Current collector bonded to a solid polymer membrane

Description

[0001] The invention relates to an improved method of manufacturing a current collector/catalyst electrode/membrane assembly which has increased electrical conductivity in the area between the catalyst electrode and the current collector. Such assemblies are useful in a variety of applications including, for example, fuel cells, water electrolysis cells, chlor-alkali cells, and the like. The assembly produced according to the present invention is substantially structurally stable which allows the membrane portion to be substantially thinner than those presently available, thereby reducing the ionic resistance of the membrane.

[0002] It is highly desirable, given the harsh conditions of many of the applications for the membrane, that the membrane portion of the assembly have substantial structural integrity. Thinner membranes have been viewed as fragile and yet thinner membranes are desirable due to their reduced ionic resistance. This requires a balance between providing adequate structural support for the assembly and yet reducing the membrane's thickness to reduce the ionic resistance of the membrane without a sacrifice in the structural integrity.

[0003] References which have a bearing on this invention include U. S. Patent No. 4,272,353, which discloses a surface abrading technique for scratching a solid polymer electrolyte (SPE) base member in preparation for subsequent treatment. U. S. Patent No. 4,272,560 describes a membrane having a cathode made of multiple coatings with a backing fabric; a dissolved copolymer is used in the fabrication of this electrode. U. S. Patent No. 4,182,670 discloses a combined cathode and diaphragm utilizing a spray coating of a metal substrate with powdered metal; a polymer impregnated diaphragm is also described. An electrode body having impregnated powdered metal (typically noble metals) is described in U. S. Patent No. 3,276,911, and it also mentions a permeable ionic electrolytic material. U. S. Patent No. 4,364,813 discloses catalytic particles deposited on an ion exchange material with a SPE membrane; additionally, this patent has an ion exchange feature mentioning a sulfonic group. U. S. Patent No. 4,366,041 describes a cathode and diaphragm assembly with a sacrificial film made of wax.

[0004] The present invention particularly describes a structurally stable electrode assembly which has lower ionic resistance in the membrane portion and which has higher electrical conductivity in the catalyst electrode and current collector portions. Membrane thinness is achieved without sacrifice of structural integrity and yet resistance to ionic movement through the membrane is reduced.

[0005] Subject matter of the present invention is a method of forming an assembly according to claim 1. Preffered embodiments thereof are subject matter of claims 2 to 12.

[0006] While the foregoing refers in general terms to the present assembly, the structure thereof and the method of manufacture are exemplified in the detailed description of the preferred embodiments following.

[0007] The invention particularly resides in a method of forming an assembly of an ion permeable membrane, electrode, and current collector, comprising the steps of:

(a) forming a foundation layer of a porous, electrically conductive material;

(b) at least partially coating a fluoropolymer binder on at least one surface of the foundation layer;

(c) applying a particulate catalyst material over the fluoropolymer binder on the foundation layer;

(d) dispersing a polymeric material as a solution or dispersion over the catalyst material in a manner to obtain penetration of the polymeric material into the porous foundation layer to form a substantially continuous coating on the catalyst material and the at least partially coated foundation layer; and

(e) applying heat and/or pressure to the assembly to enhance the flow of the polymeric material into the foundation layer and around the catalyst material to obtain adherence of the catalyst material to the foundation layer and to sinter the polymer material into a substantially non-porous layer around the catalyst material.

[0008] The foundation layer is an electrically conductive, hydraulically permeable matrix which acts as a current collector to transmit electrical energy to or from the electrode. It may be composed of a variety of substances, including carbon cloth, carbon paper, carbon felt, metallic screens, metallic felt, and porous metallic sheets. Preferably, however, the foundation layer is a carbon paper, which is readily available, performs well, is easily handled, and is relatively inexpensive.

[0009] The paper most preferably used in this invention is also one having low electrical resistivity, possessing sufficient strength for fabrication, and having adequate surface properties, such as roughness, to provide good bonding between the fluoropolymer binder and the foundation layer. It is also preferable to provide good electrical contact between the carbon paper and the catalytically active particles of the electrode.

[0010] As a beginning step, the foundation layer is at least partially coated with a suitable polymer binder. This polymer binder can be a fluorocarbon polymer, such as polytetrafluoroethylene sold under the trademark of Teflon®. Other suitable polymers can include thermoplastic, non-ionic forms of sulfonic acid copolymers; thermoplastic, non-ionic forms of carboxylic acid copolymers; and the like.

[0011] Particularly preferred as the fluoropolymer binder are thermoplastic, non-ionic forms of perfluorinated polymers described in the following U. S. Patent Nos. 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; 4,337,211; 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 European Patent Application 0,027,009. Such polymers usually have equivalent weights of from 500 to 2000.

[0012] Particularly preferred for use as the fluropolymer binder are copolymer of monomer I with monomer II (as defined below). Optionally, a third type of monomer may be copolymerized with I and II.

[0013] The first type of monomer is represented by general formula:



        CF₂=CZZ′   (I)



where:
   Z and Z′' are independently selected from -H, -Cl, -F, and -CF₃.

[0014] The second monomer consists of one or more monomers selected from compounds represented by the general formula:



        Y-(CF₂)_a-(CFR_f)_b-(CFR_f′)_c-O-[CF(CF₂X)-CF₂-O]_n-CF=CF₂   (II)



where:
   Y is selected from -SO₂Z, -CN, -COZ, and -C(R³f)(R⁴f)OH;
   Z is selected from -I, -Br, -Cl, -F, -OR and -NR₁R₂;
   R is selected from a branched or linear alkyl radical having from 1 to 10 carbon atoms or an aryl radical;
   R³f and R⁴f are independently selected from perfluoroalkyl radicals having from 1 to 10 carbon atoms;
   R₁ and R₂ are independently selected from -H, a branched or linear alkyl radical having from 1 to 10 carbon atoms or an aryl radical;
   a is 0-6;
   b is 0-6;
   c is 0 or 1;
   provided a+b+c is not equal to 0;
   X is selected from -Cl, -Br, -F, or mixtures thereof when n>1;
   n is 0 to 6; and
   R_f and R_f′ are independently selected from -F, -Cl, perfluoroalkyl radicals having from 1 to 10 carbon atoms, and fluorochloroalkyl radicals having from 1 to 10 carbon atoms.

[0015] Particularly preferred is when Y is -SO₂F or -COOCH₃; n is 0 or 1; R_f and R_f′ are -F; X is -Cl or -F; and a+b+c is 2 or 3.

[0016] The third and optional monomer is one of more monomers selected from the compounds represented by the general formula:





where:
   Y' is selected from -F, -Cl, or -Br;
   a' and b' are independently 0-3;
   c' is 0 or 1;
   provided a'b'+c' is not equal to 0;
   n' is 0-6;
   R_f and R′_f are independently selected from -Br, -Cl, -F, perfluoroalkyl radicals having from 1 to 10 carbon atoms, and chloroperfluoroalkyl radicals having from 1 to 10 carbon atoms; and
   X' is selected from -F, -Cl, -Br, or mixtures thereof when n'>1.

[0017] The binder is typically applied in a solution or dispersion to at least partially coat the foundation layer. The solution nor dispersion can be applied to the foundation layer using a variety of methods well known in the art.

[0018] When the electrode is to be used in a fuel cell, preferably, the binder is a hydrophobic material like polytetrafluoroethylene. When, however, the electrode is to be used in an electrolytic cell, such as a chlor-alkali cell, the binder is preferably a hydrophilic material like the copolymers formed from monomers I, II and, optionally III (described above).

[0019] The preferred loading, i.e. amount of application of the binder, is from 0.50 to 50 mg/cm² of foundation area with a preferred range of from 2.5 to 30 mg/cm² of foundation area.

[0020] When the binder is applied as a solution or a dispersion, the solvent/dispersant can be a variety of materials including, for example, water, methanol, ethanol, and compounds represented by the general formula:



        XCF₂-CYZ-X'



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 from 1 to 6 carbon atoms.

[0021] The most preferred solvents or dispersants are 1,2-dibromotetrafluoroethane (commonly known as Freon 114 B 2)



        BrCF₂-CF₂Br



and 1,2,2-trichlorotrifluoroethane (commonly known as Freon 113):



        ClF₂C-CCl₂F



Of these two materials, 1,2-dibromoetrafluoroethane is the most preferred solvent or dispersant.

[0022] The solution or dispersion used to apply the binder to the foundtion layer may have a concentration of from 2 to 30 weight percent of polymer in the solvent/dispersant. Preferably, the concentration is from 8 to 20 weight percent of polymer in the solvent/dispersant.

[0023] After the solution or dispersion has been applied to the foundation layer, the solvent can then be driven off using heat, a vacuum, or a combination of heat and a vacuum. Optionally, the solvent/dispersant may be allowed to evaporate under ambient conditions. Preferably, the solvent is removed at an elevated temperature. In addition to removing the solvent/dispersant, the heat sinters the binder and causes it to more completely penetrate and surround the foundation layer. As an example, when polytetrafluoroethylene is used as the binder, exposure at a temperature of from 300°C to 340°C for about 20 minutes will suffice to remove the solvent/dispersant and to sinter the polytetrafluoroethylene.

[0024] The next step in the method of the present invention is the application of catalytically active and electrically conductive particles to the coated foundation layer. The composite structure will, ultimately, form what is commonly referred to as a solid polymer electrolyte, or SPE, when the composite is used in an electrochemical cell. The electrode can be ultimately used as either a cathode or as an anode.

[0025] Materials suitable for use as electro-catalytically active anode materials include, for example, metals or metal oxides of platinum group metals, such as ruthenium, iridium, rhodium, platinum, palladium, either alone or in combination with an oxide of a film-forming metal such as Ti or Ta. Other suitable activating oxides include cobalt oxide, either alone or in combination with other metal oxides, such as those described in U. S. Patent Nos. 3,632,498; 4,142,005; 4,061,549; and 4,214,971.

[0026] Materials suitable for use as electro-catalytically active cathode materials include, for example, platinum group metals or metal oxides, such as ruthenium or ruthenium oxide. U. S. Patent No. 4,465,580 describes such cathodes.

[0027] The catalytic particles used in the present invention are preferably finely divided and have a preferred range of from 270 to smaller than 400 mesh size (U. S. Standard) (53 to less than 37 µm (microns)). The metal powder is applied to the binder-coated foundation layer by methods known to those skilled in the art including, for example, spraying, forming a sheet of catalytic particles and pressing the sheet onto the foundation layer, or forming and applying the particles in the form of liquid dispersion, for example, an aqueous dispersion. A suitable loading of catalyst particles has been found to be from 0.2 to 20 mg/cm² of foundation area with a preferred range of from 1.5 to 5.0 mg/cm² of foundation area.

[0028] Separately, a copolymer is formed. One such suitable polymer is the polymer formed from monomers I, II, and optionally III, as defined above. The polymer may be a thermoplastic, non-ionic precursor of a sulfonic acid copolymer or a thermoplastic, non-ionic precursor of a carboxylic acid copolymer, or a variety of other polymers as defined for use as the binder. Preferably, the copolymer is formed into a solution or a dispersion with a solvent for application to the catalytically active particles. On mixing with a suitable solvent or dispersant, the polymer is applied to the catalyst particle coated foundation layer. In a preferred embodiment by utilizing a vacuum on one side of the foundation layer, the polymer in the solvent or dispersant is pulled onto the catalyst and into the foundation layer. While in one sense it can be described as coated on one side, the coating nevertheless sufficiently penetrates into the porous sheet.

[0029] In the step of bonding a fluoropolymer onto the surface of the catalytic particle coated foundation layer, the cost convenient procedure is the use of conventional organic solvents. Typical solvents used are 1,2-dibromotetrafluoroethane, methanol, ethanol, and the like. The polymeric material which is applied forms a substantially non-porous ion exchange layer.

[0030] The next step is the application of heat and/or pressure to remove the solvent/dispersant and to sinter the polymer, thereby forming the polymer into a substantially continuous sheet. In addition, the heat and/or pressure enhance the coating of the polymer around the catalyst particles and the foundation layer. For example, exposure to a temperature in the range of from 260° to 320°C is generally suitable to bond the polymer to the particles and the foundation layer. The temperature range is limited primarily by the onset of thermal degradation of the polymer caused by excessive heat. The pressure is preferably sufficiently high and sustained for an interval to achieve bonding. In one example, pressure may be applied up to about 5 kg/cm² for about one minute at elevated temperature.

[0031] The next step to make the improved electrode structure ready for use is to hydrolyze the structure from the non-ionic to the ionic form. Hydrolysis may be accomplished by treating the polymer with a basic solution if the polymer is a thermoplastic, non-ionic precursor of a sulfonic acid polymer or a thermoplastic, non-ionic precursor of a carboxylic acid polymer. In addition, if the polymer is a thermoplastic non-ionic precursor of a carboxylic acid polymer, an acid solution may be used to hydrolyze the polymer. For example, in a thermoplastic, non-ionic precursor of a sulfonic acid polymer, the completed structure may be hydrolyzed in 25 weight percent sodium hydroxide for 16 hours at an elevated temperature of 80°C.

[0032] The completed article is then ready for use. As an example of typical size, it is not uncommon to encounter a membrane which is in a range of from 5 to 10 mils (0.125 to 0.25 mm) thick due to the need for structural integrity. The finished product can yield a membrane with a thickness in a range of from 1 to 2 mils (0.025 to 0.05 mm), or even less. The resistance of ionic movement through the membrane is thus lowered by a significant amount.

[0033] In an alternate application, two similar sheets of equal size are positioned in contact with one another in a manner so that the foundation layers face toward the outside of the combination and the polymer layer on each sheet is contacted against the polymer layer on the other sheet. The coterminous sheets are then placed into a press and on the application of suitable pressure/or heat, they are joined together.

Claims

1. A method of forming an assembly of an ion permeable membrane, electrode, and current collector, comprising the steps of:

(a) forming the current collector from a foundation layer of a porous, electrically conductive material;

(b) at least partially coating a fluoropolymer binder on at least one surface of the foundation layer;

(c) forming the electrode by applying a particulate catalyst material over the fluoropolymer binder on the foundation layer:

(d) applying a hydrolysable fluoropolymeric material to be converted from the non-ionic to the ionic form by hydrolysis before use as a solution or dispersion over the catalyst material in a manner to obtain penetration of the fluoropolymeric material into the porous foundation layer to form a substantially continuous coating on the catalyst material and the binder coated foundation layer; said fluoropolymeric material forming the ion permeable membrane, and

(e) applying heat and/or pressure to the assembly to enhance the flow of the fluoropolymeric material into the foundation layer and around the catalyst material to obtain adherence of the catalyst material to the foundation layer and to sinter the fluoropolymeric material into a substantially non-porous layer around the catalyst material.

2. The method of Claim 1, wherein the catalyst particles are selected from ruthenium, iridium, rhodium, platinum, palladium, or oxides thereof either alone or in combination with an oxide of a film-forming metal, and cobalt oxide either alone or in combination with other platinum group metal or metal oxide.

3. The method of Claim 1 or 2, wherein said fluoropolymer binder for the foundation layer is a thermoplastic, non-ionic precursor of a sulfonic acid copolymer having an equivalent weight in a range of from 500 to 2000.

4. The method of Claim 1 or 2, wherein said fluoropolymer binder for the foundation layer is a thermoplastic, non-ionic precursor of a carboxylic acid copolymer.

5. The method of any one of the preceding claims, wherein the fluoropolymer binder is a copolymer formed from the polymerization of one or more monomers selected from the group of monomers represented by the general formula:



        CF₂=CZZ'   (I)



where:
   Z and Z' are independently selected from -H, -Cl, -F, or -CF₃;
with one or more monomers selected from a second group of monomers represented by the general formula:



        Y-(CF₂)_a-(CFR_f)_b-(CFR_f')_c-O-[CF[CF₂X)-CF₂-O]_n-CF=CF₂   (II)



where:
   Y is selected from -SO₂Z, -CN, -COZ, and -C(R³f)(R⁴f)OH;
   Z is selected from -I, -Br, -Cl, -F, -OR, and -NR₁R₂;
   R is selected from a branched or linear alkyl radical having from 1 to 10 carbon atoms or an aryl radical;
   R³f and R⁴f are independently selected from perfluoroalkyl radicals having from 1 to 10 carbon atoms;
   R₁ and R₂ are independently selected from -H, a branched or linear alkyl radical having from 1 to 10 carbon atoms, and an aryl radical;
   a is 0-6;
   b is 0-6;
   c is 0 or 1;
   provided a+b+c is not equal to 0;
   X is selected from -Cl, -Br, -F, and mixtures thereof when n>1;
   n is 0 to 6; and
   R_f and R_f' are independently selected from -F, -Cl, perfluoroalkyl radicals having from 1 to 10 carbon atoms, and fluorochloroalkyl radicals having from 1 to 10 carbon atoms, and optionally, one or more monomers selected from a third monomer group represented by the general formula:



        Y'-(CF₂)_a'-(CFR_f)_b'-(CFR'_f)_c'-O-[CF(CF₂X')-CF₂-O]_n'-CF=CF₂   (III)



where:
   Y' is selected from -F, -Cl, or -Br;
   a' and b' are independently 0-3;
   c' is 0 or 1;
   provided a'+b'+c' is not equal to 0;
   n' is 0-6;
   R_f and R'_f are independently selected from -Br, -Cl, -F, perfluoroalkyl radicals having from 1 to 10 carbon atoms, and chloroperfluoroalkyl radicals having from 1 to 10 carbon atoms; and
   X' is selected from -F, -Cl, -Br, and mixtures thereof when n'>1.

6. The method of Claim 5, wherein Y is -SO₂F or -COOCH₃; n is 0 or 1; R_f and R_f' are -F; X is -Cl or -F; and a+b+c is 2 or 3.

7. The method of any one of the preceding claims, wherein the fluoropolymeric material contains one or more solvents or dispersants selected from ethanol, methanol, water, or a compound represented by the general formula:



        XCF₂-CYZ-X

'

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 from 1 to 6 carbon atoms.

8. The method of any one of claim 7, wherein the solvent or dispersant is selected from 1,2-dibromotetra-fluoroethane and 1,2,2-trichlorotrifluoroethane.

9. The method of Claim 1, wherein:

(a) said electrically conductive material is a porous graphite paper,

(b) said fluoropolymeric binder is polytetrafluoroethylene, and

(c) said fluoropolymeric material is a sulfonic acid copolymer in thermoplastic powder form in a liquid solvent.

10. The method of any one of the preceding claims, including the step of drawing a vacuum on the assembly to obtain penetration of the fluoropolymeric binder and fluoropolymeric material into the porous foundation layer.

11. The method of any one of the preceding claims, including the step of exposing the fluoropolymeric material to a base or to an acid at a temperature and for a time sufficient to hydrolyze substantially all of the polymer.

12. The method of any one of the preceding claims, including the step of making two similar sized assemblies, placing the two assemblies together so that the foundation layers face toward the outside of the combination and the polymer layer on each sheet is contacted against the polymer layer on the other sheet, the non-porous fluoropolymeric surfaces being in intimate contact with each other, and applying heat and/or pressure to form a single planar assembly containing two current collectors having a non-porous, ionically conductive polymer layer therebetween.

Ansprüche

1. Verfahren zum Herstellen einer Anordnung aus einer ionendurchlässigen Membran, einer Elektrode und einem Stromkollektor, umfassend die Schritte:

(a) Herstellen des Stromkollektors aus einer Grundschicht eines porösen, elektrisch leitfähigen Materials,

(b) mindestens teilweises Überziehen von mindestens einer Oberfläche der Grundschicht mit einem Fluorpolymerbindemittel,

(c) Herstellen der Elektrode durch Aufbringen eines teilchenförmigen Katalysatormaterials über das Fluorpolymerbindemittel auf der Grundschicht,

(d) Aufbringen eines hydrolysierbaren Fluorpolymermaterials, das aus der nicht-ionischen in die ionische Form durch Hydrolyse vor Verwendung umgewandelt wird, als Lösung oder Dispersion über das Katalysatormaterial auf eine Weise, um Eindringen des Fluorpolymermaterials in die poröse Grundschicht zu erreichen, so daß ein im wesentlichen kontinuierlicher Überzug auf der mit dem Katalysatormaterial und dem Bindemittel überzogenen Grundschicht gebildet wird, wobei das Fluorpolymermaterial die ionendurchlässige Membran bildet, und

(e) Zufuhr von Wärme und/oder Anlegen von Druck auf die Anordnung, um das Fließen des Fluorpolymermaterials in die Grundschicht und um das Katalysatormaterial zu verbessern, so daß Haftung des Katalysatormaterials an der Grundschicht erreicht wird und das Fluorpolymermaterial zu einer im wesentlichen nicht-porösen Schicht um das Katalysatormaterial gesintert wird.

2. Verfahren nach Anspruch 1, worin die Katalysatorteilchen aus Ruthenium, Iridium, Rhodium, Platin, Palladium oder Oxiden davon entweder alleine oder in Kombination mit einem Oxid eines filmbildenden Metalls und Kobaltoxid entweder alleine oder in Kombination mit einem anderen Metall der Platingruppe oder einem Metalloxid ausgewählt sind.

3. Verfahren nach Anspruch 1 oder 2, worin das Fluorpolymerbindemittel für die Grundschicht eine thermoplastische, nicht-ionische Vorstufe eines Sulfonsäure-Copolymers mit einem Äquivalenzgewicht im Bereich von 500 bis 2000 ist.

4. Verfahren nach Anspruch 1 oder 2, worin das Fluorpolymerbindemittel für die Grundschicht eine thermoplastische, nicht-ionische Vorstufe eines Carbonsäure-Copolymers ist.

5. Verfahren nach einem der vorhergehenden Ansprüche, worin das Fluorpolymerbindemittel ein Copolymer ist, das durch die Polymerisation von einem oder mehreren Monomeren, die aus der Gruppe von Monomeren ausgewählt werden, die durch die allgemeine Formel dargestellt sind:



        CF₂=CZZ'   (I)



worin:
Z und Z' unabhängig aus -H, -Cl, -F oder -CF₃ ausgewählt sind,
mit einem oder mehreren Monomeren, die aus einer zweiten Gruppe von Monomeren ausgewählt werden, die durch die allgemeine Formel dargestellt sind:



        Y-(CF₂)_a-(CFR_f)_b-(CFR_f')_c-O-[CF(CF₂X)-CF₂-O]_n-CF=CF₂   (II)



worin:
Y aus -SO₂Z, -CN, -COZ und -C(R³f)(R⁴f)OH ausgewählt ist,
Z aus -I, -Br, -Cl, -F, -OR und -NR₁R₂ ausgewählt ist,
R aus einem verzweigten oder linearen Alkylrest mit 1 bis 10 Kohlenstoffatomen oder einem Arylrest ausgewählt ist,
R³f und R⁴f unabhängig aus Perfluoralkylresten mit 1 bis 10 Kohlenstoffatomen ausgewählt sind,
R₁ und R₂ unabhängig aus -H, einem verzweigten oder linearen Alkylrest mit 1 bis 10 Kohlenstoffatomen und einem Arylrest ausgewählt sind,
a 0 bis 6 ist,
b 0 bis 6 ist,
c 0 oder 1 ist,
vorausgesetzt, daß a+b+c nicht gleich 0 ist,
X aus -Cl, -Br, -F und Gemischen davon, wenn n > 1 ist, ausgewählt ist,
n 0 bis 6 ist und
R_f und R_f, unabhängig aus -F, -Cl, Perfluoralkylresten mit 1 bis 10 Kohlenstoffatomen und Fluorchloralkylresten mit 1 bis 10 Kohlenstoffatomen ausgewählt sind, und gegebenenfalls einem oder mehreren Monomeren gebildet wird, die aus einer dritten Monomergruppe auswählt werden, die durch die allgemeine Formel dargestellt ist:



        Y'-(CF₂)_a'-(CFR_f)_b'-(CFR'_f)_c'-O-[CF(CF₂X')-CF₂-O]_n'-CF=CF₂   (III)



worin:
Y' aus -F, -Cl oder -Br ausgewählt ist,
a' und b' unabhängig 0 bis 3 sind,
c' 0 oder 1 ist,
vorausgesetzt, daß a'+b'+c' nicht gleich 0 ist,
n' 0 bis 6 ist,
R_f und R'_f unabhängig aus -Br, -Cl, -F, Perfluoralkylresten mit 1 bis 10 Kohlenstoffatomen und Chlorperfluoralkylresten mit 1 bis 10 Kohlenstoffatomen ausgewählt sind, und
X' aus -F, -Cl, -Br und Gemischen davon, wenn n' > 1 ist, ausgewählt ist.

6. Verfahren nach Anspruch 5, worin Y -SO₂F oder -COOCH₃ ist, n 0 oder 1 ist, R_f und R_f' -F sind, X -Cl oder -F ist und a+b+c 2 oder 3 ist.

7. Verfahren nach einem der vorhergehenden Ansprüche, worin das Fluorpolymermaterial ein oder mehrere Lösungsmittel oder Dispergiermittel enthält, die aus Ethanol, Methanol, Wasser oder einer Verbindung ausgewählt werden, die durch die allgemeine Formel dargestellt ist:



        XCF₂-CYZ-X'



worin:
X aus F, Cl, Br und I ausgewählt ist,
X' aus Cl, Br und I ausgewählt ist,
Y und Z unabhängig aus H, F, Cl, Br, I und R' ausgewählt sind,
R' aus Perfluoralkylresten und Chlorperfluoralkylresten mit 1 bis 6 Kohlenstoffatomen ausgewählt ist.

8. Verfahren nach Anspruch 7, worin das Lösungsmittel oder Dispergiermittel aus 1,2-Dibromtetrafluorethan und 1,2,2-Trichlortrifluorethan ausgewählt sind.

9. Verfahren nach Anspruch 1, worin:

(a) das elektrisch leitfähige Material ein poröses Graphitpapier ist,

(b) das Fluorpolymerbindemittel Polytetrafluorethylen ist und

(c) das Fluorpolymermaterial ein Sulfonsäurecopolymer in thermoplastischer Pulverform in einem flüssigen Lösungsmittel ist.

10. Verfahren nach einem der vorhergehenden Ansprüche, umfassend den Schritt des Anlegens eines Vakuums an die Anordnung, um Eindringen des Fluorpolymerbindemittels und des Fluorpolymermaterials in die poröse Grundschicht zu erreichen.

11. Verfahren nach einem der vorhergehenden Ansprüche, umfassend den Schritt des Behandelns des Fluorpolymermaterials mit einer Base oder mit einer Säure bei einer Temperatur und für eine Zeit, die zur Hydrolyse von im wesentlichen des gesamten Polymers ausreichend sind.

12. Verfahren nach einem der vorhergehenden Ansprüche, umfassend den Schritt des Herstellens von zwei ähnlich großen Anordnungen, des Zusammensetzens der beiden Anordnungen, so daß die Grundschichten zur Außenseite der Kombination gerichtet sind und die Polymerschicht auf jedem Blatt in Kontakt mit der Polymerschicht auf dem anderen Blatt ist, wobei die nicht-porösen Fluorpolymeroberflächen in innigem Kontakt miteinander sind, und der Zufuhr von Wärme und/oder des Anlegens von Druck, um eine einzige planare Anordnung zu bilden, die zwei Stromkollektoren mit einer nicht-porösen, ionisch leitfähigen Polymerschicht dazwischen aufweist.

Revendications

1. Procédé de formation d'un assemblage comprenant une membrane perméable aux ions, une électrode et un collecteur de courant, ledit procédé comprenant les étapes consistant à :

(a) former le collecteur de courant à partir d'une couche de base en un matériau poreux et électroconducteur,

(b) revêtir au moins partiellement, à l'aide d'un liant en polymère fluoré, au moins une surface de la couche de base,

(c) former l'électrode en déposant un matériau catalyseur en particules, par-dessus le liant en polymère fluoré, sur la couche de base,

(d) déposer un matériau polymère fluoré hydrolysable, qui sera converti de la forme non ionique à la forme ionique par hydrolyse avant usage, sous la forme d'une solution ou d'une dispersion, par-dessus le matériau catalyseur, de façon à faire pénétrer le matériau polymère fluoré dans la couche de base poreuse pour former un revêtement pratiquement continu sur le matériau catalyseur et la couche de base revêtue de liant, ledit matériau polymère fluoré constituant la membrane perméable aux ions, et

(e) le chauffage de l'assemblage et/ou l'application d'une pression sur l'assemblage, pour augmenter l'écoulement du matériau polymère fluoré dans la couche de base et autour du matériau catalyseur, afin de faire adhérer le matériau catalyseur à la couche de base, et pour agglomérer le matériau polymère fluoré en une couche pratiquement non poreuse autour du matériau catalyseur.

2. Procédé de la revendication 1, dans lequel le catalyseur en particules est choisi parmi le ruthénium, l'iridium, le rhodium, le platine, le palladium et leurs oxydes, seuls ou en combinaison avec un oxyde d'un métal filmogène, et l'oxyde de cobalt, seul ou en combinaison avec un autre métal ou oxyde métallique du groupe du platine.

3. Procédé de la revendication 1 ou 2, dans lequel ledit liant en polymère fluoré pour la couche de base est un précurseur non ionique et thermoplastique d'un copolymère à groupes sulfo, présentant un poids d'équivalent situé dans l'intervalle allant de 500 à 2000.

4. Procédé de la revendication 1 ou 2, dans lequel le liant en polymère fluoré pour la couche de base est un précurseur non ionique et thermoplastique d'un copolymère à groupes carboxy.

5. Procédé de l'une quelconque des revendications précédentes, dans lequel le liant en polymère fluoré est un copolymère formé par polymérisation d'un ou de plusieurs monomères choisis dans le groupe des monomères représentés par la formule générale :



        CF₂ = CZZ'   (I)



dans laquelle Z et Z' sont indépendamment choisis parmi -H, -Cl, -F et -CF₃,
avec un ou plusieurs monomères choisis dans un second groupe de monomères représentés par la formule générale :



        Y-(CF₂)_a-(CFR_f)_b-(CFR_f')_c-O-[CF(CF₂X)-CF₂-O]_n-CF=CF₂   (II)



dans laquelle :
Y est choisi parmi -SO₂Z, -CN, -COZ, et -C(R³f)(R⁴f)OH,
Z est choisi parmi -I, -Br, -Cl, -F, -OR, et -NR₁R₂,
R est choisi parmi les radicaux alkyle linéaires ou ramifiés comportant de 1 à 10 atomes de carbone et les radicaux aryle,
R³f et R⁴f sont choisis indépendamment parmi les radicaux perfluoroalkyle comportant de 1 à 10 atomes de carbone,
R₁ et R₂ sont indépendamment choisis parmi -H, les radicaux alkyle linéaires ou ramifiés comportant de 1 à 10 atomes de carbone et les radicaux aryle,
a vaut de 0 à 6,
b vaut de 0 à 6,
c vaut 0 ou 1,
pourvu que a + b + c ne soit pas nulle,
X est choisi parmi -Cl, -Br, -F et leurs mélanges, lorsque
n est supérieur à 1,
n vaut de 0 à 6, et
R_f et R_f' sont choisis indépendamment parmi -F, -Cl, les radicaux perfluoroalkyle comportant de 1 à 10 atomes de carbone et les radicaux fluorochloroalkyle comportant de 1 à 10 atomes de carbone,
et avec, éventuellement, un ou plusieurs monomères choisis dans un troisième groupe de monomères représenté par la formule générale :



        Y'-(CF2)_a'-(CFR_f)_b'-(CFR'_f)_c'-O-[CF(CF₂X')-CF₂-O]_n'-CF=CF₂   (III)



dans laquelle
Y' est choisi parmi -F, -Cl et -Br,
a' et b' valent indépendamment de 0 à 3,
c' vaut 0 ou 1,
pourvu que a' + b' + c' ne soit pas nulle,
n' vaut de 0 à 6,
R_f et R'_f sont indépendamment choisis parmi -Br, -Cl, -F,
les radicaux perfluoroalkyle comportant de 1 à 10 atomes de carbone et les radicaux chloroperfluoroalkyle comportant de 1 à 10 atomes de carbone, et
X' est choisi parmi -F, -Cl, -Br et leurs mélanges, quand
n' est supérieur à 1.

6. Procédé de la revendication 5, dans lequel Y représente -SO₂F ou -COOCH₃, n vaut 0 ou 1, R_f et R_f' représentent -F, X représente -Cl ou -F et a + b + c vaut 2 ou 3.

7. Procédé de l'une quelconque des revendications précédentes, dans lequel le matériau polymère fluoré contient un ou plusieurs solvants ou dispersants choisis parmi l'éthanol, le méthanol, l'eau et un composé représenté par la formule générale :



        XCF₂-CYZ-X'



dans laquelle
X est choisi parmi F, Cl, Br et I,
X' est choisi parmi Cl, Br et I,
Y et Z sont indépendamment choisis parmi H, F, Cl, Br, I et R',
R' est choisi parmi les radicaux perfluoroalkyle et les radicaux chloroperfluoroalkyle comportant de 1 à 6 atomes de carbone.

8. Procédé de la revendication 7, dans lequel le solvant ou dispersant est choisi parmi le 1,2-dibromotétrafluoroéthane et le 1,2,2-trichloro-trifluoroéthane.

9. Procédé de la revendication 1, dans lequel

a) ledit matériau électroconducteur est un papier poreux au graphite,

b) ledit liant polymère fluoré est un polytétrafluoroéthylène, et

c) ledit matériau polymère fluoré est un copolymère à groupes sulfo, sous forme de poudre thermoplastique dans un solvant liquide.

10. Procédé de l'une quelconque des revendications précédentes, comprenant l'étape consistant à mettre l'assemblage sous vide pour faire pénétrer le liant en polymère fluoré et le matériau polymère fluoré dans la couche poreuse de base.

11. Procédé de l'une quelconque des revendications précédentes, comprenant l'étape consistant à exposer le matériau polymère fluoré à l'action d'une base ou d'un acide, à une température et pendant une durée qui sont suffisantes pour que pratiquement tout le polymère soit hydrolysé.

12. Procédé de l'une quelconque des revendications précédentes, comprenant les étapes consistant à fabriquer deux assemblages de taille semblable, à disposer ensemble ces deux assemblages de telle façon que les couches de base constituent les faces extérieures de l'ensemble et que la couche de polymère de chaque feuille soit en contact avec la couche de polymère de l'autre feuille, les surfaces non poreuses de polymère fluoré étant en contact intime l'une avec l'autre, et à soumettre l'ensemble à un chauffage et/ou à une pression, pour former un assemblage plan unique comportant deux collecteurs de courant entre lesquels est disposée une couche non poreuse d'un polymère conducteur par ions.