Influence of the Electrolyte Film Thickness on Charge Dynamics of Ionic Liquids in Ionic Electroactive Devices

Abstract

Developing advanced ionic electroactive devices such as ionic actuators and supercapacitors requires the understanding of ionic diffusion and drifting processes, which depend on the distances over which the ions travel, in these systems. The charge dynamics of [C4mim][PF6] ionic liquid films and Aquivion membranes with 40 wt% [C2mim][TfO] were investigated over a broad film thickness (d) range. It was found that the double layer charging time τDL follows the classic model τDL = λDd/(2D) very well, where D is the diffusion coefficient and λD the Debye length. In the longer time regimes (t ≫ τDL) where diffusion dominates, the charge dynamics become voltage dependent. For low applied voltage, the later stage charge process seems to follow the d2 dependence. However, at high voltages (> 0.5 V) in which significant device responses occur, the charging process does not show d2 dependence so that τdiff = d2/(4D), corresponding to the ion diffusion from the bulk region, was not observed.

Evolution of morphology, segmental dynamics, and conductivity in ionic liquid swollen short side chain perfluorosulfonate ionomer membranes

“…Ion transport and storage in ionic liquid (IL)‐containing perfluorosulfonate ionomer membranes is of great interest for ionic electroactive devices, such as actuators, sensors, fuel cells, and supercapacitors . Because of the applied electric field between charged electrodes, ions move toward electrodes of opposite polarity which leads to the energy storage and the strain of the ionic electroactive polymer (IEAP) actuators . Despite the huge importance of the IL swollen membranes, many aspects of ion transport in IL swollen ionomers are not fully understood.…”

Polymer electrolytes integrated with ionic liquids for future electrochemical devices

“…Such actuators can be classified into bucky‐gel actuators,44 actuators based on interpenetrating polymer network,45 and actuators composed of ionic polymer‐metal composites 46. Among them, bucky‐gel actuators, which possess a layer of polymer electrolyte sandwiched between two electrodes composed of single‐wall carbon nanotubes (SWNTs) containing ILs, have particularly attracted immense interest 44, 47–53. Early studies on polymer electrolyte layers of the bucky‐gel actuators had focused on dry ionomers, which typically require activation fields in range 2–5 V 42.…”

“…The relative sizes of the cations and anions in the ILs play an important role in determining the volume changes of each electrode, which in turn determine the level of strain (i.e., displacement) under a given applied voltage 50, 51. There are several other factors including the polarity and mobility of ILs within the polymer matrix that affect the actuation performance 52, 53. The limitations of conventional actuators can be placed on the slow switching times and the requirement of high driving voltages, which are critical drawbacks for biomimetic applications.…”

Conductivity and transport properties of starch/glycerin-MgSO4 solid polymer electrolytes

“…Therefore, the values of the dielectric constant, ɛr, for all samples were taken at 630 kHz and were calculated at a location between 1 and 130, respectively. Another important parameter that had to be determined in the first stage was λD and thus it was calculated using the equation mentioned by Lin et al (2012). These values (ɛr, λD) were used to calculate the parameters of the diffusion coefficient, mobility of ions, the number density of charge carriers and capacitance of samples using Eqs.…”