Electrolyzer with minimised shunt-currents and use thereof

Abstract

An electrolyzer stack in which gas passages (16C, 16D) and thin and long shunt-current reducing liquid passages (16A, 16B) are provided inside a gasket that is a combination of a first and a second gasket part (12A, 12B) for ease of assembly.

Description

[0001] Electrolyzer with minimised shunt-currents and use thereof

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to an electrolyser, especially an alkaline electrolyser, and its use for production of hydrogen gas. In particular, it is configured for a combination of minimization of shunt-currents and electrolyte flow control.

[0004] BACKGROUND OF THE INVENTION

[0005] In stacks of electrochemical cells, flow of electrolyte through the electrolytic chambers is provided through liquid passages, typically with liquid flow either from one side to an opposite side of the stack or between top and bottom of the chambers. The liquid passages from each cell merge into liquid conduits, typically called manifolds, either at the top or, alternatively, at both top and bottom.

[0006] When electrolyte flows in the liquid conduits or manifolds of the electrolyzer stack, the flow will be associated with a certain pressure drop through the liquid conduits. If this pressure drop is large compared to the pressure drop related to the flow of electrolyte through the electrolytic chambers, the rate of flow of electrolyte through a specific electrolytic chamber will depend on the relative position along the liquid manifolds, extending along the stack. An electrolytic chamber positioned close to the inlet end of the liquid manifold, for example at an end of the stack, will experience a higher inlet pressure from the electrolyte in the manifold than will be the case of an electrolytic chamber positioned at a greater distance from the inlet end of the liquid manifold, for example at the opposite end of the stack. This difference in inlet pressure will cause uneven flow of electrolyte in the electrolytic chambers, with the electrolytic chambers positioned closer to the inlet end of the liquid manifold experiencing a higher electrolyte flow rate than electrolytic chambers positioned further from inlet end of the liquid manifold. Such uneven flow of the electrolyte can lead to undesirable differences in electrochemical efficiency and / or cooling efficiency. For this reason, it is customary to dimension the liquid manifolds with a relatively large cross-sectional area so as to keep the pressure drop from one end of the liquid manifold to the other, for example from one end of the stack to the opposite end, to a reasonable level, minimizing the uneven flow distribution in the electrolytic chambers.

[0007] While such relatively large cross-sectional area of the liquid manifolds has the advantage of minimizing the pressure drop through the liquid manifolds, thereby minimizing the uneven flow distribution in the electrolytic chambers, it has the associated disadvantage of increasing the so-called shunt losses through the liquid manifolds.

[0008] Since the electrolyte needs to be electrically conductive, currents will flow from one end of the electrode stack to the other in the liquid manifolds. The currents flowing through the liquid manifolds are typically designated shunt currents. This term stems from the manifolds appearing as shunts in an electrical diagram of the electrolyser stack.

[0009] Shunt currents are undesirable because the current flowing through the shunts does not contribute to hydrogen generation but is delivering waste heat only.

[0010] Since the shunt currents increase proportionally with the cross-sectional area of the liquid manifolds, and since the liquid manifolds need to have a relatively large cross- sectional area so as to keep the pressure drop from one end of the liquid manifold to the other to a reasonable level in order to minimize the uneven flow distribution in the electrolytic chambers, it follows that it is difficult to minimize the shunt currents.

[0011] For this reason, the dimensions of inflow channels to the electrolyzer cells has been the focus of considerable work.

[0012] A zinc-bromine battery with two manifolds for supply and drain of electrolyte and with a supply / drain passages from the respective manifolds to the bottom and to the top of the battery cell is disclosed in Japanese patent application JP7014617A2, issued as patent JP3198729B2. Examples are given with both supply manifold and drain manifold at the top or, alternatively, one manifold at the top and one at the bottom, without special preference with respect to one or the other configuration. In stacks of electrochemical cells, conductivity of the liquid electrolyte and the electrical field potential gradient along the stack, typically, results in shunt-currents flowing between the cells through the conductive liquid electrolyte, which reduces the capacity of the stack and decreases efficiency of the overall system.

[0013] As discussed in WO2022 / 269602, bubbles in passages reduce or even prevent such shunt-currents. In liquid passages, shunt-currents can be reduced by increasing the electrical resistance in the electrolyte pathways by increasing the length of the fluid path and reducing the cross section.

[0014] A similar discussion is found in WO2015 / 082614 for redox-flow batteries, in which pairs of manifolds on opposite sides along the stack supply electrolyte through thin supply passages to the top and drain electrolyte through drain passages at the bottom. Whereas a chamber on an anode side of the separating ion conducting membrane communicates through the long and thin passages to liquid conduits at a first side of the stack, the chamber on the cathode side of the membrane communicates through similar long and thin passage to manifolds at an opposite side of the stack. Accordingly, the stack has pairs of manifolds symmetrically on either of the two opposite sides of the stack.

[0015] A similar configuration is found in WO2013 / 049933 for a redox-flow battery. In this disclosure, the meandering shunt-channels extends between insulating sealing frames.

[0016] The approach of supply conduit and drain conduit on opposite sides of the cell and symmetrically shaped pairs of shunt-channels for the anode and cathode chamber appears to be a generally used principle in redox-flow batteries.

[0017] However, long shunt-channels as well as opposite pairs of liquid manifolds take up a substantial portion of the available cross-sectional area of a stack. It would be desirable to find an improved configuration for optimising performance. Reduction of shunt-currents by narrow passages in an electrolyzer stack has been discussed in US2350669, disclosing a supply manifold along the lower part on one side of the stack.

[0018] W02014 / 040165 discloses an electrolyzer stack with two manifolds at the top, one for the cathode chambers and one for the anode chambers in the stack. Each of the two manifolds is connected to the bottom of the respective electrolytic chamber by a liquid supply passage and to the top of the respective chamber by a gas-liquid passage. Liquid received by the manifold from the gas-liquid passages is flowing from the same manifold down to the bottom of the connected chambers through the liquid supply passages. Although, simple, due to only having two manifolds, namely one for the anode chambers and one for the cathode chambers, this system is not optimum for controlled electrolyte circulation, for example for cleaning, replenishment, and pH adjustment of the electrolyte. Also, shunt-currents have not been discussed as a problem in this disclosure and no corresponding precautions taken.

[0019] It would be desirable to find improved configurations for electrolyzer stacks, especially for hydrogen production in an alkaline electrolyzer, taking into account configuration optimization with respect to performance, including dimensional considerations as well as reduction of shunt-currents.

[0020] Furthermore, it would be desirable to find configurations for electrolyzer stacks where the reduction of shunt-currents would be combined with arrangements for flow control, minimizing the risk of uneven flow distribution in the electrolyzer cells.

[0021] DESCRIPTION / SUMMARY OF THE INVENTION

[0022] It is an objective of the invention to provide an improvement in the art. In particular, it is an objective to provide an improved combination of the liquid passages in the individual electrolyzer cells and the manifolds connecting all the electrolyzer cells in the electrolyzer stack, where this combination serves to both reduce shunt-currents and at the same time minimize the risk of uneven flow distribution in the electrolyzer cells. It is a further objective to optimize space and volume occupied by liquid flow arrangements in electrolyzer stacks, in particular for hydrogen gas production in an alkaline electrolyzer. This objective and further advantages are achieved with an electrolyzer having a stack of electrolyzer cells as described below.

[0023] In short, an electrolyzer stack is provided in which thin and long shunt-current reducing liquid passages are provided inside a gasket. The gasket is a combination of a first and a second gasket part for ease of assembly. Details are described below. Optionally, manifolds are located only at an upper side of the stack above the electrolyzer cells for saving space.

[0024] The electrolyzer stack of the alkaline electrolyzer has multiple electrolyzer cells, each cell comprising two electrolytic chambers, namely an anode chamber and a cathode chamber, separated by an ion transporting separator, for example ion-conducting membrane or other type of ion conducting separator. The term ion-transporting separator is used for any applicable type of separator that allows ions to pass for the electrolysis. In alkaline electrolysis the ions are typically OH-ions or hydroxide ions, also called anions.

[0025] Each of the electrolytic chambers is delimited by the ion-transporting separator, for example membrane, and a metal sheet that is facing the ion-transporting separator, as well as a gasket that is surrounding the electrolytic chamber and seals the space between the ion-transporting separator and the metal sheet.

[0026] The stack comprises at least one electrolyte / water supply manifold for supply of water and / or electrolyte to the electrolyzer cells in the stack. The supply manifold is used to replenish water that is used during the electrolysis, such as hydrogen production. The consumed water can be supplied as a water-addition to the electrolyte in the electrolyzer cells or supplied as replenished electrolyte. For example, the electrolyte is supplied as part of a recirculation cycle, where the electrolyte is cooled and / or the electrolyte concentration adjusted. It is customary to use two supply manifolds, one of which is connected to the electrolytic chambers on the anode sides of the ion-transporting separators, for example membranes, in the stack and the other of which is connected to the electrolytic chambers on the cathode sides of the ion-transporting separators in the stack, but a single, shared supply manifold may also be implemented. The stack also comprises two gas manifolds, one of which is connected to the electrolytic chambers on the anode sides of the ion-transporting separators, for example membranes, in the stack and the other of which is connected to the electrolytic chambers on the cathode sides of the ion-transporting separators in the stack for drain of corresponding gases, such as oxygen and hydrogen, produced in the electrolytic chambers.

[0027] It is customary to arrange the supply manifolds at the lower side of the stack and the gas manifolds at the upper side of the stack, but optionally, in order to optimise space so that the electrolyte contact area of the ion-transporting separator, for example membrane, is as large as possible, all manifolds may be arranged only at an upper side of the stack above the electrolytic cells.

[0028] The terms above, below, or on the sides of the electrolytic cell are used in relation to an orientation of the stack when in operation.

[0029] For each electrolytic chamber, a liquid passage extends from the at least one electro- lyte / water supply manifold along a side of the electrolytic chamber to a lower part of the electrolytic chamber, for example to the bottom. The liquid passage extending from the top to the bottom of the electrolytic chamber is made thin relatively to its length so that shunt-currents are minimised. When having long and thin liquid passages, not only the shunt currents are minimised due to high electrical resistance in the liquid passages but also the pressure drop in the long and thin liquid passage can be made higher than the pressure drop in the manifolds along the stack. The latter is important, as the influence of the pressure drop along the stack is reduced, and the flow through the electrolytic cells more homogeneous than in the prior art.

[0030] A useful configuration of the stack when oriented for operation is a vertical cross section that is largely rectangular. Such shape is easy in production and assembly, and it has the advantage relative to the much more common circular cross-section of alkaline electrolyzers that little or no material is wasted. If the manifolds are provided at the top, rather than at both the top and the bottom, the configuration optimises available space for the active area of the electrolyzer cells. This advantage is greater if the rectangular shape of the electrolyzer stack is oriented with the long side in the vertical direction. A further advantage of having the manifolds at the top is that the liquid passages can be made relatively long when extending from the top to the bottom of the electrolyzer cells. For example, each liquid passage extends from the liquid manifold at the top downwards along a side of the electrolytic chamber and extends along a bottom of the electrolytic chamber and connects to an liquid inlet at a bottom of the electrolytic chamber where the electrolyte flows from the liquid passage into the electrolytic chamber.

[0031] According to the invention, a liquid passage is dimensioned so that the electrical resistance of the electrolyte contained in the liquid passage is as high as possible, limiting shunt currents, while at the same time providing a desired pressure drop that is significantly higher than the pressure drop in the manifold along the stack. In this way, shunt currents are kept to a minimum, while the flow through the electrolytic cells will be almost uniform.

[0032] Assuming a fairly constant cross-section of the liquid passage, the electrical resistance R of the electrolyte contained in the liquid passage is proportional by a constant value Cl to the length L of the liquid passage and inversely proportional to the square of the diameter D (or equivalent dimension for a non-circular cross-section) of the liquid passage:

[0033] R = Ci L / D2

[0034] At the same time, the pressure drop AP through the liquid passage is proportional by a constant value C2 to the length L of the liquid passage and inversely proportional to the fourth power of the diameter D (or equivalent dimension for a non-circular crosssection) of the liquid passage:

[0035] AP = C2L / D4

[0036] Accordingly, both the pressure drop AP and the electrical resistance R are linearly dependent on the length of the liquid passage, However, the electrical resistance R scales inversely with the cross section of the liquid passage, whereas the pressure drop AP depends inversely to the square of the cross section. As the electrical resistance R and the pressure drop are equally dependent on the length of the liquid passage, but the pressure drop is more sensitive to cross sectional adjustments of the liquid passage, it is possible to adjust the electrical resistance R for a specifically desired pressure drop AP.

[0037] Dimensioning a liquid passage for a desired pressure drop AP that is sufficient to provide reasonably uniform electrolyte flow through all the electrolytic cells of the electrolyzer stack, one may, for sake of illustration, consider two different lengths of the liquid passage, Li and L2, where

[0038] L2 = 2 Li

[0039] The ratio of the diameters Di and D2 associated with the two different lengths Li and L2 of the liquid passage that will lead to the same pressure drop AP can be determined from the above equations:

[0040] AP = C2 Li / Di4= C2 L2 / D24

[0041] « D24 / Di4= L2 / Li = 2

[0042] « D2 / DI = 2(1 / 4)

[0043] It further follows from the above equations that the ratio between the electrical resistances Ri and R2 associated with the two different lengths Li and L2 of the liquid passage will be

[0044] R2 / Ri = (Ci L2 / D22) / (Ci Li / Di2)

[0045] « R2 / Ri = (2 Li Di2) / ( Li (2(1 / 4)DI)2)

[0046] « R2 / Ri = 2 / (2(1 / 4))2

[0047] « R2 / RI = V2 ~1.4

[0048] It is seen that for the same pressure drop doubling the length L of the liquid passage from Li to L2 and at the same time reducing the diameter D from Di to D2 (or equivalent dimension for a non-circular cross-section) of the liquid passage inversely proportionally with the fourth root of the length of the liquid passage will lead to an increase of the electrical resistance R by a factor of about 1.4, if the pressure drop AP is the same for the two cases.

[0049] Hence, dimensioning a liquid passage for a desired pressure drop AP that is sufficient to provide reasonably uniform electrolyte flow through all the electrolytic cells of the electrolyzer stack, one has to maximise the length of liquid passage, reducing the diameter D (or equivalent dimension for a non-circular cross-section) of the liquid passage inversely proportionally with the fourth root of the length of the liquid passage. This is simple practical relationship for adjusting the electrical resistance R for a given pressure drop AP, or vice versa.

[0050] As shown above, a simple scaling dependence has been found which has practical applicability for designing electrolyser stacks having an advantageous high pressure drop for each cell in order approximately equalize flow through the electrolyzer cells along the stack, while providing a high electrical resistance to minimize shunt current.

[0051] In practice, advantageously, the liquid passage may have a length-to-diameter ratio in the range of 50-5000.

[0052] Furthermore, for each electrolytic chamber, a gas passage connects one of the two gas manifolds with a top of the corresponding one of the electrode chambers. As gas is a good insulator, shunt-currents are also minimised with respect to the gas channels, particularly, when the cross-section of the gas channel connecting the electrode chamber to the corresponding gas manifold is sufficiently small to ensure that gas bubbles can fill the cross-section, thereby almost eliminating current passage through the gas channel.

[0053] The gasket, for example elastomeric gasket, comprises a first gasket part and a second gasket parts, assembled face-to-face, sandwiching an edge portion of the ion-transporting separator, for example membrane, or an edge portion of a separator-electrode assembly, such as membrane-electrode-assembly, MEA, for sealing the electrolytic chambers against liquid loss or gas loss other than through the correspondingly dedicated passages. At least one of the liquid passages and the gas passages, but advantageously all of them, are provided in between the first and second gasket parts.

[0054] In some concrete embodiments, the first and second gasket parts, when assembled, form walls for all of, or for at least one of, the liquid passages and the gas passages in between the first and second gasket parts. In this case, the gasket material on the inner side of one or both of the gasket parts comprises a recess that forms a wall for the corresponding passage in between the first and second gasket parts.

[0055] In alternative embodiments, at least one of the liquid passages and the gas passages is provided as a fluid passage inside a pressure-resistant pipe that is embedded in a recess in between the first and second gasket parts, for example embedded in recesses in the gasket parts. A useful material for the pipes is polyether-ether-ketone, PEEK. By providing such pipes inside the gasket, deformation or even closing of the passages due to pressure is prevented.

[0056] In some embodiments, the metal sheet on its side facing the electrolytic chamber has raised surface portions that abut the ion-transporting separator or separator-electrode assembly, for example membrane or MEA.

[0057] Optionally, the raised portions form minor channels inside the electrolytic chamber. If these minor channels are upward inclined, the bubbles formed inside such minor channel drag electrolyte along, which in turn results in increased circulation of electrolyte inside the electrolytic chamber, equalizing electrolyte concentration and temperature inside the electrolytic chamber.

[0058] For example, the minor channels extend from a vertical channel in a herringbone configuration inclined upwards on opposite sides of the vertical channel. Such configuration has been found particularly useful for increased circulation of electrolyte by bubbles formed in the minor channels by electrolysis. The metal sheet may be embossed with several sets of minor channels, for example each set provided in a herringbone pattern, each set delimited by vertical major channels. Typically, such minor channel has a depth in the range of 1 to 10 mm when measured as a distance from the ridges to the lower most portion of the minor channel.

[0059] For example, the raised surface portions are provided by embossing in the metal sheet and formed on opposite sides of the metal sheet. This is a simple production method. As the embossed minor channels are on both sides of the metal plate, the effect of increased circulation can be obtained on both sides.

[0060] For example, one side of the metal sheet is facing an electrolytic chamber and the opposite side of the metal sheet is facing a neighbouring electrolytic chamber, in which case the metal sheet is used as a single-sheet bipolar plate. The two opposite sides of the metal cell-separation plate facing the respective one of two ion-transporting separators, for example membranes, form an anode chamber and a cathode chamber with the respective ion-transporting separator.

[0061] Notice, for differentiation and correct understanding of the terms, that the ion-transporting separator is located between the cooperating anode and cathode, whereas the cell-separation plate, which is not ion-transporting, is located between the cells, each of which having a pair of cooperating electrodes.

[0062] For example, the metal sheet is used as a cell-separation plate and electrolytically active bipolar electrode abutting the ion-transporting separator, for example membrane, with the raised portions. Such an arrangement represents a “mixed gap” configuration, comprising a zero-gap arrangement where the raised surface portions of the metal cellseparation plate abut the ion-transporting separator, and a gap arrangement where the lower surface portions of the metal cell-separation plate extends as a valley between the raised portions to a certain distance from the ion-transporting separator, for example in order to form the gas-transport channels.

[0063] As an alternative to the metal sheet being used as electrode, be it as a single sheet or as part of a multi-sheet arrangement, the raised portions are in electrical contact and pressing onto electrodes abutting the ion-transporting separator, for example membrane. For example, the electrodes are in the form of perforated plated or metal meshes, optionally as part of a separator-electrode assembly, optionally a membraneelectrode assembly MEA.

[0064] For example, a porous electrode, such as a metal mesh, is positioned against the metal sheet with the porous electrode resting on the raised surface portions of the metal sheet, which is functioning as cell-separation plate. In this embodiment, a zero-gap arrangement is established by the porous electrode across the surface of the ion-transporting separator, for example membrane, and the produced gas is able to flow from the ion-transporting separator, through the pores of the porous electrode, and into the minor channels of the metal sheet.

[0065] Optionally, the metal sheet is part of a double-sheet bipolar plate with a coolant chamber in between. The minor channels formed by embossing enhance circulation and temperature equalization also in the coolant chamber on the opposite side of the sheet relatively to the electrolytic chamber.

[0066] The electrode chambers contain electrolyte, for example alkaline electrolyte, such as a NaOH or KOH based electrolyte.

[0067] Optionally, the metal sheet is manufactured from stainless steel or nickel and may be provided with surface coatings.

[0068] As an option, the first and second gasket parts are manufactured from an elastomeric material such as EPDM or Viton. However, other types of soft and hard gasket materials are also available, and selection of the preferred material will depend on a number of factors, such as pressure, oxygen saturation level, and temperature.

[0069] For example, especially for alkaline electrolysis, the ion-transporting separator comprises an open mesh polyphenylene sulfide fabric which is symmetrically coated with a mixture of a polymer and zirconium oxide. The latter is advantageous for systems in which the alkaline electrolyte is used at elevated temperatures, for example in the range of 50°C-90°C. SHORT DESCRIPTION OF THE DRAWINGS

[0070] The invention will be explained in more detail with reference to the drawing, where FIG. 1 A) is a sketch of a stack with both end plates and B) with one end plate removed;

[0071] FIG. 2 illustrates A) an end plate of the stack, B) a metal sheet on the end plate, C) a first part of a gasket on the metal sheet, D) a membrane on the first part of the gasket, E) a second part of the gasket on an edge portion of the membrane;

[0072] FIG. 3 illustrates the configuration of FIG. 2E with a mesh as part of a MEA;

[0073] FIG. 4 illustrates the first fluid passage at the bottom of the electrolytic chamber;

[0074] FIG. 5 illustrates the gasket around the manifold canal;

[0075] FIG. 6 illustrates the fluid passages for A) cathode chamber and B) anode chamber;

[0076] FIG. 7 illustrates the bottom portion of the electrolytic chamber and the first and second fluid passages;

[0077] FIG. 8 illustrates the top meanders A) without the MEA visible and B) with the MEA visible;

[0078] FIG. 9 illustrates the top portion of the fluid passages and the manifolds of the stack;

[0079] FIG. 10 illustrates the multiple fluid passages at the bottom of the stack;

[0080] FIG. 11 is a drawing of the fluid passage configuration at the top through a transparent gasket in A) an overview image and B) enlarged laid-down section;

[0081] FIG. 12 illustrates a cross section of a two-part gasket sandwiching the MEA.

[0082] FIG. 13 illustrates an embodiment where a pressure-resistant pipe is embedded in between the first and second gasket parts.

[0083] DETAILED DESCRIPTION / PREFERRED EMBODIMENT

[0084] FIG. 1 A and FIG. IB is a sketch of an electrolyzer stack 1 having a plurality of electrolyzer cells 2 stacked between end-plates 3. The term stack is used, despite the cells 2 being oriented vertical, as this is a common terminology in the technical field.

[0085] In the following, for simplicity, the ion-transporting separator is exemplified as ionconducting membrane and the term “membrane” is used, substituting any variant of ion-transporting separator that allows ions to pass, and the term “membrane” can be substituted by the term “ion transporting separator”. FIG. IB illustrates the stack 1 with one of the end plates 3 removed. As it is readily observed, through holes 4 for manifolds 14 for supply and drain of liquid and gas for the cathode chambers and anode chambers, are all provided at the top of the electrolyzer stack 1. This implies that the electrolytically active area 5 of the anode chambers and cathode chambers can be optimised relatively to an overall cross-sectional area of the stack 1 itself.

[0086] FIG. 2A illustrates an end plate 3 of the stack 1. The end plate 3 comprises through- holes 4 for fluid transport though the manifolds 14 along the stack 1. It also has mounting holes 6, which are used for bolts (not shown) that extend along the stack and clamp the cells 2 of the stack 1 in between the end plates 3.

[0087] FIG. 2B illustrates a metal sheet 7, which forms one side of an electrolytic chamber 13. Such metal sheets 7 are used in the stack 1 as cell-separation plates between the electrolytic chambers 13, for example as parts of multi-sheet cell-separation plate-arrangements, for example as parts of bipolar plates.

[0088] For example, when resting against the end plate 3, such metal sheet 7 is a monopolar plate. When inside the stack 1, such metal sheet 7 can be part of a bipolar plate, BPP. Such a BPP is optionally constructed as a multilayer plate, having such metal sheet 7 forming opposite sides of the BPP. For example, the BPP is constructed as a doublesheet BPP comprising two metal sheets, forming an anode plate and a cathode plate, which are sealingly fixed to each other back to back and have a liquid-tight coolant chamber in between. Another example is a three or four layer BPP-arrangement, with such metal sheets 7 forming an anode plate and a cathode plate and a single-sheet BPP or double-sheet BPP in between, for example the double-sheet BPP forming a coolant chamber.

[0089] As exemplified in FIG. 2B, the metal sheet 7 is at the end of the stack 1 and has a back side resting against the end plate 3 with a seal 8 that is providing fluid tightness and potentially electrical insulation. Also, fluid tightness is provided around the through holes 4 for the fluid transport in and out of the manifolds 14. The metal sheet 7 comprises also through holes 4 for the manifolds 14, such as gas manifolds 14C, 14D, and matching the through-holes 4 in the end plates 3.

[0090] As already mentioned, similar metal sheets 7 are used as cell-separation plates, for example part of a BPP, on either side of the ion-conducting membrane that separates the anode chamber from the cathode chamber.

[0091] The illustrated metal sheet 7 has embossed corrugations 9 that leave open a central vertical major channel 10 and form minor channels 11 that are arranged in a herringbone configuration extending inclined upwards in a direction away from the central major channel 10.

[0092] As an example, oxygen gas bubbles created in the anode chamber and hydrogen gas bubbles created in the cathode chamber during water splitting in alkaline hydrolysis propagate along the upwards inclined path along these minor channels 11, dragging electrolyte with them from the central major channel 10, which improves liquid circulation in the electrolytic chambers 13, promoting cooling as well as mixing of the electrolyte.

[0093] The produced gas will flow upwards in bubbles to a gas manifold 14C, 14D and leave the electrolytic chamber 13. The drag of the electrolyte through the minor channels 11 will remove electrolyte from the major channel 10 and create a circulation of the electrolyte downwards again through the other vertical channels at the sides of the electrolytic chamber 13. This arrangement of minor channels 11 and major channels 10 creates a simple path for bubble-driven electrolyte circulation in the electrode chamber 13.

[0094] Optionally, there are plural major channels 10 with upwards flow and plural major channels with downwards flow. By suitable dimensioning of the width and depth of the minor channels 11 and major channels 10, this bubble-driven circulation through the electrode chamber 13 causes rapid, self-driven circulation of the electrolyte.

[0095] Typically, such minor channel 11 has a depth in the range of 1 to 10 mm when measured as a distance from the ridges to the lower most portion of the minor channel 11. The metal sheet 7 can take the role of an electrode, abutting the membrane. Alternatively, the membrane is sandwiched between thin-walled porous plates or grids, in combination forming a MEA.

[0096] FIG. 2C illustrates a first gasket part 12A on the metal sheet 7. Onto this first gasket part 12A, a membrane 15 is provided, as illustrated in FIG. 2D, for example the membrane 15 being part of a MEA. The first gasket part 12A provides fluid tightness along an edge portion of the membrane 15 or along MEA, and, thus, around the electrolytic chamber 13 between the metal sheet 7 and the membrane 15.

[0097] The first gasket part 12A has embossed therein canals that delimit and surround fluid passages 16A, 16B, 16C, 16C. The first fluid passage 16A and the third fluid passage 16C are connected to the electrolytic chamber 13 on one side, for example anode side, of the membrane 15, and the second fluid passage 16B and the fourth fluid passage 16D are connected to the electrolytic chamber 13 on the opposite side, for example cathode side, of the membrane 15.

[0098] The first fluid passage 16A is a liquid passage for electrolyte and extends from a first liquid manifold 14A and along a first side edge of the electrolytic chamber 13 to a lower part 13B of the electrolytic chamber 13. Correspondingly, and potentially symmetric, along the opposite edge of the electrolytic chamber 13, a second liquid passage 16B extends from a second liquid manifold 14B to a lower part 13B of the electrolytic chamber 13. The liquid passages are herein also called liquid meanders according to terminology in the technical field.

[0099] For example, first fluid passage 16A is an anode liquid meander providing water and / or electrolyte to the lower part, exemplified as the bottom, of the anode chamber. Correspondingly, the second fluid passage 16B is a cathode liquid meander providing water and / or electrolyte to the lower part, exemplified as the bottom, of the cathode chamber, which is on the opposite side of the separating ion-conducting membrane 15. The first and second fluid passages 16A, 16B, which are liquid passages, are relatively long and thin so that the electrical resistance through the liquid, especially water, is high and shunt-currents minimized.

[0100] Typical dimensions of the liquid passages for the length are in the range of 0.1 to 2 m, and for the width in the range of 0.2 mm to 3 mm. Ratios of length to width of the liquid meanders are typically in the range of 50-5000.

[0101] The third fluid passage 16C and the fourth fluid passage 16D are gas passages, also called gas meanders, which extends from gas manifolds 14C, 14D to the upper part 13 A of the electrolytic chambers 13. These gas meanders transport gas from the electrolytic chambers 13 into the corresponding gas manifolds 14C, 14D. For example, the third fluid passage 16C is an oxygen meander, transporting produced oxygen out of the anode chamber, and the fourth fluid passage 16D is a hydrogen meander transporting hydrogen out of the cathode chamber during electrolysis.

[0102] Optionally, the third fluid passage 16C and the fourth fluid passage 16D may also transport some amount of electrolyte into the gas manifolds 14C, 14D, which, after gas separation and potential cooling, is then recirculated back to the liquid manifolds 14 A, 14B. Notice that the gas manifolds and the liquid manifolds are separate, which is in contrast to the disclosure in the aforementioned international patent application WO20 14 / 040165.

[0103] In some embodiments, however, only gas exits through the third fluid passage 16C and the fourth fluid passage 16D.

[0104] Due to the gas in the gas meanders, formed by the third and fourth fluid passages 16C, 16D, a good electrical insulation is achieved along the gas manifolds 14C, 14D, preventing or at least reducing shunt-currents.

[0105] FIG. 2E illustrates a second gasket part 12B placed against an edge portion of the membrane 15 on the opposite side of the membrane 15 as compared to the first gasket part 12A in order for the first gasket part 12A and the second gasket part 12B sandwiching the membrane 15 therein between along the edge portion of the membrane 15. The second gasket part 12B in combination with the first gasket part 12A seal the fluid passages 16A-16D, so that these are provided inside the combination of the first and second gasket parts 12 A, 12B.

[0106] In order to continue building up such stack with numerous electrolyzer cells 2, a metal sheet 7, as in FIG. 2B, is placed on the second gasket part 12B, and the principle of metal sheet 7, first gasket part 12A, membrane 15, second gasket part 12B, and metal sheet 7 continues for each of the electrolytic chambers 13 along the stack 1.

[0107] The gasket parts 12A, 12B also seal around the manifolds 14.

[0108] FIG. 3 is a drawing similar to FIG. 2E, however, illustrating a mesh 18 as electrode on one side of a MEA that is sandwiched between the first and second gasket parts 12A, 12B, instead of the membrane of FIG. 2E.

[0109] FIG. 4 illustrates the lowest portion of the first fluid passage 16A in the second gasket part 12B, connected to the electrolytic chamber 13, where the mesh electrode 18 of the MEA is visible. The remaining portion of the first fluid passage 16A extends inside the combination of the first gasket part 12A and the second gasket part 12B on one side of the metal plate 7.

[0110] FIG. 5 illustrates in more detail a portion of the manifold 14 with a central manifold canal 24 connected via a fluid port 21 to one of the fluid passages 16A-16D in between the first gasket part 12A and the second gasket part 12B. Notice that the manifold 14 is provided by the combinations of the various manifold portions in the gasket parts 12 A, 12B and the metal sheets 7, as well as the corresponding through holes 4 in the end plates 3.

[0111] FIG. 6A illustrates the fluid distribution in the first fluid passage 16A without the gasket material. It also shows the fluid 24A in the canal 24 of the first manifold 14A. For example, the first fluid passage 16A is a liquid meander for liquid supply to the bottom of the anode chamber. It also shows the fluid distribution in the third fluid passage 16C without the gasket material, in addition to the fluid 24C in the canal 24 of the third manifold 14C. The third fluid passage 16C is an oxygen meander for drain of oxygen gas from the anode chamber.

[0112] FIG. 6B illustrates the fluid distribution inside the second fluid passage 16B, which is a liquid meander, for example, for water supply to the bottom of the cathode chamber. It also shows the fluid distribution inside the fourth fluid passage 16D, which is a hydrogen meander, for drain of hydrogen gas from the cathode chamber.

[0113] As mentioned above and illustrated by the fluid distribution, the fluid passages 16b, 16C forming the gas meanders are short, as they do not need any substantial length because of the good insulation properties of the gas in the gas meanders, and the fluid passages 16 A, 16B forming the liquid meanders are long and thin in order to increase electrical resistance and reduce minimize currents, as well as creating pressure drop in order to equalize flow along the stack, as discussed initially.

[0114] FIG. 7 is an enlarged section of the lower part 13B of the electrolytic chambers 13 illustrating the fluid distribution inside first and second fluid passages 16 A, 16B and entering the electrolytic chambers 13 on opposite sides of the membrane 15, respectively.

[0115] FIG. 8 A is an enlarged section of the upper part 13 A of the electrolytic chambers 13 with the third and fourth fluid passages 16C, 16D entering the electrolytic chambers 13 on opposite sides of the membrane 15, respectively. Also shown, in agreement with the notation of FIG. 5, FIG. 6A and FIG. 6B are the fluid distributions 24A-24D in the canals 24 formed by the manifolds 14A-14D.

[0116] As illustrated in FIG. 8B, the MEA 20, or correspondingly a membrane 15, extends beyond the edges of the electrolytic chambers 13 because the edge portion 19 of the MEA 18 or membrane 15 is sandwiched between the gasket parts 12A, 12B, as explained in connection with FIG. 2D.

[0117] With specific reference to FIG. 8 A, it is pointed out that the gas passages 16C, 16D transition from a single canal into multiple parallel canal end portions 22, arranged as fingers, the ends of which connect to the electrolytic chamber 13. These canal end portions 22 have the function and advantage of facilitating the transition of gas bubbles from the electrode chamber to the gas channels.

[0118] FIG. 9 illustrates in more detail the upper part of the stack 1 with the manifolds 14A- 14D and the fluid distribution 24A-24D inside the manifolds 14A-14D and the fluid distribution inside the fluid passages 16A-16D to the various chambers 2. Notice that the canals themselves, defining and surrounding the fluid passages 16A-16D, are not shown, as these are formed by the gasket parts 12 A, 12B, as explained in relation to FIG. 2D and FIG. 4 and FIG. 5, which are removed for illustration in FIG. 9.

[0119] FIG. 10 illustrates the electrolyzer cells 2 of the stack 1 with the fluid distribution inside the first and second fluid passages 16A, 16B to the various electrolyzer cells 2.

[0120] FIG. 11 A is a drawing of the fluid passages 16A-16D through a transparent second gasket part 12B in an overview image and FIG. 9B shows an enlarged laid-down section of the third and fourth fluid passages 16C and 16D. The first gasket part 12A on the metal sheet 7 is shown in solid shading and the second gasket part 12B in transparent view with contour lines. Illustrated are the fourth manifold 14D with the fluid canal 24 inside the fourth manifold 14D, as well as the fourth fluid passage 16D extending into the electrolytic chamber 13.

[0121] FIG. 12 illustrates, in horizontal orientation for better illustration, a cross section of a first gasket part 12A and a second gasket part 12B sandwiching an edge portion of the membrane 15, which together with the two opposite electrode meshes 18 is part of the MEA 20. As an alternative, an edge portion of the MEA 20 could be sandwiched between the two gasket parts 12 A, 12B. The first gasket part 12A sealingly abuts the metal sheet 7, as illustrated and discussed in connection with FIG. 2. Similarly, the second gasket part 12B abuts a metal sheet 7 of the neighbouring electrolytic chamber 13, which, however, is not shown, but which was discussed in connection with FIG. 2. Illustrated is a first fluid passage 16A extending along an edge of the electrolytic chamber 13. In order to increase the tightening and clamping capability of the gasket parts 12 A, 12B on the membrane 15 or MEA 20, the first gasket part 12A or the second gasket part 12B or both have protrusions 21 which increase the pressure on the membrane 15 or MEA 20 locally and increase sealing. FIG. 13 illustrates, in horizontal orientation for better illustration, a cross section of a first gasket part 12A and a second gasket part 12B where a recess 24 extending along an edge of the electrolytic chamber 13 is fitted with a pressure-resistant pipe 23 that prevents deformation or even closing of the fluid passage 16A due to pressure. In this case, the fluid passage 16A is not provided as a recess 24 inside the gasket 12A, 12B but is provided inside the pipe 23.

Claims

CLAIMS1. An electrolyzer comprising a stack (1) of multiple electrolyzer cells (2), each of the electrolyzer cells (2) comprising two electrolytic chambers (13) separated by an iontransporting separator (15), wherein each of the electrolytic chambers (13) is delimited by the ion-transporting separator (15) and a metal sheet (7) as well as a gasket (12A, 12B) that is surrounding the electrolytic chamber (13); wherein the stack (1) comprises at least one liquid supply manifold (14A, 14B), extending along the stack (1), for supply of water and / or electrolyte to the electrolytic chambers (13) in the stack (1), and two gas manifolds (14C, 14D), extending along the stack (1), one of which being connected to electrolytic chambers (13) on anode sides of the ion-transporting separators (15) in the stack (1) and the other connected to electrolytic chambers (13) on cathode sides of the ion-transporting separators (15) in the stack (1) for drain of corresponding gases produced in the electrolytic chambers (13); wherein, for each electrolytic chamber (13), a liquid passage (16A, 16B) extends from the at least one liquid supply manifold (14A, 14B) along a side of the electrolytic chamber (13) to a lower part (13B) of the electrolytic chamber (13), and a gas passage (16C, 16D) connects one of the two gas manifolds (14C, 14D) with a top of the electrolytic chamber (13), the gas passage (16C, 16D) extending entirely only above the electrolytic chambers (13); wherein the gasket (12A, 12B) comprises a first gasket part (12A) and a second gasket parts (12B), assembled face-to-face, sealingly sandwiching an edge portion of the ion-transporting separator (15) or an edge portion of a separator-electrode-assembly (20) for sealing the electrolytic chambers (13), and wherein the liquid passages (16A, 16B) and the gas passages (16C, 16D) are provided in between the first and second gasket parts (12A, 12B).

2. The electrolyzer of claim 1, wherein all manifolds (14A, 14B, 14C, 14D) are only at an upper side of the stack (1) above the electrolytic chambers (13) when the stack (1) is oriented for operation.

3. The electrolyzer of any preceding claim, wherein the gasket parts (12A, 12B), when assembled, form walls for at least one of the liquid passages (16A, 16B) and the gas passages (16C, 16D) in between the first and second gasket parts (12A, 12B).

4. The electrolyzer of any preceding claim, wherein at least one of the liquid passages (16A, 16B) and the gas passages (16C, 16D) is provided as a fluid passage inside a pressure-resistant pipe (23) that is embedded in between the first and second gasket parts (12A, 12B).

5. The electrolyzer according to any preceding claim, wherein the liquid passages (16A, 16B) have a length in the range of 0.1 to 2 m , a width in the range of 0.2 mm to 3 mm, and a length-to- width ratio in the range of 50-5000.

6. The electrolyzer according to any preceding claim, wherein the stack (1) when oriented for operation has a vertical cross section that is largely rectangular with a height larger than a width.

7. The electrolyzer according to any preceding claim, wherein the metal sheet (7) on its side facing the electrolytic chamber (13) has raised surface portions forming minor channels (11) inside the electrolytic chamber (13), the minor channels (11) extending in a herringbone configuration upwards from a vertical channel (10) on opposite sides of the vertical channel (10) for increased circulation of electrolyte by bubbles formed in the minor channels (11) by electrolysis.

8. The electrolyzer according to claim 7, wherein the raised surface portions (50) are provided by embossing in the metal sheet (7) and formed on opposite sides of the metal sheet (7), wherein one side of the metal sheet (7) is facing the electrolytic cell and the opposite side of the metal sheet (7) is facing a neighbouring electrolytic chamber (13) or is facing a coolant chamber.

9. The electrolyzer according to any preceding claim, wherein a perforated electrode (18) is provided on either side of the ion-transporting separator (15) and abutting an edge portion of the ion-transporting separator (15) as part of a separator-electrodeassembly and wherein the perforated electrode (18) is in electrical contact with the metal sheet (7).

10. The electrolyzer according to any preceding claim, wherein each liquid passage (16A, 16B) extends from the liquid manifold (14A, 14B) downwards along a side of the electrolytic cell and extends along a bottom of the electrolytic cell and connects to an inlet at a bottom of the electrolytic chamber (13).

11. The electrolyzer according to any preceding claim, wherein the electrolytic cells (3) contain alkaline electrolyte, and wherein the gas passages (16C, 16D) are hydrogen and oxygen passages, respectively.

12. Use of the electrolyzer according to any one of the preceding claims for producing hydrogen gas.

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