METHOD FOR PRODUCING A FUEL CELL WITH A SCREEN-PRINTED SEAL

Abstract

A method is provided for producing a fuel cell that includes a stack of unit cells separated by bipolar plates. Each unit cell includes at least an anode element, a cathode element, an ion-exchange membrane, a reinforcing element, and a gas diffusion layer. The anode element and the cathode element are separated by the ion-exchange membrane. The method includes steps of: producing a silicone seal by screen printing, positioning the silicone seal on the reinforcing element, assembling constituent elements of a unit cell, and positioning a bipolar plate on each side of the unit cell. The steps of the method are repeated as many times as needed depending on a desired size of the stack.

Claims

1-6. (canceled)

7: A method for producing a fuel cell that includes a stack of unit cells separated by bipolar plates, in which each unit cell includes at least an anode element, a cathode element, an ion-exchange membrane separating the anode element from the cathode element, a reinforcing element, and a gas diffusion layer, the method comprising steps of: (a) producing a silicone seal by screen printing; (b) positioning the silicone seal on a reinforcing element; (c) assembling constituent elements of a unit cell, the unit cell having first and second sides; (d) positioning a bipolar plate on each of the first and second sides of the unit cell; and (e) repeated the steps (a) through (d) as many times as needed to obtain a desired stack size.

8: The method according to claim 7, wherein the step (a) includes: producing a screen or frame that displays a desired seal pattern, depositing a quantity of silicone on the screen or frame, the quantity being dependent upon a size of the screen or frame, passing a scraper over the screen or frame to deform the screen or frame and to pass the silicone through locations of the screen or frame corresponding to the desired seal pattern, to produce an unpolymerized seal, removing the screen or frame from the unpolymerized seal, and inserting the unpolymerized seal into an oven to allow polymerization to occur to produce the silicone seal.

9: The method according to claim 8, wherein the screen or frame is a canvas made from a PET fabric.

10: The method according to claim 9, wherein the step (a) further includes, before inserting the unpolymerized seal into the oven, resting the unpolymerized seal to allow micro-roughness to even out.

11: A unit cell of a fuel cell, the unit cell comprising: an ion-exchange membrane; two electrodes arranged on opposite sides of the membrane, such that the membrane separates the two electrodes; a reinforcer installed on the membrane; and a screen-printed seal deposited on the reinforcer.

12: A fuel cell comprising: at least one unit cell, each unit cell including: an ion-exchange membrane, two electrodes arranged on opposite sides of the membrane, such that the membrane separates the two electrodes, a reinforcer installed on the membrane, and a screen-printed seal deposited on the reinforcer; and a bipolar plate positioned on each of two sides of the unit cell, each bipolar plate being structured to enable fuel gas and oxidizing gas to flow.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0036] Other aims and advantages of the invention will appear more clearly in the following description of a preferred but non-limiting embodiment, illustrated by the following figures in which:

[0037] FIG. 1 shows an example of a bipolar plate for a fuel cell having a groove intended to allow the presence of a screen-printed seal,

[0038] FIG. 2 shows a screen for screen printing,

[0039] FIG. 3 shows a side view of a scraper used in the context of producing a seal by screen printing,

[0040] FIGS. 4 and 5 show two configurations.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION

[0041] A bipolar plate as shown in FIG. 1 comprises a central skeleton 11 made up of two thin plates, which are parallel and rigidly connected by a method such as gluing, welding or brazing. One face of this plate is intended to be placed against an anode, in a fuel cell, and the other face is intended to be placed against a cathode. The thin plates have several holes made at the periphery thereof, in order to form collectors of fuel 2, oxidizer 3, and cooling liquid 4. The plates also include a set of channels 5, which are placed in the thickness thereof, in order to allow the flow, at the surface, of fuel or of oxidizer. Furthermore, the thin plates include openings for connecting a collector to a gas flow channel.

[0042] The seal produced by screen printing is intended to be affixed to the location 10 indicated in this FIG. 1. This seal must therefore have a pattern 20 of the type of that appearing on the screen shown in FIG. 2. It is specified in this case that there are several types of bipolar plates, each having different patterns. Thus, the pattern shown in FIG. 2 does not correspond to the bipolar plate of FIG. 1. Two different patterns are intentionally shown, which are covered by the present invention, the use of which is not limited to a particular type of bipolar plate.

[0043] This screen, also called a frame, is formed from a PET fabric, the meshes and the thread diameter of which can be adapted to the various uses. The fabric is then coated with a photosensitive product known as an emulsion on which a template corresponding to the pattern to be produced is deposited. After exposure to a UV lamp, the photosensitive product hardens except for the area masked by the template. The excess is then cleaned off. Thus, all pores of the canvas, except for the area of the pattern, are blocked in order to allow the product to pass only in the desired areas.

[0044] Once this frame, or screen, has been produced, it is then possible to produce a seal, using a method as shown in FIG. 3.

[0045] Firstly, the frame is arranged on the support on which the seal will be deposited. The frame is installed slightly above the support so as to avoid contact therebetween before the scraper passes over. The product to be deposited, for example silicone, is poured in bulk into the frame.

[0046] The product is then spread out evenly over the pattern but without pressing too hard to prevent it from passing through the canvas. This operation is referred to as coating.

[0047] Then, a scraper 30 formed from a polyurethane or metal section, the hardness and stiffness of which can be adjusted, is passed along the entire section with a variable angle close to 45.

[0048] The scraper will then force the canvas 31 to deform, bringing it into contact with the support 32. The silicone is then forced, upon the passage of the scraper, to pass through the canvas in order to be deposited on the support. The scraper also makes it possible to scrape the excess silicone from the surface of the screen, the latter being subsequently close for a second removal.

[0049] It is important to note that the thickness of the seal that is intended to be obtained is dependent on many factors, even though the contour is simply defined by the screen.

The parameters having an influence on the thickness of the seal are classified in descending order. These parameters can be modified prior to the implementation of the screen-printing production method, depending on the characteristics of the desired seal. Thus, specified hereafter are examples of values for these various parameters during the implementation of an example of the invention: [0050] the type of canvas: for example, a canvas of 27-140 type is used, i.e. 27 threads per centimetre, and threads having a diameter of 140 micrometres, [0051] the viscosity of the silicone, for example 60000 pascal seconds, [0052] the angle of the scraper, preferably between 30 and 50, [0053] the pressure applied to the scraper, for example 4 kilograms per 100 millimetres of scraper, [0054] the Shore hardness of the scraper, preferably between 60 and 80 Shore, [0055] the height outside the frame, which is preferably determined depending on the size of the frame, for example height=width of the screen*0.006, [0056] the travelling speed of the scraper, for example 50 millimetres per second.

[0057] Once the seal has been deposited, it is necessary for it to harden in order to obtain the characteristics that make it possible to produce airtightness. Firstly, the deposited seal is left to rest for approximately 1-2 minutes, the time taken for the micro-roughness due to passage through the canvas to fill itself in. The seal is then passed into an oven to be set to a temperature between 80 C. and 130 C. If the oven is set to 130 C., the polymerization time will be approximately 10 minutes. The use of low temperature, of approximately 80 C., avoids degrading the element on which the seal is deposited.

[0058] Preferably, as mentioned above, an RTV2-type silicone will be used. This silicone has a long pot-life of approximately 15 h, making it possible to perform screen printing without the silicone hardening prior to shaping.

[0059] After producing the seal, it is possible to move on to the step of assembling the unit cell, and then the fuel cell. As previously indicated, the seal is used to produce the airtightness between a unit cell and the following bipolar plate in the stack.

[0060] Two different configurations of a unit cell are shown in FIGS. 4 and 5. These figures represent a sectional view of a part of a stack.

[0061] In FIG. 4, the membrane 2 is glued or welded on a reinforcer 3. [0062] The lower gas diffusion layer 1 is installed astride the membrane 2 and the reinforcer 3 on which two screen-printed seals 5 have been previously deposited on both sides. [0063] The upper gas diffusion layer 1 is only installed on the membrane 2. [0064] In FIG. 4, it is noted that the membrane 2 projects from the gas diffusion layers. It is, however, possible for the membrane to stop in line with these layers.

[0065] In the configuration shown in FIG. 5, the membrane 2 is installed between two reinforcers 3, the latter are glued or welded together and on the membrane. [0066] Each of the gas diffusion layers 1 is installed astride the membrane 2 and a reinforcer 3, respectively. [0067] In this configuration, the screen-printed seals 5 are installed on each of the reinforcers, respectively.