomposition by H recombination to H2 occurs in parallel with sulfate adsorption. The challenge associated with the inherent diffusional delay in the EC-MS response is mitigated by total H2 collection and steady-state analysis facilitated by the thin-layer EC-MS cell geometry as demonstrated for the HER on a non-hydride forming Ag electrode. Analysis of the respective transients and steady-state response on Cu(111) reveals a saturated hydride fractional coverage of 0.67 at negative potentials with an upper bound charge of 106 μC/cm2 (average electrosorption valency of ≈1.76) associated with adsorption of the () mixed sulfate-water adlayer at positive potentials.

The powder metallurgy performance of Ti-1Al-8V-5Fe alloys with unsaturated titanium hydride

ABSTRACTThe high-strength Ti-1Al-8V-5Fe alloy is synthesized with separately unsaturated titanium hydride, TiH1.5, powders and saturated titanium hydride, TiH2, powders, via cold compaction and sintering powder metallurgy process. The results show that the Ti-185 alloys with TiH2 or TiH1.5 powders have similar mechanical performances after compacted at 1000 MPa and sintering at 1350°C for 2 h. Whereas Ti-185 alloy based on TiH1.5 presents better economically advantageous and compressive formability, and the sintered density is 4.58 g cm−3 (relative density is 98.5%), which is a potential candidate to prepare high-densification and low-cost Ti-185 alloy in the future market.

Passivation of InGaAs(001)-(2 × 4) by Self-Limiting Chemical Vapor Deposition of a Silicon Hydride Control Layer.

A saturated Si-Hx seed layer for gate oxide or contact conductor ALD has been deposited via two separate self-limiting and saturating CVD processes on InGaAs(001)-(2 × 4) at substrate temperatures of 250 and 350 °C. For the first self-limiting process, a single silicon precursor, Si3H8, was dosed at a substrate temperature of 250 °C, and XPS results show the deposited silicon hydride layer saturated at about 4 monolayers of silicon coverage with hydrogen termination. STS results show the surface Fermi level remains unpinned following the deposition of the saturated silicon hydride layer, indicating the InGaAs surface dangling bonds are electrically passivated by Si-Hx. For the second self-limiting process, Si2Cl6 was dosed at a substrate temperature of 350 °C, and XPS results show the deposited silicon chloride layer saturated at about 2.5 monolayers of silicon coverage with chlorine termination. Atomic hydrogen produced by a thermal gas cracker was subsequently dosed at 350 °C to remove the Si-Cl termination by replacing with Si-H termination as confirmed by XPS, and STS results confirm the saturated Si-Hx bilayer leaves the InGaAs(001)-(2 × 4) surface Fermi level unpinned. Density function theory modeling of silicon hydride surface passivation shows an Si-Hx monolayer can remove all the dangling bonds and leave a charge balanced surface on InGaAs.

Prediction of the electronic structures, thermodynamic and mechanical properties in manganese doped magnesium-based alloys and their saturated hydrides based on density functional theory

The crystal structures, electronic structures, thermodynamic and mechanical properties of Mg2Ni alloy and its saturated hydride with different Mn-doping contents are investigated using first-principles density functional theory. The lattice parameters for the Mn-doped Mg2Ni alloys and their saturated hydrides decreased with an increasing Mn-doping content because of the smaller atomic size of Mn compared with that of Mg. Analysis of the formation enthalpies and electronic structures reveal that the partial substitution of Mg with Mn reduces the stability of Mg2Ni alloy and its saturated hydride. The calculated elastic constants indicate that, although the partial substitution of Mg with Mn lowers the toughness of the hexagonal Mg2Ni alloy, the charge/discharge cycles are elevated when the Mn-doping content is high enough to form the predicted intermetallic compound Mg3MnNi2.

A photoionization mass spectroscopic study on the formation of phosphanes in low temperature phosphine ices.

Isovalency rationalizes fundamental chemical properties of elements in the same group, but often fails to account for differences in the molecular structure due to the distinct atomic sizes and electron-pair repulsion of the isovalent atoms. With respect to main group V, saturated hydrides of nitrogen are limited to ammonia (NH3) and hydrazine (N2H4) along with ionic and/or metal-bound triazene (N3H5) and potentially tetrazene (N4H6). Here, we present a novel approach for synthesizing and detecting phosphanes formed via non-classical synthesis exploiting irradiation of phosphine ices with energetic electrons, subliming the newly formed phosphanes via fractionated sublimation, and detecting these species via reflectron time-of-flight mass spectrometry (ReTOF) coupled with vacuum ultraviolet (VUV) single photon ionization. This approach is able to synthesize, to separate, and to detect phosphanes as large as octaphosphane (P8H10), which far out-performs the traditional analytical tools of infrared spectroscopy and residual gas analysis via mass spectrometry coupled with electron impact ionization that could barely detect triphosphane (P3H5) thus providing an unconventional tool to prepare complex inorganic compounds such as a homologues series of phosphanes, which are difficult to synthesize via classical synthetic methods.

Theoretical investigation on the saturated hydrides of F5F7–C60 with in-out isomerism

The carbon polyhedrons only composed of pentagons and heptagons (F5F7–Cn) are the analogues of classical fullerenes (F5F6–Cn), but they have been neglected for a long time. Very recently, we have performed a systematical study on classical C60H60 and F5F7–C60H60 without endo C–H bonds and found that the stability of F5F7–C60H60 is comparable to their classical ones. To put further insight into the derivatives of F5F7 polyhedrons, we here performed a systematical density functional theory study on F5F7–C60H60 with 1–10 endo C–H bonds. The calculations demonstrate that some isomers of F5F7–C60H60 are lower in energy than the C60H60 obeying the isolated pentagon rule (IPR) even the parent cages of them are all higher in energy than the IPR one by as much as 350kcal/mol. Meanwhile, the F5F7–C60H60 with six endo C–H bonds is lower in energy than the IPR C60H60 without endo C–H bond by over 300kcal/mol. These results demonstrate that F5F7 polyhedrons should not be neglected at all during the search for the favorable derivatives of carbon polyhedrons and that the repulsion between the added atoms plays an important role in determining the stability of the derivatives of carbon polyhedrons.

Influence of Cr on the hydrogen storage properties of Ti-rich Ti–V–Cr alloys

In the present work, we studied the effects of Cr on the crystal structures and hydrogen storage properties of ternary alloys, Ti0.7V0.3−xCrx and Ti0.8V0.2−xCrx. Metal–hydrogen interactions were characterised by Thermal Desorption Spectroscopy (TDS) and in situ Synchrotron X-ray diffraction (SR-XRD). All initial alloys crystallise with body-centred cubic (BCC) crystal structures formed as solid solutions of V and Cr in Ti. Upon hydrogenation, the dihydrides (Ti,V,Cr)H2 with face-centred cubic (FCC) structures are formed. An increase in the Cr content leads to systematic changes in the structure and hydrogenation behaviours. The changes include (a) contraction of the unit cells for the initial alloys and for the corresponding dihydrides; (b) slower hydrogen absorption kinetics and an increase in the incubation period for hydrogenation; (c) a decrease in the thermal stability of the saturated hydrides; and (d) a reduction in the apparent activation energy of hydrogen desorption. In situ SR-XRD and TDS studies of the FCC Ti–V–Cr hydrides indicated that their decomposition consists of five individual desorption events.

Interaction in the Ce3Co8Si–H2 system

Interaction of hydrogen with Ce3Co8Si intermetallic compound (IMC) has been studied. IMC Ce3Co8Si absorbs hydrogen and forms a hydride phase at 11 atm and 50 °C. X-ray analysis of Ce3Co8Si H10.2 saturated hydride phase lattice showed that it has the symmetry of the initial compound and is expanded with strong anisotropy due to increased c parameter. Analysis of hydrogen desorption isotherms in Ce3Co8Si–H2 system has revealed that the decomposition of hydride phase occurred in one stage. The heat of hydride phase formation was calculated on the base of obtained equilibrium pressures data at 50, 60 and 70 °C. The results obtained demonstrate that Ce3Co8Si intermetallic compound may be used as reversible accumulator of hydrogen in medium temperatures interval.

Effect of cycling on hydrogen storage properties of Ti2CrV alloy

In the present work, we have studied the hydrogen absorption–desorption properties of the Ti2CrV alloy, and effect of cycling on the hydrogen storage capacity. The material has been characterized for the structure, morphology, pressure composition isotherms, hydrogen storage capacity, hydrogen absorption kinetics and the desorption profile at different temperatures in detail. The Ti2CrV crystallizes in body centered cubic (bcc) structure like TiCrV. The pressure composition isotherm of the alloy has been measured at room temperature and at 373K. The Ti2CrV alloy shows maximum hydrogen storage capacity of 4.37 wt.% at room temperature. The cyclic hydrogen absorption capacity of Ti2CrV alloy has been investigated at room temperature upto 10th cycle. The hydrogen storage capacity decreased progressively with cycling initially, but the alloy can maintain steady cyclic hydrogen absorption capacity 3.5 wt.% after 5th cycle. To get insight about the desorption behavior of the hydride in-situ desorption has been done at different temperatures and the amount of hydrogen desorbed has been calculated. The TG (Thermo gravimetric) and DTA analysis has been done on uncycled hydride shows that the surface poisoned sample gives a desorption onset temperature of 675K. The DSC measurement of uncycle and multi-cycled saturated hydrides shows that the hydrogen desorption temperature decreasing with cycling.

Structural, electronic, elastic properties and stabilities of hexagonal ZrNiAl alloy and its hydride ZrNiAlH 0.67 under pressure

The structural, electronic, elastic properties and stabilities of hexagonal prototype alloy ZrNiAl and its saturated hydride ZrNiAlH 0.67 are investigated using the pseudopotential plane wave method within the generalized gradient approximation (GGA). The calculated structural parameters are in good agreement with the available experimental data. Partial covalent characters on ZrNiAl and ZrNiAlH 0.67 are verified by the calculations of PDOS (partial density of states) and overlap population. Band structures show both ZrNiAl and ZrNiAlH 0.67 belong to metals. The elastic constants and their pressure dependences are calculated using the static finite strain technique. From the analysis of the mechanical stabilities, hexagonal ZrNiAl is unstable at higher pressure than 29.34 GPa; that its hydride ZrNiAlH 0.67 is stable up to 50 GPa is similar with the experimental result of isostructural LaNiInD 1.63− x . Hydrogenation not only leads to strong lattice anisotropy but also leads to strong mechanical anisotropy.

Improvement of hydrogen storage properties of TiCrV alloy by Zr substitution for Ti

Abstract The effects of Zr substitution for Ti on the hydrogen absorption–desorption characteristics of Ti 1− x Zr x CrV alloys ( x = 0, 0.05, 0.1 and 1.0) have been investigated. The crystal structure, maximum hydrogen absorption capacity, kinetics and hydrogen desorption properties have been studied in detail. While TiCrV crystallizes in body centered cubic (BCC) structure, ZrCrV is a C15 cubic Laves phase compound and the intermediate compositions with 5 and 10 at% Zr substitutions for Ti ( x = 0.05 and 0.1) show the presence of a small amount of ZrCr 2 Laves phase along with the main BCC phase. The pressure–composition isotherms have been studied at room temperature. TiCrV shows separation of TiH 2 phase on cycling. A small amount of Zr substitution for Ti is found to have advantageous effects on the hydrogen absorption properties of TiCrV as it suppresses TiH 2 phase separation and decreases hysteresis. It is found that the hydrogen absorption capacity of Ti 1− x Zr x CrV decreases as the Zr content increases due to the increased fraction of Laves phase. Temperature-programmed desorption studies have been carried out on the saturated hydrides in order to find the relative desorption temperatures.

Hydrogen absorption characteristics of Zr substituted [formula omitted] alloy

Hydrogen absorption properties of Ti 0.85 VFe 0.15 modified by Zr substitution (5 at%) at V site are studied. The crystal structure, maximum hydrogen absorption capacity and the hydrogen desorption properties of Ti 0.85 V 0.95 Fe 0.15 Zr 0.05 have been compared with those of Ti 0.85 VFe 0.15 . The alloys and the corresponding hydrides have been characterized by X-ray diffraction and Mössbauer spectroscopy. The kinetics of hydrogen uptake of both the alloys has been carried out and they are found to be comparable. The pressure–composition isotherms have been studied at room temperature and 373 K for both the alloys. Zr substituted composition is found to have better hydrogen absorption properties. Ti 0.85 VFe 0.15 is found to absorb a maximum of 3.83 H atoms/formula unit (3.7 wt%) to form a hydride with a composition Ti 0.85 VFe 0.15 H 3.83 , while Ti 0.85 V 0.95 Fe 0.15 Zr 0.05 absorbs a maximum of 3.74 H atoms/formula unit to form a hydride with a composition Ti 0.85 V 0.95 Fe 0.15 Zr 0.05 H 3.74 (3.5 wt%) at room temperature. Temperature programmed desorption studies have been carried out on the saturated hydrides in order to estimate the desorption temperatures.

Sorption and desorption of hydrogen in the alloys based on the ErNi2 compound

We study the process of formation of pseudobinary Laves phases on the basis of the ErNi2 compound realized as a result of the substitution of Y for Er and V for Ni and determine the hydrogen-sorption properties of these phases. The crystal structures of the original compounds and their saturated hydrides are investigated by the X-ray diffraction method. It is shown that these compounds absorb hydrogen under a pressure of 0.1–0.12 MPa without amorphization. The maximum hydrogen-sorption capacity (3.4 at. H/f.u.) is obtained for the Er0.85Y0.15Ni2 compound. The thermal stability of hydrides is determined by the method of thermodesorption spectroscopy in gaseous hydrogen at a heating rate of 5°C / min. An insignificant substitution o Y for Er and V for Ni improves the parameters of hydrogen sorption and desorption for these compounds.

Formation of a tetragonal phase hydride in Ti–Mo–H system

The structural relationship between the hydride phases in Ti–Mo–H solid solution system (Mo content up to 15 at% in the alloy) during dehydrogenation process under annealing has been studied by conventional and in situ X-ray powder diffraction and transmission electron microscopy (TEM) analysis. During dehydrogenation, the saturated hydrides of the Ti–Mo alloys with fcc δ-phase structure transfer into bcc β-phase at higher temperatures. An associated hydrogen concentration reduction for the δ-phase hydride is observed in the process. However, as the hydrogen concentrations decrease to certain values (H/M ∼ 1.1–1.7), the unsaturated δ-phase formed at high temperature would become unstable at lower temperature, and transfer into a tetragonal phase (denoted the ɛ-phase here). Unlike that of the ɛ-phase in Ti–H system, the phase transition does not occur for the saturated δ-phase with hydrogen concentration close to the stoichiometric limit. The hydrogen concentration of this ɛ-phase hydride is in between that of the tetragonal γ and ɛ-phase in Ti–H system, but more close to the γ-phase. The occurrence region of this ɛ-phase expands along with the increase of the Mo content in the alloys. The phase has a lattice similar to that of the ɛ-phase in Ti–H system with corresponding fct unit-cell c/ a < 1.

Structure transformations in the saturated hydrides ZrV2H4 &lt; x &lt; 6

Structure transformations in the saturated hydrides ZrV₂H_{4 &lt; x &lt; 6}

Vanadium-based BCC alloys: phase-structural characteristics and hydrogen sorption properties

This work was focused on the studies of vanadium-based “low-temperature” bcc alloys as H storage materials. Both as cast and annealed at 1100 ° C quaternary alloys V 92.5− x− y Zr 7.5Ti 7.5+ x− y M y (M = Cr, Mn, Fe, Co, Ni; x = 0 , 10; y = 0 , 7.5) were studied. They were characterised by XRD, PCT hydrogen absorption–desorption measurements ( T = 30 –120 ° C) and thermal desorption spectroscopy studies of H desorption from the saturated hydrides ( T = − 100 to 800 ° C). The thermodynamics of the VH ∼2↔ VH ∼1 transition and hydrogen sorption capacities ( 1.55 , … , 1.80 H/M) were found to be significantly influenced by the substituting M-element. The reversible hydrogen storage capacity ( T < 100 ° C, P > 0.1 bar) reaches 50–60% of its overall value. Complete hydrogen desorption proceeds in vacuum at T < 300 ° C. The major future challenge of the work is in increasing of the easy-reversible part of the H storage capacity corresponding to transformation VH ∼2↔ VH ∼1 by reducing the content of H in the monohydride.

Synthesis and Determination of the Crystal Structure of Hydrides of Er(M, V)2, where M = Fe or Co, Compounds

We study the process of formation of the Laves phases AB2 in Er(M, V)2 (M = Fe or Co) systems and determine their hydrogen-sorption properties. The crystal structure of parent compounds and their saturated hydrides is analyzed by the X-ray diffraction method. It is shown that these compounds absorb hydrogen at pressures of 0.1– 0.12 MPa without amorphization. The formation of the ErFe2 hydride is accompanied by the transformation of a cubic MgCu2-type structure into a trigonal TbFe2-type structure. Even an insignificant substitution of Fe with V or Co leads to an increase in the hydrogen-sorption capacity and prevents the changes in the crystal structure.

Hydrogen-induced changes in crystal structure and magnetic properties of the Zr 3MO x (M = Fe, Co) phases

It is shown that the oxygen-stabilised compounds Zr 3Fe(Co)O x ( x = 0–1.0) interact with hydrogen at ambient temperature and pressure forming saturated hydrides with filled Re 3B type structure. The hydrogen storage capacity decreases with increasing oxygen content from 6.7 H/f.u. for Zr 3Fe down to 5.35 H/f.u. for Zr 3FeO 1.0 and from 6.9 H/f.u. for Zr 3Co down to 5.3 H/f.u. for Zr 3CoO 1.0. A small change of the unit cell volumes for the Zr 3Fe(Co)O x parent compounds and a substantial increase of these parameters for the corresponding saturated hydrides were observed with increasing oxygen content. The partial hydrogen-induced lattice expansion, Δ V/at. H, increases from 2.25 Å 3 for Zr 3FeH 6.7 up to 3.38 Å 3 for Zr 3FeO 1.0H 5.35 and from 2.08 Å 3 for Zr 3CoH 6.9 up to 3.25 Å 3 for Zr 3CoO 1.0H 5.3. Rietveld refinement using neutron powder diffraction data for Zr 3FeO 0.4D 6.25 showed a distribution of deuterium atoms and a redistribution of oxygen atoms from octahedral to tetrahedral sites in a similar way as in Zr 3NiO x D y . Both 57 Fe Mössbauer spectroscopy and magnetic susceptibility measurements of Fe-containing hydrides indicated weak hydrogen-induced magnetic ordering at low temperatures. The ordering temperatures of Zr 3FeO 0.2H 6.52 and Zr 3FeO 0.6H 6.25 are 105 and 140 K, respectively.

Search for metal hydrides with short hydrogen–hydrogen separation: Ab initiocalculations

The present investigation is a part of a series on metal hydrides with extraordinary short $\mathrm{H}\mathrm{H}$ separations. The electronic structure, chemical bonding, and ground state properties of $RT\mathrm{In}$ $(R=\mathrm{La},\phantom{\rule{0.3em}{0ex}}\mathrm{Ce},\phantom{\rule{0.3em}{0ex}}\mathrm{Pr},\phantom{\rule{0.3em}{0ex}}\mathrm{Nd};\phantom{\rule{0.3em}{0ex}}T=\mathrm{Ni},\phantom{\rule{0.3em}{0ex}}\mathrm{Pd},\phantom{\rule{0.3em}{0ex}}\mathrm{Pt})$ and their saturated hydrides ${R}_{3}{T}_{3}{\mathrm{In}}_{3}{\mathrm{H}}_{4}$ $(=3RT\mathrm{In}{\mathrm{H}}_{1.333})$ are systematically studied using the full-potential linear muffin-tin-orbital method. The effect of the metal matrix on the $\mathrm{H}\mathrm{H}$ separation in $RT\mathrm{In}{\mathrm{H}}_{1.333}$ is analyzed in terms of chemical bonding, and bond strength is quantitatively analyzed using the crystal-orbital-Hamilton population. Force and volume optimizations reveal that all these hydrides violate the ``$2\text{\ensuremath{-}}\mathrm{\AA{}}$ rule.'' The insertion of hydrogen in the metal matrix causes highly anisotropic lattice changes; a large expansion along $c$ and a small contraction in the $a$ direction. Among the 12 studied hydrides the hypothetical $\mathrm{La}\mathrm{Pt}\mathrm{In}{\mathrm{H}}_{1.333}$ phase exhibits the shortest $\mathrm{H}\mathrm{H}$ separation $(1.454\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}})$. The optimized unit-cell parameters and atomic coordinates fit very well with the experimental findings for $R\mathrm{Ni}\mathrm{In}{\mathrm{H}}_{1.333}$, $R=\mathrm{La}$, Ce, and Nd. Examination of the effect of the metal matrix on the $\mathrm{H}\mathrm{H}$ separation in $RT\mathrm{In}{\mathrm{H}}_{1.333}$ suggests that on a proper choice of alloying element one may be able to reduce the $\mathrm{H}\mathrm{H}$ separation below $1.45\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. The $\mathrm{H}\mathrm{H}$ separation is reduced significantly by application of pressure.