Comparative in situ STM, cyclic voltammetry and impedance spectroscopy study of Bi(111) | 1-ethyl-3-methylimidazolium tetrafluoroborate interface

• Bi(111) electrode in EMImBF4 was studied by in situ STM, CV and EIS techniques.
• Bi(111) electrode is stable in EMImBF4 under cathodic polarisation for hours.
• Atomic resolution for Bi(111) was repeatedly obtained in EMImBF4 using STM.
• Bi(111) surface in EMImBF4 was oxidised/dissolved during anodic potential cycles.
• Ion adsorption from EMImBF4 to Bi(111) is a slow process demonstrated by EIS data.

The Bi(111) | 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) interface has been studied by in situ scanning tunnelling microscopy (STM), cyclic voltammetry and impedance spectroscopy methods within the electrode potential region from − 1.2 V to 0.0 V (vs. Ag | AgCl in EMImBF4) for 60 h. The Bi(111) | EMImBF4 interface is ideally polarisable from − 0.8 V to − 0.2 V and the atomic resolution data were established and analysed. After some oxidation/dissolution and reduction cycles within the potential region from 0.0 V to − 1.2 V the roughening of the Bi(111) surface was observed. Differently from Au(hkl) | room temperature ionic liquid interfaces, there is no potential-induced surface reconstruction at Bi(111) | EMImBF4 interface, and therefore it is not possible to restore the atomically flat Bi(111) surface by applying moderate negative potentials, observed for Au(hkl).Slow electrical double layer (EDL) formation kinetics limited by the finite-length mass transfer and adsorption steps of EMImBF4 onto the Bi(111) surface has been analysed by the impedance method. The higher series, double layer and adsorption capacitance values, calculated using non-linear least squares fitting method of impedance data, for the Bi(111) | EMImBF4 interface compared to the Bi(111) | 1-butyl-4-methylpyridinium tetrafluoroborate (BMPyBF4) interface has been explained by the lower molar volume, higher dielectric constant and lower thickness of the EDL formed.