DE102010011206A1 - Fuel cell stack i.e. proton exchange membrane fuel cell stack, for producing power, has bipolar plates whose edges rest against outer structure, where supply of fuel and oxidant and removal of products takes place over edges of plates - Google Patents

Abstract

The stack has an outer structure coherent in a stacking direction of bipolar plates (8) and separated from the bipolar plates. Edges (8a, 8b) of the bipolar plates rest against the structure. Supply of fuel i.e. hydrogen, and oxidant in flow paths of the bipolar plates and removal of reaction products from the flow paths take place over the edges of the bipolar plates via the structure. A medium gasket (5) and/or an insulating composite layer (4) surrounds a circumference of the bipolar plates. The structure comprises hollow profile elements (A, B) in the form of extruded profiles. An independent claim is also included for a method for manufacturing a fuel cell stack for producing power from reaction of fuel with oxidant to reaction product.

Description

The present invention relates to a fuel cell or Elektrolyseurstapel and a method for its preparation.

A fuel cell is a galvanic cell in which power is recovered from the reaction of a fuel with an oxidant. It comprises a solid or liquid electrolyte which is permeable to ions but impermeable to the electrons, and a catalyst which separates electrons from the fuel. The ions are transported by the electrolyte to the cathode, while the electrons are transported from the anode via an external conductor to the cathode, where the charge of the ions is balanced again. Often find hydrogen (H) as fuel and oxygen (O) or air as the oxidant use, the reaction leads to water or water vapor as a reaction product. The associated reactions are then: H ₂ ⇒ 2H ⁺ + 2e ^- (anodic reaction) 2H ⁺ + 2e ^- + ½O ₂ ⇒ H ₂ O (cathodic reaction)

In addition to hydrogen but other substances, for example. Methane or alcohols are basically considered as fuels in question. In an electrolyzer, however, the reverse reaction for the decomposition of a reactant, for example water, into its constituents, such as hydrogen and oxygen, by supplying electrical power is brought about.

An example of a typical hydrogen fuel cell is the so-called Proton Exchange Membrane Fuel Cell (PEMFC). In it, the electrolyte is formed by a permeable to protons and for electron-impermeable polymer membrane which separates a plate-shaped anode of a plate-shaped cathode also. Other typical electrolytes in fuel cells are dissolved alkalis or acids, alkali carbonate melts or ceramics.

The reaction of hydrogen and oxygen to water in such an arrangement results in a voltage of 0.6 to 0.7 volts, depending on the anode, cathode and electrolyte construction. However, since higher voltages are often required, a large number of such cells are connected in series. Such a series connection is usually realized in the form of a fuel cell stack comprising a number of bipolar plates with electrolytes therebetween. The bipolar plates have an anode side and a cathode side. The heat released in the reaction of the hydrogen with the oxygen heat is removed by a cooling medium from the fuel cell stack. Typical proton exchange membrane fuel cell stacks are, for example, in DE 10 2007 036 477 A1 or in US 2009/0297920 A1 described, fuel cell stack without polymer membranes, for example. In US 2005/0109645 A1 or in US 2009/0181272 A1 ,

State of the art is that all media, so the fuel, the oxidizing agent and the cooling fluid, are supplied and discharged through channels formed by recesses within the stacked bipolar plates. Each of these recesses must be sealed at the edges, as for example in US 2009/0181272 A1 is described. The numerous gas- and liquid-tight sealing elements lead to a complex production and are a frequent source of technical failure. In order to maintain the tightness during operation, the bipolar plates must be permanently clamped by means of a clamping device. In addition, the intermediate elastic sealing elements are an undesirable source of tension and torsions within the fuel cell stack, which have a negative effect on the reliability, reliability and service life of the fuel cell stack, especially with ever-increasing types of fuel cell stacks.

For liquid cooling, only non-conductive special cooling media may be used to avoid a short circuit of the fuel cells, which leads in practice to oxidation problems as well as to high demands in media preparation and handling. In addition, downstream heat exchangers are required to transfer the heat from the special cooling medium to a common secondary circulation medium. At temperatures above 100 ° C, the pressure of the primary cooling system above the boiling limit must be increased when using cooling water, which places additional demands on the stability of the numerous seals.

In light of the described prior art, it is a first object of the present invention to provide an advantageous fuel cell stack. A second object is to provide a method for producing fuel cell stacks, with which advantageous fuel cell stacks can be produced.

The first object is achieved by a fuel cell or Elektrolyseurstapel according to claim 1, the second object by a method for producing a fuel cell stack or electrolyzer stack according to claim 20. The dependent claims contain advantageous embodiments of the fuel cell stack or electrolyzer stack according to the invention and the inventive method. The following will only be the fuel cell stack explicitly mentioned, this term should also be understood synonymous with electrolyzer stack because of the high structural similarity between fuel cells and electrolyzers.

An inventive fuel cell stack for generating electricity from the reaction of a fuel with an oxidizing agent to a reaction product comprises a stack of bipolar plates, each having an anode surface, a cathode surface and an edge. In each case one anode surface and one cathode surface of two adjacent bipolar plates lie opposite one another in the stack. In addition, there is an electrolyte between two stacked anode and cathode surfaces. Suitable electrolytes here are all types of electrolytes, in particular polymer membranes, dissolved alkalis or acids, alkali metal carbonate melts or ceramics. The anode surfaces have flow paths for the fuel, whereas the cathode surfaces have flow paths for the oxidant and the reaction product, respectively. In the fuel cell stack according to the invention, an external structure formed separately from the stack of bipolar plates and connected in the stacking direction of the bipolar plates is provided, against which the edges of the bipolar plates rest. The supply of the fuel and the oxidant in the corresponding flow paths and the removal of the reaction product from the corresponding flow paths of the bipolar plates via the edges of the bipolar plates through the outer structure.

Since in the fuel cell stack according to the invention the supply of the fuel and the oxidizing agent and the removal of the reaction product is not through the bipolar plates in the stack direction breaking supply and discharge channels, no seals in the stacking direction (inner seals) are required between the individual bipolar plates. It is only necessary a sealing arrangement and / or an insulating arrangement on the periphery of the stack of bipolar plates, which can be arranged between the Bipolarplattenstapel and the outer structure. This can be realized in such a way that it surrounds the circumference of the stack of bipolar plates, and in particular can also be part of the external structure. The omission of the inner seals not only improves the reliability of the stack of bipolar plates, but also simplifies the production of the plates, since they can now be made in one piece, without the seals would have to be inserted. In addition, due to the elimination of the breakthroughs, the specific power density per area can be increased and, depending on the bipolar plate material used, also the power density per weight.

The sealing arrangement and / or the insulating arrangement can be formed, for example, by a potting compound. This can be applied, for example, after stacking the bipolar plates on the peripheral surface of the stack before the stack is inserted into the outer structure. If there is a gap between the outer structure and the stack of bipolar plates, the sealing arrangement and / or the insulating arrangement can also be formed by an elastomer, for example cast or injected, introduced into the gap. Alternatively, the sealing arrangement and / or the insulating arrangement may also be formed by a film wound or laminated around the circumference of the stack, such as a polymer film or a sheet of glass solder material. Another alternative is that the edges of the bipolar plates form the periphery of the stack of bipolar plates and the edges are each provided with a seal and / or insulation, which bears sealingly against the outer structure. Finally, it is also possible to attach individual seals to the openings of the stack and / or the openings of the outer structure. Preferably, the sealing arrangement is designed to be electrically insulating, so that, for example, electrically conductive cooling fluids can be used for cooling the bipolar plate stack.

A further advantage of the invention is that the bipolar plate stack is mechanically stabilized by the external structure, which may in particular also be braced, so that twisting of the stack by mechanical or thermal action or other forces influencing the shape is prevented or at least reduced.

The invention by means of external media distribution therefore enables a compact, inexpensive and mechanically stable design of cell stacks with an extremely reduced number of internal seals. This is suitable for low-, medium- and high-temperature fuel cell systems as well as for stacked electrolyzers.

In a specific embodiment of the fuel cell stack according to the invention, the anode surfaces and the cathode surfaces are assigned fuel inlet openings or oxidant inlet openings which are located in the edges of the respective bipolar plates. In addition, at least the cathode surfaces associated with reaction product outlet openings, which are located in the edges of the respective bipolar plate. For example, in the case of hydrogen as the fuel and oxygen as the oxidizing agent, reaction products are formed only by the cathodic reaction on the cathode surfaces. In contrast, in other fuels, the anodic reaction at the anode surfaces can form a reaction product (off-fluid) to be discharged. In this case, reaction product outlet openings are also assigned to the anode surfaces. The External structure has in this embodiment, in the stacking direction of the bipolar plates extending flow channels, wherein at least one fuel flow channel, an oxidant flow channel and a reaction product flow channel are present. The fuel flow passage has exit ports for the discharge of fuel, the oxidant flow passage exit ports for the exit of oxidant, and the reaction product flow passage entry ports for entry of reaction product. In this case, the outlet openings of the fuel flow channel are aligned with the fuel inlet openings of the bipolar plates, the outlet openings of the oxidant flow channel with the oxidant inlet openings of the bipolar plates and the inlet openings of the reaction product flow channel with the reaction product outlet openings of the bipolar plates.

In addition, the outer structure may have at least one cooling fluid channel for a gaseous or liquid cooling fluid extending in the stacking direction of the bipolar plates. As a result, cooling can take place on the circumference of the bipolar plate stack without the bipolar plates coming into direct contact with the cooling fluid. In particular, it may comprise at least one pair of cooling fluid passages extending in the stacking direction of the bipolar plates, in which cooling fluid flows through the two cooling fluid passages in the opposite direction. The cooling in countercurrent can be used to equalize the cooling effect of the cooling fluid.

The effectiveness of the cooling performance can be further increased if the stack of bipolar plates comprises cooling fluid plates through which a cooling fluid (gas or liquid) flows, each of which follows a number of bipolar plates, the supply and removal of the cooling fluid taking place via the external structure. In this case, the cooling fluid plates can in particular be closed off from the adjacent bipolar plates and have an edge facing the outer structure, in which cooling fluid inlet openings and cooling fluid outlet openings are present. The outer structure then has at least one cooling fluid supply channel extending in the stacking direction of the bipolar plates with cooling fluid outlet openings facing the stack of bipolar plates and at least one cooling fluid discharge channel extending in the stacking direction of the bipolar plates with cooling fluid inlet openings facing the stack of bipolar plates. In this case, the cooling fluid inlet openings and cooling fluid outlet openings of the cooling fluid plates are aligned with the cooling fluid outlet openings of the at least one cooling fluid supply channel of the outer structure or with the cooling fluid inlet openings of the at least one cooling fluid discharge channel of the outer structure. By means of the cooling plates, an internal cooling of the stack can be realized in cross section. In addition, when the cooling plates are closed against the adjacent bipolar plates, the cooling may occur without the bipolar plates themselves coming in contact with the cooling fluid. Since the cooling fluid then does not come into contact with the current-carrying bipolar plates, conductive cooling fluids can also be used, as used, for example, in vehicle construction, in building technology or in plant construction. In particular, non-deionized water can also be used as cooling fluid.

In the fuel cell stack according to the invention, the flow paths in the anode surfaces and the cathode surfaces preferably extend to the edge of the bipolar plates in order to optimally utilize their surfaces.

The outer structure of the fuel cell stack according to the invention may comprise at least one single-channel or multi-channel Hohlprofilelemt, wherein the production can be carried out by means of extrusion and for the production of the hollow profile, a variety of different Matrialien are suitable, such as ceramics and plastics, but also metals such as aluminum (Al).

Advantageously, the outer structure is at least two divided in the circumferential direction of the stack of bipolar plates, and there are clamping means which clamp the parts of the outer structure against each other and thus presses the outer structure against the stack of bipolar plates. This makes it possible, when using an elastic sealing arrangement by means of bracing the parts of the outer structure to bring about the sealing effect. Moreover, it is advantageous if the outer structure has end plates, by means of which the stack of bipolar plates is tensioned in the stacking direction, since this increases the stability of the stack. At least one of the Endgatten and / or at least a portion of the at least two-part outer structure may also comprise an adjustment for adjusting the contact pressure against the stack of bipolar cells.

According to the invention, a method for producing a fuel cell stack for generating electricity from the reaction of a fuel with an oxidizing agent to form a reaction product is also provided. They are manufactured by stacking bipolar plates, each having an anode surface with flow paths for the fuel, a cathode surface with flow paths for the oxidant or the reaction product and an edge. The stacking takes place in such a way that in each case one anode surface and one cathode surface of two adjacent bipolar plates are arranged opposite one another, wherein an electrolyte is arranged between the opposing anode and cathode surfaces. Around the stack of bipolar plates becomes a separated from the bipolar plates and arranged in the stacking direction of the bipolar plates outer structure arranged such that the edges of the bipolar plates abut the outer structure and the supply of the fuel and the oxidant in the corresponding flow paths and the removal of the reaction product from the corresponding flow paths over the edges of the bipolar plates can be done through the outer structure. Preferably, furthermore, a sealing arrangement and / or an insulating arrangement is arranged between the stack of bipolar plates and the outer structure.

With the method according to the invention, fuel cell stacks according to the invention can be produced and thus realize the advantages described with reference to the device according to the invention.

In particular, bipolar plates having fuel entry ports, oxidant entry ports, and reaction product exit ports disposed on the periphery of the bipolar plates such that the flow direction of the incoming fuel, inflow oxidant, and effluent reaction product pass through the respective openings in the plane of the anode side and cathode side flow paths, respectively, may be used Find. In order to avoid closing these openings for the inflow or outflow of the various fluids to and from the bipolar plates when attaching the sealing arrangement and / or insulating arrangement, it is advantageous if the bipolar plates have projections which surround the respective openings and in Direction of the plate plane protrude from the edge of the bipolar plates and which are removed after arranging the sealing arrangement and / or insulating arrangement. Such bipolar plates may be used in particular in connection with an outer structure with flow channels extending in the stacking direction of the bipolar plates, wherein at least one fuel flow channel, an oxidant flow channel and a Reaktionsproduktströmungskanal are present, and the fuel flow channel outlet openings for the discharge of fuel, the oxidant flow channel outlet openings for the exit of oxidant and the reaction product flow channel has inlet openings for the entry of reaction product.

Closing the openings in the bipolar plates by the seal and / or insulation can be avoided in a first alternative of attaching the sealing arrangement and / or insulating arrangement by mounting the sealing arrangement and / or insulating arrangement around the stack of bipolar plates in such a way that the Protrude projections from the sealing assembly and / or insulating assembly, and after removal of the projections, the outer structure is arranged around the stack of bipolar plates around such that the outlet openings of the fuel flow channel with the fuel inlet openings of the bipolar plates are aligned, the outlet openings of the oxidant flow channel with the oxidizing agent inlet openings of the Bipolar plates are aligned and the inlet openings of the reaction product flow channel with the reaction product outlet openings of the bipolar plates are aligned. In this case, the sealing arrangement and / or insulating arrangement can be wound or laminated around the stack of bipolar plates, in particular in the form of a gas-tight foil, for example of elastomer, glass solder, etc. The removal of the projections can be done mechanically, for example by milling, grinding, punching, cutting etc, or chemically, for example by etching.

In a second alternative of attaching the sealing arrangement and / or insulating arrangement, the outer structure is arranged around the stack of bipolar plates such that the projections into the outlet openings for the discharge of fuel, the outlet openings for the discharge of oxidizing agent and inlet openings for the entry of reaction product protrude. Subsequently, the sealing arrangement and / or insulating arrangement is introduced in the form of a potting compound between the stack of bipolar plates and the outer structure.

In a third alternative of attaching the sealing arrangement and / or insulating arrangement, the sealing arrangement and / or insulating arrangement is applied to the surfaces facing the stack of bipolar plates of the outer structure such that the outlet openings for the escape of fuel, the outlet openings for the discharge of oxidant and Inlets are covered for the entry of reaction product. This can be done, for example, by laminating film, applying elastomeric material, etc. Thereafter, the outer structure is placed around the stack of bipolar plates such that the protrusions extend through the seal and / or insulation into the exit ports for exit of fuel, exit ports for exit of oxidant and entry ports for entry of reaction product.

In both the first alternative and the second alternative, after placing the exterior structure around the stack of bipolar plates, the protrusions may be removed through the oxidant flow channel, the fuel flow channel, and the reaction product flow channel. This is necessary if the projections surrounding the openings in the bipolar plates also close these openings. Closing ensures that the for sealing and / or insulation Material used does not enter the flow paths of the bipolar plates. However, channels may also pass through the protrusions, so that removal of the protrusions is not absolutely necessary, especially in the alternative in which the gasket and / or insulation in the form of a potting compound between the stack of bipolar plates and the outer structure is introduced.

Further features, properties and advantages of the present invention will become apparent from the following description of embodiments with reference to the accompanying figures.

1 shows a first embodiment of a fuel cell stack according to the invention in a cross section perpendicular to the stacking direction of the bipolar plates.

2 Shows the first embodiment in a schematic side view.

3 shows an end plate of the fuel cell stack 1 in a cross section perpendicular to the stacking direction of the bipolar plates.

4 shows a second embodiment of a fuel cell stack according to the invention in a cross section perpendicular to the stacking direction of the bipolar plates.

5 shows a schematic representation of a bipolar plate before stacking.

6 shows a schematic cross section of the bipolar plate stack perpendicular to the stacking direction of the bipolar plates immediately after the application of a sealing arrangement and / or an insulating arrangement.

7 shows a schematic cross section of the bipolar plate stack perpendicular to the stacking direction of the bipolar plates immediately prior to installation in an external structure.

A first embodiment of a fuel cell stack according to the invention will be described below with reference to FIGS 1 to 3 described. While 1 shows a cross section of the fuel cell stack perpendicular to the stacking direction of the bipolar plates, shows 2 a side view of the fuel cell stack. The fuel cell stack is formed in the present embodiment as a proton exchange membrane fuel cell stack in which hydrogen (H) is used as fuel and oxygen (O) or air as the oxidant. The construction shown can also be realized with other types of fuel cell stacks.

The construction of the fuel cell stack consists in the present embodiment of an outer structure comprising hollow profile elements A, B in the form of extruded profiles, which may be made of metal, plastic or ceramic. The outer structure surrounds a stack of bipolar plates 8th each of which has a side formed as an anode and one formed as a cathode. In the stack, the anode sides of the bipolar plates each face the cathode sides of adjacent bipolar plates. Between adjacent anode sides and cathode sides, in the present exemplary embodiment, the electrolyte in each case is a proton exchange membrane, ie a polymer membrane which is permeable to protons and impermeable to electrons (not shown in the figures). The other common types of electrolytes are also suitable as electrolyte, for example, dissolved alkalis or acids, Alkalicarbonatschmelzen or ceramics. Over the circumference of the hollow profile elements A, B extending clamping elements 7 clamp the hollow profile elements A, B against each other and stabilize the cell stack.

The bipolar plates 8th each have an octagonal shape in the present embodiment, each having a short edge portion 8a and a long edge section 8b in the circumferential direction of the bipolar plates 8th alternate. The supply and removal of the reaction gases (in the present example, hydrogen as fuel and air as oxidant) takes place via the short edge sections 8a , A cooling of the bipolar plates 8th takes place over the long edge sections 8b , Are the edges of the bipolar plates 8th and at the same time the hollow profile walls electrically conductive, is an insulating composite layer 4 applied as an insulating arrangement at the interfaces. The composite layer 4 can also be good heat conducting and compensates for temperature-induced changes in shape of the bipolar plates elastically. Suitable composite layers can be made by wrapping or laminating the fuel cell stack with a film. The film may in this case be, for example, an elastomeric film or a glass soldering film.

The hollow profile elements A, B of the outer structure contain media channels 1a . 1b . 2a . 2 B . 3a . 3b for the supply and removal of fluidic media, ie liquids and / or gases to the stacked bipolar plates 8th , The arrangement is chosen in the present embodiment, that a media channel for fuel media supply 2a to the anode sides of the bipolar plates 8th , a media channel for off-gas removal 2 B from the anode sides of the bipolar plates 8th , a media channel for the supply of oxidant 3a to the catheter sides of the bipolar plates 8th and a media channel for reaction gas removal 3b of the Cathode sides of the bipolar plates 8th in the corners of the outer structure A, B are present. 1 shows here only one possible variant of the circuit of the media channels 2a . 2 B . 3a . 3b which can also be modified. It is possible, for example, the off-gas discharge over 3a and the oxidant supply via 2 B in dependence on the design of the flow fields indicated by the oblique lines on the anode sides and cathode sides of the bipolar plates 8th ,

The media channel for offgas removal 2 B serves in the present embodiment to dissipate unreacted fuel and impurities. In exceptional cases, with 100% pure fuels, the channels can 2a and 2 B be supplied with fuel in parallel for a more even feed.

The heat released in the reaction of the fuel ions with the oxidizing agent, ie in the present embodiment in the reaction of the hydrogen with the oxygen of the air, is removed from the fuel cell stack by a cooling medium. For this purpose, between the media channels arranged in the corners and media channels for cooling media supply 1a and media channels for cooling media removal 1b in the hollow profile elements A, B available. The coolant is in the present embodiment, only through the media channels for cooling media supply 1a and cooling media removal 1b on the outside of the stacked bipolar plates 8th passed through, without cooling medium is passed through the cross section of the stack. The media channels for cooling media supply 1a and cooling media removal 1b are as wide as possible to a large area as possible on the periphery of the stacked bipolar plates 8th to be able to cool.

The via the media channel for fuel media supply 2a and the media channel for oxidant delivery 3a supplied reaction gases pass through outlet openings 12a . 13a from the respective media channel 2a . 3a out and about with these outlet openings aligned inlet openings in the edges of the bipolar plates 8th in their anodes and cathode flow fields (flowfields) for fuel and oxidant. The offgas and the reaction gas formed in the reaction occur via outlet openings in the edges of the bipolar plates 8th in aligned with these inlet openings 12b . 13b of the media channel for offgas removal 2 B or the media channel for reaction gas removal 3b one.

Between the respective openings of the media channels 2a . 2 B . 3a . 3b and the bipolar plates 8th there is a sealing arrangement in the form of media seals 5 to avoid mixing of the media. These media seals 5 consist of - at the given operating temperatures - elastic material and are between the media channels of the hollow profile elements A and B and the bipolar plates 8th pressed. The required contact pressure can be achieved by radial clamping of the hollow profile elements A and B, for example by clamping elements 6 and 7 , be achieved. The media seals 5 can alternatively - with with straps 9 prestressed stack - also be introduced as potting compound, optionally in the same step with the composite layer 4 , It is also possible that the insulating composite layer 4 simultaneously performs the sealing function, so that separate media seals 5 can be omitted. In the case of a potting compound as a sealing arrangement and / or insulating arrangement, this can also serve the hollow profile elements A and B after their curing mechanically and / or chemically with the stacked bipolar plates 8th connect to. The use of an elastic sealing arrangement and / or insulating arrangement is advantageous because this compensating movements between the hollow profile elements A and B and the Bipolarplattenstapel be made possible in the stacking direction.

The bipolar plates 8th Even in the fuel cell stack according to the invention, only the anode / cathode flow fields (flowfields) for fuel and oxidant are contained in the fuel cell stack and can therefore be produced significantly less expensively than state-of-the-art bipolar plates. In addition, the power density of the bipolar plates 8th higher than in the prior art, since the area for the previously integrated in the bipolar plates media channels is now available for the flow fields.

The outer structure becomes at the ends of the Bipolaroplattenstapels of a front end plate 13 and a rear end plate 14 completed (see 2 ). The front end plate 13 is specially adapted to the extruded profile of the hollow profile elements A, B and has connections 15 . 16 for all gases and media. It has seals in the cross-sectional shape of the extruded profile of the hollow profile elements A, B. Laterally extending clamping elements 19 bring the required contact pressure for the tightness of the front end plate 13 opposite the media channels 1a . 1b . 2a . 2 B . 3a . 3b on. The inside of the front end plate 13 has in the present embodiment of an apparatus which is suitable, the contact pressure on cells and bipolar plates 8th of the cell stack to the required extent. Furthermore, the front end plate has 13 about executions 17 for the current collector.

As well as the front end plate 13 is the rear end plate 14 specially adapted to the extruded profile of the hollow profile elements A, B. It has integrated media redirects 10a . 10b for the cooling medium in the form of overflow channels (from the media channels 1a on the media channels 1b ) on. A cross section through the rear end plate 14 with the media diversions 10a . 10b shows 3 , The rear end plate 14 has seals in the cross-sectional shape of the extruded profile of the hollow profile elements A, B. Laterally along the cell stack extending clamping elements 19 bring the required contact pressure for the tightness of the end plate 14 towards the media channels in the extruded profile of the hollow profile elements A, B on.

The end plates 13 . 14 are considerably simplified in this design compared to the end plates in the prior art. The rear end plate 14 contains only 2 parallel or alternatively a simple mixing chamber. The material of the front and / or the rear end plate can be metal, plastic or ceramic and advantageously corresponds to the material of the extruded profile of the hollow profile elements A, B.

Should the temperature conductivity of the bipolar plates 8th not enough to heat all over the edge sections 8a . 8b can dissipate to the hollow profile elements A, B and the cooling media circulating therein, heat conducting plates with the same form factor as the bipolar plates 8th between these are layered to additionally realize a longitudinal heat dissipation from the inside of the bipolar plate stack.

A second embodiment of a fuel cell stack according to the invention will be described below with reference to 4 describes a fuel cell stack in a cross section perpendicular to the stacking direction.

The second embodiment of the fuel cell stack according to the invention differs from the first embodiment essentially in that the bipolar plate stack except the bipolar plates 108 also cold plates 112 includes. Each after a number of bipolar plates 108 is such a cooling plate 112 introduced into the stack to allow flow through the stack cross-section with cooling medium. If an electrically conductive cooling medium is used, this plate is against the adjacent bipolar plates 108 electrically isolated.

In the figure, three plates of the stack are shown cut. It is a lower bipolar plate 108a , an upper bipolar plate 108b and a cooling plate arranged therebetween 112 each partially visible.

Another difference from the first embodiment is that the outer structure A, B does not surround the entire circumference of the bipolar plate stack. Instead, the outer structure in the form of two separately formed and non-interconnected hollow profile elements A, B is formed. The hollow profile elements can be realized in the form of extruded profiles, as in the first embodiment, for which applies the analogous with respect to the first embodiment executed. The hollow profile elements A, B are by means of clamping elements 106 . 107 against the side surfaces of the bipolar cell stack 108 pressed. While the one hollow profile element A the media channel 101 for the supply of cooling medium, the media channel 102 for the fuel and the media channel 103a contains for the oxidizing agent, the second hollow profile element B contains a media channel 101b to remove the cooling medium, a media channel 102b for the offgas and a media channel 103b for the reaction gas. The media channels are each provided with the peripheral surface of the Bipolarzellenstapels facing openings, with media seals 105 are equipped. It should be noted that in the present embodiment, for each anode surface, the openings 102 and 102b are open and for a cathode surface, the openings 103a and 103b , According to shows 4 an anode surface of the upper bipolar plate 108a and a cathode surface of the underlying bipolar plate 108b ,

As in the first embodiment, the bipolar plate stack is at its peripheral surfaces with a composite layer 104 provided, which is designed to be electrically insulating. Instead of individual media seals 105 This may also be formed in the form of a surrounding the circumference of the bipolar plate stack sealing compound. The composite layer 104 and / or the sealing compound can be realized in this case, for example, as a film or as a potting, as has already been described with reference to the first embodiment. Preferably, they are elastic so as not to interfere with expansion of the bipolar plate stack during operation.

Compared to the first embodiment results from the second embodiment, a simplified embodiment of the tension of the bipolar plate stack in the stacking direction. Since there are no hollow profile elements on two opposite circumferential surfaces of the bipolar plate stack, for example, a tensioning belt can be placed around the stack, which can be passed between the stack and the front and the rear end plate. Although this is basically possible in the first embodiment, but would complicate the design of the end plates. Also, in the second embodiment, the overflow channels in at least one of the end plates can be dispensed with, since the cooling medium from the supply channel 101 through the cooling plates 112 in the discharge channel 101b can get. One of the end plates can therefore be easily formed as a lid that neither feeders, discharges or transfer channels for media needs to show. The openings for the cooling medium, unlike those in 4 be illustrated slits and in particular take the entire width of the feed channel and the discharge channel for the cooling medium, whereby the cooling capacity can be increased.

Below we refer to the 5 to 7 the application of the composite layer 4 explained. In the same way, a sealing layer can also be applied to the periphery of the bipolar plate stack. The bipolar plates 8th and - if available - the cooling plates 112 prior to assembly of the stack and before wrapping with the composite layer 4 Projections or lugs, which surround the openings in the edge of the Bipolarplattenstapels, project radially from the periphery of the stack and preferably tapered. Such a plate before stacking is in 5 shown schematically. After stacking the plates 8th then becomes the composite layer 4 attached around the circumference of the plate stack. This can be done, for example, by wrapping the stack with a film or by laminating the stack with a film. The tapered projections pierce the film, so that arise at the appropriate locations openings in the film. This condition is in 6 shown.

After application of the composite layer 4 become the projections 18 by machining, for example by milling or grinding, and so removes the inlet openings or outlet openings for the media in the bipolar plates 8th and from the bipolar plates 8th produced. The state after the machining is in 7 shown. If the film has only insulating properties, later media seals between the hollow profile elements A, B and the corresponding openings can be arranged, as shown in the 1 to 3 is shown. These media seals 5 . 105 can either be applied to the outside of the stack before the hollow profile elements A, B are arranged. On the other hand, however, they can also be attached to the sides of the hollow profile elements A, B facing the stack before the hollow profile elements A, B are arranged on the stack.

Except as a film, the composite layer 4 and / or the sealing layer are also applied as a plastic elastomer, for example as a liquid elastomer, on the peripheral surface of the stack. After the elastomer has hardened, the protrusions are removed.

In an alternative embodiment of the manufacturing process for the fuel cell stack only the hollow profile elements A, B to the still with the projections 18 arranged bipolar plate stack arranged around, wherein the projections 18 into the media openings of the media channels in the hollow profile elements A, B are guided into it. The projections 18 can also serve as guide elements, which facilitates the alignment of the openings in the hollow profile and in the Bipolarplattenstapel simultaneously. The removal of the projections by machining then takes place through the media channels of the hollow profile elements A, B.

If the hollow profile elements A, B are formed so that they enclose the entire circumference of the Bipolarplattenstapels after assembly, it is also possible to apply the film or the elastomer facing the stack surfaces of the hollow profile elements A, B such that the media openings in the hollow profiles are covered. When mounting the hollow profile elements A, B, the film or the solidified elastomer is then pierced by means of the projections, whereby the opening is produced. Subsequently, the projections 18 through the media channels.

If a one- or multi-part hollow profile is used, which encloses the entire circumference of the stack, there is a further manufacturing alternative, first to arrange the hollow profile elements A, B around the plate stack around and then to introduce a potting compound in the space between the stack and the hollow profile elements. After solidification of the potting compound, the protrusions are then removed through the media channels. The potting compound can then be used to make a connection between the stack and the outer structure. In addition, a strap for clamping the stack can be shed, which further increases the stability.

Depending on the manufacturing process, a part of the hollow profile can also serve as a mounting receptacle during the stacking of the bipolar plates.

The present invention has been described by means of exemplary embodiments. As has been stated, a large number of deviations from the respective concrete exemplary embodiments are possible within the scope of the invention.

The presented invention leads to a number of advantages: Firstly, this considerably reduces the number of seals on the bipolar plates.

Second, it allows the use of conventional conductive cooling media (such as water), in addition, even at higher pressures and temperatures above the boiling point of the cooling medium.

Third, it improves the operational safety and stability of cell stacks by increasing the reliability of the sealing structures.

Fourth, the invention provides higher power densities because the membrane electrode assemblies (MEA) located on the bipolar plates can utilize the entire area.

Fifth, the invention saves separate axial clamping elements, since this function is taken over by the hollow profile elements.

Sixth, the invention allows for the adaptation to different operating temperature ranges by installing cooling plates.

Seventh, the invention facilitates the stacking of bipolar plate MEA devices as part of the assembly of cell stacks.

Eighth, the invention simplifies the integration of the cell stack into existing cooling circuits.

Ninth, the invention allows the use of a simplified end plate without connections to the outside and thus the installation with one-sided accessibility.

Tenth, the invention prevents twisting of the cell stack.

In sum, the invention offers significant cost reduction potential.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102007036477 A1 [0005]
• US 2009/0297920 A1 [0005]
• US 2005/0109645 A1 [0005]
• US 2009/0181272 A1 [0005, 0006]

Claims (23)

Fuel cell stack for generating electricity from the reaction of a fuel with an oxidizing agent to a reaction product, with a stack of bipolar plates ( 8th . 108 ), each having an anode surface, a cathode surface and a rim ( 8a . 8b ), wherein - in the stack in each case an anode surface and a cathode surface of two adjacent bipolar plates ( 8th . 108 ), - is located between two stacked opposing anode and cathode surfaces, an electrolyte, - have the anode surfaces flow paths for the fuel and - the cathode surfaces flow paths for the oxidizing agent or the reaction product, characterized in that - one of Stack of bipolar plates ( 8th . 108 ) formed separately and in the stacking direction of the bipolar plates ( 8th . 108 ) contiguous outer structure (A, B) is present, - the edges ( 8a . 8b ) of the bipolar plates ( 8th . 108 ) on the outer structure (A, B) and - the supply of the fuel and the oxidizing agent in the corresponding flow paths and the removal of the reaction product from the corresponding flow paths of the bipolar plates ( 8th . 108 ) over the edges ( 8a . 8b ) of the bipolar plates ( 8th . 108 ) takes place through the outer structure (A, B). Fuel cell stack according to claim 1, characterized in that a sealing arrangement ( 5 ) and / or an insulating arrangement ( 4 ) surrounds the periphery of the stack of bipolar plates. Fuel cell stack according to claim 2, characterized in that the sealing arrangement ( 5 ) and / or the insulating arrangement ( 4 ) is formed by a potting compound. Fuel cell stack according to claim 2, characterized in that the sealing arrangement ( 5 ) and / or the insulating arrangement ( 4 ) is formed by a film wound or laminated around the circumference of the stack. Fuel cell stack according to claim 2, characterized in that the edges 8a . 8b ) of the bipolar plates ( 8th ) form the periphery of the stack of bipolar plates and the edges each with a sealing arrangement ( 5 ) and / or an insulating arrangement ( 4 ) are provided, which bears against the outer structure (A, B) sealingly. Fuel cell stack according to one of claims 2 to 6, characterized in that the sealing arrangement ( 5 ) and the insulating arrangement ( 4 ) are identical. Fuel cell stack according to one of claims 1 to 6, characterized in that - the anode surfaces and the cathode surfaces are assigned to fuel inlet openings or oxidant inlet openings, which in the edges ( 8a ) of the respective bipolar plates ( 8th ), and - at least the cathode surfaces are associated with reaction product outlet openings, which are located in the edges ( 8a ) of the respective bipolar plates ( 8th ), - the outer structure (A, B) in the stacking direction of the bipolar plates ( 8th ) extending flow channels ( 2a . 2 B . 3a . 3b ), wherein at least one fuel flow channel ( 2a ), an oxidant flow channel ( 3a ) and a reaction product flow channel ( 3b ), - the fuel flow channel ( 2a ) Outlet openings ( 12a ) for the discharge of fuel, the oxidant flow channel ( 3a ) Outlet openings ( 13a ) for the exit of oxidant and the reaction product flow channel ( 3b ) Inlet openings ( 13b ) for the entry of reaction product, and - the outlet openings ( 12a ) of the fuel flow channel ( 2a ) with the fuel inlet openings of the bipolar plates ( 8th ), the outlet openings ( 13a ) of the oxidant flow channel ( 3a ) with the oxidant inlet openings of the bipolar plates ( 8th ) are aligned and the inlets ( 13b ) of the reaction product flow channel ( 3b ) with the reaction product outlet openings of the bipolar plates ( 8th ) are aligned. Fuel cell stack according to claim 7, characterized in that the outer structure (A, B) at least one in the stacking direction of the bipolar plates ( 8th ) extending cooling fluid channel ( 1a . 1b ) having. Fuel cell stack according to claim 8, characterized in that the outer structure (A, B) at least one pair in the stacking direction of the bipolar plates ( 8th ) extending cooling fluid channels ( 1a . 1b ), in which the two cooling fluid channels ( 1a . 1b ) are flowed through in the opposite direction of cooling fluid. Fuel cell stack according to one of claims 1 to 9, characterized in that the stack of bipolar plates ( 108 ) cooling fluid plates through which a cooling fluid flows ( 112 ), each applied to a number of bipolar plates ( 108 ), wherein the supply and removal of the cooling fluid via the outer structure (A, B) takes place. Fuel cell stack according to claim 10, characterized in that the cooling fluid plates ( 112 ) against the adjacent bipolar plates ( 108 ) are completed, The cooling fluid plates ( 112 ) have an edge facing the outer structure (A, B), in which cooling fluid inlet openings and cooling fluid outlet openings are present, - the outer structure (A, B) has at least one cooling fluid supply channel extending in the stacking direction of the bipolar plates ( 101 ) with the stack of bipolar plates facing cooling fluid outlet openings ( 111 ) and at least one in the stacking direction of the bipolar plates ( 108 ) extending cooling fluid discharge channel ( 101b ) with the stack of bipolar plates ( 108 ) facing cooling fluid inlet openings ( 111b ), and - the cooling fluid inlet openings and cooling fluid outlet openings of the cooling fluid plates ( 122 ) with the cooling fluid outlet openings ( 111 ) of the at least one cooling fluid supply channel ( 101 ) of the outer structure or with the cooling fluid inlet openings ( 111b ) of the at least one cooling fluid discharge channel ( 101b ) of the outer structure (A, B) are aligned. Fuel cell stack according to one of claims 1 to 11, characterized in that - the flow paths in the anode surfaces and the cathode surfaces to the edge ( 8a . 8b ) of the bipolar plates ( 8th ), Fuel cell stack according to one of claims 1 to 12, characterized in that the outer structure (A, B) comprises at least one hollow profile element. Fuel cell stack according to one of claims 1 to 13, characterized in that the outer structure (A, B) in the circumferential direction of the stack of bipolar plates ( 8th . 108 ) is divided into at least two and clamping means ( 7 . 107 ) are present, which brace the parts of the outer structure (A, B) against each other. Fuel cell stack according to one of claims 1 to 14, characterized in that the outer structure (A, B) end plates ( 13 . 14 ), by means of which the stack of bipolar plates ( 8th ) is clamped in the stacking direction. Fuel cell stack according to claim 15, characterized in that the at least one of the end gates ( 13 . 14 ) and / or at least a part of the at least two-part outer structure (A, B) has an adjusting device for adjusting the contact pressure against the stack of bipolar cells (US Pat. 8th ). Method for producing a fuel cell stack for generating electricity from the reaction of a fuel with an oxidizing agent to form a reaction product, by stacking bipolar plates ( 8th . 108 ), each having an anode surface with flow paths for the fuel, a cathode surface with flow paths for the oxidant or the reaction product and a rim ( 8a . 8b ) such that in each case one anode surface and one cathode surface of two adjacent bipolar plates ( 8th . 108 ) are arranged opposite one another, wherein an electrolyte is arranged between the opposing anode and cathode surfaces, characterized in that - one of the bipolar plates ( 8th . 108 ) formed separately and in the stacking direction of the bipolar plates ( 8th . 108 ) contiguous outer structure (A, B) in such a way around the stack of bipolar plates ( 8th . 108 ) is arranged around, that the edges ( 8a . 8b ) of the bipolar plates ( 8th . 108 ) on the outer structure (A, B) and the supply of the fuel and the oxidizing agent in the corresponding flow paths and the removal of the reaction product from the corresponding flow paths over the edges ( 8a . 8b ) of the bipolar plates ( 8th . 108 ) can be done through the outer structure (A, B). Method according to claim 17, characterized in that a sealing arrangement ( 5 ) and / or an insulating arrangement ( 4 ) between the stack of bipolar plates ( 8th . 108 ) and the outer structure (A, B) is attached. Method according to claim 18, characterized in that bipolar plates ( 8th . 108 ) Are used, which have fuel inlet openings, oxidant inlet openings and reaction product outlet openings, which in such a way on the periphery of the bipolar plates ( 8th . 108 in that the flow direction of the inflowing fuel, of the inflowing oxidizing agent and of the outflowing reaction product passes through the respective openings in the plane of the flow paths of the anode side or cathode side, the fuel inlet openings, oxidant inlet openings and reaction product outlet openings of the individual bipolar plates ( 8th ) surrounding the respective opening of the fuel cell stack and in the direction of the plate plane of edge of the bipolar plates ( 8th ) protruding projections ( 18 ), which after the attachment of the sealing arrangement ( 5 ) and / or insulating arrangement ( 4 ) are removed. A method according to claim 19, characterized in that an outer structure (A, B) with in the stacking direction of the bipolar plates ( 8th ), wherein at least one of a fuel flow passage, an oxidant flow passage and a reaction product flow passage is provided, and the fuel flow passage includes exit ports for discharge of fuel, the oxidant flow passage has exit ports for exit of oxidant, and the reaction product flow passage has entry ports for entry of reaction product. Method according to claim 20, characterized in that - the sealing arrangement ( 5 ) and / or insulating arrangement around the stack of bipolar plates ( 8th ) is mounted around, that the projections of the sealing arrangement and / or insulating arrangement protrude and - after removing the projections ( 18 ) the outer structure (A, B) around the stack of bipolar plates ( 8th ) is arranged around, that the outlet openings of the fuel flow channel with the fuel inlet openings of the bipolar plates ( 8th ) are aligned, the outlet openings of the oxidant flow channel with the oxidant inlet openings of the bipolar plates are aligned and the inlet openings of the reaction product flow channel with the reaction product outlet openings of the bipolar plates ( 8th ) are aligned. A method according to claim 21, characterized in that the seal and / or insulation in the form of a gas-tight film around the stack of bipolar plates ( 8th ) is wrapped or laminated around. A method according to claim 20, characterized in that - the outer structure (A, B) in such a way around the stack of bipolar plates ( 8th ) is arranged around, that the projections ( 18 ) into the outlet openings for the exit of fuel, the outlet openings for the exit of oxidizing agent and inlet openings for the entry of reaction product protrude and, - the sealing arrangement ( 5 ) and / or insulating arrangement ( 4 ) in the form of a potting compound between the stacks of bipolar plates ( 8th ) and the outer structure (A, B) is introduced.

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