Diffusion layer for an electrochemical cell and method for producing a diffusion layer

Abstract

Method for producing a diffusion layer (5, 6) for an electrochemical cell, wherein the diffusion layer consists of a foil (5a, 6a) in which a plurality of holes are made by means of hydraulic punching.

Description

[0001] Description

[0002] Title electrochemical cell and method for producing

[0003] The present invention relates to a diffusion layer for an electrochemical cell and a method for producing a diffusion layer.

[0004] State of the art

[0005] Fuel cells are electrochemical or galvanic cells that convert the chemical reaction energy of a continuously supplied fuel and an oxidizing agent into electrical energy. In electrolysis, the electrochemical process runs in the opposite direction. Essential components of fuel cells and electrolysis cells are bipolar plates and diffusion layers. Diffusion layers for electrochemical cells are known, for example, from DE10238860A1.

[0006] The object of the present invention is to increase the perforation rate of a diffusion layer.

[0007] Disclosure of the invention

[0008] For this purpose, the diffusion layer for an electrochemical cell is now produced using hydraulic punching. The diffusion layer consists of a foil into which a large number of holes are punched using hydraulic punching. Preferably, several million holes are punched into the foil. Hydraulic punching allows more holes to be punched into the foil than previously possible, thus increasing the perforation rate of the diffusion layer produced in this way compared to the state of the art. Such a diffusion layer can improve the media supply for the electrochemical cell, increasing the performance of the electrochemical cell. Hydraulic punching is also a very fast manufacturing process.

[0009] In advantageous designs, the foil is a metallic foil. Hydraulic punching is particularly well-suited for metallic foils, as very high pressures can be achieved. Hydraulic punching is preferably carried out at a pressure of at least 10,000 bar. The foil is advantageously a maximum thickness of 0.2 mm, so that the holes can actually be punched through.

[0010] In advantageous further developments, hydraulic punching is performed as water punching. This is very simple and cost-effective due to the availability of water.

[0011] In advantageous designs, the holes have a maximum diameter of 20 pm. This can be achieved with hydraulic punching. This allows the perforation rate and homogenization of the perforations to be further increased. Both are important for improving the performance of the electrochemical cell.

[0012] In advantageous manufacturing processes, the film is clamped between a first die and a second die during punching. A plurality of through holes corresponding to the plurality of holes is formed in the first die. The through holes are fluidically connected to a pressure vessel on one side and fluidically connected to the (later) holes on the other side. As a result, each later hole in the film is subjected to pressure so that all of the holes are pierced accordingly. In advantageous further developments, a plurality of blind holes corresponding to the plurality of holes are formed in the second die, which are fluidically connected to the holes. At the start of the process, the blind holes are preferably under a pressure which corresponds at most to atmospheric pressure.Before the holes are pierced, atmospheric pressure is applied at the blind holes, so that the film has a maximum pressure difference (top - bottom) at the positions of the later holes and accordingly the local mechanical stress leads to the holes being pierced.

[0013] The invention also encompasses a diffusion layer having several million holes. The diffusion layer is preferably produced by one of the above methods.

[0014] Advantageously, the holes have a maximum diameter of 20 pm. This achieves a high and homogeneous perforation rate.

[0015] The holes are preferably cylindrical. This optimizes the flow path toward the membrane or catalytic layer of the electrochemical cell and reduces flow resistance. This is especially true compared to quasi-stochastic perforations, such as those found in nonwoven diffusion layers.

[0016] The diffusion layers according to the invention are particularly suitable for fuel cells and electrolysis cells.

[0017] Further measures improving the invention will become apparent from the following description of various exemplary embodiments of the invention, which are schematically illustrated in the figures. All features and / or advantages apparent from the claims, the description, or the figures, including structural details and spatial arrangements, may be essential to the invention both individually and in various combinations.

[0018] They show schematically: Figure 1 a section through a known from the prior art

[0019] Fuel cell, with only the essential areas shown.

[0020] Figure 2 shows a section through another fuel cell known from the prior art, with only the essential areas being shown.

[0021] Figure 3 shows a manufacturing method according to the invention for a

[0022] Diffusion layer, with only the essential areas shown.

[0023] Figure 1 schematically shows a prior art electrochemical cell 100 in the form of a fuel cell, with only the essential areas being shown. The fuel cell 100 is designed as a PEM fuel cell and has a membrane 2, in particular a polymer electrolyte membrane. A cathode chamber 100a is formed on one side of the membrane 2, and an anode chamber 100b is formed on the other side.

[0024] In the cathode chamber 100a, an electrode layer 3, a diffusion layer 5, and a distributor plate 7 are arranged, pointing outward from the membrane 2—that is, in the normal direction or stacking direction z. Similarly, in the anode chamber 100b, an electrode layer 4, a diffusion layer 6, and a distributor plate 8 are arranged, pointing outward from the membrane 2. The membrane 2 and the two electrode layers 3, 4 form a membrane-electrode assembly 1. The two diffusion layers 5, 6 are also part of the membrane-electrode assembly 1.

[0025] The distribution plates 7, 8 have channels 11 for the gas supply—for example, air in the cathode chamber 100a and hydrogen in the anode chamber 100b—to the diffusion layers 5, 6. The diffusion layers 5, 6 typically consist of a carbon fiber fleece on the channel side—i.e., toward the distribution plates 7, 8—and a microporous particle layer on the electrode side—i.e., toward the electrode layers 3, 4.

[0026] The distribution plates 7, 8 have the channels 11 and thus implicitly also ribs 12 adjacent to the channels 11. The undersides of these ribs 12 therefore form a contact surface 13 of the respective distribution plate 7, 8 to the underlying diffusion layer 5, 6.

[0027] Typically, the cathode-side distributor plate 7 and the anode-side distributor plate 8 differ from each other; advantageously, the cathode-side distributor plate 7 of an electrochemical cell 100 and the anode-side distributor plate 8 of the adjacent electrochemical cell are firmly connected, for example by welded joints, and thus combined to form a bipolar plate.

[0028] An electrochemical cell designed as an electrolysis cell can have an analogous structure.

[0029] Figure 2 schematically shows an electrochemical cell 100 known from DE10238860A1 in the form of a solid oxide fuel cell, with only the essential areas being shown. The anode-side diffusion layer 6 is a metallic foil, which simultaneously represents the so-called upper shell of a so-called cassette 60. As can be seen, this diffusion layer 6, which extends perpendicular to the plane of the drawing over a certain length, is perforated, i.e., provided with holes 30.

[0030] Together with another structure referred to as the lower shell 61, the upper shell or diffusion layer 6 forms the cassette 60, which encloses a cavity. A metallic wire mesh, for example, can be inserted into a portion of this cavity, although this is not shown here. The upper shell 6 and the lower shell 61 are welded together at their edges, i.e., they are connected to each other via a continuous weld seam in a material-to-material and thus gas-tight manner.

[0031] Essentially in the overlap area with the holes 30, on the

[0032] The membrane-electrode assembly 1 is applied to the outer side of the diffusion layer 6 facing away from the cavity, with the layer adjacent to the diffusion layer 6 being the anode-side electrode layer 4. This is applied as the first layer in the manufacturing process of an electrochemical cell 100 using a thermal powder spraying process. The electrolyte layer or membrane 2 and the cathode-side electrode layer 3 can then be applied to this.

[0033] The fuel gas required for the electrochemical cell 1 or for the electrochemical conversion process taking place therein is fed into the cavity of the cassette 60. Within the cavity, this fuel gas is appropriately distributed among the individual holes 30 so that it can then pass through them to the anode-side electrode layer 4 and react there accordingly.

[0034] In the embodiment of Figure 2, the cathode-side diffusion layer 5 is attached to the lower shell 61. Air or oxygen can then be guided through this diffusion layer 5 to the cathode-side electrode layer 3 of an adjacent electrochemical cell 100 (not shown).

[0035] An analogous structure also applies to an electrochemical cell 100 constructed as a solid oxide electrolysis cell.

[0036] The object of the invention is to increase the number of holes 30 in a diffusion layer 5, 6 of an electrochemical cell 100, preferably by a factor of 5-10. At the same time, ideally, the processing time should also be reduced. The invention is applicable to all diffusion layers 5, 6 or functional layers of electrochemical cells 100 that are designed in a foil-like manner and are intended to have a very high number of holes 30 in the foil thickness.

[0037] Previously, the holes 30 were created by laser in the metallic foil or in the diffusion layer 5, 6. This took several minutes per diffusion layer 5, 6 of a typical electrochemical cell 100. According to the invention, the foil to be perforated is now to be perforated by hydraulic punching, in particular by "water punching," in a single work step, preferably with several million holes 30, so that the diffusion layer 5, 6 is created. For this purpose, Figure 3 shows a foil 5a, 6a to be processed, which is firmly clamped between two matrices 31, 32. The first matrice 31 has through-holes 33, which can be fluidically connected to a pressure vessel 34. The pressure vessel 34 contains a pressurized liquid or a liquid to be pressurized, preferably water.The liquid can be pressurized, for example, via an inlet 35, preferably even increased to a pressure of several thousand bar, particularly preferably to a pressure of more than 10,000 bar. The water pressure then acts through the through holes 33 onto the film 5a, 6a and ultimately breaks through it, creating the holes 30 and, with them, the diffusion layer 5, 6.

[0038] The second die 32 has blind holes 36. At the beginning of the process, these blind holes 36 are preferably filled exclusively with a compressible medium, e.g., air, or even designed as a vacuum. After a hole 30 has been pierced, the corresponding blind hole 36 fills with fluid, and constant pressure prevails only for the dedicated hole 30. This ensures that all holes 30 are pierced. If the blind holes 36 were continuous and had a fluid connection in a collecting container, after a hole 30 has been pierced, all the other holes in the second die 32 would fill backwards, and an undesirable constant pressure would arise. The blind holes 36 therefore ensure that all the desired holes 30 are produced.

[0039] In preferred embodiments, the film 5a, 6a or the diffusion layer 5, 6 has a maximum thickness s of 0.2 mm. The diameter d of the through holes 33 and blind holes 36—and thus also the diameter d of the holes 30 themselves—is preferably 20 μm or less.

[0040] The liquid in the pressure vessel is advantageously pressurized to at least 10,000 bar, so that the holes 30 can also be made in a foil 5a, 6a made of stainless steel, since the tensile strength of the stainless steel is typically 70-80 kN / cm 2 The high pressure of 10,000 bar can be achieved preferably through hydraulic boosting. Since no high flow rates need to be generated, the effort is minimal.

[0041] The advantages of the inventive methods and diffusion layers 5, 6 are as follows:

[0042] • Increase the perforation rate while maintaining the same processing time.

[0043] • If the perforation rate is increased, mass transport limitations will only occur later in the later operation of the electrochemical cell 100. This means, for example, that a higher current per cm 2 active area of ​​the electrochemical cell 100 without the cell itself degrading or delamination of a ceramic or other layer due to a back pressure of media.

[0044] • The performance of an electrochemical cell 100 can be significantly increased.

[0045] • Ultimately, the cost per kW of the electrochemical cell 100 also decreases.

Claims

Claims 1. Method for producing a diffusion layer (5, 6) for an electrochemical cell (100), wherein the diffusion layer (5, 6) consists of a film (5a, 6a) into which a plurality of holes (30) are introduced by hydraulic punching.

2. The method according to claim 1, characterized in that the foil (5a, 6a) is a metallic foil.

3. Method according to claim 1 or 2 characterized in that several million holes (30) are made in the foil (5a, 6a).

4. Method according to one of claims 1 to 3 characterized in that the holes (30) are cylindrical.

5. Method according to one of claims 1 to 4 characterized in that the hydraulic punching is carried out as water punching.

6. Method according to one of claims 1 to 5 characterized in that the hydraulic punching is carried out with a pressure of at least 10,000 bar.

7. Method according to one of claims 1 to 6 characterized in that the holes (30) have a diameter (d) of a maximum of 20 pm.

8. Method according to one of claims 1 to 7 characterized in that the film (5a, 6a) has a thickness (s) of a maximum of 0.2 mm. A method according to any one of claims 1 to 8, characterized in that the film (5a, 6a) is clamped between a first die (31) and a second die (32) during the punching process, wherein a plurality of through holes (33) are formed in the first die (31) corresponding to the plurality of holes (30), which are fluidically connected to a pressure vessel (34) on one side and fluidically connected to the holes (30) on the other side. A method according to claim 9, characterized in that a plurality of blind holes (36) are formed in the second die (32) corresponding to the plurality of holes (30), which are fluidically connected to the holes (30). A method according to claim 10, characterized in that the blind holes (36) are under a pressure at the beginning of the process which corresponds at most to atmospheric pressure.A diffusion layer (5, 6) for an electrochemical cell (100) characterized in that the diffusion layer (5, 6) has several million holes (30). A diffusion layer (5, 6) according to claim 12 characterized in that the holes (30) have a diameter (d) of at most 20 pm. A diffusion layer (5, 6) according to claim 12 or 13 characterized in that the holes (30) are cylindrical.

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