Pd-cluster size effects of the hydrogen sorption properties

Clusters are agglomerates of a few to some hundred atoms. A large fraction of the atoms find themselves on a surface site. The geometrical structure of a cluster, in contrast to the structure of crystalline bulk material, can not be described with a repeated, a space filling unit cell. Clusters appear often in regular geometrical polyhedrons e.g. cuboctahedron or icosahedron. The interaction between hydrogen and palladium clusters of different sizes was investigated. The sorption properties of the clusters are compared with the well known properties of Pd bulk material. The Pd clusters reversibly absorb and desorb hydrogen. The density of states (DoS) distribution of hydrogen in die Pd cluster becomes wide with decreasing cluster size. This is an indication for a lowering of the critical temperature for the hydride formation of small Pd clusters. (C) 1999 Elsevier Science S.A. All rights reserved.