JPH036998B2 - - Google Patents

Description

[Detailed description of the invention]

The disclosed technology belongs to the technical field of electrodes for electrolysis that can withstand oxygen-generating environments such as electrolysis in sulfuric acid acidic solutions or low chlorine ion concentration solutions and have low overvoltage for desired electrode reactions. Accordingly, the present invention includes integrally coating a part or all of the surface of a corrosion-resistant conductive substrate with an electrode reactant, and a porous supported material bonded to the electrode reactant-attached substrate and the coated material. This invention relates to an electrode for electrolysis consisting of a support three-dimensionally bonded to a support, and in particular, a porous platinum metal support is integrally formed on the surface of a substrate such as titanium by electroplating or the like. Iridium oxide is formed by pyrolysis method etc.
99 mol% and one or two of ruthenium oxide and palladium oxide relative to the iridium oxide
This invention relates to an electrode for electrolysis in which a supported material composed of components distributed in an amount of 70 mol% is three-dimensionally integrated with the supported material. A commonly used electrolytic electrode is one in which an electrode reactant is coated and bonded on the surface of a corrosion-resistant conductive substrate, but when raising the basic characteristics required for this, there are basically two conditions. Firstly, the electrode reactant must have high mechanical bonding strength, strong chemical corrosion resistance, and electrical conductivity as the bonding conditions for the electrode reactant to the substrate. The internal conditions of the electrode reactant itself include high mechanical bonding strength between the components constituting the electrode reactant, strong chemical corrosion resistance, and, of course, a specified electrical conductivity. It is desirable that the overvoltage at the time is low. Incidentally, many conventional electrodes for electrolysis have been known, in which an electrode reactant having a composition containing a platinum group component is coated and bonded on the surface of a corrosion-resistant conductive substrate. Among these electrodes for electrolysis, there are two types of electrode reactants: platinum group metals consisting only of platinum group components and platinum group oxides. has been used for a very long time, and in particular, many improvements have been made to electrodes coated with platinum metal, which have a high bonding strength between the electrode reactants themselves and a strong bond to the substrate, excellent corrosion resistance, and durability. More and more electrodes are being developed. However, although the seeded platinum metal coated electrode has many excellent properties, it suffers from the disadvantage that its applications are limited. However, the main reason for this is that, compared to other electrodes used for various practical purposes, electrodes using platinum metal as an electrode reactant have overvoltage characteristics against chlorine and oxygen that are higher than other electrodes in the early stages of electrolysis. This is because although it has a low value like the electrode, it increases as the electrolysis time passes and becomes a high value, which has the disadvantage of increasing electrolysis power consumption and increasing costs.
Another problem is that the increase in overvoltage causes an electrolytic reaction other than the intended purpose, which may impede the intended electrolysis. Therefore, in order to solve this problem, in order to solve the problem that overvoltage increases over time in electrodes using platinum metal as an electrode reactant, several attempts have been made, for example, using various methods to add various metals to platinum metal. Techniques have been developed to suppress the rise in overvoltage by adding and alloying platinum metal, and to reactivate platinum metal electrodes with increased overvoltage by cathodic electrolysis. However, manufacturing electrodes using this type of development technology has the disadvantage that it is difficult to manufacture in practice due to complicated processes, etc., resulting in electrodes with poor corrosion resistance, and short-lasting active effects. It has several drawbacks, so it has not been put to practical use. On the other hand, the latter electrode, in which the reactant component is coated with a platinum group oxide such as ruthenium oxide, rhodium oxide, palladium oxide, or iridium oxide, has a low overvoltage, excellent durability, and stable catalytic function. In addition, a typical manufacturing method for platinum group oxide-coated electrodes involves applying a solution containing a compound that forms platinum group oxides by thermal decomposition onto the substrate surface. Since it is a thermal decomposition method in which a platinum group oxide can be easily obtained even if it is a combination of multiple components, it has many advantages. However, if the electrode reactant is composed only of platinum group oxides, the bonding strength of the electrode reactant to the substrate and the bonding strength of the electrode reactant itself are extremely low.
It has the disadvantage that the electrode reactant falls off during the electrolytic reaction, and in addition, the electrode has a very short lifespan.
I felt bad about its lack of practicality. Therefore, in order to increase the life of the platinum group oxide-coated electrode, it has been necessary to add a second component such as a corrosion-resistant oxide such as titanium oxide or a platinum group metal to the platinum group oxide component and form a mixture with these. Attempts have been made to increase the bond strength of electrode reactants by taking measures such as alloying, mixed crystal formation, etc. Based on these considerations, the inventors first developed a porous supported material component in which an electrode reactant component was integrally bonded on the surface of a corrosion-resistant conductive substrate, and a porous material component in which an electrode reactant component was integrally bonded on the surface of a corrosion-resistant conductive substrate. An electrode consisting of a dimensionally supported support component, i.e. a support component in which the electrode reactant component is bonded to the substrate, and a support component three-dimensionally bonded to the support component. We have developed an electrode for electrolysis that has electrode reactants divided into component compositions, and basically has excellent mechanical bonding strength to the substrate, prevents the electrode reactants from falling off, and has excellent chemical corrosion resistance. An application was filed for an electrode. Furthermore, in the above electrode for electrolysis, the supported material component is porous platinum metal, and the supported material component is a combination of iridium oxide. We have developed an electrode for electrolysis with low overvoltage and excellent durability for the desired electrode reaction in electrolysis in ion-concentrated solutions, and have filed an application for this. The purpose of this invention is to solve the problems of the electrolytic electrode based on the prior art described above, and to further improve the improved electrolytic electrode described above, and the inventors have newly solved the problems of the electrolytic electrode based on the prior art. By adding at least one of ruthenium oxide and palladium oxide to iridium oxide within a limited range, an electrode for electrolysis with lower overvoltage and greater durability has been developed, which is useful in the chemical industry. The present invention aims to provide an excellent electrode for electrolysis that is useful in the field of electrode use. In order to solve the above-mentioned problems, the structure of the present invention, which is based on the above-mentioned claims in accordance with the above-mentioned object, is to coat the surface of a corrosion-resistant conductive substrate such as titanium with an electrode reactant, The reactant is three-dimensionally supported on a porous supported material that is integrally bonded to the substrate, which increases the mechanical bonding strength to the substrate, prevents the electrode reactant from falling off, and provides corrosion resistance. 30% of the support material in the electrode reactant.
One or more of ruthenium oxide and palladium oxide is distributed as 1 to 70 mol % to ~99 mol % of iridium oxide, and the true electrode area is made larger than that in the case where only iridium oxide is supported, and the overvoltage is increased over time. Technical measures have been taken to reduce the corrosion resistance during operation, prevent deterioration of corrosion resistance, and suppress the rate of electrode reactant consumption. Therefore, in the electrode of the present invention in which one or more of ruthenium oxide and palladium oxide is added to iridium oxide in a predetermined ratio as a support component, the true electrode area is only iridium oxide. Because it is larger than the electrode of the supported component, it is possible to maintain a lower overvoltage.In addition, in electrolysis in a solution with a low chlorine ion concentration, the electrode catalytic function of ruthenium oxide and palladium oxide against chlorine generation is This is thought to be due to the fact that the overvoltage can be maintained even lower. By the way, in this invention, the amount of iridium oxide in the supported components is set to 30 to 99 mol%.
If it falls below 30 mol%, the amount of ruthenium oxide and palladium oxide, which have weak corrosion resistance in an oxygen generating environment, will increase, resulting in a decrease in corrosion resistance.As a result, the rate of consumption of the electrode reactant will accelerate and the life of the electrode will be shortened. Moreover, if it exceeds 99 mol %, the effect of increasing the true electrode area becomes low, and there is a problem that overvoltage becomes high in a high current density region. On the other hand, the reason why the amount of at least one of ruthenium oxide and palladium oxide is set to 1 to 70 mol% is that when the amount is lower than 1 mol%, the effect of increasing the true electrode area and the function of the electrode catalyst against chlorine generation are reduced. This is because the effect on the overvoltage becomes weaker and the effect of lowering the overvoltage is lost. Moreover, if it exceeds 70 mol%, corrosion resistance will decrease. Also, the ratio of iridium oxide as a support component is
As a result of the optimum ratio of 30 to 99 mol %, the optimum ratio of at least one of ruthenium oxide and palladium oxide is 1 to 70 mol %. Next, a method for manufacturing the electrode of the present invention will be described, which is based on a method previously disclosed by the inventor. That is, an electrode in which the electrode reactant is composed of a porous platinum metal component supported, 30 to 99 mol% of iridium oxide, and 1 to 70 mol% of at least one of ruthenium oxide and palladium oxide to the iridium oxide. After forming porous platinum metal by electroplating on the surface of a corrosion-resistant conductive substrate such as titanium and on the surface of the formed electrode reactant, iridium oxide and iridium oxide are bonded by thermal decomposition. A solution containing ruthenium and at least one compound selected from the group consisting of an iridium compound, a ruthenium compound, and a palladium compound among the compounds that become palladium oxide is sufficiently permeated throughout the bond-forming platinum metal in an oxidizing atmosphere. An electrode for electrolysis is obtained by forming the platinum metal group oxide in three dimensions on the platinum metal by thermal decomposition. In order to form the above-mentioned porous platinum metal, there are methods for directly forming porous platinum metal on the surface of the substrate, such as electroplating method, thermal spraying method, and pyrolysis method. , and economically superior is the electroplating method, in which the state of the electrodeposited platinum metal is porous and formed as a spherical aggregate. It is desirable to have a specific aspect. Another possible method is to perform porous treatment after forming a coating layer of platinum metal, but in this method, even if the surface of platinum metal is roughened, the solution of the compound completely penetrates and the non-platinum group oxides are completely absorbed. In some cases, it may not be possible to obtain the state that is carried in the dimension. In addition, if you want to obtain platinum metal with higher porousness, after directly forming porous platinum metal in a predetermined manner,
Furthermore, it is an effective method to apply a treatment to increase the porous state by a chemical or electrochemical method. In addition, in the manufacturing process, the platinum metal as a support is required to have a porous state to the extent that a solution containing a platinum group compound can penetrate therein, and furthermore, under the heating process of pyrolysis, the platinum metal and the substrate must be porous. It is necessary that the bonded portion with the compound be in a bonded state that does not cause deterioration due to reaction with oxidizing gas and volatile components in the compound. Therefore, in order for the porous platinum metal to have sufficient permeability to solutions containing compounds, it is preferable that the apparent density of the platinum metal be 19 g/cm ³ or less. If the density is less than 8 g/cm ³ , the mechanical strength may decrease and the life of the electrode may be shortened. On the other hand, 3 non-platinum group oxides are added to porous platinum metal.
In order for the compound that thermally decomposes during dimension formation and its solvent to penetrate smoothly into the platinum metal, it is desirable that the viscosity of the solution is low and the concentration of the compound is not high. Furthermore, a method in which ultrasonic waves are applied to the substrate to improve the penetration of the compound is also effective. Next, embodiments of the present invention will be described as follows. Example 1 A titanium metal plate was degreased with a trichlene degreasing solution, and the surface was treated with a hydrofluoric acid aqueous solution and concentrated hydrochloric acid to prepare a substrate, and then electroplated using a platinum plating bath in which dinitrodiaminoplatinum was dissolved in a sulfuric acid aqueous solution. Using this method, a sample was prepared in which porous platinum metal was formed on the surface of a titanium metal plate substrate with an apparent density of about 16 g/cm ³ and an electrodeposited amount of 1.7 mg/cm ² . Next, a solution of 1.95 g of chloroiridic acid, 0.22 g of ruthenium chloride, 20 ml of butanol, 1.95 g of chloroiridic acid, 0.015 g of palladium chloride, and hydrochloric acid.
A solution of 20 ml of 0.2 ml butanol and a solution of 1.65 g of chloroiridic acid, 0.13 g of ruthenium chloride, 0.23 g of palladium chloride, 0.2 ml of hydrochloric acid, and 20 ml of butanol were prepared. They were each applied to the platinum metal using a micropipette to give a concentration of 0.14 mg/cm ² in terms of weight, and then dried for 1 hour using a vacuum drying method at room temperature. Heating was performed for 20 minutes to produce electrodes-1, -2, and -3 of Examples. For comparison, a penetrating solution was prepared by dissolving 2.14 g of chloroiridic acid in 20 ml of butanol, and then 1.7 mg/cm ² of platinum metal was formed and supported on a titanium metal plate substrate in the same process as the electrode of the above example. The amount of iridium oxide, which is a metal, is 0.14 mg /
The infiltrating liquid was taken with a micropipette and permeated into the platinum metal in an amount of ² cm2, dried and heated in the same manner as in the example electrode manufacturing process, and the comparison electrode
1′ was prepared. Next, the electrode potential of these electrodes was measured at 10 A/dm ² in a 30 g sodium chloride aqueous solution at a liquid temperature of 30° C., and the results are shown in Table 1. Furthermore, the electrode potentials of these electrodes were measured at 10 A/dm ² in a 1M sulfuric acid aqueous solution at a liquid temperature of 60 DEG C., and the results are also shown in Table 1. From Table 1, it can be seen that Example electrodes -1, -2, and -3, in which the supported material is platinum metal and the supported material is a combination of iridium oxide and one or more of predetermined ruthenium oxide and palladium oxide, are It was observed that, unlike the comparative electrode 1', which only contained iridium oxide, the electrode exhibited a low electrode potential for chlorine and oxygen generation, that is, a low overvoltage. Example 2 Similar to Example 1 above, the apparent density was about 16 g/cm ³ and the amount of electrodeposition was 1.7 mg/cm ² on the titanium metal plate as a base.
Then, using a solution of 1.07 g of iridium chloride, 0.67 g of palladium chloride, 0.6 ml of hydrochloric acid, and 20 ml of butanol, the total amount of platinum group oxides was prepared in the same manner as in Example 1. Example electrode-4 was prepared in which 0.14 mg/cm ² of platinum group oxide in terms of metal weight was supported three-dimensionally on the platinum metal formed above. For comparison, after forming platinum metal on a titanium metal plate in the same process as the electrode of the example, 0.71 g of iridium chloride, 0.86 g of palladium chloride, and hydrochloric acid were added.
Using a solution of 0.6 ml and 20 ml of putanol, the platinum group oxide with a total amount of platinum group oxide of 0.14 mg/cm ² in terms of the weight of the metal was added to the platinum metal formed above in the same way as in the electrode of this example. Comparative electrode supported by dimensional
2' was made. Next, these electrodes, Example electrode-2 and Comparative electrode-1' were soaked in a 1M sulfuric acid solution at a temperature of 55°C.
Electrolysis was carried out at a current density of 400 A/dm ² , and the electrode potential at a current density of 1 A/dm ² was measured at regular intervals. Table 2 shows the electrode life until the potential at that time reached 1.7V versus silver chloride electrode potential. From Table 2, it was found that when the ratio of iridium oxide as a support was lower than 30 mol %, the electrode reactant consumption rate was accelerated in an oxygen generating environment, and the electrode life was shortened. As described above, according to the present invention, in an electrolytic electrode in which an electrode reactant is coated on the surface of a corrosion-resistant conductive substrate, a supported material is By supporting the support three-dimensionally, it not only basically has excellent mechanical bonding strength to the substrate, but also prevents the electrode reactant from falling off and has excellent chemical corrosion resistance. This has an excellent effect of lowering the overvoltage during operation. In particular, platinum metal is infiltrated with a solution containing at least one of a ruthenium compound and a palladium compound for an iridium compound among compounds that become iridium oxide, ruthenium oxide, and palladium oxide, and a three-dimensional structure is formed by thermal decomposition. Electrodes supported on iridium oxide have a larger true electrode area than electrodes containing only iridium oxide as a support component, so they can maintain a lower overvoltage. In electrolysis in a solution, the overvoltage can be further lowered due to the interaction of the platinum group oxides, and the electrolytic power consumption is reduced, resulting in the advantage of energy saving. In addition, the mechanical bonding strength between the electrode reactant components is strong, the chemical corrosion resistance is good, and since they are always in a uniform state, the product quality is improved. Furthermore, although the material to be supported is platinum metal, the support component is a platinum group oxide, so the increase in overvoltage during electrolysis over time that occurs at a platinum metal electrode will cause the electrode reactant component to be almost exhausted. This is an excellent effect in that it can be completely suppressed until the overvoltage rises, and in some cases, it is possible to significantly delay the time it takes for the overvoltage at the platinum metal electrode to reach the increased value. It also has the excellent effect of increasing the amount of the supported material component only when the electrode reactant component is exhausted and reaching the end of the electrode life, thereby preventing electrode deterioration, and reducing the total amount of the electrode reactant component. It has the advantage of saving resources as it does not need to be increased. In addition, even if the electrode reactant remains and reaches the end of its life at a high overvoltage, it has the effect of increasing only the supported material to extend the life, and also eliminates the need to increase the total amount of electrode reactants. There is also. Therefore, the amount of consumption of the supported material is reduced to less than a fraction of that of an electrode using only platinum group oxide, which is a component of the supported material, as an electrode reactant, and the consumption of the supported material is also reduced. There are some effects that can be done. Therefore, the electrode according to the present invention in which a supported material is three-dimensionally supported and formed on a supported material is several times as effective as an electrode in which a known platinum group metal component or a platinum group oxide component is used as an electrode reactant. It is possible to provide a well-designed electrode that extends the life of the electrode.

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Claims (1)

[Claims] 1. A porous supported object in which an electrode reactant is integrally bonded on the surface of a corrosion-resistant conductive substrate, and 3.
In an electrolytic electrode comprising a dimensionally supported material, the supported material component is porous platinum metal, and the supported material component is iridium oxide 30-30.
An electrode for electrolysis, characterized in that at least one of ruthenium oxide and palladium oxide is distributed in an amount of 1 to 70 mol% relative to 99 mol%.