Monopolar plate for fuel cell, its manufacturing process and fuel cell comprising such a monopolar plate

Abstract

Monopolar plate for a fuel cell, its manufacturing process, and a fuel cell comprising such a monopolar plate. The present invention relates to a monopolar plate (30) for a fuel cell. This monopolar plate, formed of two monopolar half-plates (32, 34), defines at least one circulation opening for a heat transfer fluid, a central zone intended to be opposite an active zone of a membrane-electrode assembly (8), and a homogenization zone comprising, between the two monopolar half-plates (32, 34), a fluidic communication space that fluidly connects the circulation opening for the heat transfer fluid to the central zone, the fluidic communication space having a volume defined by the two monopolar half-plates. At least a portion of the fluidic communication space (64) of the homogenization zone is equipped with an insert (80) for reducing its volume. Figure for the abstract: 3

Description

Title of the invention: Monopolar plate for fuel cell, its manufacturing process and fuel cell comprising such a monopolar plate

[0001] The present invention relates to a monopolar plate for a fuel cell. The present invention also relates to a method for manufacturing such a monopolar plate. Finally, the present invention relates to a fuel cell comprising, among other things, such a monopolar plate.

[0002] In the field of fuel cells, it is known to create a stack of active electrochemical cells by juxtaposing bipolar plates between which membrane-electrode assemblies, or "MEAs," are arranged. Two monopolar plates constitute the ends of the active cell stack and are potentially exposed to contact with two pressure plates that exert an axial compressive force on the stack. In some cases, the fuel cell comprises a stack of active electrochemical cells and, at at least one end of this stack, an adjacent stack of one or more so-called "dead" cells. By "dead cell" is meant a set of two adjacent plates, each geometrically analogous to a bipolar plate or a polar plate, but without an operational membrane-electrode assembly between these two plates.At each end of the stack containing dead cells, a monopolar plate is positioned between the last active electrochemical cell and the stack of dead cells.

[0003] Each bipolar or monopolar plate in the stack is traversed by a flow of heat transfer fluid whose function is to dissipate the heat generated within the various active electrochemical cells. For a bipolar plate, this heat comes from both sides of the plate, that is, from the two active electrochemical cells located on either side of it. For a monopolar plate, the heat comes from only one side of the plate, namely the side of the adjacent active electrochemical cell, so that the amount of heat to be dissipated by the heat transfer fluid is less than the amount of heat to be dissipated by the heat transfer fluid passing through a bipolar plate. Since the flow rate of the heat transfer fluid is the same for both monopolar and bipolar plates, the average temperature of the active cell delimited by a monopolar plate will be lower and may lead to operational problems with that cell.

[0004] On the other hand, it is important, from an industrial point of view, to produce the bipolar plates and monopolar plates with half-plates, respectively bipolar and monopolar, which have the closest possible geometries, in order to use the same tooling and analogous manufacturing ranges, to a large extent.

[0005] It is known from EP-A-1529321 to fabricate an electrochemical cell for a fuel cell between two bipolar plates equipped with channels inside which bimetallic strips are arranged, the geometry of which varies according to the temperature of the heat transfer fluid. This modifies the cross-sectional area of ​​a channel as a function of the heat transfer fluid temperature but does not address the specific situation of a monopolar plate located at the end of a stack. Furthermore, the bimetallic strips are complex to manufacture and increase the cost of each bipolar plate.

[0006] It is also known from DE-102021206594 to attach an intermediate plate to the outside of a conventional bipolar plate to reduce the cross-sectional area of ​​a heat transfer fluid flowing through the bipolar plate. Each intermediate plate must be specifically manufactured and installed in addition to the bipolar plate, which complicates the manufacturing process of a fuel cell stack that includes such an intermediate plate.

[0007] On the other hand, WO-A-2012 / 131267 teaches that permanent or temporary sealing means can be placed at the end of certain internal circulation channels of a bipolar plate, or that certain channels can be pinched to close them completely. The result is that some channels no longer allow the heat transfer fluid to pass through at all and are therefore no longer effective in dissipating heat from an adjacent electrochemical cell.

[0008] It is these drawbacks that the invention intends to remedy more particularly by proposing a new monopolar plate for a fuel cell which allows heat to be evacuated by circulating a heat transfer fluid in an optimized way, with the possibility of using monopolar half-plates identical or almost identical to the bipolar half-plates constituting the bipolar plates of the same stack.

[0009] To this end, the invention relates to a monopolar plate for a fuel cell, this monopolar plate being formed of two monopolar half-plates and defining a circulation opening for a heat transfer fluid, a central zone intended to be opposite an active zone of a membrane-electrode assembly, and a homogenization zone comprising a fluid communication space that connects the circulation opening for the heat transfer fluid to the central zone, the fluid communication space having a volume defined by the two monopolar half-plates. According to the invention, at least a portion of the fluid communication space of the homogenization zone is equipped with a volume-reducing insert.

[0010] Thanks to the invention, the insert present in at least a portion of the fluid communication space of the homogenization zone makes it possible to reduce its volume, and therefore the cross-sectional area of ​​this fluid communication space and consequently the flow rate of the heat transfer fluid within this fluid communication space, between the heat transfer fluid circulation opening and the central zone. The inclusion of an insert in the fluid communication space of the homogenization zone makes it possible to manufacture the monopolar plate from monopolar half-plates having a standard geometry, therefore monopolar half-plates analogous to the bipolar half-plates of the bipolar plates belonging to the same stack, while limiting the flow rate of the heat transfer fluid compared to that present in a bipolar plate.This allows the same tooling and manufacturing processes to be used to produce the half-plates intended for both bipolar and monopolar plates. Monopolar plates are configured so that the circulation of the heat transfer fluid allows for heat dissipation in an amount appropriate to their positioning at the end of the stack.

[0011] According to advantageous but not mandatory aspects of the invention, such a monopolar plate may incorporate one or more of the following features taken in any technically permissible combinations.

[0012] - The reduction in the volume of the fluidic communication space due to the insert is between 30% and 90%, preferably between 50% and 90%.

[0013] - The fluidic communication space includes channels that connect fluid- dically the opening of the circulation of the heat transfer fluid to the central zone, each channel having a passage section defined by the two monopolar half-plates and at least one channel of the homogenization zone, preferably each channel of the homogenization zone, is equipped with an insert for reducing its passage section.

[0014] - A ratio between, on the one hand, the area of ​​a cross-section of an insert, taken per pendulumwise to a direction of fluid flow in a channel, and on the other hand, the area of ​​the channel's passage section in the absence of an insert, is between 30% and 100%.

[0015] - A ratio between, on the one hand, a length of an insert, measured parallel to a direction of fluid flow in a channel, and on the other hand the length of the channel between the opening of circulation of the heat transfer fluid and the central zone, is greater than or equal to 10%.

[0016] - At least two separate channels of the homogenization zone are each equipped of an insert and the inserts of the two separate channels are connected by a junction strip.

[0017] - The channels are formed at least in part by grooves made on at least one of the two monopolar half-plates and each insert has a complete shape commentary of at least part of a groove which forms at least part of the channel in which this insert is placed.

[0018] - The channels are delimited by ribs arranged between the two half-plates monopolar and each insert has a shape complementary to at least part of the ribs that delimit the channel in which this insert is placed.

[0019] - The insert is rigid.

[0020] - The insert is a single-material part, made of metal or plastic material, or is a bi-material part.

[0021] - The insert is made of deformable three-dimensional foam or mesh.

[0022] According to a second aspect, the invention relates to a method for manufacturing a monopolar plate as mentioned above, in which the two monopolar half-plates are manufactured by stamping, hydroforming, or molding, forming at least in the homogenization zone reliefs defining, between them, in a direction perpendicular to the stacking direction, the fluidic communication space, characterized in that this method comprises at least two successive steps consisting of a. Insert between the reliefs of at least one of the two monopolar half-plates at least one insert for reducing the volume of the fluidic communication space, b. to join the two monopolar half-plates together by trapping the insert between them.

[0023] According to a third aspect, the invention relates to a fuel cell comprising a stack of active electrochemical cells defined by bipolar plates and two monopolar plates constituting the ends of this stack of active cells. In accordance with the invention, at least one of the monopolar plates is as described above or manufactured by the method mentioned above.

[0024] This fuel cell has the same advantages as the monopolar plate and the process of the invention.

[0025] Advantageously, the monopolar half-plates of the monopolar plates have the same geometry as the bipolar half-plates of the bipolar plates.

[0026] It can also be provided that the fluidic communication space comprises channels that fluidly connect the heat transfer fluid circulation opening to the central zone, each channel having a cross-section defined by the two monopolar half-plates and at least one channel of the homogenization zone, preferably each channel of the homogenization zone, is equipped with an insert for reducing its cross-section, and that the cross-section of a first channel of the monopolar plate equipped with an insert is less than the cross-section of a second channel of a bipolar plate of the stack of electrical cells active trochemicals, the first channel and the second channel being respectively disposed in the same locations in the respective homogenization zones of the monopolar plate and the bipolar plate.

[0027] The invention will be better understood and other advantages thereof will become more apparent from the following description of four embodiments of a monopolar plate, a fuel cell and a manufacturing process in accordance with its principle, given solely by way of example and with reference to the accompanying drawings in which: - [Fig.1] The [Fig.1] is a schematic cross-section, along a plane containing the stacking direction, of a part of a fuel cell according to the invention; - [Fig.2] [Fig.2] is a partial exploded view of a monopolar plate conforming to a first embodiment and belonging to the fuel cell of [Fig.1], substantially illustrating one half of the monopolar plate, the other half being symmetrical to the illustrated half; - [Fig.3] The [Fig.3] is a partial schematic cross-section of the fuel cell of the [Fig.l], at the level of line III-III in the [Fig.l]; - [Fig. 4] [Fig. 4] is an exploded view of the portion of the plate mo nopolar of the first embodiment visible in [Fig.3]; - [Fig.5] The [Fig.5] is a view analogous to the [Fig.3], for a second embodiment of the invention; - [Fig.6] The [Fig.6] is an exploded section of the portion of the monopolar plate of the embodiment visible in the [Fig.5], for the second embodiment; - [Fig.7] Fig.7 represents, on two inserts A and B, a portion of a plate monopolar conforming to a third embodiment, respectively in exploded view and in assembled view and - [Fig.8] The [Fig.8] is a view analogous to the [Fig.7], for a monopolar plate according to a fourth embodiment of the invention.

[0028] The fuel cell 2 shown in [Fig.1] comprises a stack 4, in a stacking direction, formed of polar plates between which are defined active electrochemical cells 6. Each active electrochemical cell 6 comprises a membrane-electrode assembly 8 through which ions pass, which induces an exothermic chemical reaction and a transfer of heat from the membrane-electrode assembly 8 to the adjacent plates, which is represented by the heat exchange arrows E on this [Fig.1].

[0029] The polar plates are of two types, namely bipolar plates 20 each comprising two bipolar half-plates 22 and 24, and mono- polars 30 each comprising two monopolar half-plates 32 and 34.

[0030] Each bipolar plate 20 is arranged between two active electrochemical cells 6, while each monopolar plate 30 is arranged between an active electrochemical cell 6 and a pressure plate 40, or between an active electrochemical cell and a dead electrochemical cell. In an alternative not shown and applicable to all embodiments, the fuel cell 2 comprises a stack 4 of polar plates between which active electrochemical cells 6 are defined and, at at least one end of this stack 4, an adjacent stack of one or more so-called "dead" cells. By "dead cell" is meant, for example, a set of two adjacent plates, each geometrically analogous to a monopolar plate 30 or a bipolar plate 20, but without an operational membrane-electrode assembly 8 between these two plates.A dead cell is, more generally, a cell in which no electrochemical reaction takes place. At each end of the stack 4 containing dead cells, a monopolar plate 30 is positioned between the last electrochemically active cell 6 and the stack of dead cells.

[0031] The pressure plates 40 delimit the ends of the stack 4 and belong to this stack. The stack 4 is mounted inside a housing 42 of the fuel cell 2.

[0032] Each bipolar plate 20 and each monopolar plate 30 has internal channels delimited within the thickness of the bipolar plate 20 or the monopolar plate 30 considered, between the two half-plates, which allow the flow of a heat transfer fluid. This flow of heat transfer fluid, represented by the arrows 53 in [Fig. 1], allows the heat produced by the two adjacent active electrochemical cells 6 to be dissipated in the case of a bipolar plate 20. In the case of a monopolar plate 30, only the heat produced by the single adjacent active electrochemical cell 6 is dissipated by the heat transfer fluid circulating in these channels.

[0033] As shown in [Fig.2], a monopolar plate 30 is formed of two monopolar half-plates 32 and 34, namely a first monopolar half-plate 32 and a second monopolar half-plate 34. Preferably, the two monopolar half-plates 32 and 34 are made of metal, typically stainless steel or titanium, or of carbon polymer composite, known as graphite, or of composite plastic material.

[0034] Each bipolar plate 20 has, in a known manner, two pairs of two reactive gas circulation openings, namely one pair of openings for dioxygen (or air containing dioxygen) and one pair of openings for dihydrogen, as well as one pair of two circulation openings for a ca- fluid heat transfer fluid. As is known, each pair of openings for a fluid comprises a fluid inlet opening and a fluid outlet opening, each located respectively at one of the two opposite longitudinal ends of the bipolar plate 20. Thus, in certain embodiments of a bipolar plate 20, at each longitudinal end of the bipolar plate 20, there are two reactive gas circulation openings, namely oxygen and hydrogen, as well as a circulation opening for a heat transfer fluid. The monopolar plate 30 also comprises, in such embodiments, at each longitudinal end of the monopolar plate 30, two reactive gas circulation openings 55, namely oxygen and hydrogen, at least one of the reactive gas circulation openings 55 being able to be closed, as well as a circulation opening 56 for a heat transfer fluid.

[0035] In the illustrated example, each circulation opening 55 is formed by a first portion of an opening 552 located in the first monopolar half-plate 32 and a second portion of an opening 554 located in the second monopolar half-plate 34. The circulation opening 56 is formed by a first portion of an opening 562 located in the first monopolar half-plate 32 and a second portion of an opening 564 located in the second monopolar half-plate 34. In the illustrated example, each circulation opening 55 has the shape of a closed-contour opening, the contour extending into the plane of the monopolar plate 30. A circulation opening may, however, have an open contour by being formed in an outer edge of the monopolar plate 30.

[0036] The monopolar plate 30 has a central zone 60. This central zone 60 of the monopolar plate 30 is intended to be opposite, according to the stacking direction, an active zone of the adjacent membrane-electrode assembly 8, that is, a zone of the adjacent membrane-electrode assembly 8 where the electrochemical reactions occur. The central zone 60 is formed by a first portion of the central zone 602 located in the first monopolar half-plate 32 and a second portion of the central zone 604 located in the second monopolar half-plate 34.

[0037] The monopolar plate 30 also includes a homogenization zone 62. The homogenization zone 62 is formed of a first portion of homogenization zone 622 provided in the first half-monopolar plate 32 and a second portion of homogenization zone 624 provided in the second half-monopolar plate 34. A homogenization zone extends, for a given fluid, between a circulation opening for that given fluid and the central zone.

[0038] In the example shown in the figures, for the heat transfer fluid, this homogenization zone 62 includes channels 64 which allow the flow of the heat transfer fluid and which together constitute a fluidic communication space between the heat transfer fluid circulation opening 56 and the central zone 60. The channels 64 correspond to the internal channels mentioned above. Each channel 64 is formed between the two monopolar half-plates 32 and 34 and is formed at least in part by a first groove 642 formed in the first monopolar half-plate 32 and / or by a second groove 644 formed in the second monopolar half-plate 34. Each channel 64 has, in cross-section by a plane containing the stacking direction and perpendicular to a principal direction of fluid flow in the channel 64 considered, a passage section 264, the geometry of which is defined by the one or two grooves that form it at least in part.

[0039] The sum of the internal volumes of the channels 64 constitutes a volume of the fluidic communication space.

[0040] The bipolar plates 20 have the same geometry as the monopolar plates 30 and also include circulation openings, a central zone and a homogenization zone which includes channels 164, which have the same function and the same geometry as the channels 64 of the monopolar plates 30. Each channel 164 is formed between the two bipolar half-plates 22 and 24 and is formed at least in part by a first groove 652 provided in the first bipolar half-plate 22 and / or by a second groove 654 provided in the second bipolar half-plate 24. Each channel 164 has a passage section 2164, defined by the one or two grooves which form it at least in part.

[0041] A portion of the stack 4, comprising two bipolar plates 20 and a monopolar plate 30, is shown in [Fig. 3]. The cross-sectional plane of [Fig. 3] passes through the homogenization zones 62 of the two bipolar plates 20 and the monopolar plate 30. Two membrane-electrode assemblies 8 are arranged between the two bipolar plates 20 and between one of the bipolar plates 20 and the monopolar plate 30. The monopolar plate 30 rests against a pressure plate 40. The pressure plate 40, schematically illustrated in the figures, may include, in particular, an electrical contact plate (not shown), in electrical contact with the polar plate 30, and optionally an insulating plate interposed between the electrical contact plate and the rest of the pressure plate 40.

[0042] The bipolar half-plates 22 and 24 and the monopolar half-plates 32 and 34 have identical geometries. Thus, the channels 64 and 164 have identical geometries and the passage sections 264 and 2164 are identical.

[0043] A64 denotes the area of ​​a passage section 264 or 2164.

[0044] At least one flow channel 64 of the monopolar plate 30 is equipped with a insert 80 reduces its passage cross-section by 264. In other words, the volume of the fluidic communication space is reduced by the insert 80, which is arranged in a part of this space.

[0045] This insert 80 is rigid, in one piece and made of a single material, this material being, for example, a plastic material.

[0046] Advantageously, each channel 64 of the monopolar plate is equipped with an insert 80 for reducing its cross-section 264.

[0047] Alternatively, only some of the flow channels 64 are equipped with a reducing insert 80.

[0048] Each reduction insert 80 is of complementary shape to a part of the grooves 642 of the monopolar half-plate 32 and to a part of the grooves 644 of the monopolar half-plate 34.

[0049] In the example of the first embodiment, the inserts 80 are placed in the center of the flow channels 64, halfway between the bottoms of the grooves 642 and 644.

[0050] A flow channel 64 equipped with an insert 80 has an effective flow area 2'64 for heat transfer fluid. Here, the effective flow area 2'64 comprises two subsections 2'642 and 2'644. The first subsection 2'642 is defined between the insert 80 and the monopolar half-plate 32, and the second subsection 2'644 is between the insert 80 and the monopolar half-plate 34.

[0051] We denote A'64 the area of ​​the effective passage section 2'64. The area A'64 is strictly less than the area A64.

[0052] An insert 80 thus makes it possible to reduce the cross-section 264 of the heat transfer fluid in a channel 64. The cross-section 280 of an insert 80 is defined as the cross-section of this insert taken perpendicular to the main direction of fluid flow in the channel 64. A80 denotes the area of ​​the cross-section 280 of an insert 80.

[0053] Section 264 is equal to the sum of sections 2642, 280 and 2644.

[0054] On the relation

[0055] A64 = A'64 + A80 (equation 1)

[0056] In the example of Figures 1 to 4, the length of each insert 80, measured parallel to a main direction of fluid flow in a channel 64, is equal to the length of the channel 64 between the heat transfer fluid circulation opening 56 and the central zone 60. In such a case, an insert 80 extends over the entire length of the homogenization zone 62.

[0057] In an unrepresented variant of the invention, the length of an insert 80 represents only between 10% and 95% of the total length of the channel.

[0058] As shown in [Fig. 4], the reduction inserts 80 positioned in separate channels 64, for example two adjacent channels 64, are connected to each other by means of a connecting strip 82. This connecting strip 82 is made of the same material as the two inserts 80. The two inserts 80 and the connecting strip 82 together constitute a subassembly 84 which can be manipulated as a unit during of the manufacture of the monopolar plate 30, in particular for the placement of the inserts 80 in the channels 64.

[0059] In practice, a sub-assembly with several connecting strips 82 and a corresponding number of inserts 80 can be manufactured, depending on the number of separate channels 64 to be equipped with reducing inserts 80 of their passage section.

[0060] In practice, the channels 64 of the homogenization zone 62 of the monopolar plate 30 equipped with a reduction insert 80 have an effective passage section 2'64 of area A'64 strictly less than the area A64 of the passage section 2164 of the channels 164 arranged in the same places, in the sense of places aligned along the stacking direction, in the homogenization zones 62 of the bipolar plates 20.

[0061] In general, it can be expected that the reduction in passage cross-section is identical for all channels equipped with an insert, or that the reduction in passage cross-section is proportional to the passage cross-section of the channel considered.

[0062] Depending on the geometry of the insert(s) 80, it is possible not only to obtain a reduction in the flow rate of heat transfer fluid in the monopolar plate 30, but it is also possible to influence the distribution of this fluid flow rate along a transverse direction of the monopolar plate 30.

[0063] The monopolar plate 30 according to this first embodiment is manufactured according to the following process: the grooves 642 and / or 644 of the homogenization zone 62 of the two monopolar half-plates 32 and 34 are formed by stamping. Since the grooves 642 and / or 644 of the monopolar half-plates 32 and 34 are identical to the grooves 652 and / or 654 of the bipolar half-plates 22 and 24, the same tooling and the same manufacturing processes can be used to manufacture the bipolar half-plates 22, 24 and the monopolar half-plates 32, 34.

[0064] The rigid and predefined shape reduction inserts 80 complementary to a part of the grooves 642 and 644 of the two monopolar half-plates 32 and 34 are arranged between the two monopolar half-plates 32 and 34. The two monopolar half-plates 32 and 34 are then joined together by trapping the inserts 80 in the flow channels 64.

[0065] In practice, on this occasion, the inserts 80 are manipulated within sub-assemblies of the type of sub-assembly 84.

[0066] The joining strips 82 contribute not only to the constitution of the subassemblies 84 but also to the positioning of the inserts 80 relative to the monopolar half-plates 32, 34, during the manufacturing process of the monopolar plate 30. Preferably, for a given homogenization zone, the polar plate 30 comprises a single subassembly 84 incorporating in one piece all the inserts 80 of this homogenization zone of the monopolar plate 30.

[0067] Second, third and fourth embodiments of the invention are re presented in Figures 5 to 8. In the following description, elements analogous to those of the first embodiment bear the same reference numerals and are not described in detail. If a reference numeral is mentioned in the description but not shown in a figure, or shown in a figure but not mentioned in the description, it refers to the same element as the one bearing the same reference numeral in the first embodiment. The following primarily describes what distinguishes these embodiments from the previous one.

[0068] In the second embodiment, the bipolar half-plates 22 and monopolar half-plates 32 are equipped with grooves 652, respectively 642, while the bipolar half-plates 24 and monopolar half-plates 34 are flat and equipped with ribs 52 and 54.

[0069] The ribs 52 of a bipolar half-plate 24 are turned towards the membrane-electrode assembly 8 of the active electrochemical cell 6 to which this half-plate belongs, while the ribs 54 of this half-plate are turned in the opposite direction, towards a bipolar half-plate 22 belonging to the same bipolar plate 20. The ribs 54 define between them channels 164 for the passage of heat-transfer fluid, of the same type as the channels 164 of the first embodiment. The ribs 52 of a monopolar half-plate 34 are turned towards the adjacent pressure plate 40, while the ribs 54 of this half-plate are turned in the opposite direction, towards a monopolar half-plate 32 belonging to the same monopolar plate 30. The ribs 54 define between themselves channels 64 for the passage of heat transfer fluid, of the same type as the channels 64 of the first embodiment.

[0070] In this example, the monopolar half-plate 32 is formed by stamping, while the ribs 52 and 54 of the monopolar half-plate 34 are formed by overmolding onto a flat plate, for example, overmolding in an elastomeric material such as silicone. Any other technique for creating raised features in the form of ribs can be used to manufacture the monopolar half-plate 34.

[0071] Advantageously and as in the example of the figures, the channels 64 do not all have the same geometry.

[0072] Each flow channel 64 is equipped with a rigid, single-material reduction insert 80 whose shape is complementary to a part of the ribs 54.

[0073] The inserts 80 arranged in different separate flow channels 64, possibly adjacent flow channels 64, are connected by a connecting strip 82 which acts as a support. In this example, this connecting strip 82 is made of a more rigid material than the material constituting the inserts 80, for example, metal, while the inserts 80 are made of a synthetic material.

[0074] In an alternative embodiment not shown, the inserts 80 and the joining strip 82 are made in the same material.

[0075] The inserts 80 and the joining strip 82 together constitute a subassembly 84 which can be manipulated as a unit during the manufacture of the monopolar plate 30, like the subassembly 84 of the first embodiment.

[0076] A flow channel 64 equipped with an insert 80 then presents an effective passage area 2'64 for heat transfer fluid. This effective passage area 2'64 comprises, in this embodiment, two subsections 2'642 and 2'644. The first subsection 2'642 is located between the joining strip 82 and the grooves 642 of the monopolar half-plate 32. The second subsection 2'644 is located between the insert 80, the monopolar half-plate 34, and the ribs 54.

[0077] The inserts 80 arranged on the joining strip 82 are inserted between the two monopolar half-plates 32, 34 between the ribs 54, therefore in the channel(s) 64 delimited between two adjacent ribs 54, channels 64 which the inserts 80 partially complete. The assembly of the two monopolar half-plates 32 and 34 makes it possible to enclose the insert and to form the monopolar plate 30 according to the invention, as mentioned above for the first embodiment.

[0078] In the third embodiment shown in [Fig.7], an insert 80 completely completes the reliefs of one of the monopolar half-plates 32 or 34, that is to say totally obturates a part of a channel 64 defined by a groove 642 or 644 of one of the monopolar half-plates of the monopolar plate 30.

[0079] The monopolar half-plates 32 and 34 have grooves 642 and 644 that define flow channels 64. A first rigid insert 802 fully completes a groove 642 of the monopolar half-plate 32, partially defining a first channel 64. A second rigid insert 804 fully completes a groove 644 of the monopolar half-plate 34, partially defining a second channel 64 distinct from the first channel 64. The two adjacent inserts 802 and 804 are joined by means of a connecting strip 82 and together constitute a subassembly 84. The first channel 64 equipped with its insert 802 and the second channel 64 equipped with its insert 804 present a single effective cross-section 2'64 for the passage of a fluid between this insert and the groove 642 or 644 of the monopolar half-plate 32 or 34 which is not completed by insert 80.

[0080] In the representation of [Fig.7], the inserts 802 and 804 alternately complete the grooves of the two monopolar half-plates 32 and 34. In an unrepresented variant, the multiple inserts 80 always complete the grooves of the same monopolar half-plate 32 or 34.

[0081] The grooves 642 and 644, respectively closed by the inserts 802 and 804, form at least partially separate channels 64. Thus, the effective passage area 2'64 of each channel 64 is reduced, but not made zero.

[0082] The manufacturing processes for the monopolar plates 30 of the second and third embodiments are comparable to the manufacturing process for the monopolar plate 30 of the first embodiment.

[0083] In the fourth embodiment shown in [Fig.8], the two monopolar half-plates 32 and 34 forming the monopolar plate 30 respectively have grooves 642 and 644 defining flow channels 64.

[0084] The reduction insert 80 placed between the two monopolar half-plates 32 and 34 is made of foam or deformable three-dimensional mesh whose Young's modulus is much lower than that of the monopolar half-plates 32 and 34, preferably the Young's modulus of the monopolar half-plates 32, 34 is at least ten times greater than the Young's modulus of the reduction insert 80 made of foam or three-dimensional mesh.

[0085] The insert 80 is made from a blank insert 80' of arbitrary shape, for example parallelepiped as shown in insert A) of [Fig. 8]. Due to the deformable nature of the blank 80', it takes on a shape complementary to a portion of the grooves 642 and 644 of the two monopolar half-plates 32 and 34 when these are brought together around the blank to form the monopolar plate 30. The insert 80 formed from the blank 80' extends within several distinct flow channels 64, possibly within several of the adjacent flow channels 64.

[0086] In an unrepresented variant, the deformable material insert 80 extends only within a single flow channel 64.

[0087] The two flow channels 64 comprising a portion of the insert 80 each have an effective passage cross-section 2'64 of a heat transfer fluid which comprises two subsections 2'642 and 2'644. Subsection 2'642 is located between the insert 80 and the groove 642 of the monopolar half-plate 32 and subsection 2'644 is between the insert 80 and the groove 644 of the monopolar half-plate 34.

[0088] The manufacturing process for such a monopolar plate 30 is as follows: the two monopolar half-plates 32 and 34 are manufactured by stamping. In the absence of constraints, the deformable blank 80' preferentially takes the form of a parallelepiped as shown in [Fig.8]. When the blank 80' is compressed between the two monopolar half-plates 32 and 34, it fills part of the available space and forms the insert 80. The insert 80 then occupies part of the passage cross-section 264 of several flow channels 64. The proportion of the passage cross-section 264 of each channel 64 that is closed by the insert 80 and the number of flow channels 64 having their passage cross-section reduced are determined in particular by the initial dimensions of the blank 80' and the compressive forces exerted during the assembly of the two monopolar half-plates 32 and 34.

[0089] Alternatively, in the first, second and third embodiments, the insert 80 is single-material (metal) or bi-material.

[0090] Regardless of the embodiment, the proportion, within a given homogenization zone, of the number of channels equipped with cross-sectional reduction inserts, relative to the total number of channels in the homogenization zone, is at the discretion of the fuel cell designer, depending on the desired thermal effect. This proportion is generally between 50 and 100%.

[0091] Advantageously, and regardless of the embodiment, the area A80 of the cross-section of each insert 80, 802 or 804 represents between 30% and 100% of the area A64 of the passage section 264 of the channel in which this insert is placed, this area being defined in the absence of an insert.

[0092] Advantageously, and regardless of the embodiment, the length of an insert 80, 802 or 804, measured parallel to a direction of fluid flow in a channel 64, is greater than or equal to 10% of the length of this channel between the circulation opening of the heat transfer fluid 56 and the central zone 60.

[0093] According to an embodiment of the invention not shown, the fluid communication space between the heat transfer fluid opening 56 and the active zone 60 can be achieved by means other than channels. For example, this volume can be continuous across the width of the homogenization zone 62 and provided by means of studs and a peripheral border arranged between the two monopolar half-plates 32, 34. In this case, the volume of the fluid communication space is defined around the studs and within the peripheral border. A portion of this volume is occupied by one or more inserts 80 distributed between the studs.

[0094] In a plane perpendicular to a direction of fluid flow in the fluidic communication space, the sum of the widths of the inserts 80 represents between 50% and 100% of the width of the homogenization zone 62, the widths being measured perpendicular to a direction of fluid flow in the fluidic communication space.

[0095] Regardless of the embodiment, the reduction in the volume of the fluidic communication space due to the insert 80 is between 30% and 90%, preferably between 50% and 90%. This reduction in the volume of the fluidic communication space, and the distribution of this volume reduction, particularly along the transverse direction of the plate, is obtained by determining the geometry of the insert(s).

[0096] Insofar as they are compatible, the embodiments and variants mentioned above can be combined with each other.

Claims

Demands

1. Monopolar plate (30) for a fuel cell (2), this monopolar plate being formed of two monopolar half-plates (32, 34) and defining - at least one opening (56) for the circulation of a heat transfer fluid, - a central zone (60) intended to be opposite an active zone of a membrane-electrode assembly (8), - a homogenization zone (62) comprising, between the two monopolar half-plates (32, 34), a fluidic communication space which fluidly connects the opening (56) for the circulation of the heat transfer fluid to the central zone (60), the fluidic communication space having a volume defined by the two monopolar half-plates, characterized in that at least a part of the fluidic communication space of the homogenization zone (62) is equipped with an insert (80, 802, 804) for reducing its volume.

2. Monopolar plate according to claim 1, characterized in that the reduction of the volume of the fluidic communication space due to the insert (80) is between 30% and 90%, preferably between 50% and 90%.

3. Monopolar plate according to any one of claims 1 and 2, characterized in that the fluidic communication space comprises channels (64) which fluidically connect the opening (56) of circulation of the heat transfer fluid to the central zone (60), each channel (64) having a passage section (264) defined by the two monopolar half-plates (32, 34) and in that at least one channel (64) of the homogenization zone (62), preferably each channel (64) of the homogenization zone (62), is equipped with an insert (80, 802, 804) for reducing its passage section.

4. Monopolar plate according to claim 3, characterized in that a ratio between, - on the one hand, the area (A80) of a cross-section of an insert (80), taken perpendicular to a direction of fluid flow in a channel (64), and - on the other hand, the area of ​​the section (A64) of passage (264) of the canal (64) in the absence of insert (80, 802, 804), is between 30% and 100%.

5. Monopolar plate according to any one of claims 3 and 4, characterized in that a ratio between, - on the one hand, a length of an insert (80), measured parallel to a direction of fluid flow in a channel (64), and - on the other hand the length of the channel (64) between the opening (56) of circulation of the heat transfer fluid and the central zone (60), is greater than or equal to 10%.

6. Monopolar plate according to any one of claims 3 to 5, characterized in that at least two separate channels (64) of the homogenization zone (62) are each equipped with an insert (80, 802, 804) and in that the inserts (80, 802, 804) of the two separate channels (64) are connected by a junction strip (82).

7. Monopolar plate according to any one of claims 3 to 6, characterized in that the channels (64) are formed at least in part by grooves (642, 644) formed on at least one of the two monopolar half-plates (32, 34) and in that each insert (80, 802, 804) has a shape complementary to at least part of a groove (642, 644) which forms at least in part the channel (64) in which this insert (80, 802, 804) is disposed.

8. Monopolar plate according to any one of claims 3 to 7, characterized in that the channels (64) are delimited by ribs (52, 54) arranged between the two monopolar half-plates (32, 34) and in that each insert (80, 802, 804) has a shape complementary to at least part of the ribs (52, 54) which delimit the channel (64) in which this insert (80, 802, 804) is arranged.

9. Monopolar plate according to any one of the preceding claims, characterized in that the insert (80, 802, 804) is rigid.

10. Monopolar plate according to claim 9, characterized in that the insert (80, 802, 804) is a single-material part, made of metal or plastic material, or is a two-material part.

11. Monopolar plate according to any one of claims 1 to 8, characterized in that the insert (80, 802, 804) is made of deformable three-dimensional foam or mesh.

12. A method for manufacturing a monopolar plate (30) according to any one of the preceding claims, wherein the two monopolar half-plates (32, 34) are manufactured by stamping, forming at least at the homogenization zone (62) reliefs defining, between them, the fluidic communication space, characterized in that this method comprises at least two successive steps consisting of a. inserting between the reliefs of at least one of the two monopolar half-plates (32, 34) at least one insert (80, 802, 804) for reducing the volume of the fluidic communication space, b. joining the two monopolar half-plates (32, 34) by trapping the insert (80, 802, 804) between them.

13. Fuel cell (2), comprising a stack (4) of active electrochemical cells (6) defined by bipolar plates (20) and two monopolar plates (30) constituting the ends of the stack of active electrochemical cells, characterized in that at least one of the monopolar plates (30) is according to any one of claims 1 to 11 or manufactured by a process according to claim 12.

14. Fuel cell according to claim 13, characterized in that the bipolar plates (20) each comprise two bipolar half-plates (22, 24) and in that the monopolar half-plates (32, 34) of the monopolar plates (30) have the same geometry as the bipolar half-plates (22, 24) of the bipolar plates (20).

15. Fuel cell according to any one of claims 13 and 14, wherein the monopolar plate is according to claim 3, characterized in that the area (A'64) of a passage section (2'64) of a first channel (64) of the monopolar plate (30) equipped with an insert (80, 802, 804) is less than the area (A64) of the passage section (2164) of a second channel (164) of a bipolar plate (20) of the stack (4) of active electrochemical cells (6), the first channel and the second channel being respectively disposed in the same places in the respective homogenization zones (62) of the monopolar plate (30) and the bipolar plate (20).

Images