METHOD FOR PRODUCING A CATALYTICALLY COATED MEMBRANE AND MEMBRANE ELECTRODE ASSEMBLY AND FUEL CELL STACK HAVING SAME

Abstract

The invention relates to a method for producing a catalyst coated membrane (19) for a fuel cell (10), wherein the catalyst coated membrane (19) has a membrane (11) and a catalyst layer (12, 13) of a catalytic material arranged on at least one of its flat sides, as well as a nonrectangular active area (20), which is restricted in one direction by two outer sides (30) opposite one another. The method comprises a continuous application of the catalytic material to a membrane material (33) while creating a constant coating width (B) such that an area (35) coated with the catalytic material corresponds to at least the active area (20). A provision is that the membrane material (33) be coated with the catalytic material such that a coating direction (D) has an angle with respect to the opposite outer sides (30) of the active area (20) that is not equal to 90° and not equal to 0°.

Claims

1. A method for producing a catalyst coated membrane for a fuel cell, the method comprising: producing a catalyst coated membrane that has a membrane material and a catalyst layer of a catalytic material on a flat side of the membrane material including a nonrectangular active are, which is restricted in one direction by two outer sides opposite one another and extending parallel to each other, the producing including: continuously applying the catalytic material to the flat side of the membrane material in a coating direction, the catalytic material having a constant coating width, the area of the membrane material coated with the catalytic material corresponds at least to covers the nonrectangular active area of the catalyst coated membrane, the applying including: coating the membrane material with the catalytic material such that the coating direction has an angle that is not equal to 90° and not equal to 0° with respect to two outer sides of the nonrectangular active area.

2. The method according to claim 1 wherein the nonrectangular active area has at least four corners, which is restricted by the two outer sides and at least one first pair of sides opposite one another, and wherein the coating direction has an angle that is a maximum of 10° with respect to the first pair of sides.

3. The method according to claim 2 wherein the area of the membrane material coated is bounded laterally by the first pair of sides of the nonrectangular active area.

4. A method, comprising: producing a plurality of catalyst coated membranes using a membrane material, the plurality of catalyst coated membranes each having a portion of the membrane material and a catalyst layer of a catalytic material on a flat side of the portion of the membrane material, each portion including a nonrectangular active area, which is restricted in one direction by two outer sides opposite one another and extending parallel to each other, the producing including: continuous coating of the membrane material with the catalytic material in a coating direction, the catalytic material having a constant coating width, the area of each portion of the membrane material coated with the catalytic material at least covers to the nonrectangular active area of a respective catalyst coated membrane, the coating including: coating the membrane material with the catalytic material such that the coating direction has an angle that is not equal to 90° and not equal to 0° with respect to two outer sides of each of the nonrectangular active areas; wherein the two outer sides of the nonrectangular active area of the respective catalyst coated membrane and the two outer sides of the nonrectangular active area of an adjacent catalyst coated membrane are oriented parallel with respect to one another on the membrane material.

5. The method according to claim 4 wherein the membrane material is a strip-like cut with parallel longitudinal sides and the coating direction is parallel to the longitudinal sides of the membrane material.

6. The method according to claim 5, wherein each nonrectangular active area has at least four corners bounded by the two outer sides and the first pair of sides; and wherein the plurality of catalyst coated membranes is arranged on the membrane material such that the first pair of sides are oriented parallel to the longitudinal sides of the membrane material.

7. The method according to claim 1, further comprising after applying the catalytic material, fabricating the membrane material to a desired shape of the catalyst coated membrane.

8. The method according to claim 1, further comprising: removing the catalytic material that was applied to the membrane material in areas outside of the catalyst coated membrane from the membrane material; and recycling the catalytic material that had been removed.

9. A membrane electrode assembly, comprising: a catalyst coated membrane produced with a method according to claim 1; and operating media ports arranged outside of the nonrectangular active area of the catalyst coated membrane for supplying and removing operating media to and from a fuel cell.

10. A fuel cell stack comprising, a plurality of membrane electrode assemblies alternately stacked with bipolar plates according to claim 9.

11. The method according to claim 1 wherein the nonrectangular active area has at least at least six corners.

12. The method according to claim 1 wherein the angle of the coating direction has a maximum of 5° with respect to the first pair of sides.

13. The method according to claim 1 wherein the angle of the coating direction is no more than 0° with respect to the first pair of sides.

14. The method according to claim 4 wherein the membrane material is a continuous strip.

Description

[0021] The invention is explained below in exemplary embodiments on the basis of the respective drawings. The following is shown:

[0022] FIG. 1 shows a schematic cross-sectional view of a fuel cell stack;

[0023] FIG. 2 shows a view of a membrane electrode assembly with a nonrectangular active area;

[0024] FIG. 3 shows a view of a catalyst coated membrane of the membrane electrode assembly according to FIG. 2;

[0025] FIG. 4 shows the production of a catalyst coated membrane according to FIG. 3 with a method according to the prior art;

[0026] FIG. 5 shows the production of a catalyst coated membrane according to FIG. 3 with a method according to a first embodiment of the invention;

[0027] FIG. 6 shows the continuous production of a plurality of catalyst coated membranes according to FIG. 3 with a method according to a second embodiment of the invention; and

[0028] FIG. 7 shows the continuous production of a plurality of catalyst coated membranes according to FIG. 3 with a method according to a third embodiment of the invention.

[0029] FIG. 1 shows a cutout of a fuel cell stack, designated overall with 100, of which only two individual fuel cells 10 are shown here.

[0030] Each fuel cell 10 has a polymer electrolyte membrane 11, which consists of an electrolytically conductive polymer material, which is particularly capable of conducting protons. Typically, the polymer material requires a certain humidity to maintain its electrolytic conductivity. A catalyst layer adjoins both flat sides of the membrane 11, namely an anode catalyst layer 12 and a cathode catalyst layer 13. The catalyst layers, 12 and 13, comprise a catalytic material, which is typically a precious metal, particularly platinum. Typically, the catalyst layers 12, 13 further comprise a porous, electrically conductive carrier material, on which the catalytic material is finely dispersed, for example a carbon-based material. The catalyst layers 12, 13 may further comprise components, for example polymer binder materials and the like.

[0031] A gas diffusion layer (GDL) 14 adjoins each catalyst layer 12, 13. The GDL comprises a material, through which liquids can flow, which is likewise electrically conductive. For example, the GDL 14 comprises a carbon-based foam or paper material. The structure made up of membrane 11, the catalyst layers 12, 13, as well as the gas diffusion layers 14 is also characterized as the membrane electrode assembly 15, in which the allocation of the gas diffusion layers 14 to the membrane electrode assembly 15 varies in the literature.

[0032] A bipolar plate 16, also characterized as the flow field plate or flux field plate, is arranged between each of two membrane electrode assemblies 15. On its anode side, the bipolar plate 16 has anode flow channels 17, by means of which an anode operating media (fuel), particularly hydrogen, is routed to the anode catalyst layer 12. Furthermore, on its cathode side, the bipolar plate 16 has cathode flow channels 18, by means of which a cathode operating gas, which is typically an oxygen-containing gas, usually air, is routed to the cathode catalyst layer 13. Typically, the bipolar plate 16 further has internal coolant channels, not shown here, through which a coolant can be routed for cooling the fuel cell stack 100. The bipolar plate 16 is produced from an electrically conductive material, for example a metal, a metal alloy, graphite, or an electrically conductive polymer material or polymer composite material. The bipolar plate 16 thus combines the functions of the operating media supply, the cooling, as well as the electrical connection of the catalytic electrodes 12, 13 to an external current circuit.

[0033] Typically, a plurality of such type of individual cells 10 are arranged in a fuel cell stack 100, the electrical power outputs of which accumulate. For electric vehicle applications, fuel cell stacks 100 typically comprise several hundred individual cells 10.

[0034] The catalyst layers, 12 and 13, may be present, on one hand, as a coating on the membrane 11. In this case, this is also considered to be a catalyst coated membrane or CCM, which is designated overall with 19 in FIG. 1. Alternatively, the catalyst layers, 12 and 13, may be present as a coating of the gas diffusion layers 14 such that they are then characterized as gas diffusion electrodes. The present invention primarily relates to the case of a catalyst coated membrane 19 as well as a method for the production thereof.

[0035] FIG. 2 shows a membrane electrode assembly 15 with a view of its flat sides. The membrane electrode assembly 15 has the catalyst coated membrane 19, which is also shown in FIG. 3 in isolated form. In the example shown, the catalyst coated membrane 19 has a hexagonal contour. Within this hexagonal contour, an active area 20 is arranged, which is indicated by a dashed line. Outside of the active area 20, the catalyst coated membrane 19 has inactive areas 21. The active area 20 is characterized in that the fuel cell reactions take place at the anode and cathode and thus electricity is generated in a fuel cell stack 100 in this area in the installed state of the membrane electrode assembly 15. The inactive areas 21, on the other hand, are used for other functions, for example to supply operating media to the active area 20. Ideally, the polymer electrolyte membrane 11 is only coated with the catalyst coatings, 12 and 13, in the active area 20, as is shown in FIG. 3.

[0036] The membrane electrode assembly 15 comprises various passage openings, 22 to 27, which are used to supply and remove the various operating media. Thus, a first anode port 22 is used to supply the anode operating gas to the cathodes 12 of the fuel cell stack 100 and an opposing second anode gas port 23 is used to remove the anode operating gas. Likewise, a first cathode port 24 is used to supply a cathode operating gas to the cathodes 13 of the fuel cell stack 100 and an opposing second cathode gas port 25 is used to remove the cathode operating gas. Finally, a first coolant port 26 is used to supply a coolant to the internal coolant channels of the bipolar plates 16 and an opposing second coolant port 27 is used to remove the coolant. The bipolar plates 16, which are not shown in detail, have an essentially equivalent cut as the membrane electrode assembly 15 shown, particularly corresponding ports. In this manner, in the stacked state of the membrane electrode assemblies 15 and bipolar plates 16, operating media main channels are formed, which implement the fuel cell stack 100 in its stack direction S (see FIG. 1). (These operating media main channels are not shown in FIG. 1, which only shows a section through the active area 20 of the fuel cell stack.) The anode and cathode ports, 22 to 25, are connected to the corresponding anode and/or cathode channels 17, 18 of the bipolar plates 16 so as to convey fluid by means of open distribution channels of the bipolar plates 16 adjoining in the stack 100. The coolant ports 26, 27 are connected to the internal coolant channels of the bipolar plates 16. The distribution channel structures connecting the ports 22-27 and the anode and/or cathode channels 17, 18 of the active area 20 extend into the inactive areas 21.

[0037] For mechanical support, the membrane 11 is typically enclosed on both sides by a support layer 28, which encloses the membrane 11 at its edge areas. Optionally, the membrane 11 can also extend over the entire surface of the membrane electrode assembly 15 and be laminated on its edge areas with support layers 28. Furthermore, there are seals 29 discernible in FIG. 2, which enclose the operating media passage openings, 22 to 27, as well as the catalyst coated membrane 19, in order to seal it off with respect to the outside. Optionally, the seals 29 can be arranged on the bipolar plates 16 instead of on the membrane electrode assembly 15 or may be arranged on both.

[0038] As previously explained, the fuel cell reaction takes place only in the active area 20. Thus, the target is to apply the catalyst layers, 12 and 13, only in this area to the extent possible, because the catalytic material represents the most expensive individual component of the fuel cell stack by far. On the other hand, the target is to keep the active area 20 as large as possible and the inactive areas 21 as small as possible in order to achieve the maximum extent of energy yield and to minimize the required installation space and the weight of the fuel cell. The contours of the active area 20 accordingly resulting from said targeting may deviate from the conventional rectangular contour and have an irregular contour. For example, a hexagonal contour of the active area 20 results as shown in FIGS. 2 and 3. This contour is restricted in a direction extending parallel to the main flow direction of the operating media by two parallel outer sides 30 opposite one another. The irregular hexagonal contour of the active area 20 shown further has a first pair of short sides 31 opposite one another as well as a second pair of short sides 32 opposite one another. In doing so, short sides 31 have a longer length than short sides 32.

[0039] The economical and time-saving mass production of catalyst coated membranes 19 with a nonrectangular active area has only been achieved in an unsatisfactory manner until now. For example, the production through selective coating processes can take place in which the catalytic material is exclusively applied to the active area 20 of a membrane material, for example through selective print processes such as print screening or offset screening. These processes, however, are characterized by a slow production speed (print screening) or by cost-intensive machines (offset printing). On the other hand, continuous coating processes in which the catalytic material is applied with the creation of a constant coating width on the membrane material are quicker and more cost-efficient. This is shown in the example from FIG. 4, which represents such a continuous coating process according to the prior art.

[0040] In FIG. 4, 33 designates the membrane material on which the catalytic material is applied along a continuous track of the width B, restricted by the longitudinal sides 34. FIG. 4 also shows the catalyst coated membrane 19 to be cut out in a subsequent manufacturing step of the process as well as the desired active area 20. In doing so, the application direction D according to the prior art extends in a direction that is aligned orthogonally, that is 90°, with respect to the two outer sides 30 of the active area that are aligned opposite one another. Thus, this results in a coated area 35 with rectangular contour. The coated area 35 according to the prior art, however, not only covers the active area 20 but also parts of the inactive areas 21 of the catalyst coated membrane 19 as well as protruding offcut areas that are cut off by subsequent manufacturing. Only the simply hatched areas 36 of the catalyst coated membrane 19 remain uncoated. The cross-hatched areas 37, on the other hand, are coated with catalytic material according to the conventional methods although it is not necessary at this point. This leads, on one hand, to unnecessary high costs for the catalytic material and, on the other hand, to the requirement to block these adversely coated areas 37, for example by applying gas barrier layers in order to prevent fuel cell reaction in these areas.

[0041] According to the invention, the known continuous process is thus converted in that the membrane material is coated with the catalytic material such that the coating direction D has an angle with respect to the opposite outer sides 30 of the active area 20, which is not equal to 90°, differently than in FIG. 4. This principle is represented in FIG. 5. Thus, the catalytic material is applied to the membrane material 33 in a continuous process while generating a coated surface 35 with a constant coating width B. The coating direction D here, however, does not extend orthogonally with respect to the progression of the outer sides 30 of the active area 20 as in FIG. 4 (and also not parallel to the outer sides 30, as is known from other processes). Instead, the coating direction D extends in a direction that most precisely corresponds to the direction of one of the two short side pairs 31, 32 of the active area 21, or preferably the longer short sides 31.

[0042] As can be seen using the simple hatched areas 36, which characterize the non-coated area of the membrane 19 to be cut out, the inactive areas 21 of the catalyst coated membrane 19 are completely uncoated in the example shown. After the catalyst coated membrane 19 is cut out from the membrane material 33, only the cross-hatched areas 37 remain as excessively coated areas. The comparison of the (excessively) coated areas 37 of the method according to the invention according to FIG. 5 with those according to FIG. 4 shows that the invention can reduce said excessive coating significantly. The excessively coated areas 37 created in the method according to the invention have a surface that is smaller by 6 to 10% than according to conventional processes in which the coating direction D extends orthogonally with respect to the outer sides 30 of the active area 20. Furthermore, with the coating processes according to the invention, the excessively coated areas 37 (cross-hatching) are practically completely removed from the membrane material 33 upon subsequent manufacturing of the catalyst coated membrane 19. This enables a separation of the catalyst coating and the reuse of the catalytic material such that it essentially no longer remains unused in the process. The necessity of blocking undesirable catalytic material through barrier layers is omitted or is at least reduced.

[0043] FIG. 6 shows a further exemplary embodiment for continuous production of a plurality of catalyst coated membranes 19 according to FIG. 3 from a membrane material 33, which has a strip-like cut with parallel longitudinal sides 38, particularly a continuous strip, which is supplied on a roller (not shown). The catalyst coated membranes 19 to be produced here are arranged on the membrane material 33 such that the two outer sides 30 of the active areas 20 of the adjacent catalyst coated membranes 19 are aligned parallel with respect to one another. Simultaneously, the short sides 31 of the active areas 20 are oriented parallel to the longitudinal sides 38 of the membrane material 33. Consequently, the coating direction D extends parallel to the longitudinal sides 38 of the strip-like membrane material 33. An example of an individual catalyst coated membrane 19 to be created is the uncoated area 36 to the right and left, next to the longitudinal sides 34 of the coating area, characterized by simple hatching, while the continuously coated area 35 is emphasized by cross-hatching. After the catalyst coated membranes 19 have been cut out, thus only the rectangular excessively coated areas 37 here remain. These area 37 are preferably routed to recycling of the catalytic material after cutting. In this manner, the process can be implemented in a continuous roller process, in which the catalytic material is continuously applied to a moving membrane material 33 with a constant width B.

[0044] A further advantageous embodiment of the method according to the invention is shown in FIG. 7. In this case, the catalyst coated membranes 19 to be created are arranged in two parallel rows on the membrane material 33. Their alignment regarding their outer sides 30 and short sides 31 of the catalyst areas 20 correspond to that in FIG. 6. In this process, the hexagonal membranes 19 are arranged embedded within one another such that their top ends engage with one another in an intermeshed manner. This arrangement enables the offcut of membrane material 33 to be reduced. In the example shown, about 7% membrane material 33 in relation to the overall surface area can be spared. In this example, two parallel surface-coated areas 35 are continuously created, each having a coating width B. It is obvious that also more than two parallel rows of catalyst coated membranes 19 can be produced in this manner.

REFERENCE LIST

[0045] 100 Fuel cell stack

[0046] 10 Fuel cell (individual cell)

[0047] 11 Polymer electrolyte membrane

[0048] 12 Anode catalyst layer/anode

[0049] 13 Cathode catalyst layer/cathode

[0050] 14 Gas diffusion layer

[0051] 15 Membrane electrode assembly

[0052] 16 Bipolar plate

[0053] 17 Anode flow channels

[0054] 18 Cathode flow channels

[0055] 19 Catalyst coated membrane

[0056] 20 Active area

[0057] 21 Inactive area

[0058] 22 First anode port

[0059] 23 Second anode port

[0060] 24 First cathode port

[0061] 25 Second cathode port

[0062] 26 First coolant port

[0063] 27 Second coolant port

[0064] 28 Support layer

[0065] 29 Seal

[0066] 30 Outer side of the active area

[0067] 31 Short side of the active area

[0068] 32 Short side of the active area

[0069] 33 Membrane material

[0070] 34 Longitudinal sides of the coated area

[0071] 35 Coated area

[0072] 36 Uncoated area

[0073] 37 Excessively coated area

[0074] 38 Longitudinal sides of the membrane material

[0075] B Coating width

[0076] D Coating direction

[0077] S Stack direction