JP2014530292A - High load oxygen generating anode and its manufacturing method - Google Patents

Abstract

[PROBLEMS] To provide excellent durability under high load electrolysis conditions used in industrial electrolysis such as electrolytic metal foil production such as electrolytic copper foil, feeding in aluminum liquid, continuous electrogalvanized steel sheet production, metal extraction, etc. To provide an anode for oxygen generation for load and a manufacturing method thereof. In an oxygen generating anode having a conductive metal substrate and a catalyst layer containing iridium oxide formed on the conductive metal substrate, the coating amount of iridium per catalyst layer is 2 g / The catalyst layer containing amorphous iridium oxide is formed by heating and firing in a high temperature region of 430 ° C. to 480 ° C., and then the catalyst layer containing amorphous iridium oxide is 520 ° C. An anode for oxygen generation, which is post-baked in a high temperature region of ˜600 ° C., and substantially the entire amount of iridium oxide in the catalyst layer is crystallized, and a method for producing the same. [Selection] Figure 2

Description

  The present invention relates to an oxygen generating anode used for various industrial electrolysis and a method for producing the same, and more specifically, electrolytic metal foil production such as electrolytic copper foil, feeding in aluminum liquid, continuous electrogalvanized steel plate production, metal sampling. The present invention relates to an oxygen generating anode for high load resistance having excellent durability under high load electrolysis conditions and a method for producing the same.

In industrial electrolysis such as electrolytic copper foil, feeding in aluminum liquid, continuous electrogalvanized steel sheet, metal sampling, etc., oxygen generation occurs at the anode, so the metal titanium substrate was coated with iridium oxide that is mainly resistant to oxygen generation as an electrode catalyst. Many anodes have been used. In general, this type of industrial electrolysis with oxygen generation at the anode is often electrolyzed at a constant current in terms of production efficiency and energy saving. The current density was set in a range from several A / dm ² which is mainly used in industries such as metal extraction to a maximum of 100 A / dm ² for electrolytic copper foil.

However, in recent years, electrolysis is often performed at a current density of 300 A / dm ^{2 to} 700 A / dm ² or higher in order to improve product quality or provide special performance. In order to give special performance to products obtained by electrolysis, it is necessary to install such a high current as an auxiliary anode at a specific location under high load electrolysis conditions. Conceivable.
Under such high current density electrolysis, the load on the electrode catalyst layer becomes high, and in addition, current concentration tends to occur, so that the electrode catalyst layer is consumed quickly. In addition, because organic substances and impurity elements are added to stabilize the product, various electrochemical reactions and chemical reactions occur, and the consumption of the electrode catalyst due to the increased hydrogen ion concentration (lower pH) associated with the oxygen generation reaction Will be further accelerated.

In order to solve this, it is considered as one of the solutions to increase the surface area of the electrode catalyst layer and reduce the actual current load. For example, instead of using a conventional plate base material, physically increasing the surface area by using a base material such as a mesh or punching metal is another solution. However, when these base materials were used, demerits were seen such as an increase in costs accompanied by extra processing costs. In addition, although the actual current density decreased physically due to the increase in the surface area of the substrate, the current concentration in the electrode catalyst layer was not improved, and the effect of suppressing catalyst consumption was slight.
In addition, in the thermal decomposition forming method in which the electrode catalyst layer is repeatedly applied to baked repeatedly, if the amount of iridium applied per time increases, a fluffy catalyst layer can be formed. The increase in the effective surface area of the catalyst layer was slight, and the effect of improving the durability and suppressing the consumption of the catalyst layer under high load conditions could not be clearly seen.

  As an electrode for this type of electrolysis, an electrode having a low oxygen generation potential and a long life is required. Conventionally, as this type of electrode, an insoluble electrode in which a conductive metal substrate such as titanium is coated with a catalyst layer containing a noble metal or a noble metal oxide is used. For example, Patent Document 1 discloses that a catalyst layer containing iridium oxide and a valve metal oxide is heated and fired in an oxidizing atmosphere of 650 ° C. to 850 ° C. on a conductive metal substrate such as titanium, An insoluble electrode having a partially crystallized catalyst layer is disclosed. However, since this electrode is baked at a high temperature of 650 ° C. or more, interfacial corrosion of a metal substrate such as titanium occurs, the metal substrate such as titanium becomes a defective conductor, oxygen overvoltage increases, and it cannot be used as an electrode. . In addition, the crystallite size of iridium oxide in the catalyst layer is increased. As a result, the effective surface area of the catalyst layer is decreased and the catalyst activity is inferior.

  In Patent Document 2, a catalyst layer in which amorphous iridium oxide and amorphous tantalum oxide are mixed is provided on a conductive metal substrate such as titanium, and an anode for producing copper plating and copper foil is used. It is disclosed. However, since this electrode is characterized by amorphous iridium oxide, the electrode durability was not sufficient. When amorphous iridium oxide is used, the reason why the corrosion resistance is reduced is that amorphous iridium oxide is in an amorphous state, and the bond between iridium and oxygen becomes unstable as compared with crystalline iridium oxide.

  Further, Patent Document 3 discloses a catalyst layer having a two-layer structure of a lower layer made of crystalline iridium oxide and an upper layer made of amorphous iridium oxide in order to suppress exhaustion of the catalyst layer and improve the durability of the electrode. An electrode coated with is disclosed. However, the electrode disclosed in Patent Document 3 has insufficient electrode durability because the upper layer of the catalyst layer is made of amorphous iridium oxide. Further, crystalline iridium oxide was present only in the lower layer and was not uniformly distributed throughout the catalyst layer, and the electrode durability was not sufficient.

  Further, in Patent Document 4, it is essential to contain amorphous iridium oxide on a conductive metal substrate such as titanium, and a catalyst layer in which crystalline iridium oxide and amorphous iridium oxide are mixed. An electrode for zinc electrowinning is disclosed, and in Patent Document 5, it is essential that amorphous iridium oxide is contained on a conductive metal substrate such as titanium, and iridium oxide crystalline and An anode for cobalt electrowinning provided with a catalyst layer mixed with amorphous iridium oxide is disclosed. However, since it is an essential requirement that any electrode contains a large amount of amorphous iridium oxide, it is considered that the electrode durability is not sufficient.

In order to solve these problems, the inventors of the present invention have (1) low-temperature firing (370 ° C. to 400 ° C.) when the application amount of iridium is 2 g / m ² or less per time for the main purpose of reducing the oxygen generation overvoltage. ) + High temperature post-baking (520 ° C. to 600 ° C.) and a baking method for forming a catalyst layer in which crystalline iridium oxide and amorphous iridium oxide are mixed, and (2) high temperature baking (410 ° C. to 450 ° C.) + high temperature post baking A calcining method for forming a catalyst layer containing only substantially perfect crystalline iridium oxide by (520 ° C. to 560 ° C.) was developed, and two patent applications were filed on the same date as the present application.
According to these two inventions, under the electrolysis conditions with a current density of 100 A / dm ² or less, when the amount of iridium applied per time is 2 g / m ² or less, lead-free adhesion can be achieved. At the same time, it is possible to improve durability and reduce oxygen generation overvoltage by increasing the effective area of the catalyst layer.
However, in recent years, electrolysis is often performed at a current density of 300 A / dm ^{2 to} 700 A / dm ² or more in order to improve the quality of products and to provide special performance. In order to give special performance to products obtained by electrolysis, it is necessary to install such a high current as an auxiliary anode at a specific location under high load electrolysis conditions. It came to be needed.
Under such high current density electrolysis, the load on the electrode catalyst layer is increased, and current concentration is likely to occur, so that the electrode catalyst layer is consumed quickly, and organic substances and Since the impurity element is added, various electrochemical reactions and chemical reactions occur, and the consumption of the electrode catalyst is further accelerated due to the increase in hydrogen ion concentration (decrease in pH) associated with the oxygen generation reaction. In the inventions according to the two patent applications, it has been found that the improvement in durability and the reduction in oxygen generation overvoltage may not be sufficiently achieved by increasing the effective area of the catalyst layer.

JP 2002-275697 A (Patent No. 3654204) Japanese Patent Laying-Open No. 2004-238697 (Patent No. 3914162) JP 2007-146215 A JP 2009-293117 A (Patent No. 4516617) JP 2010-1556 A (Patent No. 4516618)

  In order to solve these problems, the present invention increases the effective surface area of the electrode catalyst layer under high load conditions, thereby improving the current distribution to the electrode catalyst layer and suppressing the consumption of the electrode catalyst. An object of the present invention is to provide an oxygen generating anode for high load resistance having excellent durability under high load electrolysis conditions capable of improving the durability of an electrode catalyst and a method for producing the same.

In order to achieve the above object, the first problem-solving means in the present invention is an oxygen generating anode having a conductive metal substrate and a catalyst layer containing iridium oxide formed on the conductive metal substrate. The amount of iridium applied per catalyst layer is 2 g / m ² or more, and is fired and fired in a relatively high temperature region of 430 ° C. to 480 ° C. to form a catalyst layer containing amorphous iridium oxide, Next, the catalyst layer containing the amorphous iridium oxide is post-baked in a further high temperature region of 520 ° C. to 600 ° C., and substantially all of the iridium oxide in the catalyst layer is crystallized. Another object is to provide an oxygen generating anode.

In order to achieve the above object, the second problem-solving means of the present invention is the oxygen generating anode having a conductive metal substrate and a catalyst layer containing iridium oxide formed on the conductive metal substrate. The oxygen generation anode characterized in that the amount of iridium applied per catalyst layer is 2 g / m ² or more and the crystallinity of iridium oxide in the catalyst layer after the post-baking is 80% or more. Is to provide.

In order to achieve the above object, a third problem-solving means in the present invention is an oxygen generating anode having a conductive metal substrate and a catalyst layer containing iridium oxide formed on the conductive metal substrate. Provided is an anode for oxygen generation, wherein the application amount of iridium per catalyst layer is 2 g / m ² or more, and the crystallite diameter of iridium oxide in the catalyst layer is 9.0 nm or less. There is.

  In order to achieve the above object, a fourth problem-solving means in the present invention is an oxygen generating anode having a conductive metal substrate and a catalyst layer containing iridium oxide formed on the conductive metal substrate. Oxygen generation characterized in that an AIP underlayer containing a tantalum and a titanium component is formed on the conductive metal substrate by an arc ion plating (hereinafter referred to as AIP) method before forming the catalyst layer. It is to provide an anode.

In order to achieve the above object, the fifth means for solving the problems in the present invention is such that the amount of iridium applied per time of the catalyst layer is 2 g / m ² or more on the surface of the conductive metal substrate, and the temperature is from 430 ° C. to 480 ° C. A catalyst layer containing amorphous iridium oxide is formed by heating and firing in a relatively high temperature region of ° C. Thereafter, the catalyst layer containing amorphous iridium oxide is further heated to 520 ° C to 600 ° C. An object of the present invention is to provide a method for producing an anode for oxygen generation, characterized by post-baking in a high temperature region and crystallizing substantially the entire amount of iridium oxide in the catalyst layer.

In order to achieve the above object, the sixth problem-solving means in the present invention is such that the amount of iridium applied to the surface of the conductive metal substrate is 2 g / m ² or more on the surface of the catalyst layer, and the temperature is from 430 ° C. to 480 ° C. A catalyst layer containing amorphous iridium oxide is formed by heating and firing in a relatively high temperature region of ℃, and then the catalyst layer containing amorphous iridium oxide is further heated to 520 ° C. to 600 ° C. Another object of the present invention is to provide a method for producing an anode for oxygen generation, characterized in that post-baking is performed in a high temperature region and the crystallinity of iridium oxide in the catalyst layer is 80% or more.

In order to achieve the above object, the seventh means for solving the problem in the present invention is to heat the iridium in a relatively high temperature range of 430 ° C. to 480 ° C. with an application amount of iridium per catalyst layer of 2 g / m ² or more. By baking, a catalyst layer containing amorphous iridium oxide is formed, and then the catalyst layer containing amorphous iridium oxide is post-baked in a further high temperature region of 520 ° C. to 600 ° C., An object of the present invention is to provide a method for producing an oxygen generating anode, wherein the crystallite diameter of iridium oxide in the catalyst layer is 9.0 nm or less.

  In order to achieve the above object, an eighth problem-solving means of the present invention is to produce an anode for oxygen generation having a conductive metal substrate and a catalyst layer containing iridium oxide formed on the conductive metal substrate. A method for producing an anode for generating oxygen, comprising: forming an AIP underlayer containing a tantalum and a titanium component on the conductive metal substrate by an AIP method before forming the catalyst layer. There is to do.

In the present invention, in the formation of an electrode catalyst layer containing iridium oxide, the amount of iridium applied per catalyst layer is 2 g / m ² or more, and the crystal complete precipitation temperature of conventional iridium oxide is 500 ° C. or more. , The catalyst layer containing amorphous iridium oxide is formed by heating and firing in a relatively high temperature region of 430 ° C. to 480 ° C. By post-baking in a further high temperature region of 520 ° C. to 600 ° C., the crystallite diameter of iridium oxide in the electrode catalyst layer is kept small, preferably the crystallite diameter is 9.0 nm or less, and the iridium oxide Mostly crystallized, preferably crystallized to a crystallinity of 80% or more to suppress the growth of the crystallite diameter of iridium oxide, and the effective surface of the catalyst layer There could be increased. Therefore, according to the present invention, the growth of the crystallite diameter of iridium oxide is suppressed because the firing is performed in two stages, and first, coating and firing are performed in a relatively high temperature region of 430 ° C. to 480 ° C. Therefore, even after post-baking in a further high temperature region of 520 ° C. to 600 ° C., the crystallite diameter is larger than the crystallite diameter to a certain extent as compared with the case of high temperature firing from the beginning as in the conventional method. This is probably because it doesn't get bigger. Thus, the growth of the crystallite diameter of iridium oxide is suppressed, and the smaller the crystallite diameter, the greater the effective surface area of the catalyst layer, which can reduce the oxygen generation overvoltage of the electrode and promote oxygen generation. The reaction of generating PbO ₂ from lead ions can be suppressed. Accordingly, it becomes possible to suppress the adhesion / covering of PbO ₂ to the electrode.
Furthermore, according to the present invention, the effective surface area of the catalyst layer is increased at the same time, the current distribution is dispersed, current concentration can be suppressed, consumption of the catalyst layer due to electrolysis can be suppressed, and electrode durability can be improved. Can do.
Furthermore, according to the present invention, the application amount of iridium per one time of the catalyst layer is 2 g / m ² or more, so that the quality of the product is improved and the special performance is imparted, so that 300 A / dm ^{2 to} 700 A Electrocatalyst even when electrolysis is performed at a current density of / dm ² or higher, or when it is installed as an auxiliary anode at a specific location under high load electrolysis conditions to give special performance to products obtained by electrolysis The load on the layer can be reduced, in addition, current concentration can be prevented, and consumption of the electrode catalyst layer can be suppressed.

Graph showing changes in crystallinity of iridium oxide of the catalyst layer due to sintering temperature and the post-bake temperature (IrO _2). Graph showing changes in crystallite size of the iridium oxide of the catalyst layer due to sintering temperature and the post-bake temperature (IrO _2). The graph which shows the change of the electrode electrostatic capacitance by baking temperature and post-baking temperature. The graph which shows the dependence of baking conditions and oxygen overvoltage.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present invention, the oxygen generation overvoltage can be reduced by increasing the effective surface area of the electrode catalyst layer for the purpose of suppressing the adhesion reaction of lead oxide to the electrode surface. It has been found that the adhesion reaction of lead can be suppressed. In addition, the present invention has been completed by repeating the experiment on the assumption that the iridium oxide of the catalyst layer is mainly crystalline in order to improve the electrode durability at the same time.

In the present invention, calcination is performed in two stages. First, a catalyst layer containing amorphous IrO ₂ is formed by calcination in a relatively high temperature region of 430 ° C. to 480 ° C., and then further 520 ° C. to 600 ° C. By post-baking in a high temperature region, iridium oxide in the catalyst layer is crystallized almost completely.
According to the inventor's experiments, the catalyst layer containing amorphous iridium oxide can significantly increase the effective surface area, but the consumption of amorphous iridium oxide by electrolysis is considerably fast, and the durability is relatively high. It turned out to decline. That is, it is considered that the electrode durability cannot be improved unless iridium oxide in the catalyst layer is crystallized. Therefore, in order to achieve the object of the present invention to increase the effective surface area of the electrode catalyst layer and reduce the overvoltage of the electrode, in the present invention, the catalyst layer is obtained by performing two-step firing of high temperature firing + high temperature post-baking. The iridium oxide crystallite size can be controlled, and smaller iridium oxide crystals are deposited on the conventional product, so that the effective surface area of the electrode catalyst layer can be increased and the overvoltage can be reduced compared to the conventional product.

  In the present invention, a catalyst layer containing amorphous iridium oxide is formed on the surface of the conductive metal substrate by heating and firing in a relatively high temperature region of 430 ° C. to 480 ° C., and then the amorphous The high quality iridium oxide catalyst layer is post-baked in a further high temperature region of 520 ° C. to 600 ° C., and the iridium oxide in the catalyst layer is crystallized almost completely.

In order to give an improvement in product quality and special performance by setting the amount of iridium oxide applied to the catalyst layer of iridium oxide according to the present invention to 2 g / m ² or more, 300 A / dm ^{2 to} 700 A / dm ² Even when electrolysis is performed at a current density higher than that, or in order to give special performance to products obtained by electrolysis, even if it is installed as an auxiliary anode at a specific location under high load electrolysis conditions, The load can be reduced, in addition, current concentration can be prevented, and consumption of the electrode catalyst layer can be suppressed.

Further, the calcination temperature in the relatively high temperature range according to the present invention is 430 ° C. to 480 ° C. and the post baking temperature range 520 ° C. to 600 ° C. in the further high temperature range is the iridium oxide crystal particles formed in the catalyst layer. The catalyst layer is determined by the diameter and the degree of crystallinity, and a catalyst layer having a low oxygen overvoltage and good corrosion resistance is formed depending on the temperature range.
In the present invention, the crystallite diameter of iridium oxide in the electrode catalyst layer is kept small, preferably the crystallite diameter is 9.0 nm or less, and most of the iridium oxide is crystallized, preferably the crystallinity is By crystallizing to 80% or more, growth of the crystallite size of iridium oxide was suppressed, and the effective surface area of the catalyst layer could be increased.

If an AIP underlayer containing a tantalum and a titanium component is provided on the conductive metal substrate before forming the catalyst layer, interfacial corrosion of the metal substrate can be further prevented.
Further, instead of the AIP underlayer, an underlayer made of a TiTaO _x oxide layer may be formed.

An aqueous solution of IrCl ₃ / Ta ₂ Cl ₅ using an AIP-coated titanium substrate was applied as a coating solution at a rate of 3 g-Ir / m ² , and IrO ₂ was partially crystallized (430 to 480). The catalyst layer was formed by calcination. After repeating the said application | coating and baking process to the required catalyst carrying amount, the electrode sample was produced from having carried out the post-baking for one hour at still higher temperature (520 degreeC-600 degreeC). The prepared samples were subjected to measurement of IrO ₂ crystallinity, oxygen generation overvoltage, electrode capacitance, etc. of the catalyst layer by XRD, sulfuric acid / gelatin electrolysis evaluation and lead adhesion test evaluation.
As a result, most of the IrO _{2 in} the formed catalyst layer was crystalline, but the crystallite diameter was reduced, and the effective electrode surface area was increased. As a result of an accelerated electrolysis life evaluation, as described later, the sulfuric acid electrolysis life was about 1.4 times that of the conventional product, and the gelatin electrolysis life was about 1.5 times that of the conventional product. .

Hereinafter, experimental conditions and methods according to the present invention will be described.
In order to investigate the range of the formation temperature of amorphous iridium oxide and the post-baking temperature for subsequent crystallization, samples shown in Table 1 were prepared, X-ray diffraction, cyclic voltammetry, oxygen generation overvoltage, etc. Measurements were made.
The sample manufacturing method was as follows.
The surface of the JIS type I titanium plate was dry blasted with iron grit (G120 size), then pickled in a boiling concentrated hydrochloric acid aqueous solution for 10 minutes to clean the electrode metal substrate. The cleaned electrode metal substrate was set in an arc ion plating apparatus using a Ti-Ta alloy target as an evaporation source, and the surface of the electrode metal substrate was coated with a tantalum and titanium alloy undercoat. The coating conditions are as shown in Table 1.

Next, the coated metal substrate was heat-treated at 530 ° C. for 180 minutes in an air circulating electric furnace.
Next, iridium tetrachloride and tantalum pentachloride are dissolved in concentrated hydrochloric acid to form a coating solution, applied to the coated metal substrate, dried, and then dried in an air circulating electric furnace at the temperatures shown in Table 2. Thermal decomposition coating was performed for 15 minutes to form an electrode catalyst layer made of a mixed oxide of iridium oxide and tantalum oxide. The amount of the coating solution is set so that the coating thickness per coating solution is approximately 3.0 g / m ² in terms of iridium metal, and this operation of coating to baking is repeated nine times. An electrode catalyst layer of about 27.0 g / m ^{2 in} terms of conversion was obtained.
Next, the sample coated with the catalyst layer was further post-baked for 1 hour at the temperature shown in Table 2 in an air circulation type electric furnace to produce an electrode for electrolysis. For comparison, a sample not subjected to post-baking was prepared.
A list of the firing temperature and post-bake temperature for each sample is shown in Table 2.
Evaluation Experiment Item (1) Measurement of crystallinity and crystallite diameter IrO ₂ crystallinity and crystallite diameter of the catalyst layer were measured by X-ray diffraction method.
The crystallinity was estimated from the diffraction peak intensity.
(2) Electrode capacitance Cyclic voltammetry method Electrolyte solution: 150 g / L H ₂ SO ₄ aq.
Electrolysis temperature: 60 ° C
Electrolytic area: 10 × 10 mm ²
Counter electrode: Zr plate (20mm x 70mm)
Reference electrode: Mercury sulfate electrode (SSE)
(3) Oxygen overvoltage measurement Current interrupt method
Electrolysis solution: 150 g / L H ₂ SO ₄ aq.
Electrolysis temperature: 60 ° C
Electrolytic area: 10 × 10 mm ²
Counter electrode: Zr plate (20mm x 70mm)
Reference electrode: Mercury sulfate electrode (SSE)

焼成温度及びポストベーク温度によるＩｒＯ₂結晶性の変化は、以下の通りであった。
結晶化度の推算は従来品の結晶回析ピーク（θ＝２８°）強度を１００として、各サンプルの同結晶回析ピーク（θ＝２８°）の強度が従来品の強度との割合を結晶度とした。その結果は表２に示した。また、表２の結晶化度に関するデータを基づき作成したグラフを図１に示した。

The change in IrO ₂ crystallinity with the firing temperature and post-bake temperature was as follows.
The degree of crystallinity is estimated by taking the intensity of the crystal diffraction peak (θ = 28 °) of the conventional product as 100 and the intensity of the same crystal diffraction peak (θ = 28 °) of each sample as the strength of the conventional product. Degree. The results are shown in Table 2. Moreover, the graph produced based on the data regarding the crystallinity degree of Table 2 was shown in FIG.

As can be seen from Table 2 and FIG. 1, Sample 2 to Example 2 of the present invention (high temperature firing at a relatively high temperature range of 430 ° C. to 480 ° C. + post baking at a further high temperature range of 520 ° C. to 600 ° C.) The crystallinity of iridium oxide after post-baking of 4 and 6 to 8 was 80% or more. On the other hand, a clear peak of iridium oxide attributed to the electrode catalyst layer (sample 1) by post-baking at 430 ° C. was not observed, and it was confirmed that the catalyst layer of this sample was formed from amorphous iridium oxide. did. The degree of crystallinity of the electrode catalyst layer (sample 5) obtained by baking at 480 ° C. without post-baking was 72%, and a large amount of amorphous iridium oxide remained. In addition, the conventional sample 9 was completely crystallized and the crystallinity was 100%, but the crystallite diameter was as large as 9.1 nm. Therefore, the electric capacitance was 7.6. The effective surface area was small.
That is, regarding the change in crystallinity due to high-temperature post-baking, a clear peak of IrO ₂ attributed to the electrode catalyst layer due to further high-temperature post-baking after firing at 430 ° C. is observed. Of amorphous IrO ₂ was found to be converted to crystalline. It was also found that at any post-bake temperature, the peak intensity was the same as that of the conventional product, and amorphous IrO ₂ did not remain. On the other hand, it was found that the crystallinity of the 480 ° C. fired product was further increased by high temperature post-baking. However, it was found that a small amount of IrO ₂ amorphous remained after post-baking at 520 ° C. and 560 ° C. In contrast, the IrO ₂ crystallinity after post-baking at 600 ° C. was almost the same as that of the conventional product, indicating that it was completely crystallized.

Next, the crystallite diameter was calculated by X-ray diffraction. The results are shown in Table 2. Moreover, the graph produced based on the data regarding the crystallite diameter of Table 2 was shown in FIG.
Amorphous IrO ₂ was generated by 430 ° C. firing without post-baking and post-baking, so the crystallite diameter was set to “0”. When post-baking was performed, amorphous IrO ₂ was crystallized, but it was found that the crystallite diameter of the formed crystal was smaller than that of the conventional product. Further, almost no dependency was observed between the post-bake temperature and the IrO ₂ crystallite diameter.
On the other hand, in the post-baked 480 ° C. fired product, the formed crystallite diameter was found to be smaller than that of the conventional product regardless of the post-bake temperature. That is, although the IrO ₂ crystallinity of the catalyst layer formed by low-temperature calcination by post-baking was increased, an increase in the IrO ₂ crystallite diameter could be suppressed.

  As is clear from the data on the crystallite size in Table 2 and FIG. The crystallite size of iridium oxide after post-baking of Samples 2 to 4 and 6 to 8 by baking was 9.0 nm or less. On the other hand, a clear peak of iridium oxide attributed to the electrode catalyst layer (sample 1) by post-baking at 430 ° C. was not observed, and it was confirmed that the catalyst layer of this sample was formed from amorphous iridium oxide. did. The crystallite diameter of the electrode catalyst layer (sample 5) obtained by baking at 480 ° C. without post-baking was large, which was 9.3 nm. Moreover, the crystallite diameter of the iridium oxide of the sample 9 which is a conventional product was large and was 9.1 nm.

Next, the change in the effective surface area of the electrode catalyst layer due to high temperature firing in a relatively high temperature region of 430 ° C. to 480 ° C. + post baking in a further high temperature region of 520 ° C. to 600 ° C. was measured.
The electrode capacitance calculated by the cyclic voltammetry method is shown in Table 2. The electrode capacitance is proportional to the effective surface area of the electrode, and the higher the so-called capacitance, the higher the effective surface area. Based on the data in Table 2, the relationship between the firing conditions of the catalyst layer and the capacitance is shown in FIG.
From Table 2 and FIG. 3, Samples 2 to 4 and 6 to 8 according to examples of the present invention (high temperature baking at a relatively high temperature range of 430 ° C. to 480 ° C. + post baking at a further high temperature range of 520 ° C. to 600 ° C.) The electrode capacitance was found to be as high as 11.6 or more. On the other hand, IrO ₂ (sample 1) of the catalyst layer formed by calcination at 430 ° C. without post-baking was amorphous, and thus showed the maximum effective surface area (electrical capacitance). Since IrO ₂ crystallized after post-baking, the effective surface area (electrical capacitance) was reduced, but was found to be higher than that of the conventional product. This is probably because the crystallite diameter formed is smaller than that of the conventional product. Moreover, the tendency for the electrode effective surface area (electrical capacitance) to decrease by the increase in post-baking temperature was observed.
In addition, when post-baking after baking at 480 ° C (samples 5 to 8), the effective surface area (electrical capacitance) is almost the same regardless of the post-baking temperature, but it is twice as large as the conventional product. I found out. This is probably because the IrO ₂ crystallite diameter is smaller than that of the conventional product, and a small amount of amorphous IrO ₂ remains. Further, even when the post-bake temperature was raised, no change in the electrode effective surface area (electrical capacitance) was observed.

The oxygen generation overvoltage (V vs. SSE @ 100 A / dm ² ) of each sample was measured. The results are shown in Table 2. Further, the dependency between the firing conditions and the oxygen generation overvoltage is shown in FIG. The trend of change in the graph of FIG. 4 was opposite to that of FIG. 3, and as the electrode effective surface area increased, the oxygen generation overvoltage of the sample tended to decrease. This is considered to be because the current distribution due to the increase of the electrode effective surface area can be dispersed and the actual current is lowered.
The post-baked 430 ° C. fired product with the largest effective surface area showed the lowest oxygen overvoltage, but the oxygen overvoltage increased by reducing the effective surface area due to post-baking. A similar tendency was observed in the dependency of oxygen overvoltage and post-baking temperature on the 480 ° C. fired product. It was also found that the oxygen overvoltage of these samples was higher than that of the conventional product. This seems to be because the surface area increased compared to the conventional product.
From Table 2 and FIG. 4, samples 2 to 4 and 6 to 8 according to examples of the present invention (high temperature baking at a relatively high temperature range of 430 ° C. to 480 ° C. + post baking at a further high temperature range of 520 ° C. to 600 ° C.) It has been found that the oxygen generation overvoltage of is low.

As described above, the electrode manufactured by the high temperature baking in the relatively high temperature range of 430 ° C. to 480 ° C. + post baking in the further high temperature range of 520 ° C. to 600 ° C. is IrO in the catalyst layer as compared with the conventional product. _Two crystals were small and the electrode surface area could be increased. Since these samples were able to disperse the current distribution under high load conditions and reduced the actual current load, it is considered that the effect of suppressing the catalyst consumption is great and the durability can be expected to be improved.

  Next, examples of the present invention will be described, but the present invention is not limited thereto.

<Example 1>
The surface of the JIS type I titanium plate was dry blasted with iron grit (G120 size), then pickled in a boiling concentrated hydrochloric acid aqueous solution for 10 minutes to clean the electrode metal substrate. The cleaned electrode metal substrate was set in an arc ion plating apparatus using a Ti—Ta alloy target as an evaporation source, and the surface of the electrode metal substrate was coated with an AIP underlayer coating containing tantalum and titanium. The coating conditions are as shown in Table 1.
Next, the coated metal substrate was heat-treated at 530 ° C. for 180 minutes in an air circulating electric furnace.
Next, iridium tetrachloride and tantalum pentachloride are dissolved in concentrated hydrochloric acid to obtain a coating solution, which is coated on the coated metal substrate, dried, and then heated in an air circulating electric furnace at 480 ° C. for 15 minutes. Decomposition coating was performed to form an electrode catalyst layer made of a mixed oxide of iridium oxide and tantalum oxide. The amount of the coating solution is set so that the coating thickness per coating solution is approximately 3.0 g / m ² in terms of iridium metal, and this operation of coating to baking is repeated nine times. An electrode catalyst layer of about 27.0 g / m ^{2 in} terms of conversion was obtained.
When this sample was subjected to X-ray diffraction, a clear peak of iridium oxide attributed to the electrode catalyst layer was observed, but the intensity of the peak was lower than that of Comparative Example 1, and crystalline IrO ₂ was partially precipitated. I found out.
Next, the sample coated with the catalyst layer was further post-baked at 520 ° C. for 1 hour in an air circulation type electric furnace to produce an electrode for electrolysis.
When X-ray diffraction was performed on the post-baked sample, a clear peak of IrO ₂ belonging to the electrode catalyst layer was observed, and the intensity of the peak was higher than that before the post-baking, but still not as compared with Comparative Example 1. Low. From this, it was found that the crystallinity of the catalyst layer formed in the coating step of the previous low-temperature firing by high-temperature post-baking increased, but amorphous IrO ₂ partially remained.
Two types of life evaluation tests (both pure sulfuric acid solution and sulfuric acid solution with gelatin addition) shown in Table 3 were performed on the electrodes for electrolysis thus prepared. The results are shown in Table 4. Compared to Comparative Example 1 (conventional product) in Table 4, the sulfuric acid electrolysis life was 1.7 times longer and the gelatin electrolysis life was 1.1 times longer, so both durability against sulfuric acid or organic additives were improved. Revealed.

<Example 2>
An evaluation electrode was prepared in the same manner as in Example 1 except that the post-baking temperature in an air circulation type electric furnace was 560 ° C., and the same electrolytic evaluation was performed.
As a result of X-ray diffraction after post-baking, the degree of crystallinity and crystallite size of IrO _{2 in} the catalyst layer were found to be the same as those in Example 1.
As shown in Table 4, compared to Comparative Example 1 (conventional product) in Table 4, the sulfuric acid electrolysis life was 1.5 times longer and the gelatin electrolysis life was 1.3 times longer. It was revealed that both durability were improved.

<Comparative Example 1>
Pyrolysis coating was performed by changing the firing temperature and firing time in the air circulation type electric furnace in Example 1 to 520 ° C. for 15 minutes to form an electrode catalyst layer made of a mixed oxide of iridium oxide and tantalum oxide. . The electrodes thus prepared were not subjected to post-baking, and the same X-ray diffraction and electrolytic evaluation as in Example 1 were performed.
When this sample was subjected to X-ray diffraction, a clear peak of iridium oxide attributed to the electrode catalyst layer was observed, and it was confirmed that IrO _{2 of} the catalyst layer was crystalline.
Life evaluation similar to Example 1 was performed. From the results shown in Table 4, it was clarified that the durability against electrolysis under high load conditions was improved by the formation of the catalyst layer of low-temperature firing + high-temperature post-baking proposed in the present invention.

<Comparative example 2>
An evaluation electrode was produced in the same manner as in Example 1 except that post-baking was not performed, and then electrolytic evaluation similar to that in Example 1 was performed.
As shown in Table 4, the sulfuric acid electrolysis life and the gelatin electrolysis life of the electrode baked at 480 ° C. without post-baking were the same as those of the conventional product of Comparative Example 1, and no durability improvement effect was observed.

  The present invention relates to an oxygen generating anode used for various industrial electrolysis and a method for producing the same, and more specifically, electrolytic metal foil production such as electrolytic copper foil, feeding in aluminum liquid, continuous electrogalvanized steel plate production, metal sampling. It can be used as an oxygen generating anode for high load resistance having excellent durability under high load electrolysis conditions used in industrial electrolysis.

Claims (8)

In an oxygen generating anode having a conductive metal substrate and a catalyst layer containing iridium oxide formed on the conductive metal substrate, the amount of iridium applied per catalyst layer is 2 g / m ² or more. Yes, a catalyst layer containing amorphous iridium oxide is formed by heating and firing in a high temperature region of 430 ° C. to 480 ° C., and then the catalyst layer containing amorphous iridium oxide is 520 ° C. to 600 ° C. An oxygen generating anode, wherein the catalyst is post-baked in a high temperature region, and substantially all of iridium oxide in the catalyst layer is crystallized. In an oxygen generating anode having a conductive metal substrate and a catalyst layer containing iridium oxide formed on the conductive metal substrate, the amount of iridium applied per catalyst layer is 2 g / m ² or more. 2. The oxygen generating anode according to claim 1, wherein the degree of crystallinity of iridium oxide in the catalyst layer after the post-baking is 80% or more. In an oxygen generating anode having a conductive metal substrate and a catalyst layer containing iridium oxide formed on the conductive metal substrate, the amount of iridium applied per catalyst layer is 2 g / m ² or more. 3. The oxygen generating anode according to claim 1, wherein a crystallite diameter of iridium oxide in the catalyst layer is 9.0 nm or less.   In an anode for oxygen generation having a conductive metal substrate and a catalyst layer containing iridium oxide formed on the conductive metal substrate, arc ions are formed on the conductive metal substrate before forming the catalyst layer. The anode for oxygen generation according to any one of claims 1 to 3, wherein an arc ion plating underlayer containing tantalum and titanium components is formed by a plating method. In an anode for oxygen generation having a conductive metal substrate and a catalyst layer containing iridium oxide formed on the conductive metal substrate, iridium per coating of the catalyst layer is applied to the surface of the conductive metal substrate. A catalyst layer containing amorphous iridium oxide is formed by heating and baking in a high temperature region of 430 ° C. to 480 ° C. with an amount of 2 g / m ² or more, and then containing the amorphous iridium oxide. A method for producing an anode for generating oxygen, characterized in that the catalyst layer is post-baked in a high temperature region of 520 ° C. to 600 ° C., and substantially the entire amount of iridium oxide in the catalyst layer is crystallized. Amorphous iridium oxide is formed on the surface of the conductive metal substrate by heating and baking in a high temperature region of 430 ° C. to 480 ° C. with an application amount of iridium per catalyst layer of 2 g / m ² or more. After forming the catalyst layer containing the catalyst layer, the catalyst layer containing the amorphous iridium oxide is post-baked in a high temperature region of 520 ° C. to 600 ° C., and the crystallinity of the iridium oxide in the catalyst layer is 80%. The method for producing an anode for oxygen generation according to claim 5, which is as described above. A catalyst layer containing amorphous iridium oxide is formed by heating and firing at a high temperature region of 430 ° C. to 480 ° C. with an application amount of iridium per one time of the catalyst layer being 2 g / m ² or more, Thereafter, the catalyst layer containing the amorphous iridium oxide is post-baked in a high temperature region of 520 ° C. to 600 ° C., and the crystallite diameter of the iridium oxide in the catalyst layer is set to 9.0 nm or less. The method for producing an anode for oxygen generation according to claim 5 or 6.   In a method for producing an anode for generating oxygen having a conductive metal substrate and a catalyst layer containing iridium oxide formed on the conductive metal substrate, the catalyst layer is formed on the conductive metal substrate before forming the catalyst layer. The method for producing an oxygen generating anode according to any one of claims 5 to 7, wherein an arc ion plating underlayer containing a tantalum and a titanium component is formed by an arc ion plating method.

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