EP1525633A2

EP1525633A2 - Honeycomb structure and method for production of said structure

Info

Publication number: EP1525633A2
Application number: EP03717404A
Authority: EP
Inventors: Stéphane REVOL
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2002-02-19
Filing date: 2003-02-17
Publication date: 2005-04-27
Also published as: CN1332465C; WO2003071626A2; CN1689180A; US7115336B2; JP2006505895A; WO2003071626A3; US20050221150A1; JP4527402B2; FR2836282A1; FR2836282B1

Abstract

The invention relates to a honeycomb structure (1) comprising at least one honeycomb region (2a, 2b) partially defined by an associated sealing surface (4a, 4b). According to the invention, each honeycomb region (2a, 2b) is formed by a plurality of superimposed metallic layers (8) arranged parallel to the associated sealing surface (4a, 4b), each metallic layer (8) comprising a network of passages (10) terminating on both sides of said metallic layer (8). The invention further relates to a method for production of such a honeycomb structure (1) with application to fuel cells and heat exchangers.

Description

ALVEOLAR STRUCTURE AND METHOD FOR MANUFACTURING A

SUCH STRUCTURE

DESCRIPTION

TECHNICAL AREA

The technical field of the present invention relates to that of energy production requiring a high compactness of the components used. More particularly, the invention relates to the cellular structures used in this specific technical field. The cellular structures find particular application in the field of fuel cells, and more particularly in that of fuel cells comprising a membrane as electrolyte as well as bipolar plates, the latter being made of cellular structures.

In addition, the invention is also applicable to the field of heat exchangers using cellular structures.

Finally, the present invention also relates to the methods of manufacturing such cellular structures.

STATE OF THE PRIOR ART

In this field, fuel cells using cellular structures are known. Indeed, a fuel cell is an assembly generally comprising a plurality of elementary cells stacked one on the other. In each of the elementary cells of the fuel cell, an electrochemical reaction is created between two reagents which are introduced continuously into the elementary cells. The fuel usually used is hydrogen or methanol, depending on whether one is respectively in the presence of a cell operating with mixtures of the hydrogen / oxygen type and in the presence of a cell operating with mixtures of the methanol / type oxygen.

The fuel is brought into contact with the anode while the oxidant, in this case oxygen, is brought into contact with the cathode.

The cathode and the anode are separated by means of an electrolyte of the ion exchange membrane type. At the anode, there is an oxidation reaction of the fuel, in general hydrogen, represented by the following reaction scheme:

2H ₂ → 4H ⁺ + 4th ^" Likewise, at the level of the cathode, a reduction reaction of the oxidant, in general oxygen, takes place, according to the following reaction scheme:

0 ₂ + 4H ⁺ + 4th ^" → 2H ₂ 0 We then witness an electrochemical reaction whose created energy is converted into electric energy . H ⁺ protons flow from the anode towards the cathode by crossing the electrolyte, to join an external circuit in order to contribute to the production of electrical energy. At the same time, at the cathode, there is a production of water which is continuously discharged from the electrode-membrane-electrode assembly.

In fuel cells of the prior art, several electrode-membrane-electrode assemblies are stacked on top of each other, in order to obtain a power greater than that supplied by a single one of these assemblies. The junction and the electrical continuity between these assemblies are generally carried out using conductive plates, these plates also being called bipolar plates.

It is therefore with the aid of these bipolar plates, being of the alveolar structure type, that the cathode of an assembly can be joined with the anode of an adjacent assembly. These bipolar plates also make it possible to ensure the highest possible electrical conductivities, so as to avoid ohmic drops detrimental to the performance of the fuel cell. Bipolar plates can also perform other functions than that of providing the electrical connection.

Indeed, one can for example proceed, via these bipolar plates, to the continuous supply of reagents to the anode of a first assembly, and the cathode of an adjacent second assembly.

In addition, the bipolar plates can also be used to evacuate products at the cathode, by integrating elements for removing excess water.

The bipolar plates can also incorporate a heat exchanger serving to prevent overheating within the stack of electrode-membrane-electrode assemblies.

Finally, note that another function of these bipolar plates may reside in the mechanical strength of the electrode-menbran-electrode assemblies, in particular when the latter are stacked on top of each other. Such an assembly ensures an overall volume of the thin battery, which is entirely compatible with the intended applications, such as for example that relating to an electric vehicle.

According to the devices and methods of the prior art, there are three distinct methods for carrying out the distribution of the reagents.

We first note a method using channels machined on the ends of the bipolar plates. These channels are provided to ensure the most homogeneous distribution possible of the reagents on a surface of the electrode with which they are in contact.

These channels are usually organized so that the reagents injected into these channels wind over a large part of the surface of the electrode. The means used to obtain a such a result are horizontal sections spaced by bends descending at 180 °. Note that these sections are also capable of recovering and discharging the water produced at the cathode. However, it has been found that this particular arrangement of means does not make it possible to obtain a sufficiently large exchange surface to result in an acceptable electrochemical conversion yield for industrial application.

To overcome this drawback, a second method has been proposed in the prior art.

In this method, it is a question of using a metallic foam with high porosity to add to the metal parts in which machining is carried out, this metallic foam making it possible to ensure a good distribution of the reagents as well as the evacuation of the various products.

This type of method is described in particular in document US Pat. No. 5,482,792. Two sheets a few millimeters thick are respectively positioned against the anode and against the cathode, and also make the junction with the ends of the bipolar plate. Nevertheless, the fact of adding a metal foam at the level of the bipolar plate contributes to creating a significant resistance, which involves a reduction in the electrical conduction within the assembly. Even if the problem relating to electrical conduction can be partially solved by compressing the metal foam, it turns out in any event that corrosion problems persist, in particular due to the presence of numerous defects such as breakage of strands within the metal foam.

According to a third method known from the prior art, described in document US Pat. No. 6,146,780, the bipolar plate comprises a sealed conductive plate, as well as two parts of metal foam ensuring contact with the electrodes. This particular arrangement makes it possible to be exempt from the presence of machined metal elements and therefore expensive.

However, other drawbacks remain when using such devices.

Indeed, by using metallic foams as reagent distribution zones and evacuation of different products, one cannot correctly control the periodicity of the structure of the metallic foam type.

In addition, an additional drawback lies in the impossibility of easily controlling the internal geometry of the honeycomb structure, this resulting in the inability to vary the geometry of the distribution zone in the desired manner.

Finally, it remains to be noted that there are some of the aforementioned drawbacks in the honeycomb structures used in heat exchangers of the prior art. STATEMENT OF THE INVENTION

The object of the present invention is therefore to remedy all or part of the drawbacks of the honeycomb structures of the prior art. The invention also aims to provide a honeycomb structure of simple design, and for which it is possible to perfectly control the internal geometry of its different honeycomb areas. Another object of the present invention is to present a method of manufacturing a honeycomb structure such as that achieving the object of the invention mentioned above.

To do this, the invention firstly relates to a honeycomb structure comprising at least one honeycomb area partially delimited by an associated sealed surface. According to the invention, each alveolar zone is formed by a plurality of metallic layers superimposed parallel to the associated sealed surface, each metallic layer comprising a network of passages opening out on either side of said metallic layer.

Advantageously, the invention provides a honeycomb structure of simple design whose internal geometry of the honeycomb areas is easily adaptable according to the needs encountered.

In this type of honeycomb structure, there is no difficulty associated with assemblies of elements causing mechanical, thermal or electrical discontinuities within the bipolar plate. Preferably, the honeycomb structure is indifferently integrated into a fuel cell as a bipolar plate, to a fuel cell as a bipolar plate with integrated exchanger, or even integrated into a heat exchanger.

The present invention also relates to a method of manufacturing such a honeycomb structure. According to this method, each metal layer is produced by carrying out the following operations: - depositing a layer of metal powder; partial solidification by laser of the layer of metallic powder deposited, causing the formation of solidified parts and non-solidified parts, the solidified parts defining the periphery of the passages of the metal layer.

Preferably, for each alveolar zone, the metal layers are produced successively, the associated sealed surface constituting a support for the first metal layer to be produced, the solidified and non-solidified parts of any metallic layer produced constituting a support for the next metal layer to be made.

Preferably, for each alveolar zone, when all the metal layers have been produced, the networks for passing the metal layers are obtained by eliminating the non-solidified parts of the metal layers.

In addition, provision may be made for the operation of partial solidification by laser of a layer of deposited metal powder is also capable of joining the solidified parts obtained with the solidified parts of the metal layer on which they rest.

The metal layers are preferably made of a material selected from stainless steels, aluminum and its alloys, nickel and its alloys such as Ni-Cr, and a mixture of at least two of the above elements.

In addition, the metal layers comprise at least one binder such as bronze. This advantageously makes it possible to obtain alloys for which a sintering operation can be carried out at low temperature.

Other advantages and characteristics of the invention will appear in the non-limiting description detailed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The description will be made with reference to the appended drawings in which: FIG. 1 represents a perspective view of a honeycomb structure according to a preferred embodiment of the invention,

FIG. 2 represents a front view of the honeycomb structure of FIG. 1, in contact with two elements to be connected,

- Figure 3 shows a front view of a honeycomb structure according to another preferred embodiment of the invention, Figure 4 schematically shows a perspective view of a honeycomb area in manufacturing, after the step of depositing a layer of metal powder, and FIG. 5 schematically represents a perspective view of a cellular zone during manufacturing, after the step of partial solidification of a layer of deposited metallic powder.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to Figures 1 and 2, we see a honeycomb structure 1 according to a preferred embodiment of the invention, this honeycomb structure being in particular capable of operating with a fuel cell or with a heat exchanger (not shown).

The honeycomb structure 1 according to the invention comprises at least one honeycomb area 2a, 2b intended to be traversed by at least one fluid. According to the preferred embodiment of the invention shown in Figures 1 and 2, the honeycomb structure 1 comprises two honeycomb zones 2a, 2b, each being intended to cooperate with a respective element 16a, lβb comprising a contact surface 14a, 14b . The elements 16a, 16b visible in FIG. 2 can belong to a heat exchanger or to a fuel cell. Note that it is also possible to propose a honeycomb structure 1 having only one honeycomb area 2a, 2b.

The alveolar zones 2a, 2b are partially delimited by associated sealed surfaces 4a, 4b. The first 4a and the second sealed surface 4b belong to a conductive base plate 6, this base plate 6 also being impermeable to the fluids circulating inside the alveolar zones 2a, 2b.

Each alveolar zone 2a, 2b is formed by metal layers 8 superimposed parallel to the associated sealed surface 4a, 4b. Each metal layer 8 comprises a network of passages 10 opening on either side of the metal layer 8.

In each alveolar zone 2a, 2b, the metallic layers 8, which are substantially planar, are therefore stacked one on the other, over a large part of the associated sealed surface 4a, 4b. Each metal layer 8 comprises a network of passages comprising a plurality of passages 10, of identical or different shapes, passing through each metal layer 8 along an axis substantially perpendicular to the associated sealed surface 4a, 4b. This particular arrangement of the metal layers 8 therefore leads to the production of voluminal, conductive and porous alveolar zones 2a, 2b.

Each of the metal layers 8 may have a network of passages 10 identical to or different from the networks of passages 10 formed on the two directly adjacent metal layers 8.

Preferably and with reference to the figure

2, the structure 1 has a thickness “E” of approximately 6 mm, this thickness corresponding to the thickness “e” of the conductive base plate 6 added to the sum of the heights "ha" and "hb" of the two alveolar zones 2a, 2b.

In addition, still with reference to FIG. 2, the metal layers 8 can be of different thicknesses such as "e '" or "e", these values being preferably less than 0.5 mm, and more specifically between approximately 0.1 mm and 0.2 mm.

Thus, by varying on the one hand the thicknesses "e '" and "e''" of the metal layers 8, and on the other hand the distribution and the geometry of the networks of passages 10, it is possible to obtain alveolar zones 2a, 2b of average open porosity between a value strictly greater than 0% and 90%. In operation and with reference to Figures 1 and 2, the honeycomb structure 1 comprises two honeycomb areas 2a, 2b, each being intended to cooperate with a separate surface 14a, 14b belonging respectively to elements 16a, 16b. The elements 16a, 16b can belong to a heat exchanger or to a fuel cell. Each alveolar zone 2a, 2b is respectively supplied by a fluid F _x in the alveolar zone 2a, and by a fluid F ₂ in the alveolar zone 2b. It should be noted that these fluids Fx and F ₂ can themselves be mixtures of several fluids, and that the fluids are preferably supplied continuously.

The arrows A and B symbolize respectively • the supplies of fluids F _x and F ₂ , respectively exerted in the alveolar zones 2a and 2b. When introduced into the honeycomb structure 1, the fluids Fi and F ₂ circulate in the entire volume of the honeycomb areas 2a, 2b, and diffuse up to the surfaces 14a, 14b with which they must come into contact. The arrows C _x and C ₂ indicate a main direction of diffusion of the fluids Fi and F ₂ in each of the alveolar zones 2a, 2b.

To reach the surfaces 14a, 14b to be contacted, the fluids F _x and F ₂ pass through passages 10 made in the metal layers 8. With such an arrangement of means, the distribution of the fluids Fi and F ₂ over the surfaces to contact is guaranteed to be as homogeneous as possible. The evacuation of fluids F _x and F ₂ is respectively symbolized by the arrows Dj and D ₂ .

According to a first application of the invention, the honeycomb structure 1 is intended to be used in a fuel cell. In this specific case, the two alveolar zones 2a, 2b are reagent distribution zones, and the surfaces 14a, 14b which these distribution zones have to contact are electrode surfaces 16a, 16b each belonging to an electrode-membrane assembly. -electrode (not shown) of a fuel cell. The honeycomb structure 1 is then a bipolar plate for a fuel cell.

As in the bipolar plates of the prior art, the distribution zones constituted by the alveolar zones 2a, 2b can also be used for the evacuation of different products, such as water, formed during electrochemical reactions at the electrodes.

Note also that the alveolar structure 1, depending on the needs encountered, may include only one reagent distribution zone. This particular embodiment occurs in cases where only one electrode of a fuel cell is to be supplied with reagent.

In addition, with reference to FIG. 3 and according to a second application of the present invention, by combining two cellular structures 100 and 200, it is possible to obtain a bipolar plate comprising an integrated heat exchanger.

Indeed, a first honeycomb structure 100 comprising two honeycomb areas 102a, 102b is juxtaposed with a second honeycomb structure 200 comprising a single honeycomb area 202a. These honeycomb structures 100,200 can be brought into contact with one another, for example by simple pressing, which forms a structure comprising three distinct honeycomb zones 102a, 102b, 202a, the honeycomb region 102a being located in the middle of the other two. being a heat exchange zone and the other two zones 102b, 202a, located at the ends of the assembly, corresponding to the zones for distributing the reagents to the electrodes.

According to a third application of the invention, the honeycomb structure 1 can also be used in a device of the heat exchanger type, as a heat exchange zone. Its operation is then similar to that of the plates bipolar, and the fluids injected into the alveolar zones 2a, 2b are coolant such as water.

In such an application, the alveolar zones 2a, 2b are distribution zones for cooling liquid, this cooling liquid being intended to be distributed over all of the surfaces 14a, 14b to be cooled, then to evacuate from the alveolar structure 1 in a direction represented by the arrows Di and D ₂ of FIG. 1.

The invention also relates to a method of manufacturing a honeycomb structure 1, such as that described above. This manufacturing process consists, starting from the conductive base plate 6, in producing at least one alveolar zone 2a, 2b.

With reference to FIGS. 4 and 5, in order to end up in one of the alveolar zones 2a, 2b, two successive operations are repeated several times, making it possible to achieve the production of a metal layer 8. With reference to FIG. 4, the first operation consists in depositing a layer of metallic powder 18 on the last metallic layer 8 which has just been deposited. Note that for the production of the first metal layer 8, this first operation consists in depositing a layer of metal powder 18 on the associated sealed surface 4a, 4b.

In a second step, the operation consists in partially solidifying, by laser, the layer of metallic powder deposited 18, so as to obtain solidified parts 20 and non-solidified parts 22. It is specified that the non-solidified parts 22 consist of powder particles of the metal powder layer 18. The location and the quantities of solidified parts 20 and non-solid parts -solidified 22 are determined according to the network of passages 10 desired on the metal layer 8 in progress. Indeed, the solidified parts 20 define the periphery of the passages 10, while the location of the non-solidified parts 22 corresponds to the desired location for the passages 10 of this metal layer 8.

For each alveolar zone 2a, 2b, this succession of the two stages is therefore repeated, and this as many times as there are metallic layers 8 constituting the alveolar zone 2a, 2b concerned.

Note that after the production of any metal layer 8, the latter has solidified parts 20 and non-solidified parts 22, all of these parts 20, 22 constituting a support for depositing the metal layer 8 next .

To deposit the layers of metal powder 18, any type of method known from the prior art can be used. Preferably, the layers of metal powder 18 are deposited mechanically.

In order to carry out the partial solidification step of the layer of deposited metallic powder 18, methods known from the prior art are used which employ means of the laser type.

Examples include selective laser sintering (translated from English "selective laser sintering"), direct powder deposition (translated from English "direct powder deposition"), production and manufacturing methods. rapid (translated from English “rapid fabrication and production”), “laser sintering”, or “microsystem production”.

In general, the methods mentioned above use means of the laser type to locally provide sufficient power to sinter or melt part of the layer of metallic powder 18, at a precise and predetermined position. This operation can be carried out several times, in order to have a plurality of solidified parts 20.

It is therefore imperative to perform a precise positioning of the laser type means with respect to the layer of metallic powder 18 intended to undergo the partial solidification operation, so that this layer of metallic powder 18 is located in a focal zone of the laser type means. Thus, in certain cases encountered, it is possible to solidify part of the powder layer 18, without solidifying the non-solidified part (s) 22 of the metal layer 8 on which it rests.

Note that it is possible to carry out this process using means of the CAD type, the latter making it possible to adjust, during the course of the process, the relative positions of the laser-type means and of the different layers of metallic powder 18.

It should also be noted that the operation of partial solidification by laser of a layer of metal powder 18 also makes it possible to solidify the solidified parts 20 obtained, with the solidified part (s) of the metal layer 8 on which they rest. This characteristic is also valid for the first metallic layer 8 produced, the solidified parts 20 obtained being secured to the associated sealed surface 4a, 4b of the plate 6.

When all of the metal layers 8 intended to form a cellular zone 2a, 2b have been produced, there is then a block comprising exclusively solidified parts 20 and non-solidified parts 22. Thus, to obtain the passage networks 10 being situated at the level of the non-solidified parts 22, it is necessary to eliminate the powder constituting these parts 22. This elimination can quite simply be carried out by evacuation of the grains of powder, the latter being able to be easily extracted from the block in creating, as they are extracted, the networks of passages 10 of the metal layers 8.

After the elimination of all of the non-solidified parts 22, the alveolar zone 2a, 2b is obtained, consisting of a plurality of solidified parts 20 secured to each other. Of course, various modifications can be made by those skilled in the art to the honeycomb structure 1 and the method of manufacturing such a structure which have just been described, only by way of nonlimiting examples.

Claims

1. Honeycomb structure (1) comprising at least one honeycomb area (2a, 2b) partially delimited by an associated sealed surface (4a, 4b), characterized in that each honeycomb area (2a, 2b) is formed by a plurality of layers metallic (8) superimposed parallel to the associated sealed surface (4a, 4b), each metallic layer (8) comprising a network of passages (10) opening out on either side of said metallic layer (8).

2. Honeycomb structure (1) according to claim 1, characterized in that it is integrated into a fuel cell as a bipolar plate.

3. Honeycomb structure (1) according to claim 1, characterized in that it is integrated into a fuel cell as a bipolar plate with integrated exchanger.

4. Honeycomb structure (1) according to claim 1, characterized in that it is integrated into a heat exchanger.

5. Method for manufacturing a honeycomb structure (1) according to any one of the preceding claims, characterized in that each metal layer (8) is produced by carrying out the following operations:

- depositing a layer of metallic powder (18); partial solidification by laser of the layer of metallic powder (18) deposited, resulting in the formation of solidified parts (20) and parts non-solidified (22), said solidified parts (20) defining the periphery of the passages (10) of the metal layer (8).

6. Method according to claim 5, characterized in that for each alveolar zone

(2a, 2b), the metal layers (8) are produced successively, the associated sealed surface (4a, 4b) constituting a support for the first metal layer (8) to be made, the solidified (20) and non-solidified parts ( 22) of any metal layer (8) made constituting a support for the next metal layer (8) to be produced.

7. Method according to claim 5 or claim 6, characterized in that for each alveolar zone (2a, 2b), when all the metal layers (8) have been produced, the passage networks (10) of the metal layers (8 ) are obtained by eliminating the non-solidified parts (22) of the metal layers (8).

8. Method according to any one of claims 5 to 7, characterized in that the operation of partial solidification by laser of a layer of deposited metal powder (18) is also capable of joining the solidified parts (20) obtained with the solidified parts (20) of the metal layer (8) on which they rest.

9. Method according to any one of claims 5 to 7, characterized in that the laser solidification operation of the first layer of deposited metal powder (18) is also capable of joining the solidified parts (20) obtained with the associated sealed surface (4a, 4b) on which they rest.

10. The manufacturing method according to any one of claims 5 to 9, characterized in that the metal layers (8) consist of a material selected from stainless steels, aluminum and its alloys, nickel and its alloys such as the

Ni-Cr, and a mixture of at least two of the above.

11. The manufacturing method according to claim 10, characterized in that the metal layers (8) comprise at least one binder such as bronze.