Effect of LiBH4 on hydrogen storage property of MgH2

The effect of lithium borohydride (LiBH₄) on the hydriding/dehydriding kinetics and thermodynamics of magnesium hydride (MgH₂) was investigated. It was found that LiBH₄ played both positive and negative effects on the hydrogen sorption of MgH₂. With 10 mol.% LiBH₄ content, MgH₂–10 mol.% LiBH₄ had superior hydrogen absorption/desorption properties, which could absorb 6.8 wt.% H within 1300 s at 200 °C under 3 MPa H₂ and completed desorption within 740 s at 350 °C. However, with the increasing amount of LiBH₄, the hydrogenation/dehydrogenation kinetics deteriorated, and the starting desorption temperature increased and the hysteresis of the pressure-composition isotherm (PCI) became larger. Our results showed that the positive effect of LiBH₄ was mainly attributed to the more uniform powder mixture with smaller particle size, while the negative effect of LiBH₄ might be caused by the H–H exchange between LiBH₄ and MgH₂.     

Hydrogen storage behavior of 2LiBH4/MgH2 composites improved by the catalysis of CoNiB nanoparticles

2LiBH₄/MgH₂ system is a representative and promising reactive hydride composite for hydrogen storage. However, the high desorption temperature and sluggish desorption kinetics hamper its practical application. In our present report, we successfully introduce CoNiB nanoparticles as catalysts to improve the dehydrogenation performances of the 2LiBH₄/MgH₂ composite. The sample with CoNiB additives shows a significant desorption property. Temperature programmed desorption (TPD) measurement demonstrates that the peak decomposition temperatures of MgH₂ and LiBH₄ are lowered to be 315 °C and 417 °C for the CoNiB-doped 2LiBH₄/MgH₂. Isothermal dehydrogenation analysis demonstrates that approximately 10.2 wt% hydrogen can be released within 360 min at 400 °C. In addition, this study gives a preliminary evidence for understanding the CoNiB catalytic mechanism of 2LiBH₄/MgH₂     

Effects of MoS2 addition on the hydrogen storage properties of 2LiBH4–MgH2 systems

A 2LiBH₄–MgH₂–MoS₂ composite was prepared by solid-state ball milling, and the effects of MoS₂ as an additive on the hydrogen storage properties of 2LiBH₄–MgH₂ system together with the corresponding mechanism were investigated. As shown in the TG–DSC and MS results, with the addition of 20 wt.% of MoS₂, the onset dehydrogenation temperature is reduced to 206 °C, which is 113 °C lower than that of the pristine 2LiBH₄–MgH₂ system. Meanwhile, the total dehydrogenation amount can be increased from 9.26 wt.% to 10.47 wt.%, and no gas impurities such as B₂H₆ and H₂S are released. Furthermore, MoS₂ improves the dehydrogenation kinetics, and lowers the activation energy (E_a) 34.49 kJ mol⁻¹ of the dehydrogenation reaction between Mg and LiBH₄ to a value lower than that of the pristine 2LiBH₄–MgH₂ sample. According to the XRD test, Li₂S and MoB₂ are formed by the reaction between LiBH₄ and MoS₂, which act as catalysts and are responsible for the improved hydrogen storage properties of the 2LiBH₄–MgH₂ system.     

Effect of LiH on hydrogen storage property of MgH2

Recent works showed that the addition of LiBH₄ significantly improves the sorption kinetics of MgH₂, and LiH decomposed from LiBH₄ was supposed to play the catalytic effect on MgH₂. In order to clarify this mechanism, the effect of LiH on the hydriding/dehydriding kinetics and thermodynamics of MgH₂ was systematically investigated. The hydrogenation kinetics of LiH-doped samples, as well as the morphology after several cycles, was similar to those of pure MgH₂, which indicate that Li⁺ had no catalytic effect on the hydrogenation of Mg. Moreover, the addition of LiH strongly retarded the hydrogen desorption of MgH₂ doped with/without Nb₂O₅, and resulted in higher starting temperature of desorption, larger activation energy and larger pressure hysteresis of PCI curves of MgH₂. H₂, HD and D₂ were observed in the desorption products of MgH₂-2LiD, which confirms that H–H exchange indeed occurs between MgH₂ and LiH, hence deteriorate desorption kinetics/thermodynamics of MgH_2. The results implied that the additives containing H⁻ could retard the hydrogen desorption of MgH₂ by H–H exchange effect.     

Hydrogen storage performance of 5LiBH4 + Mg2FeH6 composite system

The hydrogen storage properties of 5LiBH₄ + Mg₂FeH₆ reactive hydride composites for reversible hydrogen storage were investigated by comparing with the 2LiBH₄ + MgH₂ composite in the present work. The dehydrogenation pathway and reaction mechanism of 5LiBH₄ + Mg₂FeH₆ composite were also investigated and elucidated. The self-decomposition of Mg₂FeH₆ leads to the in situ formation of Mg and Fe particles on the surface of LiBH₄, resulting in a well dispersion between different reacting phases. The formation of FeB is observed during the dehydrogenation of 5LiBH₄ + Mg₂FeH₆ composite, which might supplies nucleation sites of MgB₂ during the dehydrogenation process, but is not an ascendant catalyst for the self-decomposition of LiBH₄. And FeB can also transform to the LiBH₄ and Fe by reacting with LiH and H₂ during the rehydrogenation process. The dehydrogenation capacity for 5LiBH₄ + Mg₂FeH₆ composite still gets to 6.5 wt% even after four cycles. The X-ray diffraction analyses reveal the phase transitions during the hydriding and dehydriding cycle. The formed FeB in the composite maintains a nanostructure after four hydriding-dehydriding cycles. The loss of hydrogen storage capacity and de-/rehydrogenation kinetics can be attributed to the incomplete generation of Mg₂FeH₆ during the rehydrogenation process.     

Improved hydrogen storage performance of the LiNH2–MgH2–LiBH4 system by addition of ZrCo hydride

Significant improvements in the hydrogen absorption/desorption properties of the 2LiNH₂–1.1MgH₂–0.1LiBH₄ composite have been achieved by adding 3wt% ZrCo hydride. The composite can absorb 5.3wt% hydrogen under 7.0 MPa hydrogen pressure in 10 min and desorb 3.75wt% hydrogen under 0.1 MPa H₂ pressure in 60 min at 150 °C, compared with 2.75wt% and 1.67wt% hydrogen under the same hydrogenation/dehydrogenation conditions without the ZrCo hydride addition, respectively. TPD measurements showed that the dehydrogenation temperature of the ZrCo hydride-doped sample was decreased about 10 °C compared to that of the pristine sample. It is concluded that both the homogeneous distribution of ZrCo particles in the matrix observed by SEM and EDS and the destabilized N–H bonds detected by IR spectrum are the main reasons for the improvement of H-cycling kinetics of the 2LiNH₂–1.1MgH₂–0.1LiBH₄ system.     

Remarkable irreversible and reversible dehydrogenation of LiBH4 by doping with nanosized cobalt metalloid compounds

Nanosized cobalt sulfide and cobalt boride were synthesized and doped into LiBH₄ to improve the dehydrogenation properties of this important candidate for hydrogen storage. With respect to CoS_x doping, the dehydrogenation temperature (peak temperature observed by mass spectrometry) of pristine LiBH₄ can be reduced from 440 °C to 175 °C with a maximum capacity of 6.7 wt% at 50% doping. Unfortunately, B₂H₆ is liberated and the process is not reversible because the CoS_x dopant reacts with LiBH₄ to form more stable compounds. By changing CoS_x to CoB_x, a reversible dehydrogenation was realized with greatly improved reversibility. The dehydrogenation temperature was reduced to 350 °C with a maximum capacity of 8.4 wt% at 50% doping amount. It is very significant that CoB_x is stable and the release of B₂H₆ is eliminated. A reversible hydrogen desorption of about 5.3 wt% can be achieved with a LiBH₄ + 50% CoB_x mixture under a mild rehydrogenation condition of 400 °C at 10 MPa H₂. It is obvious that CoS_x acts as a reactant even though the dehydrogenation is greatly enhanced, while CoB_x behaves as a catalyst significantly promoting the dehydrogenation and reversibility of LiBH₄.     

Comprehensive hydrogen storage properties and catalytic mechanism studies of 2LiBH4–MgH2 system with NbF5 in various addition amounts

In the present work, the role of NbF₅ addition amount in affecting the comprehensive hydrogen storage properties (dehydrogenation, rehydrogenation, cycling performance, hydrogen capacity) of 2LiBH₄–MgH₂ system as well as the catalytic mechanism of NbF₅ have been systematically studied. It is found that increasing the addition amount of NbF₅ to the 2LiBH₄–MgH₂ system not only results in dehydrogenation temperature reduction and hydriding–dehydriding kinetics enhancement but also leads to the de/rehydrogenation capacity loss. Compared with other samples, 2LiBH₄–MgH₂ doping with NbF₅ in weight ratios of 40:4 exhibits superior comprehensive hydrogen storage properties, which can stably release ∼8.31 wt.% hydrogen within 2.5 h under 4 bar H₂ and absorb ∼8.79 wt.% hydrogen within 10 min under 65 bar H₂ at 400 °C even up to 20 cycling. As far as we know, this is the first time that excellent reversibility as high as 20 cycles without obvious degradation tendency in both of hydrogen capacity and reaction rate has been achieved in the 2LiBH₄–MgH₂ system. The further experimental study reveals that the highly catalytic effects of NbF₅ on the 2LiBH₄–MgH₂ system are derived from the reaction between NbF₅ and LiBH₄, which provides a fundamental insight into the catalytic mechanism of NbF₅.     

Combined effects of hydrogen back-pressure and NbF5 addition on the dehydrogenation and rehydrogenation kinetics of the LiBH4–MgH2 composite system

It is well known that the dehydrogenation pathway of the LiBH₄–MgH₂ composite system is highly reliant on whether decomposition is performed under vacuum or a hydrogen back-pressure. In this work, the effects of hydrogen back-pressure and NbF₅ addition on the dehydrogenation kinetics of the LiBH₄–MgH₂ system are studied under either vacuum or hydrogen back-pressure, as well as the subsequent rehydrogenation and cycling. For the pristine sample, faster desorption kinetics was obtained under vacuum, but the performance is compromised by slow absorption kinetics. In contrast, hydrogen back-pressure remarkably promotes the absorption kinetics and increases the reversible hydrogen storage capacity, but with the penalty of much slower desorption kinetics. These drawbacks were overcome after doping with NbF₅, with which the dehydrogenation and rehydrogenation kinetics was significantly improved. In particular, the enhanced kinetics was observed to persist well, even after 9 cycles, in the case of the NbF₅ doped sample under hydrogen back-pressure, as well as the suppression of forming Li₂B₁₂H₁₂. Furthermore, the mechanism that is behind these effects of NbF₅ additive on the reversible dehydrogenation reaction of the LiBH₄–MgH₂ system is discussed.     

Effective nanoconfinement of 2LiBH4–MgH2 via simply MgH2 premilling for reversible hydrogen storages

To improve nanoconfinement of LiBH₄ and MgH₂ in carbon aerogel scaffold (CAS), particle size reduction of MgH₂ by premilling technique before melt infiltration is proposed. MgH₂ is premilled for 5 h prior to milling with LiBH₄ and nanoconfinement in CAS to obtained nanoconfined 2LiBH₄–premilled MgH₂. Significant confinement of both LiBH₄ and MgH₂ in CAS, confirmed by SEM–EDS–mapping results, is achieved due to MgH₂ premilling. Due to effective nanoconfinement, enhancement of CAS:hydride composite weight ratio to 1:1, resulting in increase of hydrogen storage capacity, is possible. Nanoconfined 2LiBH₄–premilled MgH₂ reveals a single–step dehydrogenation at 345 °C with no B₂H₆ release, while dehydrogenation of nanoconfined sample without MgH₂ premilling performs in multiple steps at elevated temperatures (up to 430 °C) together with considerable amount of B₂H₆ release. Activation energy (E_A) for the main dehydrogenation of nanoconfined 2LiBH₄–premilled MgH₂ is considerably lower than those of LiBH₄ and MgH₂ of bulk 2LiBH₄–MgH₂ (ΔE_A = 31.9 and 55.8 kJ/mol with respect to LiBH₄ and MgH₂, respectively). Approximately twice faster dehydrogenation rate are accomplished after MgH₂ premilling. Three hydrogen release (T = 320 °C, P(H₂) = 3–4 bar) and uptake (T = 320–325 °C, P(H₂) = 84 bar) cycles of nanoconfined 2LiBH₄–premilled MgH₂ reveal up to 4.96 wt. % H₂ (10 wt. % H₂ with respect to hydride composite content), while the 1st desorption of nanoconfined sample without MgH₂ premilling gives 4.30 wt. % of combined B₂H₆ and H₂ gases. It should be remarked that not only kinetic improvement and B₂H₆ suppression are obtained by MgH₂ premilling, but also the lowest dehydrogenation temperature (T = 320 °C) among other modified 2LiBH₄–MgH₂ systems is acquired.     

An investigation on the hydrogen storage properties and reaction mechanism of the destabilized MgH2–Na3AlH6 (4:1) system

A novel hydrogen storage composite system, MgH₂–Na₃AlH₆ (4:1), was prepared by mechanochemical milling, and its hydrogen storage properties and reaction mechanism were studied. Temperature-programmed desorption results showed that a mutual destabilization effect exists between the components. First, Na₃AlH₆ reacts with MgH₂ to form a perovskite-type hydride, NaMgH₃, Al, and H₂ at a temperature of about 170 °C, which is about 55 °C lower than the decomposition temperature of as-milled Na₃AlH₆. Then, at a temperature of about 275 °C, the as-formed Al can destabilize MgH₂ to form the intermetallic compound Mg₁₇Al₁₂, which is accompanied by the self-decomposition of the residual MgH₂. This temperature is about 55 °C lower than the decomposition temperature for as-milled MgH₂. Furthermore, when heated up to 345 °C, NaMgH₃ starts to decompose into NaH, Mg, and H₂, which is followed by the decomposition of NaH at a temperature of about 370 °C. Rehydrogenation processes show that Mg₁₇Al₁₂ and NaMgH₃ are fully reversible. It is believed that the Mg₁₇Al₁₂ and NaMgH₃ formed in situ provide synergetic thermodynamic and kinetic destabilization, leading to the dehydrogenation of MgH₂, which is responsible for the distinct reduction in the operating temperatures of the as-prepared MgH₂–Na₃AlH₆ (4:1) composite system.     

Effect of Mg content on structure,hydrogen storage properties and thermal stability of melt-spun Mgx(LaNi3)100−x alloys

Amorphous Mg_x(LaNi₃)_100−x (x = 40, 50, 60, 70) alloys with ribbon shape (5 mm wide, 0.2 mm thick) have been prepared by rapid solidification, using a melt-spinning technique. Their microstructure, hydrogen storage properties and thermal stability were studied by means of XRD, SEM, PCTPro2000 and DSC analysis, respectively. The results indicated that when Mg_x(LaNi₃)_100−x alloys have been hydrogenated at 573 K under 2 MPa hydrogen pressure, LaH₃ phase is formed in the case of x (x = 40, 50, 60, 70), Mg₂NiH₄ phase formed in the case of x (x = 40, 50, 60, 70), Mg₂NiH_0.3 phase formed in the case of x (x = 40, 50), and MgH₂ phase formed in the case of x = 70. Experimental data of hydrogen desorption kinetics, tested at 523 K, 573 K and 623 K, are in good agreement with Avrami–Erofeev equation. The maximum hydrogen absorption capacity is 2.71 wt.% for Mg₇₀(LaNi₃)₃₀ and 2.35 wt.% for Mg₇₀(LaNi₃)₃₀, the increase of hydrogen desorption capacity is in the order of x = 70 > x = 60 > x = 50 > x = 40. Based on DSC analysis, the activation energies for dehydrogenation of these samples are calculated to be 122 ± 2 kJ/mol (x = 40) > 101 ± 3 kJ/mol (x = 50) > 84 ± 5 kJ/mol (x = 60) > 64 ± 3 kJ/mol (x = 70), which are in agreement with the results of hydrogen desorption kinetics.     

Improved hydrogen storage properties of LiBH4 doped Li–N–H system

Remarkable improvement of hydrogen sorption properties of Li–N–H system has been obtained by doping with a small amount of LiBH₄. The starting and ending temperatures of hydrogen desorption shift to lower temperatures and the release of NH₃ is obviously restrained by 10 mol% LiBH₄ doping. The kinetics of hydrogen desorption and absorption of Li–N–H system became faster by the addition of LiBH₄. About 4 wt.% H₂ can be released within 30 min and ∼4.8 wt.% H₂ can be reabsorbed within 2 min by LiBH₄ doped sample at 250 °C, while only 1.44 wt.% H₂ is released and 2.1 wt.% is reabsorbed for pure Li–N–H system. The quaternary hydride (LiNH₂)_x(LiBH₄)_(1−x) formed by the reaction between LiBH₄ and LiNH₂ may contribute to the enhancement of the hydrogen sorption performances by yielding a ionic liquid phase and transferring LiNH₂ from solid state to molten state with a weakened N–H bond.     

Catalytically enhanced dehydrogenation of MgH2 by activated carbon supported Pd–VOx (x=2.38) nanocatalyst

In this paper, we reported that a new multi-component catalyst of activated carbon supported nanosized Pd and VO_x (Pd–VO_x/AC, x = 2.38) prepared by wet impregnation method exhibited significant catalytic effect on hydrogen desorption of MgH₂. It is demonstrated that the nanocomposites of MgH₂ + Pd–VO_x/AC prepared by ball milling could reduce the desorption temperature, e.g. differential scanning calorimetry (DSC) measurement indicated that the peak desorption temperature decreased ∼40 °C, and also improve the desorption kinetics of MgH₂, e.g. desorbed 6.5 wt% hydrogen within 30 min at 300 °C under an initial pressure of 1 kPa. A significant decrease of activation energy (E_a) indicated that Pd–VO_x/AC catalyst is highly efficient for MgH₂ dehydrogenation, which may be ascribed to the synergistic effect of nanometric bimetals (metal oxides) and nanocarbon.     

The hydrogen storage properties and reaction mechanism of the MgH2-NaAlH4 composite system

In this study, we report the hydrogen absorption/desorption properties and reaction mechanism of the MgH₂-NaAlH₄ (4:1) composite system. This composite system showed improved dehydrogenation performance compared with that of as-milled NaAlH₄ and MgH₂ alone. The dehydrogenation process in the MgH₂-NaAlH₄ composite can be divided into four stages: NaAlH₄ is first reacted with MgH₂ to form a perovskite-type hydride, NaMgH₃ and Al. In the second dehydrogenation stage, the Al phase reacts with MgH₂ to form Mg₁₇Al₁₂ phase accompanied with the self-decomposition of the excessive MgH₂. NaMgH₃ goes on to decompose to NaH during the third dehydrogenation stage, and the last stage is the decomposition of NaH. Kissinger analysis indicated that the apparent activation energy, E_A, for the MgH₂-relevent decomposition in MgH₂-NaAlH₄ composite was 148 kJ/mol, which is 20 kJ/mol less than for as-milled MgH₂ (168 kJ/mol). X-ray diffraction patterns indicate that the second, third, and fourth stages are fully reversible. It is believed that the formation of Al₁₂Mg₁₇ phase during the dehydrogenation process alters the reaction pathway of the MgH₂-NaAlH₄ (4:1) composite system and improves its thermodynamic properties.     

Catalytic effect of Ni, Mg2Ni and Mg2NiH4 upon hydrogen desorption from MgH2

MgH₂ is a perspective hydrogen storage material whose main advantage is a relatively high hydrogen storage capacity (theoretically, 7.6 wt.% H₂). This compound, however, shows poor hydrogen desorption kinetics. Much effort was devoted in the past to finding possible ways of enhancing hydrogen desorption rate from MgH₂, which would bring this material closer to technical applications. One possible way is catalysis of hydrogen desorption. This paper investigates separate catalytic effects of Ni, Mg₂Ni and Mg₂NiH₄ on the hydrogen desorption characteristics of MgH₂. It was observed that the catalytic efficiency of Mg₂NiH₄ was considerably higher than that of pure Ni and non-hydrated intermetallic Mg₂Ni. The Mg₂NiH₄ phase has two low-temperature modifications below 508 K: un-twinned phase LT1 and micro-twinned phase LT2. LT1 was observed to have significantly higher catalytic efficiency than LT2.     

Desorption properties of MgH2 composite with a composition of 40MgH2 + 37LiBH4 + 18MgF2 + 5Ti isopropoxide

In order to increase the hydrogen storage capacity of Mg-based materials, a mixture with a composition of 2LiBH₄ + MgF₂ and LiBH₄, which has a hydrogen storage capacity of 18.4 wt%, were added to MgH₂. Ti isopropoxide was also added to MgH₂ as a catalyst. A MgH₂ composite with a composition of 40 wt%MgH₂ + 25 wt%LiBH₄ + 30 wt% (2LiBH₄ + MgF₂) + 5 wt%Ti isopropoxide (corresponding to 40 wt%MgH₂ + 37 wt%LiBH₄ + 18 wt%MgF₂ + 5 wt%Ti isopropoxide) was prepared by reactive mechanical grinding. The hydrogen storage properties of the sample were then examined. Hydrogen content vs. desorption time curves for consecutive 1st desorptions of 40 wt%MgH₂ + 37 wt%LiBH₄ + 18 wt%MgF₂ + 5 wt%Ti isopropoxide from room temperature to 823 K showed that the total desorbed hydrogen quantity for consecutive 1st desorptions was 8.30 wt%.     

Reversible hydrogen storage behavior of LiBH4–Mg(OH)2 composites

The dehydrogenation/hydrogenation properties of LiBH₄-xMg(OH)₂ were systematically investigated. The results show that the LiBH₄-0.3Mg(OH)₂ composite possesses optimal dehydrogenation properties: approximately 9.6 wt% of hydrogen is released via a stepwise reaction with an onset temperature of 100 °C. In the range of 100–250 °C, a chemical reaction between LiBH₄ and Mg(OH)₂ first occurs to give rise to the generation of LiMgBO₃, MgO and H₂. From 250 to 390 °C, the newly developed LiMgBO₃ reacts with LiBH₄ to form MgO, Li₃BO₃, LiH, B₂O₃ and Li₂B₁₂H₁₂ with hydrogen release. From 390 to 450 °C, the decomposition of LiBH₄ and Li₂B₁₂H₁₂ proceeds to release additional hydrogen and to form LiH and B. A further hydrogenation experiment indicates that the dehydrogenated LiBH₄-0.3Mg(OH)₂ sample can take up 4.7 wt% of hydrogen at 450 °C and 100 bar of hydrogen with good cycling stability, which is superior to the pristine LiBH₄.     

A synergistic effect between nanoconfinement of carbon aerogels and catalysis of CoNiB nanoparticles on dehydrogenation of LiBH4

A synergistic effect of nanoconfinement and catalyzing is a new strategy to enhance the dehydrogenation properties of complex hydrides. Herein, LiBH₄ has been infiltrated into a CoNiB-loaded carbon aerogels system (donated as LiBH₄@CA@CoNiB). It is found that the desorption performances of LiBH₄ are significantly strengthened. The onset desorption temperature of LiBH₄@CA@CoNiB is decreased to 192 °C, and majority of the liberation occurs at about 320 °C, much lower than that of pure LiBH₄. Also, about 15.9 wt% H₂ could be released below 600 °C. Furthermore, LiBH₄ doped with CA@CoNiB exhibits an excellent desorption kinetics, with a capacity of 9.33 wt% H₂ released in 30 min at 350 °C, while only 2.13 wt% H₂ is gained for bulk LiBH₄. In addition, the apparent activation energy (Ea) is reduced sharply from 59.00 kJ/mol (pure LiBH₄) to 46.39 kJ/mol.     

First-principles studies of the structures and properties of Al- and Ag-substituted Mg2Ni alloys and their hydrides

The structures and properties of hydrogen storage alloy Mg₂Ni, of aluminum and silver substituted alloys Mg_2−xM_xNi (M = Al and Ag, x = 0.16667), and of their hydrides Mg₂NiH₄, Mg_2−xM_xNiH₄ (M = Al and Ag, x = 0.125) have been calculated from first-principles. Results show that the primitive cell sizes of the intermetallic alloys and hydrides were reduced by substitution of Mg with Al or Ag. Also, the interaction of Ni–Ni was weakened by the substitution. A strong covalent interaction between H and Ni atoms forms tetrahedral NiH₄ units in Mg₂NiH₄. The NiH₄ unit near the Al/Ag atom became tripod-like NiH₃ in Mg_2−xM_xNiH₄ (M = Al, Ag), indicating that the hydrogen storage capacity was decreased by the substitution. The calculated enthalpies of hydrogenation for Mg₂Ni, Mg_2−xAl_xNi and Mg_2−xAg_xNi are −65.14, −51.56 and −53.63 kJ/mol H₂, respectively, implying that the substitution destabilizes the hydrides. Therefore, the substitution is an effective technique for improving the thermodynamic behavior of hydrogenation/dehydrogenation in magnesium-based hydrogen storage materials.