Role of chlorine adsorption in regulating surface work functions of Cu-Sn alloy system: A first-principles study

Cu-Sn alloys primarily undergo galvanic corrosion in chlorine-containing environments. The corrosion sequence is determined by the work function. In this study, the regulatory mechanism of surface work function was investigated for the adsorption of Cl atoms on the main components of Cu-Sn alloys: Cu, Sn, Cu6Sn5, and Cu3Sn. The results indicated that, on clean surfaces, the order of the work functions for the four structures did not align with the experimentally observed sequence of galvanic corrosion. However, when the Cl atom coverage on each surface exceeded 1/2, the work functions regulated by the chlorine atoms corresponded with the results observed in experiments. Through fitting, a linear relationship between the changes in surface dipole moment and work function was established. The interactions between Cl atoms on the Sn and Cu surfaces resulted in fluctuations in the work function, while the proximity of Cl atoms to the surface on the Cu3Sn structure led to a slower variation in its work function. Consequently, under the regulation of Cl atoms, the differences in work function changes among the four structures resulted in a redistribution of the work function magnitudes. This redistribution of work functions provides new insights into the corrosion mechanism of Cu-Sn alloys and suggests potential strategies for corrosion prevention.