Bipolar plate

Abstract

The invention relates to a bipolar plate (1) for an electrochemical system, having a rectangular basic shape, in which three ports (11, 12, 13, 14, 15, 16), in particular two working agent ports (11, 13, 14, 16) and one coolant port (12, 15), are arranged adjacent to one another on each of the plate narrow sides (4, 5), the coolant port (12, 15) being located between the working agent ports (11, 13, 14, 16), and the coolant port (12, 15) being located between the working agent ports (11, 13, 14, 16). The plate (1) has a plate longitudinal side (2, 3) and has a port longitudinal side (18) aligned in parallel with the plate narrow side (4, 5), and each working agent port (11, 13, 14, 16) has a port longitudinal side (20) aligned in parallel with the plate longitudinal side (2, 3), with a rectangular effective field (10) positioned between three ports (11, 12, 13) on one plate narrow side (4) and three ports (14, 15, 16) on the opposite plate narrow side (5), the active field (10) has two active field longitudinal sides (22, 22 '), each of which is arranged parallel to the plate longitudinal sides (2, 3); the effective field (10) has linear channels (10a) for guiding the flow of the working agent and the coolant parallel to the effective field longitudinal sides (22, 22 '). The product of the length (L18) of the port longitudinal side (18) of the coolant port (12, 15) and the length (L20) of the port longitudinal side (20, 20 ') of one of the two working agent ports (11, 13, 14, 16) adjacent to the coolant port (12, 15) is at least six times the product of the length (L19) of the port narrow side (19) of the coolant port (12, 15) and the length (L21) of the port narrow side (21) of the working agent port (11, 13, 14, 16).

Description

TECHNICAL FIELD

[0001] The invention relates to a bipolar plate according to the preamble of claim 1, which is intended for use in an electrochemical system and through which a coolant can flow. BACKGROUND

[0002] A bipolar plate is known, for example, from WO 2022 / 253384 A1. The known bipolar plate consists of two rectangular half-sheets, on the narrow sides of which three ports are arranged next to one another. These ports are two ports intended for passing a working medium and a port arranged between the ports and intended for passing a coolant.

[0003] WO 2006 / 054399 A1 describes a further bipolar plate having a rectangular basic shape, on each of the narrow sides of which three ports for different fluids are arranged. In this case, as in the case of WO 2022 / 253384 A1, the middle port of the three adjacent ports is rectangular, while the two outer ports have a pentagonal cross-sectional shape.

[0004] Bipolar plates intended for use in fuel cell systems and through which ports having a triangular cross-sectional shape are provided are known, for example, from DE 10 2018 128 593 A1 and WO 2014 / 102534 A1.

[0005] The bipolar plate disclosed in DE 10 2008 056 900 A1 and also as a component of a fuel cell has an arrangement of three ports, which in one case have a triangular shape, in one case a modified rectangular shape and in one case a pentagonal shape. The ports are arranged in a row next to one another. In contrast, the arrangement of the three ports describes an L shape, wherein two ports are positioned close to the narrow sides of the bipolar plate, while a third port, which is spaced apart from the narrow sides by one of the first-mentioned two ports, is arranged close to the longitudinal sides of the bipolar plate.

[0006] Various design options for bipolar plates for forming ports having a circular cross-section are described in detail, for example, in DE 10 2021 212 053 A1 and DE 10 2021 207 304 A1. SUMMARY

[0007] The invention is based on the object of specifying a fuel cell for use in an electrochemical system, in particular a fuel cell system, which is further developed with respect to the cited prior art, in particular with regard to fluidic aspects and space utilization.

[0008] According to the application, this object is achieved by a bipolar plate having the features of claim 1. The bipolar plate has a rectangular basic shape in the known basic concept, wherein on the narrow sides of the bipolar plate three ports, namely two working agent ports and one cooling water port, are arranged next to one another. The cooling water port is located between the two working agent ports. The cooling water port has a port longitudinal side which is oriented parallel to the plate narrow side, while each working agent port has a port longitudinal side which is oriented parallel to the plate longitudinal side. Between the three ports on one plate narrow side and the three ports on the opposite plate narrow side a rectangular active field is arranged, wherein the active field has two active field longitudinal sides which are arranged parallel to the plate longitudinal sides. The active field has linear channels for guiding a flow of working agent parallel to the active field longitudinal sides and for guiding a flow of coolant.

[0009] According to claim 1, the product of the length of the port longitudinal side of the coolant port and the length of the port longitudinal side of one of the two working agent ports is at least six times, in particular at least eight times, the product of the length of the port narrow side of the coolant port and the length of the port narrow side of the working agent port. The mentioned port narrow sides of the working agent ports are oriented parallel to the port longitudinal side of the coolant port. One port longitudinal side of the two working agent ports is arranged in each case in alignment, and these port longitudinal sides are arranged in alignment with the active field longitudinal sides.

[0010] The application is based on the consideration that when designing a fluid-conducting profile in a fuel cell stack or other electrochemical cell stack, partial competing objectives must be taken into account. Thus, a design which is advantageous in terms of fluidics can require a large amount of space. For example, if only the flow resistance in the channels is taken into account, a circular channel cross-section is considered to be optimal.

[0011] However, if, for example, the fluid is to be distributed as uniformly as possible in a flat area, such as can exist in the form of an active field of an electrochemical cell, for example a fuel cell, not only the flow of gaseous or liquid fluid within the channels must be taken into account, but also the transfer of the fluid out of the channels. The same applies to the case in which the fluid located in the flat area is collected and fed into the channels. Furthermore, it can be important whether the fluid is in liquid form and / or in gaseous form.

[0012] With regard to the flow of coolant through the active field or the linear channels in the active field, it is advantageous if the ports are exactly as wide as the active field. However, in such an embodiment the working agent ports must be arranged 100% laterally close to the active field. In this case, space can be saved by approximating the cross-section of the working agent ports to be circular, since this can provide the largest area for a given size.

[0013] The effective field through which the working agent and the coolant linearly flow is very advantageous in terms of particularly low pressure losses. The flow paths of the working agent and the coolant are branched off at as few branch points as possible in order to further reduce the pressure losses.

[0014] Due to the very different properties of the liquid medium, in particular the coolant, on the one hand and the gaseous medium, such as hydrogen and air or oxygen, on the other hand, medium-specific properties must also be taken into account when designing the fluid-conducting components. This relates, for example, to the design of the distributor field, which is arranged between the arrangement of the individual ports and the effective field. In the distributor field, the various media must be distributed in the transverse direction of the bipolar plate, i.e. orthogonally to the main flow direction of the media. Since the transverse distribution of the gaseous working medium is easier than the transverse distribution of the liquid coolant, the combination of a longitudinal orientation of the working agent ports with a transverse orientation of the coolant ports with respect to the longitudinal direction of the bipolar plate, which coincides with the main flow direction of the working medium, seems to be reasonable in principle. This approach is known in principle from the prior art, including from the aforementioned documents WO 2022 / 253384 A1 and WO 2006 / 054399 A1.

[0015] The solution according to the application goes beyond this approach by providing more extreme cross-sectional shapes of the ports, which deviate more from compact shapes, for example from approximately square or circular shapes. An increased flow resistance is taken into account within the ports and within the channels formed by a multitude of similar ports and extending through a cell stack comprising a multitude of bipolar plates.

[0016] According to various possible embodiments, a fraction having a numerator given by the product of the length of the port longitudinal side of the coolant port and the length of the port longitudinal side of one of the two working agent ports and having a denominator corresponding to the product of the length of the port narrow side of the coolant port and the length of the port narrow side of the working agent port is in the range between six and 30, in particular in the range between eight and 18.

[0017] According to various possible designs, the length of the port longitudinal side of the coolant port, which is parallel to the plate narrow side of the entire bipolar plate, corresponds to at least 40% of the width of the bipolar plate, in particular to at least half, the length being measured in the transverse direction of a rectangular, non-square bipolar plate. At the same time, said port longitudinal side extends, for example, over less than 80% of the length of the plate narrow side of the bipolar plate.

[0018] The coolant port can be centered between the two longitudinal sides of the bipolar plate. Alternatively, an eccentric arrangement of the coolant port can be considered. This is particularly true in the case where the two adjoining working agent ports are of unequal size.

[0019] The apparently elongated, not necessarily strictly rectangular cross-sectional shape of the coolant port can be expressed, in comparison with older solutions, by the fact that the port longitudinal sides of the coolant port, which are oriented in the transverse direction of the bipolar plate, are longer than the port longitudinal sides of the working agent port, which are oriented orthogonal to the port longitudinal sides of the coolant port and parallel to the longitudinal sides of the bipolar plate.

[0020] The rectangular shape or modified rectangular shape of the coolant port can be combined with a pentagonal cross-sectional shape of the working agent port within the bipolar plate. In particular, both working agent ports of the same three-port arrangement can be pentagonal. Optionally, the two working agent ports arranged adjacent to the coolant port are designed mirror-symmetrically with respect to one another. The length of the port longitudinal sides of the working agent port, which contains the quotient in the range between 6 and 30, will be measured on the side of the working agent port which has the shortest distance from the nearest longitudinal side of the bipolar plate.

[0021] In the case where the cross-section of the coolant port, in particular the cooling water port, is at least approximately rectangular, the ratio between the length of the port longitudinal sides of the corresponding port and the length of the port narrow sides can be greater than three, in particular in the range of four to ten.

[0022] The two port arrangements each comprising three ports can be mirror-formed with respect to a plane positioned centrally between the two narrow sides of the bipolar plate.

[0023] In a preferred embodiment, the port longitudinal sides of the two working agent ports are arranged in alignment with one another and with one of the active field longitudinal sides. This has the advantage that the base region of the bipolar plate can be utilized optimally, resulting in a saving of material and a high power density per plate due to the arrangement of the active fields and the ports on the plate.

[0024] It has proven advantageous if between the port arrangement and the active field an distributor field is arranged, and if between each cooling water port and the adjoining distributor field a plurality of mutually parallel channel portions oriented in a flow direction ST extending along the plate longitudinal sides is arranged. Preferably, each distributor field diverges from the respective channel portions towards the active field.

[0025] Preferably, the working agent ports are arranged on the side, here the inclined side, at which they adjoin the respective distributor field, so as to extend parallel to the course of the distributor field.

[0026] Alternatively, the port arrangements on either side of the plane can be designed differently. For example, the cooling water ports arranged first along the flow direction ST, i.e., the length / width ratio of the ports initially arranged on the inlet side, can be at least 50% greater than the length / width ratio of the cooling water ports subsequently arranged along the flow direction ST, i.e., the ports subsequently arranged on the outlet side. The higher pressure of the cooling water on the inlet side allows for the supply of cooling water to the effective field using particularly narrow, elongated ports. The small lateral component of the cooling water flow ensures uniform cooling across the entire width of the effective field. At the outlet end of the coolant channel extending through the bipolar plate, coolant ports with less extreme length / width ratios ensure that coolant is discharged with less flow resistance.

[0027] Bipolar plates can be constructed using known manufacturing techniques from two halves of a plate, particularly half-sheets. In these cases, coolant channels are formed between the halves of the plate. Electrochemical systems including multiple bipolar plates according to the type of this application are, for example, stationary or mobile fuel cell systems, redox flow batteries, or electrolyzers for hydrogen production. Attached Figure Description

[0028] Exemplary embodiments of the invention and unclaimed comparative examples are described in more detail below with reference to the accompanying drawings. In the drawings:

[0029] Figure 1 The diagram shows bipolar plates intended for use in electrochemical systems, i.e., fuel cell systems.

[0030] Figure 2 With Figure 1 A similar view shows a comparison example that is not claimed. Detailed Implementation

[0031] In the following text, where applicable, for those based on Figure 1 Exemplary implementations and according to Figure 2 The comparison examples use the same reference numerals for both figures; these reference numerals are used for explanation only.

[0032] The bipolar plate, generally indicated by reference numeral 1 in the accompanying drawings, is used in an electrochemical cell stack, i.e., a fuel cell stack, and defines the half-cell of a first electrochemical cell from the half-cell of another electrochemical cell. For the basic function of an electrochemical system comprising multiple bipolar plates 1 arranged in a stack, refer to the prior art cited at the beginning.

[0033] The bipolar plate 1 is constructed of two halves in a manner known in principle, with coolant flowing between the two halves. In this case, the halves are made of metal sheets; that is, the halves are designed as half-sheets. Alternatively, the half-sheets can be made of a conductive composite material containing graphite and bonded by polymer.

[0034] The working medium flows on the outer surface of the bipolar plate 1 in the cell stack, also referred to simply as the stack. The rectangular active field, denoted by 10, occupies a large part of the bipolar plate 1, in which the desired electrochemical reactions take place.

[0035] The bipolar plate 1 has an elongated rectangular shape with longitudinal sides, denoted by 2, 3, and narrow sides, denoted by 4, 5. The length of the bipolar plate 1 is denoted by LI, and the much smaller width of the bipolar plate is denoted by BI. A first port arrangement 6 is present close to the first narrow side 4, and a second port arrangement 7 is present close to the second narrow side 5. The first port arrangement 6 on the left in the arrangement according to Figure 1 and Figure 2 The first port arrangement 6 on the left in the arrangement according to

[0036] The cooling water flows through the bipolar plate 1 in the flow direction ST, i.e. essentially in the longitudinal direction of the bipolar plate 1, from left to right in the outlined case. This does not mean any statement about the actual orientation of the bipolar plate 1. In particular, the bipolar plate 1 can be oriented vertically within the cell stack.

[0037] On the second narrow side 5, there are a further three ports 14, 15, 16 belonging to the second port arrangement 7. In this case, the working medium, in particular hydrogen and atmospheric oxygen, is conducted through two outer ports 14, 16, i.e. those arranged close to the two longitudinal sides 2, 3, while the cooling water is discharged from the bipolar plate 1 through the intermediate port 15. All ports 11, 12, 13, 14, 15, 16 extend through the fuel cell stack in the stacking direction.

[0038] The rectangular active field 10 is arranged between the three ports 11, 12, 13 on the plate narrow side 4 and the three ports 14, 15, 16 on the opposite plate narrow side 5, wherein the active field 10 has two active field longitudinal sides 22, 22', which in the embodiment shown here are arranged parallel to the plate longitudinal sides 2, 3. The active field 10 has linear channels 10a for guiding the flow of the working agent, i.e. hydrogen and oxygen, and for guiding the flow of the coolant, i.e. cooling water, parallel to the active field longitudinal sides 22, 22'.

[0039] In particular, in the embodiment of the bipolar plate 1 made of two interconnected, three-dimensionally embossed thin half- sheets, the linear channels 10a in the active field 10 are formed through each half-sheet and thus exist in positive form on one side of the half-sheet and in negative form on the back side of the half-sheet.

[0040] Between the port arrangements 6, 7 and the active field 10 there is a distributor field 8, 9 in which, based on the plan view according to Figure 1 and Figure 2 different material flows cross and different materials remain separated from one another. Between the cooling water ports 12, 15 and the distributor field 8, 9, a plurality of channel portions 17 can be seen which are parallel to one another and oriented in the flow direction ST.

[0041] The extent of the flat area in which the short channel portions 17 lie has shown the clear difference between the exemplary embodiment according to Figure 1 and the comparative example according to Figure 2

[0042] According to Figure 1 the cooling water supplied to the distributor field 8 by the channel portions 17 flows through the distributor field 8 largely in a straight line direction, i.e. in the longitudinal direction of the bipolar plate 1, to the active field 10. Only in the relatively narrow edge regions of the distributor field 8 does the cooling water flow need to be significantly spread out in order to reach the active field 10 over its entire width. In the region of the second distributor field 7 and the second port arrangement 7, i.e. on the outflow side of the cooling water, there is a similar situation, in which the cooling water flow will be merged in this case.

[0043] With regard to the exemplary embodiment according to Figure 1 in the unclaimed comparative example according to Figure 2 there is a more pronounced spreading out of the cooling water flow in the first distributor field 7 and likewise a more pronounced constriction of the cooling water flow in the second distributor field 8. In the case of Figure 2 this leads to a significantly higher flow resistance. A continuous straight line flow through the bipolar plate 1 only occurs in a very narrow central region, as indicated in an idealized manner by the single long arrow oriented in the flow direction ST in Figure 2

[0044] The largely straight line low resistance flow through the bipolar plate 1 according to Figure 1 is achieved primarily by the design of the port arrangements 6, 7. The cooling water ports 12, 15 each have an elongated rectangular shape, wherein the longitudinal sides 18 of the associated port 12, 15 are parallel adjacent to the nearest plate narrow side 4, 5. The narrow sides of the cooling water ports 12, 15 are denoted by 19. The port longitudinal sides 18 of each cooling water port 12, 15 have a length L18 which is more than three times the length of the port narrow sides 19 of the same cooling water port 12, 15, denoted by L19.

[0045] ​​In contrast to the cooling water ports 12, 15, the working agent ports 11, 13, 14, 16 each have a pentagonal cross-sectional shape. In this case, the longitudinal sides 20, 20' representing the longest sides of the five sides of the working agent ports 11, 13, 14, 16 are closest to the longitudinal sides 2, 3 of the bipolar plate 1 adjacent to the relevant working agent port 11, 13, 14, 16. Thus, the longitudinal sides 20, 20' of all working agent ports 11, 13, 14, 16 are oriented orthogonally to the longitudinal sides 18 of the cooling water ports 12, 15.

[0046] Parallel to the longitudinal sides 18 of the cooling water ports 11, 15 are the narrow sides of the working agent ports 11, 13, 14, 16, which are designated by 21. The narrow sides 21 are the sides of the working agent ports 11, 13, 14, 16 which have the smallest distance from the adjacent narrow sides 4, 5 of the bipolar plate 1. The length of each port narrow side 21 is designated by L21.

[0047] Between the different lengths L18, L19, L20, L21 of the different ports 11, 12, 13, 14, 15, 16 there is the following relationship:

[0048] 6 < (L18 x L20) / (L19 x L21) < 30

[0049] The fraction given in this relationship, i.e. the quotient of the product of the lengths L18, L20 of the two longitudinal sides 18, 20 and 20' as the numerator and the product of the lengths L19, L21 of the two narrow sides 19, 21 as the denominator, is a dimensionless value, so the validity of this relationship does not depend on the chosen unit.

[0050] List of reference signs

[0051] 1 bipolar plate

[0052] 2 longitudinal side of the bipolar plate, plate longitudinal side

[0053] 3 longitudinal side of the bipolar plate, plate longitudinal side

[0054] 4 narrow side of the bipolar plate, plate narrow side

[0055] 5 narrow side of the bipolar plate, plate narrow side

[0056] 6 port arrangement, inflow side of the cooling water

[0057] 7 port arrangement, outflow side of the cooling water

[0058] 8 distributor field

[0059] 9 distributor field

[0060] 10 effective field

[0061] 10a linear channel

[0062] 11 working agent port

[0063] 12 cooling water port

[0064] 13 working agent port

[0065] 14 working agent port

[0066] 15 cooling water port

[0067] 16 working agent port

[0068] 17 channel portion

[0069] 18 longitudinal side of cooling water port, port longitudinal side

[0070] 19 narrow side of cooling water port, port narrow side

[0071] 20, 20' longitudinal side of working agent port, port longitudinal side

[0072] 21 narrow side of working agent port, port narrow side

[0073] 22, 22' effective field longitudinal side

[0074] B1 width of bipolar plate

[0075] L1 length of bipolar plate

[0076] L18 length of port longitudinal side of cooling water port

[0077] L19 length of port narrow side of cooling water port

[0078] L20 length of port longitudinal side of working agent port

[0079] L21 length of port narrow side of working agent port

[0080] ST flow direction

Claims

1. A bipolar plate for use in an electrochemical system, the bipolar plate having a substantially rectangular shape, wherein, On the plate narrow sides (4, 5) of the bipolar plate three ports (11, 12, 13, 14, 15, 16) are arranged next to each other, namely two working agent ports (11, 13, 14, 16) and one coolant port (12, 15), wherein the coolant port (12, 15) is located between the working agent ports (11, 13, 14, 16) and has a port longitudinal side (18) which is oriented parallel to the plate narrow side (4, 5), while each working agent port (11, 13, 14, 16) has a port longitudinal side (20) which is oriented parallel to the plate longitudinal side (2, 3), wherein between the three ports (11, 12, 13) on the plate narrow side (4) and the three ports (14, 15, 16) on the opposite plate narrow side (5) a rectangular active field (10) is arranged, wherein the active field (10) has two active field longitudinal sides (22, 22’), wherein these active field longitudinal sides are each arranged parallel to the plate longitudinal sides (2, 3), and wherein the active field (10) has linear channels (10a) for guiding a flow of working agent parallel to the active field longitudinal sides (22, 22’) and for guiding a flow of coolant, characterized in that the length (L18) of the port longitudinal side (18) of the coolant port (12, 15) is at least six times the product of the length (L19) of the port narrow side (19) of the coolant port (12, 15) and the length (L21) of the port narrow side (21) of the working agent ports (11, 13, 14, 16).

2. The bipolar plate of claim 1, wherein The port longitudinal sides (20, 20’) of the two working agent ports (11, 14; 13, 16) are arranged in alignment and are arranged in alignment with one of the active field longitudinal sides (22, 22’).

3. The bipolar plate according to claim 1 or claim 2, characterized in that The length (L18) of the port longitudinal side (18) of the coolant port (12, 15) is not more than 30 times the product of the length (L19) of the port narrow side (19) of the coolant port (12, 15) and the length (L21) of the port narrow side (21) of the working agent ports (11, 13, 14, 16).

4. The bipolar plate of claim 3, wherein The relationships specified in claims 1 to 3 apply to the two working agent ports (11, 13, 14, 16) adjacent to the coolant port (12, 15).

5. The bipolar plate according to any one of claims 1 to 4, characterized in that The length (L18) of the port longitudinal side (18) of the coolant port (12, 15) corresponds to at least half the width (B1) of the bipolar plate (1).

6. The bipolar plate according to any one of claims 1 to 5, characterized in that The port longitudinal side (18) of the coolant port (12, 15) is longer than the port longitudinal side (20, 20') of the working agent port (11, 13, 14, 16) which is oriented orthogonally to the port longitudinal side of the coolant port.

7. The bipolar plate according to any one of claims 1 to 6, characterized in that At least one working agent port (11, 13, 14, 16) has a pentagonal cross-sectional shape.

8. The bipolar plate of claim 7, wherein Each working agent port (11, 13, 14, 16) has a pentagonal cross-sectional shape.

9. The bipolar plate according to any one of claims 1 to 8, characterized in that The ratio between the length (L18) of the port longitudinal side (18) of the coolant port (12, 15) and the length (L19) of the port narrow side (19) of the coolant port (12, 15) is at least three.

10. The bipolar plate according to any one of claims 1 to 9, characterized in that The port arrangements (6, 7) each comprising three ports (11, 12, 13; 14, 15, 16) are mirror-formed with respect to a plane positioned centrally between the two narrow sides (4, 5) of the bipolar plate.

11. The bipolar plate according to any one of claims 1 to 10, characterized in that The first port arrangement (6) comprising three ports (11, 12, 13) arranged next to each other and adjacent to the first plate narrow side (4) is different from the second port arrangement (7) also comprising three ports (14, 15, 16) arranged next to each other and arranged on the second plate narrow side (5).

12. The bipolar plate according to any one of claims 10 or 11, characterized in that Between each of the port arrangements (6, 7) and the active field (10) a distributor field (8, 9) is arranged, and between each coolant water port (12, 15) and the adjoining distributor field (8, 9) a plurality of channel portions (17) are arranged, which are parallel to each other and oriented in a flow direction (ST) extending along the plate longitudinal sides (2, 3).

13. The bipolar plate of claim 12, wherein Each distributor field (8, 9) diverges from the respective channel portion (17) in the direction of the active field (10).

14. The bipolar plate of claim 13, wherein The working agent ports (11, 13, 14, 16) are arranged on the side of them adjoining the respective distributor field (8, 9) so as to extend parallel to the run of the distributor field (8, 9).

15. The bipolar plate according to any one of claims 12 to 14, characterized in that The length / width ratio of the coolant water port (12) arranged first in the flow direction (ST) is at least 50% larger than the length / width ratio of the coolant water port (15) arranged subsequently in the flow direction (ST).

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