Electromicrogravimetric study of thallium underpotential deposits on gold in acid medium

A study of underpotential deposits (UPD) of Tl/Au was carried out by coupling microgravimetry to cyclic voltammetry in acid perchlorate medium. In the first place, it was found that in the potential region positive to UPD formation of thallium on gold, the recorded frequency did not vary, thus implying that the adsorption of perchlorate anions does not take place before the formation of a metallic monolayer. In the second place, adsorption isotherms prepared from these systems presented similar forms to those appearing when using single-crystal electrodes of Au(111) from the literature. Besides, our results showed that the adsorption of this metal on gold substrates involves species that completely transfer their charge in accordance with the models existing in the literature. Studies performed during the time passed at the cathodic limit of the voltammogram show that there is no formation of any alloyed phase or of 2D phases in the underpotential region. Finally, a monolayer-equivalent charge was determined to be higher than the theoretical, which seems to show that, on the microscopic level, the roughness has a determinant role in the interpretation of these results. © 2007 Sociedad Chilena de Química.

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