JPS6181478A - Electrochromic display element - Google Patents

Abstract

PURPOSE:The title display element that is composed of an iron pen tacyanoferrate as a color developing material, an ion-conductive substance and oppositing electrodes, using a novel color-developing material and showing quick response with high reliability. CONSTITUTION:The objective display elements consists of an iron pentacyanoferrate of the formula: Fex[Fe(CN)6L]y (L is ligand), preferably iron pentacyanoaquoferrate, iron pentcyanoammineferrate or iron pentacyano carbonylferrate coated film made by electrodepositon, as a color developing material, an ion-conductive substance and oppositing electrodes.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an electrochromic display element, and particularly to an electrochromic display element having a fast-response coloring material.

[Background of the invention]

An electrochromic display element (hereinafter abbreviated as ECD) using a conventional thin film of a transition metal oxide such as tungsten oxide as a coloring material and an electrolyte-free or solid ionic conductive material such as LiCQO or propylene carbonate as an electrolyte. , a certain %N has a slow response speed (~0.
5s) had one drawback. 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 electrolytic deposition coloring material, is F e
(m) (F e (II) F e (II) (CN)
*) For example, in the case of Prussian blue, 10 Ms...
Through the reaction (2), insoluble Prussian blue (Fe(III)(Fe(m)Fe(■)) produced during electrolytic deposition
From (CN), ), ), M e (Fe(III)Fe(■) (CN), ) is called soluble Prussian blue.
It is thought that the chemical compound changes into a compound with the chemical formula: The blue soluble Prussian blue thus produced is oxidized to change into a green substance according to the reaction of formula (3).

M e '''Fe (m) Fe (■) (CN), - blue-green Also, by electrolytic reduction, M e '''Fa (m) Fe (II) (CN), - + M e
“Blue 101-→M e , F e (■) FA (■) (CN)
, -(4) It is thought that it will be colorless.

The reactions shown in formulas (3) and '(4) occur reversibly.

Therefore, it can be used as a coloring material for display elements. In particular, the reaction of formula (4), which has excellent reversibility, is used.

To form a coating of insoluble Prussian blue, a pair of electrodes is immersed in a solution containing ferric ions and a solution containing hexacyanoferrous (trivalent) ions, and the electrode forming the insoluble Prussian blue is immersed in a negative solution. It can be easily obtained by electrolyzing with the other electrode positive.

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 (F e "(CN)9 L ) '- is mixed with a solution containing trivalent iron ions, a blue colored precipitate can be obtained. However, it is extremely difficult to form the precipitate thus produced as a thin film on a conductor such as a transparent conductive film.

In the case of Prussian Blue, even if an aqueous solution of potassium ferricyanide, in which the oxidation state of iron is trivalent, is mixed with an aqueous solution containing trivalent iron ions, no precipitation occurs, and ? Only by the ttl MW element at r111 can an insoluble Prussian blue be formed as a molecule.

On the other hand, iron pentacyano ion is synthesized using potassium ferrocyanide as a synthetic raw material, so it is usually 1.

The oxidation state of iron is divalent, and if this aqueous solution is mixed with an aqueous solution containing trivalent iron ions, a water-insoluble precipitate will be produced. Iron pentacyanoferrate, which is insoluble in water and exhibits good color-forming and decolorizing properties, is synthesized from a mixture with an aqueous solution containing valent iron ions through an electrolytic deposition reaction. Iron pentacyanoferrate is a new color-forming material. The goal is to provide an ECD that

[Summary of the invention]

For this purpose, if an aqueous solution of pentacyanoferrate in which the oxidation state of iron is divalent is mixed with an aqueous solution containing trivalent iron ions, a precipitate will be produced, which will be analyzed to synthesize iron pentacyanoferrate. Since this is not possible, we developed a method to prepare an aqueous solution of pentacyanoferrate in which the oxidation state of iron is trivalent. That is, it has been found that by treating a pentacyanoferrate aqueous solution in which iron has a divalent oxidation state with lead dioxide, it is possible to obtain a pentacyanoferrate aqueous solution in which iron has a trivalent oxidation state.

For example, in the case of pentacyanocarbonylferrate, sodium pentacyanocarbonylferrate (Na, [Fe(CN), GO]), in which the oxidation state of iron is divalent, can be easily synthesized by a well-known method. I can do it. However, an aqueous solution of this is mixed with a salt in which the oxidation state of iron is trivalent, such as Fe.
, (So,)j immediately forms a blue precipitate. However.

After adding sulfuric acid to an aqueous solution of sodium pentacyanocarbonylferrate, in which the oxidation state of iron is divalent, to make it acidic, lead dioxide powder was added and stirred for a while.

Furthermore, even if an aqueous solution of pentacyanocarbonyl ferrate prepared by filtering lead dioxide powder and the oxidation state of iron is 3 (tl) is mixed with an aqueous solution of F ex (SO4L), no precipitation occurs. , no precipitation occurs even when an aqueous solution of pentacyanoferrate, in which the oxidation state of iron is made trivalent by treatment with lead dioxide, is mixed with an aqueous solution containing trivalent iron ions.
This applies not only to pentacyanocarbonyl ferrate but also to pentacyanoammine ferrate and pentacyanoaqua ferrate.

In addition, when an aqueous solution of pentacyanoferrate in which the oxidation state of iron is trivalent is mixed with an aqueous solution containing trivalent iron ions, and a voltage is applied with the electrode forming the coloring film set as negative and the counter electrode as positive. , a blue water-insoluble colored film is deposited on the negative electrode side.

At this time, as the aqueous solution containing trivalent iron ions, ferric sulfate, ferric chloride, and ferric perchlorate aqueous solutions can be used, and generally even soluble ferric salts can be used. In addition, the counter electrode materials used for electrodeposition include gold, platinum,
Conductors that do not react with the electrolyte, such as carbon, can be used.The electrodes that form the color-developing film include glass substrates coated with transparent conductive films containing indium oxide or tin dioxide as main components, metal substrates such as platinum, gold, etc. conductive substrates can be used.

Furthermore, a coloring film formed as described above.

An electrochromic display element can be created by combining a liquid or solid ionically conductive electrolyte with a counter electrode made of carbon, a transition metal oxide such as manganese dioxide, tungsten oxide, or a mixture thereof. By applying a voltage to the device thus created with the display electrode side negative and the counter electrode side positive, the coloring material on the display electrode becomes colorless, and by applying voltage in the opposite direction, it can be colored blue again. . This color development/decolorization reaction can be seen using iron pentacyanocarbonyl ferrate as an example.
This is thought to be based on the chemical reaction shown below. That is,
The blue colored film formed by electrolytic deposition reaction is Fe”
It is estimated to have a structure of (F e ”(,CN)sC:01, and by applying a voltage with the display electrode side negative and the counter electrode side positive, monovalent cations from the electrolyte and electrons from the electrode side is simultaneously injected into the blue film, and Fe''[F
e'(CN), GO) is colorless Me'Fe'[Fe"(
CN), Co). 1 in chemical formula
It can be expressed as equation (5).

Fe’(Fe”(CN)sco)+Me”+s-Blue This reaction is reversible.

The color of the pentacyanocarbonyl iron ferrate film is generally blue, but in detail there are considerable differences in color tone. That is, iron pentacyanocarbonylferrate is blue, but iron pentacyanoaquaferrate (F e (F e (CN) i C
HtO))), pentacyanoammineferrate (Fe
(Fe(CN)=(NH,))) is dark blue. In addition, as a result of measuring these absorption spectra, the maximum absorption wavelengths were 700 mμ, 800 mμ, and 750 mμ, respectively.
Met.

Suitable electrolytes for developing and decolorizing iron pentacyanoferrate include an aqueous solution containing monovalent cations, an organic electrolyte containing -valent cations, and a solid electrolyte using -valent cations as mobile ions.

Aqueous solutions containing monovalent cations include aqueous solutions of chlorides such as lithium chloride, sodium chloride, potassium chloride, cesium chloride, rubidium chloride, and ammonium chloride; sulfates such as lithium sulfate, sodium sulfate, and potassium sulfate; Use aqueous solutions such as lithium, borofluorides such as sodium borofluoride and potassium borofluoride, nitrates such as lithium nitrate, sodium nitrate, and potassium nitrate, and phosphates such as lithium phosphate, sodium phosphate, and potassium phosphate. be able to. In general, it only needs to be a water-soluble salt of a monovalent cation.

Solvents for organic solutions containing monovalent cations include propylene carbonate, γ-butyrolactone, acetone trile,
Solvents such as dioxane, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, etc. can be used.

Generally, any solvent that can dissolve the salt of the -valent cation is sufficient.

The counter electrode of an electrochromic display element using pentacyanoironυiron as a coloring material can be made of activated carbon, a mixture of carbon and a transition metal oxide such as tungsten oxide or molybdenum oxide, a mixture of Prussian blue and carbon, or pentacyanoferrous. mixture of iron acid and carbon,
A mixture of composite transition metal oxide such as iron tungstate and carbon can be used. In general, a material that is a mixture of a substance that causes a reversible electrochemical reaction, that is, an active material, and carbon can be used as the opposing 1tll material.

In addition, thin films of transition metal oxides such as tungsten oxide and molybdenum interstitium, transition gold complexes such as Prussian blue and iron pentacyanoferrate, and composite 'Is transferable dissimilar metal oxides such as iron tungstate can be made into metal or transparent. An electrode on a conductive film can also be used as a counter electrode.

[Embodiments of the invention]

The present invention will be specifically explained below using Examples.

Example 1 This is an example in which thin films of iron pentacyanocarbonylferrate, iron pentacyanoferrate, and iron pentacyanoaquaferrate were formed by electrolytic deposition reaction using the electrolytic shoulder shown in FIG.

In Fig. 1, 1.2 is a conductor, 3 is a platinum plate, and 4 is a substrate on which iron pentacyanoferrate is electrolytically deposited.

Reference numeral 5 indicates an electrolytic solution. The substrate on which iron pentacyanoferrate is electrolytically deposited is a transparent conductor fI! whose main component is indium oxide and has a sheet resistance of 10 Ω/d. A glass substrate coated with a film was used. At this time, the size of the substrate was 5 Ci. A 5al platinum plate was also used as the counter electrode.

An electrolytic solution for electrolytically depositing iron pentacyanocarbonyl ferrate was prepared as follows.

First, sodium pentacyanocarbonylferrate (Na,
(Fe (CN), Co)) 0.001 mol in 40 m of water
Dissolved in Q. Then, add a small amount of sulfuric acid to reduce the p of the aqueous solution.
H was set to 2.0, and 1 g of lead dioxide powder was added and stirred for 5 minutes. Keep the pH of the mixture at 2.0 even during stirring.
A small amount of sulfuric acid aqueous solution was added to maintain the temperature. Continuing,
The precipitate was filtered, and a small amount of sulfuric acid aqueous solution and water were added to the filtrate to obtain 0.02 of pentacyanocarbonyl ferrate with a pH of 2.
A 50 mQ mol/Q solution was prepared. The other solution, an aqueous ferric sulfate (F ax (SO4)-) solution, was prepared in the same manner. That is, ferric sulfate 0.00
Dissolve 1 mol in 40 ml of water, then add a small amount of potassium hydroxide and water while adjusting the pH to 2.

The total amount was 50mα. Therefore, 0.02 of ferric sulfate
Mol/a hot solution 50mQml! This means that J has been completed. The solution containing the pentacyanocarbonyl ferrate thus prepared is mixed with an aqueous ferric sulfate solution to prepare an electrolytic solution each having a concentration of 0.01 mol/Q.

The electrolytic solution for electrolytically depositing pentacyanoammine iron ferrate and pentacyano aqua iron ferrate is pentacyano,
An electrolytic solution for electrolytic deposition of carbonyl iron yokotetsu was prepared using the same procedure as above. However, in these cases, the concentrations of pentacyanoamine ferrate, pentacyanoaqua ferrate, and ferric sulfate in the electrolyte were all set to 0.001 mol/2.

When an electrolytic solution is placed in the electrolytic cell shown in FIG. 1 and electrolyzed at a constant current density with the transparent conductive film side set as negative and the platinum side set as positive, a blue colored film is deposited on the transparent conductive film. That is, in the case of iron pentacyanocarbonyl ferrate, the current density is 10
If μA/aJ and electrodeposition time are set to 8 minutes, a clear blue colored film can be obtained.

In the case of iron pentacyanoamine ferrate and iron pentacyanoaqua ferrate, I4 was 20 μA/j, and the electrodeposition time was 30 μA/j.
minutes, a dark blue colored film is obtained.

Example 2 A 1 mol/Q potassium chloride aqueous solution was electrolyzed on the films of iron pentacyanocarbonyl ferrate, iron pentacyanoamine ferrate, and iron pentacyanoaqua ferrate formed by the electrolytic deposition reaction shown in Example 1. This is an example in which the one-shot decoloring properties of a liquid were investigated by cyclic portammetry. Using a silver-silver chloride electrode as a reference electrode, the potential was repeatedly swept from +0.5V to -0.5V with respect to the reference electrode at a potential sweep rate of 0, IV/sec, and the potential/current characteristics were determined. As shown in Figures 2, 3 and 4,
Figure 2 shows the results for iron pentacyanocarbonyl ferrate, Figure 3 shows the results for iron pentacyanoammine ferrate, and Figure 4 shows the results for iron pentacyanoaqua ferrate. Note that the PI (PI) of a 1 mol/Q liquefied potassium aqueous solution was set to 4.0.

As is clear from Figures 2, 3, and 4, the color development and decolorization reactions of iron pentacyanoferrate are highly reversible, and the potential of the display electrode is -0.5V with respect to the silver-silver chloride electrode. Sometimes the monochrome film is colorless.

When it was at +0.5V, it was colored blue. Also,
Even after repeating the color development/decolorization cycle 100 times, the potential
Almost no change was observed in the 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 coloring and erasing properties.

However, when the pH of the electrolytic solution 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 the color developed and disappeared tended to decrease.

Example 3 An electrochromic display element was created using a film of iron pentacyanocarbonyl ferrate, iron pentacyanoammine ferrate, and iron pentacyanoaqua ferrate formed by the electrolytic deposition reaction shown in Example 1 as a coloring material. This is an example.

An electrochromic device shown in FIG. 5 was created using the above coloring material. In FIG.

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 conductor 22 formed of, for example, a vapor-deposited film of silicon dioxide.

25 is an electrolyte, 26 is a counter electrode, 27 is a glass substrate on the counter electrode side, 28 is a spacer, and 29 is a background material inserted into the electrolyte.

The coloring film 23 is made of iron pentacyanocarbonylferrate, iron pentacyanoammineferrate, or iron pentacyanoaquaferrate.

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

As the electrolytic solution shown in No. 25, a 1 mol/a potassium chloride aqueous solution having a pH of 4.0 was used. A porous Teflon sheet filled with titanium oxide powder as a white pigment was used as the background material 29 inserted into the electrolyte. The counter electrode 26 was formed using a fired product 26' obtained by firing carbon powder provided on the glass substrate 27, an outer transparent conductive film 26', and the conductive film. At this time, the fired product 26' was provided in a portion in contact with the electrolytic solution 25, and was bonded to the spacer 28 using an epoxy resin so that the transparent conductor 26' was in direct contact with the liquid.

Furthermore, a so-called NESA film (sheet resistance: 10 Ω/d) containing indium oxide as a main component was used as the transparent conductor 6'.

When a voltage of 0.5 V is applied to the device thus created, with the display electrode side set as negative and the counter electrode side set as positive, the colored film becomes colorless. When a voltage of 5V was applied, it immediately turned blue.

Response time during color development when applied voltage is 0.5V (
The time required for the contrast ratio to reach 2.0 is 0.1 seconds for iron pentacyanocarbonyl ferrate and 0.2 seconds for iron pentacyanoammine ferrate and iron pentacyanoaqua ferrate. Met.

Further, in the above element, no deterioration of the element was observed even after repeating color development and decolorization 10' times.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide an electrochromic display element that uses a novel color-forming material and has a fast response and high reliability, and its industrial value is high.

[Brief explanation of the drawing]

Figure 1 is a diagram showing an electrolytic cell! Figure 82, Figure 3. 4v4 is a diagram for explaining the present invention, and FIG. 5 is a diagram for explaining the present invention. FIG. 2 is a cross-sectional view of an electrochromic display. 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, 29 No. 1 Fig.'f12 Fig. 3 Ron'f-I4-Fig.

Claims (1)

[Claims] 1. General formula Fe, [Fe_x(CN)_6L]_y(L
An electrochromic display element that uses iron pentacyanoferrate represented by (denotes a ligand) as a coloring material, an ion conductive substance, and a counter electrode. 2. Iron pentacyanoferrate is iron pentacyanoaquaferrate,
The electrochromic display element according to claim 1, characterized in that it is iron pentacyanoammineferrate or iron pentacyanocarbonylferrate. 3. The electrochromic display element according to claim 1 or 2, wherein the iron pentacyanoferrate is a film formed by an electrolytic deposition reaction.