Nanocrystalline metal hydrides

Nanocrystalline hydrides are a new class of material in which outstanding hydrogen sorption may be obtained by proper engineering of the microstructure and surface. in this paper the thermodynamics and kinetics of hydride formation in a nanocrystalline alloy are presented. The role of grain size, grain boundaries, internal strain and chemical disorder is discussed, as is the effect of catalyst particles at the surface of the metal. Powders of nanocrystalline alloys, modified with a catalyst, readily absorb hydrogen, with no need for prior activation, in strong contrast to conventional hydrides. The materials show substantially enhanced absorption and desorption kinetics, even at relatively low temperatures. Examples of various nanocrystalline metal hydrides are given, based on Mg, Mg2Ni, FeTi and LaNi5.