Effect of ball milling time on the hydrogen storage properties of TiF3-doped LiAlH4

In the present work, the catalytic effect of TiF₃ on the dehydrogenation properties of LiAlH₄ has been investigated. Decomposition of LiAlH₄ occurs during ball milling in the presence of 4 mol% TiF₃. Different ball milling times have been used, from 0.5 h to 18 h. With ball milling time increasing, the crystallite sizes of LiAlH₄ get smaller (from 69 nm to 43 nm) and the dehydrogenation temperature becomes lower (from 80 °C to 60 °C). Half an hour ball milling makes the initial dehydrogenation temperature of doped LiAlH₄ reduce to 80 °C, which is 70 °C lower than as-received LiAlH₄. About 5.0 wt.% H₂ can be released from TiF₃-doped LiAlH₄ after 18 h ball milling in the range of 60 °C–145 °C (heating rate 2 °C min⁻¹). TiF₃ probably reacts with LiAlH₄ to form the catalyst, TiAl₃. The mechanochemical and thermochemical reactions have been clarified. However, the rehydrogenation of LiAlH₄/Li₃AlH₆ can not be realized under 95 bar H₂ in the presence of TiF₃ because of their thermodynamic properties.     

Destabilization of LiAlH4 by nanocrystalline MgH2

In this work, we report the synthesis, characterization and destabilization of lithium aluminum hydride by ad-mixing nanocrystalline magnesium hydride (e.g. LiAlH₄ + nanoMgH₂). A new nanoparticulate complex hydride mixture (Li–nMg–Al–H) was obtained by solid-state mechano-chemical milling of the parent compounds at ambient temperature. Nanosized MgH₂ is shown to have greater and improved hydrogen performance in terms of storage capacity, kinetics, and initial temperature of decomposition, over the commercial MgH₂. The pressure–composition isotherms (PCI) reveal that the destabilized LiAlH₄ + nanoMgH₂ possess ∼5.0 wt.% H₂ reversible capacity at T ≤ 350 °C. Van't Hoff calculations demonstrate that the destabilized (LiAlH₄ + nanoMgH₂) complex materials have comparable enthalpy of hydrogen release (∼85 kJ/mole H₂) to their pristine counterparts, LiAlH₄ and MgH₂. However, these new destabilized complex hydrides exhibit reversible hydrogen sorption behavior with fast kinetics.     

Effects of NbF5 addition on the hydrogen storage properties of LiAlH4

We investigated the effects of NbF₅ addition by ball milling on the hydrogen storage properties of LiAlH₄. Pressure-composition-temperature (PCT) experiments showed that addition of 0.5 and 1 mol% NbF₅ in LiAlH₄ improves the onset desorption temperature and results in little decrease in hydrogen capacity, with approximately 7.0 wt% released by 188 °C. Isothermal dehydriding kinetics measurements indicated that the NbF₅-doped sample shows an average dehydrogenation rate 5–6 times faster than that of the as-received LiAlH₄ sample. In the x-ray diffraction results, there are distinct peaks of Al and LiH that appear after desorption. There is no peak of NbF₅ before or after desorption. Desorption kinetics measurements indicated that the activation energy, E_A, for LiAlH₄ + 1 mol% NbF₅ is about 67 kJ/mol for first reaction stage and about 77 kJ/mol for second reaction stage. The desorption process was further characterised by differential scanning calorimetry, and the possible mechanism of the effects of NbF₅ addition is discussed.     

Carbon nanostructures as catalyst for improving the hydrogen storage behavior of sodium aluminum hydride

The present paper reports the catalytic effect of carbon nanomaterials, particularly carbon nanotubes (CNTs) and graphitic nanofibres (GNFs) with two different structure morphology, namely planar GNFs (PGNFs) and helical GNFs (HGNFs) as the catalyst for improving the dehydrogenation and rehydrogenation behavior of sodium aluminum hydride (NaAlH₄). It has been observed that HGNFs posses superior catalytic activity than other carbon nanoforms in improving the desorption kinetics and decreasing the desorption temperature of NaAlH₄. Temperature programmed desorption (TPD) reveals that HGNFs admixed NaAlH₄ undergo hydrogen desorption at a much lower temperature than PGNFs and CNTs (SWCNTs and MWCNTs) admixed NaAlH₄. Thus for the heating rate of 2 °C/min, the peak desorption temperature corresponds to initial step decomposition of NaAlH₄ admixed with 2 wt.% HGNFs and 2 wt.% PGNFs has been lowered to 143.6 °C and 152.6 °C, respectively (for pristine NaAlH₄, it is ∼170 °C). In addition to the enhancement in desorption kinetics, the HGNFs admixed NaAlH₄ undergoes fast rehydrogenation at the moderate condition. Microstructural investigation reveals that the HGNFs were present on the surface of NaAlH₄ grains, whereas CNTs were tunneled into the grains of NaAlH₄ suggesting a distinct catalytic behavior of different carbon nanovariants.     

Studies on the de/re-hydrogenation characteristic of Mg(NH2)2/LiH mixture admixed with carbon nanofibres

The effect of carbon nanofibres (CNFs) on the de/re-hydrogenation characteristics of 1:2 magnesium amide (Mg(NH₂)₂) and lithium hydride (LiH) mixture is investigated. It is found that the desorption as well as absorption characteristic of the 1:2 Mg(NH₂)₂/LiH mixture is improved with admixing of different shaped (planar and helical) CNFs separately. The different shaped CNFs were synthesized through catalytic decomposition of acetylene gas over LaNi₅ alloy. The synthesized CNFs contain Ni-metal nano particles. Among two different types of nanofibres namely planar carbon nanofibres (PCNFs) and helical carbon nanofibres (HCNFs), the later was found to act as a better catalyst. The decomposition temperature of the pristine Mg(NH₂)₂/LiH mixture is ∼250 °C, reduced to 150 and 140 °C for the PCNF and HCNF admixed Mg(NH₂)₂/LiH mixture respectively. The activation energy for dehydrogenation reaction was found to ∼97.2 kJ/mol, which is further reduced to ∼67 and ∼65 kJ/mol for the PCNF and HCNF admixed Mg(NH₂)₂/LiH mixture respectively. The lowering of decomposition temperature and enhancement in desorption kinetics, with admixing of different shaped CNFs are described and discussed.     

Significantly improved dehydrogenation of LiAlH4 catalysed with TiO2 nanopowder

The effects of TiO₂ nanopowder addition on the dehydrogenation behaviour of LiAlH₄ have been studied. The 5 wt.% TiO₂-added LiAlH₄ sample showed a significant improvement in dehydrogenation rate compared to that of undoped LiAlH₄, with the dehydrogenation temperature reduced from 150 °C to 60 °C. Kinetic desorption results show that the added LiAlH₄ released about 5.2 wt% hydrogen within 30 min at 100 °C, while the as-received LiAlH₄ just released below 0.2 wt.% hydrogen within same time at 120 °C. From the Arrhenius plot of the hydrogen desorption kinetics, the apparent activation energy is 114 kJ/mol for pure LiAlH₄ and 49 kJ/mol for the 5 wt.% TiO₂ added LiAlH₄, indicating that TiO₂ nanopowder adding significantly decreased the activation energy for hydrogen desorption of LiAlH₄. X-ray diffraction and Fourier transform infrared analysis show that there is no phase change in the cell volume or on the Al-H bonds of the LiAlH₄ due to admixture of TiO₂ after milling. X-ray photoelectron spectroscopy results show no changes in the Ti 2p spectra for TiO₂ after milling and after dehydrogenation. The improved dehydrogenation behaviour of LiAlH₄ in the presence of TiO₂ is believed to be due to the high defect density introduced at the surfaces of the TiO₂ particles during the milling process.     

Synthesis and hydrogen storage thermodynamics and kinetics of Mg(AlH4)2 submicron rods

Mg(AlH₄)₂ submicron rods with 96.1% purity have been successfully synthesized in a modified mechanochemical reaction process followed by Soxhlet extraction. ∼9.0 wt% of hydrogen is released from the as-prepared Mg(AlH₄)₂ at 125–440 °C through a stepwise reaction. Upon dehydriding, Mg(AlH₄)₂ decomposes first to generate MgH₂ and Al. Subsequently, the newly produced MgH₂ reacts with Al to form a Al_0.9Mg_0.1 solid solution. Finally, further reaction between the Al_0.9Mg_0.1 solid solution and the remaining MgH₂ gives rise to the formation of Al₃Mg₂. The first step dehydrogenation is a diffusion-controlled reaction with an apparent activation energy of ∼123.0 kJ/mol. Therefore, increasing the mobility of the species involved in Mg(AlH₄)₂ will be very helpful for improving its dehydrogenation kinetics.     

Direct synthesis of Mg(AlH4)2 and CaAlH5 crystalline compounds by ball milling and their potential as hydrogen storage materials

Mg(AlH₄)₂ and CaAlH₅ were synthesized by direct ball milling of AlH₃ and MgH₂ or AlH₃ and CaH₂ hydrides. The XRD profiles indicated crystalline compounds. Several ball-milling conditions were studied and the optimum parameters were found. Among these, the key parameter is the pause used to cool down the milling device, which allows reducing the temperature rise during milling. Thus, the maximum yield of complex hydrides was obtained by minimizing the desorbed alane amount. The decomposition properties were studied and were in agreement with those reported for different synthesis methods. Mg(AlH₄)₂ with a good hydrogen capacity and a decomposition reaction enthalpy close to 0 kJ/mol H₂ can be a candidate for one-way storage systems. As for CaAlH₅, it might be suitable for reversible hydrogen storage thanks to its dehydrogenation reaction enthalpy (26 kJ/mol H₂). However, rather high activation energy values were evaluated for both compounds (119 and 161 kJ/mol, respectively).     

The effects of the micrometric and nanometric iron (Fe) additives on the mechanical and thermal dehydrogenation of lithium alanate (LiAlH4), its self-discharge at low temperatures and rehydrogenation

LiAlH₄ containing 5 wt.% of nanometric Fe (n-Fe) shows a profound mechanical dehydrogenation by continuously desorbing hydrogen (H₂) during high energy ball milling reaching ∼3.5 wt.% H₂ after 5 h of milling. In contrast, no H₂ desorption is observed during low energy milling of LiAlH₄ containing n-Fe. Similarly, no H₂ desorption occurs during high energy ball milling for LiAlH₄ containing micrometric Fe (μ-Fe) and, for comparison, both the micrometric and nanometric Ni (μ-Ni and n-Ni) additive. X-ray diffraction studies show that ball milling results in a varying degree of the lattice expansion of LiAlH₄ for both the Fe and Ni additives. A volumetric lattice expansion larger than 1% results in the profound destabilization of LiAlH₄ accompanied by continuous H₂ desorption during milling according to reaction: LiAlH₄ (solid) → 1/3Li₃AlH₆ + 2/3Al + H₂. It is hypothesized that the Fe ions are able to dissolve in the lattice of LiAlH₄ by the action of mechanical energy, replacing the Al ions and forming a substitutional solid solution. The quantity of dissolved metal ions depends primarily on the total energy of milling per unit mass of powder generated within a prescribed milling time, the type of additive ion e.g. Fe vs. Ni and on the particle size (micrometric vs. nanometric) of metal additive. For thermal dehydrogenation the average apparent activation energy of Stage I (LiAlH₄ (solid) → 1/3Li₃AlH₆ + 2/3Al + H₂) is reduced from the range 76 to 96 kJ/mol for the μ-Fe additive to about 60 kJ/mol for the n-Fe additive. For Stage II dehydrogenation (1/3Li₃AlH₆ → LiH+1/3Al + 0.5H₂) the average apparent activation energy is within the range 77–93 kJ/mol, regardless of the particle size of the Fe additive (μ-Fe vs. n-Fe). The n-Fe and n-Ni additives, the latter used for comparison, provide nearly identical enhancement of dehydrogenation rate during isothermal dehydrogenation at 100 °C. Ball milled (LiAlH₄ + 5 wt.% n-Fe) slowly self-discharges up to ∼5 wt.% H₂ during storage at room temperature (RT), 40 and 80 °C. Fully dehydrogenated (LiAlH₄ + 5 wt.% n-Fe) has been partially rehydrogenated up to 0.5 wt.% H₂ under 100 bar/160°C/24 h. However, the rehydrogenation parameters are not optimized yet.     

Significantly improved dehydrogenation of LiAlH4 destabilized by K2TiF6

The effects of K₂TiF₆ on the dehydrogenation properties of LiAlH₄ were investigated by solid-state ball milling. The onset decomposition temperature of 0.8 mol% K₂TiF₆ doped LiAlH₄ is as low as 65 °C that 85 °C lower than that of pristine LiAlH₄. Isothermal dehydrogenation properties of the doped LiAlH₄ were studied by PCT (pressure–composition–temperature). The results show that, for the 0.8 mol% K₂TiF₆ doped LiAlH₄ that dehydrogenated at 90 °C, 4.4 wt% and 6.0 wt% of hydrogen can be released in 60 min and 300 min, respectively. When temperature was increased to 120 °C, the doped LiAlH₄ can finish its first two dehydrogenation steps in 170 min. DSC results show that the apparent activation energy (E_a) for the first two dehydrogenation steps of LiAlH₄ are both reduced, and XRD results suggest that TiH₂, Al₃Ti, LiF and KH are in situ formed, which are responsible for the improved dehydrogenation properties of LiAlH₄.     

The effects of ball milling and nanometric nickel additive on the hydrogen desorption from lithium borohydride and manganese chloride (3LiBH4 + MnCl2) mixture

A mixture of [3LiBH₄ + MnCl₂] was processed by high energy ball milling in ultra-high purity hydrogen gas for 0.5 and 1 h. The XRD patterns of milled powders show the sole diffraction peaks of LiCl. The reaction occurring during milling of [3LiBH₄ + MnCl₂] seems to have all characteristics of the metathesis-type reactions occurring between borohydrides (LiBH₄ and NaBH₄) and metal chlorides (MCl_n) induced in a solid state by a mechano-chemical activation synthesis (MCAS). Under pressure of 0.1 MPa H₂ (atmospheric) the ball milled [3LiBH₄ + MnCl₂] mixture is able to desorb ∼4.0 wt.% H₂ at 100 °C within 21,000 s and ∼4.5 wt.% H₂ at 120 and 200 °C within 8000 s and 4000 s, respectively. The addition of n-Ni with SSA = 60.5 m²/g allows desorption of ∼3.7wt.%H₂ within 8,700 s at 100 °C. This is one of the highest H₂ desorption capacities obtained for a complex hydride at 100 °C under atmospheric pressure of H₂ taking into account the fact that the microstructure contains some amount of a useless LiCl constituent. The activation energy of hydrogen desorption for a ball milled undoped [3LiBH₄ + MnCl₂] is ∼102 kJ/mol and ∼98 and 92 kJ/mol after doping with 5 wt.% of nanometric Ni having specific surface area (SSA) of 9.5 and 60.5 m²/g, respectively. After volumetric desorption from 100 to 450 °C the XRD patterns show only LiCl. The n-Ni additive slightly lowers the total quantity of desorbed H₂. Re-absorption tests, under pressure of 10 MPa H₂ at 200 °C, show that the system is, most likely, irreversible. Flammability studies show that the ball milled [3LiBH₄ + MnCl₂] mixture can be ignited by scraping the cylinder walls with a metal tool as well when it is thrown and dispersed in air in a powder form. It also reacts violently in contact with water and a nitric acid.     

TiF4-doped Mg(AlH4)2 with significantly improved dehydrogenation properties

A significant decrease in the dehydrogenation temperature of Mg(AlH₄)₂ was achieved by low-energy ball milling with TiF₄. Approximately 8.0 wt% of hydrogen was released from the Mg(AlH₄)₂-0.025TiF₄ sample with an on-set temperature of 40 °C, which represents a decrease of 75 °C relative to pristine Mg(AlH₄)₂. In contrast to the three-step reaction for pristine Mg(AlH₄)₂, hydrogen desorption from the TiF₄-doped sample involves a two-step process because the Ti-based species participates in the dehydrogenation reaction. The presence of TiF₄ alters the nucleation and growth of the dehydrogenation product, significantly decreasing the activation energy barrier of the first step in the dehydrogenation of Mg(AlH₄)₂. Further hydrogenation measurements revealed that the presence of the Ti-based species was also advantageous for hydrogen uptake, as the on-set hydrogenation temperature was only 100 °C for the dehydrogenated TiF₄-doped sample, compared with 130 °C for the additive-free sample.     

Enhancement of the H2 desorption properties of LiAlH4 doping with NiCo2O4 nanorods

Lithium aluminum hydride (LiAlH₄) is considered as an attractive candidate for hydrogen storage owing to its favorable thermodynamics and high hydrogen storage capacity. However, its reaction kinetics and thermodynamics have to be improved for the practical application. In our present work, we have systematically investigated the effect of NiCo₂O₄ (NCO) additive on the dehydrogenation properties and microstructure refinement in LiAlH₄. The dehydrogenation kinetics of LiAlH₄ can be significantly increased with the increase of NiCo₂O₄ content and dehydrogenation temperature. The 2 mol% NiCo₂O₄-doped LiAlH₄ (2% NCO–LiAlH₄) exhibits the superior dehydrogenation performances, which releases 4.95 wt% H₂ at 130 °C and 6.47 wt% H₂ at 150 °C within 150 min. In contrast, the undoped LiAlH₄ sample just releases <1 wt% H₂ after 150 min. About 3.7 wt.% of hydrogen can be released from 2% NCO–LiAlH₄ at 90 °C, where total 7.10 wt% of hydrogen is released at 150 °C. Moreover, 2% NCO–LiAlH₄ displayed remarkably reduced activation energy for the dehydrogenation of LiAlH₄.     

Understanding the effect of TiO2, VCl3, and HfCl4 on hydrogen desorption/absorption of NaAlH4

The main objective of this work was to investigate the different effects of transition metals (TiO₂, VCl₃, HfCl₄) on the hydrogen desorption/absorption of NaAlH₄. The HfCl₄ doped NaAlH₄ showed the lowest temperature of the first desorption at 85 °C, while the one doped with VCl₃ or TiO₂ desorbed at 135 °C and 155 °C, respectively. Interestingly, the temperature of desorption in subsequent cycles of the NaAlH₄ doped with TiO₂ reduced to 140 °C. On the contrary, in the case of NaAlH₄ doped with HfCl₄ or VCl₃, the temperature of desorption increased to 150 °C and 175 °C, respectively. This may be because Ti can disperse in NaAlH₄ better than Hf and V; therefore, this affected segregation of the sample after the desorption. The maximum hydrogen absorption capacity can be restored up to 3.5 wt% by doping with TiO₂, while the amount of restored hydrogen was lower for HfCl₄ and VCl₃ doped samples. XRD analysis demonstrated that no Ti-compound was observed for the TiO₂ doped samples. In contrast, there was evidence of Al–V alloy in the VCl₃ doped sample and Al–Hf alloy in the HfCl₄ doped sample after subsequent desorption/absorption. As a result, the V- or Hf-doped NaAlH₄ showed the lower ability to reabsorb hydrogen and required higher temperature in the subsequent desorptions.     

Investigation of the thermochemical transformations in the LiAlH4-LiNH2 system

The thermal transformations in the lithium alanate-amide system consisting of lithium aluminum hydride (LiAlH₄) and lithium amide (LiNH₂), mixed in a 1:1 M ratio, were investigated using the pressure-composition-temperature analysis, solid-state nuclear magnetic resonance, X-ray powder diffraction, and residual gas analysis. Below 250 °C, the alanate decomposes into Al, LiH and H₂, through the formation of Li₃AlH₆, whereas the amide remains largely intact. The release of gaseous hydrogen corresponds to approximately 5 wt%. Above 250 °C, additional ∼4 wt% of hydrogen is produced through solid-state reactions among LiNH₂, LiH and metallic Al, through the formation of intermetallic Li-Al binary alloy and an unidentified intermediate. The overall reaction of the thermochemical transformation of the LiAlH₄-LiNH₂ mixture results in the production of Li₃AlN₂, metallic Al, LiH and the release of 9 wt% of gaseous hydrogen. The reaction mechanism of the thermal decomposition is different from one identified earlier during mechanical treatment of the same system. Rehydrogenation of the thermally-decomposed products of LiAlH₄-LiNH₂ mixture using high hydrogen pressure (180 bar) and heating (275 °C) yields LiNH₂ and amorphous aluminum nitride (AlN).     

Catalytic effect of MWCNTs on the dehydrogenation behavior of LiAlH4

Dehydrogenation behavior of LiAlH₄ (lithium alanate) admixed with multi-walled carbon nanotubes (MWCNTs) was investigated by using high-pressure thermal gravimetric analysis (HPTGA) and in-situ synchrotron X-ray diffraction (XRD) technique. HPTGA results indicated that MWCNTs play a catalytic role in the dehydrogenation of LiAlH₄, subsequently decreasing the dehydrogenation temperature and improving the desorption kinetics. With the proper amount of MWCNT, the initial dehydrogenation temperature of LiAlH₄ decreased by approximately 60 °C. Furthermore, in-situ synchrotron XRD analysis confirmed the dehydrogenation reaction products and paths of LiAlH₄, with and without MWCNT addition.     

Destabilization effects of Mg(AlH4)2 on MgH2: Improved desorption performances and its reaction mechanism

Both kinetics and thermodynamics properties of MgH₂ are significantly improved by the addition of Mg(AlH₄)₂. The as-prepared MgH₂–Mg(AlH₄)₂ composite displays superior hydrogen desorption performances, which starts to desorb hydrogen at 90 °C, and a total amount of 7.76 wt% hydrogen is released during its decomposition. The enthalpy of MgH₂-relevant desorption is 32.3 kJ mol⁻¹ H₂ in the MgH₂–Mg(AlH₄)₂ composite, obviously decreased than that of pure MgH₂. The dehydriding mechanism of MgH₂–Mg(AlH₄)₂ composite is systematically investigated by using x-ray diffraction and differential scanning calorimetry. Firstly, Mg(AlH₄)₂ decomposes and produces active Al^∗. Subsequently, the in-situ formed Al^∗ reacts with MgH₂ and forms Mg–Al alloys. For its reversibility, the products are fully re-hydrogenated into MgH₂ and Al^∗, under 3 MPa H₂ pressure at 300 °C for 5 h.     

Thermal stability of Vale Inco nanonometric nickel as a catalytic additive for magnesium hydride (MgH2)

The structure stability of nanometric-Ni (n-Ni) produced by Vale Inco Ltd. Canada as a catalytic additive for MgH₂ has been investigated. Each n-Ni filament is composed of nearly spherical interconnected particles having a mean diameter of 42 ± 16 nm. After ball milling of the MgH₂ + 5 wt.%n-Ni mixture for 15 min the n-Ni particles are found to be uniformly embedded within the particles of MgH₂ and at their surfaces. Neither during ball milling of the MgH₂ + 5 wt.%n-Ni mixture nor its first decomposition at temperatures of 300, 325, 350 and 375 ^°C the elemental n-Ni reacts with the elemental Mg to form the Mg₂Ni intermetallic phase (and eventually the Mg₂NiH₄ hydride). The n-Ni additive acts as a strong catalyst accelerating the kinetics of desorption. From the Arrhenius and Johnson–Mehl–Avrami–Kolmogorov theory the activation energy for the first desorption is determined to be ∼94 kJ/mol. After cycling at 300 ^°C the activation energy for desorption is determined to be ∼99 kJ/mol. This is much lower than ∼160 kJ/mol observed for the undoped and ball milled MgH₂. During cycling at 275 and 300 ^°C the n-Ni additive is converted into Mg₂Ni (Mg₂NiH₄). The newly formed Mg₂NiH₄ has a nanosized grain on the order of 20 nm. Its catalytic potency seems to be similar to its n-Ni precursor. The formation of Mg₂Ni (Mg₂NiH₄) may be one of the factors responsible for the systematic decrease of hydrogen capacity observed upon cycling at 275 and 300 ^°C.     

Effects of REF3 (RE = Y,La, Ce) additives on dehydrogenation properties of LiAlH4

The catalytic effects of rare earth fluoride REF₃ (RE = Y, La, Ce) additives on the dehydrogenation properties of LiAlH₄ were carefully investigated in the present work. The results showed that the dehydrogenation behaviors of LiAlH₄ were significantly altered by the addition of 5 mol% REF₃ through ball milling. The destabilization ability of these catalysts on LiAlH₄ has the order: CeF₃>LaF₃>YF₃. For instance, the temperature programmed desorption (TPD) analyses showed that the onset dehydrogenation temperature of CeF₃ doped LiAlH₄ was sharply reduced by 90 °C compared to that of pristine LiAlH₄. Based on differential scanning calorimetry (DSC) analyses, the dehydriding activation energies of the CeF₃ doped LiAlH₄ sample were 40.9 kJ/mol H₂ and 77.2 kJ/mol H₂ for the first and second dehydrogenation stages, respectively, which decreased about 40.0 kJ/mol H₂ and 60.3 kJ/mol H₂ compared with those of pure LiAlH₄. In addition, the sample doped with CeF₃ showed the fastest dehydrogenation rate among the REF₃ doped LiAlH₄ samples at both 125 °C and 150 °C during the isothermal desorption. The phase changes in REF₃ doped LiAlH₄ samples during ball milling and dehydrogenation were examined using X-ray diffraction and the mechanisms related to the catalytic effects of REF₃ were proposed.