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Study on the Behavior of Halide Ions on the Au(111) Electrode Surface in Ionic Liquids Using Surface X‑ray Scattering

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journal contribution
posted on 21.01.2016, 00:00 by Kazuhisa Tamura, Yasuo Nishihata
The behavior of halide ions on the Au(111) electrode surface in two ionic liquids (ILs), 1-buthyl-1-methylpyrrolidiniun bis­(trifluoromethylsulfonyl)­amide ([BMP]­TFSA) and 1-buthyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­amide ([BMIM]­TFSA), was investigated by monitoring the structure of the electrode surface. The potential dependences of the X-ray diffraction intensity, which originate from the Au(111)-(1 × 1) structure and the surface normal structure, were measured simultaneously with cyclic voltammograms. We considered the effects of both ion concentration and ion species. The results revealed that halide ions are coadsorbed with IL molecules on the electrode surface and increase the mobility of surface atoms. By contrast, the Au(111) surface does not reconstruct to the (p × √3) structure, even in the IL containing 200 mM Br. This suggests that the interaction between halide ions and surface Au atoms is weaker than that between IL molecules and surface Au atoms; that is, the surface properties are mainly governed by adsorbed IL molecules. Furthermore, a comparison of the two ILs revealed that the effect of halide ions on the structure of the Au(111) electrode surface depends on the strength of the interaction between IL molecules and surface Au atoms.