Process for regenerating an electrolysis cell

Abstract

The invention relates to a method for regenerating an electrolysis cell configured for the electrolysis of CO2. For this purpose, an electrolyte is first drained from a water chamber. After the gas diffusion electrode is aligned horizontally, the water chamber is flooded with a catalyst binding emulsion, and an overpressure is generated relative to the gas chamber. After draining the catalyst binding emulsion, the water chamber is flushed with a solvent. Finally, drying with a drying gas takes place so that, after the electrolysis cell has been returned to an operating position, the water chamber can be refilled with the electrolyte, thus making the electrolysis cell operational again.

Description

TECHNICAL FIELD

[0001] The invention relates to an electrolysis cell for the electrolysis of CO2. This cell comprises a gas chamber containing CO2 and a water chamber containing an electrolyte, which are separated from each other by a gas diffusion electrode. Due to the aging of the gas diffusion electrode, its surface must be regularly cleaned and renewed. BACKGROUND

[0002] Renewable electricity, such as solar and wind power, can be provided in some locations in quantities that exceed local demand. The effective use of available electricity is problematic in this case. One possibility is the electrolysis of water to produce hydrogen and oxygen. However, the storage and transport of hydrogen are problematic. Furthermore, it is known that available renewable electricity can be utilized through the electrochemical conversion of CO2, capturing the greenhouse gas CO2 as a product. The electrochemical reduction reaction of carbon dioxide (CO2) to hydrocarbons through CO2 electrolysis represents a promising alternative to other energy storage strategies.

[0003] Electrolysis cells are used to reduce CO2. On one side is an anode, separated from a liquid electrolyte by a membrane. Inside the electrolysis cell is the cathode, which is in contact with the CO2 to be reduced. When the appropriate voltage is applied between the anode and cathode, electrolysis of the CO2 takes place. For this purpose, in the electrolysis cell used regularly, a cavity for holding the electrolyte is arranged adjacent to the cathode on the side facing the anode. Opposite is a cavity for holding the CO2, with the cavities separated from each other by a gas diffusion electrode.

[0004] The general functioning of an electrolysis cell for the electrolysis of CO2 is well known to those skilled in the art. This is described, for example, in WO2023 / 217624A1 or WO2019 / 096985A1. Furthermore, EP 3 626 858 A1 is cited as prior art.

[0005] In simplified terms, an electrolysis cell consists of an end plate, the anode, the membrane, the cavity for the electrolyte, the gas diffusion electrode, the cavity for the CO2 and another end plate, with the thickness of all layers being relatively small.

[0006] A technically and economically viable application is only possible if a large number of electrolysis cells are used simultaneously, which are stacked on top of each other.

[0007] During operation, the gas diffusion electrode ages due to the process. This reduces efficiency. After a certain period of operation, this requires regeneration or, if necessary, replacement of the gas diffusion electrode. This requires disassembling the stack of electrolysis cells and removing the individual gas diffusion electrodes. These can then be cleaned and treated to restore almost their original properties.

[0008] The disadvantage is the high cost of regenerating the gas diffusion electrode, which requires dismantling the stack and the individual electrolysis cells. SUMMARY OF THE INVENTION

[0009] The object of the present invention is to enable regeneration of the gas diffusion electrode with reduced effort.

[0010] The object is achieved by a method according to the invention according to the teaching of claim 1. Advantageous embodiments are the subject of the dependent claims.

[0011] An electrolysis cell for the electrolysis of CO2 comprises, in direct or indirect sequence, a cathode end plate, a gas chamber, a gas diffusion electrode, a water chamber and an anode end plate.

[0012] The invention provides that for regeneration, when the electrolysis cell is not in operation, the electrolyte is first drained from the water chamber. The water chamber is then flooded with a catalyst binding emulsion. This creates an overpressure relative to the gas chamber.

[0013] After draining the catalyst binding emulsion, the water chamber is rinsed with a solvent. Finally, it is dried with a drying gas. After the electrolysis cell has been returned to its operating position, the water chamber can be refilled with the electrolyte, making the electrolysis cell ready for operation again. DESCRIPTION OF THE INVENTION

[0014] The generic electrolysis cell is intended for the electrolysis of CO2 and includes, as a direct or indirect consequence, - a cathode end plate, - a gas chamber, - a gas diffusion electrode, - a water chamber, and - an anode end plate.

[0015] For the remainder of the description, reference is made to a left side and an opposite right side. The terms "left side" and "right side" are chosen arbitrarily in this regard; however, in the following, they should always be understood that the left side refers to the side on which the anode end plate is located, and the right side is the opposite side of the electrolysis cell from which the cathode end plate is located.

[0016] The cathode end plate and the anode end plate are the geometric ends of the respective electrolysis cell. In an arrangement of multiple electrolysis cells, a cathode end plate of one electrolysis cell can also form the anode end plate of the following electrolysis cell.

[0017] The gas chamber is a cavity in the electrolysis cell to which CO2 is supplied during operation. The water chamber is another cavity that contains an electrolyte during operation.

[0018] A gas diffusion electrode separates the gas chamber from the water chamber. For functional reasons, the gas diffusion electrode must be permeable to CO2, but the passage of liquid through the gas diffusion electrode must be prevented. The gas diffusion electrode can have a multilayer structure.

[0019] It is obvious that the gas chamber, the gas diffusion electrode, and the water chamber must be sealed all the way around to enable the gas chamber and the water chamber to be realized as cavities. Furthermore, it is obvious that appropriate connections are required for the introduction and discharge of fluids into and from the gas chamber and water chamber, respectively.

[0020] To ensure a defined distance between the gas diffusion electrode and the cathode end plate, it is particularly advantageous if at least one cathode-side spacer is inserted in the gas chamber. The cathode-side spacer is positioned against the cathode end plate and, opposite, against the gas diffusion electrode. The cathode-side spacer is intended to ensure that the distance between the cathode end plate and the gas diffusion electrode does not change due to deformation. The cathode-side spacer should have a defined position between the cathode end plate and the gas diffusion electrode.

[0021] Furthermore, depending on the dimensions of the electrolysis cell and the rigidity of the gas diffusion electrode, it may be advantageous to place at least one anode-side spacer in the water chamber. The anode-side spacer should ensure that the distance between the anode end plate and the gas diffusion electrode does not change due to deformation. The anode-side spacer should be positioned at a defined position between the anode end plate and the gas diffusion electrode.

[0022] In conjunction with the cathode-side spacer, the anode-side spacer can be used to reliably determine the position of the gas diffusion electrode.

[0023] During operation of the electrolysis cell, a voltage is present between an anode and a cathode, and the CO2 electrolysis process takes place. For the present invention, it is first necessary that the electrolysis cell is not in operation, i.e., no voltage is applied between the anode and cathode.

[0024] To reduce the effort required to regenerate the electrolysis cell, particularly the gas diffusion electrode, it is proposed to avoid disassembling the electrolysis cell. Instead, the following procedure according to the invention is carried out: a) In a first step, the electrolyte present in the water chamber is drained. c) Now the water chamber is filled with a catalyst binding emulsion.

[0025] The viscosity of the catalyst binder emulsion must be sufficiently low so that it can flow through the water chamber without causing blockages.

[0026] d) To improve the effect of the catalyst binding emulsion, it is provided that a relative overpressure is maintained between the water chamber containing the catalyst binding emulsion and the gas chamber arranged opposite the gas diffusion electrode.

[0027] Whether this involves creating a negative pressure (compared to an open system) in the gas chamber or an overpressure (compared to an open system) in the water chamber, or both a negative pressure in the gas chamber and an overpressure in the water chamber at the same time, is initially irrelevant.

[0028] At least the catalyst binding emulsion should be suitable to bring about an improvement in the properties of the gas diffusion electrode used by acting on the gas diffusion electrode.

[0029] e) After a certain contact time, the catalyst binding emulsion must be removed from the electrolysis cell. To do this, the water chamber must first be emptied.

[0030] f) To remove the catalyst binding emulsion as completely as possible, the water chamber is rinsed with a solvent in the next step.

[0031] The type of solvent is initially irrelevant, as long as the solvent promotes the removal of the catalyst binder emulsion. In this respect, it may be sufficient to reduce the viscosity by creating a mixture of the catalyst binder emulsion and the solvent.

[0032] g) At the end of the rinsing of the water chamber, it is also necessary to remove the existing solvent by draining it from the water chamber.

[0033] h) To ensure that the solvent is removed as completely as possible from the water chamber, it is further provided that the water chamber is subsequently flushed with a drying gas.

[0034] The type of drying gas is initially irrelevant. On the one hand, it can be designed so that, as the drying gas flows through the water chamber, residual solvent is entrained and thus removed. It can also be designed so that the solvent evaporates and is thus carried away by the drying gas.

[0035] j) The water chamber can now be filled with the electrolyte so that the device is ready for operation again.

[0036] The newly developed method according to the invention eliminates the otherwise necessary disassembly of the electrolysis cell and subsequent reassembly. This saves considerable time and significantly reduces the effort involved.

[0037] Regardless of the newly developed process, after a certain number of regenerations according to the inventive method, it may be necessary to disassemble the electrolysis cell in the conventional manner for complete regeneration of the gas diffusion electrode and then reassemble it after the gas diffusion electrode has been reconditioned or replaced. However, this should no longer be the rule, but rather the exception.

[0038] Since the electrolysis cell no longer needs to be disassembled, it no longer needs to be transported to a separate location for reprocessing (because, for example, the gas diffusion electrode could become contaminated at the site of operation). Advantageously, the gas diffusion electrode can be regenerated on-site using the new process. This increases flexibility, especially with regard to planning for necessary regeneration of the gas diffusion electrode.

[0039] The method according to the invention is preferably used in an electrolysis cell in which the gas diffusion electrode comprises a gas diffusion layer and an adjacent catalyst layer. In this case, the catalyst layer is located on the left side adjacent to the water chamber, and the gas diffusion layer is located on the right side adjacent to the gas chamber.

[0040] In this case, a gas diffusion layer consisting essentially of an electrically non-conductive material is preferably used. In contrast, the catalyst layer is particularly advantageously electrically conductive. For this purpose, it consists of an electrically conductive material or at least has an electrically conductive coating. The catalyst layer forms the cathode of the electrolysis cell.

[0041] Furthermore, it is possible to construct the catalyst layer or the gas diffusion layer in multiple layers. For possible and advantageous layer structures, reference is made to the known state of the art.

[0042] In any case, the gas chamber is directly adjacent to the gas diffusion electrode and, if a gas diffusion layer is present, directly adjacent to the gas diffusion layer. In a simple and advantageous manner, the gas chamber is also directly adjacent to the cathode end plate.

[0043] It is also necessary that the water chamber is directly adjacent to the gas diffusion electrode and thus, if a catalyst layer is present, directly adjacent to the catalyst layer.

[0044] In any case, an anode is required. In one embodiment, the anode end plate may also serve as the anode of the electrolysis cell. In an alternative embodiment, an anode is arranged indirectly or, preferably, directly adjacent to the anode end plate.

[0045] It is particularly advantageous if the water chamber is separated from the anode by an anode membrane and the anode membrane is therefore directly adjacent to the water chamber.

[0046] An anode chamber may be arranged between the anode membrane and the anode. However, direct contact of the anode membrane with the anode is preferred.

[0047] For functional reasons, it is necessary that a voltage can be applied to the electrolysis cell. It is particularly advantageous if the power connection to the electrolysis cell is made on the left side at the anode end plate and on the opposite right side at the cathode end plate.

[0048] Alternatively, it can also be provided that the anode and / or the catalyst layer as a cathode are contacted to the outside separately from the anode end plate or cathode end plate.

[0049] Various known solutions are available for contacting the gas diffusion electrode or the catalyst layer, so that the person skilled in the art can choose a suitable solution from these.

[0050] Both for ongoing operation and for the necessary draining and filling of the chambers, in particular the water chamber, the gas chamber and, if applicable, the anode chamber, it is advantageous if the respective chamber has at least two diagonally opposite connections.

[0051] Taking into account the operating position of the electrolysis cell with a preferred vertical orientation of the gas diffusion electrode, the particularly preferably diagonally opposite connections are located laterally on the chambers, once near a lower end of the respective chamber and on the opposite edge near an upper end of the respective chamber.

[0052] For filling the water chamber with the catalyst binding emulsion and draining the catalyst binding emulsion, it is also advantageous to have two connections on opposite sides of the water chamber. This can improve the uniformity of the exposure to the gas diffusion electrode, particularly in step d), with the horizontal orientation.

[0053] Typically, the gas diffusion electrode is oriented vertically during operation. At the very least, the electrolysis cell is in an "operating position" during operation. This position is determined by the orientation of the electrolysis cell relative to the horizontal.

[0054] However, for the subsequent regeneration process, it is particularly advantageous that the gas diffusion electrode is aligned horizontally.

[0055] b) In an advantageous step, the orientation of the electrolysis cell is changed before step c)—before or after step a)—so that the gas diffusion electrode is oriented horizontally, starting from the operating position. This step is obviously omitted if a horizontal orientation of the gas diffusion electrode corresponds to the operating position.

[0056] It is important to ensure that the left side, with the anode end plate, is above the gas diffusion electrode, and the right side, with the cathode end plate, is below the gas diffusion electrode. This means that the left side forms the top side, and the right side forms the bottom side in the subsequent process.

[0057] It should be noted that "horizontal" does not necessarily require a perfectly horizontal alignment of the gas diffusion electrode. Even with minor deviations, the method can be carried out successfully without limitations. Therefore, a deviation from the horizontal of up to 30° is considered acceptable for a "horizontal" alignment. However, the deviation should preferably not exceed 15°. A maximum inclination of 5° is considered optimal.

[0058] i) In order to restore operational readiness, it is obvious that the electrolysis cell must be returned to its original operating position in a further step before restarting. This step is therefore necessary if the position of the electrolysis cell was changed in the advantageous step b).

[0059] Advantageously, the gas diffusion electrode of the electrolysis cell is oriented vertically in an operating state with ongoing electrolysis, so that when step b) is applied, the electrolysis cell can be pivoted into the correct position in step i).

[0060] This can be done at different times after draining the catalyst binding emulsion in step e). This is advantageously done after purging with the drying gas (step h).

[0061] The composition of the catalyst binding emulsion depends on the chemical composition and structure of the gas diffusion electrode.

[0062] An exemplary gas diffusion electrode was prepared as follows:

[0063] A gas diffusion layer is provided, comprising a carbon-based, microporous support layer and an underlying macroporous support layer made of carbon fibers. A catalyst substance comprising a CuO powder and an anionic ionomer in ethanol, with an addition of isopropanol, is applied to the gas diffusion layer. An exemplary composition comprises 40 mg of CuO powder, 160 mg of a 5 wt% Sustanion XA-9 anionic ionomer in an ethanol solution, and 4 mL of isopropanol.

[0064] The catalyst binder emulsion can advantageously be a composition that corresponds to the composition used as the catalyst substance for the production of the gas diffusion electrode. A deviation from the composition of 10% is considered permissible, i.e., 90% of the amount of catalyst substance (from the production of the gas diffusion electrode) should also be contained in the catalyst binder emulsion. Particularly preferably, at least 95% of the amount of catalyst substance is contained in the catalyst binder emulsion.

[0065] To ensure flow through the water chamber during regeneration, a low viscosity for the catalyst binder emulsion is preferred, which approximately maintains the original composition of the catalyst substance.

[0066] Furthermore, attention should be paid to particle size to favorably influence particle penetration into or deposition on the gas diffusion layer during regeneration. Therefore, a small particle size is preferred, which approximately maintains the original composition of the catalyst substance.

[0067] The penetration of the catalyst binding emulsion into the gas diffusion electrode is promoted by the differential pressure between the water chamber on one side and the gas chamber on the other. It is advantageous if, simultaneously with the introduction of the catalyst binding emulsion in step c), and at least subsequently in step d), a relative overpressure of at least 5 mbar is present in the water chamber relative to the gas chamber. Preferably, a relative overpressure of at least 10 mbar is generated.

[0068] To prevent damage to the electrolysis cell, especially the gas diffusion electrode, the differential pressure should not be too high. Therefore, the relative overpressure in the water chamber relative to the gas chamber should not exceed 100 mbar. The relative overpressure is preferably limited to 50 mbar.

[0069] To remove excess catalyst binding emulsion from the electrolysis cell, especially the water chamber, various solvents can be used for rinsing. In a first variant, an alcohol-based solvent is particularly preferred. In this case, the solvent can consist of one or more alcohols or, alternatively, contain other substances, although alcohol is the main component. Preferred alcohols in this case are isopropanol and / or ethanol and / or methanol.

[0070] In a second variant, a solvent based on N-methyl-2-pyrrolidone is used. Here, too, a mixture with N-methyl-2-pyrrolidone as the main component can be used, with the solvent preferably consisting of N-methyl-2-pyrrolidone.

[0071] If the solvent remains in the electrolysis cell, especially in the water chamber, it can negatively impact the electrolysis process itself. Therefore, it is important to remove the solvent as completely as possible using a drying gas without negatively affecting the process. Therefore, a protective gas is preferred. When using the preferred solvent, it is best to use argon or helium as the drying gas.

[0072] The gas diffusion electrode regeneration process should not be carried out at temperatures below 20°C to avoid impeding the flow. The temperature of the electrolysis cell is preferably kept at least 40°C. However, the electrolysis cell should not be overheated to prevent thermal damage, especially to the gas diffusion electrode. Therefore, the temperature of the electrolysis cell should not exceed 80°C. The temperature is preferably limited to 65°C.

[0073] a') Although it would be sufficient to drain the electrolyte from the water chamber, it is advantageous to first remove as much of the CO2 as possible from the gas chamber. Whether the CO2 is removed from the gas chamber before, at the same time, or after draining the electrolyte from the water chamber is irrelevant.

[0074] c') Provision may be made for a substitute gas to be introduced into the gas chamber.

[0075] e') It is obvious that, if a substitute gas has been filled into the gas chamber, the substitute gas must also be removed before, during or after the catalyst binding emulsion is drained.

[0076] f') It is preferably provided that before, during or after the rinsing of the water chamber, the gas chamber is also rinsed, in particular with the solvent.

[0077] g') If a solvent was used to flush the gas chamber, it should obviously be removed first after flushing.

[0078] h') Furthermore, if a solvent was used to flush the gas chamber, the gas chamber should be flushed analogously and advantageously with the dry gas.

[0079] j') If the CO2 has been removed for the regeneration process, the gas chamber is preferably also flooded with CO2 when filling the water chamber with the electrolyte. This can be done before, during, or after filling the water chamber.

[0080] a") If an anode chamber is present, any anolyte present can be drained from the anode chamber. It is also irrelevant whether the anolyte is drained from the anode chamber before, at the same time as, or after the electrolyte is drained from the water chamber.

[0081] c") If an anolyte has been removed for the regeneration process, a replacement liquid should preferably be filled into the anode chamber. In this case, particular consideration must be given to the relative overpressure in the water chamber relative to the gas chamber.

[0082] e") It is obvious that, if a replacement fluid has been filled into the anode chamber, the replacement fluid must also be removed before, during or after draining the catalyst binding emulsion.

[0083] j") If an anolyte has been removed for the regeneration process, the anode chamber is preferably also filled with the anolyte when filling the water chamber with the electrolyte. This can obviously be done before, during or after filling the water chamber. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 shows a schematic exploded view of the structure of an electrolysis cell. Fig. Figure 2 shows a schematic cross-section of the electrolysis cell from Fig. 1. DESCRIPTION OF THE EMBODIMENTS

[0084] In the Fig. 1 and in the Fig.Figure 2 shows a generic electrolysis cell 01. This simplified sketch shows the structure of the electrolysis cell 01 in the sequence from the right side 02 to the left side 03.

[0085] On the right side 02 is the cathode end plate 04. The cathode-side power connection is typically made at the cathode end plate 04. Adjacent to the cathode end plate 04 is the gas chamber 06. During operation of the electrolysis cell 01, the carbon dioxide (CO2) to be converted is fed into the gas chamber through a gas connection 16a. A mixture of the converted gas and a residual amount of CO2 is discharged through the gas connection 16b.

[0086] The anode end plate 05 is located on the left side 03. The anode-side power connection is preferably made on the left side at the anode end plate 05. In the figure, the anode 09 is sketched adjacent to the anode end plate 05.

[0087] Immediately adjacent to the anode 09 in this embodiment there is an anode chamber 08 with an anode connection 18a for introducing an anolyte and an anode connection 18b for discharging the anolyte.

[0088] An adjacent water chamber 07 is separated from the anode chamber 08 by an anode membrane 14. During operation of the electrolysis cell 01, the electrolyte for enabling electrolysis is located in the water chamber 07. For this purpose, it has a water connection 17a on one side and a water connection 17b opposite. The advantageous design for the process, with two water connections on each side, is not shown.

[0089] The gas chamber 06 is separated from the water chamber 07 by a gas diffusion electrode 11. This 11 consists of a gas diffusion layer 08 and a catalyst layer 09. The gas diffusion layer 08 is electrically non-conductive, while the catalyst layer 09 is electrically conductive.

[0090] To enable CO2 electrolysis, the catalyst layer 09 must be electrically connected to a cathode terminal. This is preferably done via the connection to the cathode end plate 04, to which the cathode terminal is connected.

Claims

[1] Method for the regeneration of an electrolysis cell (01), which (01) is designed for the electrolysis of CO2 and in direct or indirect sequence from a right side (02) to a left side (03) - a cathode end plate (04), - a gas chamber (06) which (06) is at least partially filled with CO2 during operation of the electrolysis cell (01), - a gas diffusion electrode (11), - a water chamber (07), which (07) is at least partially filled with an electrolyte during operation of the electrolysis cell (01), and - comprises an anode end plate (05); wherein the electrolysis cell (01) is switched off, with the steps a) Draining the electrolyte from the water chamber (07), c) filling the water chamber (07) with a catalyst binding emulsion; d) generating a relative overpressure in the water chamber (07) relative to the gas chamber (06); e) draining the catalyst binding emulsion from the water chamber (07); f) rinsing the water chamber (07) with a solvent; g) draining the solvent from the water chamber (07); h) flushing the water chamber (07) with a dry gas; j) Filling the water chamber (07) with the electrolyte. [2] Method according to claim 1, wherein the gas diffusion electrode (11) comprises a non-conductive gas diffusion layer (13) on the right side (02) and a conductive catalyst layer (12) on the left side (03). [3] Method according to claim 1 or 2, wherein the electrolysis cell (01) between the water chamber (07) and the anode end plate (05) - an anode membrane (14) and / or - an anode chamber (08) and / or - comprises an anode (09). [4] Method according to one of claims 1 to 3, wherein the gas chamber (06) and the water chamber (07), and in particular the anode chamber (08), each have at least two connections diagonally opposite one another. [5] Method according to claim 4, wherein the water chamber (07) has at least two connections on each of two opposite sides. [6] Method according to one of claims 1 to 5, with the further steps b) storing the electrolysis cell (01) with a horizontal orientation of the gas diffusion electrode (11) before step c), wherein the right side (02) forms a bottom side and the left side (03) forms a top side; and i) Storage of the electrolysis cell (01) in the operating position after step e). [7] Method according to one of claims 1 to 6, wherein the gas diffusion electrode has been treated with a specific catalyst substance for its production, and wherein the catalyst binding emulsion corresponds to at least 90%, in particular to at least 95%, of the composition of the catalyst substance. [8] Method according to one of claims 1 to 7, wherein the relative overpressure is at least 5 mbar, in particular at least 10 mbar, and at most 100 mbar, in particular at most 50 mbar. [9] Method according to one of claims 1 to 8, wherein the solvent used is exclusively or at least predominantly an alcohol, in particular isopropanol and / or ethanol and / or methanol; and / or where N-methyl-2-pyrrolidone is used exclusively or at least predominantly as solvent. [10] Method according to one of claims 1 to 9, wherein a protective gas, in particular argon or helium, is used as the drying gas. [11] Method according to one of claims 1 to 10, wherein the drying gas and / or the electrolysis cell (01) in step h), in particular during the method, has a temperature of at least 20°C, in particular at least 40°C, and at most 70°C, in particular at most 60°C. [12] Method according to one of claims 1 to 11, wherein before or during or after step a) in a step a') the CO2 is removed from the gas chamber (06); and / or a") an anolyte is drained from the anode chamber (17); and / or wherein before or during or after step c) in a step c') a replacement fluid is introduced into the gas chamber (06); and / or c') a replacement fluid is introduced into the anode chamber (17); and / or wherein before, during or after step e) in a step e') the replacement fluid is drained from the gas chamber (06); and / or e') the replacement fluid is drained from the anode chamber (17); and / or wherein before, during or after step j) in a step j`) CO2 is introduced into the gas chamber (06); and / or j'') Anolyte is filled into the anode chamber (17).

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