Nucleation and Growth of Silver at Zeolite A-Modified Electrodes

In this paper the nucleation and growth of silver deposits at tin oxide and tin oxide modified with silver ion-exchanged zeolite A (Ag x Na12 - x A) is studied. We show via chronoamperometry that, in the case of the zeolite-modified electrodes, the lateral motion of silver cations to active sites is impeded by the zeolite layer, resulting in distinct nucleation and growth at defect sites and/or at the bulk tin oxide surface. Solution-phase silver deposition at tin oxide fits the Scharifker−Mostany model extremely well, showing that on average only one active site for silver nucleation and growth is available for each 10 zeolite particles. Furthermore, the scan rate and loading dependence of the cyclic voltammetry are explained in terms of ion-exchange kinetics and supersaturation of silver atoms around the active nucleation site. A general model pertaining to the nucleation and growth of silver at zeolite-modified electrodes is presented. Cyclic voltammetry recorded in aqueous electrolytes containing cations of different sizes (i.e., ammonium, tetramethylammonium, and sodium) supports the general model involving nucleation and growth of silver at the electrode surface.