FR3035543A1 - ENHANCED BIPOLAR FUEL CELL PLATE PROVIDING HOMOGENEOUS FLUID DISTRIBUTION - Google Patents

Abstract

Bipolar plate (2) for producing a proton exchange membrane fuel cell stack, said bipolar plate (2) comprising - a proximal region (20A) and a distal region (20B) of the bipolar plate (2) for supplying fluid, - primary fluid delivery channels (24) and secondary fluid delivery channels (25) - a central region (20C), wherein the primary (24) and secondary (24) channels ( 25) provide a flow of fluids in the longitudinal direction of the bipolar plate (2), the bipolar plate (2) being characterized in that it comprises a proximal distribution zone (30A) and a distal distribution zone (30B) , respectively provided between the proximal region (20A) and the central region (20C), and between the distal region (20B) and the central region (20C), wherein the assembled plates also form primary distribution channels configured toperforming a fluid distribution between the primary channels (24).

Description

TECHNICAL FIELD The present invention relates to the field of fuel cells, and more particularly to fuel cells intended for applications in the field of aeronautics. STATE OF THE ART The fuel cells have an operating principle associated with electrochemical reactions electrodes separated by an electrolyte. In the case of H2 and 02 fuel cells, electrochemical reactions lead to the generation of water, electricity and heat. Proton exchange membrane fuel cells are typically formed by assembling elementary cells. They consist of membrane electrode assembly "AME" or "MEA" according to the English name, seals and bipolar plates formed from thin sheets shaped and assembled in pairs, so as to form coolant channels in which a coolant circulates, reagent channels for reagent circulation, support and contact areas with the electrodes and support surfaces for positioning and compression of the sealing elements of the different canals.

The bipolar plates have wells for feeding and discharging the reagents and heat transfer fluid so as to produce a flow in a longitudinal direction of each plate.

FIG. 1 thus presents an overview of an example of a conventional bipolar plate, and FIGS. 2 and 3 are cross-sectional views illustrating two conventional channel geometries of such a bipolar plate.

FIG. 1 thus represents a bipolar plate 1 extending in a longitudinal direction marked by the X-X axis, and also defining a transverse direction marked by the Y-Y axis.

This bipolar plate 1 is formed of assembled plates, thus defining primary and secondary channels for the circulation of reagents and heat transfer fluid in the longitudinal direction of the bipolar plate 1. The bipolar plate 1 also comprises wells 11 making it possible to carry out the process. supply and fluid discharge of the various channels, these wells being disposed near the two ends of the bipolar plate 1 in the longitudinal direction. Such bipolar plates are stacked to form a stack or stack of fuel cells, the adjacent bipolar plates 1 being separated by an electrode membrane assembly.

The primary channels are formed within the bipolar plate, and entirely delimited by the forming sheets. These primary channels are typically used to achieve a circulation of heat transfer fluid, thus ensuring in particular the cooling of the bipolar plate.

The secondary channels are delimited on the one hand by the bipolar plate 1, and on the other hand by the "Membrane Electrode Assembly" or "AME", thus defining a circulation zone of the reactive gases and products of the reaction.

Figures 2 and 3 show two bipolar plate geometries, thus defining two primary and secondary 12 channel geometries 13, these figures being a partial sectional view in the transverse direction of a bipolar plate. FIG. 2 shows a bipolar plate structure formed of nested sheets 30 while FIG. 3 shows a bipolar plate structure formed of sheets joined together, as well as the AME 14 surrounding these bipolar plates.

In order to optimize the operation, and in particular the life of the fuel cell, the distribution of the fluids in the different primary and secondary channels must be as homogeneous as possible. However, it is well understood that the multiplicity of channels formed in each bipolar plate causes a non-homogeneity of the distribution of fluids (reactants and heat transfer fluid), in particular as a function of the position of each channel relative to the associated wells. In addition, the processes for manufacturing bipolar plates from two assembled sheets involve several constraints, particularly in terms of mechanical strength due to the compression force applied for the assembly of the sheets, and also in terms of geometry so to allow the assembly of two identical sheets. The use of geometries based on the assembly of two identical sheets 15 in order to obtain a bipolar plate makes it possible in fact to simplify the process of shaping the sheets and the use of a single mold. PRESENTATION OF THE INVENTION The present invention thus aims at remedying at least partially these problems, and proposes a bipolar plate for the production of a fuel cell stack with proton exchange membranes, said bipolar plate being composed of metal plates. shaped and 25, and extending in a longitudinal direction to define a proximal end and a distal end of the bipolar plate, the bipolar plate comprising - wells for feeding and discharging fluids, arranged in a proximal region and a distal region of the bipolar plate, primary fluid delivery channels and secondary fluid delivery channels providing fluid flow between the proximal region and the distal region of the bipolar plate, said primary channels being formed between said assembled sheets, 3035543 4 - a central region, in which the primary and secondary channels perform fluid circulation in the longitudinal direction of the bipolar plate, the bipolar plate being characterized in that it comprises a zone 5 of proximal distribution and a distal distribution zone, respectively arranged between the proximal region and the central region, and between the distal region and the central region, wherein the assembled plates also form primary distribution channels configured to provide fluid distribution between the different primary channels. Said primary distribution channels are for example channels arranged between adjacent primary channels, in a transverse direction of the bipolar plate, perpendicular to the longitudinal direction. For example, the primary distribution channels are formed by keeping the plates forming the bipolar plate spaced apart in the proximal and distal distribution zones.

The bipolar plate may also be such that in the proximal and distal distribution zones the assembled plates also form secondary distribution channels configured to provide a transverse fluid distribution between the different secondary channels. . Said secondary distribution channels are for example channels arranged between adjacent secondary channels, in a transverse direction of the bipolar plate, perpendicular to the longitudinal direction.

The proximal and distal distribution zones may comprise mechanical reinforcements adapted to oppose a compression force in a direction normal to the bipolar plate. Said mechanical reinforcements are for example made of conductive material, and provide an electrical connection between the sheets forming the bipolar plate. The proximal and distal distribution areas have for example a generally rectangular shape, or pentagon.

The invention also relates to a fuel cell comprising a stack in a normal direction of a plurality of elementary cells arranged between two terminal plates, each elementary cell comprising bipolar plates as defined above and a membrane-electrode assembly, the mechanical reinforcements of said bipolar plates opposing a compression force applied on the stack in the normal direction. Said bipolar plates forming the stack are for example identical, and are then typically formed by means of the same forming tool. PRESENTATION OF THE FIGURES Other characteristics, objects and advantages of the invention will emerge from the description which follows, which is purely illustrative and nonlimiting, and which should be read with reference to the appended drawings, in which: FIG. previously presented the general structure of a bipolar plate; Figures 2 and 3 previously described show examples of channel structures of a bipolar plate; FIG. 4 shows an example of a bipolar plate according to one aspect of the invention; FIG. 5 shows another example of a bipolar plate according to one aspect of the invention; FIG. 6 is a detailed view of a proximal region of a bipolar plate according to one aspect of the invention; Figure 7 is a detailed view of a portion of Figure 6; - Figures 8 to 11 are sectional views along different planes of Figure 7; FIG. 12 shows an example of distribution of the fluids in the ducts of a bipolar plate according to one aspect of the invention.

In all the figures, the elements in common are identified by identical reference numerals. DETAILED DESCRIPTION FIGS. 4 and 5 show two examples of bipolar plate 2 according to one aspect of the invention. Just as the bipolar plate described above with reference to Figures 1 to 3, this bipolar plate 2 extending in a longitudinal direction marked by the axis X-X, and also defining a transverse direction marked by the Y-Y axis. Thus, two ends, respectively proximal 2A and distal 2B, are defined for the bipolar plate 2, these ends being designated arbitrarily in the longitudinal direction of the bipolar plate 2.

Wells 21 for the supply and discharge of heat transfer fluid and reagents are arranged near the longitudinal ends of the bipolar plate 2 in two regions designated as a proximal region 20A and a distal region 20B. bipolar plate 2.

The bipolar plate 2 also comprises a central region 20C, in which primary and secondary fluid-carrying conduits 227 run, producing a circulation of reagents and coolant in the longitudinal direction. The primary and secondary channels of the central region 20C have, for example, a structure as described above, with reference to FIGS. 2 and 3. In the central region 20C, the primary and secondary channels thus extend in the longitudinal direction, and are each distinct and isolated from other channels.

It is thus possible to form a stack (or "stack") of fuel cells by stacking such bipolar plates, between which membrane-electrode assemblies are interposed. The bipolar plate 2 also includes distribution areas, respectively a proximal delivery zone 30A and a distal delivery zone 30B, respectively provided between the proximal region 20A and the central region 20C, and between the distal region 20B and the central region. 20C.

In the embodiment shown in FIG. 4, the proximal 30A and distal 30B distribution zones have a generally rectangular shape. In the embodiment shown in FIG. 5, the proximal 30A and distal 30B distribution zones are generally pentagon-shaped having three sides forming a rectangular base, and two vertex-forming sides directed toward the central region 30C. The primary and secondary channels of the central region 20C or 30C extend into the proximal 30A and distal distribution areas 30B, so as to be connected to the wells 21 for circulating reagents and coolant in the channels. The proximal 30A and distal 30B distribution zones also comprise primary distribution channels and / or secondary distribution channels, adapted to achieve a homogeneous distribution of the fluid between the wells 21 on the one hand, and the primary and secondary conduits on the other hand.

More specifically, the proximal 30A and distal 30B distribution zones may comprise primary distribution channels, adapted to achieve a homogeneous distribution of fluid from the wells 21 supplying the primary channels with fluid to said primary channels, and vice versa, from the channels primary to the wells 21 1 0 discharging fluid flowing in said primary channels. These primary distribution channels are thus configured so that in the central region 20C or 30C, the flow of fluid in the different primary channels of the bipolar plate 2 or 3 is homogeneous.

Similarly, the proximal 30A and distal 30B distribution zones may comprise secondary delivery channels, adapted to provide a homogeneous distribution of fluid from the wells 21 supplying the fluid side channels to said primary channels, and vice versa, from the secondary channels to the wells 21 for discharging the fluid flowing in said secondary channels. These secondary distribution channels are thus configured so that in the central region 20C or 30C, the flow of fluid 25 in the different secondary channels of the bipolar plate 2 or 3 is homogeneous. FIG. 6 shows an example of a detailed structure of a proximal distribution zone 30A of a bipolar plate. The bipolar plate 30 also comprises a similar distal distribution zone, not shown in this figure. This figure shows a partial view of a bipolar plate, comprising lateral wells 21 connected to primary conduits 24 producing a flow of heat transfer fluid within the bipolar plate, in particular to ensure its cooling. As seen in this figure, the bipolar plate comprises a central region 30C in which the primary 24 and secondary 25 conduits (which are identified in FIGS. 8 to 11 hereinafter described) are isolated from each other, and extend in the longitudinal direction XX of the bipolar plate. The bipolar plate also comprises a proximal region 20A in which are arranged wells 21 for supplying the primary conduits with heat transfer fluid. The bipolar plate also comprises wells (not shown) for feeding the secondary conduits with reagents. The bipolar plate also includes a similar distal region, not shown in this figure.

As seen in this figure, the proximal delivery zone 30A is interposed between the central region 30C and the proximal region 20A, and provides a homogeneous fluid distribution between the wells 21 and the primary and / or secondary channels of the plate bipolar.

In the embodiment shown, the wells 21 for supplying and discharging the heat transfer fluid circulating in the primary channels are arranged on either side of the distribution zones in the transverse direction. Wells for feeding and evacuation of reagents circulating in the secondary channels are arranged at the proximal and distal ends of the bipolar plate. In the embodiment shown, this distribution is performed by means of distribution channels, connecting the different channels of the bipolar plate. Thus, there is shown in Figure 6 primary distribution channels, 30 distributed over the width of the bipolar plate, realizing a transverse distribution of fluid through these primary channels of distribution.

The structure of the primary distribution channels is detailed in FIGS. 7 to 11 by means of detailed views and sectional views. FIG. 7 thus details the transition zone between the proximal distribution zone 30A and the central region 30C.

FIGS. 8, 9 and 10 are cross-sectional views of the bipolar plate, in various planes shown in FIG. 7. As seen in FIGS. 8 to 10, the plates forming the bipolar plate are here formed in such a way as to they are spaced apart in the distribution zones 30A and 30B, while they are contiguous in the central region 20C or 30C so as to delimit the different primary channels. These figures show the primary channels 24 delimited within the bipolar plate, and the secondary channels 25 delimited on the one hand by the bipolar plate, and on the other hand by a membrane-electrode assembly (not shown). which is arranged on the bipolar plate during the realization of the stack. As seen in FIG. 10, in the central region 20C or 30C of the bipolar plate, the primary 24 and secondary 25 channels are separated from each other by the sheets forming the bipolar plate, the sheets then being typically welded or stuck on their contact areas. Conversely, in the distribution zones, the primary channels 24 are fluidly connected to each other, due to the spacing between the plates 25 forming the bipolar plate, as shown in FIG. 8. FIG. 9 represents the transition between the central region 20C or 30C and a distribution zone; the two sheets forming the bipolar plate have, at the limit of these zones, an evolution of shape tending to locally close the space between the two sheets in order to progressively move from a wave feed sheet to the primary circuit of the zone of distribution, at a primary channel separation 3035543 11 around each secondary channel in the central region 20C or 30C. Thus, in the distribution zones 30A and 30B, the primary channels 24 are interconnected by transverse channels that are called primary distribution channels, and here form a sheet producing a distribution of the fluid in particular in the transverse direction YY of the bipolar plate, upstream of the central region 20C or 30C, so that in the central region 20C or 30C, the fluid flowing in the primary channels 24 is distributed uniformly. In addition, according to an option shown in Figures 6, 7 and 11, the distribution zones may comprise contact areas 26 between the two sheets, so as to form mechanical reinforcements. These contact zones 26 between the sheets are typically limited, in order to ensure maximum distribution of the fluid between the different primary channels 24. The two sheets can be welded or bonded to these contact zones 26. These contact zones 26 forming mechanical reinforcements have several functions.

In the first place, they improve the crush resistance of the distribution zones, and thus ensure the maintenance of the spacing between the two plates of the bipolar plate in the distribution zones. In the case where the sheets are welded or bonded to the contact areas 26, they also provide a reinforcement against the deformations that may result from the pressure in the primary channels 24, which tends to separate the two sheets. In addition, these contact zones 26 also define secondary distribution channels 27 between the secondary channels 25 of the bipolar plate. Indeed, these contact areas form local flattening of the sheets, and thus allow to arrange passages between the secondary channels 25 defined by the corrugations of the sheets. The secondary distribution channels 27 may therefore also make it possible to distribute the reagents between the different secondary channels 25. The contact zones 26 may also contribute to guiding the fluids in the distribution zones 30A and 30B.

In addition, these contact zones 26 make it possible to ensure electrical continuity between the sheets forming the bipolar plate. The proximal 30A and 30B distal distribution zones thus formed thus make it possible to distribute and homogenize the distribution of the fluid 10 in the different primary and optionally secondary channels 24, so that the flow in the central region 20C or 30C the bipolar plate is uniform. FIG. 12 represents an example of distribution of the fluid of the wells 21 1 5 towards the primary channels 24 of the central region 20C or 30C, obtained by means of partitions arranged on the bipolar plates 2 thus making it possible to form various zones in which the fluid is distributed homogeneously. Thus, in FIG. 12, arrows denote the overall direction of circulation of the fluid, so that it is homogeneously distributed in the various zones which are for their part identified by means of braces. Such homogeneous distribution of fluids in the central region 20C or 30C of the bipolar plate is advantageous. It makes it possible to reduce the pressure drop, and therefore to reduce the power required for the systems that are incidental to the fuel cell thus formed, such as pumps and compressors serving in particular for the cooling circuit, and makes it possible to improve the fuel cell efficiency.

Moreover, a homogeneous distribution of the coolant in the primary channels 24 makes it possible to avoid or at least limit the formation of a temperature gradient in the fuel cell, and thus also contributes to improving the energy efficiency. of the system, as well as its lifetime. A homogeneous distribution of the reagents in the secondary conduits 25 also makes it possible to increase the use of the reagents, ie to limit the over-stoichiometry, and thus to obtain a higher chemical potential. The performances obtained are thus improved, without requiring an increase in the active surface of the fuel cell.

Claims (11)

REVENDICATIONS1. Bipolar plate (2) for producing a proton exchange membrane fuel cell stack, said bipolar plate (2) being composed of shaped and assembled plates and extending in a longitudinal direction (XX) of defining a proximal end (2A) and a distal end (2B) of the bipolar plate (2), the bipolar plate (2) comprising - wells (21) for feeding and discharging fluid arranged in a proximal region (20A) and a distal region (20B) of the bipolar plate (2), - primary fluid delivery channels (24) and fluid-carrying fluid secondary channels (25) providing fluid circulation between the proximal region (20A) and the distal region (20B) of the bipolar plate (2), said primary channels (24) being formed between said assembled plates, - a central region (20C), wherein the primary channels (24) ) and secondary (25) perform a circul fluidization in the longitudinal direction of the bipolar plate (2), the bipolar plate (2) being characterized in that it comprises a proximal distribution zone (30A) and a distal distribution zone (30B), arranged respectively between the proximal region (20A) and the central region (20C), and between the distal region (20B) and the central region (20C), wherein the assembled plates also form primary distribution channels configured to perform a distribution of fluid between the primary channels (24). The bipolar plate (2) according to claim 1, wherein said primary distribution channels are channels arranged between adjacent primary channels (24), in a transverse direction (YY) of the bipolar plate (2), perpendicular to the longitudinal direction (XX). 3035543 15 The bipolar plate (2) according to one of claims 1 or 2, wherein said primary distribution channels are formed by keeping the plates forming the bipolar plate (2) spaced apart in the proximal (30A) and distal (30A) distribution zones ( 30B). 5 4. bipolar plate (2) according to one of claims 1 to 3, wherein in the proximal distribution zone (30A) and in the distal distribution zone (30B), the assembled plates also form configured secondary distribution channels in order to achieve a fluid distribution between the secondary channels (25) Bipolar plate (2) according to claim 4, wherein said secondary distribution channels are channels arranged between adjacent secondary channels (24), in a transverse direction (Y-1 5 Y) of the bipolar plate (2). perpendicular to the longitudinal direction (XX). 6. bipolar plate (2) according to one of claims 1 to 5, wherein the proximal (30A) and distal (30B) distribution zones 20 comprise mechanical reinforcements adapted to oppose a compression force in one direction normal to the bipolar plate (2). The bipolar plate (2) according to claim 6, wherein said mechanical reinforcements are made of conductive material, and provide an electrical connection between the laminations forming the bipolar plate (2). Bipolar plate (2) according to one of claims 1 to 7, wherein the proximal (30A) and distal (30B) distribution zones 30 have a generally rectangular, or pentagon shape. 9. Fuel cell comprising a stack in a normal direction of a plurality of elementary cells arranged between two terminal plates, each elementary cell comprising bipolar plates (2) according to one of claims 1 to 8 and a membrane assembly -electrodes, the mechanical reinforcements of said bipolar plates (2) opposing a compression force applied on the stack in the normal direction. 10. Fuel cell according to claim 9, wherein said bipolar plates (2) forming the stack are identical. 10 11. Fuel cell according to claim 9, wherein said bipolar plates (2) forming the stack consist of two identical formed sheets by means of the same tool shaped me.