DE2844495A1 - ELECTROLYTE CATALYST MADE OF THERMALLY STABILIZED, PARTIALLY REDUCED PLATINUM METAL OXIDE AND THE PROCESS FOR THE PRODUCTION OF IT - Google Patents

Description

The invention relates to an electrocatalyst, a catalytic electrode, a membrane assembly and Electrode and a method for producing the electrocatalyst. More particularly, the invention relates on catalysts and electrodes, which are particularly useful for the electrolysis of halides.

Gas extraction by electrolysis of a chemical compound into its elements, one of which may be a gas, is of course an old and well-known technique. A recently developed form of such a gas evolving Electrolyzer involves the use of a cell that contains an electrolyte in the form of a solid ion exchanging polymer membrane used. In an arrangement of this type, catalytic electrodes are provided with a suitable one Catalyst on opposite sides of the ion transport membrane, such as a sulfonated one Perfluorocarbon ion exchange membrane arranged. Through an oxidation reaction, the ionic form becomes one of the elements forming the compound on an electrode

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is generated, exemplified by hydrogen ions when H ₃ O or HCl is electrolyzed and sodium ions are another example when a sodium halide such as sodium chloride is electrolyzed. The ion is transported through the ion-exchanging membrane to the other electrode, where it is reduced to form an electrolysis product such as molecular hydrogen or NaOH. Solid ion exchange polymer membrane electrolyzers are particularly advantageous because they are efficient, small in size, and do not use corrosive liquid electrolytes.

Various metals and alloys have been used as part of the catalytic electrodes in the past electro-chemical electrolytic cells have been used. The efficiency of the catalyst on the gas-evolving Electrodes are obviously fundamental in determining effectiveness and performance the cell and thus the economic viability of the process. The selection of a catalyst for an electrochemical cell and its effectiveness depends on a complex set on variables such as the surface of the catalyst, the accessibility of the oxides thereof on the catalyst surface,

the impurities in the reactants and the type / in the cell conversion taking place. As a result, it is and always has been difficult to assess the applicability of a catalyst that in an electrochemical cell was useful to predict for another system.

In US Pat. No. 3,992,271 there is an improved oxygen evolving agent described catalytic electrode in which a platinum / iridium alloy is used, which is a very improved Efficiency and effectiveness results. Another catalytic electrode is shown in U.S. Patent 4,039,490 described for the development of hydrogen, are used in the reduced oxides of platinum / ruthenium. Of the

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Platinum / ruthenium catalyst is not only "considerably cheaper" than the reduced platinum / iridium catalyst, because it uses a cheaper material such as ruthenium to alloy with the platinum, but it is also more effective, because it has a lower oxygen overvoltage than one Platiii / iridium electrode.

V. Search, reduced ruthenium oxide electrocatalysts for the development of halogens by electrolysis of aqueous

ClnzusetizGn
Halide solutions ^ were not entirely successful, however, since harsh electrolysis conditions prevail in such cells. There can be a considerable loss of catalyst from the membrane during the evolution of chlorine, since these reduced platinum metal oxides are amenable to dissolution in an acidic environment, as can be found in the electrolysis of hydrogen halides or in the electrolysis of alkali metal halide solutions, which often become acidic . And not only is there this tendency for the platinum metals to dissolve, resulting in a loss of catalytic material, but the overvoltage of the electrodes also increases, so that the efficiency of the cell decreases and in many cases does not permit prolonged operating times.

The advantages of the invention emerge from the following Description.

According to the present invention comprises a novel electrocatalyst at least one reduced platinum group metal oxide, which subsequently in the presence of oxygen to a sufficiently high temperature is heated to thermally stabilize the oxide and the resistance of the catalyst to increase compared to the corrosive electrolysis conditions. The platinum group metal catalytic reduced oxide can optionally other reduced platinum group metal oxides, such as iridium, and optionally up to 50% by weight of electrical

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trically conductive extenders such as graphite, valve metal oxides, Titanium metal oxides and nitrides, carbides and sulfides. Examples of useful platinum group metals are platinum, Palladium, ^ .ridium, rhodium, ruthenium and osmium, where the preferred reduced metal oxide for the production of chlorine and other halogens the thermally stabilized ones, reduced ruthenium oxides are. The reduced ruthenium oxides are preferred because they are extremely low Have chlorine surges and they are stable in the electrolytic environment.

The electrocatalytic material can be a single reduced platinum group metal oxide such as ruthenium or other Platinum oxide or iridium oxide. However, it was found that mixtures or alloys of thermally stabilized, reduced platinum group metal oxides are even more stable. Such a mixture or alloy of ruthenium oxide contains up to 25% by weight of iridium oxide, the preferred range being from 5 to 25% by weight, calculated on a metal basis, is enough, although iridium is a little more expensive than ruthenium alone.

Electrically conductive extenders, such as graphite, have low overvoltages for halogens and are substantial cheaper than platinum metal oxides, and they can be easily incorporated without compromising the effectiveness of the catalyst to reduce. In addition to graphite, oxides of valve metals (the term "valve metal" is in the U.S. Patent 3,948,451 and designates a subset of transition metals z. B. Ti, Ta, Zr, Mo, Nb and W includes. These valve metals direct the current in the anodic direction and resist the passage of current in the cathodic direction. You are opposite the electrolyte and the conditions in an electrolyte cell, e.g. B. for the production of chlorine and NaOH, sufficiently resistant,

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to be used as electrode material.), how Titanium, tantalum, niobium, tungsten, vanadium, zirconium and hafnium can be added to further the electrocatalyst : j stabilize and sr ine resistance to impairing To increase electrolysis conditions.

The thermally stabilized, reduced platinum metal oxides and the extenders are made by combining with fluorocarbon. Resin particles such as that available from DuPont under the trade name Teflon material sold, formed into an electrode. The catalytic particles and the resin particles are mixed, the mixture is placed in a mold and the whole is heated until the mass is a suitable one Sintered shape that is bonded to at least one surface of the membrane by the application of heat and pressure, to create an electrode structure and a unitary membrane and electrode structure.

The inventive method for producing the electrocatalyst s involves preparing the oxides of at least one platinum group metal along with one or more Extenders, such as graphite or valve metals, reducing the oxides to a partially oxidized state and that subsequent heating of the product obtained in the presence of oxygen to a temperature which is sufficient is high to stabilize the reduced oxides.

The electrocatalyst according to the invention, which contains the thermally stabilized, reduced oxides of a platinum group metal together or in combination with other platinum group metals or optionally includes valve metals, can be made in any suitable manner which permanently, partially reduces an oxide catalyst and is thermally stabilized.

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A preferred mode of reduction is by a modification of the Adams process of platinum production by the addition of a thermally decomposable platinum halide, such as ruthenium chloride, either alone - which, if desired, together with an appropriate amount of other thermally decomposable ones Halides of platinum metals or valve metals to an excess of sodium nitrate. The Adams process of platinum production is described in an article in the Journal of the American Chemical Society, Volume 45, page 217 (1923). To mix it is ζ appropriate, the finely divided halide salts of platinum metals, such as chloroplatinic acid, in the case of platinum, the ruthenium chloride in the case of ruthenium, titanium chloride, tantalum chloride in the case of titanium and tantalum, in the same weight ratio of the metals as shown in the final alloy mixture is desirable. An excess of sodium nitrate is incorporated and the mixture was melted in an Siliziumdioxidschale for 3 hours at a temperature of 500 to 600 ⁰ C. The residue is washed thoroughly to remove the nitrates and halides still present, after which a residue of the desired platinum metal oxide remains, e.g. B. ruthenium oxide, platinum-ruthenium oxide, ruthenium-iridium oxide, ruthenium-titanium oxide, etc. The resulting suspension of mixed and alloyed oxides is then partially reduced. The reduction of the platinum group metal oxides can be carried out by any suitable known reduction method such as electrochemical reduction or by bubbling hydrogen through the mixture at room temperature so long as it is not desired to completely reduce the oxides to the metal. In a preferred embodiment, the oxides are electrochemically reduced in an acidic medium. The product, which is a reduced platinum metal oxide either alone or a mixed alloy oxide, is thoroughly dried, e.g. B. by using a heating lamp, and then ground

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cui.'h e _ .. n nylon screen with a mesh size of about 0.037 now (equivalent to 400 mesh) sieved to a fine PuIv "L * from the reduced platinum metal oxide.

The resulting reduced platinum metal oxides are then thermally stabilized by heating in the presence of oxygen for a time sufficient to obtain a catalytic material that is stable in the acidic hydrogen halide environment and in the presence of the halogens. With a thermal stabilization of the catalyst carried out in the manner described below, very much better corrosion properties are obtained in halogens such as chlorine, etc. and in the presence of halide solutions such as hydrochloric acid, etc. It is assumed that the thermal stabilization leads to the formation of a catalytic particle with a large mean pore diameter and a stable thin oxide film on the outside of the reduced oxide particle. This stabilizes the reduced oxide particles so that they have better mechanical properties for bonding to the solid polymer electrolyte membrane, and their resistance to dissolution in hydrochloric or other halide acids or to evolved halogens is also increased. The reduced oxides are preferably heated for a period of 30 minutes to 6 hours at a temperature of 350 to 75O ° C, with the preferred thermal stabilization by heating the reduced oxides for one hour to a temperature of 550-600 ⁰ C.

It was also found that the electrocatalytic Activity of the catalyst and the electrode with the catalyst is optimized by the fact that the catalytic Produces particles in the finest possible powder form. So became found that the surface of the particles as observed by the BET nitrogen absorption method,

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2
should be at least 25 m / g catalyst. The preferred one

2 The area of the surface is between 50 and 150 m / g.

The gas-permeable electrode structure of the catalytic particles and the fluorocarbon polymer particles is created by blending the catalytic particles with a Teflon dispersion, as described in U.S. Patent 3,297,484 Way to make a bonded electrode structure. In the process of connecting the electrode is it is advisable to mix the catalyst with Teflon dispersion in such a way that the dispersion is little or does not contain hydrocarbons. When the fluorocarbon polymer composition contains surface-active hydrocarbons, then this leads to a reducing Surface area of the reduced oxide catalyst. Any reduction in the surface area of the catalyst is evident undesirable as this has a potentially detrimental effect on the performance and effectiveness of the catalyst Has. The electrode should therefore be fabricated using a polytetrafluoroethylene particle composition which contains little, if any, hydrocarbons. A suitable shape of these particles for making the electrode is available from DuPont under the trade name Teflon T-30.

The mixture of the noble metal particles and Teflon particles or of graphite and the reduced oxide particles is in placed in a mold and heated until the mass is formed into a decal, which is then applied by applying pressure and heat is embedded in and associated with the surface. For example, as described in U.S. Patent 3,297,484, the electrode structure is connected to the surface of the ion exchange membrane, thereby reducing the gas-absorbing Particle mixture integrally connected and in some cases preferably incorporated into the surface of the membrane

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is bedded.

The new membrane / electrode structure produced in this way comprises a solid polymer electrolyte membrane which leads to a selective Ion transfer location capable of being with at least one Side of the membrane a thin porous gas-permeable electrode from the above-described electrocatalytic reduced Platinum group metal oxides is connected. A second electrode can be connected to the other side of the membrane and this electrode can be either the same electrocatalytic material or some other have suitable cathodic material. The selective, ion-transporting membrane is preferably a stable, hydrogenated, cationic membrane, which is characterized by ion transport selectivity. So allow Cation exchange membrane allows the passage of positively charged cations, such as hydrogen ions in the case of electrolysis of a halide such as hydrogen chloride or of sodium ions in the case of the electrolysis of aqueous sodium halides. The passage of negatively charged anions through a cation exchange membrane is kept to a minimum.

There are several types of ion exchange resins that can be made into membranes that allow the selective transport of the cations. Two classes of such resins are the so-called sulfonic acid cation exchange resins and the carboxyl cation exchange resins. Sulfonic acid exchange resins, which are preferred, include ion-exchanging groups in the form of hydrated sulfonic acid residues (SO ₃ H H "0) which are linked to the polymer chain by sulfonation. The ion-exchanging acid residues in the membrane are firmly connected to the polymer chain, which ensures that the electrolyte concentration does not change. The perfluorocarbon sulfonic acid cation exchange membranes are preferred.

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A specific class of cation exchange polymer membranes of this type is sold by DuPont under the trade name Naf: \ on. These are Nafion membranes hydrogenated copolymers of polytetrafluoroethylene and polyulfonyl fluoride vinyl ether, which contain pendant sulfonic acid groups.

The ion exchange capacity of a given sulfonic acid cation exchange membrane depends on the milliequivalent weight of SO ^ residues per gram of dry polymer. Ever The greater the concentration of sulfonic acid residues, the greater the ion exchange capacity and thus the Ability of the i-membrane to transport cations. As the ion exchange capacity of the membrane increases, however, the water content also increases and with it the ability of the membrane to repel salt. In electrolysis of alkali metal halide solutions, alkali is generated on the cathode side and the rate at which the Sodium hydroxide migrates from the cathode to the anode side, increases with the ion exchange capacity. Such Back migration reduces the effectiveness of the cathode current and also leads to the generation of oxygen at the anode, what undesirable consequences in its effect on the catalytic Has anode. The preferred ion exchange membrane for use in brine electrolysis is hence a laminate consisting of a thin film (about 0.05 mm thick) with a milliequivalent weight of 1500 and a low water content (from about 5 to 15%) with high salt repellency, combined with a film with a thickness of about 0.1 mm with high ion exchange capacity, a milliequivalent weight of 1100 combined with a Teflon fabric. One form of such a layered construction is sold by DuPont under the trade name Nafion 315. Other forms of laminates or constructions in which the cathode side layer is made of

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one thinner. Resin film layer with low water content (approx 5 to 15 5) to optimize salt repellency, are also available. Typical of such other laminates are those under the trade names Nafion 355, 376, 390, 227 and 214 available. In the case of a Schic. ', T fabric membrane, which is connected with a Teflon fabric it may be desirable to use the membrane and Teflon fabric in addition to soaking in alkali, as previously it was preferred to reflux for 3 to 4 hours in 70% nitric acid for cleaning.

In the case of the electrolysis of hydrogen halides, such as Hydrochloric acid, there is the problem of back migration of alkali or other salts, so that simpler membrane forms, such as Nafion 120, are used as ion-transporting Medium can be used.

In the case of brine electrolysis, the cation side barrier, which must be characterized by a low water content, including laminates, in which the cathode sext layer is a thin (0.05 to 0.1 mm thick) chemically modified film with sulfonamide groups or carboxylic acid groups.

In folgeiu λ reference is made to the drawing in which

Figure 1 is a schematic representation of an inventive Electrolytic cell using a solid polymer electrolyte membrane and the one with the Surface of the membrane connected new catalyst there and

Figure 2 is a schematic representation of the reactions that take place in different parts of the cell during the electrolysis of an aqueous halide solution take place.

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In Fig. 1 ie.- denoted by 10 a halogen electrolysis cell, which consists of a cathode compartment 11 and an anode compartment 12, which is formed by a solid polymer electrolyte membrane 13 are separated from one another, the membrane preferably being a hydrated, permeability-selective Cation exchange membrane is. Electrodes are connected to the opposite surfaces of the membrane 13, which Particles of a fluorocarbon, such as Teflon, include, those with thermally stabilized, reduced oxides of ruthenium (RuO) or iridium (IrO) or stabilized, reduced oxides of ruthenium-iridium (RuIr), ruthenium-titanium (RuTi), ruthenium-tantalum (RuTa), ruthenium-tantalum-iridium (RuTaIr) or ruthenium graphite or combinations of the aforementioned oxides with graphite and other valve metal oxides are connected. The cathode 14 is connected to one side of the membrane, and preferably in this embedded, and a catalytic, not shown The anode is connected to the opposite side of the membrane and is preferably embedded in it. Power collectors in the form of metal screens 15 and 16 are pressed against the electrodes. The whole unit of membrane and electrode is firmly mediated by the housing elements 11 and 12 of the seals 17 and 18, which seals are made of any material that to the cell environment, namely alkali, chlorine, oxygen, aqueous sodium chloride in the case of electrolysis of brine and HCl, HBr in the case of other hydrogen halides, is stable or inert. One form of one Gasket is a filled rubber gasket made by the Irving Moore Company, Cambridge, Mass. under under the trade name EPDM.

An aqueous alkali metal halide such as brine or a hydrogen halide such as HCl is supplied through an electrolyte inlet 19 introduced, which communicates with the chamber 20

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stands. Spent electrolyte and halogens such as chlorine are removed through an outlet line 21. A cathode inlet line 24 is provided for the case of brine electrolysis and is in connection with the cathode chamber 11 to the introduction of cathode chamber electrolyte, hereinafter abbreviated to "catholyte", water or aqueous NaOH, which is more dilute than the electrochemical at the Interface electrode / electrolyte formed to allow. In the case of the electrolysis of hydrogen halides, such as HCl, no catholyte is required and the cathode inlet conduit 24 can therefore be omitted.

In a brine electrolytic cell, the water serves two purposes separate functions. Some of the water is electrolyzed to generate hydroxyl anions and these Hydroxyl anions combine with those through the membrane transported sodium cations with the formation of alkalis (NaOH). The water also rinses over the porous bound Cathode electrode, around the membrane / electrode interface to dilute the highly concentrated lye that has formed and so cause the lye to diffuse back through the membrane in the anode electrolyte (hereinafter referred to as "anolyte") chamber as low as possible. the Cathode outlet line 22 communicates with cathode chamber 11 for removal of excess catholyte and the electrolysis products, such as caustic, in the case of brine electrolysis plus any hydrogen release the cathode in both the electrolysis of brine and hydrogen chloride. A power cable 23 is placed in the cathode compartment and a comparable cable, not shown, is placed in the anode compartment brought in. These cables connect the conductive screens 16 or 15 or any other suitable type of collector with the power source.

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Figure 2 diagrammatically illustrates those in the cell during the electrolysis of an aqueous alkali metal halide solution, reactions that take place like brine, and serves to understand the electrolysis process in such a way that in which the cell works. An aqueous solution of sodium r chloride is introduced into the anode chamber, which is passed through the cationic membrane 13 is separated from the cathode chamber. The membrane 13 is a composite membrane with a layer 26 high water content (2O to 35%, based on the dry weight of the membrane) on the anode side and one layer

27 low water content (5 to 15%, based on the Dry weight of the membrane) and high milliequivalent weight on the cathode side, both through a Teflon fabric

28 are separated from each other.

The cathode-side layer can also be on the cathode side chemically modified to form a thin layer of polymer with a low water content. In a Embodiment, this is done by modifying the polymer to form a substituted sulfonamide membrane layer. By converting the cathode side layer into a weak acid form (sulfonamide), the water content becomes this Part of the membrane is reduced and the ability of the film to repel salt is increased. As a result, the back diffusion becomes of sodium hydroxide through the membrane to the anode is kept to a minimum. While with brine electrolysis Layered membrane constructions are preferred in order to block the back migration of the sodium hydroxide other homogeneous films with a low water content can also be used, such as Nafion 150, perfluorocarboxylates, etc. Im In the case of the electrolysis of hydrogen halides such as HCl, HBr, etc., the ion-transporting membrane can obviously i.e. be a simple homogeneous film, like Nafion 120.

The TefJon-bound catalysts made from reduced noble

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metal oxides contain at least one thermally stabilized, reduced platinum metal oxide, such as one of ruthenium, Iridium or ruthenium-iridium with or without the addition of reduced oxides of titanium, niobium or tantalum and particles of Graphite. These catalysts are pressed into the surface of the membrane 13. The current collectors 15 and 16, the only partially shown in Fig. 2 for the sake of clarity are pressed against the surface of the catalytic electrodes and connected to the positive or negative terminal of the energy source, to the electrolysis potential between to create the cell electrodes. The aqueous halide ion solution, such as aqueous sodium chloride solution introduced into the anode chamber is applied to the anode 29 is electrolyzed to produce chlorine as illustrated by vesicles 30 in FIG. The chlorine will arise principally at the interface between the electrode and the membrane, but it gets through the porous electrode to the Electrode surface facing the electrolyte. The sodium ions Na become the cathode through the membrane 13 promoted. A stream of water or aqueous NaOH, designated by 31, is introduced into the cathode chamber and acts as a catholyte. This watery stream washes the surface of the Teflon-bonded catalytic cathode 14 to that formed at the membrane-to-cathode interface To dilute lye and thereby reduce the back diffusion of the lye through the membrane to the anode.

Part of the water catholyte is formed at the cathode with the formation of hydroxyl ions and gaseous hydrogen The hydroxyl ions combine with the sodium ions transported through the membrane to form of sodium hydroxide at the membrane-electrode interface. The sodium hydroxide wets the Teflon part of the bound electrode and migrates to the surface, where it is flushed over the surface of the electrode

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aqueous stream is diluted. Even when the cathode is flushed with water, it becomes concentrated at the cathode Sodium hydroxide is formed in the range of 4.5 to 6.5 molar. Some of the sodium hydroxide indicated by arrow 33, however, migrates through membrane 13 to it Anode back. This NaOH migration is a diffusion process, through the concentration gradient and the electro-chemical transport of negative ions to the anode caused. The sodium hydroxide transported to the anode is generated with the production of water and oxygen, as shown by blistering 34, oxidized. This is a parasitic reaction that reduces the effectiveness of the cathodic current should be reduced and kept as low as possible by using membranes on the cathode side have a strong salt repellency. In addition to the effect on electricity efficiency, there is also oxygen generation undesirable at the anode as this can have adverse effects on the electrode and the membrane, in particular if the electrode contains graphite. In addition, the oxygen dilutes the chlorine generated at the anode, so that a additional treatment is required to remove the oxygen. The formation of oxygen can continue as a result be reduced by acidifying the aqueous anolyte, so that the back-migrating hydroxide is more likely by neutralization is converted into water rather than being oxidized with formation of oxygen. The reactions in the various Parts of the cell in the electrolysis of NaCl are the following:

Anode reaction:
(Principle) 2 Cl- ^ Cl ₂ TH (D iiembran Transport: 2Na ⁺ "τ * rirtCJ (2) Cathode reaction: 2H ₂ O- -S »20H ~ H (3) 2Na ⁺ + 20H ~ - (4) h 2e ( E ₂ T -2e ~ -> 2NaOH

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Anode reaction: 4OH - »O ₃ + 2H ₃ O + 4e. (5)

Overall reaction: 2NaCl + 2H ₃ O- ^ 2NaOH + Cl ₃ T + H ₃ T (6) (principle)

In the electrolysis of hydrogen halide, such as HCl, the electrolysis reactions are very similar:

. Anode reaction: 2HC1- »2H ⁺ + Cl ₃ ? + 2e ~ (1)

Membrane transport: 2H ⁺ (H ₃ O, HCl) (2)

Cathode reaction: 2H ⁺ + 2e ~ - »H ₃ ^ (3)

Overall reaction: 2HC1- * H ₃ ^ + Cl ₃ ^ (4)

The new arrangement for the electrolysis of aqueous solutions of salt or HCl, which is described in the present application, is characterized by the fact that the catalytic sites of the electrodes are in direct contact with the cation exchange membrane and the ion-exchanging acid residues associated with the polymer chain are connected, are located, these acid-exchanging radicals sulfonic acid radicals SO ₃ H H ₃ O or CarboxyJsäurereste COOH χ H ₃ O are. There is therefore no noticeable voltage drop in either the anolyte or catholyte chambers. Such an electrolyte voltage drop is characteristic of the existing systems and processes in which the electrode and membrane are separated from one another, and there it can be of the order of magnitude of 0.2 to 0.5 volts. The elimination or substantial reduction of this voltage drop is one of the main advantages of the present invention as it has a very marked effect on the overall cell voltage and the economics of the process.

Since chlorine is generated directly at the interface between the anode and the membrane, there is also no voltage drop due to it

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the so-called "bubble effect" which is a gas mixing and mass transport loss due to the disruption or Blockage of the electrolyte path between the electrode and the membrane is.

In prior art systems, the chlorine-releasing catalytic electrode is separate from the membrane. The gas is formed directly on the electrode and results in a gas layer in the space between the membrane and the electrode. This interrupts the electrolyte path between the electrode collector and the membrane and blocks the passage of Na ions and in this way increases the voltage drop.

In a preferred embodiment, the Teflon-bonded noble metal electrode contains reduced oxides of ruthenium, iridium or ruthenium-iridium in order to keep the chlorine overvoltage at the anode as low as possible. The reduced ruthenium oxides are stabilized against the development of chlorine and oxygen so that a stable anode is obtained. The stabilization is initially carried out by temperature stabilization, ie by heating the reduced ruthenium ^{oxides for one hour at temperatures in the range from 550 to 600 °} C. The Teflon-bonded reduced oxides of the ruthenium anode are further stabilized by mixing or mixing with graphite and / or alloys with the reduced oxides of iridium IrO in a range of 5 to 25% iridium, with 25% being preferred, or with reduced oxides of titanium TiO, with 25 to 50% of TiO being preferred. It has also been found that a ternary alloy of reduced oxides of titanium, ruthenium and iridium (Ru, Ir, Ti) O or

Tantalum, ruthenium and iridium (Ru, Ir, Ta) O, which are with

Ji

Teflon bonded is very effective in making a sturdy long lasting anode. In the case of the ternary

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In the alloy, the composition preferably consists of 5 to 25% by weight of reduced oxides of iridium, about 50% % By weight of reduced oxides of ruthenium and the remainder is a valve metal such as titanium. Reduced for a binary alloy Oxides of ruthenium and titanium, the preferred electrode contains an amount of 50% by weight titanium and the remainder is ruthenium. Titanium has the additional advantage that it is much cheaper than ruthenium or iridium and that thus it is an effective diluent that reduces costs while at the same time keeping the electrode in an acidic environment and against the development of HCl, chlorine and oxygen stabilized. Other valve metals such as niobium, tantalum, zirconium or hafnium can be used in the electrode structure can be used instead of titanium. In addition to the valve metals, valve metal - carbides, Nitrides and sulfides are used as catalyst extenders.

The alloys of the reduced noble metal oxides are used together with the reduced oxides of titanium or others Valve metals mixed with Teflon to form a homogeneous mixture. The Teflon content of the anode can be in the range from 15 to 50 weight percent, although 20 to 30 weight percent is preferred. The Teflon used is that from DuPont Corporation under the trade designation T-30, although other fluorocarbons are alike can be used. Typical amounts of precious metals for

2
the anode is 0.6 mg / cm of the electrode surface,

2 with the preferred range being 1 to 2 mg / cm.

The current collector for the anode can be a platinum-coated niobium net with fine mesh, with which good contact is made to the electrode surface is obtained. But it can also be a stretched titanium mesh with ruthenium oxide, iridium oxide, Valve metal oxide or mixtures thereof can be used as the collector structure for the anode. Yet

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Another possible anode collector structure can be a titanium-palladium plate with one by welding or bonding attached to it be platinum-plated mesh.

The cathode is preferably a bonded mixture of Teflon particles and platinum black with a platinum black

2
amount from 0.4 to 4 mg / cm. The cathode is similar to

the anode with the ——

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Surface of the cation exchange membrane connected and in these embedded. The cathode becomes very thin, about 0.05 to 0.075 mm or less in thickness and preferably Made with a thickness of about 0.012 mm, it is porous and has a low Teflon content.

The thickness of the cathode can be quite significant because the
Cathode in reduced water or by rinsing and
Penetration of aqueous NaOH into the cathode can be reflected, which reduces the effectiveness of the cathode current. The cells were made with thin cathodes about 0.012 to about 0.05 mm thick made of platinum black with 15% Teflon
manufactured. The current efficiencies of cells with thin cathodes were about 80% with 5 molar NaOH, at 88 to 91 ^° C. and a supply of 290 g / l to the anode. With a 0.075 mm thick ruthenium and graphite cathode, the current efficiency was reduced to 54% with 5 molar NaOH.
The following Table A shows the relationship of current efficiency to thickness and indicates that thicknesses not exceeding 0.05 to 0.075 mm have the best performance.

Table A.

Current efficiency cell cathode cathode thickness (mm) in% (with n-NaOH)

1 platinum black 0.05-0.075 4.0 (64)

2 platinum black 0.05-0.075 4.5 (73)

3 platinum black 0.025-0.05 75 (3.1)

4 platinum black 0.025 - 0.05 82 (5)

5 platinum black 0.012 5.5 (78)

6 5% platinum black 0.075 78 (3.0) on graphite

7 15% Ru 0 on 0.075 54 (5.0) graphite

8 Platinized 0.25-0.37 57 (5)
Graphite fabric

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The electrode is made gas-permeable so that the development at the interface between the electrode and the membrane Gases can easily escape. It is made porous to prevent the rinsing water from penetrating to the interface between Electrode and membrane on which the NaOH is formed, and the access of the supplied brine to the membrane and the to allow catalytic electrode sites. This supports the dilution of the highly concentrated NaOH formed, before it wets the Teflon and to the electrode surface where it is further diluted by the water flowing over the electrode surface. It is important that To dilute NaOH at the interface between membrane and electrode, since this is where the concentration is greatest. To the To maximize water penetration of the cathode, the Teflon content should not exceed 15 to 30% by weight, as Teflon is hydrophobic. With a good porosity, a limited Teflon content, a thin cross-section and a flushing liquid from water or dilute lye, the NaOH concentration is controlled to allow the migration of NaOH through to diminish the membrane.

the

The current collector for / cathode must be chosen carefully as the highly corrosive alkali at the cathode forehands attacks many materials, especially during the cell not working. The current collector can be a nickel mesh, since nickel is resistant to lye. The current collector but can also be made from a plate of corrosion-resistant steel / on which a mesh of corrosion-resistant Steel is welded. Another current collector structure for the cathode, opposite to alkaline solution Is stable or inert, is graphite or graphite in combination with a nickel mesh, which is on the plate and against the surface of the electrode is pressed.

The invention is explained in more detail below with the aid of examples

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explained.

Examples

Cells were built and tested, the ion exchange membranes and Teflon-bonded electrodes with reduced precious metal oxide embedded in the membrane were to determine the effect of the various parameters on the efficiency of the cell in brine electrolysis and in particular to illustrate the operating voltage characteristics of the cell.

i) Table I illustrates the effect of the various Combinations of reduced precious metal oxides on the cell voltage. The cells were equipped with electrodes that had various specific combinations of reduced noble metal oxides bound with Teflon particles and into a 0.15 mm thick cationic ion exchange membrane were embedded. The cell was operated with a current density of about 325 mA / cm at 90 ° C, feed rates of 200 to 2000 ml / min and a concentration of the feed operated of 5 mol.

One cell was constructed in accordance with the prior art and contained a dimensionally stabilized anode at a distance '• on the membrane and a cathode network made of corrosion-resistant Steel spaced in a similar manner. This control cell was operated under the same conditions.

From the data given in Table I it can be seen that the cell operating potentials in the method according to the invention ranged from 2.9 to 3.6 volts. Compared to a prior art cell, the control cell No. 4, a voltage improvement of 0.6 to 1.5 V was achieved under the same operating conditions. Which resulting operational efficiencies and economic

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The advantages are clear.

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anode Ir) O _x
% Ir) O cathode Tabel I. Cell
No. r / 2
6 mg / cm
fcu, 25%
6 mg / cm
(Ru, 25 4 mg / cm
Platinum black
4 mg / cm
Platinum black supplied
Brine Current density
m A / cm2 1
2 5 molar
(29Og / l)
dd 323
323

Cell

Membrane current active (5 molar

8i '

6 mg / cm (Ru, 25% Ir) O

Dimensionally stable mesh anode at a distance from the membrane

4 mg / cm (Ku. 50% Ti) O

4 mg / cm (Ru 25% Ir-25% Ta) O _x

6 mg / cm (RuO graphite)

2 6 mg / cm (Ru 0)

Corrosion-resistant steel mesh at a distance from the membrane

4 mg / cm platinum black

4 mg / cm platinum black

2 mg / cm

Platinum black

. 4 mg / cm

Platinum black

323

323

323

323

323

323 voltage (V) temp

3.2-3.3

3.3 - 3.6 2.9

4.2-4.4

3.6-3.7

3.5-3.6

3.0
3.4

NaOH)

90 85% DuPont Nafion 315 Laminate 90 78% DuPont 1500 PE Nafion 90 66% DuPont 1500 PE Nafion 90 81% DuPont ' 1500 PE μ Nafion
I. 90 85 a DuPont Nafion 315 lami nat 90 86% DuPont Na - fion 315 Laminate 90 89% DuPont Well fion 315 iS3 Laminate OO 80 83% DuPont - ^ 1500 PE ^ Nafion ^. cn

Table I continued

Cell No.

anode

Cathode supplied current density cell temp. Current 5 molar Brine mA / cm voltage (V) ° C effective - NaOH

speed

σ> ft *

6 mg / cm

(Ru - 5 Ip) O

2 mg / cm

(ir O _x )

2 mg / cm

(ir O _x )

4 mg / cm platinum black

4 mg / cm platinum black

. . 4 mg / cm

Platinum black molar
(29Og / l)

323

323

323

3.4 - 3.7 90 73%
3.1-3.5 90 80%

3.2 - 3.6 90 65%

DuPont 1500 EW Nafion DuPont Nafion laminate

DuPont Nafion laminate

A cell similar to cell no. 7 of Table I was constructed and operated at 90 ° with a supply of saturated brine operated. The cell potential (V) as a function of the current density is given in Table II below.

Table II Rope tension (V) current density (mÄ / cmj

3.2 430

2.9 323

2.7 215

2.4 108

These results show that the cell operating potential decreases as the current density decreases. The relationship of However, current density versus cell voltage determines the relationship between operating and capital costs in chlorine electrolysis. It is clear, however, that even at very high

Current densities (about 325 and 430 mA / cm) marked improvements in the cell voltage in the method according to the invention for chlorine production.

Table IH illustrates the effect of the cathodic Current effectiveness on oxygen evolution. One cell with Teflon-bonded catalytic anode and cathode with reduced noble metal oxides, embedded in a cation

exchange membrane was at 90 ° C with supply of a saturated Brine with a current density of 323 mA / cm

and a feed rate of 2 to 5 ml./min/

6.25 cm of the electrode area operated. The volume percentage the oxygen in the chlorine was determined as a function of the cathodic current efficiency.

909824/0602

^"35 ~ 284U95

Table III

Cathodic
Strora effectiveness (%) Oxygen-
Development (vol-%) 89 2.2 86 4.0 84 5.8 80 8.9

Table IV illustrates the controlling effect of the Tracing the brine to the evolution of oxygen. Of the Percentage by volume of oxygen in chlorine was determined for various HCl concentrations in the brine.

Table IV O ₂ (vol%) Acid (HCl) -
concentration (Mole) 2.5 0.05 1.5 0.075 0.9 0.10 0.5 0.15 0.4 0.25

It is clear from these data that the evolution of oxygen due to the electrochemical oxidation of the OH that has migrated back is reduced by preferential reaction of the OH with the H to form H ₂ O.

A cell similar to Cell No. 1 of Table I was constructed and operated at 323 mA / cm while being fed saturated NaCl solution which had been acidified with 0.2 η HCl. The cell voltage was at different operating temperatures measured from 35 to 90 ° C.

A cell similar to cell # 7 of Table I became

2
constructed and operated at 215 mA / cm with the supply of a solution containing 290 g NaCl / l (about 5 molar) which was not acidified. The cell voltage was measured at various operating temperatures from 35 to 90 ° C. the

2 results were converted to a current density of 323 mA / cm

calculated.

Table V

Cell # 1 Voltage (V)

3.65

3.38

3.2

3.15

3.10

3.05

3.02

Cell No. 7 Voltage (V) ~ Temperature converted to 323 mA / cm ( measured at 215 mA / cm2 _j )

3.50 (3.15)

3.30 (2.98)

3.20 (2.9)

3.12 (2.78)

3.05 (2.72)

2.97 (2.65)

2.95 (2.63)

35 45 55 65 75 85 90

These results show that the best operating voltage in the range from 80 to 90 ^° C. is obtained. It should be noted, however, that even at 35 C the voltage with the catalyst and electrolyzer according to the invention is at least 0.5 volts better than with the prior art chlorine electrolyzers which were operated at 90 C.

If the NaCl electrolysis is carried out in a cell, in of the two electrodes with the surface of an ion transporting Connected to the membrane, maximum improvement is obtained. The improved efficiency of the method is achieved for all structures in which at least one of the electrodes with the surface of the Ion-transporting membrane is connected. Such a cell is called a hybrid cell. The improvement in one

909824/0602

such a hybrid cell is slightly less than a cell, in which both electrodes are connected to the membrane. Nonetheless, the improvement is in a hybrid cell significantly, namely 0.3 to 0.5 volts better than the cells according to the prior art.

A series of cells was constructed and brine electrolysis was performed executed therein to the results of cells with two electrodes connected to the membrane with the results in hybrid cells in which either only the anode or only the cathode was connected to the membrane, and compare to a prior art cell in which none of the electrodes are connected to the membrane was.

All of these cells were produced with membranes made from Nafion 315, the cells were operated at 90 ^° C., and an addition of caustic with a concentration of about 290 g / l took place. The amount of catalyst in the bonded electrode

2 wore 2 g / 930 cm at the cathode and at the for platinum black

2 anode for RuO graphite and RuO _v 4 g / 930 cm. The current effect

X «2 X

The rate at 323 mA / cm was essentially the same for all cells (84 to 85% for 5 molar NaOH). Table VI shows the cell voltages for the different cells.

Table VI

Cell anode cathode Cell voltage (V) at 323 mA / cm2

1 Ru-graphite platinum black 2.9

(bound) (bound)

2 platinum-coated platinum black 3.5 niobium mesh (bound)

(not bound)

3 platinum-coated platinum black 3,4 niobium mesh (bound)

(not bound)

809824 / 06Ö2

Table VI continued

cell anode cathode Cell voltage (V)
at 3 23 mA / cni2 , 5 4th Ru graphite
bound) Nickel mesh
(not bound) 3 , 3 5 RuO _x
(bound) Nickel mesh
(not bound) 3 ,8th 6th Platinized
Niobium mesh Nickel mesh
(not bound) 3

(not bound)

The cell voltage of the two Teflon-bonded electrodes Equipped cell # 1 is almost 1 volt better than the prior art cell in which none of the electrodes e ^ ne Teflon-bonded electrode was and the underneath Cell # 6 is listed. The hybrid cells with bound cathode ^ r. 2 and 3 and the hybrid cells with bound Anode # 4 and # 5 are 0.4 to 0.6 volts worse than those with two electrodes bonded, but still around 0.3 to 0.5 volts better than cell # 6 without a Teflon bonded electrode.

By using catalytic electrodes that are directly connected to the cation exchange membrane and in this embedded is a vastly improved method of making chlorine and other halogens from brine and, as will be shown below, from HCl and other hydrogen halides are possible.

As a result of the above-mentioned arrangement of the catalytic electrodes, the catalytic points of the electrodes are in direct contact with the membrane and the cation-exchanging acid residues in the membrane, and this leads to a method that is considerably better in terms of the required cell potential (up to 1 volt or more)

909824/0802

28U495

than the known method. The use of the very effective fluorocarbon-bonded, thermally stabilized, reduced noble metal oxide catalysts, such as the fluorocarbon / graphite reduced ones Noble metal oxide catalysts with low overvoltages have the effectiveness of the Procedure further strengthened. Electrodes were built and tested that reduced the thermally stabilized ones Precious metal oxides and so on, embedded in ion exchange membranes, showed the effect of the various parameters on the effectiveness of the cell and the catalyst in the electrolysis of hydrochloric acid.

Table VII shows the effect of various combinations of reduced noble metal oxides on cell voltage. The cells were fitted with Teflon-bonded graphite electrodes containing various specific combinations of thermally stabilized, reduced platinum metal oxides and reduced oxides of titanium, embedded in a hydrated cationic membrane with a thickness of 0.3 mm. The cell was operated with a current density of 430 mA / cm at 30 ^° C. and a feed rate of 70 ml / min with a normality of the fed solution of 9 to 11. The active cell area was 46.5 cm ² .

Tables VIII and IX show for the same cells and, under the same conditions, the effect of operating time on cell operating voltages.

Table X shows the effect of the acid concentration of the supplied solution in the range from 7.5 to 11.5 N. It was a cell similar to cell No. 5 in Table I constructed with reduced (Ru, 25% Ir) O added to the Teflon-bonded

• ft.

NEN graphite electrode was added. The cell was operated at a fixed feed rate of 150 ml / min at 30 ^° C. and 430 mA / cm. The active cell surface was 46.5 cm ² .

909824/0602

T a b j ^ 1 1 e VII

Zeil operating anode graphite / oxide cathode graphite / oxide no. time (h) fluorocarbon amount fluorocarbon amount substance plus mg / cm ^ substance plus mg / cm

Normality current cell tension density voltage led mA / cm (V) solution

6300

5300

4900

1800

4000

200

1OO

(Ru) O _x heat stabilized

(Ru, Ti) O _x heat stabilized

(Ru, Ti) O _x heat-stabilized

(Ru Ti) O _x heat stabilized

(Ru, 25% Ir) O wärmestabili- ^x Siert

0.6 (Ru) O _x 0.6

heat stabilized

0.6 (RUjTi) O _x 0.6

heat stabilized

1.0 (Ru, Ti) O _x '1.0 heat set

1.0 (Ru) O _x 1.0

heat stabilized

1.0 (Ru _f 25% Ir) O _x 1.0

heat stabilized

(Ru, Ti, 5% Ir) O ₁ 2, O _x (Ru _{/ T} i., 5% Ir) O heat stabilized - heat stabilized

(Ru, 25% Ta) O 2.2

sated

(Ru, 25% Ta) O

2.0

2.0

9-11 9-11 9-11 9-11 9-11 9-11 9-11

43O 2.10

43O 2.01

430 1.97

43O 1.91

43O 2, O7 ⁿ (1.9)

43O 1.80

430 1.64

+) The cell voltage of this cell was about 1.9 volts after 3800 hours. Because Leak, she was removed from the test.

IO

OO

-P-

-P-

J>

CO

Table VIII

Cell
No, Cell voltage
CV) after 100 h
Operating time Cell voltage
(V) for the Be
driving time from
Table II current
density"
(mA / cm) 1 1.85 2.10 430 2 1.84 2.01 430 3 1.78 1.97 430 4th 1.80 1.91 430 5 1.75 2, O7 ⁺
(1.9) 430

1.70

1.80

430

-) See footnote to Table VII.

909824/0602

Table IX

Cell
No. Between-
operating time
(H) Current density
(mA / cm ² ) Z e 11 s voltages.
(V) 1 3900 108 1, 70 215 1, 93 323 2.00 2 3400 108 1.57 215 1, 70 323 1, 83 3 1900 108 1, 58 215 1, 70 323 1, 81 4th 1000 108 1.47 215 1, 60 323 1.72 5 1200 108 1, 32 215 1.45 323 1.55

909824/0 602

Tab rush X

normality

of the supplied

solution

7.5 8
8.5

10

10.5

11.5

° 2 O , 4 O , 15 O , 04 O , 015 O , 007 O , 004 O , 003

909824/0602

From the above examples it can be seen that HCl is electrolyzed to chlorine gas which is essentially free of oxygen. The used catalyst in the electrolysis cell is characterized by a low cell voltage and a low operating temperature (.-Twa 30 ⁰ C), which enables an economic operation of such electrolytic cells. The data also show the excellent performance at various current densities, especially at 323 to 430 mA /

2
cm. This has a positive and beneficial effect on the capital cost of the chlorine electrolyzers of the present invention.

In order to show the effect of thermal stabilization on reduced noble metal and valve metal oxides, various Tests carried out. These tests show the influence on the resistance of the catalyst to harsh electrolysis conditions. There were thermally stabilized as well as unstabilized, reduced oxide catalysts highly concentrated exposed to liCl solutions, which are extremely represent harsh conditions. The color of the solution was observed as the solution darkened indicated. Increasing loss of catalyst was accompanied by more pronounced color changes.

Table XI shows the results of this corrosion resistance and stability tests for catalyst mixtures from 0.5 to 20 g.

009824/0602

Table XI

Catalyst treatment

Temp. C corrosion medium

Ru 0

(Ru 5Ir) O.

no

Thermally stabilized for 1 hour at 55O ° C

(Ru 25Nb) O none

(Ru 50Ta) O none

Thermally stabilized for 1 hour at 550 C.

for 1 more hour at 550 C thermally
stabilized

no

Thermally stabilized for 1 hour at 550 C.

(Ru 25Ir) O none

Thermally stabilized for 1 hour at 550 C.

Thermally stabilized for 1 more hour at 24 550 C.

12n HCl
12n HCl

12n HCl

12n HCl
12n HCl

Time (h) observed color

24 744

24 912

168 96

72

Stability evaluation

light brown moderate corrosion

very pale yellow, very little corrosion, good stability

light brown moderate corrosion

amber colored

pale amber

very pale yellow))

no change in color)

moderate corrosion

completely stable

12n HCl 168 Amber
Colours considerable corrosion,
unstable 12n HCl 96 no color
modification completely stable 12n HCl 168 Amber
Colours considerable corrosion,
unstable 12n HCl 96 very pale yellow) 12n HCl 72 )
no coloring)
modification completely stable

From these data it can be seen that the thermal stabilization of the reduced oxides increases the corrosion resistance Des. Improved catalyst in very concentrated HCl and gives a very good stability. The persistence of Catalysts in a much less corrosive chlorine or brine environment is excellent and the thermal one Attributed to stabilization of the reduced oxide catalysts -

After observing the improved corrosion properties of the stabilized thermally, reduced platinum group metal oxides were carried out physical and chemical tests to determine the effect of thermal stabilization at various properties to determine the catalysts determine t for improved corrosion ^properties: one could. So the oxide content, the surface in

2
m / g of the catalyst, the pore volume, the pore size distribution of the catalyst measured after it had been prepared by the modified Adams process. Namely after the reduction of the catalyst and after the thermal stabilization of the reduced catalyst. The results of these tests, which are detailed below, show that the surface area of the catalyst is somewhat reduced after reduction and that it is considerably reduced after thermal stabilization. A decrease in the oxide content after the reduction is partially held responsible for the decrease in the surface area. A significant change in the internal pore size distribution of the catalyst after thermal stabilization or a corresponding change in pore volume appears to be responsible for the considerable decrease (ratio of 2: 1) in surface area / that accompanies thermal stabilization and this would explain the improved corrosion properties, since the corrosion is directly related to the area that the

909824/0602

284U95

Attack by the corrosive agent is exposed.

First, Sample No. 1 became a ruthenium catalyst with 25 wt.% Iridium according to the modified Adams method manufactured. A portion of this catalyst was electrochemically reduced to form Sample No. 2. One Sample of the reduced (Ru 25Ir) O was thermally stabilized for one hour at 550 to 600 ° C. The surface of the unreduced catalyst of sample No. 1, the reduced catalyst of sample No. 2 and the thermally stabilized one, reduced (Ru 25 Ir) O catalyst of Sample No. 3 were tested by the three-point BET nitrogen absorption method measured. The results follow in Table XII.

Table XII

Catalyst treatment surface (Ru 25 Ir)

2 Sample No. 1 not 127.6 m / g

2 Sample No. 2 reduced 123.5 m / g

Sample no. 3 reduced and 1 hour 62.3 m / g

Thermally stabilized at 550 - 600 C.

Then the oxide content of the samples No. 1, 2 and 3 was measured as well as that of a sample No. A ₁ which had been thermally stabilized at 700 to 750 ° C. for one hour. In addition, the oxide content of platinum-iridium catalysts with 5 to 50% by weight of iridium was measured. The results can be found in Table XIII below.

909824/0602

Table XIII % Oxide content catalyst
(Ru 25 Ir) treatment 24.4 Sample # 1 no 24.3 Sample # 2 reduction 22.6 .'robe No. 3 thermal stability
1 hour at
550-600 ° C 21.5
16.5 Sample # 4
(Pt-50Ir)
Sample # 5 Reduction and thermi
cal stabilization
for 1 hour at
700-750 ° C
no 15.2 Sample # 6 reduction 13.0 Sample # 7 Reduction and thermi
cal stabilization
for 1 hour at
550-600 C.

The results of this Table XIII show a decrease in the oxide content with the reduction and the thermal stabilization just as the surface area decreases after reduction and thermal stabilization.

The decrease in the oxide content has a corresponding effect on the surface, since the surface of oxides normally is greater than that of the non-oxidic form. This reduction in oxide content partially explains the reduction of the surface, but not the dramatic reduction in the surface after thermal stabilization.

The porosity of the catalyst was therefore measured to determine whether the thermal stabilization of the catalyst causes a change in the porosity and thus a reduction in the surface area and an increase in the Corrosion resistance. From the same mixes as that

909824/0602

Sample Nos. 1, 2 and 3, catalyst samples were taken and the porosity of these samples and their particle size distribution measured. The particle size distribution was determined by a sedimentation method to find that the equivalent sphere diameter with 50% mass distribution 3.7 μm after the reduction of the catalyst and 3.1 μm after the thermal stabilization was. This shows that the outer surface area of the particles is reduced, but there are insufficient basis for total surface reduction after stabilization.

The total pore volume in ml / g was measured by capillary condensation and mercury introduction methods. the Results for Sample Nos. 1, 2 and 3 are summarized in Table XIV.

Table XIV

catalyst
(Ru-25 Ir) 1 treatment Area · ther- Total pores
volume in ml / g Sample no, 2 no 40Ä - 10 / rev O ₁ Sample no. 3 reduction Il 0, Sample no. Reduction and 0, , 80 , 72 , 76

mixed stabilization for 1 hour at 500 - 600 ° C

These results show that the total pore volume remains relatively unchanged. The porosity in g / ml or if if the sphere size and density are known it is converted into the void volume, is therefore essentially the same and ranges from 0.7 to 0.8 g / ml for Ru-25 Ir.

At the same time, the pore size distribution was measured to the pore diameter distributions in the range of 40 Sngström

909824/0602

to 10 to get. In the range from 40 to 500 Sngström Ca ^ illar condensation was used. In this procedure liquid condensation is measured at a given vapor pressure to determine the pore size distribution. The capillary condensation method has a lower limit of resolution of 40 sngstrom and an upper limit of 500 sngstrom. For pores of more than 500 Sngström (e.g. from 500 Sngström to 10 .mu.m) the pore size distribution is determined uses a mercury penetration process. The results for both ranges of pore sizes are in the following Tables XV and XVI summarized.

Table XV

Catalyst treatment

Sample # 1 none

Sample No. 2 reduction

Sample # 3

Reduction and thermal stabilization for 1 hour at 550 - 600 C

Size-pore diameter range distribution

40-5000 pore distribution below 40 S

"Pore diameter distribution below 40 Å

"Distribution in the range of 100 300 S with a maximum at 200 8

Table XVI

Catalyst treatment

Sample no,
Sample no.
Sample no.

1
2
3

Size-pore diameter range distribution

(50% point

in the distribution)

no 500fi '

Reduction "

Reduction and thermal stabilization for 1 hour at 550 - 600 ° C

■ 10 to

0.46 to 0.82 to 1.5 µm

8C9824 / 0602

These results show that the thermal stabilization of the catalyst leads to a change in the pore diameter leads. This change seems to be accompanied by a change in the number of pores, so that the total surface area reduced. Since the pore volume remains essentially constant and the pore diameter distribution changes changes so that the distribution shows a maximum at 200 Sngström and 1.5 μm, it seems quite clear that many of the Merge pores with a diameter of less than 40 Sngström and so reduce the total number of pores. The pore diameter increases above 500 Sngström. Of the The pore size diameter and the inner pore surface thus change with the thermal stabilization. All in all becomes the internal porosity and thus the pore surface during the thermal stabilization of the catalyst decreased. It is believed that this is a result of changing the morphology to a smaller number of pores to create with a larger pore diameter distribution. Because the pore volume remains relatively unchanged and a change the pore diameter distribution takes place towards a larger pore diameter, it seems to be clear that the surface reduction associated with the thermal Stabilization of the catalyst is accompanied by the change in the inner pore surface.

The porosity, expressed in pore volume in ml / g des Catalyst, the thermally stabilized, reduced platinum metal oxide catalyst is in the range from 0.4 to 1.5 ml / g, with the preferred porosity for a thermally stabilized Ru-25 Ir catalyst at 0.7 to 0.8 ml / g.

The pore diameter distribution of the thermally stabilized catalyst shows the basic distribution below from 500 Sngström than lying in the 100 to 300 Sngström range

909824/0602

284U95

with a max'.mum at 200 Angstroms. Above 500 Angstroms, the pore diameter distribution shows the largest pore volume and thus the main distribution in the range from 0.4 to 9 .mu.m, with a maximum at 1.5 .mu.m:
the distribution represents.

with a maximum at 1.5 µm, which is the 50% point

The surface area for the thermally stabilized, reduced Platinum metal oxide catalysts should be such that for any given platinum metal or combination of platinum metals with or without valve metals etc. the surface should be as small as possible (around the To reduce corrosion) for the required catalytic

2 activity. The surface should therefore be more than 10 m / g

2
with 24 to 165 m / g being a preferred range

and for a thermally stabilized Ru-25-Ir catalyst

2
the range is 60 to 70 m / g. The catalysts with the

Reduced, thermally stabilized platinum group metal oxides are large-area compared to powders, carbon blacks, etc. Catalysts that normally have a surface area of 10 to

2
15 m / g.

The oxide content of the catalyst can range from 2 to 25% by weight and preferably from 13 to 23% by weight.

909824/0602

Claims (1)

Dr. rer. near Horst pupil PATENT ADVOCATE 6000 Frankfurt / Main 1, 11.10 / 1978 Kaiserstrasse 41 ... Dr .. Telephone (0611) 235555 * W "> HH Telex: 04-16759 mapat d Postscheck account: 282420-602 Frankfurt / M. Bank account: 225 / 038y Deutsche Bank AG, Frankfurt / M. 4863-52-EE-O299 GENERAL ELECTRIC COMPANY 1 River Road Schenectady, N.Y./U.S.A. Electrolyte catalyst made from thermally stabilized, partially reduced platinum metal oxide and process for its production. Claims 1. Catalyst system with at least one electrically conductive, thermally stabilized, reduced platinum metal oxide. 2. Catalyst system according to claim 1, characterized in g that the platinum metal oxide is ruthenium or iridium oxide. 3. Katalvsatorsystem according to claim 1 or 2, characterized characterized in that it is electrically in addition to the thermally stabilized platinum oxide Contains conductive graphite. 909824/0602 ORIGINAL INSPECTED - 9 4. Catalyst system according to claims 1 to 3, characterized in that it also contains thermally stabilized oxides of a valve metal. 5. Catalyst system according to claims 2 to 4,
characterized in that the platinum metal oxide is ruthenium oxide, the at least one further thermally stabilized, reduced metal oxide of iridium, tantalum, titanium, niobium, zirconium or
Includes hafnium. 6. Catalyst system according to claim 5, characterized characterized in that it contains 5 to 25% by weight of reduced iridium oxides. 7. Catalyst system according to claim 5 or 6, characterized characterized in that it contains 25% by weight of reduced iridium oxides. 8. Catalyst system according to claim 5 to 7, characterized in that it is reduced oxides of iridium and either tantalum or titanium. 9. Catalyst system according to claims 2 to 4,
characterized in that the platinum metal oxide is iridium oxide containing reduced oxides of tantalum or titanium. 10. Catalyst system according to claims 5 to 7, characterized in that it further includes electrically conductive graphite. 11. Halogens evolving catalyst, thereby marked that he has at least one 909824/0602 includes electrically conductive, reduced platinum metal oxide, which by heating to a temperature of 300 to 750 ° C is thermally stabilized. 12. Catalyst according to claim 11, characterized in that it has a surface in the 2 range from 24 to 165 m / g. Π3 J Porous catalyst, characterized that it has at least one electrically conductive, thermally stabilized, reduced platinum 2 metal oxide with a surface area of more than 10 m / g, the porosity of the catalyst im The range is from 0.4 to 1.5 cm / g of the catalyst and the pore diameter distribution is due to the thermal stabilization is modified to the effect that the inner pore surface is reduced. 14. Catalyst according to claim 13, characterized that the pore diameter distribution has a maximum at 200 Angstroms and one 50% pore distribution point at 1.5 µm. 15. Catalyst, characterized in that that it has at least one electrically conductive, thermally stabilized, reduced platinum metal oxide includes the surface of the catalyst 2
is at least 60 m / g. 16. Combined electrolyte and electrode structure with a Ion-transporting membrane, one surface of which has at least one gas-permeable catalytic Electrode is connected, characterized in that the electrode is thermally stabilized, electrically conductive, reduced oxides of 909824/0602 comprises at least one platinum group metal. 17. Structure according to claim 16, characterized in that that the gas-permeable electrode has a plurality of thermally stabilized, electrically conductive particles of reduced platinum group metal oxides includes. 18. Structure according to claim 17, characterized that the particles include the oxides of at least two metals from the group consisting of thermally stabilized, electrically conductive, reduced platinum group metal oxides and reduced vent metal oxides wherein at least one is a reduced platinum group metal oxide. 1 9. Structure according to claim 18, characterized? The particles are shown to include thermally stabilized, electrically conductive, reduced ruthenium oxides. 20. Structure according to claim 18 or 19, characterized characterized in that the particles are thermally stabilized, electrically conductive, reduced Include oxides of ruthenium and at least one reduced metal oxide selected from the reduced ones Oxides of iridium, tantalum, titanium, niobium, zirconium or hafnium. 21. Structure according to claim 20, characterized in that the thermally stabilized, electrically conductive particles are reduced oxides of ruthenium and reduced oxides of iridium. 909624/0602 _ 5 - 2? . The structure of claim 21 characterized in that the particles include 5 to 2 5 weight percent reduced iridium oxides. 23. Structure according to claim 20 or 21, characterized in that the particles include Ge \ ^r .-% iridium. 24. Structure according to claim 18 to 21, characterized characterized in that the majority of the particles are thermally stabilized, electrically conductive Include particles of reduced noble metal oxides and reduced oxides of titanium or tantalum. 25. Structure according to claim 24, characterized that the reduced noble metal oxide is reduced iridium oxide. 26. Structure according to claims 16 to 25, characterized characterized in that the particles further include electrically conductive graphite particles. 27.Combined electrolyte and electrode structure for halogens with an ion-transporting membrane, at least one gas-permeable electrode is bonded to one surface, characterized in that that the electrode is thermally stabilized, electrically conductive, catalytically active, comprises reduced oxide particles of at least one platinum group metal, the surface of the electrode 2
comprises at least 60 m / g of the particles. Catalytic electrode structure made of an agglomerate of electrically conductive catalytic particles, which with Particles of a resinous binder are connected, 809824/0602 characterized in that the catalytic particles are thermally stabilized, reduced Include oxides of at least one platinum group metal, the electrode structure being gas-permeable, is electronically conductive and catalytically active for the electrolysis of halides. 29. The electrode structure according to claim 28, characterized in that the particles are the Oxides of at least two metals from the group include those made from electrically conductive, thermally stabilized, reduced platinum group metal oxides and thermally stabilized, reduced valve metal oxides, at least one of these Oxide is a reduced platinum group metal oxide. 30. Electrode structure according to claim 28 or 29, characterized in that the catalytic particles are thermally stabilized, reduced ruthenium oxides. 31. Electrode structure according to claims 28 to 30, characterized in that they further thermally stabilized particles of another, reduced oxide of a platinum group metal. 32. Method of making an electrocatalytic Materials, characterized at least
preparing an oxide / platinum group metal optionally containing a valve metal oxide, reducing the oxides to a partially oxidized state, heating the reduced oxides in the presence of oxygen to a temperature and for a time sufficient to stabilize the reduced oxides and that 909824/0602 then optionally up to 50% by weight of graphite is added. 33. The method according to claim 32, characterized in that - k e nn'z e ic hn et that the reduced oxides heated to 300 to 750 ° C. 34. The method according to claim 33, characterized in that the reduced oxides heated to 550 to 600 C. 809624/0602