Method for manufacturing a bipolar plate

Abstract

Method for manufacturing a bipolar plate (1), wherein - first, three non-metallic components (16, 17, 19) are prefabricated individually, namely two plate components (16, 17) made of a base material, at least one of which is three-dimensionally structured, and a channel component (19) made of an additive material different from the base material, the shape of which is adapted to the structuring (18) of the at least one plate component (16, 17), - the channel component (19) is inserted between the plate components (16, 17), thereby forming a plate body (2) as a solid intermediate product, - the plate body (2) is solidified by hot pressing, - after the production of the plate body (2) the additive material is removed from it.

Description

[0001] The invention relates to a method for manufacturing a bipolar plate suitable for use in an electrochemical system.

[0002] EP 4 117 060 A1 discloses a method for manufacturing a monopole plate for fuel cells and / or redox flow batteries. It is proposed to manufacture the monopole plate from a metal filament, which is sintered in a subsequent process. Furthermore, it is suggested that, in the case of 3D-printed parts, internal channels can be filled with water-soluble support structures and dissolved with water after the printing process.

[0003] A method for manufacturing a bipolar plate for fuel cell stacks is described in DE 102 61 483 A1. This method assumes that the bipolar plate has a frame and an inner area enclosed by the frame, containing channels for gases and coolant. A fabric is inserted into a tool for manufacturing the bipolar plate, oriented essentially perpendicular to the bipolar plate to be manufactured and extending beyond it on both sides. In the subsequent manufacturing process, the fabric is bent over on both sides so that it covers the inner area of ​​the bipolar plate.

[0004] German patent DE 103 30 832 A1 relates to a composite separator plate for a PEM fuel cell and the production of such a separator plate. During the manufacturing process, expanded graphite, which is in particle form, is dispersed in a polymer resin. The resin is then press-molded together with the graphite particles to form the separator plate.

[0005] A method for manufacturing a fuel cell component, described in WO 2007 / 021677 A2, involves the use of an easily removable masking material. This involves applying a masking material, for example diatomaceous earth or a salt, to a substrate in such a way that sections of the substrate remain exposed. After work has been carried out on the exposed sections, the masking is removed by washing, peeling, and / or scraping. Channel structures are formed, in particular, by the sections to which no masking material is applied. Hydrophilic coatings can then be applied within these channel structures.

[0006] WO 2006 / 124125 A2 concerns a porous, electrically conductive fluid distribution plate for fuel cells. A plate body of the fluid distribution plate defines a set of fluid flow channels designed such that a fluid flow is distributed over at least one side of the plate. Furthermore, the fluid distribution plate comprises a porous conductive polymer layer that is directly connected to the plate body.

[0007] A biopolar plate for fuel cell stacks described in DE 102 45 475 B4 comprises a supply plate located between two outer plates, through which cooling channels as well as inlet and outlet channels are formed. The supply plate is an injection-molded plastic part. The outer plates, on the other hand, are made of metal, for example titanium, stainless steel, aluminum, or copper.

[0008] DE 10 2021 126 237 B3 relates to a bipolar plate constructed from two half-sheets. In this case, the half-sheets provide reference markings which can be used for measurement purposes.

[0009] The invention is based on the objective of further developing the manufacturing of bipolar plates for electrochemical systems compared to the prior art, with a broad spectrum of geometric design possibilities being pursued.

[0010] This problem is solved according to the invention by a method for producing a bipolar plate as designed according to claim 1. The bipolar plate is suitable for use in an electrochemical system, for example a fuel cell system or an electrolysis system.

[0011] The bipolar plate comprises a monolithic plate body made of a single material, which constitutes the main or sole component of the bipolar plate and is traversed by a meandering cooling channel. The meandering shape of the cooling channel means that it cannot be produced by conventional machining of the single-piece plate body. The monolithic shape of the plate body distinguishes it from multi-layered plate structures, such as those made of stacked sheets.

[0012] Thanks to the one-piece design of the plate body, no sealing elements are required within the plate body itself. Depending on the surrounding structure, seals may be attached to the outer contours of the plate body.

[0013] The plate body can, in particular, comprise graphite and / or a polymer, especially in the form of a graphite-filled polymer material. In any case, the plate body is made of an electrically conductive material. This material constitutes the base material of the bipolar plate. Furthermore, a different additional material is required for the production of the bipolar plate.

[0014] During the manufacturing process of the bipolar plate, an electrically conductive, non-metallic plate body is first produced from the base material and a different additive material, such that the additive material describes a channel geometry. At this stage of production, the plate body differs from the final product in that it lacks a cavity. Only in a later step is the additive material removed from the plate body, thus completing the bipolar plate. The additive material functions as a lost-wax mold.

[0015] Regarding the shape of the cooling channel, there is considerable design freedom. For example, the cooling channel can have changing cross-sectional shapes and branches along its length. Similarly, the plate body can be permeated by multiple cooling channels. According to one possible design, the plate body has only a single cooling channel, the ends of which can be located either on the same face of the typically cuboid-shaped plate body or on different faces. This also applies to non-cuboidal plate bodies, such as those with an octagonal base.

[0016] Regardless of the basic shape of the plate body, it can be manufactured from three components: two plate components made of the base material, in particular a graphite-filled polymer mixture, and one channel component made of the additive material. At least one of the two plate components is three-dimensionally structured to match the shape of the subsequent cooling channel. Additionally, structuring can also be provided on the outer surface of the plate components.

[0017] In any case, the channel component has a shape that reflects the form of the subsequent cooling channel. The term "cooling channel" is used for simplicity regardless of whether a fluid passed through this channel during later operation is used for temperature increase or cooling.

[0018] A solid intermediate product is assembled from the three individually prefabricated plate- or channel-shaped, i.e., serpentine, components by inserting the channel component between the two plate components, which are not necessarily mirror-symmetrical to each other.

[0019] This intermediate product, which already has the basic outer shape of the future sheet body, is solidified by hot pressing. It is possible to use prefabricated components for hot pressing that only approximate the outer geometry of the final component. For example, fine structures, such as channels and feedthroughs, can still be formed during hot pressing.

[0020] In any case, the channel component is subsequently dissolved from the plate body using a solvent. An inorganic solvent, particularly water, or an organic solvent can be suitable. The choice of solvent depends on the material from which the channel component is formed. For example, this material could be a salt or a soluble polymer. Optionally, the dissolution of the channel component from the plate body is aided by the application of heat. The introduction of additional openings into the plate body for the purpose of draining the dissolved material is also optional. The removal of the salt or polymer, for example, polyvinyl alcohol, from the plate body can be facilitated by applying pressure to the solvent. In this way, the dissolution process can also be combined with a leak and pressure resistance test.

[0021] The bipolar plate can be used in fuel cell systems as well as in electrolysis systems. The individual, plate- or meander-shaped components from which the plate body is manufactured are typically formed using discontinuous processes. Alternatively, continuous processes, such as rolling processes, can be used to form these components.

[0022] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows, in part schematically: Fig. 1 and Fig. 2 a bipolar plate in cross-sectional views, Fig. 3 a stack of electrochemical cells including a plurality of bipolar plates according to Fig. 1 and Fig. 2, Fig. 4 an arrangement of different preforms for the production of the bipolar plate.

[0023] A bipolar plate 1 is intended for use in a cell stack 10, that is, a stack, of an electrochemical system, in this case a fuel cell system. Alternatively, bipolar plates 1 could be used in the Fig. The form shown in Figures 1 to 3 can also be used in other electrochemical systems, for example, electrolysis systems. In any case, the bipolar plate 1 offers the possibility of cooling and, if necessary, also of heating, i.e., generally for temperature control of the stack 10.

[0024] A plate body 2 constitutes the main component or sole component of the bipolar plate 1. If necessary, seals, for example, can be attached to the plate body 2. The plate body 2 is traversed by a meandering cooling channel 3, the ends of which are labeled 4 and 5. The orientation of the bipolar plate 1 according to the Fig. 1 and Fig. 3 denotes its underside by 6, its upper side by 7, and one narrow side by 9. This does not imply any statement about the actual orientation of the bipolar plates 1 in the stack 10. The meandering shape denoted by 8, that is, the channel geometry of the bipolar plate 1, is derived in particular from Fig. 2 stands out.

[0025] Within the cell stack 10, each bipolar plate 1 separates a half-cell 12 of a first electrochemical cell 11 from a half-cell 13 of another electrochemical cell 11. Between the half-cells 12, 13 of the same electrochemical cell 11 is a proton-permeable membrane 14. Gas diffusion layers within the half-cells 12, 13 are designated by 15.

[0026] Regarding the production of bipolar plate 1, reference is made to the Fig. 4. Two plate components 16, 17, also generally referred to as preforms, are manufactured from a graphite-filled polymer mixture using a pre-pressing tool. The first plate component 16, which is at the bottom in the sketched example, has a structure 18 that has the shape of the subsequent cooling channel 3. The second plate component 17 has completely flat surfaces in this case. In contrast to the one in Fig. In the form shown in Figure 4, the underside 6 of the first plate component 16 and / or the top side 7 of the second plate component 17 could have a three-dimensional structure, for example in the form of grooves and / or island-shaped elevations and depressions.

[0027] As a third component for the production of the bipolar plate 1, a channel component 19 is provided, which has the meander shape 8. The channel component 19 is also formed using a pre-pressing tool, whereby it is possible to fill the material from which the channel component 19 is formed directly into the cavities of the first plate component 16, which are formed by the structuring 18. Salts, for example sodium chloride or carbonates, are suitable as materials for forming the channel component 19. Alternatively, the channel component 19 can be made from a soluble polymer, for example polyvinyl alcohol.

[0028] After the plate and channel components 16, 17, 19 are assembled, the resulting intermediate product is placed in a hot-pressing tool. Hot-pressing the composite of plate and channel components 16, 17, 19 fuses the preforms 16, 17 into a single element, namely the future bipolar plate 1. This is equivalent to transforming the plate components 16, 17 into the monolithic plate body 2. During hot pressing, the shape of the future cooling channel 3 is maintained, as it is filled with the pressure-resistant, meandering channel component 19.

[0029] After cooling of the hot-pressed composite formed from the plate and channel components 16, 17, 19, the channel component 19 is dissolved with a suitable rinsing fluid, which, depending on the material used, may be water or another solvent, so that the bipolar plate 1 can be removed without further processing according to the Fig.1 to 3 are created. Reference symbol list 1 Bipolar plate 2 plate bodies 3 Cooling channel 4 End of the cooling channel 5 End of the cooling channel 6 Underside 7 Top 8 meander shape, channel geometry 9 Narrow side 10 cell stacks, Stack 11 electrochemical cell 12 half-cell 13 Half-cell 14 Membran 15 Gas diffusion layer 16 first plate component, preform 17 second plate component, preform 18 Structuring the first plate component 19-channel component

Claims

[1] Method for manufacturing a bipolar plate (1) wherein - first, three non-metallic components (16, 17, 19) are prefabricated individually, namely two plate components (16, 17) made of a base material, at least one of which is three-dimensionally structured, and a channel component (19) made of an additive material different from the base material, the shape of which is adapted to the structuring (18) of the at least one plate component (16, 17), - the channel component (19) is inserted between the plate components (16, 17), thereby forming a plate body (2) as a solid intermediate product, - the plate body (2) is solidified by hot pressing, - after the production of the plate body (2) the additive material is removed from it. [2] Method according to claim 1, characterized by, that the channel component (19) is dissolved from the plate body (2) after the plate body (2) has been completed, pressed and heated by a solvent selected from the group of solvents which includes organic as well as inorganic solvents. [3] Method according to claim 1 or 2, characterized by , that the channel component (19) is formed by a salt. [4] Method according to claim 1 or 2, characterized by , that the channel component (19) is formed by a polymer. [5] Method according to any one of claims 1 to 4, characterized by , that the channel component (19) inserted between the plate components (16, 17) is meander-shaped. [6] Method according to any one of claims 1 to 5, characterized by , that the plate body (2) composed of three components (16, 17, 19) contains graphite. [7] Method according to any one of claims 1 to 6, characterized by, that the plate body (2) composed of three components (16, 17, 19) contains a polymer. [8] Method according to any one of claims 1 to 7, characterized by , that by removing the channel component (19) from the plate body (2) a cooling channel (3) with ends (4, 5) arranged on the same side of the plate body (2) is formed.

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