Fuel cell comprising a stack of electrochemical cells and several inlet and outlet manifolds for each reactive fluid and for the heat transfer fluid

Abstract

The invention relates to a fuel cell whose bipolar plates of the electrochemical cells comprise two inlet manifolds for each reactive fluid and for the heat transfer fluid, as well as the associated outlet manifolds. The inlet and outlet manifolds are arranged so that there is an alternation of the flow direction of the heat transfer fluid and of each reactive fluid from one bipolar plate to the other. Figure for abstract: Fig. 3

Description

Title of the invention: Fuel cell comprising a stack of electrochemical cells and several inlet and outlet collectors for each reactive fluid and for the heat transfer fluid Technical field

[0001] The field of the invention is that of fuel cells, comprising a stack of electrochemical cells, the bipolar plates of which are crossed by inlet and outlet collectors ensuring the circulation of the reactive fluids and the heat transfer fluid and the evacuation of the products of the electrochemical reaction. STATE OF THE PRIOR ART

[0002] A fuel cell usually comprises a stack of electrochemical cells, each of which comprises an anode and a cathode separated from each other by an electrolyte. The cells are the site of an electrochemical reaction between two continuously introduced reactive fluids.

[0003] Generally speaking, the combustible fluid (e.g. hydrogen) is supplied to the anode, while the oxidizing fluid (e.g. oxygen contained in air) is supplied to the cathode. The electrochemical reaction is subdivided into two half-reactions, an oxidation reaction and a reduction reaction, which take place respectively between the anode and the electrolyte and between the cathode and the electrolyte. To take place, the electrochemical reaction requires the presence of an ionic conductor between the two electrodes, namely the electrolyte, for example, contained in a polymer membrane, and an electronic conductor formed by the external electrical circuit. The stack of cells is thus the location of the electrochemical reaction: the reactive fluids must be supplied there, the products and non-reactive species must be removed, as must the heat produced during the reaction.

[0004] Electrochemical cells are usually separated from each other by bipolar plates which ensure the electrical interconnection between them as well as the flow of the reactive fluids and the heat transfer fluid. The bipolar plates have an anodic face at which a hydrogen distribution circuit is formed, and an opposite cathodic face at which an oxygen distribution circuit is formed. Each distribution circuit takes the form of a network of channels arranged to bring the reactive fluid to the corresponding electrode. The bipolar plates may also have a cooling circuit formed by a network of internal conduits which ensure the flow of a heat transfer fluid, making it possible to evacuate the heat produced locally during the electrochemical reaction by the cell. The distribution and cooling circuits are su perposed to each other, and define a so-called active zone of the electrochemical cells.

[0005] [Fig.l] is a schematic and partial view, in perspective and exploded, of a stack of electrochemical cells of a fuel cell, according to an example of the prior art. The fuel cell comprises N electrochemical cells, with N>1. The successive bipolar plates are referenced by the index n, ranging from 1 to N+1.

[0006] [Fig. 2] left is a schematic and partial cross-sectional view of the stack of electrochemical cells of [Fig. 1]. [Fig. 2] right illustrates an example of variation in the temperature of the heat transfer fluid along the cooling circuit of the bipolar plates of [Fig. 2] left, as well as an example of variation in the concentration of water in the fluids flowing in the distribution circuits of the bipolar plates. In the figures, for illustration and simplicity, "H2" and "O2" are indicated to refer to the fluids circulating in the distribution circuits.

[0007] The distribution and cooling circuits are connected to inlet and outlet manifolds. The manifolds take the form of openings which pass through the stack of electrochemical cells, and more precisely the stack of bipolar plates.

[0008] Thus, each anode distribution circuit is connected to the same hydrogen inlet manifold CEH2 and to the same outlet manifold CSH2. Similarly, the cathode distribution circuits are connected to the same oxygen inlet manifold CE02 and to the same outlet manifold CS02, and the cooling circuits are connected to the same heat transfer fluid inlet manifold CEhtf and to the same outlet manifold CShtf.

[0009] The inlet manifolds CEH2, CE02 of the reactive fluids and the associated outlet manifolds CSH2, CS02 are located on either side of the active zone along a main longitudinal axis X of the distribution circuits. The inlet manifolds CEhtf and outlet manifolds CShtf of the heat transfer fluid are also located here on either side of the cooling circuits along the main longitudinal axis X (therefore located on the side of the inlet and outlet manifolds of the reactive fluids).

[0010] The inlet collectors CEH2, CE02 and outlet collectors CSH2, CS02 of the reactive fluids can be arranged so that, in each electrochemical cell Cn, the hydrogen and the oxygen flow in counter-current on either side of the electrolytic membrane Mn. Thus, the inlet collector CEH2 of the hydrogen and the inlet collector CE02 of the oxygen are arranged in an opposite manner along the main longitudinal axis X with respect to the distribution circuits.

[0011] Furthermore, the concentration of water c|J2 and C^2 in the fluids increases along the anodic and cathodic distribution circuits. Also, because the reactive fluids flow in counter-current on both sides of the membrane results in the formation of a transverse gradient of water concentration, in particular at the inlet and outlet of the active zone, thus generating a transverse flux of water 0Ac by diffusion through the electrolytic membrane. Thus, there is a transverse flux of water 0Ac from the cathode outlet where the fluid contains a high concentration of water c^2 to the anodic inlet where the fluid contains a low concentration of water C^2. And there is a transverse flux of water 0Ac from the anodic outlet where the fluid contains a high concentration of water cH2 to the cathodic inlet where the fluid contains a low concentration of water cO2. The transverse flux of water 0Ac depends on the position x along the distribution circuits.In the figures, the arrows associated with 0Ac are positioned at the ends of the distribution circuits, where the flow is particularly important, but it can be more or less important along the distribution circuits.

[0012] This configuration makes it possible to increase the hydration of the electrolytic membrane, in particular at the inlet and outlet of the active zone, which contributes to improving the performance of the electrochemical cells. Indeed, it is known that the ionic conductivity of the electrolytic membrane decreases sharply when the water concentration (e.g. the relative humidity) in the fluids flowing in the distribution circuits decreases.

[0013] However, there is a need to be able to further improve the performance of such a fuel cell. Statement of the invention

[0014] The invention aims to propose a fuel cell with improved performance. For this, the subject of the invention is a fuel cell comprising: • a stack of N electrochemical cells, with N>1; where each electrochemical cell comprises an electrolytic membrane arranged between two bipolar plates, the successive bipolar plates being identified by a rank n ranging from 1 to N+1; and where each bipolar plate comprises a distribution circuit for a reactive oxidizing fluid, a distribution circuit for a reactive combustible fluid, and a cooling circuit for a heat transfer fluid; • inlet manifolds for the reactive fluids and the heat transfer fluid, and associated outlet manifolds, the inlet and outlet manifolds passing through the bipolar plates and being connected to the distribution and cooling circuits; where the inlet and outlet manifolds are arranged so that, in each electrochemical cell, the oxidizing and combustible reactive fluids flow countercurrently on either side of the electrolytic membrane.

[0015] According to the invention, the fuel cell comprises: • first and second inlet manifolds for the oxidizing reactive fluid, and associated first and second outlet manifolds; • first and second inlet manifolds for the combustible reactive fluid, and associated first and second outlet manifolds; and • first and second heat transfer fluid inlet manifolds, and associated first and second outlet manifolds.

[0016] In addition, the first input collectors only supply the bipolar plates of odd rank n; and the second input collectors only supply the bipolar plates of even rank n.

[0017] Furthermore, in each bipolar plate: the first and second inlet collectors of the heat transfer fluid are opposite each other with respect to the cooling circuit, so that there is an alternation of the direction of flow of the heat transfer fluid from one bipolar plate to the other.

[0018] Finally, in each bipolar plate: the first and second inlet collectors of the oxidizing reactive fluid are opposite each other with respect to the distribution circuit, and the first and second inlet collectors of the combustible reactive fluid are opposite each other with respect to the distribution circuit, so that there is an alternation of the direction of flow of each reactive fluid from one bipolar plate to the other.

[0019] Some preferred but non-limiting aspects of this fuel cell are as follows.

[0020] In each bipolar plate, the first inlet manifold for the combustible fluid can be opposite the second inlet manifold for the oxidizing fluid with respect to the distribution circuits.

[0021] In each bipolar plate, the first inlet collectors of the reactive fluids can be opposite the second inlet collectors of the reactive fluids with respect to the distribution circuits.

[0022] The first heat transfer fluid inlet manifold may be located on the same side as the first reactive fluid inlet manifolds, the second heat transfer fluid inlet manifold being located on the same side as the second reactive fluid inlet manifolds, such that the first and second heat transfer fluid inlet manifolds are opposite each other with respect to the cooling circuit.

[0023] The first heat transfer fluid inlet manifold may be located on the same side as the second reactive fluid inlet manifolds, the second heat transfer fluid inlet manifold being located on the same side as the first reactive fluid inlet manifolds, such that the first and second heat transfer fluid inlet manifolds are opposite each other with respect to the cooling circuit.

[0024] Each electrolytic membrane can be a proton exchange membrane or an anion exchange membrane.

[0025] The invention also relates to a method of using the fuel cell according to any one of the preceding characteristics, in which a nominal operating temperature of the electrochemical cells is greater than or equal to 80°C.

[0026] The reactive fluids introduced into the distribution circuits may have a relative humidity less than or equal to 30%. Brief description of the drawings

[0027] Other aspects, aims, advantages and characteristics of the invention will appear better on reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the appended drawings in which:

[0028] [Fig.l], already described, is a schematic and partial view, in perspective and exploded, of a stack of electrochemical cells of a fuel cell according to an example of the prior art;

[0029] [Fig.2] left is a schematic and partial cross-sectional view of the electrochemical cell stack illustrated in [Fig.l];

[0030] [Fig.2] right illustrates an example of variation in the temperature of the heat transfer fluid in the cooling circuit of the bipolar plates of [Fig.2] left, as well as an example of variations in the concentration of water in the fluids flowing in the distribution circuits of the bipolar plates;

[0031] [Fig. 3] is a schematic and partial view, in perspective and exploded, of a stack of electrochemical cells of a fuel cell according to one embodiment;

[0032] [Fig.4] left is a schematic and partial cross-sectional view of the stack of electrochemical cells illustrated in [Fig.3];

[0033] [Fig.4] right illustrates an example of variation in the temperature of the heat transfer fluid in the cooling circuit of the bipolar plates of [Fig.4] left, as well as an example of variations in the concentration of water in the fluids flowing in the distribution circuits of the bipolar plates;

[0034] [Fig.5] is a schematic and partial view, in perspective and exploded, of a stack of electrochemical cells of a fuel cell according to one embodiment;

[0035] [Fig.6] left is a schematic and partial cross-sectional view of the electrochemical cell stack illustrated in [Fig.5];

[0036] [Fig.6] right illustrates an example of variation in the temperature of the ca- fluid carrier in the cooling circuit of the bipolar plates in [Fig.6] left, as well as an example of variations in the water concentration in the fluids flowing in the distribution circuits of the bipolar plates.

[0037] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0038] In the figures and in the remainder of the description, the same references represent identical or similar elements. In addition, the different elements are not shown to scale so as to favor the clarity of the figures. Furthermore, the different embodiments and variants are not mutually exclusive and can be combined with each other. Unless otherwise indicated, the terms "substantially", "approximately", "of the order of" mean to within 10%, and preferably to within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that the limits are included, unless otherwise indicated.

[0039] The invention relates to a fuel cell formed from a stack of electrochemical cells, connected in series with each other by bipolar plates. The bipolar plates are crossed by several inlet and outlet collectors (manifolds in English) making it possible to supply the distribution and cooling circuits with reactive fluids and heat transfer fluid.

[0040] According to the invention, the fuel cell comprises several inlet manifolds per reactive fluid and several associated outlet manifolds, as well as several inlet manifolds for the heat transfer fluid and several associated outlet manifolds. The inlet manifolds are arranged so that the reactive fluids flow in counter-current within the same electrochemical cell on either side of the electrolytic membrane, and so that there is alternation of the direction of flow of each reactive fluid and of the heat transfer fluid from one bipolar plate to the other.

[0041] This configuration makes it possible to form a transverse temperature gradient AT within each electrochemical cell, in particular at the inlet and outlet of the active zone, resulting in a transverse flow of water 0AT by diffusion through the electrolytic membrane towards the coldest bipolar plate. This transverse flow of water 0AT is of thermal origin and is thus distinguished from the transverse flow of water 0Ac generated by the transverse concentration gradient. The transverse flow of water 0AT depends on the position x along the distribution circuits. In the figures, the arrows associated with 0AT are positioned at the ends of the distribution circuits, where the flow is particularly significant, but it may be more or less significant along the distribution circuits.

[0042] This transverse flow of water 0AT of thermal origin can then be used to increase the hydration of the electrolytic membrane. Indeed, thanks to this transverse flow of water 0AT, a larger part of the water present at the outlet of a distribution circuit (where the water concentration is high) diffuses through the membrane electrolytic cell to the inlet of the opposite distribution circuit (where the water concentration is low). This further humidifies the inlet of the distribution circuit, which increases the hydration of the electrolytic membrane. In other words, a larger quantity of water is kept in each electrochemical cell, which can allow the humidification system for the reactive fluids to be relieved, or even to do without it altogether. This is particularly interesting when the nominal operating temperature of the fuel cell is high (e.g. at least 80°C). It is then possible to supply the distribution circuits with relatively dry reactive fluids and / or operate the fuel cell at a higher nominal operating temperature.

[0043] Alternatively, this transverse flow of water 0AT can also be used to reduce the concentration of water at the inlet of the distribution circuits in the case where the fuel cell needs to be uncovered.

[0044] Different embodiments and variants will be described with reference to a fuel cell, and in particular to a PEM (Proton Exchange Membrane) type fuel cell whose cathode is supplied with oxygen (e.g. contained in the air) and the anode with hydrogen. The invention, however, applies to any type of fuel cell, in particular to those operating at low temperature, i.e. at a temperature below 200°C. It can thus be applied to AEM (Anion Exchange Membrane) type fuel cells.

[0045] [Fig. 3] is a schematic and partial view, in cross-section and exploded, of a stack of electrochemical cells of a fuel cell according to one embodiment. As previously, the fuel cell comprises N electrochemical cells, with N>1. The successive bipolar plates are referenced by the index n ranging from 1 to N+1. Note that the N cells can be all or only a part of the electrochemical cells of the fuel cell. In any case, the N electrochemical cells are connected in series by the successive bipolar plates.

[0046] Here and for the remainder of the description, a direct orthogonal reference frame XYZ is defined, where the XY plane is parallel to the bipolar plates and to the electrolytic membranes, the X axis being oriented along the main longitudinal axis of flow of the reactive fluids, the Y axis being oriented along the width of the bipolar plates, and the Z axis being oriented along the stacking axis of the electrochemical cells.

[0047] The electrochemical cells each comprise an anode and a cathode, separated from each other by an electrolytic membrane, thus forming a membrane electrode assembly. The anode, the membrane and the cathode are conventional elements known to those skilled in the art and are therefore not described in detail. The MEA extends parallel to the XY plane.

[0048] Each membrane electrode assembly is separated from that of the adjacent cells by bipolar plates. Thus, as illustrated in [Fig.3], the electrochemical cell Cn comprises the bipolar plates PBn and PBn+i between which the electrolytic membrane Mn is located. This representation is obviously schematic: the anodes and cathodes, nor the gas diffusion layers, are not shown here. In addition, the electrolytic membrane can have a larger surface area and come right up to the edge of the bipolar plates.

[0049] Each bipolar plate comprises an anode face, where an anode distribution circuit is located for bringing the combustible fluid, here hydrogen, into contact with the anode of an electrochemical cell, and an opposite cathode face, where a cathode distribution circuit is located for bringing the oxidizing fluid, here oxygen contained in the air, into contact with the cathode of the adjacent electrochemical cell. The distribution circuits also make it possible to evacuate the products resulting from the electrochemical reactions and the non-reactive species.

[0050] Furthermore, the bipolar plates each comprise a cooling circuit, located between the anode and cathode distribution circuits, in which a heat transfer fluid flows, so as to allow the evacuation of the heat produced during the operation of the fuel cell.

[0051] The distribution and cooling circuits extend between an inlet and an outlet opposite each other along the main longitudinal axis X, opposite which along the axis X are located the inlet and outlet collectors for the reactive fluids and the heat transfer fluid.

[0052] The inlet and outlet collectors are openings which pass through the stack of electrochemical cells, and more precisely the stack of bipolar plates. They are intended to supply the distribution circuits with the two reactive fluids, and the cooling circuits with the heat transfer fluid. Each collector passes vertically through the bipolar plates.

[0053] The collectors of the reactive fluids are adjacent to each other (separated here by the collector of the heat transfer fluid), and are arranged opposite the same opening (inlet or outlet) of the active zone.

[0054] According to the invention, the fuel cell comprises: - first and second inlet manifolds CEI02, CE202 of the oxidizing reactive fluid (here O2), and associated first and second outlet manifolds CS102, CS202; - first and second inlet manifolds CE1H2, CE2H2 of the combustible reactive fluid (here H2), and associated first and second outlet manifolds CS1H2, CS2H2; and - first and second inlet manifolds CElhtf, CE2htf of the ca- fluid the carrier, and the associated first and second output collectors CSlhtf, CS2htf.

[0055] Furthermore, the first input collectors CE1H2, CEI02, CEhtf only supply the bipolar plates of odd index n (i.e. PBi, PB3, PB5, etc.) and not the bipolar plates of even index n (i.e. PB2, PB4, PB6, etc.). Furthermore, the second input collectors CE1H2, CEI02, CEhtf only supply the bipolar plates of even index n (i.e. PB2, PB4, PB6, etc.), and not the bipolar plates of odd index n (i.e. PBi, PB3, PB5, etc.).

[0056] In other words, the first collectors CE1H2 and CS1H2 are only connected to the anode distribution circuits of the bipolar plates of odd index n, while the second collectors CE2H2 and CS2H2 are only connected to the anode distribution circuits of the bipolar plates of even index n. Similarly, the first collectors CEI02 and CS102 are only connected to the cathode distribution circuits of the bipolar plates of odd index n, while the second collectors CE202 and CS202 are only connected to the cathode distribution circuits of the bipolar plates of even index n. Finally, the first collectors CElhtf and CSlhtf are only connected to the cooling circuits of the bipolar plates of odd index n, while the second collectors CE2htf and CS2htf are only connected to the cooling circuits of the bipolar plates of even index n.

[0057] In addition, the inlet collectors CElhtf, CE2htf and outlet collectors CSlhtf, CS2htf associated with the heat transfer fluid are arranged so that the direction of flow of the heat transfer fluid alternates from one bipolar plate to the other. This makes it possible to generate this transverse gradient (oriented along the Z axis) of non-zero temperature AT within each electrochemical cell, in particular at the inlet and outlet of the active zone.

[0058] For this, in each bipolar plate, the first inlet manifold CElhtf is opposite the second inlet manifold CE2htf with respect to the active zone, and therefore with respect to the cooling circuit. Thus, as illustrated in [Fig.3], the heat transfer fluid flows in the bipolar plates PBn and PBn+2 in the -X direction, from the inlet manifold CElhtf to the outlet manifold CSlhtf, and flows in the bipolar plate PBn+i in the +X direction, from the inlet manifold CE2htf to the outlet manifold CS2htf.

[0059] Furthermore, the inlet collectors CE1H2, CE2H2, CEI02, CE202 and outlet collectors CS1H2, CS2H2, CS102, CS202 of the reactive fluids are arranged so that, in each electrochemical cell, the reactive fluids flow in counter-current on either side of the electrolytic membrane.

[0060] Thus, as illustrated in [Fig.3], within the electrochemical cell Cn: the first inlet collector CE1H2 supplies the anode distribution circuit of the bipolar plate PBnen hydrogen, and the second inlet collector CE202 supplies the circuit of cathodic distribution of the PBn+i bipolar plate in oxygen.

[0061] In order for the reactive fluids to flow in counter-current, the first inlet collector CE1H2 is opposite the second inlet collector CE202 with respect to the active zone, and therefore the respective distribution circuits. This is the case in each bipolar plate of the electrochemical cells.

[0062] Furthermore, the inlet collectors CE1H2, CE2H2, CEI02, CE202 and outlet collectors CS1H2, CS2H2, CS102, CS202 of the reactive fluids are also arranged so that the direction of flow of each reactive fluid alternates from one bipolar plate to the other.

[0063] Thus, as illustrated in [Fig. 3], the hydrogen flows here along the -X direction in the anode distribution circuit of the bipolar plate PBn, along the +X direction in the bipolar plate PBn+i, along the -X direction in the bipolar plate PB n+2, etc. Similarly, the oxygen flows along the -X direction in the cathode distribution circuit of the bipolar plate PBn, along the +X direction in the bipolar plate PBn+i, along the -X direction in the bipolar plate PBn+2, etc.

[0064] For this, within each bipolar plate, the first hydrogen inlet collector CE1H2 is opposite the second hydrogen inlet collector CE2H2 with respect to the active zone, and therefore the anode distribution circuit. Similarly, the first oxygen inlet collector CEI02 is opposite the second oxygen inlet collector CE202 with respect to the active zone, and therefore the cathode distribution circuit.

[0065] [Fig.4] left is a schematic and partial cross-sectional view of the stack of electrochemical cells illustrated in [Fig.3]. [Fig.4] right illustrates an example of variation in the temperature of the heat transfer fluid in the cooling circuit of the bipolar plates of [Fig.4] left, as well as an example of variations in the concentration of water in the fluids flowing in the distribution circuits of the bipolar plates.

[0066] In the electrochemical cell Cn formed of the bipolar plates PBn and PBn+i and the electrolytic membrane Mn, the reactive fluids flow counter-currently on either side of the membrane Mn: the hydrogen circulates here in the -X direction from CE1H2 to CS1H2 in the anodic distribution circuit of the bipolar plate PBn, and the oxygen circulates in the +X direction from CE202 to CS202 in the cathodic distribution circuit of the bipolar plate PBn+i.

[0067] The water concentration in the distribution circuits increases along the flow. Thus, the water concentration C^x) in the fluid flowing in the anode distribution circuit of the bipolar plate PBn increases progressively along the -X direction, and the water concentration C^x) in the fluid flowing in the cathode distribution circuit of the bipolar plate PBn+i increases progressively along the +X direction.

[0068] At the inlet of each distribution circuit, the reactive fluid has a value minimum water concentration, for example a relative humidity of the order of 50%, or even less, for example less than or equal to 30%, and has a value greater than the minimum value at the outlet of the distribution circuit, for example of the order of 80% or even more, for example 100%.

[0069] Note that the variation in water concentration illustrated on [Fig.4] right is obviously very schematic. It is generally increasing, but is not necessarily linear as illustrated. Thus, it is increasing over a large part of the distribution circuit, and may be slightly decreasing or constant as one approaches the outlet of the distribution circuit. In any case, the value of the water concentration at the outlet is higher than the value at the inlet.

[0070] A transverse concentration gradient Ac is then formed along the vertical axis Z, in particular at the inlet and outlet of the active zone, which generates a transverse flow of water 4>Ac, by diffusion through the membrane Mn, oriented along the -Z direction on the side of the collectors CSlhtf and CE2htf, and oriented along the +Z direction on the side of the collectors CElhtf and CS2htf. This transverse flow of water 0Ac makes it possible to humidify the oxygen at the inlet of the cathode circuit and the hydrogen at the inlet of the cathode circuit, which makes it possible to improve the hydration of the membrane Mn in particular at the inlet and outlet of the active zone.

[0071] Furthermore, in this same electrochemical cell Cn, the heat transfer fluid flows in the -X direction in the cooling circuit of the bipolar plate PBn (from CElhtf to CSlhtf), while it flows in the +X direction in the cooling circuit of the bipolar plate PBn+i (from CE2htf to CS2htf). Thus, the temperature T(x) increases progressively with the direction of flow, and is substantially maximum at the collector CSlhtf of the bipolar plates of even rank n PBn, PB n+2, PBn+4... and at the collector CS2htf of the bipolar plates of odd rank n PBn+i, PBn+3, PBn+5--

[0072] As these two outlet collectors CSlhtf and CS2htd are opposite each other with respect to the active zone, a non-zero transverse temperature gradient AT is formed along the Z axis, in particular at the inlet and outlet of the active zone, which generates a second transverse water flow 0AT, by diffusion through the membrane Mn (the water diffuses towards the coldest bipolar plate). This transverse water flow 0AT is therefore oriented along the -Z direction on the side of the collectors CSlhtf and CE2htf, and is oriented along the +Z direction on the side of the collectors CElhtf and CS2htf. It is therefore oriented along the same direction as that of the transverse flow 0Ac, which makes it possible to further humidify the oxygen at the inlet of the cathode circuit as well as the hydrogen at the inlet of the cathode circuit, and makes it possible to further improve the hydration of the membrane Mn in particular at the inlet and outlet of the active zone.

[0073] To the extent that there is an alternation of the direction of flow of the heat transfer fluid from one bipolar plate to another, as well as an alternation of the direction of flow of each reactive fluid from one bipolar plate to another, each electrochemical cell has a non-zero transverse temperature gradient AT at the inlet and outlet of the active zone, which generates a transverse flow of water 0AT oriented in the same direction as the transverse flow of water 0Ac. Thus, each electrochemical cell has the same improvement in the hydration of the electrolytic membrane.

[0074] As indicated previously, by this transverse flow of water 0AT of thermal origin, a greater quantity of water is retained in each electrochemical cell, which makes it possible to further humidify the reactive fluids at the inlet of the distribution circuits, and therefore to improve the hydration of the electrolytic membranes. It is thus possible to supply the distribution circuits with drier reactive fluids, and / or to operate the fuel cell at a higher nominal operating temperature (at least equal to 80°C).

[0075] In the embodiment of [Fig.3] and [Fig.4], the transverse flow of water 0AT is oriented, in each electrochemical cell, in the same direction as the transverse flow of water 0Ac. This comes from the fact that, in each bipolar plate of the electrochemical cell, the heat transfer fluid flows in the same direction as the reactive fluid. Thus, in cell Cn, the heat transfer fluid and the hydrogen of the bipolar plate PBn flow along the -X direction, while the heat transfer fluid and the oxygen of the bipolar plate PBn+i flow along the +X direction.

[0076] It is however possible to provide that, in each bipolar plate of the electrochemical cell, the heat transfer fluid flows in the opposite direction to the reactive fluid. This can make it possible to cause flooding of the distribution circuits in the event that the fuel cell is initially flooded.

[0077] In this respect, [Fig. 5] is a schematic and partial view, in perspective and exploded, of a stack of electrochemical cells of a fuel cell according to one embodiment. [Fig. 6] left is a schematic and partial view, in cross-section, of the stack of electrochemical cells illustrated in [Fig. 5]; and [Fig. 6] right illustrates an example of variation in the temperature of the heat transfer fluid in the cooling circuit of the bipolar plates of [Fig. 6] left, as well as an example of variations in the concentration of water in the fluids flowing in the distribution circuits of the bipolar plates.

[0078] As previously indicated, the fuel cell differs from that of [Fig. 3] essentially in that, in each bipolar plate of the electrochemical cell, the heat transfer fluid flows in the opposite direction to the reactant fluid. In addition, this configuration is particularly advantageous when the fuel cell is initially flooded, so that the water concentration at the inlet of the distribution circuits is high and must be reduced.

[0079] Thus, in the bipolar plate PBn of the cell Cn, the heat transfer fluid flows in the direction +X from the collector CElhtf to the collector CSlhtf, while the hydrogen flows in the anode distribution circuit in the direction -X from the collector CE1H2 towards the collector CS1H2. Indeed, the inlet collector CElhtf is opposite the inlet collector CE1H2 with respect to the active zone.

[0080] Furthermore, in the bipolar plate PBn+i of the same cell Cn, the heat transfer fluid flows in the direction -X from the collector CE2htf to the collector CS2htf, while the oxygen flows in the cathode distribution circuit in the direction +X from the collector CE202 towards the collector CS202. Indeed, the inlet collector CE2 htf is opposite the inlet collector CE202 with respect to the active zone.

[0081] The fuel cell being initially flooded, the concentration of water cl]2 at the inlet of the anode distribution circuit (collector CE1H2) is particularly high, as is the concentration of water cQ-- at the outlet of the cathode distribution circuit (collector CS202). Also, the transverse gradient of concentration Ac is low there, so that the transverse flow of water 0Ac is also low.

[0082] On the other hand, the transverse temperature gradient AT remains high, as in the case of fig. 3. Here it is oriented in the +Z direction, on the side of the collectors CE1H2 and CS202, so that the transverse flow of water 0AT is oriented in the -Z direction (towards the coldest bipolar plate). Thus, the water present at the inlet of the anode distribution circuit (towards the collector CE1H2) diffuses through the membrane towards the outlet of the cathode distribution circuit (towards the collector CS202). Thus, the concentration of water C^2 at the inlet of the anode distribution circuit is reduced.

[0083] Similarly, the transverse temperature gradient AT is here oriented along the -Z direction, on the side of the collectors CS1H2 and CE202, so that the transverse flow of water 0AT is oriented along the +Z direction (always towards the coldest bipolar plate). Thus, the water present at the inlet of the cathode distribution circuit (towards the collector CE202) diffuses through the membrane towards the inlet of the anode distribution circuit (towards the collector CS1H2). Thus, the concentration of water c22 at the inlet of the cathode distribution circuit is reduced.

[0084] Since there is an alternation of the direction of flow of the heat transfer fluid from one bipolar plate to the other, as well as an alternation of the direction of flow of each reactive fluid, each electrochemical cell has a transverse temperature gradient, which generates a transverse flow of water 0AT oriented so as to reduce the concentration of water at the inlet of the anode and cathode distribution circuits. Thus, each electrochemical cell has the same local reduction in the concentration of water, thus leading to a progressive dewatering of the fuel cell.

[0085] Particular embodiments have just been described. Different variants and modifications will be apparent to those skilled in the art.

Claims

Claims

1. Fuel cell, comprising: • a stack of N electrochemical cells (Cn=i;N), with N>1; • each electrochemical cell (Cn) comprising an electrolytic membrane (Mn) arranged between two bipolar plates (PBn; PBn+i) the successive bipolar plates being identified by a rank n ranging from 1 to N+1; • each bipolar plate (PBn=i;N+i) comprising a distribution circuit for a reactive oxidizing fluid (O2), a distribution circuit for a reactive combustible fluid (H2), and a cooling circuit for a heat transfer fluid; • inlet manifolds (CE) for the reactive fluids and the heat transfer fluid, and associated outlet manifolds (CS), the inlet and outlet manifolds passing through the bipolar plates and being connected to the distribution and cooling circuits; • the inlet and outlet collectors being arranged so that, in each electrochemical cell, the reactive oxidant (O2) and combustible (H2) fluids flow counter-currently on either side of the electrolytic membrane; • characterized in that it comprises: • first and second inlet manifolds (CEI02; CE202) of the oxidizing reactive fluid (O2), and associated first and second outlet manifolds (CS102; CS202); • first and second inlet manifolds (CE1H2; CE2H2) of the combustible reactive fluid (H2), and associated first and second outlet manifolds (CS1H2; CS2H2); and • first and second inlet manifolds (CElhtf; CE2htf) of the heat transfer fluid, and associated first and second outlet manifolds (CSlhtf; CS2htf); the first input collectors (CEI02; CE1H2; CE1htf) supplying only the bipolar plates of odd rank n; and the second input collectors (CE202; CE2 H2; CE2htf) supplying only the bipolar plates of even rank n; in each bipolar plate (BPn=i;N+i): the first and second inlet collectors (CElhtf; CE2htf) of the heat transfer fluid are opposite each other with respect to the cooling circuit, so that there is an alternation of the direction of flow of the heat transfer fluid from one bipolar plate to the other; in each bipolar plate (BPn=i;N+i): the first and second inlet collectors (CEI02; CE202) of the oxidizing reactive fluid (O2) are opposite each other with respect to the distribution circuit, and the first and second inlet collectors (CE1H2; CE2H2) of the combustible reactive fluid (H2) are opposite each other with respect to the distribution circuit, so that there is an alternation of the direction of flow of each reactive fluid from one bipolar plate to the other.

2. Fuel cell according to claim 1, in which, in each bipolar plate (PBn=i;N+i), the first inlet manifold (CE1H2) of the combustible fluid is opposite the second inlet manifold (CE202) of the oxidizing fluid with respect to the distribution circuits.

3. Fuel cell according to claim 1 or 2, in which, in each bipolar plate (PBn=i;N+1), the first inlet collectors (CEI02; CE1H2) of the reactive fluids are opposite the second inlet collectors (CE202; CE2H2) of the reactive fluids with respect to the distribution circuits.

4. Fuel cell according to claim 3, in which the first inlet collector (CElhtf) of the heat transfer fluid is located on the same side as the first inlet collectors (CEI02; CE1H2) of the fluids reactive fluids, the second inlet manifold (CE2htf) of the heat transfer fluid being located on the same side as the second inlet manifolds (CE202; CE2H2) of the reactive fluids, so that the first and second inlet manifolds (CElhtf; CE2htf) of the heat transfer fluid are opposite each other with respect to the cooling circuit.

5. Fuel cell according to claim 3, wherein the first inlet manifold (CElhtf) of the heat transfer fluid is located on the same side as the second inlet manifolds (CE202; CE2H2) of the reactive fluids, the second inlet manifold (CE2htf) of the heat transfer fluid being located on the same side as the first inlet manifolds (CEI02; CE1H2) of the reactive fluids, so that the first and second inlet manifolds (CElhtf; CE2htf) of the heat transfer fluid are opposite each other with respect to the cooling circuit.

6. A fuel cell according to any one of claims 1 to 5, wherein each electrolyte membrane is a proton exchange membrane or an anion exchange membrane.

7. A method of using the fuel cell according to any one of the preceding claims, wherein a nominal operating temperature of the electrochemical cells is greater than or equal to 80°C.

8. Method of use according to the preceding claim, in which the reactive fluids introduced into the distribution circuits have a relative humidity less than or equal to 30%.

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