Improvement of color retention properties of Ag deposition-based electrochromic device by introducing anion exchange mem
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Research Letter
Improvement of color retention properties of Ag deposition-based electrochromic device by introducing anion exchange membrane Shunsuke Kimura, Ryo Onodera, Kazuki Nakamura, and Norihisa Kobayashi, Graduate School of Engineering, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba, CHIBA 263-8522, Japan Address all correspondence to Norihisa Kobayashi at [email protected] (Received 29 January 2018; accepted 26 March 2018)
Abstract Ag deposition-based multicolor electrochromic (EC) device we reported can switch various optical states among transparent, black, silver, cyan, magenta, and yellow by only using electrochemical deposition of Ag. However, the EC device had poor color retention property under open-circuit state because of dissolution of deposited Ag metal by Cu2+ ions, which is essential because it acts as redox material at counter electrode. Here, we introduced an anion exchange membrane to separate Cu2+ from the Ag deposit. The improved device achieved longer retention time of colored state. It is effective to maintain the coloring state without electric power for practical application.
Introduction Electrochromism is a reversible color change induced by electrochemical redox reactions of functional materials. The electrochromic (EC) devices have various advantages for optical modulation systems such as simple structure, large viewing angle, and low power consumption in comparison with the conventional liquid–crystal displaying system and organic lightemitting diodes. Therefore, they are expected to be applied for electronic papers, digital signages, and smart windows.[1–4] In order to develop the information displays by using EC technologies, representation of multi-color in a single device is extensively desired. Some EC molecules, especially those with low molecular weight, can show vivid color changes from clear colorless state to various colors.[5] In order to realize multi-color representation in EC devices, conventional way is the use of EC materials, which can receive multiple redox reactions related to color change as can be seen in conductive polymers and organic molecules.[6,7] However, higher oxidized or reduced states of these materials are usually unstable; therefore, it is difficult to keep a certain color at higher voltages and to achieve enough cycle stability. Other method for achieving multi-color EC devices is to combine several EC materials modified electrode in a single device. In this combination, a number of the working electrodes should be stacked in a single device for controlling each EC reaction independently.[8,9] Among these methods achieving mulch-color EC devices, we are focusing on color change of metal nanoparticles induced by localized surface plasmon resonance (LSPR).[10–12] Recently, we have reported multicolor EC device using LSPR of silver metal. This device achieved six optical states—transparent,
silver-mirror, black, cyan, magenta, and yellow—in a single device on the basis of an electrochemical Ag deposition mechanism.[13–16] The Ag depositio
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