Effect of the substituent of the cation of N-octylpyridinium hexafluorophosphate in the electrical and electrochemical response of carbon paste electrodes modified with these ionic liquids. (20th December 2017)

• Record Type: Journal Article
• Authors: Fuenzalida, Francesca; Aravena, Daniel; García, Camilo; García, Macarena; Arce, Roxana; Ramírez, Galo; Díaz, Carlos; Isaacs, Mauricio; Arévalo, María del Carmen; Aguirre, María J.
• Is Part Of: Electrochimica acta. Volume 258(2017)
• Page Start: 959
• Page End: 969
• Publication Date: 2017-12-20
• Subjects: Carbon paste electrode -- Carbon paste-ionic liquid electrode -- Substituent effect -- N-octylpyridinium hexafluorophosphate; Electrochemistry -- Periodicals; Electrochemistry, Industrial -- Periodicals; 541.37
• DOI: 10.1016/j.electacta.2017.11.147
• Languages: English
• ISSNs: 0013-4686

Abstract

Abstract: A series of N -octylpyridinium hexafluorophosphate ionic liquids (ILs), ascribed as ROpyPF6, where Opy = N -octylpyridinium and R are the substituents OCH3, CH3, CF3 and CN at the para position of the cation, were characterized and employed as binders in carbon paste electrodes (CILEs) to evaluate the electron donating or withdrawing effects of the substituent of the cation in physical and electrochemical properties of these CILEs. Substituents strongly affect the melting point of the ILs, the electric properties of the CILEs measured by electrochemical impedance spectroscopy, and the electrochemical behavior measured by the response for an outer-sphere reaction (ferro/ferricyanide redox couple) and for an inner-sphere irreversible reaction (oxidation of sulfite). Results show that ILs can be separated in two different groups: those that have withdrawing electron substituents and those that have donating-electron substituents. OpyPF6 has a behavior similar to those that have withdrawing electron substituents. Carbon paste electrode prepared with mineral oil as binder (CPE) has a very different behavior and is described for comparison purposes only. Results show that the ILs with withdrawing electron substituents have more polarized cations (a more localized positive charge) acquiring a slight ionic character in comparison to the ILs with donating substituents. The electron withdrawing effect modifies the hydrogen-fluorine interactions and also the electrostatic interactions between anion and cation, modifying the electric and electrochemical response of the CILEs, resulting in more conductive and homogeneous surfaces. Highlights: Effect of cation-substituent in electrodes modified with ionic liquids is shown. Electron-withdrawing substituents generates more conductive surfaces. Electron-donating substituents generates two kinds of active sites.