Structural investigation and hydrogen storage properties of Ca3-xLaxMg2Ni13 alloys

The phase structures and hydrogen storage properties of the Ca_3-xLa_xMg₂Ni₁₃ alloys were investigated. It was found that the La substitution is unfavorable for the formation of the Ca₃Mg₂Ni₁₃-type phase. The La-substituted alloys consist of multiple phases. Increasing La content to x = 2.25 leads to a disappearance of Ca₃Mg₂Ni₁₃-type phase. Among these alloys, the Ca_1.5La_1.5Mg₂Ni₁₃ alloy has highest equilibrium pressures of hydrogen absorption–desorption and a highest hydrogen desorption capacity of 1.34 wt.% at 318 K. The discharge capacity decreases for La-substituted alloys. However, the cycling capacity retention rate (S₃₀) increases from 13.7 to 67.6% when x increases from 0 to 3.     

An electrochemical investigation of melt-spun nanocrystalline Mg20Ni10−xCux (x = 0–4) electrode alloys

The nanocrystalline Mg₂Ni-type electrode alloys with nominal compositions of Mg₂₀Ni_10−xCu_x (x = 0, 1, 2, 3, 4) were synthesized by the melt spinning technique. The microstructures of the as-cast and spun alloys were characterized by XRD, SEM and HRTEM. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system. The results show that all the as-spun alloys hold typical nanocrystalline structure instead of an amorphous phase. The melt spinning does not modify the major phase Mg₂Ni, but it leads to the formation of crystal defects such as stacking faults, dislocations, sub-grain boundary and twin-grain boundary. The melt spinning significantly improves the electrochemical hydrogen storage capacity of the alloys, whereas it slightly impairs the electrochemical cycle stability of the alloys. The substitution of Cu for Ni significantly ameliorates the electrochemical hydrogen storage performances of the alloys, involving both the electrochemical hydrogen storage capacity and the electrochemical charging and discharging stability.     

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.     

Hydrogen absorption in beryllium substituted Mg2Ni

The alloys Mg₂Ni_1–xBe_x (x = 0.15 and 0.25) retain the Mg₂Ni structure showing a lattice dilation proportional to the beryllium content. The pressure-composition isotherms are reported for the dissociation of hydrided samples. The results suggest that there are two type of interstices able to absorb up to 4 H atoms per formula unit. The heats of formation obtained from the van't Hoff relationship show an increased stability for the hydrides of the beryllium substituted alloys compared to the pure Mg₂Ni. The results suggest that the electronic factors are more important for hydride stability than variations in the unit cell volume.     

Improved hydrogen storage behaviours of nanocrystalline and amorphous Mg2Ni-type alloy by Mn substitution for Ni

The nanocrystalline and amorphous Mg₂Ni-type alloys with nominal compositions of Mg₂Ni_1−xMn_x (x = 0, 0.1, 0.2, 0.3, 0.4) were synthesized by melt spinning technique. The structures of the as-cast and spun alloys were characterized by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system. The results show that the as-spun (x = 0) alloy holds a typical nanocrystalline structure, whereas the as-spun (x = 0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni facilitates the glass formation in the Mg₂Ni-type alloy. The hydrogen absorption capacity of the alloys first increases then decreases with rising Mn content, but the hydrogen desorption capacity of the alloys grows with increasing Mn content. Furthermore, the substitution of Mn for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving both the discharge capacity and the electrochemical cycle stability. With an increase in the amount of Mn from 0 to 0.4, the discharge capacity of as-spun (30 m/s) alloy grows from 116.7 to 311.5 mAh/g, and its capacity retaining rate at 20th charging and discharging cycle rises from 36.7 to 78.7%.     

Synergistic effects of multiwalled carbon nanotubes and Al on the electrochemical hydrogen storage properties of Mg2Ni-type alloy prepared by mechanical alloying

Mg_2−xAl_xNi (x = 0, 0.25) electrode alloys with and without multiwalled carbon nanotubes (MWCNTs) have been prepared by mechanical alloying (MA) under argon atmosphere at room temperature using a planetary high-energy ball mill. The microstructures of synthesized alloys are characterized by XRD, SEM and TEM. XRD analysis results indicate that Al substitution results in the formation of AlNi-type solid solution that can interstitially dissolve hydrogen atoms. In contrast, the addition of MWCNTs hardly affects the XRD patterns. SEM observations show that after co-milling with 5 wt. % MWCNTs, the particle sizes of both Mg₂Ni and Mg_1.75Al_0.25Ni milled alloys are decreased explicitly. The TEM images reveal that ball milling is a good method to cut long MWCNTs into short ones. These MWCNTs aggregate along the boundaries and surfaces of milled alloy particles and play a role of lubricant to weaken the adhesion of alloy particles. The majority of MWCNTs retain their tubular structure after ball milling except a few MWCNTs whose tubular structure is destroyed. Electrochemical measurements indicate that all milled alloys have excellent activation properties. The Mg_1.75Al_0.25Ni-MWCNTs composite shows the highest discharge capacity due to the synergistic effects of MWCNTs and Al on the electrochemical hydrogen storage properties of Mg₂Ni-type alloy. However, the improvement on the electrode cycle stability by adding MWCNTs is unsatisfactory.     

Electronic structure and stability of new FCC magnesium hydrides Mg7MH16 and Mg6MH16 (M = Ti,V, Nb): An ab initio study

MgH₂ is one of the most promising materials for hydrogen storage. However, its rather slow hydrogen absorption and desorption kinetics and high dissociation temperature essentially limit its application in this field. Nevertheless mixing Mg or MgH₂ with small amount of transition metals or their oxides remarkably accelerates the hydrogen kinetics. Recently a series of new hydrides Mg₇TiH_x, Mg_6.5NbH_x and Mg₆VH_x of Ca₇Ge type structure has been synthesized. The hydrogen desorption properties have been found to be better than for pure MgH₂. Here, we report on the results of our theoretical study of the electronic structure of these new hydrides carried out within the framework of the full-potential, self-consistent linearized augmented plane-wave method. We use these results, along with calculations of the heat of formation and relative stability, to discuss the bonding of these materials and their hydrogen-storage properties.     

Studies on the thermal characteristics of hydrides of Mg,Mg2Ni,Mg2Cu and Mg2Ni1−xMx (M = Fe,Co, Cu or Zn; 0 < × < 1) alloys

X-ray results on the alloys of the composition Mg₂Ni_1−xM_x (M = Fe, Co, Cu or Zn; 0 < × < 1) suggest a Mg₂Ni-type structure. The alloys, Mg₂Ni_0.75M_0.25(M = Fe, Co, Cu or Zn) upon hydriding lead to the formation of quarternary hydrides while on dehydriding yield the starting ternary alloys except for copper containing alloys which show multi-phase regions and follow a different path way for the hydriding-dehydriding process. Thermal studies (TG-DTA) on the hydrides indicate the amount of hydrogen evolved as well as the desorption temperatures. The thermodynamic quantities, namely the enthalpies and entropies of formation of the hydrides were deduced from the DTA peak maximum temperature data. The kinetic parameters such as activation energies, reaction rates and orders of the reaction for the decomposition of the hydrides formed from Mg, Mg₂Ni and Mg₂Cu alloys were evaluated from the DTA data. As to the modified Mg₂Ni system, the copper substituted alloys show lower thermal stability and also presents some interesting properties. Hence, it is considered as one of the promising ternary combinations (Mg-Ni-Cu) for hydrogen storage purposes.     

Hydrogenation and dehydrogenation behaviours of nanocrystalline Mg20Ni10−xCux (x = 0−4) alloys prepared by melt spinning

In order to improve the hydriding and dehydriding kinetics of the Mg₂Ni-type alloys, Ni in the alloy was partially substituted by element Cu, and the nanocrystalline Mg₂Ni-type Mg₂₀Ni_10−xCu_x (x = 0, 1, 2, 3, 4) alloys were synthesized by melt-spinning technique. The structures of the as-cast and spun alloys were studied by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinetics of the alloys were measured using an automatically controlled Sieverts apparatus. The results show that the substitution of Cu for Ni does not change the major phase Mg₂Ni. The hydrogen absorption capacity of the alloys first increases and then decreases with rising Cu content, but the hydrogen desorption capacity of the alloys grows with increasing Cu content. The melt spinning significantly improves the hydrogenation and dehydrogenation capacity and kinetics of the alloys.     

Electrochemical hydrogen storage properties of Mg2−xAlxNi (x = 0, 0.3, 0.5, 0.7) prepared by hydriding combustion synthesis and mechanical milling

Mg_2−xAl_xNi (x = 0, 0.3, 0.5, 0.7) hydrogen storage alloys used as the negative electrode in a nickel–metal hydride (Ni–MH) battery were successfully prepared by means of hydriding combustion synthesis (HCS) and the selected alloy Mg_1.5Al_0.5Ni was further modified by mechanical milling (MM). The structural and electrochemical hydrogen storage properties of Mg_2−xAl_xNi alloys have been investigated in detail. XRD results show that a new phase Mg₃AlNi₂ that possesses an excellent cycling stability is observed with the substitution of Al for Mg. A short-time mechanical milling has a significant effect on improving the discharge capacity of the HCS product of Mg_1.5Al_0.5Ni. The maximum discharge capacity of Mg_1.5Al_0.5Ni ascends with increasing mechanical milling time and reaches the maximum 245.5 mAh/g when milled for 10 h. The alloy milled for 5 h shows the best electrochemical kinetics, which is due to its smaller mean particle size and uniform distribution of the particles. Further increasing in mechanical milling time could not bring about better electrochemical kinetics, which might be attributed to the agglomeration of the alloy particles and thus the charge-transfer reaction and hydrogen diffusion are restrained. It is suggested that the novel method of HCS + MM is promising to prepare ternary Mg-based intermetallic compound for electrochemical hydrogen storage.     

Structural characterization and electrochemical hydrogen storage properties of Mg2Ni1−xMnx(x = 0, 0.125, 0.25, 0.375) alloys prepared by mechanical alloying

Mg₂Ni_1−xMn_x(x = 0, 0.125, 0.25, 0.375) electrode alloys are prepared by mechanical alloying (MA) under argon atmosphere at room temperature using a planetary high-energy ball mill. The microstructures are characterized by XRD and SEM. XRD analysis results indicate that the substitution of Mn for Ni could inhibit the formation of MgNi₂ phase with the increases of x from 0 to 0.375. Replacing Ni with Mn can also promote the formation of the amorphous phase when x increases from 0 to 0.25 for the MA alloys milled for 48 h. The new phase Mg₃MnNi₂ is formed only when x = 0.375 after 48 h of milling. This new phase belongs to the face-centered cubic lattice (Fd-3m) with the lattice constant a being 1.1484 nm. Estimated from the peaks broadening, the crystallite size and lattice strain of Mg₃MnNi₂ phase are 15.6 ± 3.6 nm and 1.09 ± 0.34%, respectively. Curve fit of XRD shows that amorphous and nanocrystalline Mg₂Ni coexist in the Mg₂Ni_1−xMn_x (x = 0, 0.125, 0.25) alloys milled for 48 h. The SEM observation reveals that all the MA alloys particles are mainly flaky and show cleavage fracture morphology and these particles are agglomerates of many smaller particles, namely subparticles. Electrochemical measurements indicate that all MA alloys have excellent activation properties. The discharge capacities of MA alloys increase with the prolongation of milling time. For 16 h of milling, with the increase of Mn content, the discharge capacities of Mg₂Ni_1−xMn_x (x = 0, 0.125, 0.25, 0.375) MA alloys monotonously decrease. For 24 h of milling, the discharge capacities of the Mg₂Ni_1−xMn_x (x = 0, 0.125, 0.25, 0.375) alloys also show a rough tendency to decrease with the increase of Mn content except Mg₂Ni_0.875Mn_0.125 MA alloy. On the other hand, for 48 h of milling, as the rise of Mn content from x = 0.125 to 0.375, the discharge capacities increase. Mg(OH)₂ is formed during charge/discharge cycles in the KOH solution for all MA alloys. After 48 h of milling, the substitution of Mn for Ni for x = 0.25 improves the cycle stability at the expense of decreasing the discharge capacity. In contrast, Mg₃MnNi₂ phase is relatively stable during charge/discharge cycles and therefore can significantly enhance the cycle stability under simultaneously maintaining a high discharge capacity.     

Solid solubility of Mg in Ca2Ni7 and hydrogen storage properties of (Ca2−xMgx)Ni7 alloys

The phase relations and hydrogen storage properties of the (Ca_2−xMg_x)Ni₇ alloys were investigated. It was found that the maximum solid solubility of Mg in the (Ca,Mg)₂Ni₇ phase is about x = 0.5 in the present study. The ‘inter-block-layer’ type stacking faults exist in the (Ca,Mg)₂Ni₇ phase when Mg content is very low. However, the density of stacking faults decreases and the lattice parameters reduce as Mg content increases to its maximum solid solubility. Thus the (Ca_1.5Mg_0.5)Ni₇ alloy has a good reversibility of hydrogen absorption–desorption.     

Electrochemical performances of the as-melt La0.75−xMxMg0.25Ni3.2Co0.2Al0.1 (M = Pr,Zr; x = 0, 0.2) alloys applied to Ni/metal hydride (MH) battery

The partial replacement of La by M (M = Pr, Zr) has been performed in order to ameliorate the electrochemical hydrogen storage performances of La–Mg–Ni-based A₂B₇-type electrode alloys. For this purpose, we adopt melt spinning technology to prepare the La_0.75−xM_xMg_0.25Ni_3.2Co_0.2Al_0.1 (M = Pr, Zr; x = 0, 0.2) electrode alloys. Then systemically investigate the effects that the preparation methods and M (M = Pr, Zr) substitution have on the structures and electrochemical hydrogen storage characteristics of the alloys. The analysis of XRD and TEM reveals that the as-cast and spun alloys hold a multiphase structure, containing two main phases (La, Mg)₂Ni₇ and LaNi₅ as well as a trace of residual phase LaNi₂. Besides, the as-spun (M = Pr) alloy displays an entire crystalline structure, while an amorphous-like structure is detected in the as-spun (M = Zr) alloy, implying the replacement of La by Zr facilitates forming amorphous phase. Based upon electrochemical measurements, an impact engendered by melt spinning on the electrochemical performances of the alloys appears to be evident. The cycle stabilities monotonously augment with the growing of the spinning rate. The discharge capacity and high rate discharge ability (HRD), however, exhibit difference. For the (M = Pr) alloy, they first mount up and then fall with the rising of the spinning rate, whereas for the (M = Zr) alloy, they always decline as the spinning rate elevates. Furthermore, the replacement of La by M (M = Pr, Zr) considerably enhances the cycle stability of the alloys and the replacement of La by Pr clearly increases the discharge capacity, but the Zr replacement results in an adverse impact.     

Effect of Mg3MnNi2 on the electrochemical characteristics of Mg2Ni electrode alloy

Mg₂Ni–x mol% Mg₃MnNi₂ (x = 0, 15, 30, 60, 100), the novel composite alloys employed for hydrogen storage electrode, have been successfully synthesized by a method combining electric resistance melting with isothermal evaporation casting process (IECP). X-ray diffraction (XRD) analysis results show that the composite alloys are composed of Mg₂Ni phases and the new Mg₃MnNi₂ phases. It is found on the electrochemical studies that maximum discharge capacities of the composite alloys increase with the increasing content of the Mg₃MnNi₂ phase. The discharge capacity of the electrode alloy is effectively improved from 17 mAh g⁻¹ of the Mg₂Ni alloy to 166 mAh g⁻¹ of the Mg₃MnNi₂ alloy. Among these alloys, the Mg₃MnNi₂ phase possesses a positive effect on the retardation of cycling capacity degradation rate of the electrode materials. Cyclic voltammetry (CV) results confirm that the increasing content of the Mg₃MnNi₂ phase effectively improves the reaction activity of the electrode alloys. Surface analyses indicate that the Mg₃MnNi₂ phase can enhance the anti-corrosive performance of the particle surface of these composite alloys.     

Comparative investigations on the hydrogenation characteristics and hydrogen storage kinetics of melt-spun Mg10NiR (R = La,Nd and Sm) alloys

The hydrogenation characteristics and hydrogen storage kinetics of the melt-spun Mg₁₀NiR (R = La, Nd and Sm) alloys have been studied comparatively. It is found that the Mg₁₀NiNd and Mg₁₀NiSm alloys are in amorphous state but the Mg₁₀NiLa alloy is composed of an amorphous phase and minor crystalline La₂Mg₁₇ after melt-spinning. The alloys can be hydrogenated into MgH₂, Mg₂NiH₄ and a rare earth metal hydride RH_x. The rare earth metal hydride and Mg₂NiH₄ synergistically provide a catalytic effect on the hydrogen absorption–desorption reactions in the Mg−H₂ system. The hydrogen storage kinetics is not influenced by different rare earth metal hydrides but by the particle size of the rare earth metal hydrides.     

Microstructure and electrochemical hydrogen storage characteristics of (La0.7Mg0.3)1−xCexNi2.8Co0.5 (x = 0-0.20) electrode alloys

The microstructure and electrochemical hydrogen storage characteristics of (La_0.7Mg_0.3)_1−xCe_xNi_2.8Co_0.5 (x = 0, 0.05, 0.10, 0.15 and 0.20) alloys have been investigated. The results show that all alloys consist of (La, Mg)Ni₃ and LaNi₅ phases. The cyclic stability (S₁₀₀) of the alloy electrodes increases from 58.7% (x = 0) to 69.8% (x = 0.20) after 100 charge/discharge cycles. The high rate dischargeability (HRD) increases from 66.8% (x = 0) to 69.6% (x = 0.10), then decreases to 65.1% (x = 0.20) at the discharge current density of 1200 mA/g. Moreover, the electrochemical kinetic characteristics of the alloy electrodes are also improved by increasing Ce content.     

First-principles study on the dehydrogenation properties and mechanism of Al-doped Mg2NiH4

Mg₂NiH₄, with fast sorption kinetics, is considered to be a promising hydrogen storage material. However, its hydrogen desorption enthalpy is too high for practical applications. In this paper, first-principles calculations based on density functional theory (DFT) were performed to systematically study the effects of Al doping on dehydrogenation properties of Mg₂NiH₄, and the underlying dehydrogenation mechanism was investigated. The energetic calculations reveal that partial component substitution of Mg by Al results in a stabilization of the alloy Mg₂Ni and a destabilization of the hydride Mg₂NiH₄, which significantly alters the hydrogen desorption enthalpy ΔH_des for the reaction Mg₂NiH₄ → Mg₂Ni + 2H₂. A desirable enthalpy value of ∼0.4 eV/H₂ for application can be obtained for a doping level of x ≥ 0.35 in Mg_2−xAl_xNi alloy. The stability calculations by considering possible decompositions indicate that the Al-doped Mg₂Ni and Mg₂NiH₄ exhibit thermodynamically unstable with respect to phase segregation, which explains well the experimental results that these doped materials are multiphase systems. The dehydrogenation reaction of Al-doped Mg₂NiH₄ is energetically favorable to perform from a metastable hydrogenated state to a multiphase dehydrogenated state composed of Mg₂Ni and Mg₃AlNi₂ as well as NiAl intermetallics. Further analysis of density of states (DOS) suggests the improving of dehydrogenation properties of Al-doped Mg₂NiH₄ can be attributed to the weakened Mg-Ni and Ni-H interactions and the decreasing bonding electrons number below Fermi level. The mechanistic understanding gained from this study can be applied to the selection and optimization of dopants for designing better hydrogen storage materials.     

Electrochemical hydrogen storage characteristics of Mg1.5Al0.5−xZrxNi (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) alloys synthesized by mechanical alloying

Mg_1.5Al_0.5−xZr_xNi (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) type alloys were synthesized by mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. X-ray diffraction studies showed that Zr facilitated the amorphization of Mg₂Ni phase, while Al retarded the amorphization of this phase. The increase in the Zr content was observed to bring about significant improvement in the discharge capacities at all the ball milling durations. The stepwise replacement of Al with Zr, however, caused considerable reduction in the initial discharge capacities of the alloys. Despite the adverse effect of Al on the initial discharge capacity, it prevented the rapid degradation of Mg₂Ni phase with the charge/discharge cycles. When the beneficial effects of Zr and Al were combined by designing Mg_1.5Al_0.5−xZr_xNi type alloys, Mg_1.5Al_0.2Zr_0.3Ni alloy was found to have the highest discharge capacity at almost all the charge/discharge cycle steps. Among the obtained capacity retaining rates, Mg_1.5Al_0.4Zr_0.1Ni alloy had the best performance. This alloy has kept at least 50% of its initial discharge capacity at 20th cycle. The analysis by the electrochemical impedance spectroscopy revealed that the charge transfer resistances of Al-rich alloys were low at high depth of discharges. This observation was attributed to the formation of the porous unstable Mg(OH)₂ layer due to the intercalation of Al₂O₃ layers, which have the high rate of solubility in strongly basic solutions, and thus the exposition of the underlying electrocatalytically active Ni sites.     

Hydrogen storage characteristics of the nanocrystalline and amorphous Mg–Nd–Ni–Cu-based alloys prepared by melt spinning

Nanocrystalline and amorphous Mg–Nd–Ni–Cu-based (Mg₂₄Ni₁₀Cu₂)_100−xNd_x (x = 0–20) alloys were prepared by melt spinning and their structures as well as hydrogen storage characteristics were investigated. The analysis of XRD, TEM and SEM linked with EDS reveal that all the as-cast alloys hold a multiphase structure, containing Mg₂Ni-type major phase as well as some secondary phases Mg₆Ni, Nd₅Mg₄₁ and NdNi, whose amounts clearly grow with Nd content rising. Furthermore, the as-spun Nd-free alloy displays an entire nanocrystalline structure whereas the as-spun Nd-added alloys have a mixed structure of nanocrystalline and amorphous, moreover, the amorphization degree of the alloys visibly increases with Nd content rising, implying that the addition of Nd facilitates the glass forming in the Mg₂Ni-type alloy. The addition of Nd results in a slight decrease in the hydrogen absorption capacity of the as-cast and spun alloys, but it significantly enhances their hydrogen storage kinetics and hydriding/dehydriding cycle stability of the alloy. In order to reveal the capacity degradation mechanism of the as-spun alloy, the structure evolution of the nanocrystalline and amorphous alloys during the hydriding–dehydriding cycles was investigated. It is found that the root causes of leading to the capacity degradation of the nanocrystalline and amorphous alloys are nanocrystalline coarsening, crystal defect decreasing and amorphous phase crystallizing.     

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.