Revealing the Microscopic Structure and Adsorption Mechanism of Imidazolium-Based Ionic Liquids on the Interface and...

Two-dimensional MXenes combined with ionic liquids (ILs) represent a promising class of electrode-electrolyte systems owing to their high electrochemical activity and wide electrochemical windows. However, the microscopic structure of the interaction mechanisms at MXene-IL interfaces remains insufficiently understood. In this work, first-principles calculations were employed to systematically investigate the adsorption of imidazolium-based ionic liquids on Ti₂CT₂ MXene surfaces and within MXene bilayers, with a focus on the effects of surface terminations, anion species, and cation alkyl-chain length. The results show that O-terminated Ti₂CO₂ exhibits consistently stronger adsorption toward ILs than F-terminated Ti₂CF₂, originating from its higher surface polarity and enhanced charge-transfer capability. Anion chemistry influences local adsorption configurations and interfacial charge redistribution, where small and highly polar anions ([Cl]^-, [Br]^-, and [OAc]^-) induce stronger interactions than bulky, charge-delocalized anions ([BF₄]^- and [PF₆]^-); however, their impact on overall adsorption strength is secondary compared to surface termination effects. In contrast, increasing the alkyl-chain length of imidazolium cations significantly enhances adsorption energies due to strengthened dispersion interactions and extended charge redistribution. Intercalation studies further reveal that imidazolium cations can stably reside within MXene bilayers in multiple configurations, experiencing cooperative adsorption from adjacent layers. These findings provide a microscopic understanding of MXene-ionic liquid interfacial interactions and clarify the relative roles of surface terminations, anions, and cations.