KR900007732B1 - Composite membrane electrode structure having interconnected roadways of catalytically active particles - Google Patents

Abstract

A composite membrane/electrode structure comprises a planar ion exchange membrane (I) having a plurality of inter-connected roadways of catalytically active particles (II) bonded to at least one surface of (I). Pref. the roadways cover 25-75% of (I) and (II) opt. includes electrically conductive metal particles. (II) are disposed on an electrically conductive pref. electroformed metallic, screen having openings passing therethrough, which occupy uo to 75% of the surface area of the screen. (I) is bonded such that (II) are sandwiched between (I) and the screen. The electrodes are suitable for electrolysis or fuel cells.

Description

Membrane / electrode composite structure with interconnected lines of catalytically active particulates

1 is a side view of one type of near flat screen or screen template, suitable for use in the present invention.

2 is a side view of another form of an almost flat screen or screen template suitable for use in the present invention.

3 is a partial plan view of an interconnected line pattern of catalytically active particulates attached to the membrane.

The term "M & E" refers to membranes and electrodes, which are nearly flat sheet ion exchange membranes in which a plurality of electrically conductive, catalytically active particulates are present on one or both surfaces of most of the membrane. ion exchange membrane). Catalytically active fine particles act as particulate electrodes when M & E is used in an electrochemical cell.

Sometimes M & E structures are also called solid polymer electrolyte structures or solid polymer electrolyte (SPE) structures.

An "M & E cell" is an electrochemical cell that uses an M & E structure. Such cells may operate as an electrolytic cell for producing electrochemical products or as a fuel cell for producing electrical energy. For example, electrolysers can be used to electrolyze alkali metal halides (eg sodium chloride) or to electrolyze water.

M & E batteries are known in the art and are described in U.S. Pat. 4,498,942, 4,315,805, 4,364,815, 4,272,353, and 4,394,229.

Often in M & E cells, gaseous products are produced in catalytically active particulates. The gas is bubbled into the electrolyte which contacts the M & E from the particulates while the cell is automated (acting as an electrode). However, the gaseous product produced in the pores of the particulates or at the particulate / membrane interface must be removed by diffusing through the pores of the particulate before it is bubbled into the electrolyte. Since gases are generated faster than they can escape, they accumulate in the catalytically active particulates or at the particulate / membrane interface, reducing the operational efficiency of the M & E cell. More disadvantageously, some of the gas penetrates the membrane to contaminate the product (s) produced on the other side of the membrane. In a chlor-alkali cell in which hydrogen is produced on one side of the membrane and chlorine is generated on the other side of the membrane, hydrogen can penetrate the membrane and contaminate chlorine, or chlorine can penetrate the membrane and contaminate hydrogen. Such contamination may also be dangerous due to the explosiveness of the chlorine / hydrogen mixture.

Prior art has attempted to minimize the problem of gas accumulation caused by M & E by making porous electrodes for M & E structures (US Pat. No. 4,276,146). Some porous M & E electrodes can be formed by incorporating pore formers, such as sodium chloride, into catalytically active particulates during the manufacture of M & E. Sodium chloride is then extracted from the porous M & E structure. However, since the hydrogen contamination of chlorine is not significantly reduced, this coating cannot solve the gas diffusion problem. In addition, the catalytically active porous fine particles are brittle and do not maintain a good gas evolution, resulting in the loss of catalytic fine particles, resulting in a decrease in the efficiency of the cell.

The present invention provides an M & E structure specifically designed to minimize the ingress of gaseous products through the membrane to the opposite side of the cell and to improve the electrical efficiency of the cell.

M & E electrode coatings are made using relatively expensive materials. The present invention reduces the amount of catalyst material used at the electrode without compromising the catalytic activity and efficiency of the coating.

In the M & E structure according to the prior art, an electrically conductive mesh screen is used to support the M & E. However, the reticular screen is not completely satisfactory because the surface is not flat. When the network screen is compressed with catalytically active particulate or flat sheet-like membranes, part of the screen penetrates into the membrane more than the rest of the screen. Due to this technique, the screen is inhomogeneously contacting the electrode coating and the membrane and the electrical energy is transferred unevenly to the surface of the membrane. Moreover, when the screen penetrates the membrane, part of the membrane ruptures better.

Another problem associated with the use of reticular screens is that the membrane is protected from tearing or rupturing by a mattress (elastic device) that can be used to maintain the current collector against catalytically active particulates on the surface of the membrane. Is that. Thus, reticular screens according to the prior art do not provide the protection provided by the near flat electroconductive screens according to the invention.

The present invention provides a support structure for an M & E structure that minimizes most of the problems caused by using a mesh screened structure.

In particular, the present invention relates to a membrane / electrode composite structure, characterized in that it consists of a substantially flat ion exchange membrane having a plurality of interconnected lines of catalytically active particulates bound to at least one or more flat surfaces of the membrane.

The invention also relates to a generally flat electrically conductive screen passing through the screen and having a plurality of openings that occupy less than about 75% of the surface area of the screen; Catalytically active particulates deposited on at least a portion of one flat surface of the screen and in contact with the physical and electrically flat surfaces; And an ion exchange membrane coupled to the catalytically active particulates and the flat surface of the screen such that the active particulates are interposed between the membrane and the screen.

The present invention also provides for (a) at least partially covering a plurality of catalytically active particulates with at least one surface of a substantially flat screen template through which a plurality of openings occupy less than about 75% of the surface area of the screen template; (b) contacting the ion exchange membrane with a flat surface with a coated surface of the screen template; (c) transfer catalytically active particulates from the screen template to the membrane; (d) removing the screen template; (e) a method of producing a membrane / electrode composite structure, characterized in that it comprises the step of binding the catalytically active particulates to the membrane.

Furthermore, the present invention provides a method for the preparation of (a) at least a portion of at least one surface of a substantially flat electroconductive screen through which a plurality of openings occupy less than about 75% of the surface area of the electroconductive screen. Coated with a dispersion; (b) contacting the coated surface of the screen with an ion exchange membrane; and (c) bonding the coated screen to the membrane.

Surprisingly, M & E structures with interconnected lines of catalytically active particulates attached on the membranes, when used in electrochemical cells, have significantly higher efficiencies compared to the M & E structures according to the prior art which have a substantially continuous coating of catalytically active particulates. It turns out to work. The increased efficiency is believed to result from the open area provided between the interconnected lines of catalytically active particulates present on the membrane. This open area provides an electrically inert space for removing gas produced at the catalytically active surface.

Furthermore, the interconnected lines are such that the membrane provides a minimum barrier to the gas by providing a short passage for the escape of gas formed at the interface between the catalytically active particulates and the membrane. The pattern of catalytically active particulates is designed such that the interconnected lines of particulates and passages for the escape of gas from their surroundings are less than the flow resistance through the membrane.

Thus, it is easier for the gas to pass through the interconnected lines of catalytically active particulates around the line than for the gas to penetrate the membrane and exit to the opposite cell compartment.

The size, shape and thickness of the interconnected lines of the catalytically active particulates according to the invention depend on the type of ion exchange membrane used. That is, membranes with high resistance to gas infiltration allow the interconnected lines of particulates to use larger lines, while membranes with less resistance to gas penetration may require smaller interconnected lines of particulates. . For example, in a chlor-alkali electrolyser, a polymer layer having a thickness of about 3.5 mils (0.09 mm) and having a sulfonic acid ion exchange group and a polymer layer having a thickness of about 0.5 mils (0.01 mm) and having a carboxylic acid ion exchange group, Two layer ion exchange membranes having a total thickness of about 4 mils (0.1 mm) may have interconnected lines of catalytically active particulates having desired dimensions. The term "dimension" applies herein to a line of catalytically active particulates having a predetermined width. The line may be a symmetrical or asymmetrical pattern.

Preferably, the minimum width of the line is at least 6 microns, more preferably at least 20 microns. The maximum width of the line is less than 1 cm, preferably less than 0.5 m, more preferably less than 0.2 cm.

In addition, the porosity of the catalytically active particulate layer acting as an M & E structure is also of great importance for the escape of gas formed during the operation of the cell. The M & E structure according to the prior art has microporous opeming which acts to provide a passageway for the gas to escape to a limited extent. However, rather than continuous coatings having "microporous" openings, "macroporous" coatings have been found to be quite desirable because they provide a large amount of space for the "macroporous" coating to exit the gas. Thus, the screens used in the present invention can be used to produce macroporous M & E structures (ie structures having interconnected lines of a plurality of catalytically active particulates) as compared to microporous M & E structures according to the prior art.

The macroporosity of the M & E structure according to the present invention allows the electrochemical cell to be used to operate at higher efficiency.

The screen or screen template used in the present invention is an almost flat screen having a plurality of spaced openings. The term "screen" as used herein is compatible with "screenplates" which are used as any means of providing a membrane with a line of a plurality of catalytically active particulates inserted or bonded to the membrane and then removed from the membrane. Apply as an enemy. Preferably, the screen is almost completely flat on at least one surface. Flatness is particularly preferred because flatness can form M & E structures with well-defined, controlled open regions and, alternatively, corresponding regions that can be covered using catalytically active particulates. Thus, when the catalytic coating is placed on the screen and then inserted into the membrane, most of the membrane is left exposed. This reduces the amount of catalytic material used to form the M & E structure and maximizes the area for the gaseous product to escape from the electrode coating because there is a larger amount of open area. In the case of a screen template, the screen can actually be made of any other material that can provide multiple openings, but the screen is preferably a metallic screen.

With particular reference to the drawings, FIG. 1 is a side view of one type of screen suitable for use in the present invention. The metal 100 has one flat side 130 and one round side 120. Round side 120 also has one slightly flat portion. The screen has one opening 110 that connects two opposite screen faces.

2 is a side view of another form of a screen 200 suitable for use in the present invention. Typically, the metal has rounded sides 220 and 230 that also have some flat portions. The screen has an opening 210 that connects opposite screen faces.

3 is a partial plan view of an interconnected line pattern 300 of catalytically active particulates deposited on a membrane. Between the interconnected line patterns there are a plurality of openings 310 that are not interconnected, that is, separated from each other.

The thickness of the screen does not significantly affect the successful operation according to the invention. However, for convenience and ease of handling it is desirable that the screen does not exceed the thickness of the membrane. The width or diameter of the interconnected lines of catalytically active particulates bound to the membrane is set to less than 1 cm. If the dimension is 1 cm or more, the gas of the product produced in the cell opposite, because the resistance given when the gas exits the cell across the membrane is less than the resistance received when the gas exits through the catalytically active particulates. The degree of contamination will increase.

According to the method of the invention, the interconnected lines of catalytically active particulates are suitable for the pattern of the screen or screen template used. The shape and size of the screen thus represent the shape and size of the interconnected lines of the catalytically active particulates. Generally, the screen has no more than 75% of the opening provided by the screen surface, and the screen preferably has an open area of 25 to 75%, more preferably 40 to 60%, most preferably 45 to 55%. Such screens provide enough open area on the membrane surface for the gas formed in the catalytically active particulates to escape.

In some cases, there may be no openings around the screen, so that the screen can be configured to provide a non-porous region where the gasket can be placed when the M & E structure is assembled with other components to form an electrochemical cell. have.

Particularly suitable screens for forming interconnected lines of catalytically active particulates in the membrane are electroformed screens having a plurality of openings spaced apart from one another.

The method of forming electrons is a method of electrochemically depositing a metal on a matrix in a photo-measured pattern. When the metal is deposited on the photographic plate and then removed from the photographic plate, the pattern on the photographic plate is stabilized to provide a metal matrix having a plurality of openings.

The screen created in this way is photographically complete and almost flat. Since the metal is formed around each opening to create the opening, the opening has a unique arch shape. This configuration allows the screen printed material to escape well through the openings and prevent the formation of deposits. Single-sided electroforming provides essentially conical holes, whereas double-sided electron forming methods provide biconical holes.

The holes in which the electrons are formed are preferably holes that are completely drilled, and the holes in which the electrons are formed are smooth, so that when the screen comes into contact with the membrane, the screen is formed by other means that the screen does not rupture the membrane. In addition, because the screen on which the electrons are formed is almost flat and does not penetrate the membrane unevenly when the screen is in contact with the film, the screen on which the electrons are formed is superior to the woven or mesh screen wire mesh.

The form of interconnected lines of catalytically active particulates can be symmetrical or asymmetrical. In the case of symmetry, lines can form several openings of different shapes (eg square, rectangle, triangle, etc.). As described, the lines on the membrane need not be specific patterns in particular geometric patterns that are repetitive or non-repetitive.

The improvement realized by the present invention is due to the increased ability of the gas to diffuse out of the porous electrode film and into the electrolyte solution, rather than diffusing the gas through the original membrane into the electrolyte opposite the membrane. While there are many factors measuring the diffusion path of the gas produced at the porous electrode, the open area of the membrane according to the present invention is said to be closely deposited in the catalytic area to provide a transverse path for the generated gas to reach the electrolyte solution. I think. By transverse path is meant the path of diffusion from the area producing gas in the catalytically active interconnected line to the electrolyte solution which extends essentially parallel to the membrane surface.

Moreover, if such open zones do not produce a gaseous product, the open zones may be adapted to a pressure and / or concentration gradient that acts on the desirable transfer of the gaseous product into the electrolyte solution outside the electrocatalytic region of the M & E structure. Does not provide

Experimental results show that the degree of gaseous contamination is more directly related to the percentage of open area present in the membrane rather than the width of the interconnected lines. If this is true, the limits and preferred ranges of the open area are also of great importance.

M & E structures according to the present invention include embodiments in which the catalytically active particulates and the nearly flat screen are bonded or inserted into one or both sides of the membrane. However, the present invention requires that at least one electrode is in the form of a plurality of catalytically active particulates in contact with the membrane. The electrode can act as a cathode or an anode while the cell is operating. Optionally both electrodes can be catalytically active particulates inserted opposite or into the surface of the membrane. For the purposes of the present invention, the form of the two electrodes will be described as being catalytically active particulates and may also be described as if they are separate conventional electrodes of the two electrodes.

In general, conventional anodes are produced in various shapes and patterns, including, for example, screens of expanded metal, perforated plates, punched plates, expanded metal in the form of flat diamonds or reticulated gold meshes. One is a hydropermeable, electrically conductive structure. Metals suitable for use as the anode include tantalum, tungsten, niobium, zirconium, molybdenum and include titanium and titanium alloys containing higher amounts of such metals.

Optionally, the anode may consist of a number of catalytically active particulates inserted into the membrane. Suitable materials for use as electrocatalytically active positive electrode materials include, for example, activation of oxides of platinum group metals such as ruthenium, iridium, rhodium, platinum, palladium alone, or mixtures with oxides of film-forming metals. Contains substances. Other suitable activated oxides include cobalt oxide alone or cobalt oxide mixed with other metal oxides. Such activated oxides are described in US Pat. Nos. 3,632,498, 4,142,005, 4,061,549 and 4,214,971.

In general, conventional cathodes are hydraulic impermeables made in various shapes and patterns, including, for example, screens of expanded metal, perforated plates, perforated plates, expanded metal in the form of non-flat diamonds or reticulated gold meshes, It is an electrically conductive structure. Metals suitable for use as the negative electrode are, for example, copper, iron, nickel, lead, molybdenum, cobalt, alloys containing more of these metals [eg low carbon stainless steel] and materials [eg silver, gold, Platinum, ruthenium, palladium and rhodium].

Optionally, the cathode can be a plurality of catalytically active particulates inserted therein. Suitable materials for use as the electrocatalytically active negative electrode material include, for example, platinum group metals such as ruthenium or metal oxides such as ruthenium oxide. U.S. Patent No. 4,465,580 describes such a cathode.

Whether catalytically active fine particles are used as the positive electrode or negative electrode, it is preferable to finely divide the fine particles to increase the surface area. For example, in the case of an oxygen or hydrogen electrode fuel cell, platinum black [surface area: 25 m 2 / g or more] on activated carbon powder [average particle size: 10 to 30 µ] or high surface area platinum [surface area: 800 to 1800 m 2 / g] Is quite suitable for use as an anode and a cathode. In the case of chlorine cells, catalytically active fine particles can be prepared when pyrolysis of ruthenium nitrate at a temperature of 450 ° C. for 2 hours to produce ruthenium dioxide fine particles. Subsequently, mortar and pestle may be used to pulverize the resulting oxide, and an electrode may be manufactured using a portion that passes through a 325 mesh sieve (pore diameter: less than 44 µ).

Membranes suitable for use in the present invention may consist of fluorocarbon or hydrocarbon type materials. Such membrane materials are known in the art. However, fluorocarbons are generally preferred because of their chemical stability.

Perionic polymers in the form of nonionics (thermoplastic) are particularly suitable for use in the present invention because they are easily softened by heating and can easily bond the membrane to the electrode and flat screen or screen template. Suitable membranes are described in U.S. Pat. No. 4,209,635, 4,212,713, 4,251,333, 4,270,996, 4,329,435, 4,330,654, 4,337,137, 4,337,211, 4,340,680, 4,357,218, 4,358,545, 4,358,545 4,417,969, 4,462,877, 4,470,889, 4,478,695 and European Patent Publication No. 0,027,009. Generally, membrane polymers have an equivalent range of 500 to 2000. The membrane may be a single layer or may be a multilayer membrane. More useful membranes are bilayer membranes having sulfonic acid ion exchange groups in one layer and carboxylic acid ion exchange groups in the other layer.

It is preferred that the fluorocarbon membrane is in thermoplastic form for the insertion of catalytically active particulates into the fluorocarbon membrane. The fluorocarbon membrane is in thermoplastic form before it is produced and converted to the ion exchange form. The thermoplastic form refers to, for example, SO ₂ X pendant groups, where X is —F, —CO ₂ , —CH ₃ or quaternary amine, rather than SO ₃ Na or SO ₃ H pendant groups to which the membrane is ionically bonded. It means having

Particularly preferred fluorocarbon materials for use in forming the film are copolymers of monomer (I) and monomer (II) (as defined below). Optionally, monomers of the third type can be copolymerized with monomers (I) and monomers (II).

Monomers of the first type are represented by the following general formula (I):

CF ₂ = CZZ '(I)

Wherein Z and Z 'are independently selected from -H, -Cl, -F and -CF ₃ .

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

_{Y- (CF 2) a - (} CFR f) b - (CFR f ') c -O - [CF (CF 2 X) -CF 2 -O] n -CF = CF 2 (Ⅱ)

Wherein Y is selected from -SO ₂ Z, -CN, -COZ and C (R ³ _f ) (R ⁴ _f ) OH; Z is selected from -I, -Br, -Cl, -F, -OR and -NR ₁ R ₂ ; R is a straight or branched chain alkyl radical or aryl radical having 1 to 10 carbon atoms; R ³ _f and R ⁴ _f are independently selected from perfluoroalkyl radicals having 1 to 10 carbon atoms; R ₁ and R ₂ are independently selected from —H, a straight or branched chain alkyl radical having 1 to 10 carbon atoms and an aryl radical; a is 0 to 6; b is 0 to 6; c is 0 or 1, provided that a + b + c is not 0; X is selected from -Cl, -Br, -F and mixtures thereof when n> 1, n is 0 to 6, R _f and R ^{f '} are independently -F, -Cl, 1 to 10 carbon atoms Perfluoroalkyl radicals and fluorochloroalkyl radicals having 1 to 10 carbon atoms.

Particularly preferred compounds are those wherein 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; a + b + c is a compound of 2 or 3.

Third optionally suitable monomer is one or more monomers selected from compounds represented by the following general formula (III).

Y '-(CF ₂ ) ^a' -(CFR _f ) ^{b '} -(CFR ^f' ) ^{c '} -O- [CF (CF ₂ X')-CF ₂ -O] ^{n '} -CF = CF ₂ (III )

Wherein Y 'is selected from -F, -Cl and -Br; a 'and b' are independently 0-3; c 'is 0 or 1, provided that a' + b '+ c' is not 0, n 'is 0 to 6, and R _f and R ^f' are independently -Br, -Cl, -F, 1 to Is selected from perfluoroalkyl radicals having 10 carbon atoms and chloroperfluoroalkyl radicals having 1 to 10 carbon atoms, wherein X 'is selected from -F, -Cl, -Br and mixtures thereof when n'>1; do.

Processes for converting Y to ion exchange groups are known in the art, and such methods consist of reaction with alkaline solutions. In the case of the SO ₂ F pendant group, the membrane can be converted to the membrane in ionic form by reacting the membrane with 25% by weight of NaOH under the following conditions. (1) The film is immersed in about 25% by weight sodium hydroxide at a temperature of about 90 ° C. for about 16 hours: (2) The film is washed twice with deionized water heated to about 90 ° C., each time having a cleaning time of 30 To 60 minutes. The pendant group then takes the form -SO ₃ -Na ⁺ . If in fact be non-cationic -Na ^+. [Example: -H ^+] to be produced in place of Na ⁺ is.

The method for producing a supported M & E structure according to the invention involves a number of steps. First, the membrane and flat screen are selected. A coating of catalytically active particulates is then placed on the screen. There are a number of suitable methods for depositing particulates on the surface of flat metal screens. For example, a slurry of catalytically active particulates in solution or dispersion is applied or sprayed onto a metal screen. The screen may also be immersed in a solution or dispersion of particulates. It is also possible to apply the slurry to the film using various printing techniques.

Particularly suitable methods for depositing catalytic particulates on a screen involve forming a solution / dispersion of catalytically active particulates in a solvent / dispersant.

Solvents / dispersants suitable for use in the present invention should have the following properties: boiling point [less than 110 ° C.], density [1.55-2.97 g / cm 3] and dissolution parameters [7.1 to 8.2 Hildebrand].

Solvents / dispersants of the following general formula (IV), which also meet the above-described properties (boiling point, density and dissolution parameters), have been found to be particularly preferred.

XCF ₂ -CYZ-X '(IV)

Wherein X is selected from -F, -Cl, -Br and -I, and X 'is selected from -Cl, -Br and -I; Y and Z are independently selected from -H, -F, -Cl, -Br, -I and -R '; R 'is selected from perfluoroalkyl radicals having 1 to 6 carbon atoms and chloroperfluoro radicals.

Most preferred solvents / dispersants are 1,2-dibromotetrafluoroethane [BrCF ₂ -CF ₂ Br] (mainly known as Freon 114 B 2) and 1, mainly known as Freon 113; 2,2-trichlorotrifluoroethane [ClF ₂ C-CCl ₂ F].

Of these two solvents / dispersants, 1,2-dibromotetrafluoroethane is the most preferred solvent / dispersant. Its boiling point is 47.3 ° C., density is about 2.156 g / cm 3 and dissolution parameter is about 7.2 Hildebrand.

1,2-dibromotetrafluoroethane is considered to work particularly well since it is not directly polar but has high polarization. Therefore, when 1,2-dibromotetrafluoroethane binds with a polar molecule, its electron density changes and 1,2-dibromotetrafluoroethane acts as a polar molecule. However, when 1,2-dibromotetrafluoroethane is an almost nonpolar molecule, 1,2-dibromotetrafluoroethane acts as a nonpolar solvent / dispersant. Accordingly, 1,2-dibromotetrafluoroethane has a tendency to dissolve the nonpolar skeleton and the polar pendant group of polytetrafluoroethylene. The dissolution parameter of 1,2-dibromotetrafluoroethane is measured from 7.13 to 7.28 Hildebrand.

Optionally, the solvent / dispersion may contain a binder to hold the catalytically active particulates together to bind to the screen. Preferred binders include various fluoropolymers and ionomers, including materials such as polytetrafluoroethylene, perfluorinated polymers and copolymers. Particularly preferred binders are ionomers having the same or similar composition as the ion exchange membrane. Examples of ionomers in a form suitable for use as a binder are the same as the ionomers indicated as suitable for use as ion exchange membranes, as described above. The solvent / dispersant described above is a solvent for the ion exchange polymer. Thus, solution / dispersion slurries containing catalytically active particulates, ion exchange fluoropolymers, and solvents / dispersants can be formed. These slurries help the catalytically active particulates bind together and bind to the screen or screen template.

When preparing the slurry, the concentration of the ionomer (in dry form without solvent / dispersant) is preferably 4 to 20% by weight. The concentration of catalytically active particulates is at least 0.1% by weight but typically is not at least about 30% by weight. Although there is no maximum limit level, the activity of the catalyst depends on the type of catalyst used and all catalysts behave slightly differently, so experiments with specific catalysts determine the optimum catalyst level. However, when using ruthenium oxide, it has been found that 2 to 20% by weight is a suitable level. All weight percentages are based on the total weight of the slurry.

In some cases, an electrically conductive metal can be added to the slurry to increase the electrical conductivity of the catalyst deposited on the film. For example, silver is generally added at a level of 60 to 90% by weight. Other suitable metals include nickel, tantalum, platinum and gold.

The production method of the slurry is carried out using the following production method. Other techniques may be used as appropriate. First, the ingredients are weighed and mixed with each other in a dry state. Then sufficient solvent / dispersant is added to cover the dry ingredients. The mixture is then mixed in a ball mill for 4 to 24 hours to obtain a homogeneous mixture. In addition, the ionomer is also broken up for some time and at least partially dissolved. This helps the catalytically active particulates to bind together. The mixture is then allowed to settle and the excess solvent / dispersant is decanted. Generally, the mixture at this time contains 25% by weight solids.

The flat screen or screen template is washed or treated in such a way that the flat screen or screen template on which the solution / dispersion is optionally deposited is in uniform contact with the solution / dispersion. The flat screen can be washed with a degreaser or similar solvent and then dried to remove any dirt or oil from the flat screen. The metallic screen is acid etched and then washed with a solvent to promote adhesion, and if necessary, the degreasing step is sufficient, unless the metal is a new metal.

After washing, the flat screen can be pretreated by heating or by vacuum drying before contacting the solution / dispersion in the coating operation. Preferably, in all cases it is sufficient to use a temperature of about 110 ° C. and a pressure of about 20 mmHg. Typically, however, mild heat of about 50 ° C. at atmospheric pressure is appropriate.

Various methods are suitable for applying the solution / dispersion to the screen and can also be used. One suitable method involves the steps of immersing the screen in solution / dispersion, followed by air drying and sintering with sufficient repeating at the desired temperature to form the desired thickness. Also, spraying the solution / dispersion onto the screen may advantageously be used to cover large or uneven shapes. Sometimes a step of pouring the solution / dispersion onto the screen is also used. Successfully, the step of applying the solution / dispersion with a brush or roller has also been used. Moreover, the coating can be easily applied using a tonbar, knife or rod. Typically, it is repeated-coated to form a coating or film of the desired thickness. Multiple solution / dispersion coatings may be applied to the screen to form catalytically active particulates in the desired thickness. Preference is given to removing the solvent / dispersant from the coating to dry the solution / dispersion. The drying step is carried out by evaporation of the solvent / dispersant, heating or vacuum drying. The coating may be a coating of any desired thickness. However, thicknesses of 5 to 50 microns have been found to be suitable. In some cases, the coating applied to the screen may be sintered between the coatings and then the coating may be transferred to the membrane.

When the coated screen template is used to transfer the catalytically active particulate coating to the membrane, the template is placed on one surface of the membrane opposite and the mixture is compressed. Optionally, it can be heated during compaction to enhance the migration of catalytically active particulates to the membrane and to improve adhesion of the particulates to the membrane. However, the mixture should not be heated to a temperature above about 230 ° C. because the membrane will soften too much and the membrane will stick to the screen template. Similarly, pressures above about 7 kg / cm 2 should be avoided because the membrane will squeeze and pass through the holes in the screen template. If the membrane is in the hydrogen form, the membrane should not be heated to temperatures above about 180 ° C. because the membrane tends to decompose. If both pressure and heat are used, the compression time should be relatively short. That is, it should be less than 30 seconds. The time is calculated as the time required until the temperature of the membrane fills with the stated temperature. However, if not heated at all, the mixture can be pressed for a time of up to about 5 minutes.

After moving the catalytically active particulates to the membrane, the pressure and / or heat is removed and the screen peeled off into the membrane, leaving interconnected line types of catalytically active particulates on the membrane.

The catalytically active particulates then need to be fixed to the membrane more permanently. The fixing step can be carried out by applying additional pressure and heat to the coated membrane. For example, the coated membrane may be heated to a temperature as high as about 260 ° C. for 30 seconds to 1 minute (when the coated membrane is in thermoplastic or sodium form) to allow the components to bond together. If the membrane is in the form of hydrogen, the membrane should not be heated to temperatures above about 180 ° C. because the membrane tends to decompose. This temperature softens the binder in the slurry and softens the membrane causing the binder and the membrane to bind to each other. By heating the membrane to too low a temperature or by heating the membrane for too short a time, the catalytically active particulates are not completely bound to the membrane. Heating the membrane for too long causes too much particulates to mix with the membrane. By heating the film to a temperature that is too high, the film prevents the formation of M & E structures that are superior to the structures formed by melting.

Occasionally, heating the mixture under a pressure of about 3.5 kg / cm 2 or less advantageously results in good binding of the components. However, pressures of 3.5 kg / cm 2 or more tend to make the mixture too flat.

Preferably, the heated pressure is used to combine the components. Although a variety of methods may be used, one method that has been found to be particularly useful involves forming a sandwich of components between two plates, that is, between the upper and lower platens. A screen made of polytetrafluoroethylene paper on the top of the lower platen, a membrane coated with catalytically active particulates on the film, and another screen made of polydetrafluoroethylene paper, providing elasticity. With a rubber screen, another screen made of polydetrafluoroethylene paper, and finally an upper platen. This insert is then placed in a heated compactor and heated under pressure to carry out the joining step.

The fact that the first side of the screen is nearly flat minimizes the degree of penetration of catalytically active particulates into the space between the solid portion of the screen and the membrane. In other words, when the catalytically active solution / dispersion is applied to the membrane, the solution / dispersion does not “run”. Even the screen shown in FIG. 2 is sufficiently flat to minimize the "run" of the catalytically active solution / dispersion.

Since the catalytic coating covers only part of the membrane, it uses a less catalytically active material. However, the catalytic activity of the M & E structure is at least equal to the catalytic activity of the M & E structure according to the prior art.

It has been found that the process according to the invention uses only a part of the catalytically active particulates but can further reduce the concentration of the particulates. For example, typical solutions / dispersions of catalytically active particulates contain about 75 weight percent silver, about 16 weight percent ruthenium oxide, and about 9 weight percent ionomer. However, using the technique according to the invention, a slurry containing about 83% by weight silver, about 8% by weight ruthenium oxide and about 9% by weight ionomer is in fact the same as a slurry having 16% by weight ruthenium oxide. Do it. This indicates that potential savings of about one-half the more expensive ruthenium oxide catalyst can be achieved.

Methods and techniques for using the membranes according to the invention with interconnected lines of a plurality of catalytically active particulates bound to at least one side of the membrane are methods and techniques known in the art. Generally, however, the current collector is pressed across the interconnected lines of catalytically active particulates, connected to a power supply (in the case of an electrolytic cell), or connected to a power consumer (in the case of a fuel cell or battery). Connect. The current collector conducts electrical energy to interconnected lines of catalytically active particulates (or electrical energy from interconnected lines of catalytically active particulates). Particularly suitable current collectors have been found to be electroconductive screens having the same pattern as the pattern of interconnected lines of catalytically active particulates. This fact allows the lines of catalytically active particulates to conduct electrical energy to the current collector (or to the electrical energy from the current current collector), respectively. In some cases, an elastic device (eg a mattress) may be used to hold the current collector opposite the coated membrane.

The M & E structure according to the invention is, for example, a fuel cell for continuously supplying electrical energy, for supplying chemical products such as chlorine and caustic generated from sodium chloride saline solution or hydrogen and oxygen generated from water. It is useful in a wide variety of electrochemical cells, including batteries for electrolyzers and intermediate products of electrical energy.

Example

A mixture of about 76 g silver fine particles, about 16 g ruthenium oxide fine particles and about 8 g carboxylic acid ion exchange fluoropolymer fine particles is dissolved and suspended in BrCF ₂ -CF ₂ Br under the ball. First, anhydrous ingredients are weighed and mixed together. Subsequently, sufficient solvent / dispersant is added to cover the components. Then, the mixture is mixed under the ball for about 24 hours to obtain a homogeneous mixture. In addition, the ionomer is completely milled for some time to at least partially dissolve. The mixture is then precipitated and the excess solvent / dispersant is decanted. The mixture at this time contains about 25% by weight solids.

The screen template (area: about 56 cm 2) is used to receive the solution / dispersion. The screen template is a template in which electrons are formed. Is a screen having a plurality of openings [diameter: 0.7 mm] in which the screen is uniformly distributed on the surface. There are a sufficient number of openings to provide a screen with an open surface area of about 50%. The screen template is about 0.07 mm thick.

The screen template is immersed in a silver / ruthenium oxide / ionomer suspension and dried at room temperature. For a total of six cycles, the immersion and drying steps are repeated five more times. The coating is air dried between the coatings. The coated screen is then sintered for 5-10 minutes at a temperature of about 260 ° C. The screen is then contacted with a bilayer ion exchange membrane (of thermoplastic type) having sulfonic acid ion exchange groups in one layer and carboxylic acid ion exchange groups in the other layer. The screen is contacted with the side of the membrane having carboxylic acid ion exchange groups.

The mixture is placed in a heated hydraulic press and pressed at about 3.5 kg / cm 2 for 30 to 60 seconds at a temperature of about 230 ° C. and then the membrane is bonded to the coated screen template.

Cool the mixture by removing it from the compactor. Subsequent removal of the screen template leaves a number of interconnected lines of catalytically active particulates bound to the membrane.

According to another embodiment of the present invention, the electroconductive screen is coated with catalytically active particulates, then contacted with the membrane to bond and heated for a short time under pressure. When the membrane is in thermoplastic or sodium form, the following conditions can be used to bond. The membrane is heated to a temperature of about 260 ° C. or less for 30 seconds to 1 minute. The time is calculated as the time required until the film temperature reaches the stated temperature. Heating to too low a temperature or too short a time will prevent the screen from fully bonding to the membrane. If it is heated for too long, the metal of the screen will not completely pass through the membrane and be located on the surface of the membrane. Heating to too high a temperature dissolves the film and prevents the formation of M & E structures superior to the formed structures. Sometimes it is advantageous to heat under a pressure of about 3.5 kg / cm 2 or less of the screen / membrane mixture. Pressures of about 3.5 kg / cm 2 or more tend to press the membrane and allow the membrane to pass completely through the screen. However, when the membrane is in hydrogen form, the membrane should not be heated above about 180 ° C.

In order to press the screen into the membrane, the manufacturing method mentioned in the specification is preferably used when forming an insert of components between two platens, namely the upper platen and the lower platen. The lower platen has a screen of polytetrafluoroethylene paper, a membrane, a coated screen and another screen of polytetrafluoroethylene paper, and finally an upper platen. This insert is then placed in a heated press and heated to a temperature of about 260 ° C. for about 90 seconds.

In terms of usability, the electroconductive screens according to the invention are considerably superior to the reticulated screens used in the prior art, since these reticulated screens are almost flat but the surface structure is meshed and wavy and not homogeneous or somewhat flat. Because it is a structure. The screen according to the invention is preferably metallic but may be constructed from other materials as long as the screen is electrically conductive.

Preferably, the thickness of the screen should not be thicker than the layer thickness of the film to which the screen will bind to at least about 25%. That is, in the case where the membrane is a two-layer membrane in which one layer is a sulfonic acid polymer and the other layer is a carboxylic acid polymer, when the screen is bonded to the carboxylic acid layer, the screen thickness should not be thicker than the thickness of the carboxylic acid layer which is on the order of 25% or more. If the screen is too thick, it is believed that the screen will penetrate into the membrane excessively and the screen will be chemically attacked by chemicals in the compartment opposite the cell. More preferably, the thickness of the screen should not exceed the layer thickness of the film to which the screen will bind.

The width or diameter of the catalytically active particulate layer as bonded to the membrane is preferably less than about 1 cm, more preferably less than about 0.5 cm and most preferably less than about 0.2 cm. Since it is believed that the resistance encountered when the gas travels through the membrane to the opposite cell surface is less than the resistance encountered when the gas exits through the catalytically active particulates, the dimensions above the above mentioned ranges are opposite. The degree of gas contamination of the product produced on the cell surface is raised.

Claims (21)

Membrane / electrode composite structure, comprising a substantially flat ion exchange membrane having a plurality of interconnected lines of catalytically active particulates bound to at least one flat surface of the membrane. The structure of claim 1, wherein the interconnected lines occupy 25 to 75% of the membrane surface. The structure of claim 2, wherein the interconnected lines occupy 45-55% of the membrane surface. The membrane of claim 1, wherein the membrane is selected from fluorocarbon and hydrocarbon type materials, and the plurality of catalytically active particulates are optionally mixed with oxides of the film-forming metal. A structure selected from oxides of ruthenium, iridium, rhodium, platinum, palladium and mixtures thereof, and cobalt oxide alone or a mixture of cobalt oxide and other metal oxides. The structure of claim 1 wherein the line width of the catalytically active particulates is at least 6 μ, less than 1 cm. The structure of claim 1 wherein the line width of the catalytically active particulates is between 20 μm and 0.5 cm. The structure of claim 1 containing a plurality of electrically conductive metal particulates distributed among the catalytically active particulates. 8. The structure of claim 7, wherein the electrically conductive metal particulate is selected from silver, nickel, tantalum, platinum and gold. The structure of claim 1 wherein the catalytically active particulates are present in the layer having a thickness of 5 to 20 microns. The structure of claim 1, wherein the interconnected lines of catalytically active particulates contain a binder of a fluorocarbon polymer. The device of claim 1, comprising a generally flat electroconductive screen having a plurality of openings passing through the screen and occupying about 75% or less of the surface area of the screen, wherein the catalytically active particulates are in one of the flat surfaces of the screen. A structure deposited on at least a portion and in physical and electrical contact with the flat surface, wherein the ion exchange membrane is coupled to the catalytically active particulate and the flat surface of the screen such that the active particulate is interposed between the membrane and the screen. The structure of claim 11, wherein the screen is a metallic screen with electrons formed thereon. The structure of claim 11, wherein the screen has an open area of 25 to 75% and the perimeter of the screen is nonporous. 14. The structure according to any one of claims 11, 12 and 13, wherein the thickness of the screen does not exceed the layer thickness of the film to which the screen is attached by up to 25% or more. (a) at least partially covering at least one surface of a substantially flat screen template through which a plurality of openings occupy less than about 75% of the surface area of the screen template with a plurality of catalytically active particulates; (b) contacting the flat surface of the ion exchange membrane with the coated surface of the screen template; (c) transfer catalytically active particulates from the screen template to the membrane; (d) removing the screen template and then (e) bonding the catalytically active particulates to the membrane. The method of claim 15, wherein the catalytically active particulates are coated on the screen in the form of a solution / dispersion, wherein the solution / dispersion is formed from a solvent / dispersant of the following general formula (IV). XCF ₂ -CYZ-X '(IV) Wherein X is selected from -F, -Cl, -Br and -I, and X 'is selected from -Cl, -Br and -I; Y and Z are independently selected from -H, -F, -Cl, -Br, -I and -R '; R 'is selected from perfluoroalkyl radicals having 1 to 6 carbon atoms and chloroperfluoroalkyl radicals. The method of claim 16, wherein the solution / dispersion contains 4-20% by weight ionomer. The method of claim 16, wherein the solution / dispersion contains 0.1 to 30 weight percent catalytically active particulates. 19. The method of any one of claims 16, 17 and 18, wherein the solution / dispersion contains 60 to 90% by weight of electrically conductive metal. The method of claim 15, wherein the screen template is bonded to the membrane at a temperature of about 260 ° C. or less and a pressure of about 3.5 kg / cm 2 or less. (a) coating at least a portion of at least one surface of a substantially flat electroconductive screen through which a plurality of openings occupy less than about 75% of the surface area of the electroconductive screen with a catalytically active particulate solution / dispersion in a solvent / dispersant; (b) contacting the coated surface of the screen with an ion exchange membrane, and then (c) bonding the coated screen to the membrane.

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