Achieving Low-Energy Driven Viologens-Based Electrochromic Devices Utilizing Polymeric Ionic Liquids
Journal
ACS Applied Materials and Interfaces
Journal Volume
8
Journal Issue
44
Pages
30351-30361
Date Issued
2016
Author(s)
Abstract
Herein, three kinds of viologens-based electrochromic devices (ECDs) (heptyl viologen (HV(BF4)2), octyl viologen (OV(BF4)2), and nonyl viologen (NV(BF4)2)) were fabricated utilizing ferrocene (Fc) as a redox mediator. Among them, the NV(BF4)2-based ECD exhibits the highest coloration efficiency (36.2 cm2/C) owing to the lowest driving energy. Besides, switching between 0 and 1.2 V, the NV(BF4)2-based ECD shows a desirable initial transmittance change (£_T = 56.7% at 605 nm), and long-term stability (£_T = 45.4% after 4000 cycles). Furthermore, a UV-cured polymer electrolyte containing polymeric ionic liquid (PIL, 1-allyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide) and ethoxylated trimethylolpropane triacrylate (ETPTA) was introduced to the NV(BF4)2-based ECD. By controlling the weight percentage of the PIL, different curing degrees of the polymer electrolytes were obtained and led to an improved stability of the NV(BF4)2-based ECD because of the immobilization of NV(BF4)2. This observation was explained by calculating the apparent diffusivity (Dapp) of the redox species in the NV(BF4)2-based ECD under various curing degrees. In addition, increasing the amount of PIL leads to a lower driven energy needed for the NV(BF4)2-based ECD, following the same trend as the value of Dapp. Among all NV(BF4)2-based ECDs, 20 wt % of PIL addition (20-PIL ECD) exhibits large transmittance change (£_T = 55.2% at 605 nm), short switching times (2.13 s in coloring and 2.10 s in bleaching), high coloration efficiency (60.4 and 273.5 cm2/C at 605 nm, after excluding the current density at the steady state), and exceptional cycling stability (£_T = 53.8% after 10,000 cycles, or retained 97.5% of its initial £_T). ? 2016 American Chemical Society.
Subjects
diffusion coefficient
electrochemistry
electrochromic devices (ECDs)
gel electrolytes
ionic liquids
polymer electrolytes
UV-curing
viologens
Type
journal article