Influence of chloride and nitrate anions on copper electrodeposition in ammonia media

Copper electrodeposition onto a glassy carbon electrode (GCE) was investigated using linear sweep voltammetry and a potential step technique in 5 X 10(-2) M Cu(NH3)(4)(2+), 1 M NH3 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 Cu(NH,),(2+)/Cu(NH3)(2)(+) couple managed by diffusion control, whereas in the second, the reduction of Cu(NH3)(2+) to Cu(0) is influenced by Cl- and NO3- 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 Cu(II) present in the reaction layer to form Cu(I). 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. (C) 2001 The Electrochemical Society. All rights reserved.