Electrodeposition of Ag and Tl on platinum single crystals covered with iodine




Labayen de Inza, Miguel M.

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The electrodeposition of Ag and Tl on Pt single crystal surfaces covered with iodine has been investigated, focusing on the study of the electrodeposited Pt(111)(3 x 3)-AgI structure. These crystals were prepared under atmospheric or ultra high-vacuum conditions. Multiple techniques were used for characterization: traditional electrochemical methods, A.C. impedance, LEED, Auger spectroscopy, thermal desorption spectroscopy and contact angle measurements. The surface compound Pt(111)(3 x 3)-AgI is formed during the first electrodeposition peak of Ag+ on Pt(111)(√7 x √7)R19.1°-I. The crystallographic structure of this compound was determined using tensor LEED analysis. Using stepped single crystals with (111) terraces, it was found that there is a correlation between the charge of this peak and the length of the terrace. Terraces are more reactive than steps, and ordered structures are only found for terraces wider than about 10 Å. The long-range order is associated with the directional nature of the Ag-I bonds. Cohesive and formation thermodynamic parameters of the Pt(111)(3 x 3)-AgI are calculated using a thermodynamic sequence. Two of the steps: electrodeposition of Ag on Pt(111)(√7 x √7)R19.1°-I and desorption of iodine are studied in more detail. The thermodynamic parameters calculated are partly explained by the metallic character of the Pt Ag bond, and the covalent character of the Ag-I bond. A study of Tl electrodeposition on Pt(111(√7 x √7)R19.1°-I was also undertaken. Some of the features of the voltammogram are related to specific surface structures.



Crystals, Electric properties, Electroplating, Electrochemistry