JPS6358917B2 - - Google Patents

Description

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

An "M&E battery" is an electrochemical cell using 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 batteries 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 battery 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&
E The operating efficiency of the battery 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 chlorine-alkaline batteries, 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 pass 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 problem of gaseous buildup by creating porous electrodes for M&E batteries. 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 catalytically active particles during the M&E battery manufacturing process. This sodium chloride is later leached away from the porous M&E structure. 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 battery 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 the protection 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:
consisting of a substantially planar ion exchange membrane having a number of islands of catalytically active particles attached to at least one flat surface of the membrane, wherein said islands have a diameter or width of from 6 microns to 1 cm; Also provided is a composite structure in which up to about 75% of the membrane surface is coated with the catalytically active particles.

The M&E structure of the present invention optionally includes a substantially planar, electrically conductive screen having a number of apertures passing through the screen, the apertures occupying up to about 75% of the surface area of the screen, and the ion exchange The membrane is coupled to the screen, thus leaving a portion of the membrane surface exposed through the openings in the screen, and a number of said catalytically active particles are disposed on the exposed surface portion of the membrane, and the membrane and In electrical and physical contact with the screen.

The present invention further includes forming a coating of catalytically active particles on a removable substrate; contacting the screen with the apertures occupying up to about 75% of the surface area of the screen; contacting the screen with the coated substrate; applying the coated substrate to the screen such that the catalytically active particles are in the screen; pressing with sufficient pressure to force the catalytically active particles to pass through the apertures and onto the membrane, thereby forming numerous islands of catalytically active particles on the surface of the membrane; removing the screen; and A method of manufacturing an improved membrane/electrode composite structure comprising bonding to a membrane is provided.

The present invention further provides for contacting at least one surface of the substantially planar ion exchange membrane with a substantially planar conductive screen having a plurality of apertures occupying up to 75% of the surface area of the screen. thus leaving a portion of the membrane exposed through the openings in the screen; coating the portion of the membrane exposed through the openings in the screen with catalytically active particles; and attaching the membrane to said particles and the screen. A method of manufacturing a membrane/electrode composite structure is provided.

M&G with islands of catalytically active particles deposited on the membrane
It has been found that E structures operate with very high efficiency when used in electrochemical cells, unlike prior art M&E structures which have large, substantially continuous coatings of catalytically active particles. It is speculated that the increased efficiency is due to the open areas of the membrane, ie the areas between islands of catalytically active particles that are electrically insulated from each other. These open areas provide space for the removal of gases generated at the catalytically active surface. The pattern of catalytically active particles is designed such that the escape path for gas from and around the particle islands has 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 islands of catalytically active particles than to pass through the membrane and into the opposite compartment.

The size, shape, and thickness of the catalytically active particle islands of the present invention depend on the type of ion exchange membrane used. That is, membranes with high gas permeation resistance may use larger particle islands, whereas membranes with low gas permeation resistance require smaller particle islands. For example, in a chlor-alkali electrolyzer, an entire layer consisting of a polymer layer with sulfonic acid ion exchange groups about 3.5 mils (0.09 mm) thick and a polymer layer with carboxyl ion exchange groups about 0.5 mils (0.01 mm) thick. A two-layer ion exchange membrane with a thickness of approximately 4 mils (0.1 mm) typically has a thickness of 0.5
Islands of catalytically active particles having dimensions of less than cm, preferably less than 0.2 cm can be used. The term "size" applies here to islands of catalytically active particles having a predetermined diameter or width. This diameter or width may be in a symmetrical or asymmetrical pattern. The minimum size of the island is 6
The diameter is at least micron, preferably at least 20 micron. The maximum dimension of the island is less than 1 cm, preferably 0.5 cm
It is more preferably 0.2 cm or less.

Although islands of catalytically active particles can be coated onto the membrane in a variety of ways, by using a specially designed screen that is substantially flat;
In terms of its design and operational stability, M&E structures are much superior to those obtained by prior art methods.
&E structure can be obtained. Using the screens according to the invention, M&E structures are obtained which are much superior in serviceability to M&E structures obtained using conductive screen fabrics according to the prior art. This is because prior art screen fabrics are not substantially flat and have a wavy structure typical of woven or knitted materials.

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. Prior art M&E structures have microporous openings that function, in part, to provide passageways for gas escape. However, "macroporous" coatings are much preferred over continuous coatings with "microporous" openings. This is because a large amount of space is available for gas to escape. Therefore, using the screen according to the invention, unlike the microporous M&E structures of the prior art, macroporous M&E structures
&E structures (ie, structures with multiple islands of catalytically active particles with relatively large or microporous openings or spaces between the islands) can be made. The microporous 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. As used herein, the term "screen" refers to a screen that is embedded in or bonded to a membrane and that is used as a temporary means to provide a large number of catalytically active particles to the membrane, and which is later removed from the membrane. Applies to both "screen templates". Preferably, the screen is substantially completely flat with respect to at least one surface. Flatness is particularly desirable. Because if it's flat,
Adjusted open areas with sharp contours,
and M&E structures can be formed with corresponding areas that can be coated with catalytically active particles. The screen is preferably a metal screen, but in the case of a screen template it may be made of virtually any material capable of providing a large number of apertures.

In the method of the invention, a catalyst coating is applied onto a removable substrate and then embedded into the membrane through a screen. This leaves a significant portion of the membrane exposed, ie not coated with catalytically active particles. Therefore, the amount of catalytic material used to form the M&E structure is minimized and the large amount of open area maximizes the area for gaseous matter to escape from the electrode coating.

Referring to FIG. 1, a metal screen 100
has one flat surface 130 and one round surface 120
have. The rounded surface 120 also has a slightly flattened portion. 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. Figure 3 shows the screen 30
0 and an opening 310 viewed from above.

A screen or screen template is
Up to 75% of its surface is occupied by apertures. The apertures preferably occupy 25-60%, most preferably 45-55% of the surface area. In this way,
M&G with a sufficient number of openings on the membrane surface to allow the gas formed on the catalytically active particle coating to escape.
E-structures can be created, with no gas passing through the membrane and therefore no contamination of the opposite compartment.

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 islands 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. Planar electroforming results in essentially conical holes, and double-sided electroforming results in biconical holes.

The thickness of the screen is not critical to the success of this invention. However, since the fabrication process of the present invention coats the catalytically active particles through the openings of the screen, it is preferably not too thick. Generally, the thickness of the screen should not exceed the thickness of the membrane layer by more than 25%. If the screen is too thick, it will penetrate deeper into the membrane and become more susceptible to chemical attack by chemicals in the opposite compartment.
More preferably, the thickness of the screen does not exceed the thickness of the layer of membrane to which it is bonded.

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 does not penetrate unevenly into the membrane when brought into contact with the membrane.

The shape of the holes in the conductive screen is not critical to the successful use of the present invention. The holes can be of almost any shape, such as circular, rectangular, square, rectangular, triangular, etc. However, preferably the holes are circular. This is because circular islands of catalytically active particles are formed, thus providing the shortest gas escape paths compared to other shapes.

The width or diameter of the openings in the screen is preferably less than 1 cm, more preferably less than 0.5 cm, and most preferably less than about 0.2 cm. Dimensions greater than 1 cm increase gas contamination of the product obtained on the other side of the cell. This is because the resistance to passage of gas from the membrane to the other side of the cell is less than the resistance to escape through the catalytically active particles.
The width or diameter of the openings in the screen is at least 6 microns, preferably at least 20 microns, so that very small islands of 6 microns and 1 cm
Very large islands can be formed on the membrane.

The shape of the islands of catalytically active particles is not limited and can take on several shapes, such as square, rectangular, triangular, etc. Furthermore, the arrangement of catalytically active islands on the membrane does not necessarily have to follow a particular pattern or shape (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 generated in porous electrodes,
The open areas of the membrane of the present invention are arranged in close association with the catalytic area, providing a lateral passage for the produced gases to reach the electrolyte, which is not achievable with the prior art. There is. By lateral path is meant a diffusion path from the gas production region in the catalytically active island to the electrolyte that runs essentially parallel to the membrane surface. Furthermore, since these open areas do not produce gaseous matter, these areas are subject to pressure gradients and/or that act to prevent the desired transfer of gaseous matter from the electrocatalytic region of the M&E assembly into the electrolyte. Does not create concentration gradients.

Taking into account the above, the "size" of the islands of catalytically active material is limited to such an extent that this advantage is reduced to insignificance. For example, consider the case of circular islands regularly distributed on the surface of a membrane. For each circle, the longest lateral diffusion path for the produced gas can be approximated by the radius r (center to edge). The active area, ie the area that generates gaseous substances, can be approximated by ^r2 . If the radius r is increased, the lateral diffusion path increases linearly with r and the active area increases with r ² . In other words, both of these results reduce the extent to which lateral diffusion paths play a role in the mass transfer of gaseous substances. Therefore, transport across the membrane plays an increasingly large role, which increases the contamination of the opposite electrolyte by gaseous products.

According to experiments, the degree of contamination by gaseous substances is
It has been shown to be directly related to the percentage of open area on the membrane rather than the radius of the islands. If this is true, the limits and preferred ranges for percent open 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 battery, 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 discussion of the present invention, both electrode configurations are described as if both were catalytically active particles, and also as if both were separate conventional electrodes. .

Conventional anodes are typically 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 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. Materials suitable for use in electrocatalytically active anode materials include, for example, ruthenium, iridium, rhodium, platinum,
There are activating substances such as oxides of platinum group metals such as palladium (alone or in combination with oxides of film-forming metals). Other suitable activated oxides include cobalt oxide alone or in combination with other metal oxides. Examples of such activated oxides are U.S. Pat. No. 3,632,498;
4142005; 4061549; 4214971.

Conventional cathodes are typically 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,
These include alloys containing high amounts of these metals, such as molybdenum, cobalt, low carbon stainless steel, and metals or alloys coated with materials such as silver, 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, for example, platinum group metals or oxides thereof, such as ruthenium or ruthenium oxide. Such a cathode is described in US Pat. No. 4,465,580.

Catalytically active particles, whether used as an anode or also as a cathode,
Preferably, it is finely divided and has a large surface area. For example, for oxygen or hydrogen electrode fuel cells, high surface area platinum (800-1800 m ² /g) supported on platinum black (with a surface area of 25 m ² /g or more) or activated carbon powder (average particle size 10-30 microns). is very suitable as anode and cathode. In the case of chlorine cells, catalytically active particles of ruthenium dioxide particles are made 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 also 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 makes it easier to bond the membrane to the electrode and to the flat screen or screen template. be. 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 typically range from 500 to 2000
has an equivalent weight in the range of . The membrane may be a single layer membrane or alternatively a multilayer membrane. A more useful membrane is a bilayer membrane having sulfonic acid ion exchange groups in one layer and carboxylic acid 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 has SO ₂ X side groups (X is _-F , -CO ₂ , -CH ₃ , 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 _f ) _b —(CFR _f ′) _c —O— [CF(CF ₂ X)—CF ₂ —O] _o —CF=CF ₂
() where: Y is selected from -SO ₂ Z, -CN, -COZ, and -C(R ³ f) (R ⁴ f) OH; Z is -I, -Br, -Cl, -F, -OR and-
NR ₁ R ² ; R is a branched or straight-chain alkyl group or aryl group having 1 to 10 carbon atoms; R ³ f and R ⁴ f are independent; is 1~
R ₁ and R ₂ are independently selected from about 10 perfluoroalkyl groups; -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 and 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 _f and R _f ' are independently selected from -F, -Cl, perfluorocarbon having 1 to 10 carbon atoms; an alkyl group, 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 _f and R _f ′ 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 ′―(CFR _f ) _b ′―(CFR _f ′) _c ′―O
― [CF(CF ₂ X′)―CF ₂ -O] _o ′―CF―=CF ₂
() where: Y' is selected from -F, -Cl, and -Br; a' and b' are independently from 0 to 3; c' is 0 or 1; a′+b′+c′ is not equal to 0; n′ is from 0 to 6; R _f and R _f ′ 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 aqueous solution of about 25% sodium hydroxide at about 90°C for about 16 hours; (2) The film is soaked in deionized water heated to about 90°C for 30 to 30 minutes per washing.
Wash the film twice with water for 60 minutes. This gives the side group 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. The flat screen or screen template to which the solution/dispersion is deposited is optionally cleaned or treated in a manner to ensure uniform contact with the solution/dispersion. Clean the flat screen using a degreaser or similar solvent and dry it to remove dust and oil from the screen. If the metal is new and not sufficiently degreased, the metal screen can be acid etched and then washed with a solvent to improve adhesion, if necessary. After cleaning, the flat screen may be preconditioned by heating or vacuum drying before contacting the membrane.

There are many suitable methods for attaching particles to the membrane. For example, a slurry of catalytically active particles in solution or dispersion is applied or sprayed onto the membrane through openings in the screen. The method of spraying the slurry onto the membrane through the openings in the screen is
It is used to provide the advantage of covering large or irregularly shaped openings in screens. Pouring the slurry onto the membrane through openings in the screen can also be used. Brush or roller slurry application methods may also be successfully utilized. In addition, a measuring bar,
Coating can also be easily done using a knife or rod. Usually the coating or film is
The desired thickness is deposited by repeated coatings. Various printing techniques can also be used to coat the slurry onto the membrane.

A particularly suitable method for depositing catalytically active particles on a membrane is to first prepare a slurry of catalytically active particles in a solvent/
It consists of forming a solution/dispersion of catalytically active particles on a removable substrate by forming it in a dispersant. Preferably, the solvent/dispersant used to suspend the catalytically active particles is a system that will at least partially dissolve the polymer that makes up the ion exchange membrane. Using this method,
Catalytically active particles can be more firmly bound to the membrane.

The solution/dispersion may optionally contain a binder to help retain the catalytically active particles; this is a preferred method. Preferred binders include various fluoropolymers, including materials such as polytetrafluoroethylene, perfluoropolymers, 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 solution/dispersion thus obtained facilitates mutual bonding of the catalytically active particles when they are deposited on the membrane.

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.
Optimal catalyst levels will be determined by experimentation with the particular catalyst used. 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 of all, the ingredients are measured and blended dry. Next, add enough solvent/dispersant to cover the dry ingredients. This mixture was blended in a ball mill for 4 to 24 hours.
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.

Solvents/dispersants suitable for use in the present invention include:
It 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, -
and R' is selected from a perfluoroalkyl group having 1 to 6 carbon atoms and a chloroperfluoroalkyl group.

The most preferred solvent/dispersant is 1,2-dibromotetrafluoroethane (usually Freon 114B2
): BrCF ₂ --CF ₂ Br and 1,2,2-trichlorotrifluoroethane (commonly known as Freon 113): ClF ₂ C—CCl ₂ F.

Of these two solvents/dispersants, 1,2-
Dibromotetrafluoroethane is the most preferred solvent/dispersant. This compound has a boiling point of about 47.3° C., 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 of polytetrafluoroethane, and even the polar side groups. The solubility parameter of 1,2-dibromotetrafluoroethane has been calculated to be 7.13-7.28 Hildebrand.

The slurry is then coated onto a removable substrate, such as aluminum foil. The slurry was applied repeatedly to achieve the desired thickness of the layer of catalytically active particles. Preferably, the slurry is dried by removing the solvent/dispersant between coats. This can be done by evaporating the solvent/dispersant by heating or vacuum drying. The coating can be of any desired thickness. However, a thickness of 5 to 50 microns has been found to be suitable. Optionally, the coating can be sintered between coats and transferred to the film before the next coat.

The coated removable substrate is then placed opposite one surface of the screen. When the other surface of the screen is placed opposite the membrane and pressure is applied to the combination, the catalytically active particles are forced through the pores of the screen and onto the ion exchange membrane. Optionally, heating may be applied during the pressure 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 is approximately
Do not heat above 450℃ (230℃). This is because the membrane has softened enough to bond to the screen. Similarly, pressures exceeding about 7 kg/cm ² should be avoided. This is because the membrane is pressed through the holes in the screen.
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 multiple islands of catalytically active particles on the membrane.

Next, it is necessary to permanently fix the islands of catalytically active particles in the membrane. This can be done by applying additional pressure and heat to the coated membrane. coated membrane (the membrane is now in thermoplastic form or its sodium form)
may be heated for 30 seconds to 1 minute at a high temperature of, for example, 260°C to bond the components. When the membrane is in its hydrogen form, it should not be heated to temperatures above about 180°C. This is because the film is easily 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, too much blending of the catalytically active particles with the membrane will occur. If the temperature is too high, the membrane will melt and thus prevent proper M&E structure formation.

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, if a pressure higher than 3.5Kg/ ^cm2 is applied,
The combination ends up being 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 sanderch 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 "wandering" of the catalytically active solution/dispersion is minimized.

Optionally, the catalytically active particles are covered with a conductive screen/
It may be coated onto the membrane combination and then heated to bond the combination together. If the membrane is in thermoplastic or sodium form, the following conditions can be used to induce bonding. Heat the membrane to 260°C for 30 seconds to 1 minute.
This time is believed to be the time required to raise the membrane to the above temperature. If the heating temperature is too low or the heating time is too short, the conductive screen will not completely bond to the membrane. If the heating time is too long, the metal will pass through the membrane completely and will not be fixed on the surface of the membrane. If the heating temperature is too high, the film will melt and therefore the proper M&
E structures are no longer formed. Maximum approximately 3.5Kg/cm ²
It may be advantageous to heat the electrically conductive screen/membrane combination under pressure up to . When the pressure is higher than about 3.5 Kg/cm ² , the membrane is completely pushed into the conductive screen. However, if the membrane is in the hydrogen form, it should not be heated above about 180°C.

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.

Methods of using the membranes of the present invention, in which multiple islands of catalytically active particles are bound to at least one surface of the membrane, are known in the art. Generally, a current collector is pressed against the island of catalytically active particles and is connected to a power source (in the case of an electrolyser) or a power consumer (in the case of a fuel cell or battery). (The current collector transmits electrical energy to (or from) the islands of catalytically active particles. A particularly suitable current collector has a pattern identical to the screen used to form the islands of catalytically active particles. It was found that it is a conductive screen with a
Each island of catalytically active particles is capable of transmitting electrical energy to (or from) a 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 includes, for example, a fuel cell for continuously generating electrical energy, an electrolytic cell for producing chemicals (for example, 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 batteries for intermittent generation of electrical energy.

Example 1 A mixture of about 76 g of silver particles, about 16 g of ruthenium oxide particles, and about 8 g of carboxyl ion-exchanged fluoropolymer particles was 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 contains approximately 25% solids by weight.

The mixture was sprayed onto a sheet of aluminum foil using an airless spray gun to form a 20-30 micron thick coating. This solution/dispersion was air dried. Place the resulting coating in the oven;
The coating was sintered by heating to a temperature of 250°C to 260°C in about 10 minutes.

Carboxylic layer approximately 0.01mm thick and approximately 0.01mm thick
A two-layer fluoropolymer ion exchange membrane with a 0.9 mm sulfonic layer is placed on a sheet of polytetrafluoroethylene with the sulfonic layer in contact with the polytetrafluoroethylene sheet.

An electroformed screen template (having a surface area of approximately 56 cm ² ), available from Perfluorated Products, Inc., was placed over the carboxylic layer of the membrane. This screen template has a large number of openings with a diameter of 0.7 mm evenly distributed on the surface. There are enough openings to give the screen 50% open area. The thickness of this screen is approximately 0.07mm.

An aluminum foil with a sintered coating was placed on the screen template with the coating in contact with the screen. A sheet of polytetrafluoroethylene was then placed on top of the aluminum foil.

The resulting combination was placed in a heated hydraulic press at a pressure of approximately 3.5 Kg/cm ² and at a temperature of approximately 170°C.
Treated for 30-60 seconds. This pressure forces parts of the coating through the holes in the screen and onto the membrane;
Many islands of catalytically active particles were formed on the membrane. The heat and pressure also caused islands of catalytically active particles to bond to the membrane.

The combination was removed from the press and the polytetrafluoroethylene sheet was removed. The screen template was then removed, yielding a membrane with multiple islands of catalytically active material.

Example 2 A mixture of about 76 g of silver particles, about 16 g of ruthenium oxide particles, and about 8 g of carboxylic ion exchange fluoropolymer particles was dissolved and suspended in BrCF ₂ --CF ₂ Br in a ball mill. First, the dry ingredients were weighed and blended together. Next, enough solvent/dispersant was added to cover the ingredients. This mixture was blended in a ball mill for about 24 hours to obtain a homogeneous mixture. This blending time cleaves the ionomer and
At least a portion will dissolve. The mixture was allowed to settle and excess solvent/dispersant was decanted. At this point, the mixture contains approximately 25% solids by weight.

A thickness of 20-30 microns was achieved by spraying this solution/dispersion onto a sheet of aluminum foil using an airless spray gun. The sprayed solution/dispersion was air dried to form a film. This coating is then placed in the oven for about 10 minutes.
It was heated to a temperature of 250-260°C.

A bilayer fluoropolymer ion exchange membrane having a carboxylic layer about 0.5 mils (0.01 mm) thick and a sulfonic layer about 3.5 mils (0.09 mm) thick with the sulfonic layer in contact with a polytetrafluoroethylene sheet. and place it on a sheet of polytetrafluoroethylene.

Electroformed screen template (approximately 56 cm ² ) commercially available from Perfluorated Products.
was placed on top of the carboxylic layer of the membrane. The screen has a diameter of approximately 0.7 evenly distributed over its surface
It has a large number of openings in mm. There are enough apertures to give a screen with about 50% open area. The thickness of the screen is approximately 0.1mm.

Aluminum sheet with sintered coating,
The coating was placed on the screen with it in contact with the screen. A sheet of rubber was placed on top of the aluminum foil and a sheet of polytetrafluoroethylene was placed on top of the rubber sheet.

The resulting combination was placed in an unheated hydraulic press and processed at room temperature for about 5 minutes under a pressure of about 7 Kg/cm ² . This pressure forced portions of the coating through the pores of the screen and onto the membrane, resulting in the formation of numerous islands of catalytically active particles on the membrane.

The combination was then removed from the press and the polytetrafluoroethylene sheet, rubber sheet, and screen were removed. The resulting membrane was sandwiched between two polytetrafluoroethylene sheets and placed in a heated press. The combination is heated at a temperature of about 230℃ and a pressure of about 3.5Kg/ ^cm2 for 30~
A 60 second press bonded the catalyst islands to the membrane.

Example 3 Following the procedure of Example 1, a mixture was made and spread on a sheet of aluminum foil to form a layer approximately 20-50 microns thick. Let the covering air dry, approx.
Sintering was performed at 260°C for about 5 minutes.

A two-layer ion exchange membrane was obtained having a fluoropolymer containing sulfonic ion exchange groups in one layer and a fluoropolymer containing carboxylic ion exchange groups in the other layer.
The thickness of the membrane was approximately 0.1 mm. The carboxylic layer was approximately 0.012 mm thick, and the sulfonic layer was approximately 0.09 mm thick. A nickel screen (described in Example 1) was brought into contact with the surface of the membrane containing carboxylic ion exchange groups. The other side of the screen was brought into contact with the coating of catalytically active particles formed on the aluminum foil. The combination was pressed together at a pressure of about 3.5 Kg/cm ² and a temperature of about 260° C. for about 30 seconds. This pressure pushed the coating on the aluminum foil through the holes in the screen and onto the membrane. This heat caused the catalytically active particles to bond to the membrane. After the combination was removed from the press and allowed to cool, the coated aluminum foil was removed. This resulted in a screen-bound membrane. In the open area of the screen, the catalytically active particles pressed through the pores of the screen were deposited on the membrane.

[Brief explanation of the drawing]

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 plate suitable for use in the present invention. FIG. 3 is a top view of a section of a substantially flat screen or screen template suitable for use in the present invention.

Claims (1)

Claims: 1. A membrane/electrode composite structure comprising a substantially planar ion exchange membrane having multiple islands of catalytically active particles attached to at least one planar surface of the membrane; A structure in which said islands have a diameter or width of 6 microns to 1 cm and up to about 75% of said membrane surface is covered with said catalytically active particles. 2 the islands cover 25-60% of the membrane surface,
A structure according to claim 1, wherein the diameter or width of the islands is between 20 microns and 0.5 cm. 3. A structure according to claim 1, wherein the membrane is selected from fluorocarbon-type or hydrocarbon-type materials. 4. Claims 1, 2, or 3, wherein a binder is distributed between the catalytically active particles to bind the particles to each other, wherein the binder comprises a polymer of the same composition forming at least a portion of the membrane.
Structures described in Section. 5. The structure according to claim 1, wherein a conductive metal is distributed between the catalytically active particles. 6. The structure of claim 5, wherein said conductive particles are selected from silver, nickel, tantalum, platinum, gold, and mixtures thereof. 7. said island has a thickness of less than 20 microns;
A structure according to claim 1. 8 consisting of a substantially flat conductive screen having a number of apertures, said apertures occupying up to 75% of the surface area of the screen, and said ion exchange membrane being coupled to the screen such that a portion of the membrane surface passes through the apertures of the screen. remains exposed and a number of said catalytically active particles are located on the exposed surface portion of the membrane;
8. A structure according to any of claims 1 to 7, in electrical and physical contact with the membrane and screen. 9. The structure of claim 8, wherein the conductive screen is an electroformed metal screen having an open area of 25-60%. 10 the screen is non-porous at its periphery and the thickness of the screen does not exceed the thickness of the membrane layer to which it joins by more than about 25%;
A structure according to claim 8 or 9. 11 (a) forming a coating of catalytically active particles on a removable substrate; (b) contacting a substantially planar ion exchange membrane with a substantially flat planar screen having a plurality of apertures; (c) bringing the screen into contact with the coated substrate; (d) applying the substrate to the screen and pressing with sufficient pressure; (e) forcing the catalytically active particles through openings in a screen and onto the membrane, thereby forming a number of islands of catalytically active particles on the surface of the membrane; (e) removing the screen; and (f) a method of making an improved membrane/electrode composite structure comprising bonding said catalytically active particles to said membrane. 12 (a) Cover at least one surface of the substantially planar ion exchange membrane with a substantially flat conductive screen covering up to 75 of the surface area of the screen.
(b) contacting a conductive screen having a number of apertures accounting for % of the ion exchange membrane, thereby leaving a portion of said ion exchange membrane exposed through the apertures in the screen; A method of making a membrane/electrode composite structure comprising coating a portion of a membrane with catalytically active particles; and (c) bonding the membrane to the catalytically active particles and the screen. 13. Claim 11, wherein the openings in the screen occupy 40-60% of the surface area of the screen.
The method according to item 1 or item 12. 14 Up to 350 screen/membrane combinations as described above
13. The method according to claim 12, wherein the method is heated to a temperature of (175° C.). 15 up to 7 for the above screen/membrane combination
Claim 1 applying pressure up to Kg/cm ²
The method described in Section 4. 16 Membranes coated with catalytically active particles can be coated with up to approx.
Claim 1, wherein the catalytically active particles are bonded to the membrane by heating to a temperature of up to 260° C. and pressing at a pressure of up to about 7 Kg/cm ² .
The method according to item 1 or item 12. 17 The catalytically active particles are blended with a solvent/dispersant and are in the form of a solution/dispersion when coated onto the membrane, wherein the solvent/dispersant has the following _general formula: CYZ-X' (wherein, X is -F, -Cl, -Br, and -I
X' is selected from -Cl, -Br, and -I; Y and Z are independent and -H, -F, -
is selected from Cl, -Br, -I, and -R';R' is selected from a perfluoroalkyl group having 1 to 6 carbon atoms and a chloroperfluoroalkyl group) , the method according to claim 11 or 12. 18. The solvent/dispersant is selected from 1,2-dibromotetrafluoroethane and 1,2,2-trichlorotrifluoroethane.
A method according to claim 17. 19. A method according to claim 17 or 18, wherein the solution/dispersion contains 4 to 20% by weight of ionomer. 20. Claim 17, wherein said solution/dispersion contains from 0.1 to 25% by weight of catalytically active particles.
The method according to item 18 or 19. 21. Claims 17-20, wherein said solution/dispersion contains 60-90% by weight of conductive metal.
The method described in any of the sections. 22. A method according to any of claims 17 to 21, wherein said solution/dispersion contains about 25% solids by weight. 23. The method of claim 11, wherein the substrate is coated to a thickness of 5 to 50 microns.