Electrochemical Impedance Spectroscopy (EIS) Explanation of Single Crystal Cu(100)/Cu(111) in Different Corrosion Stages.

Copper and its alloys are used widely in marine environments, and anisotropic corrosion influences the corrosion kinetics of copper. Corrosion of copper in an electrolyte containing Cl- is described as a dissolution-deposition process, which is a prolonged process. Therefore, it is laborious to clarify the corrosion anisotropy in different stages. In this paper, electrochemical impedance spectroscopy (EIS) following elapsed open circuit potential (OCP) test with 0 h (0H), 24 h (24H) and 10 days (10D) was adopted. To exclude interruptions such as grain boundary and neighbor effect, single crystal (SC) Cu(100) and Cu(111) were employed. After 10D OCP, cross-sectional slices were cut and picked up by a focused ion beam (FIB). The results showed that the deposited oxide was CuO and Cu(100)/Cu(111) experienced different corrosion behaviors. In general, Cu(100) showed more excellent corrosion resistance. Combined with equivalent electrical circuit (EEC) diagrams, the corrosion mechanism of Cu(100)/Cu(111) in different stages was proposed. In the initial stage, a smaller capacitive loop of Cu(111) suggested preferential adsorption of Cl- on air-formed oxide film on Cu(111). Deposited oxide and exposed bare metals also played an important role in corrosion resistance. Rectangle indentations and pyramidal structures formed on Cu(100)/Cu(111), respectively. Finally, a perfect interface on Cu(100) explained the tremendous capacitive loop and higher impedance (14,274 Ω·cm). Moreover, defects in the oxides on Cu(111) provided channels for the penetration of electrolyte, leading to a lower impedance (9423 Ω·cm) after 10D corrosion.