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The composites comprised of Co nanoparticle and C nanosheet were prepared though a high-temperature carbonization reaction. The catalysis of Co@C composites on the hydrogen storage behavior of Mg90Ce5Y5 alloy was investigated in detail by XRD, SEM, TEM, PCI, and DSC method. Because of the synergistic catalytic function of C and Co in C@Co nanocomposites, the Mg90Ce5Y5 alloy with 10 wt.% C@Co shows the excellent hydrogen absorption and desorption performances. Time for releasing hydrogen reduces from 150 min to 11 min with the addition of the C@Co composites at the temperature of 300 °C. Meanwhile, the dehydrogenation activation energy also declines from 130.3 to 81.9 kJ mol−1 H2 after the addition of the C@Co composites. This positive effect attributes to the C layer with the high defect density and the Co nanoparticles, which reduces the energy barriers for the nucleation of Mg/MgH2 phase and the recombination of hydrogen molecule. Besides, the C@Co composites also improve the activation property of the Mg90Ce5Y5 alloy which was fully activated in the first cycle. Moreover, the temperature for initial dehydrogenation and the endothermic peak of the alloy hydride were also decreased. Although the addition of the C@Co composites increases the plateau pressures and decreases the value of the decomposition enthalpy, these differences are so small that the improvement on thermodynamics can hardly be seen.

In this investigation, mechanical grinding was applied to fabricating the Mg-based alloys La 7 Sm 3 Mg 80 Ni 10 + 5 wt.% M (M = None, TiO 2 , La 2 O 3) (named La 7 Sm 3 Mg 80 Ni 10 –5 M (M = None, TiO 2 , La 2 O 3)). The result reveals that the structures of as-milled alloys consist of amorphous and nanocrystalline. The particle sizes of the added M (M = TiO 2 , La 2 O 3) alloys obviously diminish in comparison with the M = None specimen, suggesting that the catalysts TiO 2 and La 2 O 3 can enhance the grinding efficiency. What's more, the additives TiO 2 and La 2 O 3 observably improve the activation performance and reaction kinetics of the composite. The time required by releasing 3 wt.% hydrogen at 553, 573 and 593 K is 988, 553 and 419 s for the M = None sample, and 578, 352 and 286 s for the M = TiO 2 composite, and 594, 366, 301 s for the La 2 O 3 containing alloy, respectively. The absolute value of hydrogenation enthalpy change |Δ H | of the M (M = None, TiO 2 , La 2 O 3) alloys is 77.13, 74.28 and 75.28 kJ/mol. Furthermore, the addition of catalysts reduces the hydrogen desorption activation energy (E a de). [ABSTRACT FROM AUTHOR]

The composites comprised of Co nanoparticle and C nanosheet were prepared though a high-temperature carbonization reaction. The catalysis of Co@C composites on the hydrogen storage behavior of Mg 90 Ce 5 Y 5 alloy was investigated in detail by XRD, SEM, TEM, PCI, and DSC method. Because of the synergistic catalytic function of C and Co in C@Co nanocomposites, the Mg 90 Ce 5 Y 5 alloy with 10 wt.% C@Co shows the excellent hydrogen absorption and desorption performances. Time for releasing hydrogen reduces from 150 min to 11 min with the addition of the C@Co composites at the temperature of 300 °C. Meanwhile, the dehydrogenation activation energy also declines from 130.3 to 81.9 kJ mol−1 H 2 after the addition of the C@Co composites. This positive effect attributes to the C layer with the high defect density and the Co nanoparticles, which reduces the energy barriers for the nucleation of Mg/MgH 2 phase and the recombination of hydrogen molecule. Besides, the C@Co composites also improve the activation property of the Mg 90 Ce 5 Y 5 alloy which was fully activated in the first cycle. Moreover, the temperature for initial dehydrogenation and the endothermic peak of the alloy hydride were also decreased. Although the addition of the C@Co composites increases the plateau pressures and decreases the value of the decomposition enthalpy, these differences are so small that the improvement on thermodynamics can hardly be seen. [ABSTRACT FROM AUTHOR]

The rare earth elements are believed to catalyze the reversible reaction between magnesium and hydrogen and reduce the thermal stability of MgH 2 by weakening the Mg–H bond. This study focuses on investigating the effect of Ce partial substitution of La on the comprehensive hydrogen storage performances of La 10- x Ce x Mg 80 Ni 10 (x = 0–4) alloys (prepared by vacuum induction melting). The phase composition and microstructure were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and high-resolution transmission electron microscopy (HRTEM). The thermodynamics and kinetics of isothermal reactions were measured by the automatic Sievert apparatus. Non-isothermal dehydrogenation performance of the alloys was researched by thermogravimetry analysis (TGA) and differential scanning calorimetry (DSC). All the experimental alloys have a large capacity of hydrogen absorption and desorption and the kinetics of the Ce containing alloys is better. The additive Ce exists in the solid solution of alloy and results in the refinement of grain, making the stability of the hydride visibly lower, which is the reason for the decline in the initial dehydrogenation temperature and enthalpy (Δ H) of the hydride. Besides, the dehydrogenation activation energy of the alloys is distinctly reduced by composition adjustment, which indicates the improved hydrogen storage performances. • The as-cast La 10- x Ce x Mg 80 Ni 10 (x = 0–4) alloys were prepared by induction melting. • Ce substitution of La optimizes the activation performance of experimental materials. • Substituting La with Ce weakens the stability of Mg-based hydrides. • Adding Ce is beneficial for improving the kinetics of experimental alloys. [ABSTRACT FROM AUTHOR]

The Mg-based hydrogen storage alloy with multiple platforms is successfully prepared by ball milling Co powder and Mg-RE-Ni precursor alloy, and its hydrogen storage behavior was investigated in detail by XRD, EDS, TEM, PCI, and DSC methods. The ball-milled alloy consists of the main phase Mg, the catalytic phases Mg 2 Ni, Mg 2 Co as well as a small amount of Mg 12 Ce, and convert into the MgH 2 –CeH 2.73 -Mg 2 NiH 4 –Mg 2 CoH 5 composite after hydrogenation. The composite has three PCI platforms corresponding to the reversible de/hydrogenation reaction of Mg/MgH 2 , Mg 2 Ni/Mg 2 NiH 4 and Mg 6 Co 2 H 11 /Mg 2 CoH 5. Among them, the transformation between Mg 2 Ni and Mg 2 NiH 4 triggers the "spill-over" effect which promote the decomposition of MgH 2 phases and enhances the hydrogen desorption kinetics. Meanwhile, the conversion of the Mg 6 Co 2 H 11 to Mg 2 CoH 5 phase induces the "chain reaction" effect, which leads to preferential nucleation of Mg phase and improves the hydrogen absorption kinetics. Therefore, the Mg-RE-Ni-Co alloy has a double improvement on hydrogen absorption and desorption kinetics. Concretely, the alloy has an optimal hydrogen absorption temperature of 200 °C, at which it can absorb 5.5 wt. % H 2 within 40 s. Under the conditions, the capacity of absorption almost reaches the maximum reversible value (about 5.6 wt. %). Besides, the alloy has a dehydrogenation activation energy of 67.9 kJ/mol and can desorb 5.0 wt. % H 2 within 60 min at the temperature of 260 °C. • The Mg-based hydrogen storage alloy with multiple platforms is successfully prepared. • The Ni-/Co-multi-platform collaborative system is built. • The Mg-RE-Ni-Co alloy has a double improvement in hydrogen absorption and desorption. • The alloy can absorb 5.5 wt. % H 2 within 40 s at 200 °C. • The dehydrogenation activation energy is evaluated to be 67.9 kJ/mol. [ABSTRACT FROM AUTHOR]

In this work, the Mg 90 Y 1.5 Ce 1.5 Ni 7 sample is successfully prepared by combining the vacuum induction melting and the mechanical milling. The phase composition and microstructure characteristics are studied by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy measurements. The hydrogenated sample is composed of MgH 2 , Mg 2 NiH 4 , CeH 2.73 phases, whereas only the MgH 2 and Mg 2 NiH 4 phases are decomposed during dehydrogenation. The hydrogen storage properties of Mg 90 Y 1.5 Ce 1.5 Ni 7 samples are measured by semi-automatic Sievert type apparatus. It is found that the samples could be fully activated within three cycles of absorption and dehydrogenation, with a reversible hydrogen storage capacity of about 5.6 wt%. Also, the "optimal hydrogenation temperature" is reduced to 200 °C, and the dehydrogenation activation energy is calculated to be 68.2 kJ/mol and 65.8 kJ/mol by using the Arrhenius and Kissinger equations, respectively. This work provides a scientific approach to promote the practical application of Mg-based alloy. • Samples were prepared by combining the induction melting and the mechanical milling. • The hydrogenated Mg 90 Y 1.5 Ce 1.5 Ni 7 sample has a nanocrystalline structure. • The "optimal hydrogenation temperature" was reduced to 200 °C through ball milling. • The dehydrogenation activation energy is evaluated to be 65.8 kJ/mol. [ABSTRACT FROM AUTHOR]

Transition metals and rare-earth elements have excellent catalytic effects on improving the de-/hydrogenation properties of Mg-based alloys. In this study, a small amount of La is used to substitute the Ni in Mg 98 Ni 2 alloy, and some Mg 98 Ni 2- x La x (x = 0, 0.33, 0.67, and 1) alloys show the better overall hydrogen storage properties. The effects of La on the solidification and de-/hydrogenation behaviors of the alloys are revealed. The results indicate that different factors dominate the processes of hydrogen absorption and desorption. The Mg 98 Ni 1·67 La 0.33 alloy absorb 7.04 wt % hydrogen at 300 °C, with the highest isothermal absorption rate, the Mg 98 Ni 1·33 La 0.67 hydride show the highest isothermal desorption rates and the lowest peak desorption temperature of 327 °C. The La addition can increase the driving force of hydrogenation, thus the hydrogenation rates and capacities of the Mg 98 Ni 1·67 La 0.33 and Mg 98 Ni 1·33 La 0.67 alloys are improved. The formation of refined eutectic structures is a key factor that facilitates the desorption processes of the Mg 98 Ni 2- x La x hydrides with x = 0.67 and 1. High-density LaH 3 nanophses are in-situ formed from the LaMg x (8.5 < x < 12) phase, which results in the improved de-/hydrogenation properties. The further La addition deteriorates the hydrogen storage properties of Mg 98 Ni 2- x La x alloy. • La addition can improve the hydrogen storage properties of Mg 98 Ni 2- x La x alloy. • Mg 98 Ni 1.67 La 0.33 alloy has a hydrogen capacity of 7.04 wt. % with fast absorption rate. • The peak desorption temperature of Mg 98 Ni 1.33 La 0.67 hydride is reduced to 327C from 394 °C. • The refined eutectic in Mg 98 Ni 1.67 La 0.33 and Mg 98 Ni 1.33 La 0.67 alloys facilitate the desorption process. [ABSTRACT FROM AUTHOR]

Mechanical milling is widely recognized as the best method to prepare nano-structured magnesium based hydrogen storage materials. The composites La 7 Sm 3 Mg 80 Ni 10 + 5 wt% TiO 2 (named La 7 Sm 3 Mg 80 Ni 10 –5TiO 2) whose structures are nano-crystal and amorphous accompanied by great hydrogen absorption and desorption properties were fabricated by mechanical milling. The research focuses on the effect of milling duration on the thermodynamics and dynamics. The instruments of researching the gaseous hydrogen storing performances include Sievert apparatus, DSC and TGA. The calculation of dehydrogenation activation energy was realized by applying Arrhenius and Kissinger formulas. The calculation results show the specimen milled for 10 h exhibits the optimal activation performance and hydrogenation and dehydrogenation kinetics. Extending or shrinking the milling duration will lead to the degradation of hydrogen storage performances. The as-milled (10 h) alloy at the full activated state can absorb 4 wt% hydrogen in 87 s at 473 K and 3 MPa and release 3 wt% H 2 in 288 s at 573 K and 1 × 10−4 MPa. The changed milling durations have little impact on the thermodynamic properties of experimental samples and the enthalpy change (Δ H) of the alloy milled for 10 h is 74.23 kJ/mol. Moreover, it is found that the as-milled (10 h) alloy displays the minimum apparent activation energy of dehydrogenation (59.1 kJ/mol), suggesting the optimal hydrogen storing property of the as-milled (10 h) alloy. • The composite La 7 Sm 3 Mg 80 Ni 10 + 5 wt% TiO 2 was prepared by mechanical milling. • The effect of milling time on hydrogen storage property was investigated. • Hydriding and dehydriding rates can be affected by milling time. • The as-milled (10 h) alloy shows the optimal gaseous hydrogen storage performance. [ABSTRACT FROM AUTHOR]

Abstract Mg 80– x Ni 20 Y x (x = 0–7) alloys were successfully prepared by using the vacuum induction melting method. The structural characterizations of the alloys were performed by using X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy measurements. The effects of yttrium content on the microstructure and hydrogen storage properties of the as-cast alloys were investigated. The alloys are composed of a primary phase of Mg 2 Ni, lamella eutectic composites of Mg + Mg 2 Ni, and some amount of YNi 3. The YNi 3 has completely transformed into in situ formed nanoscale YH 2 and YH 3 , with the formation of Mg 2 NiH 4. Pulverization of the alloy particles was observed during the hydrogen absorption and desorption cycles. However, the phase composition remains unchanged even after 20 hydrogenation cycles. Yttrium addition significantly improved the hydrogen-absorption kinetic performance of the alloy. In addition, pressure-composition-temperature measurements indicated that the entropy and enthalpy changes for the formation and decomposition of MgH 2 and Mg 2 NiH 4 gradually decreased with the increase of yttrium content. Highlights • YNi 3 , Mg 2 Ni and lamella eutectic Mg + Mg 2 Ni phases were observed in the alloys. • YNi 3 fully decomposed, with the formation of nanometer YH 2 and Mg 2 NiH 4. • Increasing Y content significantly improves the hydrogen absorption kinetics. • The decomposition peak temperature was reduced from 586 K to 523 K. • Δ H and Δ S of the Mg/MgH 2 and Mg 2 Ni/Mg 2 NiH 4 transformations decreased. [ABSTRACT FROM AUTHOR]

The four Mg-based bulk metallic glass forming alloys Mg 59.5 Cu 22.9 Ag 6.6 Gd 11 , Mg 61 Cu 28 Gd 11 , Mg 54 Cu 28 Ag 7 Y 11 , and Mg 65 Cu 25 Y 10 are investigated to gain insight into their thermodynamic and kinetic properties. Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) in three point beam bending mode are used. The gathered data sets are used to evaluate the origin of the high glass forming ability of these systems, which is found in low thermodynamic driving forces for crystallization and sluggish kinetics. Furthermore, sub-T g effects are observed via dynamic mechanical analysis (DMA) and modulated differential scanning calorimetry (MDSC) of as-cast samples. These are interpreted as related to the α-relaxation time spectrum instead of being caused by a Johari-Goldstein-type relaxation mechanism. [ABSTRACT FROM AUTHOR]

Ternary alloys with the nominal composition of Mg 24 Y 3 M (M = Ni, Co, Cu, Al) have been fabricated by using vacuum induction melting method. Their microstructure and phase composition are characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The isothermal hydrogen absorption and desorption kinetics are measured by a Sievert's-type apparatus. The dehydrogenation behaviors of the full hydrogenated alloys are also analyzed by differential scanning calorimetry (DSC) method. Results show that each and every alloy has a distinct multiphase structure containing the main phase Mg 24 Y 5 and some amount of Mg. Intermetallic compounds of YCo 2 and Al 2 Y are detected in the M = Co and M = Al alloy, while long-period stacking ordered (LPSO) phase can be also observed in M = Ni and M = Cu alloy. The hydrogen absorption and desorption kinetics shows a decreased trend in the following order: (M = Ni) > (M = Al) > (M = Co) > (M = Cu). The M = Ni alloy has the best hydrogen storage performance among the investigated alloys. The dehydrogenation activation energy ( E a ) of the M = Ni alloy decreases to 66 kJ/mol, and its decomposition peak temperature is also reduced to 313 °C. Moreover, the p – c – T (pressure-composition isotherms) curves of the studied alloys are also discussed. [ABSTRACT FROM AUTHOR]

Reducing particle size and modifying surface state by ball milling are recognized as a useful method to improve the hydrogen absorption kinetics of Mg-based alloys. In order to obtain amorphous and nanocrystalline structures, ball milling was used to process the as-cast La 7 Ce 3 Mg 80 Ni 10 alloy ingot. The effects of ball milling time (5–30 h) on the structures and the thermodynamics and kinetics of hydrogen absorption/desorption of the as-milled alloys were studied. The XRD, SEM and TEM were applied to investigate the structure of the alloys. The Sievert apparatus, DSC and TGA were applied to study the isothermal and non-isothermal properties of hydrogen absorption/desorption. The Arrhenius and Kissinger methods were used to calculate the activation energy of hydrogen desorption. The results indicate that the 10 h-milled alloy has the optimal activation performance and hydrogen absorption/desorption kinetics. Prolonging or shortening the ball milling time results in the impaired hydrogen storage properties. The 10 h-milled alloy in fully activation state can absorb 4 wt% H 2 in 80 s at 473 K and 3 MPa, and it can desorb 3 wt% H 2 in 191 s at 573 K and 1 × 10−4 MPa. The hydrogen desorption enthalpy (Δ H) of the 10 h-milled alloy is 74.21 kJ/mol. Moreover, the 10 h-milled alloy has the smallest apparent activation energy for hydrogen desorption (62.9 kJ/mol), which is the reason why it has the optimal hydrogen storage properties. • The La 7 Ce 3 Mg 80 Ni 10 alloy was successfully prepared and then treated by ball milling. • Prolonging milling time does not lead to continuous improvement in hydrogen storage properties of the alloy. • The La 7 Ce 3 Mg 80 Ni 10 sample milled for 10 h shows the optimal hydrogen storage performance. [ABSTRACT FROM AUTHOR]

In this experiment, the Mg-based hydrogen storage alloys SmMg 11 Ni and SmMg 11 Ni + 5 wt.% MoS 2 (named SmMg 11 Ni-5MoS 2 ) were prepared by mechanical milling. By comparing the structures and hydrogen storage properties of the two alloys, it could be found that the addition of MoS 2 has brought on a slight change in hydrogen storage thermodynamics, an obvious decrease in hydrogen absorption capacity, an obvious catalytic action on hydrogen desorption reaction, and a lowered onset desorption temperature from 557 to 545 K. Additionally, the addition of MoS 2 could dramatically improve the alloy in its hydrogen absorption and desorption kinetics. To be specific, the hydrogen desorption times of 3 wt.% H 2 at 593, 613, 633 and 653 K were measured to be 1488, 683, 390 and 192 s respectively for the SmMg 11 Ni alloy, which were reduced to 938, 586, 296 and 140 s for the MoS 2 catalyzed SmMg 11 Ni alloy at identical conditions. The activation energies of the alloys with and without MoS 2 for hydrogen desorption are 87.89 and 100.31 kJ/mol, respectively. The 12.42 kJ/mol decrease is responsible for the ameliorated hydrogen desorption kinetics by adding catalyst MoS 2 . [ABSTRACT FROM AUTHOR]

The high-quality Mg 2 (Ni 1− x Cu x ) ( x = 0, 0.05, 0.1 and 0.15) compounds have been successfully prepared by the method combining solid solution with sintering process in this paper. These prepared Mg 2 (Ni 1− x Cu x ) compounds can exhibit a reversible hydrogen ab-/desorption process, which are strongly subject to the content of Cu, i.e., depending on x . When x ≤ 0.1, the single hydride of Mg 2 (Ni 1− x Cu x )H 4 is observed upon hydrogenation. Unfortunately, the hydrogen-induced phase decomposition would occur when x > 0.1. For instance, the Mg 2 (Ni 0.85 Cu 0.15 ) compound absorbs hydrogen to form Mg 2 (Ni 0.9 Cu 0.1 )H 4 , Mg 2 Ni and MgCu 2 . Moreover, based on the structural analysis, the maximum solid solubility of Cu in Mg 2 (Ni 1− x Cu x )H 4 is determined for the first time to be about x = 0.1. The solid solubility of Cu thus leads to a significant decrease in Δ H d value from 64.4 kJ mol −1 H 2 for Mg 2 NiH 4 to 59.8 kJ mol −1 H 2 for Mg 2 Ni 0.9 Cu 0.1 H 4 . This result provides an efficient route for destabilizing the hydrogen desorption of Mg 2 Ni-based materials. [ABSTRACT FROM AUTHOR]

Abstract: A rapidly-solidified Mg–Ni–Pd alloy is shown to exhibit reversible hydrogen-storage of 5 mass % H at a temperature of 473 K, nearly 100 K below temperatures typically required for Mg-based alloys, with an equilibrium absorption plateau near 1 atm H2 pressure. Additionally, a single plateau is observed in the pressure–composition isotherm where MgH2 and Mg2NiH4 form and decompose simultaneously during the absorption/desorption process. The increase in absorption plateau pressure to 100 kPa suggests a decrease in the free energy by as much as 15 kJ/mol resulting from either a decrease in enthalpy or an increase in entropy of reaction between the hydride and metallic phases. The improved thermodynamics are discussed in terms of the formation of a new equilibrium metallic phase, Mg6(Ni,Pd). The phase alters the thermodynamics of the hydriding reaction, allowing both MgH2 and Mg2NiH4 to form cooperatively in a single reaction. This method for reducing the free energy of the hydriding reaction is promising, and may prove useful in a variety of other metal-hydride hydrogen-storage systems. [Copyright &y& Elsevier]

In this work, the multi-element Mg-based alloys, Mg 90 Ce 10 , Mg 90 Ce 5 Ni 5 , Mg 90 Ce 3 Ni 4 Y 3 , were prepared by combination technology of induction smelting and mechanical milling. Meanwhile, the phase evolution in reversible reaction as well as hydrogen storage behaviors of these alloys were investigated in detail by X-ray diffraction, Transmission Electron Microscope, and Pressure-Capacity-Temperature characterization methods. The results showed that the reaction mechanism of the Mg 90 Ce 10 alloy can be concluded as the reversible circulation of Mg/MgH 2 catalyzed by CeH 2.73 phase. After the addition of Ni and Y elements, the new reaction path is introduced in the system, including Mg 2 Ni + H 2 ↔ Mg 2 NiH 4 and YH 2 + H 2 ↔ YH 3. Thereinto, the Ni elements have a very obvious effect on improving the hydrogen absorption and desorption kinetics of the Mg-Ce alloy, which optimizes the optimal hydrogenated temperature to 250 °C and reduces the activation energy of hydrogen desorption from127.3 to 79.7 kJ/mol H 2. Meanwhile, the Ni elements also altered the rate limiting step of hydrogen desorption process of the Mg-Ce alloy from surface control to nucleation and growth control. However, after further addition of Y elements on this basis, the desorption kinetics of the Mg-Ce-Ni-Y-alloy could not be further improved, but its hydrogen absorption kinetics had an obvious enhancement. • New promoting mechanism can be introduced by the multiple alloying. • The Ce, Ni, Y can enhance the hydrogenated behavior of Mg-based alloy step by step. • Y-induced effect are overlaid by that of Ni element for dehydrogenated reaction. • The Mg 90 Ce 3 Ni 4 Y 3 sample can absorb more than 5.5 wt% hydrogen at 250 °C in 5 min. [ABSTRACT FROM AUTHOR]

The addition of transition elements as catalyst in the ball-milling process is reckoned as a very efficient method to ameliorate the hydrogen storage property of magnesium based materials. In this study, mechanical grinding was employed to prepare the Mg-based alloys La 7 Ce 3 Mg 80 Ni 10 + x wt% TiO 2 (x = 0–10) (named La 7 Ce 3 Mg 80 Ni 10 - x TiO 2 (x = 0–10)). The microstructure characterization of as-milled alloys was achieved with the help of XRD, SEM and TEM. The isothermal and non-isothermal hydrogen storing kinetics was measured by Sievert apparatus, DSC and TGA with H 2 detector. Hydrogen desorption activation energies were evaluated by Arrhenius and Kissinger methods. According to the result, the as-milled alloys possess an amorphous and nanocrystalline structure. Besides, the particle size of alloy containing TiO 2 obviously diminishes compared with the TiO 2 -free alloy, which suggests that the additive TiO 2 enhances the efficiency of mechanical milling. Moreover, the as-milled (x = 5) alloy has the optimal activation property, hydrogenation and dehydrogenation kinetics, and it absorbs 4 wt% H 2 in 45 s at 473 K and 3 MPa, desorbing 3 wt% H 2 in 172 s at 573 K and 1 × 10−4 MPa. The effect of TiO 2 content on the thermodynamics property of alloys is slight, and the absolute value of the dehydrogenation enthalpy change (Δ H) of the as-milled (x = 5) alloy is 73.03 kJ/mol. In addition, the as-milled (x = 5) alloy has the minimum dehydrogenation apparent activation energy (57.4 kJ/mol), which also explains why the as-milled (x = 5) alloy exhibits the optimal hydrogen storage property. • The composites La 7 Ce 3 Mg 80 Ni 10 - x TiO 2 were fabricated by mechanical milling. • The additive TiO 2 improves the reaction kinetics and activation ability. • The specimen with 5 wt.% TiO 2 has the minimum activation energy of 57.4 kJ/mol. [ABSTRACT FROM AUTHOR]

To improve hydrogen storage property of Mg-based alloy, the Mg–Ce–Y–Ni + 10 wt % M (M = Zr, Ti, V) composites were prepared by the combination of alloying and ball-milling, and their microstructure, phase evolution, as well as hydrogen storage thermodynamic and kinetic properties, were investigated by XRD, PCT, and DSC methods. The result shows that the hydrogenated samples are composed of MgH 2 , Mg 2 NiH 4 and corresponding ZrH 2 , TiH 2 and VH 1.9 phases. In comparison, the |Δ H| value of M = Ti sample is larger than that of M = Zr and M = V samples, and the M = Ti sample has the highest the peak temperatures and lowest plateau pressure, which indicates that Zr and V elements are more efficient to reduce the thermodynamic stability of RE-Mg-Ni hydrogen storage alloys. Besides, the DSC curve of the M = V sample has another endothermic peak which corresponds to the decomposition reaction between VH 1.9 and VH 0.8 , which has a contribution to desorption kinetic property for the M = V sample. The apparent activation energies (E de) show an increasing trend in the following order: M = Zr (87.7 kJ/mol) < M = V (89.1 kJ/mol) < M = Ti (99.3 kJ/mol). Because the reversible cycle between VH1.9 and VH0.8 provides the driving force to activate the hydrogen desorption of MgH 2, M V sample become an exception of the electronegative rule, and shows better dynamics property than M Ti sample. Image 1 • Mg–Ce–Y–Ni-TM composites are prepared by the combination of alloying and ball-milling. • The Zr and V elements are efficient to disorganize the thermodynamic Mg-based alloy. • The positive role of reversible reaction between the VH 1.9 and VH 0.8 is confirmed. • Activation energy is determined by the both of element property and reaction path. [ABSTRACT FROM AUTHOR]