Bipolar plate of electrochemical cell allowing a reduction of short-circuit flows at the edge of the reaction zone

Abstract

The invention relates to a bipolar plate comprising upper and lower sheets (10, 20), having, along the active zone, an intermediate longitudinal zone (Zint) where there is a longitudinal alternation between at least a first anti-short-circuit region (Rsup) and at least a second anti-short-circuit region (Rinf). In the first anti-short-circuit region (Rsup), the lower sheet (20) has: a plurality of lower studs (25), projecting, in a direction opposite to the upper sheet (10), with respect to a lower intermediate recess (24) in which they are located, and having substantially equal dimensions along any two orthogonal axes in a plane parallel to the bipolar plate; and an absence of transverse ribs extending in the intermediate longitudinal zone (Zint) by joining internal (22i) and external (22e) lower longitudinal ribs. Figure for abstract: Fig.3B

Description

Title of the invention: Bipolar plate of an 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 electrolyser, usually comprises a stack of electrochemical cells, each of which comprises 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 (for example hydrogen) is supplied to the anode, while the oxidizing fluid (for example 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 location 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 which ensure the electrical interconnection between them and the flow of the reactive fluids. The bipolar plates have an anodic face at which a distribution circuit for the combustible fluid is formed, and an opposite cathodic face at which a distribution circuit for the oxidizing fluid 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 which ensure the flow of a heat transfer fluid making it possible to evacuate the heat produced locally during the electrochemical reaction by the cell.

[0005] [Fig.lA] 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. [Fig.lB] is a cross-sectional view of the bipolar plate 1 of [Fig.lA] 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 one another, 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 7. It makes it possible to prevent the reactive fluids from flowing outside the bipolar plate. Furthermore, the sheets 10, 20 comprise upper 12i and lower 21i 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 an intermediate longitudinal zone Z int located at 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 an outlet homogenization zone then an outlet injection zone, to finally reach the air outlet manifold 2 (see continuous arrows in [Fig.lA]). The same is true for the hydrogen on the anode side.

[0009] It appears, however, that air can bypass the reaction zone by flowing into intermediate longitudinal zones Zint located between the distribution circuit 7 and the external sealing line. Indeed, as shown by the dotted arrows in [Fig.lA], the air can escape from the injection zone 8 to reach the intermediate longitudinal zones Zint 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 intermediate longitudinal 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 intermediate longitudinal zones, where the conductive sheets comprise lower and upper intermediate transverse 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 intermediate longitudinal zone, is reduced, which limits the short-circuit flow of the reactive fluids.However, the cross-sectional area 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 intermediate longitudinal 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, the object of the invention is a bipolar plate of an electrochemical cell, comprising: upper and lower sheets, superimposed on each other, comprising: • upper and lower distribution circuits, superimposed on each other, adapted to bring reactive fluids respectively to upper and lower electrodes; • upper and lower internal longitudinal ribs, superimposed on each other, respectively forming a longitudinal border of the circuits upper and lower distribution; • upper and lower external longitudinal ribs, superimposed on each other, extending along the internal longitudinal ribs, laterally delimiting, with the latter, an intermediate longitudinal zone.

[0014] Furthermore, in the intermediate longitudinal zone there is a longitudinal alternation between at least one first anti-short-circuit region and at least one second anti-short-circuit region, where: • in the first anti-short-circuit region called the upper contact plane region, the upper sheet has an upper intermediate longitudinal rib extending throughout the first anti-short-circuit region; and the lower sheet has a lower intermediate recess superimposed and in contact with the upper intermediate longitudinal rib; • in the second anti-short-circuit region known as the lower contact plane region, the lower sheet having a lower intermediate longitudinal rib, extending throughout the second anti-short-circuit region; and the upper sheet having 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 region, the lower sheet has: • a plurality of lower studs, projecting, in a direction opposite to the upper sheet, with respect to the lower intermediate recess in which they are located, and having substantially equal dimensions along any two orthogonal axes in a plane parallel to the bipolar plate; • an absence of transverse ribs extending into the intermediate longitudinal zone joining the lower internal and external longitudinal ribs.

[0016] Furthermore, in the second anti-short-circuit region, the upper sheet has: • a plurality of upper studs, projecting, in a direction opposite to the lower sheet, with respect to the upper intermediate recess in which they are located, and having substantially equal dimensions along any two orthogonal axes in a plane parallel to the bipolar plate; • an absence of transverse ribs extending into the intermediate longitudinal zone joining the upper internal and external longitudinal ribs.

[0017] Some preferred but non-limiting aspects of this bipolar plate are the following.

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

[0019] The upper pads may be arranged longitudinally in a periodic manner, and the lower pads may be arranged longitudinally in a periodic manner.

[0020] The upper and lower pads may be distributed over at least two lines parallel to a longitudinal axis of the intermediate longitudinal zone.

[0021] The upper and lower pads may have a height substantially equal, respectively, to that of the upper and lower internal longitudinal ribs.

[0022] The upper and lower pads may have a circular or square base.

[0023] The upper and lower pads may be distinct respectively from the ribs upper and lower internal longitudinal ribs, and, respectively, upper and lower external longitudinal ribs.

[0024] The upper and lower external longitudinal ribs may each be in contact with a sealing gasket.

[0025] The invention also relates to an electrochemical cell, comprising at least the bipolar plate according to any one of the preceding characteristics, and membrane / electrode assemblies, one in contact with the upper sheet and the other in contact with the lower sheet.

[0026] An upper membrane / electrode assembly may be in contact with the upper pads, and a lower membrane / electrode assembly may be in contact with the lower pads.

[0027] The invention also relates to an electrochemical reactor, comprising at least one electrochemical cell according to the preceding characteristics. 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:

[0029] [Fig.1A], already described, is a top view, schematic and partial, of a bipolar plate according to an example of the prior art;

[0030] [Fig.lB], already described, is a schematic and partial view, in cross-section, of the bipolar plate of [Fig.lA], along the section line AA;

[0031] [Fig.2] is a schematic and partial top view of a bipolar plate according to one embodiment, illustrating the first and second anti-short-circuit regions located in the intermediate longitudinal zones;

[0032] [Fig.3A] is a schematic and partial perspective view of a portion of a bipolar plate according to one embodiment, illustrating a longitudinal alternation of first and second anti-short-circuit regions in an intermediate longitudinal zone (the reaction zone is not illustrated);

[0033] [Fig.3B] is a schematic and partial view, in longitudinal section in the intermediate longitudinal zone, of the bipolar plate of [Fig.3A];

[0034] [Fig.4A] is a schematic and partial view, in perspective and in cross-section in an anti-short-circuit region with a lower contact plane, of the bipolar plate of [Fig.3A];

[0035] [Fig.4B] is a schematic and partial view, in cross-section in an anti-short-circuit region with a lower contact plane, of the bipolar plate of [Fig.4A], where the upper and lower membrane / electrode assemblies are also illustrated;

[0036] [Fig.5A] is a schematic and partial view, in perspective and in cross-section in an anti-short-circuit region with an upper contact plane, of the bipolar plate of [Fig.3A];

[0037] [Fig.5B] is a schematic and partial view, in cross-section in an anti-short-circuit region with an upper contact plane, of the bipolar plate of [Fig.5A], where the upper and lower membrane / electrode assemblies are also illustrated.

[0038] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0039] 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", "in the order of" mean to within 10%, and preferably to within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that the limits are included, unless otherwise stated.

[0040] 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 intermediate longitudinal zones which extend longitudinally between the external sealing line and the distribution circuit. This structural configuration of the conductive sheets makes 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 formation of the AME or conductive sheets in the intermediate longitudinal zone.

[0041] Different 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.

[0042] [Fig. 2] is a schematic and partial top view of a portion of the bipolar plate 1 according to one embodiment. Certain elements are described with reference to [Fig. 1B]. [Fig. 3A] is a perspective view of a portion of a bipolar plate similar to that of [Fig. 2] (where the reaction zone is not illustrated), and [Fig. 3B] is a perspective and longitudinal sectional view of the bipolar plate 1 of [Fig. 3A],

[0043] Here and for the remainder of the description, a direct orthogonal reference frame XYZ is defined, 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.

[0044] 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.lB]) formed of a cathode 32 and 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 intermediate longitudinal zone along the X axis. A waterproof film 34 (material distinct from the membrane 31 or film corresponding to the membrane itself) can extend from the MEA 30 to the edge of the bipolar plates 1 and be in contact with the external seals 5.

[0045] 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 AME of the electrochemical cell.

[0046] 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.

[0047] 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 μm to 200 μm approximately in the case of metal sheets.

[0048] 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.

[0049] 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 collector of the heat transfer liquid 4 is located between the collectors of the reactive fluids 2, 3. Alternatively, they can be located along an X axis orthogonal to the longitudinal Y axis.

[0050] 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.

[0051] 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 applies to the lower sheet 20, the injection zone of which communicates with the hydrogen collector 3 and the homogenization zone. The heat transfer liquid injection zone is formed of conduits which open between the two cathode 10 and anodic 20 conductive sheets. Similar injection zones are described in particular in document EP3136492A1.

[0052] 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.

[0053] Each conductive sheet 10, 20 comprises a distribution circuit 7, formed of channels which extend between an inlet and an outlet aligned in 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 FAME. The cathode and anodic distribution circuits define in the XY plane the reaction zone of the electrochemical cell.

[0054] Furthermore, a reference plane Pref of the bipolar plate 1 is defined as being the contact plane of the conductive sheets 10, 20 at their external edges 11c and 21e (see [Fig. 1B]). This is the reference plane Pref with respect to which the ribs and the recesses are defined, when they are considered from the external face of each conductive sheet 10, 20.

[0055] Thus, a rib is obtained by local deformation of the conductive sheet 10, 20, from its internal face towards 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 Pref along the Z axis (and therefore which moves away from the other conductive sheet). In other words, a rib is a surface projecting relative to the reference plane P ref. Thus, an upper rib is a rib of the upper sheet 10 which moves away from the reference plane Pref along the +Z direction. And a lower rib is a rib of the lower sheet 20 which moves away from the reference plane Pref along the -Z direction. Furthermore, a rib has an elongated shape in the XY plane: one dimension (length) along a longitudinal axis is greater than its dimension (width) along a transverse axis.

[0056] Furthermore, an intermediate longitudinal rib is a rib located in the intermediate longitudinal zone Zint (therefore located between the internal and external longitudinal ribs) and which extends longitudinally along the same longitudinal axis Y as that of the intermediate longitudinal zone. In addition, an intermediate transverse rib is a rib located in the intermediate longitudinal zone Zint and which extends longitudinally along an inclined axis (in the XY plane), or even or- thogonal, to the longitudinal axis Y of the intermediate longitudinal zone Zint.

[0057] 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 Pref along the Z axis (and therefore which approaches the other conductive sheet). Thus, an upper recess is a recess of the upper sheet 10 which goes beyond the reference plane Pref along the -Z direction. And a lower recess is a recess of the lower sheet 20 which goes beyond the reference plane Pref along the +Z direction.

[0058] As illustrated in [Fig.lB], 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 7. They extend longitudinally at the edge of the bipolar plate 1. Seals 5, called external, 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.

[0059] 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 FAME electrode 30. Thus, the intermediate longitudinal zone Zint corresponds to the zone delimited laterally (here 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 may or may not be rectilinear).

[0060] Note furthermore that the conductive sheets 10, 20 comprise upper and lower flat portions, superimposed on each other, and in contact with each other at the reference plane Pref. Thus, external longitudinal portions 11e, 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 11i and lower 21i internal longitudinal portions extend between the internal longitudinal ribs 12i, 22i and the distribution ribs.

[0061] The bipolar plate 1 comprises, in an intermediate longitudinal zone Zint, a longitudinal alternation between at least a first anti-short-circuit region Rsup (called an upper contact plane region Pcsup) and at least a second anti-short-circuit region R inf (called a lower contact plane region Pcinf). By longitudinal alternation, it is meant that these first and second anti-short-circuit regions Rsup, Rinf follow one another, alternating along the longitudinal axis Y of the intermediate longitudinal zone Zint. This longitudinal alternation of first anti-short-circuit regions Rsup with second anti-short-circuit regions Rinf may be periodic or not.

[0062] In the first anti-short-circuit region Rsup, the contact plane between the two conductive sheets 10, 20 is an upper contact plane Pcsup, in the sense that it is located above the reference plane Pref in the +Z direction.

[0063] The upper sheet 10 has an upper intermediate longitudinal rib 16 extending throughout the first anti-short-circuit region Rsup, that is to say over its entire surface. It therefore extends over the entire length (along the Y axis) of the first anti-short-circuit region Rsup, 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 FAME over at least part of its width (as illustrated in [Fig.5B]). This upper intermediate longitudinal rib 16 extends along the longitudinal axis of the intermediate longitudinal zone Zint. Preferably, it extends in a continuously planar manner.It may be coplanar, or not, with the external upper longitudinal rib 12e and / or with the internal upper longitudinal rib 12i.

[0064] Furthermore, the lower sheet 20 has a lower intermediate recess 24, superimposed and in contact with the upper intermediate longitudinal rib 16. The contact plane between the upper intermediate longitudinal rib 16 and the lower intermediate recess 24 corresponds to the upper contact plane Pcsup. It is located above the reference plane Pref in the +Z direction.

[0065] The contact between the lower intermediate recess 24 and the upper intermediate longitudinal rib 16 may be a continuous contact, that is to say that the recess 24 is, over its entire surface, in contact with the rib 16. Alternatively, the contact may be a localized contact, that is to say that there are one or more points of contact between the recess 24 and the rib 16. Outside of these points of contact, the recess 24 and the rib 16 are spaced along the Z axis by a small distance, for example of the order of a few tens of microns, for example at most 50 μm or even less (sufficiently small to avoid the flow of the heat transfer liquid). Note that the bipolar plates may have such a localized contact before applying the clamping force to the stack, then a continuous contact after the application of this force.

[0066] According to the invention, the lower sheet 20, in the anti-short-circuit region Rsup, comprises a plurality of lower studs 25, projecting, in a direction -Z opposite to the upper sheet 10, with respect to the lower intermediate recess 24 in which they are located. They have substantially equal dimensions along any two orthogonal axes in a plane parallel to the bipolar plate 1.

[0067] Generally speaking, a stud is distinguished from a rib in the sense that it has substantially equal dimensions along any two orthogonal axes in the XY plane. The studs may thus have a substantially circular base (as here) or square, which is therefore not elongated or oblong. They have a base located at the level of the recess and a top. The top may be curved or flattened (flat). They have a height (distance between the base and the top along the Z axis) which preferably corresponds to the depth of the recess. Thus, the top is preferably substantially coplanar with the internal and / or external longitudinal ribs of the conductive sheet. However, the height of the studs may be equal to at least 50%, and preferably to at least 75% of the depth of the recess.

[0068] The lower pads 25 extend from the lower intermediate recess 24, and are preferably not connected to the inner lower longitudinal rib 22i or to the outer lower longitudinal rib 22e. They may be arranged along the longitudinal axis Y periodically or not, for example in the form of several parallel lines. Along the axis X, the lower pads 25 may be aligned or may be arranged in a staggered pattern, or even be arranged randomly.

[0069] The lower pads 25 here make it possible to ensure good mechanical strength of the conductive sheets 10, 20, and here in particular of the lower sheet 20, to prevent them from deforming in the intermediate longitudinal zone Zint, or to prevent the lower FAME from deforming in the direction of the lower intermediate recess 24. They also make it possible to ensure good mechanical contact between the bipolar plate and the lower and upper AMEs.

[0070] Furthermore, the lower sheet 20, in the anti-short-circuit region Rsup, does not have a transverse rib extending into the intermediate longitudinal zone Zint by joining the lower internal 22i and external 22e longitudinal ribs. This transverse axis can be the X axis itself or an axis inclined relative to the X axis. Indeed, such transverse ribs can allow a short-circuit flow of the heat transfer liquid, which would join the external sealing line and thus bypass the reaction zone. Also, it is understood that the lower intermediate recess 24 is a single recess which extends continuously over the entire width and length of the anti-short-circuit region Rsup by surrounding each of the lower pads 25 in the XY plane.

[0071] Thus, in the anti-short-circuit region Rsup with upper contact plane Pcsup, the air flow cross-section, at the level of the upper sheet 10 (cathodic), is greatly reduced by the presence of the upper intermediate longitudinal rib 16, which limits the short-circuit flow of the air (increase in the linear pressure drop). In addition, the conductive sheets 10, 20 have good mechanical strength thanks to the lower pads 25, which prevents their deformation as well as that of the lower AME. Finally, the short-circuit flow of the heat transfer liquid is limited or absent, since there are no lower transverse ribs connecting the internal longitudinal rib 22i to the external longitudinal rib 22e. Thus, the heat transfer liquid cannot flow there and therefore cannot enter the reaction zone.

[0072] Furthermore, in the second anti-short-circuit region Rinf, 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 Pref along the direction -Z.

[0073] The lower sheet 20 has a lower intermediate longitudinal rib 26 extending throughout the anti-short-circuit region Rinf, that is to say over its entire surface. It therefore extends over the entire length (along the Y axis) of the anti-short-circuit region Rinf, 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 (as illustrated in [Fig.4B]). This lower intermediate longitudinal rib 26 extends along the longitudinal axis of the intermediate longitudinal zone Zint. Preferably, it extends in a continuously planar manner.It may be coplanar, or not, with the external lower longitudinal rib 22e and / or with the internal lower longitudinal rib 22i.

[0074] Furthermore, the upper sheet 10 has an upper intermediate recess 14, superimposed and in contact with the lower intermediate longitudinal rib 26. 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 Pref in the direction -Z. As indicated previously for the recess 24 and the rib 16, the contact between the upper intermediate recess 14 and the lower intermediate longitudinal rib 26 may be continuous, that is to say that the recess 14 is, over its entire surface, in contact with the rib 26. Alternatively, the contact may be localized, that is to say that there are one or more points of contact between the recess 14 and the rib 26.Outside of these contact points, the recess 14 and the rib 26 are spaced along the Z axis by a small distance, for example of the order of a few tens of microns, for example at most 50 μm or even less (sufficiently small to prevent the flow of the heat transfer liquid).

[0075] According to the invention, the upper sheet 10, in the anti-short-circuit region Rinf, comprises a plurality of upper studs 15, projecting, in a direction +Z opposite the lower sheet 20, with respect to the upper intermediate recess 14 in which they are located. They have substantially equal dimensions along any two orthogonal axes in a plane parallel to the bipolar plate 1.

[0076] The upper pads 15 extend from the upper intermediate recess 14, and are preferably not connected to the upper inner longitudinal rib 12i or to the upper outer longitudinal rib 12e. They may be arranged along the longitudinal axis Y periodically or not, for example in the form of several parallel lines. Along the axis X, the upper pads 15 may be aligned or may be arranged in a staggered pattern, or even be arranged randomly.

[0077] The upper pads 15 here make it possible to ensure good mechanical strength of the conductive sheets 10, 20, and here in particular of the upper sheet 10, to prevent them from deforming in the intermediate longitudinal zone Zint, or to prevent the upper FAME from deforming in the direction of the upper intermediate recess 14. They also make it possible to ensure good mechanical contact between the bipolar plate and the lower and upper AMEs.

[0078] Furthermore, the upper sheet 10, in the anti-short-circuit region Rinf, does not have a transverse rib extending in the intermediate longitudinal zone Zint by joining the upper inner 12i and outer 12e longitudinal ribs. This transverse axis can be the X axis itself or an axis inclined relative to the X axis. Also, it is understood that the upper intermediate recess 14 is a single recess which extends continuously over the entire width and length of the anti-short-circuit region Rinf by surrounding each of the upper pads 15 in the XY plane.

[0079] Also, in the anti-short-circuit region Rinf with lower contact plane Pcinf, the cross-section of hydrogen flow, at the level of the lower sheet 20, is greatly reduced by the lower intermediate longitudinal rib 26, which limits the short-circuit flow of hydrogen (increase in the linear pressure drop). In addition, the conductive sheets 10, 20 have good mechanical strength thanks to the upper pads 15, which prevents their deformation as well as that of the upper AME. Finally, the short-circuit flow of the heat transfer liquid is limited or absent, insofar as there are no upper transverse ribs connecting the internal longitudinal rib 12i to the external longitudinal rib 12e. Thus, the heat transfer liquid cannot flow there or thus partially bypass the reaction zone.

[0080] Furthermore, let us note here, as illustrated in [Fig.3B], that the upper sheet 10 may comprise an upper curved portion 17 which ensures the longitudinal junction (along the Y axis) between the upper intermediate recess 14 and the upper intermediate rib 16. Similarly, the lower sheet 20 comprises a curved portion lower 27 which ensures the longitudinal junction between the lower intermediate rib 26 and the lower intermediate recess 24. These upper 17 and lower 27 curved portions are here offset along the longitudinal axis Y so as not to be in contact with each other, thus avoiding a transmission of mechanical stresses likely to weaken the bipolar plate 1.

[0081] [Fig.4A] is a partial perspective cross-sectional view of the bipolar plate of [Fig.3A] in the Rinf anti-short-circuit region with a lower contact plane, and [Fig.4B] is a schematic partial cross-sectional view of the bipolar plate of [Fig.4A].

[0082] The lower sheet 20 has a lower intermediate longitudinal rib 26, which extends continuously along the transverse axis X between the lower inner 22i and outer 22e longitudinal ribs, and which extends along the longitudinal axis Y as far as the anti-short-circuit region Rsup. It therefore extends throughout the anti-short-circuit region Rinf. It comes into contact with the anodic side of the lower AME, which makes it possible to reduce the short-circuit flow of hydrogen.

[0083] The upper sheet 10 has an upper longitudinal recess 14, which extends along the transverse axis X between the upper inner 12i and outer 12e longitudinal ribs, and along the longitudinal axis Y from the anti-short-circuit region Rinf. The upper longitudinal recess 14 and the lower longitudinal rib 26 are in contact with each other (continuous or localized contact) at a lower contact plane Pcinf along the axis Z (below the reference plane Pref).

[0084] The upper sheet 10 comprises upper studs 15, located in the intermediate longitudinal zone Zint, and projecting from the upper intermediate recess 14 in which they are located. They extend from the latter in the +Z direction, towards the cathode of the upper MEA with which they come into contact. These are studs and not ribs, and therefore have substantially equal dimensions along any two orthogonal axes in the XY plane. Here, they have a circular base, but a square base is also possible. Their top is rounded (see [Fig.4A]), but a flat is also possible (as illustrated in [Fig.4B]). Thus, the upper studs 15 make it possible to avoid deformation along the Z axis of the conductive sheets, but also deformation along the -Z direction of the upper MEA.They ensure good contact between the conductive sheets 10, 20 and the upper and lower AMEs.

[0085] Thus, the upper sheet 10 does not have transverse ribs extending along the transverse axis X (or inclined to the axis X) joining the upper inner 12i and outer 12e longitudinal ribs. Thus, the risks of the heat transfer liquid at least partially short-circuiting the reaction zone by crossing the intermediate longitudinal zone Zint to reach the sealing line are avoided. external.

[0086] [Fig.5A] is a partial perspective cross-sectional view of the bipolar plate of [Fig.3A] in the anti-short-circuit region Rsup with upper contact plane, and [Fig.5B] is a schematic partial cross-sectional view of the bipolar plate of [Fig.5A].

[0087] The upper sheet 10 has an upper intermediate longitudinal rib 16, which extends continuously along the transverse axis X between the upper inner 12i and outer 12e longitudinal ribs, and which extends along the longitudinal axis Y from or to the anti-short-circuit region Rinf. It therefore extends throughout the anti-short-circuit region Rsup. It comes into contact with the cathode side of the upper FAME (not shown), which makes it possible to reduce the short-circuit flow of air.

[0088] The lower sheet 20 has a lower longitudinal recess 24, which extends along the transverse axis X between the lower internal 22i and external 22e longitudinal ribs, and along the longitudinal axis Y from the anti-short-circuit region Rinf. The lower longitudinal recess 24 and the upper intermediate longitudinal rib 16 are in contact with each other (continuous or localized contact) at an upper contact plane Pcsup along the Z axis (above the reference plane Pref).

[0089] The lower sheet 20 comprises lower studs 25, located in the intermediate longitudinal zone Zint, and projecting from the lower intermediate recess 24 in which they are located. They extend from the latter in the -Z direction, towards the anode of the lower FAME with which they come into contact. Here too, they are studs and not ribs, and therefore have substantially equal dimensions along any two orthogonal axes in the XY plane. Here, they also have a circular base, but a square base is also possible. Their top is rounded (see [Fig.5A]), but a flat is also possible (see [Fig.5B]). Thus, the lower studs 25 make it possible to avoid deformation along the -Z direction of the conductive sheets, but also deformation along the +Z direction of the upper FAME.They ensure good contact between the conductive sheets 10, 20 and the upper and lower AMEs.

[0090] Thus, the lower sheet 20 does not have transverse ribs extending along the transverse axis X (or inclined to the axis X) joining the internal and external lower longitudinal ribs. Thus, the risks of the heat transfer liquid at least partially short-circuiting the reaction zone by crossing the intermediate longitudinal zone Zint to reach the external sealing line are avoided.

[0091] Finally, the fact that there is a longitudinal succession of at least one anti-short-circuit region Rsup and at least one anti-short-circuit region Rinf makes it possible to limit both the risks of short-circuit flow of air on the cathode side and of hydrogen on the anodic side.

[0092] 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: • upper (10) and lower (20) sheets, superimposed on each other, comprising: • upper and lower distribution circuits, superimposed on each other, adapted to bring reactive fluids respectively to upper and lower electrodes; • upper (12i) and lower (22i) internal longitudinal ribs, superimposed on each other, respectively forming a longitudinal border of the upper and lower distribution circuits; • upper (12e) and lower (22e) external longitudinal ribs, superimposed on each other, extending along the internal longitudinal ribs (12i, 22i), laterally delimiting, with the latter, an intermediate longitudinal zone (Zint); • in the intermediate longitudinal zone (Zint) there is a longitudinal alternation between at least a first anti-short-circuit region (Rsup) and at least a second anti-short-circuit region (Rinf), where: • in the first anti-short-circuit region (Rsup) called upper contact plane (Pcsup), the upper sheet (10) has an upper intermediate longitudinal rib (16) extending throughout the first anti-short-circuit region (Rsup); and the lower sheet (20) has a lower intermediate recess (24) superimposed and in contact with the upper intermediate longitudinal rib (16); • in the second anti-short-circuit region (Rinf) called lower contact plane (Pcinf), the lower sheet (20) having a lower intermediate longitudinal rib (26), extending throughout the second anti-short-circuit region (Rinf); and the upper sheet (10) has an upper intermediate recess (14), superimposed and in contact with the lower intermediate longitudinal rib (26); • characterized in that: • in the first anti-short-circuit region (Rsup), the lower sheet (20) has: • a plurality of lower studs (25), projecting, in a direction opposite to the upper sheet (10), with respect to the lower intermediate recess (24) in which they are located, and having substantially equal dimensions along any two orthogonal axes in a plane parallel to the bipolar plate; • an absence of transverse ribs extending in the intermediate longitudinal zone (Zint) by joining the lower internal (22i) and external (22e) longitudinal ribs;and • in the second anti-short-circuit region (Rinf), the upper sheet (10) has: • a plurality of upper studs (15), projecting, in a direction opposite to the lower sheet (20), with respect to the upper intermediate recess (14) in which they are located, and having substantially equal dimensions along any two orthogonal axes in a plane parallel to the bipolar plate; and • an absence of transverse ribs extending in the intermediate longitudinal zone (Zint) by joining the internal (12i) and external (12e) upper longitudinal ribs.;

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

3. Bipolar plate (1) according to claim 1 or 2, wherein the upper pads (15) are arranged longitudinally in a periodic manner, and the lower pads (25) are arranged longitudinally in a periodic manner.

4. Bipolar plate (1) according to any one of claims 1 to 3, in which the upper (15) and lower (25) pads are distributed on at least two lines parallel to a longitudinal axis of the intermediate longitudinal zone (Zint).

5. Bipolar plate (1) according to any one of claims 1 to 4, in which the upper (15) and lower (25) pads have a height substantially equal, respectively, to that of the upper (12i) and lower (22i) internal longitudinal ribs.

6. Bipolar plate (1) according to any one of claims 1 to 5, in which the upper (15) and lower (25) pads have a circular or square base.

7. Bipolar plate (1) according to any one of claims 1 to 5, in which the upper (15) and lower (25) pads are distinct respectively from the upper (12i) and lower (22i) internal longitudinal ribs, and, respectively, from the upper (12e) and lower (22e) external longitudinal ribs.

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

9. Electrochemical cell, comprising at least the bipolar plate (1) according to any one of the preceding claims, and membrane / electrode assemblies (30), one in contact with the upper sheet (10) and the other in contact with the lower sheet (20).

10. An electrochemical cell according to claim 9, wherein an upper membrane / electrode assembly is in contact with the upper pads (15), and a lower membrane / electrode assembly is in contact with the lower pads (25).

11. Electrochemical reactor, comprising at least one electrochemical cell according to claim 9 or 10.

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