Hydrogen storage properties of (Mg₂Ni)_100-xAg_x powder prepared by mechanical alloying

In many hydrogen storage methods, metal hydrides proposed to have some advantages such as greater volumetric efficiency, relatively low pressure, and high safety issue have attracted many R and D interests. Among a number of alloys, A₂B type Mg₂Ni intermetallic alloy due to its high hydrogen absorption capacity, lightweight and low cost is considered as a promising candidate for hydrogen storage applications. In the present study, an intermetallic powder with a desired composition of (Mg₂Ni)_100-xAg_x (x = 0, 1.0 and 5.0) was directly prepared by mechanical alloying from pure Mg, Ni and Ag elemental powders under an inert gas. The structural transformations of as-milled powder mixtures in varied milling times were examined by X-ray diffraction (XRD) technique. The hydrogen storage kinetics, pressure-composition-temperature (P-C-T) curves and thermal analysis of 15 h milled Mg₂Ni / Ag powders were evaluated. The experimental results showed that the 15 h as-milled powders were identified as a nanocrystalline mixture of Mg₂Ni, Mg and Ni. Silver addition significantly improved the hydrogen absorption capacity of Mg₂Ni, revealing that the absorbed hydrogen content and reversible hydrogen content at 350 °C were increased from 3.14 to 3.83%(ω) and from 2.40 to 3.0%(ω), respectively, for the 15 h milled Mg₂Ni powder at silver content of 1.0%.