Deciphering the corrosion inhibition of AZ91 magnesium alloy by ionic liquids: electron properties, complexation, and interface dynamics

Understanding atomic- and molecular-scales interactions at corrosion inhibitor/ metal interface is crucial for developing high-performance protective systems. This study investigates corrosion inhibition mechanisms of three ionic liquids (ILs)- 1-butyl-3-methylimidazolium tetrafluoroborate (BmimBF 4 ), N-butyl-N-methyl pyrrolidinium tetrafluoroborate (BMPBF 4 ), and 1-butyl-3-methylimidazolium chloride (BmimCl) on AZ91 magnesium alloy by integrating electrochemical measurements, surface analysis, and simulations. Density functional theory (DFT)calculations reveal that the superior performance of BmimBF 4 originates from electron transfer from BF 4 − to MgO(100), which compensates for defects in the MgO layer via subsurface electron enrichment, and its contribution is higher than that of adsorption energy. It is found that the optimal concentration of BmimBF 4 (20 mL L −1 ) corresponds to the maximum formation of the bidentate complex [Mg(H 2 O) 2 (BF 2 ) 2 ], which can self-assemble into a continuous protective layer. Molecular dynamics (MD)simulations establish, for the first time, a quantitative relationship between the diffusion coefficient of adsorbed ions and the low-frequency impedance modulus (|Z| 0.01 ), clarifying the mechanism by which molecular mobility regulates interfacial repair ability. This work provides fundamental insights into interfacial inhibition mechanisms and a predictive framework for designing green corrosion inhibitors.