Hydrogenation Of Mg Research Articles

Experimentally Observed Nucleation and Growth Behavior of Mg/MgH2 during De/Hydrogenation of MgH2/Mg: A Review.

With the increasing energy crisis and environmental problems, there is an urgent need to seek an efficient renewable energy source, and hydrogen energy is considered one of the most promising energy carriers. Magnesium is considered a promising hydrogen storage material due to its high hydrogen storage density, abundant resources, and low cost. However, sluggish kinetic performance is one of the bottlenecks hindering its practical application. The kinetic process of hydrogenation/dehydrogenation can be influenced by both external and internal factors, including temperature, pressure, elementary composition, particle size, particle surface states, irregularities in particle structure, and hydrogen diffusion coefficient. The kinetic performance of the MgH2/Mg system can be effectively improved by more active sites and nucleation centers for hydrogen absorption and desorption. Herein, we briefly review and discuss the experimentally observed nucleation and growth behavior of Mg/MgH2 during de/hydrogenation of MgH2/Mg. In particular, the nucleation and growth behavior of MgH2 during the hydrogenation of Mg is discussed from the aspect of temperature and hydrogen pressure.

Design of Bifunctional Nb/V Interfaces for Improving Reversible Hydrogen Storage Performance of MgH2

Solid-State Hydrogen Storage In article number 2200119, Xuebin Yu, Guanglin Xia, and co-workers realized uniform formation of Nb/V interfaces based on a molecular scale to promote H2 storage performance of MgH2. The onset H2 desorption temperature of MgH2 of 165 °C and the reversible hydrogenation of Mg at room temperature could be realized.

Design of Bifunctional Nb/V Interfaces for Improving Reversible Hydrogen Storage Performance of MgH2

While MgH2 has been widely regarded as a promising solid‐state hydrogen storage material, the high operating temperature and sluggish kinetics pose a major bottleneck for its practical application. Herein, V4Nb18O55 microspheres composed of nanoparticles with size of tens of nanometers are fabricated to promote H2 desorption and absorption properties of MgH2, which results in the uniform formation of Nb/V interfaces based on a molecular scale during the reversible hydrogen storage process. It is experimentally and theoretically demonstrated that the uniform building of Nb/V interfaces not only preserves the ability of Nb in weakening Mg‐H bonds but also alleviates the strong adsorption capacity of metallic Nb toward hydrogen atoms, leading to a relative energy barrier for the whole dehydrogenation process of MgH2 of only 0.5 eV, which is 0.22 and 0.43 eV lower than that of Nb and V, respectively. As a result, under the addition of V4Nb18O55 microspheres, the onset H2 desorption temperature of MgH2 is decreased to 165 °C, 125 °C lower than that of bulk MgH2, and the complete hydrogenation of Mg could be realized even at room temperature, while almost no H2 adsorption is observed for bulk Mg at a high temperature of 50 °C.

Mechanism of improving hydrogenation of Mg by in-situ formation of Al* in hydriding combustion synthesis

Magnesium hydride (MgH2) is an ideal solid hydrogen storage material and on-line hydrolysis hydrogen source. However, the synthesis of MgH2 usually requires harsh conditions of high temperature, high pressure and long duration, bringing great challenges to production cost and safety. In this paper, MgH2 is prepared by hydriding combustion synthesis (HCS) and the mechanism of improving Mg hydrogenation properties by the in-situ formation of Al* is revealed. Under low hydrogen pressure of 1 MPa, the hydrogenation degree of Mg can be greatly increased from 9.6% of pure Mg to 90.5% with 10 mol% Al added. In the activation stage, Al reacts with Mg to form Mg17Al12, which brings rich grain boundaries and provides rapid diffusion channels for hydrogen. Subsequently, in the hydrogenation stage, Mg17Al12 reacts with H2 to generate Al* in-situ, which are evenly distributed and act as nucleation sites for MgH2. Hydrogen molecules diffuse rapidly along the interface between Mg/MgH2 and Al* and are easily adsorbed and dissociated on the surface of nano-scale Al* . The unique disproportionation hydrogenation reaction of in-situ forming highly active metallic substances as excellent catalysts provides a new idea for the modification of Mg-based hydrogen storage materials.

Mechanism of Improving Hydrogenation of Mg by In-Situ Formation of Al* In Hydriding Combustion Synthesis

Mechanism of Improving Hydrogenation of Mg by In-Situ Formation of Al* In Hydriding Combustion Synthesis

Metallurgical processing of Mg alloys and MgH2 for hydrogen storage

The reversible reaction of hydrogen with metallic Mg to form MgH2 has been evaluated by more than 70 years, with particular attention in the last 20–30 years for the exceptional properties of this hydride to store energy. The main challenges to the practical use of these properties were soon identified; the high thermodynamical stability of the hydride, resulting in high temperatures for absorption / desorption of hydrogen; the low diffusion rate of hydrogen in Mg and in MgH2, which requires short diffusion distances and therefore, large surface, interface or interphase areas and the presence of catalyst to improve the absorption and desorption kinetics. Thermodynamic stability cannot be modified by the microstructure, which can, however, affect the other above-mentioned challenges. The first Mg samples to react with hydrogen were prepared by conventional metallurgical routes, but with the important addition of being crushed to be smaller than a certain particle size. Turnings of bulk Mg or Mg alloys samples were also used, resulting in the same increase in surface and interfaces area as the crushed particles. Alloys of different compositions, including eutectic alloys were designed to result in a combination of phases, with one of them in conditions to form a hydride and the other to act as catalyst, or most likely just supplying extra interphases for hydrogen diffusion. But since melting of Mg and Mg alloys is not a friendly process, mechanical alloying was considered simpler and more adequate to prepare Mg powders, resulting in the identification of the exceptional properties of nano powders to improve kinetics but also stressing the difficulties of handling nano powders and the deleterious effect of surface contamination. Severe plastic deformation was then used to prepare “bulk” nanograined material with the expectation to design microstructures with special textures and special types of grain boundaries and to avoid the problem associated with surface reactivity. Because of kinetics limitation, the SPD techniques had to be combined with other processing step, such as filing, cold rolling or milling, basically to increase the surface / interface area. Extensive plastic deformation via co-lamination had already been used but the necessity to complement SPD processing led to the use of conventional metallurgical processing such as cold rolling and cold forging to process Mg and MgH2. Such metallurgical routes prove to be simpler and cost-effective to deliver microstructures satisfying the requirement for Mg and MgH2 to act as hydrogen storage material. Other processing routes or combination of routes that could result in refined microstructure have also been studied, including melt spinning, melt spinning combined with HEBM or with cold-rolling, friction stir welding, mechanical grinding and filing and chips from lathe turnings. In this review we discuss the evolution of metallurgical processing of Mg and MgH2 based hydrogen storage material and how each processing route can lead to microstructures with the required characteristics.

Trimesic acid-Ni based metal organic framework derivative as an effective destabilizer to improve hydrogen storage properties of MgH2

Herein, a new type of trimesic acid-Ni based metal organic framework (TMA-Ni MOF) was synthesized and then, its derivative Ni@C was introduced into MgH2 as destabilizer through high energy ball milling to prepare a Mg–Ni@C–H composite. X-ray diffraction analyses indicate the formation of Mg2Ni/Mg2NiH4 as major phases after dehydrogenation/rehydrogenation of the composite, respectively. Two hydrogen absorption plateaus are observed in the Mg–Ni@C–H composite, corresponding to the hydrogenation of Mg and Mg2Ni, with the enthalpy change values of −75.8 and −52.3 kJ mol−1 H2 respectively. Thus, it can be concluded that a destabilization effect is brought by Ni@C on thermodynamic properties of MgH2. In addition, the hydriding/dehydriding kinetics of MgH2 is notably accelerated with the addition of Ni-based MOF derivative. The activation energy values of both hydrogen absorption and desorption are significantly lowered down with the assistance of Ni@C. Moreover, stable hydrogen de/absorption capacity and kinetics are remained during 25 cycles of high-rate re/dehydrogenation, which can be ascribed to the carbon-wrapped structure of the composite, with which the aggregation of the nanosized particles can be evidently avioded.

Thermochemical transformation and reversible performance of Mg(NH2)2–NaMgH3 system

Reversible hydrogen uptake of Mg(NH2)2–MgH2 system has been achieved by the introduction of Na for the first time. The thermochemical and mechanochemical transformations of Mg(NH2)2-xNaMgH3 (x = 0.5, 1 and 2) composites have been investigated through structural characterizations and gas desorption analyses. The hydrogenation property and reaction mechanism of Mg(NH2)2–NaMgH3 have been discussed. Experimental results indicate that the replacement of NaMgH3 for MgH2 can extensively suppress ammonia emission and improve the hydrogen desorption property of Mg(NH2)2–MgH2 system. For Mg(NH2)2–NaMgH3 system, its thermochemical reaction at low temperature is quite similar to the reaction under mechanochemical process. At high temperature (190 °C), the formation of NaMg(NH2)(NH) is detected. The introduction of Na alters the reaction route and enhances the reaction enthalpy of Mg(NH2)2–MgH2 system. The compound of NaMg(NH2)(NH) is synthesized by the reaction of MgNH and NaNH2 and it can reversibly store 1.8 wt% of hydrogen at 10 atm and 190 °C. The reversible cycling between NaMg(NH2)(NH) and Mg(NH2)2 is responsible for the partial reversible hydrogenation of Mg(NH2)2–NaMgH3 system.

Features of the Hydrogenation of Magnesium with a Ni-Graphene Coating

The kinetics of the hydrogenation of magnesium composites with graphene-like material (GLM) on which nickel particles are deposited (Ni/GLM) and dehydrogenation of MgH2+Ni/GLM composites is studied. The mechanism of the reactions is revealed using the obtained results and the mathematical processing of curves with the Avrami–Erofeev equation. It is found that Ni/GLM considerably accelerates the hydrogenation of Mg and the decomposition of MgH2 in the composite. The hydrogen-accumulating Mg+Ni/GLM composite is shown to have cyclic stability with rapid and virtually complete reversible hydrogenation.

Temperature- and Catalyst-Dependent Transformation from Reaction Rate-Limited to Diffusion Rate-Limited Hydrogenation of Mg with Nb2O5 Catalyst

Temperature- and Catalyst-Dependent Transformation from Reaction Rate-Limited to Diffusion Rate-Limited Hydrogenation of Mg with Nb₂O₅ Catalyst

Li-triggered superior catalytic activity of V in Li3VO4: enabling fast and full hydrogenation of Mg at lower temperatures

Li3VO4 doped MgH2 exhibits excellent hydrogen storage performance, in which the existence of Li stimulates the catalytic activity of V, and simultaneously suppresses the activity of O.

Nitrogen-stimulated superior catalytic activity of niobium oxide for fast full hydrogenation of magnesium at ambient temperature

Magnesium hydride (MgH2) is one of the most promising high-capacity hydrogen storage materials. However, limited progress has been made in storing hydrogen in Mg under ambient conditions. Here, we demonstrate for the first time that the dehydrogenated MgH2 is fully hydrogenated below 100 °C with the presence of N-containing Nb2O5 (N-Nb2O5). MgH2 composites doped with N-Nb2O5 (10 wt%) releases hydrogen from 170 °C, which is lowered by 130 °C compared with pristine MgH2, while still having 6.3 wt% hydrogen capacity available. Most importantly, full hydrogenation can be achieved by the dehydrogenated N-Nb2O5-containing sample at temperature as low as 70 °C under 50 atm of hydrogen, which is superior to other known catalyst-doped MgH2 systems. The in-situ formed NbN0.9O0.1 plays the critical catalyst role due to the joint action of N and Nb as elucidated by density functional theory (DFT) calculations. This finding remarkably facilitates the future design and exploration of much higher-performance catalysts for room-temperature hydrogen storage in metal hydrides.

The effect of oxygen coverages on hydrogenation of Mg (0001) surface

The H2 dissociation and subsequent atomic H diffusion on the oxide Mg(0001) surface have been investigated using density functional theory calculations. Our calculation indicates that at low oxygen coverages the H2 dissociation is the rate-limiting step for surface hydrogenation. The increase of oxygen coverages from 0 to 1/4 monolayer results in decreased H2 dissociation energy barriers from 0.93 to 0.76 eV, indicating that partial oxidized Mg(0001) surface facilitates hydrogenation. This can attributed to the enhancement of H binding strength on the oxidized Mg surface. However, the atomic H diffusion energy barriers increase with increasing H binding strength on the surface. At high oxygen coverage (1 monolayer) the diffusion of H atom from surface to subsurface is the rate-limiting step for the hydrogenation. The H atom diffusion pathways are blocked by surrounding O2− anions, hence H atom needs to overcome a significantly high energy barrier of 2.38 eV to diffuse from 1 monolayer oxide surface to subsurface. This indicates that high oxygen coverages would impede the surface hydrogenation.

Improvement of the Hydrogen-Storage Properties of Mg by Adding a Polymer CMC via Transformation-Involving Milling

The addition of CMC (Carboxymethylcellulose, Sodium Salt) may improve the hydrogen uptake-release properties of Mg since it has a relatively low melting point and the melting of CMC during transformation-involving milling may make the milled samples be in the good states to absorb and release hydrogen rapidly. Samples with compositions of 95 w/o Mg + 5 w/o CMC (named Mg-5CMC) were made through transformation-involving milling. Mg-5CMC was activated in about 3 hydrogen uptake-release cycles. After activation, Mg-5CMC had a higher beginning hydrogen uptake rate and a larger amount of hydrogen absorbed in 60 min, U (60 min), than milled Mg. At the third cycle (CN = 3), Mg-5CMC had a very high beginning hydrogen uptake rate (1.45 w/o H/min) and a very large U (60 min) (7.18 w/o H), showing that the activated Mg-5CMC has an effective hydrogen-storage capacity of about 7.2 w/o at 593 K in hydrogen of 12 bar at CN = 3. Mg-5CMC after transformation-involving milling contained Mg and very small amounts of β-MgH2 and MgO, with no evidence of the phases related to CMC. The milling in hydrogen of Mg with CMC is believed to fabricate defects and cracks and lessen the particle size. To the best of our knowledge, this study is the first one in which a polymer CMC is added to Mg by transformation-involving milling to improve the hydrogen uptake-release properties of Mg.

Competitive Reactions and Formation Mechanism of Microstructures in Mg/Cu Super-Laminate Composites during Initial Hydrogenation

Competitive reactions and formation mechanism of microstructures in Mg/Cu super-laminate composites (SLCs) during initial hydrogenation were studied. During initial hydrogenation of Mg/Cu SLCs, hydrogenation of Mg and alloying of Mg with Cu followed by hydrogenation of Mg2Cu are competitive. It is found that microstructures of Mg/Cu SLCs during initial hydrogenation have changed drastically depending on the order of hydrogenation of Mg and Mg2Cu. The microstructures of Mg/Cu SLCs after initial hydrogenation can be categorized in 3 types.

Relationship between initial hydrogen absorption properties and microstructures of Mg/Cu super-laminate composites with different accumulative roll bonding cycles

The relationship between initial hydrogen absorption properties and microstructures of Mg/Cu super-laminate composites (SLCs) with different accumulative roll bonding (ARB) cycles was investigated. Hydrogenation of Mg was dominant in Mg/Cu SLCs with 5 and 10 cycles of ARB, whereas that of Mg2Cu was dominant in Mg/Cu SLCs with 20 and 30 cycles of ARB. The growth rate constants did not show a significant difference among Mg/Cu SLCs with different ARB cycles. It is considered that the average thickness of Mg + Cu layers in as-rolled Mg/Cu SLCs as a function of ARB cycles has a large influence on initial hydrogenation properties and microstructure formation processes.

Development of a Hydrogen Uptake-Release Mg-Based Alloy by Adding a Polymer CMC (Carboxymethylcellulose, Sodium Salt) via Reaction-Accompanying Milling

The addition of carboxymethylcellulose, sodium salt (CMC) might improve the hydrogen uptake and release properties of Mg since it has a relatively low melting point and the melting of CMC during milling in hydrogen (reaction-accompanying milling) may make the milled samples be in good states to absorb and release hydrogen rapidly and to have a large hydrogen-storage capacity. Samples with compositions of 95 w/o Mg + 5 w/o CMC (named Mg–5CMC) and 90 w/o Mg + 10 w/o CMC (named Mg–10CMC) were prepared by adding CMC via reaction-accompanying milling. Activation of Mg–10CMC was completed after about 3 hydrogen uptake-release cycles. Mg–10CMC had a higher initial hydrogen uptake rate and a larger amount of hydrogen absorbed in 60 min, U (60 min), than Mg–5CMC before and after activation. At the cycle number of three (CN = 3), Mg–10CMC had a very high initial hydrogen uptake rate (1.56 w/o H/min) and a large U (60 min) (5.57 w/o H) at 593 K in hydrogen of 12 bar, showing that the activated Mg–10CMC has an effective hydrogen-storage capacity of about 5.6 w/o at 593 K in hydrogen of 12 bar at CN = 3. At CN = 2, Mg–10CMC released 1.00 w/o H in 2.5 min, 4.67 w/o H in 10 min, and 4.76 w/o H in 60 min at 648 K in hydrogen of 1.0 bar. The milling in hydrogen of Mg with CMC is believed to generate imperfections and cracks and reduce the particle size. The addition of 10 w/o CMC was more effective on the initial hydrogen uptake rate and U (60 min) compared with the 10 w/o additions of NbF5, TaF5, Fe2O3, and MnO, and the 10 w/o simultaneous addition of Ni, Fe, and Ti. To the best of our knowledge, this study is the first in which a polymer CMC is added to Mg by reaction-accompanying milling to improve the hydrogen storage properties of Mg.

Enhanced hydriding kinetics of Mg-10 at% Al composite by forming Al 12 Mg 17 during hydriding combustion synthesis

Abstract Mg-based alloys are widely considered as promising materials for hydrogen storage. However, owing to the high chemical activity of Mg, the surface of Mg powder is always covered with a layer of close packed MgO, which can retard the hydrogenation of Mg. In this paper, 10 at% Al was added to accelerate the hydriding kinetics of Mg through tabletting and grinding treatments. After heating to 420 °C and subsequent holding at 340 °C for 120 min under 1.5 MPa hydrogen pressure, the Mg-10 at% Al composite could absorb 6.34 wt% H2 in the process of hydriding combustion synthesis (HCS) while the same treated pure Mg powder was barely hydrided. Upon heating from room temperature to 420 °C, Al alloyed with Mg to form an Al12Mg17 phase on the surface of Mg particles and the newly formed alloy was oxide-free, which would react with H2 when the temperature decreased to 340 °C. Then hydrogen was able to get into the inner part of the Mg particle from the former Al12Mg17 sites where the MgO shell had been broken in the alloying period to further react with unhydrided Mg.

Site preference and diffusion of hydrogen during hydrogenation of Mg: A first-principles study

First-principles calculations are used to investigate the site preference and diffusion of hydrogen in the initial stage of hydrogenation of Mg. The fcc-hollow site and the tetrahedral site are found to be the energetically favorable sites for hydrogen atom on and below Mg(0001) surface, respectively. When a hydrogen atom diffuses into the bulk Mg, it has to firstly overcome an energy barrier of 0.45 eV. There exist two different diffusion pathways with this energy barrier, which start from two possible surface adsorption sites. While a lower barrier of 0.31 eV is necessary for hydrogen further diffusion into the bulk region. The effect of the subsurface vacancy on hydrogenation is also investigated in terms of hydrogen trapping and diffusion barrier. At most six hydrogen atoms can be trapped by a single Mg vacancy in the subsurface. It is required at least 0.40 eV for the trapped hydrogen to escape from the vacancy. This trapping property and relatively large diffusion barrier to escape from the vacancy would prevent further diffusion of hydrogen into Mg during the initial stage of hydrogenation. The vacancy, however, has little influence on the diffusion property of its neighboring hydrogen atom.

純MgおよびMg-Al-Zn合金における金属内部でのMg水素化物の生成

Mg is hydrogenated as core-shell type hydride in which the surface is covered with MgH2 (shell) and unreacted Mg remains at the internal side (core). Therefore, increase of absorption capacity to the theoretical hydrogen capacity is still one of the most important issues for the hydrogen storage materials, although several treatments were proposed to enhance their absorption capacity. In this study, the procedure of the core-shell structure as well as effect of Al concentration in Mg on the growth MgH2 in Mg were investigated using pure Mg and Mg-(3-9)mass%Al-1 mass%Zn alloys (AZ). MgH2 was formed on the surface as well as inside of unreacted Mg core which was apart from both gaseous H2 and the surface MgH2 layer. The inside MgH2 was formed in a granular form on Mg grain boundary and its size increased by applying plastic deformation. Thickness of the surface MgH2 and size of the internal MgH2 increased with an increase in hydrogenation time until the hydride surface was completely covered with MgH2. However, the growth of the surface and internal MgH2 came to a halt after the surface was covered with MgH2. The increase in Al concertation in AZ lead to decrease in thickness of the surface MgH2, prolongation of the halt time and increase in the internal MgH2 grain size. From these results, supplying H from metal side was dominantly contributed for growth of the surface and internal MgH2 because diffusion rate of H in Mg was much higher than that in MgH2. In addition, the growth of internal MgH2 as well as control of surface MgH2 can contribute to the promotion of the complete hydrogenation of Mg based hydrogen storage materials.