Properties Of Metal Hydrides Research Articles

Diagnostic study on laser-produced metal hydride plasmas

The characteristics of laser-produced metal hydride plasmas have been investigated in this work. The charge state and velocity of ions were determined by employing a time-of-flight technique in conjunction with an electrostatic deflection method. The ion velocities were found to be supersonic with values in the range of 104 to 105 m/s. The proportion of hydrogen ions was found to be lower than that of titanium ions. The ion emission behavior was studied by using a Faraday cup. When the total integrated space was taken into account, the ns pulsed laser was capable of producing hydrogen ion currents greater than one hundred mA. In order to understand the plasma generation process, we performed a comparative analysis between laser-generated plasma and arc plasma, and also investigated the effect of laser power density on the composition and velocity of the ions, the ablation properties of metal hydrides, and the maintainability of hydrogen ion emission.

The Effect of Severe Plastic Deformation on the Hydrogen Storage Properties of Metal Hydrides

Solid-state hydrogen storage in various metal hydrides is among the most promising and clean way of storing energy, however, some problems, such as sluggish kinetics and high dehydrogenation temperature should be dealt with. In the present paper the advances of severe plastic deformation on the hydrogenation performance of metal hydrides will be reviewed. Techniques, like high-pressure torsion, equal-channel angular pressing, cold rolling, fast forging and surface modification have been widely applied to induce lattice defects, nanocrystallization and the formation of abundant grain boundaries in bulk samples and they have the potential to up-scale material production. These plastically deformed materials exhibit not only better H-sorption properties than their undeformed counterparts, but they possess better cycling performance, especially when catalysts are mixed with the host alloy promoting potential future applications.

Effects of NH4+ doping on the hydrogen storage properties of metal hydrides

Doping can modify the properties of metal hydrogen storage materials significantly. Currently, the metal doping is a frequent strategy, while the non-metal cation doping has not been examined extensively so far. In this study, the effects of NH4+ doping on the hydrogen storage properties of different metal hydrides, including TiH2, Ti0·25V0·25Nb0·25Zr0·25H2, Ti0·5V0·5H2 and VH2, are investigated by first-principles calculations. It is found that the NH4+ presents a good affinity for metal hydrides and the NH4+ incorporation leads to charge redistribution and formation of dihydrogen bond. Furthermore, the NH4+ doping in metal hydrides is favorable for enhancing the hydrogen storage capacity and decreasing the thermal stability simultaneously. The possible reason for the NH4+ doping induced destabilization in metal hydrides is the relatively weak interaction between NH4+ and hydrogen atoms.

Energy-releasing properties of metal hydrides (MgH2, TiH2 and ZrH2) with molecular perovskite energetic material DAP-4 as a novel oxidant

Metal hydride has been used as a potential energetic material due to its high hydrogen storage density, high reactivity, high mass calorific value and large gas production. But it was still a great challenge towards optimizing and enhancing the energy-releasing properties of metal hydride. In this work, a novel molecular perovskite energetic material (H2dabco)[NH4(ClO4)3] (DAP-4) was introduced as a high energy oxidant to fabricate metal hydride (MH2, M=Mg, Ti, and Zr) based energetic composites. The thermal decomposition, ignition and combustion characteristics of MH2-based energetic composites were studied. The results showed that molecular perovskite energetic material DAP-4 was beneficial as oxidant in MH2-based high-energy solid composites, which were originated from its high energy properties and strong oxidation capacity. The ignition and combustion reaction mechanisms of MH2 with DAP-4 as oxidant were provided. This work offered an effective way to realize energy-releasing performance of MH2 by molecular perovskite energetic materials introduced for their potential application.

TiFe0.85Mn0.05 alloy produced at industrial level for a hydrogen storage plant

Moving from basic research to the implementation of hydrogen storage system based on metal hydride, the industrial production of the active material is fundamental. The alloy TiFe0.85Mn0.05 was selected as H2-carrier for a storage plant of about 50 kg of H2. In this work, a batch of 5 kg of TiFe0.85Mn0.05 alloy was synthesized at industrial level and characterized to determine the structure and phase abundance. The H2 sorption properties were investigated, performing studies on long-term cycling study and resistance to poisoning. The alloy absorbs and desorbs hydrogen between 25 bar and 1 bar at 55 °C, storing 1.0H2 wt.%, displaying fast kinetic, good resistance to gas impurities, and storage stability over 250 cycles. The industrial production promotes the formation of a passive layer and a high amount of secondary phases, observing differences in the H2 sorption behaviour compared to samples prepared at laboratory scale. This work highlights how hydrogen sorption properties of metal hydrides are strictly related to the synthesis method.

The Improvement in Hydrogen Storage Performance of MgH2 Enabled by Multilayer Ti3C2.

MgH2 has become a hot spot in the research of hydrogen storage materials, due to its high theoretical hydrogen storage capacity. However, the poor kinetics and thermodynamic properties of hydrogen absorption and desorption seriously hinder the development of this material. Ti-based materials can lead to good effects in terms of reducing the temperature of MgH2 in hydrogen absorption and desorption. MXene is a novel two-dimensional transition metal carbide or carbonitride similar in structure to graphene. Ti3C2 is one of the earliest and most widely used MXenes. Single-layer Ti3C2 can only exist in solution; in comparison, multilayer Ti3C2 (ML-Ti3C2) also exists as a solid powder. Thus, ML-Ti3C2 can be easily composited with MgH2. The MgH2+ML-Ti3C2 composite hydrogen storage system was successfully synthesized by ball milling. The experimental results show that the initial desorption temperature of MgH2-6 wt.% ML-Ti3C2 is reduced to 142 °C with a capacity of 6.56 wt.%. The Ea of hydrogen desorption in the MgH2-6 wt.% ML-Ti3C2 hydrogen storage system is approximately 99 kJ/mol, which is 35.3% lower than that of pristine MgH2. The enhancement of kinetics in hydrogen absorption and desorption by ML-Ti3C2 can be attributed to two synergistic effects: one is that Ti facilitates the easier dissociation or recombination of hydrogen molecules, while the other is that electron transfer generated by multivalent Ti promotes the easier conversion of hydrogen. These findings help to guide the hydrogen storage properties of metal hydrides doped with MXene.

Enhancing hydrogen storage properties of MgH2 by core-shell CoNi@C

Introducing multicomponent nanoparticles can improve remarkably de/hydrogenation kinetic properties of MgH2. In this work, the original core-shell CoNi@C bimetallic nanoparticles were obtained via hydrothermal and calcination reduction technology. MgH2-8 wt% CoNi@C starts to dehydrogenate at 173 °C with the dehydrogenation capacity of 5.83 wt% within 1800 s at 275 °C. Moreover, the composite absorbs 4.83 wt% H2 within 1800 s at 100 °C with prominent advantage at low temperature. The notable improvement of hydrogen storage properties of MgH2 is attributed to the reversible phase transitions of Mg2Co/Mg2CoH5 and Mg2Ni/Mg2NiH4, and the excellent thermal conductivity and confinement effect of the carbon shell. As a result, the apparent activation energy of dehydrogenation reaction reduces to 78.5 kJ/mol. This work extends the horizon of bimetallic nanoparticles with especial microstructure for enhancing the hydrogen storage properties of metal hydrides.

Atomic Imaging of Subsurface Interstitial Hydrogen and Insights into Surface Reactivity of Palladium Hydrides.

Resolving interstitial hydrogen atoms at the surfaces and interfaces is crucial for understanding the mechanical and physicochemical properties of metal hydrides. Although palladium (Pd) hydrides hold important applications in hydrogen storage and electrocatalysis, the atomic position of interstitial hydrogen at Pd hydride near surfaces still remains undetermined. We report the first direct imaging of subsurface hydrogen atoms absorbed in Pd nanoparticles by using differentiated and integrated differential phase contrast within an aberration-corrected scanning transmission electron microscope. In contrast to the well-established octahedral interstitial sites for hydrogen in the bulk, subsurface hydrogen atoms are directly identified to occupy the tetrahedral interstices. DFT calculations show that the amount and the occupation type of subsurface hydrogen atoms play an indispensable role in fine-tuning the electronic structure and associated chemical reactivity of the Pd surface.

Atomic Imaging of Subsurface Interstitial Hydrogen and Insights into Surface Reactivity of Palladium Hydrides

AbstractResolving interstitial hydrogen atoms at the surfaces and interfaces is crucial for understanding the mechanical and physicochemical properties of metal hydrides. Although palladium (Pd) hydrides hold important applications in hydrogen storage and electrocatalysis, the atomic position of interstitial hydrogen at Pd hydride near surfaces still remains undetermined. We report the first direct imaging of subsurface hydrogen atoms absorbed in Pd nanoparticles by using differentiated and integrated differential phase contrast within an aberration‐corrected scanning transmission electron microscope. In contrast to the well‐established octahedral interstitial sites for hydrogen in the bulk, subsurface hydrogen atoms are directly identified to occupy the tetrahedral interstices. DFT calculations show that the amount and the occupation type of subsurface hydrogen atoms play an indispensable role in fine‐tuning the electronic structure and associated chemical reactivity of the Pd surface.

Design tool for estimating metal hydride storage system characteristics for light-duty hydrogen fuel cell vehicles

The U.S. Department of Energy (DOE) has developed the Framework model to simulate fuel cell-based light-duty vehicle operation for various hydrogen storage systems. This transient model simulates the performance of the storage system, fuel cell, and vehicle for comparison to DOE's Technical Targets using four drive cycles. Metal hydride hydrogen storage models have been developed for the Framework model. Despite the utility of this model, it requires that material researchers input system design specifications that cannot be easily estimated. To address this challenge, a design tool has been developed that allows researchers to directly enter physical and thermodynamic metal hydride properties into a simple sizing module that then estimates the systems parameters required to run the storage system model. This design tool can also be used as a standalone MS Excel model to estimate the storage system mass and volume outside of Framework and compare it to the DOE Technical Targets. This model will be explained and exercised with existing hydrogen storage materials.

Using the copper-foam for thermal conductivity improvement of La0.9Ce0.1Ni5-alloy bed during interaction with hydrogen

One of the main obstacles to the development of hydrogen energy is the problem of heat transfer inside metal hydride beds. Thus, the problem of increasing the metal hydride beds thermal conductivity is of great interest. This study is devoted to the investigation of the hydrogen sorption properties of an intermetallic compound placed in a matrix of foam material. Copper-foam with mass of 8 g was chosen as a matrix for 50 g of powder of activated AB5-type alloy with composition of La0.9Ce0.1Ni5. PCT-isotherms of hydrogen absorption and desorption were measured at temperatures 313, 333 and 353 K. Also, the dynamics of temperature change in the sample was studied when it was heated under vacuum conditions. The obtained data were compared with the results of previous studies conducted under the same conditions for samples of pure alloy and a mixture of alloy with copper powder. It has been concluded that the use of copper-foam to improve the thermal conductivity is promising, but it is necessary to take into account its influence on the hydrogen sorption properties of metal hydrides.

Influence of Defects on the Stability and Hydrogen-Sorption Behavior of Mg-Based Hydrides.

This review deals with the destabilization methods for improvement of storage properties of metal hydrides. Both theoretical and experimental approaches were used to point out the influence of various types of defects on structure and stability of hydrides. As a case study, Mg, and Ni based hydrides has been investigated. Theoretical studies, mainly carried out within various implementations of DFT, are a powerful tool to study mostly MgH2 based materials. By providing an insight on metal-hydrogen bonding that governs both thermodynamics and hydrogen kinetics, they allow us to describe phenomena to which experimental methods have a limited access or do not have it at all: to follow the hydrogen sorption reaction on a specific metal surface and hydrogen induced phase transformations, to describe structure of phase boundaries or to explain the impact of defects or various additives on MgH2 stability and hydrogen sorption kinetics. In several cases theoretical calculations reveal themselves as being able to predict new properties of materials, including the ways to modify Mg or MgH2 that would lead to better characteristics in terms of hydrogen storage. The influence of ion irradiation and mechanical milling with and without additives has been discussed. Ion irradiation is the way to introduce a well-defined concentration of defects (Frankel pairs) at the surface and sub-surface layers of a material. Defects at the surface play the main role in sorption reaction since they enhance the dissociation of hydrogen. On the other hand, ball-milling introduce defects through the entire sample volume, refine the structure and thus decrease the path for hydrogen diffusion. Two Severe Plastic Deformation techniques were used to better understand the hydrogenation/dehydrogenation kinetics of Mg- and Mg2 Ni-based alloys: Equal-Angular-Channel-Pressing and Fast-Forging. Successive ECAP passes leads to refinement of the microstructure of AZ31 ingots and to instalment therein of high densities of defects. Depending on mode, number and temperature of ECAP passes, the H-sorption kinetics have been improved satisfactorily without any additive for mass H-storage applications considering the relative speed of the shaping procedure. A qualitative understanding of the kinetic advanced principles has been built. Fast-Forging was used for a "quasi-instantaneous" synthesis of Mg/Mg2 Ni-based composites. Hydrogenation of the as-received almost bi-phased materials remains rather slow as generally observed elsewhere, whatever are multiple and different techniques used to deliver the composite alloys. However, our preliminary results suggest that a synergic hydrogenation / dehydrogenation process should assist hydrogen transfers from Mg/Mg2 Ni on one side to MgH2 /Mg2 NiH4 on the other side via the rather stable a-Mg2 NiH0.3 , acting as in-situ catalyser.

Direct Comparison of PdAu Alloy Thin Films and Nanoparticles upon Hydrogen Exposure.

Nanostructured metal hydrides are able to efficiently detect hydrogen in optical sensors. In the literature, two nanostructured systems based on metal hydrides have been proposed for this purpose each with its own detection principle: continuous sub-100 nm thin films read out via optical reflectance/transmittance changes and nanoparticle arrays for which the detection relies on localized surface plasmon resonance. Despite their apparent similarities, their optical and structural response to hydrogen has never been directly compared. In response, for the case of Pd1–yAuy (y = 0.15–0.30) alloys, we directly compare these two systems and establish that they are distinctively different. We show that the dissimilar optical response is not caused by the different optical readout principles but results from a fundamentally different structural response to hydrogen due to the different nanostructurings. The measurements empirically suggest that these differences cannot be fully accounted by surface effects but that the nature of the film–substrate interaction plays an important role and affects both the hydrogen solubility and the metal-to-metal hydride transition. In a broader perspective, our results establish that the specifics of nanoconfinement dictate the structural properties of metal hydrides, which in turn control the properties of nanostructured devices including the sensing characteristics of optical hydrogen sensors and hydride-based active plasmonic systems.

A study on ideal distance between staggered metal hydride tanks in forced convection

There are several critical parameters in specifying the satisfactory hydrogen flow in metal hydride tanks such dynamic factors in addition to the quantity contained in the tanks. Dynamic factors could be emphasized as ambient conditions and metal hydride properties. This work aims at investigating the effects of equilibrium pressure, ambient air temperature and velocity on ideal distance among metal hydride (MH) tanks used with the purpose of storing hydrogen in fuel cell applications as theoretically and numerically by using Autodesk CFD Simulation software. The metal hydride chosen for the present study is titled as LaNi5 in the literature. A new approach was utilized in the present study to describe the ideal distance among MH tanks using a novel approach in operating different conditions. Analyses implemented in this study are based on various ambient temperatures (i.e. 290K, 300K & 310K), Reynolds Numbers (i.e. 6000, 12,000 & 30,000) and equilibrium pressures (i.e. 60 kPa, 100 kPa & 120 kPa). As emphasized here, the ideal distance among MH tanks will be rather shortened while the Reynolds numbers increase during the operation. Moreover, it is noted here that the ideal distance will not be changed while the equilibrium pressure is in decrease and the ambient temperature is on the increase. Our findings indicate that distance among the MH tanks exists for maximum heat transfer. This finding could be utilized to maximize efficiency of the integrated metal-hydride-Fuel cell system without increasing additional costs.

Review on Ammonia Absorption Materials: Metal Hydrides, Halides, and Borohydrides

Ammonia is well-known as a hydrogen carrier owing to its high hydrogen capacity (17.8 wt %). However, the toxicity and the high storage pressure limit the application of ammonia. Consequently, storing ammonia in solid state has become the promising method to utilize ammonia for practical applications. In this review, ammonia absorption properties of metal hydrides, halides, and borohydrides to form metal amides and metal ammine complexes with various coordination numbers have been systematically summarized. Through this research, we found the correlation between the reactivity with ammonia and the Pauling electronegativity of neutral atoms according to different systems. Metal hydrides with small electronegativity value of the neutral atom of the cations can react with ammonia to form metal amides, which can be used as hydrogen storage material. For metal halides or borohydrides, the lower plateau pressure of ammonia absorption can be obtained in the material with larger electronegativity value of the neu...

Transient Impurity Concentration of Absorption and Desorption in Metal Hydride

Biomass-derived hydrogen (Bio-H2) has been attracting much attention as a low environmental load type of hydrogen. Among the potential applications of Bio-H2, use as a fuel for polymer electrolyte membrane fuel cells (PEMFCs) would require the removal of contaminants. Therefore, we propose the use of metal hydride for the purification and storage of Bio-H2. Metal hydride can store a larger volumetric amount of hydrogen than that other hydrogen storage, and the hydrogenate is processed at near atmospheric pressure and room temperature. In addition, by exploiting the selective hydrogen absorption properties of metal hydride, we have successfully reduced the concentration of methane in the hydrogen using metal hydride, the storage performance of which was evaluated in our previous study. Pressure swing adsorption was used to reduce the contaminant concentration, which was measured as 3% of methane. For practical application, the hydrogen recovery rate over the hydrogen absorption and desorption processes is evaluated.

Metal-hydrogen systems with an exceptionally large and tunable thermodynamic destabilization

Hydrogen is a key element in the energy transition. Hydrogen–metal systems have been studied for various energy-related applications, e.g., for their use in reversible hydrogen storage, catalysis, hydrogen sensing, and rechargeable batteries. These applications depend strongly on the thermodynamics of the metal–hydrogen system. Therefore, tailoring the thermodynamics of metal–hydrogen interactions is crucial for tuning the properties of metal hydrides. Here we present a case of large metal hydride destabilization by elastic strain. The addition of small amounts of zirconium to yttrium leads to a compression of the yttrium lattice, which is maintained during (de)hydrogenation cycles. As a result, the equilibrium hydrogen pressure of YH2 ↔ YH3 can be rationally and precisely tuned up to five orders of magnitude at room temperature. This allows us to realize a hydrogen sensor which indicates the ambient hydrogen pressure over four orders of magnitude by an eye-visible color change.

Thermodynamic simulation of hydrogen based solid sorption heat transformer

The hydrogen absorption and desorption pressure-concentration isotherms (PCI) of La0.9Ce0.1Ni5 and LaNi4.6Al0.4 alloys are measured by static and dynamic method. The hydrogen absorption and desorption kinetics of the alloys also measured. The measured properties are used to study the performance of hydrogen based solid sorption heat transformer (MHHT). The thermodynamic simulation of MHHT is conducted using statically and dynamically measured PCI and thermodynamic properties. Due to variation in statically and dynamically measured metal hydride properties, significant variations in coefficient of performance (COP) and heat transformation capacity of MHHT are observed. In case of thermodynamic analysis using dynamically measured properties the heat transformation capacity and COP are decreased by 42.6% and 22.2% respectively, compared to statically measured data. This is due to the decrease in amount of hydrogen transmission and pressure differential between paired metal hydride reactors, and increase in reaction enthalpies. Later, the actual thermodynamic cycle for MHHT is constructed by considering the variation in pressure during hydrogen transfer processes between the metal hydride reactors.

The Effect of Magnetic Field on Thermal-Reaction Kinetics of a Paramagnetic Metal Hydride Storage Bed

A safe and efficient method for storing hydrogen is solid state storage through a chemical reaction in metal hydrides. A good amount of research has been conducted on hydrogenation properties of metal hydrides and possible methods to improve them. Background research shows that heat transfer is one of the reaction rate controlling parameters in a metal hydride hydrogen storage system. Considering that some very well-known hydrides like lanthanum nickel (LaNi5) and magnesium hydride (MgH2) are paramagnetic materials, the effect of an external magnetic field on heat conduction and reaction kinetics in a metal hydride storage system with such materials needs to be studied. In the current paper, hydrogenation properties of lanthanum nickel under magnetism were studied. The properties which were under consideration include reaction kinetics, hydrogen absorption capacity, and hydrogenation time. Experimentation has proven the positive effect of applying magnetic fields on the heat conduction, reaction kinetics, and hydrogenation time of a lanthanum nickel bed. However, magnetism did not increase the hydrogenation capacity of lanthanum nickel, which is evidence to prove that elevated hydrogenation characteristics result from enhanced heat transfer in the bed.

Effect of metal hydride properties in hydrogen absorption through 2D-axisymmetric modeling and experimental testing in storage canisters

A two-dimensional axisymmetric model is developed to study the hydrogen absorption reaction and resultant mass and heat transport phenomena inside a metal hydride canister. The model is compared against published literature and experimental data. Experimental tests are performed on an in-house fabricated setup using different cooling scenarios. An extensive study on the effects of the metal properties on charging performance is carried out through non-destructive testing (NDT). Results show that the properties that most influence the charging performance are: absorption rate constant (Ca), activation energy (Ea) and thermal conductivity (km). A Higher porosity (ε) reduces charging time and amount of hydrogen stored while a higher cooling level produces a faster charging process. These results can be used to select metal hydride materials but also to estimate the metal hydride internal state and the process can be used for future evaluation of metal hydride degradation.