The Electronic State of Hydrogen in the Phase of the Hydrogen-Storage Material PdH(D)x: Does a Chemical Bond Between Palladium and Hydrogen Exist?

The palladium-hydrogen system is one of the most famous hydrogen-storage systems. Although there has been much research on -phase PdH(D)(x), we comprehensively investigated the nature of the interaction between Pd and H(D) in -phase PdH(D)(x) (x<0.03 at 303K), and revealed the existence of Pd-H(D) chemical bond for the first time, by various insitu experimental techniques and first-principles theoretical calculations. The lattice expansion, magnetic susceptibility, and electrical resistivity all provide evidence. Insitu solid-state H-1 and (HNMR)-H-2 spectroscopy and first-principles theoretical calculations revealed that a Pd-H(D) chemical bond exists in the phase, but the bonding character of the Pd-H(D) bond in the phase is quite different from that in the phase; the nature of the Pd-H(D) bond in the phase is a localized covalent bond whereas that in the phase is a metallic bond.