MgH2 Phase Research Articles

Catalytic modification of MgH2 hydrogen storage properties by La–Ni catalysts

In this paper, it is experimentally demonstrated that the La–Ni catalyst contributes to the hydrogen storage performance of MgH2. Firstly, La–Ni (La: Ni = 1: 5.7) catalysts are prepared by CaH2 reduction method, and then MgH2+x wt.% La–Ni (x = 0, 3, 5, 7) composite alloys were prepared by ball milling method. The present work focuses on the structural and hydrogen ab/desorption properties of the composite alloys, and analysis the modulatory effect and influence mechanism of different La–Ni catalyst additions on the hydrogen storage properties of MgH2. The findings show that the composite alloys have the same diffraction peaks and that the main phase of the composite alloys is the MgH2 phase, with the addition of the LaNi5 phase, the Mg2Ni phase and a small amount of Mg phase. The mutual reversible transformations of LaH3 and Mg2Ni and Mg2NiH4 play a catalytic role in the hydrogen ab/desorption process. Moreover, the addition of La–Ni catalyst plays a dramatic improvement effect on the kinetic performance of MgH2 ab/desorption. When the addition of La–Ni catalyst is 5 wt.%, the composite alloy exhibits the most excellent hydrogen uptake and release kinetics. The MgH2+5 wt.% La–Ni composite alloy absorbs 4.2 wt.% H2 within 2 min at 473 K and releases 3.43 wt.% H2 within 150 min at 503 K. Fitting the hydrogen release activation energy of the composite alloys shows that the hydrogen release activation energy of the composite alloys decreases first and then increases, and there is a minimum hydrogen release activation energy of 101.81 kJ/mol H2 when the addition amount x = 5 wt.%.

Microstructure, hydrogen storage properties, and thermodynamic characterization of ball-milled Mg90Ni5Y5 alloy

The hydrogen storage properties of the Mg90Ni5Y5 alloy were studied, which was prepared by vacuum electromagnetic induction melting and ball milling. The microstructure and phase evolution of the ball-milled alloys during the process of hydrogen absorption and desorption were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The alloys hydrogen storage properties were measured by semi-automatic Sievert instrument. Results show that the hydrogenated sample was composed of MgH2, Mg2NiH4 and YH3 phases. After dehydrogenation, Mg2NiH4 and MgH2 phases were completely decomposed, and YH3 could only be decomposed into YH2. After 2 cycles of adsorption dehydrogenation, the alloy was completely activated, and the maximum hydrogen desorption capacity was about 5.1 wt %. According to the Arrhenius equation, the ball-milled alloy activation energy of the dehydrogenation reaction of is only 75.7 kJ/mol.

Time-Dependent Multi-Particle Model Describing the Hydrogen Absorption of Nanocrystalline Magnesium Powders: A Case Study

Classical kinetic models describing the hydrogen absorption of nanocrystalline metallic hydrides generally do not involve any parameter related to the change in the crystallite size during the hydrogenation at constant temperature. In the present investigation, ball-milled nanocrystalline Mg powders exhibiting lognormal crystallite size distribution have been subjected to hydrogen absorption in a Sievert-type apparatus. Partially absorbed states were achieved by interrupting the hydrogenation cycle at different hydrogen content, i.e., when 15%, 50%, and 90% of Mg powder transformed to MgH2. The evolution of the characteristic size of the nucleating MgH2 phase was determined from X-ray diffraction analysis. Considering the crystallite size distribution of the as-milled powder agglomerate as well as the growth during the isothermal hydrogenation process, a time-dependent multi-particle reaction function ∝CV¯t;R(t) was developed. It was shown unambiguously for this case study that the measured hydrogen absorption curve of the ball-milled Mg powder shows the best correlation with this model when it is compared to classical kinetic functions or the previously developed multi-particle reaction function excluding the change in the average crystallite size during hydrogenation.

Microstructure and hydrogen storage properties of the Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) alloys

Rare earth elements have excellent catalytic effects on improving hydrogen storage properties of the Mg2Ni-based alloys. This study used a small amount of Y to substitute Mg partially in Mg2Ni0.9Co0.1 and characterized and discussed the effects of Y on the solidification and de-/hydrogenation behaviors. The Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) hydrogen storage alloys were prepared using a metallurgy method. The phase composition of the alloys was studied using X-ray diffraction (XRD). Additionally, their microstructure and chemical composition were studied using scanning electron microscopy and energy-dispersive X-ray spectroscopy, respectively. The hydrogen absorption and desorption properties of the alloys were studied using pressure-composition isotherms and differential scanning calorimetric (DSC) measurements. The structure of the as-cast Mg2Ni0.9Co0.1 alloy was composed of the peritectic Mg2Ni, eutectic Mg–Mg2Ni, and a small amount of pre-precipitated Mg–Ni–Co ternary phases, and was converted into the Mg2NiH4, Mg2Ni0.9Co0.1H4, and MgH2 phases after hydrogen absorption. Furthermore, the XRD patterns of the alloys showed the MgYNi4 phase and a trace amount of the Y2O3 phase along with the Mg and Mg2Ni phases after the addition of Y. After hydrogen absorption, the phase of the alloys was composed of the Mg2NiH4, MgH2, MgYNi4, YH3, Y2O3, and Mg2NiH0.3 phases. With the increase of Y addition, the area ratios of the peritectic Mg2Ni matrix phase in the Mg2−xYxNi0.9Co0.1 (x = 0, 0.2, 0.3, and 0.4) alloys gradually decreased until they disappeared. However, the eutectic structure gradually increased, and the microstructures of the alloys were obviously refined. The addition of Y improves the activation performance of the alloys. The alloy only needed one cycle of de-/hydrogenation to complete the activation for x = 0.4. The DSC curves showed that the initial dehydrogenation temperatures of Mg2Ni0.9Co0.1 and Mg1.8Y0.2Ni0.9Co0.1 were 200 and 156 °C, respectively. The desorption activation energies of the hydrides of the Mg2Ni0.9Co0.1 and Mg1.8Y0.2Ni0.9Co0.1 alloys calculated using the Kissinger method were 94.7 and 56.5 kJ/mol, respectively. Moreover, the addition of Y reduced the initial desorption temperature of the alloys and improved their kinetic properties.

Construction of Mg/Zr superlattice structure to achieve efficient hydrogen storage via atomic-scale interaction in Mg-Zr modulation films

Mg-based alloys have great potential for application owing to their high hydrogen storage capacity but still suffer from too high temperature to absorb/desorb hydrogen due to overly stable de/hydriding thermodynamics and poor kinetics. To overcome this barrier, in this work, atomic-scale superlattice structures have been successfully fabricated in Mg-Zr modulation films using a self-designed semi-co-sputtering method. For comparison, Mg/Zr multilayer films with thicker layers are also prepared. The Mg/Zr interface density in Mg-Zr modulation films is much higher than in Mg/Zr multilayer films, thus exhibiting different structure changes in hydrogenation and excellent hydrogen storage properties. Transmission electron microscopy observation shows that the as-deposited Mg-Zr modulation films have ultra-thin coherent layers and grow along the [0001] direction. These modulated films keep their original lattice structure after de/hydrogenation, indicating the formation of solid solution with the entering of hydrogen atoms into the film. In contrast, the Mg/Zr multilayer films form MgH2 phase after hydrogenation. The Mg-Zr modulation film absorbs hydrogen at room temperature and begins to release hydrogen at approximately 81 °C, whereas the hydrogen release temperature of the conventional MgH2 and the present Mg/Zr multilayer film is about 287 and 171 °C, respectively. DFT calculation further reveals that the great enhancement of the above-mentioned properties can be attributed to the synergetic effect of Zr catalysis and strain induced by coherent heterointerfaces. The present work provides a new insight for developing Mg-based hydrogen storage alloys.

Conversion of CH4 and Hydrogen Storage via Reactions with MgH2-12Ni.

The main key to the future transition to a hydrogen economy society is the development of hydrogen production and storage methods. Hydrogen energy is the energy produced via the reaction of hydrogen with oxygen, producing only water as a by-product. Hydrogen energy is considered one of the potential substitutes to overcome the growing global energy demand and global warming. A new study on CH4 conversion into hydrogen and hydrogen storage was performed using a magnesium-based alloy. MgH2-12Ni (with the composition of 88 wt% MgH2 + 12 wt% Ni) was prepared in a planetary ball mill by milling in a hydrogen atmosphere (reaction-involved milling). X-ray diffraction (XRD) analysis was performed on samples after reaction-involved milling and after reactions with CH4. The variation of adsorbed or desorbed gas over time was measured using a Sieverts'-type high-pressure apparatus. The microstructure of the powders was observed using a scanning transmission microscope (STEM) with energy-dispersive X-ray spectroscopy (EDS). The synthesized samples were also characterized using Fourier transform infrared (FT-IR) spectroscopy. The XRD pattern of MgH2-12Ni after the reaction with CH4 (12 bar pressure) at 773 K and decomposition under 1.0 bar at 773 K exhibited MgH2 and Mg2NiH4 phases. This shows that CH4 conversion took place, the hydrogen produced after CH4 conversion was then adsorbed onto the particles, and hydrides were formed during cooling to room temperature. Ni and Mg2Ni formed during heating to 773 K are believed to cause catalytic effects in CH4 conversion. The remaining CH4 after conversion is pumped out at room temperature.

High-energy ball milling-induced crystallographic structure changes of AZ61-Mg alloy for improved hydrogen storage

The present study investigates the impact of ball milling on the hydrogen storage capabilities of AZ61 magnesium alloys, with a focus on understanding the underlying structure-property relationships. The structure of the hexagonal closed packed (hcp) AZ61 magnesium alloy has been studied through x-ray diffraction analysis, particle size, morphology, and Sievert's analysis. These parameters were used in the study to evaluate the effect of room temperature strain and particle size effect on hydrogen storage. The particle size of the powder samples was found to be anisotropic in all milled samples, with the exception of the as-received sample, which was spherical. The powder morphology changed from spherical to an irregular shape while the particle size decreased from the initial median of 68.33 μm to 15.9 μm for the as-received and sample 2, respectively. When the results of the diffraction peaks were compared to the theoretical positions, a slight shift in angle was observed due to the micro-regulation of metal proportion, which resulted in a change in the lattice structure. The broadening of the peaks observed was attributed to the change in particle size and deformation strain during the milling process. The hcp structure of Mg0.97Zn0.3 phase remained constant, while the size of the crystallites was observed to decrease from 173.3 Å to 22.7 Å. Hydrogen measurements revealed values as high as 5.5 wt% H2 after milling. Diffraction scanning calorimetry study revealed that AZ61 forms MgH2 (major) and AlH3 (minor) phases upon hydrogenation with a desorption activation energy of 188.9 kJ/mol similar to commercial MgH2.

The Influence of Ti + TiC Additive on Thermal Stability and Decomposition Kinetics of Nanosized MgH2 Phase in Mg-Based Mechanical Alloys

The Influence of Ti + TiC Additive on Thermal Stability and Decomposition Kinetics of Nanosized MgH2 Phase in Mg-Based Mechanical Alloys

Phase evolution, hydrogen storage thermodynamics, and kinetics of ternary Mg98Ho1.5Fe0.5 alloy

Rare earth elements and transition metals have been found to improve the hydrogen storage characteristics of magnesium-based alloys. This study investigated the Mg-Ho-Fe (MHF) ternary alloy prepared using the vacuum induction melting technique. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), pressure-composition-temperature (PCT), and differential scanning calorimetry (DSC) were used to analyze the alloy's phase transitions, microstructure, thermodynamics, and kinetic properties. The results reveal that the Mg98Ho1.5Fe0.5 alloy forms a solid solution with Ho and Fe in the magnesium matrix. Upon hydrogen absorption, the activated alloy transforms into a mixture of Mg/MgH2 phases and nanoscale HoH2 phases. Notably, only the MgH2 phase decomposes during hydrogen desorption, while the HoH2 phase remains unchanged, exhibiting a positive catalytic effect. The alloy demonstrates excellent hydrogen absorption kinetics, achieving a capacity of 5.56 wt% H2 within 10 min at 360 °C, owing to the combined catalytic effects of Ho and Fe. The activation energy for hydrogen desorption is found to be 135.87 kJ/mol, which is lower than that of the activation energies of pure MgH2 and MgFe alloys, indicating an enhancement in desorption kinetics. Moreover, the enthalpy and entropy changes for hydrogen absorption and desorption are determined to be –70.51 kJ/mol H2, –125.62 J/(K·mol) H2, 72.83 kJ/mol H2, and 128.95 J/(K·mol) H2, respectively. Furthermore, it is worth noting that the thermodynamic properties of the alloy are improved due to the catalytic effect of Ho and Fe.

Hydrogenation Effect on Interlayer Coupling and Magneto-Transport Properties of Pd/Co/Mg/Fe Multilayers.

Hydrogenation-induced modification of magnetic properties has been widely studied. A Mg spacer layer with high hydrogen storage stability was clamped in a Pd/Co/Mg/Fe multilayer structure to enhance its hydrogen storage stability and explore the structure's magneto-transport properties. After 1 bar hydrogen exposure, the formation of a stable MgH2 phase was demonstrated in an ambient environment at room temperature through X-ray diffraction. Lower magnetic coupling and enhanced magnetoresistance, compared to those of the as-grown sample, were observed using the longitudinal magneto-optical Kerr effect and a four-probe measurement. In this study, the hydrogenation stability of ferromagnetic multilayers was improved, and the concept of a hydrogenation-based spintronic device was developed.

Effet of hematite (Fe2O3) from natural iron ore as a catalyst in MgH2 as hydrogen storage materials

The main obstacle that hinders the application of fuel cell fuels for vehicles today is the hydrogen storage tube. Therefore, this paper will report the results of a study on MgH2-based hydrogen storage materials with Fe2O3 catalyst inserted (5 wt%, 10 wt%, 15wt%) and prepared by mechanical alloying technique for 10 hours. Fe2O3 samples were obtained from the Lhoong Setia Mining site in Jantang Village, Lhoong, Aceh Besar. The initial sample separation process was carried out manually using a bar magnet. Furthermore, hematite extraction was carried out with the addition of 1M HCL and NaOH each. Then the milling process of MgH2-Fe2O3 samples was carried out using a planetary ball mill. The results of the X-ray diffraction test showed that the MgH2 phase was the most dominant/mainstream phase. Thermal testing with DSC showed that the H2 desorption process experienced a decrease in temperature from 194.56 °C with a milling time variation of 7 hours.

Effect of Ti additive and preparation procedure on the temperature and decomposition kinetics of the MgH2 phase in the synthesized mechanicals alloys

The mechanical alloy Mg + 10 wt.% Ti and two mechanical alloys MgH2 + 10 wt.% Ti were synthesized by a reactive mechanical alloying (RMA) method, but in different ways. The influence of doping and the preparation procedure of mechanical alloys (MAs) on thehydrogen sorption properties, temperature and decomposition kinetics of their MgH2 phase was investigated by isobaric thermodesorption spectroscopy at a constant hydrogen pressure of 0.1 MPa. The desorption kinetics of the milled MgH2 + 10 wt.% Ti are faster than in the case of the ball milled Mg + 10 wt.% Ti. It was found that the manner of obtaining a mechanical alloys by reactive milling of MgH2 +10 wt. % Ti powder mixture rather than Mg +10 wt. % Ti powder mixture to improve the kinetic characteristics. The role of Ti as an alloying element in improving the hydrogen desorption kinetics of МAs obtained by various preparation procedures was studied. The stabilizing effect of Ti on the nanocrystalline structure and growth of the crystallites (grains) of the MgH2 phase during the cycling was also evaluated. It has been established the practical absence of the influence of Ti additive and the manner of obtaining MAs on the its thermodynamic stability.

Influence of the phase evolution and hydrogen storage behaviors of Mg-RE alloy by a multi-valence Mo-based catalyst

The Mg90Ce5Y5 alloy was prepared by the vacuum induction melting, and Mo, MoO2 and MoO3 were doped into it by mechanical ball-milling, respectively. Their microstructure, phase evolution, as well as hydrogen storage thermodynamic and kinetic properties were investigated by XRD, SEM, TEM, PCT and DSC method. The result shows that the internal phases of the Mo catalyzed alloy become MgH2, CeH2.73, YH3 and Mo phases after hydrogen absorption, while the hydrogenated alloy consists of MgH2, CeO2, YH3, MgO and Mo phases for the MoO2 catalyzed alloy and MgH2, MgO, CeO2, Y2O3 and Mo phases for the MoO3 catalyzed alloy. REDOX reaction occurred between MoO2, MoO3 and the inner phase of the alloy, respectively. In comparison, Mo catalyzed alloy has a higher hydrogen absorption saturation ratio, but the MoO2 catalyzed alloy needs a shorter time than Mo and MoO3 catalyzed alloys to release H2, and the dehydrogenation activation energy (Edes) of the samples show an increasing trend in the following order: MoO2 catalyzed alloy (110.18 kJ/mol)<MoO3 catalyzed alloy (113.72 kJ/mol)<Mo catalyzed alloy (114.24 kJ/mol). The initial dehydrogenation temperature and peak temperature of the MoO2 catalyzed alloy are the lowest, which means it has the best catalytic effect on the dehydrogenation kinetics of the alloy.

Improved hydrogen storage performance of Sm-Mg composites by adding nano-graphite

Sm5Mg41 + x wt% nano-graphite (NG) (x = 0, 2, 4, 8, 12) composites are synthesized via ball-milling. The influences of NG content on microstructure and hydrogen storage properties of the composites are researched systematically. The composites consist of Mg, Sm5Mg41, SmMg3, and NG. Nano scale Sm3H7 and MgH2 phases are observed after the hydrogen absorbing, and the newly formed Mg phase and the remaining Sm3H7 phase appear after hydrogen desorbing. NG is embedded in the surface of the composites in the form of nanosheets. Nanocrystalline Mg and some microscopic defects, including twin crystal, grain boundaries, and dislocations can be observed in the dehydrogenated sample. Such microscopic defects and nanocrystalline boundaries can reduce the total potential barrier needed to overcome during the hydrogen absorption/desorption reactions and thus the hydrogen storage kinetics of the alloy are improved. For the composites with x = 2, 4, 8 and 12, the activation energies of hydrogen desorption are 132.08, 128.06, 112.90, and 112.35 kJ/mol H2, respectively. The enthalpy changes for the hydrogen absorption are evaluated to be − 79.18, − 78.09, − 76.30, − 76.10 kJ/mol H2, indicating that the addition of NG had no obvious effect on the thermodynamic properties of the composites.

Microstructure characteristics, hydrogen storage thermodynamic and kinetic properties of Mg–Ni–Y based hydrogen storage alloys

In this paper, the Mg95-X-Nix-Y5 (x = 5, 10, 15) alloy were prepared by vacuum induction melting. The X-ray diffraction was used to analytical phase composition in different states, and the Scanning Electron Microscope and Transmission Electron Microscope were used to characterize the microstructure and crystalline state. Meanwhile, the kinetic properties of isothermal hydrogen adsorption and desorption at different temperatures also were tested by the Sievert isometric volume method. The results indicate that the hydrogenated Mg–Ni–Y samples is a nanocrystalline structure consists of MgH2, Mg2NiH4, and YH3 phases. And, the in-situ formed YH3 phase not decompose in the process of dehydrogenation and evenly dispersed in the mother alloy, which plays a paly a positive the catalytic role for the reversible cyclic reaction of Mg and Mg2Ni phases. In addition, the Ni elements are effectively to improve the thermodynamic properties of the Mg-based hydrogen storage alloy, the desorption enthalpy of the Ni5, Ni10, and Ni15 samples successively decrease to 84.5, 69.1, and 63.5 kJ/mol H2. The hydrogen absorption and desorption kinetics of the Mg–Ni–Y alloy are improved obviously with the increase of Ni content, especially for Mg80Ni15Y5 alloy, which the optimal hydrogenated temperature is reduced to 200 °C, and the 90% of the maximum hydrogen storage capacity can be absorbed within 1 min, about 5.4 wt % H2. Besides, the dehydrogenated activation energy of the Mg80Ni15Y5 alloy also is reduced to 67.0 kJ/mol, and it can completely release hydrogen at 320 °C within 5 min, which is almost reached the hydrogen desorption capability of Ni5 alloy at 360 °C. This means that Ni element is a very positive element to reduce the hydrogen desorption temperature.

Importance of thermal conductivity and stress level during a phase (hydride) transformation in magnesium

There are many different systems of an autonomous energy storage including accumulators and storage devices for renewable energy. Systems based on reversible metal hydrogenation have recently been introduced. The selection of metals is based on considerations of temperature and pressure conditions of the hydrogenation/dehydrogenation cycle, as well as the desired storage hydrogen capacity. Magnesium is one of the main challenging metals with respect to these main conditions since having a hydrogen capacity up to 7.6 w.%. For Mg forming MgH2, it was soon established that the size of particles plays a critical role since the kinetics (rate) of hydride formation accelerates when the size of the particles decreases. The present study shows that the overall diameter of the particles is the main characteristic controlling the kinetics of hydride formation because of distinct issues. A distribution of the size entails a strong dispersion transferring the heat of reaction, which characterizes Mg to MgH2 phase transition. Moreover, the formation of MgH2, is accompanied by a great increase of the unit-cell volume, developing noticeable internal stresses within the surface layers of the particles, thus turning to a systematic flaking and a systematic decrease of sizes of the powder particles. The results of the numerical modeling comply with the experimental data. This makes it possible to predict the best size of the initial Mg powder able to achieve fast kinetics during hydrogenation. Furthermore, the present analysis demonstrates the best hydrogenation kinetics, not only when using fine powders, but also when the deviation from the average particle size is minimized.

Pengaruh Waktu Milling Terhadap Sifat Desorpsi Material Penyimpan Hidrogen MgH2-Ni Melalui Teknik Mechanical Alloying

Hydrogen is a renewable energy source that can be used as a fuel and as an alternative to fossil fuels. Solid storage media in solid form are safer to use than liquid (-253 oC) or gaseous media (700 bar) media. To store hydrogen in a solid medium, it requires a metal able to interact with hydrogen . Magnesium is one of the metals which can form metal hybrids based on MgH2 which is capable of absorbing hydrogen up to (7.6wt%). However, the reaction kinetics for magnesium are very slow, it takes at least 60 minutes to absorb hydrogen and the operating temperature is always very high (300 oC). Several attempts have been made to add the catalytic converter and milling time. Hydrogen storage material based on MgH2 with a 10wt%Ni catalyst was successfully synthesized using a mechanical alloy technique with time variations of 2 hours, 5 hours, and 10 hours. From the results of the X-ray diffraction schema at a diffraction angle of 2θ=37.87o, it shows the presence of a MgH2 phase, Ni phase is at a diffraction angle of 61.85o, the diffraction peak also shows that there was a widening of the diffraction peak with increasing milling time, this explains that there was a reduction in the size of the crystal. When calculating with the Schereer method, the crystal size of the material reaches 10 nm. The results of the DSC test indicated a decrease in temperature of 383 oC in 41 minutes with a milling time of 10 hours.

Dual-tuning of de/hydrogenation kinetic properties of Mg-based hydrogen storage alloy by building a Ni-/Co-multi-platform collaborative system

The Mg-based hydrogen storage alloy with multiple platforms is successfully prepared by ball milling Co powder and Mg-RE-Ni precursor alloy, and its hydrogen storage behavior was investigated in detail by XRD, EDS, TEM, PCI, and DSC methods. The ball-milled alloy consists of the main phase Mg, the catalytic phases Mg2Ni, Mg2Co as well as a small amount of Mg12Ce, and convert into the MgH2–CeH2.73-Mg2NiH4–Mg2CoH5 composite after hydrogenation. The composite has three PCI platforms corresponding to the reversible de/hydrogenation reaction of Mg/MgH2, Mg2Ni/Mg2NiH4 and Mg6Co2H11/Mg2CoH5. Among them, the transformation between Mg2Ni and Mg2NiH4 triggers the “spill-over” effect which promote the decomposition of MgH2 phases and enhances the hydrogen desorption kinetics. Meanwhile, the conversion of the Mg6Co2H11 to Mg2CoH5 phase induces the “chain reaction” effect, which leads to preferential nucleation of Mg phase and improves the hydrogen absorption kinetics. Therefore, the Mg-RE-Ni-Co alloy has a double improvement on hydrogen absorption and desorption kinetics. Concretely, the alloy has an optimal hydrogen absorption temperature of 200 °C, at which it can absorb 5.5 wt. % H2 within 40 s. Under the conditions, the capacity of absorption almost reaches the maximum reversible value (about 5.6 wt. %). Besides, the alloy has a dehydrogenation activation energy of 67.9 kJ/mol and can desorb 5.0 wt. % H2 within 60 min at the temperature of 260 °C.

Characterization of microstructure, hydrogen storage kinetics and thermodynamics of ball-milled Mg90Y1.5Ce1.5Ni7 alloy

In this work, the Mg90Y1.5Ce1.5Ni7 sample is successfully prepared by combining the vacuum induction melting and the mechanical milling. The phase composition and microstructure characteristics are studied by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy measurements. The hydrogenated sample is composed of MgH2, Mg2NiH4, CeH2.73 phases, whereas only the MgH2 and Mg2NiH4 phases are decomposed during dehydrogenation. The hydrogen storage properties of Mg90Y1.5Ce1.5Ni7 samples are measured by semi-automatic Sievert type apparatus. It is found that the samples could be fully activated within three cycles of absorption and dehydrogenation, with a reversible hydrogen storage capacity of about 5.6 wt%. Also, the “optimal hydrogenation temperature” is reduced to 200 °C, and the dehydrogenation activation energy is calculated to be 68.2 kJ/mol and 65.8 kJ/mol by using the Arrhenius and Kissinger equations, respectively. This work provides a scientific approach to promote the practical application of Mg-based alloy.

ВПЛИВ Fe ТА Y НА ВОДЕНЬСОРБЦІЙНІ ВЛАСТИВОСТІ, ТЕРМІЧНУ СТІЙКІСТЬ ТА КІНЕТИКУ ДЕСОРБЦІЇ ВОДНЮ З ГІДРИДНОЇ ФАЗИ MgH2 МЕХАНІЧНОГО СПЛАВУ Mg + 10%ваг.Fe + 5% ваг.Y

Ефективний і безпечний спосіб зберігання водню - це його хімічне зв'язування в металогідридах. Незважаючи на те, що вчені приділяють велику увагу гідриду магнію, він ще не знайшов широке застосування в якості акумулятора водню для автомобільної промисловості через високу температуру (300 °C при 0,1 МПа H2) і повільну кінетику дисоціації. У даній роботі досліджена можливість зниження температури, поліпшення кінетики розкладу стехіометричного гідриду MgH2 за рахунок його комплексного легування Fe і Y з застосуванням методу реактивного механохімічного сплавлення (РМС). Були синтезовані механічні сплави Mg + 10% ваг. Fe + 5% ваг. Y (МС1) і Mg + 10% ваг. Fe (МС2) і досліджено їх фазовий склад, мікроструктуру, водородосорбційні властивості, термічну стабільність і кінетику десорбції водню з використанням методів рентгенівської дифракції (XRD), скануючої електронної мікроскопії (SEM) і термодесорбційної спектроскопії (TDS). Для оцінки впливу комплексного легування на температуру розкладу і термостабільність фази MgH2 отримані ізобари десорбції водню при першому нагріванні після синтезу РМС зразків механічних сплавів і після подальшого їх циклічного гідрування з газової фази. Всі ізобари отримані при тиску водню в реакторі 0,1 МПа і швидкості нагріву зразка 30/ хв. і використані для визначення як температури початку десорбції водню (Тпоч.) з гідридної фази MgH2 МС, так і температури Тмакс., що відповідає максимальній швидкості виділення водню. Кінетичні криві десорбції водню з механічних сплавів-композитів отримані при постійному тиску водню 0,1 МПа в реакторі і температурах 310 і 330 °С і були використані для визначення як часу виділення половини кількості водню (τ1/2), так і загальної кількості виходу водню (τп) з МС. Встановлено, що додавання Fe і Y до магнію призводить до значного поліпшення кінетики десорбції водню з гидридної фази MgH2, про що свідчить значне зменшення (в 15 і 6 разів) часу виділення з неї половини і всього водню при 330 0С. Розроблені матеріали можуть знайти практичне використання в стаціонарних умовах їх застосування.Бібл. 48, табл.2, рис. 9.