FI84497B - Collector which is bonded to a solid polymer membrane - Google Patents

Description

ι 84497

Current collector bound to a solid polymer membrane

The invention relates to an improved method for manufacturing a current size and / catalyst electrode / membrane structure having increased electrical conductivity in the region between the catalyst electrode and the current collector. Such structures are useful in a variety of applications, such as fuel cells, hydroelectric cells, chlor-alkali cells, and the like. The structure made according to the present invention is structurally very stable, which allows the membrane part to be much thinner than currently available, which reduces the ionic resistance of the membrane.

It is highly desirable, due to the harsh conditions of many membrane applications, that the membrane portion of the structure be structurally very strong. Thin membranes have been considered brittle, but thin membranes are desirable due to their lower ionic resistance.

This requires balancing on the one hand to obtain sufficient structural strength for the structure and on the other hand to reduce the thickness of the membrane to reduce the ionic resistance without sacrificing the structural strength.

Sources related to this invention include e.g. U.S. Patent No. 4,272,353, which describes a surface roughening technique for scraping the base of a solid polymer electrode (SPE) for subsequent processing; U.S. Patent No. 4,272,560 describes a membrane having a multilayer cathode in a backing fabric; the dissolved copolymer is used in the manufacture of this electrode. U.S. Patent No. 4,182,670 describes a combined cathode and diaphragm using a spray coating of a metal substrate with a metal powder; a polymer coated diaphragm is also described. An electrode body to which a powdered metal (typically precious metals) is attached is described in U.S. Patent No. 3,276,911, and also mentions a permeable ion electrolyte material.

U.S. Patent No. 4,844,913 to U.S. Patent No. 4,844,813 describes catalytic particles on an ion exchange material with an SPE membrane; in addition, this patent has an ion exchange moiety that mentions a sulfone group. U.S. Patent No. 4,366,041 describes a cathode and 5 diaphragm assembly having a wax degradable film.

In particular, the present invention describes a structurally stable electrode structure having a lower ionic resistance of the membrane portion and a higher electrical conductivity of the catalyst electrode and current collector portions. The thinness of the membrane is achieved without sacrificing structural durability and yet the resistance to ionic motion in the membrane is reduced.

When the above relates to this structure in the most general terms, its structure and manufacturing method are discussed in the following examples illustrating preferred embodiments.

In particular, the invention relates to a method of manufacturing an ion-permeable membrane, electrode and current collector structure comprising the steps of: a) forming a base layer of a porous electrically conductive material; b) coating at least partially at least one surface of the base layer with a fluoropolymer layer; c) coating the fluorine-25 polymer bonds on the base layer with a particulate catalyst; d) applying a polymeric substance to the catalyst material as a solution or dispersion so as to penetrate the porous base layer, forming a nearly uniform surface over the catalyst material and the at least partially coated base layer; and e) treating the structure with heat and / or pressure to enhance the flow of polymeric material into the base layer and around the catalyst material, thereby adhering the catalyst material to the base layer and sintering the polymeric material into a nearly non-porous layer around the catalyst material.

3,84497

The base layer is an electrically conductive, liquid-permeable matrix that acts as a current collector, conducting electrical energy to or from the electrode. It may consist of various materials such as carbon fabric, carbon-5 paper, carbon felt, metal mesh, metal wool and porous metal sheets. However, the most preferred base layer is carbon paper, which is readily available, easy to handle, and relatively inexpensive.

The paper 10 most preferably used in the present invention is one that has a low electrical resistance, is strong enough for processing, and has suitable surface properties, such as roughness, to provide good bonding between the fluoropolymer binder and the base layer. It is also advantageous to provide a good electrical connection between the carbon paper and the catalytically active particles of the electrode.

In the first step, the base layer is at least partially coated with a suitable polymeric binder. This polymeric binder may be a fluorocarbon binder such as poly-20 tetrafluoroethylene sold under the trademark Teflon.

Other suitable polymers may be e.g. thermoplastic nonionic forms of carboxylic acid copolymers and the like.

Particularly preferred fluoropolymer binders are the thermoplastic nonionic forms of perfluorinated polymers described in the following U.S. Patents: 3,282,875, 3,909,378, 4,025,405, 4,065,366, 4,116,888, 4,123,336, 4,126,588, 4,151,052 , 4,176,215, 4,178,218, 4,192,725, 4,209,635, 4,212,713, 4,251,333, 4,270,996, 4,329,435, 4,330,654, 4,337,137, 4,337,137, 4,337,211, 30 4,340,680, 4,357,218, 4,358,412, 4,358,545, 4,417,969, 4,462,877, 4,470,889, 4,478,695 and published EP Patent Application No. 0,027,009. The equivalent weight of such polymers is generally 500-2000.

Particularly preferred fluoropolymer binders are copolymers of 35 monomer I with monomer II (defined as 4,84497 below). If desired, a third type of monomer can be copolymerized with I and II.

The first type of monomer is represented by the general formula: CF2 = CZZ '(I) wherein Z and Z' are independently selected from -H, Cl and -CF3 ·

The second monomer consists of one or more monomers selected from compounds represented by the general formula: Y- (CP,) a- (CFRf) b- (CFRf,) c-O-fCF (CF2X) -CF ^ O] n ~ CF = CF 2 (II) 15 wherein Y is selected from -SO 2 Z / -CN, -CO 2 and -C (R 3f) (R 4f) OH; Z is selected from -I, -Br, -Cl / -F, -OR and -NR1R2; R is selected from branched or unbranched alkyl radicals having 1 to 10 carbon atoms or allyl radicals; 3 4 R f] a R f is independently selected from perfluoroalkyl radicals having 1 to 10 carbon atoms; R 1 and R 2 are independently selected from the group consisting of -H / branched or straight alkyl radicals having 1 to 10 carbon atoms or an aryl radical; a is 0-6; b is 0-6; C is 0 or 1; so that a + b + c is not 0; X is selected from -Cl / -Br, -F or mixtures thereof when n> 1; n is 0-6; and 5,84497

Rf and Rr, are independently selected from -F, -Cl, perfluoroalkyl radicals having 1 to 10 carbon atoms, and fluoroalkyl radicals having 1 to 10 carbon atoms.

It is particularly preferred when Y is SC 2 F or -COOCH 2; n is 0 or 1; and R 1, are -F, X is -Cl or -F, and a + b + c is 2 or 3.

The optional third monomer is one or more monomers selected from compounds represented by the general formula.

Y '- (CF2) a 1 ~ ^ CF ^ f} b' ”^ FR * f} c '-0 ~ ^ CH ^ CF2X' ^ -CF2" Q) n · “CF = CH2 (III) 15 where Y 'is selected from -F, -Cl or -Br; a' and b 'are independently 0-3; c' is 0 or 1; such that a '+ b' + c * is not 0; R'j is independently selected from -Br, -Cl, -F, perfluoroalkyl radicals having 1 to 10 carbon atoms, and chloroperfluoroalkyl radicals having 1 to 10 carbon atoms, and X 'is selected from -F, -Cl, -Br or mixtures thereof when n '> 1.

The binder is typically applied as a solution or dispersion so that it at least partially covers the base layer. The solution or dispersion can be applied to the base layer by various methods known per se. When the electrode is to be used in a fuel cell, the binder is most preferably a hydrophobic substance such as polytetrafluoroethylene. While the electrode will be used in an electrolyte cell such as a chlor-alkali cell, the binder is most preferably a hydrophilic material such as copolymers formed from monomers I and II and optionally III (described above).

2 6 84497

The preferred amount of binder is 0.5-50 mg / cm 2 on the surface of the base layer 2, preferably 2.5-30 mg / cm.

When the binder is applied as a solution or dispersion, various solvents / dispersants such as water, methanol, ethanol and compounds represented by the general formula: xcf2-cyz-x '10 wherein X is selected from F, Cl, Br and I; X 'is selected from Cl, Br and I; Y and Z are independently selected from H, F, Cl, Br, I and R '; and R 'is selected from perfluoroalkyl radicals and chloroperfluoroalkyl radicals having 1 to 6 carbon atoms.

The most preferred solvents or dispersants are 1,2-dibromotetrafluoroethane (commonly known as 20 Freon 114 B 2)

BrCF2-CH2Br and 1,2,3-trichlorotrifluoroethane (commonly known as Freon 113): cif2-cci2f Of the two substances, 1,2-dibromotetrafluoroethane is the most preferred solvent or dispersant.

The solution or dispersion used to apply the binder to the base layer may have a concentration of 2-30% by weight of polymer in the solvent / dispersant. The preferred concentration is 8-20% by weight and polymer 35 in the solvent / dispersant.

7 84497

Once the solution or dispersion is applied to the base layer, the solvent can be removed using heat, vacuum, or a combination of heat and vacuum. If desired, the solvent / dispersant can be allowed to evaporate under ordinary conditions. Preferably, the solvent is removed at an elevated temperature. In addition to removing the solvent / dispersant, the heat sinks the binder and causes it to more completely penetrate and surround the base layer. For example, when using polytetrafluoroethylene as a binder, exposure to 300-340 ° C for about 20 minutes is sufficient to remove the solvent / dispersant and sinter the polytetrafluoroethylene.

The next step in the process of the present invention is to add catalytically active and electrically conductive particles to the coated base layer. The structure eventually forms what is commonly referred to as a solid polymer electrolyte or SPE when the product is used in an electric cell. The electrode can be used as either a cathode or an anode.

Suitable materials for use as electrocatalytically active anode materials include platinum group metals or metal oxides such as ruthenium, iridium, rhodium, platinum, palladium, either alone or in combination with a film-forming metal such as Ti or Ta. Other suitable activating oxides include, for example, cobalt oxide, either alone or in combination with other metal oxides described in U.S. Patent Nos. 3,632,498, 4,142,005, 4,061,549, and 4,214,971.

Suitable materials for use as electrocatalytically active cathode materials include platinum group metals or metal oxides such as ruthenium or ruthenium oxide. U.S. Patent No. 4,465,580 describes such cathodes.

The catalyst particles used in this invention are most preferably finely divided and have the most preferred size of β 84497 200 to less than 400 mesh (U.S. standard) (53 to less than 37 microns). The metal powder is applied to the binder-coated base layer by methods known to those skilled in the art, such as spraying, forming a sheet from the catalyst particles, and pressing the sheet onto the base layer or forming and applying the particles as a liquid dispersion, e.g., an aqueous dispersion. A suitable amount of catalyst particles is 0.2 to 20 mg / cm per base layer area 2 and a preferred amount is 1.5 to 5.0 mg / cm.

Separately, a copolymer is formed. One such suitable polymer is a polymer formed from monomers I, II and optionally III, as described above. The polymer may be a thermoplastic nonionic sulfonic acid copolymer precursor or a thermoplastic nonionic carboxylic acid copolymer precursor or other polymer described for use as a binder. Most preferably, the copolymer is formed into a solution or dispersion with a solvent for application to the catalytic particles. When mixed with a suitable solvent or dispersant, the polymer is applied to the base layer covered with catalyst particles. Using a vacuum on one side of the base layer, the polymer in the solvent or dispersant is drawn onto the catalyst and the base layer. In a sense, when it can be said to be coated on one side, the coating, on the other hand, penetrates sufficiently the porous sheet.

In the step of bonding the fluoropolymer to the surface of the base layer coated with catalyst particles, the most practical method is to use conventional organic solvents. Typical solvents used include 1,2-dibromotetrafluoroethane, methanol, ethanol and the like. The applied polymeric material forms an almost non-porous ion exchange layer.

The next step is to use heat and / or pressure to remove the solvent / dispersant and sinter the polymer 9,84497 to form an almost uniform sheet of polymer. In addition, heat and / or pressure improve the deposition of the polymer on the catalyst particles and the base layer. For example, a temperature of 260-320 ° C is generally suitable for binding to the polymer particles and the base layer. The temperature is primarily limited by the onset of thermal decomposition of the polymer at too hot a temperature. Most preferably, the pressure is high enough and continuous long enough for binding to occur. For example, the pressure may be about 2 10 5 kg / cm for about one minute at an elevated temperature.

The next step in the fabrication of the improved electrode structure is to hydrolyze the structure from a non-ionic to an ionic form. Hydrolysis can be accomplished by treating the polymer with a basic solution if the polymer is a thermoplastic nonionic sulfonic acid polymer precursor or a thermoplastic nonionic carboxylic acid polymer precursor. In addition, if the polymer is a thermoplastic nonionic carboxylic acid polymer precursor, an acid solution can be used to hydrolyze the polymer.

For example, in a thermoplastic nonionic sulfonic acid polymer precursor, the finished structure can be hydrolyzed in 25% by weight sodium hydroxide for 16 hours at an elevated temperature of 80 ° C.

The finished article is now ready for use. As an example of size-25, it is not uncommon to find a membrane with a thickness of 5-10 mil (0.125-0.25 mm) due to the durability requirement of the structure. The final product can produce a membrane with a thickness of 1-2 mils (0.25-0.05) or even less. The resistance of the ion movement in the membrane is thus considerably reduced.

In another use, two sheets of the same size are placed together so that the base layers are outward and the polymer layers of the sheets are facing each other. The combined plates are placed in a press and joined together by suitable pressure and / or heat.

Claims (11)

A method of manufacturing a structure having an ion-permeable membrane, an electrode and a current collector, characterized in that it comprises the steps of: a) forming a current collector from a porous electrically conductive base layer material; b) at least partially coating at least one surface of the base layer with a fluoropolymer binder; c) forming an electrode by applying a particulate catalyst material over the fluoropolymer binder to the base layer; d) applying the polymeric material as a solution or dispersion to the catalyst material so that the polymeric material penetrates the porous base layer to form a substantially uniform coating on the catalyst material and at least a partially coated base layer; wherein the fluoropolymer binder of step b) and the polymeric agent of step d) form an ion permeable membrane; e) applying heat and / or pressure to the structure to assist the flow of polymeric material into the base layer and around the catalyst material so that the catalyst material adheres to the base layer and so that the polymeric material sinks into a substantially non-porous layer around the catalyst material. Process according to Claim 1, characterized in that the polymeric substance contains one or more solvents or dispersants selected from ethanol, methanol, water and a compound represented by the general formula XCF 2 -CYZ-X 'n 84497 wherein X is selected from F , Cl, Br and I; 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 and chloroperfluoroalkyl radicals having 1 to 6 carbon atoms. Process according to Claim 2, characterized in that the solvent or dispersant is selected from 1,2-dibromotetrafluoroethane and 1,2,3-trichlorotrifluoroethane. Process according to Claim 1, 2 or 3, characterized in that the catalyst particles are selected from ruthenium, iridium, rhodium, platinum, palladium and their oxides, either alone or in combination with a film-forming metal oxide, and cobalt oxide, either alone or in combination with another platinum group with metal or metal oxide. A method according to any one of the preceding claims, characterized in that it comprises the step of making two structures of the same size, placing the two structures together so that the non-porous polymer surfaces are in close contact with each other, and applying heat and / or pressure to form a single planar structure containing two current collectors with a non-porous ionically conductive polymer layer therebetween. Process according to any one of the preceding claims 30, characterized in that said base layer fluoropolymer binder is selected from a thermoplastic nonionic sulfonic acid or carboxylic acid copolymer precursor having an equivalent weight of 500 to 2,000. A method according to claim 1, characterized in that a) said electrically conductive material is graphite paper, b) said binder is polytetrafluoroethylene and c) said polymeric material is a sulfonic acid copolymer in thermoplastic powder form in a liquid solvent, and a vacuum is used to thermoplastic The powder and solvent would penetrate the porous graphite paper. A method according to claim 1, characterized in that it comprises the step of treating the polymer with a base or an acid at a temperature and for a time sufficient to hydrolyze almost all of the polymer. Process according to any one of the preceding claims, characterized in that the binder is a copolymer formed by polymerizing one or more monomers selected from the first group of monomers represented by the general formula CF 2 C 2 Z '(I), wherein Z and Z 'is independently selected from -H, -Cl, -F or -CF3; with one or more monomers selected from the group of monomers represented by the general formula 30 Y ~ (CF2) (CFRf) b- (CFRf,) c-O- [CF (CF2X) -CF2-0] n-CF = CF2 (II) wherein Y is selected from -SO 2 Z, -CN, -CO 2 and -C (R 3f) (R 4f) OH; and 84497 Z is selected from -I, -Br, -Cl, -F, -OR and -NR1R2; R is selected from branched or straight alkyl radicals having 1 to 10 carbon atoms or aryl radicals; R 3f and R 4f are independently selected from perfluoroalkyl radicals having 1 to 10 carbon atoms; Rx and R2 are independently selected from the group consisting of -H, a branched or unbranched alkyl radical of 1 to 10 carbon atoms, and an aryl radical; a is 0 to 6; b is 0 to 6; c is 0 or 1; so that a + b + c is not 0; 15. is selected from -Cl, Br, -F and mixtures thereof when n> 1; n is 0 to 6; and Rf and Rf, are independently selected from -F, -Cl, perfluoroalkyl radicals having 1 to 10 carbon atoms and fluorochloroalkyl radicals having 1 to 10 carbon atoms, and, if desired, with one or more monomers which are selected from the third monomer represented by the general formula (III) Y '- (CF2) a> - (CFRf) b, - (CFRf,) c, -O- [CF (CF2X') -CF2-0] n, -CF = CF where Y 'is selected from -F , -Cl and -Br; a 'and b' are independently 0-3; C 'is 0 or 1; so that a '+ b' + σ 'is not 0; Rf and Rf, are independently selected from -Br, -Cl, -F, perfluoroalkyl radicals having 1 to 10 carbon atoms, and chloroperfluoroalkyl radicals having 35 to 1 to 10 carbon atoms; and 14 84497 X 'is selected from -F, -Cl, -Br, and mixtures thereof when n' is> 1. Process according to Claim 9, characterized in that Y is -SO 2 F or -C00CH 3; n is 50 or 1; Rf and Rf, are -F; X is -Cl or -F; and a + b + c is 2 or 3. is 84497