Regensburg 2004 – scientific programme

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O: Oberflächenphysik

O 26: Adsorption an Oberflächen II

O 26.8: Talk

Tuesday, March 9, 2004, 17:30–17:45, H45

Electronic properties and hydrogen absorption of Pd and Ni:O nano-clusters — •Andreas Borgschulte, Ruud J. Westerwal, Sven de Man, Bernard Dam, Jan H. Rector, and Ronald Griessen — Vrije Universiteit, FEW - Vaste-stoffysica, De Boelelaan 1081, 1081 HV Amsterdam

We studied by scanning tunneling microscopy the electronic and geometric structure of Pd and Ni nano-clusters grown on oxidized yttrium surfaces. The catalytic activity of Pd and Ni nano-clusters is estimated from the optically monitored switching kinetics of the underlying yttrium layer. The electronic structure depends strongly on the cluster size and changes after hydrogenation. Small Pd clusters are insulating as evidenced by tunneling spectroscopy. The critical thickness of the metal-insulator transition coincidences with the minimal thickness for a significant catalytic Pd activity. Below the critical thickness nano-clusters have lost the special catalytic properties of (bulk) Pd. In contrast to Pd, Ni-surfaces oxidize in normal environment (air). In that case the interplay between hydrogen and oxygen chemisorbed on Ni clusters as well on crystalline surfaces is studied. Surfaces with a partially reduced oxide show the catalytically highest activity. The results are compared with X-ray diffraction studies on the interaction of hydrogen with NiO. We discuss the relevance of the results for a search of novel catalysts for hydrogen storage and fuel cells, in particular the role of oxides as catalysts.