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 technology]

[0002] A fuel cell stack usually consists of several membrane electrode assemblies (MEA) separated by so-called bipolar plates (BPP). The bipolar plates themselves usually consist of at least two electrically conductive metal plates, so-called flow field plates, which are arranged on top of each other and have a flow field for the reactants on one side and a flow field for the cooling fluid on the other side. The cooling fluid flow fields are therefore facing each other and the reactant flow fields facing the MEA. The currents generated by the MEA during the operation of the fuel cell stack will result in a potential difference between the bipolar plate assemblies. Therefore, in order to avoid short circuits, the individual bipolar plates must remain electrically isolated from each other under all circumstances.

[0003] In the ideal case, all cells in a fuel cell stack should provide equal voltages. However, it has been found that there are variations in the output voltages of different cells. The largest deviations are usually associated with 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 subject to a bias in the reactant flow, with the first cell in the flow direction usually receiving less reactants than the middle cells, while the last cell in the flow direction usually receiving more reactants than the middle 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 is reduced. Furthermore, the additional non-active bipolar plates increase the amount of work required to install the fuel cell stack. Summary of the Invention [Problem to be solved by the invention]

[0005] It is therefore an object of the present invention to provide a fuel cell stack that has a more uniform energy output across the stack. [Means for solving the problem]

[0006] This object is solved by a fuel cell stack according to claim 1.

[0007] In the following, a fuel cell stack is provided, which is composed of at least a plurality of unit fuel cells, each of which is composed of a bipolar plate and a membrane electrode assembly, stacked in a stacking direction with two bipolar plates sandwiching a multi-layer membrane electrode assembly. Each bipolar plate and / or membrane electrode assembly comprises at least one reactant inlet manifold and at least one reactant outlet manifold, which respectively form tubular channel inlets and channel outlets, which extend through the stack to supply reactant flows to / from the stack. Furthermore, the plurality of unit fuel cells are sandwiched by a cover plate and a supply plate, which comprises a reactant supply channel configured to connect the at least one reactant inlet manifold to a reactant 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 usually does not have any 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 fuel cell stack, at least one turbulence element is disposed in the reactant flow, the turbulence element configured to generate at least one turbulence in the supplied fluid flow, the at least one turbulence element being disposed on the feed plate in a region of the feed plate where the reactants flow in a stack direction, and / or the at least one turbulence element being disposed on the cover plate in a region of the cover plate perpendicular to the stack direction where the reactants flow perpendicular to the stack direction.

[0009] Preferably, the at least one turbulence element is formed as a protrusion or a recess, both shapes capable of increasing turbulence within the reactant flow.

[0010] According to a preferred embodiment, the turbulence elements have an upstream side and a downstream side, and the shape of the turbulence elements on the upstream side is different from the shape of the turbulence elements on the downstream side. This can increase the turbulence of the reactant flows. Preferably, the inclination of the turbulence elements on the downstream side is steeper than the inclination of the turbulence elements on the upstream side. This shape can improve the turbulence in the flowing reactant streams 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 reactant flow direction and / or with respect to a surface normal of the inner wall of the feed plate on which the at least one turbulence element is arranged.

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

[0012] According to a further preferred embodiment, the first and second turbulence elements have the same shape or are different in shape, for example the first turbulence element may be formed as a recess and the second turbulence element as a protrusion, this has the advantage that turbulences generated in the reactant flows can be adapted.

[0013] Preferably, the fuel cell stack comprises a plurality of turbulence elements, the plurality of turbulence elements being uniformly distributed. This may further improve uniform energy output across the fuel cell stack. Preferably, the plurality of turbulence elements form a structure on an inner wall of the reactant supply channel. Conveniently, all turbulence elements of the plurality of turbulence elements may have the same shape. Alternatively, the turbulence elements or subgroups of the turbulence elements may differ in shape. For example, the turbulence elements of a portion of the plurality of turbulence elements may be formed as protrusions, while the remaining portion may be formed as recesses. Furthermore, all or some of the turbulence elements of the plurality of turbulence elements may differ in size. Conveniently, the plurality of turbulence elements are formed during a manufacturing process of the supply plate.

[0014] According to a further preferred embodiment, the at least one reactant supply channel has a first portion with a first dimension in at least one direction perpendicular to the flow direction of the reactants, and the at least one reactant supply channel has a second portion with a second dimension in at least one direction perpendicular to the flow direction, the first dimension being smaller than the second dimension. Preferably, the dimension of the second portion is selected such that the second portion of the reactant supply channel is flush with the reactant inlet manifold and / or the shape of the first portion is adapted to the reactant supply channel. More particularly, the shape / diameter of the first portion is circular, but 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 flows. The extent and / or distribution of these velocity differences may enhance or reduce various effects such as backflow, separation, and / or bubbles in the reactant flows. By reducing the velocity difference in the reactant flows, the reactant flows themselves may become more laminar and / or have less or no bubbles, which may lead to a more uniform energy output of the unit fuel cells. Thus, by different dimensions between the first and second portions of the reactant supply channel, turbulence in the reactant flows may be further tailored such that the uniform energy output of the unit fuel cells of the fuel cell stack may be further improved.

[0015] Further preferred embodiments are defined in the description and drawings, as well as in the dependent claims, whereby an element described or shown in combination with other elements may also be present alone or in combination with other elements, without departing from the scope of protection.

[0016] In the following, preferred embodiments of the invention are described with reference to the drawings, which are for illustrative purposes and not for limiting the scope of protection, which is defined only by the appended claims. [Brief description of the drawings]

[0017] [Figure 1] 1 is a partial cross-sectional view of a fuel cell stack according to a first embodiment. [Diagram 2] FIG. 5 is a partial cross-sectional view of a fuel cell stack according to a second embodiment. [Diagram 3] 11 is a partial cross-sectional view of a fuel cell stack k according to a third embodiment. FIG. [Figure 4] 13 is a partial cross-sectional view of a fuel cell stack k according to a fourth embodiment. FIG. [Diagram 5] FIG. 5 is a cross-sectional view taken along line AA in FIG. [Figure 6] FIG. 13 is a partial cross-sectional view of a fuel cell stack k according to a fifth embodiment. [Figure 7] FIG. 13 is a partial cross-sectional view of a fuel cell stack k according to a sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In the following, elements that function identically or similarly are designated with the same reference numbers.

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

[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, each forming a tubular channel inlet 10 and channel outlet (not shown), which extend through the stack 1 to supply reactant flows, indicated by arrows 12, to / from the stack 1. Furthermore, the unit fuel cells are sandwiched by a cover plate (FIG. 3) configured to cover the fuel cell stack 1 and a supply plate 14, which includes reactant supply channels 16 configured to connect the at least one reactant inlet manifold to a reactant source and reactant outlet channels (not shown) configured to connect the at least one reactant outlet manifold to a reactant reservoir (not shown).

[0021] To achieve a more uniform energy output across the fuel cell stack 1, turbulence elements 18 are disposed in the reactant flows 12. The turbulence elements 18 in Figure 1 are formed as recesses configured to generate at least one turbulence (indicated by curved arrows 20) in the supplied reactant fluid flows 12. The turbulence elements 18 are disposed in the regions of the feed plate 14 where the reactants flow in the stack direction 8.

[0022] The turbulence element 18 has an upstream side 22 and a downstream side 24. As can be seen in Figure 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. This can increase turbulence in the reactant flow.

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

[0024] In contrast to Figures 1 and 2, Figure 3 shows the top of a fuel cell stack 1 according to a 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 Figure 3, the fuel cell stack 1 is provided with turbulence elements 18 formed as protrusions. The turbulence elements 18 in Figure 3 are arranged in areas of the cover plate 28 perpendicular to the stack direction 8, where the reactant flows 12 flow perpendicular to the stack direction 8.

[0025] FIG. 4 shows a cross-sectional view of a fuel cell stack 1 according to a fourth embodiment, and FIG. 5 shows a cross-sectional view along the line AA in FIG. 4. The fuel cell stack 1 in FIG. 4 differs from the fuel cell stack in FIG. 1 in that the fuel cell stack comprises four turbulence elements 18 formed as protrusions. Each of the turbulence elements has an upstream side 22 and a downstream side 24, the inclination of the turbulence element 18 on the downstream side 24 being steeper than the inclination of the upstream side 22 of the turbulence element 18. As can be seen more clearly in FIG. 5, the turbulence elements 18 are arranged in pairs at an incline relative 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 a fifth embodiment. The fuel cell stack 1 of Figure 6 differs from the fuel cell stack 1 of Figure 1 in that the reactant supply channel 16 has a first portion 30 having a first dimension D1 and a second portion 32 having a second dimension D2 in at least one direction perpendicular to the reactant flow direction 12, the first dimension D1 being smaller than the second dimension D2. The different dimensions between the first and second portions 30, 32 of the reactant supply channel 16 can create turbulence in the reactant flow 12, as indicated by the curved arrows 20.

[0027] FIG. 7 shows a fuel cell stack 1 according to a sixth embodiment. The fuel cell stack 1 of FIG. 7 differs from the fuel cell stack 1 of FIG. 6 in that the fuel cell stack 1 further comprises turbulence elements 18 arranged on the inner wall 26 of the first portion 30 of the reactant supply channel 16. In FIG. 7, the turbulence elements 18 are formed as protrusions. However, it is also possible to form the turbulence elements 18 as recesses, as shown in FIG. 2. The turbulence elements 18 of FIG. 7 have the advantage that they can reduce velocity differences in the reactant flows that may result from diameter differences between the first portion 30 and the second portion 32. More specifically, velocity differences in the reactant flows may lead to various effects, such as backflow, separation, and / or bubbles in the reactant flows. As the turbulence elements 18 reduce the velocity differences in the reactant flows, the reactant flows themselves may become more laminar and / or have a smaller or no amount of bubbles.

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

[0029] 1. Fuel cell stack 2 Unit Fuel Cell 4 Bipolar Plates 6. Membrane Electrode Assembly 8 Stacking Direction 10 Channel Entrance 12 Reactant Flow 14 Supply Plate 16 Reactant Supply Channel 18 Turbulence Elements 20 Turbulence 22 Upstream 24 Downstream 26 Inner wall 28 Cover Plate 30 Part 1 32 Part 2

Claims

1. A fuel cell stack (1), comprising: The fuel cell stack (1) is composed of at least a plurality of unit fuel cells (2), each unit fuel cell (2) being composed of a bipolar plate (4) and a membrane electrode assembly (6) stacked in a stacking direction (8) such that two bipolar plates (4) sandwich a multi-layer membrane electrode assembly (6), each bipolar plate (4) and / or membrane electrode assembly (6) is provided with at least one reactant inlet manifold and at least one reactant outlet manifold, each of said manifolds forming a tubular channel inlet (10) and a channel outlet, said channel inlet (10) and channel outlet being connected to a front end of the ... a fuel cell stack (1) extending through the fuel cell stack (1) to supply reactant flows (12) to / from the fuel cell stack (1), the plurality of unit fuel cells (2) being sandwiched by a cover plate (28) and a supply plate (14), the supply plate (14) comprising reactant supply channels (16) configured to connect the at least one reactant inlet manifold to a reactant source and reactant outlet channels configured to connect the at least one reactant outlet manifold to a reactant reservoir, the cover plate (28) configured to cover the fuel cell stack (1); at least one turbulence element (18) is disposed in the reactant stream, said turbulence element (18) configured to generate at least one turbulence in the supplied fluid stream (12); the at least one turbulence element (18) is arranged in a region of the feed plate (14) where the reactants flow in the stack direction (8); and / or The fuel cell stack (1), characterized in that the at least one turbulence element (18) is arranged in a region of the cover plate (28) perpendicular to the stack direction (8) where the reactants flow perpendicular to the stack direction (8).

2. The fuel cell stack (1) according to claim 1, wherein the at least one turbulence element (18) is formed as a protrusion or a recess.

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

5. 5. The fuel cell stack (1) according to claim 1, further comprising at least one second turbulence element (18), the at least one first turbulence element (18) and the at least one second turbulence element (18) being 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 with respect to each other.

7. 7. The fuel cell stack (1) according to claim 5 or 6, wherein the first and second turbulence elements (18) have the same shape or are different in shape.

8. 8. The fuel cell stack (1) according to any one of the preceding claims, wherein the fuel cell stack (1) comprises a plurality of turbulence elements (18), the plurality of turbulence elements being evenly distributed.

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

10. 10. A fuel cell stack (1) as described in any one of claims 1 to 9, 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 reactant flow direction (12) and a second portion (32) having a second dimension (D2) in at least one direction perpendicular to the flow direction (12), the first dimension (D1) being smaller than the second dimension (D2).

Images