Boosting the Dehydrogenation Properties of LiAlH4 by Addition of TiSiO4

Given its significant gravimetric hydrogen capacity advantage, lithium alanate (LiAlH4) is regarded as a suitable material for solid-state hydrogen storage. Nevertheless, its outrageous decomposition temperature and slow sorption kinetics hinder its application as a solid-state hydrogen storage material. This research’s objective is to investigate how the addition of titanium silicate (TiSiO4) altered the dehydrogenation behavior of LiAlH4. The LiAlH4–10 wt% TiSiO4 composite dehydrogenation temperatures were lowered to 92 °C (first-step reaction) and 128 °C (second-step reaction). According to dehydrogenation kinetic analysis, the TiSiO4-added LiAlH4 composite was able to liberate more hydrogen (about 6.0 wt%) than the undoped LiAlH4 composite (less than 1.0 wt%) at 90 °C for 2 h. After the addition of TiSiO4, the activation energies for hydrogen to liberate from LiAlH4 were lowered. Based on the Kissinger equation, the activation energies for hydrogen liberation for the two-step dehydrogenation of post-milled LiAlH4 were 103 and 115 kJ/mol, respectively. After milling LiAlH4 with 10 wt% TiSiO4, the activation energies were reduced to 68 and 77 kJ/mol, respectively. Additionally, the scanning electron microscopy images demonstrated that the LiAlH4 particles shrank and barely aggregated when 10 wt% of TiSiO4 was added. According to the X-ray diffraction results, TiSiO4 had a significant effect by lowering the decomposition temperature and increasing the rate of dehydrogenation of LiAlH4 via the new active species of AlTi and Si-containing that formed during the heating process.


Introduction
Concerns about the energy crisis and the environment have led to an increase in the proportion of renewable energy sources in the energy system, such as wind, hydro, and other types. The supply and utilization times are typically out of sync and have some geographical restrictions. The proper secondary energy must be selected to match them, and hydrogen is a promising alternative to meet the demands for clean and sustainable energy technologies [1]. Hydrogen energy is a perfect substitute for petroleum because of its high energy density and lack of carbon emissions [2][3][4][5][6][7].
Hydrogen can be stored in a variety of ways for application purposes. As of now, compressed gas has been the most popular technique. It can also be kept as a liquid at extremely low temperatures. Other methods of storing hydrogen are via the solid-state method through physisorption and chemisorption [8]. Storing hydrogen via the solid-state method is regarded as the most promising method. Based on the US Department of Energy (DOE), by 2025, the fuel cell materials should store 5.5 wt% (gravimetric) and 40 g L −1 (volumetric) of hydrogen [9]. Complex hydride has emerged as the most promising medium for solid-state hydrogen storage based on the DOE target due to its high hydrogen storage capacity. Additionally, based on previous research, storing hydrogen is promising in metal or complex hydrides via chemisorption. This technique involves absorbing and storing hydrogen in a metal powder made of either pure metal or an alloy. The metal/complex hydride material generates heat when hydrogen is absorbed into it, and heat is required for the metal/complex hydride to generate hydrogen again. As a result of the hydrogen's strong bonding with the metal in some materials, it requires extreme temperatures, more than 400 • C for magnesium, as an example [10,11]. This is a disadvantage of the metal/complex hydride storage method [12][13][14]. Among metal or complex hydride materials, one of the best potential candidates is said to be lithium alanate (LiAlH 4 ) [15][16][17][18][19][20]. LiAlH 4 is thought to be a promising material for storing hydrogen in solid-state form as it has a greater capacity to store hydrogen compared to other complex hydrides. Table 1 compares the properties of LiAlH 4 with other complex hydrides.  4 and other complex hydrides [21][22][23][24][25].
Complex metal oxide additives, especially secondary metal oxides, are a newly emerging research area to further enhance LiAlH 4 's dehydrogenation abilities [36][37][38]. The study of the catalysis of Al 2 TiO 5 on the dehydrogenation properties of LiAlH 4 demonstrated that the onset temperatures dropped significantly after milling with 5 wt% Al 2 TiO 5 [39]. The hydrogen began to be liberated at about 90 • C and 137 • C for both steps, respectively. Meanwhile, Zhai et al. [36] investigated how MnFe 2 O 4 affected LiAlH 4 's dehydrogenation properties and discovered that the temperature at which decomposition began was about 70 • C lower than it would have been otherwise. Moreover, the research conducted by Ismail et al. [40] proved that the onset desorption temperature of the two stages of the LiAlH 4 was reduced to 80 • C and 120 • C, respectively, when doped with SrTiO 3 , as opposed to the as-obtained LiAlH 4 . The LiAlH 4 dehydrogenation kinetics were also enhanced as the SrTiO 3 -doped LiAlH 4 composite could liberate about 3.0 wt% of hydrogen at 90 • C in 20 min as opposed to the undoped composite's 0.2 wt% in the same time frame.
However, more research is necessary to determine whether other secondary metal oxide-based catalysts could lower the decomposition temperature and improve LiAlH 4 dehydrogenation kinetic efficiency. In this study, we have used another secondary metal oxide to boost the dehydrogenation properties of LiAlH 4 . To the best of our knowledge, no research has been conducted on enhancing LiAlH 4 's ability to store hydrogen using TiSiO 4 as a catalyst.

Materials and Methods
Sigma Aldrich (Burlington, MA, USA) provided LiAlH 4 (purity 95.0%) and TiSiO 4 (purity 99.8%) powders that were used without any changes. Every stage of the sample preparation process, including loading and weighing, was completed in an MBraun Unilab glove box to avoid oxidation. The sample (LiAlH 4 + 10 wt% TiSiO 4 ) was then directly milled in an NQM-0.4 planetary ball mill for 1 h (15 min milling, followed by three cycles of 2 min rest between rotations) at a rate of 400 rpm.
A Sievert-type apparatus (Advanced Materials Corporation, Pittsburgh, PA, USA) was used to study the onset dehydrogenation temperature and the kinetic property for the liberation of H 2 from the undoped LiAlH 4 and the TiSiO 4 -added LiAlH 4 composite. The sample was heated from room temperature to 250 • C at a heating rate of 5 • C/min in a vacuum environment for the onset dehydrogenation temperature characterization. To determine the kinetics of H 2 liberation, the sample was heated at a constant temperature of 90 • C while being exposed to an H 2 pressure of 1.0 atm. Differential scanning calorimetry (DSC) from Setline STA: Simultaneous Thermal Analysis (SETARAM) was used to investigate the thermal properties of the samples. The DSC measurements were run at heating rates of 15 • C/min, 20 • C/min, 25 • C/min, and 30 • C/min. The argon gas flow rate was set to 50 mL/min, and the temperature range for this measurement was set to 300 • C. The microstructure of the sample before and after the milling process was examined using scanning electron microscopy (SEM; JEOL JSM 6360LA). The phase structure of the sample before and after the ball mill and after the dehydrogenation process was studied using an X-ray diffractometer (XRD, Rigaku Miniflex, Tokyo, Japan) and Fourier transform infrared (IR, Shimadzu Tracer-100, Tokyo, Japan). Figure 1 depicts the results of the research on the onset thermal dehydrogenation and dehydrogenation kinetics processes for both added and undoped composites (LiAlH 4 and 10 wt% TiSiO 4 systems). Two distinguishing features of each composite's dehydrogenation reaction are shown on the graph. As shown in Figure 1a, at about 146 • C, the as-obtained LiAlH 4 has initiated the liberation of hydrogen, and further heating has led to the beginning of a second stage dehydrogenation process at about 180 • C. After 1 h of the LiAlH 4 milling process, the first and second steps' onset dehydrogenation temperatures drop to about 144 • C and 174 • C, respectively. This result demonstrates how the ball milling technique insignificantly influenced the dehydrogenation temperature of LiAlH 4 . Moreover, doping 10 wt% of TiSiO 4 drastically lowered the decomposition temperatures for the two steps at 92 • C and 128 • C. Adding TiSiO 4 as a catalyst proved to enhance the dehydrogenation performance of LiAlH 4 . Figure 1b shows the isothermal dehydrogenation kinetics at 90 • C for doped and undoped samples. Less than 1.0 wt% of hydrogen was liberated in 80 min by the undoped sample. Under the same conditions, the hydrogen's liberate capacity increased significantly to 5.7 wt% after 10 wt% TiSiO 4 was added. As a result, the TiSiO 4 -added LiAlH 4 sample desorbs at a rate that is, on average, 5 to 6 times higher than the undoped LiAlH 4 . According to this result, the catalyst addition of TiSiO 4 improved the kinetics of LiAlH 4 dehydrogenation. The outcome shows that the kinetics of LiAlH 4 dehydrogenation were improved by the catalyst doping, as previous studies stated [15,41,42].  Under the same conditions, the hydrogen's liberate capacity increased significantly to 5.7 wt% after 10 wt% TiSiO4 was added. As a result, the TiSiO4-added LiAlH4 sample desorbs at a rate that is, on average, 5 to 6 times higher than the undoped LiAlH4. According to this result, the catalyst addition of TiSiO4 improved the kinetics of LiAlH4 dehydrogenation. The outcome shows that the kinetics of LiAlH4 dehydrogenation were improved by the catalyst doping, as previous studies stated [15,41,42].

Results and Discussion
The catalytic effects of TiSiO4 on the thermal properties of LiAlH4 were validated using DSC measurements on added and undoped LiAlH4. Temperatures ranging from 25 °C to 300 °C, with an argon flow rate of 50 mL/min, were used for the investigation. Figure  2 displays the DSC curves for added and undoped LiAlH4 at a rate of 15 °C/min. The thermal characteristics of as-obtained LiAlH4 have four peaks. Two are exothermic, while the other two are endothermic. The interaction of hydroxyl impurities with LiAlH4's surface caused the first exothermic peak to appear at 150 °C, while the melting of LiAlH4 caused the first endothermic peak to appear at 175 °C [37,40,43,44]. In the meantime, the dehydrogenation of liquid LiAlH4 causes the second exothermic peak (190 °C). Li3AlH6 decomposition (265 °C) was responsible for the second endothermic peak. These second exothermic and endothermic peaks were assigned to Equations (1) and (2), respectively. These similar peaks also occurred to the post-milled LiAlH4, but at lower temperatures. The catalytic effects of TiSiO 4 on the thermal properties of LiAlH 4 were validated using DSC measurements on added and undoped LiAlH 4 . Temperatures ranging from 25 • C to 300 • C, with an argon flow rate of 50 mL/min, were used for the investigation. Figure 2 displays the DSC curves for added and undoped LiAlH 4 at a rate of 15 • C/min. The thermal characteristics of as-obtained LiAlH 4 have four peaks. Two are exothermic, while the other two are endothermic. The interaction of hydroxyl impurities with LiAlH 4 's surface caused the first exothermic peak to appear at 150 • C, while the melting of LiAlH 4 caused the first endothermic peak to appear at 175 • C [37,40,43,44]. In the meantime, the dehydrogenation of liquid LiAlH 4 causes the second exothermic peak (190 • C). Li 3 AlH 6 decomposition (265 • C) was responsible for the second endothermic peak. These second exothermic and endothermic peaks were assigned to Equations (1) and (2), respectively. These similar peaks also occurred to the post-milled LiAlH 4 , but at lower temperatures.
The thermal event of LiAlH 4 is lowered from four to two after the addition of TiSiO 4 . The exothermic event peak at around 120 • C seems to correspond to the decomposition of LiAlH 4 (Equation (1)), and the endothermic event peak at around 176 • C is most likely to correspond to the decomposition of Li 3 AlH 6 (Equation (2)). The first endothermic event associated with LiAlH 4 melting has vanished from the DSC curve of TiSiO 4 -doped LiAlH 4 . The disappearance of the melting event is most likely owing to the fact that the decomposition temperature of the first stage of the doped sample is lower than the melting temperature of post-milled LiAlH 4 .
Different heating rates were measured using DSC to examine the impact of TiSiO 4 addition on the activation energy (E A ) for hydrogen desorbed from LiAlH 4 . The DSC curves for the added and undoped LiAlH 4 samples at various heating rates (15,20,25, and 30 • C/min) are shown in Figure 3a,b. The Kissinger equation used to calculate the E A values of the dehydrogenation process of the 1 h milled LiAlH 4 and LiAlH 4 -10 wt% TiSiO 4 composite is as follows: where R is the gas constant, A is a linear constant, T p is the peak temperature on the DSC dehydrogenation curves, E A is the activation energy, and β is the DSC heating rate.
Consequently, the E A was determined using the graph's slope, ln β/T 2 p vs. 1000/T p . The Kissinger plots for the dehydrogenation of LiAlH 4 (1st stage) and the dehydrogenation of Li 3 AlH 6 (2nd stage) for both composites are shown in Figure 3c,d. Based on the slopes, E A for the post-milled LiAlH 4 are 103 kJ/mol (1st stage dehydrogenation) and 115 kJ/mol (2nd stage dehydrogenation), respectively. Meanwhile, the E A for the first and second stages of dehydrogenation, respectively, are reduced to 68 kJ/mol and 77 kJ/mol for the added system with 10 wt% TiSiO 4 . The thermal event of LiAlH4 is lowered from four to two after the addition of TiSiO4. The exothermic event peak at around 120 °C seems to correspond to the decomposition of LiAlH4 (Equation (1)), and the endothermic event peak at around 176 °C is most likely to correspond to the decomposition of Li3AlH6 (Equation (2)). The first endothermic event associated with LiAlH4 melting has vanished from the DSC curve of TiSiO4-doped LiAlH4. The disappearance of the melting event is most likely owing to the fact that the decomposition temperature of the first stage of the doped sample is lower than the melting temperature of post-milled LiAlH4.
Different heating rates were measured using DSC to examine the impact of TiSiO4 addition on the activation energy (EA) for hydrogen desorbed from LiAlH4. The DSC curves for the added and undoped LiAlH4 samples at various heating rates (15,20,25, and 30 °C/min) are shown in Figure 3a,b. The Kissinger equation used to calculate the EA values of the dehydrogenation process of the 1 h milled LiAlH4 and LiAlH4-10 wt% TiSiO4 composite is as follows: where R is the gas constant, A is a linear constant, Tp is the peak temperature on the DSC dehydrogenation curves, EA is the activation energy, and β is the DSC heating rate. Consequently, the EA was determined using the graph's slope, ln [   Figure 4 shows the morphology differences between the TiSiO4, added, and undoped LiAlH4 samples. Figure 4a shows the morphology for the as-obtained TiSiO4, which is a fine particle. Figure 4b depicts the as-obtained LiAlH4's morphology, which is described as rough and asymmetrical in shape. The particle size of LiAlH4 was smaller but aggregated and inhomogeneous after a 1 h milling process (Figure 4c). The particle size of the  Figure 4 shows the morphology differences between the TiSiO 4 , added, and undoped LiAlH 4 samples. Figure 4a shows the morphology for the as-obtained TiSiO 4 , which is a fine particle. Figure 4b depicts the as-obtained LiAlH 4 's morphology, which is described as rough and asymmetrical in shape. The particle size of LiAlH 4 was smaller but aggregated and inhomogeneous after a 1 h milling process (Figure 4c). The particle size of the 10 wt% TiSiO 4 -doped LiAlH 4 sample (Figure 4d) has shrunk and is less aggregated compared to post-milled LiAlH 4 . The 10 wt% TiSiO 4 -added LiAlH 4 composite has a larger surface area due to the smaller particle sizes. Previous research has shown that surface modification significantly improves the hydrogen storage properties of metals and complex hydride materials [34,[45][46][47].  The particle size distribution of the TiSiO4, added, and undoped LiAlH4 samples were determined using the Image J software, as demonstrated in Figure 5. Based on the histogram shown in Figure 5a-d, the estimated average particle sizes for the as-obtained TiSiO4, as-obtained LiAlH4, post-milled LiAlH4, and LiAlH4 added with 10 wt% TiSiO4 were determined to be 6.10, 81.58, 61.71, and 28.13 µm, respectively. These findings demonstrated that the addition of 10 wt% TiSiO4 to LiAlH4 significantly reduced particle size. Previous studies by Ahmad et al. [22] and Cai et al. [48] stated the added LiAlH4 increased the rate of hydrogen diffusion, which resulted in fast dehydrogenation kinetics and low activation energy. Additionally, its smaller particle size results in a larger surface area and more grain boundaries [36,38,49]. The particle size distribution of the TiSiO 4 , added, and undoped LiAlH 4 samples were determined using the Image J software, as demonstrated in Figure 5. Based on the histogram shown in Figure 5a-d, the estimated average particle sizes for the as-obtained TiSiO 4 , as-obtained LiAlH 4 , post-milled LiAlH 4 , and LiAlH 4 added with 10 wt% TiSiO 4 were determined to be 6.10, 81.58, 61.71, and 28.13 µm, respectively. These findings demonstrated that the addition of 10 wt% TiSiO 4 to LiAlH 4 significantly reduced particle size. Previous studies by Ahmad et al. [22] and Cai et al. [48] stated the added LiAlH 4 increased the rate of hydrogen diffusion, which resulted in fast dehydrogenation kinetics and low activation energy. Additionally, its smaller particle size results in a larger surface area and more grain boundaries [36,38,49].  Figure 6 shows the XRD pattern of the as-obtained and post-milled LiAlH4, TiSiO4doped LiAlH4 composite, and as-obtained TiSiO4 sample. The sample of as-obtained TiSiO4 shows the high purity of TiSiO4 [50]. For the as-obtained LiAlH4 sample, as shown in Figure 6a, the peaks of LiAlH4 are dominant, and there are no other peaks detected, proving that the as-obtained LiAlH4 sample is pure, as stated by the supplier. Furthermore, as shown in Figure 6b, even after the ball milling process of 1 h, LiAlH4 initial phase remains unchanged. According to this outcome and the findings of Sazelee et al. [15] and Balema et al. [51], LiAlH4 was stable even after being subjected to ball milling. Figure 6c shows the XRD pattern of the LiAlH4-10 wt% TiSiO4 composite. In addition to the majority peaks of LiAlH4, there is a new peak corresponding to the Al for the TiSiO4-doped LiAlH4 after 1 h milling. The appearance of Al peaks indicates that with the presence of TiSiO4, hydrogen is slightly released from LiAlH4 after milling (Equation (1)). However, the peaks that correspond to Li3AlH6 could not be detected in this pattern. Additionally, due to the small amount of TiSiO4 used or the fact that TiSiO4 became amorphous after 1 h of the milling process, the peaks of TiSiO4 could not be detected with an XRD pattern [39,49,52].  Figure 6 shows the XRD pattern of the as-obtained and post-milled LiAlH 4 , TiSiO 4doped LiAlH 4 composite, and as-obtained TiSiO 4 sample. The sample of as-obtained TiSiO 4 shows the high purity of TiSiO 4 [50]. For the as-obtained LiAlH 4 sample, as shown in Figure 6a, the peaks of LiAlH 4 are dominant, and there are no other peaks detected, proving that the as-obtained LiAlH 4 sample is pure, as stated by the supplier. Furthermore, as shown in Figure 6b, even after the ball milling process of 1 h, LiAlH 4 initial phase remains unchanged. According to this outcome and the findings of Sazelee et al. [15] and Balema et al. [51], LiAlH 4 was stable even after being subjected to ball milling. Figure 6c shows the XRD pattern of the LiAlH 4 -10 wt% TiSiO 4 composite. In addition to the majority peaks of LiAlH 4 , there is a new peak corresponding to the Al for the TiSiO 4 -doped LiAlH 4 after 1 h milling. The appearance of Al peaks indicates that with the presence of TiSiO 4 , hydrogen is slightly released from LiAlH 4 after milling (Equation (1)). However, the peaks that correspond to Li 3 AlH 6 could not be detected in this pattern. Additionally, due to the small amount of TiSiO 4 used or the fact that TiSiO 4 became amorphous after 1 h of the milling process, the peaks of TiSiO 4 could not be detected with an XRD pattern [39,49,52]. Figure 7 depicts the FTIR spectrum used to investigate the effect of TiSiO 4 as a catalyst on the LiAlH 4 infrared spectroscopy band and to confirm the presence of Li 3 AlH 6 in the TiSiO 4 -doped LiAlH 4 sample after milling. In the previous studies [15,37,53], LiAlH 4 was represented by peaks with two bending modes between 800 and 900 cm −1 and two stretching modes between 1600 and 1800 cm −1 . Figure 7a,b show these peaks in the asobtained and post-milled LiAlH 4 samples. After 1 h of milling (Figure 7c), a new peak at 1403 cm −1 was discovered in the TiSiO 4 -doped LiAlH 4 sample. This new peak corresponds to the Al-H stretching mode of Li 3 AlH 6 . Although the peak of Li 3 AlH 6 could not be detected in the XRD pattern (Figure 6c), the appearance of the Al-H stretching mode of Li 3 AlH 6 in the FTIR result proves that the TiSiO 4 -doped LiAlH 4 sample slightly released hydrogen during the milling process (Equation (1)).  Figure 7 depicts the FTIR spectrum used to investigate the effect of TiSiO4 as a catalyst on the LiAlH4 infrared spectroscopy band and to confirm the presence of Li3AlH6 in the TiSiO4-doped LiAlH4 sample after milling. In the previous studies [15,37,53], LiAlH4 was represented by peaks with two bending modes between 800 and 900 cm −1 and two stretching modes between 1600 and 1800 cm −1 . Figure 7a,b show these peaks in the asobtained and post-milled LiAlH4 samples. After 1 h of milling (Figure 7c), a new peak at 1403 cm −1 was discovered in the TiSiO4-doped LiAlH4 sample. This new peak corresponds to the Al-H stretching mode of Li3AlH6. Although the peak of Li3AlH6 could not be detected in the XRD pattern (Figure 6c), the appearance of the Al-H stretching mode of Li3AlH6 in the FTIR result proves that the TiSiO4-doped LiAlH4 sample slightly released hydrogen during the milling process (Equation (1)). The XRD analysis helped to identify the catalytic and reaction mechanism behind the improvement of the dehydrogenation properties of TiSiO4-added LiAlH4. Figure 8 shows the results of 10 wt% and 20 wt% TiSiO4-added LiAlH4 composites after the dehydrogenation process at 250 °C. Due to the small amount of catalyst used, it may be challenging to identify the active species in the 10 wt% TiSiO4-added LiAlH4, so 20 wt% TiSiO4 was The XRD analysis helped to identify the catalytic and reaction mechanism behind the improvement of the dehydrogenation properties of TiSiO 4 -added LiAlH 4 . Figure 8 shows the results of 10 wt% and 20 wt% TiSiO 4 -added LiAlH 4 composites after the dehydrogenation process at 250 • C. Due to the small amount of catalyst used, it may be challenging to identify the active species in the 10 wt% TiSiO 4 -added LiAlH 4 , so 20 wt% TiSiO 4 was added to LiAlH 4 . The presence of the Al and LiH peaks in both samples (Figure 8a) indicates that LiAlH 4 has been completely dehydrogenated (Equation (2)). In addition to Al and LiH peaks, the peaks that correspond to the AlTi species can also be detected in the dehydrogenation sample. However, the peaks that correspond to the Si or Si-containing patterns could not be observed after the dehydrogenation process. This may be because the Si or Si-containing patterns were in an amorphous state. According to this research, it was hypothesized that the enhanced dehydrogenation behaviors of LiAlH 4 were attributed to the formation of AlTi and Si or Si-containing species. Furthermore, there were no new peaks found in the XRD patterns of the desorbed 20 wt% TiSiO 4 -added LiAlH 4 composite (Figure 8b), which are similar to those of the 10 wt% TiSiO 4 -added LiAlH 4 composite ( Figure 8a). The peak of Al, LiH, and AlTi did not change, and no other patterns were discovered in the dehydrogenation composite, possibly because these patterns were in an amorphous state when the dehydrogenation process was complete. Previous studies have shown that the in-situ emergence of AlTi helps to improve the dehydrogenation behavior of LiAlH4 [39,49,54]. Strong surface reactions between the Ti atom and LiAlH4 caused a reduction in the H binding energy. The correlation between the charge transfer change between Al and H and the rapid kinetic efficiency of LiAlH4 may explain the decrease in binding energy. Although the Si or Si-containing phase was not found, these species likewise play a particular role in enhancing the dehydrogenation behavior of LiAlH4. For example, the Si-containing species have been proven to play a significant role in enhancing the hydrogen storage properties of MgH2 [55]. Another study proved that SiC could enhance the hydrogen storage properties of MgH2 by reducing grain size and increasing defect concentration in MgH2 particles [56,57]. However, more research is still needed, such as using high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy to clarify the exact catalytic role of TiSiO4 on the Previous studies have shown that the in-situ emergence of AlTi helps to improve the dehydrogenation behavior of LiAlH 4 [39,49,54]. Strong surface reactions between the Ti atom and LiAlH 4 caused a reduction in the H binding energy. The correlation between the charge transfer change between Al and H and the rapid kinetic efficiency of LiAlH 4 may explain the decrease in binding energy. Although the Si or Si-containing phase was not found, these species likewise play a particular role in enhancing the dehydrogenation behavior of LiAlH 4 . For example, the Si-containing species have been proven to play a significant role in enhancing the hydrogen storage properties of MgH 2 [55]. Another study proved that SiC could enhance the hydrogen storage properties of MgH 2 by reducing grain size and increasing defect concentration in MgH 2 particles [56,57]. However, more research is still needed, such as using high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy to clarify the exact catalytic role of TiSiO 4 on the hydrogen storage properties of LiAlH 4 .

Conclusions
In conclusion, the addition of TiSiO 4 improved the dehydrogenation properties of LiAlH 4 . The introduction of TiSiO 4 to LiAlH 4 reduced the dehydrogenation temperatures for the first and second stages (start decomposing at 92 • C and 128 • C, respectively). Dehydrogenation kinetic analysis at 90 • C revealed that after 2 h, the TiSiO 4 -added LiAlH 4 composite was able to liberate more hydrogen (about 6.00 wt%) than the undoped LiAlH 4 composite (less than 1.00 wt%). The E A for hydrogen liberated from LiAlH 4 was reduced after TiSiO 4 was added. According to the Kissinger equation, the E A for hydrogen liberated in the two-step dehydrogenation of post-milled LiAlH 4 was 103 and 115 kJ/mol, respectively. The E A were lowered to 68 and 77 kJ/mol, respectively, after milling LiAlH 4 with 10 wt% of TiSiO 4 . The addition of 10 wt% of TiSiO 4 also caused the LiAlH 4 particles to shrink and become less aggregated. According to the XRD results, TiSiO 4 significantly enhanced the dehydrogenation properties of LiAlH 4 by forming active AlTi and Si-containing species during the heating process.

Data Availability Statement:
The data presented in this study are available on request from the corresponding author.