As the climate debate is hotting up, so is the (re)search for finding powerful new materials for the efficient and cost-effective removal of CO2 from flue-gas streams from power plants and other emission sources. Ionic liquids (ILs), exhibiting higher CO2 solubility than conventional organic solvents, have received considerable interest as new CO2 absorbents. The present paper evaluates the advantages and disadvantages of ILs, and provides an overview of the recent developments of ILs for CO2 capture. In conventional ILs, CO2 is absorbed by occupying the free space between the ions through physical absorption mechanisms. As another promising strategy, task-specific ILs have been studied that, by attaching functional groups to the ions, allow the formation of chemical bonds to improve the overall absorption capacity during the CO2 capture process. Other strategies include using ILs as reaction media or as selective absorption materials.
In seeking to develop ionic liquid based electrolytes for use in lithium metal batteries, we present an investigation of the electrochemical properties of
N
-propyl-
N
-methyl-pyrrolidinium bis(fluorosulfonyl)imide and lithium bis(fluorosulfonyl)imide at Ni, Pt, and Li electrodes by cyclic voltammetry, chronoamperometry, and impedance spectroscopy. While lithium electrodeposition and stripping are chemically reversible, the magnitude of peak currents during successive cycles is strongly dependent on the substrate. Severe decreases are observed at Ni, only moderate falls at Pt, while Li electrodes support modest increases in current, consistent with roughening of the electrode with each deposition cycle. We discuss this behavior on the basis of competition between (i) formation of a solid electrolyte interphase at the deposited lithium surface and (ii) strength of interaction between deposited lithium and substrate. Chronoamperometric data indicate that lithium deposition proceeds via instantaneous nucleation and growth, which favors smooth rather than nodular deposit morphology. Symmetrical
(Li|electrolyte|Li)
cells display excellent cycling behavior
(470cycles)
, at current densities up to
10mAcm−2
, with only transient evidence of dendrite formation. Initially high impedance is reduced by increasing the concentration
(∼0.5molkg−1)
of lithium salt, although all cells eventually reach relatively low values of
<10Ωcm2
. The properties of this electrolyte system make it a strong candidate for future application in lithium metal batteries.
A new series of salts, based on the N-methyl-N-alkylpyrrolidinium cation and the PF 6 -anion, are reported and their thermal properties described for alkyl ) Me, Et, Pr, Bu, Hx, and Hp. X-ray structures of several of the salts are also reported. The N,N-dimethylpyrrolidinium hexafluorophosphate has a melting point greater than 390°C; however, the N-methyl-N-butylpyrrolidinium derivative melts at 70°C. Most of the PF 6 -salts were observed to have lower melting points in comparison with the analogous iodide salts. Most of the salts exhibit one or more thermal transitions prior to melting and a final entropy of melting less than 20 J K -1 mol -1 , behavior which has previously been associated with the formation of plastic crystal phases. Good crystal structure solutions were obtained at low temperatures in the case of the alkyl ) propyl and heptyl derivatives. The loss of diffraction peaks and changes in symmetry at higher temperatures indicated the presence of dynamic rotational disorder, supporting the understanding that the plastic properties arise from rotational motions in the crystal.
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