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ABSTRACT: Magnesium is one of the most promising materials for hydrogen storage due to its high
capacity and low cost. Unfortunately, practical applications are for the moment limited by the slow
kinetics and the high operating temperature. Nanostructuring magnesium hydride MgH2, generally
by ball milling, introduces plastic deformations and catalysts that highly enhances the H2 absorption
and desorption. However a fundamental understanding of the role played by catalysts and interfaces
in MgH2 is still lacking. Microscopic characterization of MgH2-Mg system with and without heavy
metal catalysts, is achieved by combining accurate SEM observations of samples after partial
desorption process and atomic level ab-initio molecular dynamics simulations of MgH2-Mg
interfaces. The experimental method is based on low voltage SEM observations of cross sectional
powder samples, prepared by a new specific metallographic process. Identification of nucleation
sites of the sorption reaction and their correlation with the presence of catalyst particles is achieved
by suitable experimental conditions. Moreover ab-initio molecular dynamics clarifies the interplay
of interfaces and the deformations induced during desorption by the presence of catalysts that are
able to lower binding energies and free hydrogen atoms toward interfaces. Both approaches confirm
and characterize the nucleation step in the catalysts driven phase transformation.
Defect and Diffusion Forum 01/2010;
