Electrochemical measurements and atomistic simulations of Cl−-induced passivity breakdown on a Cu2O film

Highlights: • The breakdown of a Cu₂O film is due to Cl⁻ adsorption on the film/solution interface. • The inner ${\text{V}}_{\text{Cu}}^{\text{'}}$ promotes the adsorption of Cl⁻. • The involved Cl⁻ increases the diffusion coefficient ${\text{V}}_{\text{Cu}}^{\text{'}}$ by 1–3 orders of magnitude. • The proposed mechanism can be used for the local breakdown of copper. - Abstract: The mechanism of passivity breakdown on Cu₂O films was studied. The thickness and components of the film were estimated by EIS, AES and XPS analyses. The structural relaxations, energies, electronic properties and diffusion coefficients were calculated by first-principles calculations. Both the experimental and calculated results demonstrate that the film thinning is due to the adsorption of Cl⁻ on the surface instead of a penetration process. The inner point defects facilitate the adsorption of Cl⁻, and the introduction of Cl⁻, in turn, increases the transport rate of point defects. A theoretical model was proposed, which is also applicable to local breakdown.