Cold rolling of MgH2 powders containing different additives

In this study we have used cold rolling (CR) as a successful method to incorporate additives into MgH₂. The mixtures of MgH₂ + 2 Mol% X, with X = Fe, Nb, Fe₂O₃, Nb₂O₅, FeF₃, were processed by CR using a horizontal rolling mill and then followed by a detailed microstructural characterization which includes X-ray diffraction (XRD) with Rietveld refinement, Differential Scanning Calorimetry (DSC) and kinetic measurements. The CR processing resulted in a drastic crystallite size reduction, ∼8–17 nm, strong texture and partial conversion from the β to the γ-MgH₂ phase. The orthorhombic metastable NbH_x phase was detected in the XRD pattern of the mixture MgH₂ + Nb after CR, indicating the high energy involved in the CR processing. The samples containing Fe and FeF₃ as additives presented the lowest desorption temperature ranges. All additives presented beneficial effect on the dehydrogenation kinetic measurements (measured at 623 K and 598 K) compared to pure MgH₂, in especial for the samples containing Nb₂O₅ and FeF₃.     

Hydrogen desorption properties of MgH2-TiCr1.2Fe0.6 nanocomposite prepared by high-energy mechanical alloying

In the present work, high-energy mechanical alloying (MA) was employed to synthesize a nanostructured magnesium-based composite for hydrogen storage. The preparation of the composite material with composition of MgH₂-5 at% (TiCr_1.2Fe_0.6) was performed by co-milling of commercial available MgH₂ powder with the body-centered cubic (bcc) alloy either in the form of Ti-Cr-Fe powder mixture with the proper mass fraction (sample A) or prealloyed TiCr_1.2Fe_0.6 powder (sample B). The prealloyed powder with an average crystallite size of 14 nm and particle size of 384 nm was prepared by the mechanical alloying process. It is shown that the addition of the Ti-based bcc alloy to magnesium hydride yields a finer particle size and grain structure after mechanical alloying. As a result, the desorption temperature of mechanically activated MgH₂ for 4 h decreased from 327 °C to 262 °C for sample A and 241 °C for sample B. A high dehydrogenation capacity (∼5 wt%) at 300 °C is also obtained. The effect of the Ti-based alloy on improvement of the dehydrogenation is discussed.     

Influence of multiple oxide (Cr2O3/Nb2O5) addition on the sorption kinetics of MgH2

The influence of multiple additions of two oxides, Cr₂O₃ and Nb₂O₅, as additives on the hydrogen sorption kinetics of MgH₂ after milling was investigated. We found that the desorption kinetics of MgH₂ were improved more by multiple oxide addition than by single addition. Even for the milled MgH₂ micrometric size powders, the high hydrogen capacity with fast kinetics were achieved for the powders after addition of 0.2 mol% Cr₂O₃ + 1 mol% Nb₂O₅. For this composition, the hydride desorbed about 5 wt.% hydrogen within 20 min and absorbed about 6 wt.% in 5 min at 300 °C. Furthermore, the desorption temperature was decreased by 100 °C, compared to MgH₂ without any oxide addition, and the activation energy for the hydrogen desorption was estimated to be about 185 kJ mol⁻¹, while that for MgH₂ without oxide was about 206 kJ mol⁻¹.     

Enhanced hydrogen storage properties of 4MgH2 + LiAlH4 composite system by doping with Fe2O3 nanopowder

In this paper, the hydrogen storage properties and reaction mechanism of the 4MgH₂ + LiAlH₄ composite system with the addition of Fe₂O₃ nanopowder were investigated. Temperature-programmed-desorption results show that the addition of 5 wt.% Fe₂O₃ to the 4MgH₂ + LiAlH₄ composite system improves the onset desorption temperature to 95 °C and 270 °C for the first two dehydrogenation stage, which is lower 40 °C and 10 °C than the undoped composite. The dehydrogenation and rehydrogenation kinetics of 5 wt.% Fe₂O₃-doped 4MgH₂ + LiAlH₄ composite were also improved significantly as compared to the undoped composite. Differential scanning calorimetry measurements indicate that the enthalpy change in the 4MgH₂–LiAlH₄ composite system was unaffected by the addition of Fe₂O₃ nanopowder. The Kissinger analysis demonstrated that the apparent activation energy of the 4MgH₂ + LiAlH₄ composite (125.6 kJ/mol) was reduced to 117.1 kJ/mol after doping with 5 wt.% Fe₂O₃. Meanwhile, the X-ray diffraction analysis shows the formation of a new phase of Li₂Fe₃O₄ in the doped composite after the dehydrogenation and rehydrogenation process. It is believed that Li₂Fe₃O₄ acts as an actual catalyst in the 4MgH₂ + LiAlH₄ + 5 wt.% Fe₂O₃ composite which may promote the interaction of MgH₂ and LiAlH₄ and thus accelerate the hydrogen sorption performance of the MgH₂ + LiAlH₄ composite system.     

Integrated Ni/Nb2O5 nanocatalytic agent dose for improving the hydrogenation/dehydrogenation kinetics of reacted ball milled MgH2 powders

Reactive ball milling (RBM) technique was employed to synthesize ultrafine powders of MgH₂, using high energy ball mill operated at room temperature under 50 bar of a hydrogen gas atmosphere. The MgH₂ powders obtained after 200 h of continuous RBM time composed of β and γ phases. The powders possessed nanocrystalline characteristics with an average grain of about 10 nm in diameter. The time required for complete hydrogen absorption and desorption measured at 250 °C was 500 s and 2500 s, respectively. In order to improve the hydrogenation/dehydrogenation kinetics of as synthesized MgH₂ powders, three different types of nanocatalysts (metallic Ni, Nb₂O₅ and (Ni)_x/(Nb₂O₅)_y) were utilized with different weight percentages and independently ball milled with the MgH₂ powders for 50 h under 50 bar of a hydrogen gas atmosphere. The results showed that the prepared nanocomposite MgH₂/5Ni/5Nb₂O₅ powders possessed superior hydrogenation/dehydrogenation characteristics, indexed by low values of activation energy for β-phase (68 kJ/mol) and γ-phase (74 kJ/mol). This nanocomposite system showed excellent hydrogenation/dehydrogenization behavior, indexed by the short time required to uptake (41 s) and release (121 s) of 5 wt% H₂ at 250 °C. At this temperature the synthesized nanocomposite powders possessed excellent absorption/desorption cyclability of 180 complete cycles. No serious degradation on the hydrogen storage capacity could be detected and the system exhibited nearly constant absorption and desorption values of +5.46 and −5.46 wt% H₂, respectively.     

Studies on de/rehydrogenation characteristics of nanocrystalline MgH2 co-catalyzed with Ti,Fe and Ni

In the present study, we have investigated the combined effect of different transition metals such as Ti, Fe and Ni on the de/rehydrogenation characteristics of nano MgH₂. Mechanical milling of MgH₂ with 5 wt% each of Ti, Fe and Ni for 24 h at 12 atm of H₂ pressure lead to the formation of nano MgH₂-Ti5Fe5Ni5. The decomposition temperature of nano MgH₂-Ti5Fe5Ni5 is lowered by 90 °C as compared to nano MgH₂ alone. It is also found that the nano MgH₂-Ti5Fe5Ni5 absorbs 5.3 wt% within 15 min at 270 °C and 12 atm hydrogen pressures. However, nano MgH₂ reabsorbs only 4.2 wt% under identical condition. An interesting result of the present study is that mechanical milling of MgH₂ separately with Fe and Ni besides refinement in particle size also leads to the formation of alloys Mg₂NiH₄ and Mg₂FeH₆ respectively. On the other hand, when MgH₂ is mechanically milled together with Ti, Fe and Ni, the dominant result is the formation of nano particles of MgH₂. Moreover the activation energy for dehydrogenation of nano MgH₂ co-catalyzed with Ti, Fe and Ni is 45.67 kJ/mol which is 35.71 kJ/mol lower as compared to activation energy of nano MgH₂ (81.34 kJ/mol). These results are one of the most significant in regard to improvement in de/rehydrogenation characteristics of known MgH₂ catalyzed through transition metal elements.     

Effect of Nb2O5 on MgH2 properties during mechanical milling

Recently, it was shown that hydrogen absorption–desorption kinetics in magnesium were improved by milling magnesium hydride (MgH₂) with transition metal oxides. Herein, we investigate the role of the most effective of these oxides, Nb₂O₅ when added in larger volume fraction. The effect of Nb₂O₅ on magnesium crystalline structure, particle size and (ab)desorption properties has been characterised. Moreover, we report that pure MgH₂ can also show fast hydrogen sorption kinetics after a long milling time. The effects of Nb₂O₅ on MgH₂ sorption properties are rationalised in a new approach considering Nb₂O₅ as a dispersing agent, which helps reduce MgH₂ particle size during milling.     

Rehydrogenation performance of an MgH2–Nb2O5 system modified by heptane and acetone

An MgH₂ + 1 mol% Nb₂O₅ system was modified by heptane and acetone through a high-energy ball milling process, and their rehydrogenation performances were investigated. XRD results indicated that except MgH₂ and Nb₂O₅ phases Mg and MgO phases existed after ball milling. The rehydrogenation results showed that after modification by heptane the capacity increased from 3.0 wt% and 4.2 wt% to 5.0 wt% and 5.5 wt% within 110 s at 523 K and 573 K, respectively. The hydriding rate increased from 0.08 wt%/s after 20 s to 0.22 wt%/s after 10 s at 523 K. However, after modification by acetone it only absorbed 1.8 wt% and 2.0 wt% of hydrogen even within 8000 s at 523 K and 573 K, respectively. Rietveld refinement results indicated that after modification by the heptane the content of MgO was reduced from 6.8 wt% to 4.2 wt%, while after the modification by the acetone the content of MgO was significantly increased from 6.8 wt% to 23.8 wt%. The difference in the rehydrogenation performance was believed to be attributed to the different contents of the MgO phase, which led to the difference in the contents of the MgH₂ phase. It implied that the heptane acted as a solvent without oxygen element in it to prevent the MgH₂ + Nb₂O₅ system from aggregation, crystallization and oxidation. It suggested heptane was suitable for the improvement of the rehydrogenation performance of MgH₂ system.     

Synthesis of catalytically active rock salt structured MgxNb1−xO nanoparticles for MgH2 system

This communication deals with the ex-situ synthesis of rock salt type Mg_xNb_1−xO whose structural characteristics are closely related with MgO. XRD examination of 30 h ball milled MgH₂ + Nb₂O₅ confirms the formation of a rock salt product Mg_xNb_1−xO_, which is comparable to the recently reported active catalyst Mg_xNb_1−xO formed in-situ in MgH₂ milled with 8 mol.% Nb₂O₅. It is shown that MgH₂ catalyzed with the pre-made 2 wt.% Mg_xNb_1−xO desorbs hydrogen at least 50 °C lower than the in-situ 2 wt.% Nb₂O₅ catalyzed MgH₂ with improved reversible absorption. This result highlights that the proposed pathway mechanism on the basis of Nb₂O₅ catalyst may need further verification and that the addition of the Mg_xNb_1−xO catalyst in a pre-reduced state can offer distinct performance advantages over its in-situ preparation.     

The synthesis of nanoscopic Ti based alloys and their effects on the MgH2 system compared with the MgH2 + 0.01Nb2O5 benchmark

The MgH₂ + 0.02Ti-additive system (additives = 35 nm Ti, 50 nm TiB₂, 40 nm TiC, <5 nm TiN, 10 × 40 nm TiO₂) has been studied by high-resolution synchrotron X-ray diffraction, after planetary milling and hydrogen (H) cycling. TiB₂ and TiN nanoparticles were synthesised mechanochemically whilst other additives were commercially available. The absorption kinetics and temperature programmed desorption (TPD) profiles have been determined, and compared to the benchmark system MgH₂ + 0.01Nb₂O₅ (20 nm). TiC and TiN retain their structures after milling and H cycling. The TiB₂ reflections appear compressed in d-spacing, suggesting Mg/Ti exchange has occurred in the TiB₂ structure. TiO₂ is reduced, commensurate with the formation of MgO, however, the Ti is not evident anywhere in the diffraction pattern. The 35 nm Ti initially forms an fcc Mg_47.5Ti_52.5 phase during milling, which then phase separates and hydrides to TiH₂ and MgH₂. At 300 °C, the MgH₂ + 0.02 (Ti, TiB₂, TiC, TiN, TiO₂) samples display equivalent absorption kinetics, which are slightly faster than the MgH₂ + 0.01Nb₂O₅ (20 nm) benchmark. All samples are contaminated with MgO from the use of a ZrO₂ vial, and display rapid absorption to ca. 90% of capacity within 20 s at 300 °C. TPD profiles of all samples show peak decreases compared to the pure MgH₂ milled sample, with many peak profiles displaying bi-modal splitting. TPD measurements on two separate instruments demonstrate that on a 30 min milling time scale, all samples are highly inhomogenous, and samplings from the exact same batch of milled MgH₂ + 0.02Ti-additive can display differences in TPD profiles of up to 30 °C in peak maxima. The most efficient Ti based additive cannot be discerned on this basis, and milling times ? 30 min are necessary to obtain homogenous samples, which may lead to artefactual benefits, such as reduction in diffusion distances by powder grinding or formation of dense microstructure. For the hydrogen cycled MgH₂ + 0.01Nb₂O₅ system, we observe a face centred cubic Mg/Nb exchanged Mg_0.165Nb_0.835O phase, which accounts for ca. 60% of the originally added Nb atoms.     

Solid-state synthesis of amorphous TiB2 nanoparticles on graphene nanosheets with enhanced catalytic dehydrogenation of MgH2

A bi-component catalyst TiB₂/GNSs (GNSs is the abbreviation of graphene nanosheets) is synthesized by a solid-state method. Microstructural characterizations based on SEM (scanning electron microscopy), TEM (transmission electron microscopy) and N₂ physisorption show that the size of TiB₂/GNSs catalyst is at nanoscale (20–30 nm) with a surface area of 84.69 m² g⁻¹. The TiB₂/GNSs nanoparticles ball milled with MgH₂ and exhibit enhanced catalytic effects on the dehydrogenation properties of MgH₂ compares to TiB₂ and GNSs individually. DSC (differential scanning calorimetry) measurements confirm that the peak desorption temperature of MgH₂-5 wt%TiB₂/GNSs composites can be lowered more than 44 °C than the pure as-milled MgH₂. And the dehydrogenation kinetics of TiB₂/GNSs-doped MgH₂ is severalfold acceleration compares to the pure as-milled MgH₂. It is proposed that the TiB₂/GNSs nanoparticles could significantly enhance the intimate interface between TiB₂/GNSs and hydride, therefore, provide more active “catalytic sites” and H “diffusion channels” to reduce the dehydrogenation temperature and improve the dehydrogenation kinetics of MgH₂. The synergistic effect of nano-GNSs and TiB₂ nanoparticles contributes to the highly efficient for dehydrogenation of MgH₂-5wt%TiB₂/GNSs composites.     

Dehydrogenation kinetics and modeling studies of MgH2 enhanced by NbF5 catalyst using constant pressure thermodynamic forces

In this research, the effect of NbF₅ as an additive on the hydrogen desorption kinetics of MgH₂ was investigated and compared to TiH₂, Mg₂Ni and Nb₂O₅ catalysts. The kinetics measurements were done using a method in which the ratio of the equilibrium plateau pressure to the opposing pressure was the same for all the reactions. The data showed NbF₅ to be vastly superior to the other catalysts for improving the desorption kinetics of MgH₂. The rates of desorption were found to be in the order NbF₅ ? Nb₂O₅ > Mg₂Ni > TiH₂ > Pure MgH₂. Kinetic modeling measurements showed that chemical reaction at the phase boundary to be the likely process controlling the reaction rates. TPD analyses showed the mixture with NbF₅ has the lowest desorption temperature although it was accompanied with some weight penalty.     

Improved dehydrogenation of MgH2-Li3AlH6 mixture with TiF3 addition

MgH₂-Li₃AlH₆ mixture shows a mutual activation effect between the components. But the dehydrogenation kinetics is still slow, especially at temperature as low as 250 °C. Hereby, an additive (TiF₃) was introduced into the mixture in the present study. The reaction mechanisms were studied by the combined analyses of X-ray diffraction (XRD), thermogravimetric analysis (TGA), as well as thermodynamic calculations. A two-step ball milling method could reduce the mechanical decomposition of Li₃AlH₆ effectively and was adopted. During milling, Li₃AlH₆ reacts with TiF₃ and produces Al₃Ti while MgH₂ remains stable. All the species are well mixed after milling and the grain size is as small as 100 nm. During TGA test, all the reactions occur at lower temperatures compared with undoped mixture, especially the dehydrogenation of MgH₂, which shows a decrease of 60 °C. Its activation energy is reduced by 32.0 kJ mol⁻¹. The first three isothermal (250 °C) cycles indicate that the kinetics of dehydrogenation has been greatly enhanced, showing a reversible capacity of 4.5 wt.% H₂. The time needed for the 1st dehydrogenation has been shortened to 3600 s from 8000 s for the undoped mixture. These improvements are mainly attributed to the catalytic effect of the in-situ formed Al₃Ti. But there is no influence on the rehydrogenation kinetics and the enthalpy of the dehydrogenation of MgH₂ is unchanged.     

Influence of K2TiF6 additive on the hydrogen sorption properties of MgH2

In this study, the hydrogen storage properties of MgH₂ with the addition of K₂TiF₆ were investigated for the first time. The temperature-programmed desorption results showed that the addition of 10 wt% K₂TiF₆ to the MgH₂ exhibited a lower onset desorption temperature of 245 °C, which was a decrease of about 105 °C and 205 °C compared with the as-milled and as-received MgH₂, respectively. The dehydrogenation and rehydrogenation kinetics of 10 wt% K₂TiF₆-doped MgH₂ were also significantly improved compared to the un-doped MgH₂. The results of the Arrhenius plot showed that the activation energy for the hydrogen desorption of MgH₂ was reduced from 164 kJ/mol to 132 kJ/mol after the addition of 10 wt% K₂TiF₆. Meanwhile, the X-ray diffraction analysis showed the formation of a new phase of potassium hydride and titanium hydride together with magnesium fluoride and titanium in the doped MgH₂ after the dehydrogenation and rehydrogenation process. It is reasonable to conclude that the K₂TiF₆ additive doped with MgH₂ played a catalytic role through the formation of active species of KH, TiH₂, MgF₂ and Ti during the ball milling or heating process. It is therefore proposed that this newly developed product works as a real catalyst for improving the hydrogen sorption properties of 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 SiC nanoparticles with and without Ni on the hydrogen storage properties of MgH2

In this work, MgH₂–SiC–Ni was prepared by magneto-mechanical milling in hydrogen atmosphere. Scanning electron microscope mapping images showed a homogeneous dispersion of both Ni and SiC among MgH₂ particles. Based on the differential scanning calorimetry traces, the temperature of desorption is reduced by doping MgH₂ with SiC and Ni. Hydrogen absorption/desorption behaviour of the samples was investigated by Sievert's method at 300 °C, and the results showed that both capacity and kinetics were improved by adding SiC and Ni. The hydrogen desorption kinetic investigation indicated that for pure MgH₂, the rate-determining step is surface controlled and recombination, while for the MgH₂–SiC–Ni sample it is controlled as described by the Johnson–Mehl–Avrami 3D model (JMA 3D).     

Influence of different amounts of FeCl3 on decomposition and hydrogen sorption kinetics of MgH2

In the present work, the hydrogen storage properties of MgH₂-X wt.% FeCl₃ (X = 5, 10, 15 and 20) are investigated experimentally. It is found that the MgH₂ + 10 wt.% FeCl₃ sample exhibits the best comprehensive hydrogen storage properties, in terms of the onset dehydrogenation temperature, the hydrogen amounts de/reabsorbed as well as the relative de/rehydrogenation rates. The onset dehydrogenation temperature of the 10 wt.% FeCl₃-doped MgH₂ sample is reduced by about 90 °C compared to the as-milled MgH₂, and the sorption kinetics measurements indicate that the FeCl₃-doped sample displays an average dehydrogenation rate 5–6 times faster than that of the undoped MgH₂ sample. Higher levels of doping introduce negative effects, such as lower capacity and slower absorption/desorption rates compared to samples with lower FeCl₃ doping levels. The apparent activation energy for hydrogen desorption is decreased from 166 kJ•mol⁻¹ for as-milled MgH₂ to 130 kJ•mol⁻¹ by the addition of 10 wt.% FeCl₃. It is believed that the improvement of the MgH₂ sorption properties in the MgH₂/FeCl₃ composite is due to the catalytic effects of the in-situ generated Fe species and MgCl₂ that are formed during the heating process.     

Effects of nano size mischmetal and its oxide on improving the hydrogen sorption behaviour of MgH2

This paper reports the catalytic effects of mischmetal (Mm) and mischmetal oxide (Mm-oxide) on improving the dehydrogenation and rehydrogenation behaviour of magnesium hydride (MgH₂). It has been found that 5 wt.% is the optimum catalyst (Mm/Mm-oxide) concentration for MgH₂. The Mm and Mm-oxide catalyzed MgH₂ exhibits hydrogen desorption at significantly lower temperature and also fast rehydrogenation kinetics compared to ball-milled MgH₂ under identical conditions of temperature and pressure. The onset desorption temperature for MgH₂ catalyzed with Mm and Mm-oxide are 323 °C and 305 °C, respectively. Whereas the onset desorption temperature for the ball-milled MgH₂ is 381 °C. Thus, there is a lowering of onset desorption temperature by 58 °C for Mm and by 76 °C for Mm-oxide. The dehydrogenation activation energy of Mm-oxide catalyzed MgH₂ is 66 kJ/mol. It is 35 kJ/mol lower than ball-milled MgH₂. Additionally, the Mm-oxide catalyzed dehydrogenated Mg exhibits faster rehydrogenation kinetics. It has been noticed that in the first 10 min, the Mm-oxide catalyzed Mg (dehydrogenated MgH₂) has absorbed up to 4.75 wt.% H₂ at 315 °C under 15 atmosphere hydrogen pressure. The activation energy determined for the rehydrogenation of Mm-oxide catalyzed Mg is ∼62 kJ/mol, whereas that for the ball-milled Mg alone is ∼91 kJ/mol. Thus, there is a decrease in absorption activation energy by ∼29 kJ/mol for the Mm-oxide catalyzed Mg. In addition, Mm-oxide is the native mixture of CeO₂ and La₂O₃ which makes the duo a better catalyst than CeO₂, which is known to be an effective catalyst for MgH₂. This takes place due to the synergistic effect of CeO₂ and La₂O₃. It can thus be said that Mm-oxide is an effective catalyst for improving the hydrogen sorption behaviour of MgH₂.     

Stability and bonding mechanism of ternary (Mg,Fe, Ni)H2 hydrides from first principles calculations

The stability and bonding mechanism of ternary magnesium based hydrides (Mg, X, Y)H₂, X or Y = Fe or Ni, were studied by means of electronic structure and total energy calculations using the FP-LAPW method within the GGA. The influence of the selected alloying elements on the stability of the hydride was determined from the difference between the total energy of the alloyed systems and those of the pure metal and the hydride. Full relaxation was carried out against the overall geometry of the supercell and the internal coordinates of the H atoms. The bonding interactions between the alloying atoms and their surrounding H atoms were estimated using the variation of the total energy against the coordinates of H atoms. The alloying elements, Fe and Ni, destabilised MgH₂. This combined with the weak bonds between the alloying elements and H atoms improved the dehydrogenation properties of MgH₂.     

The influence of different additives on the solid-state reaction of magnesium hydride (MgH2) with Si

The possibility of increasing the solid-state reaction rate of MgH₂ with Si by modifying the mixture preparation method and adding chemical compounds or elements, such as niobium pentafluoride (NbF₅), nano-titanium (IV) oxide (TiO₂), nano-chromium (III) oxide Cr₂O₃, yttrium, and nano- and microsized nickel, was investigated. The results show that changing the milling parameters of the MgH₂ and Si mixture in a planetary ball mill greatly affects the rate of direct reaction between them and allows the reaction to take place at temperatures as low as 200 °C with an equilibrium pressure over 1 bar. Moreover, all additives significantly enhanced the reaction speed. The reaction pathway was found to be different for decomposition in a hydrogen vacuum and pressures of several bars. Reactions of the powders investigated did not occur at temperatures below 150 °C.