Bipolar plate structure with two weld planes for fuel cell

Abstract

bipolar plate (BP) adapted to a fuel cell (FC), formed of an assembly of two superimposed and welded elementary plates (Pl1, Pl2), and comprising: first inlet and outlet openings (H2In, H2Out) of a first fluid; second inlet and outlet openings (O2In, (O2+H2O)Out) of a second fluid; third inlet and outlet openings (CoolIn, CoolOut) of a third fluid intended to circulate between the two elementary plates;of the first and second weld lines (WeldOp) joining the two elementary plates around the first and second openings respectively, and of the first and second welds (WldCool) joining the two elementary plates around the third openings respectively, the first and second weld lines being formed in a first (HPlane) and a second (LPlane) plane respectively, and the welds associated with one of the third openings are formed exclusively in one or the other of these planes. Figure to be published with the abbreviation: Fig. 8(A);

Description

Title of the invention: Bipolar plate structure with two weld planes for a fuel cell. TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to the field of fuel cells, and more specifically to the structure of bipolar plates which form an essential element of the stacks of electrochemical cells forming such fuel cells. TECHNOLOGICAL BACKGROUND

[0002] Fuel cells are devices capable of generating an electrical voltage by combining an oxidizable reactant (called the fuel) and a reducible reactant (called the oxidant) in an electrochemical reaction. The reactants are fluids, usually supplied from separate external sources. The fuel cell itself essentially consists of electrodes spaced apart and ionically connected by an electrolyte.

[0003] Each electrode, anode or cathode, is electrically conductive, adsorbs the fuel or oxidant used, presents a catalyst for the reaction at the electrode, and does not oxidize unduly under the operating conditions of the cell.

[0004] When fuel and oxidant are concurrently and separately brought to the different electrodes of the fuel cell, an electrical potential appears between the terminals of the latter.

[0005] When an electric charge is connected to the electrodes, an electric current flows between them, the electrical energy thus obtained being generated by the electro-catalytic oxidation of the fuel at an anode and by the simultaneous electro-catalytic reduction of the oxidant at a cathode.

[0006] Figure 1 illustrates this operating principle at the scale of an elementary electrochemical cell, using hydrogen H2 as fuel, oxygen O2 as oxidant, and rejecting unused reactants as well as water H2O. This membrane employs a proton-exchange membrane, PrEx, often referred to by its English acronym PEM for Proton-Exchange Membrane or Polymer-Electrolyte Membrane.

[0007] During operation, a flow of hydrogen H2 is conveyed to the anode An and is catalytically split, by an oxidation reaction, at the level of a layer of catalytic anode material CatAn, into protons H+ and electrons e. The protons pass through the proton exchange membrane PrEx, which selectively transports the protons H+ to the cathode Ca. The electrons are collected by the anode An which leads them to an external electrical circuit which connects the anode An to the cathode Ca via an electric charge Ld.

[0008] In parallel, a flow of oxygen O2 is directed to the cathode Ca. At a layer of catalytic CatCa material on the cathode, the oxygen O2 molecules react with (i) protons H+ that have passed through the electrolyte El and (ii) electrons e arriving via the external electrical circuit. The product of this reduction reaction consists of water molecules H2O.

[0009] Alternatively, instead of a proton exchange membrane, an electrochemical cell comprising an anion exchange membrane can be used, as in an anion exchange membrane fuel cell. The operation is similar to that described above, with negatively charged OH ions passing through the membrane and combining with hydrogen supplied as fuel on the anode side.

[0010] The oxidation and reduction reactions taking place within the cell generate an electrical voltage of approximately 0.7 V between the two electrodes, anode and cathode. In order to obtain a usable output voltage, it is necessary to connect individual cells such as the one in [Fig. 1] in series. To do this, stacks of elementary electrochemical cells are formed. A stack can contain several hundred electrochemical cells.

[0011] Oxidation and reduction reactions, in addition to an electrical voltage, also generate heat, which is crucial to actively dissipate when considering a stack of electrochemical cells.

[0012] Fig. 2 represents a schematic diagram of the operation of a stack of electrochemical cells, from the point of view of the management of fluids, reactants and reaction products.

[0013] Each electrochemical cell incorporates an Ass assembly which comprises, in this order according to the stacking direction X, an anode diffusion DiffAn layer, an anode catalytic material CATAn layer, a proton exchange PrEx membrane, a cathode catalytic material CATCa layer, and a cathode diffusion Diff Ca layer. The Ass assembly is also referred to as the Membrane Electrode Assembly or MEA. A peripheral zone of the Ass assembly is free of catalytic material and diffusion layer. This peripheral zone is arranged to form a fluid seal at its interface with the bipolar plates, for example by bonding, using a gasket, or by direct contact, around the fluid inlets. This portion is sometimes referred to as the "sub-gasket" in English.

[0014] Diffusion layers, often referred to by the acronym GDL for Gas Diffusion Layer, allow the passage of reactant fluids and reaction products, and are electrically conductive. Thus, the DiffAn anode diffusion layer and the DiffCa cathode diffusion layer fulfill the functions of anode and cathode, respectively, and allow the reactants to be brought to the catalytic materials and the reaction products to be removed.

[0015] Bipolar plates BP are typically made of electrically conductive materials such as carbon or stainless steel. They fluidly separate the Ass assemblies from one another but electrically connect them. Electrical contacts, necessary for the practical operation of a fuel cell, can be made at these bipolar plates. Thus, the electrochemical cells Cell of a stack are electrically connected in series.

[0016] The Stack is designed to supply the reactive fluids, hydrogen (H2) and oxygen (O2), separately to the anode and cathode diffusion layers (DiffAn and DiffCa), respectively, and to remove excess reactive fluids and the produced water (H2O). The stack is also designed to allow the circulation, within the Stack, of a heat transfer fluid (Cool) as a coolant, for example, liquid water. The Cells are fluidically connected in parallel.

[0017] Thus, the Stck stack must comprise three fluid circuits isolated from each other and capable of performing the functions of supplying reactants to the diffusion layers, extracting excess reactants and reaction products, and circulating a cooling fluid. To these purposes, a Circ(H2) circuit supplies hydrogen (H2) to the DiffAn diffusion layer and recovers excess hydrogen. A Circ(O2) circuit supplies oxygen (O2) to the DiffCa diffusion layer and recovers excess oxygen and the water (H2O) produced. A Circ(Cool) circuit circulates a cooling fluid (Cool) through the stack.

[0018] These functions are conventionally performed by means of bipolar BP plates, of structures illustrated by Figures 3 to 5.

[0019] These bipolar BP plates are generally made up of two elementary metal plates, Pli and P12, stamped to form their structure and assembled together. They are held together by a WeldExt weld line following their peripheral contours, and thus the peripheral contour of the resulting bipolar plate. A bipolar plate separating a first cell and a second cell comprises a first face directed towards the anode side of the first cell and a second face directed towards the cathode side of the second cell.

[0020] The structuring of the elementary plates consists of forming reliefs that constitute channels Ch for fluid circulation. [Fig. 3] is a very schematic representation of a Stck stack, with Ass assemblies separated by bipolar plates BP. At the ends of the stack are monopolar plates MP, only one face of which is actually used from a reaction point of view, which enclose the rest of the stack. At the outer surfaces of the bipolar plates, hydrogen will flow on one side of the plate and oxygen on the opposite side. The cooling fluid will flow in channels formed between the inner surfaces of the bipolar plate, that is, between two elementary plates, sometimes called "half-plates." See [Fig. 5].The elementary plates are assembled in such a way as to ensure the sealing of the coolant against the outside, by means of a peripheral weld, designated as WldExt on the [Fig.6]. .

[0021] Figure 4 illustrates a generic configuration of a bipolar plate, viewed in the plate's extension plane, perpendicular to the X direction, with openings H2ln, Coolln, and O2ln forming fluid inlets, H2, Cool, and O2, respectively, and openings H20ut, CoolOut, and (O2+H2O)Out forming fluid outlets, H2, Cool, and a mixture of O2 and H2O, respectively. In this example, the fluids H2, Cool, and O2 are fluids comprising hydrogen, water, and oxygen (ambient air, for example), respectively. The arrows schematically represent the flows of hydrogen (H2), coolant (Cool), and oxygen (O2), respectively, circulating in a Cell, guided by the contours of the bipolar plate BP.

[0022] Bipolar plates include fluid inlets on one side and fluid outlets on the opposite side. Between the fluid inlets and outlets of a bipolar plate is an active zone Act of the plate. The active zone is designed to accommodate an assembly Ass where the electrochemical reactions will take place. Fluid distribution zones may be interposed between the active zone Act and the fluid inlets on one side and the fluid outlets on the other.

[0023] In a stack, the openings of the bipolar plates face each other in the stacking direction, forming fluid inlets through the stack in the stacking direction X and allowing the parallel fluidic connection of the Cells to each other.

[0024] It can be seen from the diagram in [Fig. 4] that the fluids intersect, and the reliefs of the elementary plates Pli and P12 are configured in such a way as to allow this crossing without mixing between the fluids and without the passage of one fluid blocking the passage of a second fluid. In order to ensure the mechanical stability of a bipolar plate and the sealing of the fluid circuits that it defines, Slnt seals and Wld weld lines are used, as illustrated by [Fig.5].

[0025] Figure 5 illustrates that the assembly of bipolar plates BP and Ass assemblies provides channels for the circulation of fluid, O2 and H2, between a bipolar plate BP and the two Ass assemblies between which it is interposed. These channels allow the reactants O2 and H2 to be conveyed to these assemblies, within which the electrochemical reactions take place, generating an electrical potential between two bipolar plates.

[0026] The elementary plates Pli and P12 have a symmetrical structure, and all the welds are made in a single BPPiane plane parallel to the extension plane of the proton exchange membrane PrEx. The height of the BPPiane plane is defined by the contact points of the two elementary plates in the active Act region of the bipolar plate.

[0027] Reference may be made, for example, to patent documents EP2715846B1, EP3985766B1, WO2019025701Al, US10615430B2 and US2006054664A1, which describe classic bipolar plate structures and explain their operating principles.

[0028] The general operating principles of fuel cells are known, but the characteristics of these cells, and in particular the geometry of the bipolar plates and their manufacturing processes, are still being developed with a view to their optimization.

[0029] In this context, the object of the present application is a bipolar plate with improved geometry and manufacturing process compared to known geometries and manufacturing processes. Description of the invention

[0030] A first object of the invention is a bipolar plate having a geometry enabling good characteristics in the transport of fluids while being able to be manufactured using limited equipment.

[0031] To achieve these objectives, a first aspect of the invention is a bipolar plate suitable for forming a stack of elementary electrochemical cells in a fuel cell, the bipolar plate being formed from an assembly of two superimposed elementary plates welded to each other, the bipolar plate comprising: first openings forming an inlet and outlet for a first fluid, and first circulation channels for the first fluid between the inlet and outlet of the first fluid, on a first side of the bipolar plate; second openings forming an inlet and outlet for a second fluid, and second circulation channels for the second fluid between the inlet and outlet of the second fluid, on a second side of the bipolar plate opposite the first side; and of the third openings forming an inlet and outlet of a third fluid, and of the third circulation channels of the third fluid between the inlet and outlet of the third fluid, between the two elementary plates, of the first and second weld lines joining the two elementary plates forming respective loops around the first and second openings, the first and second weld lines being configured so as to isolate the first and second fluids from the third fluid, respectively, and of the first welds joining the two elementary plates and surrounding a first of the third openings, and of the second welds joining the two elementary plates and surrounding a second of the third openings, in which the first weld lines are formed in a first plane,The second weld lines are formed in a second plane, distinct from the first plane; the first welds are formed exclusively in one or the other of the first and second planes; and the second welds are formed exclusively in one or the other of the first and second planes.

[0032] An advantage of this bipolar plate is that, while ensuring the normal operation of a conventional bipolar plate, it is compatible with an improvement in the regularity of the hydraulic sections, in particular of the third circulation channels.

[0033] A second advantage is that the weld lines and welds can be made in their entirety using only two welding machines, for example two fixed-focal laser welding machines, set respectively on the two weld planes.

[0034] According to additional, non-limiting features of the first aspect of the invention, considered individually or in any technically feasible combination:

[0035] - the first plane and the second plane can be located on either side of a plane defined by points of contact between the two elementary plates in an active zone of the bipolar plate;

[0036] - the active zone can be interposed between the first openings, between the second openings, and between the third openings, and the first welds can be partly formed between the active zone and the first of the third openings, and the second welds can be partly formed between the active zone and the second of the third openings;

[0037] - the bipolar plate may include a peripheral weld between the two Elementary plates, the peripheral weld can follow a peripheral contour of the bipolar plate, and can be formed in either the first or second plane;

[0038] - the weld lines and welds can be distributed between the foreground and the second plan in such a way as to minimize a difference in welding time required between the first plan and the second plan;

[0039] - the weld lines and welds can be distributed between the foreground and the second plane so as to minimize a difference between a sum of lengths of weld lines and welds formed in the first plane and a sum of weld lines and welds formed in the second plane;

[0040] - an inlet and outlet of a fluid can each consist of a number arbitrary openings included in the bipolar plate;

[0041] - one of the two elementary plates may have an arranged planar region so as to receive ribs or grooves from the other of the two elementary plates.

[0042] A second aspect of the invention relates to a stack of bipolar plates according to the first aspect of the invention, configured so as to be integrated into a fuel cell, the stack comprising assemblies each comprising, in this order, an anode diffusion layer, an anode catalytic material layer, a proton exchange membrane, a cathode catalytic material layer, and a cathode diffusion layer, each assembly being interposed between two of the bipolar plates.

[0043] A third aspect of the invention relates to a fuel cell comprising a stack according to the second aspect of the invention, compressed between two monopolar plates, the fuel cell being configured so as to, in operation, produce electrical energy.

[0044] The second and third aspects of the invention benefit from the advantages of the first aspect. BRIEF DESCRIPTION OF THE FIGURES

[0045] 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:

[0046] [Fig.1] Fig.1 illustrates the operating principle of an elementary fuel cell;

[0047] [Fig.2] [Fig.2] illustrates the operating principle of a cell stack elementary of a fuel cell;

[0048] [Fig. 3] [Fig. 3] illustrates the principle of the structure of a stack of stacks with fuel;

[0049] [Fig.4] The [Fig.4] illustrates a generic structure of a bipolar fuel cell plate;

[0050] [Fig.5] The [Fig.5] illustrates a cross-section of a conventional fuel cell stack;

[0051] [Fig.6] Fig.6 illustrates the structure of a particular bipolar plate;

[0052] [Fig.7] Figure [Fig.7] illustrates cross-sections of fluid circulation channels in stacks of bipolar plates of various geometries;

[0053] [Fig.8] Figure [Fig.8] illustrates a stack of bipolar plates according to the invention; and

[0054] [Fig.9] Fig.9 represents a fuel cell. DETAILED DESCRIPTION OF THE INVENTION

[0055] The invention is detailed in relation to Figures 1 to 9. The descriptions applying to elements identified by a certain identifier in a given figure also apply to elements identified by the same identifier in the other figures.

[0056] Figure 6 shows a plan view of a particular bipolar plate BP in its extension plane, perpendicular to the stacking direction X to form a Stck stack. In this particular case, an opening is provided for each of the inlets and outlets of the three fluids, therefore six openings in total. The number of openings for the inlets and outlets can be adjusted to more precisely control the fluid flows and is not limited to this particular case.

[0057] The bipolar plate is structured so as to form channels extending between the fluid inlets and outlets, and taking the form of sinusoidal meanders, in particular in the so-called active Act zone of the bipolar plate.

[0058] Figure 6 illustrates that a SlntEx joint forms a closed loop along the outer periphery of the bipolar plate BP. Furthermore, each of the openings H2ln, Coolln, O2ln, H20ut, Coolout, and (O2+H2O)Out is surrounded by a respective SlntOp opening joint. As is known, these joints are interposed between two bipolar plates when they are integrated into a Stck stack, as illustrated by Figure 5, possibly superimposed on ribs or grooves of the bipolar plates.

[0059] Fig. 6 also illustrates WldOp weld lines joining the two elementary plates Pli and P12 forming a bipolar plate.

[0060] The WldOp weld lines each form a continuous loop around the respective openings H2ln, O2ln, H20ut and (O2+H2O)out, outside the respective SlntOp seals. Their function is to hermetically seal these openings, which bring the reactants to or remove them from the active zone Act, with respect to the coolant Cool.

[0061] A weld line WldExt, substantially parallel to the joint SlntExt, keeps the two elementary plates forming the bipolar plate mechanically joined together, and ensures the seal between the volume defined between these plates and the outside.

[0062] WldCooi welds form loops around the Coolln and Coolom openings, respectively, and in close proximity to these openings, for example, on the inner sides of the Slntop seals surrounding these openings. The WldCooi welds could also be formed on the outer sides of these seals. The function of these welds is to stiffen the bipolar plate in the vicinity of the Coolln and CoolOut openings. Thus, the WldCooi welds do not have to form continuous lines in closed loops: simple weld points or weld lines forming dashed lines may suffice.

[0063] The WldCool welds may partly be located between the Coolln and Coolom openings and the active Act area. Where appropriate, these welds may more specifically be located between distribution channels, as discussed below and illustrated in (A2) of [Fig.8].

[0064] The bipolar plate geometry illustrated in [Fig. 6], and repeated in [Fig. 7](A), requires precise lateral alignment between the two elementary plates Pli and P12 in order to form the Cool coolant circulation channels according to the intended configuration at the fluid inlets and outlets. In these regions, outside the active Act zone, the PrEx membranes are not covered by the catalytic material and diffusion layers, and form so-called "sub-gaskets" in contact with the bipolar plates, identified as SubGask in [Fig. 7].

[0065] Fig. 7(B) illustrates the geometry resulting from a misalignment Mis between the two elementary plates. Besides the fact that achieving precise alignment between the two elementary plates complicates the fabrication of the bipolar plate, any misalignment leads to a suboptimal geometry for the sections of the coolant circulation channels, disrupting the circulation of this coolant.

[0066] Fig. 7(C) illustrates an alternative geometry, which has the advantage of eliminating the problem of misalignment of the elementary plates Pli and P12. The principle is to use asymmetrical elementary plates, with, for example, flat R regions of P12, free of grooves or ribs, these flat regions being suitable for receiving Pli ribs or grooves. Thus, fluid circulation channels with well-defined geometries can be obtained, insensitive to any alignment errors as long as they do not exceed a certain threshold. This threshold can correspond to a distance d separating the edges of the R regions from the location of P12 intended to be in contact with a Pli rib or groove edge. This improves the regularity of the hydraulic section of the channels, therefore with less turbulence and a laminar flow facilitating the movement of the transported fluid.

[0067] Ordinarily, the elementary plates Pli and P12 are symmetrical, and the welds joining these plates are all made in the same median plane BPPiane of the bipolar plate. However, the geometry illustrated in [Fig. 7](C) does not allow for such a geometry: such a solution would result in the blocking of some of the fluid circulation channels Ch due to conflicts at the crossings between the different fluid circuits Circ(H2), Circ(O2), and Circ(Cool) illustrated in [Fig. 2]. In order to avoid such conflicts, the welds sealing the openings of the Circ(H2) fluid circuit must be on one side of the median plane, while the welds sealing the openings of the Circ(O2) fluid circuit must be on a second side of the median plane, opposite the first side.

[0068] One solution consists of forming the welds associated with each of the three circuits in respective and distinct weld planes. Each of the three weld planes is distinguished from the other two by its distance from a reference plane, such as the distance to the PrEx proton exchange membrane.

[0069] From a manufacturing standpoint, the inventors determined that using a fixed assembly consisting of tooling and a welding machine for each weld level is the most advantageous configuration in terms of productivity. Each tooling piece, specifically adapted for welds in a given plane, is mounted on a welding machine. With one machine per weld plane, tooling changes on the welding machines are unnecessary, as each fixed assembly is adapted and dedicated to a particular weld plane.

[0070] This solution works. However, its implementation under industrial production conditions is inefficient. In particular, for laser welding, the most practical implementation requires three welding machines, each with a fixed focal length and configured to form welds on one of the three weld planes. This solution, although preferable to using a variable focal length laser welding machine, remains unsatisfactory.

[0071] In order to improve the efficiency of forming WldOp and WldCooi weld lines to ensure the sealing of the Circ(H2), Circ(O2), and Circ(Cool) fluid circulation circuits formed by the H2ln, Coolln, O2ln, H20ut, Coolout, and (O2+H2O)out openings, as well as the mechanical integrity of the bipolar plate, it is possible to define bipolar plate geometries that require only two weld planes. This reduction automatically results in an advantageous reduction in the number of welding machines, from three to two.

[0072] More specifically, a study of the geometric constraints concerning the possible positioning of the weld planes for the different fluid circulation circuits was carried out, considering three heights for these three planes: at the level of the BPPiane plane defined above, a low LPiane plane and a high HPiane plane located respectively below and above the BPPiane plane in the representations used in this description.It was concluded that the possible geometries are those which consist of forming (i) the welds associated with one of the two reagent circuits Circ(O2) and Circ(H2) in one of the two planes LH are and Hh ane, (ii) the welds concerning the other of the two reagent circuits Circ(O2) and Circ(H2) in the other of the two planes LPiane and HP iane, and (iii) among the welds associated with the third openings of the Circ(Cool) circuit, the welds associated with one of the same third openings are formed in the same plane, which can be either of the two planes LPiane and HP iane. More specifically, welds surrounding a coolant inlet opening are formed in either of the two planes LPiane and HPiane and, regardless of this formation plane, welds surrounding a coolant outlet opening are formed in either of the two planes LPiane and 11^.

[0073] In this document, it is considered that the welds associated with one of the reagent circuits are those which form closed loops intended to isolate the openings forming the inlets or outlets intended for this reagent from the coolant, and that the welds associated with the coolant circuit are those which are located near the inlet and outlet openings of the coolant, on the periphery of these openings, possibly between two circulation channels intended for this coolant.

[0074] [Fig.8] illustrates Stck stacks comprising a pair of bipolar plates BP as illustrated by [Fig.6], and for which (i) the welds concerning the Circ(O2) reagent circuit are formed in the lower LPiane plane, (ii) the welds concerning the Circ(H2) reagent circuit are formed in the upper HPiane plane, and (iii) the welds concerning the Circ(Cool) circuit are formed in the lower LPiane plane.

[0075] Fig. 8(A) illustrates in (A1) a plan view of the CoolOut opening taken from Fig. 6, and in (A2) a cross-sectional view of this version enlarged at the level of the dashed ellipse, a section perpendicular to the Ch channels opening into the CoolOut opening. The same structure is found on the side of the Coolln opening.

[0076] In this region, the WldCooi welds are located between two fluid circulation channels Ch which are intended to carry the cooling fluid Cool from the active zone of a bipolar plate to the CoolOut opening for cooling fluid discharge after it has passed through the active zone Act. Symmetrically, the channels bringing the cooling fluid from the Coolln opening to the active area of ​​the bipolar plate are similarly associated with other weld lines, as illustrated by [Fig.6].

[0077] The cross-section illustrated in (A2) corresponds to a section plane parallel to the SlntOp joint, comprising WldCooi welds (scales not to scale), intended to mechanically join the elementary plates Pli and P12 forming a bipolar plate BP. The welds may also be located outside this particular section plane, for example, on the outer side of the SlntOp joint. In the illustrated section plane, two identical bipolar plates BP stacked one on top of the other are shown. The peripheral zone of the assembly Ass is interposed between the two bipolar plates BP, this peripheral zone Ass forming the sub-gasket, which does not include catalytic material or a diffusion layer. In this representation, the lower plane LPiane is located below the reference plane BPPiane.We can also say that the LPiane low plane is located between the BPPiane plane and the PrExPiane extension plane of the PrEx proton exchange membrane which is located below the considered bipolar BP layer which limits the electrolytic cell of which this membrane is a part.

[0078] The figure shows the WldCooi welds related to the Circ(Cool) circuit: they maintain the physical integrity of the Ch channels through which the coolant Cool flows in an area subjected to pressure forces. In this example, these welds are located in the lower plane LPiane. In this example, the WldCooi welds are simple spot welds, but these spots could more generally form continuous weld lines or lines composed of dashed lines.

[0079] Welds located in the immediate vicinity of an opening, Coolln or CoolOut, are considered to be associated with that opening: their function is to mechanically reinforce the assembly at the opening near which they are located. Welds located between the active zone Act and one of the Coolln and CoolOut openings can also be considered to be associated with that opening.

[0080] WeldCooi welds associated with the same Coolln or CoolOut opening must be formed in the same plane, HPiane or LPiane. Welds associated with two different openings may be formed in the same plane or in two different planes. For example, welds associated with the Coolln opening may be formed in the HPiane plane and welds associated with the CoolOut opening may be formed in the LPiane plane, or vice versa. Alternatively, all welds may be formed in the same plane, HPiane or LPiane. [Fig. 8](A) illustrates in (A2) WldCooi welds associated with the CoolOut opening and formed in the LPiane plane.

[0081] Fig. 8(B) illustrates a cross-sectional view along the axis BB' defined in Fig. 6, which passes through the openings O2ln, (O2+H2O)Out and the active zone Act between these two openings. In particular, the WeldOp welds located on either side of each of the two openings are visible, at the level of the lower plane LPiane situated below the plane BPPlane*.

[0082] Fig. 8(C) illustrates a cross-sectional view along the axis CC' defined in Fig. 6, which passes through the openings H2ln, H20ut and the active area Act between these two openings. In particular, the WeldOp welds located on either side of each of the two openings are visible, at the height of the upper plane HPiane situated above the plane BPPiane.

[0083] It can be said that the lower plane LPiane and the upper plane HPiane are located on either side of the plane BPPiane defined by the points of contact between the plates Pli and P12 in the area of ​​the bipolar plate intended to form an active area of ​​an electrochemical cell, that is to say the area of ​​the bipolar plate BP intended to come into contact with an Ass assembly comprising the elements necessary for the oxidation and reduction reactions.

[0084] With the geometry illustrated by [Fig.8], the sealing of the Circ(H2) and Circ(O2) circuits with respect to the Cool coolant is ensured, while maintaining the normal functions of the Stack which is to ensure the circulation of fluids to and within the Ass assemblies.

[0085] Furthermore, this geometry allows for planar regions in the elementary plates of the bipolar plate, providing at least partial immunity to misalignment of the elementary plates relative to each other, as explained in relation to [Fig. 7](C). This feature reduces pressure losses in the Circ(Cool) circuit, and therefore the pressure required for the circulation of the cooling fluid and the risk of leakage. In addition, immunity to compression of the seals is also achieved in the event of incorrect positioning of SlntOp during assembly of the bipolar plate: slight misalignment is tolerable.

[0086] In the specific case of the bipolar plate illustrated in [Fig. 6], only one opening in the bipolar plate is provided per fluid inlet or outlet. However, more generally, each fluid inlet or outlet can be formed by an arbitrary number of openings in the bipolar plate.

[0087] During the assembly of two elementary plates PLI and PL2 to form a bipolar plate BP, two welding machines can operate in parallel to form the different weld lines and the different welds mentioned above (WldOp, WldExt, Wldcooi) in the two planes LPiane and HPiane, each welding machine being dedicated to one of the two planes. From the point of view of minimizing the Given the time required to perform the welds, it is advantageous to distribute the weld lines and welds between the two planes Hpi^ and LPiane in order to minimize the difference in welding time required for each of these planes.

[0088] In this way, the time required to form the weld lines of a bipolar plate is reduced. Thus, the welds (the WldOp and WldExt lines and the WldCooi welds) can be distributed between the first HPiane plane and the second LPiane plane so as to minimize the difference in welding time required between the first and second planes. This distribution can be characterized by the fact that the WldOp and WldExt weld lines and the WldCooi welds can be distributed between the first HPiane plane and the second LPiane plane so as to minimize the difference between a sum of the lengths of the WldOp and WldExt weld lines and the WldCooi welds formed in the first plane and a sum of the lengths of the WldOp and WldExt weld lines and the WldCooi welds formed in the second plane.

[0089] This approach can be associated with other geometries and other configurations, and can be summarized by the condition that the cooling circuit is associated with the weld plane of the reagent circuit which minimizes the cumulative length of weld lines to be made in the weld plane associated with this reagent.

[0090] A fuel cell system for generating electrical energy is formed of a stack of Stck which may include several hundred bipolar plates each interposed between two sets Ass, often referred to by the acronym MEA in English terminology.

[0091] Figure 9 illustrates in a simplified manner such a fuel cell as seen from the outside, with monopolar plates MP enclosing a stack of material Stck such as that illustrated in Figure 3. Rods R associated with compression bolts CB allow pressure to be applied to the stack of material Stck via the monopolar plates MP so as to compress the stack joints and ensure the sealing of the fluid circulation circuits. External elements not shown allow for the management of fluids (reactants, coolant) and for the electrical connection of the fuel cell to an external load to be supplied with electrical current. This load can be a vehicle or any other electrically powered device.

[0092] The fuel cell in [Fig.9] can be configured to be supplied with hydrogen as fuel, air including oxygen as oxidant, and water as coolant.

[0093] In this document, the figures are not necessarily to scale. Certain features and components may be shown exaggerated relative to other components or in a somewhat schematic form, and certain details Conventional elements may not be represented in the interest of clarity and conciseness.

[0094] 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.

Claims

1. Demands Bipolar plate (BP) capable of forming a stack of elementary electrochemical cells (Cell) in a fuel cell (FC), the bipolar plate being formed from an assembly of two superimposed elementary plates (Pli, P12) welded to each other, the bipolar plate comprising: - the first openings (H2ln, H20ut) forming an inlet and outlet of a first fluid, and the first circulation channels (Ch) of the first fluid between the inlet and outlet of the first fluid, on a first side of the bipolar plate; - second openings (O2ln, (O2+H2O)Out) forming an inlet and outlet for a second fluid, and second channels (Ch) for the circulation of the second fluid between the inlet and outlet of the second fluid, on a second side of the bipolar plate opposite the first side; and - third openings (Coolln, CoolOut) forming an inlet and outlet of a third fluid, and third channels (Ch) for the circulation of the third fluid between the inlet and outlet of the third fluid, between the two elementary plates (Pli, P12), - the first and second weld lines (WeldOp) joining the two elementary plates form respective loops around the first openings (H2ln, H20ut) and the second openings (O2ln, (O2+H20)out), the first and second weld lines (WeldOp) being configured so as to isolate the first fluid and the second fluid from the third fluid, respectively, and - the first welds (WldCooi) joining the two elementary plates and surrounding one of the third openings (Coolln), and the second welds (WldCooi) joining the two elementary plates and surrounding a second of the third openings (CoolOut), in which the first weld lines are formed in a first plane (HPiane), the second weld lines are formed in a second plane (LPiane), distinct from the first plane, the first welds are formed exclusively in one or the other of the first plane (HPiane) and the second plane (LPiane), and the second welds are formed, exclusively, in one or the other of the first plane (HPiane) and the second plane (LPiane).

2. The bipolar plate according to claim 1, wherein the first plane (HPiane) and the second plane (LPiane) are located on either side of a plane (BPPiane) defined by points of contact between the two elementary plates (Pli, P12) in an active zone (Act) of the bipolar plate.

3. 3. The bipolar plate according to claim 2, wherein the active zone (Act) is interposed between the first openings (H2ln, H20ut), between the second openings (O2ln, (O2+H20)out), and between the third openings (Coolln, CoolOut), and wherein the first welds are partly formed between the active zone (Act) and the first (Coolln) of the third openings, and the second welds are partly formed between the active zone and the second (CoolOut) of the third openings.

4. 4. The bipolar plate according to any one of claims 1 to 3, comprising a peripheral weld (WedlExt) between the two elementary plates, wherein the peripheral weld follows a peripheral contour of the bipolar plate, and is formed in either the first plane (HPiane) or the second plane (LPiane).

5. 5. The bipolar plate according to claim 4, wherein the weld lines and welds are distributed between the first plane (HPiane) and the second plane (LPiane) so as to minimize a difference in welding time required between the first plane and the second plane.

6. 6. The bipolar plate according to claim 5, wherein the weld lines and welds are distributed between the first plane (HPiane) and the second plane (LPiane) so as to minimize a difference between a sum of lengths of weld lines and welds formed in the first plane and a sum of weld lines and welds formed in the second plane.

7. 7. The bipolar plate according to any one of claims 1 to 6, wherein an inlet and an outlet of a fluid are each made up of an arbitrary number of openings included in the bipolar plate.

8. 8. The bipolar plate according to any one of claims 1 to 7, wherein one (Pli) of the two elementary plates (Pli, P12) has a planar region (R) arranged to receive ribs or grooves from the other (P12) of the two elementary plates (Pli, P12).

9. 9. Stack (Stck) of bipolar plates defined by one any of claims 1 to 8 configured to be integrated into a fuel cell (FC), the stack comprising assemblies (Ass) each comprising, in this order, an anode diffusion layer (DiffAn), an anode catalytic material layer (CATAn), a proton exchange membrane (PrEx), a cathode catalytic material layer (CATCa), and a cathode diffusion layer (DiffCa), each assembly (Ass) being interposed between two of the bipolar plates (BP).

10. 10. A fuel cell (FC) comprising a stack (Stck) according to claim 9, compressed between two monopolar (MP) plates, the fuel cell being configured so as to, in operation, produce electrical energy.

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