Ionic liquids are room-temperature molten salts, composed mostly of organic ions that may undergo almost unlimited structural variations. This review covers the newest aspects of ionic liquids in applications where their ion conductivity is exploited; as electrochemical solvents for metal/semiconductor electrodeposition, and as batteries and fuel cells where conventional media, organic solvents (in batteries) or water (in polymer-electrolyte-membrane fuel cells), fail. Biology and biomimetic processes in ionic liquids are also discussed. In these decidedly different materials, some enzymes show activity that is not exhibited in more traditional systems, creating huge potential for bioinspired catalysis and biofuel cells. Our goal in this review is to survey the recent key developments and issues within ionic-liquid research in these areas. As well as informing materials scientists, we hope to generate interest in the wider community and encourage others to make use of ionic liquids in tackling scientific challenges.

Ionic-liquid materials for the electrochemical challenges of the future.

Protic Ionic Liquids: Properties and Applications

It is widely believed that a defining characteristic of ionic liquids (or low-temperature molten salts) is that they exert no measurable vapour pressure, and hence cannot be distilled. Here we demonstrate that this is unfounded, and that many ionic liquids can be distilled at low pressure without decomposition. Ionic liquids represent matter solely composed of ions, and so are perceived as non-volatile substances. During the last decade, interest in the field of ionic liquids has burgeoned, producing a wealth of intellectual and technological challenges and opportunities for the production of new chemical and extractive processes, fuel cells and batteries, and new composite materials. Much of this potential is underpinned by their presumed involatility. This characteristic, however, can severely restrict the attainability of high purity levels for ionic liquids (when they contain poorly volatile components) in recycling schemes, as well as excluding their use in gas-phase processes. We anticipate that our demonstration that some selected families of commonly used aprotic ionic liquids can be distilled at 200-300 degrees C and low pressure, with concomitant recovery of significant amounts of pure substance, will permit these currently excluded applications to be realized.

https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=50194

The distillation and volatility of ionic liquids

In recent years, Carbon Capture and Storage (Sequestration) (CCS) has been proposed as a potential method to allow the continued use of fossil-fuelled power stations whilst preventing emissions of CO2 from reaching the atmosphere. Gas, coal (and biomass)-fired power stations can respond to changes in demand more readily than many other sources of electricity production, hence the importance of retaining them as an option in the energy mix. Here, we review the leading CO2 capture technologies, available in the short and long term, and their technological maturity, before discussing CO2 transport and storage. Current pilot plants and demonstrations are highlighted, as is the importance of optimising the CCS system as a whole. Other topics briefly discussed include the viability of both the capture of CO2 from the air and CO2 reutilisation as climate change mitigation strategies. Finally, we discuss the economic and legal aspects of CCS.

Carbon capture and storage update

Structure and nanostructure in ionic liquids.

We first succeeded in synthesizing ionic liquids from 20 natural amino acids. Amino acid ionic liquids dissolved native amino acids, despite water-free conditions. Furthermore, these ionic liquids are soluble in various organic solvents, such as chloroform. Effects of acidity, hydrogen bonding ability, and steric factors on the properties of these ionic liquids were analyzed as the function of side groups.

Room Temperature Ionic Liquids from 20 Natural Amino Acids

We describe the behavior of the conductivity, viscosity, and vapor pressure of various binary liquid systems in which proton transfer occurs between neat Bronsted acids and bases to form salts with melting points below ambient. Such liquids form an important subgroup of the ionic liquid (IL) class of reaction media and electrolytes on which so much attention is currently being focused. Such “protic ionic liquids” exhibit a wide range of thermal stabilities. We find a simple relation between the limit set by boiling, when the total vapor pressure reaches one atm, and the difference in pKa value for the acid and base determined in dilute aqueous solutions. For ΔpKa values above 10, the boiling point elevation becomes so high (>300 °C) that preemptive decomposition prevents its measurement. The completeness of proton transfer in such cases is suggested by the molten salt-like values of the Walden product, which is used to distinguish good from poor ionic liquids. For the good ionic liquids, the hydrogen bond...

Ionic Liquids by Proton Transfer: Vapor Pressure, Conductivity, and the Relevance of ΔpKa from Aqueous Solutions

We synthesized a series of imidazolium cations containing covalently-bound
anionic sites, such as sulfonate or sulfonamide groups. These zwitterionic
imidazolium salts were found to form molten salts just like ordinary imidazolium
salts. However, regardless of the high ion density, these ions cannot migrate
along potential gradients induced in the bulk. This is a new and unique characteristic
in molten salts. When other salts were added to this, the ions generated from
the newly added salts were able to behave as carrier ions. The ionic conductivity
of a pure molten salt was 10−9 S cm−1
at 25°C, but jumped to 10−5 S cm−1
by adding an equimolar amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)
at 50°C. The zwitterionic salt having a sulfonamide group instead
of sulfonate had an ionic conductivity of 10−4 S cm−1
at 50°C after adding an equimolar amount of LiTFSI. These zwitterionic
imidazolium salts having vinyl groups were synthesized and polymerized. In
spite of their rubber-like properties they showed excellent ionic conductivities
of around 10−5 S cm−1 at 50°C
following the addition of an equimolar amount of LiTFSI to the imidazolium
cation unit.

Masahiro Yoshizawa

Papers

Room Temperature Ionic Liquids from 20 Natural Amino Acids

Ionic Liquids by Proton Transfer: Vapor Pressure, Conductivity, and the Relevance of ΔpKa from Aqueous Solutions

Ion conduction in zwitterionic-type molten salts and their polymers

Development of new class of ion conductive polymers based on ionic liquids

Highly ion conductive flexible films composed of network polymers based on polymerizable ionic liquids