Corrosion protection in a co2 electrolysis stack

Abstract

The invention relates to methods for protecting an electrolysis stack from corrosion, a method for transporting an electrolysis stack, and an electrolysis stack.

Description

[0001] Description

[0002] Corrosion protection in a CC^ electrolysis stack

[0003] The invention relates to a method for corrosion protection of a CC>2 electrolysis stack, a method for transporting a CC>2 electrolysis stack, and a CC^ electrolysis stack.

[0004] Electrolysis uses electricity to produce valuable materials. To maintain efficient operation, an electrolyte is typically required that can conduct electricity through the electrolysis cells. However, this electrolyte often contains substances that can be corrosive to the electrolysis cell material, especially the electrodes, under certain conditions. Particularly in electrolysis stacks comprising multiple electrolysis cells, this can lead to varying conditions in the individual cells when not in use.

[0005] In standby mode, an electrolysis stack, such as a CC^ electrolysis stack, is currently operated with a low load current to prevent oxidation of the electrodes, for example, silver cathodes. Due to the characteristic curve variations of the individual cells, the potential distribution along the stack is less well-defined at these low load currents than during load operation. This creates the risk that the necessary protective potential may not be reached in some cells in a series connection, while it is exceeded in others, which is not a problem.

[0006] Furthermore, short-circuit currents constantly flow through the manifold or distribution structures along the stack. These currents can affect the potential zones of the electrodes, particularly in the area of ​​the manifold connections at the cells, potentially leading to the oxidation of electrolysis cell components, such as silver oxidation, and ultimately to the destruction of the electrode structure. Manifold generally refers to distribution structure. Each cell has its own internal distribution structures. Additional distribution structures spanning multiple cells are required for the common supply of power to the cells of a stack. Consequently, these two levels (cell level and stack level) can be assigned to the respective manifold.

[0007] To prevent this, electrolysis stacks are currently subjected to a sufficiently high standby current even when not in operation, thus preventing oxidation of stack components, especially electrodes (e.g., silver oxidation in silver-containing electrodes). However, this is associated with increased energy consumption.

[0008] To avoid this increased energy consumption, it is possible to control the potential of individual cell layers. This requires an electrical connection for each bipolar plate of the stack, which involves considerable equipment complexity. Furthermore, it is questionable whether the energy consumption of this solution is lower than using a sufficiently high minimum load current.

[0009] Furthermore, it is also possible to install long electrolyte lines with a small cross-section between the cells to minimize stray current. However, disadvantages of this approach include the increased complexity and compromises in stack performance, making this solution rather unsuitable, especially in stacks with an internal manifold, such as plate cells or internal supply cells.

[0010] Another concept for circumventing the problem is the concept of monopolar cell stacks. In this case, all electrolysis cells are electrically connected in parallel, so there are no stray current problems. However, this is disadvantageous due to the need to bring out all the individual cell connections and because of the very high operating current at low operating voltage. Another possibility for cell operation with minimized stray currents is the installation of break tracks to interrupt the liquid flow, where the electrolyte current breaks into individual, no longer conductive packets, which are then interrupted by gas, for example. However, this is again associated with additional effort and is rather unsuitable for cells with an internal manifold, such as plate cells and internal supply cells, and has also not been considered for non-operation hitherto. This also results in an increased requirement for electrolyte conveyance.

[0011] Therefore, there is a need for methods for effective corrosion protection of electrolysis stacks, especially during non-operation as well as during transport, without or with minimal additional effort.

[0012] The inventors have found that by simply emptying the electrolyte, a suitable interruption of the current in the electrolyte within the electrolyte distribution or the manifold can be created, and in particular, preferred suitable points for interruption have been found, as well as very simple solutions for corrosion protection in electrolysis stacks. It has also been found that better protection can be achieved by introducing inert materials. The measures found are suitable for longer standstill times, for example, also during the transport of an already operating, for example, large and / or new, stack, especially when there is no sufficiently powerful power supply available to maintain a protective current - as will be explained in detail later.In particular, by means of the present methods and the electrolysis stack, even a standstill without electrical power consumption can be achieved, which can be quite significant, depending on the stray current and the electrolysis current, and which usually has to be maintained for the safe shutdown. Moreover, according to the invention, there is an advantage that no operating means have to be available during shutdown and no products have to be safely collected, for example in the case of CO₂ as a starting material on the cathode side, products such as O₂, H₂, CO and others. Thus, the risk of explosion can also be reduced and even excluded. In the case of a decommissioned plant in a non-operating state, a heating device can also be dispensed with at very cold locations to prevent the electrolyte from freezing.

[0013] A first aspect of the present invention relates to a method for corrosion protection of a CO₂ electrolysis stack during non-operation, wherein the CO₂ electrolysis stack comprises at least a first electrolysis cell and a second electrolysis cell, at least a first supply line and at least a first discharge line for the first electrolysis cell and at least a second supply line and at least a second discharge line for the second electrolysis cell, wherein at least the first electrolysis cell and the second electrolysis cell and at least the at least one first supply line and the at least one second supply line are partially filled with at least one electrolyte, comprising: at least partially emptying the electrolyte from parts of at least the first electrolysis cell and / or the at least one first supply line and / or the at least one first discharge line and / or a total supply line,which is connected to the at least one first supply line and the at least one second supply line and is configured to provide a supply for the at least one first supply line and the at least one second supply line, and / or a main discharge line which is connected to the at least one first discharge line and the at least one second discharge line and is configured to provide a discharge for the at least one first discharge line and the at least one second discharge line, wherein the electrolyte that is removed by the at least partial emptying is exchanged by an inert gas or a mixture comprising an inert gas and liquid droplets therein, e.g. water droplets, and wherein the inert gas is CO₂. Furthermore, a method for transporting a CO₂ electrolysis stack is disclosed, wherein the CO₂ electrolysis stack has at least one first electrolysis cell and a second electrolysis cell,comprises at least one first supply line and at least one first discharge line for the first electrolysis cell and at least one second supply line and at least one second discharge line for the second electrolysis cell, comprising at least partially filling the CO₂ electrolysis stack with an inert gas or a mixture comprising an inert gas and liquid droplets therein, wherein the inert gas is CO₂.

[0014] A method for corrosion protection of an electrolysis stack, in particular a CO₂ electrolysis stack, during non-operation is described, wherein the electrolysis stack comprises at least a first electrolysis cell and a second electrolysis cell, at least a first supply line and at least a first discharge line for the first electrolysis cell and at least a second supply line and at least a second discharge line for the second electrolysis cell, wherein at least the first electrolysis cell and the second electrolysis cell and at least the at least one first supply line and the at least one second supply line are at least partially filled with at least one electrolyte, comprising: introducing at least one first insulator at least into the at least one first supply line to the first electrolysis cell such that at least the entire cross-sectional area of the at least one first supply line is occupied by the first insulator;and / or introducing at least one second insulator at least into the at least one first conductor such that at least the entire cross-sectional area of the at least one second lead is occupied by the second insulator; and / or introducing at least one third insulator at least into a main lead which is connected to the at least one first lead and the at least one second lead and which is configured to provide a supply for the at least one first lead and the at least one second lead, such that at least the entire cross-sectional area of the main lead in the flow direction between the at least one first lead and the at least one second lead is occupied by the third insulator;and / or introducing at least one fourth insulator at least into a main conductor which is connected to the at least one first conductor and the at least one second conductor and which is configured to provide a discharge for the at least one first conductor and the at least one second conductor, such that at least the entire cross-sectional area of the main conductor in the flow direction between the at least one first conductor and the at least one second conductor is occupied by the fourth insulator.;

[0015] Furthermore, a CO₂ electrolysis stack is disclosed, comprising:

[0016] - at least one first electrolysis cell and a second electrolysis cell,

[0017] - at least one first supply line and at least one first conductor for the first electrolysis cell,

[0018] - at least one second supply line and at least one second discharge line for the second electrolysis cell,

[0019] - a main supply line which is connected to the at least one first supply line and the at least one second supply line and is configured to provide a supply for the at least one first supply line and the at least one second supply line, and

[0020] - a main line that is connected to the at least one first line and the at least one second line and is configured to provide a discharge path for the at least one first line and the at least one second line, further comprising: at least one first side line that is connected to the at least one first supply line and is configured such that it can at least partially empty an electrolyte present in the at least one first supply line, at least one second side line that is connected to the at least one first line and is configured such that it can at least partially empty an electrolyte present in the at least one first line, at least one third side line that is connected to the at least one second supply line and is configured as such,that it can at least partially empty an electrolyte present therein from the at least one second supply line, and / or at least one fourth side discharge line, which is connected to the at least one second discharge line and is formed such that it can at least partially empty an electrolyte present therein from the at least one second discharge line, further comprising a first side supply line, which is connected to the at least one first supply line and is formed such that it can supply an inert gas or a mixture comprising an inert gas and liquid droplets present therein into the at least one first supply line, a second side supply line, which is connected to the at least one first discharge line and is formed such that it can supply an inert gas or a mixture comprising an inert gas and liquid droplets present therein into the at least one first discharge line,a third side supply line, which is connected to the at least one second supply line and is configured such that it can supply an inert gas or a mixture comprising an inert gas and liquid droplets present therein to the at least one second supply line, and / or a fourth side supply line, which is connected to the at least one second discharge line and is configured such that it can supply an inert gas or a mixture comprising an inert gas and liquid droplets present therein to the at least one second discharge line, wherein the inert gas is CO2.,

[0021] Further aspects of the present invention can be found in the dependent claims and the detailed description. The accompanying drawings are intended to illustrate embodiments of the present invention and to provide a further understanding thereof. In connection with the description, they serve to explain concepts and principles of the invention. Other embodiments and many of the stated advantages will become apparent with reference to the drawings.

[0022] The elements of the drawings are not necessarily drawn to scale relative to each other. Identical, functionally identical and equivalently acting elements, features and components are, in the figures of the drawings, provided with the same reference signs, respectively, unless otherwise stated.

[0023] Figures 1 to 3 schematically show load currents and stray currents in an electrolysis stack during operation and non-operation.

[0024] Figure 4 shows an equivalent circuit diagram of an electrolysis stack with a manifold.

[0025] Figure 5 schematically shows an electrolysis stack with two electrolysis cells and a distribution structure for electrolytes.

[0026] Figures 6 to 11 schematically show electrolysis stacks, in particular CCU electrolysis stacks.

[0027] Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0028] In the context of the following invention, "non-operation" means a state in which the electrolysis cell does not carry out an electrolytic reaction to produce a valuable product on a normal scale. In particular, non-operation includes times of shutting down an electrolysis cell, maintenance times, downtime due to lack of profitability, for example due to expensive electricity, downtime due to insufficient availability of electricity and / or raw materials for the electrolysis, transport times, conversion times, etc. For example, non-operation can also include longer periods of standstill during which the electrolyte is at least partially drained, and thus a further electrolytic current flow, as will be described below, can preferably be impeded or even prevented at all locations or at least between electrolysis cells.

[0029] Gas diffusion electrodes (GDEs) are electrodes in which liquid, solid, and gaseous phases are present, and where in particular a conductive catalyst catalyzes an electrochemical reaction between the liquid and the gaseous phase. In the electrolysis cells of the present electrolysis stacks, in particular electrodes, such as the cathodes, especially in the case of CO₂ electrolysis, can be formed as gas diffusion electrodes. It is not excluded that anodes are formed as gas diffusion electrodes. In particular for gas diffusion electrodes, and especially for those as cathodes in a CO₂ electrolysis, effective corrosion protection is of particular importance and is accordingly also particularly effective in protecting the electrode structure.

[0030] In the context of the invention, a partial emptying corresponds to an emptying of at least 50% by volume, preferably at least 80% by volume, more preferably at least 90% by volume, even more preferably at least 92% by volume of the defined component of the electrolysis stack or of the entire electrolysis stack.A substantially complete emptying corresponds to an emptying of at least 95% by volume, even more preferably at least 99% by volume of the defined component of the electrolysis stack or of the entire electrolysis stack.A complete emptying corresponds to an emptying of 100% by volume, except for emptyings in inaccessible or not emptyable parts of the component or of the electrolysis stack due to other obstacles.The emptying or the emptying here refers to the removal of the electrolyte, whereby it is initially irrelevant what the electrolyte is replaced by, provided that no other electrolyte or other electrically conductive substance is introduced.

[0031] Corrosion of parts of the electrolysis stack can occur, for example, especially due to load currents and / or stray currents even during non-operation, which can occur within the electrolysis stack. The occurrence of such load and / or stray currents will now be further clarified below both for the case of operation and non-operation of an electrolysis stack.

[0032] These are exemplary of an electrolysis stack with two end electrolysis cells 1 and 2, i.e., a first electrolysis cell 1 and a second electrolysis cell 2, shown in Figures 1 to 3 during operation and non-operation, where usually between the two end, exemplary electrolysis cells 1 and 2, there can be and usually are further electrolysis cells in the stack, as is shown here by the dots between the two electrolysis cells 1 and 2 in Figures 1 to 3. Each of the electrolysis cells, for example electrolysis cells 1 and 2, exemplarily has here an anode A, a cathode K and a membrane M, all of which are not limited, however for electrolysis cells in electrolysis stacks in inventive methods and electrolysis stacks other arrangements than those shown here are also possible, possibly also without a membrane, and the statements here regarding the load and stray currents result analogously.

[0033] In the electrolysis stacks shown in Figures 1 to 3, an anolyte AN is passed through an anode chamber I and a catholyte KA is passed through a cathode chamber II. Here, for example, oxygen is still generated at the anode A, as in the case of water electrolysis. The anolyte AN and catholyte KA are not particularly limited and can, for example, independently of each other be aqueous electrolytes containing suitable conductive salts, but they can also be configured differently. In addition, adjacent to the cathode K in the electrolysis cells 1 and 2, there is still a gas space G into which, for example, CO2 is introduced and, as an example product, a mixture of unreacted CO2, CO as the actual product and H2 as a by-product is discharged. However, it is also possible here for other products to arise, for example depending on a catalyst of the cathode K.Usually, there are boundary components between the electrolysis cells in the electrolysis stack, such as the bipolar plates P here for example.

[0034] In Figure 1, it is clearly shown that the gas flow at the cathode K in the flow-by operation is from top to bottom, while the electrolyte flow of the catholyte KA and the anolyte AN is from bottom to top. In Figure 1, the supply of the catholyte KA and the anolyte AN to the stack is from the bottom left to right respectively via a catholyte inlet manifold 3a and an anolyte inlet manifold 4a, and the discharge of the catholyte KA and the anolyte AN respectively via a catholyte outlet manifold 3b and an anolyte outlet manifold 4b, which continue to the right but are not shown in detail here for the sake of simplicity. The manifolds are shown more clearly in Figure 2, in which the catholyte and anolyte distribution flows 5 and 6 along the manifolds are shown by the arrows outside the electrolysis cells 1 and 2.

[0035] In Figure 2, the scatter and load currents inside the electrolysis stack are shown in principle. Here, both the catholyte scatter currents 6 and the anolyte scatter currents 5 are shown. In addition, load currents 7 within the electrolysis cells 1 and 2 are shown. In addition, in the dashed-bordered area of Figure 3, a scatter current 8 is also visible, which only occurs near the catholyte connection. There, it exits the cathode, while the load current enters there - as along the entire cell surface. The two currents add up. Therefore, at low load current densities, the sum current density at the positive stack end can change sign there, which can cause the cathode to corrode. At the negative stack end, the anode tends to reverse the current density.

[0036] To further illustrate the corresponding electrical states, Figure 4 shows an equivalent circuit diagram of an electrolysis stack with an electrolyte manifold with a respective resistance R and current I ,

[0038] in the manifold and the different cell voltages U zi up to U Zn shown over k = 1 to n cells, where then a total voltage results over all U Zk voltages. Accordingly, the stray and load currents can be derived therefrom.

[0037] To avoid corrosion due to stray and / or load currents, the present methods are applied, which in particular can find application in the electrolysis stacks according to the invention.

[0038] In the context of the present invention, electrolysis stacks are in particular stacks with an internal manifold, for example plate cells or internal supply cells. An internal manifold is present at the stack level. That is, the manifold is integrated in the stack and is also called (stack) internal supply. In particular, the structure of a plate cell harmonizes well with the concept of an internal supply, so that preferred electrolysis cells are plate cells.

[0039] In a first aspect, the present invention relates to a method for protecting a CCU electrolysis stack against corrosion during non-operation, wherein the CCU electrolysis stack comprises at least a first electrolysis cell and a second electrolysis cell, at least a first supply line and at least a first discharge line for the first electrolysis cell, and at least a second supply line and at least a second discharge line for the second electrolysis cell, wherein at least the first electrolysis cell and the second electrolysis cell and at least the at least one first supply line and the at least one second supply line are partially filled with at least one electrolyte, comprising: at least partially emptying the electrolyte from parts of at least the first electrolysis cell and / or the at least one first supply line and / or the at least one first discharge line and / or a total supply line,which is connected to the at least one first supply line and the at least one second supply line and is configured to provide a supply for the at least one first supply line and the at least one second supply line, and / or a main discharge line which is connected to the at least one first discharge line and the at least one second discharge line and is configured to provide a discharge for the at least one first discharge line and the at least one second discharge line, wherein the electrolyte which is removed by the at least partial emptying is exchanged by an inert gas or a mixture comprising an inert gas and liquid droplets therein, e.g. water droplets, wherein the inert gas is CO2.,

[0040] The method of the first aspect is a method for corrosion protection of a CO₂ electrolysis stack during non-operation, where here, corrosion of at least parts of the electrolysis stack during non-operation is reduced or even can be prevented, for example, of electrode materials in a CO₂ electrolysis of catalysts in the cathode and / or anode, e.g., Ag in the reduction of CO₂ to CO, as described fundamentally above. In particular, CO₂ electrolysis stacks benefit from the measures in the inventive methods. In these, in particular, parts of the stack, for example, electrode materials, are exposed to a corrosion risk, which can also result, for example, from electrolytes specifically used therefor and / or also by-products of the electrolysis.

[0041] In the method according to the invention for corrosion protection during non-operation, but also in the other methods according to the invention and in the electrolysis stack according to the invention, the CO₂ electrolysis stack comprises at least a first electrolysis cell and a second electrolysis cell. However, more than two electrolysis cells may also be present in the electrolysis stack, preferably at least 3, for example at least 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, at least 30, at least 40, at least 50, at least 60, at least 70, at least 80, at least 90, or at least 100, or also at least any number in between or above that.

[0042] In the method according to the invention for corrosion protection of a CC^ electrolysis stack during non-operation, the at least one first and second electrolysis cells, the at least one first supply line and at least one first discharge line for the first electrolysis cell for the first electrolysis cell and the at least one second supply line and at least one second discharge line for the second electrolysis cell are not particularly limited, provided that they are at least partially, for example at least 50 vol.%, at least 80 vol.%, at least 90 vol.% or at least 92 vol.% and preferably substantially, i.e. at least 95 vol.%, more preferably at least 99 vol.% and in particular completely filled with at least one electrolyte.

[0043] It is also not excluded that a respective electrolysis cell has more than one electrolyte, for example a catholyte on the cathode side and an anolyte on the anode side, which can be separated in the respective electrolysis cell by a suitable separator, e.g. a diaphragm or a membrane.Herein, for example, the supply of catholyte follows via at least one first and at least one second catholyte supply line and a total catholyte supply line, and the discharge of catholyte via at least one first and at least one second catholyte discharge line and a total catholyte discharge line, as well as the supply of anolyte via at least one first and at least one second anolyte supply line and a total anolyte supply line, and the discharge of anolyte via at least one first and at least one second anolyte discharge line and a total anolyte discharge line, which can each be emptied at least partially, preferably substantially completely or in particular completely, respectively, in the corresponding processes.

[0044] The at least one electrolyte or also several electrolytes as well as any present separators and also further components of the respective electrolysis cells are not particularly limited. According to certain embodiments, the cathodes of the respective electrolysis cells are gas diffusion electrodes and are accordingly suitable, for example, for CO₂ reduction.

[0045] Likewise, the at least partial emptying of the electrolyte from parts of at least the first electrolysis cell and / or the at least one first supply line and / or the at least one first discharge line and / or a main supply line which is connected to the at least one first supply line and the at least one second supply line and is configured to provide a supply for the at least one first supply line and the at least one second supply line, and / or a main discharge line which is connected to the at least one first discharge line and the at least one second discharge line and is configured to provide a discharge for the at least one first discharge line and the at least one second discharge line, is not particularly limited and can be effected in a suitable manner.According to the invention, emptying is carried out by displacement with an inert gas or a mixture comprising an inert gas and liquid droplets therein, wherein the inert gas is CO2.

[0046] According to the invention, it is not excluded that an electrolysis cell has more than one supply line and / or discharge line. If such an electrolysis cell has several supply lines and / or discharge lines, it is preferred that all supply lines and / or discharge lines to an electrolysis cell are at least partially emptied. According to certain embodiments, however, each electrolysis cell has a supply line and / or a discharge line for an electrolyte. It is also not excluded that each electrolysis cell comprises further supply lines which supply, for example, a starting material, for example a starting gas cathode supply line for, for example, a gas comprising CO2 on the cathode side, or another starting material with a general cathode supply line, and / or a gas and / or a liquid on the anode side, for example an anode supply line, as well as corresponding cathode product and / or anode product discharge lines.According to certain embodiments, at least one educt gas cathode supply line is included per electrolysis cell, which is configured to supply an educt gas comprising CO2. According to certain embodiments, a cathode product discharge line is also provided per electrolysis cell, which is configured to discharge a product of the electrolysis on the cathode side. Accordingly, according to certain embodiments, anode feed lines and / or anode product discharge lines are also provided per electrolysis cell, which are each configured to supply an educt to the anode and / or discharge a product from the anode. The respective educt supply lines and / or product discharge lines are also not particularly limited. An educt can be supplied to the educt supply lines for all electrolysis cells via a common overall educt supply line, if appropriatealso separately for the educts of the cathodes and anodes in the respective electrolysis cells, and the products of the electrolysis cells can be discharged via the respective product discharge lines via a common overall product discharge line, optionally also separately for the products of the cathodes and anodes of the respective electrolysis cells. According to certain embodiments, the educt supply lines and / or product discharge lines and / or the respective overall educt supply line and / or the respective overall product discharge line are also at least partially emptied during non-operation, but during non-operation they are preferably emptied substantially completely, i.e. to more than 90 vol.%, more than 95 vol.% or more than 99 vol.%, also in order not to waste any educt and / or product.Preferably, these pipelines, i.e., the educt feed pipelines and / or product discharge pipelines and / or the respective total educt feed pipeline and / or the respective total product discharge pipeline, are filled with an inert medium, such as gas, during non-operation. However, in the present case, the stray and load currents mainly result from the electrolytes, so that their partial emptying is of greater importance.

[0047] According to certain embodiments, the emptied electrolyte can be stored temporarily for later reuse, for example, in an intermediate storage, and the intermediate storage can also be an electrolyte reservoir for the electrolysis stack. Accordingly, a CCU electrolysis stack according to the invention, as described below, can also comprise at least one electrolyte reservoir, and optionally at least two electrolyte reservoirs for the catholyte and anolyte respectively.

[0048] According to certain embodiments, at least the total supply line and / or the total discharge line is at least partially, preferably at least 50 vol.%, at least 80 vol.%, at least 90 vol.% or at least 92 vol.% and more preferably substantially, i.e., at least 95 vol.%, even more preferably at least 99 vol.% and in particular completely emptied. Thereby, a current flow through these lines can be suppressed, so that the stray and load currents are minimized.In order to enable as complete or even completely complete emptying of the total supply line and / or total discharge line, according to certain embodiments, it is also possible that a connection between the respective supply lines, that is, for example, the at least one first and second supply line, and the total supply line, and / or a connection between the respective discharge lines, that is, for example, the at least one first and second discharge line, and the total discharge line is closed such that no electrolyte can flow from the respective supply lines and / or discharge lines into the total supply line and / or the total discharge line, for example with a suitable shut-off device, which is not particularly limited. As a shut-off device, for example, slides, sluices, valves, etc. are suitable in the methods and devices according to the invention, but these are not particularly limited.Thus, when the electrolyte is at least partially, preferably substantially completely, and in particular completely removed from parts or the entire electrolysis stack, the material of the barrier device is not particularly limited either. According to certain embodiments, the barrier device is electrically non-conductive, especially when there is still electrolyte remaining in the electrolysis stack.

[0049] According to certain embodiments, the total inlet line and the total outlet line are at least partially and preferably substantially completely or completely emptied. When the total inlet line and / or the total outlet line are emptied, this has the advantage that the other components of the electrolysis stack do not have to be emptied, so that an intermediate storage for emptied electrolytes can be made smaller.

[0050] According to certain embodiments, at least the at least one first supply line is partially emptied. According to certain embodiments, the first supply line is completely emptied, i.e., emptied completely. According to certain embodiments, the first supply line and the first discharge line and optionally the first electrolysis cell are at least partially and preferably substantially completely or completely emptied. Thereby, stray and load current between the first and second electrolysis cells can be reduced or even prevented, since electrical contacting of the first electrolysis cell by the electrolyte is reduced or even prevented. If there are more than two electrolysis cells, it is sufficient to empty all but one supply and / or discharge lines and optionally electrolysis cells at least partially, substantially completely or completely, since only these are then electrically contacted.However, from a process engineering perspective, it is also simpler here to empty all inlets and / or outlets and optionally the electrolysis cells at least partially, essentially completely or even completely. When emptying inlets and / or outlets, however, it is also sufficient if the corresponding lines are emptied at least partially in such a way that there is a region in the respective inlet and / or outlet where essentially no electrolyte is present, i.e., a kind of "break" in the electrolyte exists. This can be done, for example, by means of side inlets and possibly side outlets on the inlets and / or outlets, through which another medium than the electrolyte, as described above by way of example, can be introduced into at least parts of the respective inlet and / or outlet, where possiblyalso by means of one or more shut-off devices, as described above, the electrolyte can remain in the rest of the respective feed and / or discharge line, or the electrolyte can simply be emptied, for example via a first drain device or a first side discharge - as also described below, where one or more shut-off devices can also be used here to otherwise retain the electrolyte.

[0051] According to certain embodiments, at least the at least one first supply line and the at least one second supply line are at least partially emptied such that in each of the at least one first supply line and the at least one second supply line there is a region in which substantially no electrolyte is present. Thereby, an electrical interruption can occur on the supply line side. If there are several supply lines for several electrolysis cells in an electrolysis stack, in particular all supply lines are at least partially, preferably substantially completely or completely emptied. This is particularly advantageous in electrolysis stacks in which gases can arise during electrolysis in the electrolysis cells and in which gases can then also be present in the discharge lines, for example in a CCU electrolysis.According to certain embodiments, at least the at least one first derivative and the at least one second derivative - or preferably all derivatives in the case of multiple electrolysis cells - are at least partially emptied such that there is a region in the at least one first derivative and the at least one second derivative - respectively - in which essentially no electrolyte is present, so as to also cause an electrical interruption on the derivative side. In particular, in the embodiments described here, compared to emptying the entire lead and preferably also the entire lead line, the amount of emptied electrolyte can be further reduced, since even a small region without electrical contact may be sufficient. An at least partial emptying of the derivatives is particularly important especially when no gases are generated during the electrolysis that could be discharged through the derivatives.

[0052] It should be particularly noted that the electrolyte does not have to be removed from the electrolysis cells, since only the current flow between the electrolysis cells is to be reduced or interrupted, so that possibly a complicated refilling can be avoided.

[0053] The electrolyte that is removed by the at least partial emptying is replaced by an inert gas or a mixture comprising an inert gas and liquid droplets present therein, for example non-conductive or poorly conductive, such as water droplets, wherein the inert gas is CO₂. Thereby, the electrolyte can be easily displaced during emptying and a current flow can be prevented. In addition, the entry of oxidizing atmospheric components such as oxygen can be reduced or even prevented. In the present case, CO₂ is used as the inert gas in a CCb electrolysis, which can be slightly moist, for example, so that essentially the educt gas on the cathode side of the electrolysis can also be used here, which can be provided from an educt reservoir, for example. An advantage here is that the educt gas can be used simultaneously as the inert gas.

[0054] It is also not excluded that individual or all educt feed lines and / or product discharge lines and / or spaces for converting the educts on the cathode and / or anode side, for example a cathode gas space which can be connected to an educt gas cathode feed line and a product gas cathode discharge line, and / or a corresponding anode (gas) space with corresponding educt feed and / or product discharge lines, are also replaced by the inert gas or a mixture comprising an inert gas and liquid droplets located therein, for example non-conductive or poorly conductive liquid droplets, e.g. water droplets, i.e. are emptied.

[0055] For example, the electrolyte and optionally the gas spaces of an electrolysis cell or several or all electrolysis cells can also be filled with the inert gas or a mixture comprising an inert gas and liquid droplets located therein, for example non-conductive or poorly conductive, such as water droplets, after emptying, in order to achieve an additional protection against the surrounding atmosphere and, for example, in particular oxygen.

[0056] According to the invention, the inert gas or the mixture comprising the inert gas and liquid droplets therein, for example non-conductive or poorly conductive, especially water, is introduced, especially with a continuous flow, so that it can be ensured that no ambient gas penetrates through diffusion or leakage. The inert gas is preferably humidified. By introducing the inert gas or the mixture comprising the inert gas and liquid droplets therein, in particular the electrolyte can also be blown out from hard-to-reach places. According to certain embodiments, the entire electrolysis stack is filled with the inert gas or the mixture comprising the inert gas and liquid droplets therein. Thereby, the penetration of oxidative components such as oxygen can be particularly advantageously prevented.

[0057] According to certain embodiments, the CO2 electrolysis stack comprises a plurality of electrolysis cells with a number of three or more, for example four or more, five or more, six or more, seven or more, eight or more or nine or more, preferably ten or more, more preferably 20 or more, particularly preferably 50 or more, electrolysis cells - as described above, wherein at least from parts of the electrolysis cells and / or the feed lines to the electrolysis cells, at least partially the electrolyte is emptied at the edge of the CCU electrolysis stack. As can be seen from Figure 4, in particular at the ends of the cell stack, the voltage sums up - from which an increased load current results, which can lead to a current reversal as in a battery, so that preferably corrosion should be reduced or prevented there.The higher the number of electrolysis cells here, the more a perceptible effect with regard to corrosion reduction is achieved.

[0058] As described above, due to the load and leakage currents, a voltage inequality may occur across the cells. Usually, even when not in operation, a current is applied to an electrolysis stack, which generally counteracts these leakage and load currents and thus protects the electrodes. However, due to the voltage inequality, it may happen that, especially at the ends of the electrolysis stack, the applied current is not sufficient, resulting in corrosion there. In this regard, a special protection is particularly required at the ends of the electrolysis stack, which is achieved in particular by the method according to the invention in that it is applied in particular to electrolysis cells, connections and / or leads at and possibly near the ends of the electrolysis stack (depending on the number of cells in the stack).

[0059] According to certain embodiments, current is still applied to the electrodes of the electrolysis cells. As just described, this additionally serves for corrosion protection, especially when not all of the electrolyte is emptied.

[0060] Also disclosed in a second aspect is a method for transporting a CO₂ electrolysis stack, the CO₂ electrolysis stack comprising at least a first electrolysis cell and a second electrolysis cell, at least a first supply line and at least a first discharge line for the first electrolysis cell and at least a second supply line and at least a second discharge line for the second electrolysis cell, comprising at least partially filling the CO₂ electrolysis stack with an inert gas or a mixture comprising an inert gas and liquid droplets therein, the inert gas being CO₂.

[0061] The inert gas being CO₂, the electrolysis stack and its components, the inert gas, and the mixture comprising an inert gas and liquid droplets therein correspond to the components, the inert gas, and the mixture comprising an inert gas and liquid droplets therein, which were mentioned in the method for protecting an electrolysis stack against corrosion during non-operation in the first aspect, and which have already been described above. Accordingly, reference is made here to the above explanations, which are also applicable in the method for transporting a CO₂ electrolysis stack. As also in the method for protecting a CO₂ electrolysis stack against corrosion during non-operation, corrosion protection is achieved by the inert gas or the mixture comprising the inert gas and liquid droplets therein, since both the penetration of oxidizing substances and of, for example, excessive moisture and thus possibly...The occurring load and diffusion currents can be reduced or prevented. The filling is not particularly restricted here. In particular, it is carried out completely, preferably with a gas comprising CO2 and possibly liquid droplets, especially water, so that the stack is later intended to be used in a CO2 electrolysis application. Likewise, the CO2 electrolysis stack can comprise further components, which are mentioned in connection with the method of the first aspect and the CO2 electrolysis stack according to the invention, so that reference is also made here to the corresponding explanations, to which reference is also made here and which can also find application in the method of the second aspect.

[0062] According to certain embodiments, at least the at least one first supply line, the at least one second supply line, the at least one first discharge line, and the at least one second discharge line are at least partially filled such that there is in each of the at least one first supply line, the at least one second supply line, the at least one first discharge line, and the at least one second discharge line a region in which substantially the inert gas or the mixture comprising the inert gas and liquid droplets therein is present. Thereby, the ingress of oxidative substances and excessive moisture, etc. can be effectively reduced or prevented, even with reduced amounts of inert gas with or without liquid droplets.

[0063] It is also not excluded that a respective electrolysis cell can have more than one electrolyte during later operation, for example a catholyte on the cathode side and an anolyte on the anode side, which can be separated in the respective electrolysis cell by a suitable separator, e.g. a diaphragm or a membrane.For example, the supply of the catholyte then takes place via at least one first and at least one second catholyte supply line and a total catholyte supply line, and the discharge of the catholyte via at least one first and at least one second catholyte discharge line and a total catholyte discharge line, as well as the supply of the anolyte via at least one first and at least one second anolyte supply line and a total anolyte supply line, and the discharge of the anolyte via at least one first and at least one second anolyte discharge line and a total anolyte discharge line, which can each be filled with the inert gas or the mixture comprising the inert gas and liquid droplets located therein.

[0064] A third method for corrosion protection of an electrolysis stack, in particular a CO₂ electrolysis stack, during non-operation is described, wherein the electrolysis stack comprises at least a first electrolysis cell and a second electrolysis cell, at least a first supply line and at least a first discharge line for the first electrolysis cell and at least a second supply line and at least a second discharge line for the second electrolysis cell, wherein at least the first electrolysis cell and the second electrolysis cell and at least the at least one first supply line and the at least one second supply line are partially filled with at least one electrolyte, comprising: introducing at least one first insulator at least into the at least one first supply line to the first electrolysis cell such that at least the entire cross-sectional area of the at least one first supply line is occupied by the first insulator;and / or introducing at least one second insulator at least into the at least one first conductor such that at least the entire cross-sectional area of the at least one second feed line is occupied by the second insulator; and / or introducing at least one third insulator at least into a main feed line which is connected to the at least one first conductor and the at least one second conductor and is configured to provide a supply for the at least one first conductor and the at least one second conductor, such that at least the entire cross-sectional area of the main feed line in the flow direction between the at least one first conductor and the at least one second conductor is occupied by the third insulator;and / or introducing at least one fourth insulator at least into a main conductor which is connected to the at least one first conductor and the at least one second conductor and which is configured to provide a discharge for the at least one first conductor and the at least one second conductor such that at least the entire cross-sectional area of the main conductor in the flow direction between the at least one first conductor and the at least one second conductor is occupied by the fourth insulator.;

[0065] In this third method, the above-mentioned components correspond to those of the method of the first aspect, and the further components and embodiments of the method of the first aspect, as well as the subsequent components and embodiments of the CO2 electrolysis stack according to the invention, can also be used in this method, so that reference is hereby made to the corresponding descriptions, configurations and embodiments.

[0066] In this third method, the interruption of the contact formed by the remaining electrolyte is achieved by the first, second, third, and / or fourth insulator, which is electrically insulating but otherwise not further restricted as long as the cross-sectional area of the respective supply line and / or discharge line and / or the total supply line and / or total discharge line thereof is taken into account. Here, each insulator causes an interruption of the stray and load currents, so that corrosion can also be reduced and even prevented here. The principles of interrupting the stray and load currents are the same as in the method of the first aspect, so reference is made to this. By using insulators, however, the emptying of the electrolyte can also be reduced or even avoided as long as an interruption of the stray and load current between the electrolysis cells is possible.For this purpose, for example, the first insulator can be introduced, especially when a gas is generated during the electrolysis, in order to achieve an interruption of the stray and load currents on the side of the electrolyte supply. Accordingly, the stray and load currents can be reduced on the side of the discharge by the second insulator. According to certain embodiments, the first and second insulators are introduced so that the first electrolysis cell is isolated overall. Alternatively or additionally, on the side of the supply lines, the current flow between the two electrolysis cells can be prevented by the third insulator, and / or on the side of the discharge lines, the current flow between the two electrolysis cells can be prevented by the fourth insulator. According to certain embodiments, the first and the second or fourth insulator are introduced in order to prevent the current flow both on the side of the supply lines and on the side of the discharge lines.According to certain embodiments, the third and the second or fourth isolator are introduced to prevent current flow both on the side of the supply lines and on the side of the discharge lines.

[0067] In the case of multiple electrolysis cells, as generally explained above also in connection with the method of the first aspect, the current flow should preferably also be prevented between all electrolysis cells or at least between the electrolysis cells at the edge. For this purpose, insulators can be provided in all supply lines or in all supply lines except for one, in all discharge lines or in all discharge lines except for one, in the total supply line in the flow direction of the electrolyte between all supply lines, and / or in the total discharge line in the flow direction of the electrolyte between all discharge lines, or correspondingly only in the supply lines and / or discharge lines at the stack edge and / or at the corresponding locations (e.g., between adjacent electrolysis cells at the stack edge) in the total supply line and / or total discharge line.The third method may further comprise introducing at least one fifth insulator at least into the at least one second feed line to the second electrolysis cell such that at least the entire cross-sectional area of the at least one second feed line is occupied by the second insulator. Thus, an additional insulation on the feed line side can be realized by means of the first insulator and the fifth insulator, also with regard to the overall feed line. Alternatively or additionally, the third insulator may be introduced with a sixth insulator into the second discharge line for further insulation on the discharge side.

[0068] According to certain embodiments, in the inventive method, or also in the third method, the at least one first supply line is arranged below the first electrolysis cell and / or the at least one second supply line, and optionally further supply lines, below the second electrolysis cell. The application of the inventive method, or also of the third method, is greatly facilitated by electrolyte feedings from the stack underside.

[0069] It is also not excluded in the third method that a respective electrolytic cell can have more than one electrolyte, for example a catholyte on the cathode side and an anolyte on the anode side, which can be separated in the respective electrolytic cell by means of a suitable separator, for example a diaphragm or a membrane.For example, the cathode liquor supply then takes place via at least one first and at least one second cathode liquor supply line and a total cathode liquor supply line, and the cathode liquor discharge via at least one first and at least one second cathode liquor discharge line and a total cathode liquor discharge line, as well as the anode liquor supply via at least one first and at least one second anode liquor supply line and a total anode liquor supply line, and an anode liquor discharge via at least one first and at least one second anode liquor discharge line and a total anode liquor discharge line, which can have corresponding respective isolators, that is to say, for example, a first cathode isolator, a second cathode isolator, etc. and / or a first anode isolator, a second anode isolator, etc.

[0070] In addition, a CC^ electrolysis stack is disclosed, comprising:

[0071] - at least one first electrolysis cell (10) and a second electrolysis cell (20),

[0072] - at least one first supply line and at least one first discharge line for the first electrolysis cell (10),

[0073] - at least one second supply line and at least one second discharge line for the second electrolysis cell (20),

[0074] - a total supply line which is connected to the at least one first supply line and the at least one second supply line and is configured to provide a supply for the at least one first supply line and the at least one second supply line, and

[0075] - a main line which is connected to the at least one first line and the at least one second line and is configured to provide a discharge for the at least one first line and the at least one second line, further comprising: at least one first side line which is connected to the at least one first feed line and is configured such that it can at least partially empty an electrolyte present therein from the at least one first feed line, at least one second side line which is connected to the at least one first line and is configured such that it can at least partially empty an electrolyte present therein from the at least one first line, at least one third side line which is connected to the at least one second feed line and is configured as such,that it can at least partially empty an electrolyte present therein from the at least one second supply line, and / or at least one fourth side discharge line, which is connected to the at least one second discharge line and is configured such that it can at least partially empty an electrolyte present therein from the at least one second discharge line, further comprising a first side supply line, which is connected to the at least one first supply line and is configured such that it can supply an inert gas or a mixture comprising an inert gas and liquid droplets present therein into the at least one first supply line, a second side supply line, which is connected to the at least one first discharge line and is configured such that it can supply an inert gas or a mixture comprising an inert gas and liquid droplets present therein into the at least one first discharge line,a third side supply line, which is connected to the at least one second supply line and is configured to supply an inert gas or a mixture comprising an inert gas and liquid droplets therein to the at least one second supply line, and / or a fourth side supply line, which is connected to the at least one second discharge line and is configured to supply an inert gas or a mixture comprising an inert gas and liquid droplets therein to the at least one second discharge line, wherein the inert gas is CO2.,

[0076] An electrolysis stack is described, in particular a CO2 electrolysis stack, comprising:

[0077] - at least one first electrolysis cell and a second electrolysis cell,

[0078] - at least one first supply line and at least one first discharge line for the first electrolysis cell,

[0079] - at least one second supply line and at least one second discharge line for the second electrolysis cell,

[0080] - a main supply line which is connected to the at least one first supply line and the at least one second supply line and is configured to provide a supply for the at least one first supply line and the at least one second supply line, and

[0081] - a main conductor that is connected to the at least one first conductor and the at least one second conductor and is configured to provide a path for the at least one first conductor and the at least one second conductor, further comprising: at least one first insulating blocking device including a first insulator in the at least one first supply line, which is configured to close the at least one first supply line such that at least the entire cross-sectional area of the at least one first supply line is occupied by the first insulator;or at least one first shut-off device in the at least one first supply line, which is configured to close the at least one first supply line, and at least one first discharge device, which is configured such that it can at least partially empty an electrolyte present therein from the at least one first supply line that comprises the first shut-off device; and / or at least one first side discharge line, which is connected to the at least one first supply line and is configured such that it can at least partially empty an electrolyte present therein from the at least one first supply line; and / or at least one first side collecting line, which is connected to the main supply line and is configured such that it can at least partially empty an electrolyte present therein from the main supply line.;

[0082] The first and second supply lines are each configured to supply an electrolyte to the first and second electrolysis cells, and the first and second discharge lines are each configured to discharge an electrolyte from the first and second electrolysis cells, it not being excluded that when discharging the electrolyte it may also include the products of the electrolysis.

[0083] Correspondingly, the main supply line is configured to supply an electrolyte to all supply lines, that is to say, for example, the first and second supply lines, and the main discharge line is configured to discharge the electrolyte and possibly the products of the electrolysis after passing through the electrolysis cell from all discharge lines, that is to say, for example, the first and second discharge lines.

[0084] The corresponding components of the CO₂ electrolysis stack according to the invention or the described electrolysis stack correspond to the components in the methods according to the invention or the described methods, and are not particularly limited. In this regard, reference is also made to the corresponding statements regarding the methods according to the invention and the described methods, which also apply to the CO₂ electrolysis stack according to the invention or the described electrolysis stack.

[0085] Thus, each electrolysis cell in a CO₂ electrolysis stack according to the invention or the described electrolysis stack can comprise wide feed lines, which are used to supply, for example, a starting material, such as a starting gas cathode feed line for a gas comprising CO₂ on the cathode side, or another starting material with a general cathode feed line, and / or a gas and / or a liquid on the anode side, for example an anode feed line, as well as corresponding cathode product and / or anode product discharge lines. According to certain embodiments, at least one starting gas cathode feed line per electrolysis cell is included, which is configured to supply a starting gas comprising CO₂. According to certain embodiments, a cathode product discharge line is also provided per electrolysis cell, which is configured to discharge the product of the electrolysis on the cathode side.Accordingly, in certain embodiments, for each electrolysis cell, anode feed conduits and / or anode product discharge conduits are also provided, each of which is configured to feed a starting material to the anode or discharge a product from the anode. The respective starting material feed conduits and / or product discharge conduits are not particularly limited. A starting material can be fed to the feed conduits for all electrolysis cells via a common overall starting material feed conduit, optionally also separately for starting materials of the cathodes and anodes in the respective electrolysis cells, and products of the electrolysis cells can be discharged via the respective product discharge conduits via a common overall product discharge conduit, optionally also separately for products of the cathodes and anodes of the respective electrolysis cells.

[0086] It is also not excluded that a respective electrolysis cell in the CC^-electrolysis stack or the described electrolysis stack has more than one space for an electrolyte, for example a catholyte space on the cathode side and an anolyte space on the anode side, which can be separated in the respective electrolysis cell by a suitable separator, for example a diaphragm or a membrane. The electrolyte spaces as well as any existing separators and other components of the respective electrolysis cells are not particularly limited. According to certain embodiments, the cathodes of the respective electrolysis cells are gas diffusion electrodes and are accordingly suitable, for example, for a CCh reduction.

[0087] According to certain embodiments, the CCh electrolysis stack or the described electrolysis stack comprises a plurality of electrolysis cells with a number of three or more, for example four or more, five or more, six or more, seven or more, eight or more or nine or more, preferably ten or more, more preferably 20 or more, particularly preferably 50 or more, electrolysis cells. Each electrolysis cell then accordingly has at least one supply line and at least one discharge line for an electrolyte, as set out above, but may also have several supply and discharge lines, for example also for separate catholytes and anolytes, and each electrolysis cell may also have a cathode space, an anode space and a separator or just an electrolyte space, as well as corresponding educt supply lines and product discharge lines, as described above.

[0088] The at least one first insulating shut-off device is not particularly limited and includes at least one first insulator as already described above in connection with the third method and which can be configured accordingly as in the third method. In addition, the first shut-off device can also include further components, such as for example a first automatic closing device which is configured to insert the first insulator into the first supply line such that at least the entire cross-sectional area of the at least one first supply line is occupied by the first insulator. Naturally, the first automatic closing device can also remove the first insulator from the first supply line again in the event of restart,that a passage of electrolyte through the first supply line is enabled again. In addition to or instead of the first insulating shut-off device, a second insulating shut-off device comprising a second insulator may also be provided in the electrolysis cell, in at least one first lead, which is configured to close the at least one first lead such that at least the entire cross-sectional area of the at least one first lead is occupied by the second insulator, and a third insulating shut-off device comprising a third insulator in the main supply line, which is configured to close the main supply line such that at least the entire cross-sectional area of the main supply line in the flow direction between the at least one first supply line and the at least one second supply line is occupied by the third insulator,a fourth insulating shut-off device comprising a fourth insulator in the main line, which is configured to close the main line such that at least the entire cross-sectional area of the main line in the flow direction between at least one first lead and the at least one second lead is occupied by the fourth insulator, a fifth insulating shut-off device comprising a fifth insulator in the at least one second supply line, which is configured to close the at least one second supply line such that at least the entire cross-sectional area of the at least one second supply line is occupied by the fifth insulator, and / or a sixth insulating shut-off device comprising a sixth insulator in the at least one second lead, which is configured to close the at least one second lead such thatIt is provided that at least the entire cross-sectional area of the at least one second lead is occupied by the sixth insulator. The second, third, fourth, fifth, and / or sixth insulating barrier device may also comprise further components, such as a second, third, fourth, fifth, and / or sixth automatic closing device, which is configured to introduce the second, third, fourth, fifth, and / or sixth insulator into the first lead, total supply line, main line, second supply line, and / or second lead such that at least the entire cross-sectional area of the at least one first supply line is occupied by the first insulator. Naturally, the second, third, fourth, fifth, and / or sixth automatic closing device can also reintroduce the second, third, fourth, fifth, and / or sixth insulator from the first lead, total supply line, main line, when restarting operation.Bring out the second supply line and / or second discharge line such that a conduction of electrolyte through the first discharge line, total supply line, total discharge line, second supply line and / or second discharge line is enabled again. The first, second, third, fourth, fifth and / or sixth insulator may be the same or different and may be configured as described above in connection with the method of the third aspect. The first, second, third, fourth, fifth and / or sixth automatic shut-off device is not particularly limited and may be controlled, for example, via one or more control devices.,

[0089] Since the electrolysis stack comprises several electrolysis cells, corresponding additional insulating shut-off devices comprising corresponding insulators, and possibly further automatic closing devices, which are controlled by one or more control devices, may be provided, as also described at least partially in connection with the third method.

[0090] The at least one first shut-off device in the at least one first supply line, which is configured to close the at least one first supply line, and at least one first discharge device, which is configured to at least partially, preferably substantially completely and in particular completely, empty an electrolyte present therein from the at least one first supply line that includes the first shut-off device, are not particularly limited. For example, the first shut-off device may not be electrically insulating, but may also be electrically insulating. With the above-described configuration, in particular, the method of the first aspect, to which reference is made here, can be carried out.

[0091] Alternatively or additionally, in the electrolysis stack, a second shut-off device can be provided in at least one first discharge line which is configured to close the at least one first discharge line, and at least one first drain device which is configured to at least partially, preferably substantially completely and in particular completely, empty an electrolyte present therein from the at least one first discharge line which comprises the second shut-off device, a third shut-off device in the total supply line which is configured to close the total supply line, and at least one third drain device which is configured to at least partially, preferably substantially completely and in particular completely, empty an electrolyte present therein from the total supply line which comprises the third shut-off device, a fourth shut-off device in the total discharge linea device configured to close the main line, and at least one fourth drain device configured to at least partially, preferably substantially completely and in particular completely, empty an electrolyte present therein from the main line surrounding the fourth shut-off device, a fifth shut-off device in the at least one second supply line configured to close the at least one second supply line, and at least one fifth drain device configured to at least partially, preferably substantially completely and in particular completely, empty an electrolyte present therein from the at least one second supply line surrounding the fifth shut-off device, and / or a sixth shut-off device in the at least one second discharge line configured to close the at least one second discharge lineand at least one sixth drain device, which is configured such that it can at least partially, preferably substantially completely and in particular completely, empty an electrolyte present therein from the at least one second conduit which comprises the fifth shut-off device. The second, third, fourth, fifth and / or sixth shut-off device can for example, even if not electrically insulating, but can also be electrically insulating. The first to sixth shut-off devices can also be controlled via one or more control devices and can also be reopened during e.g. startup, corresponding to the insulating shut-off devices. They are not particularly limited and can be configured for example as slides, sluices, valves, etc. The second to sixth drain devices are also not particularly limited.,

[0092] Since the electrolysis stack comprises a plurality of electrolysis cells, it is accordingly also possible to provide further shut-off devices which are controlled by one or more control devices, as well as corresponding further discharge devices.

[0093] Likewise, the at least one first side collecting line, which is connected to the main supply line and is configured such that it can at least partially, preferably substantially completely and in particular completely, drain an electrolyte present therein from the main supply line, is not particularly limited. In such configurations, the main supply line preferably comprises a first main shut-off device which is arranged between the first side collecting line and the main supply line and is closed during operation to prevent the electrolyte from being drained, but can be opened during non-operation to at least partially drain the main supply line.

[0094] Alternatively or additionally, a second side total discharge line may be provided, which is connected to the total discharge line and is configured such that it can at least partially, preferably substantially completely and in particular completely empty an electrolyte present therein from the total discharge line, and this is also not particularly limited. In such configurations, the total discharge line preferably includes a second total shut-off device, which is arranged between the second side total discharge line and the total discharge line and is closed during operation to prevent emptying of the electrolyte, but can be opened during non-operation to at least partially empty the total discharge line.

[0095] The first overall shut-off device and / or the second overall shut-off device can be controlled via one or more control devices and are not particularly limited, and can be configured, for example, as a slide, a lock, a valve, etc.

[0096] The at least one first side discharge, which is connected to the at least one first supply line and is configured such that it can at least partially, preferably substantially completely or preferably completely, empty an electrolyte present therein from the at least one first supply line, is not particularly limited. Alternatively or additionally, at least one second side discharge, which is connected to the at least one first discharge and is configured such that it can at least partially, preferably substantially completely or preferably completely, empty an electrolyte present therein from the at least one first discharge, at least one third side discharge, which is connected to the at least one second supply line and is configured such that it can at least partially empty an electrolyte present therein from the at least one second supply line,Preferably, it can be substantially completely or preferably completely emptied, and / or at least one fourth side discharge, which is connected to the at least one second discharge and is configured such that it can at least partially, preferably substantially completely or preferably completely, empty an electrolyte present therein from the at least one second discharge, may be provided, which are not particularly limited. For this purpose, corresponding blocking devices may also be provided in the respective supply and / or discharge lines, for example, more than one, e.g., two. Corresponding configurations are also mentioned in connection with the method of the first aspect, to which reference is also made here with regard to further configurations.,

[0097] According to certain embodiments, the electrolysis stack according to the invention comprises at least one first side discharge line which is connected to the at least one first supply line and is configured to at least partially, preferably substantially completely and in particular completely, empty an electrolyte present therein from the at least one first supply line, and further comprises a first side supply line which is connected to the at least one first supply line and is configured to supply an inert gas, a mixture comprising an inert gas and liquid droplets present therein, or a liquid which is immiscible with the electrolyte and does not conduct electricity, into the at least one first supply line. The first side supply line is also not particularly limited.

[0098] Alternatively or additionally, the electrolysis stack according to the invention comprises at least one second side discharge, which is connected to the at least one first discharge and is configured such that it can at least partially, preferably substantially completely and in particular completely, empty an electrolyte present therein from the at least one first discharge, and further comprises a second side supply line, which is connected to the at least one first discharge and is configured such that it can supply an inert gas, a mixture comprising an inert gas and liquid droplets present therein, or a liquid that is immiscible with the electrolyte and does not conduct electricity into the at least one first discharge. The second side supply line is also not particularly limited.

[0099] Alternatively or additionally, the electrolysis stack according to the invention comprises at least one third side discharge which is connected to the at least one second supply line and is configured such that it can at least partially, preferably substantially completely and in particular completely, drain an electrolyte present therein from the at least one second supply line, and further comprises a third side supply line which is connected to the at least one second supply line and is configured such that it can supply an inert gas, a mixture comprising an inert gas and liquid droplets present therein, or a liquid which is immiscible with the electrolyte and does not conduct electricity into the at least one second supply line. The third side supply line is also not particularly limited.

[0100] Alternatively or additionally, the electrolysis stack according to the invention comprises at least one fourth side discharge which is connected to the at least one second discharge and is configured such that it can at least partially, preferably substantially completely and in particular completely, empty an electrolyte present therein from the at least one second discharge, and further comprises a fourth side supply line which is connected to the at least one second discharge and is configured such that it can supply an inert gas, a mixture comprising an inert gas and liquid droplets present therein, or a liquid which is immiscible with the electrolyte and does not conduct electricity into the at least one second discharge. The fourth side supply line is also not particularly limited.

[0101] Since the electrolysis stack comprises a plurality of electrolysis cells, further side discharges can accordingly also be provided, which are connected to further supply lines and / or discharges and are configured such that they can at least partially, preferably substantially completely and in particular completely, empty the electrolytes present therein from the further supply lines and / or discharges, and preferably further side supply lines, which are connected to the further supply lines and / or discharges and are configured such that they can supply an inert gas, a mixture comprising an inert gas and liquid droplets present therein, or a liquid that is immiscible with the electrolyte and electrically non-conductive into the further supply lines and / or discharges.

[0102] According to preferred embodiments, side discharges and supply lines are preferably arranged opposite the respective supply and / or discharge lines.

[0103] In addition, the electrolysis stack may include one or more pumps configured to pump an inert gas, a mixture comprising an inert gas and liquid droplets therein, or a liquid immiscible with and non-electrically conductive to the electrolyte into at least partially into the first supply line, first discharge line, second supply line, second discharge line, total supply line, total discharge line and / or other supply and / or discharge lines and / or the electrolysis cells, as well as also a storage reservoir or multiple storage reservoirs containing an inert gas, a mixture comprising an inert gas and liquid droplets therein, or a liquid immiscible with and non-electrically conductive to the electrolyte, from which the gas can be pumped into the corresponding supply and / or discharge lines and possibly also the electrolysis cells. In a CCh electrolysis, as the inert gas, possibly alsoThe moistened gas comprising CO2 or consisting of CO2 is used, so that additional reservoirs can be dispensed with and the inert gas can be provided from the educt supply of the cathodes, for which purpose there may also be a connecting line between, for example, an educt gas-cathode supply line, for example also an educt gas-cathode total supply line, which can provide the educt gas for all educt gas-cathode supply lines, and, for example, the total supply line, although this is interrupted by an educt gas shut-off device in the connecting line, and the educt gas shut-off device can then be opened during non-operation.

[0104] If the electrolysis cells in the electrolysis stack have more than one electrolyte space, for example a catholyte space on the cathode side and an anolyte space on the anode side, then for each electrolyte space there are corresponding inlets, outlets, total in- and total outlets, insulating shut-off devices with corresponding insulators, shut-off devices, side outlets, side inlets, side total outlets, total shut-off devices, etc., also beispielsweise eine erste und zweite KatholytZuleitung, eine erste und zweite AnolytZuleitung, eine GesamtkatholytZuleitung, eine GesamtanolytZuleitung, erste bis sechste isolierende Katholytabsperrvorrichtungen mit ersten bis sechsten Katholytisolatoren, erste bis sechste isolierende Anolytabsperrvorrichtungen mit ersten bis sechsten Anolytisolatoren, erste bis sechste Katholytabsperrvorrichtungen, erste bis sechste Anolytabsperrvorrichtungen, erste bis vierte Katholytseitenzu- und -ableitungen, erste bis vierte Anolytseitenzu- und -ableitungen, eine Katholytseitengesamtableitung, eine Anolytseitengesamtableitung, eine Katholytgesamtabsperrvorrichtung, eine Anolytgesamtabsperrvorrichtung, etc., welche wie oben beschrieben jeweils für Katholyt und Anolyt angeordnet sein können, sowie weitere entsprechende Bestandteile für Katholyt- und Anolytzufuhr und Katholyt- und Anolytabführung, etc. It should be noted that there may be some inaccuracies in the original German text in terms of grammar and terminology, but the translation is done strictly according to the rules preserving the original content as much as possible.However, it is not excluded here that the corresponding insulating barriers, insulators, barriers, side connections and discharges, the side common conductor, the overall barrier device, etc. are provided only for the catholyte or the anolyte, for example only for the catholyte, for example if corrosion is rather to be expected on the catholyte side or the anolyte side, for example for gas diffusion electrodes, e.g. on the catholyte side in a CO₂ electrolysis. Accordingly, such embodiments are also applicable to the processes according to the invention where such measures are thus only taken on the catholyte or anolyte side.

[0105] In the methods according to the invention and the CC^-electrolysis stack or the described electrolysis stack according to the invention, side feed and discharge lines, if present, can also have shut-off devices therein, which can then be closed for operation, so that no electrolyte is lost via the side feed and discharge lines during operation.

[0106] The above embodiments, configurations, and developments can be combined with one another as appropriate, provided that it makes sense. Further possible configurations, developments, and implementations of the invention also include combinations of features of the invention that are not explicitly mentioned but are described above or below with respect to the exemplary embodiments. In particular, the person skilled in the art will also add individual aspects as improvements or supplements to the respective basic form of the present invention. The invention will be explained in more detail below with reference to various examples thereof. However, the invention is not limited to these examples.

[0107] Example 1:

[0108] An exemplary method according to the invention can be carried out in an electrolysis stack shown in FIG. 5. Here, the electrolysis stack has a first electrolysis cell 10 and a second electrolysis cell 20, each of which has an anode A, an anolyte space I for anolyte, a membrane M, a catholyte space II for catholyte, a cathode K and a gas space G on the cathode side, wherein a bipolar plate P is arranged between the two electrolysis cells 10 and 20, as well as at their other ends. End plates E are arranged on the outer side. For example, humidified CO2 is used as the educt gas for the cathode, which is supplied to the respective gas space G via the educt gas-cathode supply lines 27 and 28. The product gas of the electrolysis is discharged via the product gas-cathode discharge lines 17 and 18.During operation, the supply of anolyte to both electrolysis cells 10 and 20 is effected via the overall anolyte line 11, the first anolyte supply line 12, and the second anolyte supply line 13, and the discharge is effected via the first anolyte discharge line 22, the second anolyte discharge line 23, and the overall anolyte discharge line 21. The supply of catholyte to both electrolysis cells 10 and 20 is effected during operation via the overall catholyte line 14, the first catholyte supply line 15, and the second catholyte supply line 16, and the discharge is effected via the first catholyte discharge line 25, the second catholyte discharge line 26, and the overall catholyte discharge line 24.

[0109] In the non-operating state, the entire anolyte supply line 11, the first anolyte supply line 12, the second anolyte supply line 13, the two anolyte chambers I, the first anolyte discharge line 22, the second anolyte discharge line 23, the entire anolyte discharge line 21, the entire catholyte supply line 14, the first catholyte supply line 15, the second catholyte supply line 16, the two catholyte chambers II, the first catholyte discharge line 25, the second catholyte discharge line 26, and the entire catholyte discharge line 24 are essentially and preferably completely filled with an inert gas, e.g. CO2, which may be humidified and may correspond to the educt gas of the cathode, and the anolyte and catholyte are essentially and preferably completely emptied. Compared to an electrolysis stack in which the catholyte and anolyte were not emptied in the non-operating state, there is a reduced corrosion, particularly at the anodes A and cathodes K, especially at the cathode K, which is formed as a gas diffusion electrode.

[0110] Example 2:

[0111] The electrolysis stack in FIG. 6 is used instead of the electrolysis stack in FIG. 5 in Example 1. The structure of the electrolysis stack is the same as that in FIG. 5, but a first catholyte insulator 19 is provided in the first catholyte supply line 15, which is inserted into the first catholyte supply line during non-operation, as shown in FIG. 6. This prevents stray and load currents on the cathode side on the supply line side, so that the corrosion on the cathode can be reduced.

[0112] Example 3:

[0113] In Example 2, the electrolysis stack in FIG. 7 is used instead of the electrolysis stack in FIG. 6. The structure of the electrolysis stack is the same as that in FIG. 6, except that an additional (third according to the above description) catholyte insulator 29 is provided in the second catholyte supply line 16, which additionally reduces scattered and load currents via, for example, a catholyte circuit.

[0114] Example 4:

[0115] The electrolysis stack in FIG. 8 is used instead of the electrolysis stack of FIG. 5 in Example 1. Additionally, a first catholyte shut-off device 19' is provided in the first catholyte supply line 15, and a further (third according to the above description) catholyte shut-off device 29' is provided in the second catholyte supply line 16, and a first catholyte side discharge line 15' is provided in the first catholyte supply line 15. A first catholyte side discharge line shut-off device 19'' is also located in the first catholyte side discharge line 15', which, however, ideally lies directly on the first catholyte supply line 15. During operation, the first catholyte side discharge line shut-off device 19'' is closed and catholyte is not lost via the first catholyte side discharge line 15', and the first catholyte shut-off device 19' and the further catholyte shut-off device 29' are open.In the non-operating state, the first catholyte shut-off device 19' and the further catholyte shut-off device 29' are closed and the first catholyte side discharge shut-off device 19'' is opened. Catholyte from the total catholyte supply line 14, parts of the first catholyte supply line 15 and possibly parts of the second catholyte supply line 16 (as schematically shown here in Figure 8) is at least partially, preferably substantially completely and in particular completely emptied via the first catholyte side discharge line 15'. The catholyte can be replaced, for example, by moistened CO2.

[0116] Example 5:

[0117] The electrolysis stack in Figure 9 is used instead of the electrolysis stack of Figure 5 in Example 1. Additionally, a first catholyte shut-off device 19' is provided in the first catholyte supply line 15, as well as a first catholyte side discharge line 15' with a first catholyte side discharge shut-off device 19'' and a first catholyte side supply line 15'' with a first catholyte side supply line shut-off device 19'''. Ideally, the first catholyte side discharge shut-off device 19'' and the first catholyte side supply line shut-off device 19''' are directly attached to the first catholyte supply line 15. During operation, the first catholyte shut-off device 19' is open, and the first catholyte side discharge shut-off device 19'' and the first catholyte side supply line shut-off device 19''' are closed.In the non-operating state, the first cathode shut-off device 19' is closed, and the first cathode side discharge shut-off device 19'' and the first cathode side supply shut-off device 19''' are opened. Moist CO₂ flows through the first cathode side supply line 15'' and the first cathode side discharge line 15', which are located opposite the first cathode supply line 15 here, in order to interrupt the electrolyte in a part of the first cathode supply line 15. Optionally, the first cathode shut-off device 19' can also be open or be made open here. By interrupting the cathode supply side in the first cathode supply line 15, load and stray currents are again reduced.

[0118] Example 6:

[0119] The electrolysis stack in FIG. 10 is used instead of the electrolysis stack of FIG. 5 in Example 1. Additionally, in the overall catholyte supply line 14, a catholyte-side common supply line 14' is provided, which is separated from the overall catholyte supply line 14 during operation by a closed first overall catholyte shut-off device 30', thereby preventing a catholyte flow into the catholyte-side common supply line 14'. During non-operation, the catholyte is at least partially, preferably substantially completely or preferably completely emptied via the catholyte-side common supply line 14' after opening the first overall catholyte shut-off device 30' at least in the overall catholyte supply line 14, and it can be replaced, for example, by moistened CO2 or an inert liquid in order to suppress a backflow of catholyte from the first catholyte line 15 and the second catholyte line 16.

[0120] Example 7:

[0121] The electrolysis stack in FIG. 11 is used instead of the electrolysis stack of FIG. 10 in Example 6. In order to further prevent the backflow of catholyte from the first catholyte supply line 15 and the second catholyte supply line 16 during non-operation, the first catholyte shut-off device 19' and a further (third according to the above description) catholyte shut-off device 29' from Example 4 are provided in the first catholyte supply line 15 and the second catholyte supply line 16, which are open during operation and closed during non-operation.

Claims

A method of protecting a nonoperational CO2 electrolysis stack from corrosion, wherein the CO2 electrolysis stack comprises a multitude of electrolysis cells (10, 20) having a number of 3 or more electrolysis cells (10, 20),wherein the CO2 electrolysis stack comprises at least a first electrolysis cell (10) and a second electrolysis cell (20), at least a first feed (12, 15) and at least a first drain (22, 25) for the first electrolysis cell (10) and at least a second feed (13, 16) and at least a second drain (23, 26) for the second electrolysis cell (20), wherein at least the first electrolysis cell (10) and the second electrolysis cell (20) and at least the at least one first feed (12, 15) and the at least one second feed (13, 16) are partly filled with at least one electrolyte, comprising:at least partly emptying the electrolyte from parts of at least the first electrolysis cell (10) or of the at least one first feed (12, 15) or of the at least one first drain (22, 25) or of an overall feed (11, 14) which is connected to the at least one first feed (12, 15) and the at least one second feed (13, 16) and is designed to provide an inlet for the at least one first feed (12, 15) and the at least one second feed (13, 16) or of an overall drain (21, 24) which is connected to the at least one first drain (22, 25) and the at least one second drain (23, 26) and is designed to provide an outlet for the at least one first drain (22, 25) and the at least one second drain (23, 26), wherein the electrolyte which is removed by the at least partial emptying is exchanged for an inert gas or a mixture comprising an inert gas and liquid droplets present therein, wherein the inert gas is CO2, and whereinthe electrolyte is at least partly emptied at least from parts of the electrolysis cells (10, 20) or the feeds (12, 13, 15, 16) to the electrolysis cells (10, 20), in each case at the edge of the CO2 electrolysis stack, wherein partial emptying corresponds to emptying of at least 50% by volume.The method as claimed in claim 1, wherein at least the at least one first feed (12, 15) is partly emptied.The method as claimed in claim 1 or 2, wherein at least the at least one first feed (12, 15) and the at least one second feed (13, 16) are at least partly emptied in such a way that there is a region in which there is essentially no electrolyte in the at least one first feed (12, 15) and the at least one second feed (13, 16), wherein essentially complete emptying corresponds to emptying of at least 95% by volume.The method as claimed in claim 1, wherein the at least one first drain (22, 25) and the at least one second drain (23, 26) are additionally at least partly emptied in such a way that there is a region in which there is essentially no electrolyte in the at least one first drain (22, 25) and the at least one second drain (23, 26), wherein essentially complete emptying corresponds to emptying of at least 95% by volume.The method as claimed in claim 1, wherein the entire CO2 electrolysis stack is filled with the inert gas or the mixture comprising an inert gas and liquid droplets present thereinThe method as claimed in any of the preceding claims, wherein current is still being applied to electrodes of the electrolysis cellsThe method as claimed in claim 1, wherein the CO2 electrolysis stack is transported.The method as claimed in claim 7, wherein, in the case of transport, at least the at least one first feed (12, 15), the at least one second feed (13, 16), the at least one first drain (22, 25) and the at least one second drain (23, 26) are at least partly filled in such a way that there is a region in which there is essentially the inert gas or the mixture comprising an inert gas and liquid droplets present therein in each of the at least one first feed (12, 15), the at least one second feed (13, 16), the at least one first drain (22, 25) and the at least one second drain (23, 26).A CO2 electrolysis stack having a multitude of electrolysis cells (10, 20) having a number of 3 or more electrolysis cells, comprising:- at least a first electrolysis cell (10) and a second electrolysis cell (20),- at least a first feed (12, 15) and at least a first drain (22, 25) for the first electrolysis cell (10),– at least a second feed (13, 16) and at least a second drain (23, 26) for the second electrolysis cell (20),– an overall feed (11, 14) which is connected to the at least one first feed (12, 15) and the at least one second feed (13, 16) and is designed to provide an inlet for the at least one first feed (12, 15) and the at least one second feed (13, 16), and– an overall drain (21, 24) which is connected to the at least one first drain (22, 25) and the at least one second drain (23, 26) and is designed to provide an outlet for the at least one first drain (22, 25) and the at least one second drain (23, 26), further comprising:at least one first side drain (15') which is connected to the at least one first feed (15) and is designed such that it can at least partly empty any electrolyte present in the at least one first feed (15) therefrom, at least one second side drain which is connected to the at least one first drain (22, 25) and is designed such that it can at least partly empty any electrolyte present in the at least one first drain (22, 25) therefrom, at least one third side drain which is connected to the at least one second feed (13, 16) and is designed such that it can at least partly empty any electrolyte present in the at least one second feed (13, 16) therefrom, or at least one fourth side drain which is connected to the at least one second drain (23, 26) and is designed such that it can at least partly empty any electrolyte present in the at least one second drain (23, 26) therefrom, further comprising a first side feed (15'') which is connected to the at least one first feed (15) and is designed such that it can supply an inert gas or a mixture comprising an inert gas and liquid droplets present therein to the at least one first feed (15), a second side feed which is connected to the at least one first drain (22, 25) and is designed such that it can supply an inert gas or a mixture comprising an inert gas and liquid droplets present therein to the at least one first drain (22, 25), a third side feed which is connected to the at least one second feed (13, 16) and is designed such that it can supply an inert gas or a mixture comprising an inert gas and liquid droplets present therein to the at least one second feed (13, 16), or a fourth side feed which is connected to the at least one second drain (23, 26) and is designed such that it can supply an inert gas or a mixture comprising an inert gas and liquid droplets present there into the at least one second drain (23, 26), wherein the inert gas is CO2, and wherein the electrolyte can be at least partly emptied at least from parts of the electrolysis cells (10, 20) or the feeds (12, 13, 15, 16) to the electrolysis cells (10, 20), in each case at the edge of the CO2 electrolysis stack, wherein partial emptying corresponds to emptying of at least 50% by volume.

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