Hydrogen absorption characteristics of Pd 1− xLi x ( x = 0.055 and 0.072) alloys and ordered Pd 7Li

Abstract

Thermodynamic quantities were determined for the absorption of hydrogen in Pd-5.5at.%Li and Pd-7.2at.%Li alloys, the latter alloy being in the two-phase field of saturated α-Pd(Li,s) solid solution and the ordered Pd 7Li phase. Data were also determined for the Pd-10.6at.%Li alloy which consists only of the ordered Pd 7Li phase. The data were determined from measurements of pressure-composition isotherms at temperatures between 273 K and 463 K and hydrogen pressures up to 1000 Torr. The PdLi alloys dissolve considerable amounts of hydrogen and form a more stable hydride phase than Pd despite the lattice contraction which occurs on alloying Pd with Li. The hydrogen solubility in the ordered Pd 7Li phase alone is a little smaller than that in the two-phase mixture. The large hydrogen absorption of PdLi alloys, which does not depend on the presence of ordered Pd 7Li, may be attributed to (i) an attractive HLi pair interaction, (ii) a decrease in the strain energies necessary for hydrogen occupation of the interstices, because of the similar lattice parameters of the α-Pd(Li,s) and ordered Pd 7Li phases, and the large compressibility of PdLi alloys, and (iii) the valence of 1 of Li in Pd compared with 3 for, for example, Y in Pd.