Method for refurbishing an electrolysis cell and electrolysis cell

Abstract

The invention relates to a method for refurbishing an electrolysis cell for alkaline water electrolysis or chloralkali electrolysis, wherein at the start of the method the electrolysis cell is in a closed starting state with an elastic current distributor being in a compressed state, holding a cathode in planar contact with one side of a sheet-like separator, wherein a second, opposite second side of the sheet-like separator is supported by a rigid anode, and wherein the method comprises the steps of opening the electrolysis cell, while releasing the compression of the elastic current distributor, interposing a first flexible anode between the rigid anode and the separator, and closing the electrolysis cell, while compressing the elastic current distributor. The invention further relates to an electrolysis cell obtainable by the above method.

Description

[0001] 29.08.2025

[0002] 1 / 14

[0003] Method for Refurbishing an Electrolysis Cell and Electrolysis Cell

[0004] Background of the Invention

[0005] The invention relates to a method for refurbishing an electrolysis cell for alkaline water electrolysis or chlor-alkali electrolysis according to the preamble of claim 1 and an electrolysis cell according to the preamble of claim 10.

[0006] In modern electrolysis cells for chlor-alkali or alkaline water electrolysis the electrodes are coated with a functional layer that enhances the efficiency and selectiveness of the electrochemical reaction the electrolysis cell is designed for. The components of the cell and, in particular, the coatings have a limited lifetime. After a certain time, the electrodes wear out resulting in an increased electrical voltage and increased Ohmic losses, and thus have to be refurbished.

[0007] In electrolysis cells of the prior art, the costs and efforts needed to refurbish the respective electrodes heavily depend on whether the cathode or the anode needs to be refurbished. This is due to the different design of anode and cathode half-cell.

[0008] For example, EP 2 165 008 B1 describes an electrolysis cell, wherein the cathode half-cell comprises an electrodic package which is comprised of a rigid current collector, an elastic current collector and flexible electrode placed on top of the elastic current collector. Upon tightening the bolts for closing the electrolysis cell, the action exerted by the partially compressed elastic collector on the two opposed surfaces of the rigid current collector and of the flexible electrode presses the latter against the separator, which is supported by the anode within the other half-cell. The anode is designed as a rigid electrode consisting of a planar surface provided with openings.

[0009] In this design, the exchange of the cathode electrode is done quickly, easily, cost-effectively and with low effort by disassembling the cell, removing the old flexible cathode, typically being made from a woven mesh, and interposing a new flexible cathode of the same type between the elastic current collector and the separator. Due to the moderate, reducing chemical conditions on the cathode side it is not necessary to fix the flexible cathode to the elastic 29.08.2025

[0010] 2 / 14 current collector and / or to join these elements e.g. by welding in order to secure sufficient electrical conductivity.

[0011] The refurbishment of the rigid anode is currently more complex, as it is welded rigidly onto webs within the anode half-cell. The rigidity of the anode is required to provide an even support of the separator being pressed onto anode by the action of the compressed elastic current collector. The welding of the anode to the webs provides superior electrical conductivity withstanding the harsh, oxidizing conditions within the anode half-cell over a long period of time.

[0012] This means that the whole anode half-cell needs to be shipped from the site of the electrolysis plant to a special, qualified workshop, where the welded joints of the rigid anode to the half-cell are carefully and precisely milled off. After cleaning and preparation, a new anode electrode can be welded onto the webs of the anode half-cell. This process is time-consuming, expensive and needs great logistical effort as many half-cells need to be transported to the workshop.

[0013] For large size projects this logistical effort is not acceptable as many hundreds to thousands of half-cells need to be refurbished over time. One strategy to solve this problem is to provide a dedicated workshop on-site. However, such a workshop has a large footprint and requires a lot of additional space, as many large-sized and expensive machines are needed for refurbishment. Moreover, the conventional refurbishment has high quality demands, because the refurbished anode half-cell needs to be dimensionally accurate in order to ensure a zero-gap configuration after re-assembly without damaging the separator. Thus, highly qualified, specially trained personnel is required to run the workshop. Finally, nickel and / or other precious metal chips as well as the milling tools from the milling process are a cost factor to be considered in conventional refurbishment.

[0014] In view of the growing demand for chlor-alkali and in particular for alkaline water electrolysis cells there is a need for a simplified method for refurbishing electrolysis cells.

[0015] Summary of Invention

[0016] It is therefore the object of the present invention, to provide a method for refurbishing electrolysis cells and an electrolysis cell which allow for simplified refurbishment with a reduced process complexity, costs and efforts. 29.08.2025

[0017] 3 / 14

[0018] This object is achieved by the method with the features of claim 1.

[0019] Hereby, a method for refurbishing an electrolysis cell for alkaline water electrolysis or chloralkali electrolysis is provided, wherein the electrolysis cell comprises an anode half-cell, a cathode half-cell and a sheet-like separator separating the anode half-cell and the cathode half-cell. The anode half-cell comprises a first back-wall, first webs and a rigid anode, wherein the anode is attached to the first back-wall by means of the first webs. The cathode half-cell comprises a second backwall, second webs, a current collector, an elastic current distributor and a cathode. The current collector is attached by means of the second webs to the second backwall. The elastic current distributor is interposed as an intermediate layer between the current collector and the cathode.

[0020] At the start of the method the electrolysis cell is in a closed starting state with the elastic current distributor being in a compressed state, holding the cathode in planar contact with one side of the sheet-like separator. The second, opposite side of the sheet-like separator is supported by the rigid anode.

[0021] The method comprises the following steps: a) Opening the electrolysis cell, while releasing the compression of the elastic current distributor, b) Interposing a first flexible anode between the rigid anode and the separator, c) Closing the electrolysis cell, while compressing the elastic current distributor.

[0022] The refurbishment method according to the invention thus, does not replace the worn out rigid anode, but an additional flexible anode is put onto the existing rigid anode. As the flexible anode is put in direct contact with the separator and is thus positioned closer to the separator than the rigid anode, the flexible anode takes over the main function of the anode, while the existing rigid anode acts mainly as a support structure for the flexible anode in the refurbished cell. The thickness of additional anode introduced into the cell is compensated by the elastic current distributor on the cathode side.

[0023] The method significantly reduces the maintenance effort for refurbishing anode electrodes of electrolysis cells. It can be carried out on site and it requires neither additional transport nor a specially qualified workshop on site. Thus, local footprint, logistics and carbon footprint are reduced. Further, the method is far less time-consuming so that downtime of the electrolysis 29.08.2025

[0024] 4 / 14 plant or module for cell refurbishment is significantly decreased. As no milling is necessary, not only the workshop, but also nickel and other precious metal chips are saved.

[0025] A rigid anode within this disclosure is defined as an anode with an inherent rigidity sufficient for providing a dimensionally stable support under the load exerted by the compressed elastic current distributor in a closed state of the electrolysis cell.

[0026] A flexible anode within this disclosure is defined as an anode being sufficiently pliable for adapting its shape under the load exerted by the compressed elastic current distributor in a closed state of the electrolysis cell.

[0027] In preferred embodiments, the rigid anode is in direct touching contact with the separator in the closed starting state and the elastic current distributor in step c) is compressed to an additional extent as compared to the closed starting state. Within these embodiments, the method can be used as a retrofit solution. Thus, the method is useful to simplify maintenance for already existing electrolysis cells with a conventional rigid anode.

[0028] In other preferred embodiments, a second flexible anode is interposed between the rigid anode and the separator in the closed starting state, which second flexible anode is removed from the electrolysis cell between steps a) and b) of the method. In these embodiments, an electrolysis cell already containing a combination of a rigid anode and a flexible anode is refurbished. This can be an electrolysis cell originally designed with an additional flexible anode, and / or an electrolysis cell that has been refurbished according to the method before.

[0029] Preferably, between steps b) and c) the first flexible anode is spot-welded to the rigid anode with a plurality of welding spots. Spot-welding improves electrical conductivity between the flexible anode and the rigid anode, in particular within the harsh chemical conditions prevailing within the anode half-cell. Spot-welding is preferred in comparison to other welding techniques, because it allows for comparatively simple automatization and results in welding patterns that allow for easy removal during the next refurbishment cycle. Due to its flexibility the spot-welded flexible anode can be ripped off the rigid anode with a low pull force. This can be done either manually or by suitable tools / robots.

[0030] In preferred embodiments, the first flexible anode and / or the second flexible anode is made from a woven wire mesh. Woven wire meshes combine a large active surface area with a 29.08.2025

[0031] 5 / 14 high degree of flexibility. They can be wound up on rolls simplifying mass production, while lying flat on the planar support of the rigid electrode. Preferably, the first flexible anode and / or the second flexible anode has a thickness within the range of 0,1 to 0,3 mm.

[0032] Preferably, the rigid anode is made from an expanded metal of punched metal sheet. The metal sheet preferably has a thickness of at least 0,5 mm.

[0033] In further preferred embodiments, the elastic current distributor is elastically compressible to a surface compression of at least 0,3 mm. Surface compression within this disclosure shall mean the difference in thickness of the elastic current distributor between an uncompressed state and a maximal elastically compressed state, i.e.. without irreversible plastic deformation to occur. Due to its elastic compressibility the current distributor - via the cathode - is able to exert a particularly even force on the separator to ensure a zero-gap configuration of the cell.

[0034] In preferred embodiments the rigid anode may comprise a coating of an electrolysis enhancing catalyst material.

[0035] The object is further achieved by an electrolysis cell for alkaline water electrolysis or chlor-alkali electrolysis, the electrolysis cell comprising an anode half-cell, a cathode half-cell and a sheet-like separator separating the anode half-cell and the cathode half-cell. The anode halfcell comprises a first back-wall, first webs and a rigid anode, wherein the anode is attached to the first back-wall by means of the first webs. The cathode half-cell comprises a second backwall, second webs, a current collector, an elastic current distributor and a cathode, wherein the current collector is attached by means of the second webs to the second back- wall. The elastic current distributor is interposed as an intermediate layer between the current collector and the cathode. The electrolysis cell further comprises a first flexible anode interposed between the rigid anode and the separator.

[0036] Hereby, a zero-gap electrolysis cell is provided that has a flexible anode on top of a rigid anode acting as a support structure. The electrolysis cell can be obtained as a retrofit design, wherein the flexible anode has been introduced into the cell during refurbishment of an electrolysis cell that did not contain any flexible anode, originally. However, the electrolysis cell may also contain the combination of a rigid anode and a flexible anode as an original design. In both cases the electrolysis cells allow for particularly easy refurbishment, once the first flexible anode is worn out, namely by replacing the flexible anode by another flexible anode. 29.08.2025

[0037] 6 / 14

[0038] In preferred embodiments the rigid anode may comprise a coating of an electrolysis enhancing catalyst material.

[0039] Further advantageous embodiments can be identified from the following description and the dependent claims.

[0040] The invention is explained in more detail below with reference to the embodiments shown in the attached drawings.

[0041] Brief Description of Drawings

[0042] Fig. 1A shows schematically an electrolysis cell in a closed starting state, before the method according to the invention is applied,

[0043] Fig. 1 B shows schematically an electrolysis cell according to the invention, obtainable by carrying out the method according to the invention, and Fig. 2 shows schematically a flow chart of a method for refurbishing electrolysis cells.

[0044] Detailed Description of Invention

[0045] In the drawings same parts are consistently identified by the same reference signs and are therefore generally described and referred to only once.

[0046] Fig. 1A shows schematically an electrolysis cell 1 for alkaline water electrolysis or chlor-alkali electrolysis in a closed starting state. The electrolysis cell 1 comprises an anode half-cell 2, a cathode half-cell 3 and a sheet-like separator 4 separating the anode half-cell 2 and the cathode half-cell 3. The sheet-like separator 4 may for example be an ion-exchange membrane or a diaphragm.

[0047] The anode half-cell 2 comprises a first back-wall 21, first webs 22 and a rigid anode 23. The rigid anode 23 is attached to the first back-wall 21 by means of the first webs 22. The rigid anode 23 forms a dimensionally stable support for the separator 4 in the closed state of the cell.

[0048] The cathode half-cell 3 comprises a second backwall 31 , second webs 32, a current collector 33, an elastic current distributor 34 and a cathode 35. The current collector 33 is attached by 29.08.2025

[0049] 7 / 14 means of the second webs 32 to the second backwall 31. The elastic current distributor 34 is interposed as an intermediate layer between the current collector 33 and the cathode 35.

[0050] In the depicted embodiments the first and second webs 22, 32 extend essentially perpendicular to the respective first and second back-wall 21 , 31. However, also other shapes of webs 22, 32 are imaginable, as e.g. webs that are V-shaped or have a Zig-Zag cross-section.

[0051] First webs 22, first backwall 21 and rigid anode 23 are preferably attached to one another by welded connections. Alternatively or in addition, the second webs 32, second backwall 32 and current collector 33 may also be attached to one another by welded connections.

[0052] In the closed starting state 100 (cf. Fig. 2) depicted in Fig. 1A the elastic current distributor 34 is in a compressed state, holding the cathode 35 in planar contact with one side 41 of the sheet-like separator 4. The second, opposite side 42 of the sheet-like separator 4 is supported by the rigid anode 23.

[0053] When the rigid anode 23 is worn out, the electrolysis cell 1 can be refurbished by carrying out the following steps (cf. Fig. 2 for a flow chart of the method steps): a) Opening 200 the electrolysis cell 1 , while releasing the compression of the elastic current distributor 34, b) Interposing 400 a first flexible anode 24 between the rigid anode 23 and the separator 4, c) Closing 600 the electrolysis cell 1 , while compressing the elastic current distributor 34.

[0054] Fig. 1B shows an electrolysis cell 1 that may be obtained after these steps have been carried out. Comparing Fig. 1A and 1B it is to be noted that in the closed starting state 100 the rigid anode 23 is in direct touching contact with the separator 4 and that the elastic current distributor 34 in step c) is compressed to an additional extent as compared to the closed starting state 100 in order to accommodate the additional first flexible anode 24 within the electrolysis cell 1.

[0055] Alternatively, the method may also start and end with the electrolysis cell 1 in a state as depicted in Fig. 1B. In this case, in the closed starting state 100, a second flexible anode 25 is interposed between the rigid anode 23 and the separator 4 as shown in Fig. 1B. This second flexible anode 25 it then removed from the electrolysis cell 1 between steps a) and b) of the 29.08.2025

[0056] 8 / 14 method, as depicted in Fig. 2, step 300. In other words, the second flexible anode 25 is replaced by the first flexible anode 24 to refurbish the electrolysis cell 1.

[0057] Preferably, the first flexible anode 24 is attached by a plurality of welding spots 26 to the rigid anode 23. The spot welding is preferably carried out between steps b) and c) as depicted in Fig. 2, step 500.

[0058] The first flexible anode 24 and / or the second flexible anode 25 may preferably made from a woven wire mesh. The first flexible anode 24 and / or the second flexible anode 25 preferably has a thickness within the range of 0,1 to 0,3 mm. Preferably, the first flexible anode 24 and / or second flexible anode 25 are made from a nickel or titanium based material. The first flexible anode 24 and / or second flexible anode 25 may preferably comprise a coating of an electrolysis enhancing catalyst material.

[0059] The rigid anode 23 is preferably made from an expanded metal of punched metal sheet. The rigid anode 23 preferably has a thickness of at least 0,5 mm. Preferably, the rigid anode 23 is made from nickel or titanium.

[0060] The rigid anode 23 may preferably comprise a coating of an electrolysis enhancing catalyst material. The coating may be a worn coating, which preferably covers between 10 % and 90 % of a total surface area of the rigid anode 23. The coating of the rigid anode 23 increases the electrical conductivity between the rigid anode 23 and the flexible anode 24, in particular at locations, where the flexible anode 24 is in mere touching contact with rigid anode 23, and hence enhances the efficiency of the electrolysis cell 1. A coated rigid anode 23 may therefore be particularly preferred in embodiments of the invention without any material bond (e.g. welded bond) between the flexible anode 24 and the rigid anode 23.

[0061] The elastic current distributor 34 is preferably elastically compressible to a surface compression of at least 0,3 mm.

[0062] The electrolysis cell 1 depicted in Figs. 1A and 1B is of the so-called single element design, wherein the half-cells 2, 3 are made from half-shells which are joined in a circumferential flange region under interposition of a gasket 5, to form an individually sealed single electrolysis cell 1. The invention, however, is also applicable to other designs of electrolysis cells, e.g. the filterpress design. In the filterpress design, the back-wall of each half-cell forms a bipolar 29.08.2025

[0063] 9 / 14 plate, acting as a back-wall for a cathodic half-cell of one electrolysis cell and for an anodic half-cell of an adjacent second electrolysis cell, at the same time.

[0064] 29.08.2025

[0065] 10 / 14

[0066] List of Reference Signs

[0067] 1 electrolysis cell

[0068] 2 anode half-cell

[0069] 3 cathode half-cell

[0070] 4 separator

[0071] 5 gasket

[0072] 21 first back- wall

[0073] 22 first webs

[0074] 23 rigid anode

[0075] 24 first flexible anode

[0076] 25 second flexible anode

[0077] 26 welding spots

[0078] 31 second back-wall

[0079] 32 second webs

[0080] 33 current collector

[0081] 34 elastic current distributor

[0082] 35 cathode

[0083] 41 first side of separator

[0084] 42 second, opposite side of separator

[0085] 100 closed starting state

[0086] 200 opening the electrolysis cell

[0087] 300 removing second flexible anode

[0088] 400 interposing first flexible anode

[0089] 500 welding of first flexible anode to rigid anode

[0090] 600 closing of electrolysis cell

Claims

29. 08.202511 / 14CLAIMS1 . Method for refurbishing an electrolysis cell (1) for alkaline water electrolysis or chlor-alkali electrolysis, the electrolysis cell (1) comprising an anode half-cell (2), a cathode half-cell (3) and a sheet-like separator (4) separating the anode half-cell (2) and the cathode half-cell (3), wherein the anode half-cell (2) comprises a first back-wall (21), first webs (22) and a rigid anode (23), the anode (23) being attached to the first back-wall (21) by means of the first webs (22), wherein the cathode half-cell (3) comprises a second backwall (31), second webs (32), a current collector (33), an elastic current distributor (34) and a cathode (35), wherein the current collector (33) is attached by means of the second webs (32) to the second backwall (31), and wherein the elastic current distributor (34) is interposed as an intermediate layer between the current collector (33) and the cathode (35), wherein at the start of the method the electrolysis cell (1) is in a closed starting state (100) with the elastic current distributor (34) being in a compressed state, holding the cathode (35) in planar contact with one side (41) of the sheet-like separator (4), wherein a second, opposite side (42) of the sheet-like separator (4) is supported by the rigid anode (23), wherein the method comprises the following steps: a) Opening (200) the electrolysis cell (1), while releasing the compression of the elastic current distributor (34), b) Interposing (400) a first flexible anode (24) between the rigid anode (23) and the separator (4), c) Closing (600) the electrolysis cell (1), while compressing the elastic current distributor (34).

2. Method according to claim 1 , characterized in that the rigid anode (23) is in direct touching contact with the separator (4) in the closed starting state (100) and that the elastic current distributor (34) in step c) is compressed to an additional extent as compared to the closed starting state (100).

3. Method according to claim 1 , characterized in that a second flexible anode (25) is interposed between the rigid anode (23) and the separator (4) in the closed starting state29.08.202512 / 14(100), which second flexible anode (25) is removed from the electrolysis cell (1) between steps a) and b).

4. Method according to any one of claims 1 to 3, characterized in that between steps b) and c) the first flexible anode (24) is spot-welded to the rigid anode (23) with a plurality of welding spots (26).

5. Method according to any one of claims 1 to 4, characterized in that the first flexible anode (24) and / or the second flexible anode (25) is made from a woven wire mesh.

6. Method according to any one of the claims 1 to 5, characterized in that the first flexible anode (24) and / or the second flexible anode (25) has a thickness within the range of 0,1 to 0,3 mm.

7. Method according to any one of the claims 1 to 6, characterized in that the rigid anode (23) is made from an expanded metal of punched metal sheet.

8. Method according to any one of the claims 1 to 7, characterized in that the elastic current distributor (34) is elastically compressible to a surface compression of at least 0,3 mm.

9. Method according to any one of the claims 1 to 8, characterized in that the rigid anode (23) comprises a coating of an electrolysis enhancing catalyst material.

10. Electrolysis cell for alkaline water electrolysis or chlor-alkali electrolysis, the electrolysis cell (1) comprising an anode half-cell (2), a cathode half-cell (3) and a sheet-like separator (4) separating the anode half-cell (2) and the cathode half-cell (3), wherein the anode half-cell (2) comprises a first back-wall (21), first webs (22) and a rigid anode (23), the anode (23) being attached to the first back-wall (21) by means of the first webs (22), wherein the cathode half-cell (3) comprises a second backwall (31), second webs (32), a current collector (33), an elastic current distributor (34) and a cathode (35), wherein the current collector (33) is attached by means of the second webs (32) to the second backwall (31), and wherein the elastic current distributor (34) is interposed as an intermediate layer between the current collector (33) and the cathode (35),29.08.202513 / 14 characterized in that the electrolysis cell (1) comprises a first flexible anode (24) interposed between the rigid anode (23) and the separator (4).

11. Electrolysis cell according to claim 10, characterized in that the first flexible anode (24) attached by a plurality of welding spots (26) to the rigid anode (23).

12. Electrolysis cell according to claims 10 or 11 , characterized in that the first flexible anode (24) is made from a woven wire mesh.

13. Electrolysis cell according to any one of the claims 10 to 12, characterized in that the first flexible anode (24) has a thickness within the range of 0,1 to 0,3 mm.

14. Electrolysis cell according to any one of the claims 10 to 13, characterized in that the rigid anode (23) is made from an expanded metal of punched metal sheet.

15. Electrolysis cell according to any one of the claims 10 to 14, characterized in that the elastic current distributor (34) is elastically compressible to a surface compression of at least 0,3 mm.

16. Electrolysis cell according to any one of the claims 10 to 15, characterized in that the rigid anode (23) comprises a coating of an electrolysis enhancing catalyst material.

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