Fuel cell membrane-electrode assembly, method of manufacturing such an assembly and fuel cell comprising at least one such assembly

Abstract

TITLE: Fuel cell membrane-electrode assembly, method for manufacturing such an assembly and fuel cell comprising at least one such assembly This fuel cell membrane-electrode assembly (2) comprises a membrane (22, 25), a frame (30) supporting the membrane, at least one diffusion layer (28) covering the membrane and a portion of the frame. The frame comprises a first half-frame (32) and a second half-frame (34) supporting the membrane and arranged on two opposite sides of the membrane. At least the second half-frame is coated, on a surface (S34) facing the first half-frame, with a layer of adhesive. First orifices (42) arranged through the first half-frame (32) are arranged facing the diffusion layer (28), in a direction (A30) perpendicular to a main plane of the membrane (π22).The diffusion layer (28) is secured to the frame (30) by a quantity (Q2) of glue which extends through the first orifices (42) and which comes from the glue coated on the facing surface (S34) of the second half-frame (34). Figure for the abstract: 3.

Description

Description Title of the invention: Fuel cell membrane-electrode assembly, method for manufacturing such an assembly and fuel cell fuel comprising at least one such assembly

[0001] — The present invention relates to a membrane-electrode assembly for a fuel cell combustible. The invention also relates to a method for manufacturing an assembly fuel cell membrane-electrode, as well as a fuel cell comprising at least one such membrane-electrode assembly.

[0002] In the field of fuel cells, it is known to insert a stack of electrochemical cells between two terminal plates, located on either side of this stacking in a stacking direction, and possibly to arrange this stacked in a casing. Electrochemical cells are formed by as- membrane-electrode assemblies and bipolar plates. A membrane- electrode is sometimes referred to as MFA, from the English "Membrane-Electrode Assembly", and generally includes a base membrane, which can be coated on one or on both sides, a catalytic layer comprising a catalyst, as well as a frame that supports this membrane. The frame may have openings which, in The stacking defines fluid flow galleries within the stack. electrochemical cells for the distribution and recovery of these fluids in the corresponding fluid compartments of each cell. This framework is the most often associated with at least one seal, sometimes called a "gasket", with which it ensures also a function of sealing against fluid flow within stacking.

[0003] …— The membrane, when coated with layers comprising a catalyst, is sometimes called CCM, from the English "Catalyst Coated Membrane" and includes in this case three layers namely, a membrane proper, a ca- layer a catalytic layer on the anode side and a catalytic layer on the cathode side.

[0004] — In the stack, a membrane-electrode assembly is intercalated between two bipolar plates and thus delimits an anodic compartment and a ca- compartment methodical. On each side, the catalyst-coated membrane is covered by a gas diffusion layer which is therefore received in the anodic compartment or ca- methodical approach corresponding to and promotes contact between the chemical species(ies), present in the corresponding anodic or cathodic compartment, with the membrane. Each gas diffusion layer also plays a role in conducting the electrons. These diffusion layers are sometimes called GDLs, from the English "Gas Diffusion Layers". Diffusion Layer. It is known to manufacture a membrane-electrode assembly by attaching the catalyst-coated membrane to the frame, which notably stiffens the membrane and facilitates its handling. This is achieved by bonding the membrane tightly to the frame. Once this operation is completed, it is known that the diffusion layer(s) can be immobilized on the pre-assembled membrane and frame in a further operation using a different adhesive. This immobilization is advantageous because it ensures that the gas diffusion layers are held in place, at least during the assembly of the electrochemical cells, sometimes called "stacking." This additional operation is time-consuming and requires the application of adhesive to the diffusion layer or the frame. In practice, this lengthens and increases the manufacturing cost of a fuel cell. WO-A-2018 / 055567 is known to use a grid for adhesive diffusion within a membrane-electrode assembly. A diffusion layer is applied and bonded to a portion of the pre-formed assembly. It is also known from US-B-11056694 to perform a membrane-electrode assembly on a bipolar plate, with a diffusion layer mounted edge-to-edge with a frame, the diffusion layer being spot-welded to an internal surface of the peripheral frame. Such an operation requires precise handling and is time-consuming. Furthermore, in known materials, the adhesive used to fix the diffusion layer to the frame is prone to capillary action. To prevent it from overflowing the diffusion layer, which could contaminate an electrochemical cell and / or the sealing gasket, a relatively wide overlap of the frame by the diffusion layer is necessary. This tends to reduce the effective surface area of ​​the membrane, unless the transverse dimensions of the cell stack are increased, thus increasing the overall size of a fuel cell with such a stack. It is these drawbacks that the invention intends to remedy in particular by proposing a new membrane-electrode assembly for a fuel cell whose manufacture can be simplified and whose cost price can be reduced compared to previous equipment. To this end, the invention relates to a fuel cell membrane-electrode assembly, this assembly comprising a membrane, a frame supporting the membrane, and at least one diffusion layer covering the membrane and a portion of the frame. The frame is bipartite and comprises a first half-frame supporting the membrane and disposed on one side of the membrane, and a second half-frame supporting the membrane and disposed on a second side of the membrane. unless the second half-frame is coated, on a surface opposite the first half-frame, with a layer of glue for joining the half-frames. According to the invention, first orifices formed through the first half-frame are arranged opposite the diffusion layer, in a direction perpendicular to a principal plane of the membrane. Furthermore, the diffusion layer is bonded to the frame by a quantity of adhesive that extends through the first orifices and originates from the adhesive coated on the opposite surface of the second half-frame. Thanks to the invention, an adhesive applied to a surface of the second half-frame can migrate through the first openings made in the first half-frame, thereby bonding the diffusion layer to the side of the first half-frame opposite the second, without the need for additional adhesive. The manufacturing of the membrane-electrode assembly is thus simplified and its cost is well controlled. According to advantageous but not mandatory aspects of the invention, such a membrane-electrode assembly may incorporate one or more of the following features, taken in any technically permissible combination: - The membrane-electrode assembly includes a first diffusion layer disposed on one side of the membrane and which partially covers the first half-frame and a second diffusion layer disposed on a second side of the membrane and which partially covers the second half-frame, while the second diffusion layer is bonded to the frame by a second quantity of glue which extends through second orifices made through the second half-frame and which comes from the glue coated on the surface opposite the first half-frame. - The first and second orifices are offset from each other in at least one direction parallel to a principal plane of the membrane, so that there is no overlap between these orifices. - Each opening made through a half-frame has a cross-section with an area less than or equal to 50 mm², preferably 20 mm², with a shape preferably circular, rectangular or oblong. - Each opening made through a half-frame has a cross-section with an area greater than or equal to 5 mm², preferably 10 mm², with a shape preferably circular, rectangular or oblong. - The glue is thermo-activatable and based on thermoplastic polymer, in particular EVA copolymer. - A strip covering the frame by the diffusion layer has a width in the range of 4 to 15 mm, preferably in the range of 5 to 10 mm. According to another aspect, the invention relates to a method for manufacturing a membrane-electrode assembly, in particular a membrane-electrode assembly as mentioned above. This method comprises a preliminary step of coating a first surface of at least the second half-frame with an adhesive, a step of bonding the frame and the membrane by applying the first surface of the second half-frame, coated with adhesive, against a first surface of the first half-frame, and a step of depositing the diffusion layer on a second surface of the first half-frame, opposite the first surface of this half-frame which is opposite the first surface of the second half-frame.According to the invention, this method includes a step of bonding the diffusion layer and the frame by adhesion of the glue, coated on the first surface of the second half-frame, to a surface of the diffusion layer, through first orifices made through the first half-frame, between its first and second surfaces. Advantageously, this process may incorporate one or more of the following characteristics, taken in any technically feasible combination: The membrane-electrode assembly comprises a first diffusion layer, positioned on the first side of the membrane and partially covering the first half-frame, and a second diffusion layer, positioned on the second side of the membrane and partially covering the second half-frame. The preliminary step involves coating the initial surfaces of the first and second half-frames with an adhesive.During the bonding stage, the first diffusion layer is bonded to the frame by the adhesion of the glue, coated on the first surface of the second half-frame, to a surface of the first diffusion layer, through the first holes made through the first half-frame, between its first and second surfaces, while the second diffusion layer is bonded to the frame by the adhesion of the glue, coated on the first surface of the first half-frame, to a surface of the second diffusion layer, through the first holes made through the second half-frame, between its first and second surfaces. - The adhesion of the glue, applied to the first surface, to the surface of the diffusion layer results from the migration of the glue from the first surface to the surface of the diffusion layer. - The bonding step includes a sub-step of pressing, a sub-step of heating and / or a sub-step of vibration for the migration of the glue through the holes made through the half-frame(s). - The step of joining the frame and the membrane and the step of joining the diffusion layer on the corresponding half-frame, by adhesion of the glue coated on the first surface of the other half-frame, are simultaneous. - The step of bonding the diffusion layer to the corresponding half-frame, adhesion of the glue, coated on the first surface of the other half-frame, is achieved by subjecting this glue to ultrasound. According to a third aspect, the invention relates to a fuel cell comprising at least one stack of electrochemical cells formed by membrane-electrode assemblies and bipolar plates. According to the invention, at least one of the membrane-electrode assemblies is as described above or manufactured by the method described above, and preferably, all the membrane-electrode assemblies are as described above or manufactured by the method described above. The invention will be better understood and other advantages thereof will become more apparent from the following description of an embodiment of a membrane-electrode assembly, a method, and a fuel cell conforming to its principle, given solely by way of example and with reference to the accompanying drawings in which: [Fig. 1] Fig. 1 is a partially exploded perspective view of an as- membrane-electrode assembly according to the invention and a plate bipolar, this assembly and this bipolar plate belonging to an em- stack of electrochemical cells of a fuel cell; [Fig.2] Fig.2 is a front view of the membrane-electrode assembly. presented in [Fig.1]; [Fig. 3] Fig. 3 is a longitudinal section of the assembly, along the line III-III to [Fig.2]; [Fig. 4] Fig. 4 is an exploded perspective view of the assembly of figures 2 and 3; and [Fig. 5] Figure 5 is a partial cross-section in principle, in the direction of the arrows. V in [Fig.1], of a stack of electrochemical cells of a battery combustible according to the invention, this stack not being in configuration exploded, unlike what is shown in [Fig.1]. In order to clearly show the characteristics of the invention, the proportions are not necessarily respected between the objects represented in the figures. A membrane-electrode assembly 2 is shown partially exploded in [Fig.1], above a bipolar plate 4. Elements 2 and 4 belong to a stack 6 of electrochemical cells 60, this stack forming part of a fuel cell 8 partially shown in [Fig.5]. A2 denotes a longitudinal axis of the membrane-electrode assembly 2. The membrane-electrode assembly 2 can be called MEA and comprises a base membrane 22 which, in the example to be described, is coated with a catalyst. More precisely, the base membrane 22 is a polymer exchange membrane of protons. The basic membrane 22 is therefore, in this example, coated, on a first side oriented upwards in Figures 3 and 4, with a first catalytic layer 23 forming the cathode and, on a second side opposite the first side and oriented downwards in [Fig. 3], with a second catalytic layer 24 forming the anode. The membrane 22 and the catalytic layers 23 and 24 together form a catalyst-coated membrane, otherwise known as a CCM. In the remainder of this description, this catalyst-coated membrane 25 is referred to as the CCM membrane. Here, the base membrane 22 is made of a polymer material, specifically of the NAFIONTM type, and has a thickness of approximately 0.005 to 0.050 mm, preferably 0.008 to 0.015 mm. The active layers 23 and 24 are made from a platinum base and each have a thickness of approximately 0.001 to 0.010 mm, preferably 0.002 to 0.005 mm. The thickness of the CCM 25 membrane is preferably between 0.010 and 0.050 mm, preferably in the order of 0.017 mm. We note 22 a median plane of the base membrane 22, which is also a median plane of the CCM membrane 25. The longitudinal axis A2 is included in the median plane 122. The CCM 25 membrane is mounted on a frame 30 consisting of two half-frames 32 and 34 which are intended to come to rest flat against each other which are, for example, made of polymer film, for example of poly(ethylene terephthalate) or PET or of poly(ethylene naphthalate) or PEN. A plane 130 is noted as the support plane of the two half-frames 32 and 34 against each other. Plane 30 is also a median plane of the frame 30 and includes the longitudinal axis A2. The two half-frames 32 and 34 are configured to enclose between them a peripheral edge 22a of the membrane 22 when they are supported against each other along plane 30. In this configuration, the half-frames 32 and 34 form a zone also called an "overlap" between the membrane 22 and the two half-frames 32, 34, an overlap which, along each longitudinal edge or each transverse edge of the frame, has a width, for example, in the range of 1 to 5 mm, preferably in the range of 2 to 4 mm. The half-frame 32 is positioned on one side of the CCM membrane 25, in the example above the membrane in [Fig. 3], while the half-frame 34 is positioned on the other side of the CCM membrane 25, in the example below the membrane in [Fig. 3]. This has the effect of immobilizing the membrane 22, i.e., in practice the CCM membrane 25, by pinching it between the half-frames 32 and 34, within the frame 30. Advantageously, the thickness of each of the half-frames 32 and 34 is between 0.020 and 0.030 mm, preferably on the order of 0.025 mm. The frame helps to stiffen the CCM 25 membrane and to hold it in position within the stack 60. In practice, the half-frames 32 and 34 are glued together at the support plane 30, using glue. We denote S32 the surface of the half-frame 32 turned towards the half-frame 34. We denote S34 the surface of the half-frame 34 turned towards the half-frame 32. In the mounted configuration of the frame 30 around the membrane 22, the surfaces S32 and S34 are in contact with each other, aligned on the plane 30 and glued to each other by means of the glue. In this configuration, the median plane 22 of the membrane 22 is also aligned with the plane 30. The glue used to assemble the half-frames 32 and 34 is preferably a thermo-activatable glue based on a thermoplastic polymer, for example an EVA copolymer-based glue, such as the glue marketed under the reference AP12 by the company Addev Materials. Advantageously, the thickness of the glue deposited on the S32 or S34 surface of each of the frames is between 0.01 and 0.02 mm, preferably on the order of 0.013 mm. Advantageously, the assembly of the two half-frames 32 and 34, enclosing the edges of the membrane 25, is achieved by activating the adhesive through the application of ultrasound. Typically, the assembly of the two half-frames 32 and 34, enclosing the membrane 25, is clamped between a sonotrode and an anvil, and the ultrasound transmitted by the sonotrode to the two half-frames 32 and 34 activates the adhesive, thus bonding the two half-frames 32 and 34 to each other and, in the overlapping area, to the membrane. Conventionally, the application of ultrasound can be implemented, in particular, by means of a grooved sonotrode, such as those known, for example, from US-B-10981245 or US-A-2013 / 213552.Typically, as illustrated in US-A-2013 / 213552, the striations can, for example, be formed by two or three networks of grooves on the surface of the sonotrode, each network having parallel grooves oriented in a direction specific to that network. The grooves of the networks thus define protruding points that are the preferred contact areas with the frame during the application of ultrasound. It should be noted that the use of a striated sonotrode can create, at least on the surface of the half-frame with which the sonotrode is in contact, a textured surface that is essentially the inverted image of the sonotrode's striations. This textured surface may have a shallower depth than the sonotrode's striations. The sonotrode may be striated over its entire surface in contact with the two half-frames 32 and 34, or only on a portion of its surface.Preferably, the entire surface of the two half-frames 32 and 34 is. assembled by ultrasound. In other words, the bonding zone of the two half-frames, which corresponds to the area where the ultrasound is applied, then corresponds to the entire surface of frame 30. In the overlap zone of frame 30 with membrane 25, the ultrasound causes each of the two half-frames 32 and 34 to bond to the corresponding face of the membrane. Preferably, the sonotrode is not allowed to come into contact with membrane 25 inside the window defined within each half-frame, to avoid heating and compressing the membrane 25 in its active portion, which will be exposed to the reagents. The sonotrode used can be frame-shaped, potentially allowing the complete assembly of frame 30 onto membrane 25 in a single operation.Alternatively, a sonotrode can be used covering only part of the desired bonding area, allowing the complete assembly of the frame 30 onto the membrane 25 to be carried out in several successive operations. Alternatively, several sonotrodes can be used, each covering only part of the bonding area, allowing the complete assembly of the frame 30 onto the membrane 25 to be carried out in a single operation for all sonotrodes simultaneously, or in several successive operations with one or more sonotrodes used in each operation. Advantageously, the frame 30 defines openings 36 intended to form fluid circulation and distribution / collection galleries within the stack 6, when several frames are juxtaposed within the stack 60, in a direction perpendicular to their median planes 30. Alternatively, particularly in the case of a so-called "external manifold" fuel cell, the frame is devoid of openings of the type of openings 36. A30 is an axis perpendicular to plane 130 and passing through the geometric center of frame 30. Axis A30 is perpendicular to the base membrane 22, as well as to the CCM membrane 25, therefore to their median plane x22. The openings 36 are formed by aligning, along directions parallel to the axis A30, individual openings 36, and 36, formed respectively in the half-frames 32 and 34. Within the stack 6, the axes A30 of the different frames 30 are coincident and the frames 30 are oriented around this axis so that the openings 36 together constitute circulation and distribution / collection galleries of fluid, in particular hydrogen, air or heat transfer fluid, within the stack 60. The bipolar plate 4 is equipped with openings 46 of the same geometry as the openings 36 and which also participate in the definition of these galleries. The geometry of the openings in Figures 1 and 2, on the one hand, and Figures 3 and 3, on the other hand, is different, given the schematic nature of these figures. In practice, this geometry results from a design choice of frame 30 and bipolar plate 4. The longitudinal ends of the half-frame 32 are denoted 32A and 32B respectively. The longitudinal ends of the half-frame 34 are denoted 34A and 34B respectively. A32 and A34 are respectively a longitudinal axis of the half-frame 32 and a longitudinal axis of the half-frame 34. In the mounted configuration of the membrane-electrode assembly 2, the axes A2, A32 and A34 are parallel and, preferably almost coincident, within the thickness of the half-frames. We denote P32 and P34 respectively as points of intersection between the axes A30 and A32, on the one hand, and between the axes A30 and A34, on the other hand. The half-frames 32 and 34 each define a central opening 32C and 34C respectively, which passes completely through them and opposite which the CCM membrane 25 is positioned in the mounted configuration of this membrane on the frame 30. The central openings of the half-frames are thus delimited by the internal edges of the half-frames. The union of the central openings 32C and 34C defines a central opening 30C of the frame 30, which is closed by the CCM membrane in the mounted configuration of the membrane-electrode assembly 2. The half-frames 32 and 34, and therefore the frame 30 they constitute, have a closed contour around the corresponding central opening. The membrane-electrode assembly 2 also includes a first gas diffusion layer 28 and a second gas diffusion layer 29 which have the function of promoting exchanges between the CCM membrane 25 and the fluids circulating between the two bipolar plates 4 of an electrochemical cell 60 to which this membrane-electrode assembly belongs. Diffusion layers 28 and 29 can be designated GDL. They also belong to the membrane-electrode assembly. Advantageously, their thickness is between 0.100 and 0.320 mm, preferably on the order of 0.250 mm. In the mounted configuration of the membrane-electrode assembly 2, the diffusion layers 28 and 29 cover the CCM membrane 25 and part of the frame 30, in the vicinity of the central opening 30C. We respectively denote S28 a surface of the diffusion layer 28 facing the CCM membrane 25 in the mounted configuration of the membrane-electrode assembly 2 and S29 a surface of the diffusion layer 29 facing the CCM membrane 25 in the mounted configuration of the membrane-electrode assembly 2. The surfaces S28 and S29 face each other through the central opening 30C and the CCM membrane 25. During the manufacture of the stack 6, the diffusion layers 28 and 29 are attached to the frame 30, on either side of the CCM membrane 25. To allow the immobilization of the diffusion layers 28 and 29 on the frame 30 equipped with the CCM membrane 25, each of the half-frames 32 and 34 is equipped with orifices 42 and 44, respectively, are arranged on either side of its opening 32C or 34C, along its longitudinal axis A32 or A34, and are intended to be covered by one of the diffusion layers 28 or 29 in the mounted configuration of the membrane-electrode assembly. In the mounted configuration of the membrane-electrode assembly, the orifices 42 and 44 are arranged opposite the diffusion layers 28 and 29, in a direction parallel to the axis A30, that is to say, in a direction perpendicular to the planes 122 and 130. In the example, openings 42 and 44 have the same geometry, as shown in the figures. However, it could be predicted that one or more of the openings in one half-frame might have a geometry different from that of the other openings in that half-frame, and / or predicted that one or more of the openings in one half-frame might have a geometry different from that of one or more openings in the other half-frame. The half-frame 32 comprises two rows of three orifices 42 which extend respectively near the ends 32A and 32B of the half-frame 32 and which connect the surface S32 of the half-frame 32 to a surface S'32 of the half-frame 32 which is opposite the surface S32 and on which the surface S28 of the diffusion layer 28 rests. The orifices 42 therefore pass through the thickness of the half-frame 32. Similarly, the half-frame 34 comprises two rows of three orifices 44 which extend respectively near the ends 34A and 34B of the half-frame 34 and which connect the surface S34 of the half-frame 34 to a surface S'34 of the half-frame 34 which is opposite the surface S34 and on which the surface S29 of the diffusion layer 29 rests. The orifices 44 therefore pass through the thickness of the half-frame 34, Let 32D1 and 32D2 be the transverse edges of the central opening 32C of the half-frame 32, each transverse edge being perpendicular to the axis A32. Let 34D1 and 34D2 be the transverse edges of the central opening 34C of the half-frame 34, each transverse edge being perpendicular to the axis A34. The transverse edges 34D1 and 34D2 are aligned respectively with the transverse edges 32D1 and 32D2, along a direction parallel to the axis A30, and together they constitute the transverse edges 30D1 and 30D2 of the central opening 30C. Let 32E1 and 32E2 be the longitudinal edges of the central opening 32C of the half-frame 32, each longitudinal edge being parallel to the axis A32. Let 34E1 and 34E2 be the longitudinal edges of the central opening 34C of the half-frame 34, each longitudinal edge being parallel to the axis A34. The longitudinal edges 34E1 and 34E2 are aligned respectively with the longitudinal edges 32E1 and 32E2, along a direction parallel to the axis A30, and together they constitute the longitudinal edges 30E1 and 30E2 of the central opening 30C. Various arrangements can be considered for the openings 42, 44. In the illustrated example, as shown in Figures 2 and 4, the openings 42 and 44 are located along a The same transverse edge 30D1 or 30D2 are offset transversely from each other in the x30 plane. More precisely, in the 130 plane and along one of the transverse edges 30D1 and 30D2, the orifices 42 belonging to one of the half-frames 32 are located at distances from the axis A2 which are different from the distances from this axis at which are located each of the orifices 44 belonging to the other half-frame 34 and located along the same edge, these distances being measured in the 30 plane, perpendicular to the axis A2. Three openings 42, arranged through the first half-frame 32, are distributed along the first transverse edge 32D1. Of these three openings, a first opening 42 is located near the first longitudinal edge 32E1, a second opening 42 is located near the second longitudinal edge 32F2, and a third opening 42 is located midway between openings 42 and 42, near axis A2. Three other openings 42, also arranged through the first half-frame 32, are distributed along the second transverse edge 32D2. Among these three orifices, a first orifice 42, is located near the second longitudinal edge 32E2, a second orifice 42,2 is located near the first longitudinal edge 32E1 and a third orifice 4273 is located midway between orifices 42,, and 42>, near axis A2. Three openings 44 arranged through the second half-frame 34 are distributed along the first transverse edge 34D1. Of these three openings, a first opening 44 is located near the first longitudinal edge 34E1, a second opening 44 is located near the second longitudinal edge 34E2, and a third opening 44 is located midway between openings 44 and 44, near axis A2. Three other openings 44, also arranged through the second half-frame 34, are distributed along the second transverse edge 34D2. Among these three orifices, a first orifice 44,, is located near the second longitudinal edge 34E2, a second orifice 44, is located near the first longitudinal edge 34E1 and a third orifice 44,, is located halfway between orifices 44,, and 44,,, near axis A2. The distance d,,; between the first longitudinal edge 32E1 of the half-frame 32 and the orifice 42,1 is strictly greater than the distance d4, between the first longitudinal edge 34E1 of the half-frame 34 and the orifice 44,,. In practice, the distance d,; is greater than the distance d4 by more than twice the radius of the orifices 42,,and44,,, so that there is no overlap, along a direction parallel to the axis A30, between the orifices 42,; and 44, which are adjacent. We number 42 and 44 the orifices 42 and 44, with i a natural number between 1 and 2 and j a natural number between 1 and 3. The index i corresponds to the number of the edge 30D1 or 30D2 near which an orifice is located, while the index j is the order number of this orifice along this edge. Here, the orifices 42 and 44 are positioned in pairs, namely one orifice 42; neighbor of an orifice 44, with the natural numbers i and j having the same value within the same pair of orifices. In particular, there is no superposition, along a direction parallel to the axis A30, between the orifices 42 and 44 of the same pair. In general, the orifices 42; and 44; are offset transversely along the transverse edges of the openings 32C and 34C, that is to say in a direction parallel to the main plane 122 of the membrane 25 and perpendicular to the axes A2, A32 and A34, such that there is no overlap between the orifices 42 and 44, in a direction parallel to the axis A30. In the example shown in the figures, and advantageously, the orifices 42 are arranged along the transverse edge 32D1, with respect to the orifices 42 arranged along the transverse edge 32D2, symmetrically along an imaginary line parallel to the transverse edge 32D1 and passing through the point P32. Similarly, the orifices 44 are arranged along the transverse edge 34D1 symmetrically with respect to the point P34 with respect to the orifices 44 arranged along the transverse edge 34D2. Along each of the transverse edges 30D1 and 30D2, the orifices 42 and 44 form a row of orifices and are arranged alternately. An orifice 42 is located between two orifices 44, and vice versa, except for the two orifices at the end of the row, which are closest to the longitudinal edges 30E1 and 30E2. In the illustrated example, there is no longitudinal offset along the axes A2, A32 and A34 between the orifices 42, 44 which are located along the same transverse edge 30D1 or 30D2. Thus, the orifices 42 belonging to a first half-frame 32 and located along the same transverse edge 30D1 or 30D2 are aligned along a straight line perpendicular to the axes A2, A32 and A34, and the orifices 44 belonging to the second half-frame 34 and located along the same transverse edge 30D1 or 30D2 are aligned along the same straight line perpendicular to the axes A2, A32 and A34. Having such a transverse offset without longitudinal offset between the orifices of the two half-frames located along the same transverse edge 30D1 or 30D2 makes it possible to limit the dimension parallel to the axes A2, A32 and A34 of the zone allowing the immobilization of the diffusion layers 28 and 29 on the frame 30. However, in some cases, other configurations can be envisaged. Thus, according to a first, unshown, embodiment of the invention, the orifices 42 belonging to a first half-frame 32 and located along the same transverse edge 30D1 or 30D2 can be aligned along a first line perpendicular to the axes A2, A32, and A34, and the orifices 44 belonging to the second half-frame 34 and located along the same transverse edge 30D1 or 30D2 can be aligned along a second line perpendicular to the axes A2, A32, and A34, offset longitudinally from the first line. In this case, it can then be envisaged that the orifices 42 belonging to the first half-frame 32 and the orifices 44 belonging to the second half-frame 34 do not show any transverse offset between two orifices 42, 44 of the same pair, i.e. neighbors but belonging to two different half-frames. According to a second variant not shown of the invention, it can be envisaged that the orifices 42 belonging to the first half-frame 32 and the orifices 44 belonging to the second half-frame 34 have, in addition to the longitudinal offset, a transverse offset between two orifices 42, 44 of the same pair. According to a third, unshown embodiment of the invention, the orifices 42, 44 belonging to the same half-frame 32 and located along the same transverse edge 30D1 or 30D2 are not aligned along a straight line. In such an embodiment, the orifices 42 belonging to the first half-frame 32 and the orifices 44 belonging to the second half-frame 34 may be arranged in a staggered pattern. Let S28 be the surface of the diffusion layer 28 facing the CCM membrane 25. Let S29 be the surface of the diffusion layer 29 facing the CCM membrane 25. In the mounted configuration of the membrane-electrode assembly 2, each orifice 42 extends, through the half-frame 32, between the surfaces S28 and S34, while each orifice 44 extends, through the half-frame 34, between the surfaces S29 and S32. A manufacturing process for the membrane-electrode assembly 2 is described below. In a preliminary step, surfaces S32 and S34 are coated with adhesive. This preliminary step can be carried out at the manufacturing site of the membrane-electrode assembly 2, either immediately before or in advance of the subsequent steps. Alternatively, this preliminary step can be carried out at a remote site, from which the adhesive-coated frame halves are transported to the manufacturing site of the membrane-electrode assembly. The application of adhesive to surfaces S32 and S34 can therefore be performed by a manufacturer other than the one producing the membrane-electrode assembly. In a second step, the two half-frames 32 and 34 are supported by their surfaces S32 and S34 along the plane 130, which has the effect of pinching the edge 22a of the membrane 22 and of joining the frame 30 and the membrane 22, i.e. the frame 30 and the CCM membrane 25. The frame 30 is formed by the adhesion of the surfaces S32 and S34 thanks to the glue which is coated there. In a third step, the diffusion layers 28 and 29 are deposited on the frame 30, more precisely on the external surfaces S'32 and S'34 of the half-frames 32 and 34. The dimensions of the aperture 30C and the diffusion layers 28 and 29 are chosen such that, at the end of the third step, the diffusion layers cover both the aperture 30C, and therefore the membrane 25, and the orifices 42 and 44. Thus, each orifice 42 or 44 is positioned, in a direction parallel to the axis A30, in view of one of the diffusion layers. This creates a seven-layer structure, namely the three layers 22, 23 and 24 of the CCM membrane 25, the two half-frames 32 and 34 and the two diffusion layers 28 and 29. This multilayer structure is visible in cross-section in [Fig.3]. The multilayer structure is subjected to a pressure force represented by the arrows P in [Fig. 3], during a pressing substep of this multilayer structure, which is part of a fourth step of the process of the invention. Concurrently with the pressing substep, a heating substep may be implemented, which has the effect, in particular, of liquefying the adhesive present on surfaces S32 and S34. This adhesive then tends to migrate towards surfaces S28 and S29, respectively, through orifices 42 and 44. In addition to, or as an alternative to, the heating substep, an ultrasonic application substep is used for the adhesive present in the multilayer structure. This ultrasonic application facilitates the migration of the adhesive from surfaces S32 and S34 to surfaces S28 and S29, within the orifices 42 and 44. Such pressure can be localized, for example, to the extent of the first and second orifices, or it can be extended to a larger area of ​​the multilayer structure, possibly even to the entire surface of the multilayer structure. The sub-steps of pressing, heating and / or vibrating together constitute the fourth step of bonding the diffusion layers 28 and 29 to the frame 30, by adhesion of the glue, initially coated on the surfaces S32 and S34, to the surfaces S28 and S29, through the orifices 42 and 44. In the fourth step, the adhesive on the solid portion of surface S34 opposite an opening 42 comes into direct contact with the portion of surface S28 located on the other side of this opening. This has the effect of bonding these two surface portions together, which, in the example shown in the figures, are in the shape of a disk with a diameter equal to that of the openings 42. This is equivalent to directly bonding the diffusion layer 28 and the half-frame 34. Similarly, or alternatively, in the fourth step, the adhesive on the solid portion of surface S32 opposite an opening 44 comes into direct contact with the portion of surface S29 located on the other side of this opening. This has the effect of directly bonding these two surface portions together. This is equivalent to directly bonding the diffusion layer 29 and the half-frame 32. This takes advantage of the fact that the diffusion layer 28, 29 is a deformable non-woven material so that, when pressed, and even more so under the pressure of the possible pressing sub-step, it can "enter" the orifices and thus come into contact with the adhesive present on the solid portion of the surface S32, S34 opposite each of the said orifices 42, 44, adhesive which is therefore directly accessible through the orifice. Moreover, the fact that the half-frames are also deformable allows the said solid portion of the surface S32, S34 opposite an orifice 44, 44 to deform towards the inside of the orifice considered, in the direction of the diffusion layer 28, 29, thus further promoting the contact of the diffusion layer 28, 29 with the glue carried by this solid portion of the surface S32, S34. During the fourth step, the first diffusion layer 28 is attached to the frame 30 by means of the glue present in the orifices 42; while the second diffusion layer 29 is attached to the frame 30 by means of the glue present in the orifices 44; Thus, at the end of the fourth step, the solid portion of the half-frame 34, which is opposite a given first orifice 42, is bonded to the corresponding solid portion of the first diffusion layer 28, notably by the adhesive initially carried by the solid portion of the half-frame 34. It can therefore be considered that at least a part of the adhesive initially carried by the half-frame 34 migrates, through the given first orifice 42, to reach the surface S28 of the first diffusion layer 28. Similarly, the solid portion of the half-frame 32, which is opposite a given second orifice 44, is bonded to the corresponding solid portion of the second diffusion layer 29, notably by the adhesive initially carried by said solid portion of the half-frame 32.We can therefore consider that at least part of the glue initially carried by the half-frame 32 migrates through the second given orifice 44; to reach the surface S29 of the second diffusion layer 29. . Furthermore, the activation of the adhesive, particularly in the case of heat-activated thermoplastic adhesives, can cause it to become more fluid, allowing some of it—specifically, the portion located near a given first and / or second orifice 42 and / or 44—to migrate into that orifice 320 and 340, respectively, towards surfaces S44 and S42. In particular, heating the adhesive on surface S34 can cause some of the adhesive present between the half-frames 32 and 34 to flow into the orifices 42.Similarly, heating the adhesive on surface S32 can cause some of the adhesive present between the half-frames 32 and 34 to flow into the orifices 44. Thus, during the fourth step, the adhesive previously coated on surfaces S32 and S34 can flow between these surfaces and migrate into the nearest hollow volumes formed by the orifices 42 and 44. From there, the adhesive flows through these orifices towards the edges of these orifices which adjoin surfaces S28 and S29 of the diffusion layers 28 and 29, which it reaches at the end of the fourth step. Following the fourth step, a quantity Q2 of glue initially present on the surface S34 is present in each orifice 42, such that it connects the surface S28 to the portion of surface S34 located opposite this orifice and possibly at the edge of this orifice 42, which adjoins surface S28. In addition, a quantity Q4 of glue initially present on surface S32 is present in each orifice 44, such that it connects surface S29 to the portion of surface S32 located opposite this orifice and possibly at the edge of this orifice 44, which adjoins surface S29. In other words, the quantity of glue Q2 comes at least in part from the glue initially coated on surface S34, while the quantity of glue Q4 comes at least in part from the glue initially coated on surface S32. In this respect, the fact that there is no overlap between the orifices guarantees that the quantities of glue Q2 and Q4 are retained in the orifices 42 and 44; and dedicated to the bonding, either of the diffusion layer 28, or of the diffusion layer 29, without direct bonding between these layers through the frame 30. The adhesive constituting quantity Q2 can be formed solely from the amount of adhesive present on the portion of surface S34 opposite an orifice 42, whereas the adhesive constituting quantity Q4 can be formed solely from the amount of adhesive present on the portion of surface S32 opposite an orifice 44. Alternatively, and as explained above, the adhesive constituting quantity Q2 can be formed from the adhesive that was present, before the fourth step, on surface S34, both at and around an orifice 42; whereas the adhesive constituting quantity Q4 is formed from the adhesive that was present, before the fourth step, on surface S32, both at and around an orifice 44. In other words, the manufacturing process of the membrane-electrode assembly 2 of the invention takes advantage of the fact that an adhesive is applied to the surfaces S32 and S34 to use it, on the one hand, to secure the half-frames 32 and 34 together and around the CCM membrane 25 and, on the other hand, to secure the diffusion layers 28 and 29 on the frame 30, without the use of an additional adhesive such as the cyanoacrylate adhesives of the prior art. Because of the composition of the glue used in the invention, which migrates through the orifices 42 and 44, it has less tendency to expand than the glues of the prior art, by capillarity, in contact with the surface S28 or S29 of the diffusion layer 28 or 29. The cross-section of the orifices 42 and 44 can be chosen with a relatively small area, less than or equal to 50 mm², preferably 20 mm². This avoids weakening the frame 30, while allowing effective bonding of the diffusion layers 28 and 29 to the frame. Furthermore, the cross-section of the orifices 42 and 44 can be chosen with an area greater than or equal to 5 mm², preferably 10 mm². This ensures that the adhesive surface in contact with a surface S28 or S29 is sufficient to guarantee effective immobilization of the diffusion layer 28 or 29. For example, the orifices 42 and 44 can be circular in shape, with a diameter of between 3 and 8 mm, preferably on the order of 5 mm, as shown in the figures. Alternatively, they can be rectangular or oblong in shape, with a length in the range of 5 to 10 mm, for example 7 mm and a width in the range of 2 to 5 mm, for example 2 or 3 mm, the length of these orifices then being parallel to the transverse edge 32D1, 32D2, 34D1 or 34D2 along which they are positioned. The peripheral edges of diffusion layers 28 and 29 are respectively noted as 282 and 292. We denote d2 a distance measured between edges 32D and 282, parallel to the longitudinal axis A2. We denote d4 a distance measured between edges 34D and 292, parallel to the axis A2. The distances d2 and d4 are the widths of two bands, adjacent to the transverse edges 32D1, 32D2, 34D1 and 34D2, on which the diffusion layers 28 and 29 overlap the frame 30. These distances represent the overlap distances between the corresponding diffusion layers and the frame 30. In the example, the distances d2 and d4 are equal. However, this is not mandatory, particularly in the case where diffusion layers 28 and 29 are of different sizes. In practice, given the method of bonding the diffusion layers 28 and 29 to the frame 30, the risk of adhesive diffusion is limited, so the distances d2 and d4 can be chosen to be relatively small. In other words, the area in which the diffusion layers 28 and 29 cover the frame 30, in the vicinity of the edges 32D1, 32D2 and 34D1, 34D2, can be reduced compared to the same area in prior art membrane-electrode assemblies, since the dimensions of the orifices 42 and 44, on the one hand, and the nature of the adhesive used, on the other hand, prevent excessive spreading of this adhesive during the bonding step of the diffusion layers 28 and 29 to the frame 30, and thus the final extent of the adhesive on the diffusion layer 28, 29 is limited. L25 denotes the length of the CCM 25 membrane, measured parallel to the axis A2 in the mounted configuration of the membrane-electrode assembly 2. In practice, an overlap distance d2 or d4 is chosen within the range of 4 to 15 mm, preferably within the range of 5 to 10 mm. This overlap distance is much smaller than the length L25, so its presence does not significantly reduce the active area of ​​the CCM 25 membrane. In the process mentioned above, it is advantageous for the operations of bonding the frame 30 and the CCM membrane 25, on the one hand, and of bonding the diffusion layers 28 and 29 to the frame 30, on the other, to take place simultaneously, under the effect of pressing, heating, and / or the application of vibrations. This is not, however, mandatory, and it is possible to carry out two successive steps, namely an earlier step, in which the frame 30 and the CCM membrane 25 are joined, and a later step, in which the diffusion layers 28 and 29 and the frame are joined by migration of the glue through the orifices 42 and 44. As seen in [Fig.5], a stack 6 of electrochemical cells 60, made within a fuel cell 8 according to the invention, comprises several membrane-electrode assemblies 2 also according to the invention which are separated by bipolar plates 4, the frames 30 of these different assemblies being kept sealed against the bipolar plates by means of sealing gaskets 50. In the stack 6 shown in [Fig. 5], at least one of the membrane-electrode 2 assemblies conforms to the invention. Preferably, for the sake of homogeneity of the electrochemical cells 60, all of these membrane-electrode 2 assemblies conform to the invention. The invention is illustrated in the figures for the case where the membrane 25 is of the CCM type, with the catalytic layers 23 and 24 supported by the base membrane 22. It is also applicable to the case where the catalytic layers 23 and 24 are supported by the diffusion layers 28 and 29, according to CCB technology (Catalyst Coated Baking). In this case, only the base membrane 22 is immobilized on the frame 30. The invention is also applicable to the case where a single diffusion layer, for example diffusion layer 28, is bonded to the frame of the membrane-electrode assembly by means of adhesive extending through holes formed in the frame. In this case, with a frame 30 formed of two half-frames 32, 34, holes are provided, for example, in only one of the two half-frames, namely half-frame 32, which is on the same side of the membrane as the diffusion layer 28 that is to be immobilized by adhesion with adhesive. The other diffusion layer 29 can then be immobilized by other means, including the known means described in the preamble to the application.According to a variant of the method of the invention, particularly adapted to such a case where a single diffusion layer is bonded to the frame of the membrane-electrode assembly by adhesion with glue through orifices provided in the frame, in the first step, only one of the surfaces S32 and S34 is coated with glue, in sufficient quantity to bond the half-frames 32 and 34 to each other and to the CCM membrane and to ensure the immobilization of the diffusion layers 28 and 29 through the orifices 42 and 44. Advantageously, only the surface S34 of the half-frame 34 which is, with respect to the CCM membrane 25, on the side opposite the diffusion layer 28 which it is thus wished to immobilize by adhesion with glue, is coated with glue. For space reasons, it is advantageous for openings 42 and 44 to be distributed along the transverse edges 32D1, 32D2, 34D1, 34D2. However, alternatively, these orifices can be distributed along the longitudinal edges 32E1, 32E2, 34E1, 34E2. In addition, orifices 42 and 44 can be provided distributed along the transverse edges 32D1, 32D2, 34D1, 34D2 and orifices distributed along the longitudinal edges 32E1, 32E2, 34E1, 34E2. The number and distribution of the holes 42 and 44 along the edges 30D1, 30D2, 30E1, and 30E2 of the frame 30 may differ from those shown in the figures. In particular, there may be one or two of these holes per edge, or four or more. Furthermore, the holes are not necessarily arranged in pairs or alternately. Regardless of the embodiment or variant considered, the quantity of glue Q2 or Q4 present in an orifice 42 or 44 does not necessarily fill the entire volume of that orifice. The embodiments and variants envisaged above can be combined to generate new embodiments of the invention.

Claims

Demands

1. Fuel cell membrane-electrode assembly (2) of a fuel cell (8), this as- assembly comprising a membrane (22, 25); a frame (30) supporting the membrane, this frame being bipartite and including a first half-frame (32) supporting the membrane and arranged on one side of the membrane; a second half-frame (34) supporting the membrane and arranged on a second side of the membrane; and at least one diffusion layer (28) covering the membrane and part of the frame, at least the second half-frame (34) being coated, on a surface (S34) opposite the first half-frame (32), a layer of glue for the solidarity of middle managers, characterized in that the first openings (42) made through the first half- frame (32) are arranged opposite the diffusion layer (28), along a direction (A30) perpendicular to a plane main membrane (22); and the diffusion layer (28) is attached to the frame (30) by a quantity (Q2) of glue that spreads through the first orifices (42) and which comes from the glue coated on the surface opposite (S34) the second half-frame (34).

2. Membrane-electrode assembly according to claim 1, characterized in what the membrane-electrode assembly includes a first diffusion layer (28) arranged on a first side of the membrane (22, 25) and which partially covers the first half-frame (32); ct a second diffusion layer (29) arranged on a second side of the membrane and which partially covers the second half-frame (34); and in that the second diffusion layer (29) is bonded to frame by a second quantity (Q4) of glue which spreads through second openings (44) arranged through the second half-frame (34) and which comes from the glue coated on the opposite surface (S32) of the first half-frame (32).

3. Membrane-electrode assembly according to claim 2, characterized in that the first and second orifices (42, 44) are offset from each other relative to others along at least one direction parallel to a plane main (122) of the membrane (22, 25), so that there is no overlap between these orifices.

4. Membrane-electrode assembly according to any one of the preceding claims preceding, characterized in that each orifice (42, 44) arranged through a half-frame (32, 34) has a section whose area is less than or equal to 50 mm?, preferably 20 mm?, with a preferred shape- typically circular, rectangular or oblong.

5. Membrane-electrode assembly according to any one of the preceding claims preceding, characterized in that each orifice (42, 44) arranged through a half-frame (32, 34) has a section whose area is greater than or equal to 5 mm, preferably 10 mm”, with a preferred shape- typically circular, rectangular or oblong.

6. Membrane-electrode assembly according to any one of the preceding claims previous, characterized in that the glue is thermo-activatable and based on thermoplastic polymer, in particular EVA copolymer.

7. Membrane-electrode assembly according to any one of the preceding claims. preceding, characterized in that a band covering the frame by the diffusion layer has a width (d2, d4) within the range from 4 to 15 mm, preferably in the range from 5 at 10 mm.

8. Method of manufacturing a membrane-electrode assembly (2) of a battery fuel (8), this assembly comprising a membrane (22, 25); a frame (30) supporting the membrane, this frame being bipartite and including a first half-frame (32) supporting the membrane (22, 25) and arranged on one side of the membrane; a second half-frame (34) supporting the membrane and arranged on a second side of the membrane; and at least one diffusion layer (28) covering the membrane and part of the frame, this process comprising at least a preliminary step of coating a first surface (S34) of at least the second half-frame (34) with glue; a step towards strengthening the framework (30) and the membrane (22, 25) by applying the first surface of the second half-frame, coated with glue, against a first surface (S32) of the first half-frame; and a deposition step the diffusion layer (28) on a second surface (S'32,) of the first half-frame (32), opposite to the first surface (S32) of this first half-frame (32) which is opposite the first surface (S34) of the second half frame (34), this process being characterized in that it includes a solida- step rization of the diffusion layer (28) and the frame (30) by adhesion of the glue, coated on the first surface (S34) of the second half-frame (34), on a surface (S28) of the diffusion layer, through first openings (42) made, through the first half-frame, between its first and second surfaces (S32, S'32). [Claim: Method according to claim 8, characterized in that the assembly membrane-electrode includes a first diffusion layer (28) arranged on the first side of the membrane (22, 25) and which partially covers the first half-frame (32); and a second diffusion layer (29) disposed on the second side of the membrane and which partially covers the second half-frame (34); in that the preliminary step is a step of coating the first surfaces (S32, S34) of the first and second half-frames (32, 34) with a glue; and in that, during the bonding stage, the first layer of diffusion (28) is secured to the frame (32) adhesion of the glue, coated on the first surface (S34) of the second half-frame (34), towards a surface (S28) of the first diffusion layer, through the first openings (42) arranged through the first half-frame, between its first and second surfaces (S32, S'32), while the second diffusion layer (29) is attached to the second half-frame (34) by adhesion of the glue, coated on the first surface (S32) of the frame {30), on a surface (S29) of the second diffusion layer, through of the first openings (44) made through the second half-frame, between its first and second surfaces (S34, S'34).

10. A method according to any one of claims 8 and 9, characterized in that the adhesion of the glue coated on the first surface (S34, S32) to the surface (S28, S29) of the diffusion layer (28, 29) results from the migration of the glue, from the first surface to the surface (S28, S29) of the diffusion layer.

11. A method according to any one of claims 8 to 10, characterized in that The bonding stage includes a pressing sub-stage, a sub heating stage and / or a vibration sub-stage for the migration of the glue through the orifices (42, 44) made through the or the half-frames (32, 34).

12. A method according to any one of claims 8 to 11, characterized in that the step of joining the frame (30) and the membrane (22, 25) and the step of bonding the diffusion layer (28, 29) to the half- corresponding frame (32, 34), by adhesion of the glue, coated on the The first surface (S32, S34) of the other half-frame are simultaneous.

13. A method according to any one of claims 8 to 12, characterized in that the step of bonding the diffusion layer (28, 29) to the half- frame (30) corresponding, by adhesion of the glue, coated on the the first surface (S32, S34) of the other half-frame, is made in subjecting this glue to ultrasound.

14. Fuel cell (8) comprising at least one stack (6) of electrochemical cells (60) formed by membrane- assemblies electrode (2) and bipolar plates (4), characterized in that one at less of the membrane-electrode assemblies (2) is according to one of the re- claims 1 to 7 or manufactured by a process according to one of the claims indications 8 to 13 and, preferably, all membrane- assemblies electrodes are according to one of claims 1 to 7 or manufactured by a process according to one of claims 8 to 13.