Fuel cell stack

Abstract

A fuel cell stack (1) is provided, the fuel cell stack (1) consisting of a plurality of unit fuel cells (2) stacked in a stack direction (8), the fuel cells (2) being sandwiched between a cover plate (28) and a supply plate (14), the supply plate (14) having reactant supply channels (16) and reactant outlet channels, the cover plate (28) covering the fuel cell stack (1), and a turbulence element (18) arranged in the reactant flow, the turbulence element (18) generating at least one turbulence in the supplied fluid flow (12), the turbulence element (18) being arranged in an area of ​​the supply plate (14) where the reactants flow in the stack direction (8) and / or the turbulence element (18) being arranged in an area of ​​the cover plate (28) perpendicular to the stack direction (8) where the reactants flow perpendicular to the stack direction (8).

Description

Technical Field

[0001] The present invention relates to a fuel cell stack.

Background Art

[0002] Generally, a fuel cell stack consists of a plurality of membrane electrode assemblies (MEAs) separated by so-called bipolar plates (BPPs). The bipolar plate itself usually consists of at least two conductive metal plates, so-called flow field plates, which are arranged on top of each other and have a flow field for reactants on one side and a flow field for a cooling fluid on the opposite side. Therefore, the cooling fluid flow fields face each other, and the reactant flow fields face the MEA. The current generated by the MEA during the operation of the fuel cell stack will cause a potential difference between the bipolar plate assemblies. Therefore, in order to avoid a short circuit, the individual bipolar plates must always be electrically separated from each other under any circumstances.

[0003] In an ideal case, all cells of the fuel cell stack should supply the same voltage. However, it has been found that there are variations in the output voltages of the individual cells. The largest deviation usually relates to the first and last cells in the stack direction. One reason for this is that the outermost cells, which are the first and last cells in the stack direction, are in a state where the reactant flow is biased. The first cell in the flow direction usually receives fewer reactants than the intermediate cells, while the last cell in the flow direction usually receives more reactants than the intermediate cells.

[0004] This can be overcome by providing non-active bipolar plates at the beginning and end of the fuel cell stack. However, this has the disadvantage that the height of the fuel cell stack itself can be increased without increasing the number of active unit fuel cells, but the voltage output decreases. Furthermore, the additional non-active bipolar plates increase the amount of work required to install the fuel cell stack.

Summary of the Invention

[0005] Therefore, an object of the present invention is to provide a fuel cell stack that has a more uniform energy output throughout the entire stack. [Means for solving the problem]

[0006] This objective is solved by the fuel cell stack described in claim 1.

[0007] In the following, a fuel cell stack is provided, the fuel cell stack comprising at least a plurality of unit fuel cells, each unit fuel cell comprising a bipolar plate and a membrane electrode assembly, which are stacked such that two bipolar plates sandwich a multilayer membrane electrode assembly in the stacking direction. Each bipolar plate and / or membrane electrode assembly comprises at least one reactant inlet manifold and at least one reactant outlet manifold, each manifold forming a tubular channel inlet and channel outlet, the channel inlet and channel outlet extending through the stack to supply reactant flow to and from the stack. Furthermore, the plurality of unit fuel cells are sandwiched by a cover plate and a supply plate, the supply plate comprising a reactant supply channel configured to connect the at least one reactant inlet manifold to a reactant supply source and a reactant outlet channel configured to connect the at least one reactant outlet manifold to a reactant reservoir. The cover plate is configured to cover the fuel cell stack and typically does not have reactant channels. More specifically, the cover plate may be configured to fluidly terminate the at least one reactant inlet manifold and the at least one reactant outlet manifold.

[0008] To achieve a more uniform energy output across the entire fuel cell stack, at least one turbulent element is positioned in the reactant flow, and the turbulent element is configured to generate at least one turbulence in the supply fluid flow. The at least one turbulent element is positioned on the supply plate, in a region of the supply plate into which the reactant flows in the stack direction, and / or on the cover plate, in a region of the cover plate perpendicular to the stack direction into which the reactant flows in perpendicular to the stack direction.

[0009] Preferably, the at least one turbulence element is formed as a projection or a recess. Both shapes can increase turbulence in the reactant flow.

[0010] In a preferred embodiment, the turbulence element has an upstream and a downstream side, and the shape of the upstream turbulence element is different from the shape of the downstream turbulence element. This can increase the turbulence of the reactant flow. Preferably, the slope of the downstream turbulence element is steeper than the slope of the upstream turbulence element. This shape can improve turbulence in the flowing reactant and can also increase the energy output of the first and / or last cell. More specifically, the at least one turbulence element may be inclined with respect to the direction of the reactant flow and / or with respect to the surface normal of the inner wall of the feed plate in which the at least one turbulence element is located.

[0011] Preferably, the fuel cell stack comprises at least one second turbulence element, wherein the at least one first turbulence element and the at least one second turbulence element are arranged adjacent to each other. Furthermore, the first and second turbulence elements may be inclined relative to each other. This further improves the uniform energy output of the fuel cell stack by increasing the turbulence of the reactant flow.

[0012] In a further preferred embodiment, the first and second turbulence elements may have the same shape or different shapes. For example, the first turbulence element may be formed as a recess, and the second turbulence element may be formed as a projection. This has the advantage that turbulence generated in the reactant flow can be accommodated.

[0013] Preferably, the fuel cell stack comprises a plurality of turbulent elements, which are uniformly distributed. This further improves the uniform energy output across the entire fuel cell stack. Preferably, the plurality of turbulent elements form a structure on the inner wall of the reactant supply channel. Conveniently, all of the plurality of turbulent elements may have the same shape. Alternatively, the turbulent elements or subgroups of the turbulent elements may have different shapes. For example, some of the plurality of turbulent elements may be formed as protrusions, while the remaining parts may be formed as recesses. Furthermore, all or some of the plurality of turbulent elements may have different dimensions. Conveniently, the plurality of turbulent elements are formed during the manufacturing process of the supply plate.

[0014] In a further preferred embodiment, the at least one reactant feed channel has a first portion having a first dimension in at least one direction perpendicular to the flow direction of the reactants, and the at least one reactant feed channel has a second portion having a second dimension in at least one direction perpendicular to the flow direction, wherein the first dimension is smaller than the second dimension. Preferably, the dimensions of the second portion are selected such that the second portion of the reactant feed channel is coplanar with the reactant inlet manifold and / or the shape of the first portion fits the reactant feed channel. More specifically, the shape / diameter of the first portion is circular, while the second portion may have any shape. For example, differences in the shape and / or diameter of the first and second portions may lead to velocity differences in the reactant flow. The range and / or distribution of these velocity differences may enhance or mitigate various effects in the reactant flow, such as backflow, separation, and / or bubbles. Reducing velocity differences in the reactant flow can lead to a more laminar reactant flow and / or a reduction or complete elimination of bubbles, potentially resulting in a more uniform energy output from the unit fuel cell. Therefore, by different dimensions between the first and second portions of the reactant supply channel, the turbulence in the reactant flow can be further adapted to further improve the uniform energy output of the unit fuel cell in the fuel cell stack.

[0015] Further preferred embodiments are provided not only in the specification and drawings but also in the dependent claims. In this regard, elements described or illustrated in combination with other elements may exist alone or in combination with other elements without departing from the scope of protection.

[0016] Preferred embodiments of the present invention will be described below with reference to the drawings, which are for illustrative purposes only and are not intended to limit the scope of protection. The scope of protection is defined solely by the appended claims. [Brief explanation of the drawing]

[0017] [Figure 1] This is a partial cross-sectional view of a fuel cell stack according to the first embodiment. [Figure 2] This is a partial cross-sectional view of a fuel cell stack according to the second embodiment. [Figure 3] This is a partial cross-sectional view of the fuel cell stack k according to the third embodiment. [Figure 4] This is a partial cross-sectional view of the fuel cell stack k according to the fourth embodiment. [Figure 5] This is a cross-sectional view along line AA in Figure 4. [Figure 6] This is a partial cross-sectional view of the fuel cell stack k according to the fifth embodiment. [Figure 7] This is a partial cross-sectional view of the fuel cell stack k according to the sixth embodiment. [Modes for carrying out the invention]

[0018] In the following, elements that are identical or function similarly are indicated by the same reference number.

[0019] Figure 1 shows a fuel cell stack 1 according to the first embodiment. The fuel cell stack 1 consists of at least a plurality of unit fuel cells 2, each unit fuel cell consisting of a bipolar plate 4 and a membrane electrode assembly 6, which are stacked such that two bipolar plates 4-1 and 4-2 sandwich the multilayer membrane electrode assembly 6 in the stacking direction 8.

[0020] Each bipolar plate 4 and / or membrane electrode assembly 6 includes at least one reactant inlet manifold and at least one reactant outlet manifold, and each of the manifolds forms a tubular channel inlet 10 and a channel outlet (not shown). The channel inlet 10 and the channel outlet extend through the stack 1 to supply the reactant flow, indicated by arrow 12, to / from the stack 1. Additionally, a plurality of unit fuel cells are sandwiched between a cover plate (FIG. 3) configured to cover the fuel cell stack 1 and a supply plate 14, and the supply plate 14 includes a reactant supply channel 16 configured to connect at least one reactant inlet manifold to a reactant supply source and a reactant outlet channel (not shown) configured to connect at least one reactant outlet manifold to a reactant reservoir (not shown).

[0021] To achieve a more uniform energy output across the entire fuel cell stack 1, a turbulence element 18 is disposed within the reactant flow 12. The turbulence element 18 in FIG. 1 is formed as a recess configured to generate at least one turbulence (indicated by the curved arrow 20) within the flow 12 of the supplied reactant fluid. The turbulence element ^{18} is disposed within the region of the supply plate 14 where the reactant flows into the stack direction 8.

[0022] The turbulence element 18 has an upstream side 22 and a downstream side 24. As can be seen in FIG. 1, the shape of the turbulence element 18 on the upstream side 22 is different from the shape of the turbulence element 18 on the downstream side 24. Thereby, the turbulence of the reactant flow can be increased.

[0023] Figure 2 shows the fuel cell stack 1 according to the second embodiment. The fuel cell stack 1 is different from the fuel cell stack 1 in FIG. 1 in that the fuel cell stack 1 in FIG. 2 is recessed from the inner wall 26 and includes three turbulence elements 18 arranged adjacent to each other. Further, they have a rectangular shape. Furthermore, the turbulence elements 18 are evenly distributed to form a structure on the inner wall 26 of the reactant supply channel 16. It should be noted that the number of the turbulence elements 18 is not limited to three. The fuel cell stack may include three or more turbulence elements 18.

[0024] Comparing with FIGS. 1 and 2, FIG. 3 shows the upper part of the fuel cell stack 1 according to the third embodiment. The fuel cell stack 1 is covered with a cover plate 28 configured to fluidly terminate at least one reactant inlet manifold 16 and at least one reactant outlet manifold (not shown). In FIG. 3, the fuel cell stack 1 includes turbulence elements 18 formed as protrusions. The turbulence elements 18 in FIG. 3 are arranged in a region of the cover plate 28 perpendicular to the stack direction 8 where the reactant flow 12 flows perpendicular to the stack direction 8.

[0025] Figure 4 shows a cross-sectional view of the fuel cell stack 1 according to the fourth embodiment, and FIG. 5 shows a cross-sectional view taken along line A-A in FIG. 4. The fuel cell stack 1 in FIG. 4 is different from the fuel cell stack in FIG. 1 in that the fuel cell stack includes four turbulence elements 18 formed as protrusions. Each of the turbulence elements has an upstream side 22 and a downstream side 24, and the inclination of the downstream side 24 of the turbulence element 18 is steeper than the inclination of the upstream side 22 of the turbulence element 18. As can be more clearly seen in FIG. 5, the turbulence elements 18 are arranged in pairs with an inclination with respect to each other. In FIG. 5, the first and second turbulence elements of each pair of turbulence elements 18 have the same shape. Alternatively, the turbulence elements may have different shapes.

[0026] Figure 6 shows a fuel cell stack 1 according to the fifth embodiment. The fuel cell stack 1 in Figure 6 differs from the fuel cell stack 1 in Figure 1 in that the reactant supply channel 16 has a first portion 30 having a first dimension D1 in at least one direction perpendicular to the reactant flow direction 12, and a second portion 32 having a second dimension D2, where the first dimension D1 is smaller than the second dimension D2. The difference in dimensions between the first and second portions 30 and 32 of the reactant supply channel 16 allows for the generation of turbulence in the reactant flow 12, indicated by the curved arrow 20.

[0027] Figure 7 shows a fuel cell stack 1 according to the sixth embodiment. The fuel cell stack 1 in Figure 7 differs from the fuel cell stack 1 in Figure 6 in that the fuel cell stack 1 further comprises a turbulence element 18 positioned on the inner wall 26 of the first portion 30 of the reactant supply channel 16. In Figure 7, the turbulence element 18 is formed as a protrusion. However, it is also possible to form the turbulence element 18 as a recess, as shown in Figure 2. The turbulence element 18 in Figure 7 has the advantage of reducing the velocity difference in the reactant flow that may arise due to the difference in diameter between the first portion 30 and the second portion 32. More specifically, the velocity difference in the reactant flow can lead to various effects such as backflow, separation, and / or bubbles in the reactant flow. Because the turbulence element 18 reduces the velocity difference in the reactant flow, the reactant flow itself can become more laminar and / or its bubble volume can be reduced or eliminated.

[0028] In summary, by increasing turbulence in the reactant flow, which is normally laminar, within the reactant supply channel 16, a more uniform energy output can be achieved throughout the fuel cell stack 1. [Explanation of Symbols]

[0029] 1 Fuel cell stack 2 Unit Fuel Cells 4 Bipolar plates 6. Membrane electrode assembly 8 Stack direction 10 Channel Inlet 12 Reactant flow 14 supply plate 16 Reactant supply channels 18 Turbulence elements 20 Turbulence 22 Upstream side 24 Downstream 26 Inner wall 28 Cover Plate 30 Part 1 32 Part 2

Claims

1. A fuel cell stack (1), The fuel cell stack (1) consists of at least a plurality of unit fuel cells (2), Each unit fuel cell (2) consists of a bipolar plate (4) and a membrane electrode assembly (6), which are stacked such that two bipolar plates (4) sandwich a multilayer membrane electrode assembly (6) in the stacking direction (8). Each bipolar plate (4) and / or membrane electrode assembly (6) comprises at least one reactant inlet manifold and at least one reactant outlet manifold. Each of the manifolds forms a tubular channel inlet (10) and a channel outlet. The channel inlet (10) and channel outlet extend through the fuel cell stack (1) to supply a reactant flow (12) to and from the fuel cell stack (1). The plurality of unit fuel cells (2) are sandwiched between a cover plate (28) and a supply plate (14), The supply plate (14) comprises a reactant supply channel (16) configured to connect the at least one reactant inlet manifold to a reactant supply source, and a reactant outlet channel configured to connect the at least one reactant outlet manifold to a reactant reservoir. The cover plate (28) is configured to cover the fuel cell stack (1), in the fuel cell stack (1), At least one turbulence element (18) is positioned in the reactant flow, the turbulence element (18) is configured to generate at least one turbulence in the supply fluid flow (12), the at least one turbulence element redirects the supply fluid flow (12) toward the first unit fuel cell and / or the last unit fuel cell in the stack direction (8), The at least one turbulence element (18) is positioned within the region of the supply plate (14) into which the reactants flow in the stacking direction (8), and The fuel cell stack (1) is characterized in that the at least one turbulence element (18) is positioned in a region of the cover plate (28), which is perpendicular to the stack direction (8), where the reactants flow in perpendicular to the stack direction (8).

2. The fuel cell stack (1) according to claim 1, wherein the turbulence element (18) of the supply plate (14) is formed as a recess.

3. The fuel cell stack (1) according to claim 1 or 2, wherein the at least one turbulence element (18) has an upstream side (22) and a downstream side (24), and the shape of the at least one turbulence element (18) on the upstream side is different from the shape of the turbulence element (18) on the downstream side.

4. The fuel cell stack (1) according to claim 3, wherein the slope of the downstream side (24) of the turbulence element (18) is steeper than the slope of the upstream side (22) of the turbulence element (18).

5. The fuel cell stack (1) according to claim 1 or 2, wherein the fuel cell stack (1) comprises at least one second turbulence element (18), and the at least one first turbulence element (18) and the at least one second turbulence element (18) are arranged adjacent to each other.

6. The fuel cell stack (1) according to claim 5, wherein the first and second turbulence elements (18) are inclined relative to each other.

7. The fuel cell stack (1) according to claim 5, wherein the first and second turbulence elements (18) have the same shape or different shapes.

8. The fuel cell stack (1) according to claim 1 or 2, wherein the fuel cell stack (1) comprises a plurality of turbulent elements (18), and the plurality of turbulent elements are evenly distributed.

9. The fuel cell stack (1) according to claim 8, wherein the plurality of turbulence elements (18) form a structure on the inner wall (26) of the reactant supply channel (16).

10. The fuel cell stack (1) according to claim 1 or 2, wherein the at least one reactant supply channel (16) has a first portion (30) having a first dimension (D1) in at least one direction perpendicular to the flow direction (12) of the reactant, and a second portion (32) having a second dimension (D2) in at least one direction perpendicular to the flow direction (12), and the first dimension (D1) is smaller than the second dimension (D2).

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