CN111052469B - Bipolar plate for improving efficiency of proton exchange membrane fuel cell - Google Patents

Bipolar plate for improving efficiency of proton exchange membrane fuel cell Download PDF

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Publication number
CN111052469B
CN111052469B CN201880058216.XA CN201880058216A CN111052469B CN 111052469 B CN111052469 B CN 111052469B CN 201880058216 A CN201880058216 A CN 201880058216A CN 111052469 B CN111052469 B CN 111052469B
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oxidant
zone
inlet
fuel
bipolar plate
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CN111052469A (en
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埃里克·潘东
让-菲利浦·普瓦罗-克鲁弗齐耶
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/0267—Collectors; Separators, e.g. bipolar separators; Interconnectors having heating or cooling means, e.g. heaters or coolant flow channels
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/0258—Collectors; Separators, e.g. bipolar separators; Interconnectors characterised by the configuration of channels, e.g. by the flow field of the reactant or coolant
    • H01M8/026—Collectors; Separators, e.g. bipolar separators; Interconnectors characterised by the configuration of channels, e.g. by the flow field of the reactant or coolant characterised by grooves, e.g. their pitch or depth
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/0258—Collectors; Separators, e.g. bipolar separators; Interconnectors characterised by the configuration of channels, e.g. by the flow field of the reactant or coolant
    • H01M8/0265—Collectors; Separators, e.g. bipolar separators; Interconnectors characterised by the configuration of channels, e.g. by the flow field of the reactant or coolant the reactant or coolant channels having varying cross sections
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M2008/1095—Fuel cells with polymeric electrolytes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Abstract

The invention relates to a bipolar plate (5) for a fuel cell having a proton exchange membrane (113), comprising: -an oxidant inlet manifold and an oxidant outlet manifold; -an oxidant flow channel (541) of the active region (54); -an inlet homogenization zone (52); -discharging the homogenized region; reynolds number for flow of oxidant exiting 1000 to 2000 in the homogenization zone: -the linear pressure loss through the discharge homogenizing zone accounts for more than 80% of the pressure loss dP2 between the active zone (54) and the oxidant discharge manifold; -dP2/dP1 has a value at least equal to 2, wherein dP1 is the pressure loss between the oxidant inlet manifold and the active zone (54).

Description

Bipolar plate for improving efficiency of proton exchange membrane fuel cell
The present invention relates to electrochemical reactors having membrane electrode assemblies such as low temperature fuel cells. The invention relates in particular to the optimisation of the energy efficiency of fuel cells with proton exchange membranes.
For example, fuel cells are envisaged as power supply systems for motor vehicles in future mass production and for a large number of applications. Fuel cells are electrochemical devices that can directly convert chemical energy into electrical energy. A fuel such as dihydro or methanol is used as a fuel for the fuel cell.
In the case of dihydro, the dihydro is oxidized and ionized at one electrode of the cell and the oxidant is reduced at the other electrode of the cell. The chemical reaction produces water at the cathode and oxygen is reduced and reacts with protons. The greatest advantage of fuel cells is the avoidance of air polluting compounds being discharged at the power generating site.
Proton exchange membrane fuel cells, known as PEM, operate at low temperatures and have particularly advantageous compactness. Each cell contains an electrolyte membrane that allows only protons to pass through, but not electrons. The membrane includes an anode on a first side and a cathode on a second side to form a membrane/electrode assembly called an AME.
At the anode, the dihydro is ionized to produce protons that pass through the membrane. Electrons generated by this reaction migrate to the flow plate and then pass through circuitry external to the cell to form an electrical current. At the cathode, the oxygen is reduced and reacts with protons to form water.
The fuel cell may comprise a plurality of so-called bipolar plates, for example made of metal, stacked on top of each other. The membrane is disposed between two bipolar plates. The bipolar plates may include flow channels and flow holes to direct reactants and products to/from the membrane, to direct coolant, and to separate the different compartments. The bipolar plates are also electrically conductive to form a manifold of electrons generated at the anode. According to a relatively common design, the bipolar plate is formed from two metal sheets assembled by welding, and a flow channel for the cooling liquid is typically provided between the two metals.
The bipolar plates also have a mechanical function for transmitting the tightening force of the stack, which is necessary for the quality of the electrical contact. The gas diffusion layer is interposed between the electrode and the bipolar plate and is in contact with the bipolar plate. Electron conduction is performed through the bipolar plate and ion conduction is obtained through the membrane.
The bipolar plate continuously supplies the reactant to the reactive surfaces of the electrodes as the reactant is consumed. The bipolar plates have a network of flow channels to ensure distribution of reactants in the reaction zone. The flow channel network is connected between the inlet manifold and the outlet manifold, typically directly from side to side through the stack. Each manifold is surrounded by seals to avoid mixing of the various fluids circulating in the cell. The homogenization zone typically connects the inlet manifold or the outlet manifold to the flow channels. The function of the homogenizing zone is to obtain a reactant flow through the different flow channels at as uniform a pressure and flow rate as possible. The passage of reactant from the inlet manifold through the flow channels of the active region to the outlet manifold causes a pressure loss.
The pressure loss in the cathode channels is typically of a sufficiently high level to allow for drainage 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 area. Thus, the pump typically compresses the oxidant to supply the oxidant under pressure to the inlet manifold and at least compensates for the pressure loss of the cathode line. In order to optimize the energy efficiency of the fuel cell system, the pressure of the oxidant must not reach an excessively high level, and the power consumption of the pump increases with the pressure level of the applied oxidant. Therefore, there is an optimum operating pressure that maximizes the efficiency of the fuel cell system.
Due to pressure losses in the inlet homogenization region between the oxidant inlet manifold and the cathode flow channels, the pressure applied by the compressor at the inlet of the oxidant inlet manifold must correspond to the optimum pressure in the active region derived from the magnitude of these pressure losses. In order to be able to maintain this optimum pressure in the active region, it is also necessary to maintain a high pressure loss downstream of the active region.
Since the pressure loss of the line in the discharge homogenizing zone is not sufficient to ensure an optimal pressure in the active zone, it is known to place a back pressure valve downstream of the oxidant outlet manifold.
However, such a valve implies that a water condenser and a gas/water separator are included between the oxidant outlet manifold and the valve in order to be able to regulate the oxidant pressure on the dry gas. In addition, such valves cause large pressure oscillations in the active area when the fuel cell is started.
It is also known to arrange a calibrated restrictor orifice downstream of the oxidant outlet manifold. These are current limiters on the cathode loop downstream of the cell. The pressure loss at these holes then increases considerably. Fig. 1 is a schematic diagram of the distribution of relative pressures in different portions of a cathode flow distributed from an inlet manifold to an exhaust manifold. The ZHE region corresponds to the inlet homogenization region, the ZA region corresponds to the active region, the ZHS region corresponds to the discharge homogenization region, and the OC region corresponds to the calibrated holes.
Such fuel cells equipped with a current limiter have drawbacks. The cathode pressure loss is insufficient to ensure that the optimum pressure is achieved over the full range of desired operating schemes. The energy efficiency of the fuel cell system deteriorates. The further the energy efficiency is theoretically from the maximum energy efficiency, the higher the compression efficiency of the oxidant pump. In addition, such fuel cells create a point of retention of parasitic water in the flow, resulting in the use of condensers and phase splitters.
The present invention is directed to addressing one or more of these shortcomings. The present invention therefore 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 variants of the dependent claims. It will be understood by those within the art that each feature of the variants of the dependent claims may be combined independently of the features of the independent claims without constituting an intermediate generalization.
The invention also relates to a fuel cell as defined in the appended claims.
Other features and advantages of the invention will become apparent from the following illustrative and in no way limiting description, given with reference to the accompanying drawings, in which:
figure 1 is a schematic diagram of the cathode relative pressure of a fuel cell according to the prior art;
fig. 2 is an exploded perspective view of an example of a stack of membrane/electrode assemblies and bipolar plates for a fuel cell;
fig. 3 is a top view of an example of a bipolar plate for a fuel cell with cross-current cooling circuits with respect to parallel flow of fuel and oxidant.
Fig. 4 is a schematic cross-sectional view of a fuel cell at an oxidant inlet homogenization zone;
fig. 5 is a schematic cross-sectional view of a fuel cell at an oxidant discharge homogenizing zone;
fig. 6 is a top view of an example of the construction of a bipolar plate at the oxidant discharge homogenizing zone;
fig. 7 is a top view of another example of the construction of a bipolar plate at the oxidant discharge homogenizing zone;
FIG. 8 is a graph comparing the relative pressures in different portions of different configurations of fuel cells;
FIG. 9 is a graph comparing the relative pressures at the inlet of different configurations of flow manifolds for fuel cells;
fig. 10 is a top view of an example of a bipolar plate for a fuel cell with parallel flow cooling circuits with respect to fuel and oxidant.
Fig. 2 is a schematic exploded perspective view of the stack of units 1 of the fuel cell 4. The fuel cell 4 includes a plurality of units 1 that overlap. The unit 1 is of the proton exchange membrane or polymer electrolyte membrane type.
The fuel cell 4 includes a fuel source 40. Here, a fuel source 40 supplies dihydro to the inlet of each unit 1. The fuel cell 4 also includes an oxidant source 42. Here, the oxidant source 42 supplies air to the inlet of each unit 1, and oxygen in the air is used as the oxidant. Each unit 1 further comprises an exhaust channel. One or more units 1 also have a cooling circuit.
Each unit 1 includes a membrane/electrode assembly 110 or AME 110, and the membrane/electrode assembly 110 includes a solid electrolyte 113, a cathode (not shown) disposed on both sides of the electrolyte and fixed on the electrolyte 113, and an anode 111. The electrolyte layer 113 forms a semi-permeable membrane that allows proton conduction while being impermeable to the gas present in the cell. The electrolyte layer also prevents electrons from passing between the anode 111 and the cathode.
Between each pair of adjacent AMEs, a bipolar plate 5 is provided. Each bipolar plate 5 defines anode and cathode flow channels on opposite outer faces. The bipolar plate 5 also advantageously defines coolant flow channels between two successive membrane/electrode assemblies. The bipolar plates 5 may each be formed in a manner known per se from two assembled conductive metal sheets, for example made of stainless steel or titanium alloy, aluminum alloy, nickel alloy or tantalum alloy. Each sheet then defines a respective outer face. The bipolar plate 5 may also be obtained by any other method, for example by moulding or injection from a carbon-polymer composite. Thus, the bipolar plate 5 may also be formed in one piece. The outer face of the bipolar plate 5 is thus defined by such a one-piece component.
The stack may also include a peripheral seal and a membrane reinforcement, not shown here. Each cell 1 may additionally comprise a gas diffusion layer (not shown) arranged between the anode and the bipolar plate, and a further gas diffusion layer arranged between the cathode and the further bipolar plate.
In a manner known per se, during operation of the fuel cell 4, air flows between the AME and the bipolar plate, and dihydro flows between the AME and the other bipolar plate. At the anode, the dihydro is ionized to produce protons that pass through the AME. Electrons generated by this reaction are collected by the bipolar plate 5. The generated electrons are then applied to the electric charge connected to the fuel cell 4 to form an electric current. At the cathode, the oxygen is reduced and reacts with protons to form water. The reactions at the anode and cathode are as follows:
at the anode: h 2 →2H + +2e - ；
At the cathode: 4H (4H) + +4e - +O 2 →2H 2 O。
During its operation, the unit 1 of the fuel cell 4 typically generates a direct voltage of about 1V between the anode and the cathode.
The oxidant source 42 typically comprises a compressor for introducing air at a given pressure at the inlet of the unit 1. Such compressors receive, for example, an air pressure set point, which can be adjusted by a variable rotational speed of the compressor.
The stacking of bipolar plates 5 and membrane/electrode assemblies 110 is intended to form a plurality of flow manifolds. For this purpose, corresponding holes (591 to 596 shown in fig. 3) are provided through the bipolar plate 5 and through the membrane/electrode assembly 110. The holes of the bipolar plate 5 and the membrane/electrode assembly 110 are oppositely disposed to form various flow manifolds.
Fig. 3 is a schematic top view of a bipolar plate 5, given by way of example, other configurations of flow channels are conceivable. Thus, bipolar plate 5 has holes 591 and 593 at a first longitudinal end, holes 595 and 596 at a second longitudinal end, hole 593 at a first lateral end, and hole 594 at a second lateral end.
The holes 591 are used, for example, to form a fuel supply manifold, and the holes 596 are used, for example, to form a manifold that discharges combustion residues and unused fuel. The holes 593 are used, for example, to form a supply manifold for the coolant, and the holes 594 are used, for example, to form a discharge manifold for the coolant. Holes 592 are used, for example, to form a supply manifold for the oxidant, and holes 595 are used, for example, to form a manifold that discharges the produced water and unused oxidant.
The outer face shown for the bipolar plate 5 has ribs defining flow channels for reactants such as fuel. The region including the flow channels corresponds to the active region 54 of the electrochemical cell. Here, the flow channels are intended to communicate the manifolds 592 and 595. The inlet homogenizing zone 52 connects the manifold 592 to the inlet 545 of the flow passage of the active region 54. The exhaust homogenization region 55 connects the manifold 595 to the outlet 546 of the flow channel of the active region 54. Figures 4 and 5 further illustrate the geometry of the different homogenization areas.
Here, the bipolar plate 5 comprises a cooling circuit of cross current with respect to the flow of fuel and oxidant. The flows of fuel and oxidant are here parallel. Of course, other configurations are contemplated within the context of the present invention.
The purpose of the bipolar plate 5 according to the invention is to optimize the energy efficiency of the fuel cell 4 without introducing excessive structural complexity. The energy efficiency of the fuel cell 4 can be defined as the ratio between the electrical energy produced by the fuel cell and the chemical energy theoretically available through fuel consumption. The bipolar plate 5 according to the invention is especially intended to avoid the need to use a condenser and a phase separator in the oxidant flow circuit.
The pressure loss distribution of the oxidation circuit within the bipolar plate 5 is as follows: dP1 between the inlet manifold 592 and the active region 54, dP2 between the active region 54 and the outlet manifold 595, and dP3 along the active region within the channel 541. Within the scope of the invention, within this bipolar plate 5, it is advantageous to try to maintain the pressure loss regulation and thus as linear and reasonably distributed as possible.
Thus, the bipolar plate 5 according to the invention is configured such that the reynolds number of the flow of the oxidant in the discharge homogenizing zone 55 is 1000 to 2000:
the linear pressure loss through the discharge homogenizing zone 55 constitutes more than 80% of the pressure loss dP2, preferably more than 90% of the pressure loss dP 2.
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 1000 to 2000 of the flow of oxidant exiting the homogenisation zone 55 is sufficient to represent a flow condition for a full power fuel cell. This range of reynolds numbers is used as a reference to verify that the pressure loss conditions are indeed met in accordance with the invention.
When the oxidant is directed to form a laminar flow, a linear pressure loss is obtained in the homogenizing zone. A linear pressure loss of a suitable magnitude can be obtained, for example, by a suitable size of the channel section in the homogenizing zone or by making the flow channel of the homogenizing zone more or less significantly inclined with respect to the flow direction in the active zone. The channel portion is defined, for example, by the width and height of the flow channel in the homogenizing zone and/or by the height and number of raised studs that may be formed in the homogenizing zone.
By configuring the discharge homogenizing zone 55 such that the pressure loss therein is substantially linear, the energy efficiency of the fuel cell 4 is improved, in particular for intermediate power levels. By configuring the value dP2/dP1 to a sufficient level, the discharge homogenizing zone 55 enables an oxidant pressure having a relatively high amplitude to be obtained at the inlet 545 of the channel 541, thereby improving the energy efficiency of the fuel cell 4. In addition, such passive management of the pressure downstream of the flow within the bipolar plate 5 enables simplified management of the water formed, since there is no need to use a condenser or a phase separator as used in prior art solutions. Thus, the oxidant exhaust circuit of the fuel cell 4 may be free of a water condenser and a gas/water separator downstream of the oxidant outlet manifold 595.
The flow downstream of the discharge homogenizing zone 55 is, for example, typically without an active back pressure valve and without a calibrated orifice of the restrictor type that is prone to cause a substantial pressure loss in the discharge homogenizing zone on the oxidant line. Such flow restrictions naturally create turbulence of the oxidant and are sensitive to the presence of water in the exiting cathode mixture.
Fig. 4 is a schematic cross-sectional view of an example of a fuel cell at an oxidant inlet homogenization zone. Fig. 5 is a schematic cross-sectional view of the fuel cell in its oxidant discharge homogenizing zone. In the illustrated construction, each membrane/electrode assembly 110 includes a stiffener 114 secured to the periphery of its membrane 113.
Here, the oxidant inlet flow channels 521 of the homogenizing zone 52 are shown (the inlet flow channels 521 are particularly present in the hatched areas of the arrows showing the flow). The flow channels 521 are formed in particular between the faces 525 of the bipolar plate 5 and the reinforcement of the membrane/electrode assembly. The height of flow channel 521 corresponds to the distance between the face 525 and the stiffener.
Between the face 526 of the bipolar plate 5 and the reinforcement 114 of the other membrane/electrode assembly 110, a flow channel 522 is formed for the exiting fuel, which is perpendicular to the oxidant inlet homogenizing zone.
Here, the height of the flow passage 521 is increased relative to the height of the flow passage 522 in order to reduce the pressure loss in the oxidant inlet homogenizing zone 52. Increasing the height of the flow passage 521 also reduces the height of the flow passage 522, which enables an increase in pressure loss at the fuel discharge, which promotes fuel homogenization in the fuel inlet homogenization region. In this example, the sum of the height of the fuel discharge homogenizing zone and the height of the oxidant inlet homogenizing zone is equal to the sum of the height of the oxidant discharge homogenizing zone and the height of the fuel inlet homogenizing zone.
Here, the height of the flow channel 521 is greater than the height of the flow channel 541 of the oxidant in the active region 54.
In this example, the bipolar plate 5 has fuel flow channels 542 on one side and oxidant flow channels 541 on the other side in its active region 54. The coolant flow channels 543 are disposed between the two faces of the bipolar plate in the active region 54.
Here, the oxidant discharge flow channel 551 of the homogenizing zone 55 is shown (the inlet flow channel 551 is particularly present in the hatched area of the arrow showing the flow). The flow channels 551 are particularly disposed between the face 525 of the bipolar plate 5 and the reinforcement of the membrane/electrode assembly. The height of the flow channel 551 corresponds to the distance between the face 525 and the stiffener.
The fuel inlet flow channels 552 are disposed between the face 526 of the bipolar plate 5 and the stiffener 114 of the other membrane/electrode assembly 110 perpendicular to the oxidant exhaust homogenization zone.
Here, the height of the flow channel 551 is reduced relative to the height of the flow channel 552 to increase the linear pressure loss in the oxidant discharge homogenizing zone 55. Here, the height of the flow channel 551 is smaller than the height of the oxidant flow channel 541 of the active region 54.
For example, it may be provided that the height of the flow channel 521 is at least twice the height of the flow channel 551.
Fig. 6 is a schematic top view of a bipolar plate at the discharge homogenization area. Here, the linear pressure loss in the discharge homogenizing zone 55 is obtained by the flow channel 551 having a reduced section.
The inlet homogenization area 52 may use a similar geometry, but with a greater depth of the flow channel 521.
The design aimed at obtaining a value of the high ratio dP2/dP1 may consist, for example, in providing an average channel section in the inlet homogenizing zone 52 that is at least twice as large as the average channel section of the outlet homogenizing zone 55.
The aim of the invention is to reduce the pressure loss (dP 1) at the oxidant inlet before the pressure loss (dP 2) at the oxidant outlet, while trying to ensure that these pressure losses are as linear as possible throughout the flow.
Advantageously, the oxidant inlet homogenizing zone 52 may be configured such that the linear pressure loss across the oxidant inlet homogenizing zone constitutes more than 80% of the pressure loss dP1 between the oxidant inlet manifold 592 and the oxidant flow channels 541, and preferably more than 90% of the pressure loss dP1.
Thus, for the same oxidant pressure in the active region 54, the pressure loss in the oxidant inlet homogenizing region 52 is reduced by reducing dP1 before dP2, and by having a large linear contribution of the homogenizing region 52 in dP1, an improvement in the overall energy efficiency of the fuel cell 4 is obtained.
To test the properties of the bipolar plate 5, pressure sensors may be placed in the oxidant inlet homogenizing zone 52 and in the oxidant outlet homogenizing zone 55. Once the bipolar plates are properly connected to the membrane/electrode assembly and their oxidant inlet manifolds fed by the oxidant compressor, the pressure loss values in these homogenization areas will be able to be checked for the reynolds number given in the oxidant outlet homogenization area 55.
Fig. 7 is a schematic top view of another example of a bipolar plate 5 at an exhaust homogenization zone 55. Here, the linear pressure loss in the discharge homogenizing zone 55 is obtained by a large number of raised studs 554 placed in the zone 55.
A similar geometry may be used for the inlet homogenization area 52, but with a greater flow depth or with a lower stud 554.
Fig. 8 is a graph comparing pressures in different segments of different fuel cell configurations. The solid line curve corresponds to a fuel cell equipped with a bipolar plate according to the invention, which has an optimal pressure loss. The dashed curve corresponds to a fuel cell equipped with a bipolar plate according to the prior art, which bipolar plate has a flow restrictor. These restrictors cause pressure losses that are proportional to the square of the oxidant velocity through them. The bipolar plates have the same active area.
Optimization in the oxidant inlet homogenization zone ZHE enables reducing the oxidant pressure that the pump must apply to the oxidant to achieve the same pressure at the inlet of the active zone. Thus reducing the power consumption of the compressor. For a bipolar plate according to the invention, the oxidant exhaust homogenizing zone has a substantially uniform pressure loss over the length of the flow between the active zone and the oxidant exhaust manifold.
Fig. 9 is a graph comparing the relative pressures at the inlet of differently configured flow manifolds for fuel cells as a function of the power generated by these fuel cells.
The dashed curve corresponds to the theoretical configuration with the best energy efficiency for an oxidant compressor with a given compression efficiency. The greater the difference between this curve for a given power and the characteristic curve of the actual fuel cell, the lower the energy efficiency of that power. The dashed curve corresponds to the use of a restrictor according to the prior art in the case of the same compression pump. The solid line curve corresponds to a bipolar plate for the flow of layered oxidant in the exhaust zone, which is the object of the invention. Especially for intermediate operating powers, the energy efficiency is improved. The bipolar plate according to the invention thus facilitates the use of a fuel cell with a certain power.
The skewed point curve corresponds to a bipolar plate of the invention for mixed laminar/turbulent flow. Even for such flows, the energy efficiency obtained by the bipolar plate according to the invention is still higher (dashed line) than that obtained by the current limiter according to the prior art.
The fluid diameter of the oxidant flow channels in the active region of a bipolar plate according to the prior art is typically 0.35 to 0.4mm. For an operating point with an average pressure of 1.5bar in the active zone, stcombant=2 (ratio of total oxidant flow to cell-consumed oxidant flow), density is 1.5A/cm 2 The Reynolds number for the flow of the oxidant in the active zone is 240. With the construction of the oxidant discharge homogenizing zone according to the prior art, the oxidant is accelerated and then the reynolds number therein is typically 500 to 1000. For a bipolar plate according to the invention dividing the oxidant channels in the oxidant discharge homogenizing zone into two, the reynolds number will reach 2000 at the most, which will allow to maintain the layered state.
It should be noted that the higher the compression efficiency of the oxidant pump, the more the invention enables the energy efficiency of the fuel cell 4 to be increased. The invention has therefore proved to be particularly advantageous when the oxidant pump has a compression efficiency of at least 75%, or preferably at least 80%. Such an efficiency is for example an efficiency corresponding to the nominal operating conditions of the pump, for example when the oxidizing agent is air.
Fig. 10 is a schematic top view of another bipolar plate 5 given as an example. Thus, bipolar plate 5 has apertures 591 to 593 at a first longitudinal end and apertures 594 to 596 at a second longitudinal end. The bipolar plate 5 here comprises a cooling circuit with parallel currents with respect to the fuel and oxidant flows.
The holes 591 form a fuel supply manifold and the holes 596 form a combustion residue exhaust manifold. The holes 593 form a coolant supply manifold and the holes 594 form a coolant discharge manifold. Holes 592 form an oxidant supply manifold and holes 595 form a manifold for discharging the produced water and unused oxidant.
Thus, the coolant channels overlap with the flow channels of the oxidant and fuel of the homogenizing zones 52 and 55.
In this example, the depth of the flow channels of the oxidant and/or fuel in the homogenizing zone 52 or 55 may be adjusted by adjusting the depth of the flow channels of the coolant in the homogenizing zone accordingly. Modifying the depth of the coolant channel has less effect on the operating parameter than modifying the depth of the flow channel of the other reactant.
Thus, to reduce the height of the oxidant flow channels in the homogenizing 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, to be able to increase the height of the oxidant inlet channels in the homogenizing zone 52, superimposed cooling liquid channels having a height smaller than the height of the cooling liquid channels in the active zone 54 may be used.

Claims (13)

1. A bipolar plate (5) for a fuel cell having a proton exchange membrane, comprising:
-an oxidant inlet manifold (592) and an oxidant outlet manifold;
-an oxidant flow channel (541) of the active region (54);
-an inlet homogenizing zone (52) comprising flow channels and connecting the oxidant flow channels (541) to an oxidant inlet manifold (592);
-an exhaust homogenization zone (55) connecting the oxidant flow channel (541) to an oxidant outlet manifold;
characterized by a Reynolds number for the flow of oxidant in the discharge homogenizing zone (55) of 1000 to 2000:
-the linear pressure loss through the exhaust homogenization zone (55) accounts for more than 80% of the pressure loss dP2 between the active zone (54) and the oxidant outlet manifold;
-dP2/dP1 has a value at least equal to 2, wherein dP1 is the pressure loss between the oxidant inlet manifold (592) and the active region (54).
2. Bipolar plate (5) according to claim 1, wherein the average channel section in the inlet homogenization zone (52) is at least twice as large as the average channel section of the outlet homogenization zone (55).
3. Bipolar plate (5) according to claim 1 or 2, wherein the discharge homogenizing zone (55) comprises flow channels, the depth of the flow channels in the inlet homogenizing zone (52) being at least twice the depth of the flow channels (551) in the discharge homogenizing zone (55).
4. A bipolar plate (5) according to claim 3, wherein the depth of the flow channels (521) of the inlet homogenization zone (52) is strictly greater than the depth of the oxidant flow channels (541) of the active zone (54).
5. The bipolar plate of claim 2, comprising:
-a fuel inlet manifold and a fuel exhaust manifold;
-a fuel flow passage of the active region;
-a fuel inlet homogenizing zone connecting the fuel flow channel to a fuel inlet manifold;
-a fuel emission homogenizing zone connecting the fuel flow channel to a fuel emission manifold;
-a portion of the fuel inlet homogenizing zone overlying the oxidant outlet homogenizing zone;
-a portion of the fuel discharge homogenizing zone overlapping the oxidant inlet homogenizing zone, the sum of the height of the fuel discharge homogenizing zone and the height of the oxidant inlet homogenizing zone being equal to the sum of the height of the oxidant discharge homogenizing zone and the height of the fuel inlet homogenizing zone.
6. The bipolar plate of claim 2, comprising:
-a coolant inlet manifold and a coolant discharge manifold;
-a coolant flow channel (543) of the active region;
-a connection area between the coolant inlet manifold and the coolant flow channels (543);
-a connection area between the coolant discharge manifold and the coolant flow channel (543);
-a portion of the connection region overlapping the oxidant discharge homogenizing region, the height of the overlapping connection region being greater than the height of the coolant flow channels (543) of the active region.
7. Bipolar plate (5) according to claim 1 or 2, wherein the inlet (52) and outlet (55) homogenizing areas have protruding studs (554).
8. Bipolar plate (5) according to claim 1 or 2, wherein the linear pressure loss through the inlet homogenization zone (52) accounts for more than 80% of the pressure loss dP1 between the active zone (54) and the oxidant inlet manifold (592).
9. A fuel cell comprising:
-bipolar plate (5) according to any of the preceding claims;
-a membrane/electrode assembly (110) comprising a proton exchange membrane and a cathode (112) covering a middle portion of the proton exchange membrane and covering an active area (54) of the bipolar plate (5).
10. The fuel cell of claim 9, comprising a pump configured to supply oxidant under pressure to the oxidant inlet manifold (592).
11. The fuel cell according to claim 10, wherein the pump has an oxidant compression efficiency of at least equal to 75%.
12. The fuel cell of claim 10 or 11, which is devoid of a water condenser and a gas/water separator downstream of the oxidant outlet manifold.
13. The fuel cell according to claim 11, wherein the pump has a compression efficiency of the oxidant at its rated operating condition of at least equal to 75% when the oxidant is air.
CN201880058216.XA 2017-08-04 2018-07-24 Bipolar plate for improving efficiency of proton exchange membrane fuel cell Active CN111052469B (en)

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FR1757528A FR3069961B1 (en) 2017-08-04 2017-08-04 BIPOLAR PLATE FOR IMPROVING THE PERFORMANCE OF A FUEL CELL WITH A PROTON EXCHANGE MEMBRANE
FR1757528 2017-08-04
PCT/FR2018/051892 WO2019025701A1 (en) 2017-08-04 2018-07-24 Bipolar plate for improving the efficiency of a proton-exchange membrane fuel cell

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ITMI20022383A1 (en) * 2002-11-11 2004-05-12 Nuvera Fuel Cells Europ Srl ELECTROCHEMICAL GENERATOR POWERED WITH REACTIVE PRESSURE GASES
JP4903770B2 (en) * 2008-11-26 2012-03-28 本田技研工業株式会社 Fuel cell
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CN101312248A (en) * 2007-05-24 2008-11-26 本田技研工业株式会社 Fuel cell
CN106571472A (en) * 2016-11-10 2017-04-19 上海交通大学 Fuel cell metal dual pole plate assembly for enhancing fluid uniformity

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WO2019025701A1 (en) 2019-02-07

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