阅读说明：本技术 燃料电池堆、用于制造燃料电池堆的方法和用于运行燃料电池堆的方法 (Fuel cell stack, method for producing a fuel cell stack and method for operating a fuel cell stack ) 是由 H·施迈瑟 U·贝尔纳 U·里格勒尔 J·韦斯内尔 F·A·克诺尔 于 2019-07-30 设计创作，主要内容包括：本发明涉及一种燃料电池堆(10)和一种用于制造这种燃料电池堆(10)的方法。在此,所述燃料电池堆(10)包括分别具有至少两个单电池(5)的至少两个燃料电池模块(58)和燃料电池堆压缩器件(82),其中,每个燃料电池模块(58)在两个电池堆外侧(66)上具有模块端板(70),所述堆叠在彼此上的燃料电池模块(58)通过所述燃料电池堆压缩器件被夹紧成燃料电池堆(10)。(The invention relates to a fuel cell stack (10) and a method for producing such a fuel cell stack (10). The fuel cell stack (10) comprises at least two fuel cell modules (58) each having at least two individual cells (5) and a fuel cell stack compression means (82), wherein each fuel cell module (58) has a module end plate (70) on two stack outer sides (66), by means of which the fuel cell modules (58) stacked on one another are clamped into the fuel cell stack (10).)

1. A fuel cell stack (10) comprising:

-at least two fuel cell modules (58) each having at least two individual cells (5), wherein each fuel cell module (58) has a module end plate (70) on two cell stack outer sides (66),

-a fuel cell stack compression means (82) by which fuel cell modules (58) stacked on one another are clamped into a fuel cell stack (10).

2. The fuel cell stack (10) according to claim 1, characterized in that module compression means (74) are provided by which the cells (5) of each fuel cell module (58) are clamped between the module end plates (70).

3. The fuel cell stack (10) of claim 2 wherein the module compression means (74) is a clamping band, wherein preferably each fuel cell module (58) has between five and eight clamping bands.

4. A fuel cell stack (10) according to claim 3, characterised in that the clamping band (74) is electrically insulated only in the region of the lateral contact faces of the individual cells (5).

5. The fuel cell stack (10) according to any one of the preceding claims, wherein each fuel cell module (58) has a current connector (71), preferably arranged on a module end plate (70).

6. The fuel cell stack (10) according to any one of the preceding claims, wherein each fuel cell module (58) has its own voltage control.

7. The fuel cell stack (10) according to any one of the preceding claims, wherein one or more module end plates (70) have a cooling distribution area (73).

8. The fuel cell stack (10) according to any one of the preceding claims, wherein one or more module end plates (70) have closable port feedthroughs (72).

9. The fuel cell stack (10) according to any one of the preceding claims, characterized in that an individual fuel cell module (58) can be separated from the current circuit (12) of the fuel cell stack (10) by means of an electrical switch (80).

10. The fuel cell stack (10) according to claim 9, characterized in that the single cells (5) of the fuel cell module (58) which can be separated from the current circuit (12) have a modified design.

11. The fuel cell stack (10) according to claim 10, characterized in that the single cells (5) of the fuel cell module (58) which can be separated from the current circuit (12) have a relatively small catalyst loading.

12. The fuel cell stack (10) according to any one of the preceding claims wherein each fuel cell stack (58) has its own hydrogen sensor.

13. A method for manufacturing a fuel cell stack (10) being a fuel cell stack according to any of the preceding claims, wherein the method comprises the steps of:

-stacking at least two single cells (5) of the fuel cell stack (10) on each other,

-arranging a module end plate (70) on two stack outsides (66) of single cells (5) stacked on each other,

-clamping the cells (5) between the module end plates (70) by means of module compression means (74) for forming a fuel cell module (58),

-checking the fuel cell module (58) for non-failure and/or tightness,

-stacking at least two fuel cell modules (58) so manufactured on top of each other,

-clamping the fuel cell modules (58) stacked on each other by means of a fuel cell stack compression device (82).

14. Method for manufacturing a fuel cell stack (10) according to claim 13, characterized in that the module compression means (74) are removed after clamping the fuel cell modules (58) stacked on each other.

15. The method for manufacturing a fuel cell stack (10) according to claim 13 or 14, characterized in that the single cells (5) are conditioned before stacking the fuel cell modules (58) on each other.

16. A method for operating a fuel cell stack (10) according to one of the preceding claims in a low-load region, wherein one or more module end plates (70) have a closable port lead-through (72), wherein an individual fuel cell module (58) can be separated from a current circuit (12) of the fuel cell stack (10) by means of an electrical switch (80), wherein the method comprises the following steps:

-separating the fuel cell module (58) from the gas supply, in particular by means of the closable port leadthrough (72).

-separating the same fuel cell module (58) from the current circuit (12) by means of at least one switch (80).

Technical Field

The invention relates to a fuel cell stack, a method for producing a fuel cell stack and a method for operating a fuel cell stack.

Background

Oxygen from the ambient air is commonly used in fuel cell systems as an oxidant to react with hydrogen in the fuel cell to form water and thus provide electrical power through electrochemical conversion.

It is known from EP 2869376 a1 to form a fuel cell stack which is composed of a plurality of fuel cell module layers which are formed beforehand by a plurality of layers of fuel cells or individual cells.

The background of the invention is that in a fuel cell stack, the greatest risk for errors in the manufacture of the stack comes from the sealing sites in the cells. Despite the high reliability of each individual cell per se for the sealing points, the overall risk of failure is increased considerably in the case of a total of several thousand sealing points per stack, so that after the production of the fuel cell stack, a higher rejection rate of the faulty fuel cell stack in the range of 10% nevertheless results. The high rejection rate of a faulty fuel cell stack thus increases the price of a non-faulty fuel cell stack. Furthermore, the design with the fuel cell module also allows better monitoring of the tightness or hydrogen leakage during operation.

Another aspect of the invention is that in an advantageous configuration and application of the fuel cell stack in the form of a modular structure, the cells can be operated at a voltage which leads to relatively little degradation, and the cells of different fuel cell modules can even be configured differently optimally, for example with regard to an optimal catalyst loading.

Disclosure of Invention

The object of the present invention is therefore to provide a fuel cell stack, a method for producing such a fuel cell stack, by means of which the rejection rate of defective fuel cell stacks is reduced, so that fuel cell stacks can be produced economically, and furthermore, a fuel cell stack having optimized individual cells, reduced degradation and increased service life is therefore provided. Furthermore, a method for operating such a fuel cell stack is to be proposed, by means of which reduced degradation and increased service life can be achieved.

This object is achieved by a fuel cell stack having the features of claim 1. Reference is made to claim 13 in connection with a method for manufacturing such a fuel cell stack. Reference is made to claim 15 in connection with a method for operating such a fuel cell stack. The dependent claims cited each represent advantageous developments of the invention.

The fuel cell stack according to the invention comprises at least two fuel cell modules, each having at least two individual cells, and a fuel cell stack compression means, wherein each fuel cell module has a module end plate on the outside of both stacks, by means of which fuel cell modules stacked on one another are clamped into a fuel cell stack.

The invention relates to a fuel cell stack (10) and a method for producing such a fuel cell stack (10). The fuel cell stack (10) comprises at least two fuel cell modules (58) each having at least two individual cells (5), and a fuel cell stack compression means (82), wherein each fuel cell module (58) has a module end plate (70) on two stack outer sides (66), by means of which fuel cell modules (58) stacked on one another are clamped into the fuel cell stack (10).

A single cell in the sense of the present invention here refers to the conventional arrangement of a gas diffusion layer with a catalytically coated membrane between a cathode-bipolar plate and an anode-bipolar plate. Here, the outside of the stack is the free side of the cathode-bipolar plate or anode-bipolar plate of the stack, which is orthogonal to the fuel flow direction over the stack. Correspondingly, the outside of the module stack is the free side of the module stack, which extends in the same plane. Here, the fuel cell stack compression means is a means which is preferably mechanically connected to two stack end plates, so that the entire module stack can be clamped between the two stack end plates.

The structure according to the invention of the fuel cell stack has the following advantages: each fuel cell module can be inspected, in particular media-tight, by the module end plates before being stacked on top of each other. Therefore, the inspection may not be performed after all the cells are assembled on the entire fuel cell stack. As a result, only the single cells stacked on one another in the fuel cell module that is correspondingly tested as faulty are rejected. This significantly reduces the costs for waste. Additionally, the probability of failure of a fully assembled fuel cell stack is significantly reduced. Thereby significantly improving the economics of manufacturing such a fuel cell stack.

In a preferred embodiment of the invention, the fuel cell stack has module compression means by which the individual cells of each fuel cell module are clamped between the module end plates. In the sense of the present invention, a module compression means is understood here to mean a means which is preferably mechanically connected to two module end plates, so that the entire cell stack can be clamped between these two module end plates. It is thereby avoided that the cells stacked on top of each other move relative to each other, so that another possible source of failure is thus avoided. Thereby further reducing the probability of failure of the fuel cell stack.

In another preferred embodiment of the invention, the modular compression device is a fastener strip. Good clamping of the fuel cell module can be achieved by means of the clamping band. In this case, it is particularly advantageous to use five to eight clamping bands per fuel cell module.

In an advantageous embodiment of the invention, the module end plates are made of metal. Here, the metal particularly preferably has good electrical conductivity. Metals have the following advantages: they generally have good mechanical stability, so that the module end plates can be correspondingly thinner. Furthermore, metals have high availability and good workability.

Alternatively, the module end plates are constructed of graphite. Graphite has the following advantages: graphite is electrically conductive and has a low material cost. Additionally, graphite has a relatively low weight, so that by providing module end plates composed of graphite, the overall weight of such a fuel cell stack is only slightly higher than conventionally manufactured fuel cell stacks.

In another alternative, the module end plates are made of electrically conductive plastic. The plastic has the following advantages: plastics are available in large quantities and in different quantities. Furthermore, plastics have a low cost and can be processed simply, for example, by injection molding. Thereby, the fuel cell stack can be manufactured more economically. Furthermore, the plastic has a relatively low weight, so that by providing module end plates consisting of plastic, the overall weight of such a fuel cell stack is only slightly higher than in conventionally manufactured fuel cell stacks.

In another alternative, the module end plates are made of the same material as the bipolar plates of the single cells. The amount of material required for manufacturing the stack can thereby be reduced. Thus, the elimination of support from such other materials allows for more economical manufacture of the stack.

Preferably, the module end plates have a thickness of 5mm-15 mm. In the sense of the present invention, the thickness is the thickness or the extension of the module end plates in the stacking direction. In this region, sufficient stability of the module end plate can be ensured. It is particularly preferred that the thickness of the module end plate is in the range of 5mm-20 mm.

Advantageously, the fuel cell stack is composed of 80 to 450 individual cells in relation to the power. A particularly preferred embodiment of the fuel cell stack comprises six to twelve fuel cell modules, which preferably each have 20 to 50 individual cells. Here, the number of the unit cells may also be different for a single fuel cell module. Such a fuel cell stack has the following advantages: sufficient power is provided. Additionally, such fuel cell stacks may be used for most applications. Particularly preferably, the fuel cell stack consists of 420 to 450 single cells. High power can be provided by means of such a fuel cell stack.

In an advantageous embodiment, the module compression means, in particular when embodied as a clamping band, is electrically insulated only in the region of the lateral contact surfaces of the cells. Thereby, the volume of the electrically insulating material is reduced, thereby reducing the material cost.

In a preferred embodiment, each fuel cell module has its own current tab, which is preferably arranged on a module end plate. The fuel cell module can thus be short-circuited when stopped, or can also be connected separately to a consumer (for example a battery) during operation. This embodiment can then also be used for an advantageous method of operating a fuel cell stack.

Advantageously, each fuel cell module has its own voltage control. Therefore, the voltage control of the individual fuel cell modules can be arranged independently of one another.

Preferably, each fuel cell module has its own hydrogen sensor. Thereby, an early and robust detection of possible internal leakage of hydrogen inside the fuel cell stack is achieved.

In a preferred embodiment, one or more of the module end plates have a cooling distribution area. By including relatively thick module end plates in the cooling circuit, cooling of the fuel cell module is performed very efficiently.

Particularly preferably, one or more of the module end plates has a closable port lead-through (portdurchfuhrung). In this way, the supply of medium to the fuel cell module or to the next fuel cell module can be interrupted or stopped. This is particularly advantageous, since not all fuel cell modules are connected to the consumer for the low-load region.

In an advantageous embodiment, the individual fuel cell modules can be separated from the current circuit of the fuel cell stack by means of an electrical switch. The fuel cell module is therefore no longer connected to the consumer, which is a preferred embodiment for low-load areas, in particular in combination with the closable port opening. The invention therefore also relates to a corresponding method for operating a fuel cell stack in a low-load region.

In a preferred embodiment, the individual cells of the fuel cell module, which can be separated from the current circuit, have a modified design, for example a relatively low catalyst loading. These cells are then connected to the consumer only at load peaks.

Additionally, the invention comprises a method for manufacturing a fuel cell stack, in particular a fuel cell stack according to the invention. Here, the method comprises the steps of: stacking at least two cells of a fuel cell stack on top of each other, arranging a module end plate on the outside of the two stacks of cells stacked on top of each other, clamping the cells between the module end plates by means of a module compression means for forming a fuel cell module, checking the fuel cell module for non-failure and/or tightness, stacking at least two fuel cell modules thus manufactured on top of each other, and clamping the fuel cell modules stacked on top of each other by means of a fuel cell stack compression means. Here, the fuel cell module may be disposed between stack end plates.

The method for manufacturing a fuel cell stack has the same advantages as the fuel cell stack described earlier. In particular, by means of the method, the fuel cell modules can be checked for failure-free, in particular sealing, before being stacked on one another. Further, the fuel cell module may be individually conditioned (kondationieren). Here, conditioning is understood firstly to mean wetting the membrane after assembly of the fuel cell module, but also to activate the catalyst. It is particularly advantageous here that the conditioning process is already carried out for individual fuel cell modules (i.e. before stacking on top of one another), since the conditioning process may be potentially faulty, so that in the worst case only the fuel cell module has to be replaced due to an incorrect conditioning process, without having to replace the entire fuel cell stack.

In a preferred embodiment of the method, the module compression means are removed after clamping the fuel cell modules stacked on one another. Thereby, the weight of the modular compression device can be saved. Thus, the module compression device also does not have to be designed for the life of the fuel cell stack.

Additionally, the invention comprises a method for operating a fuel cell stack, in particular a fuel cell stack according to the invention, in a low load region, wherein the method comprises the following steps:

the fuel cell module is separated from the gas supply, in particular by means of a closable port feedthrough.

-separating the same fuel cell module from the current circuit by means of at least one switch.

Thus, the fuel cell module or modules are separated from the supply with reducing agent (preferably hydrogen) and oxidizing agent (preferably oxygen) and from the electrical devices for the low load region. In this way, the cells remaining in the current circuit and not separated can be operated in the optimum voltage range. In an advantageous embodiment, the design of the cells is adapted accordingly; for example, the catalyst loading of the cells which are not operated in the low-load region can be reduced.

Additionally, the invention includes a motor vehicle having a fuel cell stack according to the invention. The motor vehicle has the same advantages as the fuel cell stack. Additionally, such motor vehicle failures are reduced by a subsequent failure of the fuel cell stack.

Drawings

Embodiments of the invention are illustrated in the drawings and are set forth in detail in the following description. The figures show:

fig. 1 is a cross-sectional view of an embodiment of a single cell of a fuel cell stack according to the present invention, in which only the main regions are shown;

FIG. 2 is a cross-sectional view of a first embodiment of a fuel cell stack according to the present invention, wherein only the main areas are shown;

FIG. 3 is a side view of a fuel cell module of a fuel cell stack according to the present invention, in which only the main regions are shown;

FIG. 4 is a cross-sectional view of another embodiment of a fuel cell stack according to the present invention, wherein only the primary regions are shown;

FIG. 5 is an embodiment of a module end plate in cross-section and top view, with only the major areas shown;

FIG. 6 is another embodiment of a module end plate in schematic top view;

figure 7 schematically shows another fuel cell stack;

figure 8 shows yet another fuel cell stack schematically;

fig. 9 shows the characteristic curves of the cells in the U-I diagram.

Detailed Description

Fig. 1 shows a cross-sectional view of an embodiment of a single cell 5 of a fuel cell stack 10 according to the present invention (see fig. 2 and 3). The cell 5 is formed by a cathode-bipolar plate 18 with a bead (Sicken) 14. An anode-bipolar plate 22 is arranged in mirror image opposition to the cathode-bipolar plate 18 such that the beads 14 of the two bipolar plates 18, 22 are opposed. Thereby, channels 26 are formed between the cathode-bipolar plate 18 and the anode-bipolar plate 22. A layer structure 30 is arranged within the channel 26. The layer structure 30 is exemplarily shown on the channel 26. The layer structure 30 is composed of a first and a second gas diffusion layer 34, 38, which are separated by a membrane 42. Oxygen 46 required for oxidation flows between the first gas diffusion layer 34 and the cathode-bipolar plate 18. Hydrogen 50, preferably used as a fuel, flows between the second gas diffusion layer 38 and the anode-bipolar plate 22.

Typically, the anode-bipolar plate 22 of a cell 5 is merged with the cathode-bipolar plate 18 of an adjacent cell 5 into one bipolar plate.

A seal material 54 is disposed between the membrane 42 and the bipolar plates 18, 22 at a location where the bead 14 opposes the cathode-bipolar plate 18 and the anode-bipolar plate 22. As already explained above, most faults occur at these locations.

A cross-sectional view of a first embodiment of a fuel cell stack 10 according to the present invention is shown in fig. 2. In this embodiment, for example, three fuel cell modules 58 are stacked on top of each other. Each fuel cell module 58 comprises one, here for example four, individual cells 5. Each cell 5 is configured in accordance with fig. 1. These single cells 5 are stacked on top of each other and a module end plate 70 is arranged on the stack outer side 66 on the stack 62 thus formed. The unit cells 5 stacked on each other are clamped to each other by the module compression devices 74 mechanically connected to the two module plates 70.

One preferred embodiment of the fuel cell stack 10 comprises six to twelve fuel cell modules 58, which preferably each have 20 to 50 individual cells 5. Here, the number of the unit cells 5 may be different for each fuel cell module 58.

The fuel cell modules 58 thus formed are stacked on one another against the module end plates 70. On the module stack 76 thus formed, a stack end plate 78 is arranged on the two module stack outer sides 77, on the last module end plate 70. The fuel cell modules 58 stacked on top of each other are clamped into the fuel cell stack 10 by fuel cell stack compression devices 82 that are mechanically coupled to the stack end plates 78.

Thus, each fuel cell module 58 can be checked for non-failure before introduction into the module stack 76. Therefore, it is not necessary to wait until the fuel cell stack 10 is completely manufactured before the inspection. These fuel cell modules 58 can be constructed in a single pre-assembly step on special equipment and oriented with significantly improved positioning accuracy (in the sense that all the individual cells 5 are oriented precisely in the stacking direction). Therefore, as compared with the conventional assembly of all cell components in which all bipolar plates 18, 22 and membrane-electrode units of the entire fuel cell stack 10 are stacked alternately, the force transmission between adjacent bipolar plates 18, 22 and the membrane-electrode unit located therebetween, which consists of the membrane 42, the anode-side electrode, the cathode-side electrode and the two gas diffusion layers 34, 38, in the stacking direction is performed more accurately.

Partial pressing of the edge regions of the membrane electrode unit at the transition with the bipolar plates 18, 22 is largely avoided. By means of a more precise positioning of the bipolar plates 18, 22 relative to one another, a more precise positioning of the membrane-electrode units relative to each bipolar plate 18, 22 can also be achieved by automation (reduced tolerances in the automatic placement of the membrane-electrode units by robots). Preferably, the cells 5 of the fuel cell module 58 are pressed to a desired target value (for example, displacement-controlled pressing of 60 μm/cell or force control to 15 bar). Subsequently, each fuel cell module 58 is temporarily fixed by means of a module compression device 74, preferably by means of a metal clamping band, alternatively also by means of a clamping band consisting of a very load-bearing plastic. A relatively small stack, i.e. a fuel cell module 58, is thereby achieved, which can be individually checked for tightness and subsequently conditioned.

Fig. 3 shows a side view of a fuel cell module 58 with a plurality of cells 5 which are clamped between two module end plates 70 by means of three module compression means 74. The module compression means 74 is embodied here as a clamping band. In a preferred embodiment, comprises an area of about 200x300mm²The fuel cell modules 58 of the single cells 5 have eight clamping strips, each of which is about 30mm wide.

Preferably, the clamping strip 74 is insulated only in the region of the lateral contact surfaces of the cells 5, in order to avoid short circuits between the bipolar plates.

Advantageously, one of the two module end plates 70 of the fuel cell module 58 has a current connection 71. Each fuel cell module 58 thus has its own switchable electrical contacts for tapping the voltage, so that an external circuit is supplied with power (approximately 0.6V to 1V per cell 5) via the switchable contacts of each fuel cell module 58 or a defined/desired number of fuel cell modules 58.

Preferably, each fuel cell module 58 has its own voltage control, so that a faulty cell 5 can be identified early. Ideally, the voltage control is also carried out by means of the current connections 71. By virtue of the modular design with a plurality of fuel cell modules 58, individual fuel cell modules 58 can be replaced very easily in the event of a fault or also in the event of a lack of tightness. This saves high costs, since it is not necessary to disassemble each cell 5 in the entire fuel cell stack 10 or even to replace the entire fuel cell stack 10 with only one defective cell 5. The assembly effort for the fuel cell stack 10 is reduced by reducing the inspection effort when finding a defective cell 5 and reducing the subsequent processing required in the event of a defect.

It is also preferred that each fuel cell module 58 has its own hydrogen sensor. Internal leaks of the fuel cell module 58 can thus be recognized early; such leakage can occur, for example, through damage in the membrane 42 and lead to premature failure of the fuel cell module 58 or the fuel cell stack 10.

If a hydrogen sensor is assigned to each fuel cell module 58, improved spatial resolution and correlation of the location of the cause of the leak can be achieved compared to when only one hydrogen sensor is available for the entire fuel cell stack 10. Further, a hydrogen sensor that is not mounted close enough to a position where the hydrogen concentration increases can only find an average signal of a plurality of unit cells 5. There is a relatively narrow path between the lower extreme of signal detection, preferably to a hydrogen content of 0.5%, and the ignition limit of hydrogen in air of about 4% (local observation). By assigning a hydrogen sensor to each individual fuel cell module 58, early or timely and robust detection of internal leakage of hydrogen within the interior of the fuel cell stack 10 can be achieved.

A cross-sectional view of another embodiment of a fuel cell stack 10 according to the present invention is shown in fig. 4. The fuel cell stack 10 differs from the fuel cell stack 10 of fig. 2 and 3 essentially in that the module compression devices 74 are not present in the fuel cell stack 10. In this embodiment, the module compression device 74 is eliminated after the fuel cell modules 58 stacked on one another are clamped.

By dividing the fuel cell stack 10 into a plurality of fuel cell modules 58, it is ensured that, when the fuel cell modules 58 are finally assembled, the positioning accuracy is mainly produced by the positioning errors of these fuel cell modules 58 lying on top of one another relative to one another, and that, during the final assembly, correction is effected more simply by appropriate movement of the respectively uppermost fuel cell module 58 than when an excessively large number of individual cells 5 are stacked. The same applies to the tightness of the fuel cell stack 10: this tightness is essentially determined by the module end plates 70 lying on one another, since the tightness of the fuel cell stack cannot yet be checked, and the tightness of the individual fuel cell modules 58 can already be checked before the final assembly and then possibly also subsequently improved.

At the same time, a reduced overall inspection effort for the entire fuel cell stack 10 is achieved by assembling and inspecting the fuel cell modules 58, with the result that the risk of failure of the finished fuel cell stack 10 is reduced in the final inspection. Thus, a cost advantage for the fuel cell stack 10 as a whole is achieved. Advantageously, therefore, the fuel cell modules 58 that are attractive under inspection can be simply replaced with other modules and also used in combination for special tests (e.g., performance with different platinum loads or at the end of the expected service life of the fuel cell stack 10). In a final assembly step, all fuel cell modules 58 are clamped together to a target value, and the module compression means 74 of the individual fuel cell modules 58 are cut off and removed from the fuel cell stack 10 for pre-fixing. For this purpose, the module end plate 70 preferably has a suitable clearance (about 0.5mm thick).

Fig. 5 shows an advantageous embodiment of a module end plate 70 in cross-section and top view. The module end plates 70 (like the bipolar plates 18, 22) have port feedthroughs 72 for supplying the fuel cell modules 58 or the individual cells 5 with a medium. In a preferred embodiment, one or more module end plates 70 of the fuel cell stack 10 have a cooling distribution area 73 which branches off from the port lead-throughs 72 for the cooling medium and extends in a plane x-y (in a plane, similar to the active face of the single cells 5).

The module end plate 70 thus has integrated cooling water channels that cool the distribution area 73. The inclusion of such a modular end plate 70 in the cooling circuit is a preferred embodiment.

Optionally, the module end plate 70 may preferably contain a flexible tolerance compensation element 75. In the embodiment of fig. 5, the tolerance compensation element is plate-shaped and arranged on one of the two x-y faces of the module end plate 70. The tolerance compensation element 75 can effectively improve the clamping accuracy of the fuel cell modules 58 relative to one another and homogenize the surface pressure.

Fig. 6 shows a top view of another modular end plate 70. The module end plate 70 has a closable port lead-through 72, so that the fluid flow can be interrupted if necessary, and is thus embodied as a valve plate 70. Thus, individual fuel cell modules 58 of the fuel cell stack 10 may be selectively separated from the fluid supply (particularly from the supply that supplies air and hydrogen). This may be accomplished by a slide on the module end plate 70 or by appropriate valve connections to the individual fuel cell modules 58.

To this end, fig. 7 schematically shows a fuel cell stack 10 with two (optionally also a plurality of) fuel cell modules 58. The two fuel cell modules 58 are separated by a module end plate 70 embodied as a valve plate. If the port leadthroughs 72 of the valve plate 70 are now closed, the gas flow, as shown for the gas by way of example, takes place only in the lower fuel cell module 58, while the upper fuel cell module 58 is separated from the gas supply.

Fig. 8 schematically shows the fuel cell stack 10, the fuel cell modules 58 of which are provided with electric switches 80, respectively. The fuel cell stack 10 has a current circuit 12 with a consumer 11. Advantageously, the switches 80 are in contact with the respective current terminals 71 of the fuel cell module 58. The power consuming device 11 may be a battery, for example.

Preferably, at least one module end plate 70 has a closable port lead-through 72, so that the fluid supply into the respective or a subsequent fuel cell module 58 can be interrupted.

In general, a maximum of 400 single cells 5 are arranged to overlap each other in the fuel cell stack 10. Typically, depending on the load point of the consumer 11, the gas flows through the cells 5 in matching volumes (air and hydrogen), which leads to very slow gas velocities in the active region of the cells 5 in the case of low power. Furthermore, since all the active surfaces of all 400 individual cells 5 are always used, the specific current density is very low, as a result of which very high cell voltages are achieved in the individual cells 5, which accelerates the cell aging and accordingly shortens the service life of the entire fuel cell stack 10. The main advantage of having a load modulation of the fuel cell stack 10 according to the invention, which combines the exemplary embodiments of fig. 7 and 8, is that a nearly optimal voltage is applied to the single cells 5 in both the full load region and the low load region of the fuel cell stack 10.

By using only a part of the fuel cell module 58 for the low-load region (supplying gas to only a part of the fuel cell module 58 by closing the closable port lead-throughs 72), the voltage over the single cells 5 under load can be reduced from the emergency first state 1 to the less harmful second state 2, see fig. 9. For this reason, in the illustration of fig. 8, the lower switch 80 will be closed, while the upper switch 80 is open, so that only the lower fuel cell module 58 is arranged in the current circuit 12.

The emergency area 3 represents a high voltage across the cell 5 with a low current density, which leads to degradation in the cell 5. With an effectively small total active surface of the fuel cell stack 10 (as shown in fig. 9), the operating point on the U-I characteristic curve is advantageously shifted to lower cell voltages with low power, the gas velocity increasing, which has a positive effect on the mass transfer limitation.

For the full load region, all the fuel cell modules 58 are supplied with hydrogen and oxygen, so that the electric power for the electric device 11 is increased. For this reason, in the diagram of fig. 8, the lower switch 80 will be open, while the upper switch 80 is closed, so that two fuel cell modules 58 will be arranged in the current circuit 12.

Preferably, in the full load region, the cells 5 are also operated in the second state 2. The fuel cell stack 10 is thus modulated in such a way, that is, with respect to the load point, that the entire active surface of the fuel cell stack is adapted to the load point. For this purpose, the gas supply of the individual fuel cell modules 58 (see fig. 7) is synchronized with the respective on-state of the switch 80 (see fig. 8).

Therefore, the current drop of each fuel cell module 58 is controlled by the turning on of the current. Advantageously, an additional DC/DC converter can be connected in between when a smaller number of cells 5 are used.

In an advantageous embodiment, the individual cells 5 of different fuel cell modules 58 have different designs. The individual cells 5 can differ from fuel cell module 58 to fuel cell module 58, for example, in the gas diffusion layers 34, 38, in the anode-side electrode, in the cathode-side electrode, in the membrane 42 and/or in the bipolar plates 18, 22. In this case, it is particularly preferred for the individual cells 5 to be configured differently in the anode-side electrode and the cathode-side electrode.

For the cells 5 of the fuel cell module 58, which are also supplied with gas or medium for the low-load region, the following optimized features are preferably applied:

a relatively high catalyst loading in the anode-side electrode and/or cathode-side electrode, which is adapted in particular to high (0.75-1V) and frequently changing potentials.

The anode-side and/or cathode-side electrode and/or the gas diffusion layer 34, 38 are adapted to low and varying humidity.

The membrane 42 and/or the gas diffusion layers 34, 38 have additional or increased content of radical traps.

For the individual cells 5 of the fuel cell module 58, which are separated from the gas or medium supply for the low-load region, the following optimized features are preferably applied, which are matched to the high load:

a relatively low catalyst loading in the anode-side electrode and/or cathode-side electrode, which is adapted in particular to an average, stable potential (0.6-0.75V).

The anode-side and/or cathode-side electrode and/or the gas diffusion layer 34, 38 are adapted to a high humidity, advantageously also to liquid water, in particular on the cathode side.