Nanostructured magnesium hydride MgH₂, prepared by a mechanical milling method, is considered an attractive hydrogen storage material. In particular, MgH₂ shows interesting properties such as high H₂ gravimetric storage capacity (7.6 wt%), low cost and high abundance. However, this material displays too high temperatures of decomposition, mainly owing to high thermodynamic stability and slow decomposition kinetics, so that several routes have been proposed in order to enhance the reaction and to reduce the decomposition temperature. These processes are based on the introduction of an high density of crystal defects or by ball-milling with intermetallic compounds with lower hydrogen desorption temperature than magnesium.

Since the desorption mechanism is strongly influenced by the chemical and mechanical properties at the interface between MgH₂ and Mg, a detailed study of this interface is needed. From an experimental point of view there is not a clear evidence of which interfaces are involved in the hydrogen diffusion and which is the atomic dynamics at the interfaces. However, extensive first-principle molecular dynamics simulations of the interface MgH₂-Mg give clear indications of both the equilibrium properties and the behaviour of the Mg and H atoms in terms of total energy calculations. The interface and the hydrogen desorption are studied as functions of the temperature. The atomic environment of the Mg atoms at the interface and hydrogen paths for desorption are characterized and studied. Furthermore some indications of the rearrangement of the magnesium atoms after desorption are provided to characterize the phase transition.

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