JPH0233792B2 - - Google Patents

Description

[Detailed description of the invention]

<Technical classification> The disclosed technology belongs to the technical field of electrodes for electrolysis that can withstand oxygen-generating environments such as electrolysis in acidic sulfuric acid solutions and low chlorine ion concentration solutions and has a low overvoltage with respect to the desired electrode reactant. . <Explanation of the gist> The invention is based on a porous material to be supported on a part or all of the surface of a corrosion-resistant conductive substrate such as titanium, and an electrode reaction by supporting the material on the supported material. This invention relates to an electrode for electrolysis that is integrally coated with a body, and in particular, a porous platinum metal support is integrally formed on the surface of the corrosion-resistant conductive substrate by electroplating or the like, and then thermally decomposed. A support consisting of iridium oxide with an iridium content of 40 to 99 atom % and manganese, and one or both of manganese oxide and cobalt oxide with a cobalt content of 1 to 60 atom % by a method etc. This invention relates to an electrode for electrolysis that is three-dimensionally integrally formed on the supported object. <Prior art> As is well known, there are electrodes for electrolysis that are widely used in general and include electrode reactants coated and bonded on a corrosion-resistant conductive substrate, but the basic characteristics required for such electrodes for electrolysis are Basically, there are two conditions. Firstly, there are external conditions for bonding the electrode reactant to the substrate, which include high mechanical bonding strength and chemical corrosion resistance. It is necessary that the electrode reactant itself has strong conductivity and, of course, electrical conductivity.Secondly, the internal conditions of the electrode reactant itself include mechanical bonding between the components that make up the electrode reactant. It is desired that the material has high strength, high chemical corrosion resistance, and of course has a certain electrical conductivity, and in addition, has a low overvoltage when acting as an electrode reactant. By the way, as for the above-mentioned ordinary electrolytic electrode in which an electrode reactant is coated and bonded on a corrosion-resistant conductive substrate, there have been many known electrolytic electrodes in which the electrode reactant has a composition containing a platinum group component. There is. There are two types of electrode reactants containing platinum group components: platinum group metals consisting only of platinum group components and platinum group oxides. Electrodes have been used for a long time, and in particular, many improvements have been made to those coated with platinum metal, which have increased the strength of the bond between the electrode reactants themselves and the bond to the substrate, and have improved corrosion resistance. Electrolytic electrodes that are superior and durable are being developed. However, although the electrolytic electrode coated with the seed platinum metal has many excellent properties as described above, it has the disadvantage that its applications are limited. <Problems with conventional technology> If we consider the major factors behind this problem, compared to other electrodes used for various practical purposes,
In electrolytic electrodes that use platinum metal as an electrode reactant, the overvoltage characteristics against chlorine and oxygen are similar to other electrodes at the beginning of electrolysis, but as the electrolysis time progresses, the overvoltage characteristics rise to high values. This is because, as a result, electrolysis power consumption increases, resulting in higher costs.Also, due to the increase in overvoltage, an electrolytic reaction other than the intended purpose occurs, which inhibits the intended purpose electrolysis. This is because there may be some problems. To deal with this problem, several attempts have been made to solve the problem of overvoltage increasing over time in electrodes using platinum metal as an electrode reactant. Techniques have been developed to suppress the rise in overvoltage by adding and alloying platinum by various means, and to reactivate platinum metal electrodes with increased overvoltage by cathodic electrolysis. However, manufacturing electrodes using this seed development technology has the disadvantage that it is difficult to manufacture in practice due to the complicated process, resulting in electrodes with poor corrosion resistance and poor activation effects. It has shortcomings such as short duration and has not been put to practical use. On the other hand, the latter electrode reactant component contains a platinum group oxide such as ruthenium oxide, rhodium oxide, palladium oxide, or iridium oxide, and the electrode for electrolysis coats the surface of a corrosion-resistant conductive substrate with the platinum group oxide. , it is possible to have low overcharging, excellent durability, and stable catalytic function.In addition, the typical manufacturing method for platinum group oxide coated electrodes is to produce platinum group oxides by thermal decomposition. Since this is a thermal decomposition method in which a solution containing a compound that forms is applied onto a gas surface and thermally decomposed, platinum group oxides can be easily obtained even if they are a combination of multiple components, and have many advantages. It has. However, in a component where the electrode reactant is only one type of platinum group oxide, the mechanical bonding strength of the electrode reactant to the substrate and the mechanical bonding strength of the electrode reactant itself are extremely low, and the electrode reactant falls off during the electrode reaction. This method has the drawback of causing a large amount of damage, and also has the drawback that the electrode life is extremely short, which is a practical disadvantage. Therefore, in order to increase the life of the platinum group oxide coated electrode for electrolysis, it has been necessary to add a corrosion-resistant oxide such as titanium oxide or a second raw material such as a platinum group metal to the platinum group oxide component. mixture of
The bonding strength of electrode reactants has been increased by taking measures such as alloying or mixed crystal formation. On the other hand, non-platinum group oxides such as manganese oxide and cobalt oxide are also known as electrode reactant components. However, if the electrode reactant coated on the surface of the corrosion-resistant conductive substrate is composed only of non-platinum group oxides, the electrical conductivity between the electrode reactant and the opposite substrate and the electrical conductivity of the electrode reactant itself are poor. The initial potential during the electrolytic reaction is high, and it has not yet been put to practical use. <Background of the Invention> Prior to this invention, the inventors developed a porous support component in which an electrode reactant component was integrally bonded onto the surface of a corrosion-resistant conductive substrate such as titanium, and an internal structure of the support object. , and a supported component supported three-dimensionally on the surface; that is, an electrolytic electrode consisting of a supported component having an electrode reactant component bonded to a substrate;
We have developed an electrode for electrolysis in which the electrode reactant is composed of two different independent component compositions of support components that are dimensionally combined, and has basically excellent mechanical bonding strength to the substrate and prevents the electrode reactant from falling off. He devised an electrolytic electrode with excellent chemical corrosion resistance and applied for a patent. Furthermore, in the electrode for electrolysis, the above-mentioned supported material component is a porous platinum metal, and the above-mentioned 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 chloride ion concentration solutions, and have filed a patent application for this electrode. <Objective of the Invention> The object of the invention of this application is not only to solve the problems of the electrolytic electrode based on the prior art described above, but also to further improve the electrode, although it is technically an extension of the general electrolytic electrode. The technical challenge is to
By adding at least one of manganese oxide and cobalt oxide to the iridium oxide of the support component within a predetermined range, an electrolytic product with lower overvoltage and higher durability can be obtained. It is an object of the present invention to provide an excellent electrode for electrolysis and a method for manufacturing the same, which is useful in the field of electrode use in the chemical industry. <Structure of the Invention> The structure of the invention of this application, which is based on the above-mentioned claims in accordance with the above-mentioned object, is to bond porous platinum metal onto the surface of a corrosion-resistant conductive substrate by electroplating or the like. After forming a support, the above-mentioned solution contains at least one compound among iridium compounds, manganese compounds, and cobalt compounds among compounds that become iridium oxide, manganese oxide, and cobalt oxide by thermal decomposition. The electrode reactant is made of porous platinum by sufficiently permeating the entire platinum metal of the bonded support object and supporting the oxide in three dimensions on the platinum metal by thermal decomposition in an oxidizing atmosphere. For electrolysis, consisting of a metal component supported and at least one of manganese oxide and cobalt oxide with a manganese and cobalt content of 1 to 60 at % to iridium oxide with an iridium content of 40 to 99 at % As an electrode, it reduces overvoltage over time during operation, and also prevents corrosion resistance from decreasing.
This is a technical measure that makes it possible to suppress the rate of electrode reactant consumption. <Principle of the Invention> Therefore, in the electrode for electrolysis of the present invention in which one or more of predetermined manganese oxide and cobalt oxide is added to iridium oxide as a component of the above-mentioned support, the true electrode area is only iridium oxide. Since the electrode is larger than the electrode for electrolysis of the supported component, it is possible to maintain a lower overvoltage, and the mechanical bond between the supported material, platinum metal, and the supported material, the metal oxide, is improved. Since the platinum metal that is the supported material is large and porous, the platinum metal surrounds the metal oxide that is the supported material,
It has excellent mechanical strength by supplementing the mechanical bond of the metal oxide itself, and in addition, the support itself is active and has a three-dimensional shape, which prevents the inactivation of platinum during electrolysis. This makes it possible to maintain a low electrode potential by preventing the electrolysis of manganese oxide and cobalt oxide in electrolysis in a low chlorine ion concentration solution. This is thought to be because the overvoltage can be maintained even lower due to the electrocatalytic function against chlorine generation. Further, the state of the oxide is different from the state of each oxide alone, and a shift in the lattice constant is observed from the results of X-ray diffraction, and it is presumed that it is in the form of a composite oxide. Therefore, the amount of iridium oxide among the above support components is adjusted to 40 to 99 atomic% in terms of iridium content.
The reason for this is that when the temperature is lower than 40 atomic percent with the lid on, corrosion resistance decreases because manganese oxide or simple cobalt oxide, which has poor corrosion resistance, increases in the supported components in an oxygen-generating environment. As a result, the consumption rate of the electrode reactant is accelerated, resulting in a shortened electrode life. Also, if the content exceeds 99 atomic percent, the effect of maintaining low overvoltage due to the addition of manganese oxide and cobalt oxide decreases, making it impossible to achieve true This is because the effect of increasing the electrode area and the effect on the electrode catalyst function against chlorine generation are weakened, and the function of lowering overvoltage is weakened. Therefore, the optimal amount of iridium oxide as a support component is 40 to 99 at% iridium content, and as a result, the amount of at least one of manganese oxide and cobalt oxide is relatively low. The optimum cobalt content is 1 to 60 atomic %. By the way, the next method for forming porous platinum metal as a supported material is to form porous platinum metal directly on the surface of the substrate, and to form a coating layer of platinum metal and then make it porous. However, in the latter case, even if the surface of platinum metal is roughened, it is not possible to completely penetrate the compound solution and obtain a state in which non-platinum group oxides are supported three-dimensionally. There is. Therefore, in order to form porous platinum metal in the electrode for electrolysis of the present invention, it is desirable to adopt the former means of directly forming porous platinum metal. In addition to the plating method, there are thermal spraying methods, thermal decomposition methods, etc., but among these methods, the one that has excellent characteristics and is economically convenient is the electroplating method mentioned above. Among the methods, it is preferable to use one in which the electrodeposited platinum metal forms a porous, spherical aggregate. In addition, if it is desired to obtain a platinum metal with higher porosity, that is, with a higher mechanical support strength, after directly forming a porous platinum metal, further chemical,
Alternatively, an effective method is to apply a treatment to increase the porous state by an electrochemical method or the like. In addition, in the manufacturing process, the physicochemical properties required of the platinum metal to be supported are that it should be porous to the extent that a solution containing a non-platinum group compound can permeate therein, and that it should be porous enough to be penetrated by a solution containing a non-platinum group compound; During the process, it is necessary that the joint between the gas and the platinum metal be in a joint state that does not deteriorate due to reaction with oxidizing gas or volatile components in the compound. Therefore, in the method for manufacturing electrodes for electrolysis, in order to obtain sufficient core control of a solution containing a compound using porous platinum metal as a support, the apparent density of platinum metal must be 19
g/cm ³ or less is preferable, but it significantly increases the porous state, resulting in an apparent density of 8.
If it is less than g/cm ³ , the mechanical strength will be reduced, which may conversely shorten the life of the electrode. On the other hand, when the oxide is three-dimensionally formed as a support on the porous platinum metal support, the thermally decomposed compound and its solvent penetrate smoothly into the platinum metal, so the viscosity of the solution is low. , it is desirable to prevent the concentration of the compound from becoming too high. As an auxiliary means for improving the penetration of the compound, it is also effective to irradiate the substrate with ultrasonic waves. <Example> Next, an example 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. By this method, a sample was prepared in which porous platinum metal was formed on the surface of the titanium metal plate substrate with an apparent density of about 16 g/cm ² and an electrodeposited amount of 1.7 mg/cm ² . On the other hand, 1.95 g of chloroiridic acid, manganese chloride
Solution of 0.29 g, 1 ml of ethanol, 19 ml of butanol, 1.95 g of iridic acid chloride, 0.33 cobalt chloride
g, 1 ml of ethanol, 19 ml of butanol solution, and 1.95 g of iridic acid oxide, 0.14 manganese oxide
Coating solutions of 0.15 g of cobalt oxide, 1 ml of ethanol, and 19 ml of butanol were prepared. Then, each coating solution was taken with a micropipette so that the total amount of the supported metal oxide was 0.14 mg/cm ² in terms of metal weight, and applied to each of the platinum metal surfaces, and then heated at room temperature. After drying for 1 hour using a vacuum drying method, the electrodes were heated in the atmosphere at 500° C. for 20 minutes to produce Example electrodes-1, -2, and -3. And, for comparison, 2.14 g of chloroiridic acid
was dissolved in 20 ml of butanol to prepare a penetrating solution, and on the other hand, 1.7 mg/cm ² of platinum metal was formed as a support on a titanium metal plate substrate in the same process as in the electrode production mode of the above example, The above penetrating solution was taken with a micropipette so that the amount of supported iridium oxide was 0.14 mg/cm ² in terms of the weight of the metal, and the solution was allowed to penetrate into the platinum metal. The sample was dried and heated to produce a comparative electrode-1. Next, the electrode potential of each of these electrodes was measured at 10A/ ^dm2 in a 30g/dm sodium chloride solution at a liquid temperature of 30°C, and these electrodes were placed in an IM/dm2 solution at a liquid temperature of 60°C.
The electrode potential was measured at 10 A/dm ² in an aqueous sulfuric acid solution, and the results are shown in Table 1.

[Table] From Table-1, Example electrodes-1, -2, in which the supported material is platinum metal and the supported material is a combination of iridium oxide and one or more of predetermined manganese oxide and cobalt oxide; It is recognized that, unlike comparative electrode-1, in which only iridium oxide is supported, electrode-3 exhibits a sufficiently low electrode potential against chlorine and oxygen generation, that is, a low overpotential. Example 2 In the same manner as in Example 1 above, the apparent density was about 16 g/cm ³ and the amount of electrodeposition was
1.7 mg/cm ² of platinum metal to be supported was formed. Next, 1.56 g of iridium chloride, cobalt chloride
Using a solution of 0.84 g, 2 ml of ethanol, and 18 ml of butanol, the entire amount of supported metal oxide is metal, calculated in terms of weight, in the same manner as in the case of electrode production in Example 1.
0.14mg/ ^cm2 of metal oxide was added to the above supported platinum metal.
Example electrode-4 was prepared by supporting the sample in two dimensions. For comparison, platinum metal to be supported was formed on a titanium metal plate in the same process as in the example, and then 1.24 g of iridium chloride and cobalt chloride were added.
Using a solution of 1.34 g, 2 ml of ethanol, and 18 ml of butanol, a total amount of metal oxide supported on the above-mentioned example electrode was 0.14 mg/cm ² in terms of metal weight, and the metal oxide was added to the platinum metal to be supported. Comparative electrode-2 was prepared by supporting it three-dimensionally. Next, the above Example electrodes-2, -4 and the above-mentioned Comparative electrodes-1, -2 were subjected to electrolysis at a current density of 400 A/dm ² in an IM/sulfuric acid aqueous solution at a liquid temperature of 55°C. The electrode potential was measured at a current density of 1 A/dm ² , and the electrode life until the potential reached 1.7 V versus silver chloride electrode potential is shown in Table 2.

[Table] According to Table 2, when the ratio of iridium oxide as a support falls below 40 atomic % in terms of iridium content,
It is observed that in an oxygen-generating environment, the electrode reaction pair wears out faster and the electrode life becomes shorter. <Effects of the Invention> 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 porous supported material forming the framework of the electrode reactant component is By supporting the support three-dimensionally on the object, it basically has excellent mechanical bonding strength to the substrate, prevents the electrode reaction pair from falling off, and has excellent chemical corrosion resistance. This has the effect of lowering overvoltage during reaction. Further, a solution containing a set atomic percent of at least one of iridium oxide, manganese oxide, and cobalt compound among the compounds that become iridium oxide, manganese oxide, and cobalt oxide is infiltrated into platinum metal, and 3 Dimensionally supported electrolytic electrodes have a larger true electrode area than electrolytic electrodes containing only iridium oxide as a supported component, so they can maintain a lower overvoltage. In electrolysis in a solution with a low chlorine ion concentration, it is possible to further lower the voltage due to the interaction of the metal oxides, which has the effect of reducing electrolytic power consumption and saving energy. Further, the mechanical bonding strength between the electrode reactant components is strong, the chemical corrosion resistance is good, and the excellent effects that they are always uniform are exhibited. Furthermore, although the material to be supported is platinum metal, since the supported component is a metal oxide, the increase in overvoltage caused by the electrolytic action over time that occurs at the platinum metal electrode is mostly due to the electrode reactant component. Not only can it be completely suppressed until it is consumed, but in some cases it has the effect of significantly delaying the time it takes for the overvoltage at the platinum metal electrode to reach its increased value. Furthermore, by increasing only the supported material component in a state where the electrode reactant component has been exhausted and the electrode has reached the end of its life, the electrode life can be increased, and the total amount of the electrode reactant component does not need to be increased. There are also resource advantages. In addition, 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 there is also no need to increase the total amount of electrode reactants. There is also.

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 has an iridium content of 40 to 40%.
An electrode for electrolysis comprising 99 atomic % of iridium oxide and at least one component of manganese oxide and cobalt oxide in a content of 1 to 60 atomic % of manganese and cobalt.