Bipolar plate and method for producing a bipolar plate
Patent Information
- Application Number
- EP2023724168
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-06-29
- Filing Date
- 2023-05-02
- Publication Date
- 2025-05-07
Smart Images
Figure 1.1
Abstract
Description
[0001] Bipolar plate and method for producing a bipolar plate
[0002] The invention relates to a bipolar plate intended for use in a stack of electrochemical cells according to the preamble of claim 1. Furthermore, the invention relates to a method for producing such a bipolar plate.
[0003] A generic bipolar plate and a fuel cell unit constructed therewith are known, for example, from DE 10 2005 057 045 A1. The known bipolar plate is constructed from a cathode-side and an anode-side partial plate, i.e., two half-sheets. A permeable interior space is formed between the half-sheets. Additional fluids, namely the operating media of the fuel cell unit, flow around the outer sides of the bipolar plate. In a distribution area of the bipolar plate, the two half-sheets are supported against each other by raised and negative support points.
[0004] As with the bipolar plate according to DE 102005 057 045 A1, numerous other possible bipolar plate designs feature three ports arranged side by side, namely one port for coolant and two ports for operating media. Examples in this context include documents US 10,381,675 B2 and DE 102014206333 A1. In both cases, there are overlaps between various channels formed between inlets or outlets, i.e., ports, and an active field of a fuel cell. Other possible designs of bipolar plates, including flow channels, are described, for example, in documents DE 10 2013 210 542 A1, US 9,685,664 B4, and US 9,337,498 B2.
[0005] The designs of bipolar plates and entire fuel cells disclosed in documents EP 3 577 708 B1 and EP 3 167 505 B1 are intended to achieve improved flow distributions and reactant flows. Both documents deal with fuel cells with gas diffusion layers and catalytic substances. Another fuel cell with a flow distributor is described, for example, in EP 2 926 399 B1.
[0006] The invention is based on the object of further developing bipolar plates suitable for use in fuel cell stacks compared to the aforementioned prior art under flow and manufacturing aspects.
[0007] This object is achieved according to the invention by a bipolar plate having the features of claim 1. The bipolar plate can be produced by a method according to claim 10.
[0008] The bipolar plate, which is suitable for use in a stack of electrochemical cells, in particular fuel cells, is constructed according to a known basic concept from two superimposed, interconnected half-sheets. The bipolar plate has three adjacent ports for the supply or discharge of fluids. For example, a first such arrangement of three ports is provided for the supply and a second such arrangement of three ports is provided for the discharge of fluids. It is also possible for fluids to flow in countercurrent, so that of three adjacent ports, a single port is provided for conducting a fluid that flows through or around the bipolar plate in the opposite direction to the fluids that are conducted through the other two ports in the same row of ports. The ports are also referred to as manifold openings or, for short, manifolds.
[0009] A generally central, extended section of the bipolar plate is assigned to the active field of the respective electrochemical cell, i.e., the area in which the desired electrochemical reactions take place. The term "active field" is also used for the corresponding section of the bipolar plate. In many designs, the active field of the bipolar plate has a basic rectangular shape. Furthermore, there is a distribution field of the bipolar plate, which connects the ports with the active field, i.e., is designed to conduct the three different fluids between the ports and the active field. A flow chamber for one of the three fluids is formed between the half-sheets. This is usually a flow chamber for coolant, particularly cooling water.For the other two fluids, i.e. typically for the operating media of the electrochemical cells, flow spaces are also formed on the outer sides of the half-sheets.
[0010] According to the claim, the distribution field comprises, in plan view of the half-sheets, four flat flow fields, each with a triangular basic shape:
[0011] - A coolant flow field open to the middle of the three ports,
[0012] - two two-media flow fields, each bordering the coolant flow field on the one hand and open towards one of the two outer ports on the other hand, which are each designed for the flow of coolant and an operating medium as a further fluid in mutually parallel, superimposed layers,
[0013] - a three-media flow field bordering the two two-media flow fields and open towards the active field, which is designed for the flow of coolant and the operating media as additional fluids in three mutually parallel, superimposed layers.
[0014] In each of the four flow fields, the half-sheets are structured by punctiform, i.e., island-shaped, particularly circular, embossed structures such that the half-sheets are supported both against each other and against flat components arranged outside the half-sheets. In addition to a triangular basic shape of the flow fields, flow fields with other shapes, such as square or pentagonal, can also exist. This applies in particular to the coolant flow field and the two lateral flow fields, i.e., the dual-media flow fields. During operation of the electrochemical cell stack in a typical process configuration, all four flow fields function as pressure loss-controlled flow fields.As far as parallel layers are mentioned, in each of which a medium flows, this is to be understood as meaning that the layers are arranged essentially parallel to each other, i.e. they lie one above the other, whereby flow components perpendicular to the planes defined by the individual layers can also occur.
[0015] In a top view of the bipolar plate, there may be a point where all four flow fields converge. This is especially true for designs with triangular flow fields. The first flow field, connected to the central port, can describe an isosceles triangle, as can the fourth flow field, through which all three media flow and located closest to the active field. The two two-media flow fields, which typically do not describe isosceles triangles, can be designed similarly.
[0016] In each of the four flow fields that make up the distribution field, the fluid contained in this flow field, or the two or three different fluids that flow in separate, superimposed layers, spread out over a large area. The stacking of the layers always remains consistent. This means, for example, that the medium, i.e. fluid, located in the uppermost layer is conducted exclusively in this layer. The lack of redirection of a medium from one layer to another, for example from the top side of the bipolar plate to its underside, is advantageous, particularly with regard to the flow resistance that occurs during operation of the cell stack, in particular the fuel cell stack.
[0017] According to one possible embodiment, the half-sheets in the region of the coolant flow field are each provided for flat contact with a surrounding, likewise flat component of the cell stack. Compared to the area in flat contact with the aforementioned component, there is a relatively small area portion of the coolant flow field in which round, in particular circular, supports are formed to keep the half-sheets at a distance from one another. The height of these supports corresponds, provided the embossing depth of both half-sheets is identical, to half the maximum distance between the two half-sheets. Within the flow space through which the coolant flows, the supports represent pin-shaped barriers which, on the one hand, do not significantly constrict the free flow cross-section and, on the other hand, ensure an even distribution of the coolant.This also applies to variants in which coolant is supplied or discharged through a plurality of ports.
[0018] As far as the two-media flow fields are concerned, according to one possible embodiment, the half-sheets in the region of these flow fields are provided on exactly one outer side for planar contact with a surrounding, likewise planar component, whereas the half-sheet forming the opposite outer side is provided for arrangement largely spaced from a likewise planar surrounding component. Thus, there are three distinguishable planes: a central plane in which the two half-sheets are tangent to each other, a plane in which one of the two half-sheets is in planar contact with a surrounding component, and a further plane described by the other half-sheet, which is lifted off from a planar surrounding component in a defined manner in order to provide a free, planar flow cross-section for an operating medium. The distance between the latter plane is at most half the maximum distance between the two half-sheets.At the same time, supports are formed by the same half-sheet which delimits the said flow cross-section, which supports project beyond the said plane parallel to the center plane and are intended to support the bipolar plate with respect to the planar component which is largely lifted off the said half-sheet.
[0019] The center plane is generally defined as the plane where the two half-sheets touch each other. This also applies to designs in which the different half-sheets have different drawing depths. In such cases, the two half-sheets protrude from the center plane by different distances.
[0020] In the three-media flow field, each of the two half-sheets can have a profile that, with regard to the existence of flat areas lifted from the center plane and outward-facing supports, basically corresponds to the described profile of the half-sheet of the two-media flow field, which is largely lifted from the surrounding component, whereby the distances of the half-sheets in the three-media flow field that are flat from the center plane and from a surrounding component are smaller than the distance in the two-media flow field between the center plane and a plane defined by one of the half-sheets and spaced parallel from a surrounding component. In the three-media flow field, the sum of the areas of all supports - in a plan view of the bipolar plate - is also typically less than half the total area of the corresponding flow field.
[0021] In the two-media flow fields and the three-media flow field, there are various options for designing and arranging the supports: For example, the footprint of the bipolar plate can be designed such that the inward-facing and outward-facing supports of the half-sheets are offset from each other. Alternatively, a concentric arrangement of the inward-facing and outward-facing supports of the half-sheets is possible.
[0022] According to a possible refinement, a channel-guided region of the distribution field is connected between the three-media flow field and the active field of the bipolar plate, and thus the entire electrochemical cell. Its width can correspond to the width of the active field and the width of the three-media flow field. In this configuration, the various media flows on the cathode and anode sides, respectively, as well as the coolant flow, can be distributed, to a good approximation, evenly across the entire width of the active field. In particular, the channel-guided region can be designed with channels of varying widths to achieve a uniform flow distribution across the entire width.
[0023] The metallic bipolar plate according to the invention can generally be manufactured by three-dimensionally structuring two half-sheets, in particular made of steel sheet, or alternatively, for example, of a titanium alloy, using a forming process according to claim 10 and then joining them together. The connection can be made, for example, by soldering, welding, or gluing. Continuous and / or discontinuous processes can be used to profile the half-sheets.
[0024] Two exemplary embodiments of the invention are explained in more detail below with reference to a drawing. These show, in some cases in a simplified form:
[0025] Fig. 1 shows a section of a bipolar plate for a stack of electrochemical cells in a symbolic top view,
[0026] Fig. 2 Structures of a coolant flow field in a distribution field area of the bipolar plate according to Fig. 1 ,
[0027] Fig. 3 Structures of a two-media flow field and a three-media flow field of the bipolar plate according to Fig. 1 ,
[0028] Fig. 4 shows a section through a flow field attributable to a distribution field, namely the coolant flow field, of the bipolar plate according to Fig. 1,
[0029] Fig. 5 shows a section through one of two similarly designed two-media flow fields of the bipolar plate according to Fig. 1, Fig. 6 shows a section through the three-media flow field of the bipolar plate according to Fig. 1,
[0030] Fig. 7 shows a further embodiment of a bipolar plate for a stack of electrochemical cells in a simplified plan view,
[0031] Fig. 8 shows a section of the arrangement according to Fig. 7,
[0032] Fig. 9 shows a section through the coolant flow field of the bipolar plate according to Fig. 7,
[0033] Fig. 10 shows a section through a two-media flow field of the bipolar plate according to Fig. 7, intended for the passage of a coolant and one of two operating media,
[0034] Fig. 11 shows a section through the three-media flow field of the bipolar plate according to Fig. 7.
[0035] Unless otherwise stated, the following explanations refer to both embodiments. Corresponding or essentially equivalent parts are identified by the same reference numerals in all figures.
[0036] A bipolar plate, designated overall by reference numeral 1, is part of a PEM fuel cell stack (not shown in detail). Regarding the basic structure and function of such fuel cell systems, reference is made to the prior art cited at the outset. The bipolar plate 1 can be intended for stationary or mobile use, in particular in a motor vehicle. The use of terms such as "top" or "bottom" below does not imply any statement about the actual installation position of the bipolar plate 1 in a surrounding structure. In particular, the bipolar plates 1 can be oriented vertically, unlike as shown in the figures.
[0037] The bipolar plate 1 is composed of two profiled half-sheets 2, 3. Embossed structures of the half-sheets 2, 3 are generally designated by 4. In the present case, the bipolar plate 1 has a rectangular, not square, basic shape, with one of the narrow sides and only sections of the long sides being visible in Figures 1 and 7. Deviating from this, other designs of bipolar plates 1, for example, square or bone-shaped, are also possible.
[0038] On the narrow sides of the bipolar plates 1 shown, there are several ports 5, 6, and 7. These are port 5 for the cathode cavity of the fuel cell, port 6 for the coolant, and port 7 for the anode cavity. Ports 5, 6, and 7 are arranged next to one another in a row, with port 6 for the coolant located between ports 5, 7 for the operating media. In the exemplary embodiments, ports 5, 7 are quadrangular, namely shaped as trapezoids, while port 6, in plan view, describes an elongated rectangular shape extending along the narrow side of the half-sheets 2, 3.
[0039] The arrangement of the three ports 5, 6, and 7 borders a distribution field, designated 8 overall, which is fluidically connected between the ports 5, 6, and 7 and an active field 9 of the bipolar plate 1. The width of the individual ports 5, 6, and 7, measured at the transition to the distribution field 8, is indicated by b5, b6, and b7. The distribution field 8 includes a channel-guided area, designated 18, which borders the active field 9. Furthermore, the distribution field 8, as explained in more detail below, is designed without any channeling.
[0040] Adjacent to port 6 is a coolant flow field 10, which represents one of four distinct flow fields 10, 12, 14, 16 from which the distribution field 8 is constructed, except for the channel-guided area 18. Each of the flow fields 10, 12, 14, 16 has a triangular basic shape.
[0041] Possible cross-sectional designs of the coolant flow field 10 are shown in Figures 4 and 9. The two half-sheets 2, 3 are largely raised from the center plane ME, in which the half-sheets 2, 3 touch, so that the largest possible flow cross-section is available for the coolant. The distance of the planes in which the half-sheets 2, 3 mostly lie from the center plane ME is given as hamax (anode side) and hkmax (cathode side). Further, not shown, likewise flat components of the fuel cell stack rest on the continuously flat regions of the half-sheets 2, 3, which are spaced from the center plane ME by the amount hamax and hkmax, respectively. Pin-shaped supports 11, circular in plan view, are formed directly through the half-sheets 2, 3 and keep the half-sheets 2, 3 at a distance from one another.
[0042] In flow field 12, one of the fuel cell's two operating media flows alongside the coolant. Flow field 12 thus represents a two-media flow field. The same applies to flow field 14. Compared to coolant flow field 10, there is significantly less free flow cross-section for the coolant in the two-media flow fields 12, 14. In the cases outlined in the figures, the two two-media flow fields 12, 14 are identically constructed and arranged point-symmetrically to each other. Deviating from this, for example, the anode port can be smaller than the cathode port, so that there is no symmetry.
[0043] One of the two half-sheets 2, 3 is structured in the two-media flow field 12, 14 in the same way as in the coolant flow field 10. In the case of Fig. 5, this applies to the upper half-sheet 2, and in the case of Fig. 10, to the lower half-sheet 3. The aforementioned point symmetry, which is not necessarily present and can be seen in Figures 1 and 7, refers to a point at which all flow fields 10, 12, 14, 16 collide. The second half-sheet 3, 2 lies in the two-media flow field 12, 14 largely in a plane that is lifted off the center plane ME by an amount hki, hai, where hki and hai, respectively, are smaller than hkmax and hamax, respectively. In the design according to Fig. 5, supports 13 are formed by the half-sheet 3, which in this case is largely removed from the center plane ME by the amount hki, which supports the half-sheet 3 both inwards, i.e. towards the other half-sheet 2, and outwards, i.e. towards a flat surrounding component.The cathode gas is passed through the flow field 12. Supports 13 appear ring-shaped in plan view. The same applies to supports 15, which are located in the flow field 14 through which the anode gas is passed.
[0044] In contrast to the design according to Fig. 1, in the design according to Fig. 7, in the two-media flow fields 12, 14 provided for the passage of the cathode or anode gas, as well as in a three-media flow field 16, there are different partial supports 19, 20, 21, 22, which support the half-sheets 2, 3 in different directions and are arranged next to one another in the plan view.
[0045] The three-media flow field 16, which, like the flow fields 10, 12, 14, is designed as an open flow field, borders, also in the embodiment according to Fig. 1, both the two two-media flow fields 12, 14 and the channel-guided region 18 of the distributor field 8. The width of the three-media flow field 16, indicated as b16, corresponds in the exemplary embodiments to the width b9 of the active field 9 and also to the width of the region 18. In the case of Fig. 1, numerous supports 17 are formed in the three-media flow field 16, which, like the supports 13, 15, are annular in plan view.
[0046] In the three-media flow field 16, the flow of the operating media and the cooling medium is projected in three layers, one above the other, with the coolant flow representing the middle layer. The flow cross-section available to the coolant is limited at the top and bottom by planes defined by the half-sheets 2, 3 and spaced from the center plane ME by the amount ha2 and hk2, respectively. Here, ha2 is smaller than hai and hk2 is smaller than hki. In the exemplary embodiments, hai is identical to hki, and ha2 is identical to hk2.
[0047] Reference symbol
[0048] 1 bipolar plate
[0049] 2 half sheets
[0050] 3 half sheet
[0051] 4 Embossed structure
[0052] 5 port cathode cavity
[0053] 6 port coolant
[0054] 7 port anode cavity
[0055] 8 Distribution panel
[0056] 9 Active field
[0057] 10 Coolant flow field
[0058] 11 Support in the coolant flow field
[0059] 12 Coolant and cathode-side flow field
[0060] 13 Support in the flow field 12
[0061] 14 Coolant and anode side flow field
[0062] 15 Support in the flow field 14
[0063] 16 Flow field for three fluids
[0064] 17 Support in the flow field 16
[0065] 18 channel-guided area of the distribution panel
[0066] 19 Partial support in the flow field 12
[0067] 20 partial support in the flow field 12
[0068] 21 Partial support in the flow field 16
[0069] 22 Partial support in the flow field 16 b5 Width of the port 5 b6 Width of the port 6 b7 Width of the port 7 b9 Width of the active field b16 Width of the flow field 16 hamax Maximum embossing depth anode side ha1 , ha2 Embossing depth anode side hk1 , hk2 Embossing depth cathode side hkmax Maximum embossing depth cathode side
[0070] ME mid-level
Claims
Bipolar plate (1) for electrochemical cells, constructed from two superimposed half-sheets (2, 3) with three adjacently arranged ports (5, 6, 7), an active field (9), and a distributor field (8) connecting the ports (5, 6, 7) to the active field (9), which is designed to conduct three different fluids between the ports (5, 6, 7) and the active field (9), wherein a flow space for one of the fluids is formed between the half-sheets (2, 3) and flow spaces for the two other fluids are formed on the outer sides of the half-sheets (2, 3), characterized in that the distributor field (8) comprises four planar flow fields (10, 12, 14, 16), namely - a coolant flow field (10) open towards the central port (6), - two two-media flow fields (12, 14), each bordering the coolant flow field (10) on the one hand and open towards one of the two outer ports (5, 7) on the other hand, which are each designed for the flow of coolant and an operating medium as a further fluid in mutually parallel layers, - a three-media flow field (16) bordering the two two-media flow fields (10) and open towards the active field (9), which three-media flow field is designed for the flow through of coolant and the operating media as further fluids in three mutually parallel layers, wherein in each of the four flow fields (10, 12, 14, 16) the half-sheets (2, 3) are structured by punctiform, i.e. island-shaped, embossed structures (4) in such a way that the half-sheets (2, 3) are supported both against each other and against flat components arranged outside the half-sheets (2, 3). Bipolar plate (1) according to claim 1, characterized in that the four flow fields (10, 12, 14, 16) of the distributor field (8) each have a triangular basic shape - in plan view of the half-sheets (2, 3) -, wherein a point exists at which all four flow fields (10, 12, 14, 16) meet. Bipolar plate (1) according to claim 1 or 2, characterized in that the two dual-media flow fields (12, 14) are of identical design. Bipolar plate (1) according to one of claims 1 to 3, characterized in that the half-sheets (2, 3) in the region of the coolant flow field (10) are provided for planar contact with a surrounding, likewise planar component, wherein round, in particular circular, supports (11) are formed in a comparatively small area portion of the coolant flow field (10) that keep the half-sheets (2, 3) at a distance from one another, the height (hamax, hkmax) of said supports corresponding to half the maximum distance between the half-sheets (2, 3). Bipolar plate (1) according to one of claims 1 to 4, characterized in that the half-sheets (2, 3) in the region of the two-media flow fields (12, 14) are provided on exactly one outer side for planar contact with a surrounding, likewise planar component,whereas the half-sheet metal element (3, 2) forming the respective opposite outer side is provided for arrangement at a large distance from a likewise planar surrounding component, wherein, measured from a central plane (ME) in which both half-sheet metal elements (2, 3) are tangent, the majority of the half-sheet metal element (3, 2) which is largely lifted away from the surrounding component lies in a plane which is lifted away from the central plane (ME) by an amount (hki, hai) which is at most as large as half the maximum distance between the two half-sheet metal elements, and wherein the same half-sheet metal element (3, 2) simultaneously forms supports (13, 15) which project beyond said plane parallel to the central plane (ME) and are provided for support with respect to the planar component which is largely lifted away from said half-sheet metal element (3, 2). Bipolar plate (1) according to claim 5, characterized in that in the three-media flow field (16) each of the two half-sheets (2,3) has a profiling (4) which, with regard to the existence of areas raised flat from the central plane (ME) and outwardly directed supports (17, 22), corresponds to the profiling (4) of the half-sheet (3, 2) of the two-media flow field (12, 14) which is largely raised from the surrounding component, wherein the distances (hk2, ha2) are flat from, the center plane (ME) and regions of the half-sheets (3, 2) lifted off from a respective surrounding component in the three-media flow field (16) are smaller than the distance (hki, hai) given in the two-media flow field (12, 14) between the center plane (ME) and a plane defined by one of the half-sheets (3, 2) and spaced parallel from a surrounding component.
7. Bipolar plate (1) according to claim 5 or 6, characterized in that the inwardly and outwardly directed supports (19, 20, 21, 22) of the half-sheets (2, 3) are arranged offset from one another.
8. Bipolar plate (1) according to claim 5 or 6, characterized in that the inwardly and outwardly directed supports (11, 13, 15, 17) of the half-sheets (2, 3) are arranged concentrically to one another.
9. Bipolar plate (1) according to one of claims 1 to 8, characterized in that a channel-guided region (18) of the distributor field (8) is connected between the three-media flow field (16) and the active field (9), the width of which corresponds to the width (b9) of the active field (9) and the width (b16) of the three-media flow field (16).
10. A method for producing a bipolar plate (1) for electrochemical cells, wherein two half sheets (2, 3) are three-dimensionally structured by means of forming methods according to claim 1 and then permanently connected to one another.