关键词: 电化学界面, 离子液体, Au(111), 双电层, 层状结构, AFM力曲线, 温度影响

Abstract: By utilizing in-situ AFM force curve measurements systematic investigations have been carried out on Au(111)-ionic liquid interface in BMIPF₆ and OMIPF₆ of imidazolium-based ionic liquids with different lengths of alkyl side chains. The temperature dependence of the number, thickness and stability of the layered structures of each system are studied by performing AFM force curve measurements at potentials far negative of the PZC. The layered structures at Au (111)/BMIPF₆ interface are composed of two charged interior layers and two neutral exterior layers at -1.0 V, while those at Au (111)/OMIPF₆ interface only one charged interior layer and one neutral exterior layer at -16 V. But there contains only one neutral exterior layer and one charged interior layer. Temperature influence on the layering behaviors of the two kinds of ionic liquid systems is investigated. It is shown that within the temperature range of 15 to 40 ^oC, the stability of the layered structures in both BMI⁺ and OMI⁺ systems increases as temperature decreases because of the reduced thermal perturbation. However, the temperature influence is greater for BMI⁺ than for OMI⁺ system. Variation of temperature by 5 ^oC, the rupture force of the first layer in OMIPF₆ changes only 1 ~ 2 nN at -1.6 V, while that in BMIPF6 changes 1 ~ 6 nN at -1.0 V. In addition, at low temperatures, the number of the BMIPF₆ layered structures increase, while that of OMIPF₆ layer structure maintains the same. This difference may be associated with the different molecular sizes that lead to different intermolecular interactions and interactions between the molecule and electrode surface. Meanwhile, OMIPF₆ is more viscous than BMIPF₆ so that the former could be less sensitive to temperature perturbation.

Key words: interface electrochemistry, ionic liquids, Au(111), electric double layer structure, layering structure, AFM force curves, temperature dependence