Liquide ionique

Résumé

Les liquides ioniques sont des sels possédant une température de fusion inférieure à et souvent même inférieurs à la température ambiante. Les liquides ioniques fondus à la température ambiante présentent de nombreux avantages pratiques et sont donc très utilisés. Le terme générique "liquide ionique" (en anglais : ionic liquid) a été introduit en 1943. L'ioliomique est en chimie (biologie ou médecine) l'étude du comportement des ions dans les liquides. La liste des liquides ioniques ne cesse d’augmenter. Les cations sont généralement de type dialkylimidazolium, tétraalkylammonium, tétraalkylephosphonium ou alkylpyridium. Les anions sont de type tétrafluoroborate, hexafluorophosphate, halogénure, mésylate, tosylate, ou triflate. Ils forment des liquides seulement constitués de cations et d’anions. Leur nature très modulable et leurs propriétés exceptionnelles en font des produits devenus essentiels dans certains domaines de la synthèse et de la catalyse, de l'

Source officielle

https://fr.wikipedia.org/wiki/Liquide_ionique

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Novel Ionic Liquids For Electrochemical Applications

Pui Shan Genevieve Lau

This thesis is organized into three main sections, and is concerned with the design and synthesis of novel ionic liquids (ILs), and their associated electrochemical applications. In the first section, a general introduction to the field of ionic liquids is presented, followed by the synthesis and characterization details of all novel compounds used in the study. The second section summarizes work done on the development of more stable dye-sensitized solar cells (DSCs). An introduction to the field of photovoltaics and DSCs is first delivered in Chapter 3, which is followed by two chapters of original work on ionic liqiud-based electrolytes for DSC applications. In Chapter 4, it is shown that novel triazolium-based ionic liquids can be used to fabricate dye-sensitized solar cells, giving power conversion efficiencies of up to 6.00 %. The ionic liquid-based electrolytes are found to be compatible with a range of organic and inorganic photosensitizers, although the ruthenium-based dye (coded C106) exhibits the best performance. A device employing one of these newly-developed electrolytes is also shown to be very stable, retaining ca. 90% of its initial performance even after 1000 hours of continuous full sun illumination at 60 âŠC. In Chapter 5, we focus on the development of stable porphyrin-sensitized solar cells, using IL-based electrolytes. Our studies reveal that the long-term stability of porphyrin-based DSCs are highly dependent on additives in the electrolyte. In particular, it is found that the additive, guanidinium thiocyanate, is essential for the preparation of long-lived devices. It is also shown that the beneficial effect of this additive originates from the thiocyanate anion, rather than the guanidinium cation. The third section of this thesis deals with the ionic liquid-catalyzed electroï¿Œchemical reduction of carbon dioxide. Following a general introduction on carbon dioxide mitigation using ionic liquids (Chapter 6), the results of our work in this area are presented in Chapter 7. Our studies reveal that not all ionic liquids are stable at the potentials required for CO2 reduction. However, the imidazolium-based salts generally perform quite well. The catalytic effect of the IL is found to mainly stem from the cation, with the anion playing a somewhat secondary role. Our results also demonstrate that substitutions on the imidazolium ring can have a huge impact on catalysis. Product analysis shows that the best-performing catalyst produces carbon monoxide as the dominant product, with Faradaic efficiencies of between 70 to 80 %.

EPFL2015

Chargement

Room temperature ionic liquids comprise an unique class of solvent composed of organic and inorganic-based ions that are molten under ambient conditions. They are characterised by high solvent polarity and low vapour pressure, and can be tailored to have specific physical and chemical properties. Consequently, there has been great interest in exploiting these attributes to accelerate and control organic reactions. One such reaction, the Diels-Alder reaction, is an important [4+2] cycloaddition reaction used extensively in the preparation of cyclic and heterocyclic compounds. Understanding the factors involved in the enhancing this reaction in ionic liquids remains a subject of intense interest and the centrepiece of the dissertation. The objective of the research is to explore the Diels-Alder cycloaddition reaction in ionic liquids, with a view of developing high effective reactions systems, that operate under mild reaction conditions. The role that ionic liquid media plays in facilitating the Diels-Alder reaction is discussed. A range of physical and chemical modes of activating the reaction are discussed including pressure, the application of Lewis acid catalysts, microwave irradiation and ultrasound sonication and a comparison on the various modes of activation is provided. Importantly, the results of this study can lead to a better understanding of the ionic liquids as well as their utilization for other organic reactions.

EPFL2007

Chargement

Room temperature ionic liquids (RTILs), considered as "designers' solvents", are attracting a great attention because of their possibility to be tailored based on property requirements. The ionic liquids designed and synthesized for carrying out specified task are referred as functionalized ionic liquids, which show great application potential in various processes. The efforts to produce functionalized ionic liquids, characterize them, and evaluate their properties and applications are presented in this thesis. In chapter 1 the recent developments in ionic liquid functionalization are highlighted. Chapter 2 describes the synthesis and characterization of imidazolium salts in which a nitrile group is attached to the alkyl side chain (single-armed as well as double-armed). The nitrile group was chosen as it is a promising donor to transition metals such as palladium and platinum. The physicochemical properties of these new ionic liquids are described and it is shown how the length of the alkyl unit linking the imidazolium ring and the CN group influences the melting point of the ionic liquid. The third chapter describes palladium complexation reactions with the nitrile functionalized imidazolium ionic liquids (prepared as described in Chapter 2). Their application in C-C coupling and hydrogenation reactions are described. It will be shown that the palladium complexes serve as precursors to nanoparticle catalyst reservoirs and are very efficiently stabilized by the nitrile-functionalized ionic liquids. In chapter 4, the synthesis of a series of nitrile functionalized ionic liquids based on the N-butylnitrile pyridinium cation is reported and their suitability as solvents for palladium-catalyzed biphasic Suzuki and Stille coupling reactions is demonstrated. TEM images reveal that nanoparticles are formed in situ in Stille reactions and show that the nitrile-functionalized ionic liquid exert a superior nanoparticle-stabilizing effect compared to non-functionalized ionic liquids. This allows excellent catalyst lifetimes. In the fifth chapter the synthesis and characterization of a series of ionic liquids incorporating the allyl functionality and some nascent reactions that they undergo, indicating that they are useful precursors to a wide range of other functionalized ionic liquids, will be described. Chapter 6 reports on a concept of "dual-functionalized" ionic liquids. Specifically imidazolium cations with various functionalities are combined with the nitrile functionalized anion [CH3CH(BF3)CH2CN]-, aiming at reducing the melting point and visocity of ionic liquids. In the final chapter the ionic liquid, 1-methyl-3-(4-vinylbenzyl)-imidazolium chloride, is prepared and polymerized to form a macromolecule that is subsequently used as a transition metal nanoparticle stabilizer. A methodology that enables transition metal nanoparticle transfer between liquid phases, via surface modification of the nanoparticles by anion exchange, is described.

EPFL2007

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Novel Ionic Liquids For Electrochemical Applications

Pui Shan Genevieve Lau

EPFL2015

EPFL2007