Electrochemical Stability of Zinc and Copper Surfaces in Protic Ionic Liquids

Ionic liquids are versatile solvents that can betailored through modification of the cation and anion species.Relatively little is known about the corrosive properties of proticionic liquids. In this study, we have explored the corrosion of bothzinc and copper within a series of protic ionic liquids consisting ofalkylammonium or alkanolammonium cations paired with nitrateor carboxylate anions along with three aprotic imidazolium ionicliquids for comparison. Electrochemical studies revealed that thepresence of either carboxylate anions or alkanolammonium cationstend to induce a cathodic shift in the corrosion potential. Theeffect in copper was similar in magnitude for both cations andanions, while the anion effect was slightly more pronounced thanthat of the cation in the case of zinc. For copper, the presence ofcarboxylate anions or alkanolammonium cations led to a notable decrease in corrosion current, whereas an increase was typicallyobserved for zinc. The ionic liquid-metal surface interactions were further explored for select protic ionic liquids on copper using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) to characterize the interface. From these studies,the oxide species formed on the surface were identified, and copper speciation at the surface linked to ionic liquid and potentialdependent surface passivation. Density functional theory and ab initio molecular dynamics simulations revealed that theethanolammonium cation was more strongly bound to the copper surface than the ethylammonium counterpart. In addition, thenitrate anion was more tightly bound than the formate anion. These likely lead to competing effects on the process of corrosion: thetightly bound cations act as a source of passivation, whereas the tightly bound anions facilitate the electrodissolution of the copper

Automated summary

This study investigated the corrosive properties of protic ionic liquids on zinc and copper. It was found that the presence of carboxylate anions or alkanolammonium cations led to a cathodic shift in the corrosion potential, with a noticeable decrease in corrosion current for copper and an increase for zinc. The interactions between ionic liquids and metal surface were further explored, revealing that ethanolammonium cation had a stronger binding to the copper surface compared to ethylammonium cation, and nitrate anion was more tightly bound than formate anion.