Abstract: The invention concerns a method for preparing a nanocomposite based on magnesium and another element or compound known to absorb hydrogen and hardly miscible when ground with magnesium or its hydride, such as vanadium, titanium or niobium. The method is characterised in that it consists in submitting magnesium or a compound based on magnesium known to absorb hydrogen to hydrogenation to obtain the corresponding hydride in powder form. Said resulting powder hydride is then mixed with the other element or compound or a hydride of said other element or compound and the resulting mixture is subjected to intense mechanical grinding until the corresponding nanocomposite is obtained in the form of a hydride. Finally, if necessary, the resulting nanocomposite is subjected to hydrogen desorption.

Abstract: The invention concerns a piece based on one or several metal hydrides capable of reversibly absorbing hydrogen. Said piece is in the form of a thin and dense band, having a thickness preferably not more than 1 mm and porosity preferably less than 20%. The piece is obtained by rolling a powder of selected hydride(s), with or without additional component(s), such as binders or heat-transfer elements. Said piece can easily be produced on an industrial scale. By its very nature, it is particularly adapted for use as a base element in a tank for storing and transporting hydrogen. It can also be used in a Ni-MH typre battery for storing and transporting energy.

Abstract: The invention is concerned with a process for the preparation of a supported catalyst having a nanocrystalline structure and a surface area preferably higher than 2 m2/g. The process comprises preparing by mechanical grinding a nanocrystalline material consisting of a metastable composite or alloy of at least two different elements or compounds containing at least one catalytic species and subjecting the nanocrystalline material to leaching with a leaching solution in order to eliminate totally or partially at least of one of the two elements or compounds, other than the at least one catalytic species. At least one further element or compound that is non-leachable and that acts as a support for the at least one catalytic species is added to the material during the grinding step or to the leaching solution during the leaching step.

Abstract: Leached nanocrystalline materials having a high specific surface are particularly useful for storing hydrogen or as catalysts or electrocatalysts in the manufacture electrodes, especially for fuel cells. Such materials can be manufactured by preparing a nanocrystalline material consisting of a metastable composite or alloy of at least two different chemical elements. To be nanocrystalline, this material must have a crystalline structure with the grain size lower than 100 nm. Then, the so prepared nanocrystalline material can be subjected to a leaching treatment in order to eliminate partially or totally one of the elements of the composite or alloy. This leaching results in nanocrystalline materials having a porous structure and, thereby, the requested high specific surface.