Method for operating cell stack having plurality of electrochemical cells arranged one above other and sealed to one another

Abstract

The invention relates to a method for operating a cell stack (12) having a plurality of electrochemical cells (10) which are arranged one above the other and are sealed from one another and through which a gaseous medium (38), in particular H2, flows via at least one outlet channel (32; 84, 86) from the stack. According to one aspect, an outlet channel (32) for a gaseous medium (38), in particular H2, comprises at its end an open end (52) for the outflow of the gaseous medium (38). In a second embodiment, a first outlet channel (84) for a gaseous medium (38), in particular H2, and a second outlet channel (86) for a gaseous medium (38), in particular H2, are alternately opened and closed at their ends by means of a pair (96, 98) of diagonally active valves (88, 90, 92, 94), such that the first and second outlet channels (84, 86) are arranged in the first and second outlet channels (84, 86). 86) is always provided with a closed end part (50) at one end and an open end part (52) at the end opposite to the closed end part (50).

Description

Technical Field

[0001] The invention relates to a method for operating a cell stack having several electrochemical cells arranged one above the other and sealed from one another, through which a gaseous medium, in particular H2, flows, which leaves the cell stack via at least one outlet channel. The invention also relates to the use of the method for operating a cell stack having several electrochemical cells, which is operated as an electrolysis cell or as a fuel cell for driving a vehicle. Background Art

[0002] Electrochemical cells are electrochemical energy converters and are known in the form of fuel cells or electrolyzers.

[0003] Fuel cells convert chemical reaction energy into electrical energy. In known fuel cells, in particular, hydrogen (H2) and oxygen (O2) are converted into water (H2O), electrical energy and heat.

[0004] Also known are proton exchange membrane (PEM) fuel cells, which have a centrally arranged membrane that is permeable to protons, ie, hydrogen ions. As a result, the oxidant, in particular oxygen from the air, is spatially separated from the fuel, in particular hydrogen.

[0005] A fuel cell has an anode and a cathode. The fuel is continuously directed to the anode of the fuel cell and is catalytically oxidized by releasing electrons to generate protons, which reach the cathode. The released electrons are discharged from the fuel cell and flow to the cathode via an external circuit. The oxidant is directed to the cathode of the fuel cell and reacts with the protons to generate water by absorbing electrons from the external circuit. The water thus formed is discharged from the fuel cell. The overall reaction formula is:

[0006] O2+4H + +4e - →2H2O

[0007] In this case, there is a voltage between the anode and cathode of the fuel cell. In order to increase the voltage, a plurality of fuel cells can be mechanically arranged one behind the other and electrically connected in series to form a fuel cell stack, which is also referred to as a reactor or a fuel cell body.

[0008] A stack of electrochemical cells may be referred to as an electrochemical cell assembly, which typically has end plates that press the individual cells against each other and provide stability to the stack.

[0009] The electrodes, ie, the anode and the cathode, and the membrane may be structurally combined into a membrane electrode assembly (MEA), which is also referred to as a Membrane Electrode Assembly.

[0010] The electrochemical cell stack also has bipolar plates, which are also called gas distributor plates or distributor plates. The bipolar plates are used to distribute the fuel uniformly to the anode and the oxidant uniformly to the cathode. In addition to media conduction for oxygen, hydrogen, water and, if necessary, coolant, the bipolar plates also ensure surface electrical contact with the membrane.

[0011] For example, a fuel cell stack typically has up to several hundred individual fuel cells, which are stacked on top of each other in layers. Each fuel cell has an MEA and a bipolar plate half on the anode side and on the cathode side. The fuel cell comprises in particular an anode monopolar plate and a cathode monopolar plate, which are usually each in the form of a stamped sheet material and which together form a bipolar plate, thereby forming channels for conducting gases and liquids and between which a cooling medium can flow.

[0012] Furthermore, the electrochemical cell generally includes a gas diffusion layer, which is arranged between the bipolar plate and the MEA.

[0013] In contrast to fuel cells, electrolyzers are energy converters which, when a voltage is applied, preferably decompose water into hydrogen and oxygen. Electrolyzers also have, among other components, an MEA, bipolar plates and gas diffusion layers.

[0014] The stacked electrochemical cells are often supplied with medium or the medium is discharged, especially hydrogen and oxygen, via medium channels arranged perpendicular to the membrane of the electrochemical cell. The medium channel is connected to the electrochemical cell, especially the bipolar plate fluid, through a port that can also be called a fluid connector. The medium channel is usually located at the edge of the stack and is often produced by overlapping notches arranged up and down (these notches form ports). The medium is guided from the port through the port penetration into the so-called flow field, that is, the active surface of the bipolar plate or the membrane electrode assembly. In particular, at the port, different media must be sealed to each other and to the environment.

[0015] In particular, the port openings for air or hydrogen directed toward the MEA are designed such that they provide the largest possible openings for the inflowing and outflowing media and, on the other hand, provide the best possible mechanical support for the seals arranged on the opposite side of the MEA.

[0016] DE 10158772 C1 and DE 10248531 B4 relate to a fuel cell stack having a layer formed by a plurality of fuel cells, wherein a medium is introduced or discharged via bipolar plates and a flange arrangement is provided for sealing. Summary of the invention

[0017] According to the invention, a method for operating a cell stack is proposed, the cell stack having a plurality of electrochemical cells arranged one above the other and sealed from one another, through which a gaseous medium, in particular H 2 , flows, which gaseous medium leaves the cell stack via at least one outlet channel, wherein:

[0018] a) the outlet channel for the gaseous medium, in particular H2, comprises at its end an open end for the outflow of the gaseous medium, in particular H2; or

[0019] b) A first outlet channel for a gaseous medium, in particular H2, and a second outlet channel for a gaseous medium, in particular H2, are opened and closed alternately at their ends by means of diagonally acting valve pairs in such a way that at the first and second outlet channels one end is always a closed end and the opposite end is an open end.

[0020] By means of the operating method proposed according to the invention, it is possible to achieve in an advantageous manner that the pressure distribution of the gaseous medium with respect to all electrochemical cells arranged in the cell stack is significantly homogenized. By homogenizing the pressure of the gaseous medium between the individual electrochemical cells in the cell stack, the yield of the generated gaseous medium, in particular H2, can be increased in a powerful manner, so that, viewed as a whole, a significantly more efficient operation of the cell stack formed by the electrochemical cells can be achieved.

[0021] In an advantageous development of the method according to the invention, a controllable valve is assigned to each end of the outlet channel, which closes one end and opens one end at each outlet channel. This makes it possible to alternately open and close the outlet channels at the cell stack in normal operation of the cell stack and in shutdown mode.

[0022] In an advantageous development of the method proposed according to the invention, a first outlet channel for a gaseous medium, in particular H2, has an open end at one end, wherein a second outlet channel has an open end at its end opposite to the open end of the first outlet channel on the opposite side relative to the electrochemical cell.

[0023] In an advantageous development of the method proposed according to the invention, the gaseous medium, in particular H 2 , flows out of the outlet pipe according to a) at the two open ends of the outlet pipe in mutually opposite directions.

[0024] In a method variant of the method proposed according to the invention, the maximum difference in flow path length between all electrochemical cells in the cell stack is at least halved. The significant reduction in flow path length leads to a significant homogenization of the pressure distribution in the cell stack, which concerns gaseous media, in particular H2.

[0025] In a further advantageous development of the method proposed according to the invention, according to b), the gaseous medium, in particular H 2 , leaves the cell stack via two parallel outlet channels at their open ends in opposite directions.

[0026] In the method proposed according to the invention, the sum of the flow path lengths of the gaseous medium, in particular H2, between the respective electrochemical cell and the open ends of the first and second outlet channels is substantially the same for all electrochemical cells in the cell stack.

[0027] In a development of the method proposed according to the invention, in a first operating mode of the cell stack in which a gaseous medium, in particular H2, is produced, the first diagonally arranged valve pair is switched to its open position and the gaseous medium, in particular H2, escapes from the cell stack, while the second diagonally arranged valve pair assumes its closed position in the first operating mode. Thus, a continuous production of the gaseous medium, in particular H2, is ensured in the first operating mode.

[0028] In the method proposed according to the invention, the production of a gaseous medium, in particular H2, is shut down in a cut-off mode of the cell stack, in which the first diagonally arranged valve pair is switched into the closed position, while the second diagonally arranged valve pair assumes its open position. Thus, in the cut-off mode, the gaseous medium still present in the cell stack leaves the cell stack.

[0029] In a development of the method proposed according to the invention, the gaseous medium, in particular H2, is driven out of the cell stack by flushing the cell stack with an inert gas via the second diagonally arranged valve pair in the open position. Flushing the cell stack with an inert gas, such as air or nitrogen, converts the cell stack in the shut-off mode into a safe state by removing all residues of the gaseous medium, in particular H2, from the cell stack.

[0030] The invention furthermore relates to the use of the above-described method according to the invention for operating an electrolysis cell or for operating a fuel cell for driving an electric vehicle.

[0031] Invention Advantages

[0032] By the method for operating a battery stack comprising a plurality of electrochemical cells arranged one above the other according to the present invention, the operation of the battery stack can be significantly improved. On the one hand, by the method according to the present invention, a homogenization of the pressure level can be achieved in the electrochemical cells forming the battery stack. By homogenizing the pressure level in the battery stack, more uniform flow characteristics are obtained, and thus improved full utilization of all components in the battery stack is obtained. In addition, by the operating method for the battery stack according to the present invention, the total yield of the gaseous medium, especially H2, can be increased in an advantageous manner, so that the battery stack as a whole can be operated significantly more efficiently.

[0033] By homogenizing the pressure level in the cell stack, it is also possible to counteract phenomena that occur between adjacent electrochemical cells in the cell stack due to deviations in the flow paths of the gaseous medium between the electrochemical cells. By the solution proposed according to the invention for homogenizing the pressure level, it is possible to reduce the flow resistance to the flow of the gaseous medium, which may occur in electrochemical cells located further inwards and arranged away from the outlet channel. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Embodiments of the present invention are explained in more detail with reference to the accompanying drawings and the following description.

[0035] The accompanying drawings show:

[0036] Figure 1 A perspective view of a cell stack comprising a plurality of electrochemical cells arranged one above the other, with an upper end plate and a lower end plate,

[0037] Figure 2 Different scenarios of the flow of circulating reactants through a cell stack schematically shown here with a plurality of electrochemical cells arranged one above the other,

[0038] Figure 3 A top view of a seal which is arranged between two electrochemical cells arranged one above the other and comprises channels for different media,

[0039] Figure 4.1 and 4.2 Flow through half of a stack and flow through a complete stack are shown schematically.

[0040] Figure 5 Preferred flow variants in the battery stack,

[0041] Figure 6 View of a battery stack formed of electrochemical cells with straight and curved joints,

[0042] Figure 7 a first operating mode of the cell stack for producing a gaseous medium, in particular H2, and

[0043] Figure 8 A cut-off mode of the cell stack, in which the cell stack is flushed with an inert gas. DETAILED DESCRIPTION

[0044] In the following description of the embodiments of the present invention, identical or similar elements are marked with the same reference numerals, wherein a repeated description of these elements is omitted in individual cases. The figures merely schematically illustrate the subject matter of the present invention.

[0045] Figure 1A perspective view of a battery stack 12 is shown, which comprises several electrochemical cells 10 arranged one above the other. The battery stack 12 is fixed by a connector 14 extending essentially in the vertical direction. On the upper side of the battery stack 12 there is an upper end plate 16, on which the connector is arranged; the battery stack 12 has a lower end plate 18 on its lower side. The end plates 16, 18 are equipped with insulating plates 20 on their sides facing the battery stack 12. A first current collector 22 and a second current collector 24 are shown on the side of the battery stack 12. The individual electrochemical cells 10 have bipolar plates, i.e. active areas, as known from the prior art, wherein, for example, 24 individual electrochemical cells 10 can be present in the battery stack 12. The number of electrochemical cells can vary depending on the height of the battery stack 12.

[0046] from Figure 2 , it can be seen how the gaseous medium 38, in particular H2, flows through the cell stack 12, which is only schematically illustrated in this figure. Figure 2 , at least one inlet channel 30 and at least one outlet channel 32 extending parallel thereto extend substantially in a vertical direction. Arranged between them are respective transverse connectors 34 and electrochemical cells 10. The gaseous medium 38 entering the inlet channel at the upper end of the inlet channel 30 flows through the electrochemical cells 10 arranged one above the other in the cell stack 12. The gaseous medium 38, in particular H2, leaves the electrochemical cells 10 arranged one above the other via at least one outlet channel 32 at the upper end of the outlet channel.

[0047] Figure 3 4 shows a top view of a seal 40. The seal 40 is preferably arranged between individual electrochemical cells 10 arranged one above the other in the vertical direction in the battery stack 12 so that these electrochemical cells are sealed from each other in the battery stack 12 when the connector 14 is clamped. It can be seen from the top view according to FIG. 4 that the outlet channels 32 for the gaseous medium 38, in particular H2, extend through the seal 40 opposite to each other. In addition, the seal 40 also has a porous layer 42 (PTL) in its central area. In addition, a channel 44 for gaseous hydrogen (H2) is also provided in the seal. If the individual electrochemical cells 10 are inserted in Figure 3 In the case of the seal 40 shown in the top view in FIG. 1 , if they are arranged one above the other, a channel extending through the battery stack 12 in the vertical direction into the drawing plane is formed, as shown in FIG. Figure 3 As indicated by positions 32 and 44 in FIG.

[0048] In accordance with Figure 4.1 The schematic diagram of FIG. 1 shows half 60 of the battery stack 12 , and according to FIG. Figure 4.2 The complete battery stack 12 is reflected in the schematic diagram of FIG.

[0049] from Figure 4.1It can be seen that the gaseous medium 38, in particular H2, produced in the cell stack 12 or in one half 60 of the cell stack 12 flows from the individual electrochemical cells 10 between the upper side 46 and the lower side 48 of the cell stack to the outlet channel 32. The outlet channel 32 is provided with an open end 52. As a result, the gaseous medium 38, in particular H2, can flow away via the outlet channel 32 and its open end 52 in a first partial flow 66 and a second partial flow 68. Figure 4.1 It is understood that the mentioned partial flows 66, 68 leave the outlet channel 32 in mutually opposite flow directions 72, 74, namely downwards in a first flow direction 72 and upwards in a second flow direction 74 in the direction of the upper side 46. Figure 6 Schematic diagram of Figure 4.1 Not shown are the end plates 16 , 18 that bound the battery pack 12 .

[0050] from Figure 4.2 The flow relationship in the fully illustrated cell stack 12 can be seen in more detail. In this flow relationship, the first outlet channel 84 and the second outlet channel 86 are located opposite each other on the sides of the cell stack 12. The first outlet channel 84 and the second outlet channel 86 also have open ends 52, via which the gaseous medium 38, in particular H2, leaves the cell stack 12 again at the upper side 46 or at the lower side 48. Here too, partial flows 66, 68 occur in the outlet channels 84, 86, which leave the two outlet channels 84, 86 arranged opposite each other again in opposite flow directions 72, 74 (see FIG. 1 ). Figure 4.1 ). Figure 4.1 and Figure 4.2 The flow characteristics described are different, depending on Figure 5 The flow relationship shown in the schematic diagram is another case.

[0051] from Figure 5 It can be seen that the battery stack 12 also has two outlet channels extending parallel to each other, namely a first outlet channel 84 and a second outlet channel 86. The two outlet channels 84, 86 extending parallel to each other conduct the generated gaseous medium 38, in particular H2, out of the battery stack 12. The two outlet channels 84, 86 extending parallel to each other are provided with closed ends 50 at opposite ends and also have diagonally opposite open ends 52, through which the gaseous medium 38, in particular H2, flows out of the battery stack 12. According to Figure 5 In the schematic diagram in FIG. 8 , the first outlet channel 84 is provided with an open end 52 at its upper end and a closed end 50 at its lower end. In the opposite second outlet channel 86, the closed end 50 and the open end 52 are swapped relative to the first outlet channel 84. This means that according to Figure 5The gaseous medium 38 leaves the first outlet channel 84 at the upper side 46 at the open end 52 thereof, and the gaseous medium 38, in particular H2, flows out at the lower end of the second outlet channel 86 in the region of the lower side 48. Figure 4.1 and Figure 4.2 In the flow variant shown in FIG. 1 , the gaseous medium 38, in particular H2, leaves the outlet channel 32 via the open end 52 at the upper and lower sides 46, 48 in opposite flow directions 72, 74; 84, 86. It follows that the maximum difference between the corresponding flow path lengths, with reference to all electrochemical cells 10 of the cell stack 12, is essentially halved.

[0052] In accordance with Figure 5 In the flow arrangement of , the gaseous medium 38, in particular H2, leaves the battery stack 12 via two outlet channels 84, 86, which, however, have a closed end 50 at one end and only an open end 52 at the end opposite to the closed end, through which the gaseous medium 38, in particular H2, can escape from the battery stack 12. It follows that according to Figure 5 In the flow variations in the gaseous medium 38, in particular H2, the sum of the flow path lengths between the respective electrochemical cell 10 and the open ends 52 of the two outlet channels 84, 86 is essentially the same for all electrochemical cells 10 arranged one above the other in the cell stack 12.

[0053] from Figure 6 A perspective view of the constructed battery stack 12 can be seen in FIG. The individual electrochemical cells 10 arranged one above the other are separated from one another by seals 40. Figure 6 In the cell stack 12 shown in FIG. 1 , for example, 24 electrochemical cells 10 are arranged one above the other. These electrochemical cells are bounded by an upper end plate 16 and a lower end plate 18. A connection 64 is provided on the upper end plate 16. The connection 64 for the medium flowing through the cell stack 12 or the gaseous medium 38, in particular H2, flowing out of the cell stack 12 can be oriented either vertically upward or with a 90° orientation 62, as in FIG. Figure 6 If the joint 64 is in an angled position, i.e., is provided with a 90° orientation 62, then the Figure 6 The illustration in FIG. 1 shows the structural height of the completed battery stack 12 .

[0054] from Figure 7 and Figure 8 Two different operating modes of the battery stack 12 can be seen in FIG.

[0055] Figure 7 The first operating mode of the battery stack 12 is shown. Figure 7It can be seen that the cell stack 12 has two outlet channels 84, 86 running parallel to each other. At the mutually opposite ends of these outlet channels there is a first valve 88, a second valve 90, a third valve 92 and a fourth valve 94. The valves 88, 90, 92, 94 mentioned can be switched between an open position 100 and a closed position 102.

[0056] A first diagonally arranged valve pair 96 is formed by the first valve 88 and the third valve 92 ; a second diagonally arranged valve pair 98 is illustrated by the second valve 90 and the fourth valve 94 .

[0057] The first operating mode is Figure 7 , which is a normal operating mode of the cell stack 12, in which the first diagonally arranged valve pair 96 is open and the second diagonally arranged valve pair 98 is in its closed position 102. Thus, in normal operation of the cell stack 12, the gaseous medium 38, in particular H2, flows out of the cell stack 12. Figure 7 The operating mode shown in FIG. 1 corresponds essentially to the operating mode of the gaseous medium 38 as in FIG. Figure 5 The flow relationship shown in .

[0058] If the battery stack 12 is now switched off, ie, operated in the switch-off mode, then according to Figure 8 , the first diagonally arranged valve pair 96 with the first valve 88 and the third valve 92 is transferred to its closed position 102, while the second diagonally arranged valve pair 98 with the valves 90 and 94 is adjusted to its open position 100. In this case, the gaseous medium 38 remaining in the cell stack 12 is removed in such a way that, for example, an inert gas, such as air or nitrogen, is introduced into the cell stack 12 at the fourth valve 94 in its open position 100, which flushes the cell stack and removes the gaseous medium 38, in particular H2, remaining in the outlet channels 84, 86 or in the electrochemical cells 10 arranged one above the other between them through the second valve 90 in its open position 100. Thus, according to Figure 8 In the shut-off mode of the schematic diagram in FIG. 1 , the gaseous medium 38 , in particular H 2 , remaining in the cell stack 12 can be completely removed from the cell stack, so that the cell stack 12 can be safely transferred into a stationary state, ie, a shut-off state.

[0059] In accordance with Figure 8 After flushing the cell stack 12 , all four valves 88 , 90 , 92 , 94 may be switched to their closed positions 102 as long as the cell stack 12 is not in operation, thereby preventing contaminants from entering the cell stack 12 .

[0060] Flushing the cell stack, i.e. driving off residual gaseous medium 38, in particular H2, is helpful in this respect, since otherwise even small amounts of residues can contaminate the membranes on the anode side, which makes it difficult to restart the cell stack 12 smoothly at a later point in time. Furthermore, gaseous medium 38, in particular H2, which remains in the cell stack 12 can react chemically and attack the membranes of the electrochemical cells 10 within the cell stack 12. This can be prevented by completely driving off the gaseous medium 38, in particular H2.

[0061] The present invention is not limited to the embodiments described herein and the aspects highlighted therein, but rather many variations are possible within the scope of the claims, which are within the capabilities of a person skilled in the art.

Claims

1. A method for operating a cell stack (12) having a plurality of electrochemical cells (10) arranged one above the other and sealed from one another, through which a gaseous medium (38), in particular H2, flows, which gaseous medium leaves the cell stack via at least one outlet channel (32; 84, 86), characterized in that: a) the outlet channel (32) for the gaseous medium (38), in particular H2, comprises at its end an open end (52) for the outflow of the gaseous medium (38); or b) A first outlet channel (84) for the gaseous medium (38), in particular H2, and a second outlet channel (86) for the gaseous medium (38), in particular H2, are alternately opened and closed at their respective ends by means of a pair (96, 98) of diagonally acting valves (88, 90, 92, 94) so ​​that one end of the first and second outlet channels (84, 86) is always a closed end (50) and the opposite end is an open end (52).

2. The method according to claim 1, characterized in that Each end of the outlet channels (84, 86) is assigned a controllable valve (88, 90, 92, 94), which closes one end and opens the opposite end of each outlet channel (84, 86).

3. The method according to claim 1, characterized in that The first outlet channel (84) for the gaseous medium (38), in particular H2, has an open end (52) at one end, and the second outlet channel (86) has an open end (52) at the end of the second outlet channel opposite to the open end (52) of the first outlet channel (84) on the opposite side relative to the electrochemical cell (10).

4. The method according to claim 1, characterized in that: According to a), the gaseous medium (38), in particular H2, flows out at the two open ends (52) of the outlet channel (82) in mutually opposite flow directions (72, 74).

5. The method according to claim 4, characterized in that According to a), the maximum difference in flow path length between all electrochemical cells (10) within the cell stack (12) is at least halved.

6. The method according to any one of claims 1 to 3, characterized in that According to b), the gaseous medium (38), in particular H2, leaves the cell stack (12) again via two parallel outlet channels (84, 86) at their open ends (52) in opposite flow directions (72, 74) of the outlet channels (84, 86).

7. The method according to claim 6, characterized in that The sum of the flow path lengths of the gaseous medium (38), in particular H2, between the respective electrochemical cells (10) and the open ends (52) of the first and second outlet channels (84, 86) is substantially the same for all electrochemical cells (10) within the cell stack (12).

8. The method according to any one of claims 1 to 7, characterized in that In a first operating mode of the cell stack (12) for generating a gaseous medium (38), in particular H2, a first diagonally arranged valve pair (96) assumes an open position (100) and the gaseous medium (38), in particular H2, escapes from the cell stack (12), while a second diagonally arranged valve pair (98) assumes a closed position (102).

9. The method according to any one of claims 1 to 7, characterized in that In a shut-off mode of the cell stack (12), the production of the gaseous medium (38), in particular H2, is shut down, in which the first diagonally arranged valve pair (96) assumes its closed position (102) and the second diagonally arranged valve pair (98) assumes its open position (100).

10. The method according to claim 9, characterized in that The gaseous medium (38), in particular H2, is removed by flushing the cell stack (12) with an inert gas via the second diagonally arranged valve pair (98) in the open position (100).

11. The method according to any one of claims 9 to 10, characterized in that The cell stack (12) is purged with air or nitrogen. 12 . Use of the method according to claim 1 for operating an electrolysis cell or for operating a fuel cell for driving an electric vehicle.

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