Reaction Stoichiometry and Mechanism of Pt Deposition via Surface Limited Redox Replacement of Copper UPD Layer on Au(111)

The stoichiometry and reaction mechanism of Pt deposition via surface limited redox replacement (SLRR) of Cu underpotential-deposited (UPD) monolayer on Au(111) was studied using in situ polarization dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS), scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). We proposed that Pt deposition via SLRR of Cu UPD monolayer leads to formation/deposition of Pt-surface species mainly consisting of Pt(II) chloride with a square planar local structure [PtCl4] parallel to the Au surface (60%) which has a strong interaction of the Pt complex with the Au substrate. The rest (40%) was one-monolayer Pt metal cluster. This result provides a new understanding into the mechanism and stoichiometry of the SLRR reaction, which has a wide application for synthesis of monolayer catalysts.