Intermetallic Hydrides Research Articles

One electron is enough: A chemical bonding approach on the hydrogen induced structural transformation in MPd3 (M = Mg, In, Tl) intermetallic compounds

It is crucial to understand the nature of the metal-hydrogen interactions in the intermetallic hydrides in order to develop new hydrogen storage materials with optimum metal-H interactions for desired hydrogen absorption-desorption kinetics. The MPd3 intermetallic compounds (M = Mg, In, Tl) transform to cubic anti-perovskite type (AuCu3-type with hydrogen in the octahedral intersect) structure from ZrAl3-type four-fold ccp-superstructure up on hydrogenation. According to the DFT-based orbital space electronic structure and chemical bonding analysis, this structural transformation is driven by maximizing the coordination of hydrogen surrounded by Pd, forming the Pd (4d) – H (1s), and … Pd–H–Pd … multicenter interactions. These interactions provide sufficient thermodynamic stability for the hydrides to form, with negative binding energies of hydrogen. The binding energies are found to be significantly low, with the possibility of the ease of hydrogen desorption within limited reaction conditions.

Zr-based Laves phases with nitride/hydride ions for ammonia synthesis

Early transition metal-based intermetallic compounds, such as ZrV2, ZrMn2, and ZrCr2, can reversibly absorb large amounts of hydrogen and are of great interest for hydrogen storage. The dissociative hydrogen chemisorption can proceed easily on the surface, allowing the rapid formation of intermetallic hydrides. In this study, we present the results of initial NH3 activity tests conducted on various Zr-based AB2-type intermetallic compounds, free of precious transition metals and rare earth metals. A dissociative hydrogen chemisorption together with nitrogen storage proceeds on AB2-type Laves phase intermetallic compounds accompanied by a lattice expansion. The formed intermetallic nitride hydride ZrCr2N0.4H1.4 exhibits stable catalytic activity as an ammonia synthesis catalyst.

Effects of Ni precursors on the formation of Mg-Fe-Ni intermetallic hydrides, kinetics, and reversibility.

This work focuses on the effects of Ni precursors (metallic Ni or Mg2NiH4) on the formation of Mg-Fe-Ni intermetallic hydrides as well as their de/rehydrogenation kinetics and reversibility. After ball milling and sintering, the formation of Mg2FeH6 and Mg2NiH4 are found in both samples, while MgH2 is observed only in the sample with metallic Ni. Both samples show comparable hydrogen capacities of 3.2-3.3 wt% H2 during the 1st dehydrogenation, but the sample with metallic Ni decomposes at a lower temperature (ΔT = 12 °C) and shows faster kinetics. Although phase compositions after dehydrogenation of both samples are comparable, their rehydrogenation mechanisms are different. This affects the kinetic properties upon cycling and reversibility. Reversible capacities of the samples with metallic Ni and Mg2NiH4 during the 2nd dehydrogenation are 3.2 and 2.8 wt% H2, respectively, while those during the 3rd-7th cycles reduce to ∼2.8 and 2.6 wt% H2, respectively. Chemical and microstructural characterizations are carried out to explain de/rehydrogenation pathways.

Hydrogen induced structural phase transformation in ScNiSn-based intermetallic hydride characterized by experimental and computational studies

Understanding an interrelation between the structure, chemical composition and hydrogenation properties of intermetallic hydrides is crucial for the improvement of their hydrogen storage performance. Ability to form the hydrides and to tune the thermodynamics and kinetics of their interaction with hydrogen is related to their chemical composition. Some features of the metal–hydrogen interactions remain however poorly studied, including chemistry of Sc-containing hydrides. ZrNiAl-type ScNiSn-based intermetallic hydride has been probed in the present work using a broad range of experimental techniques including Synchrotron and Neutron Powder Diffraction, 119Sn Möessbauer Spectroscopy, hydrogenation at pressures reaching several kbar H2 and hydrogen Thermal Desorption Spectroscopy studies. Computational DFT calculations have been furthermore performed. This allowed to establish the mechanism of the phase-structural transformation and electronic structure changes causing a unique contraction of the metal lattice of intermetallic alloy and the formation of the ...H-Ni-H-Ni… chains in the structure with H atoms carrying a partial negative charge. Such hydrogen absorption accompanied by a formation of a covalent Ni-H bonding and causing an unusual behavior contracts to the conventionally observed bonding mechanism of hydrogen in metals as based on the metallic bonding frequently accompanied by a jumping diffusion movement of the inserted H atoms – in contrast to the directional Metal-Hydrogen bonding observed in the present work. At high applied pressures ScNiSnH0.83 orthorhombic TiNiSi type hydride is formed with H atoms filling Sc3Ni tetrahedra. Finally, this study shows that scandium closely resembles the behavior of the heavy rare earth metal holmium.

Hydrogen sorption kinetics and mechanism of Mg2Fe(1−x)NixH6

This work aims to optimize the content of Ni substitution for Fe in Mg2FeH6 to form the quaternary intermetallic hydrides of Mg2Fe(1−x)NixH6 with the best kinetics and reversibility. Different degrees of Ni substitution (x) are obtained from varying the mole ratios of Mg2FeH6:Mg2NiH4 used as starting materials. By increasing Mg2NiH4 contents, the degree of Ni substitution enhances from x = 0.26–0.47, which is beneficial to dehydrogenation kinetics and reversible hydrogen capacities. The sample with significant Ni substitution rather decompose into Mg2Ni than Mg, which Mg2Ni reacts with Fe to reproduce Mg2Fe(1−x)NixH6 upon rehydrogenation. During cycling, Ni substitution degree of all samples enhances to the optimized composition of x∼0.5, resulting in the kinetic improvement. Furthermore, the structures of Mg2Fe(1−x)NixH6 with different Ni-substituted contents are simulated and their dehydrogenation energies are calculated to explain the role of Ni substitution on the dehydrogenation of Mg2Fe(1−x)NixH6.

Laves type intermetallic compounds as hydrogen storage materials: A review

Laves type AB 2 intermetallics belong to the most abundant group of intermetallic compounds containing over 1000 compounds. A large variety of the chemical nature of A (Mg, Ca, Ti, Zr, Rare Earth Metals) and B (V, Cr, Mn, Fe, Co, Ni, Al) metals together with the existence of the extended solid solutions formed by mixing various selected components on both A and B sites dramatically extends the list the known binary and ternary individual compounds. A vast majority of the Laves type intermetallics crystallises with C15 / FCC MgCu 2 and C14 / hexagonal MgZn 2 types of structures, both formed for a large range of ratios between the atomic radii of the A and B components outside the ideal ratio r A / r B = 1.225. Their hydrogenation performance is defined by the chemical composition and structure of the alloys and proceeds according to the following alternative / parallel mechanisms: (a) Formation of the insertion type interstitial hydrides containing up to 6–7 at. H/f.u.AB 2 ; (b) Amorphisation of the alloys on hydrogenation; (c) Disproportionation with the formation of a binary hydride of the A metal and depleted by A metal B-components based alloys/hydrides. Equilibrium pressures of hydrogen desorption from the AB 2 -type hydrides span a huge range of ten orders of magnitude and thus Laves type-based intermetallics satisfy the requirements for various applications including getters of hydrogen gas, volume- and mass-efficient hydrogen storage materials operating at ambient conditions, materials for the efficient thermally driven compression of hydrogen gas with an output pressure of several hundred bar and high capacity and high rate anode materials for the metal hydride batteries operating in a challenging temperature range - at subzero temperatures and also above 60 °C. The paper contains references to 245 publications and will guide the future work in the areas of fundamental research and also in advancing the applications of the hydrides of the Laves type intermetallics. • Laves type AB 2 intermetallics are the most abundant group of alloys. • Hydrogenation performance is defined by the chemical composition and structure. • Mechanisms of hydrogenation: interstitial hydrides / amorphization / disproportionation. • Structure-properties relationships are described. • Important applications are reviewed: H stores/MH compression/MH batteries/H getters.

Effect of oxygen on the hydrogen storage properties of TiFe alloys

Hydrogen storage is one of the critical barriers to the hydrogen-based clean energy supply chain. TiFe alloy is a prime candidate material for stationary hydrogen storage, which can play a critical role in the deployment of variable renewable energies. However, the understanding of the hydrogen storage properties of TiFe alloy and the development of industrially deployable storage technologies based on TiFe are still in their nascent stage. The properties of TiFe alloy rely strongly on the presence of oxygen due to the strong affinity of Ti to oxygen. This work systematically investigated the effects of oxygen on the equilibrium pressure of TiFe-H intermetallic hydride. We aim to understand how the oxygen content affects the (de)hydrogenation behavior of TiFe alloys. Specifically, we found that the oxygen can dissolve in the TiFe phase and form solid solutions of TiFe-O. During the thermochemical synthesis process of TiFe, with the increase of annealing time, the Ti4Fe2O phase decreases, and the oxygen in TiFe increases. The increase of oxygen content in the TiFe results in the increase of equilibrium pressure of the TiFe alloy. It suggests that the oxygen dissolved in TiFe can destabilize the TiFe-H hydride and alter the thermodynamics of the TiFe-H system.

Modeling the thermodynamics of the FeTi hydrogenation under para-equilibrium: An ab-initio and experimental study

FeTi-based hydrides have recently re-attracted attention as stationary hydrogen storage materials due to favorable reversibility, good sorption kinetics and relatively low costs compared to alternative intermetallic hydrides. Employing the OpenCalphad software, the thermodynamics of the (FeTi)1−xHx (0 ≤x≤ 1) system were assessed as a key basis for modeling hydrogenation of FeTi-based alloys. New thermodynamic data were acquired from our experimental pressure-composition-isotherm (PCI) curves, as well as first-principles calculations utilizing density functional theory (DFT). The thermodynamic phase models were carefully selected based on critical analysis of literature information and ab-initio investigations. Key thermodynamic properties such as dissociation pressure, formation enthalpies and phase diagrams were calculated in good agreement to our performed experiments and literature-reported data. This work provides an initial perspective, which can be extended to account for higher-order thermodynamic assessments and subsequently enables the design of novel FeTi-based hydrides. In addition, the assessed thermodynamic data can serve as key inputs for kinetic models and hydride microstructure simulations.

The effect of hydrogenation on the fracture of Ti2AlNb-based alloy during ball milling

In this work we have studied the effect of phase composition and microstructure of a rapidly solidified Ti2AlNb-based alloy containing hydrogen on deformation of the alloy during ball milling and production of a fine-dispersed powder. Hydrogen is introduced into the alloy up to a concentration of 2.0 wt%. The X-Ray diffraction (XRD) analysis and Scanning Electron Microscopy (SEM) show that the alloy has the following phase compositions depending on hydrogen content: β + O, β/β-hydride, β/β-hydride + intermetallic hydride (Ti2AlNbHx) or a single-phase intermetallic hydride. It is found that in the hydrogenated β + O alloy containing a small amount of hydrogen a strong decrease in ductility occurs, but this does not affect the ball milling and synthesis of the fine-dispersed powder. Efficient milling of the rapidly solidified alloy has been achieved when hydrogen content was 1.2 wt% and exceeding this value when a transformation from the H-saturated solid solution into a hydride phase is observed in the alloy or the formation of a single phase hydride occurs.

Engineering the hydrogen storage properties of the perovskite hydride ZrNiH3 by uniaxial/biaxial strain

In the present work, the bonding length, electronic structure, stability, and dehydrogenation properties of the Perovskite-type ZrNiH3 hydride, under different uniaxial/biaxial strains are investigated through ab-initio calculations based on the plane-wave pseudo-potential (PW-PP) approach. The findings reveal that the uniaxial/biaxial compressive and tensile strains are responsible for the structural deformation of the ZrNiH3 crystal structure, and its lattice deformation becomes more significant with decreasing or increasing the strain magnitude. Due to the strain energy contribution, the uniaxial/biaxial strain not only lowers the stability of ZrNiH3 but also decreases considerably the dehydrogenation enthalpy and decomposition temperature. Precisely, the formation enthalpy and decomposition temperature are reduced from −67.73 kJ/mol.H2 and 521 K for non-strained ZrNiH3 up to −33.73 kJ/mol.H2 and 259.5 K under maximal biaxial compression strain of ε = −6%, and to −50.99 kJ/mol.H2 and 392.23 K for the maximal biaxial tensile strain of ε = +6%. The same phenomenon has been also observed for the uniaxial strain, where the formation enthalpy and decomposition temperature are both decreased to −39.36 kJ/mol.H2 and 302.78 K for a maximal uniaxial compressive strain of ε = - 12%, and to −51.86 kJ/mol.H2 and 399 K under the maximal uniaxial tensile strain of ε = +12%. Moreover, the densities of states analysis suggests that the strain-induced variation in the dehydrogenation and structural properties of ZrNiH3 are strongly related to the Fermi level value of total densities of states. These ab-initio calculations demonstrate insightful novel approach into the development of Zr-based intermetallic hydrides for hydrogen storage practical applications.

Intermetallic Compounds Synthesized by Mechanical Alloying for Solid-State Hydrogen Storage: A Review

Hydrogen energy is a very attractive option in dealing with the existing energy crisis. For the development of a hydrogen energy economy, hydrogen storage technology must be improved to over the storage limitations. Compared with traditional hydrogen storage technology, the prospect of hydrogen storage materials is broader. Among all types of hydrogen storage materials, solid hydrogen storage materials are most promising and have the most safety security. Solid hydrogen storage materials include high surface area physical adsorption materials and interstitial and non-interstitial hydrides. Among them, interstitial hydrides, also called intermetallic hydrides, are hydrides formed by transition metals or their alloys. The main alloy types are A2B, AB, AB2, AB3, A2B7, AB5, and BCC. A is a hydride that easily forms metal (such as Ti, V, Zr, and Y), while B is a non-hydride forming metal (such as Cr, Mn, and Fe). The development of intermetallic compounds as hydrogen storage materials is very attractive because their volumetric capacity is much higher (80–160 kgH2m−3) than the gaseous storage method and the liquid storage method in a cryogenic tank (40 and 71 kgH2m−3). Additionally, for hydrogen absorption and desorption reactions, the environmental requirements are lower than that of physical adsorption materials (ultra-low temperature) and the simplicity of the procedure is higher than that of non-interstitial hydrogen storage materials (multiple steps and a complex catalyst). In addition, there are abundant raw materials and diverse ingredients. For the synthesis and optimization of intermetallic compounds, in addition to traditional melting methods, mechanical alloying is a very important synthesis method, which has a unique synthesis mechanism and advantages. This review focuses on the application of mechanical alloying methods in the field of solid hydrogen storage materials.

Room Temperature Metal Hydrides for Stationary and Heat Storage Applications: A Review

Hydrogen has been long known to provide a solution toward clean energy systems. With this notion, many efforts have been made to find new ways of storing hydrogen. As a result, decades of studies has led to a wide range of hydrides that can store hydrogen in a solid form. Applications of these solid-state hydrides are well-suited to stationary applications. However, the main challenge arises in making the selection of the Metal Hydrides (MH) that are best suited to meet application requirements. Herein, we discuss the current state-of-art in controlling the properties of room temperature (RT) hydrides suitable for stationary application and their long term behavior in addition to initial activation, their limitations and emerging trends to design better storage materials. The hydrogen storage properties and synthesis methods to alter the properties of these MH are discussed including the emerging approach of high-entropy alloys. In addition, the integration of intermetallic hydrides in vessels, their operation with fuel cells and their use as thermal storage is reviewed.

Intermetallic Hydrides: Magnetic Properties and Catalysis

Intermetallic hydrides (IHs) are shown to be complex dynamic systems. Hydrogen desorption and dissociative adsorption on IHs are the rate-determining stages in the heterophase exchange of hydrogen of the gas phase and hydride. The oxidative treatment of IHs leads to surface enrichment with a more noble metal, which determines the unique catalytic properties of the system along with the heterophase exchange of hydrogen.

Structure of Polycrystalline CeNi3-Based Intermetallic Hydrides at 293 and 5 K

The structure of polycrystalline CeNi3Н3.0 hydride samples at 5 and 293 K has been studied by neutron diffraction. The hydrides have a rhombic lattice (sp. gr. Pmcn, no. 62, Z = 12). The site parameters of metal and hydrogen atoms have been determined. It is established that the distribution of hydrogen atoms over the hydride structure sites at 5 K is similar to the hydrogen distribution at room temperature. A comparison of the neutron diffraction patterns obtained at different temperatures indicates a change in the sample microstructure upon cooling.

Materials for hydrogen-based energy storage – past, recent progress and future outlook

Globally, the accelerating use of renewable energy sources, enabled by increased efficiencies and reduced costs, and driven by the need to mitigate the effects of climate change, has significantly increased research in the areas of renewable energy production, storage, distribution and end-use. Central to this discussion is the use of hydrogen, as a clean, efficient energy vector for energy storage. This review, by experts of Task 32, “Hydrogen-based Energy Storage” of the International Energy Agency, Hydrogen TCP, reports on the development over the last 6 years of hydrogen storage materials, methods and techniques, including electrochemical and thermal storage systems. An overview is given on the background to the various methods, the current state of development and the future prospects. The following areas are covered; porous materials, liquid hydrogen carriers, complex hydrides, intermetallic hydrides, electrochemical storage of energy, thermal energy storage, hydrogen energy systems and an outlook is presented for future prospects and research on hydrogen-based energy storage.

Extracting an Empirical Intermetallic Hydride Design Principle from Limited Data via Interpretable Machine Learning.

An open question in the metal hydride community is whether there are simple, physics-based design rules that dictate the thermodynamic properties of these materials across the variety of structures and chemistry they can exhibit. While black box machine learning-based algorithms can predict these properties with some success, they do not directly provide the basis on which these predictions are made, therefore complicating the a priori design of novel materials exhibiting a desired property value. In this work we demonstrate how feature importance, as identified by a gradient boosting tree regressor, uncovers the strong dependence of the metal hydride equilibrium H2 pressure on a volume-based descriptor that can be computed from just the elemental composition of the intermetallic alloy. Elucidation of this simple structure-property relationship is valid across a range of compositions, metal substitutions, and structural classes exhibited by intermetallic hydrides. This permits rational targeting of novel intermetallics for high-pressure hydrogen storage (low-stability hydrides) by their descriptor values, and we predict a known intermetallic to form a low-stability hydride (as confirmed by density functional theory calculations) that has not yet been experimentally investigated.

Enhancing of hydrogen storage properties of perovskite-type MgNiH3 by introducing cobalt dopant (MgCoxNi1−xH3) using first-principle calculations

First-principle calculations have been performed to study the intermetallic alloys MgCoxNi1−x and intermetallic hydrides MgCoxNi1−xH3 using full-potential local orbital (FPLO). The electronic structure of Mg-hydride-based alloys has been elaborated to predict further modifications which destabilize the corresponding hydrides. In this paper, we have demonstrated that the insertion of Co element plays a crucial role in the stability of doped intermetallic hydrides (MgCo0.50Ni0.50H3, MgCo0.75Ni0.25H3 and MgCo0.875Ni0.125H3), by enhancing the hydrogen storage capacities which becomes around 3.488 wt%, also the desorption temperature has improved significantly. Therefore, the mixture between Co and Ni plays an important role in the hydrogen uptake mechanism in the target intermetallic matrix.

An Analysis of Thermodynamic Characteristics of Metal-Hydride Systems for Hydrogen Storage, Using a Modified Scheme of the Perturbation Theory

The use of hydrides of intermetallic compounds (IMC) to implement the working processes of thermo sorption compressors, heat pumps, storage systems, cleaning, and programmable supply of hydrogen is due to a number of unique properties of these hydrogen sorbents. These include, first of all, the fact that the saturation of IMCs with a large sorption capacity occurs under relatively mild thermodynamic conditions, as well as the selectivity of sorption processes and the presence of the effect of thermodesorptional activation of atoms and molecules of hydrogen isotopes. The work is devoted to the description of phase equilibria in IMC hydrides. The proposed approach to the problem of calculating phase equilibria in metal hydrides consists in determining the properties of the lattice gas of H atoms and the H2 molecular phase (which is in equilibrium with it) within the framework of a single method, the modified perturbation theory. The thermodynamic description of the hydrogen subsystem in the region of disordered α-, β-phases is carried out on the basis of the model of the non-ideal (interacting) lattice gas of hydrogen atoms. In this case, both the direct interaction between hydrogen atoms and the indirect deformation contributions to the potential energy due to the expansion of the lattice during hydrogen dissolution are taken into account. Simulation of phase transitions in IMC-hydrogen systems based on the modified perturbation theory scheme gives a correct description of the main features of phase diagrams in a wide range of hydrogen pressures. From the condition of the equality of the chemical potentials of the H-subsystem of the hydride and H2-phase (calculated on the H atom), equations are obtained, relating the pressure of the gaseous H2 phase to the hydride parameters c and T (phase diagrams). The proposed computational procedure does not use adjustable parameters or empirical correlations. It relies on the atomic characteristics of the hydrogen subsystem and metal matrix, which have an unambiguous physical meaning. The object of this research is the LaNi5 intermetallic hydride. Of particular interest is the position of the critical point of the β→α-transition in the LaNi5-hydrogen system, for which there are no experimentally obtained parameter values. The paper presents the calculated values of the β→α-transition critical parameters Tc=445 K, pc=87 atm. The calculated data on the thermodynamic parameters of the α→β-transition (enthalpy, entropy, and pressure on the isotherm plateau) make it possible to describe the solubility of hydrogen in LaNi5 at pressures up to 500 atm and are in good agreement with the available experimental data in the literature.

Interaction of the RNi1 –xSix (R = Dy, Gd; x = 0.05, 0.02) Compounds with Hydrogen

This paper reports the synthesis of RNi1 –xSix-based (R = Dy, Gd; x = 0.05, 0.02) intermetallic hydrides. The amount of absorbed hydrogen in the hydride phases is three to four atoms per formula unit. According to X-ray diffraction data, the synthesized hydrides have a crystal lattice with the FeB structure (sp. gr. Pnma, no. 62) at R = Dy and the CrB structure (sp. gr. Cmcm, no. 63) at R = Gd.

Metal hydride hydrogen storage tank for fuel cell utility vehicles

The “low-temperature” intermetallic hydrides with hydrogen storage capacities below 2 wt% can provide compact H2 storage simultaneously serving as a ballast. Thus, their low weight capacity, which is usually considered as a major disadvantage to their use in vehicular H2 storage applications, is an advantage for the heavy duty utility vehicles. Here, we present new engineering solutions of a MH hydrogen storage tank for fuel cell utility vehicles which combines compactness, adjustable high weight, as well as good dynamics of hydrogen charge/discharge. The tank is an assembly of several MH cassettes each comprising several MH containers made of stainless steel tube with embedded (pressed-in) perforated copper fins and filled with a powder of a composite MH material which contains AB2- and AB5-type hydride forming alloys and expanded natural graphite. The assembly of the MH containers staggered together with heating/cooling tubes in the cassette is encased in molten lead followed by the solidification of the latter. The tank can provide >2 h long H2 supply to the fuel cell stack operated at 11 kWe (H2 flow rate of 120 NL/min). The refuelling time of the MH tank (T = 15–20 °C, P(H2) = 100–150 bar) is about 15–20 min.