Electrodes for distribution of working materials in fuel cells

Abstract

An electrode (2) for a fuel cell (1), comprising a plate-shaped body (20) made of an electrically conductive foam, the plate-shaped body having an open and continuous porosity for at least one working material of the fuel cell (1). The plate-shaped body (20) ideally defines a plane (E). The plate-shaped body (20) has the following regions in the plane (E): the regions have different porosities.

Description

Technical Field

[0001] The invention relates to an electrode for distributing at least one operating material in a fuel cell, as well as a method for producing the electrode and a fuel cell having a corresponding electrode. Background Art

[0002] In a fuel cell, a fuel provided in an anode chamber reacts with an oxidant provided in a cathode chamber.

[0003] Such fuel cells are known from the prior art, for example from the publication DE 10 2009 001 153 A1. The known fuel cell comprises two gas diffusion layers, two electrode elements and an electrolyte. The electrolyte is arranged between the two gas diffusion layers with one electrode element located between them. The fuel cell is supplied with an oxidant, usually ambient air, via a supply line, and a gaseous fuel, for example hydrogen, via a fuel line. In the fuel cell, an electrochemical reaction of the fuel and the oxidant occurs with the participation of a catalyst. For this purpose, the electrolyte must be ionically conductive, preferably so that the cations of the fuel diffuse through the electrolyte. Usually, a polymer is used as an electrolyte.

[0004] In order to achieve an optimal energy density for the current generation, it is important that the fuel and the oxidant are each evenly distributed over the entire surface of the electrolyte. In other embodiments of the prior art, a distribution structure is introduced for a rough distribution to the bipolar plates or end plates, which delimit the anode space or cathode space on the side facing away from the electrolyte. A porous gas diffusion layer is attached thereto as an electrode structure. Document DE 10 2016 213 057 A1 discloses an example of a fuel cell in which the bipolar plates contain a complex distribution structure. Summary of the invention

[0005] It is an object of the present invention to design a porous gas diffusion layer in such a way that the provision of working material to the electrolyte is optimized in a plane E defined by the gas diffusion layer.

[0006] For this purpose, the electrode comprises a plate-shaped body made of an electrically conductive porous structure, such as, for example, an electrically conductive foam, which has open pores and continuous The plate-shaped body ideally defines a plane. The plate-shaped body has the following regions in the plane: the regions have different porosities.

[0007] Therefore, the plate-shaped body can be regarded as a gas diffusion layer and an electrode in the same way. The porosity of the plate-shaped body is random and behaves inversely to its density. However, the density can be increased in a targeted manner, for example by extrusion. The working material, preferably hydrogen or air, flows in this plane; this flow is influenced by the different porosities. The supply of the electrolyte with the working material is carried out in a direction perpendicular to this plane. In order to supply the electrolyte of the fuel cell with reactants or working materials as uniformly as possible, it is precisely the irregular structure of the gas diffusion layer or the electrode that is advantageous, as will be described in further detail below.

[0008] Advantageously, the plate-shaped body has a first region with a higher porosity and a second region with a lower porosity. The foam in the second region is therefore denser than the foam in the first region. This is achieved, for example, by the second region being pressed more strongly perpendicularly to the plane than the first region. As a result, the flow of the working material in the plane can be very well distributed or guided.

[0009] In an advantageous embodiment, the porosity in the second region is reduced by deformation. Thus, the first region and the second region can first be produced from the same foam with the same porosity and then the porosity of the two regions can be adjusted differently by deformation, for example extrusion, preferably by using different initial heights before extrusion. Advantageously, the porosity of the second region is reduced by a maximum of 60%.

[0010] Preferably, the flow cross section Q of the first region 1 is the flow cross section Q of the second region 2 One fifth to five times as large.

[0011] In an advantageous embodiment, the first region is formed by a first strip and the second region is formed by a second strip. Preferably, a plurality of first strips and second strips are arranged alternately side by side in the plane. The main flow direction of the working material in the plane thus extends in the strip direction, preferably the working material flows through the first strip with a higher porosity.

[0012] An advantageous method for producing such an electrode provides the following method steps:

[0013] The first strips and the second strips are arranged alternately side by side, wherein the first strips first have a first height and the second strips first have a second height,

[0014] Next, the first strip and the second strip are pressed to a uniform height, such as by conventional pressing or rolling.

[0015] This results in an electrode of uniform height, which can therefore be arranged in a known manner in a fuel cell between the electrolyte and the end plate. Preferably, the two strips are initially made of the same foam with the same random porosity, but just different heights; the different porosities are only adjusted by extrusion.

[0016] A sheet of a first height is cut from a foam block. A sheet of a second height is cut from another block or the same block. The sheet is cut into strips, that is, into a first strip and a second strip. The first and second strips are then arranged alternately side by side. Optionally, the strips can be connected by gluing, welding or preferably laser welding for better handling. As a variant, the foam of the two blocks can have different porosities and / or materials and / or the cutting is preferably conducted in such a way that sheets of different thicknesses are produced. Particularly preferably, the electrode made from the combined strips is then extruded to a uniform height h, so that in particular areas of different porosity can be formed.

[0017] Thin foams, in particular metal foams, are produced here, for example, by wire cutting large blocks into thin foam sheets, which must have a uniform thickness or height for low-tolerance stacking and can therefore be adjusted for thickness by rolling devices with optional heating.

[0018] In another advantageous embodiment, the first region is formed by a substrate and the second region is formed by a column, which is arranged in a hole in the substrate. Preferably, the column is designed as a circle in a planar cross section and is arranged here so that the columns are aligned on a plurality of parallel lines and thus form the main flow direction. Advantageously, the column has a smaller porosity than the substrate, so that the column is relatively flow-impeded. However, since the column is surrounded by a substrate with better flow permeability on its entire periphery, it is particularly uniform to supply the electrolyte with the working material, that is, by a flow perpendicular to the plane, and therefore also at the position of the column. By distributing the flow through the column in the plane of the electrolyte, a flow perpendicular to the plane can also be achieved particularly uniformly.

[0019] In a preferred embodiment, the base plate is of substantially rectangular design and the columns are arranged aligned with approximately diagonally parallel lines. This results in a diagonal main flow direction, so that the entire surface of the plate-shaped body is supplied with working material very evenly. This applies in particular when the inlet and outlet for the working material into and out of the plate-shaped body are arranged diagonally opposite and are ideally shaped in a geodesic manner.

[0020] The invention therefore also includes a fuel cell having an anode chamber, a cathode chamber and an electrolyte, the electrolyte separating the anode chamber from the cathode chamber. The anode chamber and the cathode chamber are each delimited on the side facing away from the electrolyte by an end plate. Electrodes as described above are arranged between at least one end plate on the one hand and the electrolyte on the other hand. This also has the effect that the fuel cell can be designed very thin overall.

[0021] In a preferred embodiment, the substrate of the electrode is substantially rectangular in shape and the columns are arranged aligned with approximately diagonal parallel lines. The fuel cell has an inlet and an outlet for the working material to enter and leave the plate-shaped body. The inlet and outlet are arranged diagonally opposite each other on the plate-shaped body. As a result, the connection between the inlet and the outlet corresponds almost to the main flow direction or is oriented according to parallel lines. As a result, the electrolyte is supplied with working material in a particularly uniform manner. The working material that is not supplied to the electrolyte leaves the plate-shaped body via the outlet, but can be recycled if necessary.

[0022] An advantageous method for producing an electrode having a cylindrical second region provides the following method steps:

[0023] A hole is formed in the base plate, for example by punching, which has a first height h 1 ;

[0024] A post is arranged in the hole, the post having a second height h 2 , where h 2 Greater than h 1 ;

[0025] Next, the substrate and the pillars are pressed to a uniform height h, such as by conventional pressing or rolling.

[0026] The substrate and the pillars are preferably initially made of foam having the same random porosity. After extrusion, the porosity of the pillars is significantly reduced more than the porosity of the substrate, which may even remain unchanged.

[0027] A further advantageous method for producing an electrode having a cylindrical second region provides the following method steps:

[0028] The pillars are arranged on a substrate, the substrate having a first height h 1 , the column has a height h 2 -h 1 , where h 2 >h 1 , and, as a result of subsequent processing steps, at least temporarily connecting the pillar to the substrate;

[0029] Next, the substrate and the pillars are pressed to a uniform height h, such as by conventional pressing or rolling.

[0030] Advantageously, the average pore size of the electrode material or the finished electrode is between 100 μm and 400 μm at least in some regions. The lower limit ensures that the pressure loss of the working material does not become too great. The upper limit ensures that the working material is still distributed sufficiently finely on the surface of the electrolyte.

[0031] The invention also relates to another method for producing the electrode from the electrode material. In this method, the foam of the second region, i.e., for example, the second strip or column, is at least temporarily compressed by at least 20% and at most 60% in terms of its thickness. That is, the height h is located at the second height h 2 The range of 40% to 80%.

[0032] It has been found that compression in this region changes the porosity in the electrode to such an extent that a flow of working material can be guided in the electrode, while at the same time an open porosity is retained throughout the electrode and no region is completely excluded from the supply of working material. The electrode can fulfill the dual function of distribution structure and diffusion layer for the working material particularly well, as described above.

[0033] It is taken into account here that the foam partially rebounds after the compressive force is removed. Therefore, the deformation is partly plastic and partly elastic.

[0034] Advantageously, for extrusion, at 200 N / cm 2 With 3000N / cm 2 The foam is loaded with a pressure between 100 N / cm and 200 N / cm. The loading is significantly at 150 N / cm 2 Above the typical pressure of , the finished electrode is usually subjected to this typical pressure in the case of compression in a fuel cell or a fuel cell stack. The linear pressure in this area leads to at least partial plastic deformation of the foam without completely closing or destroying too many pores. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Further measures to improve the invention are shown in greater detail below in conjunction with the description of preferred exemplary embodiments of the invention with reference to the drawings.

[0036] FIG. 1 shows a schematic embodiment of an electrode, wherein only the essential regions are shown;

[0037] Figure 2 shows another schematic embodiment of an electrode, wherein only the essential regions are shown;

[0038] Figure 3 shows another schematic embodiment of an electrode, wherein only the essential regions are shown;

[0039] Figure 4 A schematic side view of a fuel cell is shown, wherein only the essential regions are shown. DETAILED DESCRIPTION

[0040] Figure 1a , 1b and 1c show an embodiment of the electrode 2. Figure 1a and 1b shows a side view of the electrode 2, Figure 1c A top view is shown. Figure 1a The electrode 2 is shown before extrusion or before being formed; Figure 1b and 1c The electrode 2 is shown after extrusion or as a finished electrode 2 which can be arranged, for example, in a fuel cell. The finished electrode 2 has a length l, a width b and a height h, wherein the following applies: l≥b≥h. Figure 1a , 1b 1c are shown only schematically and are to be understood as not being true to scale.

[0041] The electrode 2 consists of a plate-shaped body 20 of length l and width b, which define a plane E. The subject of the invention is the flow of gas or the flow of working material in the plane E of the plate-shaped body 20 or the distribution of working material in the plane E, wherein, of course, in the case of use in a fuel cell 1, there must also be a flow of working material in the direction of height h for supplying the electrolyte 3, as will be described later. Figure 4 As shown in.

[0042] The plate-shaped body 20 is preferably implemented in metal. The plate-shaped body 20 is also implemented as a porous foam, so that gas flow, such as air or hydrogen, is possible. In particular, for applications in polymer-electrolyte-fuel cells, the foam or plate-shaped body 20 must also be able to conduct reaction water on the cathode side. In addition, the plate-shaped body 20 must be electrically conductive. In order to optimize the gas flow and, if necessary, the water conduction, the electrode 2 according to the invention has the following regions in the plate-shaped body 20, which have different porosities, i.e., a first region with a higher porosity and a second region with a lower porosity.

[0043] For this purpose, a first height h is cut from the foam, for example in block form, with a random regular porosity. 1 The first strip 21 and the second height h 2 The second strip 22, wherein h 2 >h 1 ≥h (see Figure 1a ). The first strips 21 and the second strips 22 are now arranged alternately next to each other and are then pressed or rolled to a uniform height h (see Figure 1b). Thus, the electrode 2 produced has a relatively high porosity (i.e., low density) in the first strip 21 and a relatively low porosity (i.e., high density) in the more strongly pressed second strip 22. The first strip 21 corresponds to the first region in this embodiment, while the second strip 22 corresponds to the second region.

[0044] During operation of the fuel cell, the gas flow thus occurs primarily in the first strip 21. Figure 1a , 1b 1c, the first strip 21 and the second strip 22 have a length corresponding to the width b of the electrode 2; the first strip 21 and the second strip 22 are therefore arranged so that the gas flow in the plane E along the main flow direction 70 is mainly realized in the direction of the width b. Preferably, along the main flow direction 70, the flow cross section Q of the region with higher porosity is 1 is the flow cross section Q of the region with lower porosity 2 One fifth to five times as large.

[0045] exist Figure 1b The actual flow cross section Q in plane E can be seen in 1 and Q 2 The actual flow cross section corresponds to the product of the height h and the width of the first strip 21 or the second strip 22 .

[0046] The invention is obviously similar to a gas flow achieved mainly in the direction of the length l; accordingly, the first strip 21 and the second strip 22 will have a length corresponding to the length l of the electrode 2.

[0047] Figure 2 A further exemplary embodiment of an electrode 2 is shown in a top view. Figure 3 The electrode 2 also consists of a plate-shaped body 20, which is designed as a foam and preferably metal. As in the embodiment of FIG. 1 , the foam is designed porous, but now does not have strips with different porosities, but ideally has point-different porosities, or at Figure 2 In an embodiment, the column 32 has a smaller porosity.

[0048] Manufacturing is similar to Figure 1a The embodiment of the present invention realizes that the plate-shaped body 20 is essentially composed of the foam substrate 31. The first height h of the plate-shaped body 20 1 The substrate 31 is partially punched by punching or laser cutting. A second hole 31a having a higher height h is inserted into the hole 31a thus produced. 2 The plate-shaped body 20, that is, the base plate 31 and the column 32, is then pressed to a uniform height h, where h≤h 1. As a result, a region with a lower porosity is produced at the insertion location or on the column 32, so that the pressure loss can be locally changed by means of this insertion method. The shape of the "point-like" region is arbitrary, but preferably circular. Optionally, the inserted piece or column 32 is connected to the base plate 31 by welding or laser welding before or after extrusion. In this embodiment, the base plate 31 thus forms a first region with a higher porosity, while the column 32 forms a second region with a reduced porosity.

[0049] In accordance with Figure 2 The main flow direction 70 in the plane E of the embodiment of can be realized either along the width b or along the length l of the electrode 2, depending on how the inlet and outlet are arranged on the electrode 2. Flow cross section Q with higher and lower porosity 1 and Q 2 In this case, the width b is plotted for the main flow direction 70 and is represented relative to one another as the diameter of the pillars 32 relative to the distance between two adjacent pillars perpendicularly to the main flow direction 70 .

[0050] Figure 3 Another electrode 2 is shown having a plate-shaped body 20, which has a base plate 31 and pillars 32, which originally have different heights h. 1 and h 2 And has been squeezed to a uniform height h, so that the foam of the plate-shaped body 20 has the following regions: the regions have different porosities; the base plate 31 constitutes a first region and has a relatively high porosity; the pillars 32 constitute a second region and have a relatively low porosity. However, alternatively, the same height h 1 and h 2 It is also possible to use substrates 31 and pillars 32 of different foams with different porosities with the same result.

[0051] exist Figure 3 In the embodiment of the present invention, the columns 32 are arranged diagonally or approximately diagonally, preferably at an angle between 30° and 60°, in plane E with respect to the length l and the width b of the electrode 2. Thus, the columns 32 are aligned along parallel lines 71, which extend diagonally accordingly. Therefore, the main flow direction 70 of the working material also extends diagonally accordingly, that is, parallel to the lines 71, especially when the inlet 5 and the outlet 6 of the working material are also arranged in plane E at the diagonally opposite ends of the electrode 2. Accordingly, the flow cross section Q of the regions with higher and lower porosity is depicted in plane E perpendicular to the main flow direction 70 1 and Q 2 .

[0052] Figure 4An embodiment of a fuel cell 1 is shown. The fuel cell 1 has an anode chamber 1a and a cathode chamber 1b, which are separated from each other by an electrolyte 3; the electrolyte 3 is preferably designed as a polymer electrolyte membrane. The anode chamber 1a is delimited in the thickness direction of the fuel cell 1 by a first end plate 11 on the one hand and the electrolyte 3 on the other hand. The cathode chamber 1b is delimited by a second end plate 12 on the one hand and the electrolyte 3 on the other hand. The lateral and circumferential seals are arranged on the Figure 4 Not drawn in for clarity.

[0053] An example of an electrode 2 of the type shown in FIGS. 1 to 3 is provided in each of the anode chamber 1a and the cathode chamber 1b. Figure 4 In the embodiment of , the electrodes 2 are implemented identically in the anode chamber 1a and the cathode chamber 1b, but this is by no means mandatory. For example, it is possible that the electrodes 2 are provided with an average higher porosity in the cathode chamber 1b in order to be able to optimally conduct the product water.

[0054] The electrode 2 according to the invention has the following advantages:

[0055] Possibility of using open-cell foams with high porosity and large pores in order to achieve low pressure loss;

[0056] A higher structural strength of the foam is achieved by the targeted introduction and generation of regions of greater rigidity, ie by a lower porosity.

[0057] With an overall lower pressure loss, a better lateral exchange of the flow is achieved via points or strips with a higher pressure loss.

[0058] There are regions with a layer that develops in the direction of the electrolyte 3 in order to limit the penetration of open-cell foam ends into the electrolyte 3 or into intermediate layers arranged therebetween.

Claims

1. An electrode (2) for a fuel cell (1), comprising a plate-shaped body (20) made of an electrically conductive foam, the plate-shaped body having an open and continuous porosity for at least one operating material of the fuel cell (1), wherein: The plate-shaped body (20) ideally defines a plane (E), characterized in that the plate-shaped body (20) has the following regions in the plane (E): the regions have different porosities, wherein the plate-shaped body (20) has a first region (21, 31) and a second region (22, 32), the first region has a higher porosity, and the second region has a lower porosity, wherein the first region is formed by a substrate (31), and the second region is formed by a column (32), the column is arranged in a hole (31a) of the substrate (31), and wherein the substrate (31) is constructed essentially in a rectangular shape, and the columns (32) are arranged aligned with approximately diagonal parallel lines (71).

2. The electrode (2) according to claim 1, wherein The porosity in the second region (22, 32) is reduced by deformation.

3. The electrode (2) according to claim 1 or 2, characterized in that The flow cross section Q1 of the first region (21, 31) is one fifth to five times as large as the flow cross section Q2 of the second region (22, 32).

4. A fuel cell (1) comprising an anode chamber (1a), a cathode chamber (1b) and an electrolyte (3), the electrolyte separating the anode chamber (1a) from the cathode chamber (1b), wherein: The anode chamber (1a) and the cathode chamber (1b) are respectively delimited by end plates (11, 12) on the side facing away from the electrolyte (3), wherein an electrode (2) according to any one of claims 1 to 3 is arranged between at least one end plate (11, 12) on the one hand and the electrolyte (3) on the other hand, wherein the fuel cell (1) has an inlet (5) and an outlet (6) for the working material to enter and leave the plate-shaped body (20), wherein the inlet (5) and the outlet (6) are arranged diagonally opposite each other on the plate-shaped body (20).

5. A method for producing an electrode (2) according to any one of claims 1 to 3, wherein: The substrate (31) first has a first height (h1), and the pillar (32) first has a second height (h2), characterized by the following method steps: constructing a hole (31a) in the substrate (31); Arranging the column (32) in the hole (31a); Next, the substrate (31) and the pillars (32) are pressed to a uniform height (h).

6. A method for producing an electrode (2) according to any one of claims 1 to 3, wherein: The substrate (31) first has a first height (h1), and the pillar (32) first has a second height (h2), characterized by the following method steps, Arranging a column (32) on the substrate (31) and at least temporarily connecting the column to the substrate (31) as a result of a subsequent processing step; Next, the substrate (31) and the pillars (32) are pressed to a uniform height (h).

7. A method for producing an electrode (2) according to claim 5 or 6, wherein: During compression, the foam of the second region is compressed with respect to its height by at least 20% and at most 60%.

8. The method according to claim 7, wherein: For extrusion, at 200N / cm 2 With 3000N / cm 2 The foam is loaded with pressure between.

9. The method according to claim 5, wherein: The hole (31a) is formed in the base plate (31) by punching.

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