Electrolyser with a stack of welded four-layer modules

Abstract

Electrolyser (1) comprising modules (3) that sandwich ion-transporting membranes (1) in between adjacent modules (3). The modules (3) are formed as four-layer structures of four metal plates (9, 10, 11), typically steel plates, including two separator plates (11) combined into a BPP and an anode plate (9) and a cathode plate (10) respectively on opposite sides of the BPP. The four plates (9, 10, 11 ) are welded together to form a rigid module (3) with three separate compartments, one anode compartment (9 A), one cath- ode compartment (10A) and a coolant compartment (HA).

Description

FIELD OF THE INVENTION

[0001] The present invention relates to an electrolyser for production of hydrogen gas, theelectrolyser comprising a stack of modules sandwiching ion-transporting membranes between each two of the modules, wherein each modules comprises an anode and a cathode. Inparticular, present invention relates to an electrolyser as described in the preamble of theindependent claim.BACKGROUND OF THE INVENTION

[0002] An efficient method for production of hydrogen gas is electrolysis. In an electrolyser,an ion conducting membrane is sandwiched between two electrodes, and a voltage is appliedacross the electrodes. The voltage results in water from the aqueous electrolyte being splitinto hydrogen and oxygen and a final separation of hydrogen gas and oxygen gas on oppositesides of the membrane.

[0003] Typical electrolysers comprise a stack of membrane between pairs of electrodes withseparators in between in order to increase output of hydrogen gas. The separators are typicallyprovided in the form of bipolar plates, for example two separators combined into a bipolarplate, BPP. The bipolar plates are sandwiching the membrane electrode assemblies inbetween. The number of such modules as well as the areal size of such modules determinethe possible production output at a given current per density in the cells. In order to controlthe temperature of the electrolyser, the bipolar plates are advantageously provided as twolayer plates having an internal coolant compartment guiding coolant through the BPP.Examples are illustrated in US patent applications US2021 / 0234237 and US2021 / 0202963,where opposite separator plates are welded to each other.

[0004] For proper flow and diffusion of the gas away from the membrane, there areoften provided gas diffusion layers between the membrane and the electrodes. Examples areil- lustrated in US2021 / 0234237. However, the more layers the electrolyser cell comprises,the higher is the risk that components are moving relatively to each other and cause reducesefficiency or even malfunctioning of the electrolyser. Accordingly, there is an interest ofproviding electrolyser systems with high rigidity and sturdiness.

[0005] This problem has been recognised in the international patent application WO84 / 03523.It discloses an arrangement of modules that sandwich membranes in between, where themodules comprise electrodes and separators fixed to each other. Two opposite separators areheld in shape by an intermediate rigid, solid material to which the separators are affixed. Byusing a solid and rigid material in between the separators, it is not possible to use theseparators as a bipolar plate with cooling channels inside. Accordingly, this disclosure doesonly solve a partial problem of providing rigid and sturdy electrolyser modules but does notinclude a solution of the problem of temperature control.

[0006] Chinese utility model CN212476910U discloses Dl describes an electrolyser for production of hydrogen gas and comprising a stack of modules sandwiching ion-transportingmembranes between each two of the modules. Each module comprises a cathode chamberand an anode chamber and respective outlet holes as well as a plurality of liquid inlets in themiddle part of the electrolysis chamber.

[0007] Further principles for electrolysers are disclosed in Chinese utility modelsCN211455844U, CN205676538U, CN209329036U.

[0008] JP58071382 discloses a four-layer arrangement of separators and electrodes, where thefour metallic components are welded together in a way where are the two corrugatedseparators are welded to each other and the protrusions on each side of the corresponding BPPis holding an electrode. Opposite ends of the pairs of corrugated separator sheets are open sothat electrolytes is flowing into the space between the separator plates. Accordingly, there arenot provided cooling channels through the bipolar plate.

[0009] As it appears from the above, there has been made several different attempts forproviding rigidity in modules of electrolyses but there appears to be still room forimprovement. The latter is important as there is a continuous aim to improve quality andefficiency of electrolysers.DESCRIPTION / SUMMARY OF THE INVENTION

[0010] It is therefore an objective of the invention to provide an improvement in the art. Inparticular, it is an objective to provide an electrolyser with a high degree of operationalreliability. Furthermore, it is an objective to provide an electrolyser with a plurality ofseparator / electrode modules that sandwich membranes in between, where the modulesare rigid and suitable for mass production at relatively low cost and which allow for goodtemperature control of the electrolyser. These objectives and further advantages areachieved with an electrolyser as described below and in the claims.

[0011] In short, the electrolyser comprises modules that sandwich ion-transportingmembranes in between adjacent modules. The modules are formed as four-layerstructures of four metal plates, typically steel plates, including two separator platescombined into a BPP and an anode plate and a cathode plate respectively on oppositesides of the BPP. The four plates are welded together to form a rigid module with threeseparate compartments, which are one anode compartment, one cathode compartment anda coolant compartment.

[0012] The electrolyser is used for production of hydrogen gas. However, due to thesplitting of water in the electrolyte when applying electrical power, also oxygen isproduced. The hydrogen is collected for later use, for example in fuel cells or industrialapplications.

[0013] The electrolyser comprises a stack of modules. Each pair of the consecutivelyarranged modules are sandwiching an ion-transporting membrane through which therespective ions are transported, for example OH- ions from a KOH based electrolyte.

[0014] Each module comprises a first metal plate, which is a cathode plate, a second metalplate, which is an anode plate, and third and fourth metal plates which are first and secondseparator plates and which in combination form a two-layer bipolar plate, BPP, locatedin between the anode plate and the cathode plate. The four metal plates are weldedtogether to form a rigid four-layer module with an outer anode side and an outer cathodeside, opposite to the anode side. The four plates form three compartments in between theplates, namely a first compartment, which is a cathode compartment be- tween thecathode plate and the first separator plate and containing electrolyte, a secondcompartment, which is an anode compartment, between the anode plate and the secondseparator plate and containing electrolyte, and a third compartment between the first andsecond separator plates, which is a coolant compartment with liquid-coolant flow pathinside the two-layer BPP and which contains coolant. The coolant is different fromelectrolyte and optionally containing glycol or is oil-based. Due to the BPP between theanode plate and the cathode plate, the coolant compartment is tightly separated from theanode compartment and from the cathode compartment.

[0015] For supply of water to the anode compartment and the cathode compartment inorder to replenish consumed water, the module comprises an inlet for supplying water forthe electrolysis in pure form or as part of replenished electrolyte. An option is a singlewater inlet from a common water supply conduit, which is sufficient for providing waterfor the electrolysis to both the anode and the cathode compartment. However, in somecases, it is also possible to provide more than one inlet, for example two inlets.

[0016] Optionally, water for the electrolysis is supplied to the chambers as part ofreplenished electrolyte solution. In this case, new electrolyte is replenished through theinlet and used electrolyte extracted through an outlet, which allows a circulation of theelectrolyte and possible cleaning thereof. During the circulation of the electrolyte, thewater concentration in the electrolyte is adjusted by adding water to the electrolyte in thecircuit portion outside the electrolysis chambers. This facilitates optimization of the watercon- centration in the electrolyte. Optionally, the gas outlets are also used as outlets forthe electrolyte, after which the electrolyte is separated from the gases and recirculated.

[0017] The oxygen gas produced at the anode is released from the anode compartmentthrough an oxygen-gas outlet. A hydrogen-gas outlet releases hydrogen gas from thecathode compartment. A flow of coolant through a coolant inlet, through the coolantcompartment, and through a coolant outlet is used for controlling the temperature in themodule and, thus, the temperature of the electrolyte and the electrodes.

[0018] The anode plate has anode perforations for providing electrolyte from the anodecompartment to the membrane and flow of oxygen gas into the anode compartment.

[0019] Correspondingly, the cathode plate has cathode perforations for providingelectrolyte from the cathode compartment to the membrane and flow of hydrogen gas intothe cathode compartment.

[0020] In the middle of the four plates, the module has a central plane. Typically, the fourplates are arranged in parallel and have a central plane parallel with the four plates.

[0021] In some practical embodiments, for providing tightness, the four metal plates arewelded together along a closed curve, for example by a perimeter welding at the rim.Alternatively, the four metal plates are tightened along the perimeter or close to theperimeter, by other means, such as glue or sealing gaskets.

[0022] In order to provide a high degree of rigidity, the plates are advantageously weldedtogether at a plurality of interspaced further weldings. The plurality of further weldingsare distributed across the plates within the perimeter and spaced from the perimeter andfrom each other for providing rigidity and for maintaining a predetermined distancebetween the plates. The weldings also provide a proper electrical contact between theplates. Each further welding extends over a local welding region and is connecting thecorresponding welded plates across the local welding region. For example, the furtherweldings are provided near the centre of the plates and between the centre and the rim atselected positions. The positions are optionally chosen according to a regular pattern, forexample a grid pattern with equal distance between adjacent further weldings.

[0023] For example, the further weldings connect all four plates across the local weldingregion.

[0024] Alternatively, the plates are only welded together pairwise, such that the cathodeplate and the first separator plate are welded together at a plurality of interspaced furtherweldings, and the anode plate and the second separator plates are welded together at aplurality of interspaced further weldings, but the further weldings do not connect thetwo separator plates. In this case, optionally, both separator plates have multiple contactpressure regions at which the two separator plates are in contact with each other forsecuring good conductivity between the two separator plates and for maintaining a predetermined width of the coolant compartment. These contact pressure regions are notwelded or otherwise fixed to each other than by pressure between the two separatorplates.

[0025] Advantageously, in order to facilitate assembly and welding of the module at thefurther weldings, the pairs of plates or all four plates, are shaped with depressions that areabut- ting each other and with no spacing between the plates at and across the localwelding regions before the welding. Even for a welding of all four plates at the locationof the local welding regions is a simple operation through the four tight-laid plates asthese are already stacked tightly due to the depressions. As the depressions are providedby the corresponding plate's press-deformation prior to the welding and have a fixed distance between the bottom of the depression and the general plane of the plate, the depressions also define the final distance between adjacent plates. These achieved distances further define the widths of the corresponding compartments.

[0026] For example, the depressions in the anode plate and the cathode plate are deeperthan the depressions of the separator plates. Optionally, in the case of the four plates beingwelded together, mutual abutment of the four plates at the welding region is providedcentrally between the anode plate and the cathode plate.

[0027] The welding regions have a smallest dimension when measured in parallel with thecentral plane. Optionally, smallest dimension of each of the welding regions is smallerthan 5%, for example smaller than 2%, of a distance between two opposite edges at therim. In other words, the welding regions are small as compared to the size of the plates.If the further weldings are circular, the dimensions in different directions are equal. Butfor elongate welding regions, for example oval, this is not the case, and the weldingregions would have a smallest dimension, namely a width, and a largest dimension,namely a length. For such case of elongate local welding regions, in some embodiment,the welding regions have a largest dimension when measured in parallel with the centralplane. In some embodiments, the largest dimension is smaller than 5%, for examplesmaller than 2%, of a distance between two opposite edges at the perimeter.

[0028] Optionally, for practical reasons, multiple further weldings are provided which areshaped identical.

[0029] In some practical embodiments, the oxygen-gas outlet is provided as a canal with acanal perimeter along which all four plates are welded together to form a tight sealingbetween the plates. Advantageously, all of the four plates comprise circumferential deformation regions along the canal perimeter which are inclined towards the central planefor the plates to tightly abut each other along the canal perimeter. The circumferentialdeformation region of the anode plate comprises multiple oxygen outlet holes connecting the anode compartment with the oxygen canal for flow of oxygen from the anodecompartment into the oxygen canal.

[0030] Similarly, as an option, the hydrogen-gas outlet is provided as a canal with a canalperimeter along which all four plates are welded together to form a tight sealing betweenthe plates. For example, all of the four plates comprise circumferential deformationregions along the canal perimeter which are inclined towards the central plane for theplates to tightly abut each other along the canal perimeter, and the circumferentialdeformation region of the cathode plate comprises multiple hydrogen outlet holesconnecting the cathode compartment with the hydrogen canal for flow of hydrogen fromthe cathode compartment into the hydrogen canal.

[0031] Following such principle, the coolant inlet and / or the coolant outlet comprise acoolant canal with a canal perimeter along which the cathode plate and the adjacent firstseparator plate are welded together to form a tight sealing between the cathodecompartment and the coolant compartment. Furthermore, along the canal perimeter of thecoolant canal, the anode plate and the adjacent fourth plate are welded together to form atight sealing between the anode compartment and the coolant compartment. For example,at the canal perimeter of the coolant canal, an opening is provided between the third andthe fourth plate, which are the two separator plates of the BPP, as a flow path for flow ofcoolant between the coolant canal and the coolant compartment.

[0032] In some embodiments, the anode side and / or the cathode side is abutting themembrane in a zero-gap configuration. This means that the module is abutting themembrane.

[0033] For example, the perforations through the cathode plate from the cathodecompartment to the membrane in total adds up to an open relative area A at the membraneof 20-50% of the total area by which the cathode abuts the membrane. Optionally, theperforation are provided as circular holes, for example having a diameter not smaller thanthe thickness of the cathode plate but not larger than 2 times the thickness of the cathodeplate. For example, in a cathode plate with a thickness of 0.5 mm, the holes have aminimum diameter of 0.5 mm and an optional size in the range of 0.5-0.6 mm.

[0034] A minor concrete example illustrates the advantage of these limits. For example,the open area of the perforations are 30% of the plate. A hole of with a diameter of 2 mmhas a surface are in the order of 3 mm2. If the plate has a thickness of 1.5 mm, the holeforms a canal having a surface area of the circumference multiplied by the plate thickness, which makes up about 9 mm2. Thus, the active area that is involved in theelectrolysis is actually larger than the open area of the perforation itself. Until a certainthickness of the electrode plate, a thicker plate may result in higher hydrogen productionyield than a thinner plate, however, having in mind that the electrical field quickly decreases with distance from the opposite electrode. This simple example also illustratesthat many small perforations yield a higher production rate that few large openings, dueto the added effect from the rim of the perforations.

[0035] As an option, similar to the above-described example, the perforations through theanode plate from the anode compartment to the membrane in total adds up to an openrelative area at the membrane of 20-50% of the total area by which the anode abuts themembrane. As a further option, the perforations are provided as circular, for examplehaving a diameter not smaller than the thickness of the anode plate but not larger than2 times the thickness of the anode plate. For example, in an anode plate with a thicknessof 0.5 mm, the holes have a minimum diameter of 0.5 mm and an optional size in therange of 0.5-0.6 mm.

[0036] In some embodiments, metal pressed-out sections are connected to rim portions ofthe perforations of the cathode plate and extend out of the plane of the cathode platetowards the adjacent separator plate, which is the third plate. Optionally, the pressed-outsections abut the third plate, which is used as a support to assist maintaining a constantdistance between the cathode and the BPP. The sections also may assist in a goodelectrical con- tact between the plates. As a similar option, metal pressed-out sections areconnected to rim portions of the perforations in the anode plate and extend out of theplane of the anode plate to the adjacent separator plate, which is the fourth plate, and abutthe fourth plate as a support to assist maintaining a constant distance between the anodeand the BPP. Optionally, the metal pressed-out sections are connected to two oppositerim portions of the perforations.

[0037] Typical dimensions are given in the following:Thickness of plates: 0.5 mm to 2.5 mmLength / width of the plates: 0.5 m to 3 m.Distance between electrode and BPP: 0.2 mm to 5 mmDistance between separator plates of BPP: 1 mm to 10 mm

[0038] In some embodiments, the electrolyser is part of a system in which the polarity ofthe power can be reversed, making the anode to a cathode and vice versa. Such periodicreversal prolongs the lifetime of the electrodes.

[0039] In some embodiments, the electrolyser is part of a system in which the flowdirection of the coolant through the BPP can be reversed, which may also prolong thelifetime.SHORT DESCRIPTION OF THE DRAWINGS

[0040] The invention will be explained in more detail with reference to the drawing, where

[0041] FIG. 1 is a sketch of an electrolyser stack

[0042] FIG. 2 illustrates an electrode / separator module in a head-on view; FIG. 3illustrates the four-layer principle of the module;

[0043] FIG. 4 illustrates a further welding;

[0044] FIG. 5 is a drawing with a perspective view of gas flow openings;

[0045] FIG. 6 is a drawing with A) a perspective view of coolant openings and B) a crosssectional view of coolant openings and C) an optional embodiment with bridges betweenthe openings;

[0046] FIG. 7 illustrates a perforated electrode in A) a head-on view and B) enlargedperspective view;

[0047] FIG. 8 illustrates different embodiments of a perforated electrode in A) a head-onview and B) enlarged perspective view;

[0048] FIG. 9 illustrates a further embodiment of a perforated electrode in A) perspectiveview and B) enlarged perspective view;

[0049] FIG. 10 illustrates a further embodiment of a perforated electrode in A) perspectiveview and B) enlarged perspective view;

[0050] FIG. 11 illustrates an embodiment where further welding regions connect the platespairwise.DETAILED DESCRIPTION / PREFERRED EMBODIMENT

[0051] FIG. 1 is a sketch of a principle of a stacked electrolyser 1 comprising iontransporting membranes 2 sandwiched between electrode / separator modules 3.

[0052] The modules 3 contain the necessary electrolyte for the electrolytic reaction wherewater is split into oxygen and hydrogen. In order to replenish the water that is consumedduring the reaction, the module 3 has a corresponding inlet 4, as illustrated in FIG. 2.Optionally, the inlet 4 is used for supplying water in pure form into the modules 3 for theelectrolysis or, alternatively, the inlet 4 is used for supplying water as part of replenishedelectrolyte. The modules also comprise a corresponding oxygen outlet 5 and hydrogenoutlet 6. For temperature control and cooling purposes, the module 3 is equipped withcoolant inlet 7 and coolant outlet 8.

[0053] FIG. 3 illustrates the four-layer principle of the module 3. The module comprisesfour sheets of metal, typically stainless steel, that are interconnected by weldings alongthe rim edges 27 and around the inlets 4, 7 and outlets 5, 6, 8. In the exploded view ofFIG.3, there is shown an anode 9, where oxygen is produced and released through oxygenoutlet 5, and a cathode 10, where hydrogen is produced and released through hydrogenoutlet 6. Two separator plates 11 form a bipolar plate, BPP, that mechanically separatesthe anode 9 and the anode compartment 9A from the cathode 10 and the cathode compartment 10A. However, the BPP electrically connects the anode 9 and the cathode 10,so that subsequent modules 3 of the stacked modules 3 with the membranes 2 in betweenthe modules 3 stepwise increase the voltage along the stack.

[0054] To provide stiffness and stability and in order to provide a sturdy module, the fourmetal plates of the separators 11, the anode 9, and the cathode 10 are interconnected byfurther weldings 12, which are illustrated as point-like weldings but could have othershapes. These further weldings 12 are distributed all over most of the area of the module3, as indicated in FIG. 2 and FIG. 3

[0055] FIG. 4 illustrates a further welding 12. The further welding 12 comprises a localwelding region 14. Around the welding region 14, the sheets of metal of the separators11, the anode 9, and the cathode 10 have circular deformations 13 bending inwardstowards the local welding region 14 for mutual common contact and where the weldingis performed for fastening the four plates to each other.

[0056] FIG. 5 is a drawing with a perspective view of gas flow openings 15 through whichhydrogen gas is flowing into the hydrogen outlet 6. The flow openings are provided in adepression 17 towards the central plane 26 (illustrated in FIG. 6B) and along the perimeterof the canal of the hydrogen outlet 6. In extension thereof there is also provided a weldingseam 16 that tightly connects the four plates, namely the two separator plates 11, theanode plate 9, and the cathode plate 10. A similar arrangement is optionally used for theflow of oxygen from the anode compartment 9A through the oxygen outlet 5 and into anoxygen canal.

[0057] FIG. 6A is a drawing with a perspective view of coolant openings and FIG. 6B across sectional view of coolant openings 20 from coolant inlet 7 for flow 21 of coolantinto the coolant compartment 11A between the two separator plates 11 that form the BPPbetween the anode 9 and the cathode 10. Around the coolant canal of the coolant inlet 7,there are provided tight weldings 18 that connect the first separator plate 11 with thecathode 10 and the second separator plate 11 with the anode 9. This ensures that nocoolant flows into the anode compartment 9A and the cathode compartment 10A. Alsoseen in this drawing is one of the further weldings 12.

[0058] FIG. 6c illustrates an optional embodiment with mechanically stabilizing bridges22 between the openings 20 from the coolant inlet 7 into the coolant compartment 11A.These mechanically stabilising bridges 22 are provided by bending edges of the twoseparators 11 towards each other and welding them together. Similar arrangements canbe used for the coolant outlets.

[0059] FIG. 7A illustrates a perforated electrode / separator module in a head-on view ontothe cathode 10 and FIG. 7B in an enlarged perspective view. In this embodiment, theelectrodes 9, 10 are abutting the corresponding membrane 2 in a zero-gap configuration.In order for the electrolyte, for example a KOH solution, to flow 24 to the membrane 2,the electrodes 9, 10 are provided with perforations 23. In the illustrated embodiments, theperforations 23 are circular openings through the electrode plate 10. As an example, thetotal free open area of the perforations 23, where the electrolysis takes place at themembrane 2, is in the order of 30% of the total area between the electrode 9, 10 and themembrane 2.

[0060] In practical embodiments, the hole diameter of 2 mm has been found useful. On theone hand, the diameter should not be too large because a large diameter results in a lossof active electrode surface area. On the other hand, too small diameters across theperforation 23 result in the perforation behaving like a narrow channel, perpendicular tothe membrane 2, especially when the thickness of the electrode plate 9, 10 is larger thanthe diameter of the perforation 23, which in turn may lead to a reduced transport of gasessufficiently quickly away from the perforation 23.

[0061] Accordingly, the perforation 23 shape, size and the total area of the perforations, aswell as the thickness of the electrode plates 9,10 influence the overall efficiency. Forexample, for circular openings with a diameter of 2 mm and a sheet thickness of 1.5millimetres, the total surface area of the active electrode sheet material around the holeof the perforation is approximately 9 mm2. Although, the electrical field decreases withdistance from the membrane-facing edge of the perforation 23 towards the compartmentside of the perforation, the total area that is active for the electrolysis with still reasonably high voltage is larger than the effective open area of the 2 mm perforation. All thesefactors have to be taken into account and balanced for an optimised efficiency.

[0062] This also implies that a reduction of the plate thickness of the electrodes 9, 10 forthe same size of perforations, may result in a decreased total electrolysis efficiency of themodule. However, on the other hand, thinner metal sheets use for electrodes and BPP inthe module is resulting in an overall smaller thickness of the module 3, and may allow ahigher number of modules 3 to be stacked within the same container size of theelectrolyser and, thus, may still lead to higher overall efficiency of the stack per size unitof electrolyser. As mentioned, optimization of an electrolyser is a complex balancing ofparameters.

[0063] FIG. 8A illustrates different embodiments of perforated electrode / separatormodules in a head-on view and FIG. 8B in an enlarged perspective view. In these showncases, the perforations 23 are elongate openings formed as slits oriented in differentdirections, such as vertical, horizontal, inclined.

[0064] FIG. 9A illustrates a further embodiments of perforated electrode / separatormodules in a perspective view and FIG. 9B in an enlarged perspective view. In the shownembodiment the perforation 23 are provided by pressing small sections 25 of the electrode10 out of the plane of the electrode 10. In the perforation industry, such type ofperforations are also called bridge slot perforations. These displaced sections 25 connectto the ad- jacent separator plate 11 as a support, so that the sections 25 assists inmaintaining a constant distance between the electrode, for example cathode 10 and / oranode 9, and the adjacent separator plate 11. Additionally, the sections 25 may assist inthe electrical contact between the plates. The illustrated pressed-out metal sections 25 areconnected to rim portions of the perforations 23. Although, the metal sections 25 areconnected with connections 25' to two opposite rim portions of the perforations 23, it isalso possible that they are connected to only one rim portion of the perforation.

[0065] Whereas the pressed-out sections 25 for the perforations 23 in FIG. 9 have piecewise straight portions for the connections 25' that are mutually angled, the perforations23 in FIG. 10A and FIG. 10B are curved. Also in this case, the pressed-out sections 25are used for maintaining a constant distance between the electrodes 9, 10 and the adjacentseparator plate 11, following a similar principle as illustrated in FIG. 9.

[0066] FIG. 11 illustrates a further embodiment, in which all four plates 9, 10, 11 arewelded together along the rim edge 27 by a four-layer perimeter welding 19. The cathode10 and the first separator plate 11 are welded together at further welding regions 12, whichare two-layer weldings. Furthermore, the anode 9 and the second separator plate 11 arewelded together at even further welding regions 12, which are also two-layer weldings.Both separator plates 11 have multiple contact pressure regions 29, at which the separatorplates 11 are in contact with each other for securing good conductivity between the platesand also maintaining a fixed predetermined distance between the separator plates 11, butwhich are not welded or otherwise fixed to each other than by pressure.

Claims

1. Electrolyser (1) for production of hydrogen gas by electrolysis, the electrolyser (1) comprising a stack of modules (3) sandwiching ion-transporting membranes (2) between each two of the modules, wherein each module comprises - a first metal plate, which is a cathode plate (10), and - a second metal plate, which is an anode plate (9), - an inlet (4) for supplying water in pure form or as part of replenished electrolyte to the anode compartment and the cathode compartment, - an oxygen-gas outlet (5) for outlet of oxygen from the anode compartment (9), - a hydrogen-gas outlet (6) for outlet of hydrogen gas from the cathode compartment (10A), and characterized by each module comprising - a third and fourth metal plate which are first and second separator plates (11) and which in combination form a two-layer bipolar plate, BPP, located in be- tween the anode plate and the cathode plate, wherein the four metal plates (9, 10, 11) are welded together to form a rigid four-layer arrangement of the module (3) with an outer anode side and an outer cathode side, opposite to the anode side, and with three compartments in between the plates, which are - a first compartment, which is a cathode compartment (10A) between the cathode plate (10) and the first separator plate (11) and containing electrolyte, - a second compartment, which is an anode compartment (9A), between the anode plate (9) and the second separator plate (11) and containing electrolyte, and - a third compartment between the first and second separator plates (11), which is a coolant compartment (11A) with liquid-coolant flow path inside the two- layer BPP and contains coolant that is different from electrolyte, wherein the coolant compartment (11A) is separated from the anode compartment (9A) and the cathode compartment (10A); - a coolant inlet (7) and a coolant outlet (8) for flow of coolant through the coolant compartment (11A); wherein the coolant inlet (7) and the coolant outlet (8) comprise a coolant canal with a canal perimeter along which the cathode plate (10) and the adjacent third metal plate are welded togetherto form a tight sealing between the cathode compartment(10A) and the coolant compartment(11A) and along which the anode plate (9) and the adjacent fourth metal plate (11) are welded together to form a tight sealing between the anode compartment (9A) and the coolant compartment (11A); wherein the anode plate (9A) has anode perforations (23) for flow of electrolyte from the anode compartment (9A) through the anode perforations (23) to the membrane (2) and for flow of oxygen through the anode perforations (23) into the anode compartment (9A), and wherein the cathode plate (10) has cathode perforations(23) for flow electrolyte from the cathode compartment (10A) through the cathode perforations (23) to the membrane (2) and flow of hydrogen gas through the cathode perforations (23) into the cathode compartment (10A).

2. Electrolyser according to claim 1, wherein the four metal plates (9, 10, 11) are welded together along their perimeter by a perimeter welding (19).

3. Electrolyser according to any preceding claim, wherein the cathode plate (10) and the first separator plate (11) are welded together at a plurality of interspaced further weldings (12), wherein the anode plate (9) and the second separator plates (11) are welded together at a plurality of interspaced further weldings (12), and wherein each further welding (12) is extending over a local welding region (14), wherein the plurality of local welding regions (14) are distributed across the plates (9, 10, 11) within a perimeter of the plates and spaced from the perimeter and from each other for providing rigidity and for maintaining a predetermined distance between the plates (9, 10, 11) that are welded together.

4. Electrolyser according to claim 3, wherein the further weldings (12) do not connect the two separator plates (11), wherein both separator plates (11) have multiple contact pressure regions (29) at which the two separator plates (11) are in contact with each other for securing good conductivity between the two separator plates (11), wherein the contact pressure regions (29) are not welded or otherwise fixed to each other than by pressure between the two separator plates (11).

5. Electrolyser according to claim 3, wherein the further weldings (12) connect all four plates (9, 10, 11) across the local welding region (14).

6. Electrolyser according to claim 4 or 5, wherein the plates (9, 10, 11) at the further weldings (12) are shaped with depressions (13) for abutting each other and with no spacing between the plates (9, 10, 11) at and across the local welding regions (14) before and after welding.

7. Electrolyser according to claim 6, wherein the depressions (13) in the anode plate (9) and the cathode plate (10) are deeper than the depressions (13) of the separator plates (11).

8. Electrolyser according to anyone of the claims 3-7, wherein the module (3) has a central plane (26) parallel with the four plates (9, 10, 11) and wherein the welding regions (14) have a smallest dimension when measured in parallel with the central plane (26), wherein the smallest dimension of each of the welding regions (14) is smaller than 5% of a distance between two opposite edges (27) at the perimeter.

9. Electrolyser according to claim 8, wherein the welding regions (14) have a largest dimension when measured in parallel with the central plane (26), wherein the largest dimension is smaller than 5% of a distance between two opposite edges (27) at the perimeter.

10. Electrolyser according to anyone of the claims 3-9, wherein the welding regions (14) of the plurality of further weldings (12) are shaped identical.

11. Electrolyser according to anyone of the preceding claims, wherein at least one of the anode side and the cathode side is abutting the membrane (2) in a zero-gap configuration.

12. Electrolyser according to anyone of the preceding claims, wherein the oxygen-gas outlet (5) is provided as an oxygen canal with a welded canal perimeter (16) along which all four plates (9, 10, 11) are welded together to form a tight sealing between the plates (9, 10, 11), and wherein all of the four plates (9, 10, 11) comprises circumferential deformation regions (17) along the welded canal perimeter (16) which are inclined towards the central plane (26) for the plates (9, 10, 11) to tightly abut each other along the welded canal perimeter (16), and wherein the circumferential deformation region (17) of the anode plate (9) comprises multiple oxygen outlet holes (15) connecting the anode compartment (9A) with the oxygen canal for flow of oxygen from the anode compartment (9A) into the oxygen canal, and / or wherein the hydrogen-gas outlet (6) is provided as a hydrogen canal with a welded canal perimeter (16) along which all four plates (9, 10, 11) are welded together to form a tight sealing between the plates (9, 10, 11), and wherein all of the four plates (9, 10, 11) comprises circumferential deformation regions (17) along the welded canal perimeter (16) which are inclined towards the central plane (26) for the plates (9, 10, 11) to tightly abut each other along the welded canal perimeter (16), and wherein the circumferential deformation region (17) of the cathode plate (10) comprises multiple hydrogen outlet holes (15) connecting the cathode compartment (10A) with the hydrogen canal for flow of hydrogen from the cathode compartment (10A) into the hydrogen canal,13. Electrolyser according to anyone of the preceding claims, wherein an opening (20) is provided between the third and the fourth plate (11) at the canal perimeter of the coolant canal as a flow path (21) for flow of coolant between the coolant canal and the coolant compartment (11).

14. Electrolyser according to anyone of the preceding claims, wherein the cathode perforations(23) through the cathode plate (10A) from the cathode compartment (10A) to the membrane (2) in total adds up to an open relative area A at the membrane of 20- 50% of the total area by which the cathode plate (10A) abuts the membrane (2).

15. Electrolyser according to claim 14, wherein the cathode perforations (23) are provided as circular holes having a diameter not smaller than the thickness of the plate but not larger than 2 times the thickness of the plate.

16. Electrolyser according to anyone of the preceding claims, wherein metal sections (25) are pressed out of the cathode plate (10) and connected to rim portions of the perforations(23) and extend out of the plane of the cathode plate (10) to the third plate, which is the adjacent separator plate (11), and abut the third plate (11) as a support to assist maintaining a constant distance between the cathode plate (10) and the adjacent third plate (11) and / or wherein metal sections (25) are pressed out of the anode plate (9) and are connected to rim portions of the perforations (23) in the anode plate (9) and extend out of the plane of the anode plate (9) to the fourth plate (11) and abut the fourth plate (11) as a support to assist maintaining a constant distance between the anode plate (9) and the adjacent fourth plate (11).

17. Electrolyser according to claim 16, wherein the pressed-out metalsections(25) are connected with connections (25') to two opposite rim portions of the perforations (23).