The extent to which cations and anions in ionic liquids (ILs) and ionic liquid solutions are dissociated is of both fundamental scientific interest and practical importance because ion dissociation has been shown to impact viscosity, density, surface tension, volatility, solubility, chemical reactivity, and many other important chemical and physical properties. When mixed with solvents, ionic liquids provide the unique opportunity to investigate ion dissociation from infinite dilution in the solvent to a completely solvent-free state, even at ambient conditions. The most common way to estimate ion dissociation in ILs and IL solutions is by comparing the molar conductivity determined from ionic conductivity measurements such as electrochemical impedance spectroscopy (EIS) (which measure the movement of only the charged, i.e., dissociated, ions) with the molar conductivity calculated from ion diffusivities measured by pulse field gradient nuclear magnetic resonance spectroscopy (PFG-NMR, which gives movement of all of the ions). Because the NMR measurements are time-consuming, the number of ILs and IL solutions investigated by this method is relatively limited. We have shown that use of the Stokes–Einstein equation with estimates of the effective ion Stokes radii allows ion dissociation to be calculated from easily measured density, viscosity, and ionic conductivity data (ρ, η, λ), which is readily available in the literature for a much larger number of pure ILs and IL solutions. Therefore, in this review, we present values of ion dissociation for ILs and IL solutions (aqueous and nonaqueous) determined by both the traditional molar conductivity/PFG-NMR method and the ρ, η, λ method. We explore the effect of cation and anion alkyl chain length, structure, and interaction motifs of the cation and anion, temperature, and the strength of the solvent in IL solutions.

We employ precise measuring techniques to determine the densities, viscosities, and ionic conductivities of three aqueous 1-ethyl-3-methylimidazolium [emim]+ ionic liquid (IL) systems with minimal experimental uncertainty. We simultaneously present a novel method for estimating ion dissociation relying only on these three measurements and the estimated Stokes radii of the ions based on the Stokes–Einstein and Nernst–Einstein equations. Ion dissociation values are estimated across a range of IL concentrations, emphasizing dilute IL regions, using ionic radii calculated from widely used UNIQUAC and UNIFAC values. With these approximations and assuming the presence of only ion pairs, the ion dissociation of all three ILs reaches a minimum value at a water mole fraction of about 0.98. Upon further dilution with water, the ion dissociation increases as the system approaches infinite dilution of the IL. We postulate that the apparent minimum in the ion dissociation is caused by the Stokes radii of the cation and anion increasing as the concentration becomes more dilute, due to the formation of ion triplets.

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This paper presents an experimental study of high-pressure chemical-looping combustion (CLC) of methane and synthesis gas using supported Cu and Ni oxygen carriers. The experiments were performed in an isothermal, fixed-bed reactor at the pressure range of 1–10 bar. The analysis showed that at elevated pressures, the reactivity of the CLC oxygen carriers deviates from that at atmospheric pressure. Formation of solid carbon was found favorable at high pressures for both oxygen carriers, though more extensively with Cu materials. An empirical kinetic model was used to capture the effect of pressure on the reduction and oxidation reactions. The objective of this work is to derive a kinetic model that can accurately capture the idiosyncrasies of high-pressure CLC, which can guide process design studies of CLC integration into power plants.

Typical design strategies for mixed ion−electron conduction in polymers have focused on overall ionic conductivity, without specificity for anion vs cation conduction. Here, we demonstrate that side chain chemistry can be used to control Li + conductivity in semiconducting polymers. This design principle is significant for applications that require Li + -specific transport, such as Li-ion batteries. We show that a polythiophene functionalized with an ionic liquid side chain demonstrates higher conductivity and lithium transference than a more commonly studied ether-functionalized P3AT derivative. Poly(3-(6′-(N-methylimidazolium) hexyl)thiophene TFSI − ) (P3HT-Im + TFSI − ) can solvate and conduct ions up to salt concentrations of r = 1.0 (where r = [moles of salt]/[moles of monomer]) while achieving an ionic conductivity of ∼10 −3 S/cm at 80 °C and a lithium transference number of 0.36. On the other hand, poly(3-(methoxyethoxyethoxymethyl)thiophene) (P3MEEMT) shows a peak conductivity of ∼10 −5 S/cm at r = 0.05 and 80 °C, with near-zero lithium transport. This work shows that multiple high dielectric moieties can be used to drive ion conduction in semiconducting polymers, but diffuse, cationic side chains such as imidazolium are preferred for Li-ion conduction.