Modification and implications of changes in electrochemical responses encountered when undertaking deoxygenation in ionic liquids

Chuan Zhao, Alan Maxwell Bond, Richard G Compton, A M O'Mahony, E I Rogers

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Abstract

Physicochemical changes and substantially modified electrochemical behavior have been reported when ionic liquids are degassed with nitrogen. In conventional experiments in aqueous and organic media, degassing with N-2 is commonly used to remove the electroactive dissolved oxygen. However, in hydrophilic ionic liquid media, degassing with N-2 removes not only the dissolved oxygen but also a significant amount of the adventitious water present. Given the low viscosity of water, this in turn leads to a dramatic change of the viscosity of the degassed ionic liquid and hence mass transport properties that influence voltammetric responses. In the widely used and relatively viscous room temperature ionic liquid, 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) containing the redox probe tetracyanoquinodimethane (TCNQ) and 9 (v/v) deliberately added water, 1 h degassing with very dry N-2 under benchtop conditions results in a dramatic decrease of the TCNQ reduction current obtained under steady-state conditions at a 1 mu m diameter microdisc electrode. This is reflected by a change of diffusion coefficient of TCNQ (D-TCNQ) from 2.6 x 10(-7) to 4.6 x 10(-8) cm(2) s(-1). Karl Fischer titration measurements show that almost complete removal of the deliberately added 9 water is achieved by degassing under benchtop conditions. However, displacement of oxygen by nitrogen in the ionic liquid solution results in the decrease of electrochemical reduction current by 6 , implying that dissolved gases need not be inert with respect to solvent properties. Oxygen removal by placing the BMIMBF4 ionic liquid in a nitrogen-filled glovebox or in a vacuum cell also simultaneously leads to removal of water and alteration of voltammetric data.
Original languageEnglish
Pages (from-to)3856 - 3861
Number of pages6
JournalAnalytical Chemistry
Volume82
Issue number9
DOIs
Publication statusPublished - 2010

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