Electrochemical cell with improved peripheral sealing

Abstract

The invention relates to an electrochemical cell comprising: a membrane-electrode assembly 2; two retaining plates 10; a single sealing gasket 20, extending around the membrane-electrode assembly 2 and disposed in contact with the two retaining plates 10; at least one intermediate sealing sheet 30, extending around the membrane-electrode assembly 2, disposed between the latter and the sealing gasket 20, and sealed to the membrane 4 on one side and to the sealing gasket 20 on the other. Figure for the abstract: Fig. 2A

Description

Title of the invention: Electrochemical cell with improved peripheral sealing Technical field

[0001] The field of the invention is that of electrochemical cells of the proton exchange membrane type such as electrochemical cells of fuel cells or electrolysers, and relates more precisely to the peripheral sealing of the electrochemical cell at least around the active zone thereof. STATE OF THE PRIOR ART

[0002] Proton Exchange Membrane (PEM) electrochemical cells comprise an anode and a cathode electrically separated from each other by the electrolyte membrane. The stack of electrodes and the electrolyte membrane is called a membrane electrode assembly (MEA). They may be the cells of an electrochemical reactor such as a fuel cell or an electrolyzer.

[0003] An electrochemical cell usually comprises two holding plates, between which the membrane electrode assembly is arranged. The holding plates are called bipolar plates when, in a stack of electrochemical cells, they are each in contact with the anode of a cell on one face, and the cathode of the adjacent cell on the other face. They are adapted to ensure the mechanical holding of the membrane electrode assembly, the fluid distribution of the reactive gases at the electrodes, and the electrical connection of the latter. Also, the holding plates usually comprise distribution channels located on the faces oriented towards the membrane electrode assembly, and adapted to bring the reactive fluid to the corresponding electrode and to evacuate the products of the electrochemical reaction.

[0004] For example, in the case of a fuel cell, the fuel (for example hydrogen) is brought to the anode while the oxidant (for example oxygen contained in the air) is brought to the cathode. The electrochemical reaction is subdivided into two half-reactions, an oxidation reaction and a reduction reaction, which take place respectively at the anode / electrolyte interface and at the cathode / electrolyte interface. To take place, the electrochemical reaction requires the presence of an ionic conductor between the two electrodes, namely the electrolyte contained in a polymer membrane, and an electronic conductor formed by the external electrical circuit. The cell is thus the site of the electrochemical reaction: the reactive gases are brought in, the products and non-reactive species are removed, as well as the heat produced during the reaction.

[0005] Furthermore, it is important to ensure the peripheral sealing of the electrochemical cell, that is to say the sealing around the active zone where the electrochemical reactions take place, so as to prevent the fluids circulating in the distribution channels from leaking out of the electrochemical cell.

[0006] In this respect, [Fig. 1A] illustrates an example of a PEM type electrochemical cell 1 described in document US2004 / 0209150. The peripheral sealing around the active zone is ensured by two seals 20.1, 20.2 arranged on either side of the membrane 4, and which extend continuously around the active zone (and here around inlet and outlet collectors, not shown in the figure). Thus, each seal 20.1, 20.2 is in contact with a bipolar plate 10 and a face of the membrane 4. However, the fact of using two seals 20.1, 20.2 superimposed on each other leads to greater constraints in terms of manufacturing tolerances in thickness of these seals. It is indeed necessary to precisely control the thickness of the sealing gaskets 20.1, 20.2 during manufacturing, which is particularly difficult since the seals can have a thickness of the order of a millimeter or less. Also, insufficiently low manufacturing tolerances can lead to a localized leak in the XY plane of the electrochemical cell.

[0007] To reduce these constraints in terms of manufacturing tolerances in thickness of the seals, the document US2019 / 0036130 describes another configuration of PEM type electrochemical cell 1, as illustrated in [Fig.lB]. Here, the peripheral sealing around the active zone is ensured by the same seal 20. This seal 20 is in contact with the two bipolar plates 10 on the one hand, and with an external edge of the electrolytic membrane 4 (and here of FAME 2). More precisely, the seal 20 is assembled to the AME 2 by overmolding. If the use of a single seal 20 makes it possible to reduce the constraints in terms of thickness, this configuration has the disadvantage that a localized contact defect between the seal 20 and the membrane 4 can lead to a localized leak, along the Z axis, between the two sides of the membrane 4 (here via the diffusion layers of the electrodes 3).Furthermore, this solution requires that the seal 20 be made of a material having chemical compatibility with those of PAME 2. Presentation of the invention.

[0008] The invention aims to remedy at least in part the drawbacks of the prior art, and more particularly to propose an electrochemical cell of the proton exchange membrane type having improved peripheral sealing.

[0009] For this purpose, the subject of the invention is an electrochemical cell comprising: a membrane electrode assembly, comprising a proton exchange electrolytic membrane; two holding plates, located on either side of the membrane electrode assembly, comprising distribution channels for distributing reactive fluids to the electrodes; and a single seal, extending around the membrane electrode assembly in a main plane of the electrochemical cell, and arranged in contact with the two holding plates.

[0010] According to the invention, the electrochemical cell comprises at least one intermediate sealed sheet, extending around the membrane-electrode assembly in the main plane, and arranged between the latter and the seal, made of a material impermeable to the fluids intended to circulate in the distribution channels, and assembled in a sealed manner, on the one hand to the membrane, and on the other hand to the seal.

[0011] Some preferred but non-limiting aspects of this electrochemical cell are as follows.

[0012] The intermediate waterproof sheet can be assembled by gluing, using an adhesive material, to the membrane.

[0013] The intermediate waterproof sheet may be made of a material different from that of the sealing gasket.

[0014] The intermediate waterproof sheet can be assembled by gluing, overmolding or welding to the sealing joint.

[0015] The membrane may have two faces opposite each other and parallel to the main plane of the electrochemical cell, the intermediate waterproof sheet extending over one of said faces of the membrane.

[0016] The intermediate waterproof sheet can be glued to one of said faces of the membrane.

[0017] The peripheral waterproof sheet can extend in a peripheral zone of the electrochemical cell, surrounding in the main plane an active zone where an electrochemical reaction is intended to take place.

[0018] The sealing gasket may be in contact with retaining ribs of the retaining plates, the retaining ribs projecting from the main plane and arranged opposite one another.

[0019] The seal may be in contact with retaining ribs of the retaining plates, the retaining ribs projecting from the main plane, and arranged offset from each other. This offset extends in a radial direction relative to the active zone, in the main plane.

[0020] The membrane may have first and second faces opposite each other and parallel to the main plane of the electrochemical cell, and comprising first and second intermediate sealed sheets superimposed on each other, each being sealed to the membrane and the seal, the first intermediate waterproof sheet extending on the first face, and the second intermediate waterproof sheet extending on the second face.

[0021] The first intermediate waterproof sheet may be adhered to the first face, and the second intermediate waterproof sheet may be adhered to the second face.

[0022] The invention also relates to an electrochemical reactor, comprising a stack of electrochemical cells according to any one of the preceding characteristics, the electrochemical reactor being a fuel cell or an electrolyser.

[0023] The invention also relates to a method of manufacturing an electrochemical cell according to any one of the preceding characteristics, comprising a first step of assembling the intermediate sealed sheet to the sealing gasket, followed by a second step of assembling the intermediate sealed sheet to the membrane.

[0024] The first assembly step can be carried out by gluing, welding or overmolding, and the second assembly step can be carried out by gluing.

[0025] The second assembly step can be carried out by gluing at a temperature less than or equal to 200°C. Brief description of the drawings

[0026] Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended drawings in which:

[0027] [Fig.1A], already described, is a schematic and partial cross-sectional view of an electrochemical cell according to an example of the prior art, comprising two sealing joints located on either side and in contact with the electrolytic membrane;

[0028] [Fig. 1B], already described, is a schematic and partial cross-sectional view of an electrochemical cell according to another example of the prior art, comprising a single seal located in contact with the electrolytic membrane;

[0029] [Fig.2A] is a schematic and partial cross-sectional view of an electrochemical cell according to one embodiment, comprising an intermediate sealed sheet assembled in a sealed manner to the electrolytic membrane and to the same sealing joint;

[0030] [Fig.2B] is a schematic and partial cross-sectional view of an electrochemical cell according to an alternative embodiment, in which two sealed sheets intermediates superimposed on each other, and each assembled in a sealed manner to the electrolytic membrane and to the same sealing joint;

[0031] [Fig.2C] is a schematic and partial cross-sectional view of an electrochemical cell according to an alternative embodiment, in which the sealing gasket is in contact with several retaining ribs of the retaining plates, the retaining ribs being radially offset from one another;

[0032] [Fig.3] is a top view, schematic and partial, of an electrochemical cell according to the embodiment of [Fig.2A].

[0033] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0034] In the figures and in the remainder of the description, the same references represent identical or similar elements. Furthermore, the different elements are not shown to scale so as to favor the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and can be combined with each other. Unless otherwise indicated, the terms "substantially", "approximately", "of the order of" mean to within 10%, and preferably to within 5%. Furthermore, the terms "between ... and ..." and equivalent mean that the limits are included, unless otherwise indicated.

[0035] The invention relates to an electrochemical cell of the proton exchange membrane (PEM) type. Various embodiments and variants will be described with reference to an electrochemical cell of a PEM type fuel cell, and in particular to a hydrogen cell whose cathode is supplied with oxygen and the anode with hydrogen. Such a fuel cell can also operate from methanol, among others.

[0036] The invention applies, however, to any type of PEM type fuel cell, in particular to those operating at low temperature, i.e. at a temperature below 200°C, as well as to low temperature electrochemical electrolysers, for example electrolysers generating hydrogen and oxygen from water.

[0037] [Fig.2A] is a schematic and partial cross-sectional view of an electrochemical cell 1 according to one embodiment. In this example, the holding plates 10 are made using the technology of stamped conductive sheets. However, the technology of holding plates based on graphite-filled composite can be used here. In addition, in this example, peripheral sealing is ensured around FAME 2 but it can also, in addition, be ensured around the inlet and outlet manifolds (not shown).

[0038] Here and for the remainder of the description, a direct orthonormal reference frame (X, Y, Z) is defined, where the XY plane extends parallel to the main plane of the electrochemical cell 1, the X axis is oriented along a fluid flow direction of the reactive gases, and where the Z axis is oriented along the thickness dimension of the plates. holding 10. The terms "lower" and "upper" here refer to an increasing positioning along the +Z direction. Furthermore, the terms "internal" and "external" refer to an orientation in the XY plane, directed respectively towards the active zone Za or along an opposite direction.

[0039] The electrochemical cell 1 comprises a membrane electrode assembly 2 (MEA) formed of two electrodes 3 (anode and cathode) separated from each other by an electrolytic membrane 4. The MEA 2 extends along a main plane of the electrochemical cell parallel to the XY plane. The electrodes 3 and the membrane 4 are conventional elements known to those skilled in the art.

[0040] The electrolytic membrane 4 is a proton exchange membrane. It allows the diffusion of protons from an anode to a cathode, the protons being able to be present within the membrane 4 in the form of H3O+ ions. It also ensures electrical insulation between the electrodes 3, and is made of a material impermeable to the fluids circulating in the distribution channels 11 of the holding plates 10.

[0041] Each electrode 3 is here formed of a gas diffusion layer (GDL, for Gas Diffusion Layer, in English) and an active layer in contact with the membrane 4. The active layers are the location of the electrochemical reactions. They comprise materials allowing the oxidation and reduction reactions at the respective interfaces of the anode and the cathode with the membrane 4. The diffusion layers are made of a porous material allowing the diffusion of the reactive species between the distribution channels 11 of the holding plates 10 and the active layers, as well as the diffusion of the products resulting from the electrochemical reaction.

[0042] The AME is arranged between two holding plates 10 adapted to bring reactive gases to the electrodes 3, and to ensure the electrical connection of these. They can also be adapted to evacuate the heat produced during the electrochemical reaction, and to evacuate the products resulting from the electrochemical reaction. Each holding plate 10 comprises distribution channels 11 oriented towards the corresponding electrode 3. Each distribution channel 11 is formed by a bottom wall 12, a side wall 13, and is separated from the adjacent distribution channel 11 by a contact wall 14. There is therefore a lateral alternation of distribution channels 11 and separation ribs 15 (which are formed by the walls 13 and 14).

[0043] Furthermore, the holding plates 10 here each comprise at least one holding rib 16, located in the peripheral zone Zp which surrounds the active zone Za. A holding rib 16 is a portion of the holding plate which has a projection with respect to the plane XY. It is formed of a side wall and a contact wall intended to be in contact with the seal 20. The lower and upper holding ribs 16 may be superimposed on each other (i.e. perpendicular to each other), as illustrated in [Fig. 2A], or even be radially offset from each other, as illustrated in [Fig.2C]. By "radially" is meant in a radial direction in the XY plane and opposite to the active zone Za. As detailed later, the seal 20 is in contact with the retaining plates 10 at the retaining ribs 16.

[0044] The active zone Za extends in an XY plane and corresponds to the zone where the electrochemical reactions take place. It can be defined by the zone where the electrodes 3 are located, and / or by the zone where the distribution channels 11 extend. An electrolytic ink can be arranged only in the active zone Za, and not in the peripheral zone Zp (although it can alternatively be arranged over the entire surface of the membrane 4, and therefore also in the zone Zp). The peripheral zone Zp extends in the XY plane and continuously surrounds the active zone Za. In this example, the membrane 4, and here FAME 2, has a border which is present in the peripheral zone Zp. The seal 20 is located in the peripheral zone Zp, as well as the intermediate sealing sheet(s) 30.

[0045] The electrochemical cell 1 comprises a seal 20, which ensures peripheral sealing around the active zone Za, and therefore prevents leaks out of the electrochemical cell 1 of the fluids circulating in the distribution channels 11 and in the AME 2.

[0046] The peripheral seal is ensured by the single seal 20 which ensures contact between the two holding plates 10, unlike the document US2004 / 0209150 which describes a superposition of two seals superimposed and distinct from each other.

[0047] The seal 20 here extends continuously around the active zone Za in the XY plane. As indicated in document US2004 / 0209150, the seal 20 may further extend around the inlet and outlet manifolds.

[0048] The seal 20 is here located in contact with two retaining ribs 16, lower and upper, of the retaining plates 10. In this example, the retaining ribs 16 are arranged opposite one another along the Z axis, but they may have a radial offset in the plane, as detailed later with reference to [Fig.2C].

[0049] The seal 20 is made here, depending on its thickness, of the same material and in a single piece. It ensures sealing in the XY plane by contact (and preferably compression) with the two holding plates 10. Also, depending on the thickness of the electrochemical cell 1, the same seal extends along the Z axis to contact the two holding plates 10. Furthermore, depending on its longitudinal extent in the XY plane, this seal 20 is preferably made of the same material and in a single piece, but it can be made of sections of different materials, the sections being assembled to each other in a sealed manner.

[0050] The sealing gasket 20 is preferably made of an elastic material so as to ensure a sealed contact by compression with the two holding plates 10. It may be, among other things, silicone or an elastomer (e.g. EPDM) possibly fluorinated (e.g. FKM). The sealing gasket 20 may have a thickness of the order of a millimeter, or even a tenth of a millimeter.

[0051] The electrochemical cell 1 further comprises at least one intermediate sealed sheet 30, ensuring a sealed assembly between, on the one hand, the membrane 4 and, on the other hand, the sealing gasket 20.

[0052] The intermediate waterproof sheet 30 is thus arranged between the membrane 4 and the sealing gasket 20 in the XY plane. It is made in one piece and preferably in a single material. Preferably, it continuously surrounds the active zone Za in the XY plane.

[0053] It is a sheet insofar as it has a thickness less than its width and length dimensions in the XY plane. It can extend in the XY plane in the form of a strip, its length then being greater than its width. In this respect, [Fig. 3] is a top view, schematic and partial, of the electrochemical cell 1 illustrated in [Fig. 2A]. The seal 20 can be seen extending continuously around the membrane 4. The inner limit 20i (short dotted lines) of the seal 20 is therefore laterally spaced from the limit 4e (long dotted lines) of the membrane 4. The retaining rib 16 extends in contact with the seal 20. The intermediate waterproof sheet 30 extends longitudinally in the XY plane, being continuously in contact with the membrane 4 (forming an internal junction 31i) and in contact with the seal 20 (forming an external junction 31e).

[0054] The intermediate waterproof sheet 30 is assembled in a sealed manner to the membrane 4 on the one hand and to the sealing joint 20 on the other hand. It therefore forms two sealed junctions 31, a so-called internal junction 31i with the membrane 4, and a so-called external junction 31e with the sealing joint 20. In other words, the intermediate waterproof sheet 30 comprises an internal edge assembled to the membrane 4 (internal junction 31i), an external edge assembled to the sealing joint 20 (external junction 31e), and a main part extending in the XY plane between the internal and external edges.

[0055] The intermediate waterproof sheet 30 extends over one of the main faces 5, 6 of the membrane 4, here the upper main face 6 of the membrane 4, and is assembled there in a sealed manner, possibly being in contact with the face in question. It can be assembled to the lower main face 5. The internal junction 31i is located in the peripheral zone Zp, so as not to disturb the electrochemical reactions that could result from the possible presence of the intermediate waterproof sheet 30 in the active zone Za. The radial dimension of the internal junction 3 li (in a direction opposite to the active zone Za, in the XY plane) can be of the order of a few millimeters, or even tenths of a millimeter.

[0056] Preferably, the intermediate waterproof sheet 30 is bonded to one of the faces of the membrane 4 by means of an adhesive material which can be crosslinked at low temperature, for example at a temperature less than or equal to 200°C, for example of the order of 100°C to 150°C or which can be crosslinked with ultraviolet radiation. The adhesive material may in particular be an epoxy adhesive, a silane-modified polymer adhesive (MS polymer) or a cyanoacrylate adhesive. It is chosen according to its chemical compatibility with the materials of the membrane 4 and / or of FAME 2.

[0057] The intermediate waterproof sheet 30 therefore extends over a surface of the seal 20, here its upper face 22 (although it may extend over the lower face 21, or even against the lateral face, is possible). It may be bonded to the seal 20 by means of an adhesive material that can be crosslinked at low temperature or under ultraviolet light. It may also be assembled by overmolding, as described later with reference to [Fig.2B], or even by hot welding.

[0058] The intermediate waterproof sheet 30 may be made of a material distinct from that of the sealing gasket 20, for example of a polymer material such as PEN (polyethylene naphthalate) or PET (polyethylene terephthalate). The material is waterproof to the fluids circulating in the electrochemical cell 1, and more precisely in the distribution channels 11 of the holding plates 10 and in the AME 2.

[0059] Thus, the electrochemical cell 1 has improved peripheral sealing insofar as the sealing is ensured jointly by the same sealing gasket 20 coming into contact with the two holding plates 10 along the Z axis, and by an intermediate sealing sheet 30 assembled in a sealed manner to the membrane 4 and to the sealing gasket 20.

[0060] Also, the risks of leaks in the XY plane are limited by the use of the same seal 20 coming into contact with the two holding plates 10, and not, as in the example of the document US2004 / 0209150 mentioned previously, by the use of two seals. Indeed, the manufacturing tolerances of the seals can lead, with two superimposed seals, to risks of leaks in the XY plane. These risks are reduced by the use of the same seal 20. In addition, the risks of weakening of the membrane 4 which can appear when a shear force is present between the two seals described in the document US2004 / 0209150 are limited.

[0061] In addition, the risks of leaks along the Z axis are limited by the use of the intermediate waterproof sheet 30 which is assembled in a sealed manner to at least one of the main faces 5, 6 of the membrane 4 on the one hand and to the sealing joint 20 on the other hand, and in particular the risks of leaks between the two diffusion layers are limited. 3 by bypassing the membrane 4. This clearly distinguishes it from the document US2019 / 0036130 mentioned above where the sealing gasket is overmolded to the AME 2 and therefore only comes into contact with the lateral surface of the membrane (which increases the risk of leaks by bypassing the membrane 4, at the interface with the gasket). In the invention, the internal junction between the intermediate waterproof sheet 30 and the membrane 4 may have a larger surface area than in the cited document, thus improving the sealing efficiency.

[0062] Furthermore, since the seal 20 is not assembled directly to the membrane 4, the seal 20 has fewer constraints in terms of choice of the waterproof material. Indeed, in document US2019 / 0036130 where the seal is assembled to the AME by overmolding, it is necessary to choose a waterproof material that is chemically compatible with the materials of the AME. This constraint is removed within the scope of the invention.

[0063] Furthermore, the method of manufacturing the electrochemical cell 1 may comprise two different stages of assembly of the intermediate sealed sheet 30 to the seal 20 and to the membrane 4, making it possible to limit the risks of degradation or pollution of the membrane 4 and the MEA 2.

[0064] Thus, initially, the assembly to the seal 20 can be carried out before the assembly to the membrane 4, in particular when the assembly technique is likely to cause pollution or degradation of the membrane 4 or the MEA 2, as for example in the case of overmolding or hot welding. However, low temperature bonding can be carried out.

[0065] Then, the assembly of the intermediate waterproof sheet 30 to the membrane 4 can be carried out using a technique not likely to degrade the membrane 4 or the MEA 2, for example by low-temperature bonding.

[0066] [Fig.2B] is a schematic and partial cross-sectional view of an electrochemical cell 1 according to an alternative embodiment. This differs from that illustrated in [Fig.2A] essentially in that it comprises two intermediate sealed sheets 30.1, 30.2, superimposed on each other, each assembled to the membrane 4 and to the sealing gasket 20. One is located above the membrane 4, while the other is located below the membrane 4.

[0067] The upper waterproof sheet 30.2 is then assembled in a sealed manner to the upper main face 6, and more precisely to an upper surface of the peripheral edge of the membrane 4 located in the peripheral zone Zp, preferably by gluing. In addition, it is assembled in a sealed manner to an upper surface of the peripheral internal edge of the sealing joint 20, for example by gluing, hot welding, or even overmolding.

[0068] Similarly, the lower waterproof sheet 30.1 is assembled in a sealed manner to the lower main face 5, and more precisely to a lower surface of the edge of the membrane 4, preferably by gluing. In addition, it is assembled in a sealed manner to a lower surface of the peripheral internal edge of the sealing joint 20, for example by gluing, hot welding, or even overmolding. In other words, the lower waterproof sheet 30.1 extends over a first face of the membrane 4 (possibly being in contact with the latter), and the upper waterproof sheet 30.2 extends over a second face of the membrane 4 (possibly being in contact with the latter).

[0069] This provides improved mechanical strength of the indirect assembly of the seal 20 to the membrane 4 by means of the two intermediate waterproof sheets 30.1, 30.2, thus improving the peripheral sealing of the electrochemical cell 1.

[0070] [Fig.2C] is a schematic and partial cross-sectional view of an electrochemical cell 1 according to another alternative embodiment. This differs from that illustrated in [Fig.2A] essentially in that the sealing gasket 20 is in contact with several holding ribs 16 offset from each other in a radial direction.

[0071] In this example, the upper plate 10.2 comprises two retaining ribs 16.2, and the lower plate 10.1 comprises a retaining rib 16.1, arranged radially on either side of the upper retaining rib 16.2.

[0072] Also, the sealing gasket 20 is in contact with the two holding plates 10, and here is in contact with at least a part of the three holding ribs 16. It is then deformed in the XY plane, in particular along the radial direction, thus improving the peripheral sealing of the electrochemical cell 1.

[0073] This deformation of the sealing gasket 20 in the XY plane can be obtained without affecting its assembly with the intermediate sealing sheet.

[0074] In this example, three holding ribs 16 are shown, but other configurations are of course possible.

[0075] Particular embodiments have just been described. Different variants and modifications will appear to those skilled in the art.

Claims

Claims

1. Electrochemical cell (1), comprising: • a membrane electrode assembly (2), comprising a proton exchange electrolytic membrane (4); • two holding plates (10), located on either side of the membrane electrode assembly (2), comprising distribution channels (11) for distributing reactive fluids to the electrodes (3); • a single seal (20), • extending around the membrane electrode assembly (2) in a main plane of the electrochemical cell (1), and • arranged in contact with the two holding plates (10); • characterized in that it comprises: • at least one intermediate waterproof sheet (30), • extending around the membrane electrode assembly (2) in the main plane, and arranged between the latter (2) and the sealing joint (20), • made of a material impermeable to fluids intended to circulate in the distribution channels (11);• assembled in a sealed manner, on the one hand to the membrane (4), and on the other hand to the sealing joint (20); • the sealing joint (20) being in contact with holding ribs (16) of the holding plates (10), the holding ribs (16) projecting from the main plane; • the intermediate waterproof sheet (30) is assembled to a surface of the sealing joint (20) located between the membrane electrode assembly (2) and the holding ribs (16), forming an external junction (31e).;

2. Electrochemical cell (1) according to claim 1, in which the intermediate waterproof sheet (30) is assembled by gluing, by means of an adhesive material, to the membrane (4).

3. Electrochemical cell (1) according to claim 1 or 2, wherein the intermediate sealing sheet (30) is made of a material different from that of the sealing gasket (20).

4. Electrochemical cell (1) according to any one of claims 1 to 3, in which the intermediate sealed sheet (30) is assembled by gluing, overmolding or welding to the sealing joint (20).

5. Electrochemical cell (1) according to any one of claims 1 to 4, in which the membrane (4) has two faces opposite each other and parallel to the main plane of the electrochemical cell (1), the intermediate waterproof sheet (30) extending over one of said faces of the membrane (4).

6. Electrochemical cell (1) according to claims 4 and 5, wherein the intermediate waterproof sheet (30) is bonded to one of said faces of the membrane (4).

7. Electrochemical cell (1) according to any one of claims 1 to 6, in which the peripheral sealed sheet (30) extends in a peripheral zone (Zp) of the electrochemical cell, surrounding in the main plane an active zone (Za) where an electrochemical reaction is intended to take place.

8. Electrochemical cell (1) according to any one of claims 1 to 7, in which the seal (20) is in contact with holding ribs (16) of the holding plates (10), the holding ribs projecting from the main plane, and arranged opposite one another.

9. Electrochemical cell (1) according to any one of claims 1 to 7, in which the seal (20) is in contact with holding ribs (16) of the holding plates (10), the holding ribs projecting from the main plane, and arranged offset from each other.

10. Electrochemical cell (1) according to any one of claims 1 to 9, in which the membrane (4) has first and second faces opposite each other and parallel to the main plane of the electrochemical cell (1), and comprising first and second intermediate sealing sheets (30.1, 30.2) superimposed on each other, each being assembled in a sealed manner to the membrane (4) and to the seal (20), the first intermediate sealing sheet (30.1) extending on the first face, and the second intermediate sealing sheet (30.2) extending on the second face.

11. An electrochemical cell (1) according to claim 10, wherein the first intermediate sealing sheet (30.1) is bonded to the first face, and the second intermediate sealing sheet (30.2) is bonded to the second face.

12. Electrochemical reactor, comprising a stack of electrochemical cells according to any one of the preceding claims, the electrochemical reactor being a fuel cell or an electrolyser.

13. A method of manufacturing an electrochemical cell according to any one of claims 1 to 11, comprising a first step of assembling the intermediate sealed sheet (30) to the seal (20), followed by a second step of assembling the intermediate sealed sheet (30) to the membrane (4).

14. The method of claim 13, wherein the first assembly step is performed by gluing, welding or overmolding, and the second assembly step is performed by bonding.

15. A method according to claim 14, wherein the second assembly step is carried out by gluing at a temperature less than or equal to 200°C.

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