Electrochemical cell bipolar plate for reducing short-circuit flows at the edge of the reaction zone

Abstract

The invention relates to an electrochemical cell bipolar plate, comprising upper and lower metal sheets (10, 20), the ribs of which define, along the distribution circuits (7), a lateral bypass zone (Zc) in which there is a longitudinal alternation of a first short-circuit prevention portion (P1sup) and a second short-circuit prevention portion (P2jnf), such that: • in the first short-circuit prevention portion (P1sup), the lower metal sheet (20) comprises a longitudinal series of internal ribs (25i) and external ribs (25e), each having an opposite, closed end that is not connected to the external rib (22e) or the internal rib (22i), respectively; • in the second short-circuit prevention portion (P2inf), the upper metal sheet (10) comprises a longitudinal series of internal ribs (15i) and external ribs (15e), each having an opposite, closed end that is not connected to the external rib (12e) or the internal rib (12i), respectively.

Description

DESCRIPTION TITLE: BIPOLAR PLATE OF ELECTROCHEMICAL CELL ALLOWING A REDUCTION OF SHORT-CIRCUIT FLOWS AT THE EDGE OF THE REACTION ZONE TECHNICAL FIELD

[0001] The field of the invention is that of electrochemical reactors comprising a stack of electrochemical cells, such as fuel cells and electrolysers, and relates more particularly to bipolar plates with conductive sheets. STATE OF THE PRIOR ART

[0002] An electrochemical reactor, such as a fuel cell or an electrolyzer, usually consists of a stack of electrochemical cells, each of which has an anode and a cathode electrically separated from each other by an electrolyte. The cells are the site of an electrochemical reaction between two continuously introduced reactive fluids.

[0003] Generally speaking, in the case of a fuel cell, the combustible fluid (e.g. hydrogen) is supplied to the anode, while the oxidizing fluid (e.g. air) is supplied 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, for example, contained in a polymer membrane, and an electronic conductor formed by the external electrical circuit. The stack of cells is thus the site of the electrochemical reaction: the reactive fluids must be supplied there, the products and non-reactive species must be removed, as must the heat produced during the reaction.

[0004] Electrochemical cells are usually separated from each other by bipolar plates that provide electrical interconnection between them and the flow of reactive fluids. The bipolar plates have an anodic face at which a fuel fluid distribution circuit is formed, and an opposite cathodic face at which a combustion fluid distribution circuit is formed. Each distribution circuit takes the form of a network of channels arranged to bring the reactive fluid to the corresponding electrode. The bipolar plates may also have a cooling circuit formed by a network of internal conduits that ensure the flow of a heat transfer fluid to evacuate the heat produced locally during the electrochemical reaction by the cell.

[0005] Figure 1A is a schematic and partial view of an example of a bipolar plate 1, of the conductive sheet type, seen from above and from the cathode side. Figure 1B is a cross-sectional view of the bipolar plate 1 of Fig. 1A along the section line AA.

[0006] The bipolar plate 1 comprises two upper 10 and lower 20 sheets, made of an electrically conductive material, and superimposed on each other. The sheets 10, 20 each comprise a distribution circuit 7 adapted to convey a reactive fluid to the corresponding electrode. The anodic and cathodic distribution circuits 7 are superimposed on each other, and define, in the XY plane, the reaction zone of the electrochemical cell. An air collector 2 and a hydrogen collector 3 are located opposite one another on the same side of the distribution circuit 7, and are here separated from each other by a heat transfer liquid collector 4. The air collector 2 is adapted to supply the distribution circuit 7 with air, here via an injection zone 8 then a homogenization zone 9.

[0007] The sheets 10, 20 comprise an external sealing line, formed of upper 12e and lower 22e external longitudinal ribs, superimposed on each other, each associated with a so-called external (upper and lower) sealing joint 5. The external sealing line extends continuously around the periphery of the bipolar plate 1, and surrounds in the XY plane the collectors 2 and 3 (and here also the collector 4) and the reaction zone. It prevents the reactive fluids from flowing outside the bipolar plate. Furthermore, the sheets 10, 20 comprise upper 12i and lower 22i internal longitudinal ribs, which extend longitudinally along the edge of the distribution circuits, and participate in delimiting a distribution channel.The external longitudinal ribs 12e, 22e (also called joint ribs) and the internal longitudinal ribs 12i, 22i (also called channel ribs) longitudinally delimit a lateral bypass zone Z. cc located on the edge of the distribution circuit.

[0008] Thus, in operation, the air is supplied by the inlet manifold 2, flows through the injection zone 8 then the homogenization zone 9, and comes into contact with the cathode 32 by means of the distribution circuit 7. The unconsumed air then flows through a homogenization zone, then an injection zone, to finally reach the air outlet manifold 2 (see continuous arrows in fig.lA). The same applies to the hydrogen on the anode side.

[0009] However, it appears that air can bypass the reaction zone by flowing into lateral bypass zones Z cclocated between the reaction zone and the external sealing line. Indeed, as shown by the dotted arrows in fig.1A, air can escape from the injection zone 8 to reach the lateral bypass zones Z cc (left in the figure) and flow along the longitudinal edges of the reaction zone. These flows are short-circuit flows in that they do not participate in the electrochemical reaction, which degrades the performance of the fuel cell. This is the case for air on the cathode side, but also for hydrogen on the anode side.

[0010] There is therefore a need to have bipolar plates whose structural configuration of the conductive sheets makes it possible to reduce these flows in these lateral bypass zones, both for the reactive fluids and for the heat transfer liquid.

[0011] In this respect, document EP3171439 A1 describes a structural configuration of the conductive sheets in the lateral bypass zones, where the conductive sheets comprise lower and upper transverse longitudinal ribs superimposed on each other, each of which directly connects the internal longitudinal rib to the external longitudinal rib. The intermediate transverse ribs are deformable, so that when deformed, they extend vertically in the direction of the sealing film (see film 34 in fig. 1B), between the AME and the external seal, and best match the shape of the AME. Thus, the cross-section of flow of the reactive fluids, in this lateral bypass zone Z cc, is reduced, which limits the short-circuit flow of reactive fluids. However, the flow cross-section of the heat transfer fluid is increased, which reduces the cooling efficiency and degrades the performance of the electrochemical cell. STATEMENT OF THE INVENTION

[0012] The invention aims to remedy at least in part the drawbacks of the prior art, and more particularly to propose a bipolar plate of an electrochemical cell whose structural configuration of the conductive sheets, in at least one of the lateral bypass zones, makes it possible to reduce both the short-circuit flow of the reactive fluids and that of the heat transfer liquid, while making it possible to limit the risks of mechanical deformation of the conductive sheets and / or of the membrane / electrode assemblies in the intermediate longitudinal zone.

[0013] For this purpose, the subject of the invention is a bipolar plate of an electrochemical cell, comprising upper and lower sheets, superimposed on each other, comprising: o lower and upper distribution circuits, superimposed on each other, adapted to bring reactive fluids respectively to lower and upper electrodes; o upper and lower internal longitudinal ribs, superimposed on each other, respectively forming a longitudinal border of the lower and upper distribution circuits; o upper and lower external longitudinal ribs, superimposed on each other, extending along the internal longitudinal ribs, laterally delimiting, with the internal longitudinal ribs, a lateral zone called a bypass extending longitudinally along the distribution circuits.

[0014] In the lateral bypass zone there is a longitudinal alternation: o of at least a first anti-short-circuit part, where: the upper sheet has an upper intermediate longitudinal rib, extending throughout the first anti-short-circuit part; and where the lower sheet has a lower intermediate recess, superimposed and in contact with the upper intermediate longitudinal rib; o of at least a second anti-short-circuit part, where: the lower sheet has a lower intermediate longitudinal rib, extending throughout the second anti- short circuit; and where the upper sheet has an upper intermediate recess, superimposed and in contact with the lower intermediate longitudinal rib.

[0015] According to the invention, in the first anti-short-circuit part, the lower sheet comprises a longitudinal succession of lower transverse ribs, including: internal, respectively external, lower transverse ribs, extending from the internal, respectively external, lower longitudinal rib, and having a closed opposite end not connected to the external, respectively internal, lower longitudinal rib.

[0016] Furthermore, in the second anti-short-circuit part, the upper sheet comprises a longitudinal succession of upper transverse ribs, including: internal, respectively external, upper transverse ribs, extending from the internal, respectively external, upper longitudinal rib, and having a closed opposite end not connected to the external, respectively internal, upper longitudinal rib.

[0017] Some preferred but not limiting aspects of this bipolar plate are as follows.

[0018] The bipolar plate may comprise several first anti-short-circuit parts arranged in longitudinal alternation with several second anti-short-circuit parts.

[0019] In the first anti-short-circuit portion, the inner and outer lower transverse ribs of the lower sheet may be interdigitated, so that each inner lower transverse rib extends along an outer lower transverse rib.

[0020] In the second anti-short-circuit part, the inner and outer upper transverse ribs of the upper sheet may be interdigitated, so that each inner upper transverse rib extends along an outer upper transverse rib.

[0021] The upper and lower transverse ribs can have, in a plane parallel to the bipolar plate, a rectilinear, T-shaped, L-shaped or spiral shape.

[0022] The upper and lower external transverse ribs may have a height, relative to a reference plane passing between the upper and lower external longitudinal ribs, lower than that of the upper and lower external longitudinal rib.

[0023] The lower intermediate recess may separate, along an axis orthogonal to a longitudinal axis of the lateral bypass zone, the external lower transverse rib from the internal lower longitudinal rib, and the internal lower transverse rib from the external lower longitudinal rib.

[0024] The upper intermediate recess may separate, along an axis orthogonal to a longitudinal axis of the lateral bypass zone, the upper external transverse rib from the upper internal longitudinal rib, and the upper internal transverse rib from the upper external longitudinal rib.

[0025] The upper and lower external longitudinal ribs may each be in contact with a sealing gasket.

[0026] The invention also relates to an electrochemical cell, comprising at least one bipolar plate according to any one of the preceding characteristics, and a membrane / electrode assembly in contact with the bipolar plate.

[0027] The invention also relates to an electrochemical reactor, comprising at least one electrochemical cell according to the preceding characteristic. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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: figure 1A, already described, is a top view, schematic and partial, of a bipolar plate according to an example of the prior art; figure 1B, already described, is a schematic and partial view, in cross-section, of the bipolar plate of fig.1A, along the section line AA; Figure 2 is a schematic and partial top view of a bipolar plate according to one embodiment, illustrating the first and second anti-short-circuit parts located in the lateral bypass zones; Figure 3A is a schematic and partial view of a part of an upper sheet of a bipolar plate according to one embodiment, in a lateral bypass zone; Figure 3B is a schematic and partial view of a part of a lower sheet of the bipolar plate of Fig. 3A, in the same lateral bypass zone; Figure 3C is a schematic and partial view of the same part of the upper sheet of the bipolar plate of Fig.3A, in the same lateral bypass zone, illustrating the lower transverse ribs (in dotted lines); Figures 4A to 4H are schematic and partial views, in cross-section, of a bipolar plate according to one embodiment, in a lateral bypass zone, along different cutting lines in the first and second anti-short-circuit parts; Figures 5A to 5C are schematic and partial top views of a part of an upper sheet of a bipolar plate, according to different variant embodiments of the upper transverse ribs; Figures 6A and 6B are schematic and partial views, in perspective (fig.6A) and in longitudinal section (fig.6B), of a bipolar plate according to one embodiment; Figures 7A to 7F are schematic and partial cross-sectional views of a bipolar plate according to one embodiment, in a lateral bypass zone, along different cutting lines in the first and second anti-short-circuit parts. DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0029] In the figures and in the remainder of the description, the same references represent identical or similar elements. In addition, the different elements are not shown to scale so as to enhance the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and may 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.

[0030] The invention relates to a bipolar plate of an electrochemical cell, for electrochemical reactors such as fuel cells and electrolysers. The bipolar plate is of the type with conductive sheets, which comprise ribs and recesses. The invention relates more specifically to a particular structural configuration of the bipolar plate in at least one of the lateral bypass zones which extend longitudinally between the external sealing line and the reaction zone, making it possible to reduce the short-circuit flow of the reactive fluids as well as that of the heat transfer liquid, while making it possible to limit the risks of deformation of the AME or the conductive sheets in the intermediate longitudinal zone.

[0031] Various embodiments and variants will be described with reference to a fuel cell, and in particular to a PEM (Proton Exchange Membrane) type fuel cell whose cathode is supplied with oxygen and the anode with hydrogen. The invention, however, applies to any type of fuel cell, in particular to those operating at low temperature, i.e. at a temperature below 200°C, as well as to electrochemical electrolysers.

[0032] Figure 2 is a schematic and partial top view of a part of the bipolar plate 1 according to one embodiment. Certain elements are described with reference to Fig. 1B.

[0033] Here and for the remainder of the description, we define a direct orthogonal reference frame XYZ, where the Z axis is oriented along the thickness of the bipolar plate 1 (from the lower sheet 20 to the upper sheet 10), and where the X and Y axes define a main plane along which the bipolar plate extends.

[0034] The electrochemical cells here belong to a stack of cells of a fuel cell. Each electrochemical cell comprises a membrane / electrode assembly 30 (MEA, cf. fig. 1B) formed of a cathode 32, an anode 33 separated from each other by an electrolyte 31 here comprising a polymer membrane. The MEAs 30 of the electrochemical cells are arranged between bipolar plates 1 adapted to bring reactive species to the electrodes and to evacuate the heat produced during the electrochemical reaction. The MEA here extends partly in the lateral bypass zone Z ccalong the transverse axis X. A waterproof film 34 (distinct from the membrane 31 or corresponding to the membrane) can extend from the AME 30 to the edge of the bipolar plates 1 and be in contact with the external sealing joints 5.

[0035] Each bipolar plate 1 is formed of two upper 10 and lower 20 sheets, superimposed and assembled to each other. They are made of an electrically conductive material. These conductive sheets 10, 20 are deformed locally so as to form flow channels for the reactive fluids, and in particular an injection zone 8, a homogenization zone 9 and a distribution circuit 7, as well as a cooling circuit located between the conductive sheets 10, 20. Thus, the lower sheet 20, for example anode, is intended to be in contact with the anode of the membrane / electrode assembly 30 of an adjacent electrochemical cell, while the upper sheet 10, here cathode, is intended to be in contact with the cathode 32 of the MEA of the electrochemical cell.

[0036] Each conductive sheet 10, 20 comprises an external face and an opposite internal face, the conductive sheets 10, 20 facing each other at the internal faces. An external face is called anodic when it is intended to be in contact with the anode 33, or is called cathodic when it is intended to be in contact with the cathode 32. The anodic face of a conductive sheet comprises the distribution circuit for a combustible reactive fluid, for example hydrogen here, and the cathodic face of the other conductive sheet comprises the distribution circuit for the oxidizing reactive fluid, for example air here.

[0037] The conductive sheets 10, 20 are in the form of sheets, or elementary plates of low thickness, made of an electrically conductive material, for example a metal or even a composite material for example loaded with graphite. The thickness can be of the order of a few tens of microns to a few hundred microns, for example from 50 pm to 200 pm approximately in the case of metal sheets.

[0038] Each conductive sheet 10, 20 comprises ribs and recesses, obtained for example by stamping, embossing, or any other shaping technique, the shape of which on one face is the complement of the shape on the opposite face. The ribs make it possible in particular to define the distribution circuit of a reactive fluid at the external face, as well as the cooling circuit of the heat transfer fluid at the internal face.

[0039] Collectors 2, 3, 4 are openings which pass through each of the bipolar plates 1. The collectors of the reactive fluids 2, 3 are located on either side of the reaction zone, along a main axis of flow of the reactive fluids, here along the Y axis. In this example, a heat transfer fluid collector 4 is located between the reactive fluid collectors 2, 3. Alternatively, they can be located along an X axis orthogonal to the longitudinal Y axis.

[0040] The reactive fluid collectors 2, 3 are adjacent to each other (separated or not by the heat transfer liquid collector 4), and are arranged opposite the same opening (inlet or outlet) of the reaction zone. In this example, an air inlet collector 2 and a hydrogen collector 3 (inlet or outlet) are located opposite the inlet of the cathode distribution circuit 7.

[0041] The conductive sheets 10, 20 comprise injection zones 8 to allow the circulation of fluids from or to the collectors. Thus, an air injection zone 8 ensures the fluid connection between the air collector 2 and the homogenization zone 9. It is formed of conduits which cross the sealing line of the air collector and open onto the external face of the upper sheet 10, to allow the air to flow towards the homogenization zone 9. The same is true for the lower sheet 20, the injection zone of which communicates with the hydrogen collector 3 and the homogenization zone. The injection zone of the heat transfer liquid is formed of conduits which open between the two cathode 10 and anodic 20 conductive sheets. Similar injection zones are described in particular in the document EP3136492A1.

[0042] Each conductive sheet 10, 20 here comprises a homogenization zone 9 which communicates with the injection zone 8 on the one hand, and with the distribution circuit 7 on the other hand. Such a homogenization zone 9 makes it possible to homogenize the air flow at the inlet of the distribution circuit 7. It can be formed by homogenization conduits made in the conductive sheet 10. The document EP3136492A1 also describes an example of such a homogenization zone.

[0043] Each conductive sheet 10, 20 comprises a distribution circuit 7, formed of channels which extend between an inlet and an outlet aligned along a main direction (here the Y axis). These channels are separated two by two by a separation rib which is in contact with the corresponding MEA. The cathode and anodic distribution circuits define in the XY plane the reaction zone of the electrochemical cell.

[0044] Furthermore, we define a reference plane P re f of the bipolar plate 1 as being the contact plane of the conductive sheets 10, 20 at their external edges 11e and 21e (see fig. 1B). This is the reference plane P re f with respect to which the ribs and recesses are defined, when considered from the external face of each conductive sheet 10, 20.

[0045] Thus, a rib is obtained by local deformation of the conductive sheet 10, 20, from its internal face to its external face. It is therefore a relief or a boss of the conductive sheet 10, 20, seen from the external face, which moves away from the reference plane P re f along the Z axis (and therefore which moves away from the other conductive sheet). In other words, a rib is a surface protruding from the reference plane P re f. Thus, an upper rib is a rib of the upper sheet 10 which moves away from the reference plane Pre f along the +Z direction. And a rib lower is a rib of the lower sheet 20 which moves away from the reference plane P re f along the -Z direction. Furthermore, a rib has an elongated shape in the XY plane: a dimension (length) along a longitudinal axis is greater than its dimension (width) along a transverse axis.

[0046] Furthermore, an intermediate longitudinal rib is a rib located in the lateral bypass zone Z. cc (therefore located between the internal and external longitudinal ribs) and which extends longitudinally along the same longitudinal axis Y as that of zone Z cc . In addition, an intermediate transverse rib is a rib located in the lateral bypass zone Z. cc and which extends longitudinally along an inclined axis (in the XY plane), or even orthogonal, to the longitudinal Y axis of zone Z cc .

[0047] Conversely, a recess is obtained by local deformation of the conductive sheet 10, 20, from its external face towards its internal face. It is therefore a depression or a hollow of the conductive sheet 10, 20, seen from its external face, which extends below the reference plane P re f along the Z axis (and therefore which approaches the other conductive sheet). Thus, an upper recess is a recess in the upper sheet 10 which goes beyond the reference plane P re f along the -Z direction. And a lower recess is a recess in the lower sheet 20 that goes beyond the reference plane P re f along the +Z direction.

[0048] As illustrated in Fig. 1B, the bipolar plate 1 comprises external longitudinal ribs, upper 12e and lower 22e, superimposed on each other, which entirely surround in the XY plane the collectors 2 and 3 as well as the reaction zone. They extend longitudinally at the edge of the bipolar plate 1. Seals 5, called external seals, are arranged respectively in contact with the external longitudinal ribs upper 12e and lower 22e. They are also in contact with the waterproof film 34. This configuration, which forms an external sealing line, makes it possible to prevent fluids, in particular reactive gases, from flowing outside the bipolar plate 1.

[0049] Furthermore, the bipolar plate 1 comprises internal longitudinal ribs, upper 12i and lower 22i, superimposed on each other, which extend longitudinally at the edge of the reaction zone. They form the edge ribs of the distribution circuits 7. They are in contact with the diffusion layer of the electrode of the MEA 30. Thus, the lateral bypass zone Z cc corresponds to the area delimited laterally (along the X axis) by the external sealing line and by the reaction zone, and more precisely by the external longitudinal ribs 12e, 22e on the one hand, and by the internal longitudinal ribs 12i, 22i on the other hand. Its longitudinal axis is here the Y axis (this longitudinal axis can be rectilinear or not).

[0050] It should also be noted that the conductive sheets 10, 20 comprise flat portions, upper and lower, superimposed on each other, and in contact with each other at the level of the reference plane P. re f. Thus, external longitudinal portions lie, 21e extend in the XY plane between the external longitudinal ribs 12e, 22e and the edge of the bipolar plate 1, over the entire periphery thereof. In addition, upper internal longitudinal portions lli and lower 21i extend between the internal longitudinal ribs 12i, 22i and the distribution ribs.

[0051] According to the invention, in at least one of the lateral bypass zones Z cc , the bipolar plate 1 is formed of a longitudinal succession of at least a first anti-short-circuit part PlCsup, and a second anti-short-circuit part P2j nf. By longitudinal succession, we mean that these first and second anti-short-circuit parts Pl sup , P inf follow one another along the longitudinal axis of the lateral bypass zone Z cc This longitudinal succession can be an alternation of several first anti-short-circuit parts Pl sup with several second anti-short-circuit parts P2i n r, periodically or not.

[0052] In the first anti-short-circuit part Pl sup , the contact plane between the two conductive sheets 10, 20 is an upper contact plane Pc sup , in the sense that it is located above the reference plane P re f along the +Z direction (see in particular fig. 4B to 4D, described later).

[0053] The upper sheet 10 has an upper intermediate longitudinal rib 16, which extends along the longitudinal axis of the lateral bypass zone Z cc. Preferably, it extends continuously in a planar manner. It may be coplanar, or not, with the external upper longitudinal rib 12e and / or with the internal upper longitudinal rib 12i. This upper intermediate longitudinal rib 16 extends over the entire length (along the Y axis) of the first anti-short-circuit part Pl sup , and over its entire width (along the Y axis). It thus directly connects the external upper longitudinal rib 12e with the internal upper longitudinal rib 12i, without there being an intermediate recess. The upper intermediate longitudinal rib 16 may be in contact with the AME over at least part of its width.

[0054] In addition, the lower sheet 20 has a lower intermediate recess 24, superimposed on the upper intermediate longitudinal rib 16, and in contact with the latter, which extends along the longitudinal axis of the lateral bypass zone Zcc The contact plane between the upper intermediate longitudinal rib 16 and the lower intermediate recess 24 corresponds to the upper contact plane Pc sup . It is located above the reference plane P re f (see fig.4B).

[0055] Finally, the lower sheet 20 also comprises a longitudinal succession, and preferably a longitudinal alternation, of lower transverse ribs 25i, 25e, of two different types: external lower transverse ribs 25e and internal lower transverse ribs 25i. These lower transverse ribs 25i, 25e extend vertically from the lower intermediate recess 24 in the direction -Z.

[0056] An external lower transverse rib 25e is a rib that extends along an axis transverse to the longitudinal axis Y, from the external lower longitudinal rib 22e and towards the internal lower longitudinal rib 22i. By "from the external lower longitudinal rib", it is meant that it is directly connected to the latter (without an intermediate recess that would come into contact with the upper rib 16). Thus, the section straight section delimited by the external lower longitudinal rib 22e communicates with the straight section delimited by the external lower transverse rib 25e. Furthermore, the opposite end of the external lower transverse rib 25e is closed (plugged), in the sense that the latter is not connected to the internal lower longitudinal rib 22i. Thus, the straight section delimited by the internal lower longitudinal rib 22i does not communicate with the straight section delimited by the external lower transverse rib 25e: the lower recess 24 ensures the separation along the X axis between the external lower transverse rib 25e and the internal lower longitudinal rib 22i.

[0057] An internal lower transverse rib 25i is a rib that extends along an axis transverse to the longitudinal axis Y, from the internal lower longitudinal rib 22i and towards the external lower longitudinal rib 22e. By “from the internal lower longitudinal rib”, it is meant that it is directly connected to the latter (without an intermediate recess that would come into contact with the upper rib 16). Thus, the cross-section delimited by the internal lower longitudinal rib 22i communicates with the cross-section delimited by the internal lower transverse rib 25i. Furthermore, the opposite end of the internal lower transverse rib 25i is closed (plugged), in the sense that the latter is not connected to the external lower longitudinal rib 22e.Thus, the cross section delimited by the external lower longitudinal rib 22e does not communicate with the cross section delimited by the internal lower transverse rib 25i: the lower recess 24 ensures the separation along the X axis between the internal lower transverse rib 25i and the external lower longitudinal rib 22e.

[0058] Furthermore, in the second anti-short-circuit part P2j n r, the contact plane between the two conductive sheets 10, 20 is a lower contact plane Pcinf, in the sense that it is located below the reference plane P re f along the +Z direction (see in particular fig. 4E to 4F, described later).

[0059] The lower sheet 20 has a lower intermediate longitudinal rib 26, which extends along the longitudinal axis of the lateral bypass zone Z cc. Preferably, it extends continuously in a planar manner. It may be coplanar, or not, with the external lower longitudinal rib 22e and / or with the internal lower longitudinal rib 22i. This lower intermediate longitudinal rib 26 extends over the entire length (along the Y axis) of the anti-short-circuit part P2j n r, and over its entire width (along the Y axis). It thus directly connects the external lower longitudinal rib 22e with the internal lower longitudinal rib 22i, without there being an intermediate recess. The lower intermediate longitudinal rib 26 may be in contact with the AME over at least part of its width.

[0060] In addition, the upper sheet 10 has an upper intermediate recess 14, superimposed on the lower intermediate longitudinal rib 26, and in contact with the latter, which extends along the longitudinal axis of the lateral bypass zone Zcc . The contact plane between the lower intermediate longitudinal rib 26 and the upper intermediate recess 14 corresponds to the lower contact plane Pcinf. It is located below the reference plane P re f (see fig.4E).

[0061] Finally, the upper sheet 10 also comprises a longitudinal succession, and preferably a longitudinal alternation, of upper transverse ribs 15e, 15i of two different types: external upper transverse ribs 15e and internal upper transverse ribs 15i. These upper transverse ribs 15i, 15e extend vertically from the upper intermediate recess 14 in the +Z direction.

[0062] An outer upper transverse rib 15e is a rib that extends along an axis transverse to the longitudinal axis Y, from the outer upper longitudinal rib 12e and towards the inner upper longitudinal rib 12i. By "from the outer upper longitudinal rib" is meant that it is directly connected to the latter (without an intermediate recess). Furthermore, the opposite end of the outer upper transverse rib 15e is closed (plugged), in the sense that the latter is not connected to the inner upper longitudinal rib 12i: the lower recess 14 ensures the separation along the X axis between the outer upper transverse rib 15e and the inner upper longitudinal rib 12i.

[0063] An inner upper transverse rib 15i is a rib that extends along an axis transverse to the longitudinal axis Y, from the inner upper longitudinal rib 12i and towards the outer upper longitudinal rib 12e. By "from the inner upper longitudinal rib" is meant that it is directly connected to the latter (without an intermediate recess). Furthermore, the opposite end of the inner upper transverse rib 15i is closed (plugged), in the sense that the latter is not connected to the outer upper longitudinal rib 12e: the lower recess 14 ensures the separation along the X axis between the inner upper transverse rib 15i and the outer upper longitudinal rib 12e.

[0064] So, as explained in detail later, in the anti-short-circuit part Pl sup with upper contact plane Pc sup, the air flow cross-section, at the level of the upper sheet 10 (cathodic), is greatly reduced (increase in the linear pressure drop), which limits the short-circuit flow of the air. In addition, the short-circuit flow of the hydrogen, at the level of the lower sheet 20 (anodic), is limited by the presence of the lower transverse ribs 25e, 25i. Indeed, these ribs induce an increase in the fluidic resistance (increase in the singular pressure drops), which limits the short-circuit flow at the level of the lower sheet 20. Finally, the short-circuit flow of the heat transfer liquid is limited to the extent that the internal lower transverse ribs 25i are not connected to the external longitudinal rib 22e. Thus, the heat transfer liquid cannot flow there and therefore cannot enter the reaction zone.

[0065] Similarly, in the anti-short-circuit part P2j nf with lower contact plane Pcinf, the hydrogen flow cross-section, at the level of the lower sheet 20, is strongly reduced (increase in linear pressure drop), which limits the short-circuit flow of hydrogen. In addition, the short-circuit flow of air, at the level of the upper sheet 10, is limited by the presence of the upper transverse ribs 15e, 15i (increase in fluid resistance due to singular pressure drops), which limits the short-circuit flow at the level of the upper sheet 10. Finally, the short-circuit flow of the heat transfer liquid is limited to the extent that the internal upper transverse ribs 15i are not connected to the external longitudinal rib 12e. Thus, the heat transfer liquid cannot flow therein or thus partially bypass the reaction zone.

[0066] In the example of Fig. 2, each lateral bypass zone Z cchere includes a longitudinal alternation of several anti-short-circuit parts Pl SU p with upper contact plane Pcsup and several anti-short-circuit parts P2j n f with lower contact plane Pcinf, where here each anti-short-circuit part Pl sup is directly followed by an anti-short circuit part P2j n f. Obviously, other arrangements of the anti-short-circuit parts are possible. In any case, the short-circuit flows of the reactive fluids are limited in these lateral bypass zones Z cc , so that the reacting fluids flow more into the reaction zone, which improves the performance of the electrochemical cell. Similarly, the short-circuit flow of the heat transfer fluid is limited, which also improves the performance of the electrochemical cell.

[0067] Figures 3A to 3C are schematic and partial views, in top view, of a part of the bipolar plate 1 of Fig. 2, at the level of a lateral bypass zone. Fig. 3A is a top view of the upper sheet 10, Fig. 3B is a top view of the lower sheet 20, and Fig. 3C is a top view of the bipolar plate 1, where lower transverse ribs 25e, 25i are visible in dotted lines.

[0068] With reference to Fig. 3A, the upper sheet 10 comprises the external upper longitudinal rib 12e, which helps to define the external sealing line, and extends continuously along the longitudinal axis Y. It comprises the internal upper longitudinal rib 12i, which forms the edge of the upper distribution circuit 7. It also extends here continuously along the longitudinal axis Y. It should be remembered that the ribs 12e and 12i may not extend longitudinally in parallel.

[0069] In the anti-short-circuit parts Pl SU p with upper contact plane Pc SU p, the upper sheet 10 comprises an upper intermediate longitudinal rib 16, which transversely connects along the X axis the upper external 12e and internal 12i longitudinal ribs, and which extends longitudinally along the Y axis, continuously, between the two adjacent anti-short-circuit parts P2inf.

[0070] In the P2i anti-short-circuit parts n r with lower contact plane Pcinf, the upper sheet 10 has an upper intermediate recess 14, which extends transversely along the X axis between the upper external 12e and internal 12i longitudinal ribs, and which extends longitudinally along the Y axis between the two anti-short-circuit parts P2j nf adjacent. It also includes a longitudinal alternation of external upper transverse ribs 15e and internal ribs 15i. In this example, the upper transverse ribs 15e, 15i are straight and extend along the transverse axis X.

[0071] Referring to Fig. 3B, the lower sheet 20 comprises the external lower longitudinal rib 22e and the internal lower longitudinal rib 22i.

[0072] In the anti-short-circuit parts Pl SU p with upper contact plane Pc SU p, the lower sheet 20 has a lower intermediate recess 24, which extends transversely along the X axis between the lower external 22e and internal 22i longitudinal ribs. This lower intermediate recess 24 is superimposed on the upper longitudinal rib 16 and is in contact with it. This contact is made in the upper contact plane Pc supIt also has a longitudinal alternation of external lower transverse ribs 25e and internal lower transverse ribs 25i.

[0073] In the P2i anti-short-circuit parts n r with lower contact plane Pcinf, the lower sheet 20 comprises a lower intermediate longitudinal rib 26, which connects transversely along the X axis the lower external 22e and internal 22i longitudinal ribs, and which extends longitudinally along the Y axis, continuously, between the two adjacent anti-short-circuit parts Plsup.

[0074] With reference to fig.3C, the upper sheet 10 is shown, with, in the portions Plsup, its upper longitudinal rib 16, and the alternation of the internal lower transverse ribs 25i of the lower sheet 20 is shown in dotted lines. Also shown, in the portions P2j nf, the upper intermediate recess 14 with the alternation of its upper transverse ribs 15e, 15i, superimposed on the lower longitudinal rib 26 (not shown) of the lower sheet 20.

[0075] Thus, in the Plsup portions, the short-circuit flow of air is limited by reducing the flow cross-section (due to the upper longitudinal rib 16), and the short-circuit flow of hydrogen is limited by the presence of the lower transverse ribs 25e, 25i. And in the P2j portions nf, the short-circuit flow of hydrogen is limited by reducing the flow cross-section (due to the lower longitudinal rib 26), and the short-circuit flow of air is limited by the presence of the upper transverse ribs 15e, 15i. The short-circuit flow of the heat transfer liquid is also limited to the extent that the upper internal transverse ribs 15i and 25i are not connected to the upper external longitudinal ribs 12e and 22e, respectively.

[0076] Figures 4A to 4H are schematic and partial views of a bipolar plate 1 similar to that of Fig. 2, along different section lines in the lateral area of Z bypass cc , in an anti-short-circuit part Pl SU p (fig. 4B to 4D) then in an anti-short-circuit part P2inf (fig. 4E to 4G).

[0077] Fig. 4A illustrates the bipolar plate 1 upstream of an anti-short-circuit part Pl sup . Between the external longitudinal ribs 12e, 22e and the internal longitudinal ribs 12i, 22i, the bipolar plate 1 comprises the upper 13 and lower 23 intermediate longitudinal portions, superimposed on each other, and in contact with each other at the level of the reference plane P re f.

[0078] Fig. 4B illustrates the bipolar plate 1 in an anti-short-circuit part Plsup. The upper sheet 10 comprises an upper intermediate longitudinal rib 16, which connects transversely (along the X axis) the upper external 12e and internal 12i longitudinal ribs. The lower sheet 20 comprises the lower intermediate recess 24, which extends transversely between the lower external 22e and internal 22i longitudinal ribs. The lower intermediate recess 24 is superimposed on the upper longitudinal rib 16, and is in contact with it at the upper contact plane Pc sup .

[0079] As illustrated in Fig. 4C, the lower sheet 20 comprises, in this anti-short-circuit part Plsup, lower transverse ribs, here an external lower transverse rib 25e. It is connected to the external lower longitudinal rib 22e so that the internal cross-section of the external sealing line is widened (here along the +X direction). It extends transversely (along the X axis) towards the internal lower longitudinal rib 22i, without being connected to it: its end is closed (plugged). In other words, a curved portion ensures the junction between the external lower transverse rib 25e and the lower intermediate recess 24 (which is in contact with the upper longitudinal rib 16).

[0080] As illustrated in Fig. 4D, the lower sheet 20 here comprises an internal lower transverse rib 25i. This is connected to the internal lower longitudinal rib 22i so that the internal cross-section between the internal longitudinal ribs 12i, 22i is widened (here along the -X direction). It extends transversely (along the X axis) towards the external lower longitudinal rib 22e, without being connected to it: its end is closed (plugged). In other words, a curved portion ensures the junction between the internal lower transverse rib 25i and the lower intermediate recess 24.

[0081] Fig.4E illustrates the bipolar plate 1 in an anti-short-circuit part P2i nr- The lower sheet 20 comprises a lower intermediate longitudinal rib 26, which transversely connects (along the X axis) the external 22e and internal 22i lower longitudinal ribs. The upper sheet 10 comprises the upper intermediate recess 14, which extends transversely between the external 12e and internal 12i upper longitudinal ribs. The upper intermediate recess 14 is superimposed on the lower intermediate longitudinal rib 26, and is in contact with the latter at the lower contact plane Pcinf.

[0082] As illustrated in Fig. 4F, the upper sheet 10 here comprises an external upper transverse rib 15e. It is connected to the external upper longitudinal rib 12e so that the internal cross-section of the external sealing line is widened (here following the direction +X). It extends transversely (along the X axis) towards the internal upper longitudinal rib 12i, without being connected to it: its end is closed. In other words, a curved portion ensures the junction between the external upper transverse rib 15e and the upper intermediate recess 14 (which is in contact with the intermediate lower longitudinal rib 26).

[0083] As illustrated in Fig. 4G, the upper sheet 10 here comprises an internal upper transverse rib 15i. This is connected to the internal upper longitudinal rib 12i so that the internal cross-section between the internal longitudinal ribs 12i, 22i is widened (here in the -X direction). It extends transversely in the direction of the external upper longitudinal rib 12e, without being connected to it: its end is closed. In other words, a curved portion ensures the junction between the internal upper transverse rib 15i and the upper intermediate recess 14.

[0084] As illustrated in Fig.4H, apart from the anti-short-circuit parts Pc SU p and Pcinf, the bipolar plate 1 can have a configuration identical to that of fig.4A.

[0085] Note that the transverse ribs (lower 25e, 25i as well as upper 15e, 15i) are not necessarily coplanar with the external longitudinal ribs 12e, 22e and / or internal ribs 12i, 22i. They are preferably in contact with a diffusion layer of the AME over at least part of their width along the X axis. Preferably, the external transverse ribs, for example upper 15e, are lower than the external longitudinal rib 12e, so as to maximize the mechanical crushing force of the external seal 5. By "lower", here is meant that the height of the external transverse ribs 15e (i.e. its distance from the reference plane P re f) is less than that of the external longitudinal rib 12e. This height difference can be of the order of 50pm.

[0086] Furthermore, the internal longitudinal rib 12i may be lower than the distribution ribs which transversely delimit the distribution channels, so as not to overcompress the diffusion layer of the AME outside the reaction zone. The internal transverse ribs 15i may however have the same height as that of the distribution ribs. Furthermore, the internal longitudinal rib 12i may have the same height as that of the external longitudinal rib 12e. What is said here for the upper ribs applies in the same way to the lower ribs.

[0087] Figures 5A to 5C are schematic and partial views of a bipolar plate 1 according to different embodiment variants, where the external upper transverse ribs 15e and internal ribs 15i are illustrated.

[0088] Fig. 5A illustrates an example where the transverse ribs (here the upper ribs 15e, 15i, but this is also the case for the lower ribs) extend in a straight line along the X axis. Preferably, there is interdigitation between the external transverse ribs 15e and internal 15i, in the sense that each external transverse rib 15e extends along the edge of an internal transverse rib 15i. In other words, the external ribs 15e and internal ribs 15i have a length along the X axis sufficient for an external transverse rib to extend along an internal transverse rib. Thus, the flow of the reactive fluid is a meandering flow and not a rectilinear flow along the Y axis, preferably longer by at least a ratio of 1.5 compared to the rectilinear flow, which generates singular pressure losses at each change of flow direction, and thus greatly reducing the short-circuit flow.

[0089] Fig. SB illustrates a variant where the transverse ribs 15e, 15i have a T shape formed by a rectilinear part extending along the X axis and an orthogonal rectilinear part extending along the Y axis in both directions -Y and +Y. Here, the interdigitation of these transverse ribs 15e, 15i leads to a further increase in the meandering nature of the short-circuit flow, and therefore the singular pressure losses, which further reduces this short-circuit flow.

[0090] Fig. SC illustrates another variant where the transverse ribs 15e, 15i have an L shape formed by a rectilinear part extending along the X axis and an orthogonal rectilinear part extending along the Y axis in one or other of the two directions -Y and +Y. Here also, the interdigitation of these transverse ribs 15e, 15i leads to a further increase in the meandering character of the short-circuit flow, which further reduces this short-circuit flow.

[0091] Of course, other shapes of the transverse ribs in the XY plane can be considered, for example spiral shapes. It should also be noted that the internal and external transverse ribs make it possible to improve the mechanical strength of the bipolar plate in the lateral zone, without degrading the quality of the external sealing line.

[0092] Figures 6A and 6B are schematic and partial views of a bipolar plate 1 according to one embodiment, fig. SB being a longitudinal section in the lateral bypass zone Z cc .

[0093] As shown in Fig.6A, the lateral zone Z cc has a longitudinal alternation of anti-short-circuit parts Pl SU p with upper contact plane Pc SU p and anti-short-circuit parts P2j n r with lower contact plane Pcinf. The upper external 15e and internal 15i transverse ribs are interdigitated L-shaped, as are the lower external and internal transverse ribs (not visible).

[0094] As shown in Fig.SB, in the anti-short-circuit parts Pl sup with upper contact plane Pc sup, the upper sheet 10 comprises the upper longitudinal rib 16, and the lower sheet 20 comprises a lower recess 24 superimposed and in contact with the rib upper longitudinal 16, from which extend lower external and internal transverse ribs.

[0095] Furthermore, note here that the upper sheet 10 comprises an upper curved portion 17 which ensures the longitudinal junction (along the Y axis) between the upper intermediate rib 16 and the upper intermediate recess 14. Similarly, the lower sheet 20 comprises a lower curved portion 27 which ensures the longitudinal junction between the lower intermediate recess 24 and the lower intermediate rib 26. As shown in fig.6B, the upper 17 and lower 27 curved portions are offset along the Y axis so as not to be in contact with each other, this in order not to weaken the conductive sheets 10, 20 by a local transmission of mechanical stresses, while respecting the manufacturing and positioning tolerances.

[0096] Figures 7A to 7F are schematic and partial views of the bipolar plate 1 of Fig. 6A, in cross-section along different cutting lines.

[0097] Fig. 7A illustrates the bipolar plate 1 in an anti-short-circuit part Pl SU p with upper contact plane Pc sup , where, in this section line, the lower sheet 20 has an external lower transverse rib 25e. It extends from the external lower longitudinal rib 22e towards the internal lower longitudinal rib 22i and branches off to form an L. Its opposite end is closed and has a curved portion which connects the external lower transverse rib 25e to the lower intermediate recess 24.

[0098] Fig.7B illustrates the bipolar plate 1 in the same anti-short-circuit part Pl sup with upper contact plane Pc sup , where, in this cutting line, the lower sheet 20 does not have a lower transverse rib, but the lower intermediate recess 24, superimposed and in contact with the upper longitudinal rib 16.

[0099] Fig.7C illustrates the bipolar plate 1 in the same anti-short-circuit part Pl sup with upper contact plane Pc sup , where, in this section line, the lower sheet 20 has an internal lower transverse rib 25i. It extends from the internal lower longitudinal rib 22i towards the external lower longitudinal rib 22e and branches off to form an L. Its opposite end is closed and has a curved portion which connects the external lower transverse rib 25i to the lower intermediate recess 24.

[0100] Fig.7D illustrates the bipolar plate 1 in an anti-short-circuit part P2j nf with lower contact plane Pcinf, where, in this section line, the lower sheet 20 has a lower intermediate longitudinal rib 26, and where the upper sheet 10 has an upper intermediate recess 14, superimposed and in contact with the lower intermediate longitudinal rib 26. Here, the upper sheet 10 has an internal upper transverse rib 15i. It extends from the internal upper longitudinal rib 12i towards the external upper longitudinal rib 12e, and branches off to form an L. Its opposite end is closed and has a curved portion which connects the upper internal transverse rib 12i to the upper intermediate recess 14.

[0101] Fig.7E illustrates the bipolar plate 1 in the same anti-short-circuit part P2i nf with lower contact plane Pcinf, where, in this section line, the upper sheet 10 does not have an upper transverse rib, but has the upper intermediate recess 14, superimposed and in contact with the lower intermediate longitudinal rib 26.

[0102] Fig.7F illustrates the bipolar plate 1 in the same anti-short-circuit part P2j n f with lower contact plane Pcinf, where, in this section line, the upper sheet 10 has an external upper transverse rib 15e. It extends from the external upper longitudinal rib 12e towards the internal upper longitudinal rib 12i, and branches off to form an L. Its opposite end is closed and has a curved portion which connects the external upper transverse rib 15e to the upper intermediate recess 14.

[0103] Particular embodiments have just been described. Different variants and modifications will appear to those skilled in the art.

Claims

CLAIMS 1. Bipolar plate (1) of an electrochemical cell, comprising: o upper (10) and lower (20) sheets, superimposed on each other, comprising: • lower and upper distribution circuits (7), superimposed on each other, adapted to bring reactive fluids respectively to lower and upper electrodes; • upper (12i) and lower (21i) internal longitudinal ribs, superimposed on each other, respectively forming a longitudinal border of the lower and upper distribution circuits (7); • upper (12e) and lower (22e) external longitudinal ribs, superimposed on each other, extending along the internal longitudinal ribs (12i, 22i), laterally delimiting, with the internal longitudinal ribs (12i, 22i), a lateral zone called a bypass zone (Z cc) extending longitudinally along the distribution circuits (7); o in the lateral bypass zone (Z cc ) there is a longitudinal alternation: • at least one first anti-short-circuit part (Plsup), where: the upper sheet (10) has an upper intermediate longitudinal rib (16), extending throughout the first anti-short-circuit part (Plsup); and where the lower sheet (20) has a lower intermediate recess (24), superimposed and in contact with the upper intermediate longitudinal rib (16); • at least a second anti-short-circuit part (P2i nf), where: the lower sheet (20) has a lower intermediate longitudinal rib (26), extending throughout the second anti-short-circuit part; and where the upper sheet (10) has an upper intermediate recess (14), superimposed and in contact with the lower intermediate longitudinal rib (26); o characterized in that, in the first anti-short-circuit part (Plsup), the lower sheet (20) comprises a longitudinal succession of lower transverse ribs, including: lower internal transverse ribs (25i), respectively external (25e), extending from the lower internal longitudinal rib (22i), respectively external (22e), and having a closed opposite end not connected to the lower external longitudinal rib (22e), respectively internal (22i); o and in that, in the second anti-short-circuit part (P2i nf), the upper sheet (10) comprises a longitudinal succession of upper transverse ribs, including: upper internal transverse ribs (15i), respectively external (15e), extending from the upper internal longitudinal rib (12i), respectively external (12e), and having a closed opposite end not connected to the upper external longitudinal rib (12e), respectively internal (12i).

2. Bipolar plate (1) according to claim 1, comprising several first anti-short-circuit parts (Plsup) arranged in longitudinal alternation with several second anti-short-circuit parts (P2sup).

3. Bipolar plate (1) according to claim 1 or 2, wherein, in the first anti-short-circuit part (Plsup), the internal (25i) and external (25e) lower transverse ribs of the lower sheet (20) are interdigitated, so that each internal lower transverse rib (25i) extends along an external lower transverse rib (25e).

4. Bipolar plate (1) according to any one of claims 1 to 3, wherein, in the second anti-short-circuit part (P2j n f), the inner (15i) and outer (15e) upper transverse ribs of the upper sheet (10) are interdigitated, such that each inner (15i) upper transverse rib extends along an outer (15e) upper transverse rib.

5. Bipolar plate (1) according to any one of claims 1 to 4, in which the upper (15e, 15i) and lower (25e, 25i) transverse ribs have, in a plane parallel to the bipolar plate (1), a rectilinear, T-shaped, L-shaped or spiral shape.

6. Bipolar plate (1) according to any one of claims 1 to 5, in which the upper (15e), respectively lower (25e) external transverse ribs have a height, with respect to a reference plane (P re f) passing between the upper (12e) and lower (22i) external longitudinal ribs, lower than that of the upper (12e) and lower (22e) external longitudinal rib respectively.

7. Bipolar plate (1) according to any one of claims 1 to 6, in which the lower intermediate recess (24) separates, along an axis orthogonal to a longitudinal axis of the lateral bypass zone (Z cc), the outer lower transverse rib (25e) of the inner lower longitudinal rib (22i), and the inner lower transverse rib (25i) of the outer lower longitudinal rib (22e).

8. Bipolar plate (1) according to any one of claims 1 to 7, in which the upper intermediate recess (14) separates, along an axis orthogonal to a longitudinal axis of the lateral bypass zone (Z cc ), the outer upper transverse rib (15e) of the inner upper longitudinal rib (12i), and the inner upper transverse rib (15i) of the outer upper longitudinal rib (12e).

9. Bipolar plate (1) according to any one of claims 1 to 8, in which the upper (12e) and lower (22i) external longitudinal ribs are each in contact with a sealing joint (5).

10. Electrochemical cell, comprising at least one bipolar plate (1) according to any one of the preceding claims, and a membrane / electrode assembly (30) in contact with the bipolar plate (1).

11. Electrochemical reactor, comprising at least one electrochemical cell according to the preceding claim.

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