AVS 56th International Symposium & Exhibition
    Graphene Topical Conference Monday Sessions
       Session GR-MoM

Paper GR-MoM11
Catalytic Property and Morphology of Pt Clusters on Graphite Surface

Monday, November 9, 2009, 11:40 am, Room C3

Session: Graphene and 2D Carbon Nanostructures
Presenter: J. Nakamura, University of Tsukuba, Japan
Authors: J. Nakamura, University of Tsukuba, Japan
T. Kondo, University of Tsukuba, Japan
K. Watahiki, University of Tsukuba, Japan
Y. Iwasaki, University of Tsukuba, Japan
J. Oh, University of Tsukuba, Japan
T. Suzuki, University of Tsukuba, Japan
Y. Honma, University of Tsukuba, Japan
D. Hatake, University of Tsukuba, Japan
Correspondent: Click to Email
Understanding the interface interaction between platinum nano-cluster and carbon supports composed of graphitic materials is one of the most important need in development of electrocatalysts for fuel cell. We have studied the effects of the interface interaction on the catalytic properties using model catalysts of Pt-deposited highly oriented pyrolytic graphite (HOPG) by IETS-STS-STM, TPD, and molecular/atomic beam technique. The deposited Pt clusters show unique morphology and catalytic properties. That is, the shape of Pt clusters (1-5 nm) is a raft-like structure with one or few atomic heights. The Pt clusters show quite high catalytic activity for H2-D2 exchange reaction at 24 Torr. Desorption peak of CO from the Pt was observed at a low temperature of 300 K. The significant modification is ascribed to the interface interaction between Pt atoms and graphite surface. In the STM observation, it was found that Pt atoms are located on beta-carbon, indicating the shrinkage of Pt-Pt distance about 13% compared to that of the bulk Pt. The modification in the catalytic properties and the electronic structure of the flat Pt clusters is thus ascribed to the reduction in the lattice constant of Pt. It is explained that the d-band center of Pt shifts away from the Fermi level due to the reduction in the lattice constant. We show evidence of the interface interaction between Pt and graphite here. Distinct electronic states of the graphite near the Fermi level, “non-bonding π electronic states”, were observed at the carbon atoms in the vicinity of the Pt clusters by STS measurements, which is interpreted by our newly proposed model: the conjugated bond of graphite between alpha- and beta-carbon atoms are re-hybridized into two pz-orbitals, where the pz-orbital of beta-carbon would be hybridized with a d-orbital of the Pt atom and the other pz-orbital of alpha-carbon becomes a non-bonding p-orbital. Consequently non-bonding p electronic states forms at the alpha-carbon atoms of graphite in the vicinity of the Pt cluster. The proposed model is consistent with our experimental result of scanning tunneling microscopy and inelastic electron tunneling spectroscopy (IETS) measurements as well as STS results and our first-principles density functional calculations of the graphene sheet with a Pt cluster.