34 research outputs found
Ionic Liquid Ordering at an Oxide Surface
The interaction of the ionic liquid [C4C1Im][BF4] with anatase TiO2, a model photoanode material, has been studied using a combination of synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. The system is of interest as a model for fundamental electrolyteâelectrode and dye-sensitized solar cells. The initial interaction involves degradation of the [BF4]â anion, resulting in incorporation of F into Oâ
vacancies in the anatase surface. At low coverages, [C4C1Im][BF4] is found to order at the anatase(101) surface via electrostatic attraction, with the imidazolium ring oriented 32±4° from the anatase TiO2 surface. As the coverage of ionic liquid increases, the influence of the oxide surface on the topmost layers is reduced and the ordering is lost
Energy applications of ionic liquids
Ionic liquids offer a unique suite of properties that make them important candidates for a number of energy related applications. Cationâanion combinations that exhibit low volatility coupled with high electrochemical and thermal stability, as well as ionic conductivity, create the possibility of designing ideal electrolytes for batteries, super-capacitors, actuators, dye sensitised solar cells and thermoelectrochemical cells. In the field of water splitting to produce hydrogen they have been used to synthesize some of the best performing water oxidation catalysts and some members of the protic ionic liquid family co-catalyse an unusual, very high energy efficiency water oxidation process. As fuel cell electrolytes, the high proton conductivity of some of the protic ionic liquid family offers the potential of fuel cells operating in the optimum temperature region above 100 °C. Beyond electrochemical applications, the low vapour pressure of these liquids, along with their ability to offer tuneable functionality, also makes them ideal as CO2 absorbents for post-combustion CO2 capture. Similarly, the tuneable phase properties of the many members of this large family of salts are also allowing the creation of phase-change thermal energy storage materials having melting points tuned to the application. This perspective article provides an overview of these developing energy related applications of ionic liquids and offers some thoughts on the emerging challenges and opportunities
Ionic liquids at electrified interfaces
Until recently, âroom-temperatureâ (<100â150 °C) liquid-state electrochemistry was mostly electrochemistry of diluted electrolytes(1)â(4) where dissolved salt ions were surrounded by a considerable amount of solvent molecules. Highly concentrated liquid electrolytes were mostly considered in the narrow (albeit important) niche of high-temperature electrochemistry of molten inorganic salts(5-9) and in the even narrower niche of âfirst-generationâ room temperature ionic liquids, RTILs (such as chloro-aluminates and alkylammonium nitrates).(10-14) The situation has changed dramatically in the 2000s after the discovery of new moisture- and temperature-stable RTILs.(15, 16) These days, the âlater generationâ RTILs attracted wide attention within the electrochemical community.(17-31) Indeed, RTILs, as a class of compounds, possess a unique combination of properties (high charge density, electrochemical stability, low/negligible volatility, tunable polarity, etc.) that make them very attractive substances from fundamental and application points of view.(32-38) Most importantly, they can mix with each other in âcocktailsâ of oneâs choice to acquire the desired properties (e.g., wider temperature range of the liquid phase(39, 40)) and can serve as almost âuniversalâ solvents.(37, 41, 42) It is worth noting here one of the advantages of RTILs as compared to their high-temperature molten salt (HTMS)(43) âsister-systemsâ.(44) In RTILs the dissolved molecules are not imbedded in a harsh high temperature environment which could be destructive for many classes of fragile (organic) molecules
Recommended from our members
An electrochemical in situ study of freezing and thawing of ionic liquids in carbon nanopores
Room temperature ionic liquids (RTILs) are an emerging class of electrolytes enabling high cell voltages and, in return, high energy density of advanced supercapacitors. Yet, the low temperature behavior, including freezing and thawing, is little understood when ions are confined in the narrow space of nanopores. This study shows that RTILs may show a tremendously different thermal behavior when comparing bulk with nanoconfined properties as a result of the increased surface energy of carbon pore walls. In particular, a continuous increase in viscosity is accompanied by slowed-down charge-discharge kinetics as seen with in situ electrochemical characterization. Freezing reversibly collapses the energy storage ability and thawing fully restores the initial energy density of the material. For the first time, a different thermal behavior in positively and negatively polarized electrodes is demonstrated. This leads to different freezing and melting points in the two electrodes. Compared to bulk, RTILs in the confinement of electrically charged nanopores show a high affinity for supercooling; that is, the electrode may freeze during heating
Electrochemical Stability of Imidazolium Based Ionic Liquids Containing Cyano Groups in the Anion: A Cyclic Voltammetry, XPS and DFT Study
The electrochemical stability of ionic liquids based on the 1-ethyl-3-methyl imidazolium [EMIM](+) cation and three different anions, dicyanoamide ([N(CN)(2)](-)), tricyanomethanide ([C(CN)(3)](-)) and tetracyanoborate ([B(CN)(4)](-)), has been investigated. Cyclic voltammetry, X-ray photoelectron spectroscopy (XPS) of the valence band, as well as density functional theory (DFT) calculations were performed. A clear dependence of the anodic stability on the anion can be observed by cyclic voltammetry which is confirmed by XPS valence band spectra. The experimental data are in good agreement with DFT calculations. The valence band spectra and the DFT calculations of the ionic liquids show energetic differences in the position of the highest occupied molecular orbital state and confirm the electrochemically measured stability following the sequence [EMIM][B(CN)(4)] > [EMIM][N(CN)(2)] > [EMIM][C(CN)(3)]. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.001207jes] All rights reserved