How is charge transport different in ionic liquids? The effect of high pressure

Abstract

Modern ionic liquids (ILs) are considered green solvents for the future applications due to their inherited advantages and remarkable transport properties. One of the ubiquitous properties of ILs is their intrinsic ionic conductivity. However, understanding of the super-Arrhenius behavior of the ionic conductivity process at elevated pressure still remains elusive and crucial in glass science. In this work, we investigate the ion transport properties of 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide: [Cmim][NTf], 1-butylimidazolium bis[(trifluoromethyl)-sulfonyl]imide: [CHim][NTf] and 1-butylimidazolium hydrogen sulfate: [CHim][HSO] ILs in the supercooled liquid state using dielectric spectroscopy at ambient and high pressure. We present the experimental data in the dynamic window of the conductivity formalism to examine the charge transport properties. The frequency-dependent ionic conductivity data have been analyzed using the time-temperature superposition principle. In the Arrhenius diagram, the thermal evolution of the dc-conductivity reveals similar temperature dependence for both protic and aprotic ILs thus making it difficult to distinguish the ion dynamics. However, our results demonstrate the key role of high pressure that unambiguously separates the charge transport properties of protic ILs from aprotic ones through the apparent activation volume parameter. We also highlight that the activation volume can be employed to assess the information connecting the ability of ionic systems to form H-bond networks and the impact of proton transfer involved in the conduction process.

The effect of thermal treatment on ac/dc conductivity and current fluctuations of PVDF/NMP/[EMIM][TFSI] solid polymer electrolyte

“…The normalized conductivity spectra in Fig. 3, further, demonstrate that the time-temperature superposition principle is observed, just as the Barton-Nakajima-Namikiwa (BNN) relationship σ 0 ∼ ω e is fulfilled 39,44,46,48 , inset Fig. 3.…”

“…The model assumes that hopping conduction is the main underlying mechanism in which the charge carriers hop in a random spatially varying energy landscape. Thus, the charge transport is governed by the ability of the charge carriers to overcome the randomly distributed energy barriers 39,[43][44][45][46] . The characteristic time τ e corresponds to the rate to overcome the highest energy barrier and determines the onset of the dc conductivity σ 0 43,46 .…”

“…Thus, the charge transport is governed by the ability of the charge carriers to overcome the randomly distributed energy barriers 39,[43][44][45][46] . The characteristic time τ e corresponds to the rate to overcome the highest energy barrier and determines the onset of the dc conductivity σ 0 43,46 . In other words, this characteristic time separates the dc-regime with diffusive ionic transport from the dispersive regime described by a sub-diffusive ionic motion 46 .…”

“…The characteristic time τ e corresponds to the rate to overcome the highest energy barrier and determines the onset of the dc conductivity σ 0 43,46 . In other words, this characteristic time separates the dc-regime with diffusive ionic transport from the dispersive regime described by a sub-diffusive ionic motion 46 . www.nature.com/scientificreports/ However, a fit of conductivity spectra of the ionic liquid under test exhibits an additional 'relaxation-like' process that is assumed 47 to be connected to structural reorganization of the ionic atmosphere during and after a successful ionic jump.…”

“…4). In a liquid state, this temperature dependence of conductivity is governed by Vogel-Fulcher-Tammann dependence 46,50 . Around the transition between solid and liquid states, a hysteresis loop is apparent, which can be explained as the apparition of supercooled liquid 51 .…”