EP2417663A1

EP2417663A1 - Fuel cell, fuel cell stack and method for sealing a fuel cell

Info

Publication number: EP2417663A1
Application number: EP10713834A
Authority: EP
Inventors: Christian Martin Erdmann; Eyuep Akin ÖZDENIZ; Tobias Lux
Original assignee: Daimler AG
Current assignee: Mercedes Benz Group AG
Priority date: 2009-04-08
Filing date: 2010-04-06
Publication date: 2012-02-15
Also published as: DE102009016934A1; CN102388493A; JP2012523656A; WO2010115605A1; US20120034546A1

Abstract

The invention relates to a fuel cell (1) comprising a membrane electrode assembly (2). The membrane electrode assembly (2) is arranged between two bipolar plates (5, 6) and is connected to a sealing element (3). The sealing element (3) and the bipolar plates (5, 6) contact each other while forming a contact region (10). A sliding surface (11), which can be used to apply transverse stress (15) to the membrane electrode assembly (2) arranged between the two bipolar plates (5, 6) when the two bipolar plates (5, 6) are pressed together, is provided in the contact region (10). The invention further relates to a fuel cell stack comprising such a fuel cell (1) and to a method for sealing a fuel cell (1).

Description

Fuel cell, fuel cell stack and method for sealing a fuel cell

The invention relates to a fuel cell with a membrane-electrode arrangement, which is arranged between a first distribution element for charging an anode of the membrane electrode assembly with a fuel and a second distribution element for charging a cathode of the membrane-electrode assembly with an oxidizing agent , The fuel cell comprises a sealing element, which is connected to the membrane electrode assembly. Here, the sealing element and at least one of the distribution elements are at least partially contacted, whereby a contact area is formed. Furthermore, the invention relates to a fuel cell stack with a plurality of such fuel cells and a method for sealing a fuel cell.

EP 1 614 181 B1 describes a membrane-electrode assembly with integrated seal. A sealing element arranged at an edge of the membrane-electrode arrangement is formed in a connection region between the seal and the membrane-electrode arrangement in such a way that sealing material penetrates pores of the cathode or of the anode. The porous electrodes are thus saturated in the connection region with the material of the sealing element. In the connection region, the sealing material forms a cushion whose thickness is greater than a thickness of the planar membrane-electrode arrangement. The sealing material also forms a second, more towards the edge of the outside than the cushion arranged sealing bead, wherein a thickness of the sealing bead is greater than a thickness of the pad. If the membrane-electrode assembly with the integrated seal is now arranged between two bipolar plates, then the sealing bead is received in grooves of the bipolar plates. The grooves have a width that in addition to the sealing bead and the cushion is added. If the bipolar plates are then pressed together, the peripheral sealing bead deforms. The sealing bead can be relatively compressed during compression of the bipolar plates and thereby deformed without the compression of the sealing element leads to a shear stress in the region of the pad. This ensures that the compression of the sealing element does not lead to a detachment of the seal from the membrane-electrode assembly in the connection region. Formed on the pad is a bevel which, prior to compression of the bipolar plates, is brought into abutment with a groove formed in the groove to properly align and center the bipolar plates with respect to the membrane-electrode assembly.

The object of the present invention is to provide an improved fuel cell of the aforementioned type, an improved fuel cell stack and an improved method for sealing a fuel cell.

This object is achieved by a fuel cell having the features of patent claim 1. Furthermore, this object is achieved by a fuel cell stack having the features of patent claim 13, and by methods having the features of patent claim 14. Advantageous embodiments with expedient developments of the invention are specified in the respective dependent claims.

The fuel cell according to the invention comprises a membrane-electrode arrangement which is arranged between two distribution elements. A first of the two distribution elements is used to apply a fuel to an anode of the membrane-electrode arrangement. The second distribution element is used to apply a cathode to an electrode of the membrane-electrode assembly with an oxidizing agent. A sealing element is connected to the membrane-electrode assembly. Here, the sealing element and at least one of the distribution elements at least partially in contact, so that a contact area is formed. In the contact area, a sliding surface is provided, by means of which, when the two distribution elements are compressed, a shear stress can be applied to the membrane-electrode arrangement arranged between the two distribution elements.

When pressure is applied perpendicular to the planar membrane-electrode assembly (MEA) as the two distributing members are compressed toward each other, the shear stress applied to the membrane-electrode assembly acts tangentially to the membrane-electrode assembly. As a result, when the distributor elements are compressed, the membrane-electrode arrangement arranged between them can be tensioned in the direction of the shear stress. In the unpressed state of the fuel cell, in other words, before the compression of the two distribution elements, an area occupied by the membrane-electrode arrangement and the sealing element connected thereto is smaller than a surface in the compressed state in which the two distribution elements are compressed. As a result of the sliding along the sliding surface caused when the two distributing elements are compressed, the membrane-electrode arrangement can therefore be converted into a defined clamping state.

As a result, a defined seal between the membrane electrode assembly and the respective distribution element and a defined seal between the two distribution elements can be achieved. Leaks are so particularly safe and particularly largely avoidable over a long period of operation of the fuel cell. The arranged in this way between the distribution elements sealing element also ensures a particularly good insulation of the distribution elements from each other.

Such a fuel cell allows a cost-effective, particularly reliable and reproducible assembly. In addition, the fuel cell has a particularly long life.

In an advantageous embodiment of the invention, the sliding surface is provided as a slope on the sealing element. During the compression of the two distribution elements, at least one of the distribution elements slides down along the slope and thus acts on the membrane-electrode arrangement with the shear stress.

Alternatively, but preferably in addition, a further sliding surface is provided as a slope on at least one of the two distribution elements. In particular, it is advantageous if the two distribution elements have the bevel, which correlate with a respective slope on the sealing element. Upon compression of the two distribution elements then slide the slips along each other and thus cause the tensioning of the membrane-electrode assembly. The provision of the bevels on both the sealing element and on the two distribution elements simplifies a particularly low-friction sliding along the slopes to each other.

It is particularly advantageous if, in the direction of the shear stress, a length of the slope on the sealing element is equal to a length of the slope on the distribution element. As a result, a comparatively large sliding surface is provided, which enables a particularly extensive reduction of the sliding friction of the bevels. As a further advantage, it has been shown when adjacent to at least one end of the at least one sliding surface in the direction of the shear stress a contact surface. Preferably, this contact surface is flat. Furthermore, planar contact surfaces can adjoin at both ends of the sliding surface. Such a contact surface provides - in the compressed state of the fuel cell - another contact area between the sealing element and at least one of the distribution elements, so that is provided by the sealing element in the direction of the shear stress particularly wide Dichtsaum.

If the abutment surface is of a planar design, a particularly high sealing force can be achieved in the region of the abutment surface when the distributor element is compressed with the membrane-electrode assembly arranged between the two distributor elements. In particular, a constant and constantly high surface pressure between the sealing element and the distribution elements can be achieved when the distribution elements are compressed.

If the at least one sliding surface is formed circumferentially around the membrane-electrode arrangement, when the membrane-electrode arrangement is acted upon by the shear stress, a circulating and defined clamping of the membrane-electrode arrangement takes place. Preferably learns with the

Membrane electrode assembly connected sealing element during compression of the distribution elements an equidistant, circumferential circumferential enlargement.

In a further advantageous embodiment of the invention is provided by the sealing element, in particular a more rigid frame for the membrane-electrode assembly. The membrane-electrode assembly with the connected thereto sealing element is so easy to handle.

As a further advantage, it has been shown that the, in particular an elastomer comprehensive, sealing element is welded to the membrane-electrode assembly. The joining of the membrane-electrode arrangement comprising a polymer electrolyte membrane (PEM) to the sealing element by a plastic welding process ensures a particularly secure connection of the sealing element to the membrane-electrode arrangement, which resistance is the shear stress when the distribution elements are compressed. The elastic sealing element may be formed as a thermoplastic elastomer, and / or rubber and / or silicone material. A particularly simple mounting of the fuel cell by arranging the distribution elements and the membrane-electrode assembly with the sealing element is achievable if the respective distribution element has a symmetry plane parallel to the membrane-electrode arrangement. Thus, when mounting any side of the distribution element of the membrane electrode assembly may be facing. For simple and reliable assembly of the fuel cell, it is also advantageous if the two distribution elements are the same in shape and dimensions.

In a further advantageous embodiment of the invention, a distribution space for a reaction medium is provided by at least one of the distribution elements in at least one edge region adjoining the sealing element in cooperation with the membrane-electrode arrangement. In the compressed state of the distribution element with the membrane-electrode arrangement arranged between them, a gap with a constant, defined height between the membrane-electrode arrangement and the distribution element is advantageously provided. By providing such a gap of defined height through which the oxidizing agent or the fuel can flow, the passage of the fuel cell through the reaction medium can be ensured particularly well and particularly well reproducibly. As a result, in particular the electrochemical reactions are particularly easy to control. In particular, their consistency is to ensure over a particularly long period.

Preferably, one of the distribution elements, at least on a side facing the membrane electrode assembly, has a plurality of ribs, in particular parallel to one another. In the compressed state of the distribution elements with the membrane-electrode arrangement arranged therebetween, the ribs are then brought into contact with the membrane-electrode arrangement, so that it is particularly possible to achieve a constant surface pressure between the distribution element and the membrane-electrode arrangement.

Finally, it has proven to be advantageous if the distribution elements are electrically conductive. The distribution elements thus serve not only for distributing the reaction agent on the anode or the cathode, but in particular for contacting a plurality of fuel cells coupled to one another via the electrically conductive distribution elements.

The advantages of the invention are particularly evident in a fuel cell stack, which comprises a plurality of fuel cells according to the invention. If indeed a comparatively large number, for example 200 to 350 pieces, of individual fuel cells are to form the fuel cell stack, then the defined clamping of the respective membrane electrode assemblies can be used particularly meaningfully by the sliding surface provided in the contact region. By applying the individual membrane-electrode assemblies with the shear stress so namely a high density of the fuel cell stack and a constant surface pressure can be achieved. Also undefined flow-specific channel cross-sectional constrictions and undefined length expansions of the fuel cell stack are thus avoidable.

When assembling the fuel cell stack of individual fuel cells, a distribution element within the fuel cell stack is in each case in contact with a membrane-electrode arrangement arranged on the top side of the distribution element and with a membrane-electrode arrangement arranged on the bottom side of the same distribution element. In other words, one and the same distribution element each delimits two membrane-electrode assemblies of adjacent fuel cells from each other. Only in the case of the membrane-electrode assemblies arranged at the bottom and the top in the stack, does the distribution element close to an outside of the stack.

According to another aspect of the invention, there is provided an improved method of sealing a fuel cell in which a membrane-electrode assembly is connected to a sealing member, and wherein the membrane-electrode assembly is interposed between a first manifold member for urging an anode of the membrane assembly. Electrode arrangement is arranged with a fuel and a second distribution element for charging a cathode of the membrane-electrode assembly with an oxidizing agent to form a contact area. When the two distribution elements are compressed, at least one of the two distribution elements and the sealing element slide along one another, wherein a shear stress is applied to the membrane-electrode arrangement arranged between the distribution elements. As a result, the membrane-electrode arrangement is tensioned in the direction of the shear stress, ie perpendicular to the force acting upon compression of the two distribution elements.

The preferred embodiments and advantages described for the fuel cell according to the invention also apply to the fuel cell stack according to the invention and to the method according to the invention. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or shown alone in the figures can be used not only in the respectively specified combination but also in other combinations or in isolation, without the scope of To leave invention.

Further advantages, features and details of the invention will become apparent from the claims, the following description of preferred embodiments and from the drawings. Showing:

1 shows a detail of a perspective sectional view of a fuel cell, in which a membrane-electrode assembly is held stretched between two bipolar plates in an extension plane of the membrane-electrode assembly;

FIG. 2 shows a detail of a bipolar plate of the fuel cell according to FIG. 1 with a sealing frame arranged on the bipolar plate; FIG. and

3 is an enlarged perspective sectional view of an edge region of

Fuel cell according to FIG. 1.

Fig. 1 shows in a perspective sectional view of a fuel cell 1 of a fuel cell stack. The fuel cell 1 comprises a

Membrane electrode assembly 2 in which a polymer electrolyte membrane (PEM) separates a cathode from an anode. The planar, ie, flat in the direction of an X-Y plane extending, membrane-electrode assembly 2 is connected, in particular by welding with a sealing frame 3. In this case, the membrane-electrode assembly 2 is inserted into a groove 4 formed in the sealing frame 3 (see Fig. 2).

The sealing frame 3 is made of an elastomer and, according to FIG. 1, is in contact with a first bipolar plate 5 and with a second bipolar plate 6. The bipolar plates 5, 6 serve as distributing elements for charging the anode of the membrane electrode assembly 2 with a fuel and for charging a cathode of the membrane electrode assembly 2 with an oxidizing agent. In this case, the bipolar plates 5, 6 ensure that the fuel cell 1 supplied reactant evenly distributing a continuous electrochemical reaction to the respective electrodes.

From each of the bipolar plates 5, 6 are in the direction of a Z-axis which is perpendicular to the X-Y plane, ribs 7, wherein 7 channels are formed for the reagent between the mutually parallel ribs. The ribs 7 protrude from the bipolar plates 5, 6 both in the direction of the Z-axis and in a direction opposite to the direction of the Z-axis. The bipolar plates 5, 6 are each symmetrical with respect to a plane of symmetry which is parallel to the X-Y plane.

In a bordering on the sealing frame 3 edge region 8 of the bipolar plates 5, 6 no ribs are formed (see Fig .. 2), so that in this edge region 8 in the fuel cell 1 in cooperation with the membrane-electrode assembly 2, a distribution space 9 for the respective reaction agent is provided. A height of the distribution space 9 corresponds to a height of the ribs 7.

2, which shows the lower bipolar plate 6 with the sealing frame 3 arranged thereon, but without the membrane electrode assembly 2 in a sectional view, it can be seen that a contact region 10 in which the sealing frame 3 and the bipolar plates 5 6 are in contact, includes a slope 11. Towards the inside, the bevel 11 of the sealing frame 3 adjoins a first planar contact surface 12. Furthermore, the sealing frame 3 has a further, also flat contact surface 13 which adjoins the bevel 11 towards the outside. The slope 11 thus has an inclination to the X-Y plane, while the abutment surfaces 12, 13 are parallel to the X-Y plane.

On the bipolar plates 5, 6 corresponding bevels 11 and contact surfaces 12, 13 are provided, the function of which is described in mounting the fuel cell 1 with reference to FIG. 3.

When assembling the fuel cell 1, first, the membrane-electrode assembly 2 is connected to the sealing frame 3 by welding. The present rectangular sealing frame 3 summarizes here the membrane electrode assembly 2 circumferentially. In the not yet compressed state of the fuel cell 1, that is, before the Bipolarplatten 5, 6 with a force in Fig. 3 illustrated by force arrows pressing force 14 is a surface area of an assembly, which the membrane-electrode assembly 2 and the associated with this sealing frame. 3 comprises, smaller than a respective areal extent of the bipolar plates 5, 6. After the compression of the fuel cell 1, Thus, after the compression of the bipolar plates 5, 6 and the arranged between these membrane-electrode assembly 2 by applying the Bipolarplatten 5, 6 with the pressing force 14, however, the sealing frame 3 closes in the direction of the XY plane flush with the bipolar plates 5, 6 from , The assembly thus experiences as a result of the loading of the bipolar plates 5, 6 with the pressing force 14 an equidistant increase in area. This increase in area is accompanied by a defined tensioning of the membrane electrode assembly 2 in the XY plane.

When the bipolar plates 5, 6 are compressed, the bevels 11 provided on the sealing frame 3 and on the bipolar plates 5, 6 slide along one another until the respective contact surfaces 12, 13 of the sealing frame 3 and the bipolar plates 5, 6 lie on one another. The sliding of the bevels 11 together causes the diaphragm-electrode assembly 2 to be acted upon by a shear stress 15, that is to say with a force exciting the membrane-electrode assembly 2, which acts tangentially to the X-Y plane. The shear stress 15 is illustrated in FIG. 3 by another force arrow. One end of the sliding surface 11 serving as a slope 11 in the direction of the shear stress 15 is presently formed by a kink 16. The bend 16 thus delimits the bevel 11 from the respective contact surfaces 12, 13.

As soon as the respective contact surfaces 12, 13 of the bipolar plates 5, 6 and the sealing frame 3 are in contact with each other, the pressing force acts 14 on bipolar plates 5, 6 as sealing force on these contact surfaces 12, 13. Thus, over the entire of the respective bipolar plate 5, 6 facing side of the sealing frame 3 a full-surface and thus a particularly high tightness ensuring seal provided. Due to the sealing frame 3, the bipolar plates 5, 6 are also electrically isolated from each other in the compressed state of the fuel cell 1.

A distance 17 between the bipolar plates 5, 6 is defined and constant over the entire surface of the fuel cell 1 after the compression of the bipolar plates 5, 6 and bringing the abutment surfaces 12, 13 into engagement, so that the distribution spaces 9 of the fuel cell 1 also have a constant height extent.

This is ensured on the one hand by the identical shapes and dimensions of the bevels 11 and the contact surfaces 12, 13 on the sealing frame 3 and on the bipolar plates 5, 6, and on the other hand by the defined height of the ribs 7, which in compressed state of the fuel cell 1 with the membrane-electrode assembly 2 are in abutment.

The procedure described here using the example of a single fuel cell 1 for producing a frame-distance clamping gasket of the membrane-electrode assembly 2 via the sealing frame 3 is particularly advantageous in the assembly of a fuel cell stack applicable. When assembling the fuel cell stack, a large number of membrane-electrode assemblies 2 and bipolar plates 5, 6 stacked alternately and then clamped by applying the external bipolar plates 5, 6 with the pressing force 14. In the fuel cell stack are then the respective membrane-electrode assemblies 2 in a defined clamping state in which complete the respective sealing frame 3 flush with the bipolar plates 5, 6.

LIST OF REFERENCE NUMBERS

1 fuel cell

2 membrane electrode assembly

3 sealing frame

4 groove

5 bipolar plate

6 bipolar plate

7 rib

8 border area

9 distribution room

10 investment area

11 slope

12 contact surface

13 contact surface

14 press force

15 shear stress

16 kink

17 distance

Claims

claims

1. A fuel cell with a membrane-electrode assembly (2), which between a first distribution element (5) for applying an anode of the membrane-electrode assembly (2) with a fuel and a second distribution element (6) for applying a cathode

Membrane electrode assembly (2) is arranged with an oxidizing agent, and with a sealing element (3) which is connected to the membrane-electrode assembly (2), wherein the sealing element (3) and at least one of the distribution elements (5, 6) are contacted at least in regions and thereby a contact area (10) is formed, characterized in that in the contact area (10) has a sliding surface (11) is provided, by means of which at a compression of the two distribution elements (5, 6) between the two distribution elements (5, 6) arranged membrane electrode assembly (2) with a shear stress (15) can be acted upon.

2. Fuel cell according to claim 1, characterized in that a sliding surface as a slope (11) on the sealing element (3) is provided.

3. Fuel cell according to claim 1 or 2, characterized in that a further sliding surface as a slope (11) on at least one of the two distribution elements (5, 6) is provided.

4. Fuel cell according to claim 2 and 3, characterized in that in the direction of the shear stress (15), a length of the bevel (11) on the sealing element (3) is equal to a length of the bevel (11) on the distributor element (5, 6).

5. Fuel cell according to one of claims 1 to 4, characterized in that adjacent to at least one end (16) of the at least one sliding surface (11) in the direction of the shear stress (15), in particular flat, contact surface (12, 13).

6. Fuel cell according to one of claims 1 to 5, characterized in that the at least one sliding surface (11) around the membrane electrode assembly (2) is formed circumferentially.

7. Fuel cell according to one of claims 1 to 6, characterized in that by the sealing element, in particular a more rigid, frame (3) for the membrane-electrode assembly (2) is provided.

8. Fuel cell according to one of claims 1 to 7, characterized in that the, in particular an elastomer comprehensive, sealing element (3) with the membrane-electrode assembly (2) is welded.

9. Fuel cell according to one of claims 1 to 8, characterized in that, in particular in the form and dimensions of the same distribution elements (5, 6) each have a to the membrane-electrode assembly (2) parallel plane of symmetry.

10. Fuel cell according to one of claims 1 to 9, characterized in that by at least one of the distribution elements (5, 6) in at least one of the sealing element (3) adjacent edge region (8) in cooperation with the membrane electrode assembly (2 ) a distribution space (9) is provided for a reagent.

11. Fuel cell according to one of claims 1 to 10, characterized in that one of the distribution elements (5, 6) at least on one of the membrane electrode assembly (2) side facing a plurality of, in particular parallel to each other, ribs (7) ,

12. Fuel cell according to one of claims 1 to 11, characterized in that the distribution elements (5, 6) are electrically conductive.

13. A fuel cell stack, characterized in that the fuel cell stack comprises a plurality of fuel cells (1) according to one of claims 1 to 12.

14. A method for sealing a fuel cell (1), wherein a) a membrane electrode assembly (2) with a sealing element (3) is connected, b) the membrane electrode assembly (2) between a first distribution element (5 ) is arranged for applying an anode of the membrane electrode assembly (2) with a fuel and a second distribution element (6) for applying a cathode of the membrane electrode assembly (2) with an oxidizing agent to form a contact area (10), characterized in that upon compression of the two distribution elements (5, 6) at least one of the two distribution elements (5, 6) and the sealing element (3) slide along each other, wherein between the two distribution elements (5, 6) arranged

Membrane electrode assembly (2) with a shear stress (15) is applied.

15. The method according to claim 14, characterized in that it is carried out on a fuel cell (1) according to one of claims 1 to 12 or on a fuel cell stack according to claim 13.