In situ STM studies of Bi(111)|1-ethyl-3-methylimidazolium tetrafluoroborate + 1-ethyl-3-methylimidazolium iodide interface

• Bi(111)|EMImBF4 + EMImI interface structure has been investigated by in situ STM.
• 2D-superstructure has been demonstrated at an electrode|ionic liquid mixture interface.
• Rhombohedral symmetry describes the unit cell of the iodide ions adsorbed.

Formation of an interfacial structure at an electrochemically polished Bi(111) surface in 1 wt.% 1-ethyl-3-methylimidazolium iodide + 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid mixture has been analysed using the high-resolution in situ electrochemical scanning tunneling microscopy, cyclic voltammetry and electrochemical impedance methods. At 22 ± 1 °C, a well-defined 2-dimensional superstructure has been demonstrated within the electrode potential (E) region from − 0.7 V to − 0.3 V (vs. Ag|AgCl in the same mixture of the ionic liquids), where a strong specific I− anion adsorption and coadsorption of counter-ions occurs. At E < − 0.8 V, the superstructure disappears as a result of desorption of the specifically adsorbed iodide anions from the Bi(111) surface. At E ≥ − 0.2 V, where Bi(111) surface oxidation process starts, the 2D-superstructure cannot be observed due to a quick atomic-scale roughening of the Bi(111) plane.

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