Alloying effect on heat of hydride and deuteride formation for Pd-based binary alloys

Absorption and desorption isotherms of protium and deuterium were measured for Pd-based alloys as Pd_(1-x)AE_x, where AE = Co, Ni, Cu, Rh, Ag, Pt and Au. It was observed that the heat of hydride formation decreased with increasing AE content for Co, Ni, Cu, Rh, Pt and Au, although the extent of the increase differed from each other. According to Lässer, on the other hand, alloying of Ag caused to increase the heat of hydride formation. These features were analyzed from electronic structures of the alloys inspected by use of DV-Xα package, where the inspections were carried out for small clusters as Pd_(14-y)AE_y. The DV-Xα calculations showed that the energy of the highest occupied molecular orbital of the clusters change almost linearly with their composition, suggesting that the Fermi energy of respective alloys changes in the similar manner. By assuming the Fermi energy of Pd_(1-x)AE_x to be arithmetic means of the Fermi energies of pure Pd and AE, a linear relation was found between the observed enthalpy change of hydride formation and the assumed Fermi energy.