Electrochemical Characterization of Pyrolytic Graphite and Bi(111) Electrodes in Bmimi and Pmimi Ionic Liquids

Abstract

Specific adsorption of iodide ions has been investigated in our research-group for a long time in different aqueous and classical organic solvents [1]. Recently we have showed how the iodide ions behave in different ionic liquids (ILs) mixtures and demonstrated the influence of specifically adsorbed anion on the electrochemical behaviour of Bi|RTIL and PG|RTIL interfaces [2,3]. There are some reports for platinum and glassy-carbon [4] electrodes, but for more fundamental understanding, it is better to use the monocrystal electrodes. For the electrochemical characterization cyclic voltammetry and impedance spectroscopy methods were used. Analysis of experimental and calculated data shows that the electrical double layer structure at electrode|electrolyte interface depends noticeably on the chemical nature of the electrode, electrode potential applied as well as on the chemical nature of ionic liquid used. Furthermore, even without solvation sheaths, the anion adsorption is playing the key role in determining the values of phase angle and capacitance. The phase angle values −85 degrees have been measured being characteristic for the physical adsorption step rate limited mechanism. At more positive electrode potentials, there is a clear rise in capacitance values and based on the previous studies we can conclude that this increase of C is caused by the iodide ions adsorption. Investigated systems demonstrated good stability and reversibility, which are important for using ILs in modern electrochemical devices like supercapacitors and different types of batteries. Acknowledgements This study was partially funded by the Estonian Science Foundation Grant 8786, Estonian Energy Technology Program project SLOKT10209T, Projects IUT20-13, PUT55, PUT1107, and Estonian Centres of Excellence in Science project: High-technology Materials for Sustainable Development (TK117) and TK141 “Advanced materials and high-technology devices for energy recuperation systems”