Electrochemical Interface during Corrosion of Copper in Anoxic Sulfide-Containing Groundwater-A Computational Study

Corrosion of copper is an expensive degradation process of materials in engineered infrastructures and in various technical applications. It is also an important factor in the geological disposal of spent nuclear fuel, where sulfide-induced corrosion is expected to be the predominant chemical degradation process of copper canisters used for encapsulation and isolation of the radioactive material from the biosphere. One aspect of the corrosion process that is still under intense research is the corrosion morphology and how it might be affected by the composition of the groundwater. Using density functional theory, we investigate the electrochemical interface of corroding copper in aqueous solutions containing sulfides, with and without the presence of Cl-, HCO3-, and SO42- anions. Through state-of-the-art electrochemical models, we account for the effects of pH, concentrations, and potential on the interfacial structure and composition. Results are presented for the Cu(110) surface facet and compared to the (110) and (001) facets of chalcocite (Cu2S), i.e., the main product of sulfide-induced corrosion. It is found that at low potentials, H dominates on all surfaces, and at high potentials, sulfides. In the intermediate ranges, the surfaces differ with sulfides prevailing on Cu, while adsorbed H2O, Cl, or H dominate on Cu2S. The results are summarized as surface Pourbaix diagrams and are generally applicable in corrosion science and electrochemistry. The implications of the study are discussed in light of the expected conditions of planned spent nuclear fuel repositories in Sweden, Finland, and Canada.