WO2020115450A1

WO2020115450A1 - Method for producing a membrane electrode assembly for a fuel cell

Info

Publication number: WO2020115450A1
Application number: PCT/FR2019/052983
Authority: WO
Inventors: Arnaud Grandjean; Benjamin DECOOPMAN
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2018-12-07
Filing date: 2019-12-09
Publication date: 2020-06-11

Abstract

Method for producing a membrane electrode assembly (100) for a fuel cell, comprising a proton exchange polymer membrane (10), catalytic layers (20, 30) and first and second gas diffusion layers (50, 40), the method comprising the following steps: a) forming a catalytic layer coating (20) on a first surface (14) of the membrane, the opposite surface (15) being supported by a spacer (12); b) forming a catalytic layer coating (30) on a first surface (54) of the first gas diffusion layer (50); c) bringing the first surface (54) of the first gas diffusion layer (50) into contact with the surface (15) opposite to the first surface (14) of the membrane, after removing the spacer (12), and bringing the first surface (14) of the membrane into contact with a surface of the second gas diffusion layer (40).

Description

Method of manufacturing a membrane-electrode assembly for a fuel cell

The present invention relates to fuel cells, in particular but not exclusively to fuel cells of the electrolyte type in the form of a polymer membrane (that is to say of the PEFC type for Polymer Electrolyte Fuel Cell).

This invention relates more particularly to methods of manufacturing a membrane-electrode assembly for a fuel cell.

Fuel cells are used as a source of energy in a variety of applications, including electric vehicles. In polymer membrane electrolyte (PEFC) type fuel cells, hydrogen is supplied to the anode of the fuel cell and oxygen is supplied as an oxidant to the cathode. Polymer membrane fuel cells (PEFC) include a membrane electrode assembly (MEA) comprising an electrolytic membrane made of solid proton exchange polymer and non-conductive of electricity, having the anodic catalyst on one of its faces and the cathode catalyst on its opposite face. A membrane-electrode assembly (MEA) is sandwiched between a pair of electrically conductive elements, called bipolar plates, by means of gas diffusion layers, made for example of carbon fabric. Bipolar plates are generally rigid and thermally conductive. They mainly serve as current collectors for the anode and the cathode and contain channels provided with openings suitable for distributing the gaseous reagents of the fuel cell over the surfaces of the respective anode and cathode catalysts and for eliminating the water produced at the electrode. A fuel cell is thus formed by an MEA, including the gas diffusion layers, and two bipolar plates.

A fuel cell can include a single cell or a plurality of cells formed as a stack of plates. A stack is thus made up of several individual cells connected in series.

A fuel cell is powered by a fuel which is hydrogen which is supplied to the anode and by an oxidizer which is oxygen or air which is supplied to the cathode.

The proton exchange membrane is in the form of a very thin film and is made, for example, from a sulfonated perfluorinated polymeric material. The anode and cathode side catalysts include finely divided catalytic particles, which are generally supported by carbon particles and mixed with a proton-conducting resin, such as an ionomer or a mixture of ionomers and with a solvent. The catalytic particles are generally particles of expensive precious metals, such as platinum. Thus, special attention must be paid to the manufacture of assemblies membrane-electrode (MEA) and this not only to take into account the rather high cost of its components, but especially because the quality of MEA is in direct link with the performances of a fuel cell.

Before integrating the membrane-electrode assembly, the catalysts are generally in the form of a liquid catalytic ink. This catalytic ink is deposited directly on a support of the MEA assembly, for example by spraying, by screen printing or by coating and spreading using a scraper. The catalytic ink can also be deposited indirectly on one or more constituents of an MEA by being transferred from another support impregnated with ink.

Depending on the deposition method and on the recipient medium of the catalytic ink within an MEA assembly, two methods of obtaining such an assembly are known in the prior art.

A first method consists in coating each diffusion layer of gas with catalytic ink and is known under the name CCB (for catalyst coated backing) and then applying them on either side of a polymer membrane. The performance of a fuel cell from which the MEA was obtained by this method is generally low. To improve it, hot pressing (around 130 ° C) of the assembly is carried out for a few minutes. However, such a hot pressing operation tends to deform or even deteriorate the membrane, which can cause a loss of sealing at the level of the cell. A second method which gives better results in terms of fuel cell performance, consists in coating with liquid catalytic ink the two faces of the polymer membrane and is known under the name CCM (for catalyst coated membrane). However, by its constitution, the membrane has a strong reactivity to organic or aqueous solvents which make up the catalytic ink and, therefore, it has a strong tendency to shrink and to wrinkle as soon as it comes into contact with the ink. This makes the method of applying catalytic ink on the membrane very difficult, on the one hand, and, on the other hand, it requires applying the ink on larger surfaces than that of a flat membrane, which makes it very expensive.

To overcome this problem, a solution was provided by the document US 2011/0097651 which proposes to apply detachable adhesive supports on the polymer membrane, a support being applied to one face of the membrane before the deposition of a layer of 'catalytic ink on the opposite side, and then remove these supports. However, apart from the fact that it involves multiple intermediate steps consuming time and labor, this process risks weakening the membrane, or even losing part of the catalytic coating when removing the adhesive support with which he was in touch.

Document EP 1 387 422 describes another method for applying a coating based on a catalytic ink on a gas diffusion layer or on a polymer membrane. of a fuel cell. This process comprises several successive steps consisting in applying, then leveling and drying the coating, each step being carried out under strict conditions of temperature, humidity and treatment time. Thus, by multiplying the stages and by imposing on them very severe conditions, this process proves to be complex to carry out.

An objective of the invention is to remedy the drawbacks of the aforementioned documents and to provide an original solution for a method of manufacturing an assembly

membrane electrode (MEA) for a fuel cell.

This objective is achieved by the invention which proposes a method of manufacturing a membrane-electrode assembly for a fuel cell comprising a polymer membrane proton exchange, catalytic layers and a first and a second gas diffusion layer, the method comprising the following steps:

a) forming a coating of catalytic layer on a first face of the membrane, the opposite face being supported by an interlayer;

b) forming a catalytic layer coating on a first face of the first gas diffusion layer;

c) bringing said first face of the first gas diffusion layer into contact with the face opposite to said first face of the membrane, after removing the interlayer, and said first face of the membrane with one face of the second diffusion layer carbonated. In other words, a good coating is already obtained on the membrane by applying the catalytic ink on one of its faces, corresponding to one of the electrodes, the opposite face being supported by an interlayer, which avoids that '' it shrinks or deforms during deposition. A second deposition of catalytic ink, corresponding to the other electrode, is carried out on a gas diffusion layer which is a much more rigid support and which does not deform in contact with the catalytic ink. This gas diffusion layer can be supported by an interlayer. The uncovered face of the membrane, freed from its interlayer, is then brought into contact with the face coated with catalytic ink of the gas diffusion layer. The assembly is closed by affixing the second gas diffusion layer on the coated face of the membrane.

Thus, it was found, during tests carried out in the laboratory, that the performance of such an assembly (MEA) was very close to that of an MEA obtained by applying the coating to the two faces of the membrane (which is the reference method from the point of view of the performance achieved by a fuel cell), while carrying out this assembly more easily and with much less material loss.

Advantageously, the coating formed in step a) corresponds to the cathode part of the membrane. The cathode side of the catalytic coating is that which comes into contact with oxygen (or compressed air), it has characteristics in terms of deposition which are directly linked to the performance of the fuel cell. Thus, this coating on the cathode side has a thickness of the coating less than that on the anode side and it must be well in contact with the membrane to guarantee the performance of the cell. We thus choose to apply a coating of catalytic ink to produce the MEA cathode directly on one of the faces of the membrane. Furthermore, the anode side being less sensitive to contact with the membrane, the gas diffusion layer comprising the coating of catalytic ink can be applied by simple pressure, without heating, which avoids

damage the membrane. In addition, if inadvertently the deposition on the gas diffusion layer was not consistent, it could be repeated on a gas diffusion layer much cheaper than a proton exchange membrane.

In the process of the invention, the membrane and the gas diffusion layers can be obtained by cutting steps to pre-established dimensions before step c).

The coating of catalytic layer according to the invention can be obtained by a process for the direct deposition of a catalytic ink on one of the faces of the membrane and on one of the faces of the gas diffusion layer by a process included in the group

including: screen printing, coating, flexography, spraying.

The coating deposition step according to the invention can be followed by a drying step. Drying can be done using a forced air flow heated to a temperature accepted by the membrane material, generally less than or equal to 100 ° C. The method of the invention may include an additional step of bonding on the rim of each of the faces of the membrane of a reinforcement carrying a seal.

In the process of the invention, the assembly of step c) can be done by gluing.

The invention also relates to an assembly line for carrying out the implementation of the method of manufacturing an electrode membrane assembly according to the invention.

The object of the invention is also achieved with a fuel cell comprising at least one cell comprising an electrode membrane assembly of the invention sandwiched between two bipolar plates.

The invention will be better understood thanks to the following description, which is based on the following figures:

- Figure 1 is a schematic view of an assembly line which performs the implementation of the method of the invention;

- Figure 2 is a graphical representation of the performance of a fuel cell obtained with the method of the invention compared to that of a fuel cell of the prior art; - Figure 3 is a perspective view of part of a membrane-electrode assembly obtained with the method of the invention.

In the various figures, identical or similar elements bear the same reference. Their description is therefore not systematically repeated.

FIG. 1 schematically illustrates an assembly line 1 which makes it possible to obtain a membrane-electrode assembly (MEA) 100 with the method of the invention. A membrane-electrode assembly 100 generally comprises a membrane 10, two catalytic layers 20, 30 forming electrodes arranged on either side thereof, and a gas diffusion layer 40, 50 arranged opposite each electrode.

The membrane 10 is in the form of a very thin film of a proton-conducting polymer called an ionomer. Such an ionomer is for example Nafion® N1 17 and is delivered by its manufacturer in the form of a film roll. The film is a strip a few tens of pm thick, a few tens of cm wide and a few meters long. The film is wound on a reel while being supported on an interlayer (or sometimes it is disposed between two interleaves) which can be a polyester film.

The electrodes are porous structures obtained by depositing and drying a catalytic ink on a support. The catalytic ink preferably contains particles of a catalyst of nanometric size (for example between 1 and 10 nm) supported or not by carbon particles of larger size (for example between 10 and 100 nm). The catalyst may be platinum, platinum / ruthenium or another element or group of elements chosen from the group of platinum of the periodic table. The ink further comprises a binder, such as an ionomer (for example Nafion®), a solvent (for example water, glycerol, etc.). Additives can be added to the formulation, for example a surfactant. The ink, generally in the liquid state, is deposited on the support and dried so as to obtain a catalyst charge of approximately 0.1 to 0.2 mg / cm ² .

A gas diffusion layer 40, 50 or GDL (for Gas Diffusion Layer) is a porous medium to allow the transport of the reactant from its entry towards the catalyst. It must also be electrically conductive to conduct the charges. Such a gas diffusion layer is thus advantageously made from carbon fibers which are woven or knitted together or are in the form of a non-woven fabric. One can also treat such a gas diffusion layer (for example by applying a micro coating made of PTFE and carbon particles) so that it is hydrophobic in order to better channel the water which results from the reaction within the battery. The gas diffusion layers used are of the type used in the manufacture of fuel cells. They are generally delivered in the form of a roll by their manufacturer. According to the invention, a first electrode is formed by applying a coating or catalytic layer 20 obtained based on a catalytic ink 60 on a first face 14 of the membrane 10, the opposite face 15 being supported by an interlayer 12. The first electrode or catalytic layer 20 is that corresponding to the cathode side of the membrane.

As best seen in Figure 1, we begin by unrolling a roll 19 of film 11 constituting the ion-exchange polymer membrane, the film and its support or interlayer 12 being wound together around a hub 13. To unwind the film , the hub 13 is rotated around its axis, for example using a motor (not shown) and preferably putting the film-interlayer assembly under tension. A deposit of catalytic ink 60 is then applied directly to a first face 14 of the membrane from an ink tank 61 by a direct deposition process, for example by screen printing. The opposite face 15 of the membrane is supported by the interlayer 12 having dimensions comparable to those of the film constituting the membrane. Other direct deposition methods, for example by coating with a roller or scraper, or by flexography, or even by spraying, can be used to apply the ink to the film constituting the membrane. An indirect deposition method, for example by pad printing using a PTFE transfer buffer can also be used.

The coating application step is followed by a drying step. This step can be done by exposing the film to ambient air for a predetermined period of time or using a flow of blown air, optionally heated to a temperature accepted by the material of the membrane, generally less than or equal to 100 ° C. to reduce the drying time of the coating.

Next, the interlayer 12 is separated, which is driven using a motorized roller 18 and wound around a reel 17 for recycling.

The film 11 covered with a coating formed by the first catalytic layer 20 is brought by a transfer device, which can be a movable head comprising a bar engaging the end of the film (not shown), which ensures the movement of the film until it is placed near a first cutting device 70 (which may be a knife or laser cutting device) which cuts the outline of the membrane 10.

In another variant, the film 11 coated with catalytic ink is wound on a reel before cutting the membrane, the film being tensioned in this case using intermediate tensioning rollers .

The step of cutting the membrane 10 comprising on one of these faces a catalytic coating 20 forming the first electrode is followed by an additional step of bonding on the edge of each of the faces of the membrane with a reinforcement carrying 'a joint silicone screen printed. This step is better described in document WO 2017/103475 of the applicant. FIG. 3 schematically illustrates a sub-assembly formed by the membrane 10 covered with the catalytic layer 20 which is integral with a reinforcement 21 provided with a silicone seal 23. The reinforcement 21 includes cutouts 22 allowing communication through the various assemblies and a seal 23 deposited by screen printing and which provides sealing around the periphery of the membrane and cutouts of the reinforcement.

According to the invention also, a second electrode is formed by applying a coating or catalytic layer 30 from a catalytic ink 60 on a first face of the first gas diffusion layer 50. The second electrode corresponds to the anode side of the cell fuel.

As shown in FIG. 1, a roll 59 of media 51 is unwound forming a gas diffusion layer (GDL) wound around a hub 53. To unwind the media, the hub 53 is rotated around its axis, for example using a motor (not

shown) and preferably by putting the media under tension. A coating of catalytic ink 60 is then applied directly to a first face 54 of the media 51 of the gaseous diffusion layer from an ink tank 61 by a direct deposition process, for example by screen printing. The opposite face 55 of the media 51 is not covered. Other direct deposition methods, for example by coating with a roller or scraper, or by flexography, or even by spraying can be used to apply the ink to the gas diffusion layer (GDL). An indirect deposition method, for example by pad printing using a PTFE transfer buffer can also be used. The coating application step is followed by a drying step. This step can be done by exposing the media to ambient air for a predetermined period or using a flow of blown air, possibly heated to around 100 ° C to reduce the drying time of the coating.

The media 51 forming a gas diffusion layer of the roller 59 covered with the second coating layer 30 is then brought in by a transfer device, which can be a movable head comprising a bar engaging the end of the media (not shown ), which ensures its movement until it is placed near a second cutting device 80 (which can be a knife or laser cutting device) which cuts the outline of the gas diffusion layer 50.

In another variant, the media 51 of gas diffusion layer coated with catalytic ink is wound on a coil before cutting to the dimensions of the gas diffusion layer 50, the media being tensioned in this case at using intermediate tensioning rollers. A second roll 49 of media 41 of gas diffusion layer GDL is unwound, tensioned and brought near a third cutting device 90 which cuts the outline of the second gas diffusion layer 40.

The last step in the process involves assembling the MEA components. For this, the uncovered face of the membrane 10 is brought into contact with the face covered with catalytic ink forming the electrode 30 of the first gas diffusion layer 50 and the coated covered face forming the electrode 20 of the membrane. 10 with one face of the second gas diffusion layer 40. The assembly of all the layers can be done by bonding, for example by bonding the two gas diffusion layers 40 and 50 on either side of the subassembly of Figure 3. Such bonding can be done for example by hot pressing, applying pressure to all of the layers and heating at the same time.

A MEA thus obtained is sandwiched between two bipolar plates to form an elementary cell of a fuel cell. It is then possible to produce a stack of several elementary cells as a function of the power sought for the fuel cell. The stack thus obtained is then closed by end plates and it is connected to the various circuits which ensure the operation of the fuel cell.

The graph in FIG. 2 shows, by spaced lines (triangle-shaped beacon), the performance of a fuel cell of the state of the art in which the membrane-electrode assembly (MEA) is carried out by the CCM method, judged as that giving the best results. The same graph also shows, by dotted lines (square-shaped beacon), the performance of a fuel cell of the invention in which the membrane-electrode assembly was obtained with the method of l invention (CCMix in Figure 2). Apart from the manufacturing method, the other components of the fuel cell are identical (including their materials, catalytic ink, etc.), as well as the assembly of the stack and the aging of the cells. It can be seen from this graphical representation that the performances of the two fuel cells are very close. A fuel cell is thus obtained having good operating performance, while using an easier manufacturing process.

Other variants and embodiments of the invention can be envisaged without departing from the scope of its claims. Thus, the deposition of catalytic ink on the membrane or on the gas diffusion layer can be done by other methods, such as extrusion, calendering or physical vapor deposition.

Furthermore, the method of the invention can be used to cover with a catalytic layer a membrane and a gas diffusion layer previously cut (in the form of sheets). In another variant, it is possible to cut certain components into sheets and apply them to another in the form of a roll. So we can cut the GDL into sheets covered and that not covered with a catalytic layer and then apply them each on one of the faces of the membrane previously covered with a catalytic layer on one of these faces, the membrane being in the form of a roll. In this case, the cutting of an MEA assembly will take place at the end of the assembly operation.

Claims

1. Method for manufacturing a membrane-electrode assembly (100) for a cell

fuel comprising a proton-exchange polymer membrane (10), catalytic layers (20, 30) and first and second gas diffusion layers (50, 40), the process comprising the following steps:

a) forming a catalytic layer coating (20) on a first face (14) of the membrane, the opposite face (15) being supported by an interlayer (12);

b) forming a catalytic layer coating (30) on a first face (54) of the first gas diffusion layer (50);

c) bringing said first face (54) of the first gas diffusion layer (50) into contact with the opposite face (15) to said first face (14) of the membrane, after removing the interlayer (12), and said first face (14) of the membrane with one face of the second gas diffusion layer (40).

2. Method according to claim 1, characterized in that the coating of catalytic layer (20) formed in step a) corresponds to the cathode part of the membrane (10).

3. Method according to one of the preceding claims, characterized in that the

membrane (10) and the gaseous diffusion layers (50.40) are obtained by cutting steps to predetermined dimensions before step c).

4. Method according to one of the preceding claims, characterized in that the

coating of catalytic layer (20,30) is obtained by a process of direct deposition of a catalytic ink on one of the faces of the membrane (10) and on one of the faces of the gas diffusion layer (50) by a process included in the group comprising: screen printing, coating, flexography, spraying.

5. Method according to claim 4, characterized in that the deposition is followed by a drying step.

6. Method according to one of the preceding claims, characterized in that it comprises an additional step of bonding on the rim of each of the faces of the membrane (10) of a reinforcement (21) carrying a seal of sealing (23).

7. Method according to one of the preceding claims, characterized in that

the assembly of step c) is done by gluing.

8. Assembly line for carrying out the method of manufacturing an electrode membrane assembly (100) according to the preceding claims.

9. Fuel cell comprising at least one cell comprising an electrode membrane assembly (100) obtained with the method of claims 1 to 7, the assembly being sandwiched between two bipolar plates.