JPS629385A - Electrochromic display element - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an electrochemical display element (electrochromic display element).

[Background of the invention]

Conventionally, electrochromic display elements (hereinafter abbreviated as ECD), which use a thin film of a transition metal oxide such as tungsten oxide as a coloring material and an electrolytic solution or a solid ion conductive material such as propylene carbonate of LiCQ 04 as an electrolyte, or a coloring device. ECDs that combine a film and a dielectric such as tantalum oxide have a slow response speed (~0.
5g). The slow response is thought to be mainly due to the slow diffusion of ions (protons or alkali metal ions) injected into the coloring film.

In order to overcome these drawbacks, efforts have recently been focused on developing color-forming materials with quick response. As a result, one type of new color-forming material was discovered. JP-A-56-156971, JP-A-57-158282, JP-A-57-19
Prussian Blue disclosed in Japanese Patent No. 5182 is one of them.

Prussian blue, which is an electrolytically deposited coloring material, is made of Fe(m
) 4 (F a (n ) (CN) s)] a. In this case, color development and decolorization are thought to occur according to the following reaction.

F e (m), (F e (II) (CN)s: 1.
+4 M e"Blue e Uni? M e4F e(II)4(F e (n)(
CN)s)a-(1) Colorless Here, Me represents a monovalent metal element such as Li, Na, or the like.

The reaction shown in formula (1) occurs reversibly. Therefore, it can be used as a coloring material for display devices.

In addition, a coating of insoluble Prussian blue can be made by immersing a pair of electrodes in a solution containing ferric ions and a solution containing hexacyanoferrous (trivalent) ions, and placing the electrode forming the insoluble Prussian blue on the negative side and the other. It can be easily obtained by electrolysis using the positive electrode.

Prussian Blue has long been known as a blue pigment, and is obtained as a precipitate formed by mixing an aqueous solution of potassium ferrocyanide, in which iron has a divalent oxidation state, with a solution containing trivalent iron ions.

Furthermore, even if a solution containing a series of pentacyanoferrous ions represented by (Fe (II) (CN) S L) '- is mixed with a solution containing trivalent iron ions, a blue colored precipitate can be obtained. It has been known.

[Purpose of the invention]

An object of the present invention is to provide an All-I electrochromic display element using a counter electrode material in which a reversible redox reaction occurs and the coloring accompanying this reaction is light.

[Summary of the invention]

For the above purpose, in the present invention, an electrode in which a thin film was formed on a conductive film by an electrolytic deposition reaction from a solution containing pentacyanoferrate ions and cobalt ions was used as a counter electrode.

As described above, in an aqueous solution containing hexacyanoferrate ion or pentacyanoferrate ion and cobalt ion, insoluble cobalt hexacyanoferrate or cobalt pentacyanoferrate is produced. However, these cobalt salts have a lower color density than iron salts. For this reason,
It is thought that if a thin film of cobalt salt is used for the counter electrode, an element can be obtained that is lightly colored due to a reversible electrochemical reaction at the counter electrode that accompanies the coloring and decoloring of the display electrode. If such a counter electrode is used, even if the display electrode develops color, there will be little color change at the counter electrode, so it can be used as a transmissive element.

The oxidation state of iron is trivalent, hexacyanoferrate ion, and 3
In a solution containing valent cobalt ions, an insoluble precipitate is formed, and a thin film cannot be formed by electrolytic reduction. However, a dilute aqueous solution consisting of pentacyanoammineferrate ions and pentacyanoacoferrate ions in which the oxidation state of iron is trivalent and trivalent cobalt ions does not cause precipitation. In this case, dip a pair of electrodes into the solution and negative the electrode to form an insoluble cobalt pentacyanoferrate.

An insoluble film can be easily obtained by electrolyzing with the other electrode set as positive.

The insoluble film thus obtained is rich in electrochemical activity,
Causes a reversible redox reaction. However, this oxidation and reduction reaction does not cause coloration.

The insoluble film produced by the electrolytic deposition reaction is composed of pentacyanoammine cobalt ferrate (Co(Fe(CN)).
s・N Hff)) and cobalt pentacyanoacoferrate j/ (Co (F e (CN), ・H,O))
it is conceivable that. Furthermore, it is thought that the reversible redox reaction in an aqueous potassium chloride solution can be expressed by formulas (2) and (3).

Co (F e (CN)s ・N H3) + K”
Co (F e (CN)s ・HtO) + K” In addition, Prussian blue was applied to the display electrode, and the pH of the electrolyte was 4.
0 KCQ aqueous solution, an element using cobalt pentacyanoammineferrate or cobalt pentacyanoacoferrate as the counter electrode, and the applied voltage when developing one color was 0.3 V, and the applied voltage when decoloring was 0.5 V. When driven with a square wave of , I Hz, extremely good color development and decolorization were exhibited. At this time, a voltage was applied with the display electrode side being positive and the counter electrode side being negative when coloring, and a voltage was applied in the opposite direction when decoloring.

Note that the same applies when Li or Na is used instead of the above potassium.

Furthermore, the electrode of the present invention can be used in transmission type ECD and is particularly effective.

[Embodiments of the invention]

The present invention will be specifically explained with reference to the following examples.6 Example 1 Using the electrolytic cell shown in FIG. This is an example formed by

In Figure 1, 1 and 2 are conductive wires, and 3 is a platinum plate.

4 is a substrate on which cobalt pentacyanoferrate is electrolytically deposited;
5 indicates an electrolyte. A glass substrate coated with a transparent conductive film containing indium oxide as a main component and having a sheet resistance of 10 Ω/d was used as a substrate on which cobalt pentacyanoferrate was electrolytically deposited. At this time, the size of the substrate was 5 d. Also,
A 5d platinum plate was also used as the counter electrode.

An electrolytic solution for electrolytically depositing cobalt pentacyanoammineferrate was prepared as follows.

First, sodium pentacyanoamine ferrate (N ay
(F e (CN)S-NH3) ) 0.0001
mol was dissolved in 40n+Q of water. Then, a small amount of sulfuric acid was added to adjust the pH of the aqueous solution to 2.0. moreover,
1 g of lead dioxide powder was added and stirred for 5 minutes. A small amount of sulfuric acid aqueous solution was added to keep the pH of the mixture at 2.0 during stirring. Subsequently, the precipitate was filtered, and a small amount of sulfuric acid aqueous solution and water were added to the filtrate to prepare 50 mQ of a 0.002 mol/Q solution of pentacyanoammine ferrate having a pH of 2.0. The other aqueous solution containing trivalent cobalt ions was prepared as follows. That is, cobalt sulfate 0
．． 0001 mol was dissolved in 40 mQ of water, and then a small amount of sulfuric acid was added to adjust the pH of the aqueous solution to 2.0. Furthermore, 1 g of lead dioxide powder was added and stirred for 5 minutes.

A small amount of sulfuric acid aqueous solution was added to keep the pH of the mixture at 2.0 during stirring. Subsequently, the precipitate was filtered, and a small amount of sulfuric acid aqueous solution and water were added to the filtrate to make the total amount of a solution containing cobalt ions with a pH of 2.0 to 50 mQ.

Therefore, 0.002 mol lQm solution of cobalt ions is 5
This means that 0+nQ has been prepared.

The solution containing pentacyanoammine ferrate prepared in this way and the solution containing cobalt ions are mixed,
Electrolytes each having a concentration of 0.001 mol/Q are produced.

The electrolytic solution for electrolytically depositing cobalt pentacyanoacoferrate was prepared in exactly the same manner as the electrolytic solution for electrolytically depositing cobalt pentacyanoammineferrate.

When the electrolytic solution prepared by the above method is placed in an electrolytic cell and electrolyzed at a constant current density with the transparent conductive film side set as negative and the platinum side set as positive, a colorless and transparent film is deposited on the transparent conductive film. That is, in the case of cobalt pentacyanoamine ferrate,
If the current density Id is 20 μA/ad and the electrodeposition time is 60 minutes, a colorless insoluble film can be obtained. In the case of cobalt pentacyanoacoferrate, if the Id is 2oμA/(27 and the electrodeposition time is 20 minutes, a colorless insoluble film with approximately the same thickness as cobalt pentacyanoammineferrate can be obtained.

Example 2 The coatings of cobalt pentacyanoammineferrate and cobalt pentacyanoacoferrate formed by the electrolytic deposition reaction shown in Example 1 were electrochemically activated using a 1 mol/Q potassium chloride aqueous solution as an electrolyte. This is an example in which the results were investigated by cyclic portammetry. A silver-silver chloride electrode is used as a reference electrode, and the reference electrode is +1. From Ov to 10.5V, the potential sweep speed was set to 0. As IV/sec,
The results of repeated sweeping and determination of potential/current characteristics are shown in FIGS. 2 and 3. Figure 2 shows the results for cobalt pentacyanoammineferrate, and Figure 3 shows the results for cobalt pentacyanoacoferrate. Note that the pH of the 1 mol/Q potassium chloride aqueous solution was 4.0. Figures 2 and 3
As is clear from the figure, the redox reaction of cobalt pentacyanoferrate is highly reversible. Even when the potential of the electrode is -0.5 V with respect to the silver-silver chloride electrode, it is +1. It was almost colorless when it was in Ov. Also, set the sweep cycle to 100
Even after repeating the test several times, almost no change was observed in the potential/current characteristics.

Furthermore, even when the electrolyte solution of potassium chloride was replaced with an aqueous potassium sulfate solution or a potassium hydrogen phosphate aqueous solution, no significant difference was observed in the electrochemical properties. However, p of the electrolyte
When H was 3 or less and 5 or more, it was observed that as the sweep was repeated, the value of the current that should flow as a result of oxidation and reduction tended to decrease.

Example 3 This is an example in which a transmission type electrochromic display element was created using a coating of cobalt pentacyanoammineferrate and cobalt pentacyanoacoferrate formed by the electrolytic deposition reaction shown in Example 1 as a counter electrode material.

An electrochromic device shown in FIG. 4 was created using the above counter electrode material. In FIG. 4, 21 is a glass substrate on the display electrode side, and 22 is a transparent conductive film.

23 is a coloring film, and 24 is a protective film for the transparent conductive film 22 formed of, for example, a vapor-deposited film of silicon dioxide.

25 is an electrolytic solution, 26 is a counter electrode, 27 is a glass substrate on the counter electrode side, and 28 is a spacer.

For the coloring film 23, a mixed solution (pH = 2.0) of 0.01 mol/α ferric perchlorate and 0.01 mol/Q potassium ferricyanide was used as an electrodepositing solution, and 10 μA/Q was applied.
A Prussian blue film formed by electrolysis for 8 minutes at a current density of CD was used.

The transparent conductive film 22 was made of indium oxide and had a sheet resistance of about 10 Ω/d.

As the electrolytic solution shown in No. 25, a 1 mol/Q potassium chloride aqueous solution having a pH of 4.0 was used. The counter electrode 26 includes a transparent conductive film 26' provided on a glass substrate 27 and a coating 26' of cobalt pentacyanoammineferrate or cobalt pentacyanoacoferrate formed on the conductive film according to the conditions shown in Example 1. Consisting of At this time, the film 26' was provided in a portion that comes into contact with the electrolytic solution 25, and the transparent conductive film 26' was bonded to the spacer 28 using an epoxy resin so that it was in direct contact with the spacer 28. In addition, the transparent conductive film 26' has a so-called NESA film (sheet resistance of about 10Ω/a) whose main component is indium oxide.
J) was used.

In the device thus created, a voltage of 0.5 V was applied with the display electrode side being negative and the counter electrode side being positive, regardless of whether the counter electrode was cobalt pentacyanoammineferrate or cobalt pentacyanoacoferrate. Then, the coloring film immediately became colorless, and when a voltage of 0.3 V was applied with the display electrode side being positive and the counter electrode side being negative, it was immediately colored blue. Further, at this time, no coloring occurred on the counter electrode side.

Response time during color development when the applied voltage is 0.3 V (
The time required for the contrast ratio to reach 2.0 was 0.2 seconds in both cases with the counter electrode.

In addition, no deterioration of the element was observed even after repeating color development and decolorization 104 times in the above element.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a transmission type electrochromic display element with a quick response and high reliability, and its industrial value is high.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an electrolytic cell, FIGS. 2 and 3 are diagrams for explaining the present invention, and FIG. 4 is a sectional view of an electrochromic element. 21...Glass substrate, 22...Transparent conductive film, 23.
... Coloring film, 24 ... Protective film, 25 ... Electrolyte solution, 2
6... Counter electrode, 27... Glass substrate, 28...
Spacer.

Claims (1)

[Claims] 1. An electrochromic display element in which an ion conductive substance is sandwiched between a display electrode having a coloring material and a counter electrode, wherein the counter electrode is made of cobalt pentacyanoferrate. display element. 2. Cobalt pentacyanoferrate is combined with pentacyanoacoferrate ion or pentacyanoammineferrate ion.
2. The electrochromic display element according to claim 1, wherein the electrochromic display element is a thin film deposited by an electrolytic deposition reaction from an electrodepositing solution containing valent cobalt ions.