Hydrogen sorption in elastically soft stabilized Pd-clusters

Thermodynamic properties of the Pd-H system are studied on 3.1- and 3.6-nm clusters by performing gasvolumetric measurements. To avoid interfacial str ess that occurs between an adhering particle and the substrate, the cluster s are embedded in an elastic soft polymer matrix and in a surfactant shell, respectively. A largely enhanced H-solubility was found in the alpha-phase region. Additionally the solubility Limit of the alpha-phase is shifted to a higher H-concentration whereas the minimum alpha'-phase solubility is lo wered compared to that of bulk Pd. This can be attributed to an occupation of subsurface sites. Sorption-desorption isotherms show the existence of a small hysteresis. This hysteresis can not be related to the formation of mi sfit dislocations because of the small cluster size, but can be explained w ith regard to the thermodynamics of an open two-phase system with coherent interfaces. (C) 1999 Elsevier Science S.A. All rights reserved.