Dincer Gokcen

Stoichiometry of Pt Submonolayer Deposition via Surface-Limited Redox Replacement Reaction

The work exploring the stoichiometry of Pt deposition via surface-limited redox replacement of the underpotentially deposited (UPD) Cu monolayer on Au(111) is presented. The Cu UPD monolayer is formed from 10 -3 M Cu 2+ + 0.1 M HClO 4 solution, whereas the Pt deposition via surface-limited redox replacement reaction is carried out in 10- 3 M {PtCl 6 } 2- + 0.1 M HClO 4 solution at open-circuit potential. Our results indicate that the Pt submonolayers have two-dimensional morphology and linear dependence of their coverage on the amount (coverage) of the replaced Cu UPD monolayers. Our analysis shows that the oxidation state of Cu during redox replacement reaction is 1+, suggesting that four Cu UPD adatoms are replaced by each deposited Pt adatom. This work stresses the general importance of the anions, determining the stoichiometry of metal deposition reaction via surface-limited redox replacement of the UPD monolayers.

Size Effects in Monolayer Catalysis—Model Study: Pt Submonolayers on Au(111)

The two-dimensional Pt submonolayers on Au(111) were used as model catalyst system to study kinetics of hydrogen oxidation reaction (HOR). The morphology of different Pt submonolayers was characterized by ex situ scanning tunneling microscopy combined with statistical image analysis. The HOR kinetics data were analyzed using Levich–Koutecky formalism and presented as a function of the mean size of Pt clusters for each Pt submonolayer. The Pt submonolayers with smaller Pt clusters were found less active for HOR. This trend is well correlated with the continuum elasticity analysis of the average active strain in Pt clusters indicating that smaller clusters have less tensile strain. The density functional theory calculations were found in agreement with our results demonstrating that the size-dependent strain in Pt clusters has significant effect on the energy of the d-band center, i.e., the Pt clusters’ activity.