| The underpotential deposition of silver on Pt(111) electrodes has been investigated with emphasis on the determination of the growth mechanism of the underpotentially deposited layers. Systematic variations in silver ion concentration, potential sweep rate, the presence of competing adsorbates and the electrode surface structure were employed as a means of controlling the structure of the silver adlayers.; It has been found that the voltammetry for the deposition of silver on Pt(111) is strongly dependent on the silver ion concentration, but does not follow the Nernstian behavior of 60 mV shift per decade change in concentration. At a silver ion concentration of 1.0 mM, electrodeposition takes place through adsorption of a well defined monolayer, whereas at low silver concentrations (0.005 mM) the growth mechanism involves three-dimensional nucleation and island formation. The stability of the second silver monolayer is also a strong function of the silver ion concentration, indicating the formation of different monolayer structures as the solution concentration of silver is varied.; Studies were performed to determine the effects of competing organic adsorbates on the underpotential deposition processes. The adsorbates studied were known to bind to Pt primarily through a nitrogen or sulfur hetero-atom and were chosen to represent systematic variations in both the adsorbing atom and the structure of the adsorbate. The effects of the adsorbate layer on silver deposition were found to be dependent on the nature and structure of the co-adsorbed species. Adsorbates that bind primarily through a ring nitrogen were found to inhibit the deposition of the second, but not the first, silver monolayer. In contrast, the sulfur containing adsorbates inhibited all deposition processes except that of bulk silver deposition.; The effects of the electrode surface structure on the deposition process were investigated by employing single crystal, polycrystalline and electrochemically perturbed single crystal platinum electrodes. The results indicate a strong dependence of the underpotential deposition of silver on the structural characteristics of the substrate. These differences can be explained in terms of the different surface sites and their distribution present in each case. |
