DE3022751A1 - LOW OVERVOLTAGE ELECTRODE AND METHOD FOR PRODUCING THE SAME - Google Patents

Description

"Low Overvoltage Electrode and Process for Making It"

Claimed priorities:

July 2, 1979, V.St.A., registration no. 054 335 March 27, 1980, V.St.A., registration no. 129 873

The present invention relates to an improved electrode with lower. Overvoltage, which in particular suitable for use in electrolytic cells, as well as a method for their production.

It is well known per se that the between an anode and a cathode in an electrolytic cell, in which Gases are generated at the electrodes, occurring voltage drop is due to various components and that a of these components is the gas overvoltage which occurs at the

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specially used electrode occurs. In the industrial use of electrolytic cells, it is from the standpoint In terms of operating costs, it is of the utmost importance to reduce the voltage drop in the electrolytic process to a minimum value. This means that in the corresponding System electrodes with the lowest possible level of overvoltages must be used. For example is in the electrolysis of an aqueous alkali metal halide solution such as an aqueous sodium chloride solution for the purpose of Generation of hydrogen, chlorine and sodium hydroxide the use of a cathode is highly desirable, which is one possible has a low hydrogen overvoltage.

The term overvoltage is defined by the relationship H = Ei-Eo, where Ei is the electrode potential below Load and Eo the reversible electrode potential, regardless of any overvoltage including the

mean, overvoltage generated by gases, / General methods for

Determination of these values are, among other things, in the

Il

standing literature: "Physical Chemistry,

3rd edition, Farrington Daniels and Robert A. Alberty, John Wiley & Sons, 1966, particularly pages 265-268, and in "Instrumental Methods of Analysis". Hobart H. Wxllard,

Lynne L. Merritt, Jr. and John A. Dean, D. Van Nostrand Company,

Inc., 4th edition, 1965, especially pages 620-621, and "Modern Electrochemistry", Volumes 1 & 2, John O ¹ M. Bockris

and A.K.N. Reddy, also in "Kinetics of Electrode Processes",

Wiley-Interscience, 1972, especially Chapter 2.

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Large amounts of chlorine and alkali hydroxide are required by modern industrial society and are therefore required annually Millions of tons of these materials are produced mainly by electrolysis of aqueous sodium chloride solutions. A reduction in the working voltage of an electrolytic Cell around as low as 0.05V already results in very significant economic savings, in particular with regard to the daily rising energy costs and the necessary energy-saving measures.

Electrodes consist of an electrically conductive substrate, and a wide variety of metal coatings are already available for proposed a wide variety of substrates in order to reduce the corresponding overvoltages. So in the U.S. Patent No. 4,080,278 includes coatings of nickel and molybdenum from 100 to 500 microns thick described, which can be applied to substrates made of iron, steel or nickel.

In U.S. Patent No. 4,116,804, a coating is made of Raney nickel described as having a thickness of at least 75 microns, which is preferably additionally provided with a nickel coating of 5 to 10 microns thick, around the usual to hold together the crumbling structure of Raney nickel for better mechanical strength. However, only electroplating methods or electroless plating methods are used to apply these coatings disclosed, in this US patent is admittedly

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given that overvoltages of only 6 0 mV can be achieved in this way, but in practice such low overvoltages could be achieved cannot be achieved. The overvoltages actually observed and reached were around 150 mV and above, and the coating was prone to peeling and crumbling and was generally mechanical relatively weak.

A technique known per se for applying thin layers, but which has obviously not yet been used has been used for the production of electrodes, especially for the chlor-alkali industry, is the method cathode atomization, also known as the sputtering technique. Using this sputtering technique, a first Metal components contained in a sacrificial target are bombarded in a vacuum using tiny particles. The impact of this bombarding particles leads to an energy transfer from these particles to those in the surface of the Metal component located in the sacrificial target (cathode). The surface atoms thus activated with energy become accordingly atomized from the metal component of the sacrificial target into a chamber surrounding this target, where some of the atomized Atoms of the electrically conductive to be coated Substrate is intercepted. The trapped atoms collide with the surface of the electrically conductive substrate and adhere to it in the form of a metallic film.

In view of the prior art mentioned above, there was still a need for an improved process

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for applying a metal component in film form to an electrically conductive substrate, thereby improving an To get electrode. For use in electrolysis cells, this metal film should be firmly attached to the electrically conductive substrate be liable. In addition, such an electrode should have a high electrochemical activity.

The object of the present invention was therefore to develop an electrode with a low overvoltage and, if possible, long service life. It was also an object of the invention to deposit a metal film of low overvoltage on an electrically conductive substrate, which also is significantly thinner than the metal films that can be applied according to the prior art. Furthermore, the so developed, improved electrode when used in electrolytic processes have a high electrochemical activity.

These objects are achieved by the invention. The inventive Low overvoltage electrode consisting of an electrically conductive substrate and a reducing the overvoltage, the substrate surface at least partially covering metal film, is characterized in that the metal film consists of at least two different Mixture containing metals, has a thickness of less than 100 microns and by means of the technique of Cathode atomization (sputtering technique) has been applied. In particular, the electrode according to the invention should be a metal film having a thickness in the range 0.01 to 90 microns, preferably in the range 0.05 to 20 microns and most preferably

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in the range of 0.10 to 10 microns.

According to a preferred embodiment, the inventive Electrode characterized in that the metal film contains the following components:

a) a first non-precious metal,

b) at least one further metal from group i) precious metals,

ii) the non-precious metals,
iii) the sacrificial metals.

The invention also relates to a method for producing such an improved electrode, which is characterized is that the components forming the metal film are separated or mixed by means of the sputtering technique sprayed on until the intended film thickness is reached.

In the context of the invention, any conductive material which has the required mechanical properties and the required chemical resistance in the electrolyte solution in which the electrode is inserted. In addition, the electrically conductive substrate must be applied with the corresponding Metal film must be compatible and the chemical attack of the electrolyte liquid even after the film has been applied To offer resistance. Suitable electrically conductive materials include titanium, zirconium, vanadium, niobium, tantalum,

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Chromium, molybdenum, tungsten, manganese, rhenium, iron, ruthenium, osmium, cobalt, rhodium, iridium, nickel, palladium, platinum, Copper, silver, gold, carbon, aluminum, graphite and electrically conductive polymer substances, e.g. polyacetylene, Polyelectrolytes and also semiconductors such as silicon and germanium. Mixtures or alloys of the above mentioned conductive substances are used. Are preferred in the context of the invention as electrically conductive Substrates Substrates made of iron, copper, nickel, titanium, as well as mixtures or alloys of these substances, e.g. nickel plated copper and nickel plated tin.

A particularly suitable electrically conductive substrate is nickel-plated copper in the form of an expanded, wire mesh electrode with blind-like openings, which can be designed as a single-polar or bipolar electrode. The blind-like openings of a such electrode, when used in a membrane or diaphragm type chlor-alkali cell, can be either in Be oriented towards the membrane or opposite to the membrane.

Raney nickel, such as can be produced from Ni ₃ Al ₃ as a precursor according to US Pat. No. 4,116,804, or other substrates with a surface made from Raney nickel are also suitable as electrically conductive substrates on which Technique a metal film

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can be applied. Furthermore, a cathode made of expanded steel or expanded steel with gas discharge can be used be provided according to the invention by means of the sputtering technique with a metal film without there being a A layer of Raney nickel is required, and practically the same can be achieved by means of such a coated steel electrode low overvoltages can be achieved such as with a coating made of Raney nickel.

Typical electrically conductive substrates suitable for the invention are all materials such as those used in electrolytic Cells are used as electrodes, for example in cells that are built according to the filter press principle, with monopolar or bipolar electrodes which have membranes that are selective in terms of permeability, and in particular be used for the electrolysis of aqueous solutions of alkali metal halides. Other suitable materials than Substrates are electrode materials like those in cells with porous or semi-porous diaphragms or ion exchange membranes may be used, for example membranes with selective permeability.

The electrically conductive substrate used in the context of the invention can have any shape or size is suitable for the cell in question in which the electrode is to be used as such. For example the electrically conductive substrate can take the form of wire, tube, rod, flat or curved plate,

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• / Ml ·

a perforated plate, an expanded metal, a wire gauze, a gauze or a porous mixture, for example a sintered metal powder. The surface of the relevant electrically conductive substrate can be microporous, be smooth, open-celled or sintered.

Before applying the metal film to the electrically conductive Substrate, the surface thereof is preferably carefully cleaned. This cleaning can be in any arbitrary Be carried out in a cleaning container or a cleaning bath with the aim of removing all impurities, which would affect the adhesion of the film coating to be applied to the substrate surface. Suitable Cleaning methods are, for example, degreasing in solvent vapor, treatment with an alkaline or acid solution, chemical etching or sandblasting treatment. The term "cleaning" includes within the scope of the invention, that the surfaces of the relevant electrically conductive substrate are sufficiently free of interfering organic or inorganic films are so that the metal component is then applied without difficulty by means of the sputtering technique can be. Depending on the type of electrolytic cell in which the electrode in question is to be used, only a part of the substrate surface needs to be cleaned.

The surface of the electrically conductive substrate can be rinsed and cleaned by means of conventional techniques. Ge

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For example, an acidic stain such as hydrochloric acid is suitable, which is used after the actual cleaning treatment to remove residues of an alkaline cleaning liquid to neutralize, and also one can remove oxide ions from the electrode surface by outgassing.

A preferred method of pretreating the surface of the substrate to be coated for the application of the metal film includes the following work stages:

a) washing with an organic solvent such as trichlorethylene,

b) washing with an alcohol, such as isopropyl alcohol,

c) immersion and treatment in an inorganic acid, such as aqueous hydrochloric acid solution, preferably for a period of time from about 1 to 30 minutes,

d) washing with water, preferably deionized water,

approximately
in particular during a period of 1 to 30 minutes,

e) dipping and washing with an alcohol such as isopropyl alcohol, in particular for a period of about 1 to 60 minutes, and optionally

f) drying with an inert gas, in particular nitrogen.

In this way it is possible to add a substrate surface obtained, which no longer has any traces of liquid.

The thus cleaned and dried substrate surface is
then visually assessed to ensure that

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it is perfectly pure and dry.

As non-precious metals, which are deposited on the surface of the electrically conductive substrate by means of the sputtering technique copper, nickel, molybdenum, cobalt, manganese, chromium, iron, and titanium are particularly suitable Mixtures and alloys of these metals. Suitable alloys are, for example, alloys of nickel and aluminum, made of nickel and zinc as well as of nickel and tin.

Two or more non-precious metals can be applied simultaneously or separately to the surface of the electrically conductive substrate be applied. For example, nickel and molybdenum can be used at the same time by means of cathode sputtering on one electrically conductive substrate, such as nickel or steel, are applied. According to a preferred embodiment, the composition of the metal film adjusted so that they

of the formula Ni Mo, where "a" has a value in the range a ώ

from 5 to 95 atomic percent and in particular in the range from 15 to 8 5 atomic percent, and the sum of a + b = 100 atomic percent is.

Precious metals can also be applied as a film to the surface of the electrically conductive substrate using the sputtering technique will. A noble metal is understood here to mean any metal that is chemically inert, in particular with respect to on oxygen. Suitable noble metals are silver, gold, rhodium, iridium, palladium, platinum, ruthenium, osmium as well

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Mixtures and alloys of these metals.

According to a further embodiment, together with the Precious metal or non-precious metal also sacrificial metals are applied in film form to the surface of the electrically conductive substrate and later selectively removed from the formed metal film, preferably without, however, at the same time substantial amounts of the non-precious metal are removed in the process. In this way a metal film is obtained with a relatively strongly microporous surface. The selective removal of the sacrificial metal is possible due to different Solubilities in a solvent or as a result of different electrochemical activity. All metals that alloy with the selected non-precious metal are therefore suitable as sacrificial metals are then selectively removable from the applied metal film and which do not adversely affect the voltage drop affect if a proportion of the sacrificial metal according to the selective Removal still remains in the film on the electrically conductive substrate. Sacrificial details suitable within the scope of the invention are for example aluminum, magnesium, gallium, tin, lead, cadmium, bismuth, antimony and zinc and mixtures and alloys of these metals. Furthermore, non-metallic materials such as carbon, Graphite and phosphorus. In the context of the invention, however, aluminum, zinc, magnesium are preferred as sacrificial metals and tin, as well as mixtures and alloys of these metals.

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The appropriate sacrificial metal is made depending on the non-precious metal or precious metal used and the type of procedure selected with which the sacrificial metal is removed from the applied metal film. In addition, the intended one is also provided The purpose of the electrode is important. Depending on the species of the noble metal or non-noble metal, one or more sacrificial metal components can be used.

The term "metal component ¹ or" metal mixture "used here includes all metals which are used individually or jointly as sacrificial targets for the sputtering technique. The target in question can therefore consist of a single metal or also of several metals, for example alloys, which in this way deposit the alloy components simultaneously in film form on the surface of the electrically conductive substrate.

In general, two or more of the metal components mentioned can be used are simultaneously applied to the electrically conductive substrate by means of sputtering technology. If so desired however, an alloy or a mixture of such metal components can be prepared beforehand, and the alloy or mixture can then be applied to the electrically conductive substrate as such by means of the sputtering technique Film form to be knocked down. According to another embodiment two or more alloys or mixtures can be sprayed on simultaneously in film form.

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According to one embodiment of the invention, a non-precious metal and at least one sacrificial metal is sprayed onto the electrically conductive substrate at the same time. But it can also two non-precious metals and a sacrificial metal can be applied to the surface of the substrate at the same time. At this In a special embodiment, the base metals are preferably nickel and molybdenum and the sacrificial metal is aluminum used. Thereby the composition of the metal film

preferably adjusted to be of the formula Ni Mo Al

χ y ζ

corresponds to, where "x" has a value in the range from 5 to 50 and preferably from 10 to 40 atomic percent, "z" a value in the range from 5 to 45 and preferably from 10 to 40 atomic percent and the sum of x + y + z = 100 atomic percent.

The metal film on the electrode can additionally contain built-in oxygen and / or carbon. It is believed, that these two elements are incorporated as a result of the sputtering technique used or by the fact that the metal film Oxygen or air.

According to a further embodiment of the invention, at least a noble metal and at least one non-noble metal simultaneously by means of the sputtering technique on the electrically conductive substrate are applied.

According to a further embodiment of the invention, at least a precious metal together with at least one non-precious metal and at least one sacrificial metal at the same time

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by means of sputtering technology onto the electrically conductive substrate be applied.

According to another embodiment of the invention, the contains applied metal film a mixture of a), a first non-noble metal or noble metal, and b), at least one further metal component, namely another precious metal, a sacrificial metal or a non-precious metal. The so composed Metal film preferably has a thickness in the range of 0.01 to about 90 microns.

To carry out the method of the invention, the previously dried and cleaned surface of the electrically conductive substrate using a high capacity sputtering apparatus. An inverted magnetron or a sputtering system with a hollow cathode are suitable for this, for example. One such System is for example in the trade under the name "S-Gun -Source" and is from the company Varian Associates, PaIo Alto, California. An arrangement for the sputtering technique with a preferred structure of the target connected as cathode is described in the US patent No. 4,100,055. This special arrangement is one that is profiled in a special way Cathode, which receives the metallic coating material, as well as an earthed central one arranged in a group with it arranged shielding anode, which directs the electron discharge to the area in the vicinity of the cathode surface

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limits and generates the fields that set the electron discharge in motion. In addition, a magnet arrangement is provided, which generates a magnetic field in the area of the electron discharge, and also a cooling jacket, which the entire Surrounds the cathode assembly.

A special embodiment of the electrode according to the invention, which is particularly suitable for use as a cathode in an alkaline electrolyte liquid is characterized by that they are out

a) an inner electrically conductive metal core,

b) an inner nickel-containing layer enveloping this core,

c) a middle layer which envelops the core and the inner layer and which contains Raney nickel, and

d) there is a nickel-containing outer coating layer, at least the outer coating layer by means of the Sputtering technique has been applied.

The number of metals that make up the metal film is
not limited and can be in the range from 2 to about 50, preferably in the range from 2 to about 40.

The terms "precipitation" and "precipitation" used here by means of the sputtering technique "refer to a deposition technique by means of which a mixture of metal components in the form of a film on an electrically conductive

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Substrate are deposited simultaneously, with between an anode and a sacrificial target connected as a cathode a high voltage is maintained - the metal component contained on the cathode, i.e. the sacrificial target is vaporized by bombardment with positively charged ions, and this vapor diffuses in part from the cathode and hits the object to be treated, i.e. the electrically conductive substrate, in the form of a metal film low. This can be a high-frequency or a direct current sputtering technique. Also the sputter technology by means of chemically reacting steam, the steam in question being produced by a chemical reaction at the cathode is to be understood under this term. This also includes the so-called reactive sputter technology, the generated steam or deposited film reacting with the atmosphere prevailing in the device. The ion beam sputtering technique or ion plating technique is also known bombarding a target with a focused, high energy beam of inert gas ions is, whereby the corresponding metal vapor is formed. The so-called "bias" technique is also known and the getter-sputter technique. The individual methods of the sputtering technique are described, for example, in the following literature reference described in detail: "Sputter Coating - Its Principles and Potential" by J.A. Thornton, S.A.E. Publication 730544 (May 1973). The sputtering technique also includes the direct current diode sputtering technique or the high-frequency diode sputtering technique as well as ionic magnetron cannons or

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using the triode sputtering technique or reactive sputtering technique ionic activation. For this purpose, reference is made to the detailed discussion of these techniques in the following reference referenced: "Metal Finishing", J.J. Bessot, March 1980, in particular P. 21.

With the sputtering technique, the metals of a metal mixture are applied simultaneously and in conductive form to the cleaned cathode surface is deposited, thereby forming a film on the electroconductive substrate of the electrode.

When a metallic film made of two non-precious metals and a sacrificial metal are applied using the sputtering technique should, individual targets can be used, each made of the relevant non-precious metal or the sacrificial metal exist. The electrically conductive substrate is then placed in a rotating holder and is simultaneously acted upon by the individual targets, resulting in a total metallic film on the electrically conductive substrate trains. The amount of sputtered from each individual target and deposited on the electrically conductive substrate Metal is proportional to the electrical energy directly supplied to the respective sputtering system of the individual target. Therefore, in order to produce a metal film having a desired composition, the one-target must be supplied electrical energy can be selected accordingly.

The atomization process is carried out until the

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Metal film has reached the desired thickness. Typical metal film thicknesses are in the range of about 0.01 to 90 microns, preferably in the range of about 0.05 to about 20 microns, and most preferably ranging from about 0.10 to about 10 microns. After this the desired film has been applied, the power supply to the atomizing system is turned off and that with The electrically conductive substrate provided with the film is removed from the device concerned.

If desired, electrically conductive substrates that have a metal film with one or more sacrificial metals can be further treated in a simple manner by selectively removes at least a portion of the sacrificial metal, thereby obtaining a leached metal film which is firmly connected to the electrically conductive substrate. A preferred method of removing at least one Part of the sacrificial metal is that with which the sacrificial metal containing film coated electrically conductive substrate with an alkali metal hydroxide solution, for example an aqueous solution of sodium hydroxide, potassium hydroxide and / or lithium hydroxide, the amount of the alkali is chosen so that at least a portion of the sacrificial metal is selective is removed from the film without other non-precious metals being attacked and thereby removed at the same time will. In this way, a thin leached metal film is formed. However, it is not harmful if a minor one Share of other non-precious metals present is simultaneously dissolved out of the coated substrate.

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However, this leach treatment is only one way to treat a film containing a sacrificial metal. The substrate with the film containing the sacrificial metal can also be used as an electrode directly in an electrolysis cell for the electrolysis of alkali metal halides, in which case the alkali metal hydroxide formed during the electrolysis effectively dissolves the sacrificial metal from the film applied by cathode sputtering. If, however, possible contamination by ions of the sacrificial metal should be a problem with regard to the alkali metal hydroxide to be produced, then it is necessary to leach out the sputtered film using alkali before the corresponding electrode is used. For the dissolution of the sacrificial metal from the applied metal film, alkali metal hydroxide concentrations of about 5 to 50 percent by weight and preferably of about 10 to 40 percent by weight are suitable. The temperature of the alkali metal hydroxide solution used for the treatment is expediently in the range from about 20 to 60 ^° C. and preferably in the range from about 40 to 50 ^° C.

After treatment with the alkali metal hydroxide solution can the electrically conductive substrate with the leached metal film is used as an electrode in an electrolytic cell preferably as a cathode.

By means of the method according to the invention it is possible a metal film of extremely uniform thickness

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of just a few microns on the surface of an electrically conductive substrate.

In terms of the desired evenness of the dejected For metal film it seems essential that its thickness does not exceed 100 microns, otherwise two deleterious effects may occur. First, a thicker film can crack, like the thicker one, using electroplating techniques applied coatings is known, which then the corrosion resistance is actually reduced. In addition, the surface of an electrically conductive substrate after the usual cleaning and etching treatments ^ after an acid wash and other appropriate cleaning methods a bit rough when viewed microscopically, and this Roughness can be "smoothed out" by thicker coatings as these tend to have their own surface characteristics to train. With regard to the overvoltage, such a "smoothing effect" is undesirable because it creates the effective surface is reduced, which then leads to higher current densities on the electrode surface. The phenomena of peeling or delamination are signs that the coatings applied according to the prior art are during Does not adhere well to prolonged periods of operation. According to the invention applied metallic films, however, show good adhesion to the surface of the electrically conductive substrate, though they are extraordinarily thin.

This small thickness of the metallic film according to the invention

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• OC Γ "

offers another unexpected advantage over the electrode made therewith. The electrical conductivity of the metal film is generally less than that of the electrically conductive substrate on which the metal film is placed has been knocked down. The application of a relatively thin metal film instead of a relatively thick metal film therefore causes an overall increase in electrical conductivity, and this is particularly true when the Thickness of the metallic film is only a few microns or even less.

Metal films produced according to the invention can also contain oxygen and / or incorporated carbon. It is believed that oxygen and / or carbon atoms as a result of the application can be built into the metal film using sputtering technology.

Electrodes produced by means of the sputtering technique according to the invention have, in contrast to those with a coating of Raney nickel provided electrodes of the prior art, rather than a crystalline, crumbling coating this coating appears to be amorphous or non-crystalline, so that no grain boundaries are formed in it either. Therefore there is also no possibility of a chemical attack along the grain boundaries, which would otherwise be the reason for the peeling phenomenon of the coating is viewed.

The type of metal film applied by means of the sputtering technique accordingly reduces the number of hairline cracks and leads

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thus reducing the problem of peeling of the coating on metal films from such alloys which result in the lowest overvoltages. Since metal films are formed by means of the sputtering technique, which do not have any inclination to show hairline cracking, the problems of chemical attack at the location of these hairline cracks and are also reduced thus at the grain boundaries. In addition, the metal films thus produced have surface uniformity, which is significantly larger than that of coatings made of Raney nickel, from coatings applied by electroplating or electroless plating. As already stated above, This uniformity of the surface of the coating reduces the type of chemical attack on attack not at the points of cracks, but on a uniform attack on the surface, which greatly reduces the possibilities of attack.

It is believed that by means of the sputtering technique, an electrical conducting substrate by means of the atoms or ions released from the sacrificial target, practically bombarded and these atoms or ions are implanted in the surface. This bombing leads to three main advantages of the Sputtering technique. First of all, the bombardment practically blows away the impurities and thereby the surface of the electrically conductive substrate cleaned or the impurities are deeper into the electrically conductive The substrate is driven into it and then covered by a metal film. Second, this bombing causes the

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deposited atoms in already existing very thin surface films or films of contaminants penetrate through and therefore adhere better to the substrate. Third, serve the knocked down and implanted atoms

as nails, so to speak, with which the metal film is attached to the electrically conductive substrate, so that a greater resistance to peeling or delaminating of the film results in phenomena which at virtually all other low-voltage coatings observed when such electrodes were used in electrolytic processes. Overall is therefore the sputtering technique is surprisingly superior to the other coating methods, since it creates a metal film which has virtually no hairline cracks and which is also thin enough to show the natural To preserve or reproduce irregularities of the surface of the electrically conductive substrate, thereby overall the overvoltage generated by gases is significantly reduced.

The electrodes made in accordance with the present invention are preferred used as cathodes in the electrolysis of solutions of alkali metal compounds. Typical alkali metal compounds are alkali metal halides, for example solutions of alkali metal chlorides such as sodium chloride, potassium chloride and mixtures these chlorides, also alkali metal hydroxide solutions, such as Solutions of sodium hydroxide, potassium hydroxide and lithium hydroxide and mixtures of these hydroxides. For such procedures suitable typical electrolytic cells are cells from

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Type of diaphragm cells and membrane cells, preferably constructed according to the principle of filter presses, whereby the filter press cells can be monopolar or bipolar.

However, electrodes according to the invention can also be used in others Electrolytic cells are used, for example as anodes or cathodes in the electrolysis of water.

Suitable membranes for such electrolysis cells are, for example perfluorocarbons substituted by sulfonic groups f-polymers (cf. US Pat. No. 4,036,714), furthermore polymers substituted by means of primary amine groups (cf. US Pat. No. 4,085,071) and polymers substituted with polyamine groups (cf. US Pat. No. 4,030,988JL Also with Polymers substituted by carboxylic acid groups are suitable for the membrane (see US Pat. No. 4,065,366).

The following examples illustrate the invention and the utility of the sputtering technique for the production of especially low overvoltage cathodes. Unless otherwise stated, all parts and percentages are by weight.

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. 3/1

example 1

Using the teachings of the invention, a metal film is deposited on an electrically conductive substrate with high electrochemical properties Activity and low hydrogen overvoltage are applied, and this electrode is subsequently used as the cathode used in an electrochemical cell.

Attempt a

Sections of 2.5 χ are used as the electrically conductive substrate 7.5 cm of wire mesh made of expanded nickel metal is used and metal films are applied to it. The wire mesh samples are initially cleaned in the following way:

a) washing with trichlorethylene: 5 minutes,

b) treatment in 10 percent hydrochloric acid: 10 minutes,

c) washing in deionized water: 15 minutes,

d) Treatment in isopropyl alcohol: 30 minutes, then

e) drying with dry nitrogen.

The nickel mesh thus cleaned is made using a metal mixture sprayed from three different sacrificial targets, the first target containing nickel as a non-precious metal, the second target contains molybdenum as the base metal and the third target contains aluminum as the sacrificial metal. the three targets are used as sputter guns at the same time to generate corresponding proportions of nickel and molybdenum and depositing aluminum on a first sample of the electrically conductive substrate in the form of a thin film. Included the spraying process is controlled so that a film of the

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Composition A forms about 45 weight percent nickel, about 45 weight percent molybdenum, and about 10 weight percent Contains aluminum.

A corresponding metal film of composition B is applied to a further electrically conductive nickel mesh substrate, which is adjusted to contain about 40 percent by weight nickel, about 40 percent by weight molybdenum and about Contains 20 percent by weight aluminum. In both cases, the relevant electrically conductive substrate is rotating in a Planet holder arranged (rotating planetary holder). The individual dust collectors for the Energy supply assigned to individual targets made of nickel molybdenum and aluminum is regulated in such a way that metal films of compositions A and B are obtained in the specified thicknesses (cf. Table I). After reaching the If the desired film thickness is desired, the atomization process is ended.

In combination with an etching technique, Auger electron spectroscopy applied to determine the composition of the metal film as a function of its thickness, measured by the outer surface of the metal film to the electrically conductive substrate. For analysis using Auger electron spectroscopy the metal film is bombarded with electrons, and then the secondary electrons are determines which are different from the metal atoms in the metal film.

General methods for analysis using Auger electron

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. 33.

spectroscopy are discussed in detail in the following reference: "Electronic Structure and Reactivity of Metal Surfaces ", E.G. Derouane and A.A. Lucas, Plenum Press, New York, 1976, in particular pp. 3 to 6.

When using the Auger electron spectroscopy method, the surface of the metal film is first analyzed. Afterward the metal film is removed to a certain depth by means of the sputtering technique, and then the. Repeated analysis using Auger electron spectroscopy. Then the metal film is removed to a greater depth, and the analysis by means of Auger electron spectroscopy is repeated again. The expression "ablation by means of the sputtering technique "means in connection with the Auger electron spectroscopy, that part of the metal film is removed to a desired depth, so that then the Analysis can be made using Auger electron spectroscopy at the desired depth of the original metal film can.

The. Results of the analysis by means of Auger electron spectroscopy on the first electrically conductive substrate with a non-leached metal films, which are about 0.8 microns thick, are summarized in Table I.

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Tabel

thickness

(measured from the outer metallic film surface in the direction of the electrically conductive Substrate)

micron

0.008

0.021

0.032

0.058

0.111

0.800 Existing metal type

(Atomic percent) Ni Al 0

15th 15th 42 20th 8th 48 17th 18th 10 7th 50 20th 16 8th 6th 59 25th 16 "1 <1 59 25th 16 <1 59 25th 16 <1 59 25th 16 <1

CO O , lsi

The results of the analysis by Auger electron spectroscopy on the second electrically conductive substrate with non-leached Metal films approximately 0.91 microns thick are summarized in Table II below.

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Table II

thickness

(measured from the outer metallic film surface in the direction of the electrically conductive Substrate)

Micron 0

0.008 0.016 0.032 0.058 0/111 0.800 Type of metal present

Ni (Atomic percent) 0 C. Mon 17th Al 24 18th 4th 26th 37 4th 2 34 26th 34 1 1 50 25th 24 <1 <1 51 25th 24 <1 <1 52 25th 24 <1. <1 52 25th 24 <1 <1 52 24

Attempt B

Following the procedures of Experiment A of this example, eight electrically conductive substrates are made in accordance with the invention provided with a metal coating using the sputtering technique. These eight electrically conductive substrates are first shown in divided into two groups of four substrates each. The first group of these substrates is coated with a composition A. The composition A is adjusted with regard to the individual targets and the supplied energy output in such a way that that the film is about 45 weight percent molybdenum, about 45 weight percent nickel and about 10 weight percent aluminum contains. A film of the composition is sputtered onto the second group of electrically conductive substrates B, which is adjusted to contain about 40 weight percent molybdenum, about 40 weight percent Nikkei and contains about 20 weight percent aluminum.

The metal films of these substrates are then placed in a 20 percent sodium hydroxide solution at 50 ° C. for about 60 minutes leached, and then the electrodes with a reference electrode in an aqueous solution electrically connected by about 35% sodium hydroxide at 90 ° C. The two electrodes are connected to a potentiostat, around the hydrogen overvoltage at a current density of about

To measure 2 kA / m. Those given in Table III below calculated hydrogen overvoltage is the difference the actual measured electrode potential and the reversible hydrogen potential at the same temperature

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- 33 -

door and the same concentration. The one used for the measurements Potentiostat automatically compensates for the ohmic resistance.

The use of a potentiostat to determine electrode overvoltages is described in detail in particular in the following literature: "Interfacial Electrochemistry, An Experimental Approach ", by E. Gileadi et al., Addison-Wesley Publishing Co. Inc., 1975, particularly pages 181 to 195.

Table III

Composition A first group

Composition B second group

nominal calculated Movie hydrogen thickness Overload micron (mV) 0.22 290 0.52 275 0.93 200 1.93 150 Test C.

nominal calculated Movie
thickness Hydrogen-
Overload micron (mV) 0.2 170 0.5 140 0.98 65 1.77 60

Following the measures of Experiment B of this example, another electrode is made by clicking on a electrically conductive substrate applies a metal film to a thickness of about 1.8 microns using the sputtering technique. The applied metal film has a composition corresponding to

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accordingly about 40% nickel, about 40% molybdenum and about 20% aluminum. The electrode with the non-leached metal film thus produced is used as a cathode in a divided chlor-alkali electrolytic cell used. This electrolytic cell is used to generate a 30 percent sodium hydroxide solution, hydrogen and preparing chlorine from an aqueous sodium chloride solution. The electrolysis solution had a temperature of about 85 ° C,

and a current density of about 2 kA / m was used to obtain the desired 30 percent sodium hydroxide solution to obtain. An ion exchange membrane made of substituted sulfonic acid groups was used as a separator in this cell Perfluorocarbon polymer used. From the commissioning of this cell in the course of the further Operating time determined the calculated hydrogen overvoltages given in Table IV below.

Table IV

Calculated hydrogen overtime elapsed since commissioning in days voltage at the cathode (mV)

1,189.5

3,155.4

19 128.0

24 101.5

26 79.3

33 x 71.6

42 57.5

45 73.3

49 71.9

56 80.0

60 74.0

75 87.0

81 92.3

87 91.7

90 80.1

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During operation of the cell, no metal contamination and no signs of detachment could be found on the cathode in question to be established. It is believed that the drop in the calculated hydrogen overvoltage at the cathode is from first day of operation to about the forty-second day of operation is due to the fact that the sacrificial metal aluminum slowly leached out of the metal film by the caustic soda produced in the cell, thereby activating the cathode itself will.

Example 2

A film of nickel and molybdenum with a thickness of about 0.3 is created on a nickel substrate by means of the sputtering technique Micron applied. The nickel substrate consisted of at least about 99 atomic percent nickel and was in the form of a plate. Of the applied metal coating had a composition corresponding to about 60 atomic percent molybdenum, about 28 atomic percent Nickel, about 6 atomic percent oxygen and about 6 atomic percent carbon.

A small sample of the substrate thus provided with a metal film was masked with an epoxy resin and only 1 cm of the surface remained exposed. This sample prepared in this way was made then immersed in an electrolyte solution. A corresponding section of uncoated nickel substrate was made coated in the same way with epoxy resin, and it was also left exposed only an area of 1 cm. These Nickel electrode not having a metal film served as

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Control electrode. Each sample was polarized cathodically at 8O ⁰ C in a solution containing 17 weight percent sodium hydroxide. The electrode voltage was compared by comparing the potential of the electrode with the potential of a saturated calomel electrode, which was connected to the same electrolyte via a salt bridge. The measurements were carried out by means of a potentiostat which automatically compensated for the ohmic resistance in the electrolyte solution. The measured electrode potentials are shown in FIG. According to FIG. 1, the reduced overvoltage of the electrode produced according to the invention according to this example is determined at a selected current density by determining the difference between the electrode potential of the coated electrode and the electrode potential of the non-coated nickel electrode at the relevant current density. With a current density of 2 kA / m, the reduction in overvoltage is, for example, -1.46 V - (1.22 V) = 0.24 V or -240 mV. It can be seen from FIG. 1 that the metal coating applied according to the invention has reduced the cathode potential by approximately 240 mV at a current density of 2.0 kA / m.

Example 3

The procedure of Experiment A in Example 1 is followed. Three Electrically conductive nickel substrates with cleaned surfaces are according to the invention by means of the sputtering technique with a Metal film coated.

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A metal film of composition C is deposited on a first sample, about 66 2/3% of which is molybdenum and about 33 1/3% consists of nickel.

A metal film is deposited on a second sample which has the composition D and is approximately 50% off Is made up of molybdenum and nickel.

A metal film of composition E is deposited on the third sample, about 33 1/3 of which is molybdenum and about 66 2/3 consists of nickel.

Corresponding to the measures of Experiment B of Example 1, the hydrogen overvoltage is determined using a potentiostat determined for certain film thicknesses. The results are summarized in Table V below.

<P

Λ.

Table V

First rehearsal

measured film thickness
(Micron)

0.03 0.33 0.65 ^X Composition C

calculated hydrogen over voltage (mV)

337 187 137

Second rehearsal

measured film thickness (microns)

0.03 0.19 0.65 * Composition D.

calculated hydrogen over voltage (mV)

307 247 167

Third sample

measured film thickness (microns)

0.03 0.23 0.65 * Composition E.

calculated hydrogen versus voltage (mV)

347 297 237

estimated film thickness

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L e e'rs e i t e

Claims (18)

Claims consisting of an electrically conductive substrate and one that reduces the overvoltage, at least the substrate surface partially covering metal film, thereby g e k e η η - one indicates that the metal film consists of / at least two different Mixture containing metals, has a thickness of less than 100 microns and by means of the technique of Cathode atomization (sputtering technique) has been applied. 2. Electrode according to claim 1, characterized in that the metal film has a thickness in the range of 0.01 to 90 microns, preferably in the range of 0.05 to 20 microns, and more preferably in the range of 0.10 to 10 microns. 3. Electrode according to claim 1 and 2, characterized in that the metal film contains the following components: a) a first non-precious metal, b) at least one further metal from group i) precious metals, ii) the non-precious metals, iii) the sacrificial metals. 4. Electrode according to claim 1 to 3, characterized in that that the metal film is made of copper, nickel, molybdenum, cobalt, manganese, chromium and / or iron or alloys as a non-noble metal contains these components. 030064/0695 ORIGINAL INSPECTED 5. Electrode according to claim 1 to 4, characterized in that that the metal film as noble metal iridium, palladium, platinum, Contains rhodium, silver and / or gold or alloys made from these components. 6. Electrode according to claim 1 to 5, characterized in that the metal film as sacrificial metal is aluminum, magnesium, gallium, Tin, lead, cadmium, bismuth, antimony, zinc, carbon, steel and / or phosphorus or alloys of these components contains. 7. Electrode according to claim 1 to 6, characterized in that the metal film is additionally oxygen and / or carbon contains built-in. 8. Electrode according to claim 1 to 7, in particular for use as a cathode in an alkaline electrolyte liquid, characterized in that it consists of a) an inner electrically conductive metal core, b) an inner nickel-containing layer enveloping this core, c) a middle layer which envelops the core and the inner layer and which contains Raney nickel, and d) there is a nickel-containing outer coating layer, and that at least the outer cladding layer by means of the sputtering technique has been applied. 03Q0S4 / G68S 9. Electrode according to claim 8, characterized in that the electrically conductive metal core consists of nickel or copper coated with nickel. 10. Electrode according to claim 8 and 9, characterized in that the inner cladding layer (b) is at least 50 percent by weight Contains molybdenum. 11. Electrode according to claim 8 to 10, characterized in that the middle layer (c) is at least 50 percent by weight Contains molybdenum. 12. Electrode according to claim 8 to 11, characterized in that the outer cladding layer (d) is at least 50 percent by weight Contains molybdenum. 13. A method for producing an electrode according to claim 1 to 12, characterized in that the components forming the metal film are separated or as a mixture by means of the Sputtering technique is sprayed on until the intended film thickness is reached. 14. The method according to claim 13, characterized in that when a sacrificial metal is used, the metal film is then used leached with an alkali metal hydroxide. 030084 / 068S 15. The method according to claim 13 and 14, characterized in that that nickel and molybdenum are used as non-noble metals, palladium and platinum as noble metals, each also in the form of their alloys ι and used as sacrificial metal · Aiuminium. 16. The method according to claim 15, characterized in that the composition of the meta ^ füms is admitted that it corresponds to the formula · Ni Mo, where "a ^{M is} a value im a ώ Has the range from 5 to 95 atomic percent and in particular in the range from 15 to 85 atomic percent and the sum of a + b = 100 atomic percent is. 17. The method according to claim 15, characterized in that the composition of the MetaMfume is adjusted so that it corresponds to the formula Ni Mo Al, where "x" has a value in the range from 5 to 50 and preferably from 10 to 40 atomic percent, "z" has a value in the range from 5 to 45 and preferably from 10 to 40 atomic percent and the sum of x + y + z = 100 Atomic percent is. 18. The method according to claim 13 to 17, characterized in that that the surface of the substrate to be coated is pretreated in the following way for the application of the metal film will: a) washing with an organic solvent, b) washing with an alcohol, c) immersion in an inorganic acid, d) washing with water, 030034 / 0ISB e) washing with an alcohol and optionally f) contacting with dry inert gas, in particular nitrogen. 030064 / 06SS