JP7052130B1 - Electrode for chlorine generation and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for chlorine generation having both excellent chlorine generation efficiency and durability. A chlorine generation electrode including an electrode base material made of valve metal and a coating layer made of a Pt—Ir alloy formed on the electrode base material. [Selection diagram] None

Description

The present invention relates to a chlorine generation electrode, and more particularly to a chlorine generation electrode having excellent chlorine generation efficiency and durability. The present invention also relates to a method for manufacturing the chlorine generating electrode.

The production of chlorine gas, chlorine compounds, etc. by electrolyzing salt water has been more widely practiced than before. Further, in recent years, the opportunity for hypochlorous acid to be used for the purpose of sterilization, deodorization, etc. is increasing, and electrolysis is also used for the production of the hypochlorous acid.

In the production of chlorine gas and chlorine compounds by such electrolysis, a chlorine generation reaction proceeds at the anode. For example, in the case of producing hypochlorous acid water, water (H ₂ O) is reduced at the cathode to generate hydrogen (H ₂ ), while chloride ion (Cl ⁻ ) is oxidized at the anode to produce chlorine (Cl −). ₂ ) is generated, and this chlorine reacts with water to generate hypochlorous acid (HClO).

However, in the anode, not only the above-mentioned chlorine generation due to the oxidation of chloride ions but also the generation of oxygen due to the oxidation of water occurs at the same time, and the ratio of chlorine and oxygen generation differs depending on the anode. Therefore, when the purpose is to generate chlorine, it is necessary to use an electrode having excellent chlorine generation efficiency (chlorine generation electrode) as the anode.

On the other hand, as an electrode used for water electrolysis or the like, an insoluble electrode having a coating having an electrode catalytic activity on the surface of a conductive electrode base material is widely used. Among them, Pt is used for an electrode base material made of titanium. Ti / Pt electrodes plated with Titanium are used in a wide range of applications.

However, an electrode using a metal Pt as an electrode catalyst layer, such as the Ti / Pt electrode, has excellent durability but a high chlorine overvoltage, and although the chlorine generation efficiency is sufficient for use as a chlorine generation electrode. There wasn't.

Therefore, as the chlorine generation electrode, an electrode using a noble metal oxide such as iridium oxide as an electrode catalyst is used. Electrodes using noble metal oxides have a lower chlorine overvoltage than plating with noble metals such as Pt, and therefore have excellent chlorine generation efficiency.

An electrode for chlorine generation using a noble metal oxide is usually produced by applying a solution of a noble metal compound to the surface of an electrode base material and firing it at a high temperature of around 500 ° C. Since the noble metal compound contained in the solution is thermally decomposed into a noble metal oxide, such a production method is called a thermal decomposition method.

However, the chlorine generating electrode using such a noble metal oxide as an electrode catalyst has a drawback of being inferior in durability. This durability problem becomes a problem especially when electrolysis is performed in a solution containing a large amount of mineral components such as tap water. That is, when a solution containing a large amount of mineral components is used, the mineral components in the solution are reduced and precipitated at the cathode and adhere to the cathode surface as scale, resulting in a significant decrease in electrolytic performance. Therefore, in order to remove the scale adhering to the cathode and restore the electrolysis performance, it is necessary to periodically perform so-called reverse electrolysis, in which the polarity is reversed and energization is performed. However, since the noble metal oxide of the anode undergoes reduction during reverse electrolysis, wear progresses significantly as compared with normal use.

As described above, the chlorine generation electrode using the noble metal oxide is excellent in chlorine generation efficiency but inferior in durability. Therefore, a chlorine generation electrode having both excellent chlorine generation efficiency and durability is required. ing.

Therefore, for example, Patent Documents 1 and 2 propose to form an intermediate layer made of porous platinum between an electrode catalyst layer made of a noble metal oxide and an electrode base material.

Japanese Unexamined Patent Publication No. 2008-050675 Japanese Unexamined Patent Publication No. 2017-115188

According to Patent Documents 1 and 2, by providing an intermediate layer made of porous platinum, the adhesion of the noble metal oxide is improved by the anchor effect of the intermediate layer, and the noble metal oxide is worn even when reverse electrolysis is performed. Is said to be able to reduce.

However, in the electrodes proposed in Patent Documents 1 and 2, although it is considered that the peeling of the electrode catalyst layer can be suppressed by the anchor effect of the intermediate layer, the noble metal oxide is still used as the electrode catalyst. Therefore, it is not possible to fundamentally prevent wear due to reverse electrolysis. Therefore, the durability was still insufficient.

Further, when manufacturing the electrodes proposed in Patent Documents 1 and 2, an intermediate layer is formed on the surface of the electrode base material by electroplating, and then an electrode catalyst layer is formed on the surface of the intermediate layer by a thermal decomposition method. Need to be formed. As described above, since it is necessary to form the intermediate layer and the electrode catalyst layer by different methods, the electrode is also disadvantageous in terms of productivity.

The present invention has been made in view of the above, and an object of the present invention is to provide an electrode for chlorine generation, which has excellent chlorine generation efficiency and durability, and is also excellent in productivity.

As a result of diligent research, the present inventors have found that the above problem can be solved if the electrode is provided with a coating layer made of a Pt—Ir alloy on the electrode base material. That is, as described above, Pt, which is generally used as an electrode catalyst layer for an insoluble electrode, has excellent durability but inferior chlorine generation efficiency, and therefore, it cannot be used for a chlorine generation electrode. It wasn't suitable. However, in the case of a Pt—Ir alloy in which Ir is added to Pt, a significantly superior chlorine generation efficiency can be obtained as compared with Pt. Furthermore, it was also found that the Pt-Ir alloy is not an oxide but a metal, so that it hardly wears even when reverse electrolysis is performed, and has the same level of durability as Pt.

The present invention has been made based on the above findings, and its gist structure is as follows.

1. 1. An electrode base material made of valve metal and
A chlorine generating electrode including a coating layer made of a Pt—Ir alloy formed on the electrode substrate.

2. 2. The surface roughness on the surface of the coating layer is
The chlorine generating electrode according to 1 above, which has a peak density Spd of 14.4 elements / μm ² or more.

3. 3. The surface roughness on the surface of the electrode base material is
Arithmetic mean height Sa, 2.0 μm or more, and
The chlorine generation electrode according to 1 or 2 above, which has a developed area ratio of Sdr of 3.0 or more.

4. A method for manufacturing an electrode for chlorine generation, in which a coating layer made of a Pt—Ir alloy is formed by electroplating on an electrode base material made of valve metal.

5. The method for manufacturing a chlorine generating electrode according to 4 above, wherein the electrode base material is immersed in sulfuric acid prior to the electroplating.

6. The method for producing a chlorine generating electrode according to 4 above, wherein the surface of the electrode base material is blasted prior to the electroplating, and then the electrode base material is immersed in sulfuric acid.

The electrode for chlorine generation of the present invention has excellent chlorine generation efficiency and durability, and is also excellent in productivity.

Hereinafter, embodiments of the present invention will be specifically described. The present invention is not limited to the embodiments described below.

(First embodiment)
The electrode for chlorine generation in the first embodiment of the present invention includes an electrode base material made of a bulb metal and a coating layer made of a Pt—Ir alloy formed on the electrode base material.

[Electrode substrate]
As the electrode base material, any base material can be used as long as it is made of bulb metal. As the valve metal, for example, titanium, niobium, tantalum, or an alloy thereof can be used, and among them, titanium or a titanium alloy, which is inexpensive and easy to process, is preferably used.

The shape of the electrode base material is not particularly limited, and may be any shape depending on the purpose. For example, the electrode base material may be plate-shaped, perforated plate-shaped, rod-shaped, net-shaped, expanded metal, or the like.

The thickness of the electrode base material is not particularly limited, and may be any thickness depending on the intended use and the like. Typically, the thickness of the electrode base material is preferably 10 mm or less, more preferably 0.1 to 5.0 mm, and even more preferably 0.2 to 1.0 mm.

[Coating layer]
A coating layer made of a Pt—Ir alloy is provided on the electrode base material. By using the Pt—Ir alloy, it is possible to obtain significantly superior chlorine generation efficiency as compared with Pt. Further, since the Pt—Ir alloy is not an oxide but a metal, it hardly wears even when reverse electrolysis is performed, and has the same level of durability as Pt. Therefore, by using a coating layer made of a Pt—Ir alloy, it is possible to achieve both chlorine generation efficiency and durability, which were difficult to achieve with conventional electrodes, at a high level.

The Ir content in the Pt—Ir alloy is not particularly limited, but from the viewpoint of further enhancing the chlorine generation efficiency, it is preferably 1% by mass or more, more preferably 2% by mass or more, and 5% by mass. The above is more preferable. On the other hand, from the viewpoint of further enhancing the durability, it is preferably less than 50% by mass, more preferably less than 25% by mass, and further preferably 20% by mass or less.

The method for forming the coating layer is not particularly limited, but it is preferably formed by electroplating as described later. In other words, the coating layer is preferably a Pt—Ir alloy plating layer.

The thickness of the coating layer is not particularly limited and may be any thickness. However, if it is excessively thin, it becomes difficult to cover the surface of the electrode base material, and the life of the electrode may be shortened. Therefore, the thickness of the coating layer is preferably 0.1 μm or more, and more preferably 0.3 μm or more. On the other hand, the upper limit of the thickness of the coating layer is not particularly limited, but if it is excessively thick, the coating layer may be more easily peeled off from the electrode base material due to stress. Further, since the unevenness of the surface of the electrode base material is smoothed by the coating, it becomes difficult to control the surface roughness on the surface of the coating layer as described later. Therefore, the thickness of the coating layer is preferably 10.0 μm or less, and preferably 5.0 μm or less. The thickness of the coating layer can be measured using a fluorescent X-ray film thickness meter.

A Pt layer can be provided as a base layer between the electrode base material and the coating layer. In other words, the chlorine generating electrode in one embodiment of the present invention is an electrode base material made of valve metal, a Pt layer formed on the electrode base material, and a Pt—Ir alloy formed on the Pt layer. It may be a chlorine generation electrode including a coating layer made of. By providing the Pt layer as the base of the coating layer, the adhesion of the coating layer to the electrode substrate can be improved.

The method for forming the Pt layer is not particularly limited, but it is preferably formed by plating. That is, the Pt layer is preferably a Pt plating layer.

The thickness of the Pt layer is not particularly limited, but from the viewpoint of enhancing the effect of improving the adhesion, it is preferably 0.01 μm, more preferably 0.03 μm or more, and more preferably 0.05 μm or more. Is even more preferable. On the other hand, if the Pt layer is excessively thick, the unevenness of the surface of the electrode base material is smoothed. Therefore, the thickness of the Pt layer is preferably 1.0 μm or less, more preferably 0.5 μm or less. It is more preferably 0.2 μm or less.

Since the electrode for chlorine generation of the present invention has excellent chlorine generation efficiency and durability as described above, it can be extremely suitably used for electrolytic production of chlorine or a chlorine compound.

(Second embodiment)
In the electrode for chlorine generation in the second embodiment of the present invention, the surface roughness on the surface of the coating layer is 14.4 pieces / μm ² or more at the peak density Spd of the peak. Spd is one of the indexes showing the shape of the surface defined by ISO 25178, and is defined as the number of peaks per unit area. By setting the peak density Spd of the mountain to 14.4 / μm ² or more, the durability of the chlorine generating electrode can be further improved. From the viewpoint of improving durability, it is more preferable to set Spd to 15.0 pieces / μm ² or more.

The reason why the durability is improved by controlling Spd is considered as follows. That is, the surface of the coating layer has irregularities due to irregularities on the surface of the electrode base material, and when electrolysis is performed, the current concentrates on the convex portions, that is, the vertices of the peaks. When the current is concentrated, the wear of the coating layer is likely to proceed accordingly. By increasing the peak density Spd of the peak, the current can be distributed to a large number of vertices, so that the wear of the coating layer due to the current concentration can be suppressed.

From the viewpoint of suppressing current concentration, the larger the Spd is, the more preferable it is. Therefore, the upper limit of the Spd is not particularly limited, but it is considered that the effect is saturated even if the Spd is excessively increased. It may be μm ² or less, and may be 25.0 pieces / μm ² or less.

(Third embodiment)
The chlorine generating electrode according to the third embodiment of the present invention has a surface roughness on the surface of the electrode base material of 2.0 μm or more at an arithmetic average height Sa and a developed area ratio of Sdr. It is 0.0 or more. Sa is one of the indexes showing the shape of the surface defined by ISO 25178 and JIS B 0681-2: 2018, and is a two-dimensional extension of the arithmetic mean height Ra of the line. In addition, Sdr is also one of the indexes showing the shape of the surface specified by ISO 25178 and JIS B 0681-2: 2018, and is a ratio showing how much the surface area has increased compared to the case where there is no unevenness. ..

By setting Sa and Sdr on the surface of the electrode base material within the above range, the area of the interface between the electrode base material and the coating layer is increased, so that the adhesion of the coating layer to the electrode base material is improved by the anchor effect. do. As a result, peeling of the coating layer when the electrode is used is prevented, and the durability of the electrode is further improved.

From the viewpoint of preventing peeling, the larger Sa and Sdr are, the more preferable, so that the upper limit of Sa and Sdr is not particularly limited. However, since it is considered that the effect is saturated even if it is excessively increased, for example, Sa may be 10.0 μm or less, or 5.0 μm or less. Similarly, Sdr may be 10.0 or less, and may be 5.0 or less.

The Spd, Sa, and Sdr can be measured with a laser microscope.

[Production method]
Next, a suitable manufacturing method of the chlorine generating electrode of the present invention will be described. However, the chlorine generating electrode of the present invention is not limited to that manufactured by the manufacturing method described below.

The electrode for chlorine generation of the present invention can be manufactured by forming a coating layer made of Pt—Ir alloy on an electrode base material made of Ti or a Ti alloy by electroplating.

When the coating layer is formed by electroplating, the composition of the plating solution used is not particularly limited, and any plating solution capable of forming a plating layer made of a Pt—Ir alloy, that is, a plating solution containing a Pt source and an Ir source. Any one can be used.

The Pt source is not particularly limited, and any Pt compound can be used. As the Pt compound, for example, at least one selected from the group consisting of platinum bromide, dinitrodiamine platinum, hexachloroplatinum, dinitrosulfatoplatinic acid, platinum chloride, and tetraammine platinum can be used. Above all, it is preferable to use platinum bromide salt, and it is more preferable to use sodium platinum bromide.

Similarly, any Ir compound can be used as the Ir source without particular limitation. Examples of the Ir compound include iridium bromide, iridium nitrate, iridium sulfate, iridium chloride, iridium chloride, potassium iridium chloride, hexaammine iridium chloride, hexaammine iridium hydroxide, and hexaammine iridium nitrate. At least one selected from the group can be used. Above all, it is preferable to use iridium bromide, and it is more preferable to use sodium iridium bromide.

The concentrations of Pt and Ir in the plating solution are not particularly limited, and may be adjusted so as to have a desired plating layer composition. Further, as in general plating, any electrolyte or additive can be added to the plating solution in addition to the Pt source and Ir source, if necessary.

The temperature of the plating solution at the time of plating is not particularly limited, but is preferably 50 to 95 ° C, more preferably 80 to 90 ° C.

(Sulfuric acid immersion treatment)
In one embodiment of the present invention, it is preferable to immerse the electrode base material in sulfuric acid prior to the electroplating (sulfuric acid dipping treatment). By immersing the electrode base material in sulfuric acid, fine irregularities can be formed on the surface, and as a result, the peak density Spd of the peaks of the Pt—Ir alloy coating layer formed on the surface of the electrode base material can be increased.

The conditions of the sulfuric acid immersion treatment are not particularly limited, and the apex density Spd of the peaks of the finally obtained Pt—Ir alloy coating layer may be adjusted to a desired value. Specifically, it is preferable to immerse in sulfuric acid having a concentration of 6.4 mol / L or more and a temperature of 50 ° C. or more for 5 minutes or more. On the other hand, the concentration, temperature, and upper limit of the immersion time of sulfuric acid are not particularly limited, but the effect is saturated even at an excessively high concentration, high temperature, and long time, and the burden on the manufacturing equipment becomes large. Therefore, it is preferable that the concentration is 12.8 mol / L or less, the temperature is 90 ° C. or less, and the immersion time is 24 hours or less.

(Blast treatment + sulfuric acid immersion treatment)
Further, in another embodiment of the present invention, it is preferable to blast the surface of the electrode base material prior to the electroplating, and then immerse the electrode base material in sulfuric acid (sulfuric acid dipping treatment). By forming relatively large irregularities by the blast treatment and then forming fine irregularities by the sulfuric acid immersion treatment, the arithmetic average height Sa and the developed area ratio Sdr of the electrode substrate surface can be increased.

The conditions of the blasting treatment are not particularly limited, and the arithmetic mean height Sa and the developed area ratio Sdr of the finally obtained electrode base material surface may be adjusted to be desired values. As the polishing agent used for the blast treatment, it is preferable to use a ceramic polishing agent, and it is preferable to use an alumina polishing agent. The central particle size (D ₅₀ ) of the abrasive is preferably 150 to 180 μm.

The conditions of the sulfuric acid dipping treatment when the blasting treatment and the sulfuric acid dipping treatment are used in combination may be the same as the conditions when only the sulfuric acid dipping treatment described above is performed.

(Other pretreatment)
In the present invention, prior to electroplating, any pretreatment can be performed in addition to the above-mentioned blasting treatment and sulfuric acid dipping treatment. Examples of the pretreatment include degreasing, pickling, and removal of an oxide film.

The degreasing can be performed by any method without particular limitation. The degreasing may be, for example, one or both of ultrasonic degreasing and electrolytic degreasing. By degreasing, oil and dirt adhering to the surface during the manufacturing process of the electrode base material can be removed, and a clean surface suitable for plating can be obtained.

The pickling can also be performed by any method without particular limitation. For the pickling, for example, an acid such as sulfuric acid or hydrochloric acid can be used.

A natural oxide film is usually formed on the surface of an electrode base material made of Ti or a Ti alloy. Therefore, by removing the oxide film prior to electroplating, the adhesion of the coating layer to the electrode substrate can be enhanced, and the durability of the electrode can be further improved. The removal of the oxide film can be carried out by any method without particular limitation, but it is preferable to use a solution containing a fluorine compound. As the fluorine compound, it is preferable to use at least one selected from the group consisting of hydrofluoric acid and hydrofluoric acid, and it is more preferable to use one or both of hydrofluoric acid and ammonium hydrogenfluoride. The removal of the oxide film can be performed, for example, by immersing the electrode substrate in the solution.

An oxide film is formed on the surface of the electrode base material after the blast treatment. Therefore, when performing the blast treatment, it is preferable to remove the oxide film after the blast treatment. Further, even after the sulfuric acid immersion treatment, an oxide film is formed when the electrode base material comes into contact with the atmosphere. Therefore, when the electrode substrate comes into contact with the atmosphere after the sulfuric acid immersion treatment, it is preferable to remove the oxide film after the sulfuric acid immersion treatment. When the blasting treatment and the sulfuric acid dipping treatment are performed, it is preferable to remove the oxide film both after the blasting treatment and after the sulfuric acid dipping treatment. If the electrode substrate does not come into contact with the atmosphere after the sulfuric acid immersion treatment, it is not necessary to remove the oxide film after the sulfuric acid immersion treatment.

(Post-processing)
On the other hand, after forming a coating layer made of Pt—Ir alloy by electroplating, it is preferable to wash with water as appropriate.

Further, it is preferable to fire the electrode after forming the coating layer made of Pt—Ir alloy. By firing, the durability when the electrode is used for electrolysis can be further improved. The reason is not clear, but it is expected that the improvement of the crystallinity of the plating layer by firing and the removal of impurities contribute to the improvement of durability.

It should be noted that firing may affect the surface roughness, such as smoothing the surface of the plating layer. Therefore, in the case of firing, the pretreatment conditions and plating conditions of the electrode base material may be adjusted so that the peak density Spd of the peaks in the finally obtained coating layer of the electrode satisfies the above-mentioned conditions.

When firing, the firing temperature is preferably 500 ° C. or higher, more preferably 600 ° C. or higher. On the other hand, if the firing temperature is excessively high, the oxidation of titanium, which is a component of the electrode base material, proceeds, and the durability of the electrode may decrease. Therefore, the firing temperature is preferably 700 ° C. or lower, more preferably 650 ° C. or lower.

Further, if the firing time is excessively short, the firing effect cannot be sufficiently obtained. Therefore, the firing time is preferably 30 minutes or more, and more preferably 1 hour or more. On the other hand, if the firing time is excessively long, the oxidation of titanium may proceed and the durability of the electrode may decrease. Therefore, the firing time is preferably 10 hours or less, and more preferably 5 hours or less.

Hereinafter, the effects of the present invention will be specifically described with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited thereto.

<Example 1>
First, the following experiments were conducted to evaluate the effect of the coating layer material on chlorine generation efficiency and durability.

(Invention Example 1)
The Ti plate as the electrode base material was pretreated by the following procedure.
(1) Blast treatment (2) Solvent degreasing treatment (3) Oxidation film removal (4) Pickling

The blast treatment is performed on a blast treatment device (manufactured by Fuji Seisakusho Co., Ltd., Pneumatic Blaster, SG-5BA R-306-R300) and a brown molten alumina abrasive (manufactured by Fuji Seisakusho Co., Ltd., Fujirandom A # 80, center). Particle size (150 μm to 180 μm) was used, and the pressure was 0.4 MPa.

In the degreasing treatment, Eatlex 11 manufactured by Nippon Electroplating Engineers Co., Ltd. is used as the degreasing solution, and a Ti plate is immersed in the degreasing solution and ultrasonic waves are applied for 1 minute to degreas. Was done.

The oxide film was removed by immersing the Ti plate in an aqueous solution of ammonium hydrogen fluoride for 15 seconds. The pickling was carried out by immersing in 10% sulfuric acid for 30 seconds.

Next, the Ti plate after the pretreatment was subjected to Pt plating under the following conditions to form a Pt plating layer as a base.
-Plating solution: Sulfuric acid Pt plating solution-Pt concentration: 6-9 g / L
・ Sulfuric acid: 150 g / L
-Plating liquid temperature: 60 ° C
-Thickness of Pt plating layer: Approximately 0.1 μm

Next, the surface of the Pt plating layer was further electrically plated under the following conditions to form a Pt—Ir alloy coating layer having a thickness of 0.6 μm. The Ir content in the obtained Pt—Ir alloy coating layer was about 10% by mass.
・ Plating liquid component Na solution of Pt acid bromide Aqueous solution of Na bromide Iride Iridex construction agent (manufactured by Nippon Electroplating Engineers Co., Ltd.)
-Pt concentration: 4.0 g / L
-Ir concentration: 2.5 g / L
-Plating liquid temperature: 90 ° C

After the above plating, annealing was further performed at 600 ° C. for 1 hour.

Using the obtained electrode as an anode, electrolysis was performed under the following conditions to measure the chlorine generation efficiency. The evaluation results are shown in Table 1.
-Electrolytic solution: 0.2% NaCl + 0.005% HCl / pure water-Amount of electrolytic solution: 1L
・ Cathode: Ti / Pt electrode (plate shape)
-Current: 1.8A
・ Electrolysis time: 5 minutes ・ Current density: 2.4A / dm ²
・ Distance between poles: 20 mm
・ Stirring: None during electrolysis, 300 rpm after electrolysis stopped, 30 s

The chlorine generation efficiency η was calculated using the following formula.
η (%) = (2 × F × ρ × V) / (M × 2 × 1000 × I × t) × 100
here,
F: Faraday constant (C / mol)
ρ: Hypochlorous acid concentration (mg / L) after electrolysis
V: Amount of electrolytic solution (L)
M: Atomic weight of chlorine (Cl) (g / mol)
I: Current (A)
t: time (s)

The hypochlorous acid concentration ρ after the completion of electrolysis was measured by collecting 10 mL of the electrolytic solution after the completion of electrolysis and using a handy water quality meter "Aquaab AQ-202 type" manufactured by Shibata Scientific Technology.

Further, in order to evaluate the durability of the obtained electrode, the electrode was used as an anode, and tap water was used as an electrolytic solution, and electrolysis was performed at a current density of 10 A / dm ² for 656 hours to obtain a coating layer of the anode. The rate of decrease (hereinafter referred to as "rate of decrease in film thickness") was measured. The film thickness of the coating layer before and after electrolysis was measured, and the film thickness reduction rate was calculated by dividing the reduced film thickness by the electrolysis time. The evaluation results are also shown in Table 1. In the electrolysis, normal electrolysis for 5 minutes and reverse electrolysis for 5 minutes were alternately repeated.

(Comparative Example 1)
For comparison, electrodes were prepared under the same conditions as in Invention Example 1 except that the material of the coating layer was changed to Pt, and the chlorine generation efficiency and the film thickness reduction rate were evaluated by the same procedure as in Invention Example 1. The evaluation results are also shown in Table 1.

(Comparative Example 2)
For further comparison, an electrode having a coating layer composed of iridium oxide (IrO ₂ ) and tantalum pentoxide (Ta ₂ O ₅ ) was prepared, and the chlorine generation efficiency and the film thickness reduction rate were evaluated by the same procedure as in Example 1. .. The evaluation results are also shown in Table 1.

The coating layer made of iridium oxide and tantalum oxide used in Comparative Example 2 was formed by the following procedure.

Iridium chloride and butoxytantalum were dissolved in isopropyl alcohol to prepare a solution having an Ir concentration of 7.0% by mass and a Ta concentration of 3.0% by mass. After blasting and degreasing the same Ti plate used in Example 1, the solution is applied to the surface of the Ti plate, and the temperature is 500 ° C. for 30 minutes or more in an electric furnace. It was fired to form a coating layer.

As can be seen from the results shown in Table 1, the chlorine generation electrode of the present invention has a significantly improved chlorine generation efficiency as compared with the electrode of Comparative Example 1 plated with Pt, and the film thickness reduction rate is Pt plated. It was equivalent to the electrode of Comparative Example 1 and had excellent chlorine generation efficiency and durability. On the other hand, the electrode of Comparative Example 1 plated with Pt was excellent in durability but inferior in chlorine generation efficiency. Further, the electrode of Comparative Example 2 using the coating layer composed of IrO ₂ and Ta ₂ O ₅ is excellent in chlorine generation efficiency, but the film thickness reduction rate is about 18 times that of Invention Example 1, and the durability is significantly inferior. rice field.

<Example 2>
Next, the following experiments were conducted to evaluate the effect of the pretreatment and the surface shape determined by it on the performance of the chlorine generating electrode.

A chlorine generation electrode having a coating layer made of a Pt—Ir alloy was produced by the same procedure as in Invention Example 1 except that the treatments shown in Table 2 were performed as pretreatments.

The specific procedure of the pretreatment in each invention example is as follows. In Invention Examples 3 and 4, since the electrode base material was once dried after being immersed in sulfuric acid, the oxide film was removed and pickling was performed thereafter.

(Invention Example 2)
・ Blast treatment ・ Solvent degreasing treatment ・ Oxidation film removal ・ Pickling

(Invention Example 3)
・ Solvent degreasing ・ Oxidation film removal ・ Sulfuric acid immersion ・ Degreasing ・ Oxidation film removal ・ Pickling

(Invention Example 4)
・ Blast treatment ・ Degreasing treatment ・ Oxidation film removal ・ Sulfuric acid immersion ・ Solvent degreasing ・ Oxidation film removal ・ Pickling

The sulfuric acid dipping treatment was carried out by immersing the Ti plate in sulfuric acid having a temperature of 60 ° C. and a concentration of 9.6 M for 15 minutes. Other treatments were carried out under the same conditions as in Example 1 of the above invention.

Prior to the plating treatment, the arithmetic mean height Sa and the developed area ratio Sdr on the surface of the Ti plate after the pretreatment were measured with a laser microscope (manufactured by KEYENCE, VK-X250). The measurement was performed using an objective lens having a magnification of 150 times and a monitor magnification of about 3000 times. The values of Sa and Sdr were measured at 9 randomly selected sites per sample, and the average value was used. The measurement results are also shown in Table 2.

Then, the plating treatment was carried out in the same procedure as in Invention Example 1 to obtain an electrode for chlorine generation provided with a coating layer made of a Pt—Ir alloy.

The peak density Spd of the peaks on the surface of the coating layer of the obtained electrode for chlorine generation was measured by a laser microscope (manufactured by KEYENCE, VK-X250). The measurement was performed using an objective lens having a magnification of 150 times and a monitor magnification of about 3000 times. In addition, the Spd value was measured at 9 randomly selected sites per sample, and the average value was used. The measurement results are also shown in Table 2.

Next, using the obtained electrode as an anode, electrolysis was performed under the following conditions to measure the chlorine generation efficiency. The evaluation results are also shown in Table 2.
-Electrolytic solution: 0.58% NaCl / pure water-Liquid volume: 1L
・ Current: 0.4A
・ Electrolysis time: 75 seconds ・ Current density: 1.25A / dm ²
・ Distance between poles: 4 mm
・ Stirring: None during electrolysis, 300 rpm after electrolysis stopped, 30 s

Further, using the obtained electrode as an anode, electrolysis was performed for about 1100 hours at a current density of 3.75 A / dm ² using a 30 mM NaCl aqueous solution as an electrolytic solution, and the film thickness reduction rate was measured. The evaluation results are also shown in Table 2. In the electrolysis, normal electrolysis for 2 minutes and reverse electrolysis for 2 minutes were alternately repeated.

Further, the state of the electrode surface after the electrolysis was observed, and the one in which the coating layer was not peeled off was designated as “⊚”, and the one in which peeling was observed was marked with “◯”.

From the above results, the following can be seen.
-Invention Examples 3 and 4 can obtain even higher chlorine generation efficiency as compared with Invention Example 2 in which only the blast treatment is performed.
-The rate of film thickness reduction decreases in the order of Invention Examples 2, 3 and 4, and therefore the highest durability can be realized when the blast treatment and the sulfuric acid dipping treatment are used in combination.
-Invention Example 4 in which the blast treatment and the sulfuric acid dipping treatment are used in combination is superior in adhesion to the coating layer as compared with Invention Example 3 in which only the sulfuric acid dipping treatment is performed. It is possible to demonstrate even better durability.

Claims (4)

An electrode base material made of valve metal and
A coating layer made of a Pt—Ir alloy formed on the electrode substrate is provided.
A chlorine generation electrode having a surface roughness on the surface of the coating layer of 14.4 elements / μm ² or more at the peak density Spd of the peak. The surface roughness on the surface of the electrode base material is
Arithmetic mean height Sa, 2.0 μm or more, and
The chlorine generation electrode according to claim 1, which has a developed area ratio of Sdr of 3.0 or more. A method for manufacturing an electrode for chlorine generation, in which a coating layer made of a Pt—Ir alloy is formed by electroplating on an electrode base material made of valve metal.
Prior to the electroplating, the electrode base material is immersed in sulfuric acid.
A method for manufacturing an electrode for chlorine generation, wherein the surface roughness on the surface of the coating layer is 14.4 pieces / μm ² or more at the peak density Spd of the peak . The method for producing a chlorine generating electrode according to claim 3, wherein the surface of the electrode base material is further blasted prior to immersion in sulfuric acid.