Bipolar plates with pressure chamber for electrochemical cell stacks for carbon dioxide electrolysis

Abstract

The present invention relates to metal bipolar plates with pressure chamber to be used in carbon dioxide conversion electrochemical cell stacks. The bipolar plates according to the invention are formed of two thin metal subplates (50-1000 micron in thickness, each) joined together firmly, preferably by welding, with a simultaneous forming of a cavity, i.e. a pressure chamber, between the two subplates.

Description

[0001] BIPOLAR PLATES WITH PRESSURE CHAMBER FOR ELECTROCHEMICAL CELL STACKS FOR CARBON

[0002] DIOXIDE ELECTROLYSIS

[0003] Field of the invention

[0004] The present invention relates to metal bipolar plates with pressure chamber to be used, especially, in carbon dioxide conversion electrochemical cell stacks as one of the building blocks of the cells forming said stacks.

[0005] Background art

[0006] Known electrochemical systems usually consist of multiple bipolar plates, which are arranged in a stack, so that every two adjacent plates enclose an electrochemical cell. The bipolar plates can be used to electrically contact the electrodes of the individual electrochemical cells and / or to electrically connect adjacent cells (series connection of the cells). These plates can also be used to dissipate heat that is generated in the cells.

[0007] U.S. patent No. 10601053B2 relates generally to separator plates for electrolysers, fuel cells or other electrochemical systems. The individual plates each have at least one passage opening. The passage openings of the stacked separator plates are aligned or at least partially overlap with one another in the separator plate stack of the electrochemical system. In this way, they form flow channels for the transport (inflow or outflow) of electrolyte solutions. These openings are used to create a fluidic connection between the passage opening of the separator plate and the active surface of the separator plate or between the passage opening of the separator plate and a cavity formed between the individual plates of the separator plate. The cavity is used for example to guide a coolant between the individual plates of the separator plate. The aim of the invention according to the patent is to produce a separator plate (e.g., bipolar plate) for an electrochemical system that has the best possible mechanical stability and compactness and ensures the most efficient possible media supply to the system. This description mentions that the shape of the guide channel can be asymmetrical, however, there is no reference to carbon dioxide electrolysis in it.

[0008] Chinese patent No. 114171753B outlines a bipolar plate design for fuel cells consisting of two metal plates laminated together with sealing bumps on their edges. The seal bump has a raised top with a sealing layer and a raised side portion joining it to the plate, with one side being stiffer than the other. The top portion is parallel to the plate, and the width of the top end of the raised side portion is less than the width of the bottom end. The side portion can be straight or curved, with specific angles and radii, and the length of one side segment can be different from the other. This design allows for increased seal width without losing seal stiffness, increasing the available seal compression displacement window, and improving adaptability to dimensional tolerances. In addition, the design ensures seal robustness by preventing deformation of the higher stiffness side segment after compression. The document also mentions the use of these bipolar plates in a fuel cell stack configuration, not in an electrolyser one.

[0009] The invention according to Chinese patent No. 101937998B reduces the use of sealing rings, which can effectively improve the assembly efficiency of the fuel cell stack. According to the invention, the metal bipolar plate of the proton exchange membrane fuel cell is formed by stamping and forming, which has more uniform water vapor transmission, thin plate thickness, easy processing, and low cost. The bipolar plate of the present invention has the following advantages. First, the structure of the sealed platform used on the front of the first metal plate allows the resulting bare bipolar plate to be hot-pressed with the membrane electrode assembly (MEA) into a single cell, which can reduce the use of sealing rings when assembling the stack and the deformation is obvious. Second, the first and second metal plates are provided with intermittent corner deflection grooves, which can distribute the reactive gas many times, making the gas distribution in the active area more uniform, and can effectively reduce the "water flooding" phenomenon in the fuel cell. Thirdly, since the two plates adopt equal or unequal length parallel arrangement or diagonal parallel grooves in the surrounding area of the cooling water inlet and outlet, it can not only guide the cooling water so that the cooling water distribution is more uniform, but at the same time, together with the rectangular zigzag concave and convex structure of the sealed platform area on the periphery of the first metal plate, a rigidity reinforcing structure of the metal plate is formed, which can effectively reduce the deformation of the metal plate. Finally, in this technical solution, another identical second metal plate can replace the first metal plate, so that the two second metal plates having the same structure can cooperate with each other and be assembled. It is determined that a given plate is a negative plate or an anode plate to form a bipolar metal plate having the same structure as the negative plate and the anode plate.

[0010] U.S. patent No. 6974648B2 describes one of the first stamped bipolar plates, used in PEM fuel cells. These types of cells include an MEA comprising a thin, proton-transmissive, electrically non- conductive, solid polymer electrolyte membrane having the anode catalyst on one side and the cathode catalyst on the opposite side. The MEA is sandwiched between a pair of non-porous, electrically conductive elements or plates which (1) conduct electrons from the anode of one fuel cell to the cathode of the adjacent cell of a fuel cell stack, (2) have suitable channels and / or apertures formed therein for distributing the gaseous reactants of the fuel cell over the surfaces of the respective anode and cathode catalysts, and (3) have suitable channels and / or apertures formed therein for distributing suitable coolant throughout the fuel cell stack to maintain temperature. The electrically conductive plates sandwiching the MEAs may include an array of grooves in the surfaces thereof defining a reactant flow field for distributing the gaseous reactants of the fuel cell over the surfaces of the respective cathode and anode. These reactant flow fields typically include a plurality of lands defining a plurality of flow channels therebetween through which the gaseous reactants flow from a feed header at one end of the flow channels to an exhaust header at the opposite end of the flow channels. In a fuel cell stack, a plurality of cells is stacked together in electrical series while being separated by a gas impermeable, electrically conductive bipolar plate. In some cases, the bipolar plate is an assembly formed by securing a pair of thin metal sheets with reactant flow channels formed on their outer surfaces. Typically, an internal coolant flow field is provided between the metal plates of the bipolar plate assembly. It is also known to locate a spacer plate between the metal plates to optimize the heat transfer characteristics for improved fuel cell cooling. Previously, the internal coolant flow field consumed space within the fuel cell, typically increasing the required distance between adjacent MEAs. The present invention. In accordance with a first aspect of the present invention, there is provided a fuel cell. The fuel cell comprises a pair of MEAs separated by a distance. Each of the MEAs has an anode side and a cathode side. A bipolar plate assembly is disposed between the anode side of one of the pair of MEAs and the cathode side of the other of the pair of MEAs. The bipolar plate assembly comprises a first subplate having a flow channel open to the anode side of one of the pair of MEAs. The bipolar plate assembly further comprises a second subplate having a flow channel open to the cathode side of the other of the pair of MEAs. The first subplate and the second subplate are nested to form a coolant flow channel between the first and second subplates.

[0011] U.S. patent No. 7601452B2 discloses a method of making the above-mentioned bipolar plate assembly useful in fuel cells. The method includes forming an open channel on a side of a first subplate adapted to face the anode side of an MEA. Forming an open channel on a side of a second subplate adapted to face the cathode side of an adjacent MEA. A closed channel is formed between the subplates adapted for coolant flow therethrough by nesting the first and second subplates. The method comprises forming an open channel on a side of a first subplate adapted to face the anode side of an MEA. Forming an open channel on a side of a second subplate adapted to face the cathode side of an adjacent MEA. A closed channel is formed between the subplates adapted for coolant flow therethrough by nesting the first and second subplates. There is further provided a method of operating a fuel cell having a plurality of adjacent MEAs. The method comprises passing oxygen through a flow path in communication with a cathode side of the MEA. Passing hydrogen through a flow path in communication with an anode side of the MEA. Each of the hydrogen and oxygen flow paths has a height dimension. Coolant is also passed through a flow path having a height dimension substantially aligned with the height dimension of the hydrogen flow path, the oxygen flow path, or both.

[0012] The traditional bipolar plate is a junction assembly consisting of two separate half plates. U.S. patent No. 11652219B2 represents hybrid bipolar plates for fuel cells, where only one half of them is pressed and the other half is made by other methods to improve heat dissipation. Each half plate may have an outer surface and an inner surface, the outer surface having a flow channel for gaseous reactants and the inner surface having a coolant channel. To conduct current between the anode and cathode of adjacent fuel cells in the fuel cell stack, the paired half plates of each bipolar plate assembly form the mechanical and electrical connections. For example, such bipolar plates are typically constructed with a pair of half plates joined by adhesive bonding, brazing or welding. A feature of the present solution according to the invention is the plurality of support ribs, that are provided, located in the coolant distribution area.

[0013] To improve the performance of electrochemical cells via improving contacts, several methods are known.

[0014] U.S. patent No. 8354199B2 relates to a multi-layered diffusion medium substrate that is suitable for use as a gas diffusion medium in a fuel cell. It comprises at least one rigid layer combined with a compressible layer. The rigid layer is more resistant to deformation along the x and y directions than the comparably compressible layer. In an assembled fuel cell stack, the multi-layer diffusion medium substrates are arranged such that the more compressible layers are positioned closer than the rigid layers to the MEAs of each cell, while the rigid layers are positioned closer than the compressible layers to the bipolar plates in each cell. Upon compression of the substrate between the MEA and the bipolar plate, the rigid layer provides a high degree of contact pressure against the relatively compressible layer, thereby preventing intrusion of the diffusion media into the flow field channels of the plate. In addition, the rigid layer induces a high contact pressure between the MEA and the diffusion media in the channel region, which is desired to minimize electrical and thermal resistance at this interface. The relatively compressible nature of the layer adjacent to the MEA helps maintain contact between the MEA and the diffusion media despite variations in plate and diffusion media thickness.

[0015] In another case, European patent No. 2904656B1 is directed to the design of resilient flow structures including GDL and flow field for use in electrochemical cells operating at high differential pressures, including but not limited to fuel cells, electrolysis cells, hydrogen purifiers, hydrogen expanders, and hydrogen compressors. In a typical fuel cell, the reactant gases flow through the flow fields on either side of the electrolyte membrane and then diffuse through the porous GDL to reach the electrolyte membrane. The reactant gases on either side of the electrolyte membrane are often at different differential pressures, creating a pressure difference across the MEA, which creates a force on the MEA that causes the MEA to move away from the high pressure toward the low pressure. As a result of this movement, electrical conduction is reduced, which reduces the efficiency of the fuel cell. The invention includes the use of multiple layers of materials in the flow structure, i.e., a first flow structure, a second flow structure, and a membrane electrode assembly disposed between the first and second flow structures. The first flow structure can elastically expand to maintain contact with the membrane electrode assembly under pressure differentials. The first flow structure is located on the cathode side, while the second flow structure is located on the anode side of the cell. This design can improve the performance of electrochemical cells operating under high pressure differentials. Here, the invention according to patent, there is an extra built-in elastic layer in the cell (1-1 on the cathode and anode side).

[0016] U.S. patent No. US20220259745A1, regarded as the closest prior art, generally relates to electrochemical systems for the reduction of carbon dioxide (CO2), and in particular to modular electrochemical cell designs. The system includes a stack of electrochemical cells, each cell comprising a cathode, an anode, and a separator such as a membrane or diaphragm. The design emphasizes the use of modular electrolyser cells (multi-cell stack), allowing for scalable CO2 conversion systems suited for industrial applications. A key structural feature of the stack is the application of bipolar plates, which function as both electrical interconnections and fluid distribution elements. The bipolar plates assist in guiding the reactant gases and liquids (e.g., CO2 or electrolyte), as well as managing the removal of products while also maintaining electrical conductivity across the adjacent cells. To optimize the reaction environment, minimize the ohmic losses, and manage water transport and ionic conductivity, gas diffusion electrodes and membrane-electrode assemblies (MEAs) are functionally integrated with the bipolar plates. The stack design and the functional integration of said bipolar plates allow for operation under pressurized conditions and support the implementation of flow fields and manifold systems that can distribute gases and liquids efficiently across multiple CO2 electrolyser cells. Contrary to said functional integration, the bipolar plates lacks for a design that makes them capable of actively or dynamically influencing the pressure conditions prevailing within said flow fields of the individual electrochemical cells.

[0017] Technical problem to be solved

[0018] Presently, based on the above, there is a need for improved bipolar plates that can be cost- effectively produced in large quantities and with sizes for the construction of electrochemical CO2 reduction cells and cell stacks that can be used on industrial scale.

[0019] Moreover, in the context of bipolar plates, additional challenges must be addressed, stemming from the inherent limitations of the prevailing state-of-the-art technology for the electrochemical reduction of CO2. The primary factor contributing to the asymmetry between the cathode and anode sides of the cell is the disparity between the gas and liquid feeds of cathode and anode side. This disparity manifests in the form of density differences, which necessitate distinct flow patterns. The pressure differences between these two sides require management by the bipolar plate to ensure that all components are maintained in a mechanically stable position. Secondly, a fundamental component of the membrane electrode assembly (MEA) is the porous transport electrode (PTE), which comprises a porous transport layer (PTL) and a catalyst layer. It is important to note that the PTE is inherently characterized by unevenness in thickness, a consequence of the manufacturing technology employed. This thickness variability, which ranges from 20 to 100 pm, necessitates compensatory measures to enhance electrical contact between the two elements. Thirdly, when the cells are operated at higher pressures, especially when the pressure difference between the cathode and anode side increases (i.e., differential pressure is applied), the PTL is required to maintain the mechanical stability of the other MEA elements inside the cell. This also requires passive (from design and construction) or active (varied from an external source) support from the bipolar plate. Finally, the design of the bipolar plate is intended to help avoid flooding and crystallization (of metal-carbonate and / or bicarbonate salts) on the cathode side, whether in a passive or active manner.

[0020] Underlying technical finding

[0021] In electrochemical cell stacks that are used in carbon dioxide electrolysis, bipolar plates with asymmetric flow patterns are used. These bipolar plates are made of two thin metal subplates (50- 1000 micron in thickness, each) of titanium or stainless steel, preferably titanium, that are joined together to form a cavity therebetween for using in electrochemical cell stacks as current collector means. We found that this cavity possesses the capacity to function as a pressure chamber, even if implementing substantial modifications to the material and properties of the bipolar plates' components and the ability of the cell to operate with those modifications.

[0022] We were surprised to find that when the anode side bipolar plate component (anode current collector or first subplate) was designed to be flexible (wherein the estimated relative bending stiffness was 100-200 times smaller than that of a current collector made of 4mm thick titanium plate), the electrical connection with the PTE got increased.

[0023] We also found that the pressure chamber formed as a cavity between the two subplates of a bipolar plate when said subplates are joined together can be used to actively influence the flexibility of the bipolar plate obtained, thereby helping the cell to function properly and with good performance even at high working pressures.

[0024] Furthermore, we found that when the anode side subplate delimiting the cavity is a thin, flexible plate, then it can easily change its shape in cross-section. This allows the cross-sectional area of the channels of the flow pattern to be dynamically varied. In turn, this can be used to control the flow rates of the anolyte / catholyte flowing in the cell.

[0025] Alternatively, the cavity formed between the two subplate components of the bipolar plate can also be used to provide an additional cooling capability for the cell as a separate cooling fluid could be directed / led through it which is independent of the cooling performed by the gas / anolyte taking part in the electrolysis within the cell stack as is the standard practice nowadays. Most importantly, as a result, the reaction / production rate of a cell constructed with a bipolar plate according to the invention can be controlled.

[0026] In light of the afore-mentioned, the above objects are achieved by constructing a bipolar plate in accordance with claims 1 to 10, as well as a carbon dioxide electrolyser cell and a carbon dioxide electrolyser cell stack, both comprising the bipolar plate according to claims 1 to 10 as current collector means.

[0027] Distinction from fuel cell literature / technology

[0028] In fuel cells, dry or humidified gas flows on both the anode and cathode sides, while a coolant is squeezed between the two plates to keep both sides tempered. In carbon dioxide electrolyser technology, liquid electrolyte flows on the anode side, which also acts as a heating / cooling medium inside the cell, while a humidified gas flows on the cathode side. This leaves the space between the two plates unused. In addition, due to the physical properties of the fluid flowing on either side, flow channels of different depths / patterns are required thereon. This is a significant difference from the symmetrical patterns found in fuel cells. Another difference is that the anode side of carbon dioxide electrolyser cells does not encounter a soft gas diffusion layer, but a porous transport layer (PTL), which is mechanically much stiffer than the anode side.

[0029] Definitions and abbreviations

[0030] The term "zero-gap electrolyser" is well known for the skilled person, and refers to an electrolyser, in which the separator (e.g., an ion exchange membrane) is in direct contact with the catalyst layers of the anode and the cathode. In the context of the invention, direct contact means that there is no intentional gap, and no substantial liquid layer between the ion exchange membrane and the catalyst layers, and between the catalyst layers and the electrode substrates. However, as liquid (anolyte or water originating from the humidified carbon dioxide) is present in the system, it is evident that e.g. a thin liquid film may be present. This design reduces the distance that ions must travel through the layers, compared to non-zero gap cell designs.

[0031] The term "cathode" as used herein refers to the electrode at which the cathodic reduction of carbon dioxide occurs. At a minimum, the cathode comprises a catalyst; however, it typically includes a supporting electrode positioned beneath the catalyst layer. The electrode may be composed of any electrically conductive material, although the current standard involves the use of porous electrodes, commonly referred to as gas diffusion layers.

[0032] The catalyst layer may be immobilized on the gas diffusion layer, in which case the assembly is commonly referred to as a gas diffusion electrode. Alternatively, the catalyst layer may be formed on the membrane, resulting in a catalyst-coated membrane configuration. A further technologically equivalent configuration involves the use of self-supporting catalyst layers, which may be sandwiched between the electrode and the membrane, or may themselves serve both as the catalyst and the electrode.

[0033] The term "membrane electrode assembly" refers to the combination of cathode, membrane, and anode in an electrolyser cell, regardless of the specific method or location of catalyst layer deposition.

[0034] An "electrolyser cell", or shortly "cell", is the basic functional unit of the electrolyser in which the electrochemical reactions occur. It typically comprises a cathode, an anode, an ion-conductive membrane (or separator), and compartments or chambers to manage gas and liquid flows.

[0035] An "electrolyser cell-stack", often referred to as electrolyser stack or simply stack, is comprised of multiple electrolyser cells, wherein the individual cells are connected in series in terms of the electrical connections of the cells and connected in series / parallel in terms of the flow management of the electrolyser, i.e., the liquid flows and the gaseous flows directed through the electrolyser. The overall performance of the electrolyser cell-stack comprises the cumulative performance of the contained electrolyser cells. Therefore, any process to optimise the cell performance implies a similar effect on the electrolyser stack.

[0036] In the context of the invention, "cell performance", or shortly "performance" of the CO2electrolyser refers to how effectively the electrochemical cell converts carbon dioxide (CO2) into desired or target products (like carbon monoxide (CO), methane, formate, ethylene, etc.) under certain operating conditions. Thus, the cell performance is an indicator of the energy efficiency (comparing the performance of two electrochemical cells, a lower cell voltage at the same current density means higher energy efficiency.), selectivity (CO / H2ratio in the product gas, or the faradaic efficiency values related to the target product), single pass conversion efficiency (shortly conversion), and durability of the electrolyser system.

[0037] The term "faradaic efficiency" refers to the percentage of the electric charge used for the production of a given product, relative to the total electric charge passed through the electrolyser.

[0038] Moreover, in the description the following abbreviations are used:

[0039] "GDE" means gas diffusion electrode.

[0040] "GDL" means gas diffusion layer.

[0041] "AEM" means anion exchange membrane.

[0042] "PTE" means porous transport electrode.

[0043] "PTL" means porous transport layer.

[0044] "MEA" membrane electrode assembly

[0045] Brief description of the drawings In what follows the present invention is explained in more details with reference to the appended drawings wherein

[0046] Figure 1 is a schematic illustration of the design of a zero-gap electrolyser cell stack to convert gaseous CO2 to other products.

[0047] Figure 2 shows a possible embodiment of a bipolar metal plate (100) designed by welding together a first thin plate (10) functions as the anode current collector plate and a second thin plate (20) that serves as the cathode current collector plate.

[0048] Figure 3 is the perspective view of the active surface area (30 - inside the dashed line) of the bipolar plate (100) shown in Figure 2 together with the additional gas and liquid channels used to construct an electrochemical multi-cell stack for the electrolysis of carbon dioxide.

[0049] Figure 4 illustrates a bipolar plate (100) in cross-sectional view formed from two thin metal plates (10,20) for a carbon dioxide electrolyser.

[0050] Figure 5 shows the effect of pressure in the pressure chamber (direction indicated by arrows (arrows from low pressure Pi to high pressure P2) on the shape of the anode- and cathode-side flow patterns (schematic view).

[0051] Figure 6 shows the cross-sectional schematic view of the test electrochemical cell arrangement for mechanism validation.

[0052] Figure 7 illustrates in a cross-sectional schematic view of the test electrochemical cell arrangement, before and after the pressurization of pressure chamber

[0053] Figure 8 shows two comparative measurements for a rigid and the flexible anode current collectors. Figure 9 shows example of use of the pressure chamber in the anode current collector during the measurement of electrochemical CO2 reduction.

[0054] Detailed description of the drawings

[0055] Figure 1 illustrates schematically a possible embodiment of a zero-gap electrolyser cell stack to convert gaseous CO2 to other products. Said electrolyser cell comprises (here, from a bottom bipolar plate 100 to a top one) at least an anode current collector 10 as a part of bipolar plate 100 with fluid inlet(s) 51 and fluid outlet(s) 52 on one side thereof and a flow-pattern 12 formed, a porous transport layer (PTL) with a catalyst layer (not shown) together call porous transport electrode (PTE) 303 on one side, a membrane 302, in direct contact with said catalyst layer, a cathode catalyst layer (not shown) in direct contact with the membrane 302 on one side, and the gas diffusion layer (GDL) with catalyst layer call together gas diffusion electrode (GDE) 301 on the other side, and a cathode current collector 20 as part of bipolar plate 100, on which a gas-flow pattern 22 is formed on one side thereof (in direct contact with the gas diffusion electrode 301), while gas inlet(s) 41 and outlet(s) 42 are also formed. Said electrolyser cell may also be constructed as an electrolyser cell-stack, consisting of multiple electrolyser layers (cells). In this case, multiple electrolyser layers are stacked on each other, repeating the PTE, membrane, GDE elements with the proper cathode spacers 304 and anode spacers 305. Between the adjacent layers, preferably bipolar plates 100 are used, which on one side act as anode, while serve as cathode on the other side. Such bipolar plates are known in literature.

[0056] The anode current collector 10, the cathode current collector 20, the PTE 303, the GDE 301, the flow pattern and channels 12, 22 applied in the electrolyser cell, as well as their functions and possible design are equally known in literature.

[0057] Furthermore, if the ion exchange membrane 302 is an anion exchange membrane, available under the trade names of e.g. Fumasep, Selemion, PiperlON, Aemion and Sustainion, just to mention a couple of examples only, which theoretically allows, in operation, the migration of anions (e.g., OH“, HCOa- and COa2-ions; charges) between the cathodic and anodic sides of the electrolyser cell through its bulk, while water (H2O) diffusing through said cell from the anodic to the cathodic side takes part in the electrolytic reduction of CO2 at the cathodic side. As in this case no electrons are transported through the membrane 302, said membrane 302 actually acts as an ionic conductor between the cathodic and anodic sides of the cell.

[0058] Figure 2 illustrates a bipolar metal plate (100) formed by welding two thin metal plates (10, 20) together, which can be then used to build a carbon dioxide conversion electrochemical cell stack. That is, according to the present invention, each of the metal bipolar plates used to form the cell stack consists of a first metal plate and a second metal plate. The joining of the two metal plates (one anode current collector plate 10 and one cathode current collector plate 20 - see Figure 2) results in three regions, as is shown in Figure 4: a cathode side (21), an anode side (11), and an intermediate cavity region (200) located between the two plates.

[0059] The examples to be discussed below all refer to an area 30 indicated in Figure 3. In the marked area 30, current flows through the cells towards the membrane electrode assembly (MEA - 300 in figure 6) (active surface). The marked area 30 properly distributes the electrolyte on the anode side and the wetted carbon dioxide on the cathode side within the MEA and helps the product gases to escape from the same area.

[0060] Figure 3 shows the active surface area (30 - inside the dashed line) of a bipolar plate (100) used to construct a cell of the stack in perspective view of, including the flow channels and the parts in contact with the membrane electrode assembly (MEA). The other areas outside the area 30 (i.e. recesses, weld lines, through holes and passages) are responsible for the mechanical stability of the plate and a proper fluid supply to the cell. This includes gas inlet (41) and outlet (42) chimney responsible for gas supply, electrolyte inlet (51) and outlet (52) responsible for electrolyte supply of the cells in the stack. Positioning holes (62) help the assembly of and give the stack mechanical stability against lateral impact. The pressure inside the welded bipolar plate can be controlled by using chimneys (61) connecting the pressure chambers of all bipolar plate arranged in the cell stack.

[0061] Figure 4 is a cross-sectional view of a bipolar plate 100 formed from two thin metal subplates to be used in a carbon dioxide electrolyser. Brief explanation: 21 - Cathode side surface area which contact with MEA; 11 - Anode side surface area which contact with MEA; 22 - Cathode side flow pattern channels; 12 - Anode side flow pattern channels; 200 - a cavity area between the cathode and anode current collector plates providing a pressure chamber. In the active surface area (30; in Figure 3), four preferred embodiments that are not found in fuel cells can be formed due to the differences (asymmetric flow pattern on both sides - 12 and 22, unused space forming a cavity 200 between the two plates), as one can see in Figure 4 below.

[0062] Figure 6 is a cross-sectional schematic view of the example test electrochemical cell arrangement. Brief explanation: 23 - Cathode current collector; 22 - Cathode side flow pattern; 301 - Gas diffusion electrode (GDE) which is composed of a gas diffusion layer (GDL) and a cathode catalyst layer; 302 - Ion-exchange membrane; 303 - Porous transport electrode (PTE) which is composed of a porous transport layer (PTL) and an anode catalyst layer ; 10 - Flexible (stamped) anode current collector; 12 - Anode side flow pattern and channels; 200 - Formed pressure chamber cavities; 13 - Anode holder plate; The 301, 302, 303 together also be called a membrane electrode assembly (MEA) 300.

[0063] Figure 7 presents a cross-sectional schematic view of the example test electrochemical cell arrangement, before and after pressurization of the pressure chamber between the subplates of the bipolar plates used in the cell arrangement. Brief explanation: 12A - Anode side flow pattern and channels before pressurization; 200A- Pressure chamber before pressurization; 12B - Anode side flow pattern and channels after pressurization; 200B - Pressure chamber after pressurization.

[0064] Figure 8 presents measurement results of Example 2. As illustrated in the graph on the left, the anode current collector of the cell is a rigid 4mm thick, grade 2 titanium plate manufactured using CNC milling technology. In contrast, the anode current collector on the right is a flexible, 0.1mm thick grade 2 titanium sheet based stamped thin plate on the invention. In both measurements, the other components of the cell (catalysts, membrane, endplate assembly, etc.) remained constant. As illustrated in Figure 8, the upper panels depict the cell voltages at a specified current density (two-day measurements, with a dotted line demarcating the separation), while the lower panels illustrate the selectivity as Faradaic Efficiency percentage values.

[0065] Figure 9 is an experimental example of usage of the pressure chamber during electrochemical CO2 reduction measurement. In case the A time sections (12A and 200A in figure 7), there is no pressure in the pressure chamber, in case the B time sections, 7 bar(g) is built up within two seconds (12B and 200B in Figure 7),. During the period shown in Figure 9, the two states were switched back and forth. The top graph shows the change in voltage across the cell, and the middle graph shows the change in selectivity (as a CO / H2 ratio in the product gas) when using the pressure chamber. These changes are phenomena related to example 4. The bottom graph shows the change in pressure drop in the anolyte flow through the cell when using the pressure chamber. This change indicates a change in the flow cross-section, which is also a phenomenon related to Example 4.

[0066] EXAMPLES

[0067] It is not possible to assemble only one electrochemical cell with one bipolar plate, this number is always the (number of bipolar plates + 1), minimum. This also means that if we build a multi-cell stack with the bipolar plate with a pressure chamber (according to the patent description), then during operation we can only observe an average of the expected effects as the cells work together. To understand the descripted solution and the phenomenon associated with it, we therefore need an experimental test cell that imitates the operating principle examined in the case of one cell, through which we can collect accurate and easily measurable, direct data on the effect of the pressure chamber on the cell. Based on our general knowledge of cell stack construction, we can extrapolate these results to the operation of a bipolar plate equipped with a real pressure chamber in the case of a multi-cell stack.

[0068] Materials

[0069] The CsOH-l- O and Ag nanopowder (davg< 100 nm, 99.5%, 5.0 m2g1) was purchased from Sigma- Aldrich. The PiperlON (40 pm thick PiperlON-A40-HCO3) membrane and PiperlON ionomer dispersion (PiperlON-A5-HCO3-EtOH, 5 wt% in EtOH) was purchased from Versogen. The lrOxcatalyst was purchased from FuelCellStore. The Sigracet 39BB carbon paper was purchased from SGL Carbon. MilliQ. grade (p = 18.2 MO cm) ultrapure deionised water was produced using a Millipore Direct-Q 3 UV instrument and was used to prepare all the solutions.

[0070] The CsHCOa electrolyte solution was obtained from CsOH solution by bubbling CO2 gas through it until saturation (for at least 30 minutes). General Methods

[0071] Electrode preparation

[0072] The cathode catalyst dispersion consisted of Ag nanopowder with 5 wt% PiperlON ionomer (m(ionomer) / (m(ionomer)+m(Ag)) dispersed in a 1:1 isopropanol / water solvent mixture with a concentration of 24 mg cm'3(Ag). The anode catalyst dispersion consisted of I rOxnanoparticles with 15 wt% PiperlON ionomer (m(ionomer) / (m(ionomer)+m(lrOx) dispersed in an identical solvent with a concentration of 17 mg crrr3(lrOx). The lrOxdispersion was homogenised with a magnetic stirring bar at 600 rpm. The silver nanoparticles were dispersed with a high-power immersion sonotrode (3 min) and a regular ultrasonic bath for 20 min, and the dispersion was kept sonicated in the ultrasonic bath for the duration of spray coating (while keeping the bath temperature below 35 °C by additions of ice cubes).

[0073] The GDEs were fabricated using an automata ultrasonic spray-coater machine. The Ag dispersion was spray coated onto preheated Sigracet 39BB GDLs on a hotplate at 100gC until reaching a loading of 1.0 ± 0.1 mg cm-2(Ag). The anode catalyst dispersion was spray coated similarly, onto a porous Ti frit (as a PTL) to reach a loading of 1.0 ± 0.1 mg cm-2(lrOx). The loading was calculated from the substrate weight difference before and after the spray coating.

[0074] Membrane pretreatment

[0075] The membranes were ion-exchanged before use for at least 24 hours in a 1 M CsOH solution, which was exchanged for a fresh solution after the first 5 hours. Immediately before cell assembly, the membrane was cut to size and placed into ultrapure water for 10 minutes and was thoroughly rinsed with ultrapure water.

[0076] Electrochemical measurements and cell assembly

[0077] All electrochemical measurements were performed in a custom-designed direct gas feed zerogap electrolyser cell with an active area of 95 cm2. Commercially available AEM (40 pm thick PiperlON- A40-HCO3) was used to separate the anode and the cathode chambers. The cell was assembled starting from the anode current collector, continuing with the catalyst-coated 1mm thick Ti frit (anode) as the PTE, the anion exchange membrane, the PTFE gaskets, the catalyst coated gas-diffusion layer (cathode) as the GDE and finished with the cathode current collector. The PTFE gasket was 250 pm thick to achieve the necessary compression for the approximately 310 pm thick catalyst-coated gasdiffusion layer. The cell assembly is secured with 8 bolts and nuts, tightened in three steps to 12 Nm. The CsHCOa solution was used as the anolyte, which was prepared from the respective hydroxide solution by saturating it with CO2.

[0078] An Electro-Automatik EA-PS 9040-120 power supply was used for chronoamperometry measurements. The cell voltage refers to the voltage between the anode and cathode current collector without iR compensation. The humidification of the CO2 inlet gas and the flow rate was controlled with a Bronkhorst Vapor Delivery Modul (VDM), the gas flow rate was 12.0 cm3min_1cm_2(electrochemically active area). The gas line between the humidifier and the cell was heated to avoid any condensation. An external heat exchanger heated the anolyte to achieve a cell temperature of 60°C.

[0079] Gas detection

[0080] The gas products of the CO2 electrolysis were detected using an online infrared-thermal conductivity gas analyser (Gasboard-3100, customised for CO2-CO-H2 mixtures, Hubei Cubic-Ruiyi), coupled with a McMillan S-110 Flo-Meter for continuous outlet flow rate measurement. The partial current densities were calculated from the outlet gas flow rate and the composition of the outlet gas.

[0081] Example 1 - General description of the experimental setup

[0082] The test electrochemical cell was assembled in the arrangement shown in Figure 6. In this test setup, the flexible (estimated relative bending stiffness was 100-200 times less than for the current collector made of 4mm thick titanium plate), anode current collector 10 (made by stamping from 0.1mm thick grade 2 titanium sheet) models the behavior of the stamped bipolar plate, and the pressure chamber 200 is formed in the same space as it would be in the bipolar plate (between the flexible anode current collector 10 and an anode holder plate 13). This configuration enables the examination of the impact of the flexible anode current collector 10 on the operation of the electrochemical cell (see Example 2), under both scenarios of pressure generation: the first scenario being the pressure created by the GDE 301 compression in the cathode space, and the second scenario being the (back) pressure created in the pressure chamber 200 (see Example 3). Additionally, as the pressure in the pressure chamber 200 increases, the flexible anode current collector 10 can reduce the cross-section of the anode-side liquid channels 12 by means of flexible deformation, thereby affecting the flow conditions inside the cell (Example 3). conditions:

[0083] The CO2 feed flow rate was set to 1.14 standard dm3min1at a current density of 400 mA.cm-2, while the anolyte (aqueous CsHCOa, c = 0.05 M) flow rate was set to 1 L / min. Cathode outflow gas composition was analyzed inline. As for the cathode, 1 mg cm2Ag cathode catalyst layer was immobilized on Sigracet39BB carbon paper by ultrasonic spray coating as a GDE. As for the anode, 2 mg cm2Ir black was immobilized on a porous titanium frit as a PTE. Both catalyst layers contained 15 wt% Piperion ionomer. The measurements were performed feeding 0.05 M CsHCOa anolyte continuously to the anode compartment (T = 60°C,). An external inert fluid, e.g., pressurized air or nitrogen, was introduced to the pressure chamber through the pressure chamber connecting chimney

[0084] 61.

[0085] Example 2: Flexible anode side anode current collector

[0086] In one embodiment, the anode plate component 10 is designed to remain flexible, thus providing a flexible support for the PTE during cell assembly, with a larger electrical contact area and uniform pressure. It is important for the mechanically harder PTL in PTE 303 used in carbon dioxide electrolysers, but it does not make sense for fuel cells, where there is a soft gas diffusion layer (GDL) on both sides. PTL is never uniformly flat due to its manufacturing technology, i.e. there is a 20-100 pm inequality in thickness that has to be compensated to improve electrical contact between the two elements. It reduces the resistance and thus increases the performance of the entire cell. A similar effect cannot be achieved in fuel cells because the coolant fluid squeezed between the two plates would not allow this flexibility, even with a suitable pattern.

[0087] The main goal was to compare the operation of two electrochemical cells, where the used MEAs made under the same conditions, the difference was that one case the anode current collector is rigid (4mm thick, grade 2 titanium plate milled by CNC method, estimated bending stiffness in the investigated 95 cm2electrochemical active surface area 30-100 Nm2), while in the other case we use a stamped (with ribbed pattern) flexible anode current collector made from a 0.1mm thick, grade 2 titanium sheet. 10. According to the results obtained in Figure 8, the irregularities of the rigid PTE 303 can be tracked and electrically contacted better at more points by the flexible anode current collector 10. which is associated with a decrease in contact resistance and thus an increase in cell performance. Detailed: In both measurements, two days are presented, the first at a fixed current density of 400 mA.cm'2, the second at a current density of 500 mA.cm'2, the part separating the two days in the figure is indicated by a dashed line. The left graph shows the measurements with a rigid, 4mm thick titanium anode current collector. Here, in the upper graph, the cell voltage was above 3V at both current densities. Furthermore, at a higher current density (500 mA.cm-2), more hydrogen could be measured in the product gas, as can be seen in the lower graph, ergo the selectivity of the cell deteriorated. The deterioration of selectivity at higher current densities can be attributed to the inhomogeneous current density distribution within the cell (locally higher current density within the cell produces more hydrogen at that point), which can be traced back to the inhomogeneous electrical contact between the PTE and the anode current collector. In comparison, the right-hand side of figure 8 shows the results measured on a cell assembled with an anode current collector made of 0.1mm titanium sheet by stamping. Here, the cell voltage was below 3V for both current densities. Furthermore, the selectivity of the cell did not deteriorate at a current density of 500 mA.cm-2. The value of the cell voltage and the good selectivity also lead to the conclusion that a smaller and more homogeneous contact resistance was achieved in this cell than in the case of the rigid current collector on the left, since all other cell elements were identical. The lower cell voltage and the stable and CO- selective operation mean better cell performance in the case of the flexible stamped anode current collector.

[0088] The key advantage of applying a flexible anode current collector is its ability to deliver significantly higher performance compared to previous solutions.

[0089] Example 3: Designing a pressure chamber between two plates

[0090] The space between two plates forming a cavity 200 is used to design a pressure chamber. During cell and stack assembly, the GDE 301 must be compressed to an optimal thickness value. Since GDE is a flexible material, during compression (depending on the GDL type in the GDE and the optimal spacing percentage) a pressure of 0.4-2 MPa can build up on the ion-exchange membrane 302, which stretches the cell apart, similar to when we build pressure on the cathode side. In this case the PTE is required to keep the other elements inside the cell mechanically stable. When designing the elastic pattern shown in Example 2, it should be noted that flexibility of the flexible anode current collector must be adjusted when the cells are operated at higher pressures from the GDE or from the CO2 gas flow. This will maintain the correct anode-side plate 10-PTE 303 contact and provide the correct amount of mechanical support to the PTE. Said flexibility can be controlled by the space forming the cavity 200 between the two plates, also called the pressure chamber. In this space, by increasing or decreasing the pressure (by using an external inert fluid via 61 in figure 3), flexibility of the whole bipolar plate 100 can be influenced, i.e. flexibility of the plate can be adjusted.

[0091] In another embodiment, when higher pressure (from the GDE 301 compression or the CO2 gas flow) is applied on the cathode side, it affects the elements of the cell: it stretches the cathode current collector (23 or 20) and the PTE 303 together with the ion-exchange membrane 302 apart relative to each other. If the anode current collector is flexible 10, then the ion-exchange membrane 302 and PTE 303 can bend due to the tension in that direction that means the GDE 301 is not properly compressed in the middle range of the cell, and thus the performance of the cell decreases compared to the optimal geometric arrangement - Inadequate compression of the GDE can create an inhomogeneous current density distribution within the cell, which increases the cell voltage (by increase resistivity) and reduces the selectivity towards CO, as more hydrogen can be evolved in areas with locally higher current density. By using the pressure chamber 200, the cell can resist against this pressure by harden the flexible anode current collector 10, the elements of the M EA 300 (301, 302, 303) do not move relative to each other, and the performance of the cell remains stable or it can be brought back to a more stable range by ensuring optimal cell geometry. This effect is demonstrated in Figure 9 top and middle graph: Due to the fast 7 barg pressure build-up in the pressure chamber 200 (200A to 200B in Figure 7), the cell reacts immediately and the measured cell voltage at 400 mA.cm-2current density decreases, while the selectivity towards CO increases (the 1 minute delay in the response in selectivity results from the length of the gas path between the cell and the analytical unit). The change is reversible when we remove the pressure from the pressure chamber (200B to 200A) the measured cell voltage increases while the selectivity decreases. Then the cell performance can be improved again by building up pressure in the pressure chamber 200 (200A to 200B). This kind of behavior can be explained by the cathode side and the GDE 301 have a more optimal geometry (elements moving relative to each other) when the pressure chamber 200 is under pressure due to the hardening anode current collector.

[0092] One major advantage is the stable and reliable performance of the cell even under high-pressure conditions.

[0093] Example 4: Controlling the Shape of the Anode and Cathode Side Flow Pattern

[0094] In another embodiment the shape of the anode and cathode side flow pattern (12 and 22 in Figure 4) can be varied by the pressure applied in the pressure chamber - even during cell operation - as shown in Figure 5. As illustrated in Figure 5, the impact of pressure within the pressure chamber is observed, with the direction of the arrows representing the transition from low pressure (Pl) to high pressure (P2). Additionally, the schematic representation demonstrates the alterations in the anode- and cathode-side flow patterns. With a properly designed pattern, this change can be significant (and can be designed to be minimal if this phenomenon is not desired), allowing the flow of fluids within the cell to be influenced, even during operation. This can be important on the cathode side, as well, where the depth and shape of the pattern determines the pressure drop of the gas across the cells and the extent to which the gas passes through the GDL. The variable pressure-drop (and the change in operation itself) helps to eliminate the "flooding" phenomenon by creating a greater and variable driving force on the liquid water trapped in the cell, helping it to leave.

[0095] By placing the pressure chamber 200 under pressure, the shape of the flexible anode current collector 10 is varied: this can reduce the cross-section of the anode-side liquid channels 12 by flexible deformation which has an effect on the flow conditions inside the cell. The extent of this effect is significantly influenced by the designed geometry, as well as the pattern on the anode or cathode side of the bipolar plate and the medium (gas or liquid) flowing in it. We chose the anode side flow pattern 12 to demonstrate the phenomenon, since by reducing the cross-section of these channels (12A to 12B), the amount of pressure drop in the flowing liquid in the anode side can be more easily demonstrated and studied (Figure 7). During the experiment, we monitored the pressure drop calculated from the liquid pressure before and after the cell when the liquid flowing through the cell in operation (lL / min), when 7 barg pressures were created in the pressure chamber (200A to 200B and back). As a result of the deformation (12A versus 12B), the cross-section of the flow channels 12 decreases, and since the flow velocity remains unchanged, therefore the amount of anolyte pressure drop measured on the cell change immediately towards a higher value, as presented in the bottom graph of Figure 9. Here, the dashed lines delimit the ranges in which there is no additional pressure (0 barg) in the pressure chamber 200 (case 200A) and when a pressure of 7 barg is built up in the pressure chamber 200 in 2 seconds (case 200B). Moreover, the change is reversible, as the pressure drop measured on the liquid returns to its original value when the pressure is released from the pressure chamber (200B to 200A). This cycle can be also repeated as shown in the bottom part of Figure 9. This result also proves that the pressure in the pressure chamber can indeed vary the cross-section of the flow channels in the flexible anode current collector and thus the pressure drop of the fluid flowing through the cell, under electrochemical operation. If we wanted to achieve a similar effect by changing the liquid flow rate, it would have a direct impact on the cooling of the cell, which could reduce the cell lifetime. Varying the fluid pressure drop by only changing the cross-section inside the cell does not change the cooling capacity (since the fluid flow rate is unchanged), but the change in pressure drop can help remove any gases trapped in the PTE, which increases the cell life. A similar effect is expected to be achieved on the cathode side, said help remove trapped water droplets from the GDE if the gas pressure drop values inside the cell change during electrochemical operation by influencing the crosssection of the channels in the bipolar plate.

[0096] An important advantage is its extended cell life, ensuring more durable and sustained performance over time.

[0097] Example 5: PTL attached to the anode-side component plate

[0098] - The titanium PTL is attached by welding to the anode half-plate (Figure 4).

[0099] - The advantages of this solution are that it provides additional mechanical rigidity to the entire bipolar plate, and it creates a more efficient and homogeneous electrical connection between the anode current collector plate and the PTL, which has a beneficial effect on the resistance of the entire cell stack and thus on performance.

[0100] - Advantage: mechanically stronger bipolar plates and higher cell performance.

[0101] - PTL fixed by welding on the anode current collector side passively improves the mechanical stability and electrical conductivity of the cell made with the bipolar plate according to the invention.

[0102] In what follows, a preferred manufacturing technology, i.e. stamping and welding, preferably laser welding, is described to produce a bipolar plate according to the invention. This represents merely an exemplary production process, as it is clear for a skilled person in the art. The production begins with the cleaning of the plate arriving in rolls or pre-cut to size. The purpose of cleaning is to remove any grease and dust that may have remained there during their production. The thickness of these plates can vary between 50 and 300 pm. The anode and cathode current collector plates (10 and 20 in e.g. Figure 2) are made separately with making use of respective pressing dies: the cleaned plate is placed between the pressing dies placed in the press with the help of appropriate adapter pins, then - depending on the thickness and size of the plate - pressing into the designed shape takes place with an applied pressure force of 1-400 tons, or even higher up to about 700 tons, or even higher. The shaped plate is then removed from the pressing dies. The process can be semi-automatic or automated. The pressed plate can be preheated when it is placed in the press, up to a maximum of 250°C. Depending on the pressed form, introducing a surface lubricant onto the plates before pressing improves the quality of the pressing. After the plates have been pressed, another cleaning step is performed, in which all lubricant residues are removed. This can be effected with a high-pressure liquid, steam or ultrasonic cleaning bath and a serial combination of these performed one after the other, at the end of which the plates are dried. The cleaned anode and cathode current collector plates are then placed in the welding frame, which has a threefold task: it holds the plates in the correct position relative to each other, touches them together along the welding lines and points, while making these areas accessible to a laser beam. The power of the laser used can vary between 1-30 kW depending on the thickness of the plates to be joined. After the welding is done, the quality of the finished bipolar plate is checked by any of manual, semi-automatic or automatic methods.

[0103] In summary, we found that there are several advantages over the traditionally used thick plates. First, machining costs are reduced, especially in the context of high-volume production. The cost of the expensive component, i.e., the press tool, is allocated over the number of pieces produced. Consequently, the cost of bipolar plates can be reduced to less than €10 for high-volume production (for comparison, chemical milling costs a few hundred euros per unit, while CNC milling costs a few thousand euros per unit in QI, 2024). Subsequently, the thickness of the plates is reduced. The starting plate can be as thin as 0.1 mm, from which a bipolar plate of around 1 mm thickness can be made after pressing and welding (in CNC machining, this can be 8-10 times as thick). The bipolar plate according to the invention incorporates an cell element that is elastic, eliminating the need for additional layers that could introduce contact resistance and enhance performance.

[0104] , Short description numeral _

[0105] 10 Anode current collector plate

[0106] 11 Anode side surface area of anode current collector plate which contacts with MEA

[0107] 12 Anode side flow pattern channel A Anode side flow pattern channel when NO additional pressure in pressure chamber (200) B Anode side flow pattern channel when the pressure chamber (200) is presurized

[0108] Anode holder plate

[0109] Cathode current collector plate

[0110] Cathode side surface area of cathode current collector plate which contacts with ME A

[0111] Cathode side flow pattern channel

[0112] Milled cathode current collector plate

[0113] Active surface area (inside the dashed line) of the bipolar plate

[0114] Gas inlet chimney

[0115] Gas outlet chimney

[0116] Electrolyte (anolyte) inlet chimney

[0117] Electrolyte (anolyte) outlet chimney

[0118] Pressure chamber connecting chimney

[0119] Positioning holes for bipolar plate stacking 0 Stamped and welded bipolar metal plate 0 Cavity area between the cathode and anode current collector plates providing a pressure chamber A Pressure chamber cavities when there is NO additional pressure B Pressurized pressure chamber cavities 0 Membrane electrode assembly (MEA) 1 Gas diffusion electrode (GDE) 2 Ion-exchange membrane 3 Porous transport electrode (PTE) 4 Cathode side spacers 5 Anode side spacers

Claims

CLAIMS1. A bipolar plate (100) for carbon dioxide electrolyser cell with an anode side and a cathode side to be used as current collector means of said cell, comprising a cathode side subplate (20) with a flow pattern of first flow channels (22) of a first inner flow cross-section formed in the cathode side subplate, the first flow channels being open to the cathode side of the cell; and an anode side subplate (10) with a flow pattern of second flow channels (12) of a second inner flow cross-section formed in the anode side subplate, the second flow channels being open to the anode side of the cell; the cathode side subplate (20) and the anode side subplate (10) being joined together to form the bipolar plate in such a way that, in a joined state and in orthogonal planar projection, at least one first flow channel (22) is located between each two adjacent second flow channels (22) thereby forming a cavity (200) between the cathode side subplate (20) and the anode side subplate (10); wherein the cathode side subplate (20) is configured to have a first bending stiffness and the anode side subplate (10) is configured to have a second bending stiffness, said second bending stiffness being smaller than said first bending stiffness.

2. The bipolar plate (100) according to claim 1, wherein the second bending stiffness is 100 to 200 times smaller than the bending stiffness of a titanium plate of 4 mm in thickness.

3. The bipolar plate (100) according to any of claims 1 to 2, wherein the cathode side subplate (20) is made any of a stainless steel or a titanium plate with a thickness ranging from 50 pm to 1000 pm.

4. The bipolar plate (100) according to any of claims 1 to 3, wherein the anode side subplate (10) is made any of a stainless steel or a titanium plate with a thickness ranging from 50 pm to 1000 pm.

5. The bipolar plate (100) according to any of claims 1 to 4, wherein each of the cathode side subplate (20) and the anode side subplate (10) is provided with a first opening (61) configured to connect the cavity (200) with a pressurizing means when the subplates of the bipolar plate (100) are joined.

6. The bipolar plate (100) according to any of claims 1 to 5, wherein each of the cathode side subplate (20) and the anode side subplate (10) is provided with a second opening (62), said second openings (62) are arranged in the respective subplate (10, 20) concentrically to each other to assist positioningthe cathode side subplate (20) and the anode side subplate (10) when assembling the bipolar plate (100).

7. The bipolar plate (100) according to any of claims 1 to 6, wherein each of the cathode side subplate (20) and the anode side subplate (10) is a stamped element.

8. The bipolar plate (100) according to any of claims 1 to 7 , wherein the first inner flow cross-section of said first flow channels (22) differs from the second inner flow cross-section of said second flow channels (22).

9. The bipolar plate (100) according to any of claims 1 to 8, wherein the cathode side subplate (20) and the anode side subplate (10) are joined together by welding, preferably by laser welding.

10. The bipolar plate (100) according to any of claims 1 to 9, with a total thickness of at most 1 mm.

11. A carbon dioxide electrolyser cell comprising the bipolar plate (100) according to any of claims 1 to 10 as current collector means.

12. A carbon dioxide electrolyser cell stack comprising the bipolar plate (100) according to any of claims1 to 10 as current collector means.

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