Alkaline electrolytic cell with cooled bipolar electrodes

Abstract

An electrolytic cell (1) for producing hydrogen, comprising a stack of bipolar electrodes (9) that sandwich an ion transport membrane (2) between every two of the bipolar electrodes. Each bipolar electrode comprises two metal plates (9A, 9B) welded together back to back, forming a coolant compartment between them and having a respective anode surface and an opposite cathode surface, each metal plate abutting one of the membranes. The plates (9A, 9B) are embossed with primary vertical channels (10A, 10B) and secondary channels (11A, 11B) in a herringbone pattern for conveying oxygen and hydrogen. Embossed herringbone patterns are provided on both sides of the metal plates (9A, 9B) so as to also provide herringbone-pattern coolant channels (11B) within the coolant compartments.

Description

Technical Field

[0001] The invention relates to an alkaline electrolyser for producing hydrogen, the alkaline electrolyser comprising a stack of bipolar electrodes, each two bipolar electrodes sandwiching an ion transport membrane. Each bipolar electrode forms an anode chamber on one side and a cathode chamber on the other side. Background Art

[0002] An efficient method of producing hydrogen is electrolysis. In an electrolyzer, an ion-conducting membrane is sandwiched between two electrodes, and a voltage is applied across the electrodes. The voltage causes the water in the aqueous electrolyte to split into hydrogen and oxygen, which are ultimately separated on opposite sides of the membrane.

[0003] Conventional alkaline electrolysis is based on a series of electrolytic cells. In each electrolytic cell, two electrode plates are spaced a certain distance apart. The gap between the electrodes is filled with a liquid alkaline electrolyte. When sufficient voltage is applied, hydrogen is released on the cathode surface, and oxygen is released on the anode surface. An ion-conducting membrane between the electrodes prevents the gases from mixing. The electrolyte circulates to remove the heat generated by the electrolysis process. The gap needs to be wide enough to allow hydrogen and oxygen bubbles to escape without excessively blocking the electrolyte conduction path from the anode to the cathode, and to allow the electrolyte to circulate without excessive pressure loss.

[0004] The electrode stack consists of a series of electrolytic cells. In this series of electrolytic cells, each electrode acts as an anode on one side and a cathode on the other side. In this application, the electrodes are called bipolar electrodes because they have different polarities on both sides.

[0005] In later years, the configuration of the traditional alkaline electrolyzer was replaced by the so-called zero-gap configuration. In the zero-gap configuration, the cell design works by pressing two porous electrodes onto either side of a hydroxide ion conducting membrane. This achieves a gap between the two electrodes equal to the thickness of the membrane, typically 0.5 mm or even less, rather than the 2 mm to 5 mm required for the traditional gap configuration. The smaller gap reduces the contribution of ohmic resistance to the cell losses.

[0006] In a zero-gap configuration, the electrodes need to have holes in order to allow hydrogen and oxygen bubbles to escape to the side of the electrode that is not facing the membrane. In a bipolar electrode, this arrangement would lead to mixing of hydrogen and oxygen in the chamber established between the cathode and the anode, which is undesirable. Therefore, a separator is inserted between the anode of one cell and the cathode of the adjacent cell, which prevents this mixing of the gases produced by the electrolysis process. Therefore, bipolar electrodes for zero-gap electrolysis stacks usually consist of three metal plates, namely a porous anode, a solid separator and a porous cathode. The distance from the anode to the separator and from the separator to the cathode must be of sufficient width to allow the electrolyte to circulate without excessive pressure losses and, most importantly, to allow the hydrogen and oxygen bubbles to escape without excessive obstruction, which would otherwise cause back pressure on the bubbles.

[0007] Examples of electrolytic cell arrangements in which opposing separators are welded to each other are illustrated in U.S. patent applications US2021 / 0234237 and US2021 / 0202963.

[0008] US2021 / 0234237 discusses separators for electrochemical systems and discloses a bipolar separator made of two combined corrugated plates so that the corrugations form cooling channels between the two metal plates and gas transmission channels on their outer sides. The bipolar plates are stacked and arranged on both sides of a membrane electrode assembly, i.e., an MEA, usually sandwiched between gas diffusion layers such as nonwoven materials. On their outer sides, the corrugations are in contact with the gas diffusion layer. Typically, the gas diffusion layer between the membrane and the electrode is generally used to allow the gas to flow and diffuse away from the membrane appropriately.

[0009] However, the more layers an electrolyser unit comprises, the higher the risk that the components move relative to each other and lead to reduced efficiency or even failure of the electrolyser. It is therefore of interest to provide an electrolyser system with high rigidity and robustness.

[0010] Among electrolyser systems, there is a wide variety. In some systems, the membrane is provided as part of a membrane electrode assembly, in some cases a flexible membrane electrode assembly, other systems have a metal mesh or grid pressed onto the membrane, or are provided with a flexible gas diffusion layer. Some have a single bipolar plate between the electrolyser modules in the stack, others have a double-walled electrolyser. Each principle represents an attempt to optimize hydrogen production. No conclusion has yet been found about the most efficient configuration, and for the skilled person there is no specific starting point for optimizing the system, nor direction on how to optimize in the best way. Typically, improvements are found through multiple trial and error attempts, where various features are put together in the hope of finding a further optimized system.

[0011] EP0159138 discloses an electrolysis system for producing chlorine in which a single corrugated bipolar electrode plate is sandwiched between membranes. The corrugations on either side include horizontal side channels between the main vertical channels, and the electrolyte flows from the bottom up through one main channel, then through the side channels to the adjacent main channel, then up through the adjacent channel and out of the chamber at the top. It is mentioned that this results in rapid removal of gases.

[0012] US5114547 makes up for the system in EP0159138 and discloses an electrolysis system for producing chlorine, in which the embossed corrugations in the monopolar or bipolar metal electrode plates are formed in a herringbone pattern, wherein the secondary channels extend obliquely from the vertical main channels. This is interpreted as improving the flow and circulation of the electrolyte and further rapidly removing the formed gas. Optionally, the vertical main channel is provided with an opening for electrolyte circulation. A herringbone pattern in a separator, for example formed by embossing, is also disclosed in US2007 / 0105000 as one of several alternatives.

[0013] While some systems see advantage in circulating electrolyte out of the top along with the gas, which is then separated from the electrolyte, other systems prevent such transport of electrolyte along with the gas to reduce the risk of cross currents.

[0014] WO2022 / 156869 discloses an electrolysis system having a single bipolar plate or a double bipolar plate between hydrogen production electrolysis chambers, each electrolysis chamber comprising a membrane sandwiched between perforated electrode plates adjacent to the membrane. The perforations allow gas to be transported from the membrane through the perforations to the corresponding anode chamber and cathode chamber on the opposite side of the membrane. When two bipolar plates are used, a coolant is introduced into the volume between the bipolar plates. The chamber is not completely filled with electrolyte, but space is provided at the top for gas accumulation and separation from the liquid, wherein the gas leaves the chamber through an opening above the liquid level. The separation of the gas from the electrolyte in the chamber means that only gas is transported out of the electrolyzer stack, thereby reducing the risk of shunting current through the conductive electrolyte.

[0015] These examples are just some of the attempts to improve electrolysis in different directions. However, there is still room for improvement in terms of optimization. In particular, it is desirable to provide an improved hydrogen production electrolyzer that is simple in structure but robust, reliable and efficient. Summary of the invention

[0016] It is therefore an object of the present invention to provide an improvement in the art. In particular, it is an object of the present invention to provide an electrolyser having a high degree of operational reliability. Furthermore, it is an object of the present invention to provide an electrolyser having a simple construction of a plurality of separator / electrode modules sandwiching the membrane between them, wherein these modules are rigid and suitable for large-scale production at relatively low cost and allow good temperature control of the electrolyser. These objects and further advantages are achieved by an alkaline electrolyser for the production of hydrogen as described below and in the claims.

[0017] The electrolyzer comprises a stack of bipolar electrodes, which sandwich an ion transport membrane between each two bipolar electrodes. Each bipolar electrode comprises two metal plates, in particular an anode metal plate and a cathode metal plate, which are mounted back to back to each other, such as welded together, and form a coolant compartment between them. This structure gives the bipolar electrode high rigidity.

[0018] The bipolar electrode has an anode surface and an opposite cathode surface, each of which is connected to one of the membranes. The metal plate is embossed with at least the first main vertical channel and a plurality of side channels of a herringbone pattern for conveying oxygen and hydrogen. The side channels of the embossed herringbone pattern are arranged on both sides of the metal plate so as to provide a coolant channel of the herringbone pattern in the coolant compartment. For example, the side channels of the herringbone pattern facing each other across the membrane of the anode plate and the cathode plate face each other at different angles, so that the embossed side channels in the anode metal plate intersect with the embossed coolant channels in the cathode metal plate. The herringbone pattern enhances the turbulence in the coolant compartment to effectively cool the electrolyte on the opposite side of the plate relative to the coolant compartment.

[0019] The main purpose of an electrolyser is to produce hydrogen. The hydrogen is collected for later use, for example in fuel cells or industrial applications. However, oxygen is also produced due to the decomposition of water in the electrolyte when electricity is applied. The oxygen can also be collected for later use.

[0020] The two metal plates are electrically conductive and form an anode plate and a cathode plate. The bipolar electrodes adjoin the respective two membranes and form an anode chamber and a cathode chamber respectively with the respective ion transport membrane. The electrode chambers contain an electrolyte, in particular an alkaline electrolyte, such as an electrolyte based on NaOH or KOH.

[0021] In the above arrangement of the metal plates adjacent to the membrane, the surfaces of both metal plates serve as the electrolytically active part of the electrolytic cell. Alternatively, an additional electrode layer is placed on one or both metal plate surfaces, resting on the stamped parts of the metal plates, partially or completely adjacent to the respective membrane, thereby partially or completely serving as the electrolytically active part of the electrolytic cell.

[0022] Typically, the embossed pattern includes not only one main channel but also a plurality of main vertical channels, typically vertical channels. Embossed side channels extending from each main channel in a herringbone pattern are in fluid communication with the main channels. Oxygen and hydrogen are transported from the membrane through the inclined side channels into the main channels and further upward through the main channels to release the gases from the anode and cathode chambers through corresponding gas outlets provided in the electrolyzer.

[0023] A particular advantage of this arrangement can be established by connecting a plurality of primary channels in the upper part of the electrode chamber above the secondary channels. The advantage is that a significant circulation of electrolyte is established within the volume defined by the electrode surface on one side of the electrode chamber and the membrane on the opposite side of the electrode chamber.

[0024] For example, each of the electrode metal plates is provided with a first main vertical channel, a plurality of side channels are inclined upward toward the first main vertical channel so as to form a first herringbone pattern with the first main channel, and each of the electrode metal plates is provided with a second main vertical channel, the side channels are inclined downward toward the second main vertical channel so as to form a second herringbone pattern with the second main channel, wherein the second herringbone pattern is circumferential relative to the first herringbone pattern. The side channels are also connected to the second main channel, but due to the upward inclination toward the first main channel, the bubbles drift only toward the first main channel.

[0025] Advantageously, the first main channel and the second main channel are connected above the secondary channel at the upper part of the corresponding electrode chamber and below the secondary channel at the lower part of the corresponding electrode chamber, which results in an increased circulation of the electrolyte from the lower part upward through the first main channel to the upper part above the secondary channel and then to the second main channel before flowing back to the lower part downward through the second main channel. Typically, as described above, there are a plurality of main channels of the first type with upward flow and a plurality of main channels of the second type with downward flow.

[0026] In more detail, the bubbles formed during the electrolysis process will flow in the upwardly inclined side channels formed by the depressions in the embossed herringbone pattern of the electrode and enter those first main channels in an upward path. Here, they form bubbles that flow upward. The bubbles will drag along the electrolyte, causing the electrolyte to flow upward. In the upper part of the electrode chamber, the electrolyte will flow generally horizontally to the adjacent second main channel and then flow downward. Therefore, in those adjacent second main channels, the electrolyte will flow downward. At the bottom of the electrode, the electrolyte will flow horizontally back to the adjacent first main channel, and the side channel extends toward the adjacent first main channel in an upwardly inclined path formed by the depressions in the embossed herringbone pattern of the electrode, and resumes the upward flow there.

[0027] The electrodes are cooled on opposite sides of the active surface due to the circulation of coolant in the coolant chamber between the two electrode metal plates forming the bipolar electrode. Even though the embossed herringbone pattern on the back of the electrode promotes heat transfer from the coolant to the electrode, a completely uniformly cooled electrode surface cannot be obtained. However, as described above, due to the bubble-driven circulation, a certain volume of electrolyte is in contact with a large area of ​​the electrode in a relatively short period of time. Therefore, the total volume of electrolyte in the electrolytic cell will reach a more uniform temperature than if such bubble-driven circulation did not occur.

[0028] In a practical embodiment, the gas outlet connects the anode chamber with an oxygen delivery conduit and the cathode chamber with a hydrogen delivery conduit. Optionally, the oxygen delivery conduit and / or the hydrogen delivery conduit extend along the stack through openings in the anode plate and the cathode plate. For example, a seal is provided between the bipolar electrodes so that the openings in the bipolar plate stack, optionally in addition to corresponding openings in the membrane retaining frame, also form a longitudinal gas conduit through and along the stack.

[0029] Another important advantage is achieved by the present invention, as will be described below, by comparing conventional electrolytic cells with the present invention.

[0030] In conventional arrangements of electrolyser stacks, fairly uniform cooling of the electrolyser stack can only be obtained by a significant circulation of the electrolyte and a correspondingly high pumping rate of an external pump. Since these arrangements require considerable flow volumes, the corresponding electrolyte flow paths through the electrode stack must be large in order to keep the pressure losses in the flow paths at a manageable level. When filled with a highly conductive electrolyte, these flow paths act as shunts, connecting all the cells in the stack, including the cells at the ends with the full potential difference of the stack. The shunt currents flowing in the flow paths can reach the level of several percent of the total current in the stack. Since the shunt currents do not contribute to the electrolysis at the desired locations in the stack, the ratio of the losses they generate is the same as the ratio of the shunt current to the total current.

[0031] In contrast to these conventional arrangements, the arrangement of the electrolytic cell stack according to the present invention provides internal circulation of the electrolyte in the electrolytic cell by a bubble driven circulation as described above. Therefore, no pump driven electrolyte circulation is required. The only thing required is the continuous replenishment of the electrolyte. However, the electrolyte flow required for this in the present invention is a small part of the electrolyte flow required for cooling according to conventional methods. Therefore, the electrolyte flow path through the electrode stack can have a much smaller cross-section, while still keeping the pressure losses in the flow path at a manageable level. The shunt current is proportional to the cross-section of the flow path, and the effect of the much smaller cross-section of the flow path is that the shunt losses are significantly reduced compared to the conventional arrangement, thereby reducing the losses accordingly.

[0032] In a practical embodiment, to provide sealing, the anode plate and the cathode plate can be welded together back to back, typically along a closed curve, for example by peripheral welding at the edges and advantageously around the inlet and outlet and the conduit. Alternatively, the two metal plates are pressed against each other, with sealing being achieved by glue or a sealing gasket, typically along or near the periphery and around the conduit.

[0033] The cross-section of the embossed pattern forming the channel is optionally smoothly alternating, for example approximately sinusoidal. The approximately sinusoidal cross-section reduces the contact area between the membrane and the anode surface and the cathode surface. Despite deformation of the membrane and the embossing plate, the contact area is minimized to only a few percent of the membrane surface area.

[0034] Alternatively, the cross section of the embossed pattern forming the channels is polygonal. The polygonal cross section can be made to have the same small contact area between the membrane and the anode and cathode surfaces, but can also be made to have a significant portion of the anode and cathode surfaces in close contact depending on preference.

[0035] For example, the side channels have a depth in the range of 0.3 mm to 3 mm, while the areas between the side channels abut the membrane.

[0036] In some advantageous embodiments, the secondary channel has a length of about 50 mm to 200 mm and a width of about 2 mm to 10 mm. For example, the length may be 10 to 50 times the width.

[0037] In some embodiments, a supplementary electrode may be placed on the anode and / or cathode. Such a supplementary electrode may optionally be coated with a catalytic material.

[0038] In some embodiments, the coolant channels of the herringbone pattern of the anode and cathode plates face each other at different angles so that at least some of the imprinted gas flow side channels in the anode intersect with at least some of the imprinted gas flow side channels in the cathode. The intersection of small channels in opposing plate surfaces in the coolant compartment has been shown to improve electrolyte cooling compared to channel patterns that mirror each other in the coolant compartment.

[0039] The secondary channels in the coolant compartment also include grooves and ridges between the grooves. The ridges of the secondary channels advantageously contact each other at the intersections in the coolant compartment, which not only improves the turbulence in the coolant compartment, but also ensures the rigidity of the bipolar plates and many electrical contact points. The rigidity of the bipolar plates also causes the membrane to remain firmly in place between the bipolar plates in the stack.

[0040] By properly choosing the angles of the side channels, a large number of such contact points will be established. This results in good transfer of current from the anode to the cathode, minimizing the ohmic losses caused by the need for lateral current flow in the electrode plates.

[0041] In another advantageous embodiment, the electrolyte is provided in the anode chamber and / or cathode chamber to a level below the corresponding gas outlet for separating the gas from the electrolyte and preventing the electrolyte from flowing through the gas outlet. In this case, if a circulation outlet is provided for the electrolyte, the circulation outlet is located below the electrolyte surface in the electrolyte chamber instead of at the top.

[0042] Further advantages can be achieved if the coolant compartment has a coolant inlet at the top and possibly a coolant outlet at the bottom and is arranged to cool the gas above the electrolyte and condense liquid, especially water, from the gas before the gas leaves the anode chamber and the cathode chamber through the gas outlet, thereby producing dry gas, further reducing the risk of cross flow.

[0043] In order to supply water to the anode chamber and cathode chamber to replenish the consumed water, each chamber may include one or more water inlets. Alternatively or additionally, if the water consumed during the electrolysis process is added to the electrolyte outside the electrolytic cell, each chamber may include one or more electrolyte inlets.

[0044] Typical dimensions are as follows:

[0045] Thickness of board: 0.3mm to 1.0mm

[0046] Board length / width: 0.3m to 3m

[0047] Depth of embossed secondary channels in herringbone pattern: 0.3mm to 3mm

[0048] As a separation membrane for alkaline water electrolysis, a polymer membrane is generally used. For example, a membrane comprises an open-net polyphenylene sulfide fabric symmetrically coated with a polymer and zirconium oxide mixture. The latter is advantageous for systems in which the electrolyte is used at high temperatures, for example in the range of 50°C to 90°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present invention will be described in more detail with reference to the accompanying drawings, in which

[0050] Figure 1 is a schematic diagram of an electrolyzer stack;

[0051] Figure 2A An electrode assembly in a stack is shown;

[0052] Figure 2B Shows Figure 2A A magnified cross section of

[0053] Figure 3 Anode and cathode volumes and electrolyte levels in various conduits are shown;

[0054] Figure 4 The circulation of electrolytes is shown;

[0055] Figure 5A A sinusoidal cross section of a metal plate is shown;

[0056] Figure 5B A sinusoidal cross section of a metal plate adjacent to the membrane is shown;

[0057] Figure 5C A triangular cross section of a metal plate is shown;

[0058] Figure 5D A triangular cross section of a metal plate with rounded edges is shown;

[0059] Fig. 6A is a cross section of a cathode plate combined with a perforated screen;

[0060] Figure 6B It is a cross section of a cathode plate combined with a metal mesh. DETAILED DESCRIPTION

[0061] Figure 1 is a schematic diagram of a stacked electrolyser 1 comprising an ion transport membrane 2 sandwiched between bipolar electrodes 9.

[0062] Figure 2A Some details are shown. The membrane 2 is supported by a first frame 4A and a second frame 4B. The first frame 4A forms one side of the anode chamber 5A together with the membrane 2, and the anode plate 9A forms the opposite side of the anode chamber 5A. The second frame 4B forms one side of the cathode chamber 5B together with the membrane 2, and the cathode plate 9B forms the opposite side of the cathode chamber 5B. Both chambers 5A, 5B contain the electrolyte required for the electrolysis reaction, in which water is decomposed into oxygen and hydrogen, which are extracted from the anode chamber 5A and the cathode chamber 5B, respectively.

[0063] In order to replenish the water consumed during the reaction, the frames 4A, 4B have a water inlet 6, which is supplied with water from a water supply conduit 7. In order to remove oxygen and hydrogen from the respective chambers 5A, 5B, the frames 4A, 4B have respective gas outlets 8A, 8B on opposite sides of the membrane 2 and in the upper part of the frames 4A, 4B. The gas outlets 8A and 8B lead to respective oxygen delivery conduits 13A and hydrogen delivery conduits 13B.

[0064] In practice, the anode plate 9A and the cathode plate 9B are assembled back to back into a bipolar electrode 9, with a liquid-tight coolant compartment in the volume between the anode plate 9A and the cathode plate 9B for cooling the bipolar electrode 9, and thus also cooling the electrolyte in the electrode chambers 5A, 5B. Typically, the anode plate 9A and the cathode plate 9B are provided as stainless steel plates and are welded together back to back, for example, along the edge portion of the coolant compartment. Figure 2ACoolant conduits, not shown, are provided at the top and bottom for coolant to flow through the coolant compartments between the plates 9A, 9B.

[0065] Figure 2B yes Figure 2A . It shows that the anode plate 9A and the cathode plate 9B are provided with a first main channel 10A and a second main channel 10B on the side facing the membrane, the first main channel and the second main channel are embossed into the plates 9A, 9B transversely to the membrane 2, and have an inclined side channel 11A extending toward the first main channel 10A in an upwardly directed herringbone pattern and extending toward the second main channel 10B in a downwardly directed herringbone pattern. The herringbone pattern in which the side channel 11A extends upwardly obliquely toward the first vertical main channel 10A causes bubbles to flow from the inclined side channel 11A into the first main channel 10A, thereby improving the upward flow and circulation of the electrolyte, and further quickly removing the formed gas, promoting the combined upward movement of the gas and electrolyte in the first main channel 10A.

[0066] Since the herringbone pattern of the side channels 11A is provided by stamping an alternating pattern into the metal plates of the anode plate 9A and the cathode plate 9B, the inclined side channels 11A are present not only on the side of the anode plate 9A and the cathode plate 9B facing the membrane, but the inclined side channels are also correspondingly arranged on the side between the plates 9A, 9B facing the coolant compartment and serve as inclined coolant channels 11B.

[0067] If the coolant channels 10B of the anode plate 9A are reversed relative to the coolant channels 10B of the cathode plate 9B in the coolant compartment, so that the upwardly inclined coolant channels 11B on the back of the anode plate 9A intersect with the downwardly inclined coolant channels 11B on the back of the cathode plate 9B, and vice versa, the flow and circulation of the coolant is improved. This intersection of the stamped coolant channels 11B in the coolant compartment increases the turbulence of the coolant as it flows through the coolant compartment between the anode plate 9A and the cathode plate 9B. This is an improvement over the system in the above disclosure of US5114547.

[0068] For example, two opposing embossed patterns of the coolant channel 11B in the coolant compartment are advantageously pressed together so that the ridges of the embossed patterns of the coolant channel 11B in the coolant compartment abut each other. Similar to the improvement of electrolyte flow and circulation, the flow and circulation of the coolant is also improved by the herringbone pattern. In addition, the abutting ridges provide contact points for improved electrical conduction.

[0069] refer to Figure 2A In order to prevent the electrolyte in the anode chamber 5A and the cathode chamber 5B from leaving the corresponding chambers 5A and 5B through the gas outlets 13A and 13B, the liquid level 12 of the electrolyte is lower than the liquid level of the corresponding gas outlets 8A and 8B. Figure 3 Specifically, Figure 3 The arrangement of the transport conduits, i.e. the oxygen transport conduit 13A, the hydrogen transport conduit 13B, the coolant inlet conduit 15, the coolant outlet conduit 16, the water supply conduit 7 and the electrolyte supply conduit 14 are illustrated. The cathode chamber 5B and similarly the anode chamber 5A are defined by a gasket 24 surrounding the active area of ​​the membrane 2. The electrolyte 17 extends to an uppermost layer 18 which is below the top 25 of the respective chamber 5A, 5B and therefore below the gas outlet 8A, 8B, see also Figure 2A , and is lower than the gas delivery conduits 13A, 13B, such as Figure 3 As shown, oxygen and hydrogen are separated from the electrolyte 17 before entering the respective gas delivery conduits 13A, 13B. This reduces the risk of cross current. Specifically, only hydrogen flows through the hydrogen outlet 8B, see Figure 2A , and enters the hydrogen delivery conduit 13B instead of the electrolyte or water flowing therethrough.

[0070] In the present system, further advantages are achieved by coolant flowing from the coolant inlet conduit 15 located at the top of the bipolar bi-sheet electrode plate 9 to the coolant outlet conduit 16 located at the bottom. Since the coolant enters at the top, the cooling effect is highest at the top. This means that the gas in the electrode chamber 5A, 5B is most effectively cooled at the top before leaving the electrode chamber 5A, 5B. Effective cooling causes water condensation from the gas, so that the gas leaving through the gas outlet 8A, 8B is dry, thereby even further reducing the risk of cross current. This is a special improvement relative to the system in the above disclosure of WO2022 / 156869.

[0071] Figure 4 The flow principle of the electrolyte in the cathode chamber 5B is shown by arrows 12A, 12B. As shown by the upwardly pointing arrow 12A, the bubbles flow upward in the first main channel 10A, and the side channel 11A is inclined upward toward the first main channel. The moving bubbles also drag the electrolyte 17, which causes the electrolyte 17 to circulate upward in the first main channel 10A and, as shown by the downwardly pointing arrow 12B, circulate downward in the adjacent second main channel 10B, and the side channel 11A extends in a downwardly inclined manner toward the second main channel.

[0072] By stamping on the metal plates of the anode plate 9A and the cathode plate 9B, a herringbone pattern with the secondary channels 11A in the electrode compartments 5A, 5B and a herringbone pattern of coolant channels 11B in the coolant compartment is provided.

[0073] The cross section of the embossed pattern forming the secondary channel 11A and the coolant channel 11B may be smoothly alternating, for example sinusoidal. Alternatively, the cross section of the embossed pattern forming the secondary channel 11A and the secondary coolant channel 11B is polygonal. The polygonal cross section optionally has a similar small contact area between the membrane 2 and the anode surface and the cathode surface, but can be made to make a significant portion of the anode surface and the cathode surface in close contact depending on preference.

[0074] Figure 5A , 5B , 5C and 5D show examples of possible imprints in the cathode plate 9B in cross-section along a line perpendicular to the secondary channels 11A formed by the herringbone pattern along the membrane 2. Figure 5A In the embodiment, the cross section follows a sinusoidal curve along a line transverse to the secondary channel 11A. The ridge 19 of the curve is arranged near the membrane 2. Alternatively, as Figure 5B As shown, Figure 5A The same reference numerals are valid, the embossed ridge 19 rests against the membrane 2. By the pressing force, the ridge 19 is slightly pressed into the membrane 2 to obtain good conductivity and optimized electric field strength, while the gas generated at the ridge 19 flows into the secondary channel 11A and from there into the first main channel 10A as an embossed groove, so that the gas is transported upward to the gas outlet 8A, 8B and into the corresponding gas channel 13A, 13B, as shown in conjunction with Figure 2A and Figure 3 Explained.

[0075] Other cross-sectional alternating shapes are possible, such as alternating curves with sharp edges, e.g. Figure 5C as shown, or triangular alternating curves with rounded edges, as Figure 5D shown.

[0076] Despite the deformation of the membrane 2 and the embossing plate 9B, the contact area is minimal and only a few percent of the active membrane surface area due to the abutment of the ridges 18 against the membrane 2 and the potentially embossed portion of the membrane 2.

[0077] Fig. 6A An arrangement is shown in which the electrode comprises a corrugated metal plate 9B as described above and a supplementary perforated electrode layer 21, such as a thin perforated conductive sheet, placed between the metal plate 9B and the membrane 2 and resting on a stamped portion of the metal plate 9B. Alternatively, the supplementary electrode layer may be a wire mesh with first and second lines 22A, 22B crossing each other, or it may be any other perforated conductive material, advantageously having catalytic properties.

Claims

1. An electrolyser (1) for producing hydrogen, the electrolyser (1) comprising a stack of bipolar electrodes (9) sandwiching an ion transport membrane (2) between each two bipolar electrodes therein, wherein each bipolar electrode (9) comprises an electrically conductive anode metal plate (9A) and an electrically conductive cathode metal plate (9B) mounted back to back to each other so as to form a coolant compartment therebetween, wherein the bipolar electrodes (9) abut the membrane (2) on opposite sides of the bipolar electrodes (9), and wherein the metal plates (9A, 9B) form an anode chamber (5A) and a cathode chamber (5B) with the respective membrane (2), and wherein the anode chamber and the cathode chamber (5A, 5B) contain an electrolyte (17), wherein the metal plates (9A, 9B) are embossed with a first main vertical channel (10A) and a plurality of secondary channels (10A) 1A), the plurality of side channels are inclined upward toward the first main channel (10A) so as to form a herringbone pattern with the first main channel (10A), wherein the side channels (11A) are connected to the first main channel (10A) for transporting oxygen and hydrogen from the membrane (2) into the first main channel (10) through the upwardly inclined side channels (11A), and further transporting upward in the first main channel (10A) so as to release the gases from the anode chamber and the cathode chamber (5A, 5B) through corresponding gas outlets (8A, 8B) provided in the electrolyzer (1); wherein the embossed herringbone pattern is provided on both sides of each of the metal plates (9A, 9B) so as to provide a herringbone pattern of coolant channels (11B) also in the coolant compartment.

2. An electrolytic cell according to claim 1, wherein the side channels (11A) of the anode plate (9A) and the cathode plate (9B) facing each other in a herringbone pattern across the membrane (2) face each other at different angles, so that the embossed side channels (11A) in the anode metal plate (9A) intersect with the embossed coolant channels (11A) in the cathode metal plate (9B).

3. The electrolytic cell according to any one of claims 2, wherein the herringbone pattern of the side channels (11A) is arranged so that the upwardly inclined side channels (11A) of the anode metal plate (9A) intersect with the downwardly inclined side channels (11A) of the cathode metal plate (9B), and vice versa.

4. The electrolytic cell according to claims 2 and 3, wherein the coolant channels (11B) of the herringbone pattern of the two metal plates (9A, 9B) in the coolant compartment face each other at different angles so that the embossed coolant channels (11B) in the anode metal plate (9A) intersect with the embossed coolant channels (11B) in the cathode metal plate (9B).

5. An electrolytic cell according to any one of the preceding claims, wherein each of the metal plates (9A, 9B) is provided with a second main vertical channel (10B), the secondary channel (11A) extending obliquely downwardly towards the second main vertical channel so as to form a herringbone pattern with the second main channel (10B), wherein the secondary channel (11A) is connected to the second main channel (10B), wherein the first main channel (10A) and the second main channel (10B) are connected above the secondary channel (11A) at the upper part (20A) of the corresponding electrode chamber (5A, 5B) and below the secondary channel (11A) at the lower part (20B) of the corresponding electrode chamber (5A, 5B) for increasing the circulation of the electrolyte (17) from the bottom (20B) upward through the first main channel (10A) to above the secondary channel (11A), from the first main channel (10A) to the second main channel (10B), and then downward through the second main channel (10B) to the lower part (20B).

6. An electrolyser according to any preceding claim, wherein the bipolar electrode comprises a supplementary porous conductive electrode layer (21, 22A, 22B) on the anode metal plate (9A) or the cathode metal plate (9B) or both, and adjacent to an ion-conducting membrane (2).

7. An electrolytic cell according to any preceding claim, wherein an electrolyte (17) is arranged in the anode chamber and the cathode chamber (5A, 5B) until a level (18) below the gas outlet (8A, 8B) for separating the gas from the electrolyte (17) and preventing the electrolyte (17) from flowing through the gas outlet (8A, 8B).

8. An electrolyser according to claim 7, wherein the coolant compartment has a coolant supply from a coolant conduit (15) at the top of the coolant chamber, the coolant supply being arranged to cool the gas in the electrode chamber (5) above the electrolyte (17) to cause condensation of liquid (17) in the gas before the gas leaves the electrode chamber (5A, 5B) through the gas outlet (8A, 8B).

9. The electrolytic cell according to any of the preceding claims, wherein the secondary channel (11A) has a depth in the range of 0.3 mm to 3 mm.

10. The electrolyser according to any one of the preceding claims, wherein the secondary channel (11A) has a length of about 50 to 200 mm and a width of about 2 to 10 mm, and the ratio between the width and the length is about 10 to 50.

11. An electrolyser according to any one of the preceding claims, wherein the oxygen outlet (8A) connects the anode chamber (5A) with an oxygen delivery conduit (13A), and wherein the hydrogen outlet (8B) connects the cathode chamber (5B) with a hydrogen delivery conduit (13B), wherein the oxygen delivery conduit (13A) and the hydrogen delivery conduit (13B) extend along the stack through openings in the anode plate (9A) and the cathode plate (9B).

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