Effect of Al on the hydrogen storage properties of Mg(BH4)2

The various Mg–B–Al–H systems composed of Mg(BH₄)₂ and different Al-sources (metallic Al, LiAlH₄ and its decomposition products) have been investigated as potential hydrogen storage materials. The role of Al was studied on the dehydrogenation and the rehydrogenation of the systems. The results indicate that the different Al-sources exhibit a similar improving effect on the dehydrogenation properties of Mg(BH₄)₂. Taking the Mg(BH₄)₂ + LiAlH₄ system as an example, at first LiAlH₄ rapidly decomposes into LiH and Al, then Mg(BH₄)₂ decomposes into MgH₂ and B, finally the MgH₂ reacts with Al, LiH and B, which forms Mg₃Al₂ and MgAlB₄. The system starts to desorb H₂ at 140 °C and desorbs 3.6 wt.% H₂ below 300 °C, while individual Mg(BH₄)₂ starts to desorb H₂ at 250 °C and desorbs only 1.3 wt.% H₂ below 300 °C. The isothermal desorption kinetics of the Mg–B–Al–H systems is about 40% faster than that of Mg(BH₄)₂ at the hydrogen desorption ratio of 90%. In addition, the Mg–B–Al–H systems show partial reversibility at moderate temperature and pressure. For Al-added system, the product of rehydrogenation is MgH₂, while for LiAlH₄-added system the product is composed of LiBH₄ and MgH₂.     

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).     

Preparation and dehydrogenation properties of two cobalt-based ammine borohydrides: CoCl3·3NH3/3LiBH4 and CoCl2·3NH3/2LiBH4

Two new cobalt-based ammine borohydrides were prepared via ball milling of LiBH₄ and CoCl_n·3NH₃ (n = 3, 2) with molar ratios of 3:1 and 2:1, respectively. X-ray diffraction (XRD) results revealed the as-prepared composites having amorphous state. Thermogravimetric analysis-mass spectrometry (TG-MS) measurements showed that the two composites mainly release H₂, concurrent with the evolution of a small amount of NH₃. Further results showed that the excessive addition of LiBH₄ can suppress the liberation of NH₃, resulting in the release of H₂ with a high purity (>99 mol.%). By combination with the temperature-programmed-desorption (TPD) results, the CoCl₃·3NH₃/4LiBH₄ and CoCl₂·3NH₃/3LiBH₄composites can release 7.3 wt.% (4.2 wt.% including LiCl) and 4.2 wt.% (2.0 wt.% including LiCl) pure hydrogen, respectively, in the temperature range of 25–300 °C. Isothermal dehydrogenation results reveal that CoCl₃·3NH₃/3LiBH₄ shows favorable dehydrogenation rate at low temperatures, releasing about 5.2 wt.% (2.9 wt.% including LiCl) of hydrogen within 45 min at 80 °C.     

Enhanced hydrogen desorption from the Co-catalyzed LiBH4–Mg(BH4)2 eutectic composite

Co-based catalyst can significantly improve the dehydrogenation kinetics of the eutectic composite of LiBH₄–Mg(BH₄)₂ (1/1 M ratio). The onset hydrogen desorption temperature of the composite is at about 155 °C, which is ca. 245, 110 or 27 °C lower than that of LiBH₄, Mg(BH₄)₂ or pristine LiBH₄–Mg(BH₄)₂, respectively. Upon holding the samples at 270 °C, the Co catalyzed composite can release hydrogen at a rate 1.6 times faster than that of the pristine one. Electron Paramagnetic Resonance (EPR) characterization evidenced that Co was in a reduced state of Co⁺ which may serve as the functional species in catalyzing the dehydrogenation of the composite.     

Rehydrogenation and cycle studies of LiBH4–CaH2 composite

Rehydrogenation behavior of 6LiBH₄ + CaH₂ composite with NbF₅ has been studied between 350 and 500 °C after dehydrogenation at 450 °C. The composite exhibits the best rehydrogenation feature at 450 °C in terms of the overall rehydrogenation rate and the amount of absorbed hydrogen. It is found that about 9 wt% hydrogen is absorbed at 450 °C for 12 h. Up to 10 dehydrogenation–hydrogenation cycles have been carried out for the composite. It is demonstrated that 6LiBH₄ + CaH₂ with 15 wt% NbF₅ maintains a reversible hydrogen storage capacity of about 6 wt% at 450 °C after a slight degradation between the 1st and 5th cycles. The addition of NbF₅ seems to improve the cycle properties by retarding microstructural coarsening during cycles.     

A comparative study of LiBH4-based composites with metal hydrides and fluorides for hydrogen storage

A comparative study was performed on four LiBH₄-based hydrogen storage composites 2LiBH₄ + MgX₂ and 6LiBH₄ + CaX₂ (X = H and F). The composites with fluorides and those with corresponding hydrides exhibited similar hydrogen storage properties. The dehydrogenation of 2LiBH₄ + MgF₂ demonstrated a strong dependence on the hydrogen back pressure, similar to that of 2LiBH₄ + MgH₂. The reversible hydrogen storage of 2LiBH₄ + MgF₂ was achieved under a back pressure of 5 bar at 450 °C. Dehydrogenation under lower H₂ pressures resulted in the production of Mg and thus a partial reversibility. In contrast, both 6LiBH₄ + CaH₂ and 6LiBH₄ + CaF₂ revealed reversible hydrogen storage properties regardless of the hydrogen back pressure. The structural difference between MgB₂ and CaB₆ may account for the observed differences in hydrogen storage properties of the Mg- and Ca-containing LiBH₄ reactive composites.     

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.     

Mg2FeH6–LiBH4 and Mg2FeH6–LiNH2 composite materials for hydrogen storage

Two composite hydrogen storage materials based on Mg₂FeH₆ were investigated for the first time. The Mg₂FeH₆–LiBH₄ composite of molar ratio 1:5 showed a hydrogen desorption capacity of 5.6 wt.% at 370 °C, and could be rehydrogenated to 3.6 wt.% with the formation of MgH₂, as the material was heated to 445 °C and held at this temperature. The Mg₂FeH₆–LiNH₂ composite of 3:10 molar ratio exhibited a hydrogen desorption capacity of 4.3 wt.% and released hydrogen at 100 °C lower then the Mg₂FeH₆–LiBH₄ composite, but this mixture could not be rehydrogenated. Compared to neat Mg₂FeH₆, both composites show enhanced hydrogen storage properties in terms of desorption kinetics and capacity at these low temperatures. In particular, Mg₂FeH₆–LiNH₂ exhibits a much lower desorption temperature than neat Mg₂FeH₆, but only Mg₂FeH₆–LiBH₄ re-absorbs hydrogen.     

Mechanistic investigations on significantly improved hydrogen storage performance of the Ca(BH4)2-added 2LiNH2/MgH2 system

The hydrogen storage properties and mechanisms of the Ca(BH₄)₂-added 2LiNH₂–MgH₂ system were systematically investigated. The results showed that the addition of Ca(BH₄)₂ pronouncedly improved hydrogen storage properties of the 2LiNH₂–MgH₂ system. The onset temperature for dehydrogenation of the 2LiNH₂–MgH₂–0.3Ca(BH₄)₂ sample is only 80 °C, a ca. 40 °C decline with respect to the pristine sample. Further hydrogenation examination indicated that the dehydrogenated 2LiNH₂–MgH₂–0.1Ca(BH₄)₂ sample could absorb ca. 4.7 wt% of hydrogen at 160 °C and 100 atm while only 0.8 wt% of hydrogen was recharged into the dehydrogenated pristine sample under the same conditions. Structural analyses revealed that during ball milling, a metathesis reaction between Ca(BH₄)₂ and LiNH₂ firstly occurred to convert to Ca(NH₂)₂ and LiBH₄, and then, the newly developed LiBH₄ reacted with LiNH₂ to form Li₄(BH₄)(NH₂)₃. Upon heating, the in situ formed Ca(NH₂)₂ and Li₄(BH₄)(NH₂)₃ work together to significantly decrease the operating temperatures for hydrogen storage in the Ca(BH₄)₂-added 2LiNH₂–MgH₂ system.     

Hydrogen desorption kinetics of the destabilized LiBH4AlH3 composites

LiBH₄ can be destabilized by AlH₃ addition. In this work, the hydrogen desorption kinetics of the destabilized LiBH₄AlH₃ composites were investigated. Isothermal hydrogen desorption studies show that the LiBH₄ + 0.5AlH₃ composite releases about 11.0 wt% of hydrogen at 450 °C for 6 h and behaves better kinetic properties than either the pure LiBH₄ or the LiBH₄ + 0.5Al composite. The apparent activation energy for the LiBH₄ decomposition in the LiBH₄ + 0.5AlH₃ composite estimated by Kissinger's method is remarkably lowered to 122.0 kJ mol^?1 compared with the pure LiBH₄ (169.8 kJ mol^?1). Besides, AlH₃ also improves the reversibility of LiBH₄ in the LiBH₄ + 0.5AlH₃ composite. For the LiBH₄ + xAlH₃ (x = 0.5, 1.0, 2.0) composites, the decomposition kinetics of LiBH₄ are enhanced as the AlH₃ content increases. The sample LiBH₄ + 2.0AlH₃ can release 82% of the hydrogen capacity of LiBH₄ in 29 min at 450 °C, while only 67% is obtained for the LiBH₄ + 0.5AlH₃ composite in 110 min. Johnson?Mehl?Avrami (JMA) kinetic studies indicate that the reaction LiBH₄ + Al → ‘LiAlB’ + AlB₂ + H₂ is controlled by the precipitation and subsequently growth of AlB₂ and LiAlB compounds with an increasing nucleation rate.     

Enhanced dehydrogenation properties of LiBH4 compositing with hydrogenated magnesium-rare earth compounds

LiBH₄ is regarded as a promising hydrogen storage material due to its high hydrogen density. In this study, the dehydrogenation properties of LiBH₄ were remarkably enhanced by doping hydrogenated Mg₃RE compounds (RE denotes La, Ce, Nd rare earth metals), which are composed of nanostructured MgH₂ and REH_2+x (denoted as H − Mg₃RE). For the LiBH₄ + H − Mg₃La mixture, the component LiBH₄ desorbed 6 wt.% hydrogen even at a relatively low temperature of 340 °C, far lower than the desorption temperature of pure LiBH₄ or the 2LiBH₄ + MgH₂ system. This kinetic improvement is attributed to the hydrogen exchange mechanism between the H − Mg₃La and LiBH₄, in the sense that the decomposition of MgH₂ and LaH_2+x catalyzed the dehydrogenation of LiBH₄ through hydrogen exchange effect rather than mutual chemical reaction requiring higher temperature and hydrogen pressure. However, prior to fast hydrogen release, the hydrogen exchange effect suppressed the dehydriding of MgH₂ and elevated its desorption temperature. It is expected to strengthen the hydrogen exchange effect by compositing the LiBH₄ with other nanosized metal hydrides and to obtain better dehydrogenation properties.     

The reactions in LiBH4-NaNH2 hydrogen storage system

Stepwise reactions were observed in the ball milling and heating process of the LiBH₄-NaNH₂ system by means of X-ray diffraction (XRD) and Fourier transform infrared spectrometry (FT-IR). During the ball milling process, two concurrent reactions take place in the mixture: 3LiBH₄ + 4NaNH₂ → Li₃Na(NH₂)₄ + 3NaBH₄ and LiBH₄ + NaNH₂ → LiNH₂ + NaBH₄. The heating process from 50 °C to 400 °C is mainly the concurrent reactions of Li₃Na(NH₂)₄ + 3LiBH₄ → 2Li₃BN₂ + NaBH₄ + 8H₂ and 2LiNH₂ + LiBH₄ → Li₃BN₂H₈ → Li₃BN₂ + 4H₂, where the intermediate phases Li₃Na(NH₂)₄ and LiNH₂ serve as the reagents to decompose LiBH₄. The merged equations for the mechanochemical and the heating reactions below 400 °C can be denoted as 3LiBH₄ + 2NaNH₂ → Li₃BN₂ + 2NaBH₄ + 4H₂. The maximum dehydrogenation capacity in closed system below 400 °C is 5.1 wt.% H₂, which agrees well with the theoretical capacity (5.5 wt.% H₂) of the merged equation and thus demonstrates the suggested pathway. The subsequent step consists of the decompositions of NaBH₄ and Li₃Na(NH₂)₄ within the temperature range of 400 °C-600 °C. The apparent activation energies of the two steps are 114.8 and 123.5 kJ/mol, respectively. They are all lower than that of our previously obtained bulk LiBH₄.     

Enhanced dehydrogenation and rehydrogenation properties of LiBH4 catalyzed by graphene

The investigation of thermally induced dehydrogenation of LiBH₄ reveals that LiBH₄ doped with the graphene catalysts shows superior dehydrogenation and rehydrogenation performance to that of Vulcan XC-72, carbon nanotube and BP2000 doped LiBH₄. For doping with 20 wt.% graphene, thermal dehydrogenation of LiBH₄ is found to start at ca. 230 °C and a total weight loss of 11.4 wt.% can be obtained below 700 °C. With increased loading of graphene within a LiBH₄ sample, the onset dehydrogenation temperature and the two main desorption peaks from LiBH₄ are found to decrease while the hydrogen release amount is found to increase. Moreover, variation of the equilibrium pressure obtained from isotherms measured at 350–450 °C indicate the dehydrogenation enthalpy is reduced from 74 kJ mol⁻¹ H₂ for pure LiBH₄ to ca. 40 kJ mol⁻¹ H₂ for 20 wt.% graphene doped LiBH₄. Importantly, the reversible dehydrogenation/rehydrogenation process was achieved under 3 MPa H₂ at 400 °C for 10 h, with a capacity of ca. 4.0 wt.% in the tenth cycle. Especially, LiBH₄ is reformed and new species, Li₂B₁₀H₁₀, is detected after the rehydrogenation process.     

Enhanced hydrogen storage properties of LiBH4 modified by NbF5

In this work, the hydriding–dehydriding properties of the LiBH₄–NbF₅ mixtures were investigated. It was found that the dehydrogenation and reversibility properties of LiBH₄ were significantly improved by NbF₅. Temperature-programed dehydrogenation (TPD) showed that 5LiBH₄–NbF₅ sample started releasing hydrogen from as low as 60 °C, and 4 wt.% hydrogen could be obtained below 255 °C. Meanwhile, ∼7 wt.% H₂ could be reached at 400 °C in 20LiBH₄–NbF₅ sample, whereas pristine LiBH₄ only released ∼0.7 wt.% H₂. In addition, reversibility measurement demonstrated that over 4.4 wt.% H₂ could still be released even during the fifth dehydrogenation in 20LiBH₄–NbF₅ sample. The experimental results suggested that a new borohydride possibly formed during ball milling the LiBH₄–NbF₅ mixtures might be the source of the active effect of NbF₅ on LiBH₄.     

Improved reversible dehydrogenation of LiBH4–MgH2 composite by the synergistic effects of Al and MgO

In this paper, we report a novel method of improving the reversible dehydrogenation properties of the 2LiBH₄–MgH₂ composite. Our study found that mechanically milling with small amount of Al powder can markedly shorten or even eliminate the problematic incubation period that interrupts the dehydrogenation steps of the 2LiBH₄–MgH₂ composite. But the resulting composite showed serious kinetics degradation upon cycling. In an effort to solve this problem, we found that combined usage of small amounts of Al and MgO enabled the 2LiBH₄–MgH₂ composite to rapidly and reversibly deliver around 9 wt% hydrogen at 400 °C under 0.3 MPa H₂, which compares favorably with the dehydrogenation performance of the composites with transition-metal additives. A combination of phase/microstructural analyses and series of control experiments has been conducted to gain insight into the promoting effects of Al and MgO. It was found that Al and MgO additives act as precursor and promoter for the formation of AlB₂ heterogeneous nucleation sites, respectively.     

Reversible dehydrogenation of Mg(BH4)2–LiH composite under moderate conditions

The Mg(BH₄)₂-xLiH (0.1 ≤ x ≤ 0.8) composites which exhibit favorable dehydrogenation and encouraging reversibility are experimentally investigated. LiH additive reduces the onset temperature for dehydrogenation to 150 °C. And hydrogen release exceeds 10 wt.% from the new binary material below 250 °C. Furthermore, rehydrogenation results show that 3.6 wt.% hydrogen can still be recharged after twenty cycles at 180 °C. It should be emphasized that the long-term reversibility of borohydride under 200 °C is long overdue. TPD, PCT, and high-pressure DSC measurements are used to characterize the improvements in thermodynamic and kinetic ways. In addition, FT-IR and NMR studies indicate that the composite has a significant synergistic effect during (de)hydrogenation processes. This work suggests that controlled cation stoichiometry combined with doping by metal Li⁺ subvalent to Mg²⁺ facilitate the formation of polyborane intermediates [B₃H₈]⁻ and [B₂H₆]²⁻. They improve the dehydrogenation properties and make the material reversible under mild conditions.     

Improved hydrogen storage reversibility of LiBH4 destabilized by Y(BH4)3 and YH3

In the present study, the synthesis of two different LiBH₄–Y(BH₄)₃ and LiBH₄–YH₃ composites was performed by mechanochemical processing of the 4LiBH₄–YCl₃ mixture and as-milled 4LiBH₄–YCl₃ plus 3LiH. It was found that Y(BH₄)₃ and YH₃ formed in situ during milling are effective to promote LiBH₄ destabilization but differ substantially from each other in terms of the dehydrogenation pathway. During LiBH₄–Y(BH₄)₃ dehydriding, Y(BH₄)₃ decomposes first generating in situ freshly YH₃ and subsequently, it destabilizes LiBH₄ with the formation of minor amounts of YB₄. About 20% of the theoretical hydrogen storage was obtained via the rehydriding of YB₄–4LiH–3LiCl at 400 °C and 6.5 MPa. As a novel result, a compound containing (B₁₂H₁₂)²⁻ group was identified during dehydriding of Y(BH₄)₃. In the case of 4LiBH₄–YH₃ dehydrogenation, the increase of the hydrogen back pressure favors the formation of crystalline YB_4, whereas a reduction to ≤0.1 MPa induces the formation of minor amounts of Li₂B₁₂H₁₂. Although for hydrogen pressures ≤0.1 MPa direct LiBH₄ decomposition can occur, the main dehydriding pathway of 4LiBH₄–YH₃ composite yields YB₄ and LiH. The nanostructured composite obtained by mechanochemical processing gives good hydrogen storage reversibility (about 80%) regardless of the hydrogen back pressure.     

Hydrogen sorption in MgH2-based composites: The role of Ni and LiBH4 additives

In the present work we investigate the hydrogen sorption properties of composites in the MgH₂–Ni, MgH₂–Ni–LiH and MgH₂–Ni–LiBH₄ systems and analyze why Ni addition improve hydrogen sorption rates while LiBH₄ enhance the hydrogen storage capacity. Although all composites with Ni addition showed significantly improved hydrogen storage kinetics compared with the pure MgH₂, the fastest hydrogen sorption kinetics is obtained for Ni-doped MgH₂. The formation of Mg₂Ni/Mg₂NiH₄ in Ni-doped MgH₂ composite and its microstructure allows to uptake 5.0 wt% of hydrogen in 25 s and to release it in 8 min at 275 °C. In the MgH₂–Ni–LiBH₄ composite, decomposition of LiBH₄ occurs during the first dehydriding leading to the formation of diborane, which has a Ni catalyst poison effect via the formation of a passivating boron layer. A combination of FTIR, XRD and volumetric measurements demonstrate that the formation of MgNi₃B₂ in the MgH₂–Ni–LiBH₄ composite happens in the subsequent hydriding cycle from the reaction between Mg₂Ni/Mg₂NiH₄ and B. Activation energy analysis demonstrates that the presence of Ni particles has a catalytic effect in MgH₂–Ni and MgH₂–Ni–LiH systems, but it is practically nullified by the addition of LiBH₄. The beneficial role of LiBH₄ on the hydrogen storage capacity of the MgH₂–Ni–LiBH₄ composite is discussed.     

Effect of LiBH4 on hydrogen storage property of MgH2

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

A study on the hydrogen storage properties and reaction mechanism of Na3AlH6LiBH4 composite system

In this work, the hydrogen storage properties of different molar ratio (in mole of 1:3 and 1:4) Na₃AlH₆LiBH₄ system is investigated for the first time. X-ray diffraction and Fourier transform infrared results show that the Na₃AlH₆LiBH₄ with molar ratio of 1:3 and 1:4 composite was transformed to Li₃AlH₆ and NaBH₄ phases via a metathesis reaction during a ball-milling process for 6 h. Temperature-programmed-desorption (TPD) results show three stages of decomposition for the Na₃AlH₆LiBH₄ (in mole ratio of 1:3 and 1:4) composite resulting from Li₃AlH₆ and NaBH₄ phases. From the TPD graph, the Na₃AlH₆LiBH₄ composite with molar ratio of 1:4 had showed better performance of hydrogenation properties compared to with molar ratio of 1:3. The composite began to release hydrogen at 180 °C in relation to decomposition of the Li₃AlH₆ stage into LiH and Al. The NaBH₄ stage then began to decompose at approximately 380 °C, after reacting with Al to form an intermetallic phase, AlB₂, which occurred at 100 °C lower than as-milled NaBH₄. At 430 °C, the un-reacted NaBH₄ was decomposed after catalysing with AlB₂. Kissinger analysis shows the apparent activation energy of NaBH₄ decomposition in the hydrides composite was reduced by about 75 kJ/mol compared to the as-milled NaBH₄. The rehydrogenation process evidenced the reversibility of NaBH₄. Based on these results, the intermetallic phase, AlB₂, is considered to have played an important role by lowering the operating temperature and providing access to the full hydrogen content in the Na₃AlH₆LiBH₄ composite system.