US3929608A - Catalytic material for electrodes - Google Patents

Abstract

An improved electrode having an electroconductive metal support or core at least superficially made of titanium or a titanium alloy and a catalytic coating on the titanium metal surface including (a) at least one substance from the group consisting of the platinum group metals and their oxides and (b) an oxide of tellurium. This novel electrode is particularly adapted for use in the electrolysis of aqueous solution of alkali metal halides.

Description

United States Patent Degueldre et al.

[ 1 *Dec. 30, 1975 CATALYTIC MATERIAL FOR ELECTRODES Inventors: Louis Degueldre; Yves Gobillon,

both of Brussels; Lucien Clerbois, Vilvoorde; Louis Bourgeois, Brussels, all of Belgium Assignee: Solvay & Cie, Brussels, Belgium Notice: The portion of the term of this patent subsequent to Oct. 1, 1991, has been disclaimed.

Filed: Aug. 27, 1973 Appl. No.: 391,736

Related U.S. Application Data Continuation-in-part of Ser. No. 167,189, July 29, 1971, abandoned.

Foreign Application Priority Data July 29, 1970 Luxemburg 61436 U.S. Cl. 204/290 F; 136/120 FC Int. Cl. C25B 11/08; C25B 11/10 Field of Search 204/290 F; 136/120 FC Primary ExaminerF. C. Edmundson Attorney, Agent, or FirmSpencer & Kaye 57 ABSTRACT An improved electrode having an electroconductive metal support or core at least superficially made of titanium or a titanium alloy and a catalytic coating on the titanium metal surface including (a) at least one substance from the group consisting of the platinum group metals and their oxides and (b) an oxide of tellurium. This novel electrode is particularly adapted for use in the electrolysis of aqueous solution of alkali metal halides.

13 Claims, 4 Drawing Figures FIG. I

U.S. Patent Dec. 30, 1975 Sheet 2 of2 3,929,608

CATALYTIC MATERIAL FOR ELECTRODES CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of our copending application for CATALYTIC MATERIAL FOR ELECTRODES, Ser. No. 167,189, filed July 29th, 1971, now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to a new material for electrodes, and more particularly to a material which has catalytic properties making it especially suitable as an operative surface for electrodes.

SUMMARY OF THE INVENTION According to the invention, the new catalytic material for electrodes comprises one or more of the platinum group elements in the metallic and/or oxidized state and tellurium in the oxidized state. Tellurium can be partially replaced by tungsten, molybdenum or chromium. One or more metals, selected from the group Pb, Bi, Sb, Sn, Cd, Ti, Ta and Nb, may be incorporated as oxides in the catalytic material.

The inclusion of oxidized tellurium unexpectedly and substantially improves the physical properties of the catalytic composition without adverse effect upon its electrochemical properties. There is a marked increase in the cohesiveness of the catalytic layer and, when applied to a metal, particularly to a surface of titanium or titanium alloy, the adherence of the catalyst to the metal is greatly improved.

This result may be achieved with the addition of the tellurium to the platinum group component in the ratios of from 1:100 to 1:1.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational view of a coated electrode according to the invention.

FIG. 2 is a cross-sectional view from the line 11 II of FIG. 1.

FIGS.'3 and 4 are photographs obtained with a scanning electron microscop having a magnitude of 1750, of the coating surface respectively of an electrode of the prior art and of an electrode according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIGS. 1 and 2, a coating 11 of the catalytic material of the present invention is shown placed on a strip of metal 12, such as titanium.

The catalytic material according to the present invention may constitute the whole of an electrode or only its operative surface coating.

It is preferred to place the catalytic material of the present invention on a metal support at least superficially made of titanium or a titanium metal. Advantageously, titanium is clad on a core ofa more conductive metal such as copper, aluminum, iron, or alloys of these metals.

Preferably, the material of the present invention con sists essentially of the components as set forth in the appended claims; yet more preferably, the material consists of those components.

The electrodes at least superficially made of a catalytic material according to the present invention are particularly useful as anodes in the electrolysis of aqueous solutions of alkali metal halides, especially sodium chloride, in diaphragm cells as well as in mercury-cathode cells, where they catalyze the discharge of chloride ions according to the half reaction 2c1 C1 2eunder a remarkably low overvoltage which remains substantially unvaried over an electrode lifetime. Under the conditions ruling in the cell, the anode wear is very slow, thus providing practically unlimited lifetime and avoiding the need for cell opening and electrode replacement.

More particularly, used as a coating of metal anodes for the electrolysis of aqueous solutions of sodium chloride, the material according to this invention presents a good adhesion to the underlying support and a very low overvoltage for the liberation of chlorine. It allows anodic current densities higher than 30 kA/m and even higher than 40 kA/m in some cases, in tests of long duration.

For electrode preparation, the new material is generally deposited as a coating on a conducting support. This coating is applied according to well known coating techniques. When it is applied by painting, the material is generally heated after each coat and necessarily after the last one. This heating is carried out in an oxygen containing atmosphere, preferably in the air, between 300 and 600C. Under these conditions, an important part of the noble metal can be found as on oxide in the catalytic material.

The electrodes of FIGS. 3 and 4 comprise each a sheet of titanium with a catalytic coating deposited according to the above described painting technique.

More particularly, FIG. 3 relates to an electrode of the prior art, having a coating made essentially of irid- The coating of the electrode of FIG. 4 is according to the invention and includes a compound of iridium and tellurium, with an atomic ratio TezIr 1:2.

The improved cohesiveness of the coating of the invention appears by comparison of both FIGS. 3 and 4, the coating surface of FIG. 4 having much less cracks than the coating of FIG. 3.

Further illustrative of the present invention are the following examples. All concentrations are given on a solution basis, unless indicated otherwise. Thus, for example, a solution of 0.1 g-at Ir/l means that there is 0.1 gram-atom of iridium in one liter of solution.

EXAMPLE 1 A solution of 0.1 gram-atom Ir/liter (solution A) was prepared by dissolving chloro-iridic acid H IrCl -xH O in N N- N,N-dimethylformamide (DMF), HCON(CH Additionally, 16 mg of TeO were substantially dissolved in 0.05 ml of concentrated HCl (solution B).

Several coats of the composition obtained by mixing 2 ml of solution A with the whole of solution B were painted onto titanium strips which had been previously degreased in hot trichloroethylene and immersed for 4-5 hours at about C in an aqueous solution of 10% oxalic acid to etch the surface. For painting, the titanium strips were disposed on a heating plate at -125C. After each coat had been painted on, the strips were heated at 300 to 450C for 15 minutes. After the fifth coating, the coated strips were finally heated in air, at 475C for 16 hours. The coating weight of thus deposited material was approximately 13 g/m of titanium strip surface. The coating, which analysis showed to comprise 2 g-at Ir for every 1 g-at Te, ad-

3 hered tightly to the underlying titanium support and passed successfully a test consisting of attempting to tear off the coating with an adhesive tape applied under pressure.

The thus-coated titanium strips were subjected, as anodes, to two different tests: the first one to measure the over-voltage for the liberation of chlorine under a given anodic current density kA/m the second one to determine the wear or consumption of noble metal as related to the quantity of evolved chlorine. The term overvoltage" is used herein in the same sense as it is used at pages 488-492 ofPhysical Chemistry by Walter j. Moore, Prentice-Hall, Inc., Second Edition.

In the overvoltage test, the coated strips were used as anodes for the electrolysis of a brine containing 250 g NaCl/kg, saturated with chlorine at 60C and at an approximate pH of 2. Under these conditions, the coated strips of this example showed an overvoltage of 155 mV under an anodic current density oflO kA/m In the wear test, the coated strips were used as anodes in a cell with a flowing mercury cathode for the electrolysis of a brine saturated with sodium chloride and chlorine, between 80 and 85C, under a constant anode-cathode potential difference, the test being stopped when the current density was reduced to one half of its initial value (initial value generally was between 30 and 40 kA/m Under these conditions, the tested strips produced 105 tons of chlorine per square meter of active surface under an average current density of 24 kA/m and the noble metal consumption lay below 80 mg of Ir per ton of C1 EXAMPLE 2 Six ml of the solution A used in Example 1 and 16 mg of TeO substantially dissolved in afew drops of concentrated I-ICl, were mixed together.

Five coats of this composition were applied onto titanium strips under the same conditions as in Example l and were heated in the same way.

The coating weight of the thus obtained coating was approximately 13.5 g/m Analysis showed the coating to comprise 6 g-at Ir for every I g-at Te. The coating adhered tightly to the underlying support.

In an overvoltage test carried out under the same conditions as in Example 1, the thus coated strips showed an overvoltage of 90 mV under an anodic current density of 10 kAlm In a wear test, also carried out under the conditions of Example 1, these same coated strips produced 133 tons of Cl /m under an average current density of 30 kA/m the Ir consumption being below 80 mg/ton of C1 EXAMPLE 3 Ir for every 0.9 g-at W and 0.1 g-at Te. The coating adhered tightly to the underlying titanium support.

In an overvoltage test carried out under the same conditions as in Example 1, the thus coated strips showed an average overvoltage of 95 mV under an anodic current density of 10 kA/m In a wear test also carried out as in Example I, these coated strips produced 63 tons of Cl /m under an average anodic current density of 31 kA/m The Ir consumption lay in the range 100 mg/ton of C1 EXAMPLE 4 Fifteen ml of the solution A of Example I were mixed with 10 ml of a solution of lead nitrate in DMF at 0.2 g-at Pb/l and with 79.8 mg of TeO substantially dissolved in 0.2 ml of concentrated I-ICl.

Five coats of this composition were applied onto titanium strips and heated under the conditions mentioned in Example 1.

The coating weight of the thus obtained coating was approximately 27 g/m It comprised 2 g-at Pb for every 1.5 g-at Ir and 0.5 g-at Te, and adhered tightly to the underlying support.

In an overvoltage test carried out under the same conditions as in Example 1, the thus coated strips showed an average overvoltage of 96 mV under an anodic current density of 10 kA/m In a wear test, also carried out as in Example 1, these coated strips produced 120 tons of Cl /m under an average anodic current density of 25 kA/m and the Ir consumption lay in the range of mg/ton of C1 EXAMPLE 5 One and one-half ml of the solution A of Example 1 were mixed with a solution of 77.2 mg bismuth acetate and 8 mg TeO in concentrated I-ICl.

This composition was applied onto titanium strips and heated under the conditions mentioned in Example I; but 6 coats were applied instead of 5.

The weight of the thus obtained coating was approximately 22 g/m It comprised 2 g-at Bi for every 1.5 g-at Ir and 0.5 g-at Te. It adhered tightly to the underlying support.

In an overvoltage test carried out under the same conditions as in Example 1, the thus coated strips showed an anodic overvoltage of mV under an anodic current density of 10 kA/m EXAMPLE 6 Dihydrated rhodium nitrate, Rh(NO '2I-I O, was dissolved in DMF at room temperature to give a solution of 0.1 g-at Rh/l, which was then mixed with a solution of TeO in 12 N hydrochloric acid to give a Rh/Te ratio of 2/1.

The application of this composition onto titanium strips and associated thermal treatments were carried out as set forth in Example 1.

The weight of the thus obtained coating was approximately 5 g/m it comprised 2 g-at Rh for every 1 g-at Te, and adhesion to the underlying support as checked by adhesive tape tests was good.

In an overvoltage test carried out under the same conditions as in Example 1, the thus-coated strips showed over-voltages lying between 315 and 430 mV, under an anodic current density of 10 kA/m In a wear test, also carried out as in Example 1, these coated strips produced 15 tons of Cl /m under an average anodic current density of 20 kA/m and Rh consumption lay in the range 200 mg/ton of C1 EXAMPLE 7 Hydrated rhodium trichloride and tungsten chloride, WCl were separately dissolved in DMF. Ten ml of the Rh solution containing 0.0245 g-at Rh/l were mixed with 0.166 ml of the W solution containing 0.49 g-at W/l, and with 6.5 mg of tellurium oxide previously dissolved in 0.1 ml of concentrated hydrochloric acid.

Four coats of this composition were applied at room temperature into titanium strips which were dried in the air for 30 minutes and heated at 350C for 15 minutes after each application. They were finally fired at 500C for 66 hours.

The average weight of the thus obtained coating was near to 7 g/m and adhesion was excellent. The coating comprised 6 g-at Rh for every 1 g-at Te and 2 g-at W.

In an overvoltage test carried out under the same conditions as in Example 1, the thus-coated strips showed an over-voltage of 350 mV under an anodic current density of kA/m EXAMPLE 8 CrCl '6l-I O and hydrated RuCl were separately dissolved in DMF to give a solution of 0.46 g-at Cr/l and a solution of 0.5 g-at Ru/l, respectively, which were mixed together in a given proportion; a suitable amount of TeO dissolved in 12 N HCl was then added in order to obtain a Ru/Cr/Te g-at ratio of 3/2/1.

Applied onto titanium strips under the same conditions as in Example 1, this composition gave a coating comprising 3 g-at Ru for every 2 g-at Cr and 1 g-at Te. The adhesion of this coating to the strips was satisfactory. The coating showed interesting anodic polarization properties in chlorinated brine.

EXAMPLE 9 A solution of 0.019 g-at lr/l (solution A) was prepared by dissolving chloro-iridic acid, H lrCl -H O in dimethyl sulphoxide (DMSO), CH SOCH A solution of 0.194 g-at rh/l (solution B) was prepared by dissolving rhodium nitrate, Rh(NO in glycol, l-lOCH cl-l Ol-l.

Finally, 25.3 mg of TeO were substantially dissolved in a few drops of concentrated HCl (solution C).

By mixing 50 ml of solution A 1.65 ml of solution B and the whole of solution C a composition was obtained which was applied onto titanium strips previously degreased and heated as in Example 1.

For the applications, the titanium strips were disposed in the air on a heating plate at about 100C.

After each application, the coated strips were heated for minutes at 400C.

After 12 coatings had been applied under the same conditions, 6 further coatings were applied with intermediate heatings of 15 minutes at 440C.

Finally, the coated strips were fired for 16 hours at 475C in the presence of air.

The weight of the thus deposited material was approximately 8 g/m. The coating contained 6 g-at Ir and 2 g-at Rh for every 1 g-at Te, and adhered tightly to the underlying supports as shown by tear-off tests with adhesive tape.

In an overvoltage test carried out under the same conditions as in Example 1, the thus-coated strips showed an overvoltage of 135 mV, under an anodic current density of 10 kA/m 6 In a wear test carried out as indicated in Example 1, the coated strips produced more than 63 tons of chlorine per square meter of active anodic surface, under an average current density of 24 kA/m At this stage, the use limit has not yet been reached and the wear test continued.

EXAMPLE 10 A solution A of 0.1 g-at lr/l was prepared by first dissolving chloro-iridic acid, H lrCl -H O, in a given quantity of ethanol. An equal volume of chloroform was then added to the solution together with an equal volume of turpentine a (boiling point above 150C) sulphurated to 20% through reflux heating of g turpentine a with 20 g sulphur for 3 hours.

A solution B of 0.2 g-at Tell was prepared by first dissolving tellurium chloride TeCl resulting from the action of chlorine upon tellurium, in 2 volumes of ethanol. Then 5 volumes of turpentine a sulphurated to 40% were added, the whole being heated on a water bath until the formed precipitate had completely disappeared. 7

Finally, a solution C was prepared by mixing 1 volume of ethanol, 1 volume of chloroform and 1 volume of turpentine a.

By mixing 2 ml of solution A 0.5 ml of solution B and 4.5 ml of solution C a composition was obtained which was applied onto titanium strips previously degreased and etched as described in Example 1.

This application was carried out in the air and at room temperature. After each application, the strips were heated at 500C for 15 minutes.

After 10 coatings under the said conditions, the coated strips were finally heated for 5 hours at 500C in the presence of air.

The weight of the thus obtained coating was approximately 7 g/m. The deposit contained 2 g-at Ir for every 1 g-at Te and adhered tightly to the underlying strips.

In an overvoltage test carried out under the same conditions as in Example 1, the thus-coated strips showed an overvoltage of mV under an anodic current density of 10 kA/m In a wear test, also carried out as in Example 1, the coated strips produced more than 140 tons of chlorine/m working continuously for 5 months under an average current density of 33 kA/m At this stage, the use limit had not been reached and the wear test continued.

EXAMPLE 1 l A solution A of l g-at lr/l was prepared by dissolving chloro-iridic acid, H lrCl -xl-l O in ethanol.

A solution B of 0.5 g-at Te/l was prepared by dissolving in ethanol allotelluric acid which had been obtained by keeping telluric acid H TeO '2l-i O in a sealed tube at C for 1% hours.

Finally,

1 ml of solution A 1 ml of solution B 10 ml of normal hexyl alcohol 6 ml of chloroform and 2 ml of turpentine b (boiling point between 158 and 160C) sulphurated to 20% were mixed.

Ten :coatings of the thus obtained composition were applied onto titanium strips under the conditions mentioned in Example 10. The various thermal treatments were carried out in the same way.

The weight of the thus obtained coating was approximately 7 g/m It contained 2 g-at Ir for every 1 g-at Te, and its adhesion to the underlying support was very good.

In overvoltage tests carried out as in Example 1, the thuscoated strips showed an overvoltage of 150 mV under an anodic current density of 10 kA/m In a wear test, also carried out as indicated in Example 1, the coated strips produced more than 40 tons of chlorine/m working continuously for 6 weeks under a current density near to 30 kA/m At this stage, the use limit had not been reached and the wear test continued.

EXAMPLE 12 A solution A containing 0.1 g-at Ru/l was prepared by first dissolving 0.45 g of ruthenium chloride RuCl -x- H O, in 8 ml of ethanol to which were then mixed 6 ml of chloroform and 6 ml of turpentine a sulphurated to 20% as in Example 10.

A solution B of chloro-iridic acid at 0.1 g-at Ir/l was prepared by mixing ml of the solution A of Example 8 with 13 ml of ethanol, 16 ml of chloroform and 16 ml of turpentine a sulphurated to 20% as in Example 10. Finally,

1 ml of solution A 3 ml of solution B 1 ml of solution B of Example and 7 ml of solution C of Example 10 were mixed.

Ten coatings of the thus obtained composition were applied to the titanium strips under the condition mentioned in Example 10. The various thermal treatments were carried out in the same way.

The weight of the thus obtained coating was approximately 4 g/m It contained the elements Ru-Ir-Te in respective atomic proportions 0.5/1.5/1 and its adhesion was satisfactory.

In an overvoltage test carried out as indicated in Example 1, the thus-coated strips showed an overvoltage of 140 mV under an anodic current density of 10 Kalm In a wear test carried out under the same conditions as in Example 1, the strips produced more than 120 tons of chlorine/m working continuously under current densities between 29 and 23 kA/m At this stage, the use limit had not been reached and the wear test continued.

EXAMPLE 13 Ten coatings were applied onto titanium strips under the conditions set forth in Example 10, the various thermal treatments being carried out in the same way.

The weight of the thus obtained coating was approximately 4 g/m; it contained the elements Ru-Rh-Te in the respective atomic proportions 3/2/1 and its adhesion was satisfactory.

In an overvoltage test carried out as in Example 1, the thus-coated strips showed an overvoltage of 245 mV under ananodic current density of 10 kA/lm In a wear test, also carried out under the conditions set forth in example 1, the strips produced 120 tons of chlorine/m working continuously under an average current density of 24 kA/m The consumption of noble metal lay below 20 mg of (Rh Ru) per ton of produced chlorine.

EXAMPLE 14 A solution A of 1 g-at Ru/l was prepared by dissolving ruthenium chloride, RuCl 'xI-I O, in n-pentanol.

By operating in the same way with rhodium chloride, RhCl 'xH O, a solution B of 0.5 g-at Rh/l was prepared. Finally,

5 ml of solution A 1.7 ml of solution B 0.84 ml of solution B of Example 1 1 41.5 ml of n-pentanol were mixed.

Seven coatings of the thus obtained composition were applied onto titanium strips under the conditions indicated in Example 10, but the heating conditions were different: after each application and evaporation of excess solvent the coated strips were heated for 15 minutes at 350C, and the final firing was carried out at 500C for 1 hour.

The weight of the thus-deposited material was approximately 5 g/m It contained the elements Ru-Rh- Te in the respective atomic proportions of 12/2/1. Adhesion to the underlying strips was very good.

In an overvoltage test carried out under the same conditions as in Example 1,- the thus-coated strips showed an overvoltage of 95 mV, under an anodic current density of 10 kA/m In a wear test, also carried out as indicated in Example 1, the coated strips produced more than 82 tons of chlorine/m working continuously under current densities between 36 and 25 kA/m At this stage, the use limit had not been reached and the wear test continued.

EXAMPLE 15 Hydrated RhCl and SbC1 were separately dissolved in n-hexanol, to give solutions of 0.5 g-at Rh/l (solution A) and 1' g-at Sb/l (solution B), respectively.

Mixing 5 ml of solution A 1.1 ml of solution B 1.4 ml of solution B of Example 11 and 42.5 ml of n-hexanol, a coating composition was obtained.

Seven coatings were painted onto titanium strips previously degreased and etched as in Example 1. For the applications, the strips were disposed on a heating plate at about C. After each of the first 6 applications, the strips were heated for 15 minutes at 500C, whereas after the seventh application, they were finally fired for 1 hour at 500C.

The weight of the thus obtained coating was 2.6 g/m It contained the elements Rn-Sb-Te in an atomic ratio of 7/3/2 and passed successfully a tear-off test using adhesive tape applied under pressure.

In an overvoltage test carried out as in Example 1, the thus coated strips showed an overvoltage of 450 mV under an anodic current density of -kA/m The characteristics of the above examples are 5 compiled in the following table. f

i Coating wear test Thick- Overvoltage ness in mV Example Atomic Ratio -in Adhesion at C1 Current Consumption No. g/m 1O kA/m produced density of noble in in kA/m metal in t/m? mg/t produced C1 1 2 lr/lTe 3 good 155 105 24 80 2 6 lr/lTe 13.5 excellent 95 133 3 2lr/0.9W/0.1Te 11.5 63 31 4 2Pb/l .5lr/0.5Te 27 good 96 25 75 5 2Bi/l.5lr/0.5Te 22 very good 90 6 2Rh/1Te 5 315-430 15 20 200 7 6Rh/2W/1Te 7 excellent 350 8 3Ru/2Cr/ 1 Te satisfactory interesting 9 6Ir/2Rh/1Te 8 very good 63 24 1O 21r/1Te 7 140 33 ll Zlr/lTe 7.4 60 30 12 0.5Ru/llr/1Te 4 satisfactory 140 120 29-23 13 3Ru/2Rh/1Te 3.7 245 120 24 20 14 l2Ru/2Rh/1Te 5 very good 95 82 36-25 15 7Rh/3Sb/2Te 2.6 excellent 450 A coating which has interesting overvoltage proper- 1:100.

ties is a coating for which an overvoltage of about 450 mV may be obtained in the test carried out with chlorinated brine. For industrial uses in electrolysis of NaCl brine for producing chlorine, 500 mV may be considered as the maximum overvoltage acceptable for economic viewpoint. For other electrochemical processes such as cathodic protection and all the uses where Cr and Fe, particularly, are not subject to corrosion, 500 mV is not a critical factor, and so, these coatings may be interesting.

Platinum group elements includes the following: noble transition elements of group VIII i.e. Pt, Ir, Os, Pd, Rh, Ru.

Ta and Nb having similar chemical properties as those of Sb, i.e. the same valence state these two compounds may also be used, and in the same way Sn may be used as well as Pb. Further, Zn and Cd are other elements which are convenient for the invention.

As elements of the platinum group" Os, Pd, Pt, may be also used because they have the same chemical properties as lr, Rh, Ru.

Among the platinum group metals defined above, Pt for example may be present at the metallic state, platinum oxide being only obtained by heating under high pressure. The other elements of the group may also be present at the metallic state by heating under inert atmosphere i.e without oxygen.

The atomic ratio of tellurium: platinum group metal, in the foregoing Examples and Table, varies from 1:15 to 1:20. However, as previously stated, the effective proportions are in the range of 1:100 to 1:1, the preferred range being 1:20 to 1:2.5.

The nature of this action of the tellurium oxide is not understood, but is believed to be linked to an at least partial imbrication of the tellurium into the crystal matrix of the catalyst coating.

in addition to the physical improvements, the presence of the tellurium in very favorable chlorine liberating overvoltages, as are observed for coatings containing up to l gram-atom 1r for 1 gram atom Te.

Likewise, the atomic proportion of tellurium to the additional elements lead, bismuth, antimony, tin, cadmium, titanium, tantalum or niobium, individually or collectively may be in the range 1:1.5-4.

For an atomic ratio of TezIr 1:1, the electrode has an overvoltage to the liberation of chlorine, which is too high for an economic industrial use, while for an atomic ratio of Te:Ir 1:100, tellurium has substantially no more action on the properties of the electrode coating.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What is claimed is:

1. Electrode for electrochemical processes comprising a conductive and inert substrate at least superficially comprising titanium or a titanium alloy and a protective and electrocatalytic coating covering at least a part of the surface of said substrate and adhered to said surface, said coating comprising:

a. at least one substance selected from among the group consisting of the platinum-group metals and their oxides, and

b. oxidized tellurium, the atomic ratio of bza being 2. An electrode as claimed in claim 1, further containing (c) an oxidized metal selected from the group consisting of tungsten, molybdenum and chromium, the atomic ratio of b:c being 1:2-9.

3. An electrode as claimed in claim 1, containing iridium as an element of the platinum group.

4. An electrode as claimed in claim 1, further containing at least (d) one oxidized metal selected from the group consisting of Pb, Bi, Sb, Sn, Cd, Ti, Ta, and Nb, the atomic ratio of bzd being 1:1.5-4.

5. An electrode as claimed in claim 1, said at least one component being selected from the group consisting of the oxides of the platinum-group metals.

6. An electrode for the electrolysis of alkali metal chloride solutions, comprising a conductive and inert substrate at least superficially comprising titanium or a titanium alloy and a protective and electrocatalytic coating covering at least a part of the surface of said substrate and adhered to said surface, said coating comprising: (a) at least one component selected from the group consisting of the platinum-group metals and their oxides and (b) oxidized tellurium, the atomic ratio of bza being l:2-20.

7. An electrode as claimed in claim 6, wherein said catalytic material further contains (c) an oxidized metal selected from the group consisting of tungsten, molybdenum, and chromium, the atomic ratio of bzc being 122-9.

8. An electrode as claimed in claim 6, wherein said catalytic material contains iridium as an element of the platinum group.

9. An electrode as claimed in claim 6, wherein said catalytic material further contains (d) at least one oxidized metal selected from the group consisting of Pb, Bi, Sb, Sn, Cd, Ti, Ta, and Nb, the atomic ratio of bzd being 23-8.

10; An electrode as claimed in claim 6, wherein said at least one component is selected from the group consisting of the oxides of the platinum group metals.

1]. An electrode as claimed in claim 1 wherein the atomic ratio of bza is 1:2-20.

12. An electrode as claimed in claim 1, wherein the atomic ratio of bza is 1:25-20.

13. An electrode as claimed in claim 1, wherein the atomic ratio baa is from 1:15 to 1:20.

Claims (13)

1. ELECTRODE FOR ELECTROCHEMICAL PROCESSES COMPRISING A CONDUCTIVE AND INERT SUBSTRATE AT LEAST SUPERFICIALLY COMPRISING TITANIUM OR A TITANIUM ALLOY AND A PROTECTIVE AND ELECTROCATALYTIC COATING COVERING AT LEAST A PART OF THE SURFACE OF SAID SUBSTRATE AND ADHERED TO SAID SURFACE, SAID COATING COMPRISING: A. AT LEAST ONE SUBSTANCE SELECTED FROM AMONG THE GROUP CONSISTING OF THE PLATINUM-GROUP METALS AND THEIR OXIDES, AND B. OXIDIZED TELLURIUM, THE ATOMIC RATIO OF B:A BEING 1:1-100.

2. An electrode as claimed in claim 1, further containing (c) an oxidized metal selected from the group consisting of tungsten, molybdenum and chromium, the atomic ratio of b:c being 1:2-9.

3. An electrode as claimed in claim 1, containing iridium as an element of the platinum group.

4. An electrode as claimed in claim 1, further containing at least (d) one oxidized metal selected from the group consisting of Pb, Bi, Sb, Sn, Cd, Ti, Ta, and Nb, the atomic ratio of b:d being 1:1.5-4.

5. An electrode as claimed in claim 1, said at least one component being selected from the group consisting of the oxides of the platinum-group metals.

6. An electrode for the electrolysis of alkali metal chloride solutions, comprising a conductive and inert substrate at least superficially comprising titanium or a titanium alloy and a protective and electrocatalytic coating covering at least a part of the surface of said substrate and adhered to said surface, said coating comprising: (a) at least one component selected from the group consisting of the platinum-group metals and their oxides and (b) oxidized tellurium, the atomic ratio of b:a being 1:2-20.

7. An electrode as claimed in claim 6, wherein said catalytic material further contains (c) an oxidized metal selected from the group consisting of tungsten, molybdenum, and chromium, the atomic ratio of b:c being 1:2-9.

8. An electrode as claimed in claim 6, wherein said catalytic material contains iridium as an element of the platinum group.

9. An electrode as claimed in claim 6, wherein said catalytic material further contains (d) at least one oxidized metal selected from the group consisting of Pb, Bi, Sb, Sn, Cd, Ti, Ta, and Nb, the atomic ratio of b:d being 2:3-8.

10. An electrode as claimed in claim 6, wherein said at least one component is selected from the group consisting of the oxides of the platinum group metals.

11. An electrode as claimed in claim 1 wherein the atomic ratio of b:a is 1:2-20.

12. An electrode as claimed in claim 1, wherein the atomic ratio of b:a is 1:2.5-20.

13. An electrode as claimed in claim 1, wherein the atomic ratio b:a is from 1:1.5 to 1:20.

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