Alkaline electrolysis cell with cooled bipolar electrodes

Abstract

An electrolyzer (1) for producing hydrogen gas comprises a stack of bipolar electrodes (9), with an ion transport membrane (2) sandwiched between each pair of bipolar electrodes (9). Each bipolar electrode comprises two metal plates (9A, 9B) welded back-to-back together to form a coolant compartment therebetween, each having an anode face and an opposing cathode face, each of which abuts one of the membranes. The plates (9A, 9B) are embossed with vertical major channels (10A, 10B) and minor channels (11A, 11B) in a herringbone pattern for transporting oxygen and hydrogen gases. The embossed herringbone pattern is provided on both sides of the metal plates (9A, 9B) so as to also provide herringbone-patterned coolant channels (11B) inside the coolant compartment.

Description

[Technical Field]

[0001] The present invention relates to an alkaline electrolyzer for producing hydrogen gas, which involves a stack of bipolar electrodes, each pair of which sandwiches an ion transport membrane, each bipolar electrode forming an anode chamber on one side and a cathode chamber on the other side. [Background technology]

[0002] An effective method for producing hydrogen gas is electrolysis. In an electrolytic cell, an ion-conducting membrane is sandwiched between two electrodes and a voltage is applied across the electrodes. The voltage results in water being separated from the aqueous electrolyte into hydrogen and oxygen, with the eventual separation of hydrogen and oxygen gases on either side of the membrane.

[0003] Conventional alkaline electrolysis is based on a series of electrolysis cells. In each cell, two electrode plates are separated by a specific distance. The gap between the electrodes is filled with a liquid alkaline electrolyte. When a sufficient voltage is applied, hydrogen is liberated at the cathode side and oxygen is liberated at the anode side. An ionically conductive membrane between the electrodes prevents the gases from mixing. The electrolyte is circulated to remove the heat generated by the electrolysis process. The gap must be wide enough to allow hydrogen and oxygen bubbles to escape without excessively blocking the conduction path through the electrolyte from the anode to the cathode, and to allow circulation of the electrolyte without excessive pressure loss.

[0004] The stack of electrodes comprises a series of electrolytic cells in which each electrode acts as an anode on one side and a cathode on the other side. In such applications, the electrodes are designated as bipolar electrodes because they have different polarities on their two sides.

[0005] In recent years, the traditional alkaline electrolysis cell configuration has been replaced by the so-called zero-gap configuration. In the zero-gap configuration, the cell design works by pressing two porous electrodes on either side of a proton-conducting membrane. This allows for a gap between the two electrodes equal to the thickness of the membrane, which is typically 0.5 mm or even thinner, rather than the 2-5 mm required for traditional gap configurations. The thinner gap reduces ohmic resistance, which is a source of losses in the electrolysis cell.

[0006] In a zero-gap configuration, the electrodes must have holes to allow hydrogen and oxygen bubbles to escape to the side of the electrode facing away from the membrane. In a bipolar electrode, this arrangement would result in undesirable mixing of hydrogen and oxygen in the chamber established between the cathode and anode. Therefore, a separator plate is inserted between the anode of one cell and the cathode of the adjacent cell to prevent mixing of the gases produced by the electrolysis process. Thus, a bipolar electrode for a zero-gap electrolysis stack generally consists of three metal plates: a perforated anode, a solid separator plate, and a perforated cathode. The distances from the anode to the separator plate and from the separator plate to the cathode must be wide enough to allow circulation of the electrolyte without excessive pressure loss and, most importantly, to allow the hydrogen and oxygen bubbles to escape without excessive blockage. Otherwise, back pressure would be applied to the bubbles.

[0007] Examples of electrolytic cell arrangements are shown in US Patent Application Publication Nos. 2021 / 0234237 and 2021 / 0202963, where opposing separator plates are welded together.

[0008] U.S. Patent Application Publication No. 2021 / 0234237 describes a separator plate for an electrochemical system and discloses a bipolar separator made of two interlocking corrugated metal plates, whereby corrugations form cooling channels between the two metal plates and gas transport channels on the outside of the two metal plates. The bipolar plates are stacked on either side of a membrane electrode assembly (MEA) and are sandwiched between, for example, typically nonwoven gas diffusion layers. On the outside, the corrugations contact the gas diffusion layers. Generally, gas diffusion layers between the membrane and the electrodes are often used to ensure proper flow and diffusion of gas away from the membrane.

[0009] However, the more layers an electrolyzer comprises, the greater the risk that components will move relative to one another, reducing the efficiency or even causing malfunction of the electrolyzer. Thus, there is an importance in providing an electrolyzer system with high rigidity and robustness.

[0010] Electrolyzer systems are highly diverse. In some systems, the membrane is provided as part of a membrane electrode assembly, in some cases a flexible membrane electrode assembly, while others have a metal mesh or grid pressing the membrane or are provided with flexible gas diffusion layers. Some have a single bipolar plate between stacked electrolyzer modules, while others have double-walled electrolyzers. Each principle represents an attempt to optimize hydrogen production. The most efficient configuration has not yet been determined, and for those skilled in the art, there is no specific starting point for an optimized system, nor direction on how to optimize in the best way. Often, improvements are found through multiple attempts and trials, where various features are configured to find a more optimized system.

[0011] European Patent No. 0159138 discloses an electrolysis system for producing chlorine, in which a single corrugated bipolar electrode plate is sandwiched between membranes. Corrugations on both sides provide horizontal minor channels between vertical major channels, and electrolyte flows from the bottom upward through one major channel, then through the minor channel to the adjacent major channel, then upward through the adjacent channel, and exits the chamber at the top. This is said to result in rapid gas transport.

[0012] U.S. Pat. No. 5,114,547 offsets the system in EP 0,159,138 and discloses an electrolysis system for producing chlorine, in which embossed corrugations in monopolar or bipolar metal electrode plates are formed in a herringbone pattern, with minor channels extending at an angle from a vertical major channel. This is said to result in improved electrolyte flow and circulation and more rapid transport of formed gases. Optionally, the vertical major channel is provided with openings for electrolyte circulation. A herringbone pattern in a separator plate, formed by embossing, for example, is also disclosed as one of several alternatives in U.S. Patent Application Publication No. 2007 / 0105000.

[0013] On the one hand, some systems take advantage of the circulation of electrolyte leaving the top with gas entrained, with subsequent separation of the gas from the electrolyte, and on the other hand, prevent such transport of electrolyte entrained with gas in order to reduce the risk of crossover currents.

[0014] WO 2022 / 156869 discloses an electrolysis system with single or double plates between hydrogen-producing electrolysis chambers, each chamber containing a membrane sandwiched between perforated electrode plates that abut the membrane. These perforations allow gas to pass through the perforations from the membrane into the anode and cathode chambers on either side of the membrane. When two bipolar plates are used, a coolant is introduced into the volume between the plates. These chambers are not completely filled with electrolyte, but instead have a space at the top for gas accumulation and separation from the liquid, where the gas leaves the chamber through an opening above the liquid level. Separating the gas from the electrolyte inside the chambers means that only gas is transported out of the electrolysis cell stack, thereby reducing the risk of shunt currents through the conductive electrolyte.

[0015] These examples illustrate only a few attempts in different directions for electrolyzer improvement. However, room for improvement exists for optimization. In particular, it would be desirable to provide improved hydrogen production electrolyzers that are simple to construct, yet robust, reliable, and effective. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] US Patent Application Publication No. 2021 / 0234237 [Patent Document 2] U.S. Patent Application Publication No. 2021 / 0202963 [Patent Document 3] European Patent No. 0159138 [Patent Document 4] U.S. Patent No. 5,114,547 [Patent Document 5] US Patent Application Publication No. 2007 / 0105000 [Patent Document 6] International Publication No. 2022 / 156869 Summary of the Invention [Problem to be solved by the invention]

[0017] It is therefore an object of the present invention to provide improvements in the art. In particular, it is an object to provide an electrolyzer with a high degree of operational reliability. It is a further object to provide an electrolyzer with a simple construction of a plurality of separator / electrode modules sandwiching a membrane therebetween, which modules are rigid and suitable for mass production at relatively low cost, and which allow good temperature control of the electrolyzer. These objects, and other advantages, are realized by means of an alkaline electrolyzer for producing hydrogen gas, as described below and in the claims. [Means for solving the problem]

[0018] The electrolyzer comprises a stack of bipolar electrodes, each of which has an ion transport membrane sandwiched between them. Each bipolar electrode comprises two metal plates, specifically an anode metal plate and a cathode metal plate, attached back-to-back to each other, e.g., by welding, to form a coolant compartment therebetween. This construction provides high rigidity to the bipolar electrodes.

[0019] The bipolar electrode has an anode surface and an opposing cathode surface, each of which abuts one of the membranes. The metal plate is embossed with at least a first vertical major channel and a plurality of minor channels in a herringbone pattern for transporting oxygen and hydrogen gases. The embossed herringbone-pattern minor channels are provided on both sides of the metal plate so as to also provide herringbone-pattern coolant channels inside the coolant compartment. For example, the herringbone-pattern minor channels of the anode and cathode plates facing each other between the membranes face each other at different angles, such that the minor channels embossed in the anode metal plate intersect with the coolant channels embossed in the cathode metal plate. The herringbone pattern promotes turbulence in the coolant compartment to efficiently cool the electrolyte on the opposite side of the plate relative to the coolant compartment.

[0020] The main purpose of an electrolyzer is the production of hydrogen gas, which is collected for later use, for example in a fuel cell or industrial application. However, due to the separation of water in the electrolyzer when power is applied, oxygen is also produced, which can also be collected for later use.

[0021] The two metal plates are electrically conductive and form the anode and cathode plates. The bipolar electrodes abut the two membranes, respectively, forming the anode and cathode chambers with their respective ion transport membranes. The electrode chambers contain an alkaline electrolyte, e.g., a NaOH- or KOH-based electrolyte.

[0022] In the above arrangement, where the metal plates abut the membranes, the surfaces of the two metal plates serve as the electrolytically active portion of the electrolytic cell. Alternatively, an additional electrode layer may be placed on top of one or both of the metal plate surfaces, resting on the embossments of the metal plates and partially or completely abutting the respective membranes, thereby partially or completely serving as the electrolytically active portion of the electrolytic cell.

[0023] Typically, the embossed pattern includes multiple, generally vertically oriented, major channels, rather than just one major channel. Extending from each major channel in a herringbone pattern are embossed minor channels that are in fluid communication with the major channel. Oxygen and hydrogen gases are transported from the membrane through the slanted minor channels into the major channel, and gases from the anode and cathode chambers are transported upward through the major channel for release through corresponding gas outlets in the electrolytic cell.

[0024] A particular advantage of this arrangement, realized by connecting multiple major channels to the upper portion of the electrode chamber above the minor channels, is that sufficient circulation of electrolyte is established within the volume bounded by the electrode surface on one side of the electrode chamber and the membrane on the other side of the electrode chamber.

[0025] For example, each electrode metal plate may have a first vertical major channel to which a plurality of minor channels extend at an upward angle, thereby forming a first herringbone pattern with the first major channel. Additionally, each electrode metal plate may have a second vertical major channel to which minor channels extend at a downward angle, thereby forming a second herringbone pattern with the second major channel. The second herringbone pattern is offset relative to the first herringbone pattern. The minor channels also communicate with the second major channel, but because of their upward angle toward the first major channel, gas bubbles flow only toward the first major channel.

[0026] Advantageously, the first and second major channels are connected above the minor channels at the upper portions of the respective electrode chambers and below the minor channels at the lower portions of the respective electrode chambers, thereby creating an improved circulation of electrolyte from the lower portion upward through the first major channel to the upper portion above the minor channels, then downward through the second major channel to the second major channel before returning to the lower portion. Generally, there will be a plurality of major channels of a first type with upward flow and a plurality of major channels of a second type with downward flow, as already outlined above.

[0027] More specifically, gas bubbles formed during the electrolysis process flow through the upwardly sloping minor channels formed by the depressions in the embossed herringbone pattern of the electrode and into the first major channel in an upward path. Here, they form an upward flow of gas bubbles. The gas bubbles move slowly along with the electrolyte, causing an upward flow of electrolyte. In the upper portion of the electrode chamber, the electrolyte flows primarily horizontally to the adjacent second major channels and then downward. As a result, a downward flow of electrolyte occurs in those adjacent second major channels. At the bottom of the electrode, the electrolyte flows horizontally back to the adjacent first major channel, where the minor channels extend in an upwardly sloping path formed by the depressions in the embossed herringbone pattern of the electrode, where they return to the upward flow.

[0028] The electrodes are cooled on the opposite side of their active surfaces by circulation of coolant in a coolant chamber between the two electrode metal plates that form the bipolar electrode. Even if heat transfer from the coolant to the electrodes is promoted by an embossed herringbone pattern on the backside of the electrodes, a perfectly uniformly cooled electrode surface is not achievable. Nevertheless, due to the bubble circulation, as mentioned above, the electrolyte volume comes into contact with a large area of ​​the electrodes for a relatively short period of time. As a result, the entire volume of electrolyte in the electrolytic cell reaches a more uniform temperature than would be the case without such bubble circulation.

[0029] In a practical embodiment, the gas outlets connect the anode chamber to an oxygen transport conduit and the cathode chamber to a hydrogen transport conduit. Optionally, the oxygen transport conduit and / or the hydrogen transport conduit extend along the stack through openings in the anode and cathode plates. For example, seals are provided between the bipolar electrodes, whereby openings in the stacked bipolar plates, optionally in addition to openings in the corresponding membrane-holding frames, form longitudinal gas conduits through and along the stack.

[0030] Another important advantage is obtained by the present invention as will be explained below, where a comparison is made between conventional electrolytic cells and the present invention.

[0031] In conventional configurations of electrolyzer stacks, relatively uniform cooling of the electrolyzer stack can only be achieved through significant circulation of the electrolyte and a corresponding high pumping rate by an external pump. This configuration requires a sufficient flow rate, and the corresponding electrolyte flow paths through the electrode stack must be large to keep the pressure losses in the flow paths at manageable levels. When filled with a highly conductive electrolyte, these flow paths act as shunts, connecting all the cells in the stack, including those at the end of the stack with the full potential difference. The shunt currents flowing through the flow paths can reach levels of several percent of the total current in the stack. Because the shunt currents do not contribute to electrolysis at the desired point in the stack, they incur losses in the same proportion as their ratio to the total current.

[0032] In contrast to these conventional arrangements, the electrolytic cell stack arrangement according to the present invention provides for internal circulation of the electrolyte in the electrolytic cell through the above-mentioned bubble circulation. As a result, no pumped circulation of the electrolyte is required. All that is required is a continuous replenishment of the electrolyte. However, in the present invention, the electrolyte flow required for this is only a fraction of the electrolyte flow required for cooling by conventional methods. As a result, the electrolyte flow path through the electrode stack can have a smaller cross section, while keeping the pressure loss in the flow path at a manageable level. Since the shunting is proportional to the cross section of the flow path, the effect of the smaller cross section of the flow path is that the shunting losses are significantly reduced compared to conventional arrangements, which in turn leads to a corresponding reduction in losses.

[0033] In a practical embodiment, to provide gas tightness, the anode and cathode plates may be welded together back to back, typically along a closed curve, for example by perimeter welding of the edges, and advantageously around the inlets and outlets and conduits. Alternatively, two metal plates are pressed against each other, typically along or near the periphery and around the conduits, with the seal achieved by adhesive or a sealing gasket.

[0034] The cross-section of the embossed pattern forming the channels is optionally smoothly alternating, e.g., approximately sinusoidal. The approximately sinusoidal cross-section reduces the contact area between the membrane and the anode and cathode surfaces. Despite deformation of the membrane and embossed plate, the contact area is minimized to only a few percent of the membrane's surface area.

[0035] 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 it can also be made to have a large portion of the anode and cathode surfaces in close proximity, if desired.

[0036] For example, the minor channels have depths ranging from 0.3 to 3 mm, with the regions between the minor channels abutting the membrane.

[0037] In some advantageous embodiments, the minor channel has a length of about 50-200 mm and a width of about 2-10 mm. For example, the length may be 10-50 times the width.

[0038] In some embodiments, supplemental electrodes may be placed on the anode and / or cathode, and such supplemental electrodes may optionally be coated with a catalytic material.

[0039] In some embodiments, the coolant channels in the herringbone patterned anode and cathode plates face each other at various angles, such that at least some of the embossed minor gas flow channels in the anode intersect with at least some of the embossed minor gas flow channels in the cathode. It has been found that the intersection of minor channels on opposing plate faces in the coolant compartment results in improved cooling of the electrolyte compared to channel patterns that are mirror images of each other in the coolant compartment.

[0040] The minor channels in the coolant compartment also include grooves and ridges between the grooves. The ridges of the minor channels advantageously contact each other at their intersections inside the coolant compartment, which not only improves turbulence inside the coolant compartment but also ensures the rigidity of the bipolar plates and the many electrical contacts. The rigidity of the bipolar plates also provides a firm holding position for the membranes between the bipolar plates in the stack.

[0041] By suitable selection of the minor channel angle, a large number of such contact points will be established, which will result in good current transfer from the anode to the cathode, thereby minimizing ohmic losses caused by the need for lateral current flow in the electrode plates.

[0042] In another advantageous embodiment, the electrolyte is provided in the anode chamber and / or the cathode chamber up to a level below the corresponding gas outlet for separating the gas from the electrolyte, preventing the electrolyte from flowing through the gas outlet. In this case, if a circulation outlet is provided for the electrolyte, it is below the electrolyte level in the electrolyte chamber, and not at the top.

[0043] Yet another advantage is realized when the coolant compartment has a coolant inlet at the top and, optionally, a coolant outlet at the bottom, and when the coolant compartment is arranged to cool the gas above the electrolyte and condense liquid, particularly water, from the gas before it leaves the anode and cathode chambers through the gas outlet, which further reduces the risk of cross-currents and results in dry gas.

[0044] For the supply of water to the anode and cathode chambers, each chamber may include one or more water inlets to replenish consumed water. Alternatively or additionally, each chamber may include one or more electrolyte inlets if water consumed in the electrolysis process is added to the electrolyte outside the electrolysis cell.

[0045] Typical dimensions are given below: Plate thickness: 0.3~1.0mm Board length / width: 0.3~3m Depth of embossed minor channel herringbone pattern: 0.3-3mm

[0046] Polymer membranes are commonly used as separators for alkaline water electrolysis. For example, they comprise an open-mesh polyphenylene sulfide fabric, which is symmetrically coated with a mixture of polymer and zirconium oxide. The latter is advantageous for systems where the electrolyte is used at high temperatures, e.g., in the range of 50-90°C.

[0047] The invention will now be explained in more detail with reference to the drawings. [Brief explanation of the drawings]

[0048] [Figure 1] 1 is a schematic diagram of an electrolyzer stack. [Figure 2A] FIG. 1 shows a stacked electrode assembly. [Figure 2B] FIG. 2B shows an enlarged portion of FIG. 2A. [Figure 3]FIG. 1 shows the electrolyte levels in the anode and cathode volumes and the various conduits. [Figure 4] FIG. 1 is a diagram showing the circulation of an electrolyte. [Figure 5A] FIG. 1 shows a sinusoidal cross section of a metal plate. [Figure 5B] FIG. 1 shows a sinusoidal cross section of a metal plate abutting a membrane. [Figure 5C] FIG. 1 is a diagram showing a triangular cross section of a metal plate. [Figure 5D] FIG. 1 shows a triangular cross section of a metal plate with rounded edges. [Figure 6A] FIG. 1 is a cross-sectional view of a cathode plate in combination with a perforated screen. [Figure 6B] FIG. 1 is a cross-sectional view of a cathode plate combined with a metal net. DETAILED DESCRIPTION OF THE INVENTION

[0049] FIG. 1 is a schematic diagram of the principle of a stacked electrolytic cell 1 with an ion transport membrane 2 sandwiched between bipolar electrodes 9 .

[0050] 2A shows some details. The membrane 2 is supported by a first frame 4A and a second frame 4B. The first frame 4A, together with the membrane 2, forms one side of the anode chamber 5A, and the anode plate 9A forms the opposite side of the anode chamber 5A. The second frame 4B, together with the membrane 2, forms one side of the cathode chamber 5B, and the cathode plate 9B forms the opposite side of the cathode chamber 5B. Both chambers 5A, 5B contain the electrolyte necessary for the electrolysis reaction, in which water is split into oxygen and hydrogen, which are extracted from the anode chamber 5A and the cathode chamber 5B, respectively.

[0051] To replenish water consumed during the reaction, the frames 4A, 4B have water inlets 6 through which water is supplied via water supply conduits 7. To transfer oxygen gas and hydrogen gas from the respective chambers 5A, 5B, the frames 4A, 4B have corresponding gas outlets 8A, 8B on both sides of the membrane 2 and in the upper parts of the frames 4A, 4B. The gas outlets 8A and 8B lead to corresponding oxygen gas transport conduits 13A and hydrogen gas transport conduits 13B.

[0052] In practice, the anode and cathode plates 9A and 9B are assembled back-to-back into a bipolar electrode 9, with a liquid-tight coolant compartment in the volume between the anode and cathode plates 9A and 9B for cooling the bipolar electrode 9 and thereby the electrolyte in the electrode chambers 5A, 5B. Typically, the anode and cathode plates 9A and 9B are provided as stainless steel plates, welded together back-to-back along, for example, the edges of the coolant compartment. Coolant conduits, not shown in FIG. 2A , are provided at the top and bottom to allow coolant to flow through the coolant compartment between the plates 9A and 9B.

[0053] Figure 2B is an enlarged portion of Figure 2A. Figure 2B shows that the anode plate 9A and cathode plate 9B, facing the membrane, are provided with first and second major channels 10A and 10B embossed into the plates 9A and 9B and extending across the membrane 2, and with angled minor channels 11A extending upward toward the first major channel 10A and downward toward the second major channel 10B in a herringbone pattern. The herringbone pattern, in which the minor channels 11A extend diagonally upward toward the first vertical major channel 10A, allows gas bubbles to flow from the angled minor channels 11A into the first jar channel 10A, improving the upward flow and circulation of the electrolyte and more rapidly transferring any formed gas into the combined upward movement of the gas and electrolyte in the first major channel 10A.

[0054] The herringbone pattern of minor channels 11A is provided by embossing an alternating pattern into the metal sheets of the anode plate 9A and the cathode plate 9B, so that not only do slanted minor channels 11A appear on the membrane-facing sides of the anode plate 9A and the cathode plate 9B, but slanted minor channels are also correspondingly provided on the sides toward the coolant compartment between the plates 9A, 9B, which function as slanted coolant channels 11B.

[0055] Coolant flow and circulation is improved when the coolant channels 10B of the anode plate 9A are reversed relative to the coolant channels 10B of the cathode plate 9B inside the coolant compartment, so that the upwardly inclined coolant channels 11B on the backside of the anode plate 9A intersect with the downwardly inclined coolant channels 11B on the backside of the cathode plate 9B, and vice versa. This intersection of the embossed coolant channels 11B in the coolant compartment improves turbulence of the coolant, while allowing it to flow through the coolant compartment between the anode plate 9A and the cathode plate 9B. This is an improvement over the system disclosed in the aforementioned U.S. Pat. No. 5,114,547.

[0056] For example, two embossed patterns on opposite sides of the cooling channels 11B in the coolant compartment are advantageously pressed together, so that the ridges of the embossed patterns of the cooling channels 11B in the coolant compartment abut one another. The herringbone pattern improves the flow and circulation of the coolant, as well as the improved flow and circulation of the electrolyte. Additionally, the abutting ridges provide contact points for improved electrical conductivity.

[0057] 2A, the electrolyte liquid level 12 is below the level of the respective gas outlets 8A, 8B so that the electrolyte in the anode chamber 5A and the cathode chamber 5B does not exit the respective chambers 5A, 5B through the gas outlets 13A, 13B, as shown in FIG. 3. In particular, FIG. 3 illustrates the arrangement of the transport conduits, i.e., oxygen gas transport conduit 13A, hydrogen gas transport conduit 13B, coolant inlet conduit 15, coolant outlet conduit 16, water supply conduit 7, and electrolyte supply conduit 14. The cathode chamber 5B, and similarly the anode chamber 5A, are delimited by gaskets 24 that surround the active area of ​​the membrane 2. The electrolyte 17 extends to a top level 18, which is below the top 25 of each chamber 5A, 5B, and therefore below the gas outlets 8A, 8B, also referring to FIG. 2A, and below the gas transport conduits 13A, 13B, as shown in FIG. 3. Oxygen gas and hydrogen gas are thereby separated from the electrolyte 17 before entering the respective gas transport conduits 13A, 13B. This reduces the risk of crossover currents. Specifically, referring to FIG. 2A, only hydrogen gas flows through the hydrogen gas outlet 8B and into the hydrogen gas transport conduit 13B, not the electrolyte or water.

[0058] Another advantage of the present system is realized by the coolant flow from the coolant inlet conduit 15 at the top of the cooling chamber of the bipolar double-sheet electrode plate 9 to the coolant outlet conduit 16 at the bottom. As the coolant enters at the top, the greatest cooling effect is at the top. This means that the gas in the electrode chambers 5A, 5B is most effectively cooled at the top before leaving the electrode chambers 5A, 5B. Effective cooling results in the condensation of water from the gas, thereby drying the gas exiting through the gas outlets 8A, 8B, thereby reducing the risk of further crossover currents. This is a significant improvement compared to the system disclosed in WO 2022 / 156869, mentioned above.

[0059] Figure 4 shows the principle of electrolyte flow in the cathode chamber 5B by arrows 12A and 12B. The flow of gas bubbles is directed upward in the first major channel 10A, as indicated by the upward-pointing arrow 12A, toward which the minor channel 11A is inclined upward. The moving gas bubbles also draw in electrolyte 17, which causes circulation of the electrolyte 17 upward in the first major channel 10A and downward in the adjacent second major channel 10B, as indicated by the downward-pointing arrow 12B. The minor channel 11A extends at a downward incline toward the second major channel 10B.

[0060] The herringbone pattern of minor channels 11A in the electrode chambers 5A, 5B and the herringbone pattern of coolant channels 11B in the coolant compartment are provided by embossing into the metal sheets of the anode plate 9A and cathode plate 9B.

[0061] The cross section of the embossed pattern forming the minor channels 11A and the coolant channels 11B may be, for example, smoothly alternating sinusoidal. Alternatively, the cross section of the embossed pattern forming the minor channels 11A and the coolant channels 11B is polygonal. The polygonal cross section optionally has a similarly small contact area between the membrane 2 and the anode and cathode faces, but it can also be made to closely contact a large portion of the anode and cathode faces, if desired.

[0062] 5A, 5B, 5C, and 5D show examples of possible embossings in the cathode plate 9B in cross-section along a line perpendicular to the minor channels 11A formed by a herringbone pattern along the membrane 2. In FIG. 5A, the cross-section follows a sinusoidal curve along a line transverse to the minor channels 11A. Curved ridges 19 are provided adjacent to the membrane 2. Alternatively, as shown in FIG. 5B, where the same reference numerals as in FIG. 5A are valid, the embossed ridges 19 rest against the membrane 2. Due to the pressing force, the ridges 19 press slightly into the membrane 2 for good electrical conductivity and optimized electric field strength, while the gas generated at the ridges 19 flows into the minor channels 11A and from there into the first major channel 10A. These are embossed depressions by which gas is transported upward to the gas outlets 8A, 8B and into the respective gas channels 13A, 13B as described in relation to FIGS. 2A and 3.

[0063] Other cross-sectionally alternating shapes are possible, such as alternating triangular curves with sharp edges, as shown in FIG. 5C, or with rounded edges, as shown in FIG. 5D.

[0064] Regardless of the deformation of the membrane 2 and the embossed plate 9B, the contact area is minimized, being only a few percent of the surface area of ​​the active membrane, because the ridges 19 rest against the membrane 2, and possibly even against the pressed portion of the membrane 2.

[0065] 6A shows an arrangement in which the electrodes comprise a corrugated metal plate 9B and a perforated supplemental electrode layer 21, such as a thin perforated conductive sheet, placed between the metal plate 9B and the membrane 2 and resting on the embossed portion of the metal plate 9B, as described above. Optionally, the supplemental electrode layer may be a metallic wire net with first and second wires 22A and 22B crossing each other, or any other perforated conductive material advantageously having catalytic properties.

Claims

1. An electrolytic cell (1) for producing hydrogen gas, the electrolytic cell (1) comprising a stack of bipolar electrodes (9), each bipolar electrode (9) sandwiching an ion transport membrane (2) between each pair of the bipolar electrodes (9); Each of said bipolar electrodes (9) comprises an electrically conductive anode metal plate (9A) and an electrically conductive cathode metal plate (9B) mounted back to back to each other and forming a coolant compartment therebetween; The bipolar electrode (9) abuts against a membrane (2) on both sides of the bipolar electrode (9), and the metal plates (9A, 9B) respectively form an anode chamber (5A) and a cathode chamber (5B) together with the membrane (2), and the anode chamber and the cathode chamber (5A, 5B) contain an electrolyte (17); The metal plates (9A, 9B) are embossed with a first vertical major channel (10A) and a plurality of minor channels (11A), the minor channels (11A) sloping upwardly toward the first major channel (10A) to form a herringbone pattern with the first major channel (10A); the minor channel (11A) communicates with the first major channel (10A) to transport oxygen gas and hydrogen gas, respectively, from the membrane (2) through the upwardly inclined minor channel (11A) into the first major channel (10) and further up the first major channel (10A), and release the gases from the anode and cathode chambers (5A, 5B) through corresponding gas outlets (8A, 8B) provided in the electrolytic cell (1); the embossed herringbone pattern is provided on both sides of each of the metal plates (9A, 9B) so as to also provide coolant channels (11B) in a herringbone pattern inside the coolant compartment; Electrolytic cell (1).

2. 2. The electrolytic cell according to claim 1, wherein the minor channels (11A) of the herringbone pattern in the anode plate (9A) and the cathode plate (9B) facing each other between the membranes (2) face each other at different angles, whereby the minor channels (11A) embossed in the anode metal plate (9A) intersect with the coolant channels (11A) embossed in the cathode metal plate (9B).

3. 3. An electrolytic cell according to claim 2, wherein the herringbone pattern of the minor channels (11A) is arranged such that the upwardly inclined minor channels (11A) in the anode metal plate (9A) intersect with the downwardly inclined minor channels (11A) in the cathode metal plate (9B), or vice versa.

4. 4. An electrolytic cell according to claim 2 or 3, wherein the herringbone patterned coolant channels (11B) of the two metal plates (9A, 9B) inside the coolant compartment face each other at different angles, whereby the embossed coolant channels (11B) of the anode metal plate (9A) intersect with the embossed coolant channels (11B) of the cathode metal plate (9B).

5. Each of said metal plates (9A, 9B) is provided with a second vertical major channel (10B) towards which said minor channels (11A) extend at an inclination downwards to form a herringbone pattern in said second major channel (10B); The minor channel (11A) communicates with the second major channel (10B); the first major channel (10A) and the second major channel (10B) are connected above the minor channel (11A) in the upper part (20A) of each of the electrode chambers (5A, 5B) and below the minor channel (11A) in the lower part (20B) of each of the electrode chambers (5A, 5B), improving the circulation of electrolyte (17) from the bottom (20B) upward through the first major channel (10A) to the upper part of the minor channel (11A), from the first major channel (10A) to the second major channel (10B), and then downward through the second major channel (10B) to the lower part (20B); Electrolytic cell according to any one of claims 1 to 4.

6. 6. An electrolytic cell according to any one of claims 1 to 5, wherein the bipolar electrode comprises a complementary porous and electrically conductive electrode layer (21, 22A, 22B) on the anode metal plate (9A) or the cathode metal plate (9B), or both, abutting the ion-conducting membrane (2).

7. 7. The electrolytic cell according to any one of claims 1 to 6, wherein an electrolyte (17) is provided to the anode and cathode chambers (5A, 5B) to a level (18) below the gas outlets (8A, 8B) to separate the gas from the electrolyte (17) and to prevent the electrolyte (17) from flowing through the gas outlets (8A, 8B).

8. 8. The electrolytic cell according to claim 7, wherein the coolant compartment has a coolant supply from a coolant conduit (15) at the top of the coolant chamber arranged to cool the gas in the electrode chamber (5) above the electrolyte (17), causing condensation of the liquid (17) before the gas leaves the electrode chamber (5A, 5B) through the gas outlets (8A, 8B).

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

10. 10. An electrolytic cell according to any one of claims 1 to 9, wherein the minor channel (11A) has a length of about 50 to 200 mm and a width of about 2 to 10 mm, the ratio of said width to said length being about 10 to 50.

11. 11. An electrolytic cell according to any one of claims 1 to 10, wherein the oxygen gas outlet (8A) connects the anode chamber (5A) to the oxygen gas transport conduit (13A) and the hydrogen gas outlet (8B) connects the cathode chamber (5B) to the hydrogen gas transport conduit (13B), the oxygen gas transport conduit (13A) and the hydrogen gas transport conduit (13B) extending along the stack through openings in the anode plate (9A) and the cathode plate (9B).

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