Bipolar plate structure with two welding planes for fuel cell

Abstract

The invention relates to a bipolar plate (BP) suitable for a fuel cell (FC), formed by an assembly of two superposed and welded elementary plates (Pl1, Pl2), and comprising: first inlet and outlet openings (H2In, H2Out) for a first fluid; second inlet and outlet openings (O2In, (O2+H2O)Out) for a second fluid; third inlet and outlet openings (CoolIn, CoolOut) for a third fluid intended to circulate between the two elementary plates; first and second weld lines (WeldOp) respectively securing the two elementary plates around the first and second openings, and first and second welds (WldCool) securing the two elementary plates around, respectively, third openings, the first and second weld lines being formed in a first plane (HPlane) and a second plane (LPlane), respectively, and the welds associated with one of the third openings are formed, exclusively, in one or the other of these planes.

Description

Bipolar plate structure with two weld planes for 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 supplied 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] This illustrates this operating principle at the scale of an elementary electrochemical cell, using hydrogen (H2) as fuel, oxygen (O2) as an oxidant, and rejecting unused reactants such 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 directed to the anode An and is catalytically split at a layer of material Cat An catalytic anode, by an oxidation reaction, into protons H + and in electrons e - The protons pass through the PrEx proton exchange membrane, which has the function of selectively transporting protons H +up to the cathode Ca. The electrons are collected by the anode An which conducts them to an external electrical circuit which connects the anode An to the cathode Ca via an electrical charge Ld.

[0008] Simultaneously, a flow of oxygen (O2) is delivered to the cathode (Ca). At the level of a layer of Cat material Ca In cathode catalysis, oxygen molecules (O2) react with (i) protons (H) + having passed through the electrolyte El and (ii) the electrons e - which arrive via the external electrical circuit. The product of this reduction reaction is composed 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 OH ions -negative electrical charge passing through the membrane and combining with the hydrogen supplied as fuel on the anode side.

[0010] The oxidation and reduction reactions occurring within the cell generate an electrical voltage of approximately 0.7 V between the two electrodes, anode and cathode. To obtain a usable output voltage, it is necessary to connect individual cells like the one shown here in series. This is achieved by creating stacks of elementary electrochemical cells. 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] Lare represents a schematic diagram of the operation of a Stck stack of electrochemical cells, from the point of view of the management of fluids, reactants and reaction products.

[0013] Each of the electrochemical cells incorporates an Ass assembly which includes, in this order according to the X stacking direction, a Diff layer An anode diffusion, a CAT layer An of anode catalytic material, a proton exchange PrEx membrane, a CAT layer Ca of cathodic catalytic material, and a Diff layer Cacathode diffusion. The Ass assembly is also referred to as the Membrane Electrode Assembly or MEA in English terminology. 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 terminology.

[0014] Diffusion layers, often referred to by the acronym GDL (Gas Diffusion Layer), allow the passage of reactive fluids and reaction products, and are electrically conductive. Thus, the Diff layer An anode diffusion and the Diff layer Cacathode diffusion elements 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) in a stack are electrically connected in series.

[0016] The Stck stack is designed to deliver the reactive fluids, hydrogen (H2) and oxygen (O2), separately to the Diff layers An and Diff CaThe anode and cathode diffusion systems, respectively, remove excess reactants and the produced water (H2O). The stack is also designed to allow the circulation 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 include three fluid circuits isolated from each other and capable of fulfilling the functions of supplying reactants to the diffusion layers, removing excess reactants and reaction products, and circulating a cooling fluid. For these purposes, a Circ(H2) circuit supplies hydrogen (H2) to the Diff diffusion layer. An and recovers the excess hydrogen. A Circ(O2) circuit brings oxygen O2 to the Diff diffusion layer Caand recovers the 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 using bipolar BP plates, with structures illustrated in Figures 3 to 5.

[0019] These bipolar BP plates are generally made up of two basic metal plates, Pl1 and Pl2, stamped to form their structure and assembled together. They are held together by a weld line. Ext following their peripheral contours, and therefore 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 for fluid circulation. Figure 1 is a very schematic representation of a stack, with sets of elements separated by bipolar plates. At the ends of the stack are monopolar plates, only one face of which is actually used for reaction, 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 Figure 2.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 Wld. Ext on the.

[0021] This illustrates a generic configuration of a bipolar plate, viewed in the plate's extension plane, perpendicular to the X direction, with H2 openings In , Cool In and O2 In forming fluid inlets, H2, Cool and O2, respectively, and H2 openings Out , Cool Out and (O2+H2O) Outforming 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). The arrows schematically represent the flows of hydrogen (H2), coolant (Cool), and oxygen (O2), respectively, circulating within a cell, guided by the contours of the bipolar plate (BP).

[0022] Bipolar plates have 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. This active zone is designed to accommodate a component 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 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] The diagram shows that the fluids intersect, and the reliefs of the elementary plates Pl1 and Pl2 are configured to allow this crossing without mixing between the fluids and without the passage of one fluid blocking the passage of a second. To ensure the mechanical strength of a bipolar plate and the sealing of the fluid circuits it defines, Slnt gaskets and Wld weld lines are used, as illustrated in the diagram.

[0025] This illustrates that the assembly of bipolar plates (BP) and Ass assemblies creates channels for the flow 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 carried to these assemblies, within which electrochemical reactions take place, generating an electrical potential between two bipolar plates.

[0026] The elementary plates Pl1 and Pl2 have a symmetrical structure, and all welds are made in a single plane BP Plane parallel to the extension plane of the PrEx proton exchange membrane. The height of the BP plane Plane is defined by the points of contact of the two elementary plates in the active zone Act of the bipolar plate.

[0027] Reference can be made, for example, to patent documents EP2715846B1, EP3985766B1, WO2019025701A1, 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 this application is a bipolar plate with improved geometry and manufacturing process compared to known geometries and manufacturing processes.

[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 third openings forming an inlet and outlet for a third fluid.and third circulation channels of the third fluid between the inlet and outlet of the third fluid, between the two elementary plates, the first and second weld lines joining the two elementary plates form 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 the first welds joining the two elementary plates and surrounding a first of the third openings, and 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] One 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 hydraulic sections, in particular of 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 may follow a peripheral contour of the bipolar plate, and may be formed in either the first or second plane;

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

[0039] - the weld lines and welds can be distributed between the foreground and the background in such a way as to minimize a difference between a sum of lengths of weld lines and welds formed in the foreground and a sum of weld lines and welds formed in the background;

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

[0041] - one of the two elementary plates may have a flat region arranged 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 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] This illustrates the operating principle of an elementary fuel cell;

[0047] This illustrates the operating principle of a stack of elementary fuel cell cells;

[0048] This illustrates the principle of the structure of a fuel cell stack;

[0049] Laillustre a generic structure of a bipolar fuel cell plate;

[0050] Laillustre a cross-section of a conventional fuel cell stack;

[0051] It illustrates the structure of a particular bipolar plate;

[0052] Laillustre cross-sections of fluid circulation channels in bipolar plate stacks of various geometries;

[0053] Laillustrates a stack of bipolar plates according to the invention; and

[0054] Lare 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 1 represents a planar view of a particular bipolar plate BP in its extension plane, perpendicular to the X-direction of stacking to form a Stck stack. In this specific case, an opening is provided for each of the inlets and outlets of the three fluids, therefore six openings in total. The number of inlet and outlet openings can be adjusted to more precisely control the fluid flows and is not limited to this particular case.

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

[0058] Laillustre qu'un un joint Slnt Ex forms a closed loop along the outer periphery of the bipolar plate BP. In addition, each of the H2 openings In , Cool In , O2 In , H2Out , Cool Out and (O2+H2O) Out is surrounded by an opening joint Slnt Op respective. In a known manner, these joints are interposed between two bipolar plates when they are integrated into a Stck stack, as illustrated by the, possibly superimposed on ribs or grooves of the bipolar plates.

[0059] Laillustre also shows Wld weld lines Op joining the two elementary plates Pl1 and Pl2 to form a bipolar plate.

[0060] Wld welding lines Op each form a continuous loop around the respective openings H2 In , O2 In , H2 Out and (O2+H2O) Out , outside the Slnt joints Op respective. Their function is to hermetically seal these openings, which bring the reactants to the active zone Act or evacuate them from it, with respect to the coolant Cool.

[0061] A Wld welding line Ext , substantially parallel to the Slnt joint Ex t, 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] Wld welds Cool form loops respectively around the Cool openings In and Cool Out , near these openings, for example the inner sides of the Slnt joints Op surrounding these openings. The Wld welds Cool These welds could also be formed on the outer sides of these joints. Their function is to stiffen the bipolar plate near the Cool openings. In and Cool Out Thus, the Wld welds Cool do not have to form continuous lines in closed loops: simple weld points or weld lines forming dotted lines may suffice.

[0063] The WldCool welds may be partially located between the Cool openings In and Cool Out and the active area Act. Where applicable, these welds may more specifically be located between distribution channels, as discussed below and illustrated in (A2) of the.

[0064] The bipolar plate geometry illustrated in Figure 1, and repeated in Figure 2(A), requires precise lateral alignment between the two elementary plates Pl1 and Pl2 to form the Cool fluid circulation channels according to the planned configuration at the fluid inlets and outlets. In these regions, outside the active zone Act, the PrEx membranes are not covered by the catalytic material and diffusion layers, and form elements called "sub-gaskets" in contact with the bipolar plates, identified by SubGask in Figure 1.

[0065] Figure (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 flow of this coolant.

[0066] Figure (C) illustrates an alternative geometry, which has the advantage of eliminating the problem of misalignment between the elementary plates Pl1 and Pl2. The principle is to use asymmetrical elementary plates, with, for example, flat regions R of Pl2, free of grooves or ribs, these flat regions being suitable for receiving ribs or grooves of Pl1. Thus, fluid circulation channels with well-defined geometries can be obtained, insensitive to potential 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 Pl2 intended to be in contact with a rib or groove edge of Pl1. This improves the regularity of the hydraulic cross-section of the channels, resulting in less turbulence and a laminar flow that facilitates the movement of the transported fluid.

[0067] Ordinarily, the elementary plates Pl1 and Pl2 are symmetrical and the welds joining these plates are all made in the same plane BP Plane median of a bipolar plate. However, the geometry illustrated by (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 by the figure. 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 is to form the solder joints associated with each of the three circuits in their respective and distinct solder planes. Each of the three solder 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 perspective, 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 tool, specifically adapted for welds in a given plane, is mounted on a welding machine. With one machine per weld plane, tool 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 in industrial production conditions is inefficient. In the case of laser welding, for example, 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, while preferable to using a variable focal length laser welding machine, remains unsatisfactory.

[0071] In order to improve the efficiency of Wld weld line formation Op and Wld welds Cool to ensure the sealing of the Circ(H2), Circ(O2) and Circ(Cool) fluid circulation circuits formed by the H2 openings In , Cool In , O2 In , H2 Out , Cool Out and (O2+H2O) OutAs 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 a significant 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 BP plane Plane defined above, a low plane L Plane and a high-angle shot Plane located respectively below and above the BP plan Planein 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 reactant circuits Circ(O2) and Circ(H2) in one of the two planes L Pl ane and H Pl ane (ii) the welds relating to the other of the two reactant circuits Circ(O2) and Circ(H2) in the other of the two planes L Plane and H P lane , and (iii) among the welds associated with the third openings of the Circ(Cool) circuit, the welds associated with the same third opening are formed in the same plane, which can be either of the two planes L Plane and H P lane More specifically, the welds surrounding a coolant inlet opening are formed in one of two planes L Plane and H Planeand, independently of this formation plane, the welds surrounding a cooling fluid outlet opening are formed in one or the other of the two L planes Plane and H Plane .

[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] Laillustre Stck stacks comprising a pair of bipolar plates BP as illustrated by the, and for which (i) the welds relating to the Circ(O2) reagent circuit are formed in the lower plane L Plane (ii) the welds concerning the Circ(H2) reagent circuit are formed in the upper plane H Plane , and (iii) the welds relating to the Circ(Cool) circuit are formed in the lower plane L Plane .

[0075] Figure (A) illustrates in (A1) a plan view of the Cool opening Out taken from, and in (A2) a cross-sectional view of this version enlarged at the level of the dotted ellipse, cross-section perpendicular to the Ch channels opening into the Cool opening Out The same structure is found on the Cool opening side. In .

[0076] In this region, the Wld welds Coolare located between two fluidic circulation channels Ch which are designed to bring the cooling fluid Cool from the active area of ​​a bipolar plate to the Cool opening Out coolant evacuation after passing through the active zone Act. Symmetrically, the channels bringing the coolant from the Cool opening In the active area of ​​the bipolar plate are associated in the same way with other weld lines, as illustrated by the.

[0077] The section illustrated in (A2) corresponds to a cutting plane parallel to the Slnt joint Op including Wld welds Cool (The scales are not respected), intended to mechanically join the elementary plates Pl1 and Pl2 forming a bipolar plate BP. The welds can also be located outside this particular cutting plane, for example on the outer side of the Slnt joint OpIn the illustrated cross-section, two identical bipolar BP plates stacked one on top of the other are shown. The peripheral zone of the Ass assembly is interposed between the two bipolar BP plates; this peripheral zone Ass forms the sub-gasket, which does not include catalytic material or a diffusion layer. In this representation, the bottom plane L Plane is located below the BP reference plane Plane We can also say that the low plane L Plane is located between the BP plan Plane and the PrEx plan Plan e of the extension of the PrEx proton exchange membrane which is located under the considered bipolar BP layer which limits the electrolytic cell of which this membrane is a part.

[0078] The figure shows the Wld welds CoolThese welds, which concern the Circ(Cool) circuit, maintain the physical integrity of the Ch channels through which the Cool coolant circulates in an area subjected to pressure forces. In this example, these welds are located in the lower plane L. Plane In this example, the Wld welds Cool are simple weld points, but these points could more generally form continuous weld lines or lines formed of interrupted lines.

[0079] Welds located in the immediate vicinity of an opening, Cool In or Cool Out These are considered associated with this opening: their function is to mechanically reinforce the assembly at the opening near which they are located. We can also consider the welds located between the active zone (Act) and one of the openings (Cool) as being associated with this opening. In and Cool Out are associated with this opening.

[0080] Wld welds Cool associated with the same Cool opening In or Cool Out must be formed in the same plane, H Plane or L Plane Welds associated with two different openings can be formed in the same plane or in two different planes. For example, welds associated with the Cool opening In can be formed in the plane H Plane and the welds associated with the Cool opening Out can be formed in the L plane Plane , or vice versa. Alternatively, all welds can be formed in the same plane, H Plane or L Plane Figure (A) illustrates in (A2) Wld welds Cool associated with the Cool opening Out and formed in the L plane Plane .

[0081] Figure (B) illustrates a cross-sectional view along axis BB' defined on the diagram, which passes through the openings O2 In , (O2+H2O) Outand the active zone Act located between these two openings. The Weld welds are particularly visible there. Op located on either side of each of the two openings, at the height of the lower plane L Plane located below the BP plan Plane .

[0082] Figure (C) illustrates a cross-sectional view along the axis CC' defined on the diagram, which passes through the openings H2 In , H2 Out and the active zone Act located between these two openings. The Weld welds are particularly visible there. Op located on either side of each of the two openings, at the height of the upper plane H Plane located above the BP plan Plane .

[0083] We can say that the low plane L Plane and the high plane H Plane are located on either side of the BP plan Planedefined by the contact points between the Pl1 and Pl2 plates 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 the, 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 up to and within the Ass assemblies.

[0085] Furthermore, this geometry allows for planar regions within 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 (C). This characteristic reduces pressure losses in the Circ(Cool) circuit, and therefore the pressure required for cooling fluid circulation and the risk of leaks. In addition, immunity to seal compression is also achieved in case of misalignment of Slnt. Op During the assembly of the bipolar plate: a slight misalignment is tolerable.

[0086] In the specific case of the bipolar plate illustrated in the figure, 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] When assembling two elementary plates PL1 and PL2 to form a bipolar plate BP, two welding machines can operate in parallel to form the different weld lines and welds mentioned above (Wld Op , Wld Ext , Wld Cool ) in both planes L Plane and H Plane Each welding machine is dedicated to one of the two planes. From the perspective of minimizing welding time, it is advantageous to distribute the weld lines and welds between the two H planes. Plane and L Planein order to minimize the difference in welding time required for each of these plans.

[0088] In this way, the time required to form the weld lines of a bipolar plate is reduced. Thus, the welds (the Wld lines) are less efficient. Op and Wld Ext and the Wld welds Cool ) can be distributed between the first plane H Plane and the second plan L Plane in order to minimize the difference in welding time required between the first and second layers. This distribution can be characterized by the fact that the weld lines Wld Op and Wld Ext and the Wld welds Cool can be distributed between the first plane H Plane and the second plan L Plane in order to minimize a difference between a sum of the lengths of the Wld weld lines Op and Wld Ext and Wld welds Coolformed in the foreground and a sum of the lengths of the Wld weld lines Op and Wld Ext and Wld welds Cool 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 from a stack of several hundred bipolar plates, each interposed between two sets of cells, often referred to by the acronym MEA in English terminology.

[0091] Figure 1 illustrates in a simplified manner such a fuel cell as seen from the outside, with monopolar plates MP enclosing a stack of material (Stck) like the one shown in Figure 2. Rods R, associated with compression bolts CB, allow pressure to be applied to the stack of material via the monopolar plates MP, thus compressing the stack joints and ensuring the fluid circulation circuits are sealed. External components (not shown) manage the fluids (reactants, coolant) and connect the fuel cell electrically to an external load. This load could be a vehicle or any other electrically powered device.

[0092] The fuel cell can be configured to be powered by hydrogen as fuel, air including oxygen as an oxidant, and water as a coolant.

[0093] In this document, the figures are not necessarily to scale. Some features and components may be shown exaggerated relative to other components or in a somewhat schematic form, and some details of conventional elements may not be shown for the sake of clarity and conciseness.

[0094] Of course the invention is not limited to the implementation methods described and alternative embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

Bipolar plate (BP) capable of forming a stack of elementary electrochemical cells in a fuel cell, the bipolar plate being formed from an assembly of two superimposed elementary plates (Pl1, Pl2) welded together, the bipolar plate comprising: - first openings (H2 In , H2 Out ) 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 one side of the bipolar plate; - the second openings (O2 In , (O2+H2O) Out forming an inlet and outlet of 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 (Cool In , Cool Outforming 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 (Pl1, Pl2), - of the first and second weld lines (Weld Op ) joining the two elementary plates form respective loops around the first openings (H2 In , H2 Out ) and second openings (O2 In , (O2+H2O) Out ), the first and second welding lines (Weld Op ) being configured to isolate the first and second fluids from the third fluid, respectively, and- from the first welds (Wld Cool ) joining the two elementary plates and surrounding one of the third openings (Cool In ), and second welds (Wld Cool ) joining the two elementary plates and surrounding a second of the third openings (CoolOut ), in which the first weld lines are formed in a foreground (H Plane ), the second weld lines are formed in a second plane (L Plane ), distinct from the foreground, the first welds are formed exclusively in one or the other of the foreground (H Plane ) and the second plane (L Plane ), and the second welds are formed exclusively in one or the other of the first plane (H Plane ) and the second plane (L Plane ). The bipolar plate according to claim 1, in which the first plane (H Plane ) and the second plane (L Plane ) are located on either side of a plane (BP Plane ) defined by points of contact between the two elementary plates (Pl1, Pl2) in an active zone (Act) of the bipolar plate.

3. The bipolar plate according to claim 2, in which the active zone (Act) is interposed between the first openings (H2 In, H2 Out ), between the second openings (O2 In , (O2+H2O) Out ), and between the third openings (Cool In , Cool Out ), and in which the first welds are partially formed between the active zone (Act) and the first (Cool) In ) of the third openings, and the second welds are partly formed between the active zone and the second (Cool Out ) of the third openings.

4. The bipolar plate according to any one of claims 1 to 3, comprising a peripheral weld (Wedl Ext ) between the two elementary plates, in which the peripheral weld follows a peripheral contour of the bipolar plate, and is formed in one or the other of the first plane (H Plane ) and the second plane (L Plane ).

5. The bipolar plate according to claim 4, in which the weld lines and welds are distributed between the first plane (H Plane) and the second plane (L Plane ) in order to minimize the difference in welding time required between the first and second planes.

6. The bipolar plate according to claim 5, in which the weld lines and welds are distributed between the first plane (H Plane ) and the second plane (L 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.

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

8. The bipolar plate according to any one of claims 1 to 7, in which one (Pl1) of the two elementary plates (Pl1, Pl2) has a planar region (R) arranged so as to receive ribs or grooves of the other (Pl2) of the two elementary plates (Pl1, Pl2).

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

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

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