JPS61239230A - Electrochromic display device - Google Patents

Abstract

PURPOSE:To obtain an electrochromic display device operable with low voltage and good in repeated use characteristics by using a hydrogen adsorbing alloy for an opposite electrode capable of governing coloring and decoloring of the display electrode which execute display by the coloring and decoloring reaction of an electrochromic substance. CONSTITUTION:A transparent electrode 2 made of an ITO film is formed on a glass base 1, and the electrochromic substance of tungsten oxide (WO3) 3 is vapor deposited on the electrode 2, and the WO3 is formed into a necessary pattern, and constitutes the display electrode together with the electrode 2. The WO3 3 is coated with a thick film of antimony oxide and a small amt. of binder to form an electrolyte 4, and a thick film of the hydrogen adsorbing alloy TiNiHx and a small amt. of binder is formed on the electrolyte 4 to prepare the opposite electrode 5, and a stainless steel plate 6 for leading a current is attached to the electrode 5, and these laminates 2, 3, 4, 5, 6 are covered with a sealing resin case 7, thus permitting the obtained electrochromic display device to be colored and decolored repeatedly by applying positive and negative voltages to the electrode 2 and the plate 6, and this device to be operated with low voltage and enhanced in repetition characteristics.

Description

[Detailed Description of the Invention] Technical Field> The present invention relates to an electrocomic display device C and an ECD
).

<Prior art> ECD has a structure that includes a display electrode that reversibly causes an electrochemical coloring/decoloring reaction, and a counter electrode that serves as a pair for this electrochemical reaction, with an electrolyte provided between the two electrodes. has been done. Materials for display electrodes include tungsten oxide,
There are transition metal oxides such as titanium oxide and vanadium oxide, and protons, lithium ions, sodium ions, etc. have been reported as cation species that change color and fade by moving in and out of the transition metal oxides. In addition to the above-mentioned coloring and decoloring reactions caused by the entry and exit of certain cations, there have also been reports of materials that carry out coloring and decoloring reactions by oxidation-reduction reactions such as viologen derivatives. Carbon is generally used as the material for the counter electrode, but gold, platinum, or the same material as the display electrode may also be used. Further, the electrolyte used may be a liquid or solid electrolyte that is a cationic conductor similar to ECD.

Among the general constituent materials of the ECD mentioned above, those using nifloton as the coloring species will be explained in more detail below. A display using protons as a coloring species has a metal oxide such as tungsten oxide, vanadium oxide, or titanium oxide in the display electrode, an aqueous sulfuric acid solution in the electrolyte, and a proton donor in an organic solvent.

Proton solid electrolytes such as tantalum oxide, tin oxide, and antimony oxide are used. The counter electrode is generally made of carbon as a main component, and in this case, when the display electrode is used for color display, the counter electrode is held at a positive potential. Therefore, if the electrode itself, such as carbon, does not contain emitted protons, it will decompose with water and generate oxygen gas. vice versa.

During erasing, the counter electrode is held at a negative potential, so protons are reduced and hydrogen gas is generated. In order to solve this problem of gas generation, the same material as the display electrode is added to the counter electrode side, and the above problem is solved by utilizing the opposite reaction to that of the first display electrode, or protons are adsorbed to the counter electrode. There are some that use platinum black for this purpose. However, during long-term use, gas accumulates at the electrode interface, which impairs the long-term reliability of the ECD. Furthermore, since the overvoltage of proton oxidation and reduction reactions at the counter electrode is high, driving the ECD requires a voltage 73 times higher than the equilibrium potential.

<Object of the Invention> In view of the above-mentioned current situation, the present invention provides an ECD that uses a hydrogen-absorbing alloy for the counter electrode and has good display repeatability based on a coloring/decoloring reaction and a low applied voltage during driving. With the goal.

Explanation of composition and effects〉 Hydrogen storage alloys that store hydrogen in the form of metal hydrides are
Generally, gaseous hydrogen is stored in the hydrogen storage alloy by coexisting with a hydrogen storage alloy under certain temperature and pressure conditions, and hydrogen in the hydrogen storage alloy is stored by changing the temperature and pressure to appropriate conditions. It is known to be released into the gas phase. Further, absorption and desorption of hydrogen with this hydrogen storage alloy is also possible electrochemically. In the reaction between a hydrogen storage alloy and hydrogen, the relationship between standard formation energy change ΔG0 and equilibrium dissociation pressure PH2 is ΔG = RT! nPH2・・・・・・・・・・・・(
1) (R: gas constant, T: absolute temperature).

Also, the free energy change associated with the electrochemical reaction of the electrode.
The relationship between ΔGO and electrode potential E is -ΔG −nFE ・・・・・・・・・・・・・・・
It is expressed as (2) (F: Faraday constant number).

Therefore, when the equilibrium dissociation pressure is higher than 1 atm, E<O, and the potential is less noble than the standard hydrogen electrode potential.

Further, when the equilibrium dissociation pressure is lower than 1 atm, IiE>0, which is more negative than the standard hydrogen electrode potential. That is, when a hydrogen storage alloy whose equilibrium dissociation pressure is lower than 1 atm is used as the counter electrode, the reaction at the counter electrode occurs at a potential lower than the standard hydrogen electrode potential. In addition, hydrogen storage alloys have low hydrogen overvoltage and therefore have little polarization. On the other hand, when carbon, platinum black, etc. are used for the counter electrode, the electrode potential of the counter electrode is less negative than the standard hydrogen electrode potential, and as a result, when a hydrogen storage alloy is used for the counter electrode, driving The voltage will be lower. Furthermore, since the protons attracted to the counter electrode during erasing are immediately stored in the hydrogen storage alloy, no hydrogen gas is generated. As a result of the above, a device with superior long-term stability and a longer memory effect than conventional ECDs can be realized.

The hydrogen storage alloy used in the present invention is not limited in material, shape, etc., but it is suitable that the equilibrium dissociation pressure is one atmosphere or less in the operating temperature range and that is resistant to acid corrosion. .

<Embodiment> FIG. 1 is a configuration diagram of an ECD showing an embodiment of the present invention. A transparent electrode 2 made of an ITO film is formed on a glass substrate 1, and tungsten oxide (WO3) 3, which is an electrochromic substance, is deposited thereon by electron beam evaporation. The tungsten oxide 3 is processed and formed into a required display pattern.

Together with the transparent electrode 2, it constitutes a display electrode. The tungsten oxide 3 is coated with antimony oxide and a small amount of binder to form a thick film to form an electrolyte 4. Further, a thick film of TiN1Hx, which is a hydrogen storage alloy, and a small amount of binder is formed thereon to form the counter electrode 5. The hydrogen storage alloys include I, aNis, and LaNi4F.
Those based on rare earth metals such as e, T1Co,
TiMn, CaNi5 and others can be used.

Furthermore, a stainless steel plate 6 is pasted on top of it for current collection.
EC by sealing the periphery with a dish-shaped resin envelope 7
Configure D cell. A lead wire 8 is connected to the transparent electrode 2 and the stainless steel plate 6, and the lead wire 8 is connected to a DC power source 10 via a forward/reverse switch 9. Forward/reverse changeover switch 9 is used to control ON/OFF of the drive current flowing from the RFI power source 10 to the ECD, and to switch the direction of the flow in accordance with the coloring/decoloring operation of the display pattern.

When electricity is applied between the tungsten oxide 3 and the opposing electrode 5 made of a hydrogen storage alloy through the transparent electrode 2 and the stainless steel plate 6, an electrochemical reaction proceeds between the electrolyte 4 and the tungsten oxide 3, and the tungsten oxide 3 is colored. . Display information can be obtained by observing this colored pattern from the front side of the glass substrate 1. The colored tungsten oxide 3 has a memory function in which the colored state is maintained for a certain period of time even after the energization is stopped. In addition to coloring the entire display surface, the coloring pattern can be formed by any molding pattern such as a segment-type display pattern or a nine-character graphic pattern.

The counter electrode 5 has a hydrogen storage alloy which makes it nobler than the standard hydrogen electrode potential, and the hydrogen overvoltage is also low, so that the coloring reaction proceeds with a low current. To decolor the colored tungsten oxide 3, operate the forward/reverse changeover switch 9 to reverse the current direction.

As a result, an electrochemical reaction opposite to the coloring operation proceeds between the tungsten oxide 3 and the electrolyte 4, and the tungsten oxide 3rfi is decolored and returns to its original state. in this case,
Protons at the counter electrode 5 are occluded into the hydrogen storage alloy.

Electrochromic display is performed by repeating the above operations. By using a hydrogen storage alloy as the counter electrode 5, this repetition characteristic is also improved.

FIG. 2 is a characteristic diagram showing voltage changes when coloring and decoloring the ECD with a constant current of 200 μA. Here, the curve □ is the ECD according to the above example.

Curve No. 2 corresponds to the conventional ECD shown in FIG. 1, in which the counter electrode 5 is formed into a thick film by adding a small amount of binder to acetylene black.

The driving voltage of the device according to the above embodiment is about 150 mV lower than that of the conventional device. Further, as a result of a cycle test using a rectangular wave voltage with an amplitude of ±0.8v and a pulse width of 0.59 seconds, it was confirmed that the ECD of this embodiment operates normally even after the ECDdlO cycle has elapsed. As described above, the ECD using a hydrogen storage alloy for the counter electrode has high reliability and enables low voltage driving. Further, ECD using colored species other than protons also has the effect of sucking hydrogen gas generated by side reactions, and the present invention can be applied to such cases as well.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an ECD showing one embodiment of the present invention. FIG. 2 is a voltage change characteristic diagram of the ECD shown in FIG. 1 and a conventional ECD. DESCRIPTION OF SYMBOLS 1... Glass substrate, 2... Transparent electrode, 3... Tungsten oxide, 4... Electrolyte, 5... Counter electrode, 6
... Stainless steel plate, 7... Envelope, 8... Lead wire, 9... Forward/reverse selector switch, 10... Power supply.

Claims (1)

[Claims] 1. In an electrochromic display device comprising a display electrode that performs display by a coloring/decoloring reaction of an electrochromic substance, and a counter electrode that controls the coloring/decoloring reaction as a counter electrode to the display electrode, the counter electrode has hydrogen absorption. An electrochromic display device characterized by using an alloy.