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Copper electrodeposition onto a glassy carbon electrode ͑GCE͒ was investigated using linear sweep voltammetry and a potential step technique in 5 ϫ 10 Ϫ2 M Cu͑NH 3 ͒ 4 2ϩ , 1 M NH 3 and pH 10.5, in the presence of chloride and nitrate anions. Voltammetric analysis showed that copper electrodeposition is carried out in two steps. The first step corresponds to Cu͑NH 3 ͒ 4 2ϩ /Cu͑NH 3 ͒ 2 ϩ couple managed by diffusion control, whereas in the second, the reduction of Cu͑NH 3 ͒ 2 ϩ to Cu͑0͒ is influenced by Cl Ϫ and NO 3 Ϫ anions. In the case of chloride and chloride and nitrate baths, it may be observed that only 40-60% of deposited copper is oxidized in the reverse potential sweep; these low charge recoveries are due to an disproportionation stage: the newly deposited copper reacts with the Cu͑II͒ present in the reaction layer to form Cu͑I͒. For baths containing only nitrates, the efficacy of charge recovery is even smaller ͑20%͒ due to an interaction between newly deposited copper and nitrate ions that could include a direct redox reaction and/or nitrate reduction on the surface of copper nuclei, this reaction provokes an additional dissolution of copper nuclei. The presence of chlorides in nitrate-containing baths seems to block said interaction between nitrates and newly deposited copper. Through the analysis of current transients, copper electrocrystallization on GCE is shown to be performed by means of a three-dimensional nucleation growth diffusion-limited mechanism in the presence of the three electrolytes studied here. However, the presence of anions directly influences the magnitude and dependence of kinetic parameters of copper electrocrystallization with the applied potential.

The influence of the electrode surface quality and surface morphology on the silver electrocrystallization process onto a carbon substrate from 10 -2 M Ag(NH 3 ) 2 + /1.6 M NH 3 , 1 M KNO 3 (pH ) 11) electrolyte solution was studied. Three substrates with different types of surface morphology and surface roughness were used: highly oriented pyrolitic graphite (HOPG), mechanically polished vitreous carbon (MPVC), and fractured vitreous carbon (FVC). Before the silver deposition process, the electrode surface was examined and characterized by means of Atomic Force Microscopy (AFM) analysis. Evaluation of the kinetic parameters of the silver nucleation and the growth behavior, as well as other characteristics of the silver electrocrystallization process onto carbon substrates, were based on cyclic voltammetry and chronoamperometric measurements. Cyclic voltammetry data also show that silver deposition efficiency is proportional to the increase of electrode surface roughness (from HOPG, via MPVC to FVC). The silver bulk deposition process on all three carbon substrates was characterized as 3D nucleation and diffusion-controlled growth. However, this process proceeds with different overpotentials on different substrates: the lowest for HOPG and the highest for MPVC electrode surface. The major electrocrystallization parameters, such as nucleation rate, number of active sites, and number of formed silver nuclei, strictly related to the electrode surface conditions, seem to not follow the same trends as the cyclic voltammetry data. It is clearly indicated in the nonlinear relationship between number of active sites and the surface features (recognized in AFM images). As pointed out in the discussion, it opens new questions regarding the nature of the active sites for deposition on the electrode surface and their identification by microscopic techniques.

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