Air-Stable, Self-Bleaching Electrochromic Device Based on Viologen- and Ferrocene-Containing Triflimide Redox Ionic Liquids

Abstract

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.

From Broadband to Electrochromic Notch Filters with Printed Monochiral Carbon Nanotubes

“… 2 − 6 EC materials range from inorganic oxides (e.g., tungsten trioxide) and Prussian blue to organic polyaniline, conjugated polymers (e.g., containing propylene dioxythiophene units), and redox-active molecules (e.g., viologens) and can cover broad wavelength ranges from the ultraviolet to the near-infrared (nIR). 4 , 7 − 13 A typical EC device consists of a film of the EC material on a transparent working electrode, a counter electrode, and an electrolyte sandwiched between them. The electrolyte might be liquid or solid.…”

Mechanically Robust, Highly Ionic Conductive Gels Based on Random Copolymers for Bending Durable Electrochemical Devices

“…Cospito et al prepared an EV 2+ ‐containing EC layer using conventional EC gels composed of homopolymer (poly(vinyl formal)) and organic solvent ( N ‐methyl‐2‐pyrrolidone), and an η of 118.65 cm 2 C −1 was measured from the resulting device . Gélinas et al demonstrated liquid‐type ECDs based on EV 2+ with FcNTf (anodic species) and [BMIm][NTf 2 ] (ionic liquid) that exhibited an η of 105.4–146.2 cm 2 C −1 depending on the EC solution composition …”

Viologen-Based Electrochromic Materials: From Small Molecules, Polymers and Composites to Their Applications

“…The color of this reduction state mainly depends on the substitution groups on the nitrogen of the bipyridinium salt. As illustrated in Figure 4a,b, the absorption spectra of the radical cation of ethyl viologen ( V2 ) exhibit a strong absorption peak close to 608 nm and weak absorption at near-UV irradiation (400–450 nm) region, resulting in a blue color upon reduction [29]. Other viologens substituted with alkyl chains, such as methyl viologen ( V1 ) [30], heptyl viologen ( V3 ) [31], benzyl viologen [32] and vinyl benzyl viologen ( V6 ) [33], all show similar optical characteristics to ethyl viologen with the absorption peak around 600 nm at the radical cation state, leading to a typical blue or violent-blue color.…”