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We demonstrated the preparation of Mg 17 Al 12 , a promising hydrogen storage alloy, by the method of combustion synthesis, and focused on the effects of the aluminum particle size, the synthesis temperature and the corresponding holding time on the phase composition of the products. From the X-ray diffraction patterns, it was confirmed that both the decrease of the aluminum particle size and the increase of the holding time kept at the synthesis temperature were beneficial to improve the purity of the products dramatically. It is notable that Mg 17 Al 12 single phase can be obtained with only 0.5 h holding time at 733 K when the aluminum particle size is 1–3 μm. What is more, we first proposed the alloying mechanism in the combustion synthesis of Mg–Al alloy, that is, Mg 2 Al 3 phase is synthesized first, then Mg 2 Al 3 reacts with residual Mg, forming Mg 17 Al 12 alloy.

We reported the structures and superior hydrogen storage properties of the composites Mg 90 Ni 10− x Fe x ( x = 0, 2, 4, 6 and 8) prepared by the process of HCS + MM, i.e., the hydriding combustion synthesis followed by mechanical milling. By means of X-ray diffraction (XRD), scanning electron microscopy (SEM) with an energy dispersive X-ray spectrometer (EDX) and gas reaction controller (GRC), the crystal structures, surface morphologies and hydriding/dehydriding properties of the composites were studied in detail. The Mg 90 Ni 10− x Fe x ( x = 2, 4, 6 and 8) composites consist of MgH 2 , Mg, Mg 2 NiH 4 , Mg 2 NiH 0.3 and Fe phases, while Mg 90 Ni 10 is composed of MgH 2 , Mg, Mg 2 NiH 4 and Mg 2 NiH 0.3 . It is found that Mg 90 Ni 2 Fe 8 has the best hydriding properties, requiring only 30 s to absorb 97% of its saturated hydrogen capacity of 4.80 wt.% at 373 K. The best dehydriding result is obtained with Mg 90 Ni 8 Fe 2 , which desorbs 2.02 and 4.40 wt.% hydrogen at 493 and 523 K, respectively. The microstructures of the composites prepared by HCS + MM have remarkable influences on the enhanced hydriding/dehydriding properties. In addition, the catalytic effects of Mg 2 Ni and Fe phases during hydriding/dehydriding were discussed in this study.

Magnesium chloride efficiently catalyzed the hydrolysis of Mg-based hydride prepared by hydriding combustion synthesis. Hydrogen yield of 1635 mL g(-1) was obtained (MgH(2)), i.e. with 96% conversion in 30 min at 303 K.