Properties Of MgH2 Research Articles

Hydrogen absorption-desorption properties and hydrolysis performance of MgH2-Zr3V3O0.6Hx and MgH2-Zr3V3O0.6Hx-C composites

In this work, the catalytic effect of additions of η-Zr3V3O0.6 mixed suboxide and the title intermetallic composite with graphite on the properties of MgH2 in the processes of hydrogen storage and hydrogen generation has been studied. The hydride composites were obtained by high-energy reactive ball milling (RBM). The samples were characterized by X-ray diffraction and scanning electron microscopy. The cycling performance of hydrogen desorption and absorption as well as hydrogen generation in the hydrolysis reaction were studied. We found that during the reactive ball milling the studied composites are able in a few minutes to absorb ∼6.5 wt% of hydrogen. The addition of Zr3V3O0.6 and Zr3V3O0.6 + С catalysts not only increases the rates of hydrogen absorption and release, but also lowers the activation energy and the temperature of hydrogen desorption. For a composite containing 10 wt% of suboxide and 3 wt% of graphite, the activation energy of hydrogen desorption determined by the Kissinger method was very low, just 58 kJ/mol, and this value is among the lowest described in the reference publications. We also show that the intermetallic additive forms the Zr3V3O0.6H∼10 hydride, which results in a higher gravimetric capacity of the composite as H storage material. The improved kinetics of hydrogen exchange and increased hydrogenation capacity at modest operating temperatures of 150–200 °C appear to be characteristic for the composites containing suboxide and graphite additions. The reason for the advanced performance is in the different the morphology of the synthesized samples, particularly the graphite-containing composites showing a more developed dispergation of the material (the fraction with a particle size of 1–3 μm is >80 wt%). We furthermore show that the synthesized materials can be used in the hydrolysis process resulting in hydrogen generation. The amount of hydrogen released from the hydride Mg-Zr3V3O0.6-C composite in the hydrolysis reaction reaches 1364 ml/g (the conversion degree is ∼85 % for the process duration of 120 min) when using 0.04 M MgCl2 solutions.

The adaptable effect of Ru on hydrogen sorption characteristics of the MgH2 system

In this study, a MgH2–Ru composite is prepared by mechanical ball milling of MgH2 and Ru powders. The microstructural analysis revealed the uniform distribution of Ru nanoparticles in the MgH2 matrix and the formation of intermetallic compounds (i.e. Mg6.2Ru and Mg1.5Ru) after dehydrogenation of the composite. The substantial improvements in the de/hydrogenation properties of MgH2 are due to the adjustable catalytic role of Ru under low temperature and pressure conditions. MgH2–Ru composite started to release hydrogen at an onset temperature of 300 °C, much lower than the mechanically milled pure MgH2 (350 °C). Hydrogen absorption of the MgH2–Ru composite is relatively fast at 350 °C and stored 6.1 wt% in 5 min. At the same temperature, the hydrogenated MgH2–Ru composite released all stored hydrogen in less than 5 min. Compared with the catalyst-free MgH2, the hydrogenation and dehydrogenation activation energies of the MgH2–Ru composite are reduced to 65.12 ± 2.4 kJ/mol H2, and 97.46 ± 4.15 kJ/mol H2, respectively. In addition, it further demonstrated how the reversible transformation of Mg–Ru intermetallic phases induces the thermodynamic destabilization of the MgH2 system. The presence of Ru not only facilitated the breaking of the Mg–H bond but also provided very good catalytic interfaces for enhanced de/hydrogenation properties of MgH2.

Thermally stable La-Ni-B amorphous additives for enhancing hydrogen storage performance of MgH2

In this work, we synthesized La-incorporated Ni-B amorphous composites and investigated their effects on enhancing dehydrogenation/hydrogenation properties of MgH2. MgH2 with 5 wt% 2La-3Ni-B demonstrated significantly improved dehydriding kinetics. About 6.0 wt% hydrogen could be released within 5 min at 300 °C. Moreover, no decrease in deydrogenation rate was observed within ten cycles. XRD, XPS, SEM and HRTEM examinations revealed that the La incorporation into Ni-B resulted in an amorphous La-B-O structure that could keep its disorder state up to 600 °C. The crystallization and growth of Ni dispersed in the La-B-O structure was significantly retarded. Also the alloying of Mg with Ni or La was not observed. As a result, the added La-Ni-B composites showed higher structural and catalytic stability than Ni-B during hydriding/dehydriding cycling of MgH2 at high temperatures.

Effect of TiO2 + Nb2O5 + TiH2 Catalysts on Hydrogen Storage Properties of Magnesium Hydride

AbstractMagnesium hydride (MgH2) is a prospective material for the storage of hydrogen in solid materials. It can also be envisaged for thermal energy storage applications since it has the potential to reversibly absorb hydrogen in large quantities, theoretically up to 7.6% by weight. Also, MgH2 is inexpensive, abundant, and environmentally friendly, but it operates at relatively high temperatures, and the kinetics of the hydrogenation process is slow. Mechanical milling and the addition of catalyst can alter the activation energy and the kinetic properties of the MgH2 phase. It is known that the addition of titanium hydride (TiH2) lowers the enthalpy and enhances the absorption of hydrogen from MgH2, titanium oxide (TiO2) enhances the desorption of hydrogen and niobium oxide (Nb2O5) enhances the absorption of hydrogen. In this work, the influences of the catalysts, as mentioned above on the properties of MgH2, were studied. The samples were analyzed in terms of crystal and microstructure as well as hydrogen storage properties using a pressure-composition isotherm (PCT)measurement. It has been found that the simultaneous addition of the three catalysts enhances the properties of MgH2, lowers the activation energy and operating temperature, increases the rate of intake and release of hydrogen, and provides the largest gravimetric hydrogen storage capacity.

Improved Hydrogen Absorption/Desorption Properties of MgH2 by Co–Catalyzing of YH2 and Co@C

AbstractHydrogen absorption and desorption kinetics properties of MgH2 were improved by co‐doping of commercial YH2 and a synthesized Carbon supported nano‐Co (Co@C) catalyst, which was prepared by calcination of Zeolitic Imidazolate Framework‐67 (ZIF‐67) precursor. YH2 addition shows great enhancement on the hydrogen absorption kinetics. The ball‐milled MgH2‐YH2 absorbs 6.5 wt.% of hydrogen within 100 s at 300 °C. The Co@C catalyst greatly enhances the absorption and desorption kinetics, while the absorption kinetics is slightly slower than that of MgH2‐YH2 at 250 °C and 275 °C. MgH2‐YH2‐Co@C exhibited prominent absorption and desorption kinetics, reaching full hydrogenation within 150 s at 250 °C and releasing 6 wt.% hydrogen within 1700 s at 300 °C. After hydrogenation and dehydrogenation, particle size of YH3 remains ∼500 nm, and the fine Co@C particles distributed homogeneously in the MgH2 matrix.

Highly dispersed metal nanoparticles on TiO2 acted as nano redox reactor and its synergistic catalysis on the hydrogen storage properties of magnesium hydride

In this paper, we have synthesized highly dispersed Co metal nanoparticles with the particle size about 5–10 nm on TiO2 (25–50 nm) for the first time through an extremely facile solvothermal method. It is supposed that the synthesized Co/TiO2 composite can combine the catalytic advantage of both Co and TiO2, exhibiting the superior catalytic effect on the hydrogen de/absorption properties of MgH2. The experimental data confirmed the above supposition and demonstrated that Co/TiO2 additive highly enhances the hydrogen de/absorption kinetics of MgH2 as compared to separate Co or TiO2 additive. Specifically, the MgH2Co/TiO2 composite begins to desorb hydrogen at about 190 °C with a low apparent activation energy of 77 kJ/mol. Besides, the MgH2Co/TiO2 composite has a desorption peak temperature of 235.2 °C, which is 53.2, 94.2 and 132.2 °C lower than that of MgH2TiO2 (288.4 °C), MgH2Co (329.4 °C) and ball-milled MgH2 (367.4 °C). Moreover, MgH2Co/TiO2 composite also exhibits low temperature rehydrogenation properties, which can absorb 6.07, 5.56 and 4.24 wt% H2 within 10 min at the temperature of 165, 130 and 100 °C, respectively. It is supposed that such excellent hydrogen desorption properties and low desorption energy barrier of MgH2Co/TiO2 composite are mainly ascribed to the novel synergistic catalytic effects of Co and TiO2. Herein, we propose a novel catalytic mechanism and think that Co/TiO2 acts as “nano redox reactor”, which can facilitate the dissociation and recombination process of hydrogen, thus reducing the reaction energy barrier and enhancing the de/rehydrogenation of MgH2.

A striking catalytic effect of facile synthesized ZrMn2 nanoparticles on the de/rehydrogenation properties of MgH2

Zr-based Laves phase alloys, especially ZrMn2, have been widely studied because of their good hydrogen storage properties.

Mg-based Nanocomposites for hydrogen storage containing La23Nd8.5Ti1.1Ni33.9Co32.9Al0.65 alloys as additives

Abstract Mg based nanocomposites containing different concentrations of La23Nd8.5Ti1.1Ni33.9Co32.9Al0.65 alloy has been undertaken at present work. Doped alloy was prepared by arc melting furnace and ball milled to get its nano structured. Hydrogen sorption properties of MgH2+ x wt% (x=10, 25 and 50) La23Nd8.5Ti1.1Ni33.9Co32.9Al0.65 alloy was characterized for their thermal, morphological and structural properties. Result shows that the alloy significantly reduced onset temperature of desorption. The TGA analysis showed higher desorption temperature for milled MgH2 compared to x wt% alloy added MgH2. Furthermore, the estimated activation energy for hydrogen desorption was found to be -177.90 , -204.65, -79.15 and -185.29 kJ/mol for milled ,10 wt%, 25 wt% and 50 wt % MgH2 respectively and also shows the reduction of activation energy by 98 kJ/mol due to the addition of 25 wt% alloy additives resulted the improved hydrogen storage capacity. The phase and purity of MgH2 during milling was studied by XRD and it is revealed that maximum stable and improved phase alteration for Hydrogen sorption was obtained during 25 wt % alloy milling. Morphological studies by SEM were undertaken to investigate the effect of hydrogenation of nanostructured alloy. DSC investigations were carried out to investigate the effect of alloy on hydrogen absorption behaviour of MgH2.

TiH2 as a Dynamic Additive for Improving the De/Rehydrogenation Properties of MgH2: A Combined Experimental and Theoretical Mechanistic Investigation

We report a mechanism for how low concentrations of TiH2 can function as a dynamic additive for improving both the kinetics and the thermodynamics of the Mg/MgH2–TiH2 system. We use a combination o...

Hydrogen storage properties of MgH2 co-catalyzed by LaH3 and NbH

To improve the hydrogen storage properties of Mg-based alloys, a composite material of MgH2 + 10wt%LaH3 + 10wt%NbH was prepared by a mechanical milling method. The composite exhibited favorable hydrogen desorption properties, releasing 0.67wt% H2 within 20 min at 548 K, which was ascribed to the co-catalytic effect of LaH3 and NbH upon dehydriding of MgH2. By contrast, pure MgH2, an MgH2 + 20wt%LaH3 composite, and an MgH2 + 20wt%NbH composite only released 0.1wt%, 0.28wt%, and 0.57wt% H2, respectively, under the same conditions. Analyses by X-ray diffraction and scanning electron microscopy showed that the composite particle size was small. Energy-dispersive X-ray spectroscopic mapping demonstrated that La and Nb were distributed homogeneously in the matrix. Differential thermal analysis revealed that the dehydriding peak temperature of the MgH2 + 10wt%LaH3 + 10wt%NbH composite was 595.03 K, which was 94.26 K lower than that of pure MgH2. The introduction of LaH3 and NbH was beneficial to the hydrogen storage performance of MgH2.

THE EFFECT OF MAGNETITE (Fe3O4)CATALYST FROM IRON SANDS ON DESORPTION TEMPERATURE OF MgH2 HYDROGEN STORAGE MATERIAL

One of the future technologies for a safe hydrogen storage media is metal hydrides. Currently, Mg-based metal hydride has a safety factor and efficient for vehicle applications. However, the thermodynamic properties of magnesium hydride (MgH2) found a relatively high temperature. High desorption temperatures caused MgH2 high thermodynamic stability resulting desorption enthalpy is also high. In this study, natural mineral (iron ore) has been extracted from iron sand into powder of magnetite (Fe3O4) and used as a catalyst in an effort to improve the desorption properties of MgH2. Magnetie has been successfully extracted from iron sand using precipitation method with a purity of 85 % , where the purity of the iron sand before extracted was 81%. Then, MgH2-Fe3O4 was milling using mechanical alloying method with a variety of catalysts and milling time. The observation by XRD showed the material was reduced to nanocrystalline scale. MgH2 phase appears as the main phase. DSC test results showed with the addition of Fe3O4, the desorption temperature can be reduced up to 366oC, compared to pure pure MgH2 reached by 409o C. Furthermore, based on gravimetric test, the hydrogen release occurs at a temperature of 388o C, weight loss of 0.66 mg during 16 minutes.

Phase transition and optoelectronic properties of MgH2

In this article, structural and electronic properties of MgH2 have been studied. The aim behind this study was to find out the ground state crystal structure of MgH2. For the purpose, density functional theory (DFT)-based full-potential linearized augmented plane wave (FP-LAPW) calculations have been performed in three different space groups: P42/mnm (α-MgH2), Pa3 (β-MgH2) and Pbcn (γ-MgH2). It has been found that the ground state structure of MgH2 is α-MgH2. The present study shows that α-MgH2 transforms into γ-MgH2 at a pressure of 0.41 GPa. After further increase in pressure, γ-MgH2 transforms into β-MgH2 at a pressure of 3.67 GPa. The obtained results are in good agreement with previously reported experimental data. In all the studied phases, the behavior of MgH2 is insulating and its optical conductivity is around 6.0 eV. The α-MgH2 and γ-MgH2 are anisotropic materials while β-MgH2 is isotropic in nature.

Anode properties of Al2O3-added MgH2 for all-solid-state lithium-ion batteries

All-solid-state lithium-ion batteries (LIBs) with aluminum oxide (Al2O3)-added magnesium hydride (MgH2), (100 − y)MgH2-yAl2O3 (y = 1, 5, 25 mol%) were fabricated, and their anode properties were investigated. Coulombic efficiency is increased by adding Al2O3. In addition, cycle properties are improved by adding Al2O3 as well. 27Al-magic angle spinning (MAS) nuclear magnetic resonance (NMR) and some other analyses were carried out to approach the mechanism of this additive, by which the coulombic efficiency and the cycle properties were improved. Although the niobium oxide (Nb2O5)-added MgH2 also showed the better kinetic properties compared with pristine MgH2 in our previous report, Nb2O5 should be well known as the best catalyst for hydrogen ab/desorption properties of MgH2. However, it is revealed that the hydrogen desorption temperature does not depend on Al2O3 contents. According to some detailed analyses, pentahedral-coordinated aluminum atom was successfully observed after Li insertion reaction by 27Al MAS NMR measurement. From the other experimental results, it is concluded that this pentahedral-coordinated aluminum atom could play an important role on the increasing coulombic efficiency and cycle properties.

The use of one-dimensional Niobate to improve MgH2 hydrogen sorption

A study was performed on the hydrogen absorption/desorption properties of MgH2 with the addition of Niobates synthesized by hydrothermal treatment of Nb2O5 in 10M NaOH. Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD) were used to evaluate their synthesis and show the morphological and crystallographic differences between Nb2O5 used as a precursor and the Niobates produced, the one-dimensional wired type, 1-D Niobate W and the cuboid one, Niobate C. The ball milling of MgH2 with the Niobates was performed within only 20min and afterwards the Differential Scanning Calorimetry (DSC) examination of MgH2+1-D Niobate W and MgH2+Niobate C showed the shifting of the peaks for both composites in comparison to pure MgH2. The influence of the two different types of Niobates and also the Nb2O5 on the hydrogen absorption/desorption capacity was evaluated at 350°C. The higher absorption and desorption values were attained by the MgH2+5wt.% 1-D Niobate W composite, reaching, in 10min, approximately 5.0wt.% and 6.0wt.%, respectively. The possible mechanism involved in such property improvement upon adding niobium based catalysts with different morphology and structure was discussed.

Improvement of hydrogen-storage properties of MgH2 by addition of Ni and Ti via reactive mechanical grinding and a rate-controlling step in its dehydriding reaction

In a shift from prior work, MgH2, instead of Mg, was used as a starting material in this work. A sample with a composition of 86 wt% MgH2-10 wt% Ni-4 wt% Ti was prepared by reactive mechanical grinding. Activation of the sample was completed after the first hydriding cycle. The effects of reactive mechanical grinding of Mg with Ni and Ti were discussed. The formation of Mg2Ni increased the hydriding and dehydriding rates of the sample. The addition of Ti increased the hydriding rate and greatly increased the dehydriding rate of the sample. The titanium hydride, TiH1.924, was formed during reactive mechanical grinding. This titanium hydride, which is brittle, is thought to help the mixture pulverized by being pulverized during reactive mechanical grinding and further to prevent agglomeration of the magnesium by staying as a hydride among Mg particles. A rate-controlling step for the dehydriding reaction of the hydrided MgH2-10Ni-4Ti was analyzed by using a spherical moving boundary model on an assumption that particles have a spherical shape with a uniform diameter.

Kinetic Enhancement in the Sorption Properties by Forming Mg–x wt % ZrCrCu Composites

Composite formation with Zr-based Laves phase alloys, especially the ZrCr2 family, is an effective method to improve the hydriding properties of MgH2. The present paper describes a systematic study of the reaction pathway of Mg–x wt % ZrCrCu composites (x = 25, 50) in terms of their structural, morphological, and hydrogenation properties. XRD and SEM results show no interaction between Mg and the ZrCrCu alloy phase during composite preparation by high-energy ball-milling. However, hydriding/annealing cycles lead to the formation of the Mg2Cu phase at grain boundaries of the Mg–ZrCrCu matrix. This Mg2Cu phase does not interact with the hydrogen at the studied condition, but provides several diffusion paths and stable nucleation sites for the formation of MgH2, and thus enhances the sorption kinetics. Pressure composition temperature (PCT) analysis shows a reduction in desorption temperature down to 250 °C for these composites.

The role of Mg2FeH6 formation on the hydrogenation properties of MgH2-FeFx composites

Abstract The hydrogenation properties of magnesium hydride mechanically milled with iron fluorides (FeF2 and FeF3), were investigated by Temperature Programmed Desorption (TPD) and volumetric methods using a Sieverts-type apparatus, as prepared upon dehydrogenation and finally upon subsequent hydrogenation. The activation energy of hydrogen desorption (Ea), calculated from the Kissinger formula using TPD measurements obtained with different heating rates, showed significant decreases of Ea in comparison to that of milled MgH2 without any dopants. Moreover, the influence of these metal fluorides on the thermodynamics of the decomposition process was also examined. In the case of the FeF2 dopant, rehydrogenation following desorption caused the complete decomposition of the iron fluoride to BCC iron and the formation of a predominant MgH2 phase. In contrast to FeF2, the addition of FeF3 led to the formation of β-MgH2 as a major phase coexisting with Mg2FeH6 and MgF2 compounds. The presence of pure Fe in the MgH2+FeF2 composite, as opposed to MgH2+FeF3 containing Mg2FeH6 and MgF2, did not cause any significant influence on the sorption properties of MgH2. Moreover, the original material doped with FeF3 predominantly showed iron in the Mg2FeH6 compound, while the FeF2 dopant iron mostly showed the nearly pure BCC metallic phase

Nanoscale Grain Refinement and H‐Sorption Properties of MgH2 Processed by High‐Pressure Torsion and Other Mechanical Routes

AbstractMgH2 is a promising material for solid‐state hydrogen storage due to its high gravimetric and volumetric storage capacity and its relatively low cost. Severe plastic deformation (SPD) processing techniques are being explored as an alternative to high‐energy ball‐milling (HEBM) in order to obtain more air resistant materials and reduce processing times. In this work, Mg, MgH2, and MgH2–Fe mixtures were severely mechanically processed by different techniques such as high‐pressure torsion (HPT), extensive cold forging, and cold rolling. A very significant grain refinement was achieved when using MgH2 instead of Mg as raw material. The mean crystallite sizes observed ranged from 10 to 30 nm, depending on the processing conditions. Enhanced H‐sorption properties were observed for the MgH2‐based nanocomposites processed by HPT when compared with MgH2 mixtures. Additionally, cold forging and cold rolling also proved effective in nanostructuring MgH2. These results suggest a high potential for innovative application with the use of low cost mechanical processing routes to produce Mg‐based nanomaterials with attractive hydrogen storage properties.

Changes of structural and hydrogen desorption properties of MgH2 indused by ion irradiation

Changes in structural and hydrogen desorption properties of MgH2 induced by ion irradiation have been investigated. MgH2 powder samples have been irradiated with 45 keV B3+ and 120 keV Ar8+ions, with ion fluence of 1015 ions/cm2. The effects of ion irradiation are estimated by numerical calculations using SRIM package. The induced material modifications and their consequences on hydrogen dynamics in the system are investigated by XRD, particle size distribution and TPD techniques. Changes of TPD spectra with irradiation conditions suggest that there are several mechanisms involved in desorption process which depend on defect concentration and their interaction and ordering. The results confirmed that the near-surface area of MgH2 and formation of a substoichiometric MgHx (x<2) play a crucial role in hydrogen kinetics and that various concentrations of induced defects substantially influence H diffusion and desorption kinetics in MgH2. The results also confirm that there is possibility to control the thermodynamic parameters by controlling vacancies concentration in the system.

Ab initio study of MgH 2 formation

Even if there is considerable literature dealing with structure and properties of MgH 2 compound there are still some uncertain details about nature of bonding governing its formation and decomposition. In order to better understand the processes essential for absorption and desorption of MgH 2, ab initio DFT based calculations of rutile MgH 2 compound, elemental hcp-Mg, and three different hypothetical hcp-Mg-derived hydrides are performed. Our findings show that all structures are unstable, and that MgH (Wurtzite) is a closest possible candidate for intermediate phase between the hcp-Mg and MgH 2 at 1:1 stoichiometry. An alternative hydration pathway is suggested, including promotion of hcp-Mg to bcc-Mg and consecutive transformation to rutile MgH 2 by means of hydrogen incorporation into Mg matrix. Rutile MgH 2 calculations with various hydrogen vacancies concentration are performed. Calculation shows that at high hydrogen concentration close to 1:2, stable substoichiometric hydride is possible. Calculation also shows that high vacancy (low hydrogen) concentration favors bcc-Mg 2H over rutile Mg 2H structure.