Synthesis, characterisation and hydrogen sorption properties of mechanically alloyed Mg(Ni1-xMnx)2

Abstract

Hydrogen storage materials based on the stoichiometry Mg(Ni1-xMnx)2 have been synthesized by High Energy Ball Milling (HEBM) and studied as potential candidate materials for solid state hydrogen storage. The microstructures of the as-cast and the milled alloys were characterized by means of X-ray Powder Diffraction (XRD) and Scanning Electron Microscopy (SEM) both prior and after the hydrogenation process. The storage characteristics (Pressure-Composition-Temperature isotherms) and the sorption kinetics obtained by a commercial and automatically controlled Sievert-type apparatus. The X-ray results showed that the substitution of Mn over Ni could eliminate and inhibit the MgNi2 phase. The calculation of the average crystallite size showed that the increase of the amount of Mn can reduce the size at the early stages, but for Mn content higher than 0.25 the crystallite size increases, while the microstrain levels decreased monotonically. The hydrogenation and dehydrogenation measurements took place at several temperatures (150–200–250–300 °C). The results showed that the kinetics for both the hydrogenation and dehydrogenation can be fast for operation at temperatures between 250 and 300 °C, but for temperatures below 200 °C the hydrogenation process is very slow, and the dehydrogenation process cannot be achieved.