Qiuyi Yuan

Lead Underpotential Deposition on Pt-submonolayer Modified Au(111)

Abstract Lead underpotential deposition on Au(111) surface modified with submonolayer of Pt is studied using cyclic voltammetry and in situ scanning tunneling microscopy methods. The two-dimensional Pt submonolayers (nanoclusters) on Au(111) were obtained by spontaneous Pt deposition on Au(111) from × 103 M {PtCl6}2− + 0.1 M HClO4 solution. The in situ scanning tunneling microscopy data were analyzed using statistical image processing algorithm which enabled quantification of the morphology change on Pt-modified Au(111) surface as a function of applied underpotential. The results suggest that Pb underpotential deposition starts on Au steps and other surface defects, similar to Pb underpotential deposition on Au(111). The further process proceeds by Pb monolayer nucleation and growth on Au terraces into a complete layer. In parallel, the Pb monolayer starts to nucleate on top of the Pt nanoclusters. The final stage of the Pb underpotential deposition is formation of the compact Pb nanoclusters/layer on top of the pre-existing Pt nanoclusters. The scanning tunneling microscopy data suggests that morphology of underpotentially deposited Pb monolayer on Pt-modified Au(111) is similar to the starting surface in terms of the areal density of nanoclusters, their size and shape. The morphological changes of the Pt modified Au(111) surface during Pb underpotential deposition are correlated with cyclic voltammetry results.

Finite Size Effects in Submonolayer Catalysts Investigated by CO Electrosorption on PtsML/Pd(100)

A combination of scanning tunneling microscopy, subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS), and density functional theory (DFT) is used to quantify the local strain in 2D Pt clusters on the 100 facet of Pd and its effect on CO chemisorption. Good agreement between SNIFTIRS experiments and DFT simulations provide strong evidence that, in the absence of coherent strain between Pt and Pd, finite size effects introduce local compressive strain, which alters the chemisorption properties of the surface. Though this effect has been widely neglected in prior studies, our results suggest that accurate control over cluster sizes in submonolayer catalyst systems can be an effective approach to fine-tune their catalytic properties.

Development of Surface Fluorescence X-ray Absorption Fine Structure Spectroscopy using a Laue-Type Monochromator

Surface fluorescence X-ray absorption fine structure (XAFS) spectroscopy using a Laue-type monochromator has been developed to acquire structural information about metals with a very low concentrate on a flat highly oriented pyrolytic graphite (HOPG) surface in the presence of electrolytes. Generally, surface fluorescence XAFS spectroscopy is hindered by strong scattering from the bulk, which often chokes the pulse counting detector. In this work, we show that a bent crystal Laue analyzer (BCLA) can efficiently remove the scattered X-rays from the bulk even in the presence of solution. We applied the technique to submonolayer (∼1014  atoms cm-2 ) Pt on HOPG and successfully obtained high signal/noise in situ XAFS data in combination with back-illuminated fluorescence XAFS (BI-FXAFS) spectroscopy. This technique allows in situ XAFS measurements of flat electrode surfaces to be performed in the presence of electrolytes.