WO2001089019A1

WO2001089019A1 - Fuel cell stack with frame elements

Info

Publication number: WO2001089019A1
Application number: PCT/DE2001/001860
Authority: WO
Inventors: Karl Eck; Thomas Zapp
Original assignee: Siemens Aktiengesellschaft
Priority date: 2000-05-18
Filing date: 2001-05-11
Publication date: 2001-11-22
Also published as: DE10025207A1

Abstract

The invention relates to a fuel stack that is composed of a stack of membrane-electrode units arranged with their flat sides one behind the other and separated one from the other by a bipolar plate. One simple pole flange each is provided as the final plate before the first and behind the last membrane-electrode unit. Distributing and collecting channels for the supply of the fuel cell with fuel, oxidant and coolant as well as for the discharge thereof run through the stack of membrane-electrode units, bipolar plates and final plates. Said distributing and collecting channels are disposed in respective plastic frames which enclose the individual membrane-electrode units, the bipolar plates and the final plates. Said plastic frames are firmly interlinked by welding or gluing. The invention allows for an especially inexpensive production of the fuel cell.

Description

FUEL CELL STACK WITH FRAME ELEMENTS

description

The invention relates to a fuel cell, with a stack of membrane electrode units arranged one behind the other, which are coated on both sides with a catalyst and are each separated from one another by a bipolar plate, the first and the last membrane electrode unit of the stack being behind a simple pole plate is arranged as an end plate. The stack is of distribution and collection channels for supplying and removing hydrogen and oxygen to and from the anode or. Cathode spaces, which are each formed between a membrane electrode assembly and a bipolar plate or between a membrane electrode assembly and an end plate. Branch channels branch off from the distribution and collecting channels to the corresponding anode or cathode spaces.

The sufficient and reliable availability of energy has become an indispensable part of modern industrial society. Fossil fuels are only available to a limited extent, but in such a large quantity that they will probably be available for a hundred years even if today's consumption growth rates continue. However, the pollution of humans and their environment with pollutants from the combustion processes has reached such a level in the past that the state has had to set ever stricter emission limit values.

As a further problem, the contamination of the earth's atmosphere with trace gases that are generated by humans is increasingly being recognized. It leads to dangerous climate changes. The carbon dioxide emissions from the use of fossil fuels play the greatest role. To solve these problems, increasingly non-fossil fuels have to be used. Energy efficiency on both the provision and the user side must be further increased. Fuel cells can play an important role in both ways in the future. They have therefore become a beacon of hope for an environmentally compatible energy supply.

Fuel cells for generating electrical energy by direct energy conversion from chemical energy in reverse of water electrolysis are known from the prior art.

A single fuel cell usually consists of two invariant electrodes (anode and cathode) with an invariant electrolyte between them. The fuel cell continuously supplies electricity if it has an oxidizing fuel - this is usually done with hydrogen, which, for. B. is obtained by cleavage of natural gas, methanol, hydrazine, ammonia, etc. - and an oxidizing agent is continuously added and the oxidation products formed in the fuel cell are continuously removed.

In the so-called electrochemical combustion taking place in the fuel cell, oxygen (air) is used as the oxidizing agent. In the overall reaction 2 H ₂ + O ₂ - 2 H ₂ O, which takes place at the two invariant porous electrodes, the double negatively charged oxygen ions enter the electrolyte in contact with it from one electrode (cathode). At the same time, for each oxygen ion that has entered the electrolyte, a different oxygen ion leaves the electrolyte at the other electrode (anode), where it contains a fuel molecule adsorbed there (in this case, H ₂ ), releasing its two excess electrons and under Formation of water as a combustion product reacts. The four electrons released each time consumed O ₂ moles pass from the anode into an external electrical line, which leads back to the cathode of the fuel cell via a current consumer. The circuit is closed by the electrolyte through which the O ₂ ions flow.

Fuel cells are used for stationary and mobile power generation, for road vehicles, in space travel, in connection with H ₂ storage devices (e.g. metal hydrides) as power plants in the MW range for peak loads and as O ₂ sensors. Comparatively high costs and / or insufficient long-term stability stand in the way of a broader use of fuel cells. A planar design has generally emerged as the typical fuel cell geometry. The main problems with this type of construction are to optimize the distribution of current density, concentration and temperature as well as the overall performance. In addition, efforts are being made to reduce the production costs, to make optimum use of the fuel and to keep the outlay for peripheral devices as low as possible.

In the case of the fuel cells according to the structure known hitherto, there are additional disadvantages due to the complex construction with regard to the gas tightness, the supply and removal of hydrogen and air (oxygen), and the cooling of the fuel cell which is usually required. In addition, the distribution of the gases or the coolant within the fuel cell is insufficient.

It is an object of the present invention to further develop fuel cells of the type mentioned at the outset in such a way that they can be composed of individual elements in a simple, functional and cost-saving manner, in order in this way to be able to produce the fuel cells faster and cheaper than hitherto.

This object is achieved by the features of the main claim.

Appropriate configurations of the fuel cell according to the invention are characterized in the dependent claims.

The invention provides a fuel cell in which the membrane electrode units, the bipolar plates and the end plates are each individually surrounded by a plastic frame. The distribution and collecting channels and the branch channels through which the oxygen is conducted into the cathode compartments and the hydrogen into the anode compartments, that is to say on the corresponding side of a membrane-cathode unit, are arranged in the plastic frame. The membrane electrode assemblies and bipolar plates can then simply be alternated one after the other in the desired number

Stack are arranged, with a simple pole plate is used as the end plate at the beginning and at the end. For the gas-tight connection of the distribution and collection channels to one another, the individual plastic frames are simply welded or glued to one another in alignment with one another, so that the stack is each provided with at least one distribution channel and at least one collection channel for the Oxygen (or for the cathode exhaust gas) and at least one distribution channel and at least one collection channel for the hydrogen (or for the anode exhaust gas) is continuously passed from one end plate to the other end plate. The fuel cell thus has a number of channels in the area of the plastic frame, through which various media can flow. The plastic frames are expediently produced by injection molding, the distribution and collecting channels and, if possible, also the branch channels being molded in at the same time, so that there is no need for machining.

The bipolar plates can advantageously be extrusion-coated with a plastic frame made of electrically conductive plastic. However, the bipolar plates can also be formed as an integral component in one piece from such a plastic.

The plastic used can be doped c / s-poly (acetylene) (PAC), doped ifra / 7s-poly (acetylene) (PAC), doped poly (p-phenylene) (PPP), doped poly (/ τ? -Phenylene ) (PMP), doped poly (pyrrole) (PPY), doped poly (thiophene) (PTP), doped poly (p-phenylene sulfide) (PPS) or doped poly (azasulfen) (PAS). However, other plastics are also conceivable, so that the invention is not restricted to the examples mentioned.

The bipolar plates are preferably formed with at least one cavity for the passage of a cooling medium. For example, they can be double-walled or can also be run through by cooling channels running in the plane of the bipolar plates. In the case of the double-walled design, it is advisable to fill the cavity with a nonwoven, preferably a nonwoven made of electrically conductive plastic, in order to achieve a coolant distribution that is as uniform as possible when viewed over the surface. An electrically conductive fleece creates the required electrical connection between the walls of a double-walled bipolar plate. This electrical connection could also be ensured by means of correspondingly conductive frames which surround the walls of the bipolar plate. In order to introduce the coolant into the bipolar plates (but not into the anode and cathode compartments) and to pull them out of the bipolar plates again, the plastic frames of the bipolar plates and preferably also the end plates as well as the plastic frames of the membrane electrode units are in addition to the distribution and collection channels for oxygen and hydrogen also with distribution and collection channels for a cooling medium (perpendicular to the The board). However, only in the plastic frame of the bipolar plates is there a connection of the distribution and collecting channels for the coolant to the respective cavity of the bipolar plate. This connection is preferably implemented in the same way as in the case of the distribution and collection channels for oxygen and hydrogen on the membrane electrode units in the form of branch channels (parallel to the plate level).

The membrane electrode unit can advantageously be extrusion-coated with a plastic frame made of non-conductive plastic. Suitable plastics are - but not exclusively - cis-poly (acetylene) (PAC), trans-poly (acetylene) (PAC), poly (p-phenylene) (PPP), poly (m-phenylene) (PMP), poly (pyrrole) (PPY), poly (thiophene) (PTP),

Poly (p-phenylene sulfide) (PPS) or poly (aza sulfen) (PAS).

Preferably, the distribution and collection channels for the individual media (oxygen, hydrogen, cooling medium) are each arranged in the plastic frame so that the channels for the supply and discharge of a medium are each on diametrically opposite sides of the plastic frame.

The membrane of the membrane electrode unit is regularly coated with a catalyst (vapor-coated film). The catalyst used preferably consists of noble metals, Raney nickel, tungsten carbide, molybdenum or tungsten sulfides or

Phthalocyanine or other chelate complexes. However, other catalyst materials are also conceivable.

The bipolar plates can preferably be produced in the form of a honeycomb structure made of metal or two electrically connected metal foils.

The end plates of the fuel line according to the invention preferably consist of electrically conductive plastic. The end plates expediently have connections for the gas supply and cooling and connections for tapping the current. In the interest of the best possible distribution of the gas flows in the cathode and

In anode compartments, it is advisable to arrange a fleece, preferably a fleece made of electrically conductive plastic or metal, between the membrane-electrode unit and the bipolar plate. The fuel cells according to the invention have a number of advantages. The fuel cells have a lighter design and are easier and faster to manufacture. Due to the joining technique of welding or gluing the individual plates (end plates, bipolar plates, membrane electrode units), no separate seals are necessary. Furthermore, the supply ducts for fuel gas and oxidizing agents and ducts for cooling media can be integrated into the frame by molding appropriate passages for these media during injection molding. No special clamping elements are required to hold the individual components of the fuel cell together in a sealed manner. The fuel cells according to the invention are thus significantly lighter and, above all, less expensive to manufacture in mass production. Since the individual elements and modules of the fuel cells are injection molded, stacks can be produced continuously, for example in a production line. This eliminates the traditional, expensive and complex individual production of the stacks. Furthermore, the individual elements can be tightly welded to one another by the plastic frame without the need for a gasket to be inserted between the individual elements in a complex manner. At the same time, the channels for the reactants and cooling are integrated into the plastic frame. This eliminates the otherwise complex additional laying of a large number of supply and cooling lines. Only individual feed lines need to be routed to the corresponding connections on the two end plates of a stack.

Exemplary embodiments of the invention are explained with reference to FIGS. 1 to 4. Show it:

1 is a plan view of a membrane electrode assembly,

2a to 2c cross sections through a membrane electrode unit according to Figure 1 in different sections of the frame,

Fig. 3 shows a cross section through a fuel line in a first embodiment and

4 shows a cross section through a fuel cell in a second exemplary embodiment. FIG. 1 shows a membrane-electrode unit 1, which consists of a film vapor-coated on both sides with a catalyst (eg Raney nickel) and is surrounded by a frame 2 made of an electrically non-conductive plastic. In the frame 2, channels 3, 4, 5, 6, 7 and 8 are provided which run perpendicular to the image plane and through which different media are passed. In the illustrated embodiment, the bores 3 and 4 are provided for the supply or discharge of hydrogen as the fuel gas. The oxidizing agent (oxygen or air) is supplied or discharged through the holes 6 and 7. Finally, through the further bores 5 and 8, a cooling medium can be fed in or out, which dissipates the heat generated during the combustion.

The film of the membrane electrode assembly 1 has numerous circular holes at its edges, which are penetrated on both sides by the plastic of the plastic frame 2 produced by injection molding, so that the film is held in the plastic frame 2 in a form-fitting manner. Furthermore, FIG. 1 shows two branch channels 14, 11 which branch off from the distribution channel 6 for the air supply or lead to the collecting channel 7 for the air removal. Both branch channels 14, 1 1 end, for example, on the underside of the membrane electrode unit 1. In this case, there are two branch channels (not shown) in a corresponding manner, which originate from the supply line (distribution channel 3) or from the discharge line (collecting channel 4) branch off for the fuel and end on the top of the membrane electrode assembly. Thus, one surface (cathode compartment) of the membrane electrode assembly 1 is supplied and disposed of with oxygen and the other surface (anode compartment) with fuel. The channels 5, 8 for the cooling medium have no branch channels in the frame 2 of the membrane electrode unit 1, since the cooling medium (eg water) must not penetrate into the anode and cathode compartments. Only a plastic frame of a bipolar plate has connecting channels to the respective one

Distribution and collection channels 5, 8 for the cooling medium.

Figures 2a, 2b and 2c show cross sections through a membrane electrode assembly 1 according to Figure 1. Figure 2a shows a cross section A near the distribution channel 7, Figure 2b shows a cross section B near the distribution channel 5 and Figure 2c finally a cross section C in the vicinity of the distribution channel 3. The fuel gas and the oxidizing agent are each directed at opposite corners of the frame 2 to different sides of the membrane electrode assembly 1 and reacted there. The oxidizing agent flows through the distribution channel 6 in the frame 2 and passes through the branch channel 14 (FIG. 2a) to the left side of the membrane electrode unit 1 (Cathode space) and is distributed over the surface of the membrane electrode unit 1, in order to then be discharged as cathode exhaust gas at the corner of the frame 2 diametrically opposite the valve channel 6 via the branch channel 11 (FIG. 2c) into the collecting channel 7. In a corresponding manner, the fuel (for example a hydrogen-rich gas) is passed through the distribution channel 3 and the branch channel 15 (FIG. 2c) to the right side of the

Membrane electrode unit 1 guided, distributed over a large area and, after the oxidation reaction has ended, discharged as anode exhaust gas at the corner of the frame 2 diametrically opposite the distribution channel 3 through the branch channel 16 into the collecting channel 4 (FIG. 2a). As FIG. 2b shows, the two distribution and collecting channels 5, 8 for the cooling medium do not have an opening to the membrane electrode unit 1, but only serve as a line connection to the (not shown) bipolar plates, which are directly on both sides of the membrane - Connect electrode unit 1.

A fuel cell in a first embodiment is shown schematically in FIG. Here, the membrane-electrode units 1 are injected into a frame 2 made of electrically non-conductive plastic and the bipolar plates 10, which in this case are double-walled and through which a cooling medium can flow, are injected into a frame 12 made of electrically conductive plastic. For the production of double-walled bipolar plates 10, individual plate-shaped walls can be manufactured separately and provided with a frame made of plastic, a pair of such plate-shaped walls then being placed one on top of the other (optionally with a fleece inserted between them) and welded to the frame. In the spaces between the bipolar plates 10 and the membrane electrode assemblies 1 and in the cavities of the double-walled bipolar plates 10, nonwovens 9 can be inserted, which for example consist of an electrically conductive plastic. FIG. 3 shows a section of the typical arrangement of the individual modules of a fuel cell, which consists of a first membrane electrode unit 1, a first bipolar plate 10, a second membrane electrode unit 1, a second bipolar plate 10 and a third membrane electrode unit 1 exists. In this way, any number of plate modules could be connected. The complete fuel cell is then closed on the left and right side in each case in direct connection to a membrane electrode unit by a simple pole plate as the end plate. The channels for the distribution of the media run through the frames 2, 12, but are not shown in detail. A further embodiment of a fuel cell according to the invention is now shown in FIG. 4, in which the bipolar plates 10 do not have a physically separate frame. In this case, the bipolar plates are made in one piece from a preferably conductive plastic with an expansion that corresponds to the frame 2 of the membrane electrode assembly 1. Conductive nonwovens 9 are in turn preferably arranged in the spaces between the membrane electrode assemblies 1 and the bipolar plates 10. The fleece 9 can preferably consist of conductive plastic.

For simple assembly of the fuel cells according to the invention, the membrane electrode units 1, in which the membrane is formed on a polymer basis and vapor-coated with the catalyst, and the bipolar plates 10 are in each case encapsulated with a plastic frame 2, 12, into which the distribution and collection channels 3 , 4, 5, 6, 7, 8 are molded for the individual media. The plate-shaped components formed in this way are placed one on top of the other in such a way that the corresponding channels connect flush with one another and are then welded or glued to one another to form an assembly. In this way, stacks of any size can be built.

The encapsulation of the individual plates of the fuel cell allows a particularly cheap and fast production of fuel cells of any size and performance.

The inventive shaping of channels 3, 4, 5, 6, 7 and 8 for the supply and discharge of substances required for the reaction and of coolant means that additional equipment which is expensive in terms of equipment is superfluous and previously required work steps in the production of the fuel cell are saved , The modular design of the individual elements of the fuel cell also allows the structure of the cells to be modified with little effort. By choosing electrically non-conductive plastics for the frame of the membrane electrode assemblies 1 it is achieved that the bipolar plates are insulated from one another from the outset. LIST OF REFERENCE NUMBERS

I membrane electrode unit 2 frames (non-conductive plastic)

3 distribution channel for hydrogen

4 collecting channel for hydrogen

5 distribution channel for cooling medium

6 Distribution channel for air 7 Collection channel for air 8 Collection channel for cooling medium

9 fleece

10 bipolar plate

I I branch duct (air supply)

12 frame (conductive plastic) 14 branch duct (air supply)

15 branch channel (fuel supply)

16 branch channel (fuel discharge)

Claims

claims

1. Fuel cell with a stack of flat sides arranged one behind the other

5 arranged membrane-electrode units (1) which are coated on both sides with a catalyst and which are each separated by a bipolar plate (10) and with a simple one in front of the first and one behind the last membrane-electrode unit (1) Pole plate is arranged as the first or second end plate, the stack of distribution (3, 6) and collecting channels (4, 7) for supplying and removing o and hydrogen with respect to the between a membrane electrode

Unit (1) and the two adjacent bipolar plates (10) or between a bipolar plate (10) and an end plate each formed cathode and anode spaces and with the distribution (3, 6) and collecting channels (4, 7) branch channels branch off to the corresponding cathode or anode compartments, 5 characterized in

- That the membrane electrode units (1), the bipolar plates (10) and the end plates are each individually surrounded by a plastic frame (2,12),

- That the distribution (3, 6) and collecting channels (4, 7) and the branch channels in the plastic frame (2,12) are arranged and 0 - that the plastic frame (2, 12) for the sealed connection of the distribution and

Collection channels in the individual plastic frame (2,12) are glued or welded together.

2. Fuel cell according to claim 1, 5 characterized in that the membrane electrode units (1) are in each case encapsulated with the plastic frame (12).

3. Fuel cell according to claim 1 or 2, 0 characterized in that the bipolar plates (10) are in each case encapsulated with the plastic frame (12)

4. Fuel cell according to claim 1 or 2, characterized in 5 that the bipolar plates (10) each as a whole as an integral component from one

Plastic are formed.

5. Fuel cell according to one of claims 1 to 4, characterized in that the bipolar plates (10) have at least one cavity for the passage of a cooling medium and the plastic frame (2,12) with distribution (5) and collecting channels (8) for the cooling medium are provided, the distribution (5) and

Collection channels (8) in the plastic frame (12) of the bipolar plates (10) each have a connection to the cavity, in particular a connection in the form of a branch channel.

6. Fuel cell according to claim 5, characterized in that the bipolar plates (10) are double-walled.

7. Fuel cell according to claim 6, characterized in that the bipolar plates (10) are filled with a fleece (9), in particular a fleece (9) made of electrically conductive plastic.

8. Fuel cell according to claim 5, characterized in that the bipolar plates (10) are traversed by cooling channels.

9. Fuel cell according to one of claims 1 to 8, characterized in that the distribution (3, 5, 6) and collecting channels (4, 7, 8) are integrally formed by injection molding.

10. Fuel cell according to one of claims 1 to 9, characterized in that the distribution channels (3, 5, 6) and the collecting channels (4, 7, 8) for the supply and discharge of hydrogen, oxygen and cooling medium each diametrically on each other opposite sides of the plastic frame (2,12) are arranged.

11. Fuel cell according to one of claims 1 to 10, characterized in that the bipolar plates (10) have a plastic frame (12) made of electrically conductive plastic.

12. Fuel cell according to one of claims 1 to 11, characterized in that the membrane electrode units (1) each have a plastic frame (2) made of electrically non-conductive plastic.

13. Fuel cell according to claim 12, characterized in that the electrically non-conductive plastic s-poly (acetylene) (PAC), trans-poly (acetylene) (PAC), poly (p-phenylene) (PPP), poly (-phenylene) (PMP), poly (pyrrole) (PPY), poly (thiophene) (PTP), poly (p-phenylene sulfide) (PPS) or

Poly (aza sulfen) (PAS) is.

14. Fuel cell according to one of claims 1 to 13, characterized in that the catalyst used for the membrane electrode units (1)

Precious metals, Raney nickel, tungsten carbide, molybdenum or tungsten sulfides or phthalocyanine or other chelate complexes.

15. Fuel cell according to one of claims 5 to 8, characterized in that the bipolar plates (10) are each made in the form of a honeycomb structure made of metal or two electrically connected metal foils.

16. Fuel cell according to one of claims 1 to 15, characterized in that the end plates consist of electrically conductive plastic.

17. Fuel cell according to one of claims 1 to 16, characterized in that the end plates connections for gas supply and cooling and for

Have tapping of the electrical current.

18. Fuel cell according to one of claims 11 to 17, characterized in that between a bipolar plate (10) and a membrane electrode unit (1) each have a fleece (9), in particular a fleece (9) made of electrically conductive plastic or metal , is arranged.

19. Fuel cell according to one of claims 11 to 18, characterized in that the electrically conductive plastic doped s-poly (acetylene) (PAC), doped fra / 7s-poly (acetylene) (PAC), doped poly (p-phenylene) (PPP), doped poly (m-phenylene) (PMP), doped poly (pyrrole) (PPY), doped polyfthiophene) (PTP), doped poly (p-phenylene sulfide) (PPS) or doped poly (azasulfen) (PAS) is.

20. Vehicle with a fuel cell according to one of claims 1 to 19.