We report on the concentration dependence of the underpotential deposition of silver on well-defined Pt(111) electrodes. Electrochemical as well as ultra high vacuum surface techniques have been employed. We have found that when the silver ion concentration is 1.00 mM the electrodeposition is via adsorption in a welldefined manner, whereas at a concentration of 0.005 mM the mechanism involves three dimensional nucleation and island formation. In addition, two monolayers of silver are deposited

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... t underpotentials but the stability of the second layer is a strong function of the silver ion concentration in solution. When the silver ion concentration is 1.00 mM, rinsing the electrode (with supporting electrolyte containing no silver in solution) at controlled potential results in essentially complete removal of the second layer of silver. However, when the deposition is from a solution containing silver at a concentration of 0.10 mM, the layer is stable to the same rinsing procedure. "0 ;zi":U~ZU 91.00551 91 5 24 073