Absorption of hydrogen by palladium–copper alloys. Part 2.—Theoretical analysis

Abstract

The pressure against composition data (Part 1) for the absorption of hydrogen by palladium–copper alloys containing 5, 10, 15 and 20 atom % copper are analysed. It is shown that the solubility of hydrogen (at 303 K and 760 Torr) is smaller in a Pd–Cu alloy than in an electronically equivalent Pd–Ag alloy. This result is discussed in terms of the lattice parameters of the alloys. It is also found that the limiting hydrogen solubility corresponds to filling of the d-band of the alloy, but is independent of the lattice parameter. Finally, the relative partial molar enthalpy is found to vary only slightly with copper content, and this is contrasted with the corresponding enthalpy data for Pd–Ag alloys. The difference between the two sets of alloys are attributed to a balance between elastic and electronic effects.