JP2012067390A - Pd-CONTAINING COATING FOR LOW CHLORINE OVERVOLTAGE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing an electrode bringing a low operating voltage during the electrolysis of a halogen-containing solution.SOLUTION: The invention relates to an electrocatalytic coating and an electrode having the coating thereon. The coating is a mixed metal oxide coating, preferably the oxide of platinum group metal which includes or does not include a valve metal oxide, and contains the transition metal components such as palladium, rhodium or cobalt. The electrocatalytic coating can be particularly used for the constituent of an anode in an electrolytic bath for electrolysis of a halogen-containing solution. In such a case, the palladium component lowers the operating potential of the anode, and eliminates the need of a "break-in" period for obtaining the lowest anode potential.

Description

Background of the Invention FIELD OF THE INVENTION The present invention is directed to an electrode for use in a halogen-containing aqueous solution and an electrocatalytic coating on the electrode that provides a low starting voltage and an overall low operating voltage.

2. 2. Description of Related Art Electrodes for use in electrolysis processes are known having a base metal or core metal with a metal oxide layer or coating. The core metal of the electrode may be a valve metal such as titanium, tantalum, zirconium, niobium or tungsten. If the coating is a mixture of oxides, the core or support oxide can contribute to the mixture. Such a mixture may contain at least one oxide of a metal such as platinum, iridium, rhodium, palladium, ruthenium and osmium in addition to the support metal oxide. Such electrodes are known in the art and are generally referred to as “dimensionally stable”.

  However, an inherent disadvantage of these coatings under environments that produce chlorine or chlorates is the detrimental effect on the chlorine generation potential, which is a high operating potential and a high potential within a few months over the anode. Creates the need for a voltage “break-in” period to operate at.

Attempts to overcome the disadvantages associated with chlorine generation potential are addressed in US Pat. No. 4,233,340, where palladium oxide containing a platinum compound that can be pyrolyzed to form a white metal is baked. An insoluble electrode having a coating comprising a slurry is presented. The coating contains 99-5 mol% palladium oxide and 1-95 mol% white metal. In U.S. Pat. No. 4,443,317, a coating comprising 40-90 mol% palladium oxide, 0.1-20 mol% platinum, and 5-50 mol% (Ru _x Ti _1-x )) ₂ There is a teaching on an electrode for electrolysis having:

  Accordingly, it would be advantageous to provide an electrode having a coating thereon that eliminates the need for a voltage “trial” period and provides an overall low operating potential. Furthermore, it would be desirable for such electrodes and coatings to prevent or eliminate step-wise increases in voltage following coating post-baking.

SUMMARY OF THE INVENTION It has been found that an electrode having an electrocatalytic coating thereon that results in a reduction in the operating potential of the electrode in an electrochemical cell for the oxidation of halogen-containing solutions. In addition, this coating eliminates the voltage “trial” period necessary to obtain the lowest anode potential and also eliminates the stepwise increase in anode potential observed after the post-bake or creep process. .

DESCRIPTION OF THE INVENTION In accordance with the present invention, an electrode is provided that includes an electrocatalytic coating having a low operating potential, resulting in elimination of the voltage “trial” period. The electrode of the present invention is particularly useful in the production of chlorine and alkali metal hydroxides in a membrane cell and the production of chlorates and hypochlorites by electrolysis.

  The electrode used in the present invention has an electrocatalytically active coating on a conductive support. A wide variety of metals for electrodes can be considered as any metal that can be coated. For certain applications of electrocatalytic coatings, the metal may be nickel or manganese, but it will most often be a “film-forming” metal. "Film forming metal" is connected as an anode in the electrolyte to protect the underlying metal from being corroded by the electrolyte when this coated anode is subsequently operated in the electrolyte Means metals or alloys having the property of rapidly forming passive oxide coatings, ie, metals and alloys often referred to as “valve metals”. Such valve metals include titanium, tantalum, zirconium, niobium, tungsten and silicon, and alloys containing one or more of these metals, as well as alloys containing valve metals and intermetallic mixtures, ceramics and cermets (e.g. , Ti-Ni, Ti-Co, Ti-Fe and Ti-Cu). More specifically, grade 5 titanium may contain 6.75 weight percent or less aluminum and 4.5 weight percent or less vanadium, while grade 6 titanium contains 6 weight percent or less aluminum and 3 weight percent. The following tin may contain no more than 0.25 weight percent palladium for grade 7 and 10 to 13 weight percent, preferably 4.5 to 7.5 weight percent zirconium for grade 10. There is such a thing. Of particular importance in terms of robustness, corrosion resistance and availability is titanium.

  When elemental metal is used, it means in particular the metal in the state normally available, ie a metal containing a small amount of impurities. Thus, for a particularly important metal, i.e. titanium, various grades of metal are available, including those in which other components are alloys or are impurities in addition to the alloy. Titanium grades are shown more specifically in the standard specification for titanium detailed in ASTM B 265-79.

  Titanium or other film-forming metal plates, rods, tubes, wires or braided wires and expanded mesh can be used as electrode substrates. It is also possible to use a clad of titanium or other film forming metal on the conductive core.

  Regardless of the metal and anode substrate morphology selected, the surface of such a support member is advantageously a cleaned surface. This can be obtained by any known process to achieve a clean metal surface, including mechanical cleaning. Conventional cleaning means such as chemical degreasing and electrolytic degreasing, or other chemical cleaning operations can also be advantageously used. If the substrate preparation includes annealing and the metal is grade 1 titanium, the titanium can be annealed at a temperature of at least about 450 ° C. for a time of at least about 15 minutes, but most often, Higher annealing temperatures, for example temperatures between 600 ° C. and 875 ° C., are advantageous.

  Once the cleaned or prepared and cleaned surface has been obtained, the substrate surface is further treated, particularly to provide the necessary multiple coating layers (possibly on the valve metal substrate) This may improve the adhesion (for example, the adhesion of the electrode catalyst coating layer to the valve metal). This can be done to remove intergranular etching of the support metal, high-speed grit blasting of the metal surface, peening, polishing, plasma spraying, or combinations thereof, and subsequent embedded grit (coarse grains) It will be achieved by means including surface treatment.

  To prepare a metal such as titanium for etching, it may be most useful to condition the metal, such as by annealing, thereby diffusing impurities into the grain boundaries. Thus, for example, by properly annealing grade 1 titanium, the concentration of iron impurities at the grain boundaries will increase. Again, from an etching standpoint, it may be desirable to combine a metal surface having a tailored grain boundary metallurgical morphology with an advantageous grain size. Again referring to titanium as a representative example, it is advantageous for at least a substantial amount of the grains to have a grain size number in the range of about 3 to about 7. The granularity number referred to here is in accordance with the instructions given in ASTM E 112-84. Useful metal supports under these conditions are disclosed in US Pat. No. 5,167,788.

  A suitably roughened metal surface can be obtained by special grit blasting with pointed grit and possibly subsequent removal of grit embedded in the surface. A grit that normally contains cornered particles will ablate the metal surface as opposed to peening the surface. Useful grit for such purposes includes sand, aluminum oxide, steel, and silicon carbide.

  Grit blasting can be followed by other processes such as etching or water blasting to remove embedded grit and / or clean the surface. Etching will be performed using a sufficiently active etching solution, typically an acidic solution. This results in surface roughness and / or surface morphology, possibly including strong erosion of grain boundaries. These can be carried out with hydrochloric acid, sulfuric acid, perchloric acid, nitric acid, oxalic acid, tartaric acid, and phosphoric acid, as well as mixtures thereof (eg aqua regia). Other etchants that can be used include caustic etchants such as potassium hydroxide and potassium nitrate solutions. Following etching, the etched metal surface can be subjected to a rinsing and drying step.

  An electrode having an electrocatalytic coating as described herein could be used almost always as an anode. That is, the term “anode” is frequently used herein when referring to electrodes, but this is merely for convenience and should not be construed as limiting the invention.

  In plasma sprays to obtain a suitably rough metal surface, the material will be applied in granular form, such as molten metal drops. In this plasma spray, for example as applied to metal sprays, the metal is melted and heated to a high temperature using an electric arc in an inert gas containing argon, nitrogen and optionally a small amount of hydrogen. Sprayed in the generated plasma stream. As used herein, the term “plasma spray” is understood to mean that plasma spray is preferred, but the term generally includes thermal sprays such as magnetohydrodynamic sprays, flame sprays and arc sprays. Should therefore be referred to simply as “melt spray” or “thermal spray”.

  The particulate material used may be a valve metal or an oxide thereof, such as titanium oxide, tantalum oxide and niobium oxide. Also contemplated are melt spray titanates, spinel, magnetite, tin oxide, lead oxide, manganese oxide and perovskite. In addition, various additives including dopants in the form of ions, such as niobium, tin, and indium ions, may be added to the oxide to be sprayed.

  Such plasma spray application may be used in combination with etching of the surface of the support metal. Alternatively, the electrode substrate may first be prepared by grit blasting as described above, followed by or without etching.

  From the above, it will be appreciated that the surface may then be subjected to various steps that provide pretreatment prior to coating, such as plasma spraying of the valve metal oxide coating described above. Other pretreatments may be useful. For example, it can be considered that the surface is subjected to hydrogenation or nitriding. Prior to coating with the electrochemically active material, the oxide layer may be heated by heating the support in air or by anodic oxidation of the support, as described in US Pat. No. 3,234,110. Has been proposed. Various proposals have also been made to deposit an outer layer of electrochemically active material on an underlayer, which is provided primarily as a protective and conductive intermediate. Various underlayers based on tin oxide are disclosed in U.S. Pat. Nos. 4,272,354, 3,882,002 and 3,950,240. It is also conceivable that the surface may be prepared to have an antipassivation layer.

Following surface preparation (which may include providing a pretreatment layer as described above), an electrochemically active coating layer may be applied to the support member. Often applied as typical examples of electrochemically active coatings are provided from active oxide coatings such as platinum group metal oxide, magnetite, ferrite, cobalt spinel, or mixed metal oxide coatings. Is. They may be water-based, such as aqueous solutions, or may be solution-type, such as those using alcohol solvents. However, for the electrodes of the present invention, an important aspect of the preferred coating composition solution is that which contains an oxide of a transition metal comprising one or more of palladium, rhodium or cobalt, of which Has found that palladium is preferred. The coating composition comprises a PdCl _2, RhCl ₃ or CoCl and hydrochloric acid, or will contain them in an alcohol solution. The metal salt can be used in the form of PdCl ₂ · xH ₂ O, RhCl ₃ · xH ₂ O, CoCl ₂ · xH ₂ O, and the like. For convenience, these forms are generally referred to herein simply as PdCl ₂ , RhCl ₃ or CoCl ₂ . In general, metal chlorides dissolve in alcohols, such alcohols are, for example, either isopropanol or butanol, all of which have little or no added hydrochloric acid, Of these, n-butanol is preferred.

  As will be described further below, in each embodiment of the present invention, the coating composition comprises from about 0.1 mole% to about 10 moles of transition metal component per 100 mole% of the platinum group metal oxide content of the coating. The preferred range would be from about 0.4 mol% to about 6 mol%. It will be understood that the components are present substantially as their oxides, and that referring to metals is for convenience only, and that the proportions refer to metals.

  By using such a small amount of transition metal component in the coating composition of the present invention, depending on the potential value of the coating without the transition metal component, the operating potential for the electrolysis of the halogen-containing solution is about 10 millivolts (mV). It was unexpected that the voltage was lowered to a value of about 100 mV. As described above, in the past coating, palladium oxide or a combination of this with other metals has been used in a large amount of 40% or more. Thus, it was unexpected that the desired coating composition as disclosed in the present invention could be achieved using a more simplified coating composition as described above.

In the first aspect of the present invention, PCT patent application no. As described in PCT / US04 / 14357 (the entire disclosure of which is hereby incorporated by reference), the coating composition comprises ruthenium oxide in addition to the Pd component as described above, titanium oxide. And will contain ingredients in combination with antimony oxide or tin oxide. In some cases, it is contemplated that the coating composition may contain iridium oxide. At this time, the coating composition of the first embodiment includes RuCl ₃ , TiCl ₃ or SbCl ₃ and hydrochloric acid, all of which are in an aqueous solution. For the electrochemically active coating of the first aspect, the coating formulation is preferably prepared using a water based one as opposed to an alcohol based one. Was found.

  The coating composition of the first embodiment has a ruthenium component of at least about 10 mole percent to about 30 mole percent, and preferably about 15 mole percent to about 25 mole percent per 100 mole percent of the metal content of the coating. It will contain enough to do. It will be understood that the components are present substantially as their oxides, and that referring to metals is for convenience only, and that the proportions refer to metals.

The coating composition of the first embodiment will contain a valve metal component. Various valve metals can be used, including titanium, tantalum, niobium, zirconium, hafnium, vanadium, molybdenum, and tungsten, with titanium being preferred. Dissolved metal salts are used and suitable inorganic substituents may include chlorides, iodides, bromides, sulfates, borates, carbonates, acetates, and citrates such as TiCl ₃ or TiCl ₄ in acidic solution. Good. Such coating compositions have a Ti component of at least about 50 mole percent to about 85 mole percent, and preferably about 60 mole percent to about 75 mole percent, per 100 mole percent of the metal content of the coating. Will be contained in a sufficient amount.

When the coating composition of the first aspect comprises iridium oxide, suitable precursor substituents may include IrCl ₃ or H ₂ IrCl ₆ . Iridium oxide will be present in an amount from about 1 mole percent to about 25 mole percent per 100 mole percent of the metal content of the coating.

A preferred first embodiment coating composition will comprise antimony oxide. Suitable precursor substituents may include SbCl ₃ , SbCl ₅ , or other inorganic antimony salts. Antimony oxide will generally be present in an amount from about 5 mole percent to about 20 mole percent, and preferably from about 10 mole percent to about 15 mole percent, per 100 mole percent of the metal content of the coating.

As mentioned above, it is believed that the electrocatalyst coating of the first embodiment can contain tin oxide instead of or in addition to antimony oxide. Where tin oxide is a desirable component, suitable precursor substituents may include SnCl ₂ , SnSO ₄ , or other inorganic tin salts. When tin oxide is used, it is generally present in an amount from about 2 mole percent to about 20 mole percent, and preferably from about 3 mole percent to about 15 mole percent, per 100 mole percent of the metal content of the coating. right.

  In the coating composition of the first embodiment, the ratio of ruthenium to antimony or tin is generally from about 2: 1 to about 0.1: 1, and preferably about 1.5: 1, with a titanium to antimony or tin ratio. The ratio will be from about 19: 1 to 1: 1, and preferably about 5.7: 1. If an optional iridium component is used, the ruthenium to iridium ratio will generally be from about 1: 1 to about 99: 1.

In the second aspect of the invention, as described in US patent application Ser. No. 10 / 395,939, the entire disclosure of which is hereby incorporated by reference, the preferred coating composition solution is typically In particular, it consists of RuCl ₃ , IrCl ₃ and hydrochloric acid, all in alcoholic solution and with or without the presence of the valve metal component. It is also conceivable to use chloridic acid H ₂ IrCl ₆ . It will be appreciated that RuCl ₃ may be used in a form such as RuCl ₃ .xH ₂ O, and IrCl ₃ .xH ₂ O may be used as well. For convenience, these forms will generally be referred to herein simply as RuCl ₃ and IrCl ₃ . In general, ruthenium chloride dissolves in alcohol together with iridium chloride, such alcohol is for example either isopropanol or butanol, and all of these have little or no added hydrochloric acid. Of these, n-butanol is preferred.

  Such a coating composition of the second embodiment contains sufficient ruthenium component to provide at least about 5 mole percent to about 50 mole percent ruthenium metal per 100 mole percent of the metal content of the coating; A preferred range would be from about 15 mole percent to about 35 mole percent for ruthenium. It will be understood that the components are present substantially as their oxides, and that referring to metals is for convenience only, and that the proportions refer to metals.

  The coating composition of the second embodiment contains sufficient Ir component to provide at least about 50 mole percent to about 95 mole percent iridium metal per 100 mole percent iridium and ruthenium metals, with a preferred range being From about 50 mole percent to about 75 mole percent iridium. At this time, to obtain the best coating properties, the molar ratio of Ru: Ir will be from about 1: 1 to about 1: 4, with a preferred ratio of about 1: 1.6.

  For the purpose of further stabilizing the coating and / or changing the anode efficiency, a valve metal component may optionally be included in the coating composition of the second embodiment. As described above with respect to the first aspect of the present invention, various valve metals can be used including titanium, tantalum, niobium, zirconium, hafnium, vanadium, molybdenum, and tungsten. The valve metal component can be formed from an alkoxide of the valve metal in an alcohol solvent, with or without the presence of an acid. Such valve metal alkoxides contemplated for use in the present invention include methoxide, ethoxide, isopropoxide and butoxide. For example, titanium ethoxide, titanium propoxide, titanium butoxide, tantalum ethoxide, tantalum isopropoxide or tantalum butoxide would be useful.

  When a valve metal component is present in the composition of the second aspect, the coating contains from about 0.1 mole percent to 25 mole percent or less per 100 mole percent of the metal content of the coating, with preferred compositions being It will contain from about 5 mole percent to about 15 mole percent.

  In a third embodiment, as described in US Pat. No. 5,230,780 (the entire disclosure of which is hereby incorporated by reference), the coating composition is added to the transition metal component. A solution of oxides of iridium, ruthenium, and titanium. Typically, each precursor component is a metal salt, most often a halide salt, and preferably all chloride salts for economy and efficiency of solution preparation. . However, other useful salts include iodides, bromides, and ammonium chloro salts such as ammonium hexachloroiridate or ammonium hexachlororuthenate. The coating composition applied to the metal support is aqueous, which in most cases will simply be water that is not mixed with further liquid. Preferably, deionized water or distilled water is used so as not to contain inorganic impurities.

  In the individual solution or solution combination of this third embodiment, in addition to the appropriate precursor substituents, in most cases there will be no further solution components, with one exception. Such an exception will almost always be the presence of an inorganic acid. For example, a solution of iridium trichloride may further contain a strong acid, often it is hydrochloric acid and will usually be present in an amount to provide about 5 to about 20 weight percent acid. Typically, individual solutions or combinations of solutions will have a pH of less than 1, such as a pH in the range of about 0.2 to about 0.8.

  At this time, the coating composition of the third aspect comprises at least about 15 mole percent and less than 25 mole percent iridium component, from about 35 to about 50 mole percent ruthenium component, and at least about 30 mole percent and less than 45 mole percent. Of titanium components, which are based on 100 mole percent of these components.

  In order to obtain the best coating properties, the molar ratio of ruthenium oxide to iridium oxide in the final coating will be greater than about 1.5: 1 to about 3: 1. The final coating will further have a value of less than about 1: 1 as a molar ratio of titanium oxide to the sum of the iridium and ruthenium oxides, but in most cases greater than about 0.5: 1.

In the fourth aspect of the present invention, preferred coating compositions contain ruthenium, iridium and titanium oxides. As noted above, suitable precursor components will include RuCl ₃ , IrCl ₃ , and orthobutyl titanate in an alcohol solution. At this time, the coating composition of the fourth aspect comprises from about 2 to about 20 mole percent iridium component, from about 10 to about 30 mole percent ruthenium component, and from about 50 to about 85 mole percent titanium component. Containing, which is based on 100 mole percent of these ingredients in the coating.

In each of the above embodiments, a coating composition containing an oxide of a transition metal in combination with a mixed metal oxide coating has been described as an electrochemically active coating layer. In the fifth aspect of the present invention, the top coat layer (overcoat layer) made of a transition metal containing one or more of palladium, rhodium or cobalt (preferably palladium) is used as an intermediate layer made of an electrochemically active coating layer. It is believed that it can be applied over the layer. The topcoat layer can be formed from dilute solutions of transition metals in alcohol or water, with or without the presence of acid. Generally, the transition metal component will be present in an amount of metal from about 0.2 to about 10 g / l. A preferred topcoat layer will be formed from PdCl ₂ in hydrochloric acid.

  Any of the coating compositions described above can be applied to the metal support by any means typically used to apply a liquid coating composition to the metal support. Such application methods include immersion spin methods and immersion discharge methods, brush application, roller coating, and spray application such as electrostatic spraying. Furthermore, a method combined with spray coating, for example, a combination of immersion discharge method and spray coating can be used. Spray application can be done by either conventional compressed gas application or electrostatic spray application. When using the above-described coating composition for applying an electrochemically active coating, roller coating operations may be most practical.

Regardless of the manner in which the coating is applied, the coating process is usually repeated, resulting in a more uniform application amount than can be achieved by a single coating. However, the amount of coating applied is sufficient to provide a total amount of metal ranging from about 0.1 g / m ² (grams per square meter) to about 20 g / m ² , preferably about 3 g / m 2. It will range from ² to about 12 g / m ² .

  Subsequent to application of the coating, heating the applied composition will prepare the final mixed oxide coating by pyrolysis of the precursor present in the coating composition. This prepares a mixed oxide coating containing the oxide mixed in the molar ratio as described above based on the metal of the oxide. Such heating for pyrolysis will occur at a temperature of at least about 350 ° C. for at least about 3 minutes. More typically, the applied coating will be heated at a higher temperature up to about 550 ° C. for a time of about 20 minutes or less. Suitable conditions may include heating in air or oxygen. In general, the heating method used can be any of the methods that can be used to cure the coating on the metal support. Thus, oven coatings including conveyor ovens may be used. Furthermore, an infrared curing method may be effective. Following such heating, and prior to this additional coating, if an additional application of the coating composition is made, the heated and coated support will typically be at least substantially cooled to ambient temperature. Let's go. In particular, post-baking can be used after all application of the coating composition has been completed. Typical post bake conditions for coating may include temperatures from about 400 ° C. to about 550 ° C. Bake times can vary from about 10 minutes to a length of about 300 minutes.

  As mentioned above, the coating of the present invention is particularly useful for anodes in electrolysis processes for the production of chlorates and alkali metal hydroxides. However, these electrodes will find use in other processes such as the production of chlorine and hypochlorite.

Example 1
A flat titanium plate made of unalloyed grade 1 titanium was etched in a 90-95 ° C. solution of 18-20% hydrochloric acid for 25 minutes to roughen the surface for coating application. .

  The coating composition shown in Table 1 was applied. The coating solution was prepared by adding the metals shown in the table (as chloride salts) to either butanol or water / HCl solvent. After mixing to dissolve all the salts, the solution was applied to individual samples of the prepared titanium plates. The coatings were applied in layers, where each coating was applied separately and dried at room temperature and then heated in air at the curing conditions shown in the table. After applying the final coating, some of the samples were further baked in air at the temperature / time conditions indicated in the post-bake column of the table.

  Standard Electrode Potentials (SEP) (vs SCE) were measured at 50 degrees Celsius in 300 gpl NaCl solution for the coated samples. Table 1 shows the measured values, indicating that the presence of palladium in the formulation for all the coatings listed reduces the value of SEP with and without post-baking operations. Yes.

Example 2
Three samples of the coated product were obtained from what was stored. The composition of the coating and the type of support are shown in Table 2.

  Coated substrates # 1-3 were heated in an oven to 450-470 ° C. for about 5 minutes to remove all surface contaminants. Subsequently, SEP measurement was performed on the sample, and the value is shown in Table 2. Note from the data that sample # 1 was previously post-baked and therefore has a high SEP value.

A solution of 0.7 g / l Pd (as PdCl ₂ ) in 18 wt% HCl was prepared and one coating consisting of this solution was applied to samples 1-3 to make samples 4-6. The coating was air dried and the sample was placed in an oven at 460-490 ° C. for 3-6 minutes to cure the coating. After removal from the oven and subsequent cooling period, SEP measurements were taken again on the samples. The data in Table 2 shows that Sample 4 no longer has a high SEP, and this can be attributed to the topcoat consisting of the applied palladium solution.

  Three samples 4-6 were then post-baked at 470 ° C. for 90 minutes to make samples 7-9 and SEP was recorded again. The data in Table 2 indicates that the SEP does not increase in any sample after the post-bake operation, which can be attributed to the topcoat consisting of the applied palladium solution.

  While the best mode and preferred embodiments have been shown according to the patent law, the scope of the invention is not limited thereto but is indicated by the appended claims.

Claims (51)

A method for producing an electrode for use in electrolysis of a halogen-containing solution, whereby the electrode provides a low operating potential during the electrolysis, the following steps:
a) providing a valve metal support having an intermediate electrocatalyst coating layer thereon;
b) coating the valve metal support with a topcoat layer consisting essentially of a solution of a mixture of transition metal oxides consisting of one or more of palladium, rhodium or cobalt oxides, wherein the mixture is a coating Giving a total content of transition metal oxides of from about 0.1 mol% to about 10 mol%;
Including said method.   The valve metal support is one or more of a valve metal mesh, sheet, blade, tube, perforated plate or wire member, and the valve metal is titanium, tantalum, aluminum, hafnium, niobium, The method of claim 1, wherein the method is one or more of zirconium, molybdenum or tungsten, alloys thereof and mixtures of these metals.   The surface of the valve metal electrode substrate is a roughened surface, and the roughened surface is prepared by one or more of grain boundary etching, grit blasting, peening, polishing or plasma spraying. the method of.   4. The method according to claim 3, wherein a ceramic oxide barrier layer as a pretreatment layer is fixed on the roughened surface.   The intermediate electrocatalyst coating includes a platinum group metal or platinum group metal oxide, magnetite, ferrite, cobalt oxide spinel, tin oxide, and antimony oxide, and / or at least one oxide of the valve metal and the platinum group. Comprising a crystalline material of a mixture of at least one oxide of metal and / or comprising one or more of manganese dioxide, lead dioxide, platinate substituents, nickel-nickel oxide or a mixture of nickel oxide and lanthanum oxide The method according to claim 3.   6. The method of claim 5, wherein the transition metal oxide of the topcoat layer is palladium oxide and the palladium oxide is present in an amount from about 0.4 mole percent to about 6 mole percent.   The method further comprises heating the coating, and the heating is by baking at a temperature of at least about 350 ° C to about 550 ° C for a time of at least about 3 minutes to about 20 minutes. The method according to 1.   The method of claim 1, wherein the electrode is an anode in a process for the production of one or more of chlorine, chlorate or hypochlorite.   The method of claim 1, wherein the electrode provides a reduction in operating potential in an amount from about 10 millivolts to about 100 millivolts during the electrolysis.   The intermediate electrode catalyst coating layer and the topcoat layer are applied to the valve metal support by one or more of immersion spin method, immersion discharge method, brush coating, roller coating and spray coating. The method described in 1.   An electrolytic cell for electrolysis of a halogen-containing solution comprising an electrode produced by the method of claim 1. An electrode for use in electrolysis of a halogen-containing solution, the electrode having an electrocatalytic coating thereon, the electrode comprising:
A valve metal electrode substrate;
Comprising a coating layer comprising an electrochemically active coating on the valve metal electrode substrate, the coating comprising:
a) A mixture of transition metal oxides consisting essentially of one or more of palladium, rhodium or cobalt oxides resulting in a total transition metal oxide content of from about 0.1 mole percent to about 10 mole percent of the coating. ,
b) a valve metal oxide selectively contained in a platinum group metal oxide mixture in an amount up to 25 mole percent, wherein the platinum group metal oxide mixture is essentially one or more of ruthenium and iridium oxides. The ratio is about 5 mole percent to about 50 mole percent ruthenium and about 50 mole percent to about 95 mole percent iridium per 100 mole percent of the metal present in the coating.
Including
The electrode, wherein the electrochemically active coating provides a low operating potential in the cell.   13. The electrode of claim 12, wherein the valve metal electrode substrate is a valve metal mesh, sheet, blade, tube, perforated plate or wire member.   14. The electrode of claim 13, wherein the valve metal electrode substrate is one or more of titanium, tantalum, aluminum, hafnium, niobium, zirconium, molybdenum or tungsten, alloys thereof and mixtures of these metals.   15. The surface of the valve metal electrode substrate is a roughened surface, and the surface is roughened by one or more of grain boundary etching, grit blasting, peening, polishing or thermal spraying. electrode.   The electrode according to claim 15, wherein a barrier layer of ceramic oxide as a pretreatment layer is fixed on the roughened surface.   The electrode of claim 14, wherein the electrocatalytic coating comprises the valve metal oxide.   The valve metal oxide is one or more of titanium oxide, tantalum oxide, zirconium oxide, niobium oxide, hafnium oxide, tin oxide, and the valve metal oxide is from about 0.1 mole percent to about 25 mole percent. The electrode of claim 17, wherein the electrode is present in an amount of   16. The electrode of claim 15, wherein the molar ratio of ruthenium oxide to iridium oxide is from about 1: 1 to about 1: 4.   The electrode of claim 16, wherein the molar ratio of the platinum group metal oxide to the valve metal oxide is in the range of approximately 4: 1 to approximately 1: 4.   21. The electrode of claim 20, wherein at least one topcoat layer comprising a valve metal oxide coating, a tin oxide coating, or a mixture thereof is fixed on the electrocatalyst coating.   The electrode according to claim 21, wherein the top coat layer of the valve metal oxide comprises an oxide selected from the group consisting of titanium, tantalum, niobium, zirconium, molybdenum, aluminum, hafnium, or tungsten.   The topcoat layer is a tin oxide coating layer doped with Sb, F, Cl, Mo, W, Ta, Ru, Ir, Pt, Rh, Pd, or In and one or more of these oxides; 23. The electrode of claim 21, wherein the dopant is in an amount ranging from about 0.1% to about 20%.   13. The electrode of claim 12, wherein the transition metal oxide is palladium oxide and the palladium oxide is present in an amount from about 0.4 mole percent to about 6 mole percent.   The coating further comprises iridium oxide in an amount from about 1 mole percent to about 25 mole percent per 100 mole percent of the metal content of the coating, and the ruthenium metal to iridium ratio is from about 1: 1 to about 99: The electrode according to claim 12, wherein the number is 1.   An electrode comprising a valve metal support for use in an electrocatalytic process for the electrolysis of halogen-containing solutions, the valve metal support having an electrocatalytic surface coating thereon, the coating essentially And a mixture of one or more transition metal oxides of palladium, rhodium or cobalt with one or more of ruthenium oxide, titanium oxide, and tin oxide or antimony oxide, the mixture being coated At least about 0.1 mole percent to about 10 mole percent of the transition metal oxide, at least about 10 mole percent to about 30 mole percent ruthenium, and at least about 50 mole percent per 100 mole percent of the metal content of To about 85 mole percent Chita The given, whereby said electrode catalyst coating is one that results in a low operating potential in the cell, said electrode.   The valve metal support is one or more of titanium, tantalum, zirconium, niobium, tungsten, aluminum, alloys thereof and intermetallic mixtures, and the support is a mesh, sheet, blade, tube, perforated plate or 27. An electrode according to claim 26 in the form of a wire.   28. The electrode of claim 27, wherein the surface of the valve metal support is a roughened surface and the surface is roughened by one or more of grain boundary etching, grit blasting, peening, polishing, or thermal spraying. .   For every 100 mole percent of the metal content of the coating, the ruthenium oxide is present in an amount from about 10 mole percent to about 25 mole percent, and the titanium is present in an amount from about 60 mole percent to about 75 mole percent. The electrode according to claim 28.   27. The electrode of claim 26, wherein the coating comprises from about 5 mole percent to about 20 mole percent antimony oxide per 100 mole percent of the metal content of the coating.   27. The electrode of claim 26, wherein the coating comprises from about 2 mole percent to about 20 mole percent tin oxide per 100 mole percent of the metal content of the coating.   27. The coating of claim 26, wherein the coating comprises from about 10 mole percent to about 15 mole percent antimony oxide and from about 2 mole percent to about 15 mole percent tin oxide per 100 mole percent of the metal content of the coating. Electrodes.   27. The ratio of ruthenium metal to antimony or tin is from about 2: 1 to about 0.1: 1 and the ratio of titanium to antimony or tin is from about 19: 1 to about 1: 1. The electrode as described.   27. The electrode of claim 26, wherein the coating is a water based coating.   The coating further comprises iridium oxide in an amount from about 1 mole percent to about 25 mole percent per 100 mole percent of the metal content of the coating, and the ruthenium metal to iridium ratio is from about 1: 1 to about 99: 27. The electrode of claim 26, wherein the number is 1.   27. The electrode of claim 26, wherein the electrode provides a reduction in operating potential in an amount from about 10 millivolts to about 100 millivolts during the electrolysis.   An electrolytic cell for electrolysis of chloro-alkali solutions comprising an electrode produced by the method of claim 26.   An electrode for use in electrolysis of a halogen-containing solution, said electrode comprising a valve metal support having an electrocatalytic surface coating thereon, said surface coating consisting essentially of one of palladium, rhodium or cobalt. A mixture of the above transition metal oxides in combination with ruthenium oxide, iridium oxide and titanium oxide, said mixture being at least about 0.1 mole percent for every 100 mole percent of oxide present in the coating Up to about 10 mole percent of the transition metal oxide, at least about 15 mole percent to less than 25 mole percent iridium oxide, from about 35 mole percent to about 50 mole percent ruthenium oxide, and at least about 30 mole percent to 45 moles Less than percent The coating has a titanium oxide to iridium and ruthenium oxide molar ratio of less than 1: 1, and the ruthenium oxide to iridium oxide molar ratio is greater than 1.5: 1 to 3 The electrode, wherein the electrode catalyst coating provides a low operating potential in the cell.   The valve metal support is one or more of titanium, tantalum, zirconium, niobium, tungsten, aluminum, alloys thereof and intermetallic mixtures, and the support is a mesh, sheet, blade, tube, perforated plate or 38. The electrode according to claim 37, which is in the form of a wire.   39. The electrode of claim 38, wherein the surface of the valve metal support is a roughened surface and the surface is roughened by one or more of grain boundary etching, grit blasting, peening, polishing, or thermal spraying. .   38. The electrode of claim 37, wherein the transition metal oxide is palladium oxide and the palladium oxide is present in an amount from about 0.4 mol% to about 6 mol%.   40. The method of claim 38, wherein the surface coating is heated by baking at a temperature of at least about 350 ° C to about 550 ° C for a time of at least about 3 minutes to about 20 minutes.   40. An electrolytic cell for electrolysis of a halogen-containing solution comprising an electrode produced by the method of claim 38.   40. The method of claim 38, wherein the operating potential is reduced in an amount from about 10 millivolts to about 100 millivolts.   An electrode for use in electrolysis of a halogen-containing solution, said electrode comprising a valve metal support having an electrocatalytic surface coating thereon, said surface coating consisting essentially of one of palladium, rhodium or cobalt. A mixture of the above transition metal oxides in combination with ruthenium oxide, iridium oxide and titanium oxide, the mixture comprising at least about 0.1 mole percent to about 10 mole percent of the transition metal oxide; From about 10 mole percent to about 30 mole percent ruthenium, from about 2 mole percent to about 20 mole percent iridium, and from about 50 mole percent to about 85 mole percent titanium, whereby the electrocatalytic coating is Low operating potential in the cell Those lath, said electrode.   The valve metal support is one or more of titanium, tantalum, zirconium, niobium, tungsten, aluminum, alloys thereof and intermetallic mixtures, and the support is a mesh, sheet, blade, tube, perforated plate or 46. The electrode according to claim 45, which is in the form of a wire.   47. The electrode of claim 46, wherein the surface of the valve metal support is a roughened surface and the surface is roughened by one or more of grain boundary etching, grit blasting, peening, polishing, or thermal spraying. .   46. The electrode of claim 45, wherein the transition metal oxide is palladium oxide and the palladium oxide is present in an amount from about 0.4 mol% to about 6 mol%.   48. The method of claim 47, wherein the surface coating is heated by baking at a temperature of at least about 350 ° C to about 550 ° C for a time of at least about 3 minutes to about 20 minutes.   46. An electrolytic cell for electrolysis of a halogen-containing solution comprising an electrode produced by the method of claim 45.   46. The method of claim 45, wherein the operating potential is reduced in an amount from about 10 millivolts to about 100 millivolts.