Palladium hydride is metallic palladium that contains a substantial quantity of hydrogen within its crystal lattice. At room temperature and atmospheric pressure, palladium can absorb up to 900 times its own volume of hydrogen. This remarkable property allows palladium to store substantial quantities of hydrogen in a safe manner, and may also allow for unusual chemical reactions to be performed. The details of how this absorption process works are poorly understood. Better understanding of what happens at the molecular level, such as phase changes that occur as hydrogen fills the metal and the effect of defects in the material, could give clues to designing metal hydrides that perform better.
Palladium electrodes have been used in some cold fusion experiments, under the hypothesis that the hydrogen could be "squeezed" between the palladium atoms to help them fuse at lower temperatures than would otherwise be required. No cold fusion experiments have achieved conclusive positive results, however, and the theoretical ability of palladium to accomplish this is in dispute.
