EP3662529A1

EP3662529A1 - Bipolar plate for improving the efficiency of a proton-exchange membrane fuel cell

Info

Publication number: EP3662529A1
Application number: EP18773527.9A
Authority: EP
Inventors: Eric Pinton; Jean-Philippe Poirot-Crouvezier
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2017-08-04
Filing date: 2018-07-24
Publication date: 2020-06-10
Also published as: CN111052469A; FR3069961B1; WO2019025701A1; CN111052469B; FR3069961A1

Abstract

The invention concerns a bipolar plate (5) for a proton-exchange membrane fuel cell (113), comprising: - an oxidiser inlet manifold and an oxidiser outlet manifold; - oxidiser flow channels (541) of an active area (54); - an inlet homogenisation area (52); - an exhaust homogenisation area; for a Reynolds number of the flow of oxidiser in the exhaust homogenisation area of between 1000 and 2000: - linear head losses through the exhaust homogenisation area make up more than 80% of the head losses dP2 between the active area (54) and the oxidiser outlet manifold; - the value dP2/dP1 is at least equal to 2, dP1 being the head losses between the oxidiser inlet manifold and the active area (54).

Description

BIPOLAR PLATE FOR IMPROVING THE PERFORMANCE OF A PROTON EXCHANGE MEMBRANE FUEL CELL

The invention relates to electrochemical reactors with membrane-electrode assemblies, such as low temperature fuel cells. In particular, the invention relates to optimizing the energy efficiency of a proton exchange membrane fuel cell.

Fuel cells are for example envisaged as a power supply system for motor vehicles produced in large scale in the future, as well as for a large number of applications. A fuel cell is an electrochemical device that converts chemical energy directly into electrical energy. A fuel such as dihydrogen or methanol is used as the fuel of the fuel cell.

In the case of dihydrogen, it is oxidized and ionized on one electrode of the cell and an oxidizer is reduced on another electrode in the cell. The chemical reaction produces water at the cathode, with oxygen being reduced and reacting with the protons. The great advantage of the fuel cell is that it avoids releases of atmospheric pollutants at the place of generation.

Proton exchange membrane fuel cells, called PEMs, operate at low temperatures and have particularly advantageous compactness properties. Each cell comprises an electrolyte membrane allowing only the passage of protons and not the passage of electrons. The membrane comprises an anode on a first face and a cathode on a second face to form a membrane / electrode assembly called AME.

At the anode, dihydrogen is ionized to produce protons crossing the membrane. The electrons produced by this reaction migrate to a flow plate and then pass through an electrical circuit external to the cell to form an electric current. At the cathode, oxygen is reduced and reacts with the protons to form water.

The fuel cell may comprise several so-called bipolar plates, for example made of metal, stacked on top of one another. The membrane is disposed between two bipolar plates. Bipolar plates may include channels and outlets for guiding reagents and products to / from the membrane, guiding coolant, and separating different compartments. Bipolar plates are also electrically conductive to form collectors of electrons generated at the anode. According to a relatively frequent design, a bipolar plate is formed of two metal sheets assembled by welding and generally providing between them channels for the flow of a coolant.

Bipolar plates also have a mechanical function of transmission of clamping forces of the stack, necessary for the quality of the electrical contact. Gaseous diffusion layers are interposed between the electrodes and the bipolar plates and are in contact with the bipolar plates. Electronic conduction is performed through the bipolar plates, ionic conduction being obtained through the membrane.

The bipolar plates continuously feed the reactive surfaces of the electrodes into reagents, as and when they are consumed. The bipolar plates comprise flow channel networks ensuring the distribution of reagents in the reactive zones. The flow channel arrays are connected between input and output collectors, generally traversing the stack from side to side. Each manifold is surrounded by a seal to prevent mixing of the different fluids circulating in the stack. A homogenizer zone most commonly connects an inlet or outlet manifold to flow channels. The function of the homogenization zones is to obtain a flow of a reagent with the most homogeneous pressure and flow possible through the different flow channels. The passage of reagents from an inlet manifold to an outlet manifold, through the flow channels of an active zone, induces a pressure drop.

The pressure drop in the cathode channels generally has a sufficiently high level to allow the evacuation of liquid water produced by the reaction.

The efficiency of the fuel cell increases with the oxidant pressure in the flow channels of the active zone. A pump therefore generally compresses the oxidizer to feed an inlet manifold by oxidizing under pressure, and to at least compensate for the pressure drop of the cathode line. To optimize the energy efficiency of the fuel cell system, the oxidant pressure must not reach an excessive level, the power consumption of the pump increasing with the level of oxidant pressure applied. There is therefore an optimal operating pressure which maximizes the efficiency of the fuel cell system.

Due to the pressure drop in the input homogenization zone between the oxidizer inlet manifold and the cathode flow channels, the pressure applied by the compressor at the inlet of the oxidizer inlet manifold must correspond to the optimal pressure in the active zone, relieved of the amplitude of these pressure drops. In order to maintain this optimum pressure in the active zone, it is also necessary to maintain relatively high pressure drops downstream of the active zone.

Since the pressure drop in the exhaust homogenization zone is insufficient to guarantee optimum pressure in the active zone, it is known to place a counter-pressure valve downstream of the oxidizer outlet manifold.

Such a valve, however, involves including a water condenser and a gas / water separator between the oxidizer outlet manifold and said valve to be able to regulate the oxidant pressure on a dry gas. In addition, such a valve induces large oscillations of the pressure in the active zone when starting the fuel cell.

It is also known to place calibrated flow restriction orifices downstream of the oxidizer outlet manifold. These are flow restrictors placed on the cathode circuit downstream of the cell. The pressure drops are then greatly increased at these ports. Figure 1 is a schematic diagram of the profile of the relative pressure in different sections of a cathode flow, from an inlet manifold to an exhaust manifold. The ZHE zone corresponds to the input homogenization zone, zone ZA corresponds to the active zone, the ZHS zone corresponds to the exhaust homogenization zone, and the OC zone corresponds to the calibrated orifices.

Such fuel cells provided with a flow limiter have drawbacks. The cathodic pressure drops are not sufficient to guarantee the optimum pressure over the entire range of the desired operating regime. The energy efficiency of the fuel cell system is then deteriorated. The energy efficiency is further removed from the theoretical maximum energy efficiency, the compression efficiency of the oxidizer pump is high. In addition, such fuel cells generate parasitic water retention points on the flow, inducing the use of a condenser and a phase separator.

The invention aims to solve one or more of these disadvantages. The invention thus relates to a bipolar plate for a fuel cell with a proton exchange membrane as defined in the appended claims.

The invention also relates to the variants of the dependent claims. It will be understood by those skilled in the art that each of the features of the variants of the dependent claims may be independently combined with the features of an independent claim, without necessarily constituting an intermediate generalization. The invention also relates to a fuel cell as defined in the appended claims.

Other characteristics and advantages of the invention will emerge clearly from the description which is given hereinafter, by way of indication and in no way limitative, with reference to the appended drawings, in which:

FIG 1 is a schematic diagram of the cathodic relative pressure of a fuel cell according to the state of the art;

FIG. 2 is an exploded perspective view of an exemplary stack of membrane / electrode assemblies and bipolar plates for a fuel cell;

FIG. 3 is a view from above of an example of a bipolar fuel cell plate having a cross-flow cooling circuit with respect to fuel and oxidant with parallel flows;

FIG 4 is a schematic sectional view of a fuel cell at an oxidizer inlet homogenization zone;

FIG 5 is a schematic sectional view of a fuel cell at an oxidizer exhaust homogenization zone;

FIG. 6 is a view from above of an exemplary configuration of a bipolar plate at an oxidizer exhaust homogenization zone;

FIG. 7 is a view from above of another exemplary configuration of a bipolar plate at an oxidizer exhaust homogenization zone;

FIG. 8 is a comparative diagram of the relative pressures in different sections of different fuel cell configurations;

FIG. 9 is a comparative diagram of the relative pressure at the inlet of the flow collector for different configurations of fuel cells;

FIG. 10 is a view from above of an example of a bipolar fuel cell plate having a parallel flow cooling circuit with respect to fuel and oxidant.

Figure 2 is a schematic exploded perspective view of a stack of cells 1 of a fuel cell 4. The fuel cell 4 comprises a plurality of cells 1 superimposed. The cells 1 are of the proton exchange membrane or polymer electrolyte membrane type.

The fuel cell 4 comprises a fuel source 40. The fuel source 40 supplies an inlet of each cell 1 with dihydrogen. The fuel cell 4 also includes a source of oxidant 42. The source of oxidant 42 supplies an inlet of each cell 1 with air, the oxygen of the air being used as oxidant. Each cell 1 also includes exhaust channels. One or more cells 1 also have a cooling circuit.

Each cell 1 comprises a membrane / electrode assembly 1 10 or

AME 1 10. A membrane / electrode assembly 1 10 comprises a solid electrolyte 1 13, a cathode (not shown) and an anode 1 1 1 placed on either side of the electrolyte and fixed on this electrolyte 1 13. The electrolyte layer 1 13 forms a semipermeable membrane allowing proton conduction while being impervious to gases present in the cell. The electrolyte layer also prevents the passage of electrons between the anode 11 and the cathode.

Between each pair of adjacent MEAs, a bipolar plate 5 is disposed. Each bipolar plate 5 defines anode flow channels and cathodic flow channels on opposite external faces. Bipolar plates 5 advantageously also define coolant flow channels between two successive membrane / electrode assemblies. The bipolar plates 5 may be each formed in a manner known per se from two conductive metal sheets assembled, for example stainless steel, or titanium alloy, aluminum alloy, nickel alloy or tantalum alloy. Each sheet then defines a respective outer face. Bipolar plates can also be obtained by any other method, for example molding or injection from carbon-polymer composites. The bipolar plates 5 can thus also be formed in one piece. The outer faces of the bipolar plate 5 are then defined by such a piece in one piece.

The stack may also include peripheral seals and membrane reinforcements not shown here. Each cell 1 may further comprise a gas diffusion layer (not shown) disposed between the anode and a bipolar plate, and another gas diffusion layer disposed between the cathode and another bipolar plate.

In a manner known per se, during the operation of the fuel cell 4, air flows between an AME and a bipolar plate, and dihydrogen flows between this AME and another bipolar plate. At the anode, dihydrogen is ionized to produce protons that pass through ΑΜΕ. The electrons produced by this reaction are collected by a bipolar plate 5. The electrons produced are then applied to an electrical charge connected to the fuel cell 4 to form an electric current. At the cathode, oxygen is reduced and reacts with the protons to form water. The reactions at the anode and the cathode are governed as follows: ¾ ^→ ^ ⁺ + 2 at the anode;

H ^' + 4e + (. ~ → 2H ₂ 0 _{at the} level of the cathode.

During its operation, a cell 1 of the fuel cell 4 usually generates a DC voltage between the anode and the cathode of the order of 1 V.

The source of oxidant 42 typically comprises a compressor for introducing air at a given pressure to the inlet of cells 1. Such a compressor receives for example an air pressure setpoint, the air pressure can be regulated by a variable speed of rotation of the compressor.

The stack of bipolar plates 5 and membrane / electrode assemblies 1 10 is intended to form a plurality of flow collectors. For this purpose, respective orifices (591 to 596, illustrated in Figure 3) are formed through the bipolar plates 5 and through the membrane / electrode assemblies 1 10. The orifices of the bipolar plates 5 and the membrane / electrode assemblies 1 10 are arranged vis-à-vis to form the different flow collectors.

Figure 3 is a schematic top view of an exemplary bipolar plate 5, other flow channel configurations may be contemplated. The bipolar plates 5 thus have orifices 591 and 593 at a first longitudinal end, orifices 595 and 596 at a second longitudinal end, an orifice 593 at a first lateral end, and an orifice 594. at a second lateral end.

The orifice 591 serves for example to form a fuel supply manifold, the orifice 596 serves for example to form an exhaust collector exhaust combustion and unused fuel. The orifice 593 serves for example to form a coolant supply manifold, the orifice 594 serves for example to form a coolant discharge manifold. The orifice 592 serves, for example, to form an oxidizer supply manifold, and the orifice 595 serves, for example, to form a collector for discharging produced water and unused oxidant.

The outer face illustrated for the bipolar plate 5 comprises ribs delimiting flow channels for a reagent, for example the fuel. The zone comprising the flow channels corresponds to the active zone 54 of the electrochemical cell. The flow channels are here intended to connect the collectors 592 and 595. An inlet homogenization zone 52 connects the collector 592 to the inlet 545 of the flow channels of the zone 54. An exhaust homogenization zone 55 connects the manifold 595 to the outlet 546 of the flow channels of the active zone 54. FIGS. 4 and 5 further illustrate the geometry of various homogenization zones.

The bipolar plate 5 here comprises a cross-flow cooling circuit with respect to the fuel and oxidant flows. The fuel and oxidant flows are here parallel. Other configurations may of course be considered in the context of the invention.

The purpose of a bipolar plate 5 according to the invention is to optimize the energy efficiency of the fuel cell 4 without inducing excessive structural complexity. The fuel efficiency of the fuel cell 4 can be defined as the ratio between the electrical energy generated by the fuel cell and the chemical energy theoretically available by the fuel consumption. A bipolar plate 5 according to the invention aims in particular to avoid the need for the use of a condenser and a phase separator in the oxidizer flow circuit.

The pressure drops of the combustion circuit in the bipolar plate 5 are distributed as follows: dP1 between the inlet manifold 592 and the active zone 54, dP2 between the active zone 54 and the outlet manifold 595 and dP3 the along the active zone within the 541 canals. In the context of the invention within this bipolar plate 5, it is advantageous to ensure that the pressure drops remain regular and therefore linear as much as possible and judiciously distributed.

Thus, the bipolar plate 5 according to the invention is configured so that, for a Reynolds number of the flow of the oxidant in the exhaust homogenization zone 55 between 1000 and 2000:

the linear pressure losses across the exhaust homogenization zone 55 constitute more than 80% of the pressure losses dP2, and preferably more than 90% of the pressure drops dP2;

the value dP2 / dP1 is at least equal to 2, preferably at least equal to 3. The value dP2 / dP1 is advantageously at most equal to 10.

A Reynolds number of the oxidant flow in the exhaust homogenization zone 55 between 1000 and 2000 is fairly representative of the flow conditions for a full power fuel cell. This Reynolds number range serves as a reference for verifying that the pressure drop conditions are well met according to the invention.

Linear pressure losses in a homogenization zone are obtained when this oxidant is channeled so as to form a laminar flow. For example, linear pressure drops of suitable amplitude are obtained by adequate sizing of the passage section in this homogenization zone, or by inclination more or less marked flow channels of the homogenization zone with respect to the direction of flow in the active zone. This passage section is for example defined by the width and height of flow channels in this homogenization zone, and / or the height and the number of raised studs possibly formed in this homogenization zone.

By configuring the exhaust homogenization zone 55 so that the pressure drops therein are essentially linear, the fuel efficiency of the fuel cell 4 is improved, in particular for intermediate power levels. By setting the value dP2 / dP1 to a sufficient level, the exhaust homogenization zone 55 makes it possible to obtain an oxidant pressure at the inlet 545 of the channels 541 having a relatively high amplitude, favoring the energy efficiency of the battery In addition, this passive management of the pressure downstream of the flow within the bipolar plate 5 allows a simplified management of the water formed because it does not require the use of a condenser or of a phase separator as in the case of the solutions of the state of the art. Thus, the oxidant exhaust system of the fuel cell 4 may be devoid of water condenser and gas / water separator downstream of the oxidizer outlet manifold 595.

The flow downstream of the exhaust homogenization zone 55 is, for example, typically without an active counter-pressure valve and without calibrated orifices of the flow restrictor type on the oxidizer line, which is likely to cause the majority of the losses. charge in this exhaust homogenization zone. Such flow restrictions are such as to form a turbulent flow of the oxidant and to be sensitive to the presence of water in the cathodic output mixture.

Figure 4 is a schematic sectional view of an example of a fuel cell at an oxidizer inlet homogenization zone. FIG. 5 is a schematic cross-sectional view of this fuel cell at its oxidizer exhaust homogenization zone. In the configuration illustrated, each membrane / electrode assembly 1 10 comprises a reinforcement 1 14 fixed to the periphery of its membrane 1 13.

An oxidizer inlet flow channel 521 of the homogenization zone 52 is here illustrated (inlet flow channels 521 are in particular present in a shaded area of the arrow illustrating a flow). This flow channel 521 is formed in particular between a face 525 of the bipolar plate 5 and a reinforcement of a membrane / electrode assembly. The height of the flow channel 521 corresponds to the distance between this face 525 and this reinforcement. A fuel exhaust flow channel 522 is provided between a face 526 of the bipolar plate 5 and a reinforcement 11 of another membrane / electrode assembly 1 10, vertically above the inlet homogenization zone. of oxidizer.

The height of the flow channel 521 is here increased relative to the height of the flow channel 522, in order to reduce the pressure drops in the oxidizer inlet homogenization zone 52. The increase in the height of the channels flow 521 also makes it possible to reduce the height of the flow channels 522, which makes it possible to increase the pressure losses at the fuel exhaust, which favors the homogenization of the fuel in the homogenization zone of fuel input. In this example, the sum of the height of the fuel discharge homogenization zone and the height of the oxidizer inlet homogenization zone being equal to the sum of the height of the homogenization zone of the oxidizer exhaust and the height of the fuel inlet homogenization zone.

The height of the flow channel 521 here is greater than that of the oxidizer flow channels 541 of the active zone 54.

In this example, the bipolar plate 5 has fuel flow channels 542 on one side and oxidizer flow channels 541 on another side in its active zone 54. Coolant flow channels 543 are formed in the active zone 54 between the two faces of the bipolar plate. An oxidizer exhaust flow channel 551 of the homogenization zone 55 is here illustrated (inlet flow channels 551 are in particular present in a hatched area of the arrow illustrating a flow). This flow channel 551 is in particular formed between the face 525 of the bipolar plate 5 and a reinforcement of a membrane / electrode assembly. The height of the flow channel 551 corresponds to the distance between this face

525 and this reinforcement.

A fuel inlet flow channel 552 is provided between the face

526 of the bipolar plate 5 and a reinforcement 1 14 of another membrane / electrode assembly 1 10, vertically to the oxidizer exhaust homogenization zone.

The height of the flow channel 551 is here reduced relative to the height of the flow channel 552, to increase the linear pressure losses in the oxidizer exhaust homogenization zone 55. The height of the flow channel 551 is here lower than that of the oxidant flow channels 541 of the active zone 54. For example, the height of the flow channels 521 may be at least twice that of the flow channels 551.

FIG. 6 is a schematic top view of an example of a bipolar plate 5 at its exhaust homogenization zone 55. The linear pressure losses in this exhaust homogenization zone 55 are here obtained by means of FIG. flow channels 551 having reduced sections.

A similar geometry can be used for the input homogenization zone 52, with greater depths of the flow channels 521.

A design to obtain a high dP2 / dP1 ratio may for example consist in having an average passage section in the inlet homogenization zone 52 which is at least twice that of the homogenization zone. Exhaust 55.

The aim of the invention is both a reduction in the oxidant input (dP1) pressure losses in front of the output losses (dP2), while seeking to make them as linear as possible all along the flow.

Advantageously, it is possible to configure the oxidizer inlet homogenization zone 52 so that the linear pressure losses therethrough constitute more than 80% of the pressure losses dP1 between the oxidizer inlet manifold 592 and the oxidant flow channels 541, and preferably more than 90% of dP1 pressure drops.

Thus, the pressure drop in the oxidizer inlet homogenization zone 52 is reduced for the same oxidant pressure in the active zone 54 by decreasing dP1 in front of dP2 and an improvement in the overall energy efficiency of the fuel cell is obtained. 4 having a strong linear contribution of the homogenization zone 52 in dP1.

To test the characteristics of a bipolar plate 5, it will be possible to position pressure sensors in the oxidizer inlet homogenization zone 52 and in the oxidizer outlet homogenization zone 55. Once the bipolar plate is contiguous with suitable for a membrane / electrode assembly and its oxidant inlet collector fed by an oxidizer compressor, it will then be possible to check the pressure drop values in these homogenization zones, for the Reynolds number values given in FIG. oxidizer outlet homogenization zone 55. FIG. 7 is a schematic top view of another example of a bipolar plate 5 at its exhaust homogenization zone 55. The linear pressure losses in this exhaust homogenization zone 55 are here obtained by a multitude of relief studs 554 positioned in zone 55.

A similar geometry can be used for the inlet homogenization zone 52, with greater depths of flow or with pads 554 less high. Figure 8 is a comparative diagram of pressures in different sections of different fuel cell configurations. The curve in solid line corresponds to a fuel cell provided with a bipolar plate according to the invention, with an optimization of the pressure losses. The dashed curve corresponds to a fuel cell provided with a bipolar plate according to the state of the art having flow limiters. These flow limiters induce load losses proportional to the square of the velocity of the oxidant passing through them. The bipolar plates have the same active zone.

Optimization in the oxidizer inlet ZHE homogenization zone makes it possible to reduce the oxidant pressure that the pump must apply to the oxidant to obtain the same pressure at the inlet of the active zone. The power consumption of the compressor is thus reduced. The oxidizer exhaust homogenization zone for the bipolar plate according to the invention has substantially uniform pressure drops along the length of the flow between the active zone and the oxidizer exhaust manifold.

Figure 9 is a comparative diagram of the flow manifold inlet relative pressure for different fuel cell configurations, as a function of the electrical power generated by these fuel cells.

The dashed curve corresponds to a theoretical configuration presenting the optimum energy efficiency, for an oxidizer compressor having a given compression efficiency. The greater the difference between this curve and a characteristic curve of a real fuel cell is important for a given power, the lower the energy efficiency for this power. The dashed curve corresponds to the use of a flow limiter according to the state of the art with the same compression pump. The solid line curve corresponds to a bipolar plate for a flow of laminar oxidant in the exhaust zone, object of the invention. Energy efficiency is improved especially for power operating intermediates. A bipolar plate according to the invention thus promotes the use of a fuel cell with a certain dynamic.

The dash-dot curve corresponds to a bipolar plate according to the invention, for a mixed laminar / turbulent flow. Even for such a flow, the energy yield obtained with a bipolar plate according to the invention remains better than that obtained with a flow limiter according to the state of the art (dashed curve).

The hydraulic diameter of an oxidant flow channel in the active zone of a bipolar plate according to the state of the art is typically between 0.35 and 0.4 mm. For an operating point with an average pressure of 1.5 bar in the active zone, with Stcomburant = 2 (ratio of the total oxidant flow rate to oxidizer flow consumed by the cell), a density of 1.5A / cm ² , the number Reynolds of the oxidant flow in the active zone is 240. With a configuration of an oxidizer exhaust homogenization zone according to the state of the art, the oxidant is accelerated and the Reynolds number is then typically between 500 and 1000. With a bipolar plate according to the invention which would halve the section of oxidant passage in the oxidizer exhaust homogenization zone, the Reynolds number would reach at most 2000, which would keep a laminar regime.

It should be noted that the higher the compression efficiency of the oxidizer pump, the more the invention makes it possible to increase the fuel efficiency of the fuel cell 4. Thus, the invention proves particularly advantageous when the oxidizer pump has a compression yield at least equal to 75%, or preferably at least equal to 80%. Such a yield is for example that corresponding to nominal operating conditions of the pump, for example when the oxidizer is air.

Figure 10 is a schematic top view of another exemplary bipolar plate. The bipolar plates 5 thus have orifices 591 to 593 at a first longitudinal end, orifices 594 to 596 at a second longitudinal end. The bipolar plate 5 here comprises a parallel current cooling circuit with respect to fuel and oxidant flows.

The orifice 591 forms a fuel supply manifold, the orifice 596 forms a combustion residue evacuation manifold. Port 593 forms a coolant supply manifold, port 594 forms a coolant discharge manifold. Port 592 forms a oxidizer feed manifold, and the orifice 595 forms a waste water discharge manifold and unused oxidant.

Coolant channels are thus superimposed on the oxidizer and fuel flow channels of the homogenization zones 52 and 55.

In this example, it is possible to modulate the depth of the oxidant and / or fuel flow channels in a homogenization zone 52 or 55, correspondingly adapting the depth of the coolant flow channels in this zone. homogenization. Changing the depth of the coolant channels may have less impact on the operating parameters than changing the flow channel depth of another reagent.

Thus, to reduce the height of the oxidizer flow channels in the homogenization zone 55, superimposed coolant channels having a height greater than the height of the coolant channels in the active zone 54 may be used.

Similarly, in order to increase the height of the oxidizer inlet channels in the homogenization zone 52, superimposed coolant channels having a height less than the height of the coolant channels in the zone may be used. active 54.

Claims

Bipolar plate (5) for a proton exchange membrane fuel cell (4), comprising:

an oxidizer inlet manifold (592) and an oxidizer outlet manifold (595);

oxidant flow channels (541) of an active zone (54);

an inlet homogenization zone (52) having flow channels and connecting the oxidant flow channels (541) to the oxidizer inlet manifold (592);

an exhaust homogenization zone (55) connecting the oxidizer flow channels (541) to the oxidizer outlet manifold (595); Characterized in that, for a Reynolds number of the oxidant flow in the exhaust homogenization zone (55) between 1000 and 2000:

linear pressure losses across the exhaust homogenization zone (55) constitute more than 80% of the pressure losses dP2 between the active zone (54) and the oxidizer outlet manifold (595);

the value dP2 / dP1 is at least equal to 2, with dP1 the losses of charges between the oxidizer inlet manifold (592) and the active zone (54).

A bipolar plate (5) according to claim 1, wherein the average passage section in the input homogenization zone (52) is at least twice that of the exhaust homogenization zone (55).

A bipolar plate (5) according to claim 1 or claim 2, wherein the exhaust homogenization zone (55) comprises flow channels, the flow channels in the input homogenization zone (52). ) having a depth at least twice that of the flow channels (551) in the exhaust homogenization zone (55).

A bipolar plate (5) according to claim 3, wherein the depth of the flow channels (521) of the input homogenization zone (52) is strictly greater than that of the oxidant flow channels (541) of the active area (54).

A bipolar plate according to any one of claims 2 to 4, comprising: a fuel inlet manifold (591) and a fuel evacuation manifold (596);

fuel flow channels (542) of the active zone; a fuel input homogenization zone connecting the fuel flow channels to the fuel inlet manifold (591);

a fuel evacuation homogenization zone (596) connecting the fuel flow channels (542) to the fuel evacuation manifold (596);

a part of the fuel inlet homogenization zone being superimposed on the oxidizer exhaust homogenisation zone; part of the fuel evaporation homogenization zone being superimposed on the oxidizer inlet homogenization zone, the sum of the height of the fuel evaporation homogenisation zone and the height of the an oxidizer inlet homogenization zone being equal to the sum of the height of the oxidizer exhaust homogenization zone and the height of the fuel inlet homogenization zone.

Bipolar plate according to any one of claims 2 to 4, comprising:

a coolant inlet manifold (593) and a coolant discharge manifold (594);

coolant flow channels (543) of the active zone;

a connection zone between the coolant inlet manifold

(593) and said coolant flow channels (543); a connection zone between the coolant outlet manifold

(594) and said coolant flow channels (543); a part of a connecting zone being superimposed on the oxidizer exhaust homogenization zone, the height of the superimposed connecting zone being greater than the height of the coolant flow channels (543) of the active area. 7. Bipolar plate (5) according to any one of the preceding claims, wherein the inlet homogenization zone (52) and the exhaust homogenization zone (55) comprise studs (554) in relief.

8. bipolar plate (5) according to any one of the preceding claims, wherein linear pressure losses across the input homogenization zone (52) constitute more than 80% of the pressure losses dP1 between the active zone (54) and the oxidizer inlet manifold (592). 9. Fuel cell (4), comprising a bipolar plate (5) according to any one of the preceding claims;

a membrane / electrode assembly (1 10) comprising a proton exchange membrane (1 13) and a cathode (1 12) covering a median portion of the proton exchange membrane and covering the active zone (54) of the bipolar plate ( 5).

The fuel cell (4) of claim 9 including a pump configured to supply the oxidizer inlet manifold (592) with pressure oxidizer.

1 1. The fuel cell (4) of claim 10, wherein said pump has an oxidizer compression efficiency of at least 75%. Fuel cell according to claim 10 or 11, the fuel cell being devoid of water condenser and gas / water separator downstream of the oxidizer outlet manifold (595).

13. Fuel cell (4) according to claim 1 1, wherein said pump has an oxidizer compression efficiency at least equal to 75% under its nominal operating conditions, when the oxidizer is air.