Bipolar plates for fuel cells

Abstract

The invention relates to a bipolar plate (1) for a fuel cell, consisting of two half-plates (2, 3), with mutually facing surfaces (13, 15) and, in the area of ​​these surfaces (13, 15), alignment elements (9) with protrusions (14) having a height (H) and corresponding recesses (12) having a depth (T). The invention is characterized in that all protrusions (14) and corresponding recesses (12) have a greater extent (L1, L2) in the longitudinal direction (L) than in the transverse direction (Q), and in that on each surface (13, 15) four corresponding parts of the alignment elements (9) are arranged, two of which are located on a common straight line (10, 11) and oriented in the same orientation.

Description

[Technical Field]

[0001] The invention relates to a bipolar plate for a fuel cell according to the type more precisely defined in the preamble of claim 1, consisting of two half plates which are in particular glued together. [Background technology]

[0002] A bipolar plate of this type is basically known from DE 10 200 04 14 56 A1, in which the bipolar plate consists of two half-pieces or layers that are materially connected to one another, for example welded in the case of a metal bipolar plate, as described in the above-mentioned German publication. To enable the most efficient orientation of the two half plates or layers relative to each other, alignment elements are provided on the opposing surfaces of the half plates. The alignment elements consist of a protrusion with a height and a corresponding recess with a depth. When the two half plates or layers are positioned on top of each other, the protrusion engages with the recess, thereby helping to orient these components relative to each other. This is also clearly illustrated in the example shown in Figure 4 and subsequent figures in the German publication. In this case, alignment is achieved via one element in one direction and via two elements in the other direction. To this end, the recess on one plate is significantly larger than the protrusion on the other plate and has a different shape from the recess. This is relatively complicated. Furthermore, the alignment elements are located next to the actual flow field, which can adversely affect the outer shape of the bipolar plate or result in significant additional manufacturing costs if these elements have to be separated later. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] DE102009036039A1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Therefore, the problem of the present invention here is to present an improved bipolar plate composed of two half plates of the type more specifically defined by the preamble of claim 1.

Means for Solving the Problems

[0005] According to the present invention, this problem is solved by a bipolar plate having the features of claim 1, here in particular the features of the characterizing part of claim 1. Advantageous forms and developments of this bipolar plate become apparent from the dependent claims dependent on claim 1.

[0006] In the bipolar plate according to the present invention, it is contemplated that, as in the prior art according to the field, the bipolar plate is composed of two half plates. Both half plates have alignment elements in the surface area at least on their surfaces facing each other, and these alignment elements consist of convex portions having a height and corresponding concave portions having a depth. According to the present invention, all convex portions and corresponding concave portions have a greater extent in a first longitudinal direction than in a second transverse direction, the longitudinal direction and the transverse direction being perpendicular to each other and located in the same plane. Here, four alignment elements are arranged on each surface. In this case, two of the alignment elements are located on a common straight line and have the same orientation. That is to say, this means that the longitudinal directions of both alignment elements located on the common straight line are similarly oriented with respect to, for example, the outer edge of the half plate or the symmetry line at the center of the half plate, while the other two alignment elements located on a second straight line that preferably intersects the first straight line similarly have the same orientation. In this way, the orientations are the same for each pair, but are preferably different between the two pairs. This enables correspondingly easy and efficient positioning of both half plates, and then enables these half plates to be easily joined in a form-fitting manner, in particular to be adhered to each other. This adhesion can in this case preferably be carried out via a sealant and adhesive inserted or applied to one of the half plates.

[0007] According to a particularly preferred development of the bipolar plate according to the present invention, it is contemplated in this case that the longitudinal directions of both alignment elements extend along a straight line with the same orientation. That is to say, the longitudinal direction is arranged along or coincides with the straight line connecting both respective alignment elements. As a result, adjustment of the position along this straight line and the longitudinal direction becomes possible to a certain extent. This "certain extent" results from the inevitable minimum size difference between the concave portion on the one hand and the corresponding convex portion on the other hand, but here a tolerance in the range of only a few tenths of a millimeter is compensated, so this "size difference" is actually very small.

[0008] According to a further highly advantageous form of the bipolar plate according to the invention, in this case at least one of the straight lines does not coincide with the symmetry line in the middle of the outer dimensions of the half plate. In principle, the two alignment elements can be positioned on the same straight line at the center of the corresponding half plate. However, it has proven to be advantageous if the straight line extends eccentrically and is offset from such a symmetry line in the center of the structure. In particular, this straight line may extend inclined with respect to the symmetry line, so that the alignment elements arranged in the same orientation will be arranged, for example, at the corner portions on the diagonal lines of the respective half plates.

[0009] However, according to a further highly preferred form, it may further be contemplated that the straight line offset from the symmetry line is oriented parallel to the symmetry line and is offset parallel to this symmetry line by a distance shorter than twice the longitudinal dimension. In this way, in this particularly preferred form, by the straight line being offset "slightly" with respect to the symmetry line, the rotation of the half plates relative to each other that may occur before orientation and bonding is efficiently prevented. Therefore, errors during manufacturing are very unlikely to occur.

[0010] Here, in a further highly advantageous form of the bipolar plate according to the invention, it may further be contemplated that the convex portions and the corresponding concave portions have the same shape. In this case, the convex portions are formed smaller than the concave portions in the longitudinal direction, the transverse direction, and their height, and in the longitudinal direction, the transverse direction, and their depth. By the shapes being the same and the convex portions being configured to be only minimally smaller than the concave portions in all three spatial directions, it becomes possible to efficiently receive each convex portion by the respective concave portion, and thus a stable and reliable orientation is achieved. Therefore, it becomes possible to orient the two half plates relative to each other with a very small tolerance, and at the same time, it becomes possible to efficiently compensate for the minimum manufacturing tolerances in the plate.

[0011] In this case, according to an advantageous form of the bipolar plate according to the present invention, the half plate is formed from a plastic base material in which a carbon-containing material is dispersed and arranged therein. This type of bipolar plate is often also referred to as a graphite plate or a bipolar plate made of a carbon composite material, and is usually manufactured using an appropriate mold. Therefore, since the shape can be forcibly realized with slight tolerances by the mold, such bipolar plates have relatively small manufacturing tolerances. Accordingly, making the convex portion and the corresponding concave portion have the same shape can be ideally applied to optimally connect such plates to each other. In that regard, for example, the metal bipolar plates described in the prior art mentioned at the beginning are different. Since they expand correspondingly during welding, it is almost impossible to make the outer shapes of the convex portion and the corresponding concave portion identical.

[0012] A further very advantageous form contemplates that the surface of the convex portion extending laterally with respect to the surface is arranged at the same angle as the corresponding surface of the concave portion with respect to the surface. That is, it is particularly preferable if both the convex portion and the concave portion have the same angle in those regions where they both extend laterally with respect to the surface within the alignment element. This angle may be, for example, about 5 to 15°, whereby both half plates can be reliably inserted into each other in the region of their alignment elements, and at the same time, the position of one half plate can be oriented with respect to the other half plate in order to bond both half plates.

[0013] According to a very advantageous form, in this case, in order to reliably define the target preferred direction, the spread in the lateral direction of the alignment element may be smaller than one-third of the spread in the longitudinal direction. In this case, the height and the depth are smaller than half of the spread in the lateral direction. Thereby, it is surely prevented that the convex portion abuts against the bottom of the concave portion, and the joining and sealing are performed by adhesion in the region provided therefor between the original half plates and the surfaces of these half plates.

[0014] In this case, in the case of a normal bipolar plate, the longitudinal direction may have an extent of, for example, 2 to 10 mm, preferably 5 to 7 mm. Such a structure is small enough that this structure can be arranged between the flow guiding region of the half plate and the outer edge, and at the same time, large enough that reliable positioning of the half plates relative to each other is possible. Then, different from the prior art mentioned at the beginning, additional elements such as protrusions or projections for appropriately positioning the elements for orientation are not required. Such elements then either unnecessarily occupy space and result in unnecessary weight during later use, or have to be removed from the completed bipolar plate with considerable effort.

[0015] A further advantageous form of the bipolar plate according to the present invention will also become apparent from the embodiments described in more detail below with reference to the drawings.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

DETAILED DESCRIPTION OF THE INVENTION

[0017] In the depiction of FIG. 1, a bipolar plate 1 is seen, which is schematically suggested by an exploded view. The bipolar plate 1 consists of two half - plates 2, 3, and in the illustrated embodiment, the half - plates 2, 3 are connected to each other via a sealant and adhesive 4. In this case, on the surface represented upward, a flow field 5 for one of the free bodies of a fuel cell assembled using such a bipolar plate 1, particularly for atmospheric oxygen or hydrogen, is provided by a method known per se. Between both half - plates 2, 3, a refrigerant flow field is usually enclosed, and only one half thereof, namely the half located in the lower half - plate 3, is distinguishable. This refrigerant flow field is labeled 6. Additionally, the bipolar plate 1 is provided with openings 7 formed by a method known per se for supplying and discharging media. A detailed illustration is not very important for the present invention here and can be formed in any arbitrary method well - known to those skilled in the art, so it is omitted here. Now, in the depiction of FIG. 2, a view of, for example, the lower half - plate 3 and the corresponding flow field 6 for the refrigerant is shown again. The flow field 6 is located inside the outer peripheral edge 8 of each of the half - plates 2, 3 and the bipolar plate 1 formed by adhesion from these half - plates 2, 3, together with the openings 7 already mentioned. Each half - plate 2, 3 in this case results from a press mold and consists of a mixture, for example, of a carbon - containing material such as graphite and a suitable plastic base material. In this case, the completed half - plates 2, 3 are formed mostly identically over the entire stack of the fuel cell. For only both bipolar plates 1, also referred to as interface plates, in the peripheral region of the fuel cell, only one of the half - plates 2, 3 is required and is combined with an alternative interface half - plate or two compatible half - plates are used. However, the same applies to these elements as to the half - plates 2, 3 of the bipolar plate 1, which will be described in detail below.

[0018] Here, in order to facilitate the orientation of the two half plates 2 and 3 with respect to each other, alignment elements 9 are provided on the surfaces of the half plates 2 and 3 facing each other. The alignment elements 9 are each formed from a raised portion or convex portion 14 (see FIG. 6) on one of the half plates 2 and 3 and a corresponding recess 12 (see FIG. 4) in the same region of the other half plates 3 and 2, respectively. In the depiction of FIG. 2, two alignment elements 9 are formed substantially centrally with respect to the flow field 6 in this case and at right angles to the main direction of the flow path that is flowed through here. The alignment elements 9 are formed in the illustrated embodiment in the outer shape of two rectangles with rounded corners and are arranged to be connected to each other via a straight line depicted by a dashed line with 10 attached. The alignment elements 9 are located inside the outer peripheral portion 8 of the half plate 3 and outside the original flow field 6. Also, another pair of alignment elements 9 are located between the outer peripheral portion 8 and the opening 7 and can be connected to each other via another straight line 11. These two pairs of alignment elements 9 are each arranged in the same orientation. This orientation, in the embodiment shown in FIG. 2, coincides with or is oriented along the straight line 11 or 10 together with the longitudinal direction of each alignment element 9 further explained in FIGS. 4 and later below. In this case, since the straight lines 10 and 11 intersect at approximately right angles, the longitudinal directions of the alignment elements 9 that are paired with each other also form right angles with respect to each other accordingly. By arranging at least one of the straight lines, here the straight line 11, parallelly shifted with respect to the symmetry line S of the half plate 3 in this case, it is stably prevented that the half plates 2 and 3 are attached in a rotated state. In this case, the shift between the symmetry line S and the straight line 11 is smaller than twice the spread in the longitudinal direction of the alignment element 9 and is thus relatively small with respect to the dimensions of the half plate 3 or the bipolar plate 1 as a whole.

[0019] The depiction of FIG. 3 shows an alternative arrangement of the individual alignment elements 9. The straight lines 10 and 11 are formed here so as to extend from one corner to the other diagonally and intersect at approximately the center of the half plate 3. Here again, both alignment elements 9 connected to each other via the respective straight line 10 or 11 are formed in the same orientation respectively, but as distinguishable in the depiction of FIG. 3, they do not have to be oriented to match the respective straight lines 10, 11. The orientation of each pair of alignment elements 9 connected to each other via the respective straight lines 10, 11 may be, for example, an angle larger than the intersection angle between both straight lines 10, 11, so that the orientations are, for example, within an angular range between 80° and 100° relative to each other.

[0020] Now, in the depictions from FIG. 4 onwards, enlarged views of possible configurations of the recess 12 and the protrusion 14 of the alignment element 9 can be seen. The depiction of FIG. 4 shows, on the upper half plate in the depiction of FIG. 1, the half plate 2 here, which corresponds to the anode plate as a pure example. The recess 12 can be seen in the longitudinal section along the longitudinal direction L in the left drawing and in the cross section along the transverse direction Q shown next to it on the right. The recess 12 has a first spread L1 in the longitudinal direction L and a first spread Q1 in the transverse direction Q in a region, for example, facing the surface 13 of the half plate 2 along the longitudinal direction L. In this case, the depth between the surface 13 and the deepest point of the recess 12 is T.

[0021] As an example, the spread L1 in the longitudinal direction may be, for example, about 6 mm, while the depth T is 0.5 mm, and the spread in the transverse direction Q can be realized as Q1 = 1.5 mm. The recess 12 may, in this case, have a rounded rectangular outer shape, or an outer shape of two semi - circles connected by straight sides, as represented in the line - of - sight direction according to the arrow V in FIG. 4 in the depiction of FIG. 5.

[0022] Now, in the depiction of FIG. 6, a convex portion 14 corresponding to the concave portion 12 in the depiction of FIG. 4 is shown. Here too, a longitudinal section is seen on the left side and a cross section is seen on the right side. In this case, the convex portion 14 protrudes correspondingly from the surface 15 of the second half plate 3. The convex portion 14 has a dimension L2 in the longitudinal direction L, also in the region of the intersection line with the surface 15, and a dimension Q2 in the transverse direction Q. The convex portion 14 has a height H with respect to the surface 15. As shown from the illustration of FIG. 7 corresponding to the arrow VII in FIG. 6, in this case the shape is the same as the configuration of the concave portion 12. However, since the dimensions are slightly smaller, L2 is smaller than L1. For example, when L1 = 6 mm, L2 = 5.8 mm. Q2 is correspondingly smaller than Q1. For example, Q1 = 0.5 mm and Q2 = 0.135 - 0.145 mm. The height H is also correspondingly smaller than the depth T, so that while achieving centering, it does not interfere with the joining of the surfaces 13 and 15 with respect to each other, or the joining to the adhesive and sealant 4 disposed therebetween. For this purpose, while the height H is only 0.45 mm, the depth T may be, for example, 0.5 mm as already mentioned above.

[0023] The above dimensions should be understood purely as examples and it is obvious to those skilled in the art that they can be changed as appropriate. In this case, in particular, the depth T is desirably designed to be smaller than one-third of the total thickness of the half plates 2 and 3 in order to avoid unnecessarily reducing the stability of the half plate 2.

[0024] FIG. 8 shows a modification of the embodiment according to FIG. 2. The arrangement of the alignment element 9 according to FIG. 2 could be called a cross shape. The arrangement of the alignment element 9 according to FIG. 8 is, similarly, likely to be called a cross shape as well, but the cross in FIG. 8 is tilted laterally or rotated by 45° compared to FIG. 2.

[0025] The embodiment according to FIG. 9 combines the design elements of the embodiment according to FIG. 3, in which the arrangement of the alignment elements 9 can be called a cross shape, and the embodiment according to FIG. 8. That is, the alignment elements 9 in both the lower left and upper right are arranged as in FIG. 3, and the alignment elements 9 in both the upper left and lower right are arranged as in FIG. 9.

[0026] Of course, other shapes, as well as the reverse arrangement, that is, a configuration in which the half plate 3 has the recess 12 and the half plate 2 has the protrusion 14, are also possible. Of course, for each of the four alignment elements 9 provided, it is possible to appropriately interchange the positions of the recess 12 and the corresponding protrusion 14 in the respective half plates 2 and 3. In this way, it would also be possible for each pair of alignment elements 9 to include a recess 12 and a protrusion 14 on the respective half plates 2 and 3, respectively. It would also be conceivable to make these pairs of configurations different from each other.

Claims

1. A bipolar plate (1) for a fuel cell, which consists of two half plates (2, 3), having surfaces (13, 15) facing each other, and alignment elements (9) provided with convex portions (14) having a height (H) and corresponding concave portions (12) having a depth (T) within the regions of the surfaces (13, 15). In the bipolar plate (1), all of the convex portions (14) and the corresponding concave portions (12) have a spread (L1, L2) that is larger in the longitudinal direction (L) than in the lateral direction (Q). Four corresponding portions of the alignment element (9) are arranged on each of the surfaces (13, 15), two of which are located on a common straight line (10, 11) and are oriented in the same direction. At least one of the straight lines (10, 11) does not coincide with the symmetry line (S) in the middle of the outer dimensions of each of the half plates (2, 3), and at least one of the straight lines (10, 11) is parallelly spaced from the symmetry line (S) by a distance shorter than twice the dimensions (L1, L2) of the alignment element (9) in the longitudinal direction (L). The bipolar plate (1).

2. The bipolar plate (1) according to claim 1, characterized in that the longitudinal directions (L) of the two alignment elements (9) extend along the respective straight lines (10, 11) in the same direction.

3. The bipolar plate (1) according to claim 1 or 2, characterized in that the convex portion (14) and the concave portion (12) have the same shape, and the convex portion (14) is formed to be smaller than the corresponding dimensions of the concave portion (12) in the longitudinal direction (L), the lateral direction (Q), and the height (H).

4. The bipolar plate (1) according to claim 1 or 2, characterized in that a surface extending laterally with respect to the surfaces (13, 15) of the convex portion (14) extends at the same angle as the corresponding surface of the concave portion (12) with respect to the surfaces (12, 13).

5. The bipolar plate (1) according to claim 1 or 2, characterized in that the spread (Q1, Q2) in the lateral direction (Q) is smaller than one-third of the spread (L1, L2) in the longitudinal direction (L), and the height (H) and the depth (T) are smaller than half of the spread (Q1, Q2) in the lateral direction (Q).

6. The bipolar plate (1) according to claim 1 or 2, wherein the spread (L1, L2) in the longitudinal direction (L) is 2 to 10 mm.

7. The bipolar plate (1) according to claim 1 or 2, wherein the half plates (2, 3) are formed of a carbon-containing material dispersed in a plastic base material.

8. The bipolar plate (1) according to claim 1 or 2, wherein the alignment element (9) is disposed between the flow guiding region (6) and the outer edges (8) of the respective half plates (2, 3).

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