Gas diffusion electrode

Abstract

A gas diffusion electrode for a membrane electrode assembly is provided with expanded metal layers each having a mesh configuration defining a length orientation of the expanded metal layers. The expanded metal layers each have opposed flat sides and are stacked in a layered arrangement such that the flat sides of the expanded metal layers that are neighboring each other in the layered arrangement are facing each other as facing flat sides, respectively. The facing flat sides are connected to each other by pulsed resistance welding at welded contact points. Due to the mesh configuration, the welded contact points are distributed evenly across the entire surface area of the facing flat sides. At least one of the expanded metal layers is oriented with its length orientation so as to be rotated by 90° relative to the length orientation of one of the neighboring expanded metal layers.

Claims

1. A gas diffusion electrode for a membrane electrode assembly, the gas diffusion electrode comprising: first expanded metal layers each comprising a mesh configuration defining a length orientation of the first expanded metal layers; the first expanded metal layers each comprising opposed flat sides; the first expanded metal layers stacked in a layered arrangement such that the flat sides of the first expanded metal layers that are neighboring each other in the layered arrangement are facing each other as facing flat sides, respectively; the facing flat sides connected to each other by pulsed resistance welding at welded contact points; wherein, due to the mesh configuration of the first expanded metal layers, the welded contact points are distributed evenly across the entire surface area of the facing flat sides; wherein at least one of the first expanded metal layers is oriented with its length orientation so as to be rotated by 90° relative to the length orientation of one of the neighboring first expanded metal layers.

2. The gas diffusion electrode according to claim 1, wherein the first expanded metal layers each have a defined mesh width, wherein at least two of the first expanded metal layers differ from each other with regard to the defined mesh width.

3. The gas diffusion electrode according to claim 2, wherein the first expanded metal layers include a membrane-contacting expanded metal layer that is configured to contact directly a membrane of a membrane electrode assembly, wherein the mesh width of the membrane-contacting expanded metal layer is the smallest mesh width of the defined mesh widths of the first expanded metal layers.

4. The gas diffusion electrode according to claim 3, wherein the defined mesh widths of the first expanded metal layers decrease in a direction of thickness of the layered arrangement toward the membrane-contacting expanded metal layer.

5. The gas diffusion electrode according to claim 3, further comprising a second expanded metal layer, wherein the first expanded metal layers include a membrane-remote expanded metal layer opposite the membrane-contacting expanded metal layer, wherein the second expanded metal layer is connected to the membrane-remote expanded metal layer.

6. The gas diffusion electrode according to claim 5, wherein the second expanded metal layer is connected to the membrane-remote expanded metal layer by spot welding.

7. The gas diffusion electrode according to claim 1, comprising a linear-elastic behavior in a direction of thickness of the layer arrangement.

8. A method for producing a gas diffusion electrode for a membrane electrode assembly, the method comprising: stacking first expanded metal layers, each comprising a mesh configuration defining a length orientation of the first expanded metal layers and each comprising opposed flat sides, on top of each other to form a layered arrangement such that at least one of the first expanded metal layers is oriented with its length orientation so as to be rotated by 90° relative to the length orientation of one of the neighboring first expanded metal layers and such that the flat sides of the first expanded metal layers that are neighboring each other in the layered arrangement are facing each other as facing flat sides, respectively; in one working step with flat welding electrodes compressing the layered arrangement of the first expanded metal layers, and connecting by pulsed resistance welding the neighboring first expanded metal layers to each other at their facing flat sides by welded contact points that are evenly distributed across the entire surface area of the facing flat sides of the first expanded metal layers due to the mesh configuration of the first expanded metal layers.

9. The method according to claim 8, further comprising generating a compression force by the flat welding electrodes, the compression force sufficiently great for welding and low enough to avoid plastic deformation of the first expanded metal layers.

10. The method according to claim 9, wherein the compression force applied by the flat welding electrodes is 1.0 N/mm.sup.2 to 3.5 N/mm.sup.2.

11. The method according to claim 10, wherein the compression force applied by the flat welding electrodes is 1.3 N/mm.sup.2 to 3.0 N/mm.sup.2.

12. The method according to claim 11, wherein the compression force applied by the flat welding electrodes is 1.5 N/mm.sup.2 to 2.8 N/mm.sup.2.

13. The method according to claim 12, wherein the compression force applied by the flat welding electrodes is 1.7 N/mm.sup.2 to 2.5 N/mm.sup.2.

14. The method according to claim 8, further comprising generating a welding energy by the flat welding electrodes of 1.0 J/mm.sup.2 to 3.0 J/mm.sup.2.

15. The method according to claim 14, wherein the welding energy is 1.2 J/mm.sup.2 to 2.6 J/mm.sup.2.

16. The method according to claim 15, wherein the welding energy is 1.4 J/mm.sup.2 to 2.4 J/mm.sup.2.

17. The method according to claim 15, wherein the welding energy is 1.6 J/mm.sup.2 to 2.2 J/mm.sup.2.

18. The method according to claim 8, further comprising connecting a second expanded metal layer to the layered arrangement.

19. The method according to claim 18, further comprising connecting the second expanded metal layer by resistance spot welding.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Further features and advantages of the invention result from the following description with the aid of the drawings. In this context, the figures show purely schematic illustrations.

(2) FIG. 1 is an exploded view of a membrane electrode assembly.

(3) FIG. 2 is an exploded view of a gas diffusion electrode.

(4) FIG. 3 is a detail view an expanded metal layer.

(5) FIG. 4 shows the first step of a method according to the invention.

(6) FIG. 5 shows the second step of the method according to the invention.

(7) FIG. 6 shows the third step of the method according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) FIG. 1 shows in a purely schematic illustration a membrane electrode assembly 1 (MEA for short). In the illustrated embodiment, the membrane electrode assembly 1 comprises a membrane 2 which is provided on both sides with a catalyst layer 3. Neighboring these catalyst layers 3, a first gas diffusion electrode 4 and a second gas diffusion electrode 5 are provided, respectively. In this context, the gas diffusion electrode 4 can form the anode side, for example, and the gas diffusion electrode 5 the cathode side.

(9) According to the invention, the gas diffusion electrodes 4, 5 are comprised of individual expanded metal layers 6, 7, 8 that are welded to each other, as is shown in an exemplary fashion with the aid of the gas diffusion electrode 4 in FIG. 2.

(10) As shown in FIG. 2, the gas diffusion electrode 4 in the illustrated embodiment comprises a total of six first expanded metal layers wherein expanded metal layers with differently sized meshes are provided. Two first expanded metal layers 6 with comparatively small mesh width, three expanded metal layers 7 with larger mesh width as well as an expanded metal layer 8 with a comparatively coarse mesh width are provided. In this context, the mesh width decreases from coarse to fine in the direction of arrow 11, i.e., with reference to the illustration of FIG. 1, in the direction toward the membrane 2 contacting the gas diffusion electrode 4, 5 in the final mounted state.

(11) FIG. 3 shows a detail view of the expanded metal layer 8. As can be seen in the illustration, the expanded metal layer 8 comprises a plurality of diamond-shaped meshes 9 which each have a mesh width W. In this context, the length orientation 10 of the expanded metal layer 8 is oriented in the direction of the mesh width W that determines the mesh size.

(12) According to the invention, it is provided that the individual expanded metal layers of the gas diffusion electrode 4, 5 are connected to each other by welding. In this context, at least one of the expanded metal layers 6, 7 and/or 8 is rotated in regard to its length orientation 10 by 90° relative to its neighboring expanded metal layer 6, 7 or 8, i.e., the expanded metal layers are oriented relative to each other in rotated arrangement such that the mesh width of the meshes of the associated expanded metal layers are oriented transversely, preferably rotated by 90°, relative to each other in respective neighboring layers.

(13) The first expanded metal layers 6 and 7 are connected to each other by means of pulsed resistance welding, namely at contact points of their facing flat sides 15, 16. Accordingly, a contact connection between neighboring first expanded metal layers is provided that, as a whole, can be said to be areally connected.

(14) The further (second) expanded metal layer 8 is not areally connected to the composite that is formed of the first expanded metal layers 6 and 7 but only spot-wise, which is achieved by spot welding.

(15) FIGS. 4, 5 and 6 illustrate the method according to the invention schematically.

(16) For welding the first expanded metal layers 6 and 7 by pulsed resistance welding, welding electrodes 12 of a flat (areal) areal configuration are used. In this context, the expanded metal layers which are to be welded to each other are introduced into the gap between the two welding electrodes 12. Then the two welding electrodes 12 are moved toward each other causing a compression of the first expanded metal layers 6 and 7 arranged between the welding electrodes 12. The movement of the welding electrodes 12 is stopped when the first expanded metal layers 6, 7 have been compressed by a defined force F that is predetermined, for example, by a control unit. In this context, the compression force F is selected in particular based on the geometric configuration and/or the material of the first expanded metal layers 6 and 7 to be connected to each other and can be adjusted as needed.

(17) Onto the first expanded metal layers 6 and 7 which are pressed against each other by the two welding electrodes 12, a welding pulse is applied via the welding electrodes 12, namely for a certain pulse duration at a defined welding energy. The pulse duration is preferably in the range of a few milliseconds, for example, between 5 ms and 100 ms. The welding energy can be, for example, between 1.4 J/mm.sup.2 and 2.4 J/mm.sup.2.

(18) The first expanded metal layers 6 and 7 that are welded to each other form the joined composite 13. The further or second expanded metal layer 8 is then applied and spot-welded thereto for which purpose a spot-welding electrode 14 is used, as shown in the illustration of FIG. 6. In this way, the connection between the second expanded metal layer 8 and the joined composite 13 is not areally connected, but is formed by individual spot welds.

(19) The specification incorporates by reference the entire disclosure of European priority document 14 181 052.3 having a filing date of Aug. 14, 2014.

(20) While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

LIST OF REFERENCE NUMBERS

(21) 1 membrane electrode assembly 2 membrane 3 catalyst layer 4 gas diffusion electrode 5 gas diffusion electrode 6 expanded metal layer 7 expanded metal layer 8 expanded metal layer 9 mesh 10 length orientation 11 arrow 12 welding electrode 13 composite 14 spot welding electrode 15 flat side 16 flat side W mesh width F compression force