Metal-hydrogen Systems Research Articles

Hydride formation in single palladium and magnesium nanoparticles studied by nanoplasmonic dark-field scattering spectroscopy.

Scrutinizing functional nanosystems and relating details in their size, chemistry, and geometry to functionality remains a significant experimental challenge. Following the concept of indirect nanoplasmonic sensing (INPS), the exploitation of truncated Au nanocones with functionalized tips, nanofabricated in a one step, are used as single nanoplasmonic sensors for dark-field scattering spectroscopy measurements of the hydride formation Au in single Pd and Mg nanoparticles.

Reducing Hydrogen Permeation through Metals

Metal–hydrogen systems are of great basic and technological interest in connection to the role of hydrogen as a clean energy carrier. Frequently, metal systems are involved in hydrogen purification, storage, and engines making use of this fuel. The presence of hydrogen in a metallic matrix gives rise to modifications of electrical, optical and mechanical properties. Hydrogen accumulation in metals may cause damage to the material by also producing fracture, thus limiting operating lifetime. Reducing the hydrogen permeation is an important task also for the fusion reactors: it is well known, indeed, that tritium is radioactive so that it is very important to be able to confine tritium during the nuclear fusion process. The theoretical study of permeation is thus of fundamental importance to obtain efficient barriers to permeation. Hydrogen trapping sites have a great influence on the hydrogen permeation through a slab sample. The diffusion of the hydrogen in a crystal is generally described by a parabolic partial differential equation with appropriate boundary conditions. The numerical simulation code PHM (Permeation of Hydrogen through Metals), realized for the study of the permeation of hydrogen in presence of trapping sites, is here described and utilized for the analysis of the influence of reversible and irreversible traps on the diffusion of hydrogen in a metal.

H2-Binding by Neutral and Multiply Charged Titaniums: Hydrogen Storage Capacity of Titanium Mono- and Dications.

Given that transition metal-hydrogen systems have been studied as a predecessor for hydrogen storage materials, we have investigated the neutral and multiply charged titanium-H2 systems (Ti-H2, Ti(+)-H2, Ti(2+)-H2, Ti(3+)-H2, and Ti(4+)-H2) using density functional theory (DFT) and high-level ab initio calculations, including coupled cluster theory with single, double, and perturbatively triple excitations [CCSD(T)]. These systems show different types of hydrogenation depending on their charged state. The neutral Ti-H2 system shows dihydride structure with covalent interaction where the Ti-H distance is 1.76 Å, while H2 is dissociated into two neigboring hydride ions by withdrawing electrons from Ti. The charged Ti(+)-H2, Ti(2+)-H2, and Ti(3+)-H2 systems show dihydrogen structures with noncovalent interaction, where the Ti(+)-H, Ti(2+)-H, and Ti(3+)-H distances are 2.00, 2.14, and 2.12 Å, respectively. The main binding energies in these systems arise from the hydrogen polarizability driven interaction by the positive charge of Ti(n+) (n = 1-3). Among Ti(n+)-H2 (n = 1-3) the Ti(+)-H2 has the shortest distance against our common expectation, while Ti(2+)-H2 has the longest distance. The Ti(+)-H2 distance is the shortest because of the d-σ* molecular orbital (MO) interaction which is not present in Ti(2+)-H2 and Ti(3+)-H2. The Ti(4+) ion does not bind H2. In this regard, we have investigated the maximal hydrogen binding capacity by Ti complexes. The coordination of titanium mono- and dications complexed with dihydrogen (H2) [Ti(+)(H2)n and Ti(2+)(H2)m] is studied along with their structures, binding energies, electronic properties, and spectra. The titanium monocations of the quartet ground state have up to the hexacoordinaton, while titanium dications of the triplet ground state have up to the octacoordination at very low temperatures. At room temperature, the monocations favor penta- to hexacoordination, while the dications favor hexacoordination. This information would be useful for the design of hydrogen storage devices of Ti complexes, such as Ti-decorated/dispersed polymer-graphene hybrid materials.

Low T Study of PdH x System by Torsional Oscillator Technique: x Dependent Responses

Hydrogen atoms dissolve in Pd at densities up to one H atom per Pd, which provides higher atomic H density than in solid H2. They are known to have large diffusion coefficient due to quantum tunneling. Torsional oscillator (TO) technique is employed to investigate the phases of H in Pd, which is known to show phase boundaries at the lowest T among metal-hydrogen (MH) systems. Specific heat measurements have been performed for PdHx with x up to high H concentration specimens as well as studies of the resistivity study to establish the unique x−T phase diagram. We have, in addition, been performing TO experiments, in order to study the effect of atomic H intrusion and the dynamics in the PdH(D)x system. The TO is a well-established, powerful instrument method to investigate superfluidity and quantum vortices of liquid He, especially in thin films, as well as dislocation dynamics in solids. In our TO experiments on PdHx specimens have shown a resonance frequency shift for PdHx, with 0.16≤x≤0.75 at the lowest T’s, which can be largely explained by the lattice deformation by H intrusion. This x dependent contribution has a smaller, additional change depending on x and T above ∼50 K. We will show the details of experimental data and discuss the correspondence to the phonon modes change and further possibility of studying occurrence of quantum phenomena for the hydrogen system.

High pressure in situ diffraction studies of metal–hydrogen systems

“Hybrid” hydrogen storage, where hydrogen is stored in both the solid material and as a high pressure gas in the void volume of the tank can improve overall system efficiency by up to 50% compared to either compressed hydrogen or solid materials alone. Thermodynamically, high equilibrium hydrogen pressures in metal–hydrogen systems correspond to low enthalpies of hydrogen absorption–desorption. This decreases the calorimetric effects of the hydride formation–decomposition processes which can assist in achieving high rates of heat exchange during hydrogen loading—removing the bottleneck in achieving low charging times and improving overall hydrogen storage efficiency of large hydrogen stores. Two systems with hydrogenation enthalpies close to −20 kJ/mol H 2 were studied to investigate the hydrogenation mechanism and kinetics: CeNi 5–D 2 and ZrFe 2− x Al x ( x = 0.02; 0.04; 0.20)–D 2. The structure of the intermetallics and their hydrides were studied by in situ neutron powder diffraction at pressures up to 1000 bar and complementary X-ray diffraction. The deuteration of the hexagonal CeNi 5 intermetallic resulted in CeNi 5D 6.3 with a volume expansion of 30.1%. Deuterium absorption filled three different types of interstices, Ce 2Ni 2 and Ni 4 tetrahedra, and Ce 2Ni 3 half-octahedra and was accompanied by a valence change for Ce. Significant hysteresis was observed between deuterium absorption and desorption which profoundly decreased on a second absorption cycle. For the Al-modified Laves-type C15 ZrFe 2− x Al x intermetallics, deuteration showed very fast kinetics of H/D exchange and resulted in a volume increase of the FCC unit cells of 23.5% for ZrFe 1.98Al 0.02D 2.9(1). Deuterium content, hysteresis of H/D uptake and release, unit cell expansion and stability of the hydrides systematically change with the amount of Al content. In the deuteride D atoms exclusively occupy the Zr 2(Fe,Al) 2 tetrahedra. Observed interatomic distances are Zr–D = 1.98–2.11; (Fe, Al)–D = 1.70–1.75 Å. Hydrogenation slightly increases the magnetic moment of the Fe atoms in ZrFe 1.98Al 0.02 and ZrFe 1.96Al 0.04 from 1.9 μ B at room temperature for the alloy to 2.2 μ B for its deuteride.

NMR study of metal-hydrogen systems for hydrogen storage

In this contribution we report on the results of our recent 1H NMR studies of different metal hydrides of interest for reversible hydrogen storage applications: Ti–V–Cr alloys of various compositions, pure and with Zr 7Ni 10 or Hf 7Ni 10 additives, and in additives themselves. The temperature dependences of 1H spin-lattice relaxation have been treated within an exchange model.

Nanostructured Metal Hydrides for Hydrogen Storage Studied by In Situ Synchrotron and Neutron Diffraction

AbstractThis work was focused on studies of the metal hydride materials having a potential in building hydrogen storage systems with high gravimetric and volumetric efficiencies of H storage and formed / decomposed with high rates of hydrogen exchange. In situ diffraction studies of the metal-hydrogen systems were explored as a valuable tool in probing both the mechanism of the phase-structural transformations and their kinetics. Two complementary techniques, namely Neutron Powder Diffraction (NPD) and Synchrotron X-ray diffraction (SR XRD) were utilised. High pressure in situ NPD studies were performed at D2 pressures reaching 1000 bar at the D1B diffractometer accommodated at Institute Laue Langevin, Grenoble. The data of the time resolved in situ SR XRD were collected at the Swiss Norwegian Beam Lines, ESRF, Grenoble in the pressure range up to 50 bar H2 at temperatures 20-400°C.The systems studied by NPD at high pressures included deuterated Al-modified Laves-type C15 ZrFe2-xAlx intermetallics with x = 0.02; 0.04 and 0.20 and the CeNi5-D2 system. D content, hysteresis of H uptake and release, unit cell expansion and stability of the hydrides systematically change with Al content.Deuteration exhibited a very fast kinetics; it resulted in increase of the unit cells volumes reaching 23.5 % for ZrFe1.98Al0.02D2.9(1) and associated with exclusive occupancy of the Zr2(Fe,Al)2 tetrahedra.For CeNi5 deuteration yielded a hexahydride CeNi5D6.2 (20°C, 776 bar D2) and was accompanied by a nearly isotropic volume expansion reaching 30.1% (∆a/a=10.0%; ∆c/c=7.5%). Deuterium atoms fill three different interstitial sites including Ce2Ni2, Ce2Ni3 and Ni4. Significant hysteresis was observed on the first absorption-desorption cycle. This hysteresis decreased on the absorption-desorption cycling.A different approach to the development of H storage systems is based on the hydrides of light elements, first of all the Mg-based ones. These systems were studied by SR XRD. Reactive ball milling in hydrogen (HRBM) allowed synthesis of the nanostructured Mg-based hydrides.The experimental parameters (PH2, T, energy of milling, ball / sample ratio and balls size), significantly influence rate of hydrogenation. The studies confirmed (a) a completeness of hydrogenation of Mg into MgH2; (b) indicated a partial transformation of the originally formed -MgH2 into a metastable -MgH2 (a ratio / was 3/1); (c) yielded the crystallite size for the main hydrogenation product, -MgH2, as close to 10 nm. Influence of the additives to Mg on the structure and hydrogen absorption/desorption properties and cycle behaviour of the composites was established and will be discussed in the paper.

Hydrogen-induced soliton-like coherent swellings moving across the surface of palladium-hydrogen alloys

Coherently conjugate wave-like swellings moving across the surface of PdH0.1 alloy at additional saturation with hydrogen under significantly nonequilibrium conditions have been detected and video recorded for the first time. The shape and character of motion of these swellings are similar to those of solitary waves of translation—solitons. The detected moving soliton-like swelling has been phenomenologically analyzed based on the modern concepts of metal-hydrogen systems. It is emphasized that the formation of these soliton-like coherent moving swellings is a peculiar (unknown previously) mechanism of relaxation and equalization of internal stress in metal-hydrogen alloys.

Novel device for simultaneous volumetric and x-ray diffraction measurements on metal-hydrogen systems

Hydrogen storage materials can form more than one hydride phase. These different phases, in turn, display different hydrogen absorption/desorption capacities, kinetics, and stabilities. Studies aimed at characterizing and improving these materials usually need to correlate hydrogen intake with the precise determination of the hydride phase involved in the process. Here, we present a device designed to perform measurements of well known volumetric techniques with simultaneous x-ray diffraction on the material under study. The compact design can stand up to 6000 kPa of internal pressure while the sample can be heated up to 450 degrees C. The design process was assisted by finite element modeling and by the use of mock-up prototypes in order to optimize the thermal and under load behaviors. We provide two examples of use for this new device: (1) hydride decomposition in LaNi5 at 115 degrees C and (2) formation of MgCo during the programmed thermal desorption of the Mg2CoH5 hydride.

Anodic Polarisation Characterisation of Absorbed Hydrogen in Modified Mm(B<sub>5</sub>)<sub>x</sub> Alloys

Anodic polarisation curves of Mm(Ni3.6Co0.7Mn0.4Al0.3)x (Mm = mischmetal, 0.85  x  1.15) electrodes were measured under the conditions of various initial concentrations of absorbed hydrogen (H/M), potential sweeping rates (v), temperatures (T), and amounts of reducing agent (y = [NaBH4]) in alkaline solution. Anodic peak current (Ip) at the Mm(B5)x electrodes increased with an increase in T, x and y values. In addition, the Ip value depended linearly on initial hydrogen concentration and square root of potential sweeping rate, irrespective of T, x and y values. Furthermore, the activation energy for hydrogen diffusion decreased with an increase in x and y values. From these results, it is considered that the surface reduction treatment of the Mm(B5)x alloys, performed in alkaline solution with sodium borohydride, the nonstoichiometry and the initial concentration of absorbed hydrogen, are important factors for improving the charge-discharge performance of negative electrodes for metal-hydrogen energy systems.

F2-5 A One-Way Coupled Crystalline Plasticity-Transient Hydrogen Diffusion Analysis to Simulate the Effect of the Heterogeneity of Stress-Strain States on Hydrogen Distributions in Microstructure

Hydrogen embrittlement is a well identified cause of material degradation and is the origin of major failure in industry. The deleterious effect of hydrogen uptake in metals and alloys is especially observed on mechanical properties. For most of the metal-hydrogen systems, fracture strength and fracture toughness are decreased and fatigue crack propagation is increased. Many attempts have already been made to investigate the metal-hydrogen interactions at macro-scale but the microstructure is generally not introduced into the analyses. The aim of this work is to propose a coupled mechanical-diffusion analysis taking into account explicitly the microstructure and using the finite element method. The stress-strain fields in artificial polycrystalline aggregates are obtained in the crystalline plasticity framework. A one-way coupled crystalline plasticity-transient hydrogen diffusion analysis is then employed to solve a boundary value problem of a large elasto-plastic deformation. The hydrogen distributions on all over the polycrystal including the hydrogen concentration within the grains and close to the grain boundaries are determined.

Effect of Coexistent Hydrogen Isotopes on Tracer Diffusion of Tritium in Alpha Phase of Group-V Metal-Hydrogen Systems

Tracer diffusion coefficients of tritium in the alpha phase of group-V metal-hydrogen systems, α-MH(D)xTy (M = V and Ta; x >> y), were measured in order to clarify the effects of coexistent hydrogen isotopes on the tritium diffusion behavior. The hydrogen concentration dependence of such behavior and the effects of the coexistent hydrogen isotopes (protium and deuterium) were determined. The results obtained in the present (for V and Ta) and previous (for Nb) studies revealed that tritium diffusion was definitely dependent on hydrogen concentration but was not so sensitive to the kind of coexistent hydrogen isotopes. By summarizing those data, it was found that the hydrogen concentration dependence of the tracer diffusion coefficient of tritium in the alpha phase of group-V metals could be roughly expressed by a single empirical curve.

Effect of Coexistent Hydrogen Isotopes on Tracer Diffusion of Tritium in Alpha Phase of Group-V Metal-Hydrogen Systems

Tracer diffusion coefficients of tritium in the alpha phase of group-V metal-hydrogen systems, � - MH(D)xTy (M ¼ V and Ta; xy), were measured in order to clarify the effects of coexistent hydrogen isotopes on the tritium diffusion behavior. The hydrogen concentration dependence of such behavior and the effects of the coexistent hydrogen isotopes (protium and deuterium) were determined. The results ob- tained in the present (for V and Ta) and previous (for Nb) studies revealed that tritium diffusion was def- initely dependent on hydrogen concentration but was not so sensitive to the kind of coexistent hydrogen isotopes. By summarizing those data, it was found that the hydrogen concentration dependence of the trac- er diffusion coefficient of tritium in the alpha phase of group-V metals could be roughly expressed by a single empirical curve.

Hydrogenography of PdH x thin films: Influence of H-induced stress relaxation processes

Hydrogenography is a new optical thin film combinatorial method that follows hydrogenation and determines its associated thermodynamic properties. Due to clamping to the substrate, stresses generated in thin films are larger than in bulk. This must be taken into account for a comparison between these two types of systems. In this article, we follow the microstructure, surface morphology and in-plane stress changes of thin polycrystalline PdH x films upon several hydrogen ab/desorption cycles and correlate them to the evolution in shape and hysteresis of pressure–optical transmission isotherms (PTIs) recorded by hydrogenography. The in-plane stress in the first instance is relaxed inhomogeneously by buckling, and a more complete, homogeneous relaxation is only reached after the creation of a buckle-and-crack network that is the two-dimensional analogue of bulk decrepitated grains. This sequence of changes is clearly visible in the PTIs, demonstrating another useful facet of hydrogenography for characterizing metal–hydrogen systems.

Experimental Study on the Delivery Rate and Recovery Rate of ZrCo Hydride for ITER Application

To investigate the key design aspects of the storage and delivery system (SDS) bed in ITER, rates of a hydriding, dehydriding and isotope effects on the H/D composition during a rapid delivery were experimentally investigated by using small tube-type reactors with different packing heights. Hydrogen recovery times for a shorter packing-height bed (20~40mm) decreased exponentially with an increasing initial hydrogen pressure, but increased by approximately two orders of a magnitude in a longer packing-height bed (145mm). Dehydriding rate increases exponentially with an increase in the relative heating area per unit weight of ZrCo powder and decreases in the packing-height of ZrCo hydride. Continuous isotopic compositional change inevitably occurs during the entire delivery time due to the known isotope effect in the metal-hydrogen systems. To overcome the isotope effect during a delivery from the SDS beds, an alternative operation method was suggested for the fuel supply from the SDS.

Isotope effect in the hydrogen distribution in the solid solution TiN0.40H0.19D0.19

The structure of a solid solution with a combined isotope composition based on TiN0.40H0.19D0.19 (space group \( P\overline 3 m1 \)) has been studied by neutron diffraction. The isotope effect in the distribution of H and D isotopes has been found: the isotopes are located in tetrahedral interstices of the same type but with different z coordinates; there is splitting of 2d tetrahedral interstices into two groups, the protium (H) and deuterium (D). Therefore, in the ordered “layered” structure of the TiN0.40H0.19D0.19 solid solution, two different isotopes of the same element cannot be located at the same plane perpendicular to the threefold axis. The crystal-chemical analysis of the surroundings of H and D has been performed, and considerable differences have been revealed between the coordination polyhedra surrounding different hydrogen isotopes. It has been found that, in some metal-hydrogen systems, protium and deuterium should be treated as independent chemical components.

The mathematical modelling of the hydroelastic effect of slowing down of the diffusion processes in metal-hydrogen systems

Computations were carried out involving the lifetime of macroscopic ball-shaped Hydrogen Concentration (HC) inhomogeneities in palladium. It was shown that hydrogen-elastic stresses slow down the solubility of HC inhomogeneities. The influence of hydrogen-elastic stresses increases considerably as inhomogeneity dimensions increase.

Experimental observation of a soliton-like moving swell on the surface of a palladium-hydrogen alloy

Upon additional saturation of a PdH0.1 alloy with hydrogen under highly nonequilibrium conditions, moving coherently conjugate undulatory swells, (whose shape and character of motion resemble those of solitary translational waves—solitons) on the surface have been for the first time fixed and recorded on video tape. Based on modern concepts about the metal-hydrogen systems, the observed soliton-like moving swell and the mechanism of its formation and motion have been discussed. Emphasis has been placed on the fact that the incipient formation of soliton-like coherent moving swells is a special previously unknown mechanism of relaxation and leveling-off of internal stresses in metal-hydrogen alloys.

Experimental requirements for measuring pneumatochemical impedances

Hydrogen storage remains a bottleneck process on the way to the hydrogen economy. For practical applications, metal hydride systems offer interesting features, in particular, the possibility of reversibly storing large amounts of hydrogen at low or moderate pressure. However, they still suffer from unfavorable specific energy, with mass-fraction values ranging from 0 up to 5 wt % whereas transport applications require 6 wt % and more. Besides this, higher sorption/desorption kinetics and better chemical stability over long-term cycling are also needed. This is why many studies are carried out in the research community on hydride-forming systems, to develop new materials meeting these requirements. Development and optimization of metal hydride reactors require coupled thermodynamic and kinetic characterization of metal-hydrogen systems. In particular, it is necessary to analyze the kinetics in terms of reaction mechanism, in order to identify the different steps of commonly observed multistep reaction paths, and to measure their individual rate parameters. By analyzing hydriding kinetics in the frequency (Fourier) domain, pneumatochemical impedance spectroscopy (PIS) now offers the possibility of measuring experimental impedances and identifying reaction steps. However, measurement of such impedances is indirect and nontrivial. The purpose of this paper is to detail the experimental requirements needed for correctly measuring gas-phase impedance diagrams. In particular, practical conditions of data sampling and data treatment are described. Experimental results obtained with the model LaNi(5)-H(2)(g) system are presented to illustrate the potentialities of PIS analysis.

Modeling of phase transformations in metal-hydrogen systems by using multicenter potentials of interatomic interaction

We present the results of modeling of phase transformations in Fe-H, V-H, Ti-H, and Mg-H systems performed by using multicenter potentials constructed in the quasifermionic approximation. These potentials take into account the short-term interatomic interactions and the contributions made to the bonding energy by the delocalization and transfer of the electron charges. This enables us to model the structural transformations of metals in broad ranges of the concentrations of hydrogen.