Influence of the electrode potential and in situ STM scanning conditions on the phase boundary structure of the single crystal Bi(1 1 1)|1-butyl-4-methylpyridinium tetrafluoroborate interface

• The formation of 1-butyl-4-methylpyridinium tetrafluoroborate superstructures at Bi(1 1 1) is a slow process.
• The multilayered ionic liquid structure depends on electrode potential and in situ STM scanning parameters.
• The atomic resolution of Bi(1 1 1) surface structure has been observed at low STM tip potential and slow scanning rate.

Interfacial structure of the Bi(1 1 1)|1-butyl-4-methylpyridinium tetrafluoroborate (BMPyBF4) interface has been studied applying the in situ scanning tunnelling microscopy (STM), cyclic voltammetry, impedance spectroscopy (EIS), and also computational chemistry methods. Influence of electrode potential and in situ STM scanning conditions on the interfacial superstructure formation process has been demonstrated. Slow electrical double layer formation limited by the mass transfer step of BMPyBF4 adsorption onto the Bi(1 1 1) surface, established by using EIS and verified also by STM data, has been explained by the BMPyBF4 multilayered superstructure formation. Possible reasons for the low values of series capacitance for the Bi(1 1 1)|BMPyBF4 interface have been analyzed on the basis of modern theoretical models and explained by the semimetallic nature of bismuth, i.e., by the potential drop inside the Bi(1 1 1) electrode surface layer, and by the strong van der Waals type attractive forces between the adsorbed BMPy+ cations, generating compact adsorbed structures with the low effective dielectric constant.It was found that at the fixed Bi(1 1 1) potential, the observed multilayered structure depends on the STM image scanning rate, the tip potential (bias) and on the tunnelling current. Multilayered formations of BMPyBF4 at the Bi(1 1 1) electrode were observed within potential range from −1.2 V to −0.6 V (vs. Ag|AgCl in BMPyBF4), for the positively charged tungsten STM tip and at the high scanning rates. At more negative Bi(1 1 1) potentials (and the slower scanning rates), the atomic resolution was observed similarly to the Bi(1 1 1)|Na2SO4 + H2SO4 aqueous solutions interface.