Hydrogenation Properties of Mg-Al-Zn-CaO-Hx Prepared by Hydrogen Induced Mechanical Alloying (HIMA).

Mg and Mg-system alloys are the materials of choice among hydrogen energy storage media due to their high hydrogen storage capacity (7.6 wt.%) and lighter weight (Huot, J., et al., 1999. Structural study and hydrogen sorption kinetics of ball-milled magnesium hydride. Journal of Alloys and Compounds, 293, pp.495-500). However, the formation of hydrogen products at high temperatures, the phenomenon of rapid alloy deterioration, and the low rate of reaction in the hydriding and dehydriding processes have been the main hindrances to commercialization of these alloys for hydrogen storage. In this study, to increase the reaction rate with hydrogen, Mg-Al-Zn-CaO-Hx hydrogen storage alloys were fabricated HIMA (Seok, S., et al., 2005. Evaluations of microstructure and hydrogenation properties on Mg2NiHx. Transactions of the Korean Hydrogen and New Energy Society, 16(3), pp.238-243). The Alloying times of 72 and 96 h and BCR of 30:1 and 66:1 were used for the HIMA process; the rotation speed was fixed at 200 rpm and the hydrogen pressure was 3 Mpa. SEM was used to confirm the shape of the particles. The crystal structure of the synthesized materials was analyzed by XRD, and BET measurements were performed to determine the correlation between the BCR and specific surface area. The weight change of the composite material was measured by TGA, and the kinetics was evaluated to determine the hydrogen adsorption rate (at 150, 250, and 350 °C).

Effect of MWCNT (Multi-Walled Carbon Nano-Tube) Doping on Hydrogenation Kinetics of Mg-CaO Alloys.

Magnesium hydride has a high hydrogen storage capacity (7.6 wt.%), and is cheap and lightweight, thus advantageous as a hydrogen storage alloy. However, Mg-based hydrides undergo hydrogenation/ dehydrogenation at high temperature and pressure due to their thermodynamic stability and high oxidation reactivity. Various attempts have been made to lower the reaction rate and dehydrogenation temperature by adding transition elements (e.g., Ti, Fe, Co, Ni, Ce), metal oxides, and intermetallic compounds to overcome these shortcomings. On the other hand, carbon materials have been mainly studied in the field of hydrogen storage with high specific surface area and lightweight properties; however, results show that they cannot store a large amount of hydrogen. Recently, it has been theoretically reported that carbon materials act as adsorbents in hydrogen storage. This study focuses on the hydrogenation behavior of MgHx-CaO and MgHx-CaO-MWCNT composites prepared by hydrogen-induced mechanical alloying, and investigates the properties of these composite materials.