Hydrogen desorption kinetics of nanostructured MgH 2 composite materials

Abstract

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 microstructure typically shows additive particles covered with a film of MgH 2 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 MgH 2 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, MgH 2 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 MgH 2 composite materials with a high storage capacity of hydrogen accessible at moderate temperatures.