METHOD FOR PRODUCING A MEMBRANE ELECTRODE ASSEMBLY FOR A FUEL CELL

Abstract

A method for producing a membrane electrode assembly for a fuel cell comprising a proton exchange polymer membrane, catalyst layers, and first and second gas diffusion layers, the method comprising the following steps: a) forming a catalytic layer coating on a first surface of the membrane, the opposite surface being supported by a spacer; b) forming a catalytic layer coating on a first surface of the first gas diffusion layer; c) bringing the first surface of the first gas diffusion layer into contact with the surface opposite to the said first surface of the membrane, after removing the spacer, and bringing the first surface of the membrane into contact with a surface of the second gas diffusion layer.

Claims

1. A method for producing a membrane electrode assembly for a fuel cell comprising a polymeric proton exchange membrane, catalyst layers, and first and second gas diffusion layers, the method comprising the following steps: a) forming a catalytic layer coating on a first surface of the membrane, the opposite surface being supported by a spacer; b) forming a catalytic layer coating on a first surface of the first gas diffusion layer; c) bringing said first surface of the first gas diffusion layer into contact with the opposite surface to the first surface of the membrane, after removing the spacer, and bringing said first membrane surface into contact with a surface of the second gas diffusion layer.

2. The method according to claim 1, wherein the catalytic layer coating formed in step a) corresponds to the cathode portion of the membrane.

3. The method according to claim 1, wherein the membrane and the gas diffusion layers are obtained by steps of cutting to preset dimensions prior to step c).

4. The method according to claim 1, wherein the catalytic layer coating is obtained by a method of direct deposit of a catalytic ink on one surface of the membrane and on one surface of the gas diffusion layer by a method included in the group comprising screen printing, coating, flexography, spraying.

5. The method according to claim 4, wherein the deposit is followed by a drying step.

6. The method according to claim 1, comprising further an additional step of bonding a reinforcement to the edge of each of the membrane surfaces, carrying a seal.

7. The method according to claim 1, wherein the assembly of step c) is carried out by gluing.

8. An assembly line for carrying out the method for producing a membrane electrode assembly according to claim 1.

9. A fuel cell comprising at least one cell comprising a membrane electrode assembly obtained with the method of claim 1, the assembly being sandwiched between two bipolar plates.

Description

[0028] The invention will be better understood from the following description, which is based on the following figures:

[0029] FIG. 1 is a schematic view of an assembly line that implements the method of the invention;

[0030] FIG. 2 is a graphical representation of the performance of a fuel cell obtained with the method of the invention compared to that of a state-of-the-art fuel cell;

[0031] FIG. 3 is a perspective view of a portion of a membrane-electrode assembly obtained with the method of the invention.

[0032] In the various figures, identical or similar elements bear the same reference. Their description is therefore not systematically repeated.

[0033] FIG. 1 schematically illustrates an assembly line 1 that 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 surface thereof, and a gas diffusion layer 40, 50 arranged opposite each electrode.

[0034] The membrane 10 is in the form of a very thin film of a proton conducting polymer called ionomer. Such an ionomer is, for example, Nafion® N117 and is supplied by its manufacturer in the form of a film roll. The film is a strip with a thickness of a few tens of μm, a width of a few tens of cm and a length of a few meters. The film is wound into a reel and supported on a spacer (or sometimes it is placed between two spacers) which can be a polyester film.

[0035] 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 selected from the platinum group of the periodic table of elements. The ink further comprises a binder, such as an ionomer (e.g., Nafion®), a solvent (e.g., water, glycerol, etc.). Additives may be added to the formulation, such as a surfactant. The ink, which is generally in a liquid state, is deposited on the substrate and dried to a catalyst loading of about 0.1 to 0.2 mg/cm.sup.2.

[0036] A gas diffusion layer 40, 50 or GDL (for Gas Diffusion Layer) is a porous media to allow the transport of the reactant from its inlet to the catalyst. It must also be electrically conductive to conduct the charges. Such a gas diffusion layer is thus advantageously made of carbon fibers that are woven or knitted together or are in the form of a non-woven textile. Such a gas diffusion layer can also be treated (for example by applying to it a micro-coating made of PTFE and carbon particles) so that it is hydrophobic in order to better channel the water that results from the reaction within the cell. The gas diffusion layers used are of the type used in the manufacture of fuel cells. They are generally supplied in roll form by their manufacturer.

[0037] According to the invention, a first electrode is formed by applying a coating or catalytic layer 20 obtained from a catalytic ink 60 to a first surface 14 of the membrane 10, the opposite surface 15 being supported by a spacer 12. The first electrode or catalytic layer 20 is the one corresponding to the cathode surface of the membrane.

[0038] As best seen in FIG. 1, a roll 19 of film 11 constituting the polymeric ion exchange membrane is first unwound, the film and its support or spacer 12 being wound together around a hub 13. To unwind the film, the hub 13 is rotated about its axis, for example by means of a motor (not shown) and preferably by tensioning the film-spacer assembly. A catalytic ink deposit 60 is then applied directly to a first surface 14 of the membrane from an ink reservoir 61 by a direct deposit method, such as screen printing. The opposite surface 15 of the membrane is supported by the spacer 12 having dimensions comparable to the film forming the membrane. Other direct deposit methods, such as coating with a roller or wiper, or flexography, or even spraying can be used to apply the ink to the membrane film. An indirect deposit method, for example by pad printing using a PTFE transfer pad, can also be used.

[0039] 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 time or by using a blown air stream, possibly heated to a temperature accepted by the membrane material, generally less than or equal to 100° C. in order to reduce the drying time of the coating.

[0040] The spacer 12 is then separated and driven by a motorized roller 18 and wound around a reel 17 for recycling.

[0041] The coated film 11 formed by the first catalytic layer 20 is fed by a transfer device, which may be a moving head comprising a bar engaging the end of the film (not shown), which moves the film until it comes to lie in the vicinity of a first cutting device 70 (which may be a knife or laser cutting device) which performs the cutting of the contour of the membrane 10.

[0042] In another embodiment, the film 11 coated in catalytic ink is wound into a spool before cutting the membrane, in which case the film is tensioned by intermediate tensioning rolls.

[0043] The step of cutting the membrane 10 comprising a catalytic coating 20 one of its surfaces, forming the first electrode, is followed by an additional step of gluing a reinforcement to the edge of each of the membrane surfaces, carrying a screen-printed silicon seal. This step is best described in the applicant's WO 2017/103475. FIG. 3 schematically illustrates a sub-assembly formed by the membrane 10 covered with the catalytic layer 20 that is integral with a reinforcement 21 provided with a silicone seal 23. The reinforcement 21 comprises cut-outs 22 allowing communication through the various assemblies and a seal 23 deposited by silk-screen printing and which ensures the sealing around the perimeter of the membrane and the cut-outs of the reinforcement.

[0044] Also, according to the invention, a second electrode is formed by applying a catalytic coating or layer 30 from a catalytic ink 60 to a first surface of the first gas diffusion layer 50. The second electrode corresponds to the anode surface of the fuel cell.

[0045] As seen in FIG. 1, a roll 59 of media 51, forming a gas diffusion layer (GDL) wrapped around a hub 53, is unwound. To unwind the media, the hub 53 is rotated about its axis, for example by means of a motor (not shown) and by preferably putting the media under tension. A catalytic ink coating 60 is then applied directly to a first surface 54 of the gas diffusion layer media 51 from an ink reservoir 61 by a direct deposit method, such as screen printing. The opposite surface 55 of the media 51 is uncovered. Other direct deposit methods such as roller or doctor blade coating, or flexography, or even spraying can be used to apply ink to the gas diffusion layer (GDL). An indirect deposit method, such as pad printing using a PTFE transfer pad can also be used.

[0046] 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 time or by using a blown air stream, possibly heated to about 100° C. to reduce the drying time of the coating.

[0047] The media 51 forming a gas diffusion layer of the roll 59 covered with the second coating layer 30 is then fed by a transfer device, which may be a moving head comprising a bar engaging the end of the media (not shown), which ensures its movement until it comes to lie in the vicinity of a second cutting device 80 (which may be a knife or laser cutting device) which performs the cutting of the contour of the gas diffusion layer 50.

[0048] In another variant, the catalytic ink coated gas diffusion layer media 51 is wound in a reel prior to cutting to the dimensions of the gas diffusion layer 50, with the media tensioning in this case being done with intermediate tensioning rolls.

[0049] A second roll 49 of GDL (gas diffusion layer) media 41 is unwound, tensioned and brought close to a third cutting device 90 which performs the contour cutting of the second gas diffusion layer 40.

[0050] The final step of the method involves the assembly of the MEA components. This is accomplished by bringing the uncovered surface of the membrane 10 into contact with the catalytic ink-covered surface forming the electrode 30 of the first gas diffusion layer 50 and the coating-covered surface forming the electrode 20 of the membrane 10 with a surface 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 surface of the subassembly of FIG. 3. Such bonding can be done for example by hot pressing, by applying pressure to the assembly of layers and heating it at the same time.

[0051] A MEA obtained in this way is sandwiched between two bipolar plates to form an elementary cell of a fuel cell. A stack of several elementary cells can then be produced depending on the power required for the fuel cell. The stack thus obtained is then closed by end plates and connected to the various circuits that ensure the operation of the fuel cell.

[0052] The graph in FIG. 2 shows, by spaced lines (triangle-shaped marker), the performance of a state-of-the-art fuel cell in which the membrane-electrode assembly (MEA) is carried out by the CCM method deemed to give the best results. The performance of a fuel cell of the invention in which the membrane-electrode assembly was obtained with the method of the invention (CCMix in FIG. 2) is also represented on the same graph by dotted lines (square marker). Apart from the production method, the other fuel cell components are identical (including their materials, catalytic ink, etc.), as well as the stack assembly and the aging of the cells. It can be seen from this graphical representation that the performance of the two fuel cells is very close. This results in a fuel cell with good performance in operation, while using an easier producing method.

[0053] Other variants and embodiments of the invention can be envisaged without going beyond the scope of its claims. For example, the deposit of catalytic ink on the membrane or on the gas diffusion layer can be done by other methods, such as extrusion, calendaring or physical vapor deposit.

[0054] Alternatively, the method of the invention can be used to coat a previously cut membrane and gas diffusion layer (in sheet form) with a catalytic layer. In another embodiment, some components can be cut into sheets and applied to another in roll form. For example, the GDL covered with a catalytic layer and the GDL not covered with a catalytic layer can be cut into sheets and then each of them can be applied to one surface of the membrane previously covered with a catalytic layer on one of these surfaces, the membrane being in the form of a roll. In this case, the cutting of a MEA assembly will take place at the end of the assembly operation.