Dehydrogenation Properties Of Mg Research Articles

Understanding the dehydrogenation properties of Mg(0001)/MgH2(110) interface from first principles

Magnesium hydride is one of the most promising solid-state hydrogen storage materials for on-board application. Hydrogen desorption from MgH2 is accompanied by the formation of the Mg/MgH2 interfaces, which may play a key role in the further dehydrogenation process. In this work, first-principles calculations have been used to understand the dehydrogenation properties of the Mg(0001)/MgH2(110) interface. It is found that the Mg(0001)/MgH2(110) interface can weaken the Mg–H bond. The removal energies for hydrogen atoms in the interface zone are significantly lower compared to those of bulk MgH2. In terms of H mobility, hydrogen diffusion within the interface as well as into the Mg matrix is considered. The calculated energy barriers reveal that the migration of hydrogen atoms in the interface zone is easier than that in the bulk MgH2. Based on the hydrogen removal energies and diffusion barriers, we conclude that the formation of the Mg(0001)/MgH2(110) interface facilitates the dehydrogenation process of magnesium hydride.

2D transition metal carbides trigger enhanced dehydrogenation and reversibility properties in Mg(BH4)2

Although Mg(BH4)2 has been widely studied in the hydrogen storage field for its high hydrogen density, its terrible dehydriding kinetics and cycling features remain impediments to practical applications. Herein, introducing different MXenes (Ti3C2, Ti2C, Nb2C) with novel two-dimensional structures as catalysts into Mg(BH4)2 has been demonstrated to be an efficient approach to boosting the hydrogen storage properties. 30 wt% MXenes in Mg(BH4)2 causes a considerable reduction in its hydrogen release temperature, remarkable increases in its dehydrogenation rate and capacity, and an enhancement to its reversibility. The Mg(BH4)2-30Ti2C as the most excellent composite starts to liberate hydrogen from 132 °C, 143 °C lower than that of Mg(BH4)2. Furthermore, at 260 °C, the Mg(BH4)2-30Ti2C composite desorbs 10.2 wt% H2, which is much higher than that of Mg(BH4)2 (1.5 wt%). Theoretical calculations elucidate the weakening of B-H bonds caused by the electron transfer at the Mg(BH4)2/MXenes interfaces, and the dehybridization effect between the B and H orbits. X-ray photoelectron spectroscopy (XPS) analyses prove the in-situ formation of multiphase interfaces resulting from the interaction of Mg(BH4)2 and MXenes during milling and dehydrogenation processes, which could increase electron conduction and facilitate hydrogen diffusion. These factors contribute to the outstanding dehydrogenation properties of Mg(BH4)2.

Enhancement of the Hydrogenation and Dehydrogenation Characteristics of Mg by Adding Small Amounts of Nickel and Titanium

We compared the hydrogenation and dehydrogenation properties of Mg-based alloys to which small amounts of transition elements (Ni and Ti), halides (TaF5 and VCl3), and complex hydrides (LiBH4 and NaAlH4) were added through grinding in a hydrogen atmosphere (reactive milling). Mg-1.25Ni-1.25Ti is one of the samples compared, having a composition of 97.5 wt.% Mg + 1.25 wt.% Ni and 1.25 wt.% Ti. Even though Mg-1.25Ni-1.25Ti did not have the highest initial hydrogenation rate, it had the largest quantities of hydrogen absorbed and released for 60 min and the highest initial dehydrogenation rate. In addition, Mg-1.25Ni-1.25Ti did not show the incubation period in the dehydrogenation. We thus investigated the hydrogenation and dehydrogenation properties of Mg-1.25Ni-1.25Ti in more detail. Activated Mg-1.25Ni-1.25Ti absorbed 5.91 wt.% H in 12 bar H2 and released 5.80 wt.% H in 1.0 bar H2 at 593 K for 60 min at n = 3. For 5 wt.% hydrogen absorption by Mg-1.25Ni-1.25Ti, 18.7 min was required at 593 K in 12 bar H2 at n = 3. Although only small amounts of Ni and Ti were added, the hydrogenation and dehydrogenation properties of Mg were greatly improved. Ni and Ti-added Mg had a higher initial dehydrogenation rate and a larger Hd (60 min) than only Ni-added Mg, suggesting that the TiH1.924 and NiTi formed in Mg-1.25Ni-1.25Ti play roles in the increases in the initial dehydrogenation rate and Hd (60 min), probably acting as active sites for the nucleation of the Mg-H solid solution phase.

The dehydrogenation kinetics and reversibility improvements of Mg(BH4)2 doped with Ti nano-particles under mild conditions

Magnesium borohydride, Mg(BH4)2, is ball-milled with Ti nano-particles. Such catalyzed Mg(BH4)2 releases more hydrogen than pristine Mg(BH4)2 does during isothermal dehydrogenation at 270, 280, and 290 °C. The catalyzed Mg(BH4)2 also exhibits better dehydrogenation kinetics than the pristine Mg(BH4)2. Based on kinetics model fitting, the activation energy (Ea) of the catalyzed Mg(BH4)2 is calculated to be lower than pristine Mg(BH4)2. During partial dehydrogenation, the catalyzed Mg(BH4)2 releases 4.23 wt % (wt%) H2 for the second dehydrogenation at 270 °C, comparing to 4.05, and 3.75 wt% H2 at 280, and 290 °C. The reversibility of 4.23 wt% capacity is also one of the highest for Mg(BH4)2 dehydrogenation under mild conditions such as 270 °C as reported. 4 cycles of Mg(BH4)2 dehydrogenation are conducted at 270 °C. The capacities degrade during 4 cycles and tend to be stable at about 3.0 wt% for the last two cycles. By analyzing the hydrogen de/absorption products of the catalyzed sample, Mg(BH4)2 is found to be regenerated after rehydrogenation according to Fourier Transform Infrared (FTIR) spectroscopy. Ti nano-particles can react with Mg(BH4)2 during ball-milling and de/rehydrogenation. The products include TiH1.924, TiB, and TiB2, which can improve the dehydrogenation properties of Mg(BH4)2 from a multiple aspect.

Improved reversible dehydrogenation properties of Mg(BH4)2 catalyzed by dual-cation transition metal fluorides K2TiF6 and K2NbF7

Two dual-cation transition metal fluorides K2TiF6 and K2NbF7 are introduced into Mg(BH4)2 by ball-milling to catalyze the dehydrogenation of Mg(BH4)2. According to the DSC and TPD results, the onset dehydrogenation temperature of Mg(BH4)2 doped with K2TiF6 and K2NbF7 are remarkably reduced to 105.4 and 118.0 °C, respectively. Meanwhile, both the K2TiF6 and K2NbF7 catalyzed systems can release more than 6.4 wt% H2 under 280 °C, showing an improvement in dehydrogenation kinetics. In addition, the reversible capacity of the Mg(BH4)2–3%K2TiF6 system is 2.7 wt% at 280 °C in 250 min, which is enhanced comparing to that of pristine Mg(BH4)2. X-ray diffraction, Fourier-transformed infrared and 11B nuclear magnetic resonance investigations reveal that the K2TiF6 actually acts as a catalytic precursor to react with Mg(BH4)2, forming active hydrides of KBH4 and TiH2, which further serve as catalyzing agents to facilitate the re-generation of Mg(BH4)2 from intermediates under moderate conditions.

LiAlH4 as a “Microlighter” on the Fluorographite Surface Triggering the Dehydrogenation of Mg(BH4)2: Toward More than 7 wt % Hydrogen Release below 70 °C

Mg(BH4)2 is one of the most promising hydrides for hydrogen storage. Herein, the dehydrogenation properties of Mg(BH4)2 are significantly improved by LiAlH4 and fluorographite (FGi) addition. The m...

Nano-inducement of Ni for low-temperature dominant dehydrogenation of Mg–Al alloy prepared by HCS+MM

Magnesium hydride is one of the most ideal solid hydrogen storage materials (HSMs). However, its sluggish absorption/desorption kinetics and undesirable thermodynamics create a burden for industrial-scale applications. In this paper, the effects of micro-Ni and nano-Ni on the dehydrogenation properties of Mg–Al alloys were compared and studied. All the samples were prepared by hydriding combustion synthesis (HCS) and mechanical milling (MM). Temperature programmed desorption (TPD) and differential scanning calorimeter (DSC) analyses showed that the catalytic effect of nano-Ni was vastly superior to that of micro-Ni and the catalytic effect of Ni was more excellent than Al3Ni2 on the dehydrogenation of Mg–Al alloy. Mg90Al10-5nanoNi-MM exhibited the best dehydrogenation property, in which, two dehydrogenation peaks at 260 °C and 343 °C in the DSC curve (10 °C/min) were observed and the main dehydrogenation occurred at the lower temperature. The apparent activation energy for dehydrogenation of MgH2 was reduced from 144.8 kJ/mol to 88.8 and 65.5 kJ/mol for the two dehydrogenation peaks. Ex-situ X-ray differential (XRD) and high resolution transmission electron microscope (HRTEM) were conducted to understand the microstructure evolution during dehydrogenation. Nano-inducement of nano-Ni dramatically promotes the regulation of Al on MgH2 thus improving the dehydrogenation performance.

Hydrogen Storage Properties of Mg Alloy Prepared by Incorporating Polyvinylidene Fluoride via Reactive Milling

In the present work, we selected a polymer, polyvinylidene fluoride (PVDF), as an additive to improve the hydrogenation and dehydrogenation properties of Mg. 95 wt% Mg + 5 wt% PVDF (designated Mg-5PVDF) samples were prepared via milling in hydrogen atmosphere (reactive milling), and the hydrogenation and dehydrogenation characteristics of the prepared samples were compared with those of Mg milled in hydrogen atmosphere. The dehydrogenation of magnesium hydride formed in the as-prepared Mg- 5PVDF during reactive milling began at 681 K. In the fourth cycle (n=4), the initial hydrogenation rate was 0.75 wt% H/min and the quantity of hydrogen absorbed for 60 min, Ha (60 min), was 3.57 wt% H at 573 K and in 12 bar H2. It is believed that after reactive milling the PVDF became amorphous. The milling of Mg with the PVDF in hydrogen atmosphere is believed to have produced defects and cracks. The fabrication of defects is thought to ease nucleation. The fabrication of cracks is thought to expose fresh surfaces, resulting in an increase in the reactivity of the particles with hydrogen and a decrease in the diffusion distances of hydrogen atoms. As far as we know, this investigation is the first in which a polymer PVDF was added to Mg by reactive milling to improve the hydrogenation and dehydrogenation characteristics of Mg. (Received August 8, 2018; Accepted October 11, 2018)

Increase in the Dehydrogenation Rate of Mg–CMC (Carboxymethylcellulose, Sodium Salt) by Adding Ni via Hydride-Forming Milling

In our previous work, samples with a composition of 95 wt% Mg + 5 wt% CMC (Carboxymethylcellulose, Sodium Salt, [C6H7O2(OH)x(C2H2O3Na)y]n) (named Mg–5 wt% CMC) were prepared through hydride-forming milling. Mg–5 wt% CMC had a very high hydrogenation rate but a low dehydrogenation rate. Addition of Ni to Mg is known to increase the hydrogenation and dehydrogenation rates of Mg. We chose Ni as an additive to increase the dehydrogenation rate of Mg–5 wt% CMC. In this work, samples with a composition of 90 wt% Mg + 5 wt% CMC + 5 w% Ni (Mg–5 wt% CMC–5 wt% Ni) were made through hydride-forming milling, and the hydrogenation and dehydrogenation properties of the prepared samples were investigated. The activation of Mg–5 wt% CMC–5 wt% Ni was completed at the 3rd hydrogenation–dehydrogenation cycle (N = 3). Mg–5 wt% CMC–5 wt% Ni had an effective hydrogen-storage capacity of 5.83 wt% at 593 K in 12 bar hydrogen at N = 3. Mg–5 wt% CMC–5 wt% Ni released hydrogen of 2.73 wt% for 10 min and 4.61 wt% for 60 min at 593 K in 1.0 bar hydrogen at N = 3. Mg–5 wt% CMC–5 wt% Ni dehydrogenated at N = 4 contained Mg and small amounts of MgO, β-MgH2, Mg2Ni, and Ni. Hydride-forming milling of Mg with CMC and Ni and Mg2Ni formed during hydrogenation–dehydrogenation cycling are believed to have increased the dehydrogenation rate of Mg–5 wt% CMC. As far as we know, this study is the first in which a polymer CMC and Ni were added to Mg by hydride-forming milling to improve the hydrogenation and dehydrogenation properties of Mg.

Synthesis of a Mg-based alloy with a hydrogen-storage capacity of over 7 wt% by adding a polymer CMC via transformation-involving milling

Carboxymethylcellulose sodium salt (CMC) was added to magnesium via milling in hydrogen (transformation-involving milling), and samples with compositions of 95 wt% Mg + 5 wt% CMC (named Mg-5CMC) and 90 wt% Mg + 10 wt% CMC (Mg-10CMC) were prepared. At the cycle number (CN) of three, Mg-5CMC had a very high initial hydrogenation rate (1.45 wt% H/min) and a very large effective hydrogen-storage capacity of about 7.2 wt%. It is believed that the CMC melted during milling, and that because the melted CMC was highly viscous, sliding between the Mg particles and hardened steel balls was prevented, which led to effective milling (the generation of defects and cracks and the reduction of particle sizes). To the best of our knowledge, this study is the first in which a polymer CMC was added to Mg in order to improve the hydrogenation and dehydrogenation properties of Mg.

Raising the Dehydrogenation Rate of a Mg-CMC (Carboxymethylcellulose, Sodium Salt) Composite by Alloying Ni via Hydride-Forming Milling

In our previous work, samples with a composition of 95 wt% Mg + 5 wt% CMC (Carboxymethylcellulose, Sodium Salt, [C6H7O2(OH)x(C2H2O3Na)y]n) (named Mg-5 wt%CMC) were prepared through hydride-forming milling. Mg-5 wt%CMC had a very high hydrogenation rate but a low dehydrogenation rate. Addition of Ni to Mg is known to increase the hydrogenation and dehydrogenation rates of Mg. We chose Ni as an additive to increase the dehydrogenation rate of Mg-5 wt%CMC. In this study, samples with a composition of 90 wt% Mg + 5 wt% CMC + 5 wt% Ni (named Mg-5 wt%CMC-5 wt%Ni) were made through hydride-forming milling, and the hydrogenation and dehydrogenation properties of the prepared samples were investigated. The activation of Mg-5 wt%CMC-5 wt%Ni was completed at the 3rd hydrogenation-dehydrogenation cycle (N=3). Mg-5 wt%CMC-5 wt%Ni had an effective hydrogen-storage capacity (the quantity of hydrogen stored for 60 min) of 5.83 wt% at 593 K in 12 bar hydrogen at N=3. Mg-5 wt%CMC-5 wt%Ni released hydrogen of 2.73 wt% for 10 min and 4.61 wt% for 60 min at 593 K in 1.0 bar hydrogen at N=3. Mg-5 wt%CMC-5 wt%Ni dehydrogenated at N=4 contained Mg and small amounts of MgO, β-MgH2, Mg2Ni, and Ni. Hydride-forming milling of Mg with CMC and Ni and Mg2Ni formed during hydrogenation-dehydrogenation cycling are believed to have increased the dehydrogenation rate of Mg-5 wt%CMC. As far as we know, this study is the first in which a polymer CMC and Ni were added to Mg by hydride-forming milling to improve the hydrogenation and dehydrogenation properties of Mg. Key words: hydrogen absorbing materials, mechanical milling, scanning electron microscopy (SEM), X-ray diffraction, a polymer CMC (Carboxymethylcellulose, Sodium Salt) addition, Ni addition

Improving dehydrogenation properties of Mg/Nb composite films via tuning Nb distributions

To investigate the effect of Nb on the dehydrogenation properties of Mg–Nb composite films, Mg/Nb eight-layer film and Mg-10 at% Nb alloy film with the similar Mg-to-Nb atomic ratio were prepared by magnetron sputtering. Results show that both Mg/Nb eight-layer film and Mg-10 at% Nb alloy film exhibit excellent de/hydrogenation properties. Mg-10 at% Nb alloy film starts to release hydrogen at 108 °C, and its desorption peak temperature is lower to 146 °C, which is much better than that of pure MgH2 under the same condition. Scanning electron microscopy (SEM) results demonstrate that the dispersive Nb nanoparticles in Mg/Nb eight-layer film may serve as nucleation sites for Mg ↔ MgH2 reactions, which can provide channels for H diffusion. For Mg-10 at% Nb alloy film, the uniform distributions of Nb can accelerate the hydrogen diffusion and effectively improve the dehydrogenation kinetics for MgH2. This study provides an enlightening way for designing and preparing Mg-based composite films with excellent dehydrogenation properties.

Study on the dehydrogenation properties and reversibility of Mg(BH4)2[sbnd]AlH3 composite under moderate conditions

Mg(BH4)2 has been considered as one of the promising light metal complex hydrides due to its high hydrogen capacity and low cost. But its higher thermal stability (dehydrogenation at above 300 °C) needs to be improved for the practical application. In this study, the aluminum hydride AlH3 was introduced into complex borohydride Mg(BH4)2 to synthesize a new Mg(BH4)2AlH3 composite by ball milling method. It is found that the active Al∗ formed from the self-decomposition of AlH3 can effectively improve the dehydrogenation properties of Mg(BH4)2, the Mg(BH4)2AlH3 composite starts to release hydrogen at 130.8 °C with a total hydrogen capacity of 11.9 wt.%. The dehydrogenated products of the composite is composed of Mg2Al3 and B at 350 °C, resulting in the improved hydrogen desorption properties of Mg(BH4)2AlH3 composite. The Mg2Al3 and B products would be further transformed into MgAlB4 and Al at 500 °C. Moreover, the Mg2Al3 and B dehydrogenated products show better reversible hydrogen storage property than that of the MgAlB4 and Al products. This research shows a way to alter hydrogen de/hydrogenation route and reversibility of Mg(BH4)2 complex hydride by compositing with AlH3 and controlling the dehydrogenation temperature.

Remarkable enhancement in dehydrogenation properties of Mg(BH4)2 modified by the synergetic effect of fluorographite and LiBH4

Mg(BH4)2 is considered as one of the most promising light metal complex hydrides because of its high volumetric and gravimetric hydrogen capacities and world-wide abundance. However, its higher major desorption temperatures (above 300 °C) and poor reaction kinetics have to be improved for the practical application. Herein, Mg(BH4)2 was successfully synthesized via wet-chemical technique and a significant enhancement in dehydrogenation performance of Mg(BH4)2 is achieved by the synergetic effect of fluorographite (FGi) and LiBH4. Under the effect of FGi, the hydrogen desorption of 6 Mg(BH4)2-4FGi composite could be completed below 170 °C in seconds. However, the hydrogen released from 6 Mg(BH4)2-4FGi suffers from impurities of B2H6 and HF. More importantly, it is demonstrated that almost all the B2H6 and HF impurities can be suppressed by synergetic modifying Mg(BH4)2 with FGi and LiBH4. The 3 Mg(BH4)2–3LiBH4-4FGi composite exhibits a capacity over 8.0 wt% H2 and starts to release hydrogen at 125.7 °C, which is 143.8 °C and 254.3 °C lower than that of pure Mg(BH4)2 and LiBH4, respectively. These significant improvements could be attributed to both the novel morphology that numerous nano-scale borohydride spots formed on the surface of FGi, and the formations of stable fluorides (MgF2 and LiF) from the interaction between borohydrides and FGi.

Improved dehydrogenation properties of Mg(BH4)2·2NH3 combined with LiAlH4

The decomposition properties of Mg(BH4)2·2NH3 combined with LiAlH4 mixtures were investigated systematically. It revealed that the hydrogen desorption temperature shifted to 100 °C with the superior suppression of ammonia, and desorption rates were improved with the increased LiAlH4 ratio (0.5, 1, 2), respectively. When the LiAlH4 ratio was increased to 2, the binary system exhibited three dehydrogen steps with an onset temperature at 98 °C and 5.4 wt % H2 desorbed rapidly at the same temperature, while no apparent evolution of H2 was observed for individual Mg(BH4)2·2NH3 and LiAlH4 below 150 °C. The dehydrogenation rate of the system was improved by about 92% more than that of Mg(BH4)2·2NH3. These results indicate that the dehydrogenation of Mg(BH4)2·2NH3 is enhanced significantly by the introduction of LiAlH4. The synergetic factor of the aided-cation effect and dihydrogen interaction may contribute to prevent the NH3 group from being dissociated as ammonia.

Influence of titanium and nickel dopants on the dehydrogenation properties of Mg(AlH4)2: Electronic structure mechanisms

The structures and dehydrogenation properties of pure and Ti/Ni-doped Mg(AlH4)2 were investigated using the first-principles calculations. The dopants mainly affect the geometric and electronic structures of their vicinal AlH4 units. Ti and Ni dopants improve the dehydrogenation of Mg(AlH4)2 in different mechanisms. In the Ti-doped case, Ti prefers to occupy the 13-hedral interstice (TiiA) and substitute for the Al atom (TiAl), to form a high-coordination structure TiHn (n = 6, 7). The Ti 3d electrons hybridize markedly with the H 1s electrons in TiAl and with the Al 3p electrons in TiiA, which weakens the Al–H bond of adjacent AlH4 units and facilitates the hydrogen dissociation. A TiAl3H13 intermediate in TiiA is inferred as the precursor of Mg(AlH4)2 dehydrogenation. In contrast, Ni tends to occupy the octahedral interstice to form the NiH4 tetrahedron. The tight bind of the Ni with its surrounding H atoms inhibits their dissociation though the nearby Al–H bond also becomes weak. Therefore, Ti is the better dopant candidate than Ni for improving the dehydrogenation properties of Mg(AlH4)2 because of its abundant activated hydrogen atoms and low hydrogen removal energy.

Improved dehydrogenation properties of the combined Mg(BH4)2·6NH3–nNH3BH3 system

A combined strategy via mixing Mg(BH4)2·6NH3 with ammonia borane (AB) is employed to improve the dehydrogenation properties of Mg(BH4)2·6NH3. The combined system shows a mutual dehydrogenation improvement in terms of dehydrogenation temperature and hydrogen purity compared to the individual components. A further improved hydrogen liberation from the Mg(BH4)2·6NH3–6AB is achieved with the assistance of ZnCl2, which plays a crucial role in stabilizing the NH3 groups and promoting the recombination of NHδ+⋯HBδ−. Specifically, the Mg(BH4)2·6NH3–6AB/ZnCl2 (with a mole ratio of 1:0.5) composite is shown to release over 7 wt.% high-pure hydrogen (>99 mol%) at 95 °C within 10 min, thereby making the combined system a promising candidate for solid hydrogen storage.

Influence of transition metals Fe, Ni, and Nb on dehydrogenation characteristics of Mg(BH4)2: Electronic structure mechanisms

First principles calculations on Fe, Ni, and Nb doped Mg(BH4)2 were carried out to study the influence of dopants on dehydrogenation properties of Mg(BH4)2. It was shown that all dopants considered prefer to substitute for Mg with relatively smaller occupation energies comparing to the B substitution and the interstitial occupation. However, the B substitution shows smaller hydrogen dissociation energy than the Mg substitution. Mechanisms that dopants used to improve dehydrogenation properties of Mg(BH4)2 are different. For Mg substitution, Fe strongly interacts with one H atoms of the [BH4] group, distorts its structural stability and therefore lowers the hydrogen dissociation energy, Ni may attract one particular H atom of the [BH4] group and weakens the interactions between the B and other H atoms reducing the hydrogen dissociation energy, and the Nb however may drive the formation of NbB2 and improves the dehydrogenation properties as well. In the B substitution, Fe interacts with the one of H atoms and decreases its structure stability, the Ni will attract its neighbor atoms to form a regular group which is almost identical in structure to that of the NiH4 group in Mg2NiH4, and the NbH2 and MgH2 are likely to be generated by Nb doping.

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A combined strategy via mixing Mg(BH4)2·6NH3 with ammonia borane (AB) is employed to improve the dehydrogenation properties of Mg(BH4)2·6NH3. The combined system shows a mutual dehydrogenation improvement in terms of dehydrogenation temperature and hydrogen purity compared to the individual components. A further improved hydrogen liberation from the Mg(BH4)2·6NH3–6AB is achieved with the assistance of ZnCl2, which plays a crucial role in stabilizing the NH3 groups and promoting the recombination of NHδ+⋯HBδ−. Specifically, the Mg(BH4)2·6NH3–6AB/ZnCl2 (with a mole ratio of 1:0.5) composite is shown to release over 7 wt.% high-pure hydrogen (>99 mol%) at 95 °C within 10 min, thereby making the combined system a promising candidate for solid hydrogen storage.

Effect of Al on the hydrogen storage properties of Mg(BH4)2

The various Mg–B–Al–H systems composed of Mg(BH4)2 and different Al-sources (metallic Al, LiAlH4 and its decomposition products) have been investigated as potential hydrogen storage materials. The role of Al was studied on the dehydrogenation and the rehydrogenation of the systems. The results indicate that the different Al-sources exhibit a similar improving effect on the dehydrogenation properties of Mg(BH4)2. Taking the Mg(BH4)2 + LiAlH4 system as an example, at first LiAlH4 rapidly decomposes into LiH and Al, then Mg(BH4)2 decomposes into MgH2 and B, finally the MgH2 reacts with Al, LiH and B, which forms Mg3Al2 and MgAlB4. The system starts to desorb H2 at 140 °C and desorbs 3.6 wt.% H2 below 300 °C, while individual Mg(BH4)2 starts to desorb H2 at 250 °C and desorbs only 1.3 wt.% H2 below 300 °C. The isothermal desorption kinetics of the Mg–B–Al–H systems is about 40% faster than that of Mg(BH4)2 at the hydrogen desorption ratio of 90%. In addition, the Mg–B–Al–H systems show partial reversibility at moderate temperature and pressure. For Al-added system, the product of rehydrogenation is MgH2, while for LiAlH4-added system the product is composed of LiBH4 and MgH2.