FR3132394A3 - Fuel cell membrane-electrode assembly, method of manufacturing such an assembly and fuel cell comprising at least one such assembly - Google Patents

Abstract

TITLE: Membrane-electrode assembly for a fuel cell, method of manufacturing such an assembly and fuel cell comprising at least one such assembly This membrane-electrode assembly (2) of a fuel cell comprises a membrane (22, 25), a frame (30) supporting the membrane at least one diffusion layer (28) covering the membrane and part of the frame. The frame includes a first half-frame (32) and a second half-frame (34) supporting the membrane and disposed 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 glue. 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 holes (42) and which comes from the glue coated on the facing surface (S34) of the second half-frame (34). Figure for abstract: 3

Description

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

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

In the field of fuel cells, it is known to insert a stack of electrochemical cells between two end plates, located on either side of this stack in a stacking direction, and possibly to arrange this stack in a casing. . Electrochemical cells are formed by membrane-electrode assemblies and bipolar plates. A membrane-electrode assembly is sometimes called MEA, from the English “Membrane-Electrode Assembly”, and generally comprises a base membrane, which can be coated on one or both of its faces, with a catalytic layer comprising a catalyst, as well as a frame which supports this membrane. The frame may include openings which, in the stack, define fluid flow galleries within the stack of electrochemical cells for distribution and recovery of these fluids in the corresponding fluidic compartments of each cell. This frame is most often associated with at least one seal, sometimes called a “gasket”, with which it also provides a sealing function to the flow of fluids within the stack.

The membrane, when coated with layers comprising a catalyst, is sometimes called CCM, from the English "Catalyst Coated Membrane" and in this case comprises three layers, namely, a membrane itself, a catalytic layer on the anode side and a catalytic layer on the cathode side.

In the stack, a membrane-electrode assembly is inserted between two bipolar plates and thus delimits an anode compartment and a cathode compartment. On each side, the membrane coated with catalyst is covered by a gas diffusion layer which is therefore received in the corresponding anodic or cathodic compartment and promotes contacting of the chemical species, present in the corresponding anodic or cathodic compartment. , with the membrane. Each gas diffusion layer also has a role in conducting electrons. These diffusion layers are sometimes called GDL, from the English “Gas Diffusion Layer”.

It is known to manufacture a membrane-electrode assembly by attaching the membrane coated with catalyst to the frame, which in particular makes it possible to stiffen this membrane and facilitate its handling. This takes place by sealing the membrane to the frame.

Once this operation has been carried out, it is known to immobilize, on the pre-assembled membrane and frame, the diffusion layer(s), during an additional operation and by means of another glue. This immobilization is advantageous so that the gas diffusion layers are held in place at least during the formation of the stack of electrochemical cells, sometimes called “stacking”. This additional operation takes time and requires the application of glue to the diffusion layer or to the frame. In practice, this extends and increases the cost of manufacturing a fuel cell.

It is known from WO-A-2018/055567 to use a grid for the diffusion of glue within a membrane-electrode assembly. A diffusion layer is added and glued to part of the pre-constituted assembly.

It is also known from US-B-11056694 to produce a membrane-electrode assembly on a bipolar plate, with a diffusion layer mounted edge to edge with a frame, the diffusion layer being welded point by point on an internal surface of the frame peripheral. Such an operation requires precise maneuvers and takes time.

In addition, in known materials, the glue used to fix the diffusion layer on the frame risks spreading by capillarity. To prevent it from overflowing the diffusion layer, at the risk of polluting an electrochemical cell, and/or at the risk of polluting the seal, it is necessary to provide a relatively large covering of the frame by the diffusion layer. . This tends to reduce the useful surface area of the membrane, except to enlarge the transverse dimensions of a stack of cells, which increases the bulk of a fuel cell comprising such a stack.

It is these drawbacks that the invention more particularly intends to remedy by proposing a new membrane-electrode assembly for a fuel cell whose manufacturing can be simplified and whose cost price can be reduced compared to previous materials.

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 part of the frame. The frame is bipartite and comprises a first half-frame supporting the membrane and arranged on a first side of the membrane, as well as a second half-frame supporting the membrane and arranged on a second side of the membrane. At least the second half-frame is coated, on a surface facing the first half-frame, with a layer of glue for securing the half-frames.

In accordance with the invention, first orifices provided through the first half-frame are arranged facing the diffusion layer, in a direction perpendicular to a main plane of the membrane. In addition, the diffusion layer is secured to the frame by a quantity of glue which extends through the first orifices and which comes from the glue coated on the surface facing the second half-frame.

Thanks to the invention, an adhesive coated on a surface of the second half-frame can migrate through the first orifices provided through the first half-frame, which has the effect of securing the diffusion layer on the side of the first half. -frame opposite the second half-frame, without having to use additional glue. The manufacturing of the membrane-electrode assembly is thus simplified and its cost price is well controlled.

According to advantageous but not obligatory aspects of the invention, such a membrane-electrode assembly can incorporate one or more following characteristics, taken in any technically admissible combinations:

- The membrane-electrode assembly comprises a first diffusion layer disposed on a first 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 secured to the frame by a second quantity of glue which extends through second orifices provided through the second half-frame and which comes from the glue coated on the facing surface of the first half-frame.

- The first and second orifices are offset relative to each other in at least one direction parallel to a main plane of the membrane, so that there is no superposition between these orifices.

- Each orifice arranged through a half-frame has a section whose area is less than or equal to 50 mm², preferably 20 mm², with a preferably circular, rectangular or oblong shape.

- Each orifice arranged through a half-frame has a section whose area is greater than or equal to 5 mm², preferably 10 mm², with a preferably circular, rectangular or oblong shape.

- The glue is heat-activatable and based on thermoplastic polymer, in particular EVA copolymer.

- A strip covering the frame with the diffusion layer has a width in the range from 4 to 15 mm, preferably in the range from 5 to 10 mm.

According to another aspect, the invention relates to a method of manufacturing a membrane-electrode assembly, in particular a membrane-electrode assembly as mentioned above. This process comprises a preliminary step of coating a first surface of at least the second half-frame with an adhesive, a step of joining the frame and the membrane, by applying the first surface of the second half-frame, coated with glue, 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. In accordance with the invention, this method comprises a step of joining the diffusion layer and the first half-frame by migration of the glue coated on the first surface of the second half-frame, towards a surface of the diffusion layer, at through first holes provided through the first half-frame, between its first and second surfaces.

Advantageously, this process can incorporate one or more of the following characteristics, taken in any technically admissible combination:

- The membrane-electrode assembly comprises a first diffusion layer, arranged on the first side of the membrane and which partially covers the first half-frame, and a second diffusion layer, arranged on the second side of the membrane and which covers partially the second half-frame. The preliminary step is a step of coating the first surfaces of the first and second half-frames with glue. During the joining step, the first diffusion layer is joined to the first half-frame by migration of the glue coated on the first surface of the second half-frame, towards a surface of the first diffusion layer, through first orifices arranged through the first half-frame, between its first and second surfaces, while the second diffusion layer is secured to the second half-frame by migration of the glue coated on the first surface of the first half-frame, towards a surface of the second diffusion layer, through first orifices provided through the second half-frame, between its first and second surfaces.

- The joining step includes a pressing sub-step, a heating sub-step and/or a vibrating sub-step for the migration of the glue through the orifices provided 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 migration of the glue coated on the first surface of the other half-frame, are simultaneous .

- The step of securing the diffusion layer to the corresponding half-frame, by migration of the glue coated on the first surface of the other half-frame, is carried out by subjecting this glue to ultrasound.

According to a third aspect, the invention relates to a fuel cell which comprises 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 mentioned above or manufactured by the method mentioned above and, preferably, all the membrane-electrode assemblies are as mentioned above or manufactured by the process mentioned above.

• La est une vue en perspective partiellement éclatée d’un assemblage membrane-électrode conforme à l’invention et d’une plaque bipolaire, cet assemblage et cette plaque bipolaire appartenant à un empilement de cellules électrochimiques d’une pile à combustible ;
• La est une vue de face de l’assemblage membrane-électrode représenté à la ;
• La est une coupe longitudinale de l’assemblage, selon la ligne III-III à la ;
• La est une vue en perspective éclatée de l’assemblage des figures 2 et 3 ; et
• La est une coupe partielle de principe, dans le sens des flèches V à la , d’un empilement de cellules électrochimiques d’une pile à combustible selon l’invention, cet empilement n’étant pas en configuration éclatée, à la différence de ce qui est représenté à la .

The invention will be better understood and other advantages thereof will appear more clearly in the light of the description which follows of an embodiment of a membrane-electrode assembly, of a method and of a battery. fuel conforming to its principle, given solely by way of example and made with reference to the appended drawings in which:

• There is a partially exploded perspective view of a membrane-electrode assembly according to the invention and of a bipolar plate, this assembly and this bipolar plate belonging to a stack of electrochemical cells of a fuel cell;
• There is a front view of the membrane-electrode assembly shown in ;
• There is a longitudinal section of the assembly, along line III-III at ;
• There is an exploded perspective view of the assembly of Figures 2 and 3; And
• There is a partial cut in principle, in the direction of arrows V at the , of a stack of electrochemical cells of a fuel cell according to the invention, this stack not being in exploded configuration, unlike what is represented in .

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 at the , above a bipolar plate 4. Elements 2 and 4 belong to a stack 6 of electrochemical cells 60, this stack constituting part of a fuel cell 8 partially represented in the .

We denote A2 as 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 which will be described, is coated with catalyst. More precisely, the base membrane 22 is a proton exchange polymer membrane. The base membrane 22 is therefore, in the example, coated, on a first side facing upwards in Figures 3 and 4, with a first catalytic layer 23 forming a cathode and, on a second side opposite the first side and oriented down to the , a second catalytic layer 24 forming an anode. The membrane 22 and the catalytic layers 23 and 24 together form a catalyst-coated membrane, otherwise called CCM. In the remainder of this description, this membrane coated with catalyst 25 is called CCM membrane.

Here, the base membrane 22 is made of polymer material, in particular of the NAFION™ type, and has a thickness of the order of 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 the order of 0.001 to 0.010 mm, preferably 0.002 to 0.005 mm.

The thickness of the CCM membrane 25 is preferably between 0.010 and 0.050 mm, preferably of the order of 0.017 mm.

We note π22 as 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 π22.

The CCM membrane 25 is mounted on a frame 30 consisting of two half-frames 32 and 34 which are intended to come into plane support against each other which are, for example, made of polymer film, for example poly( ethylene terephthalate) or PET or poly(ethylene naphthalate) or PEN.

We note π30 a support plane of the two half-frames 32 and 34 against each other. The plane π30 is also a median plane of the frame 30 and it includes the longitudinal axis A2. The two half-frames 32 and 34 are configured to trap between them a peripheral edge 22a of the membrane 22 when they rest against each other along the plane π30. In this configuration, the half-frames 32 and 34 form a zone also called "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, presents a width for example included in the range from 1 to 5 mm, preferably in the range from 2 to 4 mm.

The half-frame 32 is arranged on a first side of the CCM membrane 25, in the example above the membrane at the , while the half-frame 34 is arranged on a second side of the CCM membrane 25, in the example below the membrane at the . This has the effect of immobilizing the membrane 22, that is to say 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 of the order of 0.025 mm.

The frame makes it possible to stiffen the CCM membrane 25 and hold it in position within the stack 60.

In practice, the half-frames 32 and 34 are glued against each other at the level of the support plane π30, using glue.

We denote S32 the surface of the half-frame 32 facing the half-frame 34. We denote S34 the surface of the half-frame 34 facing 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 π30 plane and stuck to each other using glue.

In this configuration, the median plane π22 of the membrane 22 is also aligned with the plane π30.

The glue used to assemble the half-frames 32 and 34 is preferably a heat-activatable glue based on a thermoplastic polymer, for example an glue based on an EVA copolymer, such as the glue marketed under the reference AP12 by the company Addev Materials .

Advantageously, the thickness of the glue deposited on the surface S32 or S34 of each of the frames is between 0.01 to 0.02 mm, preferably of the order of 0.013 mm.

Advantageously, the frame 30 defines openings 36 intended to form circulation and fluid distribution/collection galleries within the stack 6, when several frames are juxtaposed within the stack 60, in a direction perpendicular to their median planes π30.

Alternatively, particularly in the case of a so-called fuel cell with “external manifolds”, the frame does not have openings of the type openings 36.

We note A30 an axis perpendicular to the plane π30 and passing through the geometric center of the frame 30. The axis A30 is perpendicular to the base membrane 22, as well as to the CCM membrane 25, therefore to their median plane π22.

The openings 36 are formed by aligning, in directions parallel to the axis A30, individual openings 36 ₂ and 36 ₄ formed respectively in the half-frames 32 and 34.

Within the stack 6, the axes A30 of the different frames 30 are merged and the frames 30 are oriented around this axis so that the openings 36 together constitute circulation and fluid distribution/collection galleries, 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 36 in Figures 1, on the one hand, and 2 and 3, on the other hand, is different, taking into account the schematic nature of these figures. In practice, this geometry results from a design choice of the frame 30 and the bipolar plate 4.

We denote respectively 32A and 32B the longitudinal ends of the half-frame 32. We denote respectively 34A and 34B the longitudinal ends of the half-frame 34.

We respectively note A32 and A34 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 -confused, to the nearest thickness of the half-frames.

P32 and P34 are respectively points of intersection between axes A30 and A32, on the one hand, and between axes A30 and A34, on the other hand.

The half-frames 32 and 34 each define a central opening 32C respectively 34C which passes right through them and opposite which the CCM membrane 25 is arranged in the mounted configuration of this membrane on the frame 30. The central openings of the half-frames are therefore delimited by internal edges of the half-frames. The meeting 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 which They constitute, present 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 has 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.

The diffusion layers 28 and 29 can be called GDL. They also belong to the membrane-electrode assembly. Advantageously, their thickness is between 0.100 and 0.320 mm, preferably of 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 note 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, respectively 44, which are arranged on either side of its opening 32C or 34C, along its longitudinal axis A32 or A34, and which 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 assembled configuration of the membrane-electrode assembly, the orifices 42 and 44 are arranged facing 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 π22 and π30.

In the example, the orifices 42 and 44 have the same geometry, as shown in the figures. However, one could provide that one or more of the orifices of a half-frame have a geometry different from that of the other orifices of this half-frame, and/or provide that one or more of the orifices of a half-frame frame has a geometry different from that of one or more holes 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 bears. The orifices 42 therefore pass through the thickness of the half-frame 32.

In the same way, 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 bears. The orifices 44 therefore pass through the thickness of the half-frame 34.

We note 32D1 and 32D2 the transverse edges of the central opening 32C of the half-frame 32, each transverse edge being perpendicular to the axis A32. We note 34D1 and 34D2 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 respectively aligned with the transverse edges 32D1 and 32D2, in a direction parallel to the axis A30, and with them constitute the transverse edges 30D1 and 30D2 of the central opening 30C.

We denote 32E1 and 32E2 as the longitudinal edges of the central opening 32C of the half-frame 32, each longitudinal edge being parallel to the axis A32. We denote 34E1 and 34E2 as 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 respectively aligned with the longitudinal edges 32E1 and 32E2, in a direction parallel to the axis A30, and with them constitute the longitudinal edges 30E1 and 30E2 of the central opening 30C.

We can consider different arrangements for the orifices 42, 44. In the example illustrated, as can be seen from Figures 2 and 4, the orifices 42 and 44 located along the same transverse edge 30D1 or 30D2 are offset transversely from each other by compared to the others in the π30 plane. More precisely, in the plane π30 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 by relative to this axis at which each of the orifices 44 belonging to the other half-frame 34 and located along the same edge are located, these distances being measured in the plane π30, perpendicular to the axis A2.

Three orifices 42 provided through the first half-frame 32 are distributed along the first transverse edge 32D1. Among these three orifices, a first orifice 42 ₁₁ is located near the first longitudinal edge 32E1, a second orifice 42 ₁₂ is located near the second longitudinal edge 32E2 and a third orifice 42 ₁₃ is located halfway between the orifices 42 ₁₁ and 42 ₁₂ , near axis A2. Three other orifices 42 also provided through the first half-frame 32 are distributed along the second transverse edge 32D2. Among these three orifices, a first orifice 42 _{2 1} is located near the second longitudinal edge 32E2, a second orifice 42 _{2 2} is located near the first longitudinal edge 32E1 and a third orifice 42 _{2 3} is located halfway between the orifices 42 _{2 1} and 42 _{2 2} , near axis A2.

Three orifices 44 arranged through the second half-frame 34 are distributed along the first transverse edge 34D1. Among these three orifices, a first orifice 44 ₁₁ is located near the first longitudinal edge 34E1, a second orifice 44 ₁₂ is located near the second longitudinal edge 34E2 and a third orifice 44 ₁₃ is located halfway between the orifices 44 ₁₁ and 44 ₁₂ , near axis A2. Three other orifices 44 also provided through the second half-frame 34 are distributed along the second transverse edge 34D2. Among these three orifices, a first orifice 44 _{2 1} is located near the second longitudinal edge 34E2, a second orifice 44 _{2 2} is located near the first longitudinal edge 34E1 and a third orifice 44 _{2 3} is located halfway between the orifices 44 _{2 1} and 44 _{2 2} , near axis A2.

The distance of₂₁₁between the first longitudinal edge 32E1 of the half-frame 32 and the orifice 42₁₁is strictly greater than the distance d₄₁₁between the first longitudinal edge 34E1 of the half-frame 34 and the orifice 44₁₁. In practice the distance d₂₁₁is greater than the distance d₄₁₁ more than twice the radius of the orifices 42₁₁ And 44_{1 1}, so that there is no superposition, in a direction parallel to axis A30, between the orifices 42₁₁and 44₁₁who are neighbors.

The orifices 42 and 44 are numbered 42 _ij and 44 _ij , 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 is located an orifice, 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 an orifice 42 _ij close to an orifice 44 _ij , with the natural integers i and j which have the same value within the same pair of orifices. In particular, there is no superposition, in a direction parallel to the axis A30, between the orifices 42 and 44 of the same pair.

Generally, the orifices 42 _ij and 44 _ij 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 π22 of the membrane 25 and perpendicular to the axes A2, A32 and A34, so that there is no overlap between the orifices 42 and 44, in a direction parallel to the axis A30.

In the example of the figures and advantageously, the orifices 42 _1j are arranged, along the transverse edge 32D1, relative to the orifices 42 _2j arranged along the transverse edge 32D2, symmetrically of an imaginary line parallel to the edge transverse 32D1 and passing through point P32. Likewise, the orifices 44 _1j are arranged along the transverse edge 34D1 symmetrically from the point P34 with respect to the orifices 44 _2j arranged along the transverse edge 34D2.

Along each of the transverse edges 30D1 and 30D2, the orifices 42 and 44 constitute a row of orifices and are arranged alternately. An orifice 42 is arranged between two orifices 44, and vice versa, except for the two orifices located at the end of the row, which are closest to the longitudinal edges 30E1 and 30E2.

In the example illustrated, 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 considered are aligned along a straight line perpendicular to the axes A2, A32 and A34, and the orifices 44 belonging to the second half-frame frame 34 and located along the same transverse edge 30D1 or 30D2 considered are aligned along the same straight line perpendicular to the axes A2, A32 and A34. The fact of 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 immobilization diffusion layers 28 and 29 on frame 30.

However, in certain cases, other configurations can be provided.

Thus, according to a first variant of the invention not shown, it can be provided that the orifices 42 belonging to a first half-frame 32 and located along the same transverse edge 30D1 or 30D2 considered are aligned along a first 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 considered either aligned along a second straight line perpendicular to the axes A2, A32 and A34, offset longitudinally from the first RIGHT. In this case, we can then envisage that the orifices 42 belonging to the first half-frame 32 and the orifices 44 belonging to the second half-frame 34 do not present any transverse offset between two orifices 42, 44 of the same pair, that is, that is to say neighbors but belonging to two different half-frames.

According to a second variant of the invention not shown, 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 present, in addition to the longitudinal offset, a transverse offset between two orifices 42, 44 of the same pair.

According to a third variant of the invention not shown, 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 a variant, it can be provided that the orifices 42 belonging to the first half-frame 32 and the orifices 44 belonging to the second half-frame 34 are arranged in a staggered manner.

We denote S28 the surface of the diffusion layer 28 facing the CCM membrane 25. We denote S29 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 surfaces S29 and S32.

A method of manufacturing the membrane-electrode assembly 2 is described below.

During a first preliminary step, surfaces S32 and S34 are coated with glue. This preliminary step can be carried out on the manufacturing site of the membrane-electrode assembly 2, just before the following steps or in advance. Alternatively, this preliminary step can be carried out at a remote site, from where the half-frames coated with glue are transported to the manufacturing site of the membrane-electrode assembly. The operation of coating surfaces S32 and S34 with glue can therefore be carried out by a manufacturer different from the one manufacturing the membrane-electrode assembly.

During a second step, the two half-frames 32 and 34 are supported by their surfaces S32 and S34 along the plane π30, which has the effect of pinching the edge 22a of the membrane 22 and securing the frame 30 and the membrane 22, that is to say the frame 30 and the CCM membrane 25. The frame 30 is constituted by the adhesion of the surfaces S32 and S34 thanks to the glue which is coated there.

During 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 opening 30C and diffusion layers 28 and 29 are chosen such that, at the end of the third step, the diffusion layers cover both the opening 30C, therefore the membrane 25, and the orifices 42 and 44. Thus, each orifice 42 or 44 is arranged, in a direction parallel to the axis A30, facing one of the diffusion layers.

A seven-layer structure is thus formed, 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 section to the .

The multilayer structure is subjected to a pressure force represented by the arrows P at the , during a sub-step of pressing this multilayer structure which is part of a fourth step of the process of the invention. Concomitantly with the pressing sub-step, a heating sub-step can be implemented, which has the particular effect of fluidizing the glue present on the surfaces S32 and S34, this glue then having a tendency to migrate towards the surfaces S28 and S29, respectively through the orifices 42 and 44.

In addition or as an alternative to the heating sub-step, a sub-step of applying ultrasound to the glue present in the multilayer structure. This application of ultrasound facilitates the migration of the glue from the surfaces S32 and S34 to the surfaces S28 and S29, within orifices 42 and 44.

The sub-steps of pressing, heating and/or vibration together constitute the fourth step of securing the diffusion layers 28 and 29 on the frame 30, by migration of the glue coated on the surfaces S32 and S34 towards the surfaces S'32 and S'34, therefore in the direction of surfaces S28 and S29, through orifices 42 and 44.

By migration, we mean that the glue previously coated on the surfaces S32 and S34 flows between these surfaces into the nearest hollow volumes which are constituted by the orifices 42 and 44. From there, the glue flows, into these orifices, towards the 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_ij, so that it connects the surface S28 to the edge of this orifice and to the portion of the surface S34 located opposite this orifice. In addition, a quantity Q4 of glue initially present on the surface S32 is present in each orifice 44_ij, so that it connects the surface S29 to the edge of this orifice and to the portion of the surface S32 located opposite this orifice. In other words, the quantity of glue Q2 comes from the glue initially coated on the surface S34, while the quantity of glue Q4 comes from the glue initially coated on the surface S32. In this regard, 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_ij And 44_ijand dedicated to the bonding, either of the diffusion layer 28, or of the diffusion layer 29, without direct connection between these layers through the frame 30.

In other words, the method of manufacturing 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, for 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 glue such as cyanhydric glues of the prior art.

Due to 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, on contact with the surface S28 or S29 of the diffusion layer 28 or 29.

The section of the orifices 42 and 44 can be chosen with a relatively small area, less than or equal to 50 mm ² , preferably 20 mm ² . This avoids weakening the frame 30, while allowing effective joining of the diffusion layers 28 and 29 to the frame. In addition, the section of the orifices 42 and 44 can be chosen with an area greater than or equal to 5 mm ² , preferably 10 mm ² . This allows the glue surface in contact with a surface S28 or S29 to be sufficient to ensure 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 of the order of 5 mm, as shown in the figures. Alternatively, they may be in the shape of a rectangle or oblong, with a length in the range from 5 to 10 mm, for example 7 mm and a width in the range from 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.

We denote respectively 282 and 292 the peripheral edges of the diffusion layers 28 and 29.

We note d2 as a distance measured between the edges 32D and 282, parallel to the longitudinal axis A2. We note d4 as a distance measured between the edges 34D and 292, parallel to the axis A2. The distances d2 and d4 are the widths of two strips, adjacent to the transverse edges 32D1, 32D2, 34D1 and 34D2, on which the diffusion layers 28 and 29 cover the frame 30. These distances represent the overlapping distances between the diffusion layers corresponding and frame 30.

In the example, the distances d2 and d4 are equal. This is however not obligatory, particularly in the case where the diffusion layers 28 and 29 are of different sizes.

In practice, taking into account the method of joining the diffusion layers 28 and 29 to the frame 30, the risk of diffusion of the glue is limited, so that the distances d2 and d4 can be chosen relatively small. In other words, the area of the zone 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 the membrane assemblies -electrode of the prior art, since the dimensions of the orifices 42 and 44, on the one hand, and the nature of the glue used, on the other hand, avoid a strong spreading of this glue during the joining step of the diffusion layers 28 and 29 on the frame 30, and therefore the final extension dimension of the glue on the diffusion layer 28, 29 is limited.

We denote L25 as the length of the CCM membrane 25, 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 in the range from 4 to 15 mm, preferably in the range from 5 to 10 mm. This overlapping distance is much less than the length L25, so that its presence does not significantly reduce the active area of the CCM 25 membrane.

In the method mentioned above, it is advantageous for the operations of joining the frame 30 and the CCM membrane 25, on the one hand, and of joining the diffusion layers 28 and 29 to the frame 30 to take place simultaneously. , under the effect of pressing, heating and/or the application of vibrations. This is however not obligatory and it is possible to provide two successive stages, namely an earlier stage, in which the frame 30 and the CCM membrane 25 are joined together, and a later stage, 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 visible at , a stack 6 of electrochemical cells 60, produced within a fuel cell 8 in accordance with the invention, comprises several membrane-electrode assemblies 2 also in accordance with the invention which are separated by bipolar plates 4, the frames 30 of these different assemblies being maintained in a sealed manner with respect to the bipolar plates thanks to seals 50.

In stack 6 shown in , at least one of the membrane-electrode assemblies 2 conforms to the invention. Preferably, for the sake of homogeneity of the electrochemical cells 60, all of these membrane-electrode assemblies 2 conform to the invention.

The invention is shown in the figures in the case where the membrane 25 is of the CCM type, the catalytic layers 23, 24 being carried by the base membrane 22. It is also applicable to the case where the catalytic layers 23, 24 are carried by diffusion layers 28 and 29, according to CCB technology, from the English “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 the diffusion layer 28, is secured to the frame of the membrane-electrode assembly by migration of the glue through orifices made in the frame. In this case, in the presence of a frame 30 formed of two half-frames 32, 34, we provide, for example, orifices in only one of the two half-frames, namely the half-frame 32 which is on the same side of the membrane as the diffusion layer 28 which we thus wish to immobilize by glue migration. The other diffusion layer 29 can then be immobilized by other means, including the known means exposed in the preamble of the application. According to a variant of the method of the invention, particularly suitable for such a case where a single diffusion layer is secured to the frame of the membrane-electrode assembly by migration of the glue through orifices made in the frame, during the first step, only one of the surfaces S32 and S34 is coated with glue, in sufficient quantity to secure the half-frames 32 and 34 together and with the CCM membrane and to migrate through the orifices 42 and 44. Advantageously, only the surface S34 of the half-frame 34 is coated with glue which is, relative to the CCM membrane 25, on the side opposite the diffusion layer 28 which it is thus desired to immobilize by glue migration.

For reasons of space, it is advantageous for the orifices 42 and 44 to be distributed along the transverse edges 32D1, 32D2, 34D1, 34D2.

However, as a variant, 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 orifices 42 and 44 along the edges 30D1, 30D2, 30E1 and 30E2 of the frame 30 may be different from those shown in the figures. In particular, these orifices may be 1 or 2 per edge, or greater than or equal to 4. In addition, the orifices are not necessarily arranged in pairs, nor in an alternating manner.

Whatever 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 this orifice.

The embodiments and variants considered above can be combined to generate new embodiments of the invention.

Claims (13)

Membrane-electrode assembly (2) of fuel cell (8), this assembly comprising

• a membrane (22, 25);

a frame (30) supporting the membrane, this frame being bipartite and comprising

• a first half-frame (32) supporting the membrane and disposed on a first side of the membrane;
• a second half-frame (34) supporting the membrane and disposed 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) facing the first half-frame (32), with a layer of glue for securing the half-frames,
characterized in that

• 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); And
• 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).

Membrane-electrode assembly according to claim 1, characterized in that the membrane-electrode assembly comprises

• a first diffusion layer (28) arranged on a first side of the membrane (22, 25) and which partially covers the first half-frame (32); And
• 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 secured to the frame by a second quantity (Q4) of glue which extends through second orifices (44) provided through the second half-frame (34) and which comes from the glue coated on the facing surface (S32) of the first half-frame (32). Membrane-electrode assembly according to claim 2, characterized in that the first and second orifices (42, 44) are offset relative to each other in at least one direction parallel to a main plane (π22) of the membrane (22, 25), so that there is no overlap between these orifices. Membrane-electrode assembly according to one of the preceding claims, 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 mm², preferably 20 mm², with a preferably circular, rectangular or oblong shape. Membrane-electrode assembly according to one of the preceding claims, 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 mm², preferably 10 mm², with a preferably circular, rectangular or oblong shape. Membrane-electrode assembly according to one of the preceding claims, characterized in that the glue is heat-activatable and based on thermoplastic polymer, in particular EVA copolymer. Membrane-electrode assembly according to one of the preceding claims, characterized in that a strip covering the frame by the diffusion layer has a width (d2, d4) in the range from 4 to 15 mm, preferably in the range going from 5 to 10 mm. Method for manufacturing a membrane-electrode assembly (2) of a fuel cell (8), this assembly comprising

• a membrane (22, 25);

a frame (30) supporting the membrane, this frame being bipartite and comprising

• a first half-frame (32) supporting the membrane (22, 25) and arranged on a first side of the membrane;
• a second half-frame (34) supporting the membrane and disposed 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 of joining the frame (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 step of depositing the diffusion layer (28) on a second surface (S'32,) of the first half-frame (32), opposite the first surface (S32) of this first half-frame (32) which is in view of the first surface (S34) of the second half-frame (34),

this method being characterized in that it comprises a step of joining the diffusion layer (28) and the first half-frame (32) by migration of the glue coated on the first surface (S34) of the second half-frame ( 34), towards a surface (S28) of the diffusion layer, through first orifices (42) provided, through the first half-frame, between its first and second surfaces (S32, S'32). Method according to claim 8, characterized in that the membrane-electrode assembly comprises

• a first diffusion layer (28) disposed 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 an adhesive;
and in that, during the joining step, the first diffusion layer (28) is joined to the first half-frame (32) by migration 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 first orifices (42) provided through the first half-frame, between its first and second surfaces (S32, S'32), while the second diffusion layer (29) is secured to the second half-frame (34) by migration of the glue coated on the first surface (S32) of the first half-frame (32), towards a surface (S29) of the second layer of diffusion, through first orifices (44) arranged through the second half-frame, between its first and second surfaces (S34, S'34). Method according to one of claims 8 and 9 characterized in that the joining step comprises a pressing sub-step, a heating sub-step and/or a vibrating sub-step for the migration of the glue to through the orifices (42, 44) provided through the half-frame(s) (32, 34). Method according to one of claims 8 to 10, characterized in that the step of joining the frame (30) and the membrane (22, 25) and the step of joining the diffusion layer (28, 29) on the corresponding half-frame (32, 34), by migration of the glue coated on the first surface (S32, S34) of the other half-frame, are simultaneous. Method according to one of claims 8 to 11, characterized in that the step of securing the diffusion layer (28, 29) to the corresponding half-frame (30), by migration of the glue coated on the first surface (S32, S34) of the other half-frame, is carried out by subjecting this glue to ultrasound. Fuel cell (8) comprising at least one stack (6) of electrochemical cells (60) formed by membrane-electrode assemblies (2) and bipolar plates (4), characterized in that at least one of the membrane assemblies -electrode (2) is according to one of claims 1 to 7 or manufactured by a process according to one of claims 8 to 12 and, preferably, all the membrane-electrode assemblies are according to one of claims 1 to 7 or manufactured by a process according to one of claims 8 to 12.