Mechanosynthesis and reversible hydrogen storage of Mg 2 Ni and Mg 2 Cu alloys

Abstract

A series of MgNi or MgCu alloys with Mg content comprised between 55 and 77 at% Mg was prepared by mechanical alloying with the aim of synthesizing Mg 2 Ni and Mg 2 Cu phases, respectively. Their morphology and structural properties were characterized by scanning electron microscopy (SEM) and X-ray Diffraction (XRD). High Pressure Differential Scanning Calorimetry (HP-DSC) was used to evaluate their hydrogenation properties. For the MgNi series, 8 hours of milling were enough to synthesize the Mg 2 Ni alloy. The highest reversible hydrogen capacity (2.8 mass%) was obtained for 70 at% Mg sample without the need of any activation treatment. For MgCu series, 83 mass% of Mg 2 Cu was obtained after 4 hours of milling. From the view point of alloying composition, Mg-rich samples show better crystallinity of Mg 2 Cu phase. Under hydrogen, the Mg 2 Cu powder mixtures decompose and form MgH 2 hydride storing 1.56 mass% of hydrogen for 66 at% Mg. For the MgNi series, Cu or Al elements (1 to 10 mass%) were added during milling. HP-DSC runs show that they destabilize the hydride phase due to alloying effects.