Atomistic insights into chloride-induced depassivation mechanisms of protective Cu2O films in marine environments

Copper (Cu) is widely utilized in industrial and marine engineering due to its exceptional thermal and electrical conductivity. In alkaline environments, a passivation layer, primarily composed of Cu₂O, forms on copper surfaces, effectively inhibiting corrosion. However, in marine environments, this protective film becomes vulnerable to attack by aggressive Cl^- ions, leading to film detachment. Several mechanisms have been proposed to explain the depassivation of Cu₂O, including stress-induced fracture, local thinning, and void-induced collapse mechanisms. Nevertheless, the precise atomic-scale processes at the Cu₂O/seawater interface remain poorly understood, leaving the exact mechanism by which Cl^- promotes Cu₂O depassivation debated. To elucidate the atomic-scale mechanism of Cl^--induced Cu₂O corrosion, this study employs advanced computational techniques: ab initio thermodynamics, machine learning potential-based molecular dynamics, and constrained molecular dynamics. Our results reveal that under marine conditions, Cl^- undergoes extensive chemisorption on the Cu₂O(111) surface. This adsorption markedly reduces the energy barrier for lattice copper dissolution. Furthermore, we demonstrate that the formation rate of surface Cu⁺ vacancies far exceeds their longitudinal diffusion rate into the bulk. Based on this kinetic disparity, we propose that Cl^--mediated Cu₂O depassivation primarily proceeds via the local thinning mechanism. Overall, this work clarifies the breakdown mechanism of passive films on copper and provides a critical theoretical basis for designing corrosion-resistant Cu-based alloys used in marine environments.