Co-adsorption of CO onto a Ag-modified Pt(111) — Restructuring of a Ag UPD layer monitored by EC-STM

Abstract

The effect of co-adsorption of CO on an underpotentially deposited (UPD) silver monolayer on a Pt(111) single crystal electrode in 0.05 M sulfuric acid is investigated for the first time by means of electrochemical scanning tunneling microscopy (EC-STM). Pure electrochemical experiments suggest that the co-adsorption of CO onto Pt single crystal electrodes previously modified by a monolayer of Ag, forces Ag atoms of the first UPD monolayer into a second adlayer. The present EC-STM studies reveal the formation of a large-area Ag network after the co-adsorption of CO. The resulting Ag nanostructures formed on wide Pt(111) terraces are approximately 0.5 nm high and 10 nm wide. The desorption of the newly formed second Ag adlayer, the oxidation of CO and the desorption of Ag atoms from the first adlayer are monitored by EC-STM and simultaneously detected in the corresponding CVs in three different oxidation peaks. EC-STM images recorded afterwards show the unchanged Pt surface. The presence of Ag on the surface leads to a downward shift of the onset of oxygen adsorption on the Pt(111) surface.

The formation of two Ag UPD layers on stepped Pt single crystal electrodes and their restructuring by co-adsorption of CO

“…Motivated by an older note by Clavilier and Klein [1], we recently confirmed that co-adsorption of carbon monoxide onto a surface which is covered by a monolayer of Ag(upd) forces silver atoms of the first into a second adlayer on Pt(1 1 1) [2]. EC-STM experiments confirmed the formation of long-range Ag networks over the terraces of the Pt(1 1 1) crystal.…”

“…The dimensions of the resulting Ag structures on stepped Pt electrodes are in the same range as found for Pt(1 1 1) though on the broad terraces of Pt(1 1 1), the Ag islands never grow across the step edges because the terrace width is larger than the size of the adlayer structure (compare Fig. 7b in [2]). …”

“…6a in comparison to the resulting Ag structure on Pt(1 1 1) recorded at a similar low potential (Fig. 6b, E = 0.5 V [2]). The picture shows many small clusters of approximately 10 nm width that are spread on the surface.…”

“…The charge densities found for Ag 2nd are considerably lower than the value found in [19] for iodine coated Pt (160 vs 245 C cm −2 ). This fact is in part due to the lattice expansion in the bilayer [2,13]. (The lattice constant of bulk Ag is 4% larger than that of Pt, the surface density therefore smaller by about 8%.…”

“…Due to its strong affinity to Pt, CO is able to displace Ag atoms of the first into a second Ag adlayer [1,2]. Presumably, CO adsorbs at defect sites of the Ag monolayer at first and then proliferates across the substrate.…”