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