Three-dimensional plate for fuel cell, corresponding cell, use and production method

Abstract

The invention relates to a bipolar or monopolar plate for a proton-exchange membrane fuel cell, each having first channels for the circulation of reactive gases, dihydrogen and air respectively, and second channels for the circulation of a heat-transfer fluid. The first and second channels extend in orthogonal directions (D1, D2) along the length and the width, respectively, of the plate and follow a path defining undulations in an undulation plane substantially perpendicular to the main plane of the plate, and the channels have a cross-section varying between a maximum cross-section (Smax) and a minimum cross-section (Smin), the minimum cross-section (Smin) corresponding to the locations in which one of the first channels crosses one of the second channels.

Description

[0001] DESCRIPTION

[0002] TITLE: Three-dimensional plate for fuel cell, corresponding cell, use and manufacturing method.

[0003] 1. Field of the invention

[0004] The field of the invention is that of hydrogen fuel cells. More specifically, the invention relates to the improvement of such fuel cells, and in particular of the bipolar and monopolar plates of which they are made.

[0005] Such plates, and therefore such batteries, find applications in many fields, whenever it is necessary to produce electrical energy, particularly autonomously, for example in vehicles (cars, utility vehicles, trucks, buses, trains, boats, aircraft, etc.), generator sets, etc.

[0006] 2. Prior art

[0007] The principle of the fuel cell has been known for many years. It has been implemented in the space sector, and numerous projects have also been developed by various car manufacturers.

[0008] A hydrogen fuel cell is based on the principle illustrated in Figure 1, and produces electrical energy by a chemical reaction between hydrogen (H2) and oxygen (O2). This chemical reaction is described by the equations below:

[0009] [Chem 1] H2-> 2H + + 2nd

[0010] O2+ 4 H + + 2nd -> 2H2O

[0011] H2+ I / 2O2 -> H2O r H < 0

[0012] The optional term A r H < 0 only indicates that the reaction is exothermic.

[0013] This reaction occurs in what is called an active zone of an assembly of an electrolyte membrane and electrodes (MEA), i.e. a stack of membranes allowing the exchange of H ions. + , placed between an anode, receiving dihydrogen from a tank, and a cathode receiving dioxygen (O2) from the outside air. As illustrated in Figure 1, the fuel, dihydrogen (F ), is introduced (Fl) into the cell, to come into contact with the anode A. A part of the dihydrogen enters (F2) into the anode A, in which the dihydrogen molecules are separated into electrons e" and ions H + which pass through the electrolyte E towards the cathode C. The latter is in contact with the air brought from outside (F3) whose oxygen O2 molecules (F4) combine with the H ions +and the electrons e" to produce (F5) water (H2O). This water (F6) and the unused air (F7) are evacuated.

[0014] Anode A is therefore the element in which oxidation occurs: H2 ->2H + + 2nd _ , and the cathode C is the element in which the reduction occurs: O2 + 4H + + 4th _ -> 2H2O. The electrons e" circulate (F8) between the anode A and the cathode C, producing an electric current E, which is used to drive an electric motor and / or charge a battery.

[0015] This reaction is exothermic, and the various components of the battery can heat up quickly. The entire system must therefore be cooled. The design of the mechanical parts must therefore be adapted to be supplied with coolant, or heat transfer fluid.

[0016] The structure of a fuel cell, implementing this chemical reaction, is illustrated in Figure 2. The cell 21 consists of a stack of cells 22, placed between two end plates 23i and 232.

[0017] The constituent elements of a 22 cell are detailed, exploded, in Figure 3. It comprises two plates, bipolar or monopolar, between which is placed an electrolyte membrane. The monopolar plates are the first and last plates in the cell stack. They generally have the same design as a bipolar plate, but inlets are closed so that the plate does not receive one of the gases. The cell thus comprises a monopolar cathode plate not receiving dihydrogen and a monopolar anodic plate not receiving dioxygen.

[0018] The bipolar plates, stacked between the two monopolar plates, are formed by the assembly of two metal half-plates 31, 32 (one anode half-plate 31 and one cathode half-plate 32), which can be welded, brazed or glued. A space between the two metal half-plates is defined by the forming of these to define on the one hand zones 33, 34 receiving a cooling liquid and on the other hand channels allowing the circulation of gases, respectively dihydrogen and dioxygen (extracted from the air). MEA membranes 35 are interposed between the half-plates.

[0019] One of the difficulties in the design of fuel cells, and of these plates in particular, is the optimization and homogenization of the path of this coolant, which is generally imposed by what has been designed for the circulation of gases from the anode and cathode parts.

[0020] Different types of channels are known for the circulation of gases, including straight channels, parallel to each other, serpentine or zigzag, extending over an active part of the plate.

[0021] The efficiency of these plates is not perfect. Despite the designers' efforts, there are significant variations in gas pressure, particularly oxygen, in the active surface, and an uneven distribution of the heat transfer fluid, particularly partial in the middle of the plate. This introduces thermal inhomogeneity, notably the presence of hot spots.

[0022] As a result, this introduces an inhomogeneity in the creation of the electric current in the plate.

[0023] Such plates are also difficult to manufacture and assemble. In particular, they have poor rigidity along their length, which leads to the use of relatively thick, and therefore heavy, strips and requires the use of manufacturing techniques that are not well-suited to mass production, such as brazing or multiple welds.

[0024] There is therefore a need for a new approach to the production of such plates, to enable production more suited to series requirements and / or to improve their efficiency.

[0025] 3. Main characteristics of the invention

[0026] The invention meets at least part of this need using a new type of bipolar or monopolar plate for a proton exchange membrane fuel cell, each having first channels for circulating reactive gases, respectively dihydrogen and air, and second channels for circulating a heat transfer fluid.

[0027] According to the invention, said first and said second channels extend in orthogonal directions (DI, D2), respectively along the length and width of said plate and follow a path defining undulations in a corrugation plane substantially perpendicular to the main plane of said plate, and said channels have a variable section between a maximum section (S ma x) and a minimal section (S m in), said minimum section (S m in) corresponding to the locations where one of said first channels crosses one of said second channels.

[0028] In other words, the plate, and in particular its active surface, that is to say the surface ensuring the exchange of protons, located opposite the membrane, is defined in three dimensions, and not according to a plane. It has undulations, or "hollows" and "bumps", determined in such a way as to optimize the pressure of said gases and / or the flow rate of said heat transfer fluid.

[0029] Furthermore, said first channels extend in a direction orthogonal to the direction of said second channels, and parallel to the length and width of the plate respectively, crossing each other and following the corrugations.

[0030] Finally, the channels have a variable section, in order to optimize the pressure of said gases and / or the current density delivered by said plate.

[0031] This combination of channel crossing and variable sections improves the performance of the plates, while optimizing their rigidity and limiting their thickness.

[0032] According to a particular embodiment, said lines defining undulations and / or said variable sections are defined by the finite element method, according to at least one criterion belonging to the following group: optimization of the fluid distribution in said channels; optimization of the rigidity of each plate; limitation of the thickness of a battery cell, formed by a first plate, a membrane and a second plate.

[0033] This approach makes it possible to efficiently characterize the dimensions and shapes of the plates.

[0034] In particular, it is thus possible to industrially produce a battery cell, formed by a first plate, a membrane and a second bipolar plate, less than 1 mm. According to a particular embodiment, the plate is produced by assembling two complementary half-plates, formed in three dimensions, so as to define said undulations.

[0035] Half-plates can be obtained by hydroforming.

[0036] According to a particular embodiment, said undulations have a radius (R) and a period (P) such that R = P ± 20%.

[0037] According to a particular embodiment, said section varies so that the ratio between the maximum section S ma x and the minimum section S m in is between 1.2 and 2, of the order of 1.6 for example.

[0038] According to a particular embodiment, said half-plates are made from thinner strips than those conventionally used, for example 316L stainless steel with a double carbon coating, with a thickness of 0.075 mm.

[0039] The invention also relates to fuel cells comprising a stack of plates as described above.

[0040] The invention also relates to the uses of such batteries, in particular for at least one of the applications belonging to the group comprising: motor vehicles; utility vehicles; buses or trucks; boats; aircraft; railway vehicles; generator sets;

[0041] The invention also relates to a method for manufacturing a bipolar or monopolar plate as described above, comprising in particular the following steps: manufacturing two complementary half-plates in which said first and said second channels extend in orthogonal directions (DI, D2), respectively along the length and width of said plate and follow a path defining undulations in a corrugation plane substantially perpendicular to the main plane of said plate, and said channels have a variable section between a maximum section (S ma x) and a minimal section (S m in), said minimum section (S min) corresponding to the locations where one of said first channels crosses one of said second channels; assembly of said complementary half-plates, so that said first and / or said second channels follow a path defining undulations in a corrugation plane substantially perpendicular to the main plane of said plate.

[0042] The production of half-plates can be carried out in particular by hydroforming.

[0043] 4. list of figures

[0044] Other characteristics and advantages of the invention will appear more clearly on reading the following description of an example of implementation, given as a simple illustrative and non-limiting example, and the appended figures among which:

[0045] [Fig 1]: Figure 1, already described in the preamble, illustrates the general principle of a fuel cell;

[0046] [Fig 2]: Figure 2, already described in the preamble, shows the structure of a fuel cell, comprising a stack of cells;

[0047] [Fig 3]: Figure 3, already described in the preamble, presents the constituent elements of a cell of Figure 2, exploded;

[0048] [Fig 4]: Figure 4 schematically illustrates the main elements of a bipolar plate of the cell of Figure 3;

[0049] [Fig 5A], [Fig 5B]: Figures 5A and 5B illustrate respectively the path of the gas flow (dihydrogen or air) and the path of the heat transfer fluid, following undulations (only a portion of the half-plate is shown);

[0050] [Fig 6]: Figure 6 is another view of a portion of the half-plate, showing the undulations in the two orthogonal directions defined by the channels;

[0051] [Fig 7]: Figure 7 schematically illustrates an example of undulation;

[0052] [Fig 8]: Figure 8 illustrates the variation of the section of a gas channel.

[0053] 5. Description of a particular embodiment

[0054] 5.1 Main elements of a bipolar plate

[0055] The invention applies to the manufacture of plates, bipolar or monopolar, intended to form a fuel cell. For information purposes, the main aspects of a bipolar plate are described below. As illustrated schematically in the example of Figure 4, there are several essential zones in a bipolar plate: active zone AZ: this is the location where the reaction takes place, consisting of numerous channels. One of the difficulties in designing these plates is the need to provide a homogeneous distribution of the gas and not to overfeed or underfeed the channels. The surface area of ​​the active zone of the plate is the same as that of the active zone of the MEA;

[0056] Homogenization zone HZ: location in which the flows mix to supply the channels of the active zone with the same quantity of gas / coolant. It is similar to a funnel, going from a flow inlet towards the start of the active zone;

[0057] ABP anti-bypass zone: an anti-bypass zone is necessary for mechanical reasons such as good retention of the AME and / or good compression of the seal. It is then necessary to avoid a bypass effect for the gases, which could induce drops in gas pressure, and therefore the efficiency of the entire system;

[0058] M-manifolds: Manifolds are sizing elements, including inlets and outlets for each gas and the refrigerant. Generally, their position and dimensions define the overall dimensions of the plate;

[0059] Inlets I: The inlets are what allow the gas and refrigerant to go from the headers to the gas or refrigerant side of the plate;

[0060] G-guide interfaces: elements helping to hold the stack in position during the stacking process;

[0061] V measuring electrodes: allowing a pin or special device to be connected between the anode and the cathode to take measurements;

[0062] Data matrix: allowing precise identification of the plate. It can include a serial number, a supplier identification number, a time, a manufacturing date, etc. Its dimensions are generally 4x4 or 5x5 mm; Poka-Yoke: mechanical element which constrains the positioning of the half-plates;

[0063] Welds: holding the half-plates together, they can be waterproof or simply intended to reinforce the structure.

[0064] 5.2 three-dimensional (3D) topology

[0065] The invention therefore proposes a new approach to bipolar or monopolar plates, according to which the active zone of the latter, that is to say substantially the zone opposite the membrane, allows the flows of gas and heat transfer fluid to move in the three dimensions of space.

[0066] More specifically, as illustrated by Figures 5A and 5B, respectively representing the path of the gas flow (dihydrogen or air) and the path of the heat transfer fluid, the channels 51 intended for the gas and the channels 52 intended for the heat transfer fluid extend in orthogonal directions DI, D2, respectively according to the length and width of the plate, and intersect. In addition, these channels have undulations in both directions, the surface of the active part therefore not being flat, but having "hollows" and "bumps", as can be seen in particular in Figure 6.

[0067] This approach presents, compared to the prior art according to which the channels extend in a plane, the plane defined by the plate, can present numerous advantages, depending on the implementations: improvement of thermal convection, making it possible to reduce the flow rate and / or improve the efficiency of the system; better rigidity of the plate and / or weight saving, making it possible to reduce the thickness of the strip; improvement of electrical contact and reduction of electrical contact resistance; facilitation of the assembly of the battery, and in particular of the alignment of the cells with each other, making it possible in particular to avoid sealing problems; homogenization of the partial pressure of oxygen along the active surface; homogenization of the creation of current and improvement of the current density.Figure 7 schematically illustrates an example of a ripple, characterized by its length, or period, P and its radius R, or maximum height of the ripple. Of course, the shape of the ripple may be different from that illustrated.

[0068] The inventors determined, taking into account in particular the tangency constraints of the fluid channels, a difference between the radius R and the half-period %P less than or equal to 20% was effective, so as not to make the couple (radius; half-period) too strong and to obtain a balance between undulations that are too pronounced and undulations that are too tenuous. We thus choose values ​​of %P and R that are identical or close, for example: R = P ± 20%.

[0069] As an indication, the dimensions can be of the order of:

[0070] %P: between 8 and 12 mm;

[0071] A: Between 16 and 24 mm.

[0072] As illustrated in Figure 7, we can, for example, implement a radius R of 20 mm and a half-period of 10 mm.

[0073] The relative proportions of these geometric constraints allow a significant reduction in the thickness of the assembly of two strips, independently of the material thickness of the strip. The proportional links between the channel sections, their respective directions and the arrangement of the "bumps" allow, while ensuring very good fluid distribution, to obtain a plate rigidity allowing industrialization and a classic assembly, a very low thickness of battery cell (bipolar plate - membrane assembly - bipolar plate), which can be less than one mm.

[0074] It is important to note that the determination of these dimensions is not based on simple choices among a few possibilities, but is based on the results of long and non-obvious research, to meet several requirements of efficiency and industrialization, much superior to the plates previously known.

[0075] More generally, the dimensions of the half-plate can be of the order of: length: between 250 and 350 mm; width: between 150 and 200 mm.

[0076] The number of gas channels is for example between 50 and 100. The number of heat transfer fluid channels can also be between 50 and 100. 5.3 variable section channels

[0077] According to another aspect of the invention, which can, if necessary, be implemented independently of the 3D topology described above, the cross-section of the channels is varied. Indeed, the inventors have found that the active zones according to the prior art, which have channels for conveying fluids of constant cross-section, introduce heating and generate inhomogeneous partial pressures. In addition, this is detrimental to the rigidity of the plate.

[0078] To overcome these problems, gas channels are provided in particular whose section varies periodically, as illustrated by figure 8, in which it can be seen that, along the path 81 of the fluid, the section of the channel varies between a maximum section S ma x 82 and a minimum section S m in 83.

[0079] This makes it possible in particular to improve the rigidity of the plate, to obtain better thermal convection, to balance partial pressures and / or to obtain better electrical contact.

[0080] According to one embodiment, the maximum section S ma x corresponds to a location where the maximum height H of the gas channel and the minimum section S m in at a location where the gas channel crosses a heat transfer fluid channel (crossing, or "cross-channel" in English), the height being reduced to the minimum height h.

[0081] The minimum section corresponds to a location where a first channel crosses a second orthogonal channel.

[0082] The ratio between H and h is preferably between 2 and 3, and for example such that H = 2.5 * h.

[0083] For simplification, we consider that the width L of the channel, which varies little, is constant. Thus, the section S max is approximately L * H, and the section S m in approximately (H - h) * L.

[0084] We therefore preferably choose a section variation ratio S ma x / S m in between 1.5 and 2, for example of the order of 1.6.

[0085] It should be noted that this figure 8 illustrates a portion of a half-plate, and therefore a half-section of the channels which are obtained by assembling two half-plates, to form a complete plate. The ratios, however, obviously remain the same.

[0086] As an indicative example, the dimensions may be of the order of: H: between 0.2 and 0.35 mm; h: between 0.1 and 0.15 mm;

[0087] L: between 0.5 and 1.3 mm.

[0088] The lines defining the undulations and / or the variable sections can in particular be defined by the finite element method, so as to maximize one or more criteria, and in particular: optimization of the fluid distribution in said channels; optimization of the rigidity of each plate; limitation of the thickness of a battery cell, formed by a first plate, a membrane and a second plate.

[0089] These traces can define a channel pattern repeated several times.

[0090] 5.4 manufacturing and assembly

[0091] The inventive approach makes it possible to manufacture half-plates from thinner strips than those conventionally used, for example 316L stainless steel with a double carbon coating, with a thickness of 0.075 mm. Indeed, three-dimensional forming makes it possible to increase rigidity (a conventional flat plate can tend to deform), and therefore to limit possible alignment defects. This makes it possible to produce batteries requiring less material, and therefore less heavy and less expensive.

[0092] Of course, the three-dimensional shape, the half-plates with corrugations in two orthogonal directions (corresponding to the directions of the channels) and / or the presence of channels with variable sections require special care during the production of the half-plates, for example by stamping or molding. A preferred manufacturing method is hydroforming, which has many advantages, such as precision in the repeatability of the process, elasticity after forming, homogeneity of the wall thickness, efficiency of the contact zones, adaptability...

[0093] On the other hand, this shape and / or the reduced thickness of the strips can allow a simpler and more reliable assembly of the two half-plates forming each plate, in particular for the joining of the half-plates, for example by welding, and for the assembly of the plates to form a stack. The stacking of 300 plates, for example, to form a stack, is therefore simplified and more efficient, which in particular reduces the risk of loss of sealing.

[0094] According to the prior art, it is necessary to carry out homogenization of the surface of the plate. On the other hand, this is not necessary according to the approach of the invention, which makes it possible to obtain a homogeneous current, as much as possible, and therefore to avoid the presence of hot spots, introducing risks of deterioration and contamination, without additional treatment.

[0095] The invention thus makes it possible to obtain highly efficient plates and batteries, suitable for numerous applications, for example in motor vehicles, and more generally in any type of vehicle or means carrying fuel cells.

[0096] The invention can also be used with membranes of different formats depending on the stacks, so as to define several active zone dimensions, and therefore stacks of different power from identical plates. This is made possible in particular by the homogeneity obtained thanks to the approach of the invention.

Claims

DEMANDS 1. Bipolar or monopolar plate for a proton exchange membrane fuel cell, each having first reactive gas circulation channels, respectively dihydrogen and air, and second heat transfer fluid circulation channels, characterized in that said first and second channels extend along orthogonal directions (DI, D2), respectively along the length and width of said plate, and follow a pattern defining undulations in a corrugation plane substantially perpendicular to the principal plane of said plate, and in that said channels have a variable cross-section between a maximum cross-section (Smax) and a minimum cross-section (S m in), said minimum section (S m in) corresponding to the locations where one of said first channels crosses one of said second channels.

2. Plate according to claim 1, characterized in that said tracings defining undulations and / or said variable sections are defined by the finite element method, according to at least one criterion belonging to the following group: optimization of the fluidic distribution in said channels; optimization of the rigidity of each plate; limitation of the thickness of a pile cell, formed by a first plate, a membrane and a second plate.

3. Plate according to any one of claims 1 and 2, characterized in that it is made by assembling two complementary half-plates, formed in three dimensions, so as to define said undulations.

4. Plate according to any one of claims 1 to 3, characterized in that said undulations have a radius (R) and a period (P) such that R = P ± 20%.

5. Plate according to any one of claims 3 to 6, characterized in that said section varies such that the ratio between the maximum section (S ma x) and the minimum section (S m in) or of the order of 1.

6.

6. Plate according to any one of claims 1 to 5, characterized in that it enables the realization of a battery cell, formed by a first plate, a membrane and a second plate, of thickness less than 1 mm.

7. Fuel cell comprising a stack of plates according to any one of claims 1 to 6.

8. Use of a fuel cell according to claim 7 for at least one of the applications belonging to the group comprising: motor vehicles; commercial vehicles; buses or trucks; boats; aircraft; railway vehicles; generator sets.

9. A method for manufacturing a bipolar or monopolar plate for a proton exchange membrane fuel cell, each having first reactive gas circulation channels, respectively dihydrogen and air, and second heat transfer fluid circulation channels, characterized in that it comprises the following steps: manufacturing two complementary half-plates in which said first and second channels extend along orthogonal directions (DI, D2), respectively along the length and width of said plate, and follow a pattern defining undulations in a corrugation plane substantially perpendicular to the principal plane of said plate, and said channels have a variable cross-section between a maximum cross-section (S ma x) and a minimal section (S m in), said minimum section (S m(in) corresponding to the locations where one of said first channels crosses one of said second channels; assembly of said complementary half-plates, so that said first and / or said second channels follow a path defining undulations in a corrugation plane substantially perpendicular to the principal plane of said plate.

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