palladium hydride is metallic palladium that contains a substantial quantity of hydrogen within its crystal lattice. despite its name, it is not an ionic hydride but rather an alloy of palladium with metallic hydrogen that can be written pdhx . at room temperature, palladium hydrides may contain two crystalline phases, α and β (sometimes called α'). pure α phase exists at x < 0.017 whereas pure β phase is realised for x > 0.58; intermediate x values correspond to α-β mixtures.
hydrogen absorption by palladium is reversible and therefore has been investigated for hydrogen storage. 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.