Effect of potential on the early stages of nucleation and growth during silver electrocrystallization in ammonium medium on vitreous carbon

In this work, a systemic study of silver electrocrystallization process was performed on a vitreous carbon (VC) electrode in a medium of 1.6 M NH3, 1 KNO3 at pH 11. The analysis of current transients, using different theoretical models, shows that the systematic evolution of electrocrystallization process is observable through the gradual modification of energetic conditions of the interface by either changing the concentration of electroactive species [10(-4) to 0.1 M Ag(NH3)(2)(+)] or the potential imposed to the electrode. At low concentrations of electroactive species (less than or equal to10(-3) M) and not so negative potentials, 2D-2D growth of silver may be observed forming deposits less than the monolayer coverage. At more negative potentials 2D-3D growths are obtained. In this type of transition, two kinds of silver growth sites are identifiable, first on the VC and afterward, on the recently deposited silver. At concentrations greater than or equal to10(-2) M and less negative potentials, 3D growth of nuclei can be seen, forming deposits far beyond a monolayer. Their growth is influenced by either diffusion of Ag(NH3)(2)(+) or the incorporation of silver adatoms into the substrate lattice, depending on the conditions of imposed potential. At concentrations greater than or equal to10(-1) M and very negative potentials, where the deposited silver was much greater than a monolayer, 2D growths were found associated with the growth of Agdegrees on the previously deposited silver. It is worth noting that this is the first time, that in the same chemical system, the systematic evolution of electrocrystallization of 2D and 3D stages of nuclei growth on heterogeneous VC surfaces can be observed, through the gradual modification of energetic conditions at the interface by either changing the concentration of electroactive species or the potential imposed to the electrode. (C) 2004 The Electrochemical Society.