JPH0417689A - Electrode for electrolyzing water and production thereof - Google Patents

Abstract

PURPOSE:To produce an electrode for electrolyzing water wherein ozone is generated without deteriorating current efficiency by utilizing an electrode base body as an anode and utilizing a soln. contg. lead component suspended with fluororesin contg. sulfone group as an electrolyte and performing electrolysis. CONSTITUTION:After activating the surface of an electrode base body such as porous and corrosion resistant titanium, a conductive interlayer is preferably formed. This interlayer is obtained by applying the surface of the electrode base body with liquid contg. a compd. having a component for forming the interlayer and thermally decomposing it. The electrode base body which has this interlayer or has not it is utilized as an anode. An aq. soln. such as lead nitrate which has lead component suspended with fluororesin contg. sulfone group is utilized as an electrolyte and electrolysis is performed. Thereby PbO2 layer having fluororesin contg. sulfone group is preferably formed via the interlayer on the surface of the electrode base body. This PbO2 layer is preferably constituted of a two-layer structure which is formed of both an alpha-PbO2 layer on the electrode base body and a beta-PbO2 layer impregnated with the resin and positioned on the alpha-PbO2 layer. Thereby the electrode for electrolyzing water is obtained wherein reaction for uniformly generating ozone is performed as a whole with high current efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electrode for producing ozone gas or ozone-containing water, which can be used for disinfection, water treatment, cleaning, etc., by an electrolytic method, and a method for producing the same.

(Prior art and its problems) Hydrogen and oxygen (and ozone) have been obtained by electrolyzing water for a long time. manufacture,
Conventionally, ozone has been used for sterilization and the like.

In the production of ozone through water electrolysis, attention has been focused on how to reduce the electricity consumption rate and how to manufacture the electrodes used at low cost to achieve efficient electrolysis. A so-called ion exchange membrane made of a fluororesin having A solid electrolyte electrolysis method is used.In this electrolysis method, electrolysis is generally performed with the electrode close to or in close contact with the diaphragm.
Since the sulfone groups and fluorine compounds (fluorine resins) in the diaphragm function as cocatalysts, it is only the electrode material near the sulfone groups, that is, near the ion exchange membrane, such as lead dioxide, that mainly contributes to electrolysis. It is thought that.

Of course, if the electrolyte is of sufficiently high purity and the conductivity is about 1 μS/C or less, the electrode material other than the part that is in contact with the ion exchange membrane will come into contact with the ion exchange membrane through an insulator. Since it does not contribute to electrolysis, no particular problem arises unless the electrode material is relatively expensive and it is not possible to reduce the cost of manufacturing the electrode. However, the conductivity of the liquid that comes into contact with the ion exchange membrane usually increases to 10 μS/cm or more due to carbon dioxide in the liquid and eluates from the electrodes, so electrolysis occurs even in areas other than those that do not directly contact the ion exchange membrane.

Since this part of the electrolysis is performed in the absence of a catalyst, there is a problem in that the ozone generation efficiency is reduced and the overall current efficiency is reduced.

For example, in Japanese Unexamined Patent Publication No. 1983-100190, two anodes are used.
An electrode structure has been disclosed in which an electrode material is present only in the layer that contacts the ion exchange membrane (solid electrolyte) to improve current efficiency, but this electrode structure substantially limits the electrode area. There are problems in that the actual current density increases, which may shorten the life span, and the structure becomes complicated.Currently, no solution to this problem has been found yet.

(Objective of the Invention) Therefore, an object of the present invention is to provide an electrode for water electrolysis and a method for manufacturing the same, which can maintain the current efficiency of ozone generation substantially constant without reducing the effective electrode area.

(Means for Solving the Problems) An electrode for water electrolysis according to the present invention includes an electrode base and a lead dioxide layer having a fluororesin containing a sulfone group formed on the surface of the electrode base. A conductive intermediate layer may be formed between the electrode base and the lead dioxide layer. In addition, the method for producing an electrode for water electrolysis according to the present invention is to conduct electrolysis using an electrode substrate as an anode and a solution containing a sulfone group and a lead component in which a fluororesin is suspended as an electrolyte, thereby forming a sulfone group on the surface of the substrate. 1. A method for producing an electrode for water electrolysis, comprising forming a lead dioxide layer having a fluororesin containing: a conductive intermediate layer by a pyrolysis method on the electrode substrate before electrolytically coating the lead dioxide layer. may be formed.

The present invention will be explained in detail below.

The present invention uses normal solid electrolysis in a lead dioxide layer that functions as an electrode material for ozone production in an electrode for water electrolysis.
A fluororesin having a sulfone group that functions as a cocatalyst in the (ion exchange membrane) is added. As a result, in conventional water electrolysis, only the electrode material in contact with the solid electrolyte effectively functions to generate ozone, whereas in the water electrolysis electrode according to the present invention, the electrode material does not come into contact with the solid electrolyte. Since it can come into contact with the fluororesin having a sulfone group that functions as a cocatalyst for ozone generation regardless of its presence or absence, the current density can be made uniform and a decrease in current efficiency can be suppressed.

The shape of the electrode substrate of the present invention is not particularly limited as long as it is in close contact with the solid electrolyte to allow a uniform current to flow therethrough and the generated oxygen gas and ozone gas can be taken out behind it, but it usually allows good gas release. It is desirable that the porous material has through holes as small as 50 to 300 μm. The material of the electrode substrate is not particularly limited as long as it is conductive and resistant to ozone gas and ozone-containing water, but examples include metals and alloys such as titanium and titanium alloys, or titanium oxide sintered bodies and carbon sintered bodies. It is preferable to use ceramics such as

The substrate may be used as it is to cover the intermediate layer or lead dioxide layer described later, but if the surface is activated by pretreatment, the intermediate layer or lead dioxide layer can be coated firmly. . This pretreatment method includes expanding the surface area by blasting, roughening the surface, activating the surface by pickling, and cleaning the surface by generating hydrogen gas from the substrate surface through cathodic polarization in an electrolytic solution such as an aqueous sulfuric acid solution. There is also a method of activation using a hydride partially generated by the hydrogen gas.

A lead dioxide layer may be formed directly on this electrode substrate, but
An intermediate layer can also be provided to prevent passivation. This intermediate layer may be made of a material such as platinum that is conductive itself and can act as an electrode catalyst, but if the intermediate layer is exposed, electrolysis will occur and the current efficiency will be reduced. It is desirable that the intermediate layer be formed of a substance that does not have the function of an electrode catalyst or has a weak function. As the material forming the intermediate layer, for example, a material in which platinum is dispersed in a composite oxide of titanium and tantalum in a molar ratio of about X can be used. To coat this material on the electrode substrate, for example, a predetermined amount of chloroplatinic acid is dissolved in a dilute hydrochloric acid aqueous solution of titanium chloride and tantalum chloride to prepare a coating solution, and the coating solution is applied to the surface of the electrode substrate and dried. , pyrolyzed by firing at 450 to 600°C, and this operation may be repeated multiple times if necessary. The intermediate layer thus obtained is a mixture of rutile-type crystals of titanium-tantalum oxide and metallic platinum, and even if electrolysis is performed using this as an anode, its potential is much higher than that of lead dioxide; It cannot be used for electrolysis with a current density of about dm2. However, the electrical resistance of the intermediate layer is 10-2 to 10-
It has a resistance of about 3 Ωcm, making it ideal for current-carrying purposes.

The electrode substrate with or without the intermediate layer is then coated with a lead dioxide layer.

The lead dioxide that forms this lead dioxide layer includes α-lead dioxide and β-lead dioxide.Although β-lead dioxide, which is highly active as an electrode material, may be directly coated, the β-lead dioxide layer may be uniformly coated on the entire surface. To form the lead dioxide layer, it is desirable to first coat an α-lead dioxide layer and then coat the β-lead dioxide layer thereon.

To coat the α-lead dioxide layer on the electrode substrate, use the substrate as an anode, and use a solution of lead oxide (PbO) dissolved in a 25% sodium hydroxide aqueous solution to saturation as an electrolyte. Electrodeposition can be carried out by electrolysis at ~60°C with a relatively low current density of about 2A/d+n2, and the thickness of this α-lead dioxide layer is preferably 5 to 100μ, just enough to cover the surface.
The optimum value is about m.

Next, a preferably β-type lead dioxide layer containing a sulfone group-containing fluororesin is directly coated on this α-lead dioxide layer or on the electrode substrate with or without the aforementioned intermediate layer.

The fluororesin is not particularly limited as long as it contains a sulfonic group, but it is desirable to use a perfluorosulfonic acid-based ion exchange resin that has high resistance to ozone and the like.

It is desirable that the lead dioxide layer be coated by electrodeposition, and electrodeposition can be carried out using an aqueous solution of a lead compound in which the fluororesin is suspended as an electrolyte. Typical conditions for forming β-lead dioxide by electrodeposition are as follows: 200 to 800 g/j2 of lead nitrate aqueous solution in which 1 to 10% of fluorine resin containing sulfonic groups is suspended is used as the electrolyte, and the temperature is 40 to 80°C. 0.1-1 at temperature
Electrolysis is performed at a current density of about 0 A/dm2 using the substrate as an anode. The thickness of the lead dioxide layer impregnated with this fluororesin may be appropriately selected by adjusting the electrolytic conditions, but it is usually 30 to 300 μm, and this thickness is sufficient for ozone generation.

Under these conditions, it is possible to impregnate lead dioxide with about 0.5 to 5 percent of fluororesin. Since this fluororesin is almost uniformly dispersed throughout the lead dioxide, there is also the secondary effect that electrodeposition distortion, which is always a problem with lead dioxide coatings, is virtually eliminated.

The lead dioxide electrode produced in this manner is pressed against, for example, a perfluorosulfonic acid-based ion exchange membrane that is a solid electrolyte, and electrolysis is performed while supplying ion exchange water. According to this electrolysis, the current efficiency of ozone generation can be maintained at about 13% or more even if the conductivity of ion-exchanged water becomes 10 to 100 μS/cm, whereas carbon dioxide, which does not have a fluororesin containing sulfone groups, can maintain the current efficiency of ozone generation at about 13% or more. Electrodes made of lead layers can generally achieve a current efficiency of only about 10% or less, and the electrode for water electrolysis according to the present invention can generate ozone in a much more stable state than conventional electrodes. .

(Examples) The present invention will be described in detail below, but the examples are not intended to limit the present invention.

Fruit size: 40~ made by sintering and solidifying titanium fibers with a thickness of 2mm
A porous filter of 200 μm is used as a base, and the base is rotated at an angle of 90°.
After pickling in 20% sulfuric acid of C, a solution containing 10% dilute hydrochloric acid of chloride of each metal, consisting of 60 mol% titanium, 15 mol% tantalum, and 25 mol% platinum, was applied to the surface and dried. The material was pyrolyzed at 510°C for 10 minutes in a Matsufuru furnace with air flowing through it. This operation was repeated five times to form an intermediate layer. An interlayer consisting of rutile-type titanium-tantalum oxide and platinum metal was formed.

25 g/f of lead oxide (Pb0) was dissolved in a 25% aqueous sodium hydroxide solution as an electrolyte.
Using the substrate as an anode, electrolysis was performed at a current density of 0.2 A/dm2 for 1 hour to form a thin layer of α-lead dioxide on the substrate.

Furthermore, a solution prepared by adding 2% of commercially available Nafion (trade name) solution to an 800 g/1 lead nitrate aqueous solution was used as an electrolyte.
Using the above substrate as an anode, electrolysis was carried out for 2 hours at a current density of IA/dI of 11" and a liquid temperature of 65°C.The apparent current efficiency was 85.
%, on the surface of the substrate, β containing about 3% Nafion in the layer.
- A layer of lead dioxide was formed. A thin layer of α-lead dioxide was formed on the substrate to form an electrode for water electrolysis.

The electrode on which this lead dioxide layer was formed was brought into contact with a perfluorosulfonic acid-based ion exchange membrane Nafion 117 to serve as an anode, and the electrode was heated at 100 A/dm2 while adding ion exchange water.
Ozone-containing gas was produced by water electrolysis at a current density of . After 24 hours of preliminary electrolysis, electrolysis was continued without exchanging the ion-exchanged water, and the initial current efficiency for ozone generation was 14.5%, and the current efficiency after 10 hours was 13%.

At this time, the conductivity of ion exchange water on the anode side is 50 uS/a
It was n.

An electrode was manufactured in which no fluorine-containing resin was contained in the β-lead dioxide layer formed without adding Nafion liquid to the electrolyte during the formation of the lead dioxide layer, and the electrode was subjected to the same conditions as in Example 1. When used as an anode in the production of ozone-containing gas, the initial current efficiency for ozone generation was 14%, but after 10 hours the current efficiency decreased to 9%, and the conductivity of ion-exchanged water decreased by 50%.
It became μS/cm. When the ion exchange water was replaced, the current efficiency recovered to 13.5%.

Example 1 A porous sintered body made of titanium oxide in the Magneli phase was used as a substrate, and an α-lead dioxide layer and then a fluororesin were impregnated on the substrate under the same conditions as in Example 1 without forming an intermediate layer. A β-lead dioxide layer was formed and used as an electrode.

This electrode is attached as an anode of an electrolytic layer using Nafion 117 as a solid electrolyte in close contact with the solid electrolyte (100).
Ozone-containing gas was produced by electrolysis of pure water with a conductivity of 10 uS/cm at a current density of A/dm2. The current efficiency during preliminary electrolysis for 24 hours was 13.8%, and the current efficiency rose to 14.2% after one week.

(Effects of the Invention) The electrode for water electrolysis according to the present invention comprises an electrode base and a lead dioxide layer impregnated with a fluororesin containing a sulfone group formed on the surface of the electrode base. Claim 1) Or an electrode for water electrolysis (Claim 3) in which a conductive intermediate layer is formed between the electrode base and the lead dioxide layer.

Therefore, in the electrode of the present invention, since a fluororesin containing a sulfone group having a promoter function is present in the lead dioxide layer having an electrode function, water electrolysis is performed by bringing the electrode into close contact with an ion exchange membrane, which is a solid electrolyte. In this case, the lead dioxide in the lead dioxide layer that is not in contact with the fluororesin containing sulfone groups in the solid electrolyte also comes into contact with the fluororesin containing similar sulfone groups in the lead dioxide layer, and the ozone generation reaction is promoted. . Therefore, even if the electrolytic solution has high conductivity, the ozone generation reaction occurs uniformly over almost the entire lead dioxide layer without reducing the effective electrode area, and the current efficiency of ozone generation can be maintained at a high level. Furthermore, if a conductive intermediate layer is formed between the electrode base and the lead dioxide layer, passivation of the electrode base is prevented and a sufficient amount of current is ensured.

The lead dioxide layer of the electrode for water electrolysis according to the present invention preferably has a 2N structure of an α-lead dioxide layer and a β-lead dioxide layer having a fluororesin containing a sulfone group (Claim 2), and is configured in this way. By doing so, the entire surface of the electrode substrate can be uniformly coated with a β-lead dioxide layer having a high function as an electrode catalyst.

Further, it is preferable that the conductive intermediate layer is formed as a layer in which platinum is dispersed in a composite oxide of titanium and tantalum (claim 4), and such an intermediate layer has a weak function as an electrode catalyst and a conductive layer. is high, it is possible to prevent passivation and ensure a sufficient amount of current without inhibiting ozone generation by the lead dioxide layer.

Furthermore, in the method for producing an electrode for water electrolysis according to the present invention, an electrolytic method is used when coating the lead dioxide layer impregnated with the fluororesin containing a sulfone group, and a conductive intermediate layer is formed. In this case, the intermediate layer is coated by a pyrolysis method, and a lead dioxide layer is further formed by the electrolytic method (claim 6).
That's what I do. Therefore, in the water electrolysis electrode manufactured by the method of the present invention, as described above, the ozone generation reaction occurs uniformly over almost the entire lead dioxide layer, and the current efficiency of ozone generation can be maintained at a high level, and the electrode has an intermediate layer. A sufficient amount of current is ensured at the electrodes.

Claims (6)

[Claims] (1) An electrode for water electrolysis comprising an electrode base and a lead dioxide layer having a fluororesin containing sulfone groups formed on the surface of the electrode base. (2) A claim in which the lead dioxide consists of an α-lead dioxide layer formed on the electrode base and a β-lead dioxide layer impregnated with a fluororesin containing a sulfone group formed on the α-lead dioxide layer. 1. The water electrolysis electrode according to 1. (3) For water electrolysis, comprising an electrode base, a conductive intermediate layer formed on the surface of the electrode base, and a lead dioxide layer having a fluororesin containing a sulfone group formed on the surface of the conductive intermediate layer. electrode. (4) The electrode for water electrolysis according to claim 3, wherein the conductive intermediate layer is a layer in which platinum is dispersed in a composite oxide of titanium and tantalum. (5) Using the electrode substrate as an anode, electrolysis is performed using a solution containing a lead component in which a fluororesin containing a sulfone group is suspended as an electrolyte, and a lead dioxide layer having a fluororesin containing a sulfone group is formed on the surface of the substrate. A method for producing an electrode for water electrolysis, comprising: (6) Forming an intermediate layer on the substrate by applying a coating liquid containing a compound of an intermediate layer forming component to the surface of the electrode substrate and thermally decomposing the coating liquid, and removing the substrate on which the intermediate layer is formed. The method comprises forming a lead dioxide layer having a fluororesin containing a sulfone group on the intermediate layer by performing electrolysis using a solution containing a lead component in which a fluororesin containing a sulfone group is suspended as an anode as an electrolyte. A method for manufacturing an electrode for water electrolysis.