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 in which the bipolar plates of the electrochemical cells have two inlet manifolds, one for each reactive fluid and one for the heat transfer fluid, as well as the associated outlet manifolds. The inlet and outlet manifolds are arranged so that the flow direction of the heat transfer fluid and each reactive fluid alternates from one bipolar plate to the other. Figure for the abstract: Fig. 3

Description

Title of the invention: Fuel cell comprising a stack of electrochemical cells and several inlet and outlet manifolds 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, whose bipolar plates are traversed by inlet and outlet manifolds ensuring the circulation of the reactant fluids and the heat transfer fluid and the evacuation of the products of the electrochemical reaction. PRIOR TECHNOLOGY

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

[0003] Generally, the fuel fluid (e.g., hydrogen) is supplied to the anode, while the oxidizing fluid (e.g., oxygen from 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. For the electrochemical reaction to occur, an ionic conductor is required 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 cell stack is thus the site of the electrochemical reaction: the reactive fluids must be supplied to it, the products and non-reactive species must be removed, as well as the heat produced during the reaction.

[0004] Electrochemical cells are usually separated from each other by bipolar plates that provide electrical interconnection between them as well as the flow of reactant fluids and the heat transfer fluid. The bipolar plates have an anodic face on which a hydrogen distribution circuit is formed, and an opposite cathodic face on which an oxygen distribution circuit is formed. Each distribution circuit takes the form of a network of channels arranged to deliver the reactant fluid to the corresponding electrode. The bipolar plates may also include a cooling circuit formed by a network of internal conduits that ensure the flow of a heat transfer fluid, allowing the heat produced locally during the electrochemical reaction by the cell to be dissipated. The distribution and cooling circuits are... positioned opposite each other, and define what is called the active zone of electrochemical cells.

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

[0006] Figure 2 on the left is a schematic and partial cross-sectional view of the stack of electrochemical cells in Figure 1. Figure 2 on the right illustrates an example of the temperature variation of the heat transfer fluid along the cooling circuit of the bipolar plates in Figure 2 on the left, as well as an example of the variation in water concentration in the fluids flowing in the distribution circuits of the bipolar plates. In the figures, "H2" and "O2" are indicated, for illustrative purposes and simplicity, 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 that pass through the stack of electrochemical cells, and more specifically the stack of bipolar plates.

[0008] Thus, each anodic distribution circuit is connected to the same hydrogen inlet manifold CEH2 and the same outlet manifold CSH2. Similarly, the cathodic distribution circuits are connected to the same oxygen inlet manifold CEO2 and the same outlet manifold CSO2, and the cooling circuits are connected to the same heat transfer fluid inlet manifold CEhtf and the same outlet manifold CShtf.

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

[0010] The inlet manifolds CEH2, CEO2 and outlet manifolds CSH2, CSO2 of the reactive fluids can be arranged so that, in each electrochemical cell Cn, hydrogen and oxygen flow in counter-current on either side of the electrolytic membrane Mn. Thus, the inlet manifold CEH2 of hydrogen and the inlet manifold CEO2 of oxygen are arranged oppositely along the main longitudinal axis X with respect to the distribution circuits.

[0011] Furthermore, the water concentration c|J2 and C^2 in the fluids increases along the anodic and cathodic distribution circuits. Also, because the reactive fluids The counter-current flow across the membrane results in the formation of a transverse water concentration gradient, particularly at the inlet and outlet of the active zone, thus generating a transverse flux of water (OAc) by diffusion across the electrolytic membrane. Therefore, there is a transverse flux of water (OAc) from the cathodic outlet, where the fluid has a high water concentration (c^2), to the anodic inlet, where the fluid has a low water concentration (C^2). Similarly, there is a transverse flux of water (OAc) from the anodic outlet, where the fluid has a high water concentration (cH2), to the cathodic inlet, where the fluid has a low water concentration (cO2). The transverse flux of water (OAc) 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 high, but it can be more or less high along the distribution circuits.

[0012] This configuration increases the hydration of the electrolytic membrane, particularly at the inlet and outlet of the active zone, which helps improve the performance of electrochemical cells. Indeed, it is known that the ionic conductivity of the electrolytic membrane decreases sharply when the water concentration (e.g., relative humidity) in the fluids flowing through the distribution circuits decreases.

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

[0014] The invention aims to provide a fuel cell with improved performance. To this end, the object 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 disposed between two bipolar plates, the successive bipolar plates being identified by a rank n 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 fuel fluid, and a cooling circuit for a heat transfer fluid; • inlet manifolds for reactive fluids and 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 fuel reactive fluids flow counter-currently on either side of the electrolytic membrane.

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

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

[0017] Furthermore, in each bipolar plate: the first and second inlet manifolds of the heat transfer fluid are opposed to 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 manifolds of the oxidizing reactive fluid are opposed to each other with respect to the distribution circuit, and the first and second inlet manifolds of the combustible reactive fluid are opposed to 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 not limiting aspects of this fuel cell are the following.

[0020] In each bipolar plate, the first inlet manifold of the fuel fluid can be opposed to the second inlet manifold of the oxidizing fluid with respect to the distribution circuits.

[0021] In each bipolar plate, the first reactive fluid inlet manifolds can be opposed to the second reactive fluid inlet manifolds with respect to the distribution circuits.

[0022] The first heat transfer fluid inlet manifold can 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, so 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 can 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, so 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 of less than or equal to 30%. Brief description of the drawings

[0027] Other aspects, objects, advantages and features of the invention will become more apparent upon reading the following detailed description of preferred embodiments thereof, given by way of non-limiting example, and made with reference to the accompanying drawings in which:

[0028] Fig. 1, already described, is a schematic and partial view, in perspective and exploded view, of a stack of electrochemical cells of a fuel cell according to an example of the prior art;

[0029] the left [Fig.2] is a schematic and partial cross-sectional view of the stack of electrochemical cells illustrated in the [Fig.1];

[0030] The [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 the [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 view, of a stack of electrochemical cells of a fuel cell according to one embodiment;

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

[0033] The [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 the [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 view, of a stack of electrochemical cells of a fuel cell according to one embodiment;

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

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

[0037] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0038] In the figures and throughout the description, the same reference numerals represent identical or similar elements. Furthermore, the various elements are not drawn to scale in order to enhance the clarity of the figures. Moreover, the different embodiments and variants are not mutually exclusive and may be combined. Unless otherwise indicated, the terms "approximately," "about," and "in the order of" mean within 10%, and preferably within 5%. Furthermore, the terms "between ... and ..." and equivalents mean that the limits are inclusive, unless otherwise stated.

[0039] The invention relates to a fuel cell formed from a stack of electrochemical cells connected in series by bipolar plates. The bipolar plates are traversed by several inlet and outlet manifolds allowing the distribution and cooling circuits to be supplied with reactive fluids and a heat transfer fluid.

[0040] According to the invention, the fuel cell comprises several inlet manifolds for each 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 flow within the same electrochemical cell on either side of the electrolytic membrane, and so that the direction of flow of each reactive fluid and the heat transfer fluid alternates from one bipolar plate to the other.

[0041] This configuration allows the formation of a transverse temperature gradient AT within each electrochemical cell, particularly at the inlet and outlet of the active zone, resulting in a transverse flow of water 0AT by diffusion across the electrolytic membrane towards the coldest bipolar plate. This transverse flow of water 0AT is of thermal origin and is thus distinct 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 can be more or less significant along the distribution circuits.

[0042] This transverse flow of thermally generated water 0AT can then be used to increase the hydration of the electrolytic membrane. Indeed, thanks to this transverse flow of water 0AT, a larger proportion of the water present at the outlet of a distribution circuit (where the water concentration is high) diffuses through the membrane The electrolytic fluid flows to the inlet of the opposite distribution circuit (where the water concentration is low). This further humidifies the inlet of the distribution circuit, increasing the hydration of the electrolytic membrane. In other words, a larger quantity of water is retained in each electrochemical cell, potentially reducing the need for the reactive fluid humidification system or even eliminating it entirely. This is particularly advantageous when the fuel cell's nominal operating temperature is high (e.g., at least 80°C). It then becomes 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 water concentration at the inlet of the distribution circuits in the event that the fuel cell needs to be dewatered.

[0044] Various 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., from air) and whose anode is supplied with hydrogen. However, the invention applies to any type of fuel cell, particularly those operating at low temperatures, i.e., below 200°C. It can thus be applied to AEM (Anion Exchange Membrane) type fuel cells.

[0045] Figure 3 is a schematic and partial cross-sectional exploded view of a stack of electrochemical cells in a fuel cell according to one embodiment. As before, 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 may represent all or only some of the electrochemical cells in the fuel cell. In any case, the N electrochemical cells are connected in series by the successive bipolar plates.

[0046] Here and for the rest of the description we define a direct orthogonal frame XYZ, where the XY plane is parallel to the bipolar plates and 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] Each electrochemical cell comprises 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 AME extends parallel to the XY plane.

[0048] Each membrane-electrode assembly is separated from that of 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 lies the electrolytic membrane Mn. This representation is obviously schematic: the anodes and cathodes, as well as the gas diffusion layers, are not shown here. Furthermore, the electrolytic membrane may have a larger surface area and extend to the edge of the bipolar plates.

[0049] Each bipolar plate has an anodic face, where an anodic distribution circuit is located for bringing the fuel fluid, here hydrogen, into contact with the anode of an electrochemical cell, and an opposite cathodic face, where a cathodic distribution circuit is located for bringing the oxidizing fluid, here oxygen from the air, into contact with the cathode of the adjacent electrochemical cell. The distribution circuits also allow for the removal of the products of the electrochemical reactions and non-reactive species.

[0050] Furthermore, the bipolar plates each include a cooling circuit, located between the anodic and cathodic 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 manifolds of the reactive fluids and the heat transfer fluid.

[0052] The inlet and outlet manifolds are openings that pass through the stack of electrochemical cells, and more specifically through the stack of bipolar plates. They are designed to supply the distribution circuits with the two reactive fluids, and the cooling circuits with the heat transfer fluid. Each manifold passes vertically through the bipolar plates.

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

[0054] According to the invention, the fuel cell comprises: - the first and second inlet manifolds IEC02, CE202 of the oxidizing reactive fluid (here O2), and the associated first and second outlet manifolds CS102, CS202; - the first and second inlet manifolds CE1H2, CE2H2 of the combustible reactive fluid (here H2), and the associated first and second outlet manifolds CS1H2, CS2H2; and - of the first and second inlet manifolds CE1htf, CE2htf of the ca- fluid loporteur, and the first and second output collectors CSlhtf, CS2htf associated.

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

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

[0057] Furthermore, the inlet manifolds CE1htf, CE2htf and outlet manifolds CS1htf, 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 non-zero transverse temperature gradient (oriented along the Z-axis) AT within each electrochemical cell, in particular at the inlet and outlet of the active zone.

[0058] To achieve this, in each bipolar plate, the first inlet manifold CElhtf is positioned 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 CSihtf, and flows in the bipolar plate PBn+1 in the +X direction, from the inlet manifold CE2htf to the outlet manifold CSihtf.

[0059] Furthermore, the inlet manifolds CE1H2, CE2H2, CEI02, CE202 and outlet manifolds 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 input collector CE1H2 supplies the anodic distribution circuit of the bipolar plate PBn with hydrogen, and the second input collector CE202 supplies the circuit of cathodic distribution of the bipolar plate PBn+i in oxygen.

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

[0062] Furthermore, the inlet manifolds CE1H2, CE2H2, CEI02, CE202 and outlet manifolds 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], hydrogen flows here in the -X direction in the anodic distribution circuit of the bipolar plate PBn, in the +X direction in the bipolar plate PBn+i, in the -X direction in the bipolar plate PBn+2, etc. Similarly, oxygen flows in the -X direction in the cathodic distribution circuit of the bipolar plate PBn, in the +X direction in the bipolar plate PBn+i, in the -X direction in the bipolar plate PBn+2, etc.

[0064] To this end, within each bipolar plate, the first hydrogen inlet collector CE1H2 is opposed to the second hydrogen inlet collector CE2H2 with respect to the active zone, and therefore to the anodic distribution circuit. Similarly, the first oxygen inlet collector CEIO2 is opposed to the second oxygen inlet collector CE2O2 with respect to the active zone, and therefore to the cathodic distribution circuit.

[0065] Fig. 4 on the left is a schematic and partial cross-sectional view of the stack of electrochemical cells illustrated in Fig. 3. Fig. 4 on the right illustrates an example of temperature variation of the heat transfer fluid in the cooling circuit of the bipolar plates of Fig. 4 on the left, as well as an example of variations in water concentration 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: hydrogen flows here in the direction -X from CE1H2 to CS1H2 in the anodic distribution circuit of the bipolar plate PBn, and oxygen flows in the direction +X from CE2O2 to CS2O2 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 anodic 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 cathodic 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 around 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 around 80% or more, for example 100%.

[0069] Note that the variation in water concentration illustrated in [Fig. 4] on the right is obviously very schematic. It is generally increasing, but 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 water concentration value at the outlet is higher than the value at the inlet.

[0070] A transverse concentration gradient Ac is then formed along the vertical Z axis, particularly at the inlet and outlet of the active zone, which generates a transverse flow of water 4>Ac, by diffusion across the Mn membrane, oriented along the -Z direction on the side of the collectors C1htf and CE2htf, and oriented along the +Z direction on the side of the collectors C1htf and CS2htf. This transverse flow of water 0Ac allows the oxygen inlet of the cathodic circuit to be moistened, as well as the hydrogen inlet of the cathodic circuit, thereby improving the hydration of the Mn membrane, particularly 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 CSihtf), 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 CSihtf of the bipolar plates of even rank n PBn, PBn+2, PBn+4... and at the collector CS2htf of the bipolar plates of odd rank n PBn+i, PBn+3, PBn+5--

[0072] Since these two outlet collectors C1htf and C2htd are opposite each other with respect to the active zone, a non-zero transverse temperature gradient AT is formed along the Z-axis, particularly at the inlet and outlet of the active zone. This gradient generates a second transverse water flow 0AT by diffusion across the Mn membrane (the water diffuses towards the colder bipolar plate). This transverse water flow 0AT is therefore oriented in the -Z direction on the side of the C1htf and C2htf collectors, and in the +Z direction on the side of the C1htf and C2htf collectors. It is thus oriented in the same direction as the transverse flow 0Ac, which further humidifies the oxygen and hydrogen entering the cathode circuit, and further improves the hydration of the Mn membrane, particularly at the inlet and outlet of the active zone.

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

[0074] As previously stated, this transverse flow of thermally generated water (0AT) retains a larger quantity of water in each electrochemical cell, thereby increasing the humidification of the reactive fluids entering the distribution circuits and thus improving the hydration of the electrolytic membranes. This allows the distribution circuits to be supplied with drier reactive fluids and / or the fuel cell to operate at a higher nominal operating temperature (at least 80°C).

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

[0076] However, it is 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 allow for the unflooding of the distribution circuits in the event that the fuel cell is initially flooded.

[0077] Accordingly, [Fig. 5] is a schematic and partial view, in perspective and exploded view, of a stack of electrochemical cells of a fuel cell according to one embodiment. [Fig. 6] left is a schematic and partial cross-sectional view of the stack of electrochemical cells illustrated in [Fig. 5]; and [Fig. 6] right illustrates an example of the temperature variation 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 water concentration in the fluids flowing in the distribution circuits of the bipolar plates.

[0078] As previously stated, 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 reactive fluid. Furthermore, 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 +X direction from the collector CElhtf to the collector CSihtf, while the hydrogen flows in the anodic distribution circuit in the -X direction 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 -X direction from the manifold CE2htf to the manifold CS2htf, while the oxygen flows in the cathodic distribution circuit in the +X direction from the manifold CE202 towards the manifold CS202. Indeed, the inlet manifold CE2htf is opposite the inlet manifold CE202 with respect to the active zone.

[0081] Since the fuel cell is initially flooded, the water concentration cl]2 at the inlet of the anodic distribution circuit (collector CE1H2) is particularly high, as is the water concentration cQ-- at the outlet of the cathodic distribution circuit (collector CS2O2). Therefore, the transverse concentration gradient Ac is low, so the transverse water flux 0Ac is also low.

[0082] In contrast, the transverse temperature gradient AT remains high, as in the case of Fig. 3. Here, it is oriented along the +Z direction, towards the collectors CE1H2 and CS2O2, so that the transverse water flow 0AT is oriented along the -Z direction (towards the colder bipolar plate). Thus, the water present at the inlet of the anodic distribution circuit (towards the collector CE1H2) diffuses through the membrane towards the outlet of the cathodic distribution circuit (towards the collector CS2O2). This reduces the water concentration C^2 at the inlet of the anodic distribution circuit.

[0083] Similarly, the transverse temperature gradient AT is oriented along the -Z direction, towards the collectors CS1H2 and CE2O2, so that the transverse water flow 0AT is oriented along the +Z direction (always towards the colder bipolar plate). Thus, the water present at the inlet of the cathodic distribution circuit (towards the collector CE2O2) diffuses through the membrane towards the inlet of the anodic distribution circuit (towards the collector CS1H2). This reduces the water concentration c2O at the inlet of the cathodic distribution circuit.

[0084] Since the flow direction of the heat transfer fluid alternates from one bipolar plate to the other, as does the flow direction of each reactive fluid, each electrochemical cell exhibits a transverse temperature gradient, which generates a transverse flow of water oriented to reduce the water concentration at the inlet of the anodic and cathodic distribution circuits. Thus, each electrochemical cell exhibits the same local reduction in water concentration, leading to a progressive dewatering of the fuel cell.

[0085] Specific embodiments have just been described. Different variants and Changes will be apparent to a person skilled in the art.

Claims

Demands

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 from 1 to N+1; • each bipolar plate (PBn=i ;N+i) comprising a distribution circuit for an oxidizing reactive fluid (O2), a distribution circuit for a combustible reactive fluid (H2), and a cooling circuit for a heat transfer fluid; • inlet manifolds (IM) for reactive fluids and heat transfer fluid, and associated outlet manifolds (AB), the inlet and outlet manifolds passing through the bipolar plates and being connected to the distribution and cooling circuits; • the inlet and outlet manifolds being arranged so that, in each electrochemical cell, the reactive oxidizing (O2) and fuel (H2) fluids flow counter-currently on either side of the electrolytic membrane; • characterized in that it comprises: • the first and second inlet manifolds (IEC02; CE202) of the oxidizing reactive fluid (O2), and the associated first and second outlet manifolds (CS102; CS202); • the first and second inlet manifolds (CE1H2; CE2H2) of the combustible reactive fluid (H2), and the associated first and second outlet manifolds (CS1H2; CS2H2); and • the first and second inlet manifolds (CE1htf; CE2htf) of the heat transfer fluid, and the associated first and second outlet manifolds (CS1htf; 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 manifolds (CE1htf; 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 manifolds (CE1O2; CE2O2) of the oxidizing reactive fluid (O2) are opposite each other with respect to the distribution circuit, and the first and second inlet manifolds (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, wherein, in each bipolar plate (PBn=i ;N+i), the first inlet manifold (CE1H2) of the fuel fluid is opposed to the second inlet manifold (CE202) of the oxidizer fluid with respect to the distribution circuits.

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

4. Fuel cell according to claim 3, wherein the first inlet manifold (CE1H1) of the heat transfer fluid is located on the same side as the first inlet manifolds (CE1H2; CE1H2) of the fluids reactive, 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 (CE1htf) 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 (CE102; CE1H2) of the reactive fluids, so that the first and second inlet manifolds (CE1htf; CE2htf) of the heat transfer fluid are opposite each other with respect to the cooling circuit.

6. Fuel cell according to any one of claims 1 to 5, wherein each electrolytic 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. A method of use according to the preceding claim, wherein the reactive fluids introduced into the distribution circuits have a relative humidity less than or equal to 30%.

Images