Background: Cyclic voltammetry is widely employed in electroanalytical studies because
it provides fast information about the redox potentials of the electroactive species and the influence of
the medium on the redox processes. Azole compounds have been found to be effective corrosion inhibitors
for copper in chloride-containing solutions. The aim of this work was to investigate in detail
the influence of the addition of various azole compounds on the oxidation mechanism of copper in
chloride-containing solutions, using cyclic voltammetry.
Methods: The influence of thirteen azole compounds, at three different concentrations on the electrochemical/
chemical reactions of pure copper immersed in 3 wt.% NaCl solution was studied using cyclic
voltammetry at different scan rates. The change of the peak current and potential with the scan
rate were investigated. The possible linearity was compared with the theoretically derived mechanism.
The possible reaction mechanisms were discussed based on the linearity of these parameters (peak
current and potential) with the scan rate compared to theoretically derived models.
Results: Both the peak current and peak potential of the copper samples immersed in chloridecontaining
solutions with additions of the majority of azole compounds showed linearity with the
square root of the scan rate, suggesting that copper follows the Müller-Calandra passivation model.
The same behavior was also found for copper in chloride-containing solutions without additions of azole
compounds. A linear variation of the peak potential with the natural logarithm of the scan rate and
linear variation of the peak potential with the square root of the scan rate was observed for the copper
samples immersed in chloride-containing solutions with the addition of 10 mM of 2-mercapto-1-
methylimidazole, imidazole, or 2-aminobenzimidazole. This suggests that copper follows irreversible
redox reactions under a diffusion controlled process. No other linear relations of the peak current and
peak potential with the scan rate were found.
Conclusion: Copper oxidation in chloride-containing solutions is controlled by passivation (following
the Müller-Calandra passivation model) upon the addition of the majority of the selected azoles. In the
minority of cases, irreversible redox reactions that follow a diffusion-controlled process were identified.
None of the systems followed an adsorption-controlled process. Moreover, none of the tested
systems underwent reversible redox reactions that followed a diffusion controlled process.