Metal hydrides such as MgH2 and NaBH4 are among the materials for with the highest potential solid-state hydrogen storage. However, unlike gas and liquid storage, a dehydrogenation process has to be done prior to hydrogen utilization. In this context, the hydrolysis method is one of the possible methods to extract or generate hydrogen from the materials. However, problems like the MgH2 passivation layer, high cost and sluggish self-hydrolysis of NaBH4 are the known limiting factors for this process, but they can be overcome with the help of catalysts. In this works, selected studies have been reviewed on the performance of catalysts like chloride, oxide, fluoride, platinum, ruthenium, cobalt and nickel-based on the MgH2 and NaBH4 system. These studies show a significant enhancement in the amount of hydrogen released as compared to the hydrolysis of the pure MgH2 and NaBH4. Therefore, the addition of catalysts is proven as one of the options in improving hydrogen generation via the hydrolysis of MgH2 and NaBH4.

Summary A ball milling technique was used to prepare a 4MgH2‐LiAlH4 doped TiO2 sample. The hydrogen storage behaviour of the system 4MgH2‐LiAlH4‐TiO2 and the role played by TiO2 have been systematically investigated. The result shows the decrement of the initial decomposition temperature from the 4MgH2‐LiAlH4‐TiO2 composite when contrasted with the 4MgH2‐LiAlH4 system. The initial dehydrogenation temperature of 4MgH2‐LiAlH4‐10 wt% TiO2 destabilized system decreased from 100°C and 270°C of undoped composite to 70°C and 200°C, respectively, for the desorption process in the first two stages. It was also found that the re/dehydrogenation kinetics performances of the 4MgH2‐LiAlH4‐10 wt% TiO2 destabilized system was improved when contrasted with the non‐catalyzed sample. On the other hand, the activation energy for the MgH2‐relevant decomposition is reduced from 133.3 kJ/mol (4MgH2‐LiAlH4 sample) to 102.5 kJ/mol (4MgH2‐LiAlH4‐TiO2 sample). In addition, this synergistic effect of TiO2 on the improvement of the absorption/desorption performances was related to the formation of Al3Ti and TiH2 phases in the doped sample upon desorption, which reinforces the interaction of MgH2 with LiAlH4. This further changes the thermodynamics of the reactions by modifying the absorption/desorption pathway. In conclusion, the TiO2 catalyst showed a good catalytic impact in ameliorating the hydrogen sorption behaviour of the 4MgH2‐LiAlH4 sample.

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Summary The 4MgH2‐Li3AlH6 destabilized system is deemed as a propitious composite to store hydrogen in a solid form. The catalytic effects of strontium titanate (SrTiO3) on the hydrogen sorption performances of the 4MgH2‐Li3AlH6 system which was prepared by the ball milling were studied for the first time. It was found that SrTiO3 demonstrates a good catalytic ability to the 4MgH2‐Li3AlH6 system by reducing the onset decomposition temperature as well as enhancing its rehydrogenation kinetics performance. The SrTiO3/4MgH2‐Li3AlH6 composite has started to release hydrogen at 135°C and 215°C, for the first two steps of desorption, respectively. These temperature values are about 35°C lower for both stages as opposed to the pure 4MgH2‐Li3AlH6 system. In terms of the rehydrogenation kinetics, the composite of SrTiO3/4MgH2‐Li3AlH6 composite absorbed approximately 4.23 wt% of hydrogen within 30 minutes of adsorption at 320°C. In contrast, the 4MgH2‐Li3AlH6 destabilized system showed a hydrogen adsorption capacity of 3.53 wt% under similar conditions. The inclusion of SrTiO3 to the 4MgH2‐Li3AlH6 system did not result in the enhancement of its desorption kinetics performance at 320°C. The apparent activation energy for the hydrogen desorption of SrTiO3/4MgH2‐Li3AlH6 composite that was obtained by the Kissinger analysis was calculated to be 119 kJ/mol, which is significantly lower than the pure composite (151 kJ/mol). The images observed by the scanning electron microscopy demonstrated that all the materials are well mixed after the ball milling process and it can be proposed that the key role played by the SrTiO3 was based on the alteration of the microstructure of the composite. From the X‐ray diffraction analysis, it was observed that SrTiO3 is a stable and inert catalyst. Thus, the improvement in the hydrogen sorption performances of the 4MgH2‐Li3AlH6 composite is mainly ascribed to the pulverization effect introduced by SrTiO3.

In this work, the catalytic effects of FeCl3 toward the hydrogen storage properties of the MgH2–Na3AlH6 composite were investigated for the first time. The temperature-programed desorption results indicated that the onset temperature of the hydrogen release of a 10 wt % FeCl3-doped MgH2–Na3AlH6 composite was ∼30 °C lower than that of the undoped MgH2–Na3AlH6 composite. The addition of FeCl3 into the MgH2–Na3AlH6 composite resulted in improved absorption and desorption kinetics performance. The absorption/desorption kinetics measurements at 320 °C (under 33 and 1 atm hydrogen pressure, respectively) indicated that within 10 min, the doped sample absorbed ∼4.0 wt % and desorbed ∼1.5 wt % hydrogen. By comparison, the undoped sample absorbed only ∼2.1 wt % and desorbed only ∼0.6 wt % hydrogen under the same conditions and time. Comparably, the apparent activation energy value of the doped composite is 128 kJ/mol, which is 12 kJ/mol lower than that of the undoped composite (140 kJ/mol). The formation of the new species of MgCl2 and Fe in the doped composite was detected from X-ray diffraction analysis after heating and absorption processes. These two components were believed to play a vital role in reducing the decomposition temperature and kinetics enhancement of the MgH2–Na3AlH6 composite.