DE102017101954A1 - Membrane electrode assembly and fuel cell stack - Google Patents

Abstract

The invention relates to a membrane electrode arrangement (14) for a fuel cell stack (10) comprising a membrane (152), two catalytic electrodes (143) adjoining on both sides and a supporting and / or arranged on at least one edge of the membrane (152). or sealing layer (150), and a fuel cell stack (10) in which a plurality of such membrane-electrode assemblies (14) and bipolar plates (16) are stacked alternately. It is provided that an edge (151) of the membrane electrodes Arrangement (14) extending at the edge, in cross section has a greater height (h) than a height (h) of the stack of membrane (152) and catalytic electrodes (143).

Description

The invention relates to a membrane-electrode assembly for a fuel cell stack comprising a membrane, two catalytic electrodes adjoining on both sides and a supporting and / or sealing layer surrounding the membrane and forming peripheral regions, wherein supply openings for supplying and discharging operating media are provided in the peripheral regions available. The invention further relates to a fuel cell stack having such a membrane electrode assembly and a fuel cell system having such a fuel cell stack or such a membrane-electrode assembly.

Fuel cells use the chemical transformation of a fuel with oxygen to water to generate electrical energy. For this purpose, fuel cells contain as a core component the so-called membrane electrode assembly (MEA for membrane electrode assembly), which is a microstructure of an ion-conducting (usually proton-conducting) membrane and in each case on both sides of the membrane arranged catalytic electrode (anode and cathode). The latter mostly comprise supported noble metals, in particular platinum. In addition, gas diffusion layers (GDL) can be arranged on both sides of the membrane-electrode assembly on the sides of the electrodes facing away from the membrane. As a rule, the fuel cell is formed by a multiplicity of stacked MEAs whose electrical powers add up. As a rule, bipolar plates (also called flow field plates or separator plates) are arranged between the individual membrane electrode assemblies, which ensure that the individual cells are supplied with the operating media, ie the reactants, and are usually also used for cooling. In addition, the bipolar plates provide an electrically conductive contact to the membrane-electrode assemblies.

During operation of the fuel cell, the fuel (anode operating medium), in particular hydrogen H ₂ or a hydrogen-containing gas mixture, is supplied to the anode via an anode-side open flow field of the bipolar plate, where an electrochemical oxidation of H ₂ to protons H ⁺ takes place with release of electrons (H ₂ → 2 H ⁺ + 2 e ^- ). Via the electrolyte or the membrane, which separates the reaction spaces gas-tight from each other and electrically isolated, takes place (water-bound or anhydrous) transport of the protons from the anode compartment into the cathode compartment. The electrons provided at the anode are supplied to the cathode via an electrical line. The cathode is supplied via a cathode-side open flow field of the bipolar plate oxygen or an oxygen-containing gas mixture (for example, air) as a cathode operating medium, so that a reduction of O ₂ to 2 O ^2- taking up the electrons takes place (½ O ₂ + 2 e → O ^{2 -} ). At the same time, the oxygen anions in the cathode compartment react with the protons transported via the membrane to form water (O ^2- + 2 H ⁺ → H ₂ O).

The supply of the fuel cell stack with its operating media, ie the anode operating gas (for example hydrogen), the cathode operating gas (for example air) and the coolant, via main supply channels, which are formed by corresponding present in the membrane electrode assemblies and bipolar plates supply openings and the Enforce stack in its entire stacking direction. From the main supply channels, the operating media are supplied to the individual cells via the bipolar plates. For each operating medium at least two such main supply channels are present, namely one for feeding and one for discharging the respective operating medium.

Within a fuel cell stack, the individual cells must be electrically isolated from each other to prevent electrical shorting or sparking. In the course of ever-increasing current densities of fuel cells, however, the cell heights of the individual cells are increasingly reduced. As a result, however, reduces the gap between two individual cells, in particular between two adjacent bipolar plates, whereby the creepage distance shortened and thus increases the risk of electrical short circuit or sparkover.

A known measure to counteract this problem is to increase the plate sizes of the membrane-electrode units slightly opposite to those of the bipolar plates, so that edge regions of the membrane-electrode assemblies protrude beyond the edges of the bipolar plates something. In this way, the creepage distance is increased. A disadvantage of this solution, however, is that an enlargement of the overall volume of the entire stack is accompanied by the enlargement of the MEA. Thus, the extent of the overhang of the MEA over the bipolar plates are limited. In addition, a centering by means of stop due to lack of rigidity of the membrane is not possible or only with difficulty.

In addition, is off EP 1 612 877 B1 It is known to impregnate the edge regions of the membrane-electrode assembly and to compress the non-impregnated region more strongly.

To increase the creepage distance beats the US 7,033,694 A further, to make the membrane-electrode assembly taper to the outside, to increase the outer circumference. In this case, however, centering by means of a stop is impossible.

The present invention is therefore based on the object to enable improved internal electrical insulation of the individual cells of a fuel cell stack, without taking an excessive space expansion of the stack in purchasing.

This object is achieved by a membrane electrode assembly, a fuel cell stack and a fuel cell system with the features of the independent claims.

Thus, a first aspect of the invention relates to a membrane electrode assembly for a fuel cell stack comprising a membrane, two catalytic electrodes adjoining on both sides and a supporting and / or sealing layer arranged on at least one edge of the membrane, wherein supply openings for the supply and discharge of Operating media are available. According to the invention, it is provided that an edge of the membrane-electrode arrangement which runs along its edge has a greater height (h _D ) in cross-section than a height (h _MEA ) of the stack of membrane and catalytic electrodes.

The membrane-electrode arrangement according to the invention has improved insulation properties compared with membrane-electrode arrangements of the prior art. In particular, a creepage distance is increased, thus increasing the dielectric strength of a membrane-electrode arrangement according to the invention arranged in a fuel cell. The creepage distance is increased in the edge region by the arrangement of the support and / or sealing layer, since this layer has a larger circumference than the membrane in the edge region. This is ensured in particular by the height h _D , which according to the invention is greater than the height h _{MEA of} the stack of catalytic layer / membrane / catalytic layer. Depending on the configuration of the support and / or insulation layer, the creepage distance corresponds at least to the height h _D. Since the insulation properties of the membrane electrode assembly are proportional to the length of the creepage distance, these are increased in the membrane electrode assembly according to the invention.

In other words, according to the invention, the supporting and / or sealing layer projects over based on a cross section by an amount h _Ü over the surface of the catalytic layer. This supernatant is preferably formed as an edge or as a step. Depending on the configuration of the supporting and / or sealing layer, the height h _D may correspond to the sum of anode and cathode-side projection h _Ü and thickness of the stack of membrane and catalytic coating or even exceed this.

In addition, the membrane-electrode assembly according to the invention exhibits an increased rigidity compared to known membrane-electrode assemblies. Depending on the design of the support and / or insulation layer, the membrane is reinforced on at least one edge by the support and / or insulation layer. Since the height of the layer h _D exceeds that of the stack h _MEA , the rigidity is increased at least along the edge. With the increased stiffness better centerability and better stability of the membrane-electrode assembly are connected. The outer edge of the support and / or sealing layer forms a centering edge, which can be used as a stop. A conventional membrane, which has no support element, can not be centered by means of a stopper, especially not when, to achieve a set minimum creepage distance, the membrane projects beyond the edge of an adjacent bipolar plate.

The support and / or sealing layer has a supporting and / or sealing function. In a particularly preferred embodiment, both properties come to you simultaneously. The support and / or sealing layer is arranged on at least one edge of the membrane. In this case, it extends along the edge and encloses the outer edge of the membrane along the edge, so that the support and / or sealing layer on a side facing away from the active region of the membrane-electrode assembly extends beyond the membrane. Thus, the support and / or sealing layer (S / D layer) is preferably arranged on both sides of the membrane. Preferably, the S / D layer is disposed on the catalytic coating. Alternatively, the membrane-electrode assembly has no catalytic coating in the region of the S / D layer.

In the cross-section of the membrane-electrode assembly, there are three mutually adjacent regions which are formed from the inside to the outside (ie from the active region of the membrane-electrode assembly to the edge) as a layer stack as follows: catalytic coating / membrane / catalytic coating, S / D layer / catalytic coating / membrane / catalytic coating / S / D layer and S / D layer.

The S / D layer is designed as an electrical insulator and preferably comprises a plastic or a polymer which can be applied liquid, in particular can be sprayed. The S / D layer is preferably arranged by injection molding on the membrane-electrode assembly.

In a preferred embodiment, the support and / or sealing layer runs on at least two, in particular adjacent edges of the membrane. This embodiment increases the rigidity of the entire membrane-electrode assembly.

With particular advantage, the support and / or sealing layer extends like a frame along all edges of the membrane. This embodiment has the greatest rigidity of the membrane-electrode arrangement among those mentioned. Compared to the embodiment in which two or less edges have an S / D layer, a frame-like S / D layer increases the rigidity and stability of the membrane-electrode assembly even at smaller dimensions. In other words, with a small number of coated edges, the S / D layer continues to project over the membrane. With respect to the adjacent regions described above, this means that the region in which the layer stack S / D layer / catalytic coating / membrane / catalytic coating / S / D layer is formed is narrower relative to a membrane surface, the more edges of the membrane-electrode assembly have an S / D layer. Particularly preferably, the range has a width in the range of 5 to 30 mm.

In a preferred embodiment it is further provided that the support and / or sealing layer in cross-section has a profile flattened on one or both sides and the edge has an outwardly tapered, in particular trapezoidal profile. In this embodiment, the creepage distance is further increased and thus further improves the insulation properties of the membrane electrode assembly. If a membrane-electrode arrangement is arranged in a fuel cell to form a bipolar plate, the S / D layer does not adjoin the adjacent bipolar plate over the entire adjacent area due to the tapered profile. The trapezoidal shape ensures the formation of a centering edge, as in 5 becomes clear.

Preferably, the outwardly tapering profile is symmetrical relative to the cross section of the membrane-electrode assembly, in particular mirror-symmetrical, wherein a median plane of the membrane in the extension direction forms the mirror plane.

Another aspect relates to a fuel cell stack having a plurality of alternately stacked bipolar plates and a membrane electrode assembly according to the invention. The fuel cell stack according to the invention is characterized even with reduced cell height by an increased life and good isolation of the individual cells.

Advantageously, the support and / or sealing layer extends at least partially between two bipolar plates and the bipolar plates have a recess in this region, which extends from the edge over a part of the support and / or sealing layer. This embodiment of the bipolar plate makes it possible that the height h _{D of} the S / D layer, in particular the projection height h _Ü , is greater than that of the stack h _MEA , without a pressure increase occurring in the edge regions during the pressing of the stack.

In a preferred embodiment, the recess has a height which corresponds at least to the supernatant h _{Ü of} the S / D layer over the surface of the catalytic coating. Furthermore, the recess extends from the outer edge of the bipolar plate to an edge of the S / D layer, that is to say to an interface of the areas of catalytic coating / membrane / catalytic coating / and S / D coating / catalytic coating / membrane / catalytic coating / S / D layer.

The S / D layer preferably adjoins the bipolar plate at least in this area.

On this basis, in a preferred embodiment, the S / D layer is no longer adjacent to the bipolar plate. In other words, a gap is then formed in the recess at least partially between the bipolar plate and the S / D layer, which, depending on the design of the S / D layer, tapers inwards, ie towards the active surface. This is achieved in particular by the arrangement of a membrane electrode assembly according to the invention in the embodiment with an outwardly tapering profile, when the return of the bipolar plate is formed with respect to a cross section substantially rectangular. These embodiments have the advantage that the creepage distance is increased by the length of the joint and thus contribute to a further increased insulation.

In an alternative embodiment, the recess is filled by the support and / or sealing layer. In other words, no gap is formed between the S / D layer and the bipolar plate, but instead their surfaces adjoin one another in a material-locking manner.

In both cases, it is preferred that the supporting and / or sealing layer protrudes from the fuel cell stack by a length (L). The resulting outer circumference of the S / D layer is significantly increased compared to a flush conclusion, whereby the creepage distance and thus the insulation are further increased.

With particular advantage, the S / D layer encloses a part of the edge of the bipolar plate, so is with the bipolar plate not only in the region of the recess, but also partially with a on the return adjacent the outer edge of the bipolar plate connected conclusively. This is particularly preferred when the return from the S / D layer is filled. This is done on one side of the membrane-electrode assembly, ie either on the anode-side or the cathode-side bipolar plate. Based on a cross-section results in an L-shape of the S / D layer, as in 7 shown as an example. Alternatively, a T-shape or double-L shape of the S / D layer is formed, that is, the S / D layer overlaps both with the anode-side and with the cathode-side bipolar plate (by way of example in FIG 6 shown).

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics.

The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with each other.

• 1 ein Blockschaltbild eines Brennstoffzellensystems gemäß einer bevorzugten Ausgestaltung;
• 2 eine Draufsicht auf eine Membran-Elektroden-Einheit;
• 3 eine Draufsicht auf eine Bipolarplatte;
• 4 eine Schnittansicht einer Einzelzelle eines Brennstoffzellenstapels gemäß einer bekannten Ausführung;
• 5 eine Schnittansicht einer Einzelzelle eines Brennstoffzellenstapels gemäß einer ersten Ausführung der Erfindung;
• 6 eine Schnittansicht einer Einzelzelle eines Brennstoffzellenstapels gemäß einer weiteren Ausführung der Erfindung;
• 7 eine Schnittansicht einer Einzelzelle eines Brennstoffzellenstapels gemäß einer weiteren Ausführung der Erfindung; und
• 8 eine Draufsicht auf eine Membran-Elektroden-Einheit in einer bevorzugten Ausführungsform der Erfindung.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

• 1 a block diagram of a fuel cell system according to a preferred embodiment;
• 2 a plan view of a membrane electrode assembly;
• 3 a plan view of a bipolar plate;
• 4 a sectional view of a single cell of a fuel cell stack according to a known embodiment;
• 5 a sectional view of a single cell of a fuel cell stack according to a first embodiment of the invention;
• 6 a sectional view of a single cell of a fuel cell stack according to another embodiment of the invention;
• 7 a sectional view of a single cell of a fuel cell stack according to another embodiment of the invention; and
• 8th a plan view of a membrane-electrode assembly in a preferred embodiment of the invention.

1 shows a fuel cell system generally designated 100 according to a preferred embodiment of the present invention. The fuel cell system 100 is part of a not further illustrated vehicle, in particular an electric vehicle having an electric traction motor, by the fuel cell system 100 is supplied with electrical energy.

The fuel cell system 100 comprises as a core component a fuel cell stack 10 containing a plurality of stacked single cells 11 having alternately stacked membrane-electrode assemblies (MEAs) 14 and bipolar plates 16 be formed (see detail). Every single cell 11 thus includes one MEA each 14 , which has an ion-conducting polymer electrolyte membrane (not shown in more detail here) and catalytic electrodes arranged on both sides, namely an anode and a cathode, which catalyze the respective partial reaction of the fuel cell conversion and in particular can be formed as coatings on the membrane. The anode and cathode electrodes comprise a catalytic material, such as platinum, supported on an electrically conductive high surface area support material, such as a carbon based material. Between a bipolar plate 16 and the anode thus becomes an anode compartment 12 formed and between the cathode and the next bipolar plate 16 the cathode compartment 13 , The bipolar plates 16 serve to supply the operating media in the anode and cathode rooms 12 . 13 and further provide the electrical connection between the individual fuel cells 11 ago. Optionally, gas diffusion layers may be interposed between the membrane-electrode assemblies 14 and the bipolar plates 16 may be arranged.

To the fuel cell stack 10 to supply with the operating media, the fuel cell system 100 on the one hand, an anode supply 20 and on the other hand, a cathode supply 30 on.

The anode supply 20 includes an anode supply path 21 which feeds an anode operating medium (the fuel), for example hydrogen, into the anode spaces 12 of the fuel cell stack 10 serves. For this purpose, the anode supply path connects 21 a fuel storage 23 with an anode inlet of the fuel cell stack 10 , The anode supply 20 further includes an anode exhaust path 22 that removes the anode exhaust gas from the anode spaces 12 via an anode outlet of the fuel cell stack 10 dissipates. The anode operating pressure on the anode sides 12 of the fuel cell stack 10 is about an actuating means 24 in the anode supply path 21 adjustable. In addition, the anode supply can 20 as shown, a fuel recirculation line 25 comprising the anode exhaust path 22 with the anode supply path 21 combines. The recirculation of fuel is common in order to return and utilize the fuel, which is mostly used in excess of stoichiometry, in the stack. In the fuel recirculation line 25 is another adjusting agent 26 arranged, with which the recirculation rate is adjustable.

The cathode supply 30 includes a cathode supply path 31 which is the cathode spaces 13 of the fuel cell stack 10 supplying an oxygen-containing cathode operating medium, in particular air which is drawn in from the environment. The cathode supply 30 further includes a cathode exhaust path 32 , which the cathode exhaust gas (in particular the exhaust air) from the cathode compartments 13 of the fuel cell stack 10 dissipates and optionally this feeds an exhaust system, not shown. For conveying and compressing the cathode operating medium is in the cathode supply path 31 a compressor 33 arranged. In the illustrated embodiment, the compressor 33 designed as a mainly electric motor driven compressor whose drive via a with a corresponding power electronics 35 equipped electric motor 34 he follows. The compressor 33 may also be through a in the cathode exhaust path 32 arranged turbine 36 (optionally with variable turbine geometry) are supported by a common shaft (not shown) driven. The turbine 36 represents an expander, which causes an expansion of the cathode exhaust gas and thus a reduction of its pressure.

The cathode supply 30 may also according to the illustrated embodiment, a wastegate line 37 having the cathode supply line 31 with the cathode exhaust gas line 32 connects, so a bypass of the fuel cell stack 10 represents. The wastegate pipe 37 allows the operating pressure of the cathode operating medium in the fuel cell stack in the short term 10 reduce without the compressor 33 shut down. One in the wastegate pipe 37 arranged adjusting means 38 allows control of the amount of the fuel cell stack 10 immediate cathode operating medium. All adjusting means 24, 26, 38 of the fuel cell system 100 can be designed as controllable or non-controllable valves or flaps. Corresponding further actuating means can be in the lines 21 , 22, 31 and 32 to the fuel cell stack 10 isolate from the environment.

The fuel cell system 100 may also be a humidifier module 39 exhibit. The humidifier module 39 on the one hand is in the cathode supply path 31 arranged so that it can be flowed through by the cathode operating gas. On the other hand, it is so in the cathode exhaust path 32 arranged so that it can be flowed through by the cathode exhaust gas. The humidifier 39 typically has a plurality of water vapor permeable membranes formed either flat or in the form of hollow fibers. In this case, one side of the membranes is overflowed by the comparatively dry cathode operating gas (air) and the other side by the comparatively moist cathode exhaust gas (exhaust gas). Driven by the higher partial pressure of water vapor in the cathode exhaust gas, there is a transfer of water vapor across the membrane in the cathode operating gas, which is moistened in this way.

Various other details of the anode and cathode supply 20 . 30 are in the simplified 1 not shown for reasons of clarity. Thus, in the anode and / or cathode exhaust path 22 . 32 a water separator may be installed to condense and drain the product water resulting from the fuel cell reaction. Finally, the anode exhaust gas line 22 into the cathode exhaust gas line 32 lead, so that the anode exhaust gas and the cathode exhaust gas are discharged via a common exhaust system.

The 2 and 3 each show in a plan view of an exemplary membrane-electrode assembly 14 or bipolar plate 16 which the fuel cell stack 10 constitute.

Both components are subdivided into an active area AA and inactive areas IA , The active area AA is characterized by the fact that fuel cell reactions take place in this area. For this purpose, the membrane electrode assembly 14 in the active region AA on both sides of the polymer electrolyte membrane, a catalytic electrode 143 on. The inactive areas IA , each can be divided into service areas SA and distribution areas THERE divide. Within the service areas SA are supply openings 144 to 147 from the membrane electrode assembly 14 respectively 164 to 169 from the bipolar plate 16 arranged in the stacked state substantially aligned with each other and form main supply channels in the fuel cell stack. The anode inlet openings 144 and 164 serve to supply the anode operating gas, ie the fuel, for example hydrogen. The anode outlet openings 145 or 165 serve the discharge of the anode exhaust gas after overflow of the active area AA , The cathode inlet openings 146 respectively 166 serve to supply the cathode operating gas, which is in particular oxygen or an oxygen-containing mixture, preferably air. The cathode outlet openings 147 respectively 167 serve the discharge of the cathode exhaust gas after overflow of the active area AA , The coolant inlet openings 148 respectively 168 serve the supply and the coolant outlet 149 respectively 169 the discharge of the coolant.

The MEA 14 has an anode side 141 on that in 2 is visible. Thus, the illustrated catalytic electrode 143 formed as an anode, for example as a coating on the polymer electrolyte membrane. In the 2 invisible cathode side 142 has a corresponding catalytic electrode, here the cathode. The polymer electrolyte membrane can spread over the entire spread of the membrane electrode assembly 14 extend, but at least over the active area AA ,

The MEA 14 also has a, the membrane enclosing and this frame-like surrounding support and sealing layer 150 in the example shown, over the entire inactive area IA extends, as it were formed, and the electrodes 143 enclosing all around. The support and sealing layer 150 also forms a border area 151 out, the MEA 14 along its entire circumference revolves and has a flattened profile, which will be explained later in more detail. In addition, also the supply openings 144 to be formed 149 with such a flattened edge (not shown here).

In the 3 illustrated bipolar plate 16 also has a visible cathode side in the illustration 162 on and an invisible anode side 161 , In typical embodiments, the bipolar plate is 16 composed of two joined plate halves, the anode plate and the cathode plate. On the illustrated cathode side 162 Operating fluid channels 163 are formed as open channel-like channel structures, which the cathode inlet opening 166 with the cathode outlet opening 167 connect. Only five exemplary resource channels are shown 163 , where usually a much larger number is available. Likewise, the not visible here anode side 161 corresponding resource channels, which the anode inlet opening 164 connect to the anode outlet port 165. These operating medium channels for the anode operating medium are also designed as open, channel-like channel structures. Inside the bipolar plate 16 , in particular between the two plate halves, extend enclosed coolant channels, which the coolant inlet opening 168 with the coolant outlet opening 161 connect. With the broken lines are in 3 Seals indicated.

As already mentioned, those in the 2 and 3 shown membrane-electrode assemblies 14 and bipolar plates 16 alternately arranged on each other and pressed fluid-tight between two end plates, so as to form a fuel cell stack 10 train. This will be the bipolar plates 16 interconnected via an external circuit to remove the generated power. On the other hand, the individual cells, especially the bipolar plates 16 , electrically isolated from each other.

The 4 . 5 . 6 and 7 show a section through an edge region of a single cell 11 a corresponding fuel cell stack 10 according to the in 2 and 3 shown section plane. 4 shows a known embodiment and the 5 . 6 and 7 each represent an embodiment according to the present invention. Corresponding elements are designated by the same reference numerals.

Each of the membrane-electrode assemblies 14 of the 4 to 7 has a polymer electrolyte membrane 52 which is in the active region AA through the two catalytic electrodes 143 will be contacted. The electrodes 143 may be present as a coating of the membrane, as a self-supporting layer or as a coating of gas diffusion layers, not shown here, which are on both sides of the MEA 14 connect. In the 4 to 7 is also recognizable that the support and / or sealing layer 150 in one piece to the edge of the membrane 152 is formed. This can be done for example by an injection molding process or the like. For example, the layer 150 made of a silicone material. It may also have a bead (not shown here), which is a circumferential seal to the bipolar plates 16 forms. In an alternative embodiment, the membrane 152 in its edge region also be laminated on one side by one or both sides with two support and / or sealing layers (not shown).

According to the execution according to 4 overlaps the membrane-electrode assembly 14 the bipolar plates 16 in the form of an overhang with a length L , This results in a creepage distance, resulting from the distances designated K in 4 results and which of electrical charge carriers must be overcome to the two bipolar plates 16 short-circuit. The longer the creepage distance K is, the lower the probability that it will be overcome by electric charge carriers and the better the single cells 11 electrically isolated from each other. Thus, the insulation effect can be improved by the overhang length L is enlarged. However, this leads to an increase in the volume of the fuel cell stack 10 which is particularly undesirable in mobile applications in which space is limited.

The 5 . 6 and 7 show a corresponding sectional view of a single cell 11 a fuel cell stack 10 with a membrane electrode assembly 14 according to one embodiment of the invention. The membrane electrode assembly 14 has a supporting and / or sealing layer (S / D layer) 150 on the edge shown. This has a height h _D on, which is greater than the height h _MEA the membrane or the stack catalytic coating / membrane / catalytic coating. The S / D layer 150 thus projects beyond a surface of the membrane 152 arranged catalytic coating. The proportions are for illustrative purposes only and are not intended to be quantitative. The bipolar plates 16 The individual cells shown each have a return 170 on. This is formed substantially rectangular and has a height corresponding to a degree to which the S / D layer 150 projects beyond the surface of the catalytic coating. The S / D layer 150 protrudes by one length L from an escape of the edges of the bipolar plates 16 out. The creepage distance K , which results from the distances indicated by K and which must be overcome by electrical charge carriers to the two bipolar plates 16 Short circuit results from the length L based on the anodically adjacent bipolar plate 16 , from the height h _D the S / D layer 152 and again the length L , based on the cathodic to the membrane 152 adjacent bipolar plate 16 , Because of the difference h _D - h _MEA and the specific configuration of the shape of the S / D layer 150 is the resulting creepage distance K in a fuel cell stack according to the invention at a defined volume in comparison to that in FIG 4 shown enlarged fuel cell stack.

The profile of the S / D layer 150 is in the embodiments of 5 and 6 formed symmetrically to a plane of symmetry, that of the median plane of the membrane 152 equivalent.

In 5 The S / D layer 152 has a trapezoidal cross section. The result is a gap between bipolar plate 16 or the edge of the return 170 and the S / D layer 150.

The in the 6 and 7 shown embodiments show an S / D layer, the return 170 the bipolar plate 16 fills. It is in 6 3 shows a symmetrical configuration in which the profile of the membrane electrode assembly (FIG. 14 ) on both sides of the membrane has the same profile and also the recesses 170 the two adjacent bipolar plates 16 are designed point-symmetrically. On the other hand shows the 7 an asymmetrical profile of the S / D layer 150 and different sized recesses 170 the adjacent bipolar plates 16 ,

In 6 For example, the S / D layer 150 has an L-profile with a leg along a depth of the recess 170 extends and a leg along the edge of the bipolar plate 16 runs. Throughout the area, the S / D layer is adjacent to the bipolar plate 16 at. There is no fugue. In 7 is the described profile of the S / D layer on both sides of the membrane 152 formed so that a double-L profile or a T-profile is formed.

LIST OF REFERENCE NUMBERS

100

The fuel cell system

10

fuel cell stack

11

single cell

12

anode chamber

13

cathode space

14

Membrane electrode assembly (MEA)

141

anode side

142

cathode side

143

catalytic electrode / anode

144

Supply opening / anode inlet opening

145

Supply opening / anode outlet opening

146

Supply opening / cathode inlet opening

147

Supply opening / cathode outlet opening

148

Supply opening / coolant inlet opening

149

Supply opening / coolant outlet opening

150

Support and / or sealing layer

151

centering edge

152

Membrane / polymer electrolyte membrane

16

Bipolar plate (separator plate, flow field plate)

161

anode side

162

cathode side

163

Resource channel (reactant channel)

164

Supply opening / anode inlet opening

165

Supply opening / anode outlet opening

166

Supply opening / cathode inlet opening

167

Supply opening / cathode outlet opening

168

Supply opening / coolant inlet opening

169

Supply opening / coolant outlet opening

170

return

20

anode supply

21

Anode supply path

22

Anode exhaust gas path

23

fuel tank

24

actuating means

25

Brennstoffrezirkulationsleitung

26

actuating means

30

cathode supply

31

Cathode supply path

32

Cathode exhaust path

33

compressor

34

electric motor

35

power electronics

36

turbine

37

Waste gate line

38

actuating means

39

humidifier

AA

Active area (reaction area, active area)

IA

Inactive area

SA

Supply area

THERE

Distribution area

L

Overhang

K

creepage

B

Width of the flattened edge

h _MEA

Height of the stack of membrane and adjacent catalytic coatings

h _D

Height of the support and / or sealing layer

h _R

Height return

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

• EP 1612877 B1 [0007]
• US7033694A [0008]

Claims (10)

Membrane-electrode arrangement (14) for a fuel cell stack (10) comprising a membrane (152), two catalytic electrodes (143) adjoining on both sides and a supporting and / or sealing layer (150) arranged on at least one edge of the membrane (152) ), wherein supply openings (144-149) for supply and discharge of operating media are present, characterized in that an edge of the membrane-electrode assembly (14) extending at the edge, in cross-section has a height (h _D ) greater than a height (h _MEA ) of a stack of membrane (152) and catalytic electrodes (143). Membrane electrode assembly (14) according to Claim 1 , characterized in that the support and / or sealing layer (150) extends on at least two, in particular adjacent, edges of the membrane (152). Membrane electrode assembly (14) according to Claim 1 , characterized in that the support and / or sealing layer (150) extends along all edges of the membrane (152). Membrane-electrode assembly (14) according to any one of the preceding claims, characterized in that the support and / or sealing layer (150) has a flattened profile in cross-section and the edge has an outwardly tapering, in particular trapezoidal profile. A fuel cell stack (10) comprising a plurality of alternately stacked bipolar plates (16) and membrane electrode assemblies (14) according to any one of Claims 1 to 4 , Fuel cell stack (10) after Claim 5 , characterized in that the support and / or sealing layer (150) extends at least partially between two bipolar plates (16) and the bipolar plates (16) in these areas have a recess (170) extending from the edge along a portion of the support - and / or sealing layer (150) extends. Fuel cell stack (10) according to one of Claims 5 or 6 , characterized in that at least in regions between the support and / or sealing layer (150) and the bipolar plate (16) is formed a gap which, in particular in the direction of a center of the membrane (152), tapers. Fuel cell stack (10) according to one of Claims 5 to 7 , characterized in that the recess (170) of the support and / or sealing layer (150) is filled. Fuel cell stack (10) according to one of Claims 5 to 8th , characterized in that the support and / or sealing layer (150) protrudes by a length (L) from an alignment of the fuel cell stack (10). Fuel cell system comprising a fuel cell stack (10) according to one of Claims 5 to 9 ,

Images