Fuel Cell Stack

Abstract

The present invention relates to a fuel cell stack (1) comprising a plurality of individual cells stacked into a stack, in which at least one humidification section (4) integrated into the stack is arranged at an end of the plurality of individual cells as electrochemical sections (3). The present invention is characterized in that a heat exchange section (5) is arranged on the side of the at least one humidification section (4) facing away from the electrochemical section (3), and in that the flow plates (10, 10') for distributing fluids have the same external shape in at least three sections (3, 4, 5) of the stack.

Description

[Technical field]

[0001] The present invention relates to a fuel cell stack of the type more precisely defined in the preamble of claim 1, comprising a plurality of individual cells stacked in a stack. [Background technology]

[0002] Besides the actual fuel cell stack with its electrochemically active individual cells, various peripheral components are necessary for the operation of the fuel cell stack. These components include, in particular, components for treating the intake air used as an oxygen source, which may include an intake air cooler and a humidifier. In this context, the applicant's US Pat. No. 5,399,433 describes a fuel cell device comprising a fuel cell stack, an intake air cooler and a humidifier, which are combined into a single constructional unit. [Patent Document 1] DE102007038880A1

[0003] Therefore, Patent Document 2 describes integrating a humidifier for each individual electrochemical cell, but this involves considerable costs. [Patent Document 2] DE102007008214B4

[0004] A simplification is offered by a construction in which flow-through plates similar to those for the construction of the electrochemical individual cells can also be used for the humidifier. These flow-through plates can then be integrated relatively easily into the stack of individual cells, much more efficiently than in the initially mentioned documents where various parts are combined. Such a construction is described in US Pat. No. 5,399,433. [Patent Document 3] US5,200,278A Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to further optimize the fuel cell stack in order to make it possible to realize a fuel cell system in which the fuel cell stack is installed in a compact and cost-effective manner. [Means for solving the problem]

[0006] According to the invention, this problem is solved by a fuel cell stack having the features recited in claim 1, and here in particular in the characterizing part of claim 1. Advantageous configurations and developments emerge from the subclaims dependent on claim 1.

[0007] In the fuel cell stack according to the invention, like the last-mentioned prior art fuel cell stack, the fuel cell stack comprises a number of stacked individual cells, and a humidifier arranged at the end of the individual cells is integrated into the stack. In principle, two humidifiers at both ends of the individual cells of the stack are also conceivable. According to the invention, a charge air cooler is arranged on the side of at least one humidifier facing away from the individual cells. The flow plates, which are provided in at least three parts of the stack for distributing the fluids, have the same external shape in the fuel cell stack according to the invention. The flow plates used are therefore designed identically with respect to their external shape, so that they can be stacked without problems to form the entire stack. The concepts for sealing between the individual flow plates and for connecting the individual cells and the parts of the entire stack can be transferred to the further parts of the humidifier and charge air cooler as for conventional electrochemical individual cells.

[0008] This results in a very simple structure which, by integrating the humidifier and charge air cooler into the fuel cell stack and by using the same geometry for all flow plates, can be made compact and low cost.

[0009] In this case, according to a very advantageous development of the fuel cell stack according to the invention, it is provided that the flow plates of the sections are parallel, at least three sections are passed in succession, and the incoming air first passes through the charge air cooler, then through the humidifier, and then through the cathode side of the individual cells. This design ensures that the entire incoming air flow is uniformly cooled and humidified before entering the individual cells. In principle, this design can also be used for hydrogen flows, which will be correspondingly preheated and then humidified after relaxation, and the humidification of the air flow, which has a much larger volumetric flow, is generally sufficient to sufficiently humidify the membranes of the individual cells realized in PEM technology.

[0010] According to a very advantageous development of the fuel cell stack according to the invention, it is further provided that the connection openings of the flow plates of at least three parts have the same shape and that a distribution plate for the medium is attached between each part. The connection openings, which in the stack typically form a continuous volume for distributing the medium to the parallel flow fields of the individual cells, are thus preferably embodied identically in all flow plates. That is to say, each flow plate, similar to the flow plates of the electrochemical individual cells, comprises openings corresponding to the inlet and outlet of the anode side, openings corresponding to the inlet and outlet of the cathode side and openings corresponding to the coolant inlet and outlet of the coolant. In order to ensure that the flow through the individual parts as intended in accordance with the above-mentioned advantageous embodiments occurs in succession, corresponding distribution plates for the medium are arranged between the individual parts, which ensure any necessary fluid redirection for this purpose and the sealing of the flow paths of the individual parts formed by the aligned connecting openings relative to one another or, if, for example, the cooling medium is simply guided through the region of the charge air cooler and / or humidifier, also in the connecting openings for this cooling medium accordingly.

[0011] According to a further very advantageous embodiment of the fuel cell stack according to the invention, in the part used as the charge air cooler, a heat-conductive and heat-resistant film is arranged between two flow plates, through which the incoming and outgoing gases pass alternately. Thus, in both the heat exchanger and the humidifier parts, the individual flow plates can be formed in such a way that on one side of the flow plate a flow passage is formed for one of the gas flows, for example the incoming gas, and on the opposite side of the flow plate a flow passage is formed for the outgoing gas. In that case, the plate elements are arranged alternately, so that between the plate elements a heat-conductive and heat-resistant film is arranged in the case of the heat exchanger part, and a water vapor-permeable membrane is arranged in the case of the part used as the humidifier. This allows a simple and efficient construction.

[0012] In this case, this structure can be realized on one or both sides of the individual cells at the respective stack end, which also contributes to a corresponding improvement in the temperature management of the individual cells located in the end region of the stack, since these individual cells are now located adjacent to the humidifier and are not cooled to a greater extent due to their arrangement adjacent to the end plates of the stack, which was partially difficult in the prior art structures. This allows the structure of the end plates to be further simplified, since electrical heating of the end plates in the stack structure according to the invention can at least be dispensed with if the end plates are arranged adjacent to the arrangement of the charge air cooler and humidifier, rather than adjacent to the individual cells.

[0013] In the part of the fuel cell stack used as a charge air cooler, as a complement or alternative to the described structures for heat exchange between the inflowing and outflowing gases, a structure with flow fields can also be realized, similar to the structure of the flow fields in electrochemical cells, with a flow field for one of the media on one side and a flow field for the cooling medium on the other side. If two such plate elements are connected back to back, a structure is formed through which, for example, the intake air can flow on one side of the sandwich and the exhaust air on the other side, and the cooling medium can flow in between. If these plate elements are again arranged alternately with films arranged between them, for example made of metal or graphite, on the one hand, the heat exchange between the media takes place through these films, and on the other hand, additional temperature regulation takes place, in particular additional cooling by the cooling medium already used to cool the individual cells. In this case, the flow in the ideal case is such that the individual cells are first circulated by the cooling medium and then the part of the fuel cell stack configured in this way used as a charge air cooler.

[0014] This can also be realized in the region of the humidifier, so that the structure can be realized here as well, corresponding to the structure of the electrochemical individual cell, but without gas diffusion layers and catalysts.In principle, the same membrane can even be used here, and a cheaper membrane here provides an additional advantage.Here too, a cooling medium could be used together to realize the cooling of the incoming gas during humidification.

[0015] In this case, a fuel cell stack of this kind can be preferably made in PEM technology and is used in particular, but not exclusively, in vehicles, for example passenger cars or especially utility vehicles such as trucks, in which the fuel cell stack is used to provide electric motive power from hydrogen supplied and air as oxygen source drawn from the surroundings.

[0016] Further advantageous configurations of the fuel cell stack according to the invention will become apparent from the following detailed description of the preferred embodiments with reference to the drawings. [Brief description of the drawings]

[0017] [Figure 1] 1 is a schematic diagram of a first possible embodiment of a fuel cell stack according to the present invention; [Diagram 2] 2 is a view similar to that of FIG. 1 of an alternative possible configuration of a fuel cell stack according to the invention; [Diagram 3] FIG. 13 is a top view of a flow plate that can be used, for example, in the region of a part utilized as a charge air cooler or humidifier. [Figure 4] FIG. 4 is a schematic cross-sectional view of a portion of a flow plate in a portion used as an air cooler and / or humidifier with a flow plate according to FIG. 3. [Diagram 5] FIG. 4 is a diagram of a flow plate similar to that of FIG. 3 in an alternative configuration. [Figure 6] FIG. 6 is a diagram of a structure similar to that of FIG. 4 with a flow plate according to the structure shown in FIG. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In the diagram of FIG. 1, a possible structure of a fuel cell stack 1 in one embodiment according to the invention is shown. In this case, three parts are located between two end plates marked 2. The electrochemical part 3 is provided with a number of individual cells for supplying electrical power. This part 3 is composed of stacked individual cells in PEM technology and corresponds essentially to a conventional fuel cell stack or fuel cell stack. This is followed by a humidification part 4 and then a heat exchange part 5. The humidification part 4 serves to humidify the supply air entering the electrochemical part 3 by utilizing the moisture from the exhaust air of the electrochemical part 3 for humidification. In this case, the structure is a plate humidifier with a membrane 22 permeable to water vapor, which will be further shown later.

[0019] The heat exchanger section 5 serves as an air cooler for correspondingly cooling the hot, dry air supply after compression, for example from a typical temperature after compression of 200-250° C. to a temperature level of about 100° C., for example 80-120° C. Here, the flow paths are indicated by arrows. The air supply enters and flows through the heat exchanger section 5 at one side of the heat exchanger section 5 at a point marked 6. This air then flows in parallel through the flow plates of the heat exchanger section 5 before being redirected by a distribution plate, not shown here. Following this, the air supply flows through the humidification section 4, inside which it also flows parallel to one another through the individual flow plates. The thus cooled and humidified air flow then reaches the electrochemical section 3 in the region of a further distribution plate, here at a point marked 7, and flows in parallel through its individual cells. The moist exhaust air from the electrochemical section 3 then re-enters the humidification section 4 at point 8 and releases the moisture contained in the exhaust air to the supply air. The exhaust air then enters the heat exchange section 5 where it absorbs heat from the supply air stream before exiting the fuel cell stack 1 again at point 9.

[0020] In this case, the entire structure is provided in the embodiment shown here at the end of the electrochemical part 3 and is integrated between the end plates 2 of this structure. Alternatively, it would also be possible to configure the structure as suggested in FIG. 2. In this case, the fluids are not again explicitly shown here, but the structure is accordingly integrated at both ends of the electrochemical part 3, which would require additional connecting lines. In addition, both end plates 2 are arranged directly adjacent to the electrochemical part 3 in a conventional manner, on both sides of which the humidification part 4 and the heat exchange part 5 as charge air cooler are provided on the outside of the end plates 2. In this case, both structures according to FIG. 1 and FIG. 2 can be combined with each other in any way. The structure could therefore be provided, for example, on both sides of the electrochemical part 3 on the inside of the end plates 2, or only on one side, similar to the view in FIG. 1, but on the outside of the end plates 2 as suggested in FIG. 2.

[0021] Here, the individual parts 3, 4, 5 contain flow-through plates 10, 10'. These flow-through plates 10, 10' are often formed as bipolar plates and are in principle basically known to the person skilled in the art of electrochemical parts and here individual cells. Flow-through plates of this kind can be used correspondingly to a large extent in the other parts 4, 5 without changing the shape of these flow-through plates, in particular with regard to the external shape and the shape of the connection openings, here also with the possibility of changing in particular to cheaper materials and manufacturing methods for the flow-through plates. It is then possible to stack the entire structure in the manner known for the electrochemical part 3 and to seal it easily, reliably and in a manner known per se via sealing elements between the individual flow-through plates 10, 10'.

[0022] In the diagram of FIG. 3, a top view of a possible construction of two such flow plates 10, 10' is seen. These flow plates contain three connection openings on each side, which are designated 11, 12 and 13 on the one side and 14, 15, 16 on the other side. In the case of the flow plate 10 depicted here on the left, the connections 11 and 16 are now connected to one another on the side facing the viewer via a flow field 17, which is correspondingly indicated by the corresponding area between the flow field 17 and the respective connection openings 11 and 16, which is a so-called manifold 18. In this way, a flow channel designated 20 is formed. On the opposite side of the flow plate 10, which is not visible here, the two cooling water connections 12, 15 are thereby connected to one another. This results in a coolant flow channel designated 19. In the next flow plate 10', shown here on the right, the cooling water connections 12 and 15 are again connected to one another on one side, and the connections 13 and 14 are connected to one another on the visible side. This results in the formation of the flow channels marked 21. As is known from the field of flow plates 10, 10' for electrochemical parts 3, these flow plates 10, 10' are now arranged with their rear sides against one another, so that channels 19 for the cooling medium are formed between the flow plates 10, 10'. If these structures 100 of flow plates 10, 10' connected to one another are now stacked in mirror images, then between the individual structures 100 of flow plates 10, 10' the channels 20 circulated by one medium and the channels 21 circulated by the other medium are always located opposite each other. This can be seen in the schematic cross-section of FIG. 4 by a small part of each part 4, 5. Between the individual plate elements 10, 10' of the structure 100, channels for the cooling medium, here designated 19, arise on one side of the structure, for example on the surface of the flow plate 10, and opposite the channels for one medium, designated 20, channels for the other medium arise on the surface of the other flow plate 10', which channels are designated 21. Between the channels 20, 21 for the one and the other medium, here a membrane or film 22 is arranged, as can be seen in the diagram in FIG.In the region of the humidification section 4, this membrane or film 22 may be a membrane permeable to water vapor, which allows the exchange of water vapor between the media flowing in the channels 20 and 21. Thus, the dry inlet air and the moist exhaust air can be humidified in the humidification section 4 by directing them here into the respective channels 20, 21. Such membranes are not usually suitable for the region of the heat exchange section 5, since they cannot withstand or cannot sustainably withstand the relatively high temperatures of the compressed dry hot inlet air. For this reason, metal or graphite films or the like can be used here as membrane or film 22, which are correspondingly heat-resistant and allow good heat exchange between the hot inlet air and the significantly cooler exhaust air. Additionally, in both cases, temperature regulation can be achieved jointly via a cooling medium flowing in the cooling channels 19, similar to the structure of the individual cells in the electrochemical area 3.

[0023] However, instead of this structure described in FIGS. 3 and 4, a correspondingly simpler variant is also conceivable, which does not require an additional flow of cooling medium and the cooling channels 19 required for this. For this, only one flow plate 10 is necessary, as correspondingly suggested in the diagram of FIG. 5. This flow plate 10 corresponds in shape to the flow plate 10 shown previously. On the rear side, which is not visible here, in this case the openings 13 and 14, rather than the openings 12 and 15, are connected to one another, so that a structure is obtained, so to speak, with one side of the previously described flow plate 10 on one side and one side of the previously described flow plate 10' on the other side. These flow plates 10 can then be directly stacked with the membrane or film 22, alternating with one another in mirror image, as suggested in the diagram of FIG. 6, analogous to the diagram of FIG. 4. This structure can be realized even more simply and compactly, and in particular can be dispensed with active cooling of the parts 4 and 5. In this case, it would of course be conceivable to actively cool only one of these parts, i.e. to construct the structure according to Figures 3 and 4, and not to actively cool the other of these parts, thereby adopting the structure according to Figures 5 and 6.

[0024] In this case, the general shape of the connecting openings 11 to 16 can also be used here, in order to keep the shape of the stack the same across all parts 3, 4, 5, especially in the arrangement integrated between the end plates. In this case, the openings 12 and 15, which are usually provided for cooling water, can for example be omitted or integrated with other openings. This makes it possible, for example, to use the openings 11 and 12 as a common inlet for one medium and the openings 15 and 16 accordingly as a common outlet. This can be done, for example, by connecting the individual openings in the upper and lower end regions, or the openings can each be connected to the flow field 17 by means of their own manifold 18. In principle, it is also conceivable to provide separate sections for the one and the other fluid in the flow field 17. Depending in particular on the design of the humidification part 4 or the heat exchange part 5, as well as on the volume flows and flow cross-sections that are required in the respective parts 4, 5 according to this design, all variants are conceivable and possible here.

Claims

1. A fuel cell stack (1) comprising a plurality of individual cells stacked in a stack, at least one humidification section (4) integrated in the stack and arranged at an end of the plurality of individual cells as electrochemical sections (3), a heat exchange section (5) is arranged on the side of the at least one humidification section (4) facing away from the electrochemical section (3); a flow plate (10, 10') for distributing a fluid has the same external shape in at least three of the sections (3, 4, 5) of the stack; and the fluid is passed through the at least three sections (3, 4, 5) in succession; In the humidification section (4) and the heat exchange section (5), two of the flow plates (10, 10'), each having a cooling medium flow path (19) on the back side opposite to the front side of the flow plates (10, 10'), are combined on the back side to form one structure (100), and a fluid flowing into a flow path (20) formed on the front side of the flow plate (10) on one side of the structure (100) and a fluid flowing out of a flow path (21) formed on the front side of the flow plate (10') on the other side of the structure (100) adjacent to the structure (100) flow in opposite directions to each other. In the heat exchange portion (5), a thermally conductive and heat resistant film (22) is disposed between the flow path (20) on one side of the structure (100) and the flow path (21) on the other side of another structure (100) adjacent to the structure (100); and The fuel cell stack (1), characterized in that in the humidification portion (4), a membrane (22) permeable to water vapor is arranged between the flow path (20) on one side of the structure (100) and the flow path (21) on the other side of another structure (100) adjacent to the structure (100).

2. 2. The fuel cell stack (1) according to claim 1, characterized in that the flow plates (10, 10') of each of the sections (3, 4, 5) are arranged in parallel and the compressed air entering as the fluid flows first through the heat exchange section (5), then through the humidification section (4) and then through the cathode side of the electrochemical section (3).

3. 3. A fuel cell stack (1) according to claim 1 or 2, characterized in that the connection openings (11, 12, 13, 14, 15, 16) of the flow-through plates (10, 10') of the at least three parts (3, 4, 5) have the same shape and distribution plates for air, hydrogen and cooling medium are arranged between the parts (3, 4, 5).

4. A fuel cell stack (1) according to any one of claims 1 to 3, characterised in that the humidification section (4) and the heat exchange section (5) are arranged on one side of the electrochemical section (3).

5. 4. Fuel cell stack (1) according to any one of claims 1 to 3, characterized in that the humidification section (4) and the heat exchange section (5) are arranged on either side of the electrochemical section (3).

6. Use of a fuel cell stack (1) according to any one of claims 1 to 5 for powering an at least partly electrically driven vehicle.

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