JPS6147231B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention generally relates to electrodes for electrolysis and the manufacture of such electrodes, comprising an outer coating suitable for electrolysis, a conductive intermediate mixed oxide layer, and a base of valve metal. Electrodes used in industrial electrolyzers usually meet several stringent requirements, namely with regard to conductivity, physicochemical stability, corrosion resistance, manufacturing and electrochemical performance, and more specifically catalytic activity and selectivity. Must meet strict requirements. However, no material has yet been found that satisfies all of the above requirements for providing satisfactory performance to industrial electrodes. Although there are only a limited number of materials that can withstand severe anodic attack, their use alone is usually not possible in the production of electrodes with reasonable electrochemical performance under industrial operating conditions. Therefore, various types of composite electrodes have been proposed, consisting of various combinations of different materials, in order to provide reasonable industrial performance and to be able to meet the various technical and economic requirements as far as possible. . Various electrodes with catalyst coatings on metal bases have been proposed and can be found in numerous patents relating to these electrode coatings. As an outstanding success in this field, DSA
For example, there is a dimensionally stable anode known under the trade name U.S. Pat. No. 3,632,498. This anode, which has a catalytic coating of titanium-ruthenium oxide on a titanium base, has fundamentally transformed the world's chlorine industry over the past decade. Titanium is preferred as the electrode base. Because titanium and other suitable valve metals
This is because it exhibits extremely high corrosion resistance due to its film-forming properties and therefore forms a protective oxide film under anodic operating conditions. Platinum group metals are known to act as excellent electrocatalysts for various electrode reactions. However, because they are expensive, these metals must be used in as small a quantity as possible, and specifically, they must be replaced with cheaper electrode materials where possible. Ruthenium is of particular interest because it is cheaper and more readily available than other platinum group metals. The dimensionally stable anode (DSA) described above exhibits excellent stability performance and long service life when used in chlorine production electrolyzers. However, the manufacture and operation of this DSA must be carried out under controlled conditions and must not produce an insulating layer of titanium oxide on the electrode base. The presence of this insulating layer renders the anode electrochemically inactive and increases its operating potential excessively. Another anode is described, for example in U.S. Pat. No. 3,776,834, whose catalytic coating is
Approximately half of the ruthenium normally present in DSA's standard titanium-ruthenium oxide coating is replaced with titanium. This anode, which replaces some of the ruthenium with titanium, has a higher oxygen overpotential in the presence of anode-generated oxygen and better oxidation resistance than the standard DSA currently used in the chlor-alkali industry. Various inexpensive electrode materials based on metals other than noble metals have been proposed, but their use remains relatively low for various reasons. Lead dioxide is also a stable, inexpensive, and promising anode material for use in various electrolysis methods, but lead dioxide anode bodies have insufficient electrical conductivity. On the other hand, lead dioxide coatings formed on electrode bases have not generally exhibited satisfactory stability over long lifetimes in industrial use to date. Lead dioxide electrodes and techniques for their manufacture and use are disclosed in U.S. Pat. No. 4,040,039;
No. 4026786, No. 4008144, No. 3751301, No.
3629007 and British Patent No. 1416162, no.
Nos. 1378884 and 1377681. Manganese dioxide also shows great promise as a stable, inexpensive anode material for oxygen generation, especially in electrowinning of metals from acid solutions. However, its widespread use has so far not been realized due to manufacturing difficulties. There was no technology available for making a satisfactory electrode body consisting entirely of manganese dioxide, while the manganese dioxide coating formed on the electrode base usually possessed stable and satisfactory performance with a sufficient industrial life. I hadn't done it. Lead dioxide and manganese dioxide coatings can be produced by depositing a metal salt on the electrode base and pyrolyzing it to create a coating substrate. However, the resulting oxide film is usually very porous and has poor adhesion to the electrode base. On the other hand, by electrodepositing it on the electrode base, it is possible to create an oxide film that is dense and has good adhesion.
However, the coatings are still porous and generally still have insufficient protection against electrode base oxidation. Metal electrode bases with an intermediate protective coating covered with an external coating of lead dioxide or manganese dioxide have also been proposed. The technology related to this intermediate protective coating is disclosed in U.S. Patent No. 4028215, U.S. Pat.
No. 4040937 (tin/antimony oxide lower coating), Japanese Patent Application No. 51-156740 (Special Publication No. 53-79771)
Electrochimica Acta Vol.23, p.331-333
(Platinum Group Metal Oxide Bottom Coating), U.S. Patent No.
No. 4072586 (RuO ₂ /TiO ₂ bottom coating), U.S. Patent No.
No. 4,180,445 (TiO ₂ /SnO ₂ /RuO ₂ bottom coating), US Pat. No. 4,060,476 (TiN bottom coating). This intermediate protective coating must act as an effective inhibitor against oxidation of the electrode base and, for that purpose, must have the following characteristics: adhesion, conductivity, price, impermeability, antioxidant properties, physicochemical stability. The requirements related to the above shall be satisfied. When used industrially, it is not easy to achieve all of these properties. Various proposals have also been made to use various polymers in electrode manufacture. For example, in US Reissue Patent No. 29419, a composite coated catalyst formed on a valve metal base consists of ruthenium dioxide finely dispersed in an organic polymer. The intended role of the organic polymer is as a binder for mechanical support of the dispersed electrocatalyst, adhesion to the base, and protection thereof. Ruthenium dioxide is prepared in the form of ultrafine particles smaller than 1 micron and uniformly dispersed in a polymer at a weight ratio of 6:1 to 1:1 to form a coating with electrical and catalytic properties. The electrical conductivity of this composite coating is therefore largely determined by the amount, particle size, and distribution of the dispersed electrocatalyst in the polymer (binder). Technologies related to electrodes containing polymeric materials include:
Additionally, U.S. Patent Nos. 3,626,007, 3,751,301,
No. 4118294, No. 3972732, No. 3881957, No.
4090979, German Patent Application No. 2035918. The lifetime of coated electrodes as described above is usually short when these electrodes are used industrially under the well-known anodic oxygen evolution. The particular problem in this case is
It is necessary to adequately protect the electrode base from oxygen attack, which can lead to electrode destruction due to corrosion or electrochemical inactivation of the electrode base. As can be seen from the above, in addition to the selection of appropriate electrode materials, the manufacture of electrodes with satisfactory long-term performance in industrial electrolysis processes is generally extremely problematic and involves complex technical issues. I'm leaving it behind. The purpose of the present invention is to provide a valve metal base, a stable outer coating suitable for electrolysis, an intermediate layer (a layer that sufficiently prevents the electrode base from oxidizing and firmly adheres to the base, and the outer coating is applied to this layer). The object of the present invention is to provide an electrode for electrolysis consisting of an intermediate layer (intermediate layer) which adheres firmly and is stable under the industrial operating conditions under which the electrode is used. Another object of the invention is to provide an electrode with a protective intermediate layer which can be easily fabricated on the electrode base and which then allows the production of an outer coating in a satisfactory manner without any deterioration of the electrode base. Our goal is to provide the following. Yet another object of the present invention is to provide an electrode that exhibits excellent antioxidant properties, long life, and stable electrochemical performance under industrial operating conditions. A further object of the invention is to prevent deactivation of the base by means of an intermediate layer containing as little platinum group metal as possible, advantageously less than 2 g and preferably less than 1 g per m ² of electrode base. is to provide valve metal electrodes. Another object of the invention is to provide an electrode containing a minimum amount of noble metal. Yet another object of the present invention is to provide an electrode having a protective intermediate layer and an outer coating catalyst of manganese dioxide. Another object of the invention is to provide an electrode having a protective intermediate layer as well as an outer coating of lead dioxide. Yet another object of the invention is to provide a simple manufacturing method for making electrodes with a protective interlayer. Another object of the invention is a valve having a protective intermediate layer as described above and an inexpensive, stable, electroplated outer coating of desired free thickness for carrying out electrolysis, in particular electrolysis with anodic oxygen evolution. The object of the present invention is to make it possible to produce electrodes having a satisfactory long-term performance, consisting of a metal base. The above objects are essentially fulfilled by the claimed invention. The present invention essentially provides an electrode in which a very thin protective oxide layer is created between the base of the valve metal and the outermost applied outer coating, specifically the electroplated coating. be. To create the protective oxide layer, the valve metal electrode base surface is converted to a mixed oxide. The mixed oxide layer is made of a mixed oxide of the valve metal and a noble metal selected from the group consisting of iridium, rhodium, and ruthenium. The mixed oxide is prepared by subjecting the surface of the valve metal base to a special oxidation treatment under carefully controlled conditions according to the claimed method. The valve metal base used in the present invention may be a suitable electrode base consisting essentially of a valve metal such as titanium, zirconium, tantalum, niobium or an alloy based on a valve metal, or at least the surface of the base may be a valve metal or its like. Any electrode base may be made of an alloy and serve as a valve metal substrate for making the mixed oxide layer according to the invention. The solution applied to the base contains a sufficient amount of hydrogen chloride, which corrodes the base surface and causes the valve metal on the surface to coexist with the precious metal chloride applied with the solution, replacing the corresponding chloride, causing thermal decomposition. A mixture of chlorides must be formed to form a mixed oxide. The amount of base valve metal replacing chloride clearly depends on the HCl concentration in the solution on the one hand and on the time during which this conversion takes place on the other hand. As a result, the coating solution must be allowed to dry slowly without significantly increasing the temperature, allowing the necessary time for conversion to the precious metal chloride.
Furthermore, the base surface is moderately moistened with the coating solution,
The above conversion of valve metal must be ensured. The present invention was successfully implemented using isopropyl alcohol (IPA) as the solvent for the coating solution.
However, other alcoholic solvents such as ethanol and butanol have been used with similar success. On the other hand, water is clearly unsuitable as a solvent when carrying out the invention. This is because solutions using water do not sufficiently wet the valve metal and/or the hydrochloric acid evaporates too quickly. The HCl concentration required to give a constant molar ratio of valve metal to noble metal to convert into a mixed oxide is:
It can be calculated theoretically. However, some excess of HCl is usually added to ensure the desired conversion. Furthermore, in order to ensure the formation of mixed oxides on the surface of the valve metal base according to the present invention, the molar ratio of HCl to noble metal chloride present in the coating solution must fall within a certain range. In each case, this molar ratio depends on the desired ratio of valve metal to noble metal in the resulting mixed oxide, as well as the amount of valve metal that is effectively converted to chloride, and more specifically on the valve metal surface. Depends on the amount of HCl that reaches and effectively erodes. It is further noted in this connection that the number of solution layers applied and thermally converted into mixed oxide according to the present invention is
It depends on various factors, in particular the concentration of noble metal in the coating solution in each case. The invention was successfully carried out using IrCl ₃ dissolved in IPA at a concentration corresponding to about 7 g of metallic iridium per portion. Mixed oxides were also prepared in accordance with the present invention with iridium concentrations ranging from 3.5 to 35 g/g. However, the noble metal chloride concentration can be selected from a wide range of concentrations starting from about 1.times.10.sup. ^-2 moles per solution. However, in order to ensure satisfactory mixed oxide formation according to the present invention, a narrow range of 2×10 ^-2 to 10×
10 ⁻² mol, particularly 2.5×10 ⁻² to 7.5×10 ⁻² mol is preferred. However, as explained above, in both cases
The concentration of HCl is determined by the concentration of noble metal chloride present in the coating solution, and the molar ratio of HCl and noble metal chloride must be within a certain range to form a mixed oxide as specified. The HCl concentration can therefore also be selected from a relatively wide range, ie from about 14.times.10.sup. ^-2 to 3 mol per solution. However, the chosen HCl concentration in each case depends on the choice of the concentration of noble metal chloride present in the coating solution. When carrying out the present invention, the above range of the molar ratio of HCl and noble metal chloride concentration is from 1:1 to 100:
1, preferably in the range of 3:1 to 30:1. However, both concentrations must be increased or decreased at the same time. The mixed oxide according to the invention does not form when the HCl concentration is extremely high (e.g. 200 g/) and the precious metal concentration is extremely low (e.g. 2-3 g/), in which case it is important to provide an electrode with reasonable long-term performance. It was found that no useful results could be obtained. On the other hand, as shown in the Examples shown below, when the molar ratio is selected from the above fixed range based on the present invention, excellent performance as an oxygen generating anode can be obtained. According to the present invention, in order to convert the mixed chloride obtained by coating a solution containing HCl and noble metal chloride in a certain ratio, and slowly drying the coating solution into a mixed oxide, the mixed chloride is oxidized. in a sexual mood
The heat treatment is performed at a relatively high temperature in the range of 400-600°C, more specifically about 450-520°C. This heat treatment successfully converted the mixed oxide in about 5-10 minutes at about 480 DEG C. in a stream of air. In the case of heat treatment at a lower temperature than this, it seems that it takes more time, and vice versa. On the other hand, when heat treatment was performed at a relatively low temperature of 400°C for a relatively long time of one hour, satisfactory results were not obtained. The time and temperature of the heat treatment must therefore be chosen appropriately in each case to effect a satisfactory conversion of the mixed chloride to the mixed oxide. In that case, oxidation of the underlying base of the valve metal is undesirable and must be avoided. According to the invention, the successive process consisting of application of a suitable component-controlled solution, slow drying and controlled heat treatment to convert the mixed chlorides into mixed oxides is carried out several times in cycles, i.e. at least twice. The process must be repeated to gradually produce a mixed oxide of appropriate thickness containing a sufficient amount of precious metal. The first layer of mixed oxide thus formed is relatively porous, so that the subsequently applied solution soaks into this first porous layer, eroding the underlying valve metal and converting it to the corresponding valve metal chloride. conversion, resulting in the new formation of the above-mentioned mixed chlorides. This mixed chloride is converted to a mixed oxide, some of which forms in the pores of the first layer. Therefore, the porosity of the resulting mixed oxide layer gradually decreases with each repetition of the steps in the above cycle for mixed oxide formation, until the conversion of the base valve metal from chloride to mixed oxide is almost complete. It is no longer practiced. Even if the above cycle process is repeated, the mixed oxide of the present invention is no longer produced, and it is no longer desirable to carry out the process any further. This is because only precious metal oxides are produced, and as we know,
This is because they are less stable than mixed oxides containing significant amounts of valve metal. By repeating a series of simple, well-controlled process cycles in accordance with the present invention, an extremely stable, homogeneous, relatively dense, impermeable, conductive mixed oxide can be produced as a base for valve metals. It can be made gradually. However, as stated above, the amount of mixed oxide produced in accordance with the present invention is limited in each case and application of the solution in excess of this limit should be avoided. This is because oxides with low stability are produced, which is not preferable. The number of solution layers that can be effectively applied for the production of the mixed oxides of the invention depends primarily on the noble metal concentration in the solution applied in each case. Thus, for example, in the case of a solution containing IrCl ₃ corresponding to 7 g of iridium per solution, excellent results were obtained when the above series of steps for mixed oxide formation was repeated four times according to the invention. Ta. However, if the noble metal concentration in the coating solution is significantly lowered to approach the lower limit of the above-mentioned equivalent concentration, the number of repetitions of the above series of steps can be increased to 20 times or perhaps more. On the other hand, when using precious metals at relatively high concentrations,
The number of applications of the solution is reduced, for example, from 2 to 4 times, so that only the mixed oxide is formed, so that a large amount of precious metal is deposited on the valve metal base in the form of a relatively unstable mixed oxide with a reduced proportion of the valve metal. must be prevented from generating. It is further noted that the solution for producing mixed oxides according to the invention can be applied by any suitable method, such as by brush or sprayer. Regarding the amount of solution applied in each case (V), apply 10 to 20 of the above solution per 1 m ² of surface of the valve metal base.
Good results were obtained based on the present invention. Furthermore, amounts such as 50 ml/m ² could be applied by spraying, and smaller amounts such as 5 ml/m ² could probably also be used. The total amount of precious metal (L) produced in the form of mixed oxide per unit area of the base surface of the valve metal obviously depends on the concentration of precious metal in the coating solution (CNM), the number of coats (N), and the number of coats applied each time. It is proportional to the amount of solution (Vml/m ² ). According to the invention, from 0.5 to 0.5 of the precious metal in the form of mixed oxides per unit surface area of the valve metal base
Good results were obtained by depositing an amount (L) of noble metal equivalent to 1 g. Satisfactory results can be obtained with precious metal coatings somewhat less than 0.5 g/ ^m2 ;
Since this level is already quite low, further reductions in noble metal loading are unlikely to yield significant economic benefits any further. On the other hand, we have discovered that when using a reasonable number of solution applications (N), extremely low noble metal coverage (approximately 0.2 g/m ² ) does not give satisfactory results. Furthermore, if necessary, the amount of precious metal deposited may be reduced by 1
For example, 1.2 g/m ² at a location somewhat higher than g/m ²
We have found that it is possible to increase the amount to 1.5 g/m ² , or perhaps up to about 1.5 g/m 2 . It is therefore clear from the above description that reasonable compromises should be found for the above parameters falling within each indicated range, and in each case the best result according to the respective electrode requirements should be sought. Therefore, for example, the number of times each solution application is followed by drying and heat treatment should clearly remain within a reasonable range. On the one hand, this number of applications should be increased to take advantage of all the advantages of the invention, but too many applications are too cumbersome and undesirable, and all the advantages of the invention cannot be fully exploited. According to the present invention, large industrial electrodes can also be easily manufactured. That is, it is manufactured according to the special technique of the present invention for producing mixed oxides using the valve metal obtained from the electrode base itself and the noble metal supplied from the coating solution. As explained below, the conductive intermediate mixed oxide layer thus formed on the valve metal base and thus fully integrated with the electrode base surface provides excellent protection to the valve metal base due to its relatively low noble metal loading. while its electrical resistance is practically negligible. In a very simple and economical manner, the conductive intermediate mixed oxide layer thus forms a highly conductive layer for the subsequent electrodeposition of a stable and inexpensive outer coating, in particular of manganese dioxide or lead dioxide. Provide an intermediate substrate. This electrically conductive intermediate mixed oxide layer produced according to the special technology of the invention has, in addition, not only a good protective power and a low potential drop, but also a good electrodeposition property - so that the electroplated coating can be applied to the valve metal base. Gives a strong adhesion to -. This superior adhesion improves the quality and performance of the resulting electrode, thereby greatly improving its long-term performance and lifespan. The method of manufacturing the electrode according to the invention is illustrated by the following examples using the table below. Listed in the table below are the electrode samples, the amount of noble metal in the mixed oxide, the amount of oxide in the outer coating, and the test data for each sample: anodic current density, anodic potential relative to a normal hydrogen electrode, and test time. It is. Test times are shown in the last column of the table, with underlined data being when the anode had stopped working, and asterisked data being when the anode was still working. It is something. Example 1 An electrode sample in which a manganese dioxide film was coated on a titanium base was prepared by the following method. Titanium plates (10 x 2 cm) were degreased, washed with water, dried and etched in oxalic acid for 30 minutes. Next, add 10ml of IPA to the pre-treated titanium plate.
A fresh solution S6 consisting of 0.06 ml of hydrochloric acid and 0.16 g of an aqueous IrCl ₃ solution (48% by weight of Ir) was applied with a brush and then allowed to dry slowly in air to treat the surface of the titanium plate. Then, heat treatment was performed at 480° C. for 7 minutes in an air flow of 60/h to form a mixed oxide of titanium and iridium on the surface of the titanium plate base. The series of steps of solution application, drying, and heat treatment was repeated four times (five times in the case of CH1), which gradually formed a conductive intermediate mixed oxide layer consisting of base titanium and a certain amount of iridium, and produced electricity. This is to prepare a mixed oxide intermediate substrate for plating. The mixed oxide substrate was then top coated by anodically depositing manganese dioxide. Topcoat is done in a 2M manganese nitrate bath at 90-95°C, usually for 1.5 hours at a current density of 1.5 mA/ ^cm2 , or for SM3.
3 hours at 10mA/ ^cm2 , for SM2 and D40b
It was carried out for 1.5 hours at 20 mA/cm ² . At the end of the MuO ₂ top coat, a heat treatment at 400° C. for 20 minutes in an air flow of 60/h was performed to improve electrode performance. For each electrode sample of the generated MnO ₂ coating, 150
at 45-55 °C in an electrolytic cell containing g/g H ₂ SO ₄
Accelerated tests as an oxygen generating anode were performed at constant anode current densities ranging from 500 to 7500 A/ ^m2 .
The initial anodic potential of each sample was measured against a regular hydrogen electrode without correction for resistance drop. The final anode potential at the end of the test was also measured, but was not measured if the anode potential showed a sudden and rapid increase (end of life of the anode). For reference, the manufacturing methods of the electrode samples Me1, C49, and B03 in Table 1 were different from those described above. That is, the titanium substrate of Me1 was etched with hydrochloric acid instead of oxalic acid, and the MnO 2 top coat of B03 was heat treated at 330°C instead of 400°C, and the MnO ₂ top coat of B03 was etched at 330°C instead of 400°C.
MnO ₂ topcoating was done at 400°C but in steady air. The CH1 electrode sample was removed from the test chamber after 1000 hours of stable operation at 7500 A/ ^m2 , and X-ray diffraction was performed. Approximately 75-80% of the initial _βMnO2 coating still remained, which was noticeable. No structural changes occurred at all.

【table】

[Table] Example 2 Comparative sample B65,
A mixed oxide substrate was applied to F12 and SM5. However, the MnO ₂ topcoat was not electrodeposited, but instead was produced by pyrolyzing a manganese nitrate solution onto the mixed oxide surface layer for comparison. The data in Table 2 for these samples was obtained in the same manner as in Table 1. Comparing the results of Tables 1 and 2, Example 1
Electrodeposited coating of MnO ₂ shows a longer electrode life under similar conditions.

[Table] Example 3 An electrode sample in which lead dioxide was coated on a titanium mesh base was prepared in the following manner. To pre-treat the titanium mesh pieces (50 x 25 x 2 mm), grit blast and 96°C in 25% hydrochloric acid.
Etching was performed at ℃ for 30 minutes. 1 g of IrCl ₃ aqueous solution (Ir56%) was added to n-butanol.
A solution was prepared by dissolving the mixture in 60 ml and 3 ml of 36% hydrochloric acid. This solution was evenly applied to the surface of the pretreated titanium mesh using a brush, dried in air for 10 minutes, and heat treated at 480° C. for 7 minutes in a stream of air. The above surface treatment was repeated four times in order to gradually transform the titanium surface into a mixed oxide substrate containing 0.5 g/m ² of Ir. Next, Pb(NO ₃ ) ₂ 400g/, Cu(NO ₃ ) ₂ 14
g/, HNO ₃ 10g/, surfactant (product name
Lead dioxide was electroplated onto the mixed oxide substrate produced above in a plating bath containing an aqueous solution of 12 g/triton-X). 50~ in this metsuki bath
Lead dioxide was anodically electrodeposited at 75°C, but two successive
It was carried out in steps: 40 mA/cm ² for 5 minutes and 20 mA/cm ² for 55 minutes. Approximately 1000g after drying at 100℃ for 5 minutes
A coat of lead dioxide corresponding to PbO ₂ /m ² was obtained.
The battery voltage of the electric plating was about 1.5V, and the current efficiency with respect to PbO ₂ was 50%. For titanium mesh sample 51 with lead dioxide top coated on the surface of the conductive intermediate mixed oxide layer,
An accelerated test as an oxygen generating anode was conducted at 50° C. and 8000 A/m ² in 150 g of H ₂ SO ₄ . The unipolar initial potential was 2.26 V (not corrected for resistance drop) relative to the standard hydrogen electrode. Battery voltage is approximately 5V (initial approx.
4.5V) and the anode life under accelerated test conditions was approximately 680 hours, the test was discontinued.

[Table] Example 4 Electrode samples A to F, each having a titanium plate base coated with lead dioxide, were prepared in the following manner. The preliminary treatment of titanium plate pieces (100 x 20 x 1 mm) is as follows:
After grit blasting, in 15% hydrochloric acid at 100℃, 60
I etched it for a minute. A solution was prepared by dissolving 0.1 g of IrCl ₃ aqueous solution (48% Ir) in 6 ml of IPA and 0.4 ml of 36% hydrochloric acid. This solution was applied evenly with a brush to the surface of the pretreated titanium sample, dried in air at 60°C for 5 minutes, and then aged in a stream of air at 480°C for 7.5 minutes. The above surface treatment was repeated four times in order to gradually transform the titanium surface into an oxide substrate containing 0.8 g/m ² of Ir. Lead dioxide was then electroplated onto the resulting oxide substrate in the same bath as in Example 1. However, it was carried out in one step for 2 hours at 20 mA/cm ² . Next, drying was performed at 120°C for 120 minutes, and the substrate surface 1
A coat of lead dioxide corresponding to 1430-1700 g PbO ₂ per m ² was obtained. Sample A was further treated at 400°C for 20 minutes. Four electrode samples (A to D) thus obtained
On the other hand, an accelerated test was conducted as an oxygen generating anode at 45° C. in 150 g of H ₂ SO ₄ . Table 3 shows the amount of lead dioxide coating, anode test current density, and test time for anode samples A to D. Electrode sample E prepared as described above was subjected to an accelerated test under the same conditions as sample A. However, 10 ppm of sodium fluoride was added to the sulfuric acid electrolyte. No decisive influence by fluoride ions was found under these test conditions. Sample F was also prepared using the same method, but the total amount of noble metal coating on the surface of the mixed oxide substrate was Ir0.2g/m ² and Ru0.6.
A portion of the IrCl ₃ was replaced by RuCl ₃ in the solution so that the amount of IrCl 3 was 100 g/m ² . Next, lead dioxide was top coated and an anodic test was performed. The anode life under accelerated test conditions at 7500 A/m ² was 780 hours. Industrial Applicability Electrodes produced according to the present invention can be advantageously used in various electrolytic methods that require inexpensive, stable, and anti-oxidizing electrodes based on valve metals. The electrode according to the invention can be advantageously utilized as an anode for use under conditions where oxygen is anodically generated, more particularly in acid electrolytes. The electrode of the present invention having a manganese dioxide coating can be advantageously used as a lightweight, small-capacity, inexpensive oxygen-generating anode that operates with low electromotive force without contaminating the electrolyte, and therefore can be used advantageously as an oxygen-generating anode that is lightweight, has a small capacity, operates with low electromotive force, and is therefore superior to conventional methods currently in use. Instead of lead or lead alloy anodes, they can be advantageously used in metal (Cu, Zn, Co, Ni, Cr, etc.) electrowinning processes from acid electrolytes. The electrode of the present invention having a lead dioxide coating can contain organic substances, fluorides, chlorides, bromides, chlorates, sulfates, nitrates, cyanides, carbonates, C ₂ H ₃ O ₂ , chromates, dichromates. It can be advantageously used as an insoluble anode for electrolysis in aqueous solutions of salts.
These electrodes are used in the recovery, purification, and electrowinning of metals (Cu, Zn, Co, Ni, Cr, etc.). These electrodes can also be usefully used in processes such as chromic acid production, chrome plating, perosalt, persulfate, and perchlorate production, and iodic acid oxidation. Similarly, these electrodes can be usefully utilized as anodes for electroflotation or for organic oxidation reactions requiring relatively high oxygen overpotentials.

Claims (1)

[Scope of Claims] 1. An electrolytic electrode comprising an electrode base material of a valve metal, a conductive intermediate mixed oxide layer, and an outer coating of manganese dioxide or lead dioxide on the layer, wherein the conductive intermediate mixed oxide An electrode for electrolysis, characterized in that the layer is made of a mixed oxide formed from a valve metal on the surface of the electrode base material and at least one platinum group metal. 2. The conductive intermediate mixed oxide layer contains at least one of platinum group metals: iridium, ruthenium, and rhodium.
Claim 1 characterized in that it includes a type.
Electrode as described in Section. 3. The electrode according to claim 1 or 2, wherein the electrode base material is made of titanium. 4. In a method for producing an electrolytic electrode comprising a valve metal electrode base material, a conductive intermediate mixed oxide layer, and an outer coating of manganese dioxide or lead dioxide, (a) on the surface of the valve metal electrode base material, the valve metal and Forming a conductive intermediate mixed oxide layer with at least one platinum group metal, which is constituted by the following method; A solution consisting of a chloride of a platinum group metal and hydrochloric acid is applied, and the molar ratio of hydrogen chloride to platinum group metal chloride in the solution is from 1:1 to
(b) Bringing hydrochloric acid into contact with the surface of the valve metal substrate for a sufficient period of time to convert the valve metal on the surface into a sufficient amount of chloride to achieve the above molar ratio. Slowly dry the treatment solution to produce a chloride mixture of valve metal chloride and platinum group metal chloride in corresponding predetermined proportions; (c) apply the resulting chloride mixture to the surface of the valve metal substrate; The above chloride mixture was heated for 400 min in an oxidizing atmosphere in order to convert it into a mixed oxide integrated with
heat treatment at a temperature range of ~600°C; (d) repeating a series of steps of solution application, drying, and heat treatment to gradually form a layer of the mixed oxide having the desired thickness; and (b) the above. forming the outer coating on the mixed oxide layer produced by the series of steps; A method for producing an electrode for electrolysis, characterized by comprising the steps (a) and (b) above. 5. The manufacturing method according to claim 4, characterized in that the manganese dioxide or lead dioxide is electrodeposited in an amount equivalent to at least 100 g per square meter of the surface of the valve metal substrate. 6. The manufacturing method according to claim 4, characterized in that the chloride mixture is heat-treated at a temperature range of 450 to 520°C. 7. Process according to claim 4, characterized in that the molar ratio is selected between 3:1 and 30:1. 8. Claim 4, characterized in that the molar concentration of the platinum group metal chloride present in the solution is selected from the range of 1 x 10 ^-2 to 25 x 10 ^-2 mol per solution.
Manufacturing method described in section. 9. The production method according to claim 8, wherein the molar concentration of the platinum group metal chloride is selected within the range of 2×10 ⁻² to 10×10 ⁻² mol per solution. 10 If the above molar concentration of platinum group metal chloride is solution 1
10. The production method according to claim 9, wherein the amount is selected in the range of 2.5×10 ^-2 to 7.5×10 ^-2 mol per mol. 11 The molar concentration of HCl in the solution per solution
The manufacturing method according to claim 4, characterized in that the amount is selected between 14×10 ⁻² and 3.0 mol. 12. The manufacturing method according to claim 4, wherein the solution applied to the surface of the valve metal electrode substrate contains a non-aqueous solvent, and the solvent is slowly evaporated during the drying step. 13. The production method according to claim 12, wherein the solvent is alcohol. 14. The manufacturing method according to claim 13, wherein the solvent is isopropyl alcohol.