The use of imidazolium-based ionic liquids (ILs) as corrosion inhibitors for iron is studied using first-principles based approaches, to understand their adsorption structure, stability, and mechanism. A total of 36 ionic liquids were selected, where we varied the anion type (Cl–, Br–, I–, N(CN)2–, BF4– and PF6–) and the alkyl chain length (Cn, n = 0, 1, 2, 4 and 6) of the cation. By density functional theory (DFT) and ab-initio molecular dynamics calculations, we identified the stable adsorption configurations and found that the ILs exhibit strong chemisorption on the metal surface through net electron donation from the iron slab to the imidazolium ring. Employing dispersion corrected DFT methods (DFT-D3), we demonstrated that the alkyl chain length of the cation greatly influences adsorption energy due to interfacial interactions between the iron slab and the IL. The anion within the IL also significantly affects adsorption properties, and those with halide anions show exceptionally strong adsorption energy. Combining DFT-based quantum chemical parameters and force field based molecular dynamics calculations, we developed a quantitative-structure activity relationship (QSAR) model to predict the calculated adsorption energies. Among several commonly used machine learning algorithms tested, support vector regression performs the best, with predicted adsorption energies within 10% root mean square error of the actual calculated adsorption energies. The results from this computational study agree with past experimental findings and provide insight into the nature of the adsorption process of ILs involved in corrosion inhibition.

Adsorption of imidazolium-based ionic liquids on Fe(100) surface for corrosion inhibition: A first-principles computational study

ACS Spring 2022

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