JPH0219442B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an electrochromic device that exhibits a color change due to an electrochemical redox reaction, and particularly to a device in which an organic polymer performs an electrochromic function. [Background Art] In today's information-overloaded society, display technology plays an important role in processing large amounts of information. One such display means is liquid crystals, which are used in a wide range of applications such as calculators and watches. However, since liquid crystals utilize changes in the orientation of polymers, they have limitations in terms of viewing characteristics, brightness, and multicolorization. Therefore, electrochromic devices have been developed as an alternative to liquid crystals. This electrochromic element causes color changes such as coloring and decoloring through electrochemical redox reactions, and can also be applied to light switches. As an inorganic compound, tungsten oxide (WO ₃ ) is a substance that has an electrochromic effect.
Examples of organic compounds include methyl viologen or conductive polymers such as polypyrrole, polyaniline, and polythiophene. In particular, when using the above-mentioned conductive polymer, it has the advantage that it can be used in a wider range of applications by making it into a membrane, and it is easy to synthesize the membrane and control its area, and it is also possible to increase the area. . An electrochromic device using this conductive polymer is composed of an electrolyte solution containing a supporting electrolyte and a pair of electrodes in contact with the electrolyte solution. It is installed on the electrode. When a voltage is applied to this pair of electrodes, the conductive polymer exhibits a color change due to an oxidation-reduction reaction that occurs at the working electrode. It has been reported that polyaniline is the most stable among these conductive polymers, has a large absorbance change (ΔOD (optical density)) during coloring/decoloring, and has good electrochromic properties ( Journal of Electroanalytical Chemistry, 177 (1984)
281). By the way, it is believed that protons (H ⁺ ) are involved in the electrochromic reaction of polyaniline, and it has been reported that polyaniline is electrochemically inactive and does not exhibit electrochromic properties at a pH of 3 to 4 or higher. ing. That is, conventional electrochromic devices using polyaniline use strong acid aqueous solutions with a pH of 1 or less as electrolyte solutions, and none use neutral, alkaline aqueous solutions or non-aqueous solutions. However, the stability of the substrate electrode is a problem in a strong acid aqueous solution, for example, ITO, which is a transparent conductive glass,
When glass coated with an (indium tin oxide) film is used as a substrate electrode, the ITO film easily dissolves, and the polyaniline peels off from the substrate electrode, resulting in deterioration of the electrode. Furthermore, when metal electrodes are used as substrate electrodes instead of ITO film-coated glass, those that are stable in acidic aqueous solutions are limited to noble metals such as platinum, and the device itself becomes very expensive. Furthermore, in the electrochromic device using the above-mentioned strong acid aqueous solution, the maximum △OD is about 0.4 when the color changes reversibly, but higher characteristics are required to work as a practical device. It is. [Problems to be Solved by the Invention] The present invention has been made in view of the above-mentioned problems, and the substrate electrode is stabilized and △
The aim is to provide an electrochromic device with a large OD. [Means for Solving the Problems] The electrochromic device of the present invention comprises a nonaqueous electrolyte solution containing a supporting electrolyte in a polar organic solvent, and a first electrode and a second electrode in contact with the nonaqueous electrolyte solution. The first electrode is composed of a conductive base material and a polyaniline film in close contact with the conductive base material, and the polyaniline film forms stable quaternary ammonium ions of polyaniline in the polar organic solvent. It is characterized by containing a counter anion. The basic structure of the electrochromic device of the present invention consists of a pair of electrodes, a first electrode and a second electrode, and an electrolyte solution. The first electrode consists of a conductive base material, which is a substrate electrode, and a polyaniline film in close contact with the conductive base material. This polyaniline film exhibits electrochromic action,
The first electrode acts as a working electrode. The polyaniline membrane contains a counter anion that forms stable quaternary ammonium ions in the polar organic solvent used in the non-aqueous electrolyte solution. This is a necessary condition for polyaniline to exhibit electrochromic action in a nonaqueous electrolyte solution, as explained below. In conventional electrochromic devices using a strong acid aqueous solution as an electrolyte solution, protons (H ⁺ ) in the strong acid aqueous solution dope and undope polyaniline, thereby exhibiting an electrochromic effect. That is, as shown in the following reversible reaction formula [1], polyaniline exhibits coloring and decoloring due to the involvement of protons. Compared to the above, in the case of an electrochromic device using the non-aqueous electrolyte solution of the present invention, anion (X ^- ) performs doping/undoping of polyaniline as shown in the reversible reaction formula [2] below. Therefore, it exhibits electrochromic action. In order to smoothly perform doping and dedoping of the anion (X ^- ), it is necessary that the anion be easily dissolved in the nonaqueous electrolyte solution. That is, 4 of polyaniline on the right side of the above formula [2]
It is necessary that ammonium ions exist stably in polar organic solvents. Therefore, in order for polyaniline to exhibit electrochromic action in a non-aqueous electrolyte solution, it is necessary that polyaniline contain a counter anion that stably exists the quaternary ammonium ion of polyaniline in a polar organic solvent. This counter anion varies depending on the polar organic solvent, but generally includes perchlorate ion (ClO ₄ ^- ), borofluoride ion (BF ₄ ^- ), phosphorous ion (PF ₆ ^- ), etc. One or more of these may be used. These counter-anions are dissolved in various polar organic solvents to be described later, so that the quaternary ammonium ion of polyaniline exists stably. On the contrary, Cl ^- , SO ₄ ^2- , NO ₃ ^- are anions that hardly dissolve in polar organic solvents.
etc., and the use of such anions is avoided in the present invention. There is a method for adding counter anions such as ClO ₄ ^- and BF ₄ ^- to polyaniline during polymerization of polyaniline. This polyaniline polymerization is carried out by electrolytic polymerization, polymerization using a catalyst, or the like. For example, in the case of electrolytic polymerization, an aniline monomer is dissolved in an aqueous solution of an acid, such as perchloric acid or hydroborofluoric acid, which is a source of the above-mentioned counteranions to form a solution for electrolytic polymerization, and a positive electrode is added to the solution. and immerse the negative electrode. Thereafter, by applying a DC voltage between the positive and negative electrodes, a polyaniline film is deposited on the positive electrode. This polyaniline film contains counteranions such as perchlorate ions and borofluoride ions. In the case of this electrolytic polymerization, the concentration of the acid in the electrolytic polymerization solution is preferably within the range of 0.1 to 5 mol/l, and optimally within the range of 0.1 to 2 mol/l. The concentration of aniline monomer in the electrolytic polymerization solution is preferably in the range of 0.1 to 5 mol/l, most preferably in the range of 0.1 to 2 mol/l. In addition, the applied voltage is 10μA per unit area of the positive electrode.
It is desirable to have a current with a current density of 5mA/ ^cm2 , and optimally the current density is between 50 and 500μA/cm2.
It is preferably within the range of ^cm2 . In addition, when polyaniline is polymerized using a catalyst, the counteranion is contained in the polymerized polyaniline by polymerizing in the coexistence of a compound that supplies the counteranion, such as LiClO ₄ or LiBF ₄ , with the aniline monomer. Ru. The polyaniline is made into a film-like material that exhibits a remarkable electrochromic effect. The film thickness is preferably within the range of 500 Å to 2 μm. The film thickness is
If the thickness is less than 500 Å, it is difficult to observe noticeable color changes such as coloring or decoloring, while if it is thicker than 2 μm, decoloring becomes difficult. Even better electrochromic properties are obtained when the film thickness is in the range of 1000 Å to 1 μm. Further, the conductive base material of the first electrode serves as a substrate electrode. The conductive substrate serves as a support material for the polyaniline film and also transfers electrons between the power supply for operating the electrochromic device and the polyaniline film. However, its materials include metals such as stainless steel, platinum, gold, and nickel, as well as ITO (indium tin oxide).
Examples include transparent conductive materials such as glass or transparent plastic film coated with a film, a SnO ₂ film or a gold-deposited film. Especially when displaying an electrochromic effect through the conductive substrate,
The conductive base material is transparent. The first electrode is made of a polyaniline film and a conductive base material that are brought into close contact with each other, and methods for bringing the polyaniline film and the conductive base material into close contact include compression bonding or vapor deposition.
Furthermore, as described above, there is a method in which a conductive base material is used as a positive electrode for electrolytic polymerization of a polyaniline film, and the polyaniline film is deposited on the conductive base material of the positive electrode during electropolymerization. Among these methods, it is desirable to use electrolytic polymerization from the viewpoint of adhesion and film formability. Note that if polyaniline contains water, the protons in the water will affect the electrochromic action. Therefore, in order to remove moisture from the polyaniline membrane, it is desirable to wash the polymerized polyaniline membrane with an organic solvent such as propylene carbonate, acetonitrile, methanol, or ethanol, and then heat and vacuum dry it. The second electrode is made of a conductive base material such as carbon, graphite, stainless steel, glass coated with an ITO film, or glass coated with a SnO ₂ film, and serves as a counter electrode to the first electrode. Next, the non-aqueous electrolyte solution according to the present invention enables current to be passed between the first electrode and the second electrode by immersing the two electrodes, and furthermore, the non-aqueous electrolyte solution of the present invention allows current to be passed between the first electrode and the second electrode. It is involved in the electromic action of The non-aqueous electrolyte solution is one in which a supporting electrolyte is dissolved in a polar organic solvent. The supporting electrolyte is one that is soluble in a polar organic solvent, and includes lithium perchlorate, sodium tetrafluoroborate, tetramethylammonium perchlorate, and tetramethylammonium tetrafluoroborate. Therefore, one or more of these supporting electrolytes are used. Further, examples of the polar organic solvent include propylene carbonate, acetonitrile, sulfolane, nitromethane, benzonitrile, etc., and one or more of them are used. The concentration of the supporting electrolyte in the non-aqueous electrolyte solution is preferably in the range of 0.01 to 2 mol/l.
If it is less than 0.01 mol/l, the electrochromic properties will deteriorate, and if it exceeds 2 mol/l, the supporting electrolyte may not be completely dissolved in the solvent. The electrochromic device of the present invention is arranged such that the non-aqueous electrolyte solution and the first and second electrodes are in contact with each other. Since the electrolyte solution and both electrodes are in contact with each other, all or part of the electrodes are actually immersed in the electrolyte solution stored in the container. Alternatively, the electrolyte solution may be impregnated into a liquid-absorbing polymer such as cellulose or an ion exchange membrane, and the electrode may be placed in contact with the liquid-absorbing polymer. The container for storing the non-aqueous electrolyte solution is preferably made of a material that is not susceptible to the electrolyte solution and has electrical insulation properties, such as polyethylene, polypropylene, glass, etc. Note that the first electrode and the second electrode are prevented from coming into direct contact with each other in the nonaqueous electrolyte solution. Therefore, an insulator such as a separator made of polypropylene, cellulose, etc., an electrolyte holding material, a spacer, etc. may be arranged between the two electrodes. The first electrode and the second electrode are connected to a power source by respectively attaching appropriate lead portions. Next, various examples of arrangement of the first electrode and the second electrode are shown in FIGS. 2 to 8. Although each figure shows only the first electrode and the second electrode in plan view, both electrodes are actually in contact with the electrolyte solution. In the figure, 1 indicates the first electrode, 2 indicates the second electrode, and the arrow indicates the viewing direction. Since the first electrode 1 performs an electrochromic reaction and exhibits changes in coloring and decoloring, the first electrode 1 is arranged so as to be present in the field of vision. When the conductive base material 11 of the first electrode is transparent,
There is an arrangement in which both electrodes are arranged in series as shown in FIG. 2, or an arrangement in which both electrodes are located at right angles as shown in FIG. Further, when the conductive base material of the second electrode 2 is also transparent, there is an arrangement in which both electrodes are lined up in parallel as shown in FIG. In both FIGS. 2 to 4, when the polyaniline film 10 of the first electrode is colored, light is blocked, and when the polyaniline film 10 of the first electrode is discolored, light is transmitted. In addition, when the conductive base material 12 of the first electrode 1 is opaque, an arrangement in which both electrodes are arranged in series as shown in FIG. 5, an arrangement in which both electrodes are located at right angles as shown in FIG. As shown in the figure, there is an arrangement in which both electrodes are arranged in parallel and the second electrode is located behind the field of view of the first electrode. Further, when the conductive base material of the second electrode 2 is transparent, there is an arrangement in which both electrodes are lined up in parallel as shown in FIG. In both cases, the polyaniline film 10 of the first electrode 1 is placed in the field of vision. In this case, when the polyaniline film 10 is decolored, the conductive base material 12 appears, and especially in the case of a base material with a high light reflectance, the base material becomes a mirror surface. Further, when the polyaniline film 10 is colored, the base material 12 becomes soft. As mentioned above, when the conductive base material of the first electrode is transparent such as glass coated with an ITO film, the electrochromic device of the present invention can be applied as an anti-glare mirror or a light control glass. Furthermore, when the conductive base material is opaque such as metal, it can be used as an anti-glare mirror or a display board. The electrochromic device of the present invention exhibits a color change of coloring and decoloring by applying a voltage. For example, when the voltage applied to the first electrode (working electrode) (to the second electrode, the same applies hereinafter) is - 1.5V, +
At 1.0V and +2.0V, it exhibits pale yellow, green, and dark blue, respectively, and by applying an intermediate voltage between them, each intermediate color can be obtained. Note that the light yellow color appears visually transparent. [Operation of the invention] When a constant voltage power source is connected between the first electrode and the second electrode of the electrochromic device of the present invention, and a voltage of -1.5V is first applied to the first electrode, the polyaniline film of the first electrode is in a transparent (light yellow) state. Next, when the applied voltage was changed to +2.0V, the transparent (light yellow) polyaniline film of the first electrode was colored dark blue. This is thought to be due to the oxidation reaction shown in the chemical reaction formula [2 ^] (in the formula, ). That is, the polyaniline film is colored dark blue by doping the anion (X ^- ) into the polyaniline film. This reaction is reversible, and when the applied voltage is set to -1.5V again, the anion (X ^- ) is dedoped from the polyaniline film and the polyaniline film turns transparent (light yellow). Also, the first electrode +
When a voltage of 1.0V is applied, the polyaniline film has the left side (reduced form) and the right side (oxidized form) of the above formula [2].
It becomes an intermediate state and exhibits a green color. All of the above reactions are electrochemically reversible, and can be changed to a desired color by controlling the applied voltage. The reason why polyaniline membranes exhibit electrochromic action even when using non-aqueous electrolyte solutions as described above is because polyaniline is stable in polar organic solvents.
This is because the polyaniline film contains a counter anion that forms a class ammonium ion, and this counter anion performs doping and dedoping of the polyaniline film. [Effects of the Invention] According to the present invention, an electrochromic element having a long life and a large ΔOD can be provided. This is because the electrolyte solution of the electrochromic device of the present invention is non-aqueous, and there is no adverse effect such as melting of the electrodes or generation of hydrogen gas, which occurs in the case of devices using conventional strong acid aqueous solutions. This is because it has stabilized. The electrochromic device of the present invention can be applied to anti-glare mirrors, light control glasses, blinds, large display elements, small display elements, light amount adjustment filters, etc. of automobiles, etc. [Examples] Examples of the present invention will be described below. Example 1 First, a first electrode was formed as follows.
A 1 mol/l aniline-2 mol/l perchloric acid aqueous solution was prepared as an electrolytic polymerization solution, and after immersing ITO film-coated glass as a positive electrode and graphite as a negative electrode in the solution, a current was applied between the two electrodes. Electrolytic polymerization was performed by applying a voltage so that a direct current with a density of 100 μA/cm ² (per unit area of the positive electrode) flowed. A polyaniline film with a thickness of approximately 2000 Å was deposited on glass coated with an ITO film. This was immersed in a propylene carbonate solution and then vacuum dried at 100° C. for 30 minutes to obtain a first electrode. Next, an electrochromic device according to the present invention was formed as shown in FIG. Note that FIG. 1 is a perspective view of the element. The electrochromic element is arranged such that the first electrode 3 and the second electrode 4 are located at right angles, and the transparent glass 61
It is a hollow rectangular body arranged so that the and are surrounding the circumference. The first electrode 3 is made of glass coated with an ITO film and a polyaniline film deposited thereon, and the second electrode 4 is made of graphite.
2 are the side and rear surfaces of the transparent glass, respectively.
A propylene carnate solution 5 of 1 mol/l lithium perchlorate as an electrolyte solution is placed in this rectangular cavity. Note that a polypropylene separator 7 is interposed between the first electrode 3 and the second electrode 4 so that they do not come into contact with each other.
In addition, the polyaniline film of the first electrode is located inside the rectangular body.
That is, it is arranged so as to be in contact with the electrolyte solution. Lead portions 8 were attached to the first electrode 3 and second electrode 4 of this element, respectively, and a constant voltage power source 9 was connected to them. Voltages of +2.0 V and -1.5 V were applied to the first electrode 3 of the device, respectively, and the visible light absorption spectrum was measured in the direction of the arrow in FIG. 1 to evaluate the spectral characteristics of the first electrode. The results are shown in the visible light absorption spectrum curve in FIG. When the applied voltage was -1.5V, the polyaniline film of the first electrode showed almost no absorption in the visible light region and was a pale yellow color that was almost transparent, but when the applied voltage was +2.0V, it was dark blue. Moreover, when +1.0V, which is an intermediate voltage between these, was applied, the polyaniline film turned green. Note that all of these color changes were reversible. For comparison, a comparative electrochromic device was formed having the same structure as the above device except that the electrolyte solution was a 1 mol/l perchloric acid aqueous solution. A cycle life characteristic test was conducted on the above two types of electrochromic devices. In this test, voltages of +2.0V and -1.5V were applied to the first electrode for 1 second each, and the absorbance change (△OD) was approximately 0.4.
The ΔOD ratio was measured when it was set to 100%.
The results are shown in FIG. As is clear from Fig. 10, in the comparative example element,
10 The △OD ratio decreases after about ³ cycles, but
It can be seen that the product of the present invention exhibits stable electrochromic action for 3×10 ⁴ cycles or more. Furthermore, ΔOD with respect to the amount of electricity injected per unit area of the first electrode was measured for the above two types of electrochromic devices. The relationship is shown in FIG.
The relationship between the amount of injected electricity and △OD is almost proportional for both types of devices, but in the case of the device of the present invention, the △OD change per unit amount of electricity is 0.036 cm ² /mc, and in the case of the comparative example, it is 0.024. cm ² /mc. This shows that the electrochromic device of the present invention requires less electricity to change color than the comparative example. Example 2 First, to make the first electrode, the ITO film-coated glass was immersed in a 1 mol/l aniline-2 mol/l hydroborofluoric acid aqueous solution as a positive electrode and carbon as a negative electrode, and then the current density was 100 μA/cm ² ( Electrolytic polymerization was performed using a positive electrode (per unit area of the positive electrode) to deposit a polyaniline film with a thickness of approximately 3000 Å on the ITO film-coated glass.
This was immersed in a propylene carbonate solution and then vacuum dried at 100° C. for 30 minutes to obtain a first electrode.
Using this first electrode, an electrochromic device having the same structure as in Example 1 was formed. For comparison, 1 mol/l as an electrolyte solution
A comparative electrochromic device was formed in the same manner as above except that an aqueous hydrochloric acid solution was used. The above two types of devices were left at room temperature and the behavior of the polyaniline film of the first electrode was observed. The result is the first
Shown in the table. As is clear from Table 1, the electrochromic device of the present invention shows no change in the polyaniline film even after being left for 30 days, indicating that it has excellent storage stability.

[Table] Example 3 This example shows the influence of anions contained in a polyaniline film on electrochromic properties. First, an aqueous solution for electrolytic polymerization of polyaniline as shown in Table 2 was prepared. Add ITO as a positive electrode to the aqueous solution.
The membrane-coated glass and the negative electrode were immersed, and a voltage was applied so that a direct current with a current density of 100 μA/cm ² (per unit area of the positive electrode) flowed between the two electrodes to perform electrolytic polymerization. This results in a film thickness of approx.
A 2000 Å polyaniline film was deposited. This was washed with methanol, and then vacuum dried at 100°C for 30 minutes to form a first electrode. In addition, sample No. in Table 2.
1 was the same as in Example 1. Further, each polyaniline film contains anions shown in Table 2. Next, using the above four types of first electrodes, Example 1
An electrochromic device with a similar configuration was formed. A cycle life characteristic test was conducted on the above four types of electrochromic devices. In this test, voltages of +2.0V and -2.0V are applied to the first electrode for 1 second each, and the change in absorbance (△OD) is determined, and when the initial value is taken as 100%, the △OD ratio is 90%. This was done by measuring the number of cycles until the decrease (cycle life). The results are shown in Table 2. As is clear from Table 2, when polyaniline has a counter anion that does not form a quaternary ammonium ion, which is stable in polar organic solvents such as Cl ^- and NO ₃ ^- , ClO ₄ ^- and BF of the present invention It can be seen that both ΔOD and cycle life are reduced compared to the element with ₄ ^- .

【table】 [Brief explanation of drawings]

1 and 9 are perspective views of the electrochromic device of the present invention in Example 1 and diagrams showing visible light absorption spectrum curves of the first electrode, and FIGS. 10 and 11 are diagrams showing the electrochromic device of Example 1. Figures 2 to 8 show examples of the arrangement of the first and second electrodes of the electrochromic element of the present invention. FIG. 1, 3...first electrode, 2,4...second electrode, 1
0... Polyaniline membrane, 5... Electrolyte solution.

Claims (1)

[Scope of Claims] 1. An electrochromic device comprising a non-aqueous electrolyte solution containing a supporting electrolyte in a polar organic solvent, and a first electrode and a second electrode in contact with the non-aqueous electrolyte solution, which The electrode is composed of a conductive base material and a polyaniline film in close contact with the conductive base material, and the polyaniline film contains a counter anion that forms a stable quaternary ammonium ion of polyaniline in the polar organic solvent. Tsuku Motoko. 2. The electrochromic device according to claim 1, wherein the polar organic solvent is one or more of propylene carbonate, acetonitrile, sulfolane, nitromethane, and benzonitrile.