DD153397A5 - ELECTRODE WITH AN ELECTROCATALYTIC COVER - Google Patents

Abstract

An electrode for use in electrolytic processes comprises a substrate of film-forming metal such as titanium having a porous electrocatalytic coating comprising at least one platinum-group metal and/or oxide thereof possibly mixed with other metal oxides in an amount of at least about 2 g/m<2> of the platinum-group metal(s) per projected surface area of the substrate. Below the coating is a preformed barrier layer constituted by a surface oxide film grown up from the substrate. This preformed barrier layer has rhodium and/or iridium as metal or compound incorporated in the surface oxide film during formation thereof in an amount of up to 1 g/m<2> (as metal) per projected surface area of the substrate.

Description

1AO-54070

description

Title of the invention

Electrode with an electrocatalytic coating

Field of application of the invention

The invention relates to electrodes for electrolytic processes, which can be termed dimensionally stable electrodes, from a base metal body of a valve metal, e.g. Titanium, tantalum, zirconium, niobium, tungsten, aluminum or their alloys or ferrosilicon, i. which can coat with a passivating oxide film, an intermediate layer and a special electrocatalytically active coating.

C characteristic of the known technical solutions

From GB-PS 855 107 and 869 865 are titanium electrodes with a coating of a platinum metal and

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an inert barrier layer of titanium oxide / known, wherein the barrier layer is preferably formed or reinforced by a heat treatment. According to GB-PS 925 080, the inert barrier layer of titanium oxide is produced electrolytically or by heating the titanium substrate in an oxidizing atmosphere prior to the application of the platinum metal. The pre-formation of such a barrier layer was carried out according to GB-PS 1 147 422 also with regard to a better anchoring of an active layer or containing oxides of platinum metals.

The development of coatings based on mixed crystals or solid solutions of deposited oxides of valve metals and platinum group metals (US Pat. No. 3,632,498) has resulted. to economically viable electrodes that revolutionized the chloralkali industry and found wide application for other purposes as well. , These electrodes gave excellent performance without the need for a reinforcement or preformed inert barrier layer on the electrode base body. Today, it is generally believed that preformed or reinforced inert barrier layers are disadvantageous in terms of electrode performance. Looking back, it can now be said that the previous proposals for preformed or reinforced inert barrier layers were apparently unsuccessful attempts to avoid defects that arose with the previous coatings and not so much with the electrode base body.

Some attempts have been made to improve the inert barriers, e.g. by applying a coating of titania from a tetravalent * in the pores of the coating

Titanium ion-containing solution; however, this affected the performance of the electrodes.

Other efforts have been to provide non-passivating interlayers below the electrocatalytic layer, e.g. doped intermediate layers of tin dioxide; thin intermediate layers of one or more platinum metal (s) such as a platinum iridium alloy; Intermediate layers of cobalt oxide or lead oxide or the like. Although, according to some patents, an improvement of these electrodes is mentioned in certain applications, none of these proposals resulted in any appreciable improvement or widespread commercial application.

Object of the invention

The object of the invention is now a dimensionally stable electrode made of a valve metal base body with a porous electrocatalytic layer, which is a large-scale application, especially as anodes for chloralkali electrolysis, for electrometallurgy in chloride and sulfate-containing electrolytes and the like, due to their high efficiency and long working capacity.

Explanation of the essence of the invention

In the electrode according to the invention is located on the electrode body of a valve metal, a porous electrocatalytically active outer layer containing at least about 2 g / m ^ at least one platinum metal and / or its oxide - based on the projected surface of the body -

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optionally in admixture with other metal oxides, wherein there is a non-passivating intermediate or barrier layer between the base body and the electrocatalytic coating.

The barrier layer according to the invention is a preformed oxide skin, grown on the valve metal of the base body, containing rhodium and / or iridium within the oxide skin, which are introduced during their formation, in an amount up to 1 g / m (calculated as metal, based on the projected area of the main body).

The oxide skin of the barrier layer is made non-passivating by incorporation of metallic rhodium and / or iridium or in the form of a compound, usually the oxide or a partially oxidized compound. :

The preparation of the electrode according to the invention is carried out in the manner that a very dilute acidic solution is applied to form the intermediate layer, e.g. containing a small amount of a heat-decomposable iridium and / or rhodium compound, so that with simultaneous decomposition and. Formation of the oxide skin of the valve metal iridium and / or rhodium are completely absorbed in the metal oxide. In general, this diluted solution contains about 1 to 15 g / l of iridium and / or rhodium.

The solution usually contains an organic solvent such as isopropyl alcohol and an acid such as hydrogen chloride, hydrogen bromide or hydrogen iodide, or as another means, for example, sodium fluoride, which attacks the valve metal comparable

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224,371

and allows the formation of its oxide during the subsequent heat treatment. Furthermore, the solution contains one or more heat-decomposed salts of iridium and / or rhodium. In general, the solution is at least 5 times more dilute, preferably at least about 10 times, diluted T _{x in} terms of noble metal content than the solution used to make the porous electrocatalytic layer, ie, the amount of iridium and / or rhodium is, for example, 1/5 or 1/10, or even 1/100, of the amount corresponding to the platinum metal in the solution applied with approximately the same amount of solvent and acid to form the outer layer.

The action of the acid or other agent capable of attacking the valve metal and promoting the formation of its oxide skin is of great importance in the subsequent heat treatment. Without such an agent causing this effect, the formation of the oxide skin of the valve metal would be substantially hindered if not prevented _f be.

It has been observed that when a given mixture of solvent and acid is applied to the valve metal of the electrode base previously cleaned and etched in a conventional manner and then solvent evaporated by heating, a given amount of valve metal oxide is formed; this can be repeated a few times - usually 4 or 5 times in one

 z -z '

4 cm ^ HCl in 60 cnr isopropyl alcohol is applied to titanium of the main body and then heated to 500 ⁰ C for 10 min, before the Ventilmetalloxid skin so

has grown so much that further treatments do not lead to success. The first layer of the whole oxide skin is relatively porous. As a result, during the subsequent application of the solution, it can penetrate into the first layer during the drying stage, as a result of which the acid is able to attack the uncovered valve metal underneath. Valve metal ions are thus provided from the body for oxide formation during subsequent heating. This oxide is now partially formed within the pores of the first layer. As a result, the porosity of the oxide skin decreases with each renewed Lage.bis no more valve metal from the electrode body for conversion into the oxide is available. In this way, an extremely stable, relatively compact and impermeable skin of valve metal oxide can be prepared by applying a limited number of layers with the aid of the acidic solution, followed by drying and heating.

In the preparation of the intermediate layer according to the invention, each layer contains such a small amount of iridium and / or rhodium compound, so that the catalyst obtained by thermal decomposition. is fully incorporated into the oxide skin of the valve metal. Each applied solution contains at most about 0.2 g / m of iridium xmdjb of rhodium, based on the projected area of the electrode body, but usually much less. Moreover, the application of further layers of the dilute solution is discontinued after the number of layers after which the oxide skin no longer increases or the oxide formation is prevented. This is how to set the optimal amount

of electrocatalytic agent in the dilute solution and the optimum number of layers for forming a satisfactory compact impermeable interlayer for each particular electrode body, / ratio of solvent to acid, and the type of electrocatalytic material. In many cases you will apply 2 to 10 layers with the diluted solution. After each application, it is dried and heated to about 400 to 600 ^° C. for about 5 to 15 minutes. After the last application, it is possible to heat for a long time, for example a few hours or days to 450 to 600 ° C in air or in a reducing atmosphere, for example ammonia / hydrogen.

Examination of the thus prepared intermediate layer on an unetched or un-etched or unetched titanium electrode base body generally exhibits the same appearance as titanium oxide layers, but prepared in the same manner without introduction of electrochemically active iridium and / or rhodium are, namely a bright blue, yellow and / or red as the interference color of the skin.

The dilute acidic solution for producing the intermediate layer according to the invention preferably contains only one heat-decomposable iridium and / or rhodium compound, since the valve metal required for the oxide skin is provided by the electrode base body. However, the diluted solution may also contain small amounts of other substances than other platinum metals (ruthenium, palladium, platinum, osmium, in particular

* for each

/8th

Ruthenium), gold, silver, tin, chromium, cobalt, antimony, molybdenum, iron, nickel, manganese, tungsten, vanadium, titanium, tantalum, zirconium, niobium, bismuth, lanthanum, tellurium, phosphorus, boron, beryllium, sodium, lithium , Calcium, strontium, lead and copper, their compounds and their mixtures. If any small amount of a valve metal compound is used, it should be © in a metal other than that of the electrode base body to contribute to the doping of the oxide skin. Excellent results are obtained with iridium / ruthenium compounds in a weight ratio of iridium: ruthenium of about 2: 1. If the solution contains such additives, they must of course be present in compatible amounts with the small amount of the main electrocatalytically active component, iridium and / or or rhodium, so that substantially all of the electrocatalytically active metal and the additives can be incorporated into the oxide skin. In any case, the total amount of iridium and / or rhodium and the other metals should be <1 g / m, preferably <0.5 g / m _f and the additional metal should be present in lesser amount than rhodium and / or iridium. The iridium and / or rhodium compounds and the compounds of the other metal are expected to decompose in the heat to the metals or their oxides, but in no case complete decomposition is required. For example, an intermediate layer of partially undecomposed iridium chloride has excellent properties up to about 5% by weight of the original chlorine content. Intermediate layers with only 0.1 to 0.3 g / m (calculated as metal) Iridium and / or rhodium oxide and / or chloride give excellent results. Experiments showed that an intermediate layer containing 0.5

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to 0.6 g / m (as metal) iridium gives optimum effect in terms of extending the working capacity of the electrodes according to the invention. An increase in the iridium content above these levels generally does not result in any further extension of working capacity.

If an electrode base body made of titanium is used, titanium dioxide is mainly present in the oxide skin in the rutile modification. Possibly, the formation of the rutile, for example, at about 400 to 500 ⁰ G is catalyzed by the applied with the dilute solution of rhodium and / or iridium.

The intermediate layer thus applied is impermeable to electrolyte and developed oxygen. The porous, outer electrocatalytically active layer is then applied in a conventional manner, for example to the intermediate layer in a plurality of sub-layers by means of a relatively concentrated solution containing a heat-decomposable compound of a platinum metal _{ and heat. Each outer layer can be at least 0.4 g / m platinum metal, based on the projected area of the base body _; contain. The coating is repeated until an application of at least about 2 gm of platinum metal oxide (s) is deposited. The selection of the compounds for the electrocatalytic layer is performed with regard to forming a coating, which mainly consists of a solid solution of at least one valve metal and at least one platinum group (U.S. Patent No. 3,632,498). Preferably, the layer is a solid solution of the oxides of ruthenium and titanium in an atomic ratio of 1: 1 to 1 s 4. In this

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In this case, the electrocatalytic layer consists of several sublayers with an appearance which reveals microcracks and is quite porous. This electrocatalytic layer in conjunction with the intermediate layer according to the invention leads to a significant increase in the performance of the electrode in the standardized rapid test with evolution of oxygen. Under conditions of conventional large scale industrial electrolysis to recover chlorine, the electrode of the present invention will then exhibit a much longer life because it is known that one cause of failure of these electrodes after prolonged use in chloralkali electrolysis as the anode is the oxygen attack on the electrode body , On the other hand, it is also possible to achieve the same life with a much lower layer thickness of the electrocatalytic coating, which saves Beschikntungsmaterial and labor and energy for the production of the layer must be used to a lesser extent.

The thus formed electrocatalytically active layer of one or more platinum metal (s), such as a platinum / iridium alloy _/ is suitable for chlorate production and to a limited extent in diaphragm or the membrane cells for the chlorine extraction in conventional bit platinum and iridium coated electrodes the layers are relatively thick, ie at least about 5 g / m, to avoid the problems associated with passivation Electrodes according to the invention having the improved interlayer allow thinner and more porous electrocatalytically active layers based on platinum metals without oxidation

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the body comes to problems, or that disadvantages occur that were previously expected with a passivation of the barrier layer of titanium oxide.

It is also possible to prepare the electrocatalytically active layer by plasma spraying a solid solution of the valve metal oxide and the platinum metal oxide. For example, according to US Pat. No. 3,677,975, a powder of solid solution can be prepared by flame spraying, whereupon this powder is then applied to the electrode base body by plasma spraying. However, it is also possible, by plasma spraying, to apply at least one valve metal oxide to the preformed intermediate layer and then to introduce the platinum metal (s) and / or their oxides into this coating obtained by plasma spraying as valve iron oxide (US Pat. No. 4,140,813). Even in these cases, the improved interlayer according to the invention improves the lifetime of the electrode and enables a reduction in the noble metal content of the electrocatalytic layer.

In a preferred method of mass producing electrodes, a series of electrode bases are subjected to a series of pretreatments including etching and build-up of the intermediate layer by immersing the bases in the appropriate dilute solution and heating the bases, whereupon the electrocatalytically active coatings are applied to the various electrodes can be applied. This avoids the disadvantages in the production of electrodes in large-scale industry, which result from a "bottleneck"

between the etching bath and the coating line. In conventional mass production, a series of bases is pretreated by sandblasting, then etching, rinsing and drying, whereupon these bases are then further processed individually in a production line for coating and firing. However, it was necessary to synchronize the etching with the coating and firing because the etched body can not be left in the air for a long time (more than about 2 days) without adverse influence on the performance of the electrode due to oxidation of the body before coating , This is especially true when dust or dirt settle in the thin oxide skin. The precoating of a series of basic bodies immediately after the etching with an improved intermediate layer according to the invention avoids this bottleneck in the production process and the base bodies treated in this way can be stored without the risk of further oxidation. Any dust or dirt settling on the intermediate layer can easily be blown off before being coated with the electrocatalytically active compound, since it does not adhere to the oxide layer or is anchored therein.

In addition, the dip coating is suitable for a number of basic bodies according to the invention, which is not the case for conventional coating methods in which each different sub-layers of certain thickness must be applied, yes, these sub-layers of oxide are extremely thin.

The electrode base body may consist of any valve metal, with titanium being preferred for reasons of cost. The electrode base body can be constructed in the form of a rod, a pipe, a triangular metal or the like of titanium or another valve metal. It is also possible to cover an electrically conductive core with titanium or another valve metal. For most applications, the base is first etched to roughen the surface and provide anchoring for the layers to be applied. However, it is also possible to treat porous, sintered or plasma-sprayed titanium in the same way with the dilute solutions, but it is preferred that the electrode base body is not porous and that the surface of the titanium is only superficially roughened.

The electrodes according to the invention are particularly suitable as anodes for the chloralkali electrolysis; ^They also exhibit superior properties in the electrowinning when chloride and sulfate is carried out with an electrolyte containing, and there is a chlorine and oxygen evolution.

embodiments

The invention will be further illustrated by the following examples.

example 1

A titanium sheet 75 x 20 mm was degreased, rinsed with water, dried and etched for 0.5 h with oxalic acid. A solution was prepared from 6 c-n-propanol, 0.4 cc of concentrated hydrochloric acid

and 0.1 g iridium and / or rhodium chloride and brushing this solution on both sides of the sheet, in four thin layers. The sheets were heated to evaporate the solvent and finally held in air at 500 ^° C. for 10 minutes for the first three coats and 30 minutes after the last coat. In this way, an intermediate layer containing about 0.2 to 0.3 g / m of iridium and / or rhodium (calculated as metal) was obtained, depending on the amount of solution applied to each intermediate layer, which resulted from the increase in weight.

Now a solution containing 6 cnr n-propanol, 0.4 cnr concentrated hydrochloric acid, 3 cnr butyl titanate and 1 g RuCl ^) was determined using a solid solution of oxides of titanium and ruthenium by heating in air at 400 ⁰ C for 5 In this layer, the atomic ratio of titanium: ruthenium was about 2: 1 (note that this solution was about 10 times more concentrated on noble metal in the solvent than the dilute solution used to make the intermediate layer); This coating was repeated until the catalytically active layer had a thickness of about

ρ ρ

10 g / m, i. about 4 g / m ruthenium.

The electrodes produced in this way and similar electrodes (a) with an intermediate layer of TiO.sub.p produced in the same way, however, with a solution which contained only 6% n-propanol and 0.4 c / l of concentrated hydrochloric acid or with electrodes (b) without Interlayer were subjected to comparative electrochemical tests. It was found that the electrode according to the invention

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a much longer lifetime in the quick test

naxte. As an anode, at which oxygen evolved / In the chloralkali electrolysis, the life should

of which multiples are / the / comparison anode (a) and much longer than the / comparative anode (b).

Example 2

According to Example 1, a titanium sheet was degreased, rinsed with water, dried, etched and treated with a solution containing iridium and ruthenium chlorides in a weight ratio of 2: 1, 4 times, so that the titania skin was about 0.2 g / m iridium and 0.1 g / m ruthenium, each calculated on metal. After each layer application was baked at 40O ⁰ C for 10 min and applied to the resulting intermediate layer, the electrocatalytically active layer of TH ^ and RuOp according to Example 1 and carried out the same comparative experiments. The results obtained with these electrodes corresponded to those according to Example 1.

Example 3

According to Example 1 titanium sheets were degreased, rinsed with water, dried and etched and then treated with an iridium chloride solution similar to that of Example 1. The solution was applied 4 times and solvent evaporated each time and fired at 480 ^° C. for 7 minutes. The iridium concentration in the intermediate layer was varied between Q3, 0.6 and 0.8 g / m iridium.

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According to Example 1, a catalytically active layer of titanium dioxide and ruthenium dioxide was applied, but in this case in a layer thickness corresponding to 20 g / m or 8 g / m ruthenium. These electrodes were subjected to the rapid test in oxygen evolution. The maximum life resulted in the electrode with an intermediate layer containing 0.6 g / m iridium; this corresponds to an increase in the life of a similar electrode without an intermediate layer or with an intermediate layer of titanium dioxide only by a factor of 10.3. In a further comparison, a similarly coated electrode with no interlayer was investigated, but the layer contained 0.6 g of iridium dispersed therein, thus achieving only a very moderate increase in the lifetime.

Example 4

Electrodes were made as in Example 1 except that dilute solutions of chlorides of various platinum metals including palladium, platinum and ruthenium alone and rhodium and iridium were used to make the intermediate layer; these electrodes were tested for oxygen evolution life at the anode. Only electrodes with an intermediate layer containing rhodium and / or iridium showed a marked increase in the lifetime in these investigations. Combinations of rhodium and / or iridium with minor amounts of other platinum metals or their compounds, particularly ruthenium and palladium, also provided significant improvements.

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Example 5

According to Example 1, titanium sheets with Zwischenschicken

Then, a solution containing 0.5 g of iridium chloride and 1 g of platinum chloride in 10 cnr isopropyl alcohol and 10 cnr linalool / and then heated to 350 ⁰ C was heated to about 0.2 g / m of iridium and / or rhodium. A mixture of ammonia and hydrogen was then passed over about 30 seconds to yield a layer containing 70 % platinum and 30 % iridium. The whole was repeated until a layer of 4 g / m of the platinum / iridium alloy was obtained. For similarly constructed

Electrodes with <7 g / m platinum / iridium alloy but without intermediate layer according to the invention could be observed that passivation occurred at higher current density and at least 7 g / m must be applied in order to allow a satisfactory operation over long periods. This problem is apparently overcome with the intermediate layer according to the invention, since the electrode according to the invention requires only an electrocatalytic layer of 4 g / m for satisfactory operation.

Example 6 ·.

According to Example 1 titanium sheets were provided with intermediate layers of about 0.2 g / m iridium and / or rhodium. Then, in a conventional manner a layer of about 400 g / m ¹ "titanium oxide was applied by plasma spraying. The plasma-sprayed titanium oxide layer was overlaid with 2 g / m (as metal basis) of ruthenium oxide and / or iridium oxide in various amounts by applying a solution of 6 car propanol and 1 g RuCl, and / or IrCl ₇ , and firing

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each order in air for 10 min at 500 ⁰ C. An electrochemical preliminary test showed that these electrodes have extremely long lifetimes as anodes in mercury-chlor-alkali electrolysis cells at high current densities. From the data given in US Pat. No. 4,140,813, it is apparent that the electrode according to the invention has the same outstanding lifetime but only 1/5 precious metal content.

Example 7

j ..

According to Example 1, titanium sheets having intermediate layers containing about 0.3 g / m of iridium, rhodium and iridium / ruthenium alloy in a weight ratio of 2: 1 were prepared, but in some cases, the final heating was carried out for several hours.

An aqueous solution of iridium chloride and tantalum chloride (iridium and equivalent weight tantalum) was brushed on both sides of the panels, with 5 × 10 and 15 coatings. Each application contained about 0.5 g / m of iridium. After each application, the sheets were dried and kept in the air at 450 ⁰ C for 10 min. During the last application this heat treatment lasted 1 h. The intermediate layer was a solid solution of the two oxides containing about 2.5, 5 and 7.5 g / m of iridium, respectively.

The electrodes were used as anodes in 10 -6% sulfuric acid at 60 ° C and a current density of 1.2 kA / m

tested, the current was interrupted after every 24 h 15 min, without the electrodes

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were taken out of the bathroom. The results show the superiority of the electrodes according to the invention compared to electrodes with titanium titanium only or a basic body of a titanium / palladium alloy with 0.15% palladium. Of course, the titanium base with the interlayer according to the invention is much cheaper than the titanium / palladium alloy and provides a substantially improved resistance to interruption of operation and to the passivating effect of the nascent oxygen. It is apparent from preliminary experiments that the electrodes according to the invention with a low iridium content (2.5 g / m + 0.3 g / m in the intermediate layer) provide superior operating times over electrodes without this intermediate layer.

Claims (18)

Invention test 1. Electrode of an electrode base body, consisting of a valve metal _t and thereon a porous electrocatalytically active layer of at least one platinum metal and / or its oxide and optionally other metal oxides, wherein the proportion of platinum metal fen) is at least about 2 g / m, and between the base body and the electrocatalytic layer is an intermediate layer, characterized in that the intermediate layer is an oxide skin of the metal of the base body with embedded rhodium and / or iridium in an amount up to 1 g / m, based on the surface of the base body. \ 2. Electrode according to item 1, characterized in that the porous electrocatalytically active layer consists of several partial layers with microcracks. 3. The electrode according to item 2, characterized in that the porous electro-catalytic layer is mainly a solid solution of at least one valve metal oxide and at least one platinum metal oxide. 4. An electrode according to item 3, characterized in that the porous catalytically active layer is a solid solution of ruthenium and titanium oxide, in which the atomic ratio of ruthenium: titanium is 1: 1 to 1: 4. 5. The electrode according to item 1, characterized in that the porous catalytically active layer consists essentially of one or more PlatinmetalYen). 6. Electrode according to item 5, characterized g e -v indicates that the porous electrocatalytically active layer is a platinum / iridium alloy. 7. Electrode according to item 1, characterized in that the porous electrocatalytically active layer is a plasma-sprayed layer of at least one valve metal containing one or more platinum metals and / or their oxides. 8. The electrode according to item 1 to 7, characterized in that the intermediate layer contains at least one further metal in addition to rhodium and / or iridium and this is present in lesser amount than rhodium and / or iridium, wherein the total metal content of the intermediate layer to 1 g / m is. 9. The electrode of item '8, characterized in that the intermediate layer to 0.5 g / m of iridium and ruthenium in a weight ratio of about 2: 1. 10. An electrode according to item 1 to 9, characterized in that the electrode base body made of titanium and the intermediate layer mainly consists of rutile. 11. A method for producing an electrode according to claim 1 to 10 by forming the intermediate layer on the electrode body and on this the porous electrocatalytically active layer containing at least one platinum metal and / or its oxide and optionally further oxides in an amount of at least about 2 g / m platinum metals characterized in that: to form the intermediate layer, the electrode base body is coated one or more times with a very dilute acidic solution containing a decomposable in the heat compound of rhodium and / or iridium, drying this order and the formation of the Ventilmetalloxid -Heaten with simultaneous at least partial decomposition of the compounds, with each application of the very dilute solution so much of the compound is applied that the rhodium and / or iridium is completely absorbed in the heat treatment in the Ventilmetalloxid) and such a number of Fulfilled orders lgt that the intermediate layer bis'1 g / m rhodium and / or Iridium, based on the area of the Elektrodengrundkörpersj contains. 3.1 - κ- 224 37i 12, method according to point ti, characterized ge ke nnzeichnet that with one or each application of the solution, a layer with up to 0.2 "g / m rhodium and / or iridium is obtained. Process according to item 11 or 12, characterized in that the dilute solution is applied 2 to 5 times and after each application heated to 300 to 600 ° C for about 5 to 15 minutes and for a long time after the last application. 14. ^ Process according to item 11 to 13 * characterized in that heated only until incomplete decomposition of the compounds. 15. The method according to item 11 to 14, characterized marked ze ichnet that one prepares the electrocatalytic layer in several sub-layers by means of a relatively concentrated solution containing a decomposable in the heat platinum metal compound _v and heating. 16. The method according to item 15, characterized in that the electrocatalytic layer contains at least 0.4 g / m platinum metal, based on electrode base body. 17. "Process according to item 11 to 14, characterized in that applying the electrocatalytic layer by plasma spraying. 18. The method according to item 11 to 14, characterized in that applying the electrocatalytic layer by plasma spraying of at least one valve metal on the preformed AH - 224 371 Intermediate layer and then the platinum metals and / or their oxides in the plasma sprayed valve · metal oxide brings. 19. The method according to item 11 to 18, characterized in that subjecting a number of Elektrodengrundkorpem together a series of pretreatments including the etching and the formation of the intermediate layer by immersion in the dilute solution and heating, whereupon the electrocatalytic layer is applied äääe . 20. Using the electrodes by point 1 to 10 or the electrodes produced according to claims 11 to 19 as an anode in the chloralkali electrolysis.