Hydrogen storage in encapsulated magnesium nickel alloys prepared by intergranular diffusion

Mg-Ni metal hydrides have been considered as materials to store hydrogen in solid state as they reversibly adsorb considerable amounts of hydrogen. However, the method of preparation affects the hydrogen storage capacity of the material. Samples containing 1% Ni through 4% Ni (balance Mg) were prepared by powder metallurgical techniques slightly above the eutectic temperature to enhance intergranular diffusion and were investigated. It was found that this approach produced Mg grains encapsulated by a non-stoichiometric Mg-Ni intermetallic layer. The encapsulation resulted in enhanced hydrogen storage due to rapid dissociation of hydrogen by the intermetallic layer and adsorption into stabilized Mg grains. Increasing the concentration of Ni improved the performance of this hydrides layer up to 3 weight percent Ni. It was found using DTA that these hydrides must be carefully managed using lower temperatures and heating rates, as the metastable phase responsible for hydrogen adsorption decomposed at higher temperatures leading to significant reduction in hydrogen uptake.