GREEN PAPER FOR PRODUCING A GAS DIFFUSION LAYER FOR A FUEL CELL

Abstract

A green paper is provided for producing a gas diffusion layer (GDL) for a fuel cell. A process is for producing a green paper for producing a gas diffusion layer (GDL) for a fuel cell. The green paper includes at least one first, watermarked paper web. The watermark forms the patterning for the flow field or gas distribution structure of the gas diffusion layer (GDL) produced from the green paper. The first paper web is admixed with metal powder and/or metal fibres. The eventual GDL is formed after debindering, sintering, coating, deposition of atomic layers (ALD—atomic layer deposition) and further operating steps.

Claims

1.-15. (canceled)

16. A green paper for producing a gas diffusion layer (GDL) for a fuel cell, wherein the green paper has at least one first paper web, in which at least one watermark is made, where the watermark forms a patterning for the flow field of the gas diffusion layer produced from the green paper.

17. The green paper according to claim 16, wherein the watermark is a true watermark, in which the thickness of the paper varies but the density of the paper does not vary, and/or in that the watermark is a false watermark, in which the thickness of the paper is reduced but at the same time the density of the paper is increased.

18. The green paper according to claim 16, wherein the green paper has a first paper web and at least one second paper web.

19. The green paper according to claim 16, wherein the watermark is configured as a recess in the form of at least one channel.

20. The green paper according to claim 16, wherein the watermark has little or virtually no patterning so as in the GDL to generate registration marks, positioning aids, centering aids or starting points for passages.

21. The green paper according to claim 16, wherein the patterns of the watermark of the anode side and of the cathode side of the fuel cell are not identical but are instead exactly mirror-symmetrical in the area and in the material-thickness direction.

22. A process for producing a green paper for producing a gas diffusion layer (GDL) for a fuel cell, wherein at least one first paper web, admixed with metal powder and/or metal fibers, is generated, with at least one watermark being made in the paper web, in order to form a patterning for the flow field of the gas diffusion layer produced from the green paper.

23. The process according to claim 22, wherein the watermark is formed by a true watermark, in which the thickness of the paper varies but the density of the paper does not vary, and/or in that the watermark is formed by a false watermark, in which the thickness of the paper is reduced but at the same time the density of the paper is increased.

24. The process according to claim 22, wherein a first paper web is formed, and a second paper web is formed, the web in the still-wet state being brought together with and firmly joined to the first paper web, where the first paper web and the second paper web together form a green paper for the GDL.

25. The process according to claim 24, wherein the first and/or second paper web is generated in a cylindrical paper machine.

26. The process according to claim 24, wherein the first and/or second paper web is generated in a short former wherein the paper stock is applied via nozzle to a cylindrical wire.

27. The process according to claim 24, wherein the first paper web has a higher density than the second paper web, where the first paper web has a density of 3 g/cm.sup.3 to 10 g/cm.sup.3 and the second paper web has a density of 1 g/cm.sup.3 to 5 g/cm.sup.3.

28. The process according to claim 27, wherein the first paper web is formed by a finer paper fiber slurry than the second paper web.

29. The process according to claim 24, wherein the first paper web forms a diffusion layer for a membrane coated with catalytic metal, platinum, in the gas diffusion layer produced from the green paper, and the second paper web forms a distribution layer with flow field in the gas diffusion layer produced from the green paper.

30. The use of a gas diffusion layer (GDL) produced from a green paper according to claim 16, in a proton exchange membrane fuel cell (PEMFC), in a proton exchange membrane electrolyzer cell (PEMEC), in electrolyzer cells or in another power-to-X technology which requires correspondingly porous, conductive material for gas/power/reactant distribution.

Description

[0038] The advantages of the invention are elucidated with reference to the exemplary embodiments below and to the supplementary figures. The exemplary embodiments constitute preferred embodiments, but without any intention at all for the invention to be confined to them. Furthermore, for greater ease of understanding, the representations in the figures are highly schematized and do not reflect the actual circumstances. In particular, the proportions shown in the figures do not match the conditions present in reality, and serve solely to improve clearness. Furthermore, the embodiments described in the exemplary embodiments below are reduced to the essential core information, for greater ease of understanding. In the practical implementation, substantially more complex designs or images may be employed.

[0039] In detail and schematically:

[0040] FIG. 1 shows a double-cylindrical paper machine for producing a green paper of the invention,

[0041] FIG. 2 shows a cylindrical paper machine and a short former in schematic representation,

[0042] FIG. 3 shows a two-ply GDL having a serpentine channel shaped by a watermark, in plan view on the left and in sectional representation along the section A-B on the right,

[0043] FIG. 4 shows the two-ply GDL from FIG. 3, additionally with registration marks, positioning aids and centering aids,

[0044] FIG. 5 shows a combination of two 3D mirror-symmetrical anode and cathode GDLs, in each case in plan view on the left and in sectional representation along the section A-B on the right,

[0045] FIG. 6 shows a GDL having channels shaped by a watermark, these channels leading outward from the middle of the GDL, with ray-shaped channels in FIG. 6a, with ray-shaped and concentric channels in FIG. 6b, and with spiral-shaped channels in FIG. 6c.

[0046] FIG. 1 shows in schematic representation a double-cylindrical paper machine 10, as is known for the production of security paper from WO 2006/099971 A2, for example. The paper machine 10 contains two cylindrical paper machines 12 and 14, which are connected to one another via a transfer felt 16.

[0047] In the first paper machine 12, a paper web 20 is formed on a cylindrical wire 18. In the second paper machine 14, in parallel with this, a second, homogeneous paper web 30 is produced, is taken from the cylindrical wire 34 by means of the transfer felt 16 and is passed to the first paper machine 12, where it is joined to the first paper web 20 in the region of the pinch roller 36. The paper webs 38 joined to one another together form the GDL and are passed to further processing stations.

[0048] As represented in FIG. 2, the second paper web 30 may also be generated with a short former 40, in which the paper stock is applied with a head-box nozzle 42 onto the surface of a cylindrical wire 44. With a short former of this kind it is possible to generate particularly thin paper plies, having a grammage for example of 15 to 25 g/m2.

[0049] It is appreciated that with the paper machines 12, 14, 40 shown, it is also possible analogously to generate and bring together three or more paper webs.

[0050] FIG. 3 shows schematically a two-ply GDL 1 having a serpentine channel 2 shaped by a watermark, in plan view on the left and in sectional representation along the section A-B on the right.

[0051] In the section A-B, the black region 3 shows the cylindrical wire ply with patterned watermark as channel 2, and the shaded region 4 shows the former ply with fine pore structure. Depending on configuration, the individual plies 3 and 4 may have a different basic thickness. Apparent along the serpentine pattern of the channel 2 in the example above is a sectional profile shaped by the watermark, apparent as a thickness modulation through the cylindrical wire ply, which in the drawing has a semicircle shape. In principle, any conceivable profile shape is possible here that does not possess undercuts and forms a wall angle <80°. The large arrows show the gas inlet/outlet. The gasket around the GDL must be designed accordingly.

[0052] FIG. 4 shows schematically the two-ply GDL from FIG. 3, supplemented by registration marks, positioning aids and centering aids.

[0053] By means of highlight watermarks it is possible to incorporate registration marks, positioning aids, centering aids, and starting points for passages, in order to simplify the further processing of the GDL to form the fuel cell stack. Such incorporation ensures that, using transmitted-light/reflected-light image processing systems, for example, precise positioning of the GDL relative to the other components, such as BPP or CL, is possible.

[0054] The lines 5 are intended to represent cutting marks for the GDL, realized for example as highlight watermarks, and the circles 6 are intended to represent centering/positioning aids. They may of course be made in any desired form. It would also be possible to employ HD watermark laser screens.

[0055] FIG. 5 shows schematically a combination of an anode GDL 7.1 and of a cathode GDL 7.2, formed with 3D mirror symmetry to said anode, the figure showing at the top left a plan view of the surface of the anode GDL 7.1, at the bottom left a plan view of the surface of the cathode GDL 7.2, and on the right in each case a sectional representation along the section A-B.

[0056] The elevations and depressions in the green paper and in the completed GDL, these elevations and depressions being generated by the watermark and forming flow field channels 8.1 and 8.2, may be damaged again, pressed back or even levelled by pressing and other mechanical loads, meaning that the channels 8.1 and 8.2 may no longer be fully effective.

[0057] This problem can be eliminated by the patterns, generated by watermark, in the GDLs of the anode side and of the cathode side being not identical but instead exactly mirror-symmetrical in the area, but also in the material-thickness direction. This means, when the anode GDL 7.1 is placed by the flow field side onto the flow field side of the cathode GDL 7.2, the elevations and depressions of the channels 8.1 and 8.2 arranged in parallel cancel one another out exactly. The combination of two anode/cathode GDLs with 3D mirror symmetry hence produces a planar piece of sinter paper which can be densified with any pressure without losing its channel pattern.

[0058] Furthermore, the anode GDL 7.1 and the cathode GDL 7.2 may have a different porosity. For example, the anode GDL 7.1 may have a porosity of 20% to 75% and the cathode GDL 7.2 a porosity of 30% to 90%, with the cathode GDL 7.2 therefore acting hardly as resistance for the gas, but instead only as a spacer with respect to the bipolar plate.

[0059] FIG. 6, in plan view in FIGS. 6a, 6b and 6c, shows three embodiments in which the gases are coupled into the GDL in the middle of the bipolar plates (not represented) and then distributed toward the outside or toward the outer edge of the GDL via various watermark patterns and/or channels in the GDL.

[0060] According to FIG. 6a, the channels of the watermark patterns have a ray-shaped design, starting from the middle of the GDL. The gases are supplied via the circular opening in the middle of the GDL; the regions shown in black constitute the regions of the watermark which have a higher thickness of the GDL than the regions shown in white, with reduced thickness of the GDL, which form the channels.

[0061] FIG. 6b shows an exemplary embodiment in which radial channels of the watermark patterns are supplemented by concentric annular channels, so producing a pattern resembling a spider's web. The gases are supplied via the circular opening in the middle of the GDL; the regions shown in black constitute the regions of the watermark which have a higher thickness of the GDL than the regions shown in white, with reduced thickness of the GDL, which form the channels.

[0062] FIG. 6c shows an exemplary embodiment in which the channels of the watermark patterns have a spiral-shaped design, starting from the middle of the GDL. The gases are supplied via the circular opening in the middle of the GDL; the regions shown in black constitute the regions of the watermark which have a higher thickness of the GDL than the regions shown in white, with reduced thickness of the GDL, which form the channels.