Abstract
The electrochemical behaviour of copper electrodes in NaOH solutions with the addition of Na 2S was studied through the analysis of current transients under constant potential and complementary voltammetric and scanning electron microscopy data including energy dispersive X-ray analysis. The overall process can be described by the following three stages. The first stage corresponds to the nucleation and growth of a complex copper sulphide layer at potential values close to the equilibrium potentials of the Cu/Cu 2S and Cu/CuS reversible electrodes. The second stage is related to the rupture of the copper sulphide film at potentials more positive than a certain critical value leading to pitting corrosion of copper metal and yielding a poorly protective copper sulphide layer. The third stage occurs in the copper oxide electroformation range, where the presence of copper sulphide accelerates the electrodissolution of the base metal and copper oxide hinders the sulphidization processes. The current transients of each stage are interpreted through a model based on the nucleation and growth mechanism.
Highlights
EXPERIMENTALThe electrochemical behaviour of copper in solutions containing sulphide ions is very complex as it involves different processes depending on the potential range considered[l]
This work shows that the complex kinetics of polycrystalline copper electrodes in alkaline solutions containing sodium sulphide can be related to the nucleation and growth of different phases at least in three distinguishable ranges of potentials
The voltammetric results of copper in base solutions containing sodium sulphide show a multiplicity of anodic and cathodic current peaks related to already well established electrochemical reactions[l]. This allows a reasonable interpretation of the current transients run under a constant potential step and the evaluation of the various contributions participating in the copper anodization in alkaline sulphide solution
Summary
The electrochemical behaviour of copper in solutions containing sulphide ions is very complex as it involves different processes depending on the potential range considered[l]. This work shows that the complex kinetics of polycrystalline copper electrodes in alkaline solutions containing sodium sulphide can be related to the nucleation and growth of different phases at least in three distinguishable ranges of potentials. In this respect the study is mainly based on the analysis of potentiostatic current transients complemented with voltammetry and scanning electron microscopy. The electrode was immersed in the solutions containing sulphides with the potentiostat already turned on at the preset potential (E,) to avoid spontaneous formation of copper sulphides at open circuit This procedure was repeated for each measurement and was found to yield reproducible results[4].
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