Kinetics of hydrogen isotope absorption for well-annealed palladium-platinum alloys

Absorption kinetics of protium and deuterium for Pd, Pd-4 at%Pt and Pd-8 at%Pt were studied in a dilute hydrogen concentration region in a temperature region from 274 to 357 K by means of constant volume method, where samples were annealed well at 973 K under vacuum before measurements to remove defects induced by sample preparation. It was found that protium had larger rate constants for adsorption, lower rate constants for desorption and larger diffusion constants than those of deuterium within the examined temperature region. The activation energy of hydrogen absorption for both hydrogen isotopes was almost null for all of the samples used. The activation energy of desorption for deuterium was smaller than that for protium. It was attributed to the difference in the enthalpy of hydrogen absorption into metal in dilute hydrogen concentration region between protium and deuterium. These features and trends observed in the alloying effect were supported by the ab initio calculations for small clusters.