Relation Between Thermodynamic and Kinetics Aspects of Pt Deposition Via Slrr and Resulting Properties of Catalyst Monolayers

Thursday, May 15, 2014: 11:40
Floridian Ballroom F, Lobby Level (Hilton Orlando Bonnet Creek)
S. Brankovic and Q. Yuan (University of Houston)
The deposition method based on surface limited replacement reaction i.e. galvanic displacement of under potentially deposited (UPD) metal monolayers has been extensively used for preparation of highly active catalysts monolayers1-[i],[ii],[iii][iv]. The physical and chemical behavior of these monolayers is altered due to different structural and electronic effects dominating their properties. In the case where ligand (substrate) effect is weak, their properties are predominantly affected by the level of coherent strain.

The two dimensional Pt submonolayers/nanoclusters on Au(111) and Pd(hkl) were used as model system to study size/strain effect on catalyst monolayer properties. The probe ion/molecule was CO and Pb2+, and the Pt submonolayers were obtained by galvanic displacement of Cu UPD monolayers using surface limited red-ox replacement process. The morphology of Pt monolayers was studied by scanning tunneling microscopy and statistical image processing. The electrosorption characteristics of Pt submonolayers were studied using SNIFTIR, STM and conventional electrochemical methods.

The results indicate that Pt submonolayers have quite different electrosorption properties as compared to Pt bulk electrode. In both cases, with strong (Pd(111)) and weak (Au(111)) ligand effect of substrate, a lower reactivity of Pt submonolayers is observed as compared to Pt(111) electrode. In the case of CO adsorption on Pt/Pd(111), the spectroscopic and electrochemical data indicate weaker bond than on  both bulk Pt(111) and Pd(111) electrodes. In the case of Pb2+adsorption, (UPD), the Pt sub-monolayers remain passive for UPD process until several hundred milivolts more negative potentials as compared to Pb UPD on Pt(111). These results suggest that lateral strain developed in Pt submonolayers/nanoclusters, which is function of their size, is a dominant force determining their electrosorption behavior.

The presented work correlates the theoretical analysis of the size effects on the active strain in different Pt submonolayer catalysts with their experimentally observed electrosorption properties.

[#] SRBrankovic@uh.edu

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[[iv]]E. Kamshoff, E. Hahn, and K. Kern, Phys. Rev. Lett., 73, (1994) 704.