EA024356B1

EA024356B1 - Electrode for electrolytic cell

Info

Publication number: EA024356B1
Application number: EA201390927A
Authority: EA
Inventors: Кристиан Урджеге; Антонио Лоренцо Антоцци
Original assignee: Индустрие Де Нора С.П.А.
Priority date: 2010-12-22
Filing date: 2011-12-21
Publication date: 2016-09-30
Also published as: ITMI20102354A1; EA201390927A1; JP2014505166A; EP3118351A1; IL225905A; ZA201302944B; CN103249872A; MX2013006271A; KR20180043398A; EP2655693A2; US20130228450A1; WO2012085095A3; DK2655693T3; WO2012085095A2; CN103249872B; CO6741167A2; AR083989A1; CA2815137C; BR112013014015B1; KR20130143624A

Abstract

The invention relates to an electrode for evolution of gaseous products in electrolysis cells comprising a metal substrate coated with at least two catalytic compositions, the outermost catalytic composition being deposited by means of chemical or physical phase vapour deposition technique and having a composition comprising noble metals selected from the group of platinum group metals or oxides thereof.

Description

The invention relates to an electrode suitable for operation as an anode in electrolysis cells, for example, as a chlorine emitting electrode in an alkali chloride cell of an electrolyzer.

Background of the invention

The use of metal electrodes equipped with catalytic coatings in electrolytic applications is known in the art: electrodes consisting of a metal substrate equipped with a coating based on noble metals or their oxides are used, for example, as cathodes for hydrogen evolution in the process of electrolysis of water or chlorides alkali metals, as anodes for oxygen evolution in electrometallurgical processes of various types or for chlorine emission during chloride electrolysis herringbone metal. Electrodes of this type can be manufactured thermally, i.e. proper thermal decomposition of solutions containing metal-deposited precursors by electroplating from suitable electrolytic baths, direct metallization using flame or plasma spraying methods, or chemical or physical vapor deposition.

Electrolysis of sodium chloride brine, aimed at obtaining chlorine and caustic soda, for example, is often carried out using anodes consisting of a substrate made of titanium or another valve metal, activated by the surface layer or ruthenium dioxide (KIO ₂ ) to reduce the overvoltage of the chlorine anode reaction. For electrolysis of this type, catalytic compositions are also known, based on mixtures of ruthenium, iridium and titanium oxides, which are all capable of reducing the overvoltage of the anodic chlorine release reaction.

As a rule, electrodes of this type are made by thermal scheme.

Catalytic compositions can be deposited on a substrate using vapor deposition methods, which have the advantage of providing extremely precise control of coating deposition parameters. However, in essence, they are characterized as batch processes that require loading the substrate into a suitable precipitation chamber, which should be subjected to a slow evacuation process that takes several hours to get the ability to process a single part. In addition to the length of the process (usually several hours are required, depending on the specific content of the noble metal required), the application of large amounts of catalytic coatings leads to coatings with a very limited service life.

Summary of Invention

The various aspects of the invention are set forth in the appended claims.

According to a first aspect, the present invention relates to an electrode for separating gaseous products in electrolysis cells, consisting of a valve metal substrate coated with at least one first catalytic composition and an external catalytic composition, said at least one first catalytic composition comprising a mixture of valve metal oxides or tin and noble metals selected from the group of platinum metals (PM) or their oxides, taken individually or in a mixture, and mentioned at least one first catalytic composition obtained by thermal decomposition of precursors, said external catalytic composition contains noble metals selected from the group of platinum metals or their oxides, taken separately or in a mixture, said external catalytic composition is precipitated by chemical or physical vapor deposition , the amount of noble metal in said first catalytic composition is above 5 g / m ^{2 of the} surface, and the amount of noble one metal in said external catalytic composition is between 0.1 and 3.0 g / m ^{2 of} surface.

The inventors have unexpectedly found that the deposition of one last catalytic layer with specific characteristics by chemical or physical vapor deposition allows an electrode with unexpected properties to be obtained in terms of both durability and potential reduction.

In one embodiment, the first catalytic electrode composition according to the invention comprises titanium, iridium, ruthenium in the form of metals or oxides.

In one embodiment, the implementation of the outer catalytic composition contains ruthenium and / or iridium in the form of metals or oxides.

In one embodiment, the specific content of the noble metal in the first catalytic composition is between 6 and 8 g / m ² , and the specific metal content in the outer catalytic composition is between 1.5 and 2.5 g / m ² .

In another aspect, the invention relates to a method for producing an electrode, comprising depositing an outer catalytic composition by chemical or physical vapor deposition, preferably by reactive sputtering of noble metals selected from the group of platinum metals.

In another aspect, the invention relates to the reactivation of a used electrode, including chemical or physical vapor deposition of an external catalytic composition, including noble metals selected from the group of platinum metals or their oxides, taken

- 1 024356 individually or in a mixture.

According to an additional aspect, the invention relates to an electrolysis cell of alkali metal chloride solutions, for example, a sodium chloride brine electrolysis cell, intended to produce chlorine and caustic soda, which acts with anodic release of chlorine on the electrode described above.

The following examples are included to demonstrate specific embodiments of the invention, the practical applicability of which has been thoroughly tested in the claimed range of values.

Specialists in this field of technology should be clear that the compositions and methods disclosed in the following examples are those compositions and methods that are found by the authors of the invention as well acting in the practical implementation of the invention; however, those skilled in the art will appreciate in view of the present disclosure that in the disclosed specific embodiments, many changes can be made and still get a similar or similar result without going beyond the scope of the invention.

Counterexample 1

A sample of titanium mesh with a size of 10x10 cm was subjected to blasting with corundum, cleaned of residues with a stream of compressed air. Then the sample was 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 ΝαΟΗ and 50 g / l ΚΝΟ ₃ , at about 100 ° C for 1 h. After this alkaline treatment, the sample was washed three times with demineralized water at 60 ° C, changing liquid each time. The last wash was carried out with the addition of a small amount of HCl (approximately 1 ml per liter of solution). Air drying was performed, observing the formation of a brown tint due to the growth of a thin ΤίΟ _χ film. Then, 100 ml of a water-alcohol solution containing KiCl ₃ -3H ₂ O, H ₂ 1gC1 ₆ -6H ₂ O, PS.'1 ₃ in a mixture of water and 2-propanol, acidified with HC1, having a molar composition of 36% Ci, 20% 1g were prepared , 44% Τι in terms of metals.

The solution was applied to the sample titanium mesh with a brush in five layers; after applying each layer, drying was performed at 100-110 ° C for about 10 minutes, followed by heat treatment for 15 minutes at 450 ° C. The sample was cooled in air each time before applying the next layer.

At the end of the whole procedure, the total specific content of the noble metal was 9 g / m ² , expressed as the sum of Ki and 1 g in terms of metals.

The electrode thus obtained was designated sample no. 1.

Counterexample 2

A sample of titanium mesh with a size of 10x10 cm was subjected to blasting with corundum, cleaned of residues with a stream of compressed air. Then the sample was 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 of UN and 50 g / l ΚΝΟ ₃ at about 100 ° C for 1 hour. After this alkaline treatment, the sample was washed three times with demineralized water at 60 ° C, changing each time the liquid . The last wash was carried out with the addition of a small amount of HCl (approximately 1 ml per liter of solution). Air drying was performed, observing the formation of a brown tint due to the growth of a thin film of TU _X.

Then the mesh sample was placed in a vacuum chamber of the jet spraying unit.

After establishing a dynamic vacuum of about 50x10 ^-4 mbar with the supply of a mixture of oxygen with 20% argon, the sputtered targets were polarized at the following powers: ruthenium 35 W, iridium 24 W, titanium 250 W. The distance from the target to the electrode substrate was about 10 cm.

The deposition process was carried out under the same conditions alternately on two sides of the titanium mesh with a total duration of 220 minutes. The electrode thus obtained had a catalytic coating with a thickness of about 1 μm and a total specific content of the noble metal of about 9 g / m ² , expressed as the sum of Cu and 1 g in terms of metals.

The electrode thus obtained was designated sample no. 2.

Example 1

A sample of titanium mesh with a size of 10x10 cm was subjected to blasting with corundum, cleaned of residues with a stream of compressed air. Then the sample was 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 NaΟH and 50 g / l ΚΝ ₃ at about 100 ° C for 1 hour. After this alkaline treatment, the sample was washed three times with demineralized water at 60 ° C, changing liquid each time. The last wash was carried out with the addition of a small amount of HCl (approximately 1 ml per liter of solution). Air drying was performed, observing the formation of a brown tint due to the growth of a thin ΤίΟ _χ film.

Then, 100 ml of a water-alcohol solution containing KiS ^ -EH ^, H ₂ I ^ C1 ₆ · 6H ₂ Ο, PS1 ₃ in a mixture of water and 2-propanol, acidified with HC1, having a molar composition of 36% Ci, 20% 1g, 44 were prepared % Вι in terms of metals.

- 2 024356

At the end of the whole procedure, the total specific content of the noble metal was 7 g / m ² , expressed as the sum of CI and 1 g in terms of metals.

Then the prefabricated electrode was introduced into the vacuum chamber of the jet spraying unit.

After establishing a dynamic vacuum of approximately 100x10 ^-4 mbar with the supply of a mixture of oxygen with 20% argon, the sputtered targets were polarized at the following powers: ruthenium 30 W, iridium 35 W. The distance from the target to the electrode substrate was about 10 cm. To impart optimum properties to the resulting coating, the substrate was also subjected to a residual polarization of about 150 V.

The deposition process was carried out under the same conditions alternately on two sides of the titanium mesh with a total duration of 40 minutes. The electrode thus obtained had an outer catalytic coating with a thickness of approximately 0.1 μm and a total specific content of the noble metal of approximately 9 g / m ² , expressed as the sum of Ki and 1 g in terms of metals.

The electrode thus obtained was designated sample No. 3.

Samples of the previous examples were characterized as anodes for the release of chlorine in a laboratory cell, which was supplied with sodium chloride brine with a concentration of 200 g / l, strictly controlling the pH value at level 3. Tab. 1 results in an overvoltage of chlorine release, measured at a current density of 4 kA / m ² , and the volume percentage of oxygen in the product, chlorine.

Table 1

Samples of previous examples were also subjected to a durability test. The mentioned durability test is a simulation in a separate cell of the conditions of industrial electrolysis on the electrolyte concentration and temperature, but at a current density, mostly increased to a value 2-3 times greater than the nominal, in order to accelerate the experimental result. Tab. 2 leads the value of the loss of precious metal per unit current.

table 2

Sample No. Loss of precious metal per current unit (mGd _ragmetall / kA -h) one 0, 016 2 0, 5 3 0, 005

The above description is not intended to limit the invention, which can be used according to various embodiments without departing from its scope and the scope of which is determined solely by the attached claims.

Throughout the description and claims of this application, the terms contain, include and variations thereof, such as containing, including, containing and including, do not imply the exclusion of the presence of other elements or additives.

Discussion of documents, actions, materials, devices, products, etc. included in this description only to provide a context for the present invention. It is not intended or implied that any or all of these objects were part of the basic level of technology or were well known information in the field relevant to the present invention, prior to the priority date of each claim of this application.

Claims

1. An electrode for isolating gaseous products in electrochemical cells, consisting of a valve metal substrate coated with a first catalyst composition and an external catalyst composition, said first catalyst composition comprising a mixture of a valve metal or tin or its oxide and noble metals selected from the group platinum metals or 3,035,356 metals or their oxides, taken individually or in mixture, said outer catalyst composition contains noble metals selected from the pl atine metals or their oxides, taken individually or in a mixture, said first catalyst composition is obtained by thermal decomposition of precursors, said external catalyst composition is deposited by chemical or physical vapor deposition, the amount of noble metal in said first catalyst composition is above 5 g / m ² , and the amount of the noble metal in said outer catalyst composition is 0.1-3.0 g / m ² .

2. The electrode according to claim 1, wherein said first catalyst composition comprises titanium, iridium and ruthenium.

3. The electrode according to claim 1, in which the outer catalytic composition contains ruthenium and / or iridium.

4. The electrode according to any one of claims 1 to 3, in which the specific noble metal content of the first catalytic composition is from 6 to 8 g / m ² and the specific noble metal content of the outer catalyst composition is from 1.5 to 2.5 g / m ² .

5. A method of manufacturing an electrode according to any one of claims 1 to 4, including chemical or physical vapor deposition of an external catalytic composition of noble metals selected from the group of platinum metals or their oxides, taken individually or in a mixture, on a metal substrate coated with the first a catalytic composition obtained by thermal decomposition of the precursors of valve metals, or tin, or its oxide and noble metals selected from platinum group metals or their oxides, taken individually or in mixtures.

6. The method according to claim 5, including the deposition of the aforementioned external catalytic composition in the form of a mixture of oxides by reactive spraying of noble metals selected from the group of platinum metals.

7. The method according to claim 5, in which said metal substrate is a spent electrode.

8. The method according to claim 7, in which the deposition of the external catalytic composition in the form of a mixture of oxides is carried out by reactive spraying of iridium and ruthenium onto said spent electrode.

9. An electrolysis cell including a cathode compartment and an anode compartment for an alkali metal chloride brine separated by a membrane or diaphragm, wherein the anode of said anode compartment is an electrode according to any one of claims 1 to 4.