Self-assembled monolayers (SAMs) have significant importance in many modern applications^1-2. The properties of SAMs depend on many aspects, such as the characteristics of individual molecules, forming the monolayer; by the interactions between these molecules; and SAM interactions with the electrolyte; the crystalline surface of the substrate; etc³. Therefore, the fundamental studies of these systems are crucial in determining the function of SAMs in various applications^4-5.

The aim of the current work was to study the adsorption characteristics of 4,4’- bipyridine from ionic liquid media at different electrodes⁶.

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were conducted to characterize the electrochemical behavior of the self-assembled 4,4’-bipyridine (4,4’-BP) layers at the Sb(111) and Cd(0001) | 4,4’-BP+1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF₄) interface. All the experiments were carried out in a three-electrode electrochemical cell in a glove-box, i.e., a nitrogen-controlled atmosphere.

CV method was used to examine the electrochemical characteristics of the system under investigation within the potential region −0.9 V < E < 0.0 V for Sb(111) and −2.1 V < E < -0.8 V for Cd(0001) vs. Ag|AgCl. The current values increase rapidly at the more negative end of the studied potential region, indicating that reduction processes started at the Sb(111) and Cd(0001) | 4,4’-BP+EMImBF₄ interface. In contrast with the data measured in EMImBF_4, where the system shows ideal polarisable behaviour in the whole potential range. Interfacial capacitance (C_s) values were calculated using the relation C_s=−(Z′′2𝜋f)⁻¹. Capacitance values calculated depend on the composition of the electrolyte (i.e., on the concentration of 4,4’-BP), electrode material as well as on applied potential. C_s values are lower in the mixture than those measured in pure EMMImBF₄ at a certain potential region in the case of both electrode materials. This effect is caused by the adsorption of 4,4’-BP molecules at the electrode surface. The shape of the phase angle vs. frequency (f) curves shows that mixed kinetic processes occur in the whole f range measured (i.e. diffusion and charge transfer steps in addition to adsorption).

Acknowledgments:

This work was supported by the Estonian Research Council grant PSG249, and by the EU through the European Regional Development Fund under project TK141 (2014-2020.4.01.15-0011).

References:

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6. H. Ers et al., DOI: 10.26434/chemrxiv-2022-5lcrq