We demonstrate an electrochromic device with self-bleaching ability that uses ethyl viologen- ([EV]) and ferrocene-based redox ionic liquids ([FcNTf]) as the electroactive species. These electroactive compounds are insensitive to atmospheric O and HO in both their oxidized and reduced states once dissolved in a typical ionic liquid electrolyte ([BMIm][NTf]), allowing for the device to be assembled outside a glovebox without any encapsulation. This device could generate a deep blue color by the application of a 2.0 V potential between two fluorine-doped tin oxide (FTO) substrates to oxidize the ferrocenyl centers to [FcNTf] while reducing viologen to [EV]. Self-bleaching occurs at OCP as [EV] and [FcNTf] undergo homogeneous electron transfer in the electrolyte. The mass transport of ethyl viologen and ferrocenylsulfonyl(trifluoromethylsulfonyl)imide ([FcNTf]) anion was evaluated by double potential step chronoamperometry to study the impact of the diffusion coefficient on the self-bleaching mechanism. The electrochromic device demonstrated here shows a contrast ΔT (610 nm) around 40% at 2.0 V as colored cell voltage, a switching time in the order of few seconds for coloration and bleaching, coloration efficiency of 105.4 to 146.2 cm C at 610 nm, and very high stability (94.8% ΔT after 1000 cycles) despite the presence of O and HO in the electrolyte.

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Here, we report on the electrochemistry and transport of ions in mixtures of carbonates and an electroactive ionic liquid, in which lithium bis­(trifluoromethylsulfonyl)­imide (Li­[NTf2]) is dissolved. The electroactive ionic liquid was obtained by linking a ferrocene moiety to the [NTf2]−, resulting in a redox anion (ferrocenylsulfonyl­(trifluoromethylsulfonyl)­imide, [FcNTf]−) that can be used as a redox shuttle additive in Li-ion battery electrolytes. Electrochemical and transport properties of the [FcNTf]− electroactive anion and of Li+ are investigated by ionic conductivity, cyclic voltammetry, and self-diffusion PFGSE NMR measurements. The study of the transport properties demonstrates the formation of solvated species and ion aggregation which affects the electrochemical behavior of the [FcNTf]− anion. This study highlights that the fractional lithium ion and total ionic conductivity were significantly decreased with a high concentration of ionic liquid and lithium salt. Finally, the electroactive ionic liquid was applied in lithium-ion cells as a proof of concept of their use as redox shuttles.

Entropic changes inherent within a redox process typically result in significant temperature sensitivity. This can be utilised positively or can be a detrimental process. This study has investigated the thermoelectrochemical properties (temperature-dependant electrochemistry) of the ferrocenium|ferrocene redox couple in an ionic liquid, and in particular the effect of covalently tethering this redox couple to fixed positive or negative charges. As such, the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide was employed to dissolve ferrocene, as well as cationic-tethered ferrocene (the 1-ethyl-3-(methylferrocenyl)imidazolium cation) and anionic-tethered ferrocene (the ferrocenylsulfonyl(trifluoromethylsulfonyl)imide anion). These systems were characterised in terms of their voltammetry (apparent formal potentials, diffusion coefficients and electron transfer rate constants) and thermoelectrochemistry (temperature coefficients of the cell potential or 'Seebeck coefficients', short circuit current densities and power density outputs). The oxidised cationic species behaved like a dicationic species and was thus 6-fold more effective at converting waste thermal energy to electrical power within a thermoelectrochemical cell than unmodified ferrocene. This was almost exclusively due to a significant boost in the Seebeck coefficient of this redox couple. Conversely, the oxidised anionic species was formally a zwitterion, but this zwitterionic species behaved thermodynamically like a neutral species. The inverted entropic change upon going from ferrocene to anion-tethered ferrocene allowed development of a largely temperature-insensitive reference potential based upon a mixture of acetylferrocene and ferricenyl(iii)sulfonyl(trifluoromethylsulfonyl)imide.