Copper Dissolution in Ammonia Solutions: Identification of the Mechanism at Low Overpotentials

Corrosion of copper in ammonia solutions is significantly affected by a large number of parameters such as the concentration of ammonia, pH, temperature, concentration of , the presence/absence of dissolved oxygen, the chemical nature, and the concentration of the anion but also by selected corrosion products, in particular, , various adsorbed intermediates, and finally passive films. In the present work we try to elucidate the corrosion of copper in a wide potential window [from −1.4 to 0 vs mercury/mercurous sulfate electrode (MSE)] and in a broad range of concentrations of various species (0.2–3.5 mol/L , 0–0.1 mol/L , pH 10–12.5). Then, we focus on the first peak occurring within −1.0 to −0.6 V vs MSE with the aim to explain the underlying mechanism. We show that the reaction order of the dissolution reaction with respect to ammonia is 2. We further show that using conventional electrochemical methods in combination with an optical method (scanning electron microscopy), a two-step (electrochemical-chemical) reaction yielding is identified as the most likely passivation mechanism, consistent with previous assumptions by other authors. Finally, we confirm this mechanism by performing impedance analysis at various experimental conditions.