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Microelectrode studies in low ionic strength media

Microelectrode studies in low ionic strength media
Microelectrode studies in low ionic strength media

Several electrochemical reactions have been investigated in low ionic strength media using microelectrodes under pseudo steady state conditions. The current-potential responses recorded for charged reactants in aqueous solution do not show any distortion due to iR drop as expected from the theory. However, for a neutral reactant in aprotic solvent (reduction of nitrobenzene) distortion due to iR drop were observed in solutions containing no added electrolyte. Nevertheless, it was still possible to record non distorted steady state voltammograms for solutions containing very low concentrations of electrolyte.

As the current-potential responses for charged reactant species are not distorted by iR drop at low electrolyte concentrations, the influence of ionic strength on the kinetics and thermodynamics of electron transfer reactions of metal complexes was investigated. This study was carried out on the hexacyanoferrate, heaammineruthenium and hexachloroiridate couples which are likely to undergo outer sphere electron transfer reactions. The formal potential was found to shift to more negative potentials for the Fe(CN)64-/Fe(CN)63- and IrCl62-/IrCl63- and to more positive potentials for theRu(NH3)63+/Ru(NH3)62+ as the electrolyte concentration decreases. This effect reflects the relative interaction between the metal complexes and the electrolyte ion. The rate of electron transfer measured using fast potential scan rates as well as steady state experiments was also found to decrease as the electrolyte concentration in the solution was reduced. For the hexacyanoferrate couple, the effects were large and the reproducibility of the current-potential curves was poor when the kinetics of electron transfer was slow. These effects were therefore interpreted in terms of chemical reactions leading to a passivating film in the absence of excess electrolyte. Hence, one role of the electrolyte is to ion pair the hexacyanoferrate anions thereby stabilising them. For the other couples, no complications in the steady state voltammograms were observed and the decrease in the standard rate constants measured is likely to come from a double layer effect.

University of Southampton
Beriet, Carine
Beriet, Carine

Beriet, Carine (1993) Microelectrode studies in low ionic strength media. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

Several electrochemical reactions have been investigated in low ionic strength media using microelectrodes under pseudo steady state conditions. The current-potential responses recorded for charged reactants in aqueous solution do not show any distortion due to iR drop as expected from the theory. However, for a neutral reactant in aprotic solvent (reduction of nitrobenzene) distortion due to iR drop were observed in solutions containing no added electrolyte. Nevertheless, it was still possible to record non distorted steady state voltammograms for solutions containing very low concentrations of electrolyte.

As the current-potential responses for charged reactant species are not distorted by iR drop at low electrolyte concentrations, the influence of ionic strength on the kinetics and thermodynamics of electron transfer reactions of metal complexes was investigated. This study was carried out on the hexacyanoferrate, heaammineruthenium and hexachloroiridate couples which are likely to undergo outer sphere electron transfer reactions. The formal potential was found to shift to more negative potentials for the Fe(CN)64-/Fe(CN)63- and IrCl62-/IrCl63- and to more positive potentials for theRu(NH3)63+/Ru(NH3)62+ as the electrolyte concentration decreases. This effect reflects the relative interaction between the metal complexes and the electrolyte ion. The rate of electron transfer measured using fast potential scan rates as well as steady state experiments was also found to decrease as the electrolyte concentration in the solution was reduced. For the hexacyanoferrate couple, the effects were large and the reproducibility of the current-potential curves was poor when the kinetics of electron transfer was slow. These effects were therefore interpreted in terms of chemical reactions leading to a passivating film in the absence of excess electrolyte. Hence, one role of the electrolyte is to ion pair the hexacyanoferrate anions thereby stabilising them. For the other couples, no complications in the steady state voltammograms were observed and the decrease in the standard rate constants measured is likely to come from a double layer effect.

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Published date: 1993

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Local EPrints ID: 462509
URI: http://eprints.soton.ac.uk/id/eprint/462509
PURE UUID: a5dc55ad-a8d1-44f4-91b9-caa869162988

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Date deposited: 04 Jul 2022 19:10
Last modified: 04 Jul 2022 19:10

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Author: Carine Beriet

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