KR20130143624A - Electrode for electrolytic cell - Google Patents

Abstract

The present invention relates to an electrode for gas product generation in an electrolytic cell comprising a metal substrate coated with two or more catalyst compositions, wherein the outermost catalyst composition is deposited by chemical or physical vapor deposition and is selected from platinum group metals. Or a composition comprising an oxide thereof.

Description

Electrode for electrolytic cell {ELECTRODE FOR ELECTROLYTIC CELL}

The present invention relates to an electrode suitable for functioning as an anode in an electrolytic cell, for example as a chlorine generating anode in a chlor-alkali cell.

The use of metal electrodes with a catalyst coating in the field of electrolysis is known in the art: Electrodes consisting of metal substrates with coatings based on noble metals or oxides thereof are, for example, in water or alkali chloride electrolysis. As a cathode for generating hydrogen in the process, it is used as an oxygen generating anode in various kinds of electrometallurgical processes or as a chlorine generating anode in alkali chloride alkali electrolysis. Electrodes of this kind can be prepared by thermal methods, ie by suitable pyrolysis of a solution containing a precursor of the metal to be deposited; By galvanic electrodeposition from a suitable electrolytic bath; It can be produced by a flame or plasma spraying process or by direct plating via chemical or physical vapor deposition.

Electrolysis of sodium chloride brine, which leads to the production of chlorine and caustic soda, is often a titanium or other valve activated by the surface layer or ruthenium dioxide (RuO ₂ ), for example, to lower the overvoltage of the anode chlorine generating reaction. It is performed by an anode made of a metal substrate. Also known for this type of electrolysis are catalyst formulations based on mixtures of oxides of ruthenium, iridium and titanium, all of which are capable of lowering the overvoltage of the anodic chlorine evolution reaction.

Electrodes of this kind are generally produced by thermal methods.

The catalyst formulation can be deposited on the substrate by phase vapor deposition, which has the advantage of allowing extreme precise control of the coating deposition factor. However, the method is characterized in nature as a batch-type process, and in order to enable the processing of the pieces, loading of the substrate into a suitable deposition chamber is required, which lasts for several hours through a slow depressurization process. Should be. In addition to the significant duration of the process (typically several hours depending on the loading of the noble metal required), the application of a large amount of catalyst coating results in a coating with a very limited lifetime.

Various aspects of the invention are set forth in the appended claims.

In a first aspect, the invention relates to an electrode for gas product generation in an electrolytic cell consisting of a valve metal substrate coated with at least one first catalyst composition and an outer catalyst composition, wherein the at least one first catalyst composition is a valve metal. Or an oxide of tin and a mixture of a noble metal or oxide thereof (selected alone or in combination) selected from the platinum metal (PM) group, wherein the at least one first catalyst composition is obtained by pyrolysis of the precursor, The external catalyst composition comprises a noble metal selected from a platinum metal group or an oxide thereof (selected alone or in combination), the external catalyst composition is deposited by chemical or physical phase vapor deposition, and on the first catalyst composition the amount of the noble metal 5g / m ² greater than the surface, the external ear in the catalyst compositions The amount is in the range of 0.1 to 3.0g / m ² of surface.

The inventors have surprisingly found that the deposition of one last catalyst layer through chemical or physical phase vapor makes it possible to obtain electrodes with unexpected features in terms of both duration and potential reduction, together with the specified features.

In one embodiment, the first catalyst composition of the electrode according to the invention comprises titanium, iridium, ruthenium in metal or oxide form.

In one embodiment, the external catalyst composition comprises ruthenium and / or iridium in metal or oxide form.

In one embodiment, the specific precious metal loading in the first catalyst composition is in the range of 6 to 8 g / m ² and the specific metal loading in the external catalyst composition is in the range of 1.5 to 2.5 g / m ² .

In another aspect, the present invention relates to a method for preparing an electrode comprising vapor deposition of an external catalyst composition by chemical or physical vapor deposition, preferably by reactive thin film deposition of a noble metal selected from the platinum metal group.

In a further aspect, the present invention relates to the reactivation of a used electrode comprising chemical or physical vapor deposition of an external catalyst composition comprising a noble metal selected from a platinum metal group or an oxide thereof (selected alone or in combination). will be.

In a further aspect, the present invention relates to an electrolytic cell of an alkali chloride solution, for example, a sodium chloride saline electrolytic cell which leads to the production of chlorine and caustic soda, which is an anode of chlorine on an electrode, as described herein above. Brings sex occurrences.

The following examples are included to illustrate certain embodiments of the present invention, the utility of which has been largely demonstrated in the claimed numerical range. It is to be understood by those skilled in the art that the compositions and techniques described in the following examples work well in the practice of the invention, as found by the inventors. However, those of ordinary skill in the art should, in light of the present specification, understand that certain aspects described herein may be modified in many ways and still obtain the same or similar results without departing from the scope of the present invention.

Control Example 1

Titanium mesh samples of 10 cm × 10 cm size were blasted with corundum and the residue was washed with compressed air jet. The sample was then degreased using acetone in an ultrasonic bath for about 10 minutes. After drying, the sample was immersed in an aqueous solution containing 250 g / l NaOH and 50 g / l KNO ₃ at about 100 ° C. for 1 hour. After alkali treatment, the samples were washed three times with deionized water at 60 ° C., with the liquid changing each time. The last wash was performed by adding a small amount of HCl (about 1 mL per 1 liter of solution). As a result of air drying, the formation of brown coloration was observed due to the growth of the TiO _x thin film. Then 100 mL of a hydroalcoholic solution containing RuCl ₃ * 3H ₂ O, H ₂ IrCl ₆ * 6H ₂ O, TiCl ₃ in a mixture of 2-propanol and water acidified with HCl were prepared, wherein Ru 36% , Ir 20%, Ti 44% molar composition.

The solution was applied to the titanium mesh sample by a 5-ply coating by brushing, after each coating it was dried at 100-110 ° C. for about 10 minutes and then heat treated at 450 ° C. for 15 minutes. The sample was cooled in air each time before applying the subsequent coating.

At the end of the whole procedure, a total precious metal load of 9 g / m ² expressed as the sum of Ru and Ir for the metal was obtained.

The electrode thus obtained was referred to as sample number 1.

Control Example 2

Titanium mesh samples of 10 cm × 10 cm size were blasted with corundum and the residue was washed with a compressed air jet. The sample was then degreased with acetone in an ultrasonic bath for about 10 minutes. After drying, the sample was immersed in an aqueous solution containing 250 g / l NaOH and 50 g / l KNO ₃ at about 100 ° C. for 1 hour. After alkali treatment, the samples were washed three times with deionized water at 60 ° C., with the liquid changing each time. The last wash was performed by adding a small amount of HCl (about 1 mL per 1 liter of solution). As a result of air drying, the formation of brown coloration was observed due to the growth of the TiO _x thin film.

The mesh sample was then introduced into the vacuum chamber of the reactive thin film deposition apparatus.

When setting a dynamic vacuum of about 50 E-4 mbar supplying a mixture of 20% argon and oxygen, the thin film deposition targets were polarized at the following sources: ruthenium 35W, iridium 24W, titanium 250W. The object-electrode substrate spacing was about 10 cm.

Under the same conditions, the deposition process was performed alternately on both sides of the titanium mesh for a total duration of 220 minutes. The electrode thus obtained exhibited a total precious metal loading of about 9 g / m ² expressed as the sum of Ru and Ir for the catalyst coating and metal of about 1 μm.

The electrode thus obtained was referred to as sample number 2.

Example 1

Titanium mesh samples of 10 cm × 10 cm size were blasted with corundum and the residue was washed with a compressed air jet. The sample was then degreased with acetone in an ultrasonic bath for about 10 minutes. After drying, the sample was immersed in an aqueous solution containing 250 g / l NaOH and 50 g / l KNO ₃ at about 100 ° C. for 1 hour. After alkali treatment, the samples were washed three times with deionized water at 60 ° C., with the liquid changing each time. The last rinse was carried out by addition of a small amount of HCl (about 1 ml per liter of solution). As a result of air drying, the formation of brown coloration was observed due to the growth of the TiO _x thin film.

Then 100 mL of a hydroalcoholic solution containing RuCl ₃ * 3H ₂ O, H ₂ IrCl ₆ * 6H ₂ O, TiCl ₃ in a mixture of 2-propanol and water acidified with HCl were prepared, wherein Ru 36% , Ir 20%, Ti 44% molar composition.

The solution was applied to the titanium mesh sample with a 5-ply coating by brushing, after each coating it was dried at 100-110 ° C. for about 10 minutes and heat treated at 450 ° C. for 15 minutes. The sample was cooled in air each time before applying the subsequent coating.

At the end of the whole procedure, a total precious metal load of 7 g / m ² expressed as the sum of Ru and Ir for the metal was obtained.

A semi-finished electrode was then introduced into the vacuum chamber of the reactive thin film deposition apparatus.

When setting a dynamic vacuum of about 100 E-4 mbar supplying a mixture of 20% argon and oxygen, the thin film deposition targets were polarized at the following sources: ruthenium 30W, iridium 35W. The object-electrode substrate spacing was about 10 cm. In addition, the substrate was subjected to a residual polarization of about 150V to give optimum properties to the coating result.

Under the same conditions, the deposition process was performed alternately on both sides of the electrode for a total duration of 40 minutes. The electrode thus obtained has a total precious metal loading of about 9 g / m ² expressed as the sum of Ru and Ir for the outer catalyst coating and metal about 0.1 μm thick.

The electrode thus obtained was referred to as sample number 3.

The sample of this example was characterized as an anode for chlorine generation in a lab cell fed with sodium chloride brine at a concentration of 200 g / l with strict control of pH to 3. Table 1 shows the chlorine overvoltage and the volume percentage of oxygen in the chlorine product measured under a current density of 4 kA / m ² .

Table 1

A duration test was also performed on the samples of the above examples. The duration test is a simulation in a separate cell with current densities for electrolyte concentration and temperature, but conveniently increased to 2 to 3 times higher than nominal to accelerate the experimental reaction. Table 2 shows the precious metal losses per unit current.

Table 2

The above description is not intended to limit the invention, but may be used in accordance with different embodiments without departing from the scope of the invention, the scope of the invention being limited only by the appended claims.

Throughout the description and claims of this application, the terms "comprises" and variations thereof, such as "comprising" and "comprising", are not intended to exclude the presence of other elements or adducts.

Discussion of literature, statutes, materials, devices, articles and the like is included herein for the sole purpose of providing the context of the invention. Any or all of these matters do not form part of the prior art base or imply or indicate that they are common general knowledge in the relevant field of the invention before the priority date of each claim of this application.

Claims (9)

An electrode for gas product generation in an electrolytic cell consisting of a valve metal substrate coated with at least one first catalyst composition and an outer catalyst composition, the at least one first catalyst composition comprising a valve metal or tin or an oxide thereof, and platinum A mixture of a noble metal selected from the group metal or an oxide thereof (selected alone or in combination), wherein the at least one first catalyst composition is obtained by pyrolysis of the precursor, and the external catalyst composition is prepared by chemical or physical vapor deposition Deposited by the amount of the precious metal in the at least one first catalyst composition in excess of 5 g / m ² and the amount of the precious metal in the outer catalyst composition in the range of 0.1 to 3.0 g / m ² of the surface. The electrode of claim 1, wherein the mixture of the one or more first catalyst compositions comprises titanium, iridium and ruthenium. The electrode of claim 1, wherein the external catalyst composition comprises ruthenium and / or iridium. The process of claim 1, wherein the specific precious metal loading of the at least one first catalyst composition is 6-8 g / m ² and the specific precious metal loading of the external catalyst composition is 1.5-2.5 g. electrode, which is / m ² . The method of producing an electrode according to any one of claims 1 to 4, comprising depositing the external catalyst composition by chemical or physical vapor deposition. The method of producing an electrode according to any one of claims 1 to 4, comprising depositing the external catalyst composition as a mixture of oxides by reactive thin film deposition of a noble metal selected from the group of platinum metals. A method of reactivating a consumed electrode consisting of a metal substrate and a spent catalyst coating, comprising the deposition of an external catalyst composition as a mixture of oxides by reactive thin film deposition of iridium and ruthenium on the spent catalyst coating. Reactivation method of the electrode. 8. The method of claim 7, comprising vapor deposition by chemical or physical vapor deposition of an external catalyst composition comprising a noble metal selected from a group of platinum metals or an oxide thereof (selected alone or in combination). . An electrolytic cell comprising a cathode compartment containing a cathode and an anode compartment containing an anode, separated by a membrane or diaphragm, wherein the anode compartment is fed with alkali chloride brine and the anode of the anode compartment Is an electrode according to any one of claims 1 to 4, an electrolytic cell.