Regenerating an electrolysis cell

Abstract

The invention relates to a method for operating at least one electrolysis cell (12) of an electrolysis system (10), wherein the electrolysis cell (12) is supplied with an electrolysis power in normal electrolysis operation (64) in order to produce at least one electrolysis product from a substance to be electrolyzed. According to the invention, at least one predetermined electrical power pulse that has a predetermined power amplitude is applied to the at least one electrolysis cell (12) outside of normal electrolysis operation (64) in regeneration operation (66) in order to regenerate the at least one electrolysis cell (12).

Description

[0001] 2024PF00738

[0002] Description

[0003] Regenerating an electrolysis cell

[0004] The invention relates to a method for operating at least one electrolysis cell of an electrolysis plant, wherein the electrolysis cell is supplied with an electrolysis current in intended electrolysis operation in order to produce at least one electrolysis product from a substance to be electrolyzed. Furthermore, the invention relates to an electrolysis plant with a plurality of electrolysis cells, which are at least partially connected electrically in series, a power supply unit electrically coupleable to the electrolysis cells and configured to provide electrical electrolysis power in order to supply the electrolysis cells with an electrolysis current in intended electrolysis operation, and a cell supply unit at least for supplying a substance to be electrolyzed to the electrolysis cells and for removing at least one electrolysis product in intended electrolysis operation.

[0005] Processes of this type, as well as electrolysis plants, are extensively known in the prior art, so that no separate printed evidence is required. Electrolysis plants serve to convert one or more chemical substances, as the substance to be electrolyzed, into other chemical substances, namely electrolysis products, by means of electricity. For this purpose, the electrolysis plant has a plurality of electrolysis cells, with the corresponding electrochemical conversion taking place in each of the electrolysis cells. For this purpose, the electrolysis cells are supplied with an electric electrolysis current or an electric electrolysis power during intended electrolysis operation. As a rule, this is done with the aid of 2024PF00738

[0006] 2

[0007] The electrolysis current causes a chemical reaction, i.e., a transformation of matter. This is called electrolysis. A well-known and frequently used form of electrolysis is water electrolysis. In water electrolysis, water is broken down into its components, namely hydrogen and oxygen, using the electrolysis current. In principle, however, other substances can also be subjected to electrolysis, such as carbon dioxide or the like.

[0008] Both the substance to be electrolyzed and the electrolysis product are generally fluids that are supplied to and removed from the electrolysis cells via appropriate supply lines. These supply lines are usually connected to, or at least partially encompassed by, a cell supply unit. The cell supply unit serves to supply the electrolysis cells with the respective substances, or at least one operating fluid, for the intended electrolysis operation. In this context, "supply" therefore means not only the introduction of the operating fluid or the substance to be electrolyzed, but also the removal of the respective electrolysis product.

[0009] The supply of hydrogen is proving particularly relevant to industry, especially since hydrogen can be a versatile energy carrier. Hydrogen can be produced using an electrolysis plant, also called an electrolyzer, particularly when powered by renewable electricity. One method of hydrogen production involves using an electrolysis plant to perform water electrolysis.

[0010] The electrolysis cells utilize, for example, proton exchange membranes (PEMs). The principle of a PEM-based electrolysis device 2024PF00738

[0011] 3

[0012] A PEM-based electrolysis cell is known in the prior art, therefore further explanation is omitted here. An electrolysis cell of this type for producing hydrogen and oxygen from water is disclosed, for example, in DE 10 2011 007 759 Al.

[0013] Electrolysis devices of this type typically consist of multiple electrolysis cells, often connected in series. Depending on the design of the electrolysis system and the electrolysis cells, however, the electrolysis cells may also be connected in parallel, at least partially. During electrolysis operation, the electrolysis cells are electrically coupled to an electrical power supply unit of the electrolysis system, which provides a suitable electrical current—specifically, the electrolysis current or power—for the intended electrolysis process. This allows the electrolysis cells to carry out the intended electrochemical conversion process.

[0014] Furthermore, the electrolysis cells in an electrolysis system are often arranged sequentially in a stacking direction, forming a cell stack. This stacked arrangement allows for direct electrical contact between the successive electrolysis cells, simplifying series connection. Additionally, separate electrical connections for the electrolysis cells can be largely reduced or even eliminated. Finally, a compact, mechanically stable design can be achieved.

[0015] Within a cell stack, a supply line arrangement with cell connection lines can also be used. 2024PF00738

[0016] 4

[0017] (English: manifold) or a supply structure of a cell supply unit is provided, which serves, among other things, to supply the at least one operating material or the at least one substance to be electrolyzed to the electrolysis cells and / or to remove the at least one electrolysis product from the electrolysis cell. The cell stack is generally operated with a specific electrolysis power or electrolysis current such that the electric current of the cell stack is as low as possible, while at the same time the electric voltage across the cell stack is as high as possible. This is achieved by appropriately stacking the electrolysis cells within the cell stack.This allows the electrical voltages of the individual electrolysis cells in the cell stack to add up to a cell stack voltage, while the electrolysis cells connected in series in this way can be operated with an essentially identical electrolysis current.

[0018] The electrolysis power is provided by the power supply unit, which can be connected to the respective opposing electrical terminals of the cell stack for this purpose. The power supply unit is preferably connectable to a power supply network such as the public power grid. A large number of electrolysis cells can be arranged in the cell stack, for example, more than about 100 electrolysis cells, in particular several hundred electrolysis cells, but preferably not more than about 400 electrolysis cells. In the electrolysis of water to hydrogen and oxygen, for example, the electrical voltage at each of the electrolysis cells is about 1.5 V to about 2.5 V. It follows that in a cell stack of such electrolysis cells, the cell stack voltage often exceeds 100 V and can even be several hundred volts. 2024PF00738

[0019] 5

[0020] In addition to the cell stack, the electrolysis system can include other components, such as pumps, heat exchangers, and separators, which are necessary for proper electrolysis operation. These components can be provided collectively by the cell supply unit. The electrolysis system also typically includes a control unit that manages the electrolysis process.

[0021] During normal operation of the electrolysis plant, it becomes apparent that the electrolysis cells are subject to aging and a decrease in efficiency. This aging and efficiency degradation can be caused by impurities affecting the electrolysis cells, particularly their components such as the proton exchange membrane. These impurities can originate from components of the electrolysis cells themselves, materials and components of the cell stack or the electrolysis plant, or from substances that come into contact with the electrolysis cells. Furthermore, the presence of impurities can also depend on the operating conditions and profiles of the electrolysis plant and the electrolysis cells, and can consequently lead to corrosion and aging.This can include, for example, cations, particularly from metals, which may be released from metallic parts made of stainless steel or titanium. Any aging can negatively affect the performance of the electrolysis cells or cell stack and therefore impair electrolysis efficiency and lifespan.

[0022] While reuse or reprocessing is possible for many metallic components, this is not the case, for example, for 2024PF00738

[0023] 6

[0024] Catalyst-coated proton exchange membranes, for example those of membrane electrode assemblies (MEAs), are not readily available. Therefore, in the prior art, it is common practice to incinerate catalyst-coated membranes (CCMs) and, in a subsequent step, recover only some valuable substances such as platinum group metals (PPMs) in order to reuse them in the production of the catalyst.

[0025] The prior art already includes attempts to partially regenerate catalyst-coated membranes using acid, such as sulfuric acid, carbonic acid, or the like. However, it has been shown that such regeneration is only effective if it immediately follows a corresponding contamination or is at least intended for an artificial and precisely dosed contamination. This, however, cannot be achieved in normal electrolysis operation, particularly in electrolysis plants.

[0026] Overall, the fact that an electrolysis cell must be replaced when it reaches a certain stage of aging or a low efficiency proves to be a disadvantage in terms of the state of the art. This is not only costly, but also a drawback for electrolysis systems that consist of a large number of such cells. Replacing an electrolysis cell requires deactivating the electrolysis system, or at least the corresponding cell stack. It is problematic that the electrolysis cells in an electrolysis system do not age uniformly or change their efficiency uniformly. This can lead to the electrolysis system having to be deactivated far too often to replace aged or particularly efficient electrolysis cells.

[0027] Furthermore, it should be noted that any exchange 2024PF00738

[0028] 7

[0029] Replacing a complete stack of cells represents an enormous effort, especially in terms of cost.

[0030] The invention is based on the objective of providing an improvement in this regard and, in particular, achieving an improvement in terms of the intended operation of electrolysis cells or an electrolysis system.

[0031] The invention proposes a method, an electrolysis plant and a regeneration unit according to the independent claims as a solution.

[0032] Advantageous further training opportunities arise from the characteristics of the dependent requirements.

[0033] With regard to a generic method, the invention particularly proposes that the at least one electrolysis cell is subjected to at least one predetermined electrical power pulse, having a predetermined power amplitude, in a regeneration mode outside of the intended electrolysis operation in order to regenerate the at least one electrolysis cell.

[0034] With regard to a generic electrolysis system, the invention particularly proposes that the electrolysis system has a regeneration unit configured to subject at least one of the electrolysis cells to at least one predetermined electrical power pulse having a predetermined power amplitude in a regeneration mode outside of the intended electrolysis operation, in order to regenerate the at least one electrolysis cell.

[0035] The invention further proposes, in particular, a regeneration unit for the electrolysis system. 2024PF00738

[0036] 8

[0037] The invention is based, among other things, on the idea that impurities, which can cause aging and / or degradation with regard to efficiency and which have settled in components of the electrolysis cell, can be remobilized. This makes it possible to remove the remobilized impurities from the electrolysis cell and at least partially reverse or reduce their impact on aging or efficiency degradation. The invention utilizes, among other things, the knowledge that an electrolysis cell can be at least partially regenerated by means of an electrical power pulse, in particular an electrical current pulse, so that the aging process can be at least partially reversed, or efficiency degradation can be at least partially reversed.The effect of the invention can be based, at least in part, on the fact that impurities or substances causing aging or efficiency degradation, such as metal cations, can be mobilized by one or more power pulses so that they can be removed from the electrolysis cell. It has been shown that aging or efficiency degradation can depend, among other things, on impurities. By removing these impurities from the electrolysis cell through regeneration, the resulting negative effects on aging or efficiency can be at least partially reversed. This allows the intended operation of the electrolysis cell, and in particular the electrolysis system, to be reliably maintained for a longer period without the need for intervention.Overall, the invention makes it possible to improve the operation of the electrolysis system, in particular its electrolysis cells. Extensive maintenance work. 2024PF00738.

[0038] 9

[0039] They can be reduced, for example by only needing to be carried out at longer intervals.

[0040] Furthermore, the operation of a cell stack can also be improved, even if the electrolysis cells are not homogeneously exposed to impurities. The inhomogeneous exposure of the electrolysis cells in a cell stack to impurities can lead to the electrolysis cells themselves aging differently, or to their efficiency changing differently, particularly reducing it, depending on their individual exposure to the impurities. The invention makes it possible to regenerate the electrolysis cells, thereby at least partially reducing, and in particular reversing, this uneven development of aging or degradation states of the electrolysis cells with regard to efficiency. This allows operation to be improved, and in particular extended, even under unfavorable operating conditions.

[0041] The regeneration mode of the electrolysis cell differs from the intended electrolysis mode in that the electrolysis cell is no longer supplied with the electrolysis power or current, but instead with at least one predetermined electrical power pulse. The power amplitude is appropriately predetermined so that the regeneration effect can preferably be at least partially achieved in regeneration mode.

[0042] In normal electrolysis operation, the electrolysis cell is supplied with the specified electrolysis current or power, enabling electrolysis to occur under these operating conditions. In water electrolysis, hydrogen and oxygen are produced from water. (2024PF00738)

[0043] 10

[0044] Carbon dioxide electrolysis produces carbon monoxide and oxygen from supplied carbon dioxide during normal electrolysis operation.

[0045] Electrolysis is not required during regeneration mode. Ideally, electrolysis should not occur at all during regeneration. However, it may be possible to allow for partial electrolysis even during regeneration mode.

[0046] Furthermore, it can be provided that, during regeneration operation, at least one electrolysis cell, preferably the cell stack, and particularly preferably the electrolysis system, can be supplied with a purging fluid, for example a purging gas, a purging liquid, or the like. This can assist in the removal of mobilized impurities.

[0047] Regeneration can be carried out over a predetermined period. Depending on requirements, the electrolysis cell can be subjected to more than one power pulse during regeneration. These power pulses can, for example, have the same predetermined power amplitude. Alternatively, the power pulses can have different predetermined power amplitudes. The number of power pulses and the predetermined power amplitudes can be selected based on the electrolysis cell's design, the degree of aging or efficiency degradation, and / or similar factors.

[0048] The regeneration unit can include a regeneration control unit that implements the necessary control functionalities for regeneration operation. The regeneration control unit can communicate with the control unit of the electrolysis plant. (See 2024PF00738 for further details.)

[0049] 11

[0050] Is it possible to implement the electrolysis operation and the regeneration operation in a suitable manner?

[0051] According to a further development, it is proposed that the at least one electrolysis cell be operated with a regeneration power that is at least 50% of the rated power, preferably at most 30% of the rated power, and particularly preferably at most 20% of the rated power, of the at least one electrolysis cell, or at least 200% of the rated power, and preferably 300% of the rated power, of the at least one electrolysis cell. It has been shown that in many applications of regeneration operation, such power increases are suitable for mobilizing impurities. This makes it possible to remove these impurities from the electrolysis cell using the rinsing fluid or during subsequent normal operation.

[0052] Furthermore, it is proposed that the at least one predetermined power pulse extend over a period of at most 15 minutes, preferably at most 6 minutes, and particularly preferably at most 1 minute. This makes it possible to supply the electrolysis cell with a correspondingly large predetermined power pulse, with which the electrolysis cell can be supplied with a power output greater than its rated power. This allows the regeneration process to be further improved.

[0053] Furthermore, it is proposed that the at least one predetermined power pulse has a slope of at least 10% of the rated power per second, preferably at least 80% of the rated power per second, and particularly preferably at least 100% of the rated power per second, at least on a rising or falling edge. The steepness of the power pulse's edge can particularly advantageously achieve the mobilization of impurities.

[0054] 12

[0055] The process can at least be improved. Preferably, the slope can be implemented for both the rising and falling edges of the specified power pulse. The slope of the edge can be the same for the rising and falling edges, or it can be chosen differently. With multiple power pulses, each pulse can have the same slope on its respective edge. However, depending on requirements, the slope of the respective edges can also be chosen to differ, at least partially, for multiple power pulses. This makes it possible to implement specific mobilization scenarios for the contaminants. The regeneration process can be further improved.

[0056] Furthermore, it is proposed that the at least one electrolysis cell, during regeneration, be subjected to at least two successive predetermined power pulses, with the power pulses being spaced at least one minute apart, preferably at least 15 minutes. The interval between successive, and in particular immediately successive, predetermined power pulses makes it possible, for example, to perform a flushing process between two successive power pulses. Moreover, it is possible to thermally relieve the electrolysis cell if the predetermined power pulses are greater than a rated power.

[0057] It is further proposed that the operating temperature of the at least one electrolysis cell during regeneration should be at most 80%, preferably 60%, and particularly preferably 50%, of the operating temperature of the at least one electrolysis cell during normal electrolysis operation. This will further improve the regeneration process. The temperature can be controlled, for example, by means of a temperature control unit or the flushing fluid 2024PF00738.

[0058] 13

[0059] and / or similar settings. For example, the electrolysis cell can at least be heated or cooled.

[0060] According to a further training, it is proposed that the start of the regeneration process be separated from the end of the intended electrolysis operation by a preparation period. This ensures that the electrolysis operation can be reliably completed before the regeneration process begins. Generally, it can be planned that the regeneration process follows an intended electrolysis operation. To ensure that the regeneration process can be carried out reliably as intended, it can be advantageous for the intended electrolysis operation to be reliably completed, in particular for no further electrolysis to take place. This can be beneficial if, during the intended electrolysis operation, the electrolysis cell may be contaminated with impurities that are precisely what the regeneration process is intended to remove. This can further improve the regeneration process.The preparation period can last for one or more minutes, for example. It can also last for half an hour or more.

[0061] According to a further embodiment, it is proposed that the process be carried out at least once a day, preferably at least ten times a day, and particularly preferably at least 100 times a day. This makes it possible to integrate the regeneration process into the intended operation of the electrolysis plant and thus improve the overall reliability of the electrolysis plant. This also applies, in principle, to the individual electrolysis cell that is subjected to the regeneration process.

[0062] It is further proposed that an electrolysis efficiency of at least one electrolysis cell be recorded, the electrolysis efficiency being measured with a 2024PF00738

[0063] 14

[0064] A predefined reference value is compared, and the regeneration process is triggered based on this comparison. This allows for automation of the regeneration process. The regeneration process can therefore be triggered based on this comparison. Triggering the regeneration process can include, among other things, terminating the intended electrolysis operation, if it is running, before activating the regeneration process. Furthermore, it can also be stipulated that the preparation period is activated first. The duration of this preparation period can also be determined based on the comparison.

[0065] It is further proposed that the regeneration unit be designed to electrically isolate at least one electrolysis cell from the power supply unit during regeneration. The power supply unit is a component of the electrolysis system that serves to supply the electrolysis cells, or at least one cell stack, with the electrolysis power during normal electrolysis operation. This is generally a substantially constant electrical power output over a longer period than the duration of a power pulse. For regeneration, however, the provision of the specified power pulse is required. The power supply unit is generally not designed for this purpose.Therefore, it can be provided that the regeneration unit electrically isolates the at least one electrolysis cell from the power supply unit so that the at least one electrolysis cell can be supplied with the specified power pulse during regeneration operation. Preferably, the regeneration unit is connected to the at least one electrolysis cell and provides the at least one power pulse. 2024PF00738.

[0066] 15

[0067] Furthermore, it is proposed that the regeneration unit includes a regeneration power unit configured to provide at least one power pulse to at least one electrolysis cell during regeneration operation. For this purpose, the regeneration unit can be electrically coupled to the at least one electrolysis cell, allowing the electrolysis cell to be supplied with the at least one power pulse. The regeneration power unit can have its own power source. Alternatively, the regeneration power unit can be connected to a power supply network, in particular the public electrical power grid.

[0068] Furthermore, it is proposed that the regeneration unit shall have a service unit which is designed to disconnect at least one electrolysis cell from the other electrolysis cells, at least electrically or mechanically, for the purpose of carrying out the regeneration operation and to connect it to the regeneration unit instead.

[0069] This makes it possible to continue operating the other electrolysis cells in their intended electrolysis mode and simply connect the electrolysis cell designated for regeneration to the regeneration unit. Naturally, this can also be implemented for a cell stack. For this purpose, a transport unit, a robot, and / or similar device can be used to perform the necessary functionalities.

[0070] It is further proposed that the regeneration unit includes a rinsing unit that can be coupled to the at least one electrolysis cell and is configured to supply the at least one electrolysis cell with a rinsing fluid for the purpose of carrying out the regeneration operation. This makes it possible to rinse the at least one electrolysis cell so that impurities, which are present by means of the 2024PF00738

[0071] 16

[0072] At least one predetermined power pulse must be mobilized to remove at least some of the residue from the electrolysis cell. The purge fluid can be, for example, a suitable purge gas, a suitable purge liquid, and / or the like. Furthermore, the purge fluid can be used to temperature-control at least one electrolysis cell, that is, to support or enable the electrolysis cell to reach a predetermined temperature.

[0073] The advantages and effects stated for the process according to the invention naturally apply equally to the electrolysis plant and the regeneration unit according to the invention, and vice versa. In this respect, process features can also be formulated as device features and vice versa.

[0074] The embodiments described below are preferred embodiments of the invention. The features and combinations of features specified above in the description, as well as those mentioned in the following description of embodiments and / or shown individually in the figures, are not only usable in the combinations specified, but also in other combinations. Thus, embodiments are also encompassed by the invention or are considered disclosed that are not explicitly shown and explained in the figures, but can be derived and produced from the described embodiments by separate combinations of features.The features, functions, and / or effects illustrated by the embodiment examples can each, in themselves, represent individual features, functions, and / or effects of the invention, which must be considered independently of one another and which further develop the invention independently. Therefore, the embodiment examples should also include combinations other than those in the described embodiments. Furthermore, the described embodiments can also be modified by further embodiments of the 2024PF00738.

[0075] 17

[0076] The invention may be supplemented with features, functions and / or effects already described.

[0077] In the figures, the same reference symbols denote the same features and functions.

[0078] They show:

[0079] FIG 1 shows a schematic circuit diagram of an electrolysis plant with a plurality of electrolysis cells connected in series, arranged in cell stacks, and a regeneration unit for regenerating the electrolysis cells;

[0080] FIG 2 shows a schematic diagram representation of a current density profile of an electrolysis cell of a cell stack of the electrolysis plant according to FIG 1;

[0081] FIG 3 shows a schematic diagram of the cell voltage profile of the electrolysis cell according to FIG 2; and

[0082] FIG 4 shows a schematic diagram of the temperature profile of the electrolysis cell according to FIG 2.

[0083] FIG. 1 shows a schematic circuit diagram of an electrolysis plant 10 with a plurality of electrolysis cells 12, which are arranged in cell stacks 18 and electrically connected in series. FIG. 1 shows four cell stacks 18 as an example. However, the electrolysis plant 10 can also have a plurality of cell stacks 18.

[0084] Each cell stack 18 has a plurality of electrolysis cells 12 connected in series. The series connection of each cell stack 18 is established via a first switching element 26 with a positive electrical 2024PF00738

[0085] 18

[0086] Supply line 58 and, via a second switching element 28, can be electrically coupled to a negative electrical supply line 56. An electrolysis voltage is provided between the supply lines 56 and 58, so that the cell stack 18, specifically the electrolysis cells 12 comprised of each cell stack 18, are supplied with a corresponding electrolysis voltage. The electrolysis cells 12 of each cell stack 18, connected in series, are subjected to an electrolysis current. This ensures that, for intended electrolysis operation 64 (FIG 2), each of the electrolysis cells 12 is supplied with an individual electrolysis power. Thus, in intended electrolysis operation 64, a substance to be electrolyzed, supplied to the electrolysis cells 12, can be subjected to electrolysis, so that each electrolysis cell 12 provides respective electrolysis products due to the intended electrolysis operation 64.In the present embodiment, the electrolysis plant 10 is designed for the electrolysis of water, such that water is the substance to be electrolyzed. The electrolysis products are therefore hydrogen and oxygen. In the present embodiment, the electrolysis cells 12 are essentially identical. However, in alternative embodiments, the electrolysis cells 12j can be at least partially different from one another.

[0087] The electrolysis plant 10 further comprises a cell supply unit 32, which is coupled to each of the electrolysis cells 12 via a line assembly 52. ​​The water to be electrolyzed can be supplied to the electrolysis cells 12 via the line assembly 52. ​​In addition, the line assembly 52 is designed to remove the hydrogen and oxygen produced during normal electrolysis operation 64 from the electrolysis cells 12. The 2024PF00738

[0088] 19

[0089] Electrolysis products can then be used, for example, in a respective hydrogen storage system or…

[0090] Oxygen storage is supplied. Furthermore, it is of course also possible to supply these substances to another industrial plant that uses them for its intended operation. In the intended electrolysis operation 64, the switching elements 26, 28 are in the switched-on state.

[0091] The electrolysis plant 10 has a control unit 14 that controls the operation of the electrolysis plant 10, and in particular the intended electrolysis operation 64. For this purpose, the control unit 14 is connected, among other things, via communication technology to the switching elements 26, 28 and thus determines their switching state. Depending on requirements and available power, the number of cell stacks 18 activated for electrolysis can be varied by switching the switching elements 26, 28.

[0092] The electrolysis plant 10 also includes a power supply unit 20, which is electrically connected to a public power supply network 16 and is supplied with electrical energy via this power supply network 16. Depending on the energy available from the power supply network 16, the number of activated cell stacks 18 is controlled during normal electrolysis operation.

[0093] The power supply unit 20 includes a transformer 22. A primary side of the transformer 22 is connected to the power supply network 16. This allows an alternating voltage supplied by the power supply network 16 to be converted to a suitable alternating voltage value for the operation of the electrolysis plant 10, which is supplied at a secondary side of the transformer 22. 2024PF00738

[0094] 20

[0095] A rectifier unit 24 is connected to the secondary side of the transformer 22. This unit is capable of providing rectification functionality and controlling rectification power. In the present embodiment, the rectifier unit 24 comprises thyristors, which are controlled by the control unit 14 according to the required power. On the DC side, the rectifier unit 24 provides the electrolysis voltage between the supply lines 56 and 58. Thus, on the DC side, the rectifier unit 24 is electrically connected to the switching elements 26 and 28.

[0096] The electrolysis plant 10 further comprises a regeneration unit 30, which is configured to subject the electrolysis cells 12 to at least one predetermined electrical power pulse with a predetermined power amplitude outside of the intended electrolysis operation 64 in a regeneration operation 66 (FIG 2). This allows the electrolysis cells 12 to be regenerated.

[0097] It has been shown that the electrolysis cells 12 are subject to aging, or rather a degradation of their efficiency, during normal electrolysis operation 64. This effect can be due, among other things, to unwanted cations that are deposited, particularly in PEM electrolysis cells, in the respective membrane or catalyst. This undesirable effect can reduce efficiency and accelerate aging. The regeneration unit 30 makes it possible to at least partially reverse this effect, as will be explained below.

[0098] For this purpose, the regeneration unit 30 has its own regeneration power unit 34, which provides the electrical power required for regeneration operation 66. In the present embodiment, 2024PF00738

[0099] 21

[0100] The regeneration power unit 34 is provided to have a regeneration rectifier 48, which in this case is also connected to the secondary side of the transformer 22. On the AC side, the rectifier unit 24 and the regeneration rectifier 48 are thus connected in parallel.

[0101] On the DC side, the regeneration rectifier 48 is electrically connected to an energy storage device 36, the regeneration power unit 34. The energy storage device 36 can comprise one or more accumulators, one or more capacitors, and / or the like to store electrical energy. The energy storage device 36 serves to provide electrical energy to a pulse unit 38 of the regeneration power unit 34 connected to the energy storage device 36.

[0102] The pulse unit 38 provides power pulses, as will be explained below. For this purpose, the pulse unit 38 is connected to a positive pulse line 60 and a negative pulse line 62. The pulse lines 60 and 62 can be electrically coupled to a respective cell stack 18 via respective service units 40, so that a power pulse from the pulse unit 38 can be applied to the respective cell stack 18.

[0103] For this purpose, the service unit 40 has a switching element 42 which, depending on the respective switching state, electrically couples one end of the cell stack 18 to the positive pulse line 60. Furthermore, the service unit 40 of the regeneration unit 30 has another switching element 44 which electrically couples the opposite end of the respective cell stack 18 to the negative pulse line 62, depending on the respective switching state. The switching elements 42 and 44 are actuated together by a regeneration control unit 46, which is designed to implement the functionality of the regeneration unit 30. In2024PF00738

[0104] 22

[0105] The present design provides that a respective service unit 40 is provided for each cell stack 18.

[0106] With the service unit 40, it is possible to electrically couple the respective cell stack 18 to the pulse unit 38 for carrying out the regeneration operation 66. In regeneration operation 66, it is therefore provided that the respective switching elements 26, 28 for the respective cell stack 18 for which the regeneration operation 66 is to be carried out are in the switched-off position.

[0107] The switching state is switched, whereas the switching elements 42, 44 are switched to the on switching state. It is provided that the pulse unit 38 is configured to perform the regeneration operation 66 for exactly one cell stack 18. In alternative embodiments, it is of course also possible that the pulse unit 38 is configured to perform the regeneration operation 66 simultaneously for more than one single cell stack 18.

[0108] The regeneration unit 30 further comprises a flushing unit 50, which is connected to each of the electrolysis cells 12 via a regeneration line arrangement 54. The flushing unit 50 enables the respective electrolysis cells 12 to be flushed during regeneration operation 66 in order to flush out impurities released or mobilized during regeneration operation 66. This makes it possible to remove the impurities at least partially from the electrolysis cells 12, thus achieving an improvement with regard to the aging state of the electrolysis cells 12 or an improvement with regard to the efficiency of the electrolysis cells 12.

[0109] The control unit 14 communicates with the regeneration control unit 46. This allows either only the switching elements 26, 28 or the 2024PF00738 to be activated.

[0110] 23

[0111] Switching elements 42, 44 can assume the switched-on switching state with respect to a respective cell stack 18. A respective cell stack can thus be selectively coupled to the regeneration unit 30.

[0112] FIG. 2 shows a schematic diagram of the current density profile of one of the electrolysis cells 12, a cell stack 18 of the electrolysis plant 10 according to FIG. In FIG. 2, an ordinate is assigned to a current density, whereas an abscissa is assigned to time. A graph 70 represents the current density profile. As can be seen from FIG. 2, the electrolysis cell 12 is in intended electrolysis operation 64 for a period t0 to tl. In this specific configuration, the cell current or electrolysis current for the electrolysis cell 12 has a current density of approximately 1.5 A / cm². 2This is caused and is essentially constant over this period. During the period from tO to tl, the electrolysis cell 12 is therefore operating as intended in electrolysis mode 64.

[0113] At time tl, a regeneration cycle 66 is initiated. For this purpose, the cell current is first reduced at time tl, so that the current density decreases until it reaches a current density of approximately 0.3 A / cm². 2 This current density is then present for the further period from tl to t2 and is essentially constant. The period from tl to t2 is referred to as preparation period 68.

[0114] At time t2, the preparation period 68 is complete, and the regeneration operation 66 begins. During regeneration operation 66, the electrolysis cell 12 is subjected to ten successive current pulses 76, one of which is shown in FIG. 2. The current pulses 76 are spaced apart by at least one minute. After the last current pulse 76 has been executed, the intended electrolysis operation 642024PF00738 begins.

[0115] 24

[0116] It is automatically reactivated. For this purpose, switching elements 26, 28, 42, 44 are actuated accordingly.

[0117] FIG 2 shows that the amplitude of the current pulse 76 is approximately 3 A / cm. 2which is approximately twice the current density in the intended electrolysis operation 64. FIG. 2 further shows that the current pulse 76 has a rising edge 82 and a falling edge 84.

[0118] Current pulse 76 lasts for approximately one minute. After pulse 76 ends, the current density drops back to approximately 0.3 A / cm². 2 from and remains essentially constant until the following current pulse 76 .

[0119] FIG. 3 shows a schematic diagram of the cell voltage profile of electrolysis cell 12 according to FIG. 2. The voltage profile of the cell voltage is represented by a graph 72. One ordinate is assigned to the cell voltage and one abscissa to time. The time scale of the abscissa corresponds to that of FIG. 2.

[0120] Figure 3 shows that the cell voltage of electrolysis cell 12 is approximately 2 V during electrolysis operation 66. Graph 72 shows the time course of the cell voltage corresponding to graph 70. Figure 3 shows that the cell voltage is essentially constant and approximately 2 V during the period from t0 to tl.

[0121] At time tl, the cell voltage drops and, after a brief undershoot, reaches a value of approximately 1.5 V, which remains essentially constant until time t2. At time t2, the cell voltage initially rises according to current pulse 76 and then falls according to current pulse 76, resulting in a voltage pulse 78. The voltage pulse 78 has a time course that is essentially similar to the time course of the 2024PF00738.

[0122] 25

[0123] The current pulse 76 corresponds to a voltage pulse amplitude of approximately 2.5 V. After the current pulse 76 or voltage pulse 78 has subsided, the cell voltage reaches a value of approximately 1.5 V, which remains essentially constant until the next current pulse 76 or voltage pulse 78.

[0124] Figures 2 and 3 show that the pulse unit 38 provides a power pulse for regeneration operation 66 that is approximately 2.5 times the power provided during normal electrolysis operation 64. The resulting power pulses mobilize impurities, allowing them to be removed from the electrolysis cell 12 by the flushing fluid supplied by the flushing unit 50. This reduces aging and / or a decrease in efficiency.

[0125] FIG. 4 shows a further schematic diagram depicting the temperature profile of the electrolysis cell 12 according to FIG. 2. The abscissa represents time and the ordinate represents temperature. The diagram according to FIG. 4 has the same time axis as the diagrams according to FIGS. 2 and 3. It can be seen that during the period from t0 to tl, i.e., during electrolysis operation 64, the temperature in the electrolysis cell 12 is approximately 60 °C. During the period from tl to t2, the temperature in the electrolysis cell 12 drops from 60 °C to approximately 40 °C and then remains constant. This temperature is essentially maintained during regeneration operation 66. Thus, in the present configuration, regeneration operation 66 is carried out at a reduced cell temperature. After completion of regeneration operation 66, the cell temperature is increased again to 60 °C when the 2024PF00738

[0126] 26

[0127] The intended electrolysis operation 64 is to be continued.

[0128] In alternative configurations, the number of pulses and their parameters can, of course, be adjusted or changed as needed. In the present configuration, the pulses are intended to be essentially the same. However, it is also possible for successive pulses to have different properties or parameters.

[0129] The invention is naturally not only suitable for use in electrolysis cells 12 intended for the electrolysis of water. It can equally be used in electrolysis cells intended for the electrolysis of another substance, for example carbon dioxide or the like.

[0130] Furthermore, the invention is not only suitable for regenerating a single electrolysis cell 12, but also for regenerating several electrolysis cells 12 simultaneously. In particular, it can of course be provided that a complete cell stack 18 is subjected to regeneration. This is also provided for in FIG. 1. The embodiment according to FIG. 1 also provides that the electrolysis cells 12 can remain integrated in the electrolysis system 10, in particular in the cell stack 18, for regeneration. In alternative embodiments, however, it can be provided that the electrolysis cells 12 or even a cell stack 18 are removed from the electrolysis system 10 and connected to the regeneration unit 30 electrically, mechanically, and fluidically in order to carry out the regeneration.

[0131] The exemplary embodiments serve solely to illustrate the invention and are not intended to limit it.

Claims

2024PF00738 27 Patent claims 1. Method for operating at least one electrolysis cell ( 12 ) of an electrolysis plant ( 10) , wherein the electrolysis cell ( 12 ) is subjected to an electrolysis power in an intended electrolysis operation ( 64 ) in order to produce at least one electrolysis product from a substance to be electrolyzed, characterized by the fact that the at least one electrolysis cell ( 12 ) outside of the intended electrolysis operation ( 64 ) in a regeneration operation ( 66) is subjected to at least one predetermined electrical power pulse having a predetermined power amplitude in order to regenerate the at least one electrolysis cell ( 12 ).

2. Method according to claim 1, characterized in that the predetermined power amplitude is selected such that the at least one electrolysis cell (12) is operated with a regeneration power that is at most 50% of a rated power, preferably at most 30% of the rated power, particularly preferably at most 20% of the rated power, of the at least one electrolysis cell (12) or at least at least 200% of the rated power, preferably 300% of the rated power, of the at least one electrolysis cell (12).

3. Method according to one of the preceding claims, characterized in that the at least one predetermined power pulse extends over a period of at most 15 minutes, preferably at most 6 minutes, particularly preferably at most 1 minute.

4. Method according to one of the preceding claims, characterized in that the at least one predetermined power pulse has a gradient of at least 10% of the rated power per second, preferably at least 2024PF00738, at least on a rising or falling edge in time. 28 exhibits 80% of the rated power per second, particularly preferably at least 100% of the rated power per second.

5. Method according to one of the preceding claims, characterized in that the at least one electrolysis cell ( 12 ) in regeneration mode ( 66) is subjected to at least two successive predetermined power pulses, wherein the power pulses are spaced apart from each other by at least one minute, preferably at least 15 minutes.

6. Method according to one of the preceding claims, characterized in that the operating temperature of the at least one electrolysis cell ( 12 ) in regeneration operation ( 66) is at most 80%, preferably 60%, particularly preferably 50%, of the operating temperature of the at least one electrolysis cell ( 12 ) in the intended electrolysis operation ( 64 ).

7. Method according to one of the preceding claims, characterized in that the start of the regeneration operation ( 66) is separated in time from the end of the intended electrolysis operation ( 64 ) by a preparation period ( 68 ).

8. Method according to one of the preceding claims, characterized in that the method is carried out at least once a day, preferably at least 10 times a day, particularly preferably at least 100 times a day.

9. Method according to one of the preceding claims, characterized in that the electrolysis efficiency of the at least one electrolysis cell (12) is detected, the electrolysis efficiency is compared with a predetermined reference value, and the regeneration operation (66) is triggered depending on the comparison. 2024PF00738 29 10. Electrolysis plant (10) with a plurality of electrolysis cells (12) which are at least partially connected electrically in series, a power supply unit (20) which can be electrically coupled to the electrolysis cells (12) and which is configured to provide electrical electrolysis power in order to supply the electrolysis cells (12) with the electrolysis power in an intended electrolysis operation (64), and a cell supply unit (32) at least for supplying a substance to be electrolyzed to the electrolysis cells (12) and for removing at least one electrolysis product in an intended electrolysis operation (64), characterized by a regeneration unit (30) which is configured to subject at least one of the electrolysis cells ( 12 ) outside of the intended electrolysis operation ( 64 ) in a regeneration operation ( 66) to at least one predetermined electrical power pulse having a predetermined power amplitude in order to regenerate the at least one electrolysis cell ( 12 ).

11. Electrolysis system according to claim 10, characterized in that the regeneration unit (30) is configured to electrically disconnect at least one electrolysis cell (12) for regeneration operation (66) from the power supply unit (20).

12. Electrolysis system according to claim 10 or 11, characterized in that the regeneration unit (30) has a regeneration power unit (34) which is configured to provide at least one power pulse for at least one electrolysis cell (12) during regeneration operation (66).

13. Electrolysis system according to one of claims 10 to 12, characterized in that the regeneration unit (30) has a service unit (40) which is configured to have at least one electrolysis cell (12) for carrying out 2024PF00738 30 to separate the regeneration unit ( 66) from the other electrolysis cells ( 12 ) at least electrically or mechanically and instead connect it to the regeneration unit (30).

14. Electrolysis plant according to one of claims 10 to 13, characterized in that the regeneration unit (30) has a rinsing unit (50) that can be coupled to the at least one electrolysis cell (12) and is configured to supply the at least one electrolysis cell (12) with a rinsing fluid for carrying out the regeneration operation (66).

15. Regeneration unit (30) of the electrolysis system (10) according to one of claims 10 to 14.

Images