In-situ X-ray diffraction of palladium cathodes in electrolytic cells

Stability of a hydrogen molecule in a vacancy of palladium hydrides

“…The lattice parameters of palladium hydrides were determined by minimization of total energy versus lattice parameters. The calculated values agree well with experimental lattice parameters, giving 3.88 Å (experimentally 3.89 Å ) for Pd and 4.06 Å (4.08 Å ) for PdH [14]. A vacancy was created by removing a Pd atom in a supercell of palladium or palladium hydrides with the appropriate lattice parameters obtained by minimization of their total energies, but atomic positions were still kept at fcc lattice sites.…”

“…The energy barrier is 0.84 eV for dissociation of the H 2 molecule in the vacancy to two positions near T-sites. This means it is difficult for the H 2 molecule to thermally escape from the vacancy once the H 2 molecule is trapped at a high loading ratio, because the energy of 0.84 eV is not easily thermally accessed at 300 K. Experimentally, it is usually difficult to have a palladium hydride with H/Pd > 1 [14], but having H/Pd > 1 in some local areas like defects may still be possible. We thus tested the H 2 molecule in the supercell matrix of Pd 31 vH 34 , where 32 hydrogen atoms occupy all O-sites and 2 hydrogen atoms occupy the nearest neighbored T-sites along the [111] direction.…”