Hydrogen storage properties of the Mg/Fe system

Magnesium hydride is a very attractive material for solid state hydrogen storage due to their high mass and volume capacity, but its slow absortion/desortion kinetics does not favours its practical use in mobile applications. Recently it has been observed that the addition of small quantities of transition metals or their oxides has an important catalytic effect on its hydrogen sorption kinetics. Although this effect is well documented very little is known about the precise mechanisms involved in the observed sorption rate improvement. We present here a study of the sorption properties of several samples in the MgH2/Fe system prepared by mechanical alloying in H2 atmosphere and starting from mixtures of Mg or MgH2 with Fe or Fe2O3 of varying composition. The samples were characterized by X-ray diffraction and Mössbauer spectroscopy, before and after milling and after several H2 absorption and desorption cycles in a Sievert-type volumetric apparatus. Some differences were found in the desorption kinetics that can be correlated with the microstucture resulting from the milling process.