Effect of Anions in Imidazolium-Based Ionic Liquids on the Corrosion Inhibition of Copper in Seawater

Ionic liquids (ILs) have attracted increasing attention as environmentally friendly corrosion inhibitors because of their low toxicity, high stability, and tunable structures. In this study, the effect of anions in imidazolium-based ionic liquids, including 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl), bromide ([EMIM]Br), and iodide ([EMIM]I), on the corrosion inhibition of copper in seawater was systematically investigated. Electrochemical measurements, surface characterization, density functional theory calculations, and molecular dynamics simulations were employed to evaluate inhibition performance and clarify the adsorption mechanism. The results show that inhibition efficiency increased with inhibitor concentration, and [EMIM]I exhibited the best performance. The superior inhibition of [EMIM]I is attributed to the stronger adsorption ability and the formation of a denser and more compact protective film on the copper surface. Specifically, the larger atomic radius and lower electronegativity of the iodide anion (I – ) promote its strong specific adsorption on the copper substrate, which subsequently facilitates the electrostatic attraction and parallel alignment of the [EMIM] + cations. These findings demonstrate the key role of anions in regulating the cation–anion–metal interaction and provide theoretical support for the design of efficient and environmentally friendly ionic liquid inhibitors.