Alexandre Augusto Cesario Asselli

Formation reaction of Mg2FeH6: effect of hydrogen absorption/desorption kinetics

In this paper we address some aspects of the kinetics of hydrogen absorption and desorption of Mg 2 FeH 6 nanocomposite powder. The Mg 2 FeH 6 material was prepared from a 2Mg-Fe composition by reactive milling under H 2 pressure at room temperature. After mechano-chemical processing, the material was mainly constituted of Mg 2 FeH 6 having a hydrogen gravimetric capacity corresponding to 94% of the theoretical capacity. The kinetics of hydrogen absorption at constant temperature and the transformation of phases during this process were studied. The kinetics of hydrogen absorption presented a two-step behaviour. First, β-MgH 2 was formed with faster kinetics than Mg 2 FeH 6 under constant temperature and H 2 pressure. Then, β-MgH 2 reacted with α-Fe forming Mg 2 FeH 6 in a much slower reaction. Unexpectedly, reaction of hydrogen desorption showed an one-step kinetics, even if Mg 2 FeH 6 and β-MgH 2 phases were previously present in the powder.

The Influence of Morphology on the Hydrogen Storage Properties of Magnesium Based Materials Processed by Cold Rolling

In this communication we report the effect of macro and microstructure on the hydrogen storage properties of magnesium based materials. Magnesium hydride is an attractive material for hydrogen storage applications since it has a high hydrogen volumetric density. Furthermore, the high enthalpy of hydride formation makes it attractive for thermal energy storage applications. Besides, magnesium is an abundant and low cost material. However, the Mg/MgH2 system requires high operating temperatures due to its thermodynamic stability and slow hydrogen absorption and desorption kinetics. Magnesium’s first hydrogenation is a very long and costly process. This work aims to ameliorate this process which would effectively reduce the cost of MgH2. Commercial pure magnesium samples were processed by cold rolling. After processing, the samples presented limited hydrogen absorption due to their small surface area to volume ratio. To overcome this problem the samples were then reduced to powder using a bastard file. The samples were characterized by scanning electron microscopy and presented different morphology. Hydrogen storage properties and morphology are discussed and correlated. Results show an important improvement on the hydrogen absorption and desorption kinetics for the comminuted samples.