Hydrogen desorption kinetics of nanostructured MgH2 composite materials

In order to investigate the microscopic mechanism of hydrogen desorption we have studied ball-milled magnesium-composite materials with a relatively large volume fraction of additives. After ball milling the rnicrostructure typically shows additive particles covered with a film of MgH2 as investigated by scanning electron microscopy and energy-dispersive X-ray microanalysis. Depending on the milling time and material used as additive, the desorption of hydrogen takes place at a far lower temperature than in pure MgH2 as studied by thermal desorption spectroscopy. In the next step we developed a new method to use only small volume fractions of additives in order to minimize the amount of additive material and maximize the percentage of hydrogen storage material. Therefore, MgH2 was sputter-deposited by palladium and successively ball milled to achieve a composite material with finely dispersed metallic additives. The desorption kinetics could be strongly improved even though only small amounts of palladium were added. The new method of ultra-fine dispersion may lead to MgH2 composite materials with a high storage capacity of hydrogen accessible at moderate temperatures. (C) 2002 Elsevier Science B.V. All rights reserved.