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 stress that occurs between an adhering particle and the substrate, the clusters are embedded in an elastic soft polymer matrix and in a surfactant shell, respectively. A largely enhanced H-solubility was found in the α-phase region. Additionally the solubility limit of the α-phase is shifted to a higher H-concentration whereas the minimum α′-phase solubility is lowered 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 misfit dislocations because of the small cluster size, but can be explained with regard to the thermodynamics of an open two-phase system with coherent interfaces.