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Accueil du site > Productions scientifiques > Séminaires à PHENIX > 2012 > Séminaire 11.07.2012 à 14h00

Séminaire 11.07.2012 à 14h00

par Mathieu Salanne - 5 juillet 2012

Austen Angell, du département de chimie et biochimie de l’Arizona State University, présentera un séminaire le 11 juillet 2012 à 14h00 dans la bibliothèque du laboratoire PECSA (7e étage, bâtiment F, porte 754) intitulé :

Ionic liquids as oxidic media for electron and proton transfer studies

Résumé

We review the basic ideas underlying the electron free energy level diagrams that have been found useful in considering the thermodynamics of redox processes in molten silicates and related high temperature ionic liquid solvents and their relation to aqueous solutions(1, 2) and then show how closely they link to behavior observable in ambient temperature ionic liquids.

Much of the information available on redox levels in molten oxides has been gleaned from chemical analysis and spectroscopic species distribution studies, but it is simpler to obtain the data electrochemically. Here we report some cyclic voltammetry measurements of the Fe(II)/Fe(III) redox equilibrium in aprotic ionic liquids whose anions provide oxide environments for the redox species that are of different electronic polarizability character from those of the high temperature solvents, and relate the observations to those of the earlier studies. Quasireversible behavior is found in each of the cases studied. As might be expected, the Fe(II)/Fe(III) equilibrium experiences a more basic environment in an acetate IL than it experiences in any of the common glassforming oxide media, while triflate anions contrast by providing a more acid environment than does the most acid of the molten oxide glassformers studied (an alkali phosphate). The difference can amount to well over 1 V(3), suggesting the possibility of a "basicity cell" where the same redox couple locates in anode and cathode compartments of the cell, and only the anion environment is different.

To make a contrast, we then make a related discussion of the energy levels of protons, the other fundamental particle, in ionic liquids of the protic variety(4). We identify the condition under which superacidc ionic liquids, which are also superprotonic, may be prepared.

Références

1. C.A. Angell, Electron free energy levels in oxidic solutions : relating oxidation potentials in aqueous and non-aqueous systems, J. Solid State Electrochem., 13, 981 (2009)

2. J. Wong, C.A. Angell, Glass : Structure by Spectroscopy, p 864 (chap 6.2) (available at http://www.public.asu.edu/angell). Marcel Dekker, New York, Amsterdam (1976)

3. K. Ueno, C.A. Angell, Ionic liquids as oxidic medial for electron transfer studies, J. Chem. Phys., in press (2012)

4. C.A. Angell, Y. Ansari, Z.-F. Zhou, Ionic Liquids : Past, Present and Future, Faraday Discuss., 154, 9 (2012)

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