End plate, fuel cell stack and fuel cell system

Abstract

The invention relates to an end plate (10) for a fuel cell stack (12) of a fuel cell system (14), the end plate comprising: a first connection portion (16) which has at least one first connector (18) for supplying and / or discharging at least one reactant and / or a reaction product and / or a coolant; and a second connection portion (20) which has at least one second connector (22) for supplying and / or discharging at least one reactant and / or a reaction product and / or a coolant; wherein: a reaction region (24) is situated between the first connection portion (16) and the second connection portion (18); the at least one first connector (18) of the first connection portion (16) has a first transfer region (26) for transferring the at least one reactant and / or the reaction product and / or the coolant into the fuel cell stack (12) or out of the fuel cell stack (12); and / or the at least one second connector (22) of the second connection portion (20) has a second transfer portion (28) for transferring the at least one reactant and / or the reaction product and / or the coolant into the fuel cell stack (12) or out of the fuel cell stack (12);and the first transfer region (26) and / or the second transfer region have / has a surface structure (30).

Description

[0001] Description

[0002] State of the art

[0003] The invention relates to an end plate having the features of independent patent claim 1, a fuel cell stack having the features of independent patent claim 6 and a fuel cell system having the features of independent patent claim 12.

[0004] For the efficient operation of a fuel cell stack in the low-load range, humidification of the membrane by the inflowing gases in the cathode and anode paths is particularly important to prevent the membrane from drying out, avoid its premature degradation, and prevent high ohmic losses in the membrane. Current state-of-the-art anode subsystems with water separators are used to remove excess water (as condensate and water vapor) from the anode exhaust gas before it is recirculated, enriched with fresh gas (hydrogen), into the anode inlet of the stack, sometimes with recirculation fans. However, the efficiency of the water separator, at 90% to 95%, is insufficient to completely prevent the penetration of liquid water in the form of droplets or wall film into the inlet channel of the stack.

[0005] The liquid water takes the first possible path through the first cell of the fuel cell stack, causing the cell to become unstable. This can lead to a local and, later, global hydrogen deficiency in the cells, resulting in damage. Disclosure of the Invention

[0006] The invention proposes an end plate with the features of independent patent claim 1, a fuel cell stack with the features of independent patent claim 6, and a fuel cell system with the features of independent patent claim 12. Further features and details of the invention emerge from the subclaims, the description, and the drawings. Features and details described in connection with the end plate according to the invention naturally also apply in connection with the fuel cell stack according to the invention and / or in connection with the fuel cell system according to the invention, and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is or can always be made to each other.

[0007] A first aspect of the invention is an end plate for a fuel cell stack of a fuel cell system, comprising a first connection section with at least one first nozzle for supplying and / or discharging at least one reactant and / or a reaction product and / or a coolant, with a second connection section with at least one second nozzle for supplying and / or discharging at least one reactant and / or a reaction product and / or a coolant, wherein a reaction region is arranged between the first connection section and the second connection section.

[0008] The at least one first nozzle of the first connection section has a first transition region for the transition of the at least one reactant and / or the reaction product and / or the coolant into the fuel cell stack or out of the fuel cell stack.

[0009] Additionally or alternatively, the at least one second nozzle of the second connection section has a second transition section for the transition of the at least one reactant and / or the reaction product and / or the coolant into or out of the fuel cell stack. The first transition region and / or the second transition region have a surface structure.

[0010] The proposed measures have different physical effects on the inlet and outlet sides of the end plate during operation of the fuel cell stack. However, the surface structure of the first transition section and the second transition section leads to a reduction in the amount of liquid water in the first nozzle and the second nozzle, and thus also in the area of ​​the cell adjacent to the end plate. This occurs through the capillary forces on the wall surface and the high gas velocity present at this point during flow into or out of the fuel cell stack.

[0011] The surface structure can have grooves or elevations.

[0012] In this context, reactants are understood to be the media involved in the reaction to produce the reaction product. These can be, for example, hydrogen and oxygen or air.

[0013] On the inlet side, the surface structure causes the liquid water to penetrate the grooves (or the rough structure of the warm wall) of the nozzles as a wall film, and is slowed down by the extended flow path. This increases both the ratio of the contact surface area of ​​the liquid wedge / wall to the liquid volume. At the same time, the residence time of the liquid water at the wall increases, so that it evaporates more rapidly through wall heat transfer with the hot wall.

[0014] On the outlet side, the mechanism of capillary forces is crucial for drawing the escaping liquid water into the surface structure of the nozzles, thus reducing the liquid water in this area. This reduces the risk of flooding the lowest cell and reduces the extent of premature degradation.

[0015] Depending on the design of the fuel cell stack, the first

[0016] The connection section with at least one first nozzle can be the inlet side or the outlet side, wherein the second connection section with the at least one second nozzle is then correspondingly the outlet side or the inlet side.

[0017] Within the scope of the invention, it may be advantageous that the surface structure of the first transition region and / or the second transition region has a roughness between 2 to 20 pm, preferably 3 to 15 pm, more preferably 4 to 10 pm.

[0018] The roughness allows the surface area for the evaporation of liquid water to be enlarged and adapted to the requirements of the respective fuel cell stack. It is conceivable that the surface structure of the first transition area differs from the surface structure of the second transition area in order to adapt the respective physical effects to the function of the first nozzle and the second nozzle.

[0019] Within the scope of the invention, it is conceivable that the first transition region and / or second transition region has a height of 0.5 to 4.0 cm, preferably 0.75 to 3.0 cm, more preferably 1.0 to 2.5 cm.

[0020] The height of the respective transition areas determines how much liquid water remains on the respective surface structure of the first nozzle and / or the second nozzle and can thus evaporate. A minimum height of 0.5 mm is sufficient to cause the liquid water to adhere to the surface structure.

[0021] Within the scope of the invention, it can be provided that the first transition region and / or the second transition region has a hydrophilic coating.

[0022] A hydrophilic coating is a special coating or surface treatment that has a high affinity for water. The word "hydrophilic" comes from the Greek and literally means "water-loving." A hydrophilic coating causes water to spread in a thin, even layer on the treated surface, rather than beading up.

[0023] An additional hydrophilic coating therefore has a positive effect on the distribution of the liquid water in the first transition area of ​​the first nozzle and the second transition area of ​​the second nozzle and thus optimizes the evaporation of the liquid water.

[0024] It is further conceivable that the at least first nozzle of the first connection section is designed to supply an anode medium as a reactant and the at least one second nozzle is designed to discharge the anode medium as a reactant, and wherein at least one third nozzle of the first connection section is provided for supplying and / or discharging a cathode medium as a reactant and / or a reaction product and / or a coolant, and wherein at least one fourth nozzle of the second connection section is provided for supplying and / or discharging a cathode medium as a reactant and / or a reaction product and / or a coolant.

[0025] This allows the respective media flows to be divided during operation of the fuel cell stack with the end plate. It is particularly advantageous if the third nozzle has a third transition area and / or the fourth nozzle has a fourth transition area. The roughness of the third transition area and / or the fourth transition area can differ from the roughness of the first transition area and / or the second transition area.

[0026] A second aspect of the invention is a fuel cell stack having a plurality of fuel cells, wherein the plurality of fuel cells is arranged between a first end plate according to the first aspect of the invention and a second end plate. A sealing element for sealing the fuel cell stack is provided between the first end plate and a first fuel cell. The sealing element between the first end plate, which has the transition region with the surface structure, and the first fuel cell supports the effect of the surface structure. If liquid water is present in the fuel cell stack during outflow, it is drawn via the sealing element into the surface structure of the first nozzle or the second nozzle in order to be quickly discharged from the fuel cells.During the inflow, the sealing element ensures that the liquid in the inflowing medium (reactant) is held in the area of ​​the surface structure of the first nozzle or the second nozzle in order to remove or at least reduce the liquid from the reactant in the sense of an evaporator or heat exchanger.

[0027] It is conceivable that the second end plate is also designed according to the first aspect of the invention, and a sealing element is arranged between the second end plate and the last fuel cell.

[0028] Within the scope of the invention, it is conceivable that the sealing element is a seal or a sub-sealing sleeve.

[0029] A sub-gasket can contain channels or capillaries to absorb and transport liquid water away. This can enhance the effects of the surface structure. At the same time, the sub-gasket is intended to isolate the end plate from the cells and ensure a reliable seal.

[0030] The seal can seal outwards and ensure that no liquid water leaks from the fuel cell stack or moisture from the environment enters.

[0031] Both the seals and the sub-gasket must be chemically inert to withstand the aggressive environmental conditions within the fuel cell. They must also exhibit good resistance to the electrolytes and reaction gases used in the fuel cell. It is also conceivable for the sealing element to have the first connection section with at least one first connection opening for contact with the at least one first nozzle, and the second connection section with at least one second connection opening for contact with the at least one second nozzle.

[0032] This allows for simplified insertion of the sealing element into or onto the first end plate, since the first connection opening and the second connection opening can be used as a positioning aid.

[0033] Within the scope of the invention, it is optionally possible for the at least one first connection opening to have a first sealing lip, wherein the first sealing lip is arranged at least in sections in the at least one first connecting piece.

[0034] On the inlet side, the sealing lip of the first connection opening causes the liquid water to penetrate the surface structure of the transition area of ​​the first nozzle or the second nozzle end as a wall film, and is slowed down by the protruding additional sealing lip of the sealing element. This increases both the ratio of the contact surface of the liquid / wall to the volume of the liquid by at least a factor of ten, as well as the residence time of the liquid water at the wall, so that it evaporates more rapidly through wall heat transfer with the hot wall.

[0035] On the outlet side, the mechanism of capillary forces is crucial for drawing the escaping liquid water into the superhydrophilic surface of the nozzle via the additional sealing lip of the sealing element, thereby reducing its presence on the upper side of the lowest sealing element (i.e., in the fuel cell stack of the lowest cell). This reduces the risk of flooding of the lowest cell and reduces the extent of premature degradation. Furthermore, within the scope of the invention, it can be provided that the circumference of the first sealing lip of the first connection opening is smaller than the circumference of the first nozzle.

[0036] The respective circumference is the circumference of the opening defined by the sealing lip or the circumference of the inlet opening or the outlet opening of the nozzle.

[0037] This ensures that the first sealing lip protrudes, i.e., extends into the opening of the first nozzle or the second nozzle. This creates the desired effects when reactants flow in or out.

[0038] With regard to the present invention, it is conceivable that the at least one second connection opening has a second sealing lip, wherein the second sealing lip is arranged at least in sections in the at least one second nozzle.

[0039] Accordingly, a sealing lip can be provided on both the outlet side and the inlet side to create the above-mentioned effects in order to evaporate the liquid water as well as possible at both the inlet and the outlet.

[0040] The circumference of the second sealing lip of the first connection opening is smaller than the circumference of the second nozzle.

[0041] It is also conceivable that additional nozzles are provided. Connection openings for these nozzles can also be provided in the sealing element. It is also conceivable that sealing lips are provided at the additional connection openings.

[0042] Furthermore, it is conceivable that the at least one first connection opening of the sealing element is arranged on the first nozzle of the first connection section for supplying an anode medium as a reactant, and that the at least one second connection opening of the sealing element is arranged on the second nozzle for discharging the anode medium as a reactant, and that at least one third connection opening is arranged on the at least one third nozzle of the first connection section and that at least one fourth connection opening is arranged on the at least one fourth nozzle of the second connection section.

[0043] This allows the respective connection openings to be adapted to the associated nozzle, so that different diameters and / or shapes can be used for the first nozzle and the first connection opening than for the second nozzle and the second connection opening. This allows the nozzles to be adapted to the respective task or reactant composition.

[0044] A third aspect of the invention is a fuel cell system having at least one fuel cell stack according to the second aspect of the invention.

[0045] Advantages described in detail with respect to the end plate for a fuel cell stack of a fuel cell system according to the first aspect of the invention equally apply to the fuel cell stack having a plurality of fuel cells according to the second aspect of the invention and the fuel cell system according to the third aspect of the invention.

[0046] Further advantages, features, and details of the invention will become apparent from the following description, which describes several embodiments of the invention in detail with reference to the drawings. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination. The invention is illustrated in the following figures:

[0047] Figure 1 is a schematic representation of an end plate according to the invention,

[0048] Figure 2 is a schematic representation of a fuel cell stack according to the invention, Figure 3 is a schematic representation of a section of the fuel cell stack along a section AA,

[0049] Figure 4 is a schematic representation of a fuel cell system.

[0050] Fig. 1 shows an end plate 10 for a fuel cell stack 12 of a fuel cell system 14 with a first connection section 16 with at least one first nozzle 18 for supplying and / or discharging at least one reactant and / or a reaction product and / or a coolant and with a second connection section 20 with at least one second nozzle 22 for supplying and / or discharging at least one reactant and / or a reaction product and / or a coolant.

[0051] A reaction region 24 is arranged between the first connection section 16 and the second connection section 18.

[0052] The at least one first nozzle 18 of the first connection section 16 has a first transition region 26 for the transition of the at least one reactant and / or the reaction product and / or the coolant into the fuel cell stack 12 or out of the fuel cell stack 12. Alternatively or additionally, the at least one second nozzle 22 of the second connection section 20 has a second transition section 28 for the transition of the at least one reactant and / or the reaction product and / or the coolant into the fuel cell stack 12 or out of the fuel cell stack 12.

[0053] In order to prevent the liquid water from entering the fuel cell stack 12 when the reactants are fed in and, on the other hand, to accelerate the liquid water from leaving the fuel cell stack 12 when the reaction products are removed, the first transition region 26 and / or the second transition region 28 has a surface structure 30.

[0054] Depending on the liquid water content of the reactants or the reaction product, the surface structure 30 of the first transition region 26 and / or the second transition region 28 has a roughness between 2 to 20 pm, preferably 3 to 15 pm, more preferably 4 to 10 pm.

[0055] The surface structure 30 extends over a height H of the first transition region 26 and / or the second transition region 28 of 0.5 to 4.0 cm, preferably 0.75 to 3.0 cm, more preferably 1.0 to 2.5 cm.

[0056] To increase the effects of the surface structure 30, a hydrophilic coating 32 is provided on both the first transition region 26 and the second transition region 28.

[0057] In this case, at least the first nozzle 18 of the first connection section 16 is designed to supply an anode medium 54 as a reactant, and at least one second nozzle 22 is designed to remove the anode medium 54 as a reactant. In addition, at least one third nozzle 34 of the first connection section 16 is provided for supplying a cathode medium 56 as a reactant, and at least one fourth nozzle 36 of the second connection section 20 is provided for removing the cathode medium 56 as a reactant and the reaction product. In addition, a fifth nozzle 58 is provided for supplying a coolant, and a sixth nozzle 60 is provided for removing the coolant. In this exemplary embodiment, the cathode medium 56 and the anode medium 54 flow into the fuel cells in cocurrent flow, but in countercurrent flow to the coolant.It is conceivable that the anode medium and the cathode medium flow in countercurrent, in which case the fourth nozzle 36 serves to supply the cathode medium 56 and the third nozzle 34 serves to discharge the cathode medium 56.

[0058] 2 and 3 show a fuel cell system 14 with a plurality of fuel cells 38, wherein the plurality of fuel cells 38 is arranged between a first end plate 10 according to FIG. 1 and a second end plate 10, wherein a sealing element 40 for sealing the fuel cell stack 12 is provided between the first end plate 10 and a first fuel cell 39. As can be seen in the detail of FIG. 3, the sealing element 40 has the first connection section 16 with at least one first connection opening 42 for placing on the at least one first connecting piece 18 and the second connection section 20 with at least one second connection opening 44 for placing on the at least one second connecting piece 22. The sealing element 40 is in this case a sub-sealing sleeve. The detail also applies to the second connection section 20.

[0059] The at least one first connection opening 42 has a first sealing lip 46, wherein the first sealing lip 46 is arranged at least in section in the at least one first nozzle 18. In addition, the at least one second connection opening 44 has a second sealing lip 48, wherein the second sealing lip 48 is arranged at least in section in the at least one second nozzle 22. Via the channels of the flow field provided in the sealing element 40, the liquid water on the sealing element 40 can be guided via the sealing lip into the fourth nozzle 36. Here, the sealing element 40 has sealing lips at the connection openings of the third nozzle, the fourth nozzle, the fifth nozzle, and the sixth nozzle.

[0060] As can be seen in Fig. 3, the circumference U of the first sealing lip 46 of the first connection opening 42 is smaller than the circumference U of the first nozzle. This also applies to the second sealing lip 48 and the further sealing lips of the third nozzle, the fourth nozzle, the fifth nozzle, and the sixth nozzle.

[0061] According to the structure of the end plate 10 according to Fig. 1 , the at least one first connection opening 42 of the sealing element 40 is arranged on the first nozzle 18 of the first connection section 16 for supplying an anode medium 54 as a reactant, and the at least one second connection opening 44 of the sealing element 40 is arranged on the second nozzle 22 for removing the anode medium 54 as a reactant. The at least one third connection opening 50 of the sealing element 40 is arranged on the at least one third nozzle 34 of the first connection section and the at least one fourth connection opening 52 is arranged on the at least one fourth nozzle 36 of the second connection section 20. The third nozzle 34 is used to supply the cathode medium 56 and the fourth nozzle 36 is used to remove the cathode medium 56 and the reaction product.The same applies to the further connection openings for the fifth nozzle 58 and the sixth nozzle 60, which are used to supply and discharge the coolant.

[0062] Fig. 4 shows a fuel cell system 14 with at least one fuel cell stack 12 according to Figs. 2 and 3.

Claims

Claims 1. End plate (10) for a fuel cell stack (12) of a fuel cell system (14), comprising a first connection section (16) with at least one first nozzle (18) for supplying and / or discharging at least one reactant and / or a reaction product and / or a coolant, a second connection section (20) with at least one second nozzle (22) for supplying and / or discharging at least one reactant and / or a reaction product and / or a coolant, a reaction region (24) being arranged between the first connection section (16) and the second connection section (18), the at least one first nozzle (18) of the first connection section (16) having a first transition region (26) for the transition of the at least one reactant and / or the reaction product and / or the coolant into or out of the fuel cell stack (12),and / or wherein the at least one second nozzle (22) of the second connection section (20) has a second transition section (28) for the transition of the at least one reactant and / or the reaction product and / or the coolant into the fuel cell stack (12) or out of the fuel cell stack (12), wherein the first transition region (26) and / or the second transition region have a surface structure (30).

2. End plate (10) according to claim 1, characterized in that the surface structure (30) of the first transition region (26) and / or the second transition region (28) has a roughness between 2 and 20 pm, preferably 3 to 15 pm, more preferably 4 to 10 pm.

3. End plate (10) according to claim 1 or 2, characterized in that the first transition region (26) and / or second transition region (28) has a height (H) of 0.5 to 4.0 cm, preferably 0.75 to 3.0 cm, more preferably 1.0 to 2.5 cm.

4. End plate (10) according to one of the preceding claims, characterized in that the first transition region (26) and / or the second transition region (28) has a hydrophilic coating (32).

5. End plate (10) according to one of the preceding claims, characterized in that the at least one first nozzle (18) of the first connection section (16) is designed to supply an anode medium (54) as a reactant and the at least one second nozzle (22) is designed to discharge the anode medium (54) as a reactant, and wherein at least one third nozzle (34) of the first connection section (16) is provided for supplying and / or discharging a cathode medium (56) as a reactant and / or a reaction product and / or a coolant, and wherein at least one fourth nozzle (36) of the second connection section (20) is provided for supplying and / or discharging a cathode medium (56) as a reactant and / or a reaction product and / or a coolant.

6. A fuel cell stack (12) comprising a plurality of fuel cells (38), wherein the plurality of fuel cells (38) is arranged between a first end plate (10) according to one of the preceding claims and a second end plate (10), wherein a sealing element (40) for sealing the fuel cell stack (12) is provided between the first end plate (10) and a first fuel cell (39).

7. Fuel cell stack (12) according to claim 6, characterized in that the sealing element (40) has the first connection section (16) with at least one first connection opening (42) for placing on the at least one first nozzle (18) and the second connection section (20) with at least one second connection opening (44) for placing on the at least one second nozzle (22).

8. Fuel cell stack (12) according to claim 6 or 7, characterized in that the sealing element (40) is a seal or a sub-sealing sleeve.

9. Fuel cell stack (12) according to one of the preceding claims 6 to 8, characterized in that the at least one first connection opening (42) has a first sealing lip (46), wherein the first sealing lip (46) is arranged at least in sections in the at least one first nozzle (18).

10. Fuel cell stack (12) according to one of the preceding claims 6 or 9, characterized in that the circumference (U) of the first sealing lip (46) of the first connection opening (42) is smaller than the circumference (U) of the first nozzle.

11. Fuel cell stack (12) according to one of the preceding claims 6 to 10, characterized in that the at least one second connection opening (44) has a second sealing lip (48), wherein the second sealing lip (48) is arranged at least in sections in the at least one second nozzle (22).

12. Fuel cell stack (12) according to one of the preceding claims 6 to 11, characterized in that the at least one first connection opening (42) of the sealing element (40) is arranged on the first nozzle (18) of the first connection section (16) for supplying an anode medium (54) as a reactant, and in that the at least one second connection opening (44) of the sealing element (40) is arranged on the second nozzle (22) for discharging the anode medium (54) as a reactant, and in that at least one third connection opening (50) is arranged on the at least one third nozzle (34) of the first connection section and in that at least one fourth connection opening (52) is arranged on the at least one fourth nozzle (36) of the second connection section (20).

13. Fuel cell system (14) with at least one fuel cell stack (12) according to one of the preceding claims 6 to 12.

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