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

Abstract

The invention relates to a bipolar or unipolar plate for a proton exchange membrane fuel cell, each plate having a first channel for the circulation of reaction gases, respectively hydrogen and air, and a second channel for the circulation of a heat transfer fluid. The first and second channels respectively extend in orthogonal directions (D1, D2) along the length and width of the plate and follow a path defining an undulation on an undulation plane substantially perpendicular to the main plane of the plate, and the channels have a variable cross-section between a maximum cross-section (Smax) and a minimum cross-section (Smin), a minimum cross-section (Smin) corresponds to a position where one of the first channels intersects one of the second channels.

Description

1. Technical Field

[0001] The field of the invention is that of hydrogen fuel cells. More precisely, the invention relates to improvements in such fuel cells and in particular to improvements in the bipolar plates and monopolar plates used to form fuel cells.

[0002] Such panels and such batteries have uses in many areas wherever electrical energy needs to be generated, in particular independently, for example in vehicles (motor vehicles, utility vehicles, trucks, buses, trains, ships, aircraft, etc.), engine generators, etc. 2. Background technology

[0003] The principle of fuel cells has been known for many years. They are used in particular in the aerospace sector and are also being developed in many projects by various vehicle manufacturers.

[0004] Hydrogen fuel cells are based on Figure 1 The principle shown in Figure 1 is to generate electrical energy through a chemical reaction between hydrogen (H2) and oxygen (O2). The chemical reaction is described by the following formula:

[0005] [Chemical formula 1] H2-->2H + +2e -

[0006]

[0007] Optional term Δ r H < 0 simply means that the reaction is exothermic.

[0008] The reaction takes place in the so-called active zone of the electrolyte membrane and electrodes (MEA, i.e. “Membrane Electrode Assembly”), that is, a stack of H + An ion exchange membrane is located between an anode that receives hydrogen from a tank and a cathode that receives oxygen (O2) from the outside air.

[0009] like Figure 1 As shown, fuel hydrogen (H2) is introduced (F1) into the cell and contacts the anode A. A portion of the hydrogen permeates (F2) into the anode A, where the hydrogen molecules are separated into - The electrons and H pass through the electrolyte E toward the cathode C + The cathode contacts the air brought in from the outside (F3), and the O2 oxygen molecules (F4) in the air react with H + Ions and e - The electrons combine to produce (F5) water (H2O). This water (F6) and unused air (F7) are exhausted.

[0010] Therefore, the anode A is the element that undergoes oxidation: H2 → 2H + +2e -, and the cathode C is the element that undergoes reduction: O2+4H + +4e - →2H2O.e - The electrons circulate between the anode A and the cathode C (F8), generating an electric current E which is used to drive a motor and / or charge a battery pack.

[0011] The reaction is exothermic and the various elements forming the battery can heat up quickly. The entire system must therefore be cooled. Therefore, the mechanical parts must be designed to be supplied with a coolant or heat transfer fluid.

[0012] Figure 2 The structure of a fuel cell that realizes this chemical reaction is shown. The cell 21 is composed of a stack 22 of unit cells placed between two end plates 231 and 232.

[0013] Figure 3 The elements forming the unit cell 22 are described in detail in an exploded view. It comprises two types of plates, bipolar or monopolar, between which an electrolyte membrane is placed. The monopolar plates are the first and last plates of the unit cell stack. They generally have the same design as the bipolar plates, but the input ends are closed so that the plates do not receive one of the gases. Thus, the unit cell comprises a cathode monopolar plate that does not receive hydrogen and an anode monopolar plate that does not receive oxygen.

[0014] The bipolar plate superimposed between two monopolar plates consists of an assembly of two metal half-plates 31, 32 (anode half-plate 31 and cathode half-plate 32) which can be welded, brazed or glued. The space between the two metal half-plates is defined by the formation of the two metal half-plates, on the one hand defining the zones 33, 34 receiving the coolant and on the other hand defining channels allowing the circulation of gases, respectively hydrogen and oxygen (extracted from the air). The membrane MEA 35 is inserted between the half-plates.

[0015] One of the difficulties in the design of fuel cells and in particular of the plates is the optimization and homogenization of the coolant trajectory, which is usually imposed by the trajectory designed for the circulation of the gases of the anode and cathode parts.

[0016] Different types of channels for the circulation of gases are known, in particular straight channels, channels parallel to one another, serpentine or zigzag channels, channels extending over the active part of the plate.

[0017] The efficiency of these plates is not perfect. Despite the efforts of the designers, significant variations in gas pressure, especially oxygen pressure, at the active surface were observed, as well as inhomogeneous distribution of the heat transfer fluid, especially in the middle of the plate. This can cause thermal inhomogeneities, especially hot spots.

[0018] This, therefore, leads to non-uniformity in the current generation in the plate.

[0019] Furthermore, such plates are also not easy to manufacture and assemble. They have particularly poor rigidity over their length, which results in the use of relatively thick and therefore heavy metal strips, and they require the use of manufacturing techniques such as brazing or multiple welding that are not well suited to mass production.

[0020] Therefore, there is a need for a novel method of manufacturing such panels in order to make the production more adaptable to the requirements of the series and / or to increase its efficiency. 3. Summary of the invention

[0021] The present invention at least partially meets this need by a novel bipolar plate or monopolar plate for a fuel cell with a proton exchange membrane, each plate having a first channel for circulation of a reactant gas, hydrogen and air respectively, and a second channel for circulation of a heat transfer fluid.

[0022] According to the invention, the first channel and the second channel extend respectively according to orthogonal directions D1 and D2 along the length and width of the plate and follow a path defining an undulation in an undulation plane substantially perpendicular to the main plane of the plate, and the channels have a maximum cross section (S max ) and minimum cross section (S min ) between the variable cross-sections, the minimum cross-section (S min ) corresponds to the position where a first channel among the first channels intersects with a second channel among the second channels.

[0023] In other words, the plate, and in particular its active surface, that is to say the surface ensuring proton exchange, positioned facing the membrane, is defined in three dimensions and not according to a plane. It has defined reliefs or "cavities" and "ridges" to optimize the pressure of the gas and / or the flow rate of the heat transfer fluid.

[0024] Furthermore, the channels extend in a direction orthogonal to the direction of the second channel and parallel to the length and width of the respective plates by crossing each other and following the undulations.

[0025] Finally, the channels have a variable cross section in order in particular to optimize the pressure of the gas and / or the current density delivered through the plate.

[0026] This combination of channel crossing and variable cross-section makes it possible to increase the efficiency of the plate while optimizing its rigidity and limiting its thickness.

[0027] According to a particular embodiment, said path defining the relief and / or said variable cross section is defined by a finite element method according to at least one criterion belonging to the following group:

[0028] - Optimizing the fluid distribution in the channel;

[0029] -Optimize the rigidity of each plate;

[0030] - limiting the thickness of the unit cell of the fuel cell formed by the first plate, the membrane and the second plate.

[0031] This approach allows for efficient characterization of plate size and shape.

[0032] In particular, a fuel cell can thus be produced industrially which is formed from a first plate, a membrane and a second bipolar plate and which is smaller than 1 mm.

[0033] According to a particular embodiment, the panel is formed by the assembly of two complementary half-panels formed in three dimensions so as to define said relief.

[0034] In particular, the half-plates can be obtained by hydroforming.

[0035] According to a specific embodiment, the undulations have a radius R and a period P such that R=P±20%.

[0036] According to a specific embodiment, the cross-sectional variation is such that the maximum cross-sectional area S max With minimum cross section S min The ratio between is between 1.2 and 2, for example about 1.6.

[0037] According to a particular embodiment, the half-plates are made of a metal strip thinner than conventionally used, for example 316L stainless steel with a double carbon coating having a thickness of 0.075 mm.

[0038] The invention also relates to a fuel cell consisting of a stack of plates as described above.

[0039] The invention also relates to the use of such a battery, in particular for at least one of the following uses:

[0040] - motor vehicles;

[0041] -Multi-purpose vehicles;

[0042] - a bus or a truck;

[0043] -Boat;

[0044] - Aircraft;

[0045] - Railway vehicles;

[0046] -Engine generator;

[0047] -other.

[0048] The present invention also relates to a method for manufacturing the above-mentioned bipolar plate or monopolar plate, in particular, the method comprises the following steps:

[0049] - manufacturing two complementary half-plates, wherein the first channel and the second channel extend respectively according to orthogonal directions D1 and D2 along the length and width of the plate, following a path defining an undulation in an undulation plane substantially perpendicular to the main plane of the plate, and wherein the channels have a maximum cross section (S max ) and minimum cross section (S min ) between the variable cross-sections, the minimum cross-section (S min ) corresponds to a position where one of the first channels intersects one of the second channels;

[0050] - Assembling the complementary half-plates such that the first channel and / or the second channel follows a path defining an relief in a relief plane substantially perpendicular to the main plane of the plate.

[0051] In particular, the production of the half-panels can be carried out by hydroforming. 4. Description of the drawings

[0052] Other characteristics and advantages of the invention will become more apparent from a reading of the following description of exemplary embodiments given as simple illustrative and non-limiting examples, and of the accompanying drawings, in which:

[0053] [ Figure 1 ]: Figure 1 It has been described in the previous text, showing the general principle of a fuel cell;

[0054] [ Figure 2 ]: Figure 2 As has been described above, the structure of a fuel cell including a stack of unit cells is shown;

[0055] [ Figure 3 ]: Figure 3 As described above, the formation is shown in the form of an exploded view. Figure 2 Elements of the battery;

[0056] [ Figure 4 ]: Figure 4 Schematically shows Figure 3 The main elements of the bipolar plates of the unit cells;

[0057] [ Figure 5A ]、[ Figure 5B ]: Figure 5A and Figure 5BThe trajectories of the gas (hydrogen or air) flow and the heat transfer fluid are shown, respectively, along the undulations (only a portion of the half plate is shown);

[0058] [ Figure 6 ]: Figure 6 is another view of a portion of a half-plate showing undulations according to two orthogonal directions defined by the channels;

[0059] [ Figure 7 ]: Figure 7 An example of an undulation is schematically shown;

[0060] [ Figure 8 ]: Figure 8 The variation of the cross section of the gas channel is shown. 5. Specific implementation methods

[0061] 5.1 Main Elements of Bipolar Plates

[0062] The invention is suitable for use in the manufacture of bipolar plates or monopolar plates intended for forming fuel cells.

[0063] For ease of explanation, the main aspects of the bipolar plate are described below. Figure 4 As shown schematically in the example of FIG. 1 , there are several basic areas in the bipolar plate:

[0064] - Active zone AZ: This is where the reaction takes place and the active zone AZ consists of many channels. One of the difficulties in the design of these plates is that they must provide a homogeneous gas distribution and not over- or under-gas the channels. The surface of the active zone of the plate is the same as that of the active zone of the MEA;

[0065] - Homogenizing zone HZ: the location where the fluids are mixed, supplying the channels of the active zone with the same amount of gas / coolant. It is similar to a funnel, from the flow inlet to the beginning of the active zone;

[0066] - Anti-bypass zone ABP: the anti-bypass zone is necessary for mechanical reasons such as a well-maintained MEA and / or a good compression joint. Then, the gas bypass effect must be avoided, as this may cause a drop in gas pressure, thus reducing the efficiency of the entire system;

[0067] - Manifolds M: the manifolds are the elements that contribute to the dimensions and include the inlet and outlet for each gas and refrigerant. In general, their location and their dimensions define the overall dimensions of the plate;

[0068] - Inlet I: The inlet is the one that allows gas and refrigerant to enter the gas side or refrigerant side of the plate from the manifold;

[0069] - Guiding interface G: an element that helps keep the unit cells in place during stacking;

[0070] - Measuring electrode V: allows the insertion of a pin or a special device between the anode and cathode for measurement;

[0071] - Data Matrix: allows the precise identification of the board. It can carry in particular the serial number, the supplier's identification number, the time, the date of manufacture, etc. Its dimensions are usually 4×4 mm or 5×5 mm;

[0072] - Poka-yoke: mechanical element that limits the positioning of the half panels;

[0073] -Welds: hold the half plates together, they can be impermeable or serve only to reinforce the structure.

[0074] 5.2 Three-dimensional topology (3D)

[0075] The present invention thus proposes a new approach to bipolar or monopolar plates, according to which the active area of ​​the bipolar or monopolar plate (ie the area substantially facing the membrane) allows the movement of gas and heat transfer fluid in three dimensions of space.

[0076] More precisely, if Figure 5A and Figure 5B As shown, Figure 5A and Figure 5B The paths of the gas (hydrogen or air) flow and the paths of the heat transfer fluid are shown, respectively, the channels 51 intended for the gas and the channels 52 intended for the heat transfer fluid extending in orthogonal directions D1, D2 along the length and width of the plate, respectively, and crossing each other. Moreover, these channels have undulations in both directions, so that the surface of the active part is not flat, but has "depressions" and "protrusions", as shown in particular in Figure 6 Observed in .

[0077] Compared to the prior art, where the channels extend in the plane defined by the plates, this approach according to embodiments may have a number of advantages:

[0078] - Improved heat convection, allowing for reduced flow rates and / or increased system efficiency;

[0079] - Greater rigidity and / or increased weight of the plate, which allows the thickness of the metal strip to be reduced;

[0080] - Improve electrical contact and reduce electrical contact resistance;

[0081] - facilitate the assembly of the batteries, in particular the alignment of the batteries with respect to one another, thus allowing in particular to avoid sealing problems;

[0082] - Homogenization of oxygen partial pressure along the active surface;

[0083] - Homogenizes the current and increases the current density.

[0084] Figure 7 Examples of undulations are schematically shown, characterized by the length or period P of the undulations and the radius R of the undulations or the maximum height of the undulations. Of course, the shape of the undulations may differ from that shown.

[0085] The inventors have taken into account the limitation of the tangent line of the fluid channel and determined that it is effective when the difference between the radius R and the half period 1 / 2P is less than or equal to 20%, so that the pair (radius; half period) is not too strong and a balance is achieved between too obvious undulations and too small undulations. For example, the same or close 1 / 2P value and R value are selected: R = P ± 20%.

[0086] For reference only, the dimensions can be approximately:

[0087] -1 / 2P: between 8mm and 12mm;

[0088] -R: between 16mm and 24mm.

[0089] like Figure 7 As shown, for example, a radius R of 20 mm and a half period of 10 mm can be achieved.

[0090] The relative proportions of these geometrical constraints allow the thickness of the assembly of the two metal strips to be significantly reduced, independently of the thickness of the metal strip material. The proportional relationship between the cross sections of the channels, their respective orientations and the arrangement of the "bumps", while ensuring very good fluid distribution, also allows obtaining plate rigidity, thus allowing industrialization and routine assembly, making the thickness of the fuel cell (bipolar plate-membrane assembly-bipolar plate) very small, which can be less than 1 mm.

[0091] It is important to note that these dimensions were not determined based on a simple choice from several possibilities, but were the result of long and non-obvious research to meet several requirements for efficiency and industrialization, far exceeding those of previously known panels.

[0092] More generally, the dimensions of a half plate can be approximately:

[0093] - Length: between 250mm and 350mm;

[0094] -Width: between 150mm and 200mm.

[0095] For example, the number of gas channels is between 50 and 100. The number of heat transfer fluid channels may also be between 50 and 100.

[0096] 5.3 Channels with variable cross-section

[0097] According to another aspect of the invention, which can if necessary be implemented independently of the above-mentioned 3D topology, the cross section of the channel is varied.

[0098] In fact, the inventors have observed that the active zone according to the prior art, which has a channel for supplying a fluid and has a constant cross section, introduces heat and generates inhomogeneous partial pressures. Furthermore, this has a negative impact on the rigidity of the plate.

[0099] In order to overcome these problems, there are in particular gas channels whose cross-section varies periodically, e.g. Figure 8 As shown, it is observed that along the trajectory 81 of the fluid, the cross section of the channel is at the maximum cross section S max 82 and minimum cross section S min Varies between 83.

[0100] This allows, in particular, to increase the rigidity of the plate, to obtain better heat convection, to balance the voltage divisions and / or to obtain better electrical contact.

[0101] According to one embodiment, the maximum cross-section S max corresponds to the position of the maximum height H of the gas channel, while the minimum cross section S min Corresponds to the location where the gas channel intersects (intersects, or "cross channels") the heat transfer fluid channel, where the height reaches a minimum height h.

[0102] The minimum cross section corresponds to where the first channel intersects the orthogonal second channel.

[0103] The ratio between H and h is preferably between 2 and 3 and is for example such that H=2.5*h.

[0104] By simplification, it is assumed that the width L of the channel does not change much and is constant. Therefore, the cross section S max is equal to approximately L*H, and the cross-sectional area S min Equal to approximately (Hh)*L.

[0105] Therefore, it is preferred to select the cross-sectional variation ratio S max / S min Between 1.5 and 2, for example about 1.6.

[0106] It should be noted that Figure 8 A portion of a half plate is shown, thus showing a half cross section of a channel obtained by assembling two half plates to form a complete plate. But obviously the ratio remains the same.

[0107] For example, just for reference, the dimensions can be approximately:

[0108] -H: between 0.2mm and 0.35mm;

[0109] -h: between 0.1mm and 0.15mm;

[0110] -L: between 0.5mm and 1.3mm.

[0111] The path defining the relief and / or the variable cross section may in particular be defined by a finite element method to maximize one or more criteria, and in particular:

[0112] - Optimizing the fluid distribution in the channel;

[0113] -Optimize the rigidity of each plate;

[0114] - limiting the thickness of the unit cell of the fuel cell formed by the first plate, the membrane and the second plate.

[0115] These paths may define channel patterns that are repeated several times.

[0116] 5.4 Manufacturing and Assembly

[0117] The method of the invention allows the half-plates to be manufactured from finer metal strips than those conventionally used, for example from 316L stainless steel with a double carbon coating of 0.075 mm thickness. In fact, three-dimensional shaping allows the rigidity to be enhanced (conventional flat plates may have a tendency to deform), thus limiting possible defects in alignment. This results in less material required to manufacture the battery, therefore lighter and less expensive.

[0118] Of course, during the production of the half-plates (e.g. by stamping or molding), special attention needs to be paid to the three-dimensional shape, the half-plates with undulations in two orthogonal directions (corresponding to the direction of the channels) and / or the presence of channels with variable cross-section. A preferred mode of production is hydroforming, which has many advantages, such as precision of process repeatability, elasticity after forming, homogeneity of the thickness of the wall, efficiency of the contact zone, adaptability, etc.

[0119] However, this shape and / or reduced thickness of the metal strip can make it possible to make the assembly of the two half-plates forming each plate simpler and more reliable, in particular for the rigid connection of the half-plates (for example by welding) and for the assembly of the plates to form a battery. Thus, the stacking of 300 plates, for example to form a battery, is simplified and more efficient, which in particular allows reducing the risks of leaktightness.

[0120] According to the prior art, it is necessary to homogenize the surface of the plate. However, according to the method of the invention, this is not necessary since it allows obtaining a current as homogeneous as possible, thus avoiding the risk of degradation and contamination due to hot spots, without requiring additional treatments.

[0121] The invention thus allows to obtain very efficient plates and cells suitable for numerous uses, for example in motor vehicles and more generally in any type of vehicle or device carrying a fuel cell.

[0122] Furthermore, the invention can also be used with membranes having different forms, depending on the cell, so as to define active areas of several sizes and therefore cells with different power outputs from the same plate. This is made possible in particular by the homogeneity obtained by the method according to the invention.

Claims

1. A bipolar plate or a monopolar plate for a fuel cell having a proton exchange membrane, each plate having a first channel for circulation of a reaction gas and a second channel for circulation of a heat transfer fluid, the reaction gases being hydrogen and air, respectively, It is characterized in that the first channel and the second channel extend in orthogonal directions (D1, D2) along the length and width of the plate, respectively, and follow a path defining an undulation in an undulation plane substantially perpendicular to a main plane of the plate, And wherein the channel has a maximum cross section (S max ) and minimum cross section (S min ) between the variable cross-sections, the minimum cross-section (S min ) corresponds to the position where a first channel among the first channels intersects with a second channel among the second channels.

2. The plate according to claim 1, characterized in that The path defining the relief and / or the variable cross section are defined by a finite element method according to at least one criterion belonging to the following group: - Optimizing the fluid distribution in the channel; -Optimize the rigidity of each plate; - limiting the thickness of the unit cell of the fuel cell formed by the first plate, the membrane and the second plate.

3. The plate according to any one of claims 1 to 2, characterized in that The panel is formed by the assembly of two complementary half-panels formed in three dimensions to define the relief.

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

5. A plate according to any one of claims 3 to 6, characterized in that The cross-sectional variation is such that the maximum cross-sectional area (S max ) and the minimum cross section (S min ) is about 1.

6.

6. A plate according to any one of claims 1 to 5, characterized in that The plate allows the manufacture of a fuel cell which is formed by the first plate, the membrane and the second plate and which has a thickness of less than 1 mm.

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

8. Use of the fuel cell according to claim 7 for at least one of the following uses: - motor vehicles; -Multi-purpose vehicles; - a bus or a truck; -Boat; - Aircraft; - Railway vehicles; -Engine generator.

9. A method of manufacturing a bipolar plate or a monopolar plate for a fuel cell having a proton exchange membrane, each plate having a first channel for circulation of a reactant gas, hydrogen and air respectively, and a second channel for circulation of a heat transfer fluid, It is characterized in that The method comprises the following steps: - manufacturing two complementary half-plates, wherein the first channel and the second channel extend in orthogonal directions (D1, D2) respectively along the length and width of the plate and follow a path defining an undulation in an undulation plane substantially perpendicular to the main plane of the plate, and wherein the channels have a maximum cross section (S max ) and minimum cross section (S min ) between the variable cross-sections, the minimum cross-section (S min ) corresponds to a position where one of the first channels intersects one of the second channels; - Assembling the complementary half-plates such that the first channel and / or the second channel follows a path defining an relief in a relief plane substantially perpendicular to the main plane of the plates.

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