NO832090L - Electrode assembly for electrolytic cells and methods of manufacture thereof - Google Patents

Description

Field of the invention

The invention relates to electrolytic cells, and more particularly cells, which produce an alkaline cathode product,

e.g. cells for the production of chloralkali. The invention relates more particularly to improved cathodes and cathode assemblies for use in chemical cells, and methods for producing these improved cathodes and assemblies.

The background of the invention

Electrolysis cells for the production of chemical reaction products are widely used. One area where these cells have found particularly extensive use is in the production of halogens and caustic compounds from salts of halogen. In such cells, the halogen is generally evolved on the anode, while the caustic compound is evolved near the cathode.

Considerable effort has recently been directed toward the development of improved anode designs that enable more efficient operation of the electrochemical cell. These efforts have borne fruit in the development of such improvements as dimensionally stable anodes sold under the trade name DSA. Anode improvements have facilitated the achievement of improved economics in the operation of chlor-alkali cells.

In cells where a separator, such as a diaphragm, separates the cell-defining anode and cathode compartments, considerable effort has been devoted to the development of improved separators. Separators which are based, for example, on perfluorocarbon copolymers and have pendant functional cation exchange groups, have been determined under certain cell operating conditions to offer the possibility of obtaining significant economic advantages in the operation of a cell.

A remaining inadequacy in the operation of electrochemical cells is associated with poor power yield, which originates in the distance between the separator and the anode and cathode used in the cell, as in most ordinary cells. There can be a number of reasons for maintaining this distance. A common reason concerns, for example, difficulties in releasing gas bubbles if an electrode is pressed into a relatively soft separator, such as a diaphragm-type separator.

The distance between the anode and the cathode in the electrochemical cell makes it necessary for the electric current to follow a path through the cell electrolyte or electrolytes where the resistance to electric current can be relatively high. The greater the distance between the anode and the cathode, the higher the voltage applied to the cell must generally be for the desired electrochemical reaction to take place. This requirement for increased voltage leads to increased electrical power consumption when operating the cell and thus to higher costs when operating the cell.

There are a number of proposals aimed at reducing the anode-cathode distance in a cell and thereby reducing the power consumption when operating the cell. A reduced anode-cathode distance has been proposed for cells separated by a hydraulically permeable diaphragm and a hydraulically impermeable membrane.

In diaphragm cells, for example, the distance between anode and cathode has been reduced until one or both electrodes come into contact with the diaphragm. A number of diaphragms are made of materials that cause the diaphragm to swell under cell conditions. Electrodes used in such cells are often made of a wire cloth or mesh cloth. Swelling of the diaphragm in contact with such an electrode can cause partial clogging of openings in the electrode and lead to poor release of gas bubbles formed near the electrode, and to limited flow of electrolyte from the anode compartment to the cathode compartment via the diaphragm. An unfortunate effect of this can be an overvoltage on the electrode which at least partially cancels power consumption gains that have been achieved by means of a reduced anode-cathode distance.

In membrane cells, the membrane, which generally consists of a cation exchange material, is normally quite thin, on the order of a few hundredths of a millimetre. Moreover, such membranes often exhibit significant dimensional stability, which makes it possible to replace electrodes near the membranes without significant risk of expansion of the membrane plugging openings in the electrode. However, when mesh electrodes or wire cloth electrodes are placed close to a membrane so that the electrodes will be within a distance of a few hundredths of a millimeter from each other, electrical current lines between the individual electrode elements will not always include all the membrane material that separates the anode and cathode from each other, and this will lead to to inefficient utilization of the membrane and to a corresponding increase in the voltage drop which can be attributed to an electrolyte flow through the membrane that is less than optimal.

Furthermore, when an electrode of the grid or mesh type comes into contact with a membrane, gas bubbles tend to agglomerate in openings in the grid, and these gas bubbles can often lead to an overvoltage on the electrode.

According to a proposal to achieve a closer anode-cathode distance, as described e.g. in US Patents 4,253,924, 4,253,922 and 4,250,013, a porous, possibly conductive, secondary electrode material is used to fill in particular the cathode compartments of the cell and to press a primary electrode into contact with a cell membrane. An interface between the primary electrode and the porous secondary electrode material can significantly contribute to the electrode resistance between these two and at least partially negate the advantages otherwise obtainable due to the large electrode surface area potentially offered by the secondary electrodes. materials.

A cell construction where a primary foam or network electrode is in contact with a cell dividing device offers opportunities for improved economy when operating the electrolysis cell.

Description of the invention

The invention relates to an electrode assembly for use in electrochemical cells, where a separator divides the cell into anode and cathode compartments. A porous network, generally in the form of a foam-like material with open pores, fills essentially the entire electrode compartment and is in strong physical contact with the separator. A current collector is intermetallically bonded to the electrode so that voltage losses associated with the transfer of electric current between the electrode and the current collector become negligible. An electrolyte distribution device is used to introduce electrolyte into and remove electrolyte from the electrode.

The electrode assembly according to the invention is produced by essentially completely filling an electrode compartment in a cell with the porous electrode material which is generally of the foam type, so that the foam will come into strong physical contact with the separator. The foam which has been made conductive is deposited by such methods where an electrode metal is coated on the foam to form a network electrode. A current supply device is arranged to be in electrical contact with the foam and is intermetallically bonded to the foam electrode in strong electrical contact with the foam or network electrode.

These network electrodes, generally cathodes, can be made conductive using common methods, such as impregnation with carbon or electroless plating. Electrodeposition can be carried out using common methods. These methods can be carried out in situ in the electrolysis cell or externally in relation to the cell.

An advantage of the method according to the invention for producing electrode assemblies is that the steps can be carried out in varying order. This means that the foam can first be cut to the right size, first made conductive or made conductive and electroplated before being cut. This flexibility enables a wide choice in the manufacture of cells for a variety of end applications.

When a porous foam or network electrode is in contact with the separator, only the thickness of the separator needs to form a distance between the anode and the cathode in the cell, whereby the voltage requirement associated with the passage of the electric current through the cell electrolyte is reduced. Forced circulation of electrolyte through the porous electrode can facilitate the suppression of the accumulation of bubbles near the surface of the separator in contact with the electrode, and it can act to reduce concentration gradients in the electrode compartment, especially near the separator. As concentration gradients and bubble formation can both contribute to overvoltages, a reduction of these can lower the voltages necessary to operate an electrochemical cell in which the electrode assembly according to the invention is used.

The above-mentioned and other special features and advantages of the present invention will be apparent from the detailed description of the invention below in connection with the accompanying drawing.

Description of the drawing

The drawing shows a cross-section through an electrochemical cell containing a cathode assembly according to the invention.

Best embodiment of the invention

In the drawing, an electrochemical cell 10 is shown in cross-section, according to the best embodiment a chloralkali cell. The cell comprises a housing 12, an anode assembly 14, a separator 16 and a cathode assembly 18.

The housing 12 can be made of any suitable or common material which is relatively chemically inert to the contents of the cell. If the electrochemical cell is to be used for the production of chlorine and caustic products from a solution of an alkali metal halide salt, which represents the best embodiment of the invention, the housing can be made of a plastic, such as polypropylene. In general, a cell lid (not shown) is placed over the upper part of the cell when it is operated.

The cell is divided into anode 22 and cathode 24 compartments by means of the separator 16. This separator can be hydraulically porous, like a diaphragm, or hydraulically impermeable, like a cation exchange membrane. If the separator is of the diaphragm type, the diaphragm may be produced using any of a number of well-known methods for producing a hydraulically permeable separator. Such diaphragm separators generally include asbestos fibers if they have been made for use in a chloralkali cell.

If the cell is divided by a membrane, the membrane will

in general separate the departments 22, 24 from each other on

such a way that free movement of fluid between the departments

is excluded. It is necessary for this membrane to transfer electrical current between the compartments, and such membranes are therefore generally able to transfer a particular ion or charged materials between the compartments. If the electrolyte content in the electrochemical cell comprises aggressive compounds, it is desirable that the membrane is made of a compound which is essentially resistant to aggressive attack by the electrolyte in the compartments.

For a chloralkali cell according to this best embodiment, the membrane can be made of a suitable or common material which is resistant to aggressive materials in electrolytes in each compartment 22, 24. A highly preferred material is a perfluorinated copolymer with pendant functional cation exchange groups. These perfluorocarbons are a copolymer of at least two monomers, one monomer consisting of vinyl fluoride, hexafluoropropylene, vinylidene fluoride, trifluoroethylene, chlorotrifluoroethylene, perfluoroalkyl vinyl ether, tetrafluoroethylene or mixtures thereof.

The second monomer is often selected from a group of monomers which generally contain a pendant SC₂F group or sulfonyl fluoride group. Examples of such other monomers can generally be represented by the formula CF2=CFR-^SO2F. R-^ in the general formula is a bifunctional, perfluorinated radical which generally comprises 1-8 carbon atoms, but which can occasionally be as many as 25. A limitation regarding the general formula is a general requirement that at least one fluorine atom must be present on the carbon atom which is a neighboring atom in relation to the -SC^F group, especially if the functional group is in the -(-SC^NHjmQ form. In this form, Q can be hydrogen or an alkali or alkaline earth metal cation, and m is the valency of Q. in the general formula may have any suitable or conventional structure, but it has been found preferred that the vinyl radical comonomer is linked to the R₂ group via an ether bond.

Such perfluorocarbons are generally available

in trade, such as under the trademark NAFION^ Perfluorocarbon copolymers containing perfluoro-(3,6-dioxa-4-methyl-

7-octenesulfonylfluoride) comonoras, have been shown to be particularly useful for Cl2~ cells. If sodium chloride salt solution is used for the production of chloralkali products from an electrochemical cell, it has proven advantageous to use membranes whose main mass consists of a perfluorocarbon copolymer with suspended functional groups derived from sulfonyl fluoride, and a relatively thin layer of perfluorocarbon copolymer with carbonyl fluoride derived functional groups near one membrane surface.

The anode compartment 22 comprises an anode 26 and an anodic power supply device 28. The power supply device 28 is connected to an electrical power supply (not shown). An electrolyte 30 generally fills voids in the anode compartment. This electrolyte 30 or anolyte is generally constituted by a solution of an alkali metal halide salt prepared in accordance with well-known methods. The composition of these "salt solutions" is well known in the industry.

The anode 26 is made of a suitable or ordinary material which is suitably resistant to the anolyte and halogen compounds which are formed in the electrolysis cell. Titanium with an applied coating of one or more metals or metal oxides, such as ruthenium oxide, is typically used. DSA anodes are suitable for use in a cell of the type shown in this preferred embodiment.

The anode 26 can be placed immediately close to the separator or at a distance from it. According to an equally preferred alternative embodiment of this preferred embodiment, a catalyst, such as ruthenium oxide, is attached directly to the separator, i.e. a membrane, in contact with a grid or mesh-like current collector.

The cathode compartment 24 comprises a cathode assembly 34. It comprises a foam-like network cathode 36, a cathode current supply device 38 and an inlet 40 and outlet 42 for electrolyte. The cathode compartment is generally filled with an electrolyte 4 2 or catholyte comprising a hydroxide of the alkali metal for the halide salt which forms the salt solution. This catholyte also fills the part of the cathode compartment that is not occupied by the cathode 36.

The cathode is of the network type with open pores. Although the pores may be of any suitable or customary size, pores with a size between 0.5 and 10 µm are preferred, with pores having a size between 1 and 5 µm being strongly preferred. By open pores is meant that the cathode is essentially hydraulically permeable over its structure.

The cathode 36 comprises a substrate which is formed from

a resin-like material or plastic material, such as urethanes, polyesters, olefin polymers, such as polypropylene or polyethylene, or other suitable or common materials. The substrate is used in the form of a foam which does not need to be a rigid foam.

The substrate is at least partially encapsulated in one or more coatings of at least one conductive cathode metal. These coatings can be applied to the substrate in any suitable or conventional manner, e.g. by electrodeposition. For electrodeposition, it is generally necessary that the resin-like substrate or plastic foam substrate is electrically conductive. The foam substrate can generally be made conductive by using

by suitable or common well-known methods, such as electrolysis-free plating or by impregnation with a conductive material, such as carbon.

The application of the coating metal makes the foam network electrically conductive and thereby suitable for use as a cathode. Although a variety of cathode metals are known, nickel and/or copper are preferred for the best embodiment of a chloralkali cell according to the present disclosure. Nickel in particular seems to act in such a way that it supports the electrochemical reaction at the cathode. The metal coating on the substrate need only have a sufficient thickness and a sufficient continuity that it will offer a negligible resistance to electric current through the cathode to a point of collection of electric current.

The network cathode is held in the cathode compartment 24 generally in contact with the separator. As the foam network becomes relatively rigid when the metal coating is applied, it is often preferred that the foam has such a size that it can be received in

the cathode compartment before the metal coating is applied.

The network cathode acts as the primary electrode in the cell. Electrical current is supplied to the primary network cathode via the cathode current supply device 38. It is highly preferred that the electrical resistance due to any electrical connection between the network cathode and the current supply device 38 be negligible. This low electrical resistance is preferably achieved by making the connection intermetallic - One method of attaching the cathode current supply device to the network cathode is to introduce the current supply device 38

in the foam substrate for the network cathode 36 before the plating metal is applied. the introduction can be done by splitting up the foam substrate of the network construction and introducing the power supply device, the power supply device being heated to a temperature higher than the foam's melting temperature and immersed in the foam, and simultaneously extruding or shaping the foam with the power supply device embedded in it. Intermetallic connection between the current supply device and the network cathode can then be achieved by electrically depositing the metal for coating the foam substrate, while the current supply device is used to supply electric current for the electrical deposition of the coating metal.

The inlet 40 and the outlet 4 2 are arranged so that the catholyte can be circulated through the foam network cathode. As the network cathode is porous, the catholyte is relatively easily forced through the cathode using any or ordinary means, such as e.g. pumping. One or more inlets and/or outlets can be arranged depending on the size of the cathode, the desired degree of circulation or other variables.

During use of the electrolytic chloralkali cell according to the best embodiment, metal ions, usually sodium ions, will pass through the separator from the anode compartment and at least partially in accordance with the electrical current through the cell. These sodium ions react at the cathode with hydroxyl radicals that are formed by the splitting of water at the cathode, but remain ionized in solution. As operation of the electrochemical cell continues, the concentration of these metal ions from the separator can typically increase and cause a concentration gradient resistance to further migration of metal ions. In order to overcome this resistance, a higher cell voltage between the anode and the cathode in the cell will normally be required, with the resulting increased power requirement for operating the cell. Circulation which tends to reduce this concentration gradient resistance or the overvoltage can prevent increased power consumption when operating the cell.

The splitting of water that takes place at the cathode can form hydrogen, which is obtained in the form of bubbles. If these bubbles adhere to the cathode, the bubbles can effectively reduce cathode surfaces available for the electrochemical reaction and lead to electrical resistance or overvoltage. Circulation of catholyte through the network cathode can reduce the adhesion of the bubbles and thereby prevent an increased working voltage for the cells that would otherwise have been necessary to compensate for this bubble overvoltage.

The catholyte volume that it is desired to circulate through the cathode can vary, as lower current amounts per unit of time is generally preferred to achieve a favorable power consumption. Flow rates of 1- - 250 liters per minute per m 3 network cathode will generally be preferred. However, it is only necessary to use a flow rate which is sufficient to avoid bubble formation and concentration overvoltage.

It is not necessary that the network cathode 36 fills the cathode compartment 24 completely. The network foam cathode only needs to fill parts of the cathode compartment near the separator and be in physical contact with the separator. If the network cathode does not completely fill the cathode compartment, the remainder of the cathode compartment may be filled with a resistant material, such as a foam, which is capable of acting to keep the network cathode biased in contact with the separator. Alternatively, a network cathode which does not completely fill the cathode compartment may be held in tensioned contact with the separator in any suitable or conventional manner, e.g. by using a springy grid.

According to an alternative to the best embodiment, the cathode current collector is first embedded in the foam substrate for the network cathode. The foam substrate is adapted to the cathode section of the cell. If the foam substrate has not previously been made electrically conductive by impregnation with carbon or a similar process, a preliminary metal coating is applied to the foam substrate by plating without the use of electrolysis. This plating without the use of electrolysis can be carried out in the electrolysis cell, and according to the most preferred embodiments it is primarily carried out to make the foam substrate conductive for subsequent electrodeposition of cathode metal.

The subsequent electrodeposition of metal on the network cathodic disassembly that is created is preferably carried out in the electrolysis cell. Plating solution is introduced into the cathode compartment, and the cathodic current supply device is connected to an electrical current source. Metal ions in the plating solution will thereby be deposited on the network foam substrate using well-known plating methods.

When using the electrochemical cell, this catholyte metal which has been deposited on the foam substrate is cathodically protected against the impact of aggressive chemicals in the catholyte. In a chloralkali cell where the separator is a cation exchange membrane, metal ions, such as sodium ions, will pass through the membrane from the anode compartment and react with the hydroxyl radicals formed on the network cathode, producing a metal hydroxide solution comprising the catholyte. Hydrogen gas is emitted. By periodically removing part of the catholyte from the catholyte which is circulated through the network cathode and by supplementing water, the metal hydroxide concentration in the catholyte can be regulated within desired well-known preferred limits in the operation of a membrane chloralkali cell.

If the network separator is in contact with a porous separator, such as a diaphragm, salt solution containing ions of the metal will flow through the diaphragm to the cathode compartment and be carried along with catholyte circulating through the cathode compartment. Removal of circulating catholyte will, in a well-known manner, compensate for the used volume of salt solution passing through the separator, and regulate the metal hydroxy concentration in the circulating catholyte.

Anodes can be made for use in electrolytic cells in the same way as the formation of the foam or network cathode assemblies described above. Such foam or network anodes can be used in electrochemical cells and essentially in physical contact with a separator that separates the anode and cathode compartments in the cell. It is often advantageous that anodes which have been manufactured according to the present invention comprise a top coating or electrocatalytic coating which has been applied after the foam or network anode assembly has been formed. Typical coatings will include coating systems commercially designated as DSA or TIR-200J3, or other suitable or common electrode coatings.

The invention is described in more detail in the examples below.

Example 1

A nickel network cathode was fabricated by first attaching a nickel current distributor, which had been fabricated from a nickel grid plate, to a conducting rod. The grid and conductive rod were then heated to above the melting point of polyurethane foam, the foam having been sized to occupy substantially the entire cathode compartment of an electrolysis cell. The hot conducting rod with the grid was introduced into the foam and cooled. On cooling, foam was melted due to the heat from the conductive rod and grid and fused to the grid. The resulting cathode assembly was then plated. Such plated cathodes worked effectively in an electrolysis cell when the foam contained between 4 and 18 pores per cm (ppc).

For plating, the cathode assembly was immersed in a bath that had room temperature and consisted of an aqueous solution of 10 g/l stannous chloride and 10 ml hydrochloric acid (20° Be) per litres. After 5 minutes, the cathode assembly was gently rinsed with

water at room temperature and then immersed in an aqueous solution of 0.5 g/l PdCl2 and 10 ml hydrochloric acid per liter for 5 minutes. After rinsing with water, the foam cathode assembly was i

10 minutes and at 50° C immersed in a mixture comprising 1 liter of an aqueous solution of 4 5 g/l nickel chloride hexahydrate, 50 g/l ammonium chloride, 100 g/l sodium nitrate, 0.5 1 ammonium hydroxide per liter and 27.3 ral of a 450 g/l aqueous solution of sodium hypophosphite. At these initial steps, a nickel coating was electrolytically deposited on the cathode assembly. The electrolytic plating was followed by electrolytic nickel plating. The cathode assembly was immersed in an aqueous solution of 141 g/l nickel chloride hexahydrate, 2 91 g/l nickel sulfate hexahydrate and 4 5 g/l phosphoric acid, the pH of the solution being regulated to 4.5 - 6.5 using hydrochloric acid. Cathode disassembly was done cathodically in relation to nickel anodes that were mounted approx. 3.8 cm from the surfaces of the foam cathode assembly, and plating was performed at 2.25 V for 3 hours at 30-40° C. Plating was continued until a coating 10 µm or thicker had formed on the foam.

After 1.5 hours of plating, the polyurethane foam can possibly be ashed by placing the network in a flame or an oven until the foam has burned out. After rinsing, plating can continue.

Example . 2

A nickel network cathode was prepared as described in Example 1, except that after the electroless plating was completed, the cathode assembly was immersed in an aqueous solution of 250 g/l nickel chloride hexahydrate and 50 g/l zinc chloride. The solution was kept at 45° C and at a pH of approx. 4.5 which was regulated by the addition of HC1. Nickel and nickel-zinc anodes were placed close to surfaces of the cathode assembly for approx. 1 hour and made anodic relative to the cathode assembly at 2.0 V. The solution was stirred during the electrolytic plating.

After the electrolytic plating was finished, the cathode assembly was immersed in an aqueous solution of 200 g/l sodium hydroxide for 1 hour at 75°C.

Example 3

The preparation steps according to Example 1 were repeated, except that electrolytic plating was carried out with an aqueous solution of 265 g/l cobalt chloride hexahydrate, 90 g/l zinc chloride and 30 g/l boric acid at 50°C and a pH of 4 which was maintained by adding of hydrochloric acid. Zinc anodes that were installed approx. 3.8 cm from the surfaces of the cathode assembly, was used to plate zinc on the cathode assembly at 0.6 V during 1 hour.

Example 4

A cathode assembly was prepared as described in Example 1, except that the current distribution grid was made of copper instead of nickel. A copper coating was deposited on the polyurethane foam without electrolysis by submerging the cathode assembly for 5 minutes in sequence in two baths at room temperature. The first bath contained 10 g/l stannous chloride and 10 ml/g hydrochloric acid (20 Be°). The second bath contained 0.5 g/l palladium chloride and 10 ml/l hydrochloric acid (20 Be°). After each bath, rinsing with water at room temperature was carried out. The cathode assembly was then impregnated for 20 minutes at room temperature in a commercially available copper solution for electroless plating made by mixing 777A and 777M "Cu Electroless Makeup" in a ratio of 1:1:8 in water, and then gently rinsed.

The cathode assembly was then immersed in an electrolytic plating bath of an aqueous solution of 40 g/l copper in the form of copper sulphate and 10 g/l sulfuric acid and with a pH of 1 which was maintained by the addition of sulfuric acid at room temperature. Electrolytic deposition of copper was carried out by placing the copper anode at a distance of 3.8 cm from the radiation surface of the cathode assembly which was made cathodic in relation to the copper anodes, and by applying a voltage of 1.5 V across these for approx. . 1 hour. The polyurethane foam can optionally be washed as described in Example 1, after approx. half of the electrolytic deposition has taken place.

As copper as such can be highly susceptible to corrosion/attack in a chloralkali cell cathode compartment, the copper electrolytically plated cathode assembly was then advantageously coated with nickel by carrying out the electrolytic plating step described in Example 1.

Example 5

A cathode assembly was produced by attaching a current supply device to a current distribution grid made of nickel as described in Example 1. The current distribution grid and the current supply device were, in a heated state, immersed in polyurethane foam as described in Example 1, and a foam or network cathode assembly was obtained.

The foam cathode assembly was then electrolytically plated with copper as described in Example 4, and it was then applied with an electrolytically deposited copper coating as described in Example 4. An electrolytically deposited nickel coating was then applied to the foam cathode assembly as described in Example 1.

Nickel and zinc were then electrolytically deposited

on the network cathode disassembly as described in Example 2.

Example 6

A cathode assembly was prepared as described in Example 1. After the electrolytic deposition of nickel, a palladium oxide-zirconium oxide coating was applied to the cathode. The application was carried out by grinding a slurry of 10 ml of water, 1 ml of acetic acid, 1.5 g of palladium chloride particles and 2 g of zirconium nitrate in a ball mill for 2 hours to stabilize the palladium chloride and reduce the size of any undissolved material particles. The coating was then coated on the nickel-plated network cathode assembly of Example 1 which had been ashed as described in Example 1. The coated coating and cathode were heated for 3 minutes at 125°C and then cured for 7 minutes at 500°C in air to convert the palladium chloride to palladium oxide and the zirconyl nitrate to zirconium dioxide. Four further coats of the coating were then applied and cured. In other manufacturing methods, as much as half of the palladium chloride was replaced with cobalt and/or nickel when manufacturing the cathode.

Example 7

A foam or network cathode assembly was made in accordance with the steps described in Example 1, including electrolytically. application of a nickel coating. After the electrolytic plating with nickel, the foam cathode assembly was immersed in an electrolytic plating bath of 3.8 liters of water, 20 g of sulfamic acid and 20 g of ruthenium in the form of ruthenium sulfamate. The bath was maintained at a temperature of 27 - 38°C, and the electrolytic "deposition" was carried out using platinum anodes placed at a distance of about 3.8 cm from the surfaces of the foam cathode assembly. This was made cathodic, and current was conducted between the platinum anodes and the foam cathode assembly with a current density of 0.15 A/cm<2> and a voltage of 1.75 V.

Example 8

A foam or network cathode assembly was prepared as described in Example 1, including electrolytic deposition of a nickel coating. After the electrolytic nickel plating, the foam cathode assembly was immersed in a stirred plating solution containing 5 ml of H 3 Pt(SO 3 ) 2 OH in 150 ml of water and was adjusted to a pH of 3 using 1 N NaOH and comprising approx. 15 ml of a 30% hydrogen peroxide solution. The foam cathode assembly was impregnated in this peroxide-containing solution for approx. 1 hour during which the pH gradually decreased to 1. The pH of the solution was then readjusted to 3 using 1 N alkali hydroxide solution, and the solution and cathode assembly were heated to 80°C while the peroxide-containing solution was stirred until all peroxide was evolved - bubbles stopped. After washing, the foam cathode assembly was dried at 125 - 150°C.

Example 9

A foam cathode assembly was prepared as described

in Example 1, comprising electrolytic application of a nickel coating. Sintering or ashing was carried out as described in Example 1. After the nickel coating was electrolytically deposited, an aluminum coating was applied by plasma spraying to the surfaces of the foam cathode assembly. The assembly was then heat treated for 8 hours at 760° C in a nitrogen atmosphere, whereby the nickel and aluminum diffused into each other.

When operating a chloralkali cell using such a cathode, the aluminum will be leached from the surfaces where the mutual diffusion has taken place, by the action of hot NaOH in the cell. The leaching provides a greater surface area on the foam cathode assembly than the area that would have been available without the mutual diffusion and leaching.

Example 10

A foam or network cathode assembly was prepared as described in Example 1, except that electrolytic plating was carried out by immersing the foam cathode assembly in an aqueous solution of 240 g/l divalent iron sulphate at a pH of 2.8 - 3.5 and a temperature of 32 - 66° C. Cathode disassembly was done cathodically in relation to iron anodes which were placed at a distance of approx. 3.8 cm from the surfaces of the cathode assembly. The plating was carried out for 1 - 3 hours at 0.04 - 0.11 A/cm 2 . The bath of divalent iron sulfate was stirred during the electrolytic deposition to help achieve a uniform coating on the foam cathode assembly.

Example 11

A foam or network cathode assembly was made as described in Example 4 and then electrolytically applied an iron coating as described in Example 10.

Example 12

A foam or network cathode assembly was made as described in Example 1, including intermediate sintering or ashing during the electrolytic deposition process. The cathode assembly was then plasma sprayed with a mixture of 80% nickel, 10% molybdenum and 10% aluminium. The molybdenum and aluminum were then leached with hot sodium hydroxide while operating in a chloralkali cell. A cathode assembly with a substantially increased surface area was achieved.

Example 13

Example 1 was repeated, except that polyurethane foam with a thickness of 1.25 cm was used as the starting material and produced by laminating four foam layers each with a thickness of 0.32 cm. A structure was obtained that could not be distinguished from the structure obtained in Example 1.

Example 14

Two electrolysis cells were operated in parallel. One cell was provided with an anode made as described in Example 1. The cathode in this first cell was a perforated nickel plate. The cell contained a separator of Nafion<®>295 which is a cation exchange material suitable for use in chloralkali electrolysis cells. The cell was supplied with an aqueous stream of sodium bicarbonate and sodium carbonate in a ratio of 1:1.

The second cell was equipped in the same manner as the first cell, except that the cathode in the second cell was a porous foam or network cathode made as described in Example 1. This second cell was operated with the same feed materials as the first cell. .

In both cells, the electrodes were in substantial physical contact with the separator. The first cell was operated at a voltage of 2.82 V and a current density of 0.15 A/cm 2 , while the second cell was operated at a voltage of 2.63 V and a current density of 0.15 A/cm 2 The first cell exhibited a voltage of 3.33 V at a current density of 0.31 A/cm 2 , while the second cell exhibited a voltage of 3.05 V at a current density of 0.31 A/cm<2 >. The current yield of the cells was the same within the limits of experimental error. Due to the presence of the nickel network or foam cathode assembly in the second cell, this was operated at a significantly lower voltage which, in technical terms, would result in a lower need for electrical power to operate the cell. The nickel network or foam cathode assembly provided an operating advantage of 200 mV at 0.15 A/cm<2> and 280 mV at 0.15 A/cm<2>.

Example 15

Two electrolysis cells were operated in parallel. One cell comprised an anode which was made of a titanium mesh cloth with diamond-shaped openings of approx. 0.64 cm x 0.32 cm and coated with a DSA electrocatalytic coating for the production of chlorine. DSA-coated titanium mask cloth is commercially available and generally includes ruthenium oxide in the form of a surface coating. The cathode in the first cell was made of a nickel mesh cloth with diamond-shaped openings also of approx. 0.64cm x 0.32cm. The cell contained a separator of Nafion^295, and both the anode and cathode were in intimate contact with the Nafion^ separator. The cell compartment delimited by the separator and containing the anode was supplied with a sodium chloride solution (170 g/l).

The second cell of the parallel cell pair was equipped in the same manner as the first cell, except that its cathode was a foam or mesh cathode assembly made as described in Example 1. This cathode as well as the anode 1 of the second cell were in intimate contact with the separator. The feed material to the second cell was the same as the feed material to the first cell. Both cells were operated at 0.31 A/cm<2> of membrane surface area, the first cell requiring 3.84 V and the second 3.18 V for electrolysis. The current yields were the same. The use of a network foam electrode gave the second chlorine production cell a voltage advantage of 660 mV at 0.31 A/cm .

Example 16

Two cells were operated in parallel. One cell contained a titanium mesh anode with an applied electrocatalytic DSA coating. The openings in the cloth were approx. 0.32cm x 0.32cm. The cathode in this first cell was made of a nickel mesh cloth with the same opening dimensions. The anode and cathode were in contact with and separated from each other by a Nafion® 2 90 cation exchange membrane. An aqueous solution containing 170 g/l sodium chloride was introduced into a compartment of the cell which was bounded by the separator and contained the anode.

The second cell of this parallel pair contained an identical anode and separator, but had been made using a nickel foam or network cathode assembly prepared as described in Example 1. The feed material to this second cell was the same as the feed material to the first cell. The first cell was operated at 3.28 V in the production of chlorine at a current density of approx. 0.3 A/cm<2>measured on the separator, and the second cell achieved a working voltage of 3.13 V at the same current density. The current yields for the two cells were the same.

Example 17

Two cells were operated in parallel. In one cell, the anode was made of efl porous foam network anode construction made as described in Example 1. The first cell contained a cathode made of a perforated nickel plate. The foam or mesh anode assembly and nickel plate were substantially in contact with a microporous polypropylene separator. 300 g/l sodium carbonate was introduced into this cell.

The second cell contained an identical anode and separator, but included a foam or mesh cathode assembly in contact with the separator, and the foam or mesh cathode was made as described in Example 1. The same feed material was introduced into this second cell. The first cell was operated at 2.72 V and a current density of 0.15 A/cm 2 , while the second cell had an operating voltage of 2.44 V at the same current density. The current yields for the two cells were the same within the limits of experimental error. The cell with a network cathode achieved an operating voltage advantage of 280 mV compared to an identical cell without a network cathode.

Example 18

Two cells were operated in parallel. The first cell contained a cathode made of a perforated nickel plate in intimate contact with a porous ceramic aluminum oxide separator. The anode in this first cell was a sheet of metallic titanium mesh with openings of approx. 0.64 cm x 0.32 cm and coated with TIR2000 which is an anode coating from Diamond Shamrock and which is useful for the development of oxygen. This first cell was fed with 300 g/l sodium carbonate.

The other cell was equipped in the same way as

the first cell, except that the anode in the second cell was a foam or mesh anode made as described in Example 1. The feed material for this second cell was the same as for the first cell. The first cell was operated at 3.4 V at 0.15 A/cm<2>, while the second cell with the foam or network anode assembly was operated at 2.72 V and the same current density. The current yield for two de., two \ cells

were the same within the limits of experimental error. The second cell with the foam or mesh anode assembly in contact with the separator achieved an operating voltage advantage of 0.68 V compared to a cell with a perforated nickel plate anode in contact with the separator.

Claims (20)

1. Electrolysis cell with anode and cathode compartments which are delimited by a separator, characterized in that it comprises (a) a primary open-pore network cathode that at least partially fills one of the compartments and is in substantial physical contact with the separator, (b) a power supply device intermetallically bonded to the electrode, whereby electric current is distributed to the electrode with negligible electrical resistance between the electrode and the power supply device, and (c) a distribution device, by which electrolyte can be circulated into the electrode compartment and out of the electrode compartment. 2. Electrolysis cell according to claim 1, characterized in that the electrode is an anode. 3. Electrolysis cell with anode and cathode compartments delimited by a separator, characterized in that it contains a cathode assembly comprising (a) a primary network cathode with open pores which substantially fills the cathode compartment and is in substantial physical contact with the separator, (b) a cathodic power supply device intermetallically bonded to the cathode, whereby electric current is distributed to the cathode with negligible electrical resistance between the cathode and the power supply device, and (c) a cathode distribution device, whereby catholyte can be circulated into the cathode compartment and out of the cathode compartment. 4. Electrolysis cell with a narrow spacing, where the anode and cathode compartments in the cell are delimited by a separator and at least one electrode in the cell is in substantial physical contact with the separator, characterized in that it contains an electrode assembly with a narrow spacing comprising (a) at least one open pore primary network electrode with a size of 0.0127 - 0.254 mm and in substantial physical contact with the separator, substantially filling at least one compartment of the cell, (b) a power supply device which intermetallically connects the electrode to a source of electric current, whereby electrical resistance between the power supply device and the electrode is rendered negligible, and (c) at least one electrolyte inlet for introducing electrolyte into the electrode construction and at least one outlet for removing catholyte from the electrode construction. 5. Electrolysis cell according to claim 4, characterized in that the electrode is an anode. 6. Narrowly spaced electrolysis cell, where anode and cathode compartments in the cell are delimited by a separator where the cathode in the cell is in substantial physical contact with the separator, characterized in that it contains a narrowly spaced cathode assembly comprising (a) a primary network cathode with open pores with a size of 0.0127 - 0.254 mm in substantial physical contact with the separator and as it substantially fills the cathode compartment of the cell, (b) a cathodic power supply device which intermetallically connects the cathode to a source of electric current, whereby electrical resistance between the power supply device and the electrode becomes negligible, and (c) at least one catholyte inlet for introducing catholyte into the cathode structure and at least one catholyte outlet for removing catholyte from the cathode structure. 7. Method for in situ producing an electrode assembly for use in an electrolysis cell with anode and cathode compartments that are delimited by a separator, and with at least one electrolyte inlet and outlet to the compartments, characterized in that (a) at least one compartment is substantially completely filled with an open cell plastic skin such that the foam is in substantial physical contact with the membrane; (b) an electrically conductive metallic power supply device is provided for each compartment filled with foam, the power supply device being at least partially submerged in the plastic foam, (c) an electrolytic deposition plating solution is brought into contact with the open pore plastic foam until an electrically conductive coating of the desired thickness has been deposited on the foam; (d) the foam is made cathodic, and (e) an electroplating solution is circulated through the foam electrode until an electrolytically deposited deposit of the desired thickness has been formed on the foam. 8. Method according to claim 7, characterized in that the foam is removed with heat during the electrolytic deposition. 9. Method according to claim 7, characterized in that the foam has an open porosity of 0.5 - 10.0 um. 10. Method according to claim 7, characterized in that a metallic nickel coating is deposited on the foam cathode using the plating solutions. 11. Method for in situ producing an .-electrode assembly for use in an electrolysis cell with anode and cathode compartments that are delimited by one separator, and with at least one electrolyte inlet and outlet to each compartment, characterized in that (a) at least one compartment is substantially completely filled with an open cell conductive plastic skin, the foam being in substantial physical contact with the membrane, and (b) an electrically conductive metallic power supply device is provided for each foam-filled compartment and is at least partially submerged in the plastic foam; (c) the foam is made cathodic, and (d) an electrolytic plating solution is brought into contact with the foam electrode until an electrolytically deposited deposit of the desired thickness has been deposited on the foam. 12. Method according to claim 11, characterized in that the foam is of a type which is impregnated with an electrically conductive material. 13. Method according to claim 11, characterized in that a solution for electrolytic triple plating is brought into contact with the foam cathode in order to deposit a desired metal coating on it before the cathode is made cathodic. 14. Method according to claim 7 or 11, characterized in that an electroplating solution is used which comprises a significant proportion of nickel ions for electrolytic deposition on the foam cathode. 15. Method according to claim 7 or 11, characterized in that a separator is used which is a membrane which is hydraulically impermeable to liquid between the compartments, but which will easily enable free movement of cations between the compartments. 16. Method according to claim 15, characterized in that a membrane is used which comprises a significant proportion of a perfluorocarbon copolymer with suspended sulfonyl- or carbonyl-based functional cation exchange groups. 17. Assembly according to claim 1, 2, 3, 4, 5 or 6, characterized in that the separator is a membrane which is hydraulically impermeable to liquid between the compartments, but which will easily enable the cations to move freely between the compartments. 18. Assembly according to claim 17, characterized in that the membrane comprises a significant proportion of a perfluorocarbon copolymer with suspended sulfonyl- or carbonyl-based functional cation exchange groups. 19. Method according to claim 7 or 11, characterized in that the current collector is immersed in the foam by the current collector being heated and immersed in the foam. 20. Method for producing a cathode assembly for use in an electrochemical cell with anode and cathode compartments that are delimited by a separator and have at least one catholyte inlet and at least one catholyte outlet, characterized in that (a) a porous network foam cathode material is selected and fitted into the cathode compartment of the cell such that the foam substantially fills the cathode compartment and is in substantial physical contact with the separator; (b) the foam is made electrically conductive; (c) a cathodic current supply device is provided and placed in electrical contact with the cathode, and (d) a cathode metal is electrolytically deposited on the foam cathode.