JP2021050376A - Electrolysis electrode - Google Patents

Abstract

To provide an electrolysis electrode that can suppress deterioration of an electrode and can hold performance of the electrode for a long period of time by protecting the end portion of the electrode.SOLUTION: An electrolysis electrode 1 comprises: a conductive substrate 2 composed of a valve metal; a catalyst layer 3 having a chlorine activity by electrolysis; and a protective layer 5. The catalyst layer 3 is arranged on the surface of the conductive substrate 2. The protective layer 5 is arranged on the surface of the electrode end face 6 and on the surface of the protective layer 5 of the range between the end of the conductive substrate 2 and a distance D1. The ratio between the distance D1 and the thickness D2 of the conductive substrate 2 is D1/D2=1.0-5.0.SELECTED DRAWING: Figure 2

Description

The present invention relates to an electrode for electrolysis that produces a component that contributes to sterilization and deodorization using hypochlorous acid or the like by an electrolytic reaction via an electrolyte.

Conventionally, by applying an electric current between the electrodes for electrolysis, an electrolyte such as tap water is electrolyzed to generate various electrolyzed water, and the electrolyzed water is used to float bacteria, viruses, and odors in the air. An air purification device that removes substances and the like has been proposed (see, for example, Patent Document 1).

Further, the above-mentioned air purification device is provided with an electrode for electrolysis that produces an active ingredient by electrolysis. The electrode for an electrode via an electrolyte generally has a structure in which a catalyst layer is laminated on a conductive base material (see, for example, Patent Document 2).

The electrode for electrolysis has a catalyst layer laminated on the surface of a conductive base material to form a relatively uniform catalyst layer, which can cause an electrolytic reaction to generate an active ingredient against bacteria, viruses, odorous substances, and the like. ..

Japanese Unexamined Patent Publication No. 2002-181358 JP-A-2019-119930

In such a conventional electrode for electrolysis, deterioration of the electrode due to local elution of the catalyst layer may hinder long-term use.

Therefore, an object of the present invention is to provide an electrode for electrolysis with less local elution of the catalyst layer.

Then, in order to achieve this purpose, an investigation and analysis of the electrode for electrolysis was carried out, and it was found that cracks were generated in the catalyst layer. Further, it was found that a large amount of bubbles due to the electrochemical reaction are likely to be generated in the catalyst layer around the crack, and in particular, it is highly likely that the catalyst layer is peeled off from the crack at the end of the electrode for electrolysis.

Focusing on the electrode manufacturing process, it is presumed that in many cases, the electrode is die-cut after the catalyst layer is applied, and cracks are likely to occur at the end portion from the viewpoint of manufacturing cost.

When a large-sized electrode coated with a catalyst layer is die-cut into a predetermined shape, physical stress is likely to be applied to the end of the electrode, so that the catalyst layer is affected by the stress, and the end of the electrode is affected. Relatively large cracks occur from the initial stage of production. Further, even when the catalyst layer is applied after the electrode is die-cut, thermal stress is applied during firing of the catalyst layer due to the influence of cracks generated in the conductive base material, and cracks are generated in the catalyst layer.

When the electrolyte enters the cracks at the ends, a large amount of bubbles are likely to be generated due to the electrochemical reaction, and the cracks at the ends induce peeling of the catalyst layer. If the catalyst layer is peeled off at the end portion, the conductive base material is exposed at the peeled portion, so that the current concentrates on the peeled portion and the deterioration is accelerated, and the deterioration progresses from the electrode end portion to the electrode center portion. I will do it.

In the crack region at the end of the electrode, the ratio _{of the distance D 1} from the end of the electrode, which is the end of the conductive base material, to the thickness D _{2 of the conductive base material is D 1} / D ₂ = 1.0 to 5. It has also been revealed that they are concentrated in the D ₁ region of 0.

Therefore, the electrode for electrolysis according to the present invention is an electrode for electrolysis provided with a plate-shaped conductive base material made of valve metal, a catalyst layer having chlorine activity by electrolysis, and a protective layer, and the catalyst layer. Is arranged on the surface of the conductive base material, and the protective layer is arranged on the surface of the protective layer within a range of a _{distance D 1 from the electrode end face and the end portion of the conductive base material, and the distance D 1} is. The ratio is D ₁ / D _{2 = 1.0 to 5.0 with respect to the thickness D 2} of the conductive substrate, thereby achieving the intended purpose. is there.

According to the present invention, the electrode for electrolysis is an electrode for electrolysis including a plate-shaped conductive base material made of valve metal, a catalyst layer having chlorine activity by electrolysis, and a protective layer, and the catalyst layer. is disposed on the surface of the conductive substrate, wherein the protective layer is arranged in a range from the end portion of the electrode end surface and the electrically conductive substrate of the distance D ₁ to the surface of the protective layer, the distance D ₁ is The ratio is D ₁ / D _{2 = 1.0 to 5.0 with respect to the thickness D 2} of the conductive base material, and the protective layer is the end of the electrode for electrolysis. By covering the crack portion existing in the portion, it is possible to suppress the electrolyte from entering the crack portion and suppress the activity of the surface of the catalyst layer and the crack portion at the end portion. That is, the presence of the protective layer alleviates the concentration of electrolysis on the end portion, suppresses the progress of peeling from the end portion, elutes the protective layer, and the catalyst layer at the end portion is the outermost surface of the electrode. In the central portion of the electrode other than the end portion, the effect of peeling from the end portion can be removed, and only deterioration is caused by elution of the pure catalyst layer, so that improvement in electrode life can be expected.

That is, it is possible to provide an electrode for electrolysis with less local elution of the catalyst layer.

Schematic diagram of the electrode for electrolysis (single-sided electrode) according to the first embodiment of the present invention ((a) plan view, (b) cross-sectional view) A diagram showing the deterioration status of the electrode for electrolysis according to the first embodiment of the present invention ((a) a diagram showing an initial stage of manufacturing when there is no protective layer, (b) a diagram showing a middle stage of use when there is no protective layer, (C) A diagram showing the final stage of use when there is no protective layer, (d) a diagram showing the initial stage of production when there is a protective layer, (e) a diagram showing the middle stage of use when there is a protective layer, (f). ) Figure showing the final stage of use when there is a protective layer) Sectional drawing of electrode (double-sided electrode) for electrolysis of Embodiment 1 of this invention

The electrode for electrolysis according to claim 1 of the present invention is an electrode for electrolysis including a plate-shaped conductive base material made of valve metal, a catalyst layer having chlorine activity by electrolysis, and a protective layer. The catalyst layer is arranged on the surface of the conductive base material, and the protective layer is arranged on the surface of the protective layer within a range of a _{distance D 1 from the electrode end face and the end portion of the conductive base material, and the distance D. Reference numeral 1} denotes a ratio of D ₁ / D ₂ = 1.0 to 5.0 with _{respect to the thickness D 2} of the conductive substrate.

Thereby, in the region where cracks are likely to occur, the cracks at the end of the electrode can be filled by laminating the protective layer from the upper part of the catalyst layer. That is, the conductive base material can be made into a structure that does not come into contact with the electrolyte, and local electrolytic concentration can be avoided.

Further, in the electrode for electrolysis according to claim 2, the protective layer is composed of a platinum component and has a thickness of 50 nm or less.

As a result, since the platinum component having high chemical stability is used, it is strong against polarity reversal of the electrode and elution to the electrolyte is less likely to occur. In particular, when the thickness is 50 nm or less, electric field concentration does not occur near the boundary between the protective layer and the catalyst layer in the center of the electrode, and a uniform line of electric force can be formed between the electrode electrodes.

Hereinafter, embodiments of the electrode for electrolysis in the present invention will be described with reference to the drawings. The contents described below are merely examples of implementation, and are not limited thereto.

(Premise example)
In this embodiment, an example of electrolysis using an electrode for electrolysis is shown. Hypochlorite water will be described as an example of electrolyzed water generated by electrolysis.

As the electrolyzed water generation mechanism in the present embodiment, when an electrolyte in which sodium chloride is dissolved in tap water is used and an electrolytic cell having no diaphragm is used, the electrolysis reaction of the electrodes is as follows.
(anode)
2H ₂ O → O ₂ ↑ + 2H ⁺ + 2e ⁻
2Cl ⁻ → Cl ₂ + 2e ⁻
Cl ₂ → H ₂ O ⇔ HClO + HCl
(cathode)
2H ₂ O + 2e ⁻ → H ₂ ↑ + 2OH ⁻
Na ⁺ + OH ⁻ → NaOH
Cl ₂ + 2 NaOH → 2 NaClO + H ₂
On the surface of the anode, electrons are deprived of water molecules and chloride ions to form oxygen gas and chlorine gas, respectively. Of these, chlorine gas rapidly reacts with water to produce hypochlorous acid.

On the other hand, at the cathode, water molecules receive electrons and hydrogen gas is generated.

The electrode for electrolysis of the present embodiment can realize that the electrode end portion of the catalyst layer having high chlorine activity is covered with a protective layer to maintain high electrolysis performance for a long period of time.

The configuration will be described below.

(Embodiment 1)
As shown in FIGS. 1 (a) and 1 (b), the electrode 1 for electrolysis shown in the first embodiment has, for example, a rectangular shape, and the catalyst layer 3 is formed on the surface of the plate-shaped conductive base material 2. It has. In the region where the ratio _{of the distance D 1} from the electrode end 4 which is the end of the conductive base material 2 to the thickness D _{2 of the conductive base material 2 is D 1} / D ₂ = 1.0 to 5.0. , The protective layer 5 is laminated from the upper part of the catalyst layer 3. The protective layer 5 preferably covers not only the front surface of the catalyst layer 3 but also the electrode end surface 6 which is the cut surface of the conductive base material 2 or the back surface of the conductive base material 2, and the back surface of the conductive base material 2 It may cover the whole.

Examples of the material forming the conductive base material 2 include simple substances of titanium, iron, copper, niobium, and tantalum, or alloys thereof. Titanium or a titanium alloy is particularly preferable in consideration of ease of processing at the time of manufacturing and manufacturing cost. It is preferable that the conductive base material 2 is a valve metal that is difficult to take in elements and compounds other than oxygen even in a state where an oxide film is formed on the surface and is in contact with the electrolyte and the catalyst layer 3. In addition, the material should be selected with the expectation that the adhesion to the catalyst layer 3 will be improved.

For the conductive base material 2, it is preferable to adjust the roughness of the base material surface in advance before applying the catalyst layer 3. As a result, it is expected that the contact establishment between the electrolysis electrode 1 and the electrolyte will be improved and the adhesion between the conductive base material 2 and the catalyst layer 3 will be improved. The roughness adjustment of the surface of the base material includes, and is not particularly limited, a method of etching a chemical solution such as oxalic acid or hydrochloric acid, a method of blasting, and the like.

The shape of the conductive base material 2 is not particularly limited, and should be a shape suitable for the usage environment. For example, a flat plate, a curved plate, a perforated plate and the like can be mentioned.

The material forming the catalyst layer 3 may be in any metal state such as metal, alloy, metal oxide, etc. For example, Pt, Ir, Pb, Au, Ni, Cu, Ag, Fe, Pd, Ru, Examples include carbon, and there is no problem with metal oxides or mixtures of the above materials.

The thickness of the catalyst layer 3 is preferably 50 nm to 2000 nm, more preferably 50 nm to 500 nm. If the thickness of the catalyst layer 3 becomes too thick than necessary, a large number of cracks are likely to occur in the entire area of the catalyst layer 3, and the deterioration of the electrode performance may be accelerated.

The method for forming the catalyst layer 3 on the conductive substrate 2 includes, but is not limited to, a coating firing method, a plating method, a sputtering method, and a CVD method.

For example, a coating firing method will be described. The solvent in which the above-mentioned noble metal compound is dispersed is applied onto the conductive base material 2. The coating method includes brush coating, dipping, spraying, and the like, and is not limited. After coating, the catalyst layer 3 is fixed on the conductive base material 2 by a drying treatment at a relatively low temperature of about 25 ° C. to about 250 ° C. After that, the catalyst layer 3 can be supported by firing in a general firing furnace such as an electric furnace in a temperature range of about 450 ° C. to about 700 ° C., preferably about 500 ° C. to about 650 ° C. The above steps can be repeated until the required thickness of the catalyst layer 3 is reached. Further, the firing atmosphere may be any of an atmospheric atmosphere, a reducing atmosphere, and a vacuum atmosphere.

Further, as shown in FIG. 3, the catalyst layer 3 may be supported on both surfaces of the conductive base material 2 depending on the usage conditions of the electrode 1 for electrolysis.

The material for forming the protective layer 5 is a platinum component, and after the catalyst layer 3 is formed, the protective layer 5 is fixed and dried in a region of 2500 μm from the electrode end portion 4 by a method such as brush coating, dipping, or spraying. Then, it is baked by firing to support the protective layer 5.

Further, in the protective layer 5, the ratio _{of the distance D 1} from the electrode end 4 which is the end of the conductive base material 2 to the thickness D _{2 of the conductive base material 2 is D 1} / D ₂ = 1.0 to In the region of 5.0, it is preferable that not only the catalyst layer 3 is laminated from the upper surface but also the electrode end surface 6 where each layer is exposed is protected. Further, when the catalyst layer 3 is supported on both sides of the conductive base material 2, the protective layer 5 is also supported on both sides in the same region.

The thickness of the protective layer 5 is preferably 50 nm or less. When the thickness of the protective layer 5 is thicker than 50 nm, the electric field tends to concentrate on the boundary portion 9 between the protective layer 5 and the catalyst layer 3, and the deterioration of the electrode may progress from that point.

In the electrode 1 for electrolysis, as the energization time, that is, the electrolysis time elapses, the noble metal forming the catalyst layer 3 elutes into the electrolyte due to the redox action of the noble metal due to the coordination of chloride ions and the polarity inversion, and the electrode deteriorates. Goes on.

In the vicinity of the crack 7 of the electrode end 4 generated during manufacturing, the conductive base material 2 is exposed, and the activity is increased due to the concentration of the electric field and the permeation of the electrolyte into the crack 7, and bubbles are generated. As a result, the peeling of the catalyst layer 3 is promoted, and the disappearance of the catalyst layer proceeds from the electrode end portion 4 to the electrode center portion 8.

The process of electrode deterioration will be described below by comparing the case where the protective layer 5 with platinum is present and the case where the protective layer 5 is not provided.

2 (a), (b), and (c) show the case where the protective layer 5 is not present, and FIGS. 2 (d), (e), and (f) show the case where the protective layer 5 is present.

First, the middle stage of use is compared with reference to FIGS. 2 (b) and 2 (e).

When the protective layer 5 is not provided, the catalyst layer 3 is peeled and deteriorated from the crack 7 at the electrode end portion 4, and electric field concentration is generated at the electrode end portion 4. Along with this phenomenon, the deterioration of the catalyst layer 3 tends to proceed from the electrode end portion 4 to the electrode center portion 8.

On the other hand, when the protective layer 5 is provided, the thickness of the catalyst layer 3 at the central portion 8 of the electrode is reduced based on a normal deterioration factor, as in the case where the protective layer 5 is not provided. However, at the electrode end 4 where the protective layer 5 is located, only the elution of the platinum protective layer 5 which is resistant to polarity reversal has progressed, and the catalyst layer 3 of the electrode end 4 remains in a state where the thickness is maintained. That is, peeling deterioration can be suppressed while maintaining the activity of the electrode end portion 4.

Next, the final stages of use are compared with reference to FIGS. 2 (c) and 2 (f).

When the protective layer 5 is not provided, the thickness of the catalyst layer 3 in the central portion 8 of the electrode is reduced due to a normal deterioration factor, and the peeling deterioration from the electrode end portion 4 progresses, so that the exposure ratio of the conductive base material 2 is increased. Increases, and the power supply becomes abnormal, making it unusable.

On the other hand, when the protective layer 5 is present, the catalyst layer 3 in the central portion 8 of the electrode is deteriorated in the same manner as when the protective layer 5 is not present, but at the electrode end portion 4, although the protective layer 5 is eluted, the electrode end portion 4 The catalyst layer 3 remains in the water, and the activity is maintained. That is, when the protective layer 5 is provided, the catalyst layer 3 can be maintained for a long period of time, and an improvement in the electrode life can be expected.

That is, according to the above configuration, when electrolyzed water is generated by electrolysis of the electrode for electric field, conventionally, cracks existing at the end of the electrode for electrolysis are the starting points, and the peeling deterioration of the catalyst layer progresses. However, in the present invention, by covering the crack at the electrode end with a protective layer, peeling deterioration from the electrode end can be suppressed. That is, since the progress of deterioration from the electrode end can be suppressed, the catalyst layer remains in the electrode center and the electrode end even at the end of the electrode use, and the electrode performance is maintained for a long period of time. It is possible to continue to do so.

As described above, the electrode for electrolysis in the present invention can maximize the activity of the catalyst layer while suppressing the deterioration of the electrode by utilizing the protective action of the platinum component, so that sterilization, deodorization, etc. can be performed. It can be used as an electrode for electrolysis provided in a target air purification device.

1 Electrode for electrolysis 2 Conductive base material 3 Catalyst layer 4 Electrode end 5 Protective layer 6 Electrode end face 7 Crack 8 Electrode center 9 Boundary

Claims (2)

It is an electrode for electrolysis including a plate-shaped conductive base material made of valve metal, a catalyst layer having chlorine activity by electrolysis, and a protective layer, and the catalyst layer is arranged on the surface of the conductive base material. ,
The protective layer is disposed on a surface of the protective layer in a range from the end portion of the electrode end surface and the electrically conductive substrate of the distance D _1,
The electrode for electrolysis, wherein the distance D ₁ has a ratio of D ₁ / D ₂ = 1.0 to 5.0 with _{respect to the thickness D 2} of the conductive base material. The electrode for electrolysis according to claim 1, wherein the protective layer is composed of a platinum component and has a thickness of 50 nm or less.

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