Bipolar plate for electrochemical cells limiting unwanted leakage outside an active region

Abstract

The invention relates to a bipolar plate (1) for electrochemical cells. The bipolar plate (1) is formed of two sheets (10a, 10b) joined together, each having patterns composed of recessed and raised reliefs. These patterns define, on each of the sheets (10a, 10b), an active zone (Za) extending longitudinally between a first fluid distributor (D1) and a second fluid distributor (D2), and two lateral bands (B1, B2) bordering the active zone (Za). Each lateral band (B1, B2) has at least one indentation (R, R') extending in a plurality of meanders (m) over at least one longitudinal portion (P1) of the lateral band (B1, B2). At least one meander (m) of a recess (R) in one of the plates (10a, 10b) is nested within at least one meander (m) of a recess (R') in the other plate (10a, 10b). Figure 5

Description

Title of the invention: BIPOLAR PLATE FOR ELECTROCHEMICAL CELLS LIMITING STIRRED FLOWS OUTSIDE AN ACTIVE REGION FIELD OF INVENTION

[0001] The present invention relates to a bipolar plate for electrochemical cells, in particular fuel cell cells. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] Electrochemical systems, for example fuel cells, are usually formed from a stack of cells, defined and separated from each other by bipolar plates.

[0003] In proton exchange membrane fuel cells (PEMFCs), and as illustrated in [Fig.1A], each cell C of a stack E consists of a membrane-electrode assembly 6 (referred to more simply as AME in the remainder of this description) arranged between an anodic face la of a first bipolar plate 1 and a cathodic face 1b of an adjacent bipolar plate 1.

[0004] The AME 6 comprises a solid electrolyte membrane 6b based on a polymer, for example a fluorinated polymer, and a catalyst layer formed on each face of the solid electrolyte membrane 6b. The catalyst layers form the electrodes of cell C (anode and cathode). As shown in [Fig. 1C], the AME 6 may incorporate other layers, such as gas diffusion layers 6a or a sealing strip 6c for fluidically isolating two half-cells of a cell C from each other. Reference may be made in this regard to US patent 2006 / 0078781.

[0005] An electrochemical system is formed from a stack comprising one hundred, or even several hundred, cells. In this description, the repeated stacking of a bipolar plate and an AME (Aggregate Electrochemical Element) forming an electrochemical system will be referred to as the "stacking".

[0006] As recalled in document CA2701366, the functions of bipolar plates include: - to ensure electrical contact between the anode and cathode of the two AMEs with which the bipolar plate is in contact, thus allowing the cells to be connected in series; - to supply the cells with reactive fluids, hydrogen and air for example, and to remove the products of the electrochemical reaction; - to dissipate the residual heat generated during the electrochemical reaction, for example using a heat transfer fluid; - to ensure the sealing of the various channels of reactive or cooling fluids between each other and with respect to the outside.

[0007] The bipolar plates must also exhibit sufficient mechanical robustness to maintain these functions in the stack forming the electrochemical system and when the fluids are under significant pressure.

[0008] Figures IB and IC illustrate an example of a bipolar plate of the prior art enabling these functions to be performed, respectively in top view and in partial section AA.

[0009] The bipolar plate 1 illustrated in these figures is formed of two conductive sheets 10a, 10b, respectively designated "anodic sheet" and "cathodic sheet" in this application, assembled together at an assembly plane Pref. The free face of the anodic sheet 10a defines the anodic face 1a of the bipolar plate 1 intended to be exposed to the fuel fluid (e.g., hydrogen) and, similarly, the free face of the cathodic sheet 10b defines the cathodic face 1b of the bipolar plate 1, intended to be exposed to the oxidizing fluid (e.g., air). Fig. 1A is a view of the cathodic face 1b.

[0010] In general, the conductive sheets 10a, 10b are provided with patterns composed of "recessed" reliefs tending to bring the anodic face 1a and the cathodic face 1b closer together and "raised" reliefs tending to move the anodic face 1a and the cathodic face 1b further apart. These relief patterns are typically formed by embossing the conductive sheets 10a, 10b before their assembly and enable the bipolar plate 1 to be functionalized.

[0011] The cathodic plate 10b and anodic plate 10a each include, in particular, a sealing line formed by a raised peripheral pattern on which a sealing element 5 rests. In a stack E, the sealing element 5 is pressed between two adjacent bipolar plates 1, which prevents reactive fluids from flowing outside a cell C. The sealing line of each plate 10a, 10b forms the contour of an internal region Zi of the plate, and these lines therefore define respectively two internal regions Zi of the cathodic face 1b and the anodic face 1a of the bipolar plate 1 (visible in [Fig. 1A]).

[0012] In this internal region Zi, each sheet 10a, 10b has a so-called "active" zone Za where the electrochemical reaction is intended to occur. More precisely, the active zones Za of a cathodic face 1b and an anodic face 1a of two adjacent bipolar plates 1 of a stack E define the cell volume in which the electrochemical reaction takes place. The AME 6 is arranged in cell C to cover the active areas Za of the two faces, anodic and cathodic, which face each other.

[0013] An active zone Za extends longitudinally (along the Y direction in the orthonormal coordinate system of Figures IB and IC) between a first distributor DI and a second distributor D2 arranged in the internal zone Zi of a face la,lb. These two distributors D1, D2 allow the reactive fluids to be injected at the level of the two active zones Za of a cell and these fluids and / or reaction residues to be collected after they have passed through these zones. For simplicity, these elements are referred to as "distributors," whether they are used to inject or collect a fluid. The two distributors D1, D2 also allow the heat transfer fluid to circulate in the bipolar plate 1, between the two plates 10a, 10b, so that this fluid circulates at the level of the active zone Za carried by each face la,lb of the bipolar plate 1.

[0014] As can be seen in [Fig. IC], an active zone Za is usually formed by a network of longitudinal ribs (i.e., protruding features) N on each of the plates 10a, 10b of the bipolar plate 1. These ribs N extend from the first distributor DI to the second distributor D2 to ensure the continuity of fluid flow. Two adjacent longitudinal ribs N of the network define a channel C, a recessed feature, allowing the reactive fluids to be distributed over a large area of ​​the electrode. The longitudinal ribs N of the active zones Za of the two plates forming a bipolar plate 1 define internal channels CI within this plate. These internal channels CI allow the heat transfer fluid to circulate at the active zones Za of the cathodic face 1b and the anodic face 1a of the bipolar plate 1.

[0015] In the example shown in [Fig.1B], the distributors D1,D2 comprise an air collector 2 and a hydrogen collector 3 separated from each other by a heat transfer fluid collector 4. On the cathodic face 1b of the bipolar plate 1 shown in [Fig.1B], the air collector 2 is adapted to supply channels of the active zone with air, via an injection zone 8 and a homogenization zone 9. The second distributor D2 has a similar arrangement to collect the airflow having passed through the active zone.

[0016] On the anodic face of the bipolar plate, not shown in [Fig. IB], in the first distributor DI and in the second distributor D2 there is an injection zone and a homogenization zone associated this time with the hydrogen collector.

[0017] The heat transfer fluid collector 4 is adapted to introduce and circulate this fluid in the internal channels CI of the bipolar plate 1, at the level of the active areas Za of the cathodic face 1b and the anodic face la of the bipolar plate 1.

[0018] Finally, the anodic plate 10a and the cathodic plate 10b of a bipolar plate 1 each have two lateral bands B, consisting of a raised pattern, arranged at least partially in the internal region Zi and laterally bordering the active zone Za carried by each plate 10a, 10b. The lateral bands B accommodate a peripheral contour of the AME 6, the gas diffusion layers 6a, and the sealing layer 6c. One lateral band extends laterally (along the X direction) between the active zone Za and the sealing line.

[0019] As revealed in documents EP3171441, US20140272661, or CA2701366, these lateral bands B constitute bypass zones of the reactive zone Za for the reactive fluids or for the heat transfer fluid. When at least some of these fluids bypass and short-circuit the active zone Za, the electrochemical reaction is, of course, much less efficient.

[0020] In the bipolar plate 1 of the prior art shown in figures IB and IC, the lateral bands B define a bypass passage P for the heat transfer fluid.

[0021] The aforementioned documents provide, in order to reduce the parasitic flow of fluid in the side bands, for the creation of ribs and / or recesses in the anodic and cathodic plates in order to make it more difficult for fluids to flow around the active area. SUBJECT OF THE INVENTION

[0022] One object of the invention is to provide an improvement to prior art solutions. More specifically, one object of the invention is to provide a bipolar plate for a fuel cell having lateral bands configured to limit the flow of fluids bypassing the active zone, more effectively than the solutions envisaged in the prior art. BRIEF DESCRIPTION OF THE INVENTION

[0023] To achieve one of these objectives, the object of the invention proposes a bipolar plate for electrochemical cells, the bipolar plate being formed of two sheets joined together, each having patterns composed of recessed and raised reliefs. The patterns define on each of the sheets, arranged opposite each other: - an active zone at which an electrochemical reaction is intended to occur, the active zone extending longitudinally between a first fluid distributor and a second fluid distributor; - two lateral bands formed of protruding reliefs and bordering laterally the active area.

[0024] According to the invention: - each lateral band has at least one indentation, forming a hollow relief, the indentation extending in a plurality of meanders over at least one longitudinal portion of the lateral band; - a recess in a lateral strip of one of the sheets of the bipolar plate contacts a longitudinal portion without any recess in the lateral strip arranged opposite it on the other sheet; - at least one meander of a recess in one of the sheets is nested in at least one meander of a recess in the other sheet.

[0025] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: - the longitudinal portions in which the indentations of one sheet are formed are complementary to the longitudinal portions in which the indentations of the other sheet are formed; - the bipolar plate further includes a sealing line on which a sealing element is intended to bear, the sealing line forming a contour of an internal region; - the active zone of each of the sheets is arranged in the internal region of that sheet; - the first distributor and the second distributor include an air manifold, a hydrogen manifold and a heat transfer fluid manifold; - the first distributor and the second distributor respectively comprise an injection zone and a homogenization zone; - the active zone of each sheet is formed by a network of longitudinal ribs defining channels for the circulation of reactive fluids and defining internal channels for the circulation of a heat transfer fluid.

[0026] According to another aspect, the invention proposes an electrochemical system, such as a fuel cell, comprising a stack of bipolar plates as defined above, an electrode membrane assembly being disposed between each pair of adjacent bipolar plates.

[0027] According to other advantageous and non-limiting features of this aspect of the invention, taken alone or in any technically feasible combination: - the electrochemical system further includes a sealing element arranged peripherally between each pair of adjacent bipolar plates; - the membrane electrode assembly comprises a solid electrolyte membrane having faces provided with a catalyst layer; - the membrane electrode assembly also includes gas diffusion layers arranged on either side of the solid electrolyte membrane and / or a sealing strip. Brief description of the drawings

[0028] Other features and advantages of the invention will become apparent from the detailed description of the invention which follows with reference to the accompanying figures in which:

[0029] [Fig.1A]

[0030] Fig. 1A represents an electrochemical stack-up of the prior art;

[0031] [Fig.1B]

[0032] [Fig.lC]

[0033] Figures 1B, 1C respectively represent a view of the cathode face and a cross-section of a bipolar plate of the prior art;

[0034] [Fig.2]

[0035] Fig. 2 represents respectively a view of an anodic face (left) and a view of a cathodic face (right) of a bipolar plate according to the invention;

[0036] [Fig.3]

[0037] Fig. 3 represents a membrane electrode assembly compatible with a bipolar plate according to the invention;

[0038] [Fig.4]

[0039] Fig. 4 illustrates a serpentine recess arranged in a lateral band of a bipolar plate according to the invention;

[0040] [Fig.5]

[0041] Fig. 5 illustrates an interlocking of two serpentine recesses arranged in two contiguous longitudinal portions of the lateral bands of a bipolar plate according to the invention;

[0042] [Fig.6]

[0043] Fig. 6 is the cross-sectional view, along axis BB of Fig. 5, of a part of a bipolar plate according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0044] For the sake of simplicity in the following description, the same references are used for identical elements or elements performing the same function in the different modes of implementation of the invention or in the presentation of the prior art.

[0045] The bipolar plate described herein is intended to constitute an electrochemical system, and more particularly a proton exchange membrane fuel cell as presented in the introduction. Such a system comprises a large number of electrochemical cells, and therefore bipolar plates, stacked one against the other, alternating with a proton exchange membrane.

[0046] A bipolar plate according to the invention is compatible with a stack consisting of identical bipolar plates. It is also compatible with a mixed stack of bipolar plates of different types, as is the case, for example, in the electrochemical system proposed by document EP2707921. Although they may be of different types, the bipolar plates in a stack have the characteristics of a bipolar plate that is the subject of the remainder of this description.

[0047] Figure 2 includes schematic and partial top views of the anodic face 1a and the cathodic face 1b of a bipolar plate 1 according to one embodiment. Figure 6 shows a partial cross-section of this bipolar plate 1. An XYZ coordinate system is defined in these figures, where the X and Y axes define a principal plane along which the bipolar plate 1 extends.

[0048] The bipolar plate 1 of these figures, taken as an illustration only, incorporates certain characteristics of a bipolar plate of the prior art, described in the introduction to the application, which are summarized succinctly in the following paragraphs.

[0049] Thus, and with reference to Figures 2 and 6, such a bipolar plate 1 is formed of an electrically conductive anodic plate 10a and an electrically conductive cathodic plate 10b joined together. The two plates 10a, 10b may be made of a single metal and held together only at their edges Zb, for example by welding, so as to allow the flow of a heat transfer fluid in the bipolar plate 1, between the two plates 10a, 10b.

[0050] The free face of the anodic plate 10a (the face of this plate that is not assembled to the cathodic plate 10b) defines the anodic face 1a of the bipolar plate 1. This face is intended to be exposed to the fuel fluid (for example, hydrogen). Similarly, the free face 1b of the cathodic plate 10b defines the cathodic face 1b of the bipolar plate 1, this face being intended to be exposed to the oxidizing fluid (for example, air).

[0051] The anodic plate 10a and the cathodic plate 10b each comprise a sealing line Le formed by a raised peripheral motif on which a sealing element 5 can bear. This bearing can be vertical, i.e., perpendicular to the face of the plate, or lateral. "Lateral bearing" refers to a bearing against a raised feature that allows the sealing element 5 to be contained during its compression or during its installation.

[0052] The sealing line Le of each sheet forms the contour of an internal region Zi of the cathodic face 1b of the bipolar plate 1 and the contour of an internal region Zi of the anodic face of the bipolar plate 1.

[0053] In this internal region Zi, each plate 10a, 10b has an active zone Za that extends longitudinally (along the Y direction on the two faces shown in [Fig. 2]) between a first fluid distributor DI and a second fluid distributor D2. The active zones Za of the two plates 10a, 10b of the bipolar plate 1 are opposite each other. The two distributors D1, D2 allow the circulation of reactive fluids and a heat transfer fluid at the level of the active zone Za of each plate 10a, 10b, which together constitute the bipolar plate 1.

[0054] Each active zone Za can be traversed by a network of longitudinal ribs N (protruding patterns), extending between the first distributor DI and the second distributor D2, two adjacent ribs N defining a longitudinal channel C (recessed pattern) allowing to guide the circulation of reactive fluids between the two distributors and for this circulation to be distributed over the entire extent of the active zone Za.

[0055] In the embodiment shown, the two distributors D1,D2 include an air collector 2 and a hydrogen collector 3 separated from each other by a heat transfer fluid collector 4. The distributors D1,D2 also include injection zones 8 and homogenization zones 9 allowing a reactive fluid flow to be established extending between the collectors 2,3 of the first distributor DI and the collectors 2,3 of the second distributor D2, for example a hydrogen flow on the active zone Za of the anodic face 1a and an air flow on the active zone Za of the cathodic face 1b.

[0056] But the invention does not require the presence of these two zones, and any means allowing the respective flow of reactive fluids at the level of the active zones Za of each sheet is suitable.

[0057] A heat transfer fluid flow can be established between the two sheets 10a,10b of the bipolar plate 1, from one heat transfer fluid collector to the other, via internal channels CL. This heat transfer fluid flow is likely to circulate between the anodic sheet 10a and the cathodic sheet 10b, at the level of the active areas Za which face each other, in order to evacuate the heat produced by the electrochemical reaction.

[0058] The anodic plate 10a and the cathodic plate 10b of a bipolar plate 1 each have, arranged at least in part in the internal region Zi of the plate considered, two lateral bands B1,B2 bordering the active zone Za. The two lateral bands B1,B2 are respectively made up of protruding motifs, arranged on one side and the other of this active zone Za, between this active zone Za and the sealing line Le.

[0059] A first lateral band B1 of one face of the bipolar plate 1 located on one side of the active zone is positioned opposite the first lateral band B1 of the other face of the bipolar plate 1 located on the same first side of the active zone Za. Similarly, a second lateral band B2 of one face of the bipolar plate 1 located on a second side of the active zone Za is opposite the second lateral band B2 on the other side of the bipolar plate 1 arranged on the same second side of the active zone Za.

[0060] A lateral band B1,B2 extends in projection over at least the entire longitudinal extent of the active zone Za, from the first distributor DI to the second distributor D2.

[0061] As a reminder, these side bands allow to receive, on a lateral overlap portion, a peripheral contour of FAME 6.

[0062] Figure 3 illustrates, respectively in top view and in cross-section, an example of such an AME 6. As presented in the introduction, this assembly 6 consists of a solid electrolyte membrane 6a, each face of which is provided with a catalyst layer forming an electrode. This layer, here rectangular in shape, has dimensions that correspond approximately to the dimensions of an active zone Za, slightly larger than this active zone Za.

[0063] The AME 6 also includes, on either side of the membrane 6b, two gas diffusion layers 6a. These layers, also rectangular, have slightly larger dimensions than the membrane 6b so that they extend beyond its periphery. Finally, the AME of [Fig. 3] includes a sealing strip 6c, this strip surrounding the membrane 6b peripherally, without completely covering it, particularly in a central portion.

[0064] When the AME 6 is suitably arranged between two adjacent bipolar plates 1 of an electrochemical stack, the opposite faces, anodic la and cathodic 1b, of these two plates defining an electrochemical cell, the membrane 6b and the gas diffusion layers 6a completely cover the active areas Za. They extend over a portion of the lateral bands B1,B2. The sealing band 6c extends laterally at least as far as the sealing line Le, to come into contact with the sealing element 5 and thus separate the cell into two half-cells, which are not in fluidic communication.

[0065] In this arrangement in which the two adjacent bipolar plates 1 are placed against each other, the two lateral bands B1, B2 of one of the bipolar plates 1 come into contact with the two lateral bands B1, B2 of the other bipolar plate. The AME is held "sandwiched" between the two adjacent bipolar plates, at the level of the lateral bands B1, B2.

[0066] The forced and extensive contact of the lateral strips B1, B2 tends to limit the parasitic flow of reactive fluids between these two strips and towards the sealing line. This limits the flow of reactive fluids bypassing the active zone, and the lateral strips tend to channel this flow so that it passes through the active zone Za and maximizes the amount of reactive fluid that participates in the electrochemical reaction.

[0067] The two lateral bands B1, B2 arranged on each of the two plates 10a, 10b of a bipolar plate 1 having a "protruding" pattern are liable to define, within the bipolar plate 1 and between these two plates, an internal bypass passage into which the heat transfer fluid may enter, and thus form a parasitic flow of this fluid. To avoid this phenomenon, a bipolar plate 1 of the present description includes recesses R, formed in the lateral bands B1, B2.

[0068] To avoid any doubt, the term "recess" refers to any recessed pattern formed in the lateral bands B1, B2 of the sheets of the bipolar plate 1, which are generally protruding. A recess R formed in a sheet is such that its bottom contacts the opposite sheet of the bipolar plate, this other sheet being, on the opposite side, without any recess. In other words, a recess R in a lateral band B1, B2 of one of the sheets 10a, 10b of the bipolar plate 1 contacts the lateral band B1, B2 of the other sheet 10a, 10b, arranged opposite, and which, on the other hand, is without any recess at that point. A recess R therefore has the capacity to block, at least locally, the parasitic flow of the heat transfer fluid since it closes off a possible passage for this flow.

[0069] According to the invention, a recess R is "serpentine," that is, it is composed of a plurality of successive meanders m. This recess extends continuously in a general longitudinal direction along the lateral band. The meanders m of the serpentine recess R extend laterally from the active zone Za to the sealing line Le. Figure 4 shows an example of such a recess R, according to the invention, comprising a plurality of successive meanders m, each meander m defining an open loop.

[0070] The longitudinal extension L of the recess R blocks the parasitic flow of the heat transfer fluid along a bypass zone of the active zone Za. Its lateral extension 1, generated by the meanders m, primarily limits the flow of the heat transfer fluid across the width of the lateral bands B1, B2. This lateral extension 1 also improves the robustness of the bipolar plate, notably by limiting the sagging or crushing of the lateral bands in a stack of bipolar plates. By preventing or limiting the sagging of the lateral bands B1, B2 thanks to the serpentine recess R of the invention, their function of blocking parasitic flows of reactive fluids, obtained in a stack when two adjacent bipolar plates 1 are stacked, is maintained.The lateral extension 1 of the recess R can cover the largest possible portion of the lateral band B1,B2 in which it is arranged, without however extending below the sealing line.

[0071] It is advantageous for a recess R not to extend continuously along the entire longitudinal extent of a lateral band Bl, B2 of a plate 10a, 10b, from one distributor to the other, but only over a portion thereof. Indeed, if this were the case, reactive gases that would seep between two bands B1, B2 in contact with two adjacent bipolar plates of a stack could circulate in this recess R and along the entire length of the active zone Za, which would constitute a possible bypass zone for these gases.

[0072] Also, each lateral band B1,B2 is advantageously divided into longitudinal portions P1,P2. Some longitudinal portions P1 of the lateral bands B1,B2 of a sheet 10a, 10b have indentations R. Other longitudinal portions P2 of the lateral bands B1,B2 of a sheet 10a, 10b are without any indentations. Each band B1,B2, on each of the sheets, can be formed from an alternation of longitudinal portions having indentations P1 and longitudinal portions without indentations P2.

[0073] As can be clearly seen in [Fig.2], a longitudinal portion PI of a sheet 10a,10b of a bipolar plate 1 bearing a recess is arranged opposite a longitudinal portion without any recess P2 of the other sheet 10a, 10b of the bipolar plate 1.

[0074] The longitudinal portions PI of one sheet 10a,10b in which indentations are formed, and the longitudinal portions PI of the other sheet 10a,10b, in which other indentations are also formed, are complementary. This is naturally also the case for the longitudinal portions P2 without indentations.

[0075] Thus, when the two sheets 10a, 10b are joined together to form the bipolar plate 1, the longitudinal portions PI of the sheets in which indentations are respectively formed fit into the longitudinal portions P2 of the sheets without any indentations. In this way, the longitudinal portions PI of the two sheets in which the indentations are formed combine to extend over the entire longitudinal extent of a lateral strip, and the indentations R carried by the two sheets therefore completely border, in combination, the active zone Za. In such an embodiment, the lateral strips B1, B2 are made up of a plurality of contiguous longitudinal portions PI in which indentations are formed, these portions PI being arranged alternately on one and then the other sheet of the bipolar plate 1.

[0076] Consequently, each lateral band B1,B2 of the anodic plate 10a and each lateral band B1,B2 of the cathodic plate 10b of a bipolar plate 1 according to the invention may each have one or more recesses R. When such a lateral band B1,B2 has several recesses R, these do not communicate with each other and are arranged on longitudinal portions PI of These lateral bands are separated by a longitudinal portion P2 without any indentation. In the bipolar plate 1 shown as an example in [Fig. 2], each lateral band B1, B2 of the anodic plate 10a (left part of [Fig. 2]) has two longitudinal portions PI, each with a indentation, separated by a longitudinal portion P2 without an indentation. And each lateral band B1, B2 of the cathodic plate 10b (right part of the figure) has a single longitudinal portion PI with an indentation, this longitudinal portion PI being complementary to the two longitudinal portions PI with indentations of the anodic plate 2a.

[0077] Such a configuration, where the recesses R are arranged on the lateral bands B1, B2 of the two sheets 10a, 10b, in complementary longitudinal portions PI, is nevertheless insufficient to limit the parasitic flow of heat transfer fluid. This can in fact infiltrate at the junction of these two complementary longitudinal portions PI, this junction forming a straight leak line extending from the active zone Za to the sealing line Le.

[0078] To avoid or limit this residual leakage, the serpentine recesses R,R' of two complementary and contiguous longitudinal portions PI (carried by the cathode plate 10a and the anodic plate 10b) are nested one inside the other. More precisely, one of the two recesses R formed on the lateral band B1,B2 of one of the two plates extends into the open loop defined by an end meander of the other recess R' formed on the other plate. Such a configuration is shown in [Fig. 5]. In such a nested configuration, it is not possible to form a straight line extending from the active zone Za to the sealing line Le without intersecting a recess R, thus limiting heat transfer fluid leakage.

[0079] Figure 6 shows a view along section BB of Figure 5, at the point where the recesses interlock. As indicated by the arrows in Figure 5, this prevents the formation of a straight leakage path between the active zone Za and the sealing line Le, since any leaks must bypass the interlocking meanders, resulting in relatively high fluid resistance. In effect, the longitudinal sections with complementary and contiguous recesses PI overlap, eliminating the straight junction that could have formed a leakage path with low resistance.

[0080] Of course the invention is not limited to the modes of implementation described and alternative embodiments can be made without departing from the scope of the invention as defined by the claims.

[0081] A sealing line of a sheet 10a,10b arranged at the same elevation as the lateral strips of this sheet has thus been described and illustrated. But this in no way forms an essential feature of the invention, and it could be envisaged that the sealing line could be placed at any suitable elevation.

Claims

Demands

1. Bipolar plate (1) for electrochemical cells, the bipolar plate (1) being formed of two sheets (10a,10b) assembled to each other and each having patterns composed of recessed and raised reliefs, the patterns defining on each of the sheets (10a,10b), arranged opposite each other: - an active zone (Za) at the level of which an electrochemical reaction is intended to occur, the active zone (Za) extending longitudinally between a first fluid distributor (D1) and a second fluid distributor (D2); - two lateral bands (B1,B2) formed of raised reliefs and bordering laterally the active zone (Za);the bipolar plate (1) being characterized in that: - each lateral band (B1,B2) has at least one indentation (R,R'), forming a recessed relief, the indentation (R,R') extending in a plurality of meanders (m) over at least one longitudinal portion (PI) of the lateral band (B1,B2); - a indentation (R,R') of a lateral band (B1,B2) of one of the plates (10a,10b) of the bipolar plate (1) contacts a longitudinal portion (P2) devoid of any indentation of the lateral band (B1,B2) arranged opposite it on the other plate (10a, 10b); - at least one meander (m) of a recess (R) of one of the sheets (10a,10b) is nested in at least one meander (m) of a recess (R') of the other sheet (10a,10b).;

2. Bipolar plate (1) according to the preceding claim in which the longitudinal portions (PI) in which the recesses (R) of one sheet (10a,10b) are formed are complementary to the longitudinal portions (PI) in which the recesses (R) of the other sheet (10a,10b) are formed.

3. Bipolar plate (1) according to any one of the preceding claims further comprising a sealing line (Le) on which a sealing element is intended to bear, the sealing line forming a contour of an internal region (Zi).

4. Bipolar plate (1) according to the preceding claim in which the active area (Sa) of each of the sheets (10a,10b) is arranged in the internal region (Zi) of that sheet.

5. Bipolar plate (1) according to any one of the preceding claims wherein the first distributor (D1) and the second distributor (D2) comprise an air manifold (2), a hydrogen manifold (3) and a heat transfer fluid manifold (4).

6. Bipolar plate (1) according to the preceding claim in which the first distributor (D1) and the second distributor (D2) respectively comprise an injection zone (8) and a homogenization zone (9).

7. Bipolar plate (1) according to any one of the preceding claims in which the active zone (Za) of each plate (10a, 10b) is formed of a network of longitudinal ribs (N) defining channels (C) for the circulation of reactive fluids and defining internal channels (CI) for the circulation of a heat transfer fluid.

8. Electrochemical system, such as a fuel cell, comprising a bipolar plate stack (1) according to any one of the preceding claims, an electrode membrane assembly (6) being disposed between each pair of adjacent bipolar plates.

9. Electrochemical system according to the preceding claim further comprising a sealing element (5) disposed peripherally between each pair of adjacent bipolar plates.

10. Electrochemical system according to any one of claims 8 or 9 wherein the membrane electrode assembly (6) comprises a solid electrolyte membrane (6b) having faces provided with a catalyst layer.

11. Electrochemical system according to the preceding claim wherein the membrane electrode assembly (6) also includes gas diffusion layers (6a) arranged on either side of the solid electrolyte membrane (6) and / or a sealing strip (6c).

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