Submolecular insights into the adsorption mechanism of imidazolium-based corrosion inhibitors: A novel quantum parameter for predicting inhibition superiority

Despite extensive research, there are still debates about distinct aspects of corrosion inhibition by organic inhibitors. In this study, two novel ionic liquids (ILs) were synthesized and investigated as model inhibitors for mild steel in 0.5 M HCl. Electrochemical methods and surface characterization through FTIR, XPS, and FE-SEM, along with thermodynamic and first-principles calculations, were employed to evaluate inhibition efficacy and to unravel the underlying mechanism. Results revealed that, following a one-layer adsorption isotherm, the ILs predominantly exhibited anodic spontaneous physicochemical interactions with the corroding substrate. As a result, at least 84 % of the acidic corrosion was mitigated using 4 mM of the ILs, according to impedance studies. Furthermore, chloride-mediated cooperative (indirect) adsorption, apart from direct surface binding, was confirmed experimentally for the first time, providing better justification for the dominant anodic performance. Utilizing quantum calculations, it was demonstrated how the data computed for standalone inhibitors can contribute to estimate the most stable adsorption configurations. In addition, the role of each functional group and atomic constituent in the adsorptive corrosion inhibition was elaborated, given different possible adsorbate-adsorbent interaction modes. Finally, a novel quantum parameter was introduced, and its potential application as an indicator for identifying superior corrosion inhibition was described.