Electrochromism of Ferrocene- and Viologen-Based Redox-Active Ionic Liquids Composite

ACS Appl Mater Interfaces. 2019 Jan 9;11(1):1-6. doi: 10.1021/acsami.8b16410. Epub 2018 Dec 27.

Abstract

Redox-active ionic liquids (RAILs) require no other additional reagents such as solvent and supporting electrolyte for electrochemical reactions under undiluted condition. Viologen-based RAILs are one of the electrochromic (EC) ionic liquids with sharp color contrast and high chemical stability. An operation of an EC cell requires two electroactive elements, an EC material and a charge compensating material. In this study, an equimolar composite of a viologen-based RAIL as the EC material and a ferrocene-based RAIL as the charge compensation material, was synthesized and applied to an EC cell. The EC cell with the composite RAIL of as high concentration as 0.92 M each redox species showed good coloration efficiency (91.4 cm2 C-1 at 540 nm on 1.0 V). The coloration process of the EC cell was diffusion-limited process. The current and absorbance of the EC cell reached constant values at large enough bias voltage because of the charge recombination between reduced viologens and oxidized ferrocenes. The recombination affected rapid color erasing process. Almost no deterioration of the composite RAIL was found by 1H NMR after 13 000 potential cycle durability experiment.

Keywords: composite ionic liquids; electrochromic materials; ferrocene-based ionic liquids; redox-active ionic liquids (RAILs); viologen-based ionic liquids.