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

Abstract

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 (Formula presented.) 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 (Formula presented.) and Cu (Formula presented.) 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 Cu2O and Cu (Formula presented.) /Cu (Formula presented.) experienced different corrosion behaviors. In general, Cu (Formula presented.) showed more excellent corrosion resistance. Combined with equivalent electrical circuit (EEC) diagrams, the corrosion mechanism of Cu (Formula presented.) /Cu (Formula presented.) in different stages was proposed. In the initial stage, a smaller capacitive loop of Cu (Formula presented.) suggested preferential adsorption of (Formula presented.) on air-formed oxide film on Cu (Formula presented.). Deposited oxide and exposed bare metals also played an important role in corrosion resistance. Rectangle indentations and pyramidal structures formed on Cu (Formula presented.) /Cu (Formula presented.), respectively. Finally, a perfect interface on Cu (Formula presented.) explained the tremendous capacitive loop and higher impedance (14,274 Ω·cm2). Moreover, defects in the oxides on Cu (Formula presented.) provided channels for the penetration of electrolyte, leading to a lower impedance (9423 Ω·cm2) after 10D corrosion.