Magnesium-based alloys are promising hydrogen storage materials because of their high storage capacity and low cost. It was found that the electrochemical activity of nanocrystalline hydrogen storage alloys can be improved in many ways, by alloying with other elements, by ball-milling the alloy powders with a small amount of nickel or graphite powders. The surface modification of nanocrystalline hydrogen storage alloys with graphite by ball-milling leads to an improvement in both discharge capacity and charge-discharge cycle. In this work, nanostructured composite Mg₂Ni/LaNi₅ materials have been synthesized using the mechanical alloying process. The new composites have been investigated by XRD, TEM, SEM and electron energy dispersion spectrum for their phase compositions, crystal structure, grain size, particle morphology and the distribution of catalyst elements. Hydrogen storage capacities and the hydriding-dehydriding kinetics of the new materials have been measured at different temperatures using a Sieverts apparatus. The results show that nanostructured  Mg_1.5Mn_0.5Ni/LaNi_3.75Mn_0.75Al_0.25Co_0.25 composite material releases 1.6 wt% hydrogen at 295K. It is believed that the dehydriding temperature is largely controlled by the thermodynamic configuration of magnesium hydride. Additionally, doping Mg₂Ni nanocomposite materials with palladium or graphite reduces the hydriding and dehydriding temperatures, as well. The nanocrystalline metal hydrides offer a breakthrough in prospects for practical applications. Their excellent properties (significantly exceeding traditional hydrides) are a result of the combined engineering of many factors: alloy composition, surface properties, microstructure, grain size and others.

This work was supported by the Polish National Committee for Scientific Research under the contract No PBZ-KBN-117/T08/07.

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