The first systematic study on the mutual destabilization between MgH₂ and LiAlH₄ was reported by Zhang et al. (Zhang et al., 2008). They studied the different molar ratios (1:1, 2:1, and 4:1) of MgH₂–LiAlH₄. The result showed that the initial desorption temperature for the MgH₂–relevant decomposition in all the different molar ratios of the MgH₂–LiAlH₄ composite was decreased to ∼250°C, which is 50°C lower than the milled MgH₂, as shown in Figure 3. By using the Kissinger method, the activation energy value of MgH₂–relevant decomposition in the composite was reduced dramatically compared to the undoped MgH₂. The dehydrogenation enthalpies of the MgH₂–LiAlH₄ composites with different molar ratios 4:1, 2:1, and 1:1 are 61, 48.66, and 45 kJ/mol, respectively. These enthalpy values were smaller than the undoped MgH₂ (76 kJ/mol), which indicates that MgH₂ was destabilized by LiAlH₄. Further study revealed that the dehydrogenation process in the MgH₂–LiAlH₄ system can be divided into two steps: the first step is due to the two-step decomposition of LiAlH₄ (The first step is the decomposition of LiAlH₄ to Li₃AlH₆ and Al (as in Eq. 1), and the second step is the decomposition of Li₃AlH₆ to LiH and Al (as in Eq. 2) and the second step is due to the reaction between LiH and Al phases to form Li_0.92Mg_4.08 and Mg₁₇Al₁₂ phases, as indicated in Eqs 4, 5. 4.08 M g H 2 + 0.92 L i H → L i 0.92 M g .08 + 4.54 H 2 , (4) 17 M g H 2 + 12 A l → A l 12 M g 17 + 17 H 2 . (5)

Moreover, rehydrogenation measurement shows that Li_0.92Mg_4.08 and Mg₁₇Al₁₂ are the fully absorbed hydrogen, as shown in Eqs 6, 7. L i 0.92 M g 4.08 + 4.5 H 2 → 4.08 M g H 2 + 0.92 L i H , (6) A l 12 M g 17 + ( 17 − 2 y ) H 2 → y M g 2 A l 3 + ( 17 − 2 y ) M g H 2 + ( 12 − 3 y ) A l . (7)

Lin and Tsai (Lin & Tsai, 2017) in their study exposed that the diffraction peak intensity of LiAlH₄ decreased with an increasing amount of MgH₂ addition, as in Figure 4. No other compounds were found after milling, indicating that no reaction occurred between LiAlH₄ and MgH₂ during the milling process. This result is in agreement with a previous study by Hsu et al. (Hsu et al., 2014b), in which the diffraction peak intensity of MgH₂ increased with a decreasing amount of LiAlH₄ in the MgH₂–LiAlH₄ mixture.

Next, the temperatures of desorption and the amount of hydrogen released from the composites of MgH₂–LiAlH₄ were quantitively evaluated by the thermogravimetric analysis (TGA), as shown in Table 2. It was evident that with the increasing MgH₂ content in the composites, the first desorption temperature was lowered. These findings showed that MgH₂ played an effective role in reducing the initial desorption temperature of these composites. As soon as the desorption of these composites was completed, absorption kinetics was initiated with a temperature maintained at 400°C, while charging hydrogen to the target pressure. As displayed in Table 2, the total amount of hydrogen absorbed (wt.%) increased from 0.3 to 3, and the onset desorption temperature also decreased to 85°C compared to 100°C with an increase in the MgH₂ content in the composites. The results proved that MgH₂ was the main compound that exhibited reversibility concerning the hydrogen absorption/desorption reaction. As shown in Table 2, the ability of the MgH₂–LiAlH₄ composite to absorb hydrogen increased as the MgH₂ ratio increased.

The LiAlH₄–MgH₂ hydrogen storage system was studied by Chen et al. (Chen et al., 2010). The commercial LiAlH₄ was decomposed at 163°C; meanwhile, the commercial MgH₂ decomposed at 405°C. However, LiAlH₄ and MgH₂ mixtures start to release hydrogen at ∼107°C, indicating that the combination of LiAlH₄ and MgH₂ may improve their thermodynamic properties. Measurement of the XRD was performed after desorption, and the results showed that in all the LiAlH₄–xMgH₂ composites (LiAlH₄–MgH₂, LiAlH₄–2.5MgH₂, and LiAlH₄–4MgH₂), the Mg₁₇Al₁₂ phase was formed. In addition, the LiAlH₄–4MgH₂ composite contained major Li_0.92Mg_4.08 phases, whereas LiAlH₄–2.5MgH₂ contained minor Li_0.92Mg_4.08 phases, as shown in Figure 5. This indicates that Li_0.92Mg_4.08 can be formed while the ratio of MgH₂/LiAH₄ is relatively high. These composites also undergo an absorption process at 350°C under a pressure of 10 MPa hydrogen. In 60 min, the LiAlH₄–4MgH₂ composites reach 90% of their maximum absorption capacity. In brief, these reported studies indicated that the combination of LiAlH₄ and MgH₂ may have been shown to affect the thermal stability of both LiAlH₄ and MgH₂ by the formation of intermetallic Mg₁₇Al₁₂ and Li_0.92Mg_4.08.

Based on the abovementioned discussions, the different molar ratios of the MgH₂–LiAlH₄ composites also affected the performance of the Mg–Li–Al system. This review article outlined that 4MgH₂–LiAlH₄ shows the best performance compared to the other ratios (e.g., 1:1, 2:1, and 2.5:1). The 4MgH₂–LiAlH₄ composite created an intermediate compound of Li_0.92Mg_4.08 and Mg₁₇Al₁₂ that helps to enhance the hydrogen storage performance of the Mg–Li–Al system.

Vittetoe et al. (Vittetoe et al., 2009) explored the destabilization effects of the combination of LiAlH₄ with a nanocrystalline MgH₂ by mechanical–chemical milling concerning reversibility and kinetics problems. Interestingly, they investigated the LiAlH₄–MgH₂ composite with different durations of milling (1, 2, 3, and 5 h). They discovered that the LiAlH₄–MgH₂ samples that have been milled for 1, 2, and 3 h started to decompose at ∼100°C. Researchers verified that for an optimal ball milling period of 2 h, a three-step hydrogen desorption response with an early-onset temperature and greater amount of hydrogen release is required. In addition, further study elucidates LiAlH₄–MgH₂ and LiAlH₄–nanoMgH₂ of TGA and differential scanning calorimetry (DSC) profiles milled for 2 h, as seen in Figure 6. The LiAlH₄–nanoMgH₂ systems show a greater weight loss of approximately 5.2 wt.% (∼200°C), at least 1.0 wt.% higher capacity than the commercial-grade sample (LiAlH₄–MgH₂).

As LiAlH₄–nanoMgH₂ showed better performance than LiAlH₄–MgH₂, this material underwent repeated absorption of hydrogen (80 bars) and desorption at two different temperatures (300 and 350°C). After numerous attempts of hydrogen absorption–desorption experiments, these samples were carefully examined under a scanning electron microscope (SEM), as shown in Figure 7. SEM images of LiAlH₄–nanoMgH₂ after cycling indicated that the sample had a relatively smaller grain with a highly porous matrix and uniform (as in Figure 7B) as compared to LiAlH₄–nanoMgH₂ (as in Figure 7A). This is due to the host structure’s effective uptake and release of hydrogen.

Milanovic et al. (Milanović et al., 2013) investigated the catalytic influence on the desorption of hydrogen from MgH₂. Indeed, when mixing MgH₂ with a 5 wt.% of LiAlH₄ for 15 min, the peak of the hydrogen desorption shifts to a lower temperature than as received MgH₂ and as milled MgH₂. In this study, milling up to 30 and 60 min of the MgH₂–LiAlH₄ composites may reduce the catalytic activity of the LiAlH₄ additive, as revealed by the shift to a higher peak of desorption temperatures. According to Leon et al. (Léon et al., 2009), experiments conducted under various conditions revealed that the milling parameters, in particular the milling speed and milling time, can be of great importance through reactive ball milling for the formation of the new hydride phase. Next, Ding et al. (Ding et al., 2013) studied the MgH₂–LiAlH₄ composites milled at different milling times (2, 5, and 9 h). The result revealed that MgH₂–LiAlH₄ composites milled for 2 h decompose in the temperature ranges of ∼130–183°C; meanwhile, after the MgH₂–LiAlH₄ composites were milled for 5 h, the composites start to release hydrogen at 102°C. However, the capacity of hydrogen released decreased compared with 2 h milled composites. In addition to that, the initial desorption temperature decreases to 86°C when the milling time increases to 9 h, but the amount of hydrogen released also decreases. The XRD pattern showed that the peaks of Li₃AlH₆ and Al appeared after milling the MgH₂–LiAlH₄ composites up to 5 h. Interestingly, milling up to 9 h proved that the intensity peaks of Li₃AlH₆ and Al become stronger. This indicated that more LiAlH₄ has been decomposed into Li₃AlH₆ and Al, accounting for the lowest onset desorption temperature. Based on the results obtained, the lower decomposition temperature was attributed to the decomposition of LiAlH₄ that had occurred, and more LiAlH₄ decomposed as the milling time increased. In addition, the peaks of the Mg₁₇Al₁₂ phase can also be detected when the MgH₂–LiAlH₄ composites were heated to 250°C. Furthermore, Ding et al. (Ding et al., 2013) also studied the reversibility of the destabilized MgH₂–LiAlH₄ composite under a hydrogen pressure of 3 MPa and at 300°C, and the results show that the MgH₂–LiAlH₄ composite exhibits fast ab/desorption kinetics in the first two cycles, but the ab/desorption kinetics worsened during the third cycle, as shown in Figure 8. Moreover, SEM images indicated that the morphology of MgH₂–LiAlH₄ composites was smaller. A reduction in the particle size and crystallite size results in the introduction of high surface defect density and the creation of more grain boundaries. In addition to that, a high density of the nanosized catalyst particles forms a large number of nucleation sites at the surface of the LiAlH₄ matrix, leading to the larger surface area of LiAlH₄ particles, as indicated by Zhai et al. (Zhai et al., 2012). Xia et al. (Xia et al., 2020) also stated that the morphological change should be beneficial for the enhancement of the desorption properties of LiAlH₄, owing to the reduction of the particle size and the process of creating small crystallite sizes. Halim Yap et al. (Halim Yap et al., 2019), in their study, revealed that the decrement of the grain sizes led to the increment of the contact surface area. As a result, the desorption reaction of hydrogen has been improved due to the reduction of the hydrogen diffusion length. A study conducted by Czujko et al. (Czujko et al., 2011) revealed that the average particle size of MgH₂+50 wt% LiAlH₄ composites was reduced to ∼3.5 ± 2.7 µm. It demonstrated that during MgH₂ ball milling, lithium alanate could act as a lubricant, and the reduction of particle size is much less efficient when the LiAlH₄ additive level reaches 50 wt.%. Based on this subsection, appropriate milling time is beneficial to the Mg–Li–Al systems. This indicates that the milling time at a suitable time is helpful to improve the hydrogen storage performance of the Mg–Li–Al system. The variation of the milling duration has obvious effects on the onset desorption temperature, activation energy, and morphology of the samples.

A study conducted by Halim Yap and Ismail (Halim Yap & Ismail, 2017) indicated that the hydrogen sorption properties of the MgH₂–LiAlH₄ system can be enhanced by the addition of K₂ZrF₆. The onset desorption temperature for 4MgH₂–LiAlH₄ exhibited two significant stages. For the 4MgH₂–LiAlH₄ systems, the onset desorption temperature was 135 and 275°C for the first and second desorption stages, with the total amount of hydrogen desorption being 7.5 wt.%. After the addition of 10 wt.% K₂ZrF₆, the desorption temperature for the first and second stages was decreased by 40 and 25°C, respectively. In addition, 4MgH₂–LiAlH₄ + 10 wt.% K₂ZrF₆ demonstrates better kinetics of desorption, and the value of activation energy was decreased to 102.9 kJ/mol compared to the undoped composites (129.8 kJ/mol). However, the absorption kinetics under 33.0 atm at 320°C exposed that adding 10 wt.% of K₂ZrF₆ to 4MgH₂–LiAlH₄ showed no improvement in the absorption of hydrogen. Meanwhile, the SEM images for comparing the morphology of undoped and doped samples are shown in Figure 9. The doped samples show that the particles size is less agglomerated and smaller as in Figure 9D than the undoped samples (Figure 9C). This result was also supported by Ranjbar et al. (Ranjbar et al., 2010) who suggested that the smaller particle size improves hydrogen ab/desorption as it makes the particle larger surface area and reduces the diffusion length of hydrogen.

Further research indicated that the new peaks of Al₃Zr and KH (indicating LiAlH₄ react with K₂ZrF₆) were formed after 4MgH₂–LiAlH₄ + 10 wt.% K₂ZrF₆ were heated at 200°C. In addition, the peaks of MgH₂ were also present as well as LiH and Al (illustrated the decomposition as in Eq. 2). Heating up to 450°C, the peaks of Mg, Li_0.92Mg_4.08, and Mg₁₇Al₁₂ were detected, whereas the Al₃Zr and KH peaks remained unchanged. Furthermore, the XRD pattern of absorption for K₂ZrF₆-doped 4MgH₂–LiAlH₄ sample at 300°C also exposed the peaks of Al₃Zr, KH, LiH, and Al remain unchanged. However, the peaks of the Mg₁₇Al₁₂ and Li_0.92Mg_4.08 disappeared, and it is suggested that a reaction occurred during the absorption process, as indicated in Eqs 6, 7. The amount of K₂ZrF₆ was increased to 20 wt.% to obtain a better insight into the F-containing, Zr-containing, and K-containing phase structures. New minor peaks attributed to LiF were detected along with the KH and Al₃Zr phases. Therefore, it is recognized that the new LiF, KH, and Al₃Zr products created during the heating process worked together as active components to work on improving the 4MgH₂–LiAlH₄ system of the hydrogen storage performance. The hydrogen storage properties of MgH₂/LiAlH₄ were improved by the addition of SrFe₁₂O₁₉, as suggested by Sulaiman and Ismail (Sulaiman & Ismail, 2017). The result disclosed that the addition of 5 wt.% of SrFe₁₂O₁₉ resulted in a decrease of 40 and 10°C in the first and second stages of desorption, respectively, compared to the MgH₂/LiAlH₄ system. The doped samples begin to release hydrogen at ∼80°C for the first stages and ∼260°C for the second stages. Interestingly, the hydrogen released by the doped samples was 7.1 wt.%, which is the amount of hydrogen released equivalent to milled MgH₂. The energy barriers for the release of hydrogen affected the kinetic desorption performance of the samples. From the calculation of as-received MgH₂, the activation energy was 175 kJ/mol. However, the activation energy was decreased to 133 kJ/mol after MgH₂ was milled for 1 h. This proves that the value of the activation energy is also affected by the milling process (Sabitu & Goudy, 2012; Ismail, 2015; Lin et al., 2015; Zhang et al., 2017). Furthermore, after destabilizing MgH₂ with LiAlH₄, the activation energy was reduced to 121 kJ/mol, which showed a reduction of 12 kJ/mol compared to the milled MgH₂ (133 kJ/mol). The improvement of desorption kinetics is related to the energy barrier for the hydrogen release from the composite. Lower activation energy means faster kinetics. In this context, the activation energy is the least energy required to instigate the decomposition process of the system (Ismail et al., 2020). The activation energy decreased to 104 kJ/mol, after the addition of 5 wt.% SrFe₁₂O₁₉ to 4MgH₂–LiAlH₄. Furthermore, these findings appear to be comparable to the previous studies reporting on the role of catalysts in reducing the activation energy, leading to improved dehydriding kinetics (Sazelee et al., 2019). Conversely, the newly developed products formed during the heating process of in situ Li₂Fe₃O₄ and Al₂Sr exhibit a synergistically catalytic effect on the improvement of the 4MgH₂–LiAlH₄ composites.

According to Mao et al. (Mao et al., 2011), dehydrogenation has been improved after LiAlH₄ was combined with MgH₂, in which the first-stage desorption temperature is close to LiAlH₄ (∼150°C), while the second-stage desorption was completed at 233°C. This suggested that in the binary LiAlH₄–MgH₂ system, a mutual destabilization occurred. However, after being doped with TiF_3, hydrogen starts to release at ∼60°C (100°C lower than the undoped LiAlH₄–MgH₂ system). The desorption and absorption kinetics were also improved after the addition of TiF₃. For the LiAlH₄–MgH₂–TiF₃ system, the amount of hydrogen desorbed was 2.48 wt.% after 10 min, compared to the LiAlH₄–MgH₂ system (1.59 wt.%) at 300°C. Furthermore, the reversibility of this system was performed at 300°C under ∼2 MPa for both samples. LiAlH₄–MgH₂–TiF₃ systems demonstrate the ability to absorb 2.68 wt.% hydrogen after 5 min, which is greater than the LiAlH₄–MgH₂ system (1.75 wt.%). Further study showed that the intermediate phase of Mg₁₇Al₁₂ and Li₃Mg₇ produced during the heating process is mainly due to the Al/LiH reaction with MgH₂, as shown in Eqs 5, 8: 3 L i H + 7 M g H 2 → L i 3 M g 7 + 8.5 H 2 . (8)

The hydrogen sorption properties of 4MgH₂–LiAlH₄ were greatly improved after the addition of 5 wt.% Fe₂O₃, as eloquently stated by Mustafa et al. (Mustafa & Ismail, 2014). As-milled MgH₂ can release hydrogen at 350°C; meanwhile, the as-milled LiAlH₄ can release at 135–160°C. For the destabilized system of 4MgH₂–LiAlH₄, the onset desorption temperature was reduced similar to the as-milled LiAlH₄. However, after the addition of Fe₂O₃, the onset of desorption was decreased to 95°C. The desorption and absorption kinetics were also improved after the addition of Fe₂O₃. The apparent activation energy of 4MgH₂–LiAlH₄ + Fe₂O₃ was reduced to 117 kJ/mol compared to the undoped 4MgH₂–LiAlH₄ systems. Further research exposed that the Li₂Fe₃O₄ was developed by heating 4MgH₂–LiAlH₄ + Fe₂O₃ up to 400°C and revealed that the Li₂Fe₃O₄ also plays a crucial role in reducing the value of desorption temperature and activation energy in the 4MgH₂–LiAlH₄ systems.

According to Wan et al. (Wan et al., 2013), the hydrogen storage performance of MgH₂–LiAlH₄ was effectively improved after the addition of MnFe₂O₄ nanoparticles. As indicated in Table 3, the onset desorption temperature for MgH₂–LiAlH₄ + 5 mol% of MnFe₂O₄ and MgH₂–LiAlH₄ + 7 mol% of MnFe₂O₄ revealed the lowest onset desorption temperature. However, the total amount of hydrogen released for MgH₂–LiAlH₄ + 5 mol% of MnFe₂O₄ is higher than the addition of 7 mol% of MnFe₂O₄. Nonetheless, the addition of MnFe₂O₄ can reduce the onset desorption temperature of the MgH₂–LiAlH₄ systems.

For the desorption kinetics at 200°C, under 0.1 MPa, the MgH₂–LiAlH₄ systems release 0.94 wt.% hydrogen, whereas the MgH₂–LiAlH₄ + 5 mol% of MnFe₂O₄ can release 2.91 wt.%. Furthermore, the reversibility for those samples was investigated at 300°C under 3 MPa, and the doped samples show better absorption kinetics than the undoped samples. For MgH₂–LiAlH₄ + 5 mol% of MnFe₂O₄, a hydrogen absorption capacity of 3.64 wt.% was achieved within 300 s. In the meantime, the MgH₂–LiAlH₄ systems only absorbed 2.81 wt.% of hydrogen under the same conditions. Moreover, after heating up to 400°C, the XRD pattern shows the peaks of Li_0.92Mg_4.08 and Mg₁₇Al₁₂. Furthermore, the new peak of Fe_0.872O observed also indicated that the interaction between LiAlH₄ and MnFe₂O₄ had occurred. However, no Mn-containing peak has been seen due to the low amount of MnFe₂O₄ that has been used. Also, the XRD pattern observed after the absorption kinetics at 300°C stated that no peaks of Li_0.92Mg_4.08 and Mg₁₇Al₁₂ have been detected. The peaks of Fe_0.872O can still be seen in the XRD pattern of the absorption results. Therefore, they concluded that the in situ formed Fe oxide and the Mn-containing peak enhanced hydrogen storage performances of the MgH₂–LiAlH₄ system.

The impact of various additives on the hydrogen storage properties of the MgH₂-LiAlH₄ system was studied by Ismail et al. (Ismail et al., 2011). Milled MgH₂ starts to decompose at 330°C and desorb about 7.1 wt.% of hydrogen at 420°C. Meanwhile, the as-milled LiAlH₄ decomposes at ∼142°C for the first and ∼173°C for the second stage. After the two hydrides (MgH₂–LiAlH₄) with ratio 4:1 have been mixed, the samples began to decompose at 130°C for the first stage (attributed to the decomposition of LiAlH₄), while at 270°C for the second stages (corresponding to the decomposition of Li₃AlH₆). The 4MgH₂–LiAlH₄ was completed at ∼360°C with 7.5 wt.% of hydrogen released (attributed to the decomposition of MgH₂). After the addition of metal halides, the temperature-programmed desorption (TPD) curves of 4MgH₂–LiAlH₄ systems were significantly improved. TiF₃ followed by NiF₂, CrF₂, NbF₅, and YF₃ showed a strong catalytic influence on the decomposition of MgH₂–LiAlH₄, as shown in Figure 10. The MgH₂–LiAlH₄ composite doped with TiF₃ begins to decompose at 70°C. However, the desorption kinetics of the MgH₂–LiAlH₄ composite were significantly enhanced after the addition of 5 wt.% of metal halides. Furthermore, the addition of metal halide additives could reduce the activation energy of the MgH₂–LiAlH₄ composite. The apparent activation energy for the MgH₂–LiAlH₄ composite with the selected different metal halides is shown in Table 4.

In order to study the phase structure of these samples, the 4MgH₂–LiAlH₄ samples were characterized by using XRD. After the samples were heated up to 400°C, apart from Mg, the intermediate phases of Li_0.92Mg_4.08 and Al₁₂Mg₁₇ were eventually created in the composite system. The XRD measurements were also carried out on the absorption kinetics. The results showed that the peaks of Li_0.92Mg_4.08 and Al₁₂Mg₁₇ disappeared; meanwhile, the appearance of peaks of Al₃Mg₂ indicated that the reaction, as in Eqs 6, 7, occurred during the absorption process. For the doped samples, further research showed that LiF and Al₃Ti are believed to act as the actual catalyst that can enhance the interaction of the MgH₂–LiAlH₄ system, while speeding up the hydrogen desorption process of the MgH₂–LiAlH₄ system. According to Mustafa et al. (Mustafa et al., 2015), the addition of K₂TiF₆ improves the 4MgH₂–LiAlH₄ system of hydrogen storage performance. The desorption temperature of the 4MgH₂–LiAlH₄ system was reduced to 80 and 250°C for the first and second stages, respectively, after the addition of K₂TiF₆. Meanwhile, the 4MgH₂–LiAlH₄ composite decomposed at 130 and 270°C for the first and second stages, respectively. In addition, after the addition of K₂TiF₆, desorption and absorption kinetics were also enhanced. The activation energy for 4MgH₂–LiAlH₄ systems has also been reduced from 126 to 107 kJ/mol. The XRD analysis was conducted on 4MgH₂–LiAlH₄ + K₂TiF₆ for the possible reaction of catalytic additives on the 4MgH₂–LiAlH₄ systems. The intermediate phases of Li_0.92Mg_4.08, Al₁₂Mg_17, and Mg were eventually formed after desorption at 400°C. The complete recovery of LiH and MgH₂ from the Li–Mg and Al–Mg alloys was accomplished in the absorption samples due to the reaction of Al₁₂Mg₁₇ and Li_0.92Mg_4.08 with hydrogen. Further verification stated that the peaks of TiH₂, LiF, and Al₃Ti act as the real catalyst, thus proving that the addition of K₂TiF₆ enhanced the sorption properties of the 4MgH₂–LiAlH₄ systems.

Recently, Sulaiman et al. (Sulaiman et al., 2021a) observed an improvement in the onset desorption temperature and the morphology of the 4MgH₂–LiAlH₄ systems when 5 wt.% of Al₂TiO₅ was added. The hydrogen started to release at 85°C which is decreased by 35°C for the undoped systems. It is important to note that the inclusion of Al₂TiO₅ to the 4MgH₂–LiAlH₄ systems resulted in significantly smaller particle sizes which help to shorten the diffusion length and larger nucleation sites. Moreover, based on the XRD result, the new in situ active species of LiTi₂O₄, TiH_2, and AlTi₂ were detected after the de/rehydrogenation process which is believed to act as a true catalyzer in improving the hydrogen storage performance of the Al₂TiO₅-doped Mg–Li–Al systems. From the results, it is noted that the addition of additives ameliorates the performance of the MgH₂–LiAlH₄ composite by reducing the onset decomposition temperature and fastening the sorption kinetics performance than the unary MgH₂ and LiAlH₄, as demonstrated in Table 5. Table 5 presents the onset desorption temperature, total desorption, absorption capacity, and activation energy for the MgH₂–LiAlH₄ system doped with several additives. The undoped MgH₂, LiAlH₄, and MgH₂–LiAlH₄ systems are also included in Table 5 for comparison purposes.

Based on the abovementioned discussion and Table 5, it can be stated that the addition of the additives significantly enhanced the hydrogen storage performance of the MgH₂–LiAlH₄ systems. It is reported that the active species that are in situ formed during the heating process are believed to play a catalytic role in enhancing the hydrogen sorption performance of the MgH₂–LiAlH₄ additive system. Up to this date, the addition of MnFe₂O₄ to Mg–Li–Al composites has presented the best performance which can release hydrogen approximately at 55°C (Wan et al., 2013). In addition, the MgH₂–LiAlH₄–MnFe₂O₄ system can absorb 3.64 wt.% of hydrogen in only 300 s and desorb more hydrogen (approximately 4 wt.% in 200 s), which shows a better performance in the sorption kinetics of MgH₂–LiAlH₄ systems.