JP2004360067A - Electrode for electrolysis, and its production method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode for electrolysis which contains an intermediate layer more excellent in peeling resistance and corrosion resistance than the conventional electrode for electrolysis, has an electrolysis life longer than that of the same and causes a large electric current at an industrial level to flow, and to provide its production method. <P>SOLUTION: The electrode for electrolysis is obtained by coating the surface of a high temperature oxide film for a valve metal or valve metal alloy electrode substrate 1 whose surface is oxidized to form the high temperature oxide film 2, with an electrode catalyst 3. The high temperature oxide film is integrated with the electrode substrate to improve its peeling resistance. Further, by the heating of the high temperature oxide film together with the electrode catalyst, the non-electronic conductivity of the intermediate layer is reformed into electronic conductivity, so that the large electric current can be caused to flow. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an electrode for electrolysis used for various industrial electrolysis and a method for producing the same, and more particularly, to oxygen generation used in industrial electrolysis such as production of electrolytic copper foil, power supply in aluminum liquid, production of continuous electrogalvanized steel sheet, and the like. The present invention relates to an anode for use and a method for producing the same.

  In recent years, in industrial electrolysis such as electrolytic copper foil, power supply in an aluminum solution, and continuous electrogalvanized steel sheet, an anode obtained by coating a metal titanium substrate mainly with iridium oxide as an electrode catalyst has come into wide use. However, the anode for chlorine generation, which is mainly used in salt electrolysis and mainly uses ruthenium oxide as an electrode catalyst, is closely related to the purity of chlorine and caustic soda products. However, in the above-mentioned industrial electrolysis, which produces a value-added product mainly at the cathode, organic substances and impurity elements are added for the purpose of stabilizing the product. For this reason, various electrochemical reactions and chemical reactions occur near the anode where oxygen is generated without a diaphragm, and the consumption of the electrode catalyst due to an increase in the hydrogen ion concentration (pH decrease) accompanying the oxygen generation reaction is reduced. It will be even faster.

Also, while ruthenium oxide electrocatalysts commonly used for chlorine generation can use up to about 90% of the supported catalyst amount, iridium oxide electrocatalysts often used for oxygen generation can only use up to about 50%. In many cases, the electrode potential rises and electrolysis becomes impossible.
The increase in the potential of the oxygen generating electrode is started by the above-described consumption of the electrode catalyst and the corrosion of the electrode substrate due to a common cause. Further, it is considered that current concentration on the remaining electrode catalyst is added due to partial internal consumption and peeling of the electrode catalyst, and the current proceeds in a chained and accelerated manner.

In order to suppress the corrosion and dissolution of the electrode substrate and the accompanying peeling of the effective electrode catalyst from the electrode substrate, many methods have been adopted mainly for providing an intermediate layer between the titanium substrate and the electrode catalyst layer.
Usually, the electrode activity of the intermediate layer is selected to be lower than that of the electrode catalyst layer.Either type has electron conductivity, and by keeping the electrode substrate away from the corrosive electrolytic solution and the oxygen generation site that causes a decrease in pH, It plays a role in mitigating damage to the substrate.

As an intermediate layer satisfying such conditions, Japanese Patent Publication No. Sho 60-21232 discloses that an oxide of tantalum and / or niobium is provided in a thickness of 0.001 to 1 g / m ^{2 in} terms of metal, and titanium formed on the surface of the substrate. An intermediate layer having an oxide film provided with conductivity has been proposed. Furthermore, Japanese Patent Publication No. 60-22074 proposes a valence control semiconductor in which a tantalum and / or niobium oxide is added to a titanium and / or tin oxide, all of which are widely used industrially. I have. However, in recent years, with the trend of placing importance on economic efficiency, operating conditions have become increasingly severe, and there has been a demand for electrodes having higher durability.
As a simple and practical means, there is a case where the application amount of the electrode catalyst is increased to cope with the problem, but the application amount and the electrode life are not always directly proportional. As described above, in a severe environment, deterioration proceeds near the interface between the electrode substrate and the electrode catalyst, so that not all of the increased amount of the electrode catalyst is necessarily used effectively. As a result, valuable electrode catalyst is wasted. become.
JP-A-7-90665 (Claim 4, [0025] to [0037])

In order to solve such a problem of the formation of the intermediate layer, the titanium electrode base itself is electrolytically oxidized to convert titanium on the surface of the electrode base into titanium oxide to form an intermediate layer (a titanium oxide single layer). The method is described in Patent Document 1. However, in the electrode described in Patent Document 1, sufficient corrosion resistance cannot be obtained because the intermediate layer that can be formed by electrolytic oxidation is extremely thin ([0034]). Therefore, the surface of the first titanium oxide single layer is thermally decomposed. To form a thick second titanium oxide single layer, and an electrode catalyst layer thereon. Although it is also disclosed that the first titanium oxide single layer is formed by heating in an oxygen-containing atmosphere, the second titanium oxide single layer is also formed in this case.
The method described in Patent Literature 1 requires two steps for forming the intermediate layer, in particular, a step requiring completely different facilities such as electrolysis and thermal decomposition. Therefore, the workability is poor and the burden is large economically, and sufficient practicality is required. Could not have.

  In view of the drawbacks of the prior art, the present invention provides an intermediate layer (high-temperature oxide film) that is rich in corrosion resistance, dense, can be firmly bonded to the electrode substrate, and can be manufactured in a single process, between the electrode substrate and the electrode catalyst. An object of the present invention is to provide a formed electrode for electrolysis and a method for manufacturing the same.

According to the present invention, first, a valve metal or a valve metal alloy electrode substrate, and a valve metal or a valve metal alloy electrode substrate formed on the surface by a high-temperature oxidation treatment so that the weight increase is 0.5 g / m ² or more. A high-temperature oxide film, and an electrode for electrolysis characterized by comprising an electrode catalyst layer formed on the surface of the high-temperature oxide film. A high-temperature oxide film is formed on the surface of the electrode substrate so that the weight increase is 0.5 g / m ² or more (1.25 g / m ² or more in terms of TiO ₂ ), and then an electrode catalyst layer is formed on the high-temperature oxide film Thirdly, a high-temperature oxidation treatment of a valve metal or valve metal alloy substrate to form a high-temperature oxide film on the surface of the substrate, and then forming an electrode on the high-temperature oxide film Form catalyst layer In the method for producing an electrode for electrolysis, when a high-temperature oxide film of the electrode substrate is formed on the interface between the electrode substrate and the electrode catalyst, the weight increase of the high-temperature oxide film is maintained at a heating temperature of 600 ° C. in air. A method for producing an electrode for electrolysis, characterized in that the amount of weight increase of a high-temperature oxide film of a valve metal or a valve metal alloy electrode substrate generated in one hour is not less than one hour.

Hereinafter, the present invention will be described in detail.
In the present invention, unlike the prior art, a valve metal or a valve metal alloy electrode substrate (hereinafter referred to as a “valve metal substrate” or “electrode substrate” or simply “substrate”) is formed in a single step of substantially only high-temperature oxidation in an oxidizing atmosphere. ), A high-temperature oxide film formed of an oxide of a valve metal or a valve metal alloy and functioning as an intermediate layer between the valve metal substrate and an electrode catalyst layer described later is formed.

The high-temperature oxide film obtained by high-temperature oxidation of the electrode substrate is rich in corrosion resistance, dense and firmly bonded to the electrode substrate, protecting the electrode substrate and further bonding the electrode catalyst mainly composed of oxide to oxide-oxide bonding. Should be able to be supported more reliably, but in practice, the high-temperature oxide film had a drawback that it had poor electron conductivity. When the thickness was increased, this defect became more prominent.
By baking the electrode catalyst layer on this high-temperature oxide film by a coating pyrolysis method, the present inventors have found that a high-temperature oxide film (with a weight increase of 0.5%) in a region where the effect of protecting the electrode substrate is large but the electron conductivity is poor is obtained. g / m ² or more, 1.25 g / m ² or more in terms of TiO ₂ ), resulting in an increase in electron conductivity as a result, allowing the flow of a large current at the industrial electrolysis level. It is a solution. The increase in weight is remarkable particularly effective at 0.67 g / m ² or more (1.68 g / m ² or more in terms of TiO _2), the upper limit is 17 g / m ² (about 42 g / m ² in terms of TiO ₂₎ . Above this upper limit, the film thickness becomes 10 μm or more, the oxide film turns from gray to white, and the adhesion between the oxide film and the electrode substrate deteriorates.

In other words, the high-temperature oxide film thus formed is an oxide and usually has poor electron conductivity. However, by performing a heat treatment at a high temperature of 300 ° C. or more after the formation of the high-temperature oxide film, the electron conductivity can be modified. This allows a large current at the level of industrial electrolysis to flow. This heat treatment is performed separately from the heat treatment at the time of forming the high-temperature oxide film, and can be performed simultaneously with the formation of the electrode catalyst layer, or before and after the formation. The reforming at the same time as the formation of the electrode catalyst layer means that, in the formation of the electrode catalyst layer involving heating such as a coating pyrolysis method, the reforming of the high-temperature oxide film is caused by the heating at the same time as the formation of the electrode catalyst layer. .
The high-temperature oxide film (intermediate layer) thus formed is integrated with the electrode substrate and does not peel off from the electrode substrate. Further, the high-temperature oxide film is dense and rich in corrosion resistance, and thus sufficiently protects the electrode substrate. In addition, since the electrode catalyst is formed as an oxide film, the electrode catalyst mainly composed of an oxide can be reliably supported on the electrode substrate by an oxide-oxide bond.

  As the base material in the present invention, titanium and a titanium alloy can be preferably used, but tantalum, niobium, zirconium and their alloys, which are so-called valve metals, can also be used because of the possibility of modifying the oxide film as a valve. . Titanium and titanium alloys are preferred because, besides their corrosion resistance and economy, their strength / specific gravity, that is, their specific strengths, are large and their processing such as rolling is relatively easy, and their processing techniques such as cutting have been greatly improved in recent years. It is. The shape may be a simple one in the shape of a bar or a plate, or one having a complicated shape by machining, and the surface may be smooth or porous. Here, the surface refers to a portion that can be in contact with the solution when immersed in the electrolyte.

Contaminants such as oils, cuttings, and salts on the surface of the substrate adversely affect the properties of the high-temperature oxide film, and thus it is desirable to remove as much as possible by washing in advance. For washing, water washing, alkali washing, ultrasonic washing, steam washing, scrub washing and the like can be used.
By roughening the surface by blasting or etching to increase the surface area, the bonding strength can be increased and the electrolytic current density can be substantially reduced. Etching increases the cleanliness of the surface rather than simply cleaning the surface. When blasting is performed, it is very preferable to perform etching in order to remove blast particles stuck on the surface. Etching is performed at a temperature near or at the boiling point using a non-oxidizing acid such as hydrochloric acid, sulfuric acid, oxalic acid, or a mixed acid thereof, or at about room temperature using nitric hydrofluoric acid.
As a finish, rinse with pure water and dry thoroughly. It is also possible to rinse with a large amount of tap water before using pure water.

Next, a high-temperature oxidation treatment is performed on such an electrode substrate to form a high-temperature oxide film on the surface of the electrode substrate.
The method for forming a high-temperature oxide film according to the present invention is basically not significantly different from annealing performed in air.
The heating method of the heat treatment furnace can be any of atmosphere (convection) heating, direct heating of nichrome or Kanthal wire, near-infrared lamp, far-infrared panel, radiant tube, etc., conduction heating of hot plate, etc., or electromagnetic induction heating. However, for example, the thermal conductivity of pure titanium at 600 ° C. is as small as about half that of pure iron, and in order to obtain a temperature distribution as uniform as possible, a heating method having many convection heating elements is preferable. The atmosphere may be oxidizing, and any of air, oxygen, water vapor, carbon dioxide, city gas combustion gas, and gas obtained by mixing ozone gas with an inexpensive carrier gas can be used. If hydrogen gas or an ammonia decomposition gas containing the same is mixed, titanium and titanium alloys are hydrogenated and become brittle to the deepest part. Needless to say, an inert gas such as argon or a vacuum is ineffective and unsuitable.

Next, the substrate formed into a predetermined shape and subjected to pretreatment such as cleaning is inserted into a furnace by hanging it on a hanger or placing it on a gantry. In any case, care must be taken so that the plurality of substrates are not brought into close contact with each other and the gas in contact with the substrates is renewed without interruption. If the supply of the oxidizing gas is rate-determining, the growth of the oxide film near the center of the superposed substrate surface is delayed, which is not preferable.
The substrate may be inserted into the furnace after the inside of the furnace has been heated to a predetermined temperature. However, in order to obtain a uniform temperature distribution, it is desirable to insert the base at a temperature as low as possible before raising the temperature.
After reaching a predetermined temperature, in order to obtain a high-temperature oxide film having a constant thickness, the temperature is maintained for a predetermined time and then lowered.

The thickness of the high-temperature oxide film of titanium observed in the present invention is usually 0.1 μm or more, and methods of evaluating this level of thickness include measurement of weight gain, cross-sectional observation by SEM, SIMS, GDS, X-ray diffraction, There are electron beam diffraction, ellipsometer, etc., each of which has a length and a shortness, but the measurement of the weight gain is simple and suitable.
Here, the form of the intermediate layer of the high-temperature oxide film will be described focusing on the weight increase which should be an index.
In the present invention, the value of the surface area expressed in units of mm ² , cm ² , m ^{2 and the} like means, for example, in the case of a rectangular parallelepiped having three sides a, b and c, (a × b + b × c + c × a) × 2. In other words, the surface area corresponds to the shape of the base, and in the case of a mesh or punch metal, it is approximated by a three-dimensional shape model divided into polygons and cylinders. Further, this is distinguished from the specific surface area by the BET method calculated from the adsorption amount of the monolayer gas.

Assuming that the weight increase due to high-temperature oxidation is ΔW g / m ² , O = 16.00, and Ti = 47.88, the weight W _TiO2 g / m ² of the high-temperature oxide film of titanium is converted as follows.
W _TiO2 = ΔW / (16.00 × 2) × (47.88 + 16.00 × 2)
Further, since only the TiO _{2 in the} rutile phase is detected from the identification of the crystal phase of the high-temperature oxide film of titanium by X-ray diffraction, if the density of the TiO _{2 in} the rutile phase is 4.27 g / ml, the thickness t (μm) becomes Is converted as follows.
t = w / (16.00 × 2) × (47.88 + 16.00 × 2) / 100 ² /4.27×10000

The larger the surface roughness of the substrate actual surface area is increased, thus because the greater increase in weight, the corresponding value of the thickness is thicker calculated, the oxide film is sufficient that oxygen deficiency than the stoichiometric composition of TiO ₂ It is calculated to be thinner if oxygen is dissolved in the base metal titanium. Actually, the influence of the surface roughness of the substrate is the largest, and the thickness tends to be calculated to be larger than the thickness as an actually measured value by cross-sectional observation.
In addition, the growth of a high-temperature oxide film is generally suppressed in a titanium alloy as compared with pure titanium.

The projections of the actual surface roughness by cross-section observation have a large area that receives heat radiation or gas, so the oxide film grows thickly, whereas the concave parts have a small area that receives heat radiation or gas. Therefore, the oxide film is thin. A smooth, non-roughened mirror-finished titanium substrate is not used as an actual substrate for industrial electrolysis, and the thickness of the high-temperature oxide film varies greatly depending on the surface irregularities and its shape. It is not appropriate to define it as a quantitative evaluation method.
For example, using a titanium substrate having a surface roughness Ra of 12.5 μm, a heating temperature of 600 ° C. in air, and a measured value from a cross-sectional SEM photograph when a high-temperature oxide film was formed with a holding time of 1 hour, the projections of The thickness of the thick part generally reached 0.5 to 0.7 μm, but the thickness of the thinnest part of the recess was only about 0.1 μm. The actual weight increase at this time was 0.67 g / m ² (0.067 mg / cm ² ), the TiO ₂ equivalent weight increase by the above formula was 1.67 g / m ² , and the rutile TiO ₂ thickness equivalent The value was 0.39 μm.

Several documents are known about the weight increase of the high-temperature oxide film of pure titanium in air. In one of the documents, from the rate constant of high temperature oxidation of pure titanium in air at 600 ° C. Kp = 33.46 × 10 ⁻⁴ (40 hours or less), the weight increase of the high temperature oxide film at 600 ° C. for 1 hour is: It is calculated to be 0.058 mg / cm ² (AMChaze and C. Coddet, Oxidation of Metals, Vol. 27, Nos. 1/2, 1-20 (1987).).
The increase in the weight of the high-temperature oxide film on the titanium substrate formed at a heating temperature of 600 ° C in air and a holding time of 1 hour in the above-mentioned 0.67 g / m ² (0.067 mg / cm ² ) is slightly larger than this literature value. The reason is that a substrate having a surface roughness that is not smooth and has a surface roughness close to that of a substrate to be used for industrial electrolysis is used. Therefore, the weight increase of the high-temperature oxide film intermediate layer essentially effective in the present invention is set to 0.50 g / m ² (0.050 mg / cm ² ) or more. At this time, the TiO ₂ weight conversion value is 1.25 g / m ² , and the rutile TiO ₂ thickness conversion value is 0.29 μm. The lower limit of the weight increase may be an actual weight increase of 0.67 g / m ² .

Next, an electrode catalyst layer having a platinum-group metal or a platinum-group metal oxide as a main catalyst is provided on the high-temperature oxide film thus formed. Corresponding to various electrolysis, platinum, ruthenium oxide, iridium oxide, rhodium oxide, palladium oxide, etc., as appropriate, selected alone or in combination, in order to enhance the adhesion to the substrate and the electrolytic durability It is desirable to mix titanium oxide, tantalum oxide, tin oxide, and the like.
As a coating method of the electrode catalyst layer, a coating pyrolysis method, a sol-gel method, a paste method, an electrophoresis method, a CVD method, a PVD method, and the like can be used. In particular, JP-B-48-3954 and JP-B-46- The coating pyrolysis method as described in detail in 21888 is preferred.

When heat treatment is performed at the same time as or before and after the formation of the electrode catalyst layer of the electrode for electrolysis of the present invention, it is theoretically possible that the electron conductivity of such a high-temperature oxide film having poor electron conductivity increases. It is not clear, but with a few reasonable assumptions, we can infer the following:
Generally, it is known that when two adjacent phases are in equilibrium, the chemical potential of each component is the same in either phase. That is, if two adjacent phases containing oxygen are in equilibrium at the interface, the chemical potential of oxygen should be continuous at the two-phase interface. Long-range diffusion of oxygen is necessary to achieve equilibrium of the entire two phases, but diffusion of only a few angstroms is required to reach local equilibrium at the interface (Paul G Shewmon: Diffusion in solids, translated by Kazuo Fueki and Koichi Kitazawa (Corona Publishing Co., 1976) p148).

The oxygen concentration profile in the depth direction of the high-temperature oxide film of titanium and titanium alloy has the highest surface layer due to the mechanism of diffusion of oxygen from the substrate surface to the inside of the substrate, and the outermost surface of the high-temperature oxide film with poor electron conductivity. It is considered that the layer is close to stoichiometric TiO ₂ .
As for the electrode catalyst layer, for example, iridium oxide (rutile IrO ₂ ) which is most frequently used for oxygen generation, in the X-ray diffraction pattern, the peak on the high angle side is broader than on the low angle side. , A clear lattice distortion is observed. This distortion is considered to be caused by IrO _2-x having oxygen deficiency instead of IrO ₂ having a stoichiometric composition.
Therefore, during the heat treatment of the electrode catalyst layer, oxygen on the surface of the high-temperature oxide film diffuses into the electrode catalyst layer, and the chemical potential of oxygen approaches equilibrium at the two-phase interface between the high-temperature oxide film and the electrode catalyst layer. Guessed. Since the outermost surface layer of platinum metal is also a platinum oxide, it may be considered in the same manner as other platinum group metal oxides.

  The high-temperature oxide film of the present invention has both denseness and adhesiveness on the surface of the valve metal substrate, while generating a high-temperature oxide film having poor electron conductivity from the substrate itself, and has conventionally been used as an intermediate layer. An oxide such as tantalum or niobium as shown in JP-B-60-21232 or JP-B-60-22074 or a mixed oxide of these with an oxide such as titanium or tin before and after forming a high-temperature oxide film May be provided on the surface. Other conventionally proposed conductive intermediate layers can also be used in combination with the high-temperature oxide film according to the present invention.

The formation of the high-temperature oxide film is effective only in the step before forming the platinum group electrode catalyst layer, as shown in Example 1 and Comparative Example 2 described below. The formation of the intermediate layer is not limited thereto. As shown in Embodiments 2 and 3, it is effective to provide the high-temperature oxide film simultaneously with the provision of the high-temperature oxide film or in the pre-process and post-process.
The electrode for electrolysis according to the present invention is mainly used for an electrode for oxygen generation exposed to severe conditions during electrolysis. Can be effectively used not only for a dilute salt water electrolysis electrode typified by alkali-alkali-on water / acidic water but also for a chlorine generation electrode in which the electrode substrate corrodes depending on the electrolysis conditions.

The present invention provides a valve metal or a valve metal alloy electrode substrate, a weight increase of 0.5 g / m ² or more on the surface of the valve metal or the valve metal alloy electrode substrate by a high-temperature oxidation treatment of the valve metal or the valve metal alloy electrode substrate, preferably. Is an electrode for electrolysis characterized by comprising a high-temperature oxide film formed to be 0.67 g / m ² or more, an electrode catalyst layer formed on the surface of the high-temperature oxide film, and a method for producing the same.

Heat treatment of the valve metal or valve metal alloy electrode substrate in an oxidizing atmosphere to form a high-temperature oxide film with poor electron conductivity of 0.5 g / m ² or more in weight gain and 1.25 g / m ² or more in TiO ₂ conversion. By baking the electrode catalyst layer using a coating pyrolysis method as a high-temperature oxide film, the electronic conductivity of the high-temperature oxide film is increased, and a large current of the industrial electrolytic level can be passed. An electrode for electrolysis is obtained.
This high-temperature oxide film is rich in corrosion resistance, is dense and firmly bonded to the electrode substrate, protects the electrode substrate from corrosive electrolytes and electrolytic reactions, and securely carries the electrode catalyst by oxide-oxide bonding As a result, the electrode catalyst in the catalyst layer can be effectively used.

FIG. 1 is a conceptual diagram showing an example of the electrode for electrolysis according to the present invention.
The electrode substrate 1 made of a valve metal such as titanium or an alloy thereof and having a roughened surface has its surface oxidized by high-temperature heat treatment to form a high-temperature oxide film 2 made of a corresponding oxide film of a valve metal oxide. Is done. Since the high-temperature oxide film 2 is integrated with the electrode substrate 1, it does not peel off from the electrode substrate 1 and has high corrosion resistance, so that the electrode substrate is reliably protected.

Next, an electrode catalyst layer 3 containing a metal such as iridium or titanium or a metal oxide as a catalyst is formed on the surface of the high-temperature oxide film 2. When the formation of the electrode catalyst layer is performed under heating conditions, or when the entire electrode obtained after the formation of the electrode catalyst layer 3 is heated, reforming at the interface between the high-temperature oxide film 2 and the electrode catalyst layer 3 results in a non-electronically conductive material. Electronic conductivity is imparted to a certain high-temperature oxide film 2 so that a large current at the level of industrial electrolysis can be passed.
The high-temperature oxide film 2 forms an oxide-oxide bond with the electrode catalyst layer 3, which is mainly an oxide, and reliably carries the electrode catalyst layer.
Further, when the valve metal is contained in the electrode catalyst layer, a stronger bond is generated between the valve metal in the high-temperature oxide film and the valve metal in the electrode catalyst layer, and the durability is sufficiently improved.

  Next, as a reference example of the present invention, an example in which the contact resistance value of a high-temperature oxide film of metallic titanium was actually measured will be described.

[Reference example]
Mercury was used as a contact material in order to avoid abrasion and peeling of the oxide film due to strong contact and errors due to partial contact.
First, mercury was poured into a nickel cylindrical container having an inner diameter of 20 mm and a depth of 20 mm. Next, a metal titanium rod having a diameter of 3 mm and a length of 100 mm was subjected to a high-temperature oxidation treatment at a predetermined temperature and for a predetermined time, and one end was ground to peel off the high-temperature oxide film so that electricity could be supplied. A titanium rod was semi-fixed, and one end where the high-temperature oxide film remained was immersed in mercury by a length of about 9.9 mm so that the contact area with mercury was about 100 mm ² (1 cm ² ). A predetermined current value was applied while the titanium rod side was positive and the nickel container side was negative, and the voltage between the titanium rod and the nickel container was measured and converted to a resistance value. The results are shown in Table 1 (actually measured contact resistance of high-temperature oxide film).
The unit of Ωcm ^{2 in} the table represents a resistance value Ω corresponding to a unit area cm ² when a current is passed in a direction perpendicular to the oxide film. These values are different from the values obtained by placing a probe on a surface, such as a four-probe method, and measuring the resistance in the horizontal direction of the cross section of the oxide film.

Originally When a current is supplied to the 3A / cm ² as in this embodiment in Table 1 in the oxide film layer with an average value 0.070,0.298,0.599,0.682,2.327,15.126Omucm ² of the film resistor, respectively 0.2,0.9,1.8, Although voltage rises of 2.0, 7.0, and 45.4V should occur, when the electrode catalyst layer is actually formed by pyrolysis and then subjected to electrolysis, the cell voltage of any electrode shows around 4.5V. , Leveled and the difference disappeared.

  Next, Examples and Comparative Examples relating to the electrode for electrolysis according to the present invention and the production thereof will be described, but these do not limit the present invention.

[Example 1]
The surface of each of a total of 15 3 mm-thick titanium plates for general industrial use was roughened by blasting with # 20 alumina particles, and then immersed in boiling 20% hydrochloric acid to perform surface cleaning, and a total of 15 sheets were obtained. Electrode substrate. The substrate is heated in air at a rate of about 5 ° C./minute from a room temperature, heat-treated at a predetermined holding time (see Table 2) at each of the reached temperatures, and then cooled in a furnace to obtain a high temperature of the titanium substrate. An oxide film was obtained. Table 2 shows the weight increase (g / m ² and the value converted to mg / cm ² ) of the high-temperature oxide film of each substrate (Examples 1-1 to 1-15).
Next, a 10% hydrochloric acid mixed solution of iridium chloride containing 70 g / l of iridium and tantalum chloride containing 30 g / l of tantalum was applied to each of the titanium substrates on which these high-temperature oxide films were formed. This was fired for 10 minutes in a muffle furnace maintained at ℃, and this operation was repeated 12 times to produce an electrode containing a mixed oxide of iridium oxide and tantalum oxide containing about 12 g / m ² of iridium as an electrode catalyst. .

Each electrode was subjected to an electrolytic life test in a 150 g / l sulfuric acid aqueous solution at 60 ° C. with a platinum plate as a cathode at a current density of 3 A / cm ² . The point at which the cell voltage increased by 1 V was determined as the life of the electrode.
Each of these electrodes can maintain a stable electrolysis and have an electrolysis test life of 1300 hours or more, which is sufficient to exhibit sufficient performance in industrial electrolyzers whose main reaction is oxygen generation. It was confirmed.
Table 2 shows the conditions for forming the high-temperature oxide film on each electrode and the results of the electrolytic life test.
FIG. 2 shows the relationship between the increase in the weight of the high-temperature oxide film and the life of the electrolytic test (part of Examples 1-1 to 1-15). Note that FIG. 2 also includes the results of Comparative Examples 1-1 and 1-2 in which the amount of increase in the weight of the high-temperature oxidation is merely different.

The electrolysis life increased while having a logarithmic relationship with the weight increase, except for a few points (shown by white circles in FIG. 2) present in a specific region of 1.5 to 3.5 g / m ^{2 in} terms of oxidized weight gain. . Specific region is consistent with the gray surface oxide film from the pink and area color changes, since the weight 3.5 g / m ² or more does not change gray tones be increased, the surface oxide film light It is considered to be a special phenomenon in the transition region where the semiconductor characteristics change greatly, but its theoretical nature is unknown. Electrodes with a high-temperature oxide film with a weight increase of 0.5 g / m ² or more exhibited longer life than electrodes with a high-temperature oxide film intermediate layer with a weight increase of less than 0.5 g / m ² .
FIG. 3 shows a SEM photograph of a cross section of the electrode sample of Example 1-7 at a magnification of about 5,000.

[Comparative Example 1]
Heat treatment was performed at an ultimate temperature and a holding time of 500 ° C. for 1 hour (Comparative Example 1-1) and 500 ° C. for 3 hours (Comparative Example 1-2), respectively, followed by furnace cooling to obtain a high-temperature oxide film on a titanium substrate. Except for this, a sample was prepared in the same manner as in Example 1, and an electrolytic life test was performed. Increase in weight Comparative Example 1-1 In 0.18 g / m ^2, was 0.30 g / m ² in Comparative Example 1-2.
In these electrodes, the cell voltage rapidly increased in a short time of 406 hours (Comparative Example 1-1) and 814 hours (Comparative Example 1-2). Table 2 shows the results.

[Comparative Example 2]
When providing an electrode catalyst layer by a coating pyrolysis method on a titanium or titanium alloy substrate, high-temperature oxidation is effective only when it is performed as a pretreatment of the substrate. During formation of the electrode catalyst layer, it is conceivable that the electrode catalyst layer is formed. In this comparative example, the role of the high-temperature oxidation step was verified by comparing these efficiencies.

The iridium chloride containing 70 g / l of iridium and the tantalum chloride containing 30 g / l of tantalum were directly formed on the electrode substrate obtained by roughening and washing in the same manner as in Example 1 without forming a high-temperature oxide film. A 10% hydrochloric acid mixed solution is applied, and after drying, 500 ° C. (Comparative Example 2-1), 550 ° C. (Comparative Example 2-2), 600 ° C. (Comparative Example 2-3), 650 ° C. (Comparative Example 2-4) B) for 10 minutes each in a muffle furnace, and repeat this operation 12 times to produce an electrode containing a mixed oxide of iridium oxide and tantalum oxide containing about 12 g / m ² of iridium as an electrode catalyst. did.
In addition, one of the electrode samples fired at 500 ° C. was taken out, and the temperature was raised from room temperature at a rate of about 5 ° C./min. Was heat-treated at 650 ° C. for 3 hours (Comparative Example 2-5), and then cooled in a furnace. The heat treatment after forming the electrode catalyst layer is hereinafter referred to as post bake.

These electrodes were subjected to an electrolytic life test at a current density of 3 A / cm ^{2 in} a 150 g / l sulfuric acid aqueous solution at 60 ° C. using a platinum plate as a cathode. The point at which the cell voltage increased by 1 V was determined as the life of the electrode.
All electrodes were 329 hours (Comparative Example 2-1), 281 hours (Comparative Example 2-2), 197 hours (Comparative Example 2-3), 161 hours (Comparative Example 2-4), and 77 hours (Comparative Example). 2-5), the cell voltage rapidly increased in a very short time.

Two combined causes were considered for the remarkably inferior life of the electrode compared to Example 1.
According to the analysis by X-ray diffraction of the electrode before the electrolysis test, when the catalyst layer was formed by baking at 550 ° C. or more, metal Ir having a slightly lower resistance was produced as a by-product in addition to IrO ₂ having resistance as an anode catalyst. I found out. This means that the electrode catalyst layer has been consumed more quickly.
Furthermore, from the EPMA analysis of the cross section of the electrode before electrolysis, it was found that, for all electrodes, the interface at the side of the metal titanium substrate in contact with the electrode catalyst layer was much higher than the normal high-temperature oxide film when compared at the same temperature. It was found that a thick abnormal high-temperature oxide layer had formed. When the electrolysis is performed, this abnormal high-temperature oxide layer is significantly embrittled or corroded as compared with the high-temperature oxide film formed on the titanium substrate in Example 1, and even when the temperature is lower than 600 ° C., it is even dissolved. Was seen. It is considered that the high-temperature oxide film formed on the titanium substrate in Example 1 also had an effect of suppressing the formation of the abnormal high-temperature oxide layer when the electrode catalyst was fired at a normal firing temperature.

[Example 2]
The surface of each of a total of eight 3 mm-thick titanium plates for general industrial use was roughened by blasting with # 20 alumina particles, and then immersed in boiling 20% hydrochloric acid to perform surface cleaning, and the electrode substrate and (Examples 2-1 to 2-8).
First, before forming the high-temperature oxide film on the substrate, the formation of the high-temperature oxide film described in Example 1 of JP-B-60-21232 was applied to the six electrode substrates of Examples 2-1 to 2-6. A 10% hydrochloric acid solution of tantalum chloride TaCl ₅ containing 10 g / l of tantalum is applied once as a coating solution for drying, and after drying, the substrate is further dried in air at a rate of about 5 ° C./minute from room temperature. The temperature was raised, each substrate was subjected to a predetermined heat treatment shown in Table 3, and then cooled in a furnace to obtain a high-temperature oxide film on a titanium substrate.
X-ray diffraction analysis of this high-temperature oxide film shows that, in addition to the titanium metal substrate, TiO ₂ (rutile type) inevitably generated as its oxide and Ta ₂ O ₅ generated from the coating layer And a diffraction peak of Ti ₃ O, which is considered to be present at the interface between the high-temperature oxide film and the substrate, was detected.

Separately, before forming a high-temperature oxide film on the substrate, the two electrode substrates of Examples 2-7 and 2-8 were coated with 10 g / l molybdenum chloride as a coating solution for forming a high-temperature oxide film. A 10% hydrochloric acid solution of molybdenum MoCl ₅ is applied once, and the substrate is heated in air at a rate of about 5 ° C./min from room temperature. And then cooled in a furnace to obtain a high-temperature oxide film on the titanium substrate.
X-ray diffraction analysis of this high-temperature oxide film suggests that in addition to the titanium metal of the substrate, TiO ₂ (rutile type) inevitably generated as its oxide and the interface between the high-temperature oxide film and the substrate The diffraction peak of Ti ₃ O was detected. However, no molybdenum oxide was identified. The melting point of molybdenum oxide MoO ₃ is 795 ° C., and at 650 ° C., the vapor pressure is high and it is considered that the molybdenum oxide evaporates during firing. In the firing at 500 ° C. performed in Comparative Example 3-2 described later, a clear diffraction peak of molybdenum oxide MoO ₃ was observed.

Next, a 10% hydrochloric acid mixed solution of iridium chloride containing 70 g / l iridium and tantalum chloride containing 30 g / l tantalum was applied onto the titanium substrate on which the high-temperature oxide film was formed, dried, and then heated to 500 ° C. Firing in a held muffle furnace for 10 minutes, this operation was repeated 12 times, and a total of eight electrodes containing about 12 g / m ² of iridium and a mixed oxide of iridium oxide and tantalum oxide as an electrode catalyst were used. Produced.
Each of these electrodes was subjected to an electrolytic life test at a current density of 3 A / cm ^{2 in} a 150 g / l sulfuric acid aqueous solution at 60 ° C. using a platinum plate as a cathode. The point at which the cell voltage increased by 1 V was determined as the life of the electrode. The life of each electrode was as shown in Table 3.
Each of these electrodes can maintain a stable electrolysis and have an electrolysis test life of 1300 hours or more, which is sufficient to exhibit sufficient performance in industrial electrolyzers whose main reaction is oxygen generation. It was confirmed.

[Consideration of Examples and Comparative Examples]
In Examples 2-1 to 2-6 in which high-temperature oxidation was performed after the application of tantalum chloride, there was a tendency that the electrolytic life was longer than that in the high-temperature oxide film simply subjected to high-temperature oxidation. This is an example in which the corrosion resistance of tantalum oxide is added to the high-temperature oxide film, that is, an additive / synergistic effect is observed.
On the other hand, Examples 2-7 and 2-8 in which high-temperature oxidation was performed after application of molybdenum chloride also obtained a sufficient electrolytic life, but did not show any additive / synergistic effects due to application of molybdenum chloride. . However, no negative effects were observed.
Table 3 shows these conditions and electrolysis results.

The net weight of the resulting tantalum oxide is 0.05 g / m ² before and after, but increase in weight after the high-temperature oxidation after tantalum chloride coating, conversely from the increase in weight of the high-temperature oxidation film of the simple titanium substrate It has run out. It is assumed that the oxidation of the titanium substrate was suppressed by the tantalum oxide. Molybdenum oxide evaporates during high-temperature oxidation at 650 ° C. or higher, but it is considered that the same action was performed while remaining.

[Comparative Example 3]
After applying the coating solution and drying, heat treatment was performed with the ultimate temperature and holding time at 500 ° C. for 10 minutes, followed by furnace cooling to obtain a high-temperature oxide film on the titanium substrate in the same manner as in Example 2. Samples were prepared and subjected to an electrolytic life test. In Comparative Example 3-1, thermal oxidation was performed after applying tantalum chloride, and in Comparative Example 3-2, thermal oxidation was performed after applying molybdenum chloride. The weight increase of the titanium substrate of Comparative Example 3-1 was 0.07 g / m ² , and the weight increase of the titanium substrate of Comparative Example 3-2 was 0.08 g / m ² .
In these electrodes, the cell voltage rose rapidly in a short time.
Table 3 shows these conditions and electrolysis results.

[Example 3]
The surface of each of the three general industrial titanium plates having a thickness of 3 mm was roughened by blasting with # 20 alumina particles, and then immersed in boiling 20% hydrochloric acid to perform surface cleaning, and the total of three plates were washed. Electrode substrate.
One of these substrates was subjected to Ta ion implantation at an implantation energy of 45 keV and an implantation amount of 1 × 10 ¹⁶ ions / cm ² (Example 3-1), and the other substrate was implanted at an implantation energy of 45 keV and an implantation amount of 45 keV. Ta ions were implanted at 1 × 10 ¹⁷ ions / cm ² (Example 3-2). Further, another substrate is first subjected to Ta ion implantation at an implantation energy of 45 keV and an implantation amount of 1 × 10 ¹⁷ ions / cm ² , followed by Ni ion implantation at an implantation energy of 50 keV and an implantation amount of 5 × 10 ¹⁶ ions / cm ^2. A composite ion implantation of Ta and Ni was performed (Example 3-3).

These samples were subjected to crystal structure analysis using a transmission electron microscope. In the Ta ion-implanted substrate, a diffraction ring of the α-phase of metallic titanium and a diffraction ring of the β-phase due to the implantation of Ta ion as a β-phase stabilizing element were observed. On the other hand, in the composite ion-implanted substrate of Ta and Ni, diffraction rings of the intermetallic compound Ti ₂ Ni were observed in addition to the α and β phases of titanium metal, but Ni-Ta metal such as nickel metal and Ni ₃ Ta was observed. No intermediate compounds were found. The surface layers of these substrates can be considered to be composed of a Ti-Ta alloy and a Ti-Ta-Ni alloy, respectively.

Further, each of these three substrates was heated at a rate of about 5 ° C./min from room temperature in air, and heat-treated at an ultimate temperature of 650 ° C. for a holding time of 3 hours, and then cooled in a furnace to obtain a titanium substrate. A high temperature oxide film was obtained. Increase in weight of the titanium substrate, respectively 2.79 g / m ² (Example 3-1) was 2.36 g / m ² (Example 3-2) and 2.34 g / m ² (Example 3-3) .
These samples were analyzed by X-ray diffraction. From the Ta ion-implanted substrate, the metallic titanium of the substrate, TiO ₂ (rutile type) inevitably generated as an oxide thereof, Ta ₂ O _5, and Ti ₃ O which seems to exist at the interface between the high-temperature oxide film and the substrate Was detected. On the other hand, in the composite ion-implanted substrate of Ta and Ni, a fine peak of NiTiO ₃ was observed in addition to these diffraction peaks.

Next, a 10% hydrochloric acid mixed solution of iridium chloride containing 70 g / l iridium and tantalum chloride containing 30 g / l tantalum was applied onto the titanium substrate on which the high-temperature oxide film was formed, dried, and then heated to 500 ° C. This was fired for 10 minutes in a held muffle furnace, and this operation was repeated 12 times to produce an electrode containing about 12 g / m ² of iridium and a mixed oxide of iridium oxide and tantalum oxide as an electrode catalyst.
These electrodes were subjected to an electrolytic life test at a current density of 3 A / cm ^{2 in} a 150 g / l sulfuric acid aqueous solution at 60 ° C. using a platinum plate as a cathode. The point at which the cell voltage increased by 1 V was determined as the life of the electrode.

Each of these electrodes can maintain a stable electrolysis and have an electrolysis test life of 1300 hours or more, which is sufficient to exhibit sufficient performance in industrial electrolyzers whose main reaction is oxygen generation. It was confirmed.
When a high-temperature oxidation treatment was performed as a post-treatment on a metal titanium substrate alloyed near the surface by ion implantation, the type and amount of implanted elements had various effects on the electrolytic life.
For example, in the case of Ta ion implantation, as shown in Example 3-1 and Comparative Example 4-1 when the amount is small, the high-temperature oxidation treatment exerts a very large effect, but in Example 3-2 and Comparative Example As shown in 4-2, when the amount was large and sufficient electrolytic life could be obtained without originally performing high temperature oxidation, the effect was limited or additive.
On the other hand, in the case of composite ion implantation of Ta and Ni, Ti ₂ Ni, which has poor electrolytic resistance at the anode, is present from the beginning, and this also becomes NiTiO ₃ , which also has poor corrosion resistance due to high-temperature oxidation. Led to This is presumably because NiTiO ₃ present in the form of fine particles was included in the high-temperature oxide film and was isolated to suppress the adverse effect. This is one of the effects of the high-temperature oxide film.
Table 4 shows these conditions and electrolysis results.

[Comparative Example 4]
Same as Examples 3-1 to 3-3 except that the substrate after ion implantation of each of Examples 3-1 to 3-3 was not subjected to high-temperature oxidation as a post-treatment, and was directly coated with an electrode catalyst. Was prepared and subjected to an electrolytic life test (comparative examples 4-1, 4-2, and 4-3 in this order).
The cell voltage of these electrodes rapidly increased in a short time except for Comparative Example 4-2.
Table 4 shows these conditions and electrolysis results.

The conceptual diagram which shows an example of the electrode for electrolysis which concerns on this invention. 4 is a graph showing the relationship between the amount of increase in the weight of the high-temperature oxide film obtained in Examples and Comparative Examples and the life of the electrolytic test. 14 is a SEM photograph of a cross section of the electrode sample of Example 1-7 at a magnification of about 5,000.

Explanation of reference numerals

1 electrode substrate 2 intermediate layer 3 electrode catalyst layer

Claims (5)

A valve metal or a valve metal alloy electrode base, a high temperature oxide film formed on the surface by a high temperature oxidation treatment of the valve metal or the valve metal alloy electrode base so that the weight increase becomes 0.5 g / m ² or more; and An electrode for electrolysis comprising an electrode catalyst layer formed on a surface of an oxide film. ^{2. The} electrode for electrolysis according to claim 1, wherein the weight increase is 0.67 g / m ² or more. By subjecting the valve metal or valve metal alloy electrode substrate to high-temperature oxidation treatment, a high-temperature oxide film is formed on the surface of the electrode substrate so that the weight increase is 0.5 g / m ² or more, and then an electrode catalyst is formed on the high-temperature oxide film. A method for producing an electrode for electrolysis, comprising forming a layer.   A method for producing an electrode for electrolysis in which a high-temperature oxidation treatment of a valve metal or a valve metal alloy substrate is performed to form a high-temperature oxide film on the surface of the substrate, and then an electrode catalyst layer is formed on the high-temperature oxide film. When forming, the weight increase of the high-temperature oxide film should be equal to or greater than the weight increase of the high-temperature oxide film of the valve metal or valve metal alloy electrode substrate generated at a heating temperature of 600 ° C in air and a holding time of 1 hour. A method for producing an electrode for electrolysis characterized by the following.   The method for producing an electrode for electrolysis according to claim 3 or 4, wherein when the electrode catalyst layer is provided on the high-temperature oxide film, the electrode catalyst layer is formed by a coating pyrolysis method.

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