WO2014131619A1 - Fuel cell stack - Google Patents

Abstract

The invention relates to a fuel cell stack, comprising a plurality of individual fuel cells, which are combined to form a stack, with bipolar plates (2) and channels provided apart from the chemically active surfaces of the individual fuel cells for the supply of the reactants to and the discharge of the reaction products from the individual fuel cells and a cooling channel (1) carrying cooling fluid for the individual fuel cells, wherein at least one of the bipolar plates (2) protrudes into the cooling channel (1) and thus forms a flow obstacle for the cooling fluid guided therein. Preferably, the section (2*) of the bipolar plate (2), which protrudes into the cooling channel (1), has an enlarged surface with respect to a simple planar extension of the bipolar plate (2).

Description

 FUEL CELL STACK The present invention relates to a fuel cell stack with a plurality of stacked individual fuel cells with bipolar plates and provided away from the chemically active surfaces of the individual fuel cells channels for the supply of reactants and removal of the reaction products to / from the individual fuel cells and a cooling fluid for the individual fuel cells leading cooling channel. Reference is made to the prior art, for example, to EP 1 830 426 B1.

Fuel cell stacks realize high power densities with their chemically active surfaces, for example of the order of 200 to 350 cm ² , which requires cooling of the individual fuel cells. For this purpose, cooling plates are usually provided, in which, in cooperation with profiled bipolar plates for producing a suitable flow field, a cooling fluid (also called coolant or heat transfer medium) is guided over the planes of the respective individual fuel cells. The cooling fluid, as well as the reactants and reaction products of these individual fuel cells, are each guided or led away to the stacked individual fuel cells via a duct which extends generally perpendicular to the planes of the individual fuel cells or bipolar plates, these ducts usually at the edge region of the individual fuel cells lie, ie run away and usually outside the chemically active region of the individual fuel cells. The walls of these channels may well be formed by the individual bipolar plates and other stacked elements of the fuel cell stack. The high power densities of the fuel cell stacks require a complex cooling concept for the bipolar plates, which can be known to be one or more metal plates or metal foil (s), so that each bipolar plate in the chemically active region has a gas-impermeable electrically conductive surface Layer describes. In particular, if within the bipolar plate, ie between two metal foils or the like. A cooling fluid is to be led, the complexity of the bipolar plates is significantly increased, which is why a fuel cell stack according to the preamble of claim 1, a measure to increase the cooling effect to be shown, which is a simpler Cooling concept allows (= object of the present invention).

The solution to this problem is characterized in that at least one of the bipolar plates protrudes into the said cooling channel and thus forms a flow obstacle for the cooling fluid guided therein. Advantageous embodiments and further developments are content of the dependent claims.

As a result of the embodiment according to the invention, a significantly increased heat transfer between the cooling fluid guided in the cooling channel and any bipolar plate projecting into the cooling channel occurs at least within the cooling channel. In particular, if each bipolar plate is designed in accordance with the invention, it may be possible to completely dispense with guiding the cooling fluid in the planes of the bipolar plates. But even if, as usual, the cooling fluid is diverted from the cooling channel into the planes of the bipolar plates, bipolar plates designed according to the invention undergo enhanced cooling, in particular in that their section protruding into the cooling channel forms a flow obstacle, which causes an increased heat transfer between the cooling fluid and the bipolar plate. If - as already mentioned - the further cooling takes place in the plane of the individual Bipolarpiatte only by heat conduction, so that so in the plane of the Bipolar plates no cooling fluid is performed, so the height of a fuel cell stack according to the invention compared to the prior art significantly reduced and it will be required less elaborately shaped bipolar plates.

The heat transfer between the cooling fluid and the bipolar plate projecting into the cooling channel can be further increased if its section protruding into the cooling channel has a larger surface area than a simple planar extension of the bipolar plate into the cooling channel. Such a surface-enlarging embodiment can be realized in different ways: For example, the protruding into the cooling channel section may be formed meandering. Also, this section may have the shape of a closed rectangle. Another embodiment provides a shape as a U-shaped channel, which can also be closed with a lid. Extremely easy to represent and yet effective is a surface enlarging design such that the projecting into the cooling channel portion of the bipolar plate is at least partially inclined relative to the non-protruding into the cooling channel portion of the bipolar plate and / or twisted. With a twisting or partial twisting of the section of the bipolar plate projecting into the cooling channel, the flow profile of the cooling fluid in the cooling channel can advantageously be influenced in a desired manner. The same applies to a further proposed embodiment, according to which the section of the bipolar plate protruding into the cooling channel has an opening.

It can be provided that the ends of the sections of the bipolar plates protruding into the cooling channel are connected to the wall of the cooling channel and / or to one another, for example via a depression or other suitable other structures and / or an introduced material, for example in the form of an elastomer in the cooling channel or be fixed relative to this, of course, without an electrical short circuit dar- to deliver. With such a mechanical, but not electrically conductive connection, a displacement or deformation of the bipolar plates in the cooling channel during operation of the fuel cell stack, which could lead to contacting at least two bipolar plates with each other, be excluded. In this sense, the cooling channel wall can be shaped in such a way that during the manufacturing process of the fuel cell stack, the protruding into the cooling channel portions of the bipolar plates or at least the ends are deformed in a desired manner. For example, the ends of a bipartite bipolar plate, ie such a bipolar plate, which is formed by two stacked plates, in different directions through a projecting from the cooling channel wall tip in different directions, namely the end of the upper sheet and the end of the lower Bleed down, be bent up. These quasi Y-shaped bent ends can then be fixed in a recess of the cooling channel wall. This virtually creates a fuel cell stack with a bipolar plate formed from at least two metal sheets whose sections projecting into the cooling channel are shaped differently, it being understood that other embodiments of the last-mentioned embodiment of the present invention are possible.

However, an inventively designed fuel cell stack in which at least one, but preferably all, bipolar plate (s) is or are each formed from a single metal sheet is particularly advantageous. This not only sets a lower pressure drop in the flow of cooling fluid, as this does not need to be performed within the stack and / or distributed homogeneously within a bipartite bipolar plate, but this reduces in particular the height of the fuel cell stack. An optionally existing profiling of the bipolar plates for the targeted guidance of the reactants can then be made simpler or provided only in some areas. For the sake of completeness, it should be mentioned that the sections projecting into the cooling channel Incidentally, the bipolar plates do not have to be integral with the bipolar plate material in the chemically active region, but these sections can also preferably be connected in a materially bonded manner to the material of the respective bipolar plate in the chemically active region.

Similar to the supply channels and discharge channels for reactants, reaction products and a cooling fluid in the known prior art (see, for example, the above-mentioned document), the walls of a cooling channel according to the invention, projecting into the edge sections of the bipolar plates, also from the bipolar plates the stacked individual fuel cells be formed, between which, of course, suitably shaped sealing elements or the like. Are provided. Alternatively, the one or more cooling channels provided, for example, or preferably on two opposite edge regions of each bipolar plate or individual fuel cell, may be formed by independent channel structures.

DETAILED DESCRIPTION OF THE INVENTION FIGS. 1 and 2 each show a cooling channel 1 perpendicular to the plane of the drawing, the wall 3 or walls 3 of which are not formed by bipolar plates and in which bipolar plates 2, which lie in a plane lying perpendicular to the plane of the drawing, protrude with an edge section 2 ^* . In the figures, on the right side of the cooling channel 1, the chemically active regions of the individual fuel cells, not shown in the figure, are stacked one above the other, of which a number of bipolar plates 2 are represented in sections. Not shown is a commonly provided, but not mandatory in all embodiments coolant distribution channel which extend at the front and / or rear end of the coolant channel 1, preferably in the vertical direction, ie in the stacking direction of the individual fuel cells can. In some of the following embodiments, such a distribution channel is not required at all.

FIGS. 3, 4 show various embodiments of edge sections 2 ^* of bipolar plates 2 according to the invention in a view analogous to FIGS. 1, 2 without a surrounding cooling channel.

FIGS. 5-7 again show with cooling channel 1 in a view analogous to FIGS. 1, 2 further embodiments of a fuel cell stack according to the invention, while FIGS. 8-10 show further shapes according to the invention on sections 2 ^* of bipolar plates of individual fuel cells projecting into a cooling channel a fuel cell stack on the essential abstracted are shown in perspective.

All embodiments have in common that these projecting into the cooling channel 1 sections 2 ^{* of} the bipolar plates form a flow obstacle for the cooling fluid flowing in the cooling channel 1.

In Figure 1, only two superimposed bipolar plates 2 of a fuel cell stack are shown, each consisting of two superimposed and interconnected profiled sheets 2a, 2b, protrude the end portions 2 * in one or the cooling channel 1 and bent Y-shaped as a whole are, ie it is the end portion of the upper profile sheet 2a upwards and that of the lower profile sheet 2b bent downwards.

FIG. 2 also shows in the upper illustration (letter A) a bipolar plate 2 consisting of two interconnected profiled sheets 2 a, 2 b. To increase the flow around the surface and thus increase the heat transfer between the cooling fluid flowing in the cooling channel 1 and the bipolar plate 2 while projecting into the cooling channel 1 sections 2 * of the individual profile sheets 2a, 2b of different lengths. The two middle representations (letters B, C) in FIG. 2 show embodiments of simple bipolar plates 2 in which the section 2 ^* projecting into the cooling channel 1 is not formed in a special way, whereby under the letter B one of two is superimposed on one another connected profiled sheets 2a, 2b existing bipolar plate 2 is shown, while under the letter C is made of a single profiled sheet bipolar plate 2 is shown.

In the lower part of FIG. 2, a bipolar plate 2 consisting of a single profile sheet is shown under the letter D, the section 2 ^{* of which} projecting into the cooling channel 1 is meander-shaped for enlarging the surface.

Figure 3 shows in the three upper figures under the letters A, B, C each consist of two interconnected profiled sheets 2a, 2b existing bipolar plate (2) or substantially their in a cooling channel (1) not shown protruding portion 2 *.

According to the uppermost embodiment A of FIG. 3, each of the sections 2 * of the profiled sheets 2a, 2b extending into the cooling channel 1 is designed as a U-shaped channel, the open sides of the two channels facing one another. In the following illustration B, two U-shaped channels are formed on each of the sections 2 ^{* of} the profiled sheets 2a, 2b which extend into the cooling channel 1. Also in this embodiment, the open sides of the channels face each other, so that in each case a closed channel K is formed.

In the middle illustration C in FIG. 3, a V-shaped channel is formed in each of the sections 2 * of the profiled sheets 2 a, 2 b extending into the cooling channel 1, whereby the open sides of the channels form a closed channel K with a large heat-transferring surface facing each other.

The two lower representations (letters D, E) in FIG. 3 show a bipolar plate consisting of a single profiled sheet and with its edge section 2 * in the cooling channel 2. In this case, in order to increase the surface area, the section 2 * extending into the cooling channel 1 is designed as a U-shaped channel in its end region, which is closed according to embodiment D with a separate cover part 3.

Alternatively, according to the lowermost representation E in FIG. 3, the section 2 * reaching into the cooling channel can also be formed into a closed rectangle.

4, further embodiments are shown under the letters A, B, C, D, which show a larger surface area of the sections 2 * of a cooling channel (here optionally formed of two profiled sheets 2 a, 2 b), compared to the prior art (FIG. 2) show. Here are sections 2 ^{* of} the two profile sheets 2a, 2b formed differently.

According to the uppermost embodiment A in FIG. 4, one of the sections 2 * extending into the cooling channel is designed as a U-shaped channel, while the other section extending into the cooling channel is rectilinear and the open channel of the other (first-mentioned) profiled sheet 2b covers.

In the following illustration B two U-shaped channels are formed on one of the extending into the cooling channel 1 sections 2 ^* , while the other in the cooling channel 1 reaching in profile sheet 2a is rectilinear or planar and the open channels of the other (the former) profile sheet 2b covers.

In the third illustration C in FIG. 4, a V-shaped channel is formed in the section 2 ^{* of} the profiled sheet 2 ^b extending into the cooling channel, while the other section of the profiled sheet 2 a extending into the cooling channel is rectilinear or planar and the open channel of the other (former)

Profile sheet 2b covers.

In the lower illustration D in FIG. 4, each of the sections 2 * of the profiled sheets 2 a, 2 b reaching into the cooling channel 1 has a V-shaped one Channel formation, wherein the open sides of these V-shaped channels facing each other, but offset from each other and again cover the open channel of the other profile sheet. By forming each bipolar plate 2 at its end at least one closed channel in the embodiments shown in Figures 3 and 4, this can also act as a cooling fluid channel, which in a fuel cell stack with bipolar plates designed in this way practically as many individual cooling fluid channels or if this configuration at the two Be provided opposite edges of the bipolar plate, twice as many cooling channels branch off from a supply channel for cooling fluid and could open with its other end again in a common discharge channel for cooling fluid, as in this fuel cell stack bipolar plates are present.

FIG. 5 shows an embodiment in which the sections 2 ^{* of} the bipolar plates 2 projecting into the cooling channel 1 analogously to FIGS. 1, 2 completely pass through this cooling channel 1 and into one of those walls through which the bipolar plate 2 is led into the cooling channel 1 , opposite wall of the cooling channel 1 provided recess 5 are held. This or each recess 5 acts as a spacer and thus prevents the bipolar plates 2 of the stacked individual fuel cells can come into contact with each other. In addition, the recess 5 can also serve for positioning and supporting the respective bipolar plate 2 in the fuel cell stack. The reference numeral 6 in this figure 5 for the embodiment A a of said opposite wall of the cooling channel 1 in this a certain extent in projecting tip 6 is characterized, which may be provided to one of two initially analogous to the Ausfüh- form B of Fig. 5 superimposed profile sheets 2a, 2b composite bipolar plate 2 in the assembly process of the fuel cell stack, for example. By laterally pushing the with this Tip 6 provided channel wall 3 according to arrow P at its projecting into the cooling channel 1 section 2 * to transform such that the first free end of the upper profile sheet 2a as shown figuratively slightly upwards and that of the lower profile sheet 2b is bent slightly downward, so that a further enlarged heat transfer surface of the bipolar plate 2 is formed in the cooling channel 1.

The embodiment C of Figure 5 shows two each formed from a single sheet of bipolar plates 2 of two adjacent Einzelbrennstoffzel- len with due to the bending also slightly enlarged heat transfer surface in the cooling channel 1. Of course, in these embodiments of Figure 5 to ensure that over the wall 3 having the recesses 5 does not form an electrically conductive connection between the bipolar plates 2 of the various individual fuel cells, which may be realized, for example, by the said wall 3 being made in an electrical insulator material or in the recesses 5 an electrical insulation layer is provided. The latter is not necessary if, according to the embodiments of Figure 6, the free ends of reaching into the cooling channel 1 sections 2 * of the bipolar plates 2 via an introduced electrically non-conductive and thereby a mechanical, for example. Bonding compound producing material 91, 93 with the said " In this case, either by such a support on the wall 3 and a mutual support of the bipolar plates 2 of two adjacent individual fuel cells is possible, as shown in Figure 6 for the reference numeral 93rd or the material 2 2 'of the bipolar plates 2 of two adjacent individual fuel cells projecting into the cooling channel 1 can only be supported against one another, as indicated by the material 92. Finally, the reference numeral 94 a suitable material is characterized, which securely holds the sections 2 ^{* of} the profiled sheets 2a, 2b of a bipolar plate 2 apart in the Y-shape already shown several times. As shown in FIG. 7, a material 1 1 introduced between the sections 2 ^{* of} the bipolar plates 2 of adjacent individual fuel cells protruding into the cooling channel 1 can not only be provided to mutually support the mutually adjacent sections 2 * in an electrically insulating manner but can instead by such material 1 1 in the cooling channel 1 also different flow zones or sub-channels are formed, which are marked in Figure 7 with the letters A, B. In the flow zone A, a low flow resistance prevails here than in the flow zone B. Such a subdivision can be advantageous, for example, if different coolant flows can be supplied to the flow zones or partial channels A and B via different coolant distribution channels or the like.

In the figures 8-10 additional shapes according to the invention and advantageous are in a not shown cooling passage (1) protruding sections 2 ^* of bipolar plates of individual fuel cells of a fuel cell stack to the essential abstracted shown in perspective, wherein the cooling channel extends in each case in the direction of arrow P , In the embodiment according to Fig.8 are on a single sheet over its (viewed in the direction of arrow P) length alternately sections 21 up or down (reference numeral 22) bent, which additionally twisted slightly in the embodiment of Figure 9, ie a are rotated perpendicular to the arrow P in the plane of the sheet extending axis. Thus, not only an enlarged flow obstacle is formed, which leads to an increased heat transfer between the cooling fluid flowing in the cooling channel and the section 2 * of the respective bipolar plate 2, but it can thus the Strö- tion profile of the cooling fluid flow can be influenced or adjusted in the desired manner. Also in the embodiment according to FIG. 10, the flow profile of the cooling fluid flow is influenced by apertures or passage openings 23 for the cooling fluid provided in the said section 2 *, wherein here the design is advantageously such that indentations or the like are shown in the figure 24, which force the cooling fluid flowing toward it to pass through the respective passage opening 23. In particular, when viewed in the direction of flow of the cooling fluid, these nozzles 24 are alternately provided alternately on the upper side and on the underside of the sheet forming said section 2 *, the heat transfer between this projecting into the cooling channel section 2 * of the bipolar plate and guided in the cooling channel cooling fluid increased significantly.

The foregoing description of the present invention is for illustrative purposes only, and not for the purpose of limiting the invention. In the context of the invention, various changes and modifications are possible without departing from the scope of the invention and their equivalents.

Claims

Patent claims 1. Fuel cell stack with several individual fuel cells combined into a stack with bipolar plates (2) and channels provided away from the chemically active surfaces of the individual fuel cells for the supply of the reactants and removal of the reaction products to/from the individual fuel cells and a cooling channel carrying a cooling fluid for the individual fuel cells (1), characterized in that at least one of the bipolar plates (2) projects into the cooling channel (1) and thus forms a flow obstacle for the cooling fluid guided therein. Fuel cell stack according to claim 1, wherein the section (2 ^* ) of the bipolar plate (2) which projects into the cooling channel (1) has an enlarged surface compared to a simple flat extension of the bipolar plate (2). Fuel cell stack according to claim 1 or 2, wherein the section (2 ^* ) of the bipolar plate (2) which projects into the cooling channel (1) is designed as a closed rectangle or as a U-shaped channel or in a meandering shape. 4. Fuel cell stack according to one of the preceding claims, wherein the section (2 ^* ) of the bipolar plate (2) which projects into the cooling channel (1) is at least partially opposite to the section of the bipolar plate (2) which does not project into the cooling channel (1). is tilted and/or twisted. 5. Fuel cell stack according to one of the preceding claims, wherein the section (2 ^* ) of the bipolar plate (2) which projects into the cooling channel (1) has an opening (23). 6. Fuel cell stack according to claim 5, wherein the opening (23) is spanned by a hood (24). 7. Fuel cell stack according to one of the preceding claims, wherein the section (2*) of the bipolar plate (2) which projects into the cooling channel (1) is connected to the wall (3) of the cooling channel and/or which projects into the cooling channel (1). Section of the adjacent bipolar plate (2) is connected mechanically, but not electrically conductively. 8. Fuel cell stack according to one of the preceding claims with a bipolar plate (2) formed from a single sheet. 9. Fuel cell stack according to one of claims 1 - 7 with a bipolar plate (2) formed from at least two sheets (2a, 2b), the sections of which protrude into the cooling channel (1) are shaped in different ways. 10. Fuel cell stack according to one of the preceding claims, wherein the wall of the cooling channel (1) is also formed by the bipolar plates.