JPH0121231B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The term "M&E" refers to a combination of a membrane and an electrode, with an electrically conductive and catalytically active membrane present on one or both major planar surfaces of the membrane. A structure consisting of a substantially planar sheet-like ion exchange membrane having a large number of particles. Catalytically active particles act as particulate electrodes when M&E is used in electrochemical cells. M&
The E structure is a solid polymer electrolyte.
electrolyte) or SPE structure.

An "M&E cell" is an electrochemical cell that uses an M&E structure. Such cells can be operated as electrolyzers to produce electrochemical products, or alternatively as fuel cells to produce electrical energy. The electrolytic cell can be used, for example, for the electrolysis of alkali metal halides, such as sodium chloride, or alternatively for the electrolysis of water.

M&E cells are known in the art and are disclosed in numerous US patents, including: 4293394; 4299674; 4299675; 4319969;
4345986; 4386987; 4416932; 4457822;
4469579; 4498942; 4315805; 4364815;
4272353; and 4394229.

In M&E cells, gaseous substances often form on the catalytically active particles. While the M&E cell is in operation,
Gas bubbles away from the particles (which act as electrodes) and into the electrolyte that is in contact with the M&E cell. However, gaseous substances that form within the particle pores or at the particle/membrane interface must diffuse through the particle pores before entering the electrolyte and being removed. Since gas is produced faster than it can escape, it can accumulate within the catalytically active particles or at the particle/membrane interface, thus causing M&
The operating efficiency of the E cell will decrease. Even more undesirably, some of the gas permeates through the membrane and contaminates the resulting product on the other side of the membrane. In a chlorine-alkali cell, hydrogen is produced on one side of the membrane and chlorine on the other side of the membrane, but it is possible for hydrogen to permeate through the membrane and contaminate the chlorine, or vice versa. things happen. The explosive nature of chlorine/hydrogen mixtures makes such contamination even more dangerous.

The prior art has attempted to overcome the gaseous buildup problem by creating porous electrodes for M&E cells. For example, U.S. Pat.
This is disclosed in No. 4276146.
Porous M&E electrodes can be formed by incorporating pore formers, such as sodium chloride, into the catalytically active material during the M&E cell manufacturing process. This sodium chloride is later leached out,
Exclude from porous M&E structures. However, the use of such a coating does not solve the gas diffusion problem, since hydrogen contamination with chlorine is not significantly reduced. Furthermore, porous catalytically active particles have low strength and cannot withstand the effects of gas evolution. Therefore, the number of catalytically active particles decreases, and the efficiency of the cell decreases.

The present invention utilizes specially designed M &
Provide an E structure.

M&E electrode coatings are made using fairly expensive materials. The present invention can reduce the amount of catalytic material used in the electrode without sacrificing the catalytic activity and efficiency of the coating.

In prior art M&Es, conductive window screen fabrics are used to support the M&Es. However, screen fabrics are not completely satisfactory because their surfaces are not uniform.
When pressing a screen fabric onto catalytically active particles or a planar sheet-like membrane, some portions of the screen penetrate deeper into the membrane than other portions. This method results in uneven contact of the electrode coating and membrane with the screen and uneven transfer of electrical energy across the surface of the membrane. Furthermore, as the screen penetrates the membrane, some parts of the membrane become more susceptible to rupture.

Another problem with the use of screen fabrics is that the membrane can be torn or broken by the pine tresses (elastic devices) used to support the current collector for the catalytically active particles on the surface of the membrane. This is something that must be prevented from happening. Therefore, prior art screen fabrics do not provide as much protection as is provided by the substantially flat, conductive screen of the present invention.

The present invention provides a M
&E support structures.

In particular, the present invention is a membrane/electrode composite structure comprising:
A membrane/electrode composite structure comprising a substantially planar ion exchange membrane having multiple interconnecting paths of catalytically active particles bound to at least one surface of the membrane is provided.

The present invention further relates to a substantially planar, electrically conductive screen having a large number of apertures passing through the screen, the apertures occupying up to about 75% of the surface area of the screen and containing a large number of catalytically active particles. disposed on at least a portion of one planar surface of the screen and in physical and electrical contact with said planar surface, an ion exchange membrane disposed between the catalytically active particles and the planar surface of the screen. The particles are bound together in such a way that they are sandwiched between the membrane and the screen. The present invention further provides coating at least one surface of a substantially planar screen template with a plurality of catalytically active particles, wherein the screen template has a plurality of apertures, the apertures being the largest of the surface areas of the screen template. contacting the ion exchange membrane with the coated surface of the screen template; transferring the catalytically active particles from the screen template to the membrane; removing the screen template; and transferring the catalytically active particles to the membrane. A method of making an improved membrane/electrode composite structure is provided.

The present invention further provides for coating a portion of at least one surface of a substantially planar conductive screen with a solution/dispersion of catalytically active particles and a solvent/dispersant, wherein said screen has a plurality of apertures. contacting the coated surface of the screen with an ion exchange membrane; and bonding the coated screen to the membrane. /Provides a method for producing an electrode composite structure.

M&E structures with interconnecting channels of catalytically active particles deposited on a membrane, unlike prior art M&E structures with substantially continuous coatings of catalytically active material, are very difficult to use in electrochemical cells. It was found to operate with high efficiency. It is speculated that the increased efficiency is due to the open area present between interconnecting channels of catalytically active particles on the membrane. These open areas provide an electrically inert space for the removal of gases generated at the catalytically active surface. Additionally, the width of the interconnect is such that it provides a short path for the escape of the gas generated at the interface between the catalytically active particles and the membrane, so that blockage of the membrane by gas is minimized. The pattern of catalytically active particles is designed such that the interconnections of the particles and the escape paths for gas from around them have a flow resistance that is less than the flow resistance when passing through the membrane. Therefore, it is easier for gas to escape from and around the interconnections of the catalytically active particles than to pass through the membrane and into the opposite compartment. The size, shape, and thickness of the interconnecting channels of the catalytically active particles of the present invention depend on the type of ion exchange membrane used. That is,
Membranes with high gas permeation resistance can use larger particle interconnections, whereas membranes with low gas permeation resistance require smaller particle interconnections. For example, a chlor-alkali electrolyzer consists of a polymer layer with sulfonic ion exchange groups about 3.5 mils (0.09 mm) thick and a polymer layer with carboxylic ion exchange groups about 0.5 mils (0.01 mm) thick. A two-layer ion exchange membrane having a total thickness of about 4 mils (0.1 mm) can have interconnecting channels of catalytically active particles having predetermined dimensions. The term "dimensions"
Here it is applied to interconnecting channels of catalytically active particles having a predetermined width. The interconnecting paths may be in a symmetrical or asymmetrical pattern. The minimum width of the interconnection path is typically greater than or equal to 6 microns, preferably greater than or equal to 20 microns.
The maximum width of the interconnecting channel is usually less than 1 cm, preferably less than 0.5 cm, more preferably less than 0.2 cm.

The porosity of the layer of catalytically active particles that acts as the M&E structure is also critical in allowing the escape of gases formed during cell operation. That is, the gas generated at the membrane/electrode interface serves to escape into the room through the porous portions of the catalytically active particles. This can cause gas to accumulate on the membrane/electrode surface, reducing the operating efficiency of the cell, or some of the gas can permeate through the membrane and contaminate the product obtained on the other side of the membrane. It disappears.

Screens according to the invention can also be used to create macroporous M&E structures (ie, structures with a large number of interconnecting channels of catalytically active particles). The macroporous nature of the M&E structures of the present invention allows the electrochemical cells used to operate with high efficiency.

The screen or screen template used in the present invention is a substantially flat, planar screen having a large number of regularly spaced apertures. The term "screen" as used herein refers to a screen that is embedded in or associated with a membrane, and that is used as a temporary means to provide an interconnection path for a large number of catalytically active particles in the membrane, and which is Both apply to the "screen template" which is removed from the membrane at. Preferably, the screen is substantially completely flat with respect to at least one surface. Flatness is particularly desirable. because,
This is because flatness allows the formation of M&E structures with contoured and controlled opening areas and corresponding areas that can be coated with catalytically active particles. Therefore, if a catalyst coating is placed on the screen and embedded in the membrane,
A large portion of the membrane remains exposed.
This minimizes the amount of catalytic material used to form the M&E structure, and the large open area provides an area for gaseous matter to escape from the electrode coating. Maximum.

Referring to the drawings, FIG. 1 is a side view of one type of screen suitable for use in the present invention. Metal 100 has one flat surface 130 and one rounded surface 120. round surface 120
It also has a slightly flattened part. This screen has apertures 110 connected on two opposite sides.

FIG. 2 is a side view of another type of screen 200 suitable for use in the present invention. The metal screen has generally rounded surfaces 220 and 230, which also have slightly flattened portions. The screen has connected openings 210 on opposite sides.

FIG. 3 is a top view of a portion of an interconnect pattern 300 of catalytically active particles deposited on a membrane. There are a number of openings 31 between the interconnecting path patterns.
0 and these openings are not interconnected, ie isolated from each other.

The thickness of the screen is not critical to the success of this invention. However, for convenience of handling, it is preferred that the thickness of the screen does not exceed the thickness of the membrane.

Preferably, the width or diameter of the interconnecting channels of catalytically active particles bound to the membrane is less than 1 cm. Above 1 cm, gas contamination of the product obtained on the other side of the cell increases. This is because there is less resistance to passing through the membrane and into the other side of the cell than escaping through the catalytically active particles.

According to the method of the invention, the interconnecting paths of the catalytically active particles match the pattern of the screen or screen template used. The shape and size of the screen will therefore represent the shape and size of the interconnecting channels of the catalytically active particles. The screen typically has up to 75% of its surface area occupied by apertures, and the screen preferably has an area of 25 to 75
% open area, more preferably 45-55
% open area. This provides a sufficient number of open areas on the surface of the membrane for the escape of the gas produced by the catalytically active particles.

Optionally, the screen can be constructed to have no openings along the periphery, thus preventing M&E
When the structure is assembled with other components to form an electrochemical cell, a pore-free area is provided in which a gasket can be placed.

A particularly suitable screen for forming interconnections of catalytically active particles on the membrane is an electroformed screen having a number of regularly spaced and mutually insulated openings.

Electroforming is a method of electrochemically depositing metal onto a matrix in a photographically defined pattern. The pattern on the photographic plate is such that upon depositing metal on the photographic plate and then removing the metal from the photographic plate, a metal matrix having a large number of openings is obtained.
Screens made in this manner are photographically perfect and substantially flat. The apertures have a distinctive arched shape because they are created by depositing metal around each. This shape allows for the smooth passage of screen printed material through the apertures and reduces the likelihood of deposits building up. Single-sided electroforming results in essentially conical holes, and double-sided electroforming results in biconical holes.

Electroformed holes are preferred over punched holes and holes formed by other means. This is because the electroformed holes are smooth and therefore do not tear the membrane when the screen comes into contact with it. Similarly, electroformed screens are superior to woven or screened wire mesh fabrics. This is because the electroformed screen is substantially flat and will not penetrate unevenly into the membrane when brought into contact with the membrane.

The shape of the interconnecting channels of the catalytically active particles may be symmetrical or asymmetrical. In the case of symmetry, the interconnecting channels can form any number of differently shaped openings, such as squares, rectangles, triangles, etc. As mentioned above, the interconnecting paths on the membrane do not necessarily have to follow a particular pattern (repeating or not). The improvement provided by the present invention is that rather than the generated gas diffusing through the membrane and into the electrolyte on the opposite side of the membrane, the generated gas diffuses out of the porous electrode coating and into the electrolyte. This is thought to be due to an increased ability to penetrate inside. Although there are many factors that determine the diffusion path of gas produced in a porous electrode, the opening area of the membrane of the present invention is aligned in close relation to the catalytic area, allowing the produced gas to reach the electrolyte. A horizontal passage is now available. By lateral path is meant a diffusion path from the production region of the gas in the catalytically active interconnection path to the electrolyte that runs essentially parallel to the membrane surface. Additionally, since these aperture areas do not produce gaseous matter, these aperture areas are susceptible to pressure gradients and /or does not create a concentration gradient.

According to experiments, the degree of contamination by gaseous substances is
It has been shown to be directly related to the percent open area on the membrane rather than the width of the interconnect. If this is true, the limits and preferred ranges for percent aperture area become extremely important.

M&E structures of the present invention also include embodiments in which the catalytically active particles and substantially flat screen are bonded to or embedded in one or both sides of the membrane. . However, the invention requires that at least one of the electrodes be in the form of a large number of catalytically active particles in contact with the membrane. During operation of the cell, this electrode can act as a cathode or an anode. Optionally, both electrodes may be catalytically active particles embedded on either side or surface of the membrane. For purposes of this discussion, both electrode configurations are described as if they were both catalytically active particles, and as if they were separate conventional electrodes. .

Conventional anodes are typically hydraulically permeable conductive structures, including, for example, expanded metal screens, perforated plates, stamped plates, unflattened diamond-shaped expanded metal, or metal wire fabrics. , built in various shapes and styles. Metals suitable for use in the anode include tantalum, tungsten, columbium, zirconium, molybdenum, and preferably titanium and titanium alloys rich in the above metals.

Optionally, the anode may be made of multiple catalytically active particles embedded within the membrane. Suitable materials for use in electrocatalytically active anode materials include, for example, oxides of metals of the platinum group (alone or in combination with oxides of film-forming metals) such as ruthenium, iridium, rhodium, platinum, palladium, etc. There are activating substances such as Other suitable activated oxides include:
There are cobalt oxides used alone or cobalt oxides and other metal oxides in combination. Examples of such activated oxides are U.S. Patent Nos. 3,632,498; 4,142,005;
4061549; described in No. 4214971.

Conventional cathodes are usually hydraulically permeable conductive structures, such as expanded metal screens, perforated plates, stamped plates, unflattened diamond-shaped expanded metal, or woven metal wire. They are made in a variety of shapes and styles, including: Metals suitable for use in the cathode include, for example, copper, iron, nickel, lead, molybdenum, cobalt, alloys containing high amounts of the above metals, such as low carbon stainless steel, and silver,
These include metals or alloys coated with materials such as gold, platinum, ruthenium, palladium, and rhodium.

Optionally, the cathode may be made of multiple catalytically active particles embedded within the membrane. Suitable materials for use in the electrocatalytically active cathode material include platinum group metals or their oxides, such as ruthenium or ruthenium oxide. Such a cathode is described in US Pat. No. 4,465,580.

Whether used as an anode or a cathode, the catalytically active particles are preferably finely divided and have a large surface area. For example, in the case of oxygen or hydrogen electrode fuel cells,
High surface area platinum (800-1800 m ² /g) supported on platinum black (with a surface area of more than 25 m ² /g) or activated carbon powder (average particle size 10-30 microns) is very suitable as anode and cathode. For chlorine batteries, the catalytically active particles of ruthenium dioxide particles are
It is produced by pyrolyzing ruthenium nitrate at a temperature of 450°C for 2 hours. The resulting oxide is then ground using a pestle and mortar, and the portion that passes through a 325 mesh sieve (44 microns or less) is used to make electrodes.

Membranes suitable for use in the present invention may be made of fluorocarbon type materials and
Alternatively, it may be made of a hydrocarbon type material. Such membrane materials are known in the art. However, fluorocarbon materials are generally preferred from the standpoint of chemical stability.

Nonionic (thermoplastic) forms of perfluoropolymers are particularly suitable for use in the present invention. This is because these polymers soften easily upon heating and the use of such polymers simplifies bonding the membrane to electrodes and flat screens or screen templates. Suitable membranes are described in the following US and other patents: 3282875; 3909378; 4025405; 4065366;
4116888; 4123336; 4126588; 4151052;
4176215; 4178218; 4192725; 4209635;
4212713; 4251333; 4270996; 4329435;
4330654; 4337137; 4337211; 4340680;
4357218; 4358412; 4358545; 4417969;
4462877; 4470889; 4478695; and European Patent Publication 0027009.

Membrane polymers usually have an equivalent weight in the range 500-2000. The membrane may be a single layer membrane or a multilayer membrane. More useful membranes are bilayer membranes, such as those having sulfonic ion exchange groups in one layer and carboxylic ion exchange groups in the other layer.

Desirably, the fluorocarbon membrane is in thermoplastic form so that the catalytically active particles can be embedded within the fluorocarbon membrane. Fluorocarbon membranes are in thermoplastic form during fabrication and prior to conversion to ion exchange form. The thermoplastic form referred to here means, for example, that the membrane does not have ionically bonded side groups such as SO ₃ Na or SO ₃ H, but instead has SO ₂ X side groups (X is -F, -CO ₂ ,
_-CH3 or quaternary amine).

Particularly preferred fluorocarbon materials for membrane formation are monomers and copolymers of monomers (specified below). Optionally, a third type of monomer can also be copolymerized with the monomer and the monomer.

The first type of monomer is represented by the general formula:

CF ₂ =CZZ′ () where: Z and Z′ are independent, -H, -Cl, -
F, and -CF ₃ .

The second type of monomer consists of one or more monomers selected from compounds represented by the following general formula.

Y-(CF ₂ )a-(CFR)b-(CFR')c -O-[CF(CF ₂ X)-CF ₂ -O]n-CF=
CF ₂ () where: Y is -SO ₂ Z, -CN, -COZ, and -C
(R ³ ) (R ⁴ )OH; Z is selected from -I, -Br, -Cl, -F, -OR, and -NR ₁ R ² ; R is the number of carbon atoms is a branched or straight-chain alkyl group or aryl group having 1 to 10 carbon atoms; R ³ and R ⁴ are independent and have 1 to 10 carbon atoms;
selected from about 10 perfluoroalkyl groups: R ₁ and R ² are independently selected from -H, a branched or straight-chain alkyl group having 1 to 10 carbon atoms, or an aryl group; a is 0 to 6; b is 0 to 6; c is 0 or 1; a+b+c is not equal to 0; X is -Cl, -Br when n>1 , -F, or a mixture thereof; n is 0 to 6; and R and R' are independently selected from -F, -Cl, perfluoroalkyl having 1 to 10 carbon atoms; and a fluorochloroalkyl group having 1 to 10 carbon atoms.

It is particularly preferred that Y is -SO ₂ F or -
COOCH ₃ ; n is 0 or 1; R and R' are -
F; X is -Cl or -F; and a+b+c is 2
Or when it's 3.

Suitable third (optional) monomers are one or more monomers selected from compounds represented by the following general formula.

Y′―(CF ₂ )a′―(CER)b′―(CFR′)c′ ―O―[CF(CF ₂ X′)―CF ₂ ―O]n′―CF―
=CF ₂ () where: Y' is selected from -F, -Cl, and -Br; a' and b' are independently 0 to 3; c' is 0 or 1 a'+b'+c' is not equal to 0; n' is 0 to 6; R and R' are independent and -Br, -Cl, -
F, perfluoroalkyl group having 1 to 10 carbon atoms,
and a chlorperfluoroalkyl group having 1 to 10 carbon atoms; and when n'>1, X' is selected from -F, -Cl, -Br, and mixtures thereof. be.

The conversion of Y into an ion exchange group is known in the art and consists of a reaction using an alkaline solution. In the case of -SO ₂ F side groups, the membrane can be converted to its ionic form by reacting it with 25% by weight NaOH under conditions such as:
(1) The film is immersed in an approximately 25% by weight aqueous sodium hydroxide solution at approximately 90°C for approximately 16 hours; (2) The film is soaked in deionized water heated to approximately 90°C for 30 to 60% per washing.
Wash the film twice with water. This causes the side group to be in the form -SO ₃ ^- Na ⁺ . It is also possible to replace −Na ⁺ with a cation other than −Na ⁺ (for example, −H ⁺ ).

Fabrication of the supported M&E structure of the present invention consists of many steps. The first step is the selection of the membrane and flat screen. A coating of catalytically active particles is placed on the screen. There are many suitable methods for depositing catalytically active particles onto the surface of a flat metal screen. For example, a slurry of catalytically active particles in solution or dispersion is applied or sprayed onto the membrane through openings in the screen. Alternatively, the screen may be immersed in a solution or dispersion of catalytically active particles. Various printing techniques can also be used to coat the membrane with the slurry.

A particularly suitable method for depositing the catalytically active particles on the screen consists of mixing the catalytically active particles with a solvent/dispersant to form a solution/dispersion.

Solvents/dispersants suitable for use in the present invention must have the following properties: boiling point below 110°C; density between 1.55 and 2.97 g/ ^cm3 ; and Hildebrand solubility parameter between 7.1 and 8.2. .

It has been found that a solvent/dispersant represented by the following general formula is particularly preferred. However, the above properties (boiling point, density, and solubility parameters) must be met: XCF ₂ -CYZ-X' where: X is selected from -F, -Cl, -Br, and -I. ; X' is selected from -Cl, -Br, and -I; Y and Z are independent; -H, -F, -
It is selected from Cl, -Br, -I, and -R'; and R' is selected from a perfluoroalkyl group having 1 to 6 carbon atoms and a chloroperfluoroalkyl group.

The most preferred solvents/dispersants are 1,2-bromotetrafluoroethane (commonly known as Freon 114B2): _BrCF2 - _CF2Br and 1,2,2-trichlorotrifluoroethane (commonly known as Freon 114B2). 113): ClF ₂ C—CCl ₂ F.

Among these two solvents/dispersants, 1,
2-dibromotetrafluoroethane is the most preferred solvent/dispersant. This compound is approximately 47.3℃
, a density of about 2.156 g/cm ³ , and a solubility parameter of about 7.2 Hildebrand.

1,2-dibromotetrafluoroethane, although not directly polar, is thought to work particularly well because it can be highly polarized. Therefore, when 1,2-dibromotetrafluoroethane is combined with a polar molecule, its electron density shifts, resulting in it behaving as a polar molecule. However, when 1,2-dibromotetrafluoroethane is present around non-polar molecules, this compound behaves as a non-polar solvent/dispersant. Therefore, 1,2-dibromotetrafluoroethane tends to dissolve the nonpolar backbone and even polar side chains of polytetrafluoroethane. The solubility parameter of 1,2-dibromotetrafluoroethane is 7.13-7.28
It is calculated as Hildebrand.

The solution/dispersion may optionally contain a binder to help retain the catalytically active particles and bond them to the screen, which is a preferred method. Preferred binders include various fluoropolymers, including materials such as polytetrafluoroethylene, perfluoropolymers and copolymers, and ionomers. Particularly preferred as the binder are ionomers having the same or similar composition as the ion exchange membrane. Examples of types of ionomers suitable for use as binders are the same as examples of types suitable for use as ion exchange membranes (described above). The aforementioned solvents/dispersants are solvents for ion exchange polymers. Thus, a slurry can be formed that includes catalytically active particles, ion exchange fluoropolymer, and solvent/dispersant. The resulting slurry facilitates bonding of the catalytically active particles to each other and to the screen or screen template.

When making the slurry, the concentration of ionomer (in dry form, without solvent/dispersant) is preferably between 4 and 20% by weight. The concentration of catalytically active particles is at least 0.1% by weight, but usually does not exceed about 30% by weight. There is no set maximum limit, but catalytic activity varies depending on the type of catalyst used, and all catalysts behave slightly differently.
Experimentation with the particular catalyst used will determine the optimal catalyst level. However, when using ruthenium oxide, 2 to 20% by weight has been found to be suitable. All weight percent values are based on the total weight of the slurry.

Optionally, a conductive metal may be added to the slurry to increase the conductivity of the catalyst deposited on the membrane. Usually silver is added, for example at a level of 60-90% by weight. Other suitable metals include nickel, tantalum, platinum, and gold.

The slurry can be produced by the following procedure. Note that there are several other methods that can be used appropriately. First, the ingredients are measured and blended in a dry state. Next, add enough solvent/dispersant to cover the dry ingredients. This mixture is blended in a ball mill for 4 to 24 hours to obtain a homogeneous mixture. Blending for such a period of time cleaves the ionomer and also causes at least a portion to dissolve. This makes it easier for the catalytically active particles to bond with each other. The mixture is then allowed to settle and excess solvent/dispersant is decanted. At this point, the mixture typically contains 25% solids by weight.

The flat screen or screen template to which the solution/dispersion is optionally deposited is cleaned or treated to ensure uniform contact with the solution/dispersion. Flat screens can be cleaned by cleaning using a degreaser or similar solvent and then drying to remove dust and oil from the screen. If the metal is new and not well degreased, the metal screen can be acid etched and then cleaned with a solvent to improve adhesion, if necessary.

After cleaning, the flat screen may be preconditioned by heating or vacuum drying before contacting with the solution/dispersion in the coating operation. Preferably, the following ranges of temperature and pressure are used. The conditions of approximately 20 mmHg at a temperature of approximately 100°C are sufficiently satisfactory in all cases. However, normal mild heating conditions (approximately 50° C. at atmospheric pressure) are sufficient.

There are a variety of suitable methods for applying the solution/dispersion to the screen that can be used. One suitable method consists of dipping the screen into the solution/dispersion, then drying and sintering it repeatedly at the desired temperature to deposit it to the desired thickness. The method of spraying the solution/dispersion onto a screen is utilized to the advantage of coating large or irregular shapes. Pouring the solution/dispersion onto a screen is also sometimes used. Brush or roller application of the solution/dispersion may also be successfully utilized. In addition, measuring bars, knives,
Alternatively, coating can be easily performed using a rod. Typically, the coating or film is deposited to the desired thickness by repeated coatings.
The solution/dispersion can be applied to the screen multiple times to deposit the catalytically active particles to the desired thickness. Preferably, the solution/dispersion is dried by removing the solvent/dispersant after each coating operation. This can be done by evaporating the solvent/dispersant by heating or vacuum drying. The coating can be of any desired thickness. However, thicknesses of 5 to 50 microns have been found to be suitable. Optionally, the coating applied to the screen may be sintered after each coating operation to transfer the coating to a membrane before performing the next coating operation.

With coated screen template,
When transferring a coating of catalytically active particles to a membrane, the template is placed opposite one side of the membrane.
Optionally, heating may be applied during the pressurization cycle to enhance the transfer of the catalytically active particles to the membrane and to increase the adhesion of the catalytically active particles to the membrane. However, this combination should not be heated above about 230°C. This is because the film becomes too soft and bonds to the screen template. Similarly, pressures above about 7 Kg/cm ² should be avoided. This is because the membrane is pressed through the holes in the screen template. If the membrane is in hydrogen form, it must not be heated to temperatures above 180°C. This is because the film may be thermally decomposed. If both pressure and heat are used, the pressurization time should be relatively short, ie, 30 seconds or less. It is assumed that this time is the time required to raise the membrane to the above temperature. However, if no heat is used, the combination can be pressurized for up to about 5 minutes.

After transferring the catalytically active particles to the membrane, the pressure and/or heat is removed and the screen is stripped from the membrane, forming an interconnected path pattern of catalytically active particles on the membrane.

Next, it is necessary to permanently fix the interconnecting paths of the catalytically active particles by means of a membrane. This can be done by applying additional pressure and heat to the coated membrane. Coated membranes (if the membrane is in thermoplastic or sodium form)
may be heated for 30 seconds to 1 minute at a high temperature of, for example, 260°C to bond the components. If the membrane is in the hydrogen form, it must not be heated to temperatures above approximately 180°C. This is because the film may be thermally decomposed. At such temperatures, the binder and film in the slurry soften and become bonded to each other. Furthermore, if the temperature is too low or the heating time is too short, the catalytically active particles will not be completely bonded to the membrane. If the heating time is too long, there will be too much blending of the catalytically active particles with the membrane. Too high a temperature will melt the membrane and thus prevent formation of a proper M&E structure.

To ensure that the combination of ingredients occurs, up to approx.
It may be advantageous to heat the combination under pressure of up to 3.5 Kg/cm ² . However, applying a pressure higher than 3.5 Kg/cm ² causes the assembly to become too flat.

Preferably, a heated press is used to combine the components. Although there are a variety of procedures available, one that has been found to be particularly useful consists of sandwiching the ingredients between platens (an upper platen and a lower platen) to form a sandwich structure. Above the lower platen is a screen of polytetrafluoroethylene paper (this membrane has catalytically active particles coated on the membrane), another screen of polytetrafluoroethylene paper, and a rubber one to provide elasticity. A screen, another screen of polytetrafluoroethylene paper, and finally an upper surface plate. The sandwich structure is placed in a heated press and heated under pressure to cause bonding.

The fact that the first side of the screen is substantially flat minimizes the ingress of catalytically active particles into the space between the solid portion of the screen and the membrane. In other words, the catalytically active solution/dispersion does not "move around" as it is applied to the membrane. The screen shown in FIG. 2 is also sufficiently flat so that "running around" of the catalytically active solution/dispersion is minimized.

Since the catalyst coating covers only a small portion of the membrane, materials with lower catalytic activity are used. However, the catalytic activity of the M&E structures of the present invention is at least comparable to the catalytic activity of prior art M&E structures.

Although only small amounts of catalytically active particles are used in the present invention, it has been found that the concentration of particles can be further reduced. For example, a typical solution/dispersion of catalytically active particles is about 75% silver by weight, about 16
% by weight of ruthenium oxide, and about 9% by weight of ionomer. However, using the method of the present invention, a slurry containing about 83% by weight silver, about 8% by weight ruthenium oxide, and about 9% by weight ionomer can be substantially It works equally well. This fact means that the amount of expensive ruthenium oxide catalyst used can be saved by about half.

Membranes of the invention, in which a number of interconnecting channels of catalytically active particles are attached to at least one surface of the membrane.
Methods of using are known in the art. Typically, a current collector is pressed against the interconnection of the catalytically active particles, and this is used as a power source (in the case of an electrolyser) or a power consumer (in the case of a fuel cell or battery).
Connect with. The current collector transmits electrical energy to (or from) the interconnects of the catalytically active particles. A particularly suitable current collector has been found to be a conductive screen having a pattern identical to the pattern of the interconnections of the catalytically active particles. This allows each interconnection of catalytically active particles to transfer electrical energy to and from the current collector. A resilient device, such as a mattress, may optionally be used to hold the current collector against the coated membrane.

The M&E structure of the present invention can be used, for example, in a fuel cell for continuously generating electrical energy, or an electrolytic cell for producing chemicals (e.g., producing chlorine and caustic soda from an aqueous sodium chloride solution, hydrogen and oxygen from water, etc.). It is useful in a wide variety of electrochemical cells, including electrolytic cells (such as electrolytic cells) and batteries for intermittently producing electrical energy.

Example: Approximately 76g of silver particles, approximately 16g of ruthenium oxide particles,
and about 8 g of carboxylic ion-exchange fluoropolymer particles were dissolved and suspended in BrCF ₂ --CF ₂ Br in a ball mill. The dry ingredients were first weighed and blended together. Sufficient amount of solvent/dispersant was added to cover the ingredients. This mixture was then blended in a ball mill for about 24 hours to obtain a homogeneous mixture. Such blending time cleaves and at least partially dissolves the ionomer. The mixture was then allowed to settle and excess solvent/dispersant was decanted.
At this point, the mixture contained approximately 25% solids by weight.

A screen template with an area of approximately 56 cm ² was used to apply the solution/dispersion. The screen template is an electroformed screen template commercially available from Perfluorated Products, Inc., having a number of 0.7 mm diameter apertures evenly distributed over its surface. The screen template has a sufficient number of openings to give a screen with approximately 50% open area. The thickness of the screen template is approximately 0.07mm
It is.

The screen template was dipped into the silver/ruthenium oxide/ionomer suspension and then dried at room temperature. The immersion and drying operations were repeated 5 more times, for a total of 6 times. The coatings were air-dried after each coating run. The coated screen was sintered at about 260°C for 5-10 minutes. The screen was contacted with a two-layer ion exchange membrane (in thermoplastic form) having sulfonic ion exchange groups in one layer and carboxylic ion exchange groups in the other layer. Note that the screen was brought into contact with the surface of the membrane having carboxylic ion exchange groups.

The resulting combination was placed in a heated hydraulic press and heated for 30 minutes at a pressure of about 3.5 Kg/cm ² and a temperature of about 230 °C.
Press for ~60 seconds to bond the membrane to the coated screen template.

The combination was removed from the hydraulic press and allowed to cool. After cooling, the screen template was removed, leaving a large number of interconnecting channels of catalytically active particles bound to the membrane.

In accordance with another embodiment of the invention, coating a conductive screen with catalytically active particles and contacting the membrane with the conductive screen;
Heat briefly under pressure. If the membrane is in thermoplastic or sodium form, the following conditions are used for bonding. Heat to a maximum temperature of about 260℃ in 30 seconds to 1 minute. This time is
This is considered to be the time required to raise the temperature of the membrane above. If the heating temperature is too low or the heating time is too short, it will be difficult for the screen to completely bond to the membrane. If the heating time is too long, the screen will completely pass through the membrane and will not be located on the surface of the membrane. If the heating temperature is too high, the membrane will melt and a proper M&E structure will not be formed. It may be advantageous to heat the screen/membrane combination under pressure up to about 3.5 Kg/cm ² . When the pressure exceeds 3.5Kg/cm ² , the membrane tends to be pushed and completely enter the screen. However, if the membrane is in the hydrogen form, it should not be heated above about 180°C.

In order to force the screen into the membrane, it is preferable to use a method in which the components are sandwiched between two surface plates (an upper surface plate and a lower surface plate) to form a sandwich structure. Above the lower platen is a screen of polytetrafluoroethylene paper, a membrane, a coated screen, another screen of polytetrafluoroethylene paper, and finally an upper platen. This sandwich structure is placed in a heated press and heated to a temperature of about 260° C. for about 90 seconds.

The conductive screen of the present invention is far superior in its usefulness to the window-screen types used in the prior art. This is because such window-screen types are not substantially flat, but are constructed of woven fabric, resulting in a wavy, uneven or somewhat non-planar structure. The screen of the present invention is preferably made of metal, but may be made of other materials as long as they are electrically conductive.

Preferably, the thickness of the screen does not exceed the thickness of the layer of membrane to which it is bonded by more than about 25%. In other words, if the membrane is a bilayer membrane with one layer of sulfonic polymer and another layer of carboxylic polymer, and the screen is bonded to the carboxylic layer, then the thickness of the screen is the same as that of the carboxylic layer. The thickness shall not be exceeded by more than 25%. If the screen is too thick, it will penetrate deeper into the membrane, making it more susceptible to attack by chemicals in compartments on opposite sides of the cell. It is further preferred that the thickness of the screen does not exceed the thickness of the layer of membrane to which it is bonded.

The width or diameter of the layer of catalytically active particles attached to the membrane is preferably about 1 cm or less, more preferably about 0.5 cm or less, and most preferably about 0.2 cm or less. If the dimensions are larger than these ranges, gas contamination of the product produced on the other side of the cell will increase.
This is because gas has less resistance passing through the membrane to the other side of the cell than escaping through the catalytically active particles.

[Brief explanation of drawings]

FIG. 1 is a side view of one type of substantially flat screen or screen template suitable for use in the present invention. FIG. 2 is a side view of another type of substantially flat screen or screen template suitable for use in the present invention. FIG. 3 is a top view of a section of the interconnect pattern of catalytically active particles deposited on the membrane.

Claims (1)

Claims: 1. A membrane/electrode composite structure comprising a substantially planar ion exchange membrane having a number of interconnections containing a number of catalytically active particles, the interconnections containing a binder. a composite structure comprising catalytically active particles attached to at least one planar surface of the membrane. 2. The membrane/electrode composite structure of claim 1, wherein the interconnecting passageway covers 25-75% of the membrane surface. 3. The membrane/electrode composite structure of claim 2, wherein the interconnecting passageway covers 45-55% of the membrane surface. 4. said membrane is selected from fluorocarbon-type or hydrocarbon-type materials, and a number of catalytically active particles are selected from ruthenium oxide, iridium oxide, rhodium oxide, platinum oxide, palladium oxide and Claims selected from mixtures of oxides, these substances optionally in combination with oxides of film-forming metals, cobalt oxide alone, and cobalt oxide in combination with other metal oxides. The membrane/electrode composite structure according to item 1, 2 or 3. 5. The membrane/electrode composite structure according to any one of claims 1 to 4, wherein the width of the interconnection path of the catalytically active particles is greater than 6 microns and less than 1 cm. 6. Claims 1 to 4, wherein the interconnection path of the catalytically active particles has a width of 20 microns to 0.5 cm.
The membrane/electrode composite structure according to any one of Items 1 to 9. 7. The membrane/electrode composite structure according to any one of claims 1 to 6, wherein a large number of conductive metal particles are distributed between the catalytically active particles. 8. The membrane/electrode composite structure according to claim 7, wherein the conductive metal particles are selected from silver, nickel, tantalum, platinum, and gold. 9. Claims 1 to 8, wherein the catalytically active particles are present in a layer having a thickness of 5 to 50 microns.
The membrane/electrode composite structure according to any one of Items 1 to 9. 10. A membrane/electrode composite structure according to any one of claims 1 to 9, wherein the interconnecting paths of the catalytically active particles contain a fluorocarbon polymer binder. 11 comprising a generally planar conductive screen having a plurality of apertures, the apertures occupying up to about 75% of the surface area of the screen, and the catalytically active particles are disposed on at least a portion of one planar surface of the screen; the ion exchange membrane is in physical and electrical contact with the planar surface, the ion exchange membrane is interposed between the catalytically active particles and the planar surface of the screen, and the catalytically active particles are sandwiched between the membrane and the screen. Claim 1 combined in such a manner that
The membrane/electrode composite structure described in . 12. The membrane/electrode composite structure according to claim 11, wherein the screen is an electroformed metal screen. 13. The screen has an open area of 25-75% and is non-porous along its periphery.
A membrane/electrode composite structure according to claim 11 or 12. 14. The thickness of the screen does not exceed the thickness of the membrane layer to which the screen joins by more than about 25%;
The membrane/electrode composite structure according to claim 11, 12, or 13. 15 (a) at least one surface of a substantially planar screen template is at least partially coated with a plurality of catalytically active particles, the catalytically active material comprising a binder, and wherein the screen template has a plurality of apertures. (b) contacting a planar surface of the ion exchange membrane with the coated screen template surface; (c) Transferring catalytically active particles from the screen template to the membrane; (d) removing the screen template; and (e) binding the catalytically active particles to the membrane. A method for making a composite membrane/electrode structure. 16 The catalytically active particles are coated on the screen in the form of a solution/dispersion, wherein the solution/dispersion
The dispersion has the general formula XCF ₂ -CYZ-X', where X is selected from -F, -Cl, -Br, and -I; Y and Z are independently -H, -F, -Cl, -Br, -I, and -
R′ is selected from R′; R′ has a carbon number of 1 to
16. The method according to claim 15, wherein the solvent/dispersant is selected from the perfluoroalkyl group and the chloroperfluoroalkyl group of No. 6. 17. The method of claim 16, wherein said solution/dispersion contains 4 to 20% by weight of ionomer. 18. Claim 1, wherein said solution/dispersion contains from 0.1 to 30% by weight of said catalytically active particles.
The method described in Section 6. 19. Claim 16, 1, wherein said solution/dispersion contains 60-90% by weight of conductive metal.
7, or the method according to item 18. 20. The method of claim 15, wherein the screen template is bonded to the membrane at a temperature up to about 260<0>C and a pressure up to about 3.5 Kg/cm ^<2> . 21 (a) coating at least a portion of the surface of at least one of the substantially planar conductive screens with a solution/dispersion obtained by mixing catalytically active particles in a solvent/dispersant, wherein said screen (b) contacting the surface of the coated screen with an ion exchange membrane; and (c) A method of making a membrane/electrode composite structure comprising the steps of bonding said coated screen to said membrane.