Plate arrangement for an electrochemical cell

Abstract

The invention relates to a plate arrangement (2) for an electrochemical cell (1), in particular a fuel cell, said plate arrangement comprising: a lattice which is provided for sandwich-like arrangement between a first plate (5) lying in a base plane and a second plate (4) parallel thereto, is designed as an expanded metal (3), and has a plurality of nodes (6) and webs (10, 11) that connect the nodes (6), wherein rows of nodes (KR1, KR2) are formed which run parallel to one another in a plan view of the lattice (3) and define a longitudinal direction (LR), wherein all nodes (6) have a planar, bent shape with a bending line that is oriented transversely to the longitudinal direction (LR) and separates two node sections (7, 8) from one another. At least in a subset of the nodes (6), one of the node sections (7) is arranged at least approximately parallel to said plates (4, 5).

Description

[0001] Plate arrangement for an electrochemical cell

[0002] The invention relates to a plate arrangement according to the preamble of claim 1, intended for use in an electrochemical cell, in particular a fuel cell, which comprises a grid designed as expanded metal.

[0003] Such a plate arrangement of an electrochemical cell is known, for example, from DE 11 2009 004 658 B4. The known plate arrangement is intended for use in a fuel cell and comprises a so-called gas channel formation element, which is in the form of an expanded metal grid, wherein connecting sections, i.e., nodes, of the expanded metal have distinguishable sections which are inclined in different ways with respect to plates, inter alia in the form of a separator, between which the expanded metal is inserted. In this case, acute angles can be included between the node sections and the plates. An angle included between a section of the node and the separator is smaller than an angle included between another section of the node and a gas diffusion layer.DE 11 2009004 658 B4 provides for the production of expanded metal from titanium.

[0004] DE 11 2007 000017 T5 relates to a method for forming a gas diffusion layer for a fuel cell. This method utilizes a metal mesh processing device to process a stainless steel sheet. The stainless steel sheet can be fed to a holding mechanism using feed rollers. A cutting tool, which is also part of the metal mesh processing device, forms through holes in a grid-like, staggered arrangement. The through holes have a hexagonal shape and provide free cross-sections when the grid is installed in a fuel cell. A separator for a fuel cell described in US Pat. No. 8,206,865 B2 is contacted by a collector formed from a metal mesh. The possibility of stacking a plurality of metal meshes to form the collector is also mentioned.A contact area between the collector and an electrode layer should be greater than or equal to a contact area between the collector and the separator body.

[0005] Another element forming a gas flow path in a fuel cell battery is disclosed in US Pat. No. 9,160,026 B2. In this case, too, the element forming the gas flow path is in the form of a metal mesh structure. Said element has a plurality of annular sections forming through-openings.

[0006] US Patent No. 9,450,253 B2 describes possible geometric details of a fuel cell cell structure made of expanded metal. In this case, too, the meshes of the expanded metal describe hexagonal or other polygonal shapes.

[0007] The invention is based on the object of further developing elements for electrochemical cells, in particular fuel cells, compared to the cited prior art, in particular with regard to fluid dynamics and manufacturing aspects, whereby a robust structure of the end product, i.e. the fuel cell system or other electrochemical system, in particular in the form of a fuel cell stack, is sought, which is also suitable for mobile applications.

[0008] This object is achieved according to the invention by a plate arrangement suitable for use in an electrochemical cell having the features of claim 1. The plate arrangement is suitable for forming a stack of electrochemical cells according to claim 10.

[0009] The plate arrangement comprises, in a known basic concept, a sandwich-like

[0010] Arrangement between a first plate lying in a base plane and a second plate parallel thereto, provided as an expanded metal grid, which has a plurality of nodes and webs connecting the nodes, wherein in a plan view of the grid parallel rows of nodes are formed which define a longitudinal direction, wherein all nodes have a flat, bent shape with a bend line oriented transversely to the longitudinal direction, which separates two node sections of the respective node from one another.

[0011] According to claim 1, at least in a subset of the nodes, one of the two node sections is arranged at least approximately parallel to the mentioned plates. In the present case, an approximately parallel arrangement is said to occur if the node section in question forms an angle of no more than 15° with the adjacent plate of the electrochemical system. In particular, the node section in question lies flat on the mentioned plate, which can be formed by a membrane-electrode arrangement.

[0012] This form of expanded metal fulfills several functions of the plate arrangement equally: Firstly, the numerous node sections of the expanded metal, which are at least approximately parallel to the plates, provide generously dimensioned contact surfaces that absorb forces within the plate stack with moderate surface pressures and conduct electrical currents. Secondly, the angled plate sections, together with the webs of the grid, i.e., the expanded metal, ensure targeted flow-guiding effects, whereby media flowing between the plates also experience flow components perpendicular to the plates.

[0013] Each node section that is parallel to the plates or only slightly inclined to the plates, i.e., at an angle of less than 15°, is connected via two webs to node sections that are more inclined to the plates, one of which defines the base plane, i.e., form a larger angle with the plates, unless located at the edge of the grid. This means that the webs are twisted. This contributes to both the flow conduction and the mechanical stability of the expanded metal.

[0014] According to one possible embodiment, for some nodes of the expanded metal, in particular for nodes arranged in certain rows, the first node section lies flat on the ground plane, which can be provided by the membrane-electrode arrangement, whereas for other nodes, typically also arranged in rows, there is a distance between the nodes and the aforementioned plane, wherein the first node sections are arranged in a plane parallel to the ground plane. In this embodiment, although there is a smaller overall contact area between the nodes and one of the plates applied to the expanded metal compared to embodiments in which the first node section of each node contacts the ground plane, expanded free cross-sections exist for the medium flowing through the plate arrangement precisely because of the node sections raised from the ground plane.

[0015] The nodes resting on the ground plane and the nodes raised from the ground plane can be arranged alternately in a row of nodes extending in the longitudinal direction of the expanded metal. Likewise, for example, variants of the expanded metal can be realized in which two adjacent rows of nodes always rest on the ground plane and every third row of nodes is raised from the ground plane.

[0016] When manufacturing expanded metal from a sheet initially without openings, a variable feed rate of the sheet can be used. This is reflected in the finished product, i.e., expanded metal, by the presence of node sections of varying lengths. The length is measured in the feed direction. The feed direction forms a right angle with the bend line, which represents the boundary between the two node sections. For each node section, its length is measured on the surface of the respective edge section, i.e., not on a projection of the node onto the ground plane.

[0017] With the help of the variable feed rate of the sheet metal being processed into expanded metal, four different types of nodes can be produced within one and the same expanded metal grid in a single manufacturing process: In a first row of nodes there are nodes made up of two long node sections, one of which can lie flat on the ground plane. Between every two such so-called large nodes there is a node called a small node, made up of two comparatively short node sections, in which case both node sections are arranged at an angle to the ground plane. In a second row of nodes, which is completely raised from the ground plane, there are various variants of medium-sized nodes.In this case, one of the node sections is spaced from the ground plane and from the second plate, for example spaced parallel, whereas the second node section, which is the only section inclined or more strongly inclined, contacts the second plate in a linear manner.

[0018] The first node variant consists of a short node section, particularly parallel to the plates, and a second, comparatively long node section. The opposite applies to the second variant: In this case, a long node section parallel to the plates is followed by a comparatively short, slanted node section extending to the second plate. The webs connecting the nodes extend either from one long node section to another long one or between two short node sections, so that each web has a constant width.

[0019] In addition, by varying the feed length during production, expanded metal mesh with more than two different node rows, for example, three or four different node rows, can be realized. It is also conceivable for different types of node rows to be constructed exclusively from nodes whose adjacent sections have different lengths in each individual case.

[0020] The node sections are also commonly referred to as half nodes. If a node section is arranged parallel to the ground plane, it is also referred to as a horizontal node section for simplicity, regardless of the actual orientation of the panel arrangement in space. In various forms of expanded metal, for example, an angle of at least 90° and a maximum of 150° can be enclosed between the two node sections of a node.

[0021] The plate, generally referred to as the second plate, is in particular a bipolar plate. The bipolar plate can be constructed in a conventional manner from two half-sheets, between which channels for a coolant are formed. The second plate can also be designed as a monopolar plate. In both the case of a bipolar plate and a monopolar plate, the term "separator" is also used for the second plate.

[0022] The first plate-shaped arrangement, which defines the base plane and is referred to as the first plate for short, comprises, in particular, a proton-permeable polymer electrolyte membrane (PEM). In a typical configuration, the PEM is bordered by porous anode and cathode catalyst layers as well as porous gas diffusion layers, which are also part of the first plate. Thus, within a plate stack comprising a plurality of similar plate arrangements, there are contacts between the various gas diffusion layers and the expanded metal grids. Regardless of the geometric design of the expanded metal, the expanded metal grids always form flow fields for the operating media of the electrochemical system.

[0023] In the embodiment already described, in which an expanded metal produced with a variable feed is used, the row of nodes which is lifted from the base plane can, for example, be removed from the base plane by a distance which corresponds to at least 30% and at most 60% of the distance between the two plates, i.e. the thickness of the expanded metal grid.

[0024] According to a further possible embodiment, the nodes of a node row of the first type only contact the first plate of the plate arrangement, whereas the nodes of a node row of the second type only contact the second plate. In this case, the node sections of all nodes can have a uniform length, wherein - viewed in the transverse direction of the expanded metal - the node rows of the first and second types are arranged alternately. Assuming a horizontal arrangement of the plate arrangement, the nodes of the various node rows are located at different heights, which can be viewed as a corrugated shape of the expanded metal in its transverse direction. The corrugated shape keeps particularly large flow cross-sections free within the plate arrangement. In this case, all webs have a uniform width, which is predetermined by the feed rate during the manufacturing process.

[0025] In a further developed embodiment, a variable feed, expressed in node sections of non-uniform width, is combined with corrugation of the expanded metal. In this case, as in the embodiment already explained in detail, there are various rows of nodes, with one row of nodes alternating between long and short nodes, while the second row of nodes contains medium-length nodes of varying sizes. In contrast to the embodiment already explained, the further developed embodiment can be characterized in particular by the fact that the medium-length nodes are raised particularly far from the first plate.By setting the horizontal node sections of these nodes at a distance from the first plate in the range of, for example, 50% ± 10%, in particular 50% ± 5%, of the plate spacing, particularly generously dimensioned flow channels are formed that run longitudinally through the plate arrangement and can extend from the inlet to the outlet of a flow field. Four exemplary embodiments of the invention are explained in more detail below with reference to a drawing. These show:

[0026] Fig. 1 shows a first embodiment of an expanded metal grid for an electrochemical cell,

[0027] Fig. 2 shows a plate arrangement of an electrochemical cell including the expanded metal grid according to Figure 1,

[0028] Fig. 3 to 5 the expanded metal grid according to Figure 1 in further representations,

[0029] Fig. 6 shows a second embodiment of an expanded metal grid for an electrochemical cell,

[0030] Fig. 7 shows a plate arrangement of an electrochemical cell including the expanded metal grid according to Figure 6,

[0031] Fig. 8 to 12 the expanded metal grid according to Figure 6 in further representations,

[0032] Fig. 13 shows a third embodiment of an expanded metal grid for an electrochemical cell,

[0033] Fig. 14 shows a plate arrangement of an electrochemical cell including the expanded metal grid according to Figure 13,

[0034] Fig. 15 to 19 show the expanded metal grid according to Fig. 13 in further representations, Fig. 20 shows a fourth embodiment of an expanded metal grid for an electrochemical cell,

[0035] Fig. 21 shows a plate arrangement of an electrochemical cell including the expanded metal grid according to Figure 20,

[0036] Fig. 22 to 26 show the expanded metal grid according to Figure 20 in further representations.

[0037] Unless otherwise stated, the following explanations refer to all exemplary embodiments. Parts or contours of parts that correspond to one another or have essentially the same function are identified by the same reference numerals in all figures.

[0038] In the exemplary embodiments, an electrochemical cell, designated overall by reference numeral 1, is a fuel cell comprising a plurality of identical, stacked plate arrangements 2. Regarding the basic structure and function of the stack of electrochemical cells 1, reference is made to the prior art cited at the outset.

[0039] The plate assembly 2 includes an expanded metal grid 3, which is also referred to as expanded metal or grid for short. The plate assembly 2 further comprises a first plate-shaped assembly 5, namely a membrane-electrode assembly including gas diffusion layers, which is also referred to as the first plate for simplicity. Furthermore, the plate assembly 2 includes a second plate 4, which is part of a bipolar plate.

[0040] The surface of plate 5 that contacts the expanded metal 3 defines a base plane of the plate arrangement 2. There are significant differences in mechanical load-bearing capacity between the two plates 4, 5. Both plates 4, 5 are designed to conduct electrical currents, with electrical currents flowing in particular through contact areas between the grid 3 and the various plates 4, 5. The expanded metal 3 also performs an important function in conducting liquid and / or gaseous media, i.e., the operating media of the electrochemical cell 1.

[0041] The grid 3 has a plurality of nodes 6, each of which has a first node section 7 and a node section 8 inclined relative thereto, and which are shown in the figures partly in simplified form. In the exemplary embodiments, the first node section 7 is arranged parallel to the plates 4, 5. The node sections 7, 8 adjoin one another at a bend line. The angle between the node sections 7, 8 is designated α.

[0042] The nodes 6 of the grid 3 are connected to one another by webs 10, 11, forming openings 9 with a basic diamond shape. A flow channel formed by the grid 3 between the plates 4, 5 is generally designated 12. The medium flowing through the plate arrangement 2 flows overall in the longitudinal direction of the plate arrangement 2, designated LR. The dimension SWD (Short Way Diagonal) of the meshes of the grid 3 is to be measured in the longitudinal direction LR. The dimension LWD (Long Way Diagonal) is to be measured transversely to the longitudinal direction LR in a likewise conventional manner. KB indicates the node width, i.e. the matching width of the node sections 7, 8. SH indicates the expanded metal height, i.e. the distance between the plates 4, 5. The essentially uniform wall thickness of the grid 3, measured at the horizontal sections 7, is indicated by WS. The nodes 6 are arranged in node rows KR1, KR2, which run in the longitudinal direction LR.

[0043] In the exemplary embodiment according to Figures 1 to 5, unlike the exemplary embodiments according to Figures 6 to 14 and 20 to 26, all node rows KR1, KR2 are designed identically. Here, all node sections 7 lie flat on the first plate 5, i.e., the membrane electrode assembly. The second plate 4, which is flat in the illustrated areas in the exemplary embodiments, is only contacted by the edges of the second node sections 8, which is, however, tolerable due to the given current-carrying capacity and mechanical load-bearing capacity of the second plate 4. In the flow direction, i.e., in the longitudinal direction LR, each node 6 of the expanded metal 3 according to Figure 1 represents a barrier filling the space between the plates 4, 5, wherein the inclined position of the sections 8 contributes to the medium being directed past the node 6 in the direction of the adjacent webs 10, 11.Each web 10, 11 connects a horizontal node section 7 with an inclined node section 8, which means that the web 10, 11 is twisted. Such twisting of the webs 10, 11 is also present in all other embodiments and contributes to the flowing medium experiencing a movement component in the normal direction to the plates 4, 5. Furthermore, the twisting of the webs 10, 11, together with the bent shape of the nodes 6, increases the stability of the entire expanded metal 3.

[0044] The embodiment according to Figures 6 to 12 differs significantly from the embodiment according to Figures 1 to 5 in that the adjacent sections 7, 8 of the nodes 6 have different lengths. This is achieved by a variable feed of the sheet from which the expanded metal 3 is manufactured.

[0045] In the expanded metal grid 3 according to Figure 6, as can be seen particularly from Figure 12, all nodes 6 of the first node row KR1 are raised from the membrane electrode assembly 5. In contrast, the nodes 6 of the second node row KR2, as can be seen from Figure 11, lie either flatly or linearly against the membrane electrode assembly 5. In the latter case, the node row KR2 is formed by alternating longer and shorter nodes 6. The length of the first node section 7 of a longer node 6 is designated LI. The inclined node section 8 adjoining the longer node section 7 has a length L2, which in the illustrated case corresponds to the length LI. The next node 6 in the node row KR2 is a short node, whereby in this case both node sections 7, 8 are inclined in different ways to plates 4, 5.Each of the node sections 7, 8 has a length L3 which is shorter than the length LI. Due to the more pronounced inclination of the short nodes 6 compared to the longer nodes 6, the shorter nodes 6 also extend from the surface of the bipolar plate 4 to the surface of the first plate 5. Thus, all nodes 6 of the node row KR2 of the grid 3 according to Figure 6 extend over the entire expanded metal height SH. In contrast to node 6 of the node row KR2, all nodes 6 of the first node row KR1 contact the second plate 4, but not the first plate 5. In the case of the first node row KR1, each node 6 comprises a combination of a short and a long node section 7, 8. If the first node section 7 is designed as a short node section with a length L3, the second, inclined node section 8 is a long node section with a length L2.In contrast, the next node 6 in the node row KR1 has the opposite length ratio: The first, horizontal node section 7 is designed as a long node section of length LI. The adjoining, inclined node section 8 is a short section of length L3. In the exemplary embodiment according to Figures 6 to 12, the distance d is less than half the expanded metal height SH. Depending on the relationship between the distance d and the expanded metal height SH as well as the flexibility of the first plate 5, the first plate 5 can also rest against the node 6 of the first node row KR1. Otherwise, as can be seen from Figure 12, a free space is formed between the nodes 6 of the first node row KR1 and the plate 5, which space is to be attributed to the flow channel 12.

[0046] In the exemplary embodiment according to Figures 13 to 19, the nodes 6 of the node row KR1 are also lifted off the first plate 5, as can be seen from Figure 18. At the same time, these nodes 6 contact the bipolar plate 4, as can also be seen from Figure 18. The opposite applies to the nodes 6 of the second node row KR2. In this case, all node sections 7 lie on the first plate 5, whereas the inclined node sections 8 are spaced from the bipolar plate 4. In cross-section, all nodes 6 of the node row KR1, KR2 have a uniform cross-sectional shape, as can be seen from a comparison of Figures 18 and 19. The length of the node sections 7, 8 is LI in all cases. Overall, the embodiment according to Figures 13 to 19 consists of a corrugated expanded metal 3.

[0047] In the embodiment according to Figures 24 to 26, features of the embodiment according to Figures 13 to 19 are combined with features of the embodiment according to Figures 6 to 12. Accordingly, in the case of Figures 20 to 26, a corrugated expanded metal 3 produced with a variable feed is present. Figure 25 shows the cross-sectional shape of the nodes 6 in the second node row KR2. A commonality with the embodiment according to Figure 11 exists in that in the longitudinal direction LR, nodes 6, which are formed from two long node sections 7, 8, and nodes 6, which are formed from two short node sections 7, 8, each having the length L3, are arranged in a row, maintaining distances which are present as openings 9. In contrast to the embodiment according to Figure 11, however, in the case of Figure 25, all nodes 6 of the node row KR2 are spaced from the bipolar plate 4.As far as the first node row KR1 is concerned, the cross-sectional design shown in Figure 26 is fundamentally comparable to the cross-sectional design according to Figure 12. This means that all inclined node sections 8 contact the bipolar plate 4, whereas the horizontal node sections 7 are raised from the first plate 5. The distance d between the horizontal node sections 7 and the first plate 5 in the case of Figure 27 corresponds approximately to half the expanded metal height SH. The longer node sections 7, each having the length LI, are somewhat further away from the first plate-shaped arrangement 5 than the shorter node sections 7, each having the length L3. Overall, the embodiment according to Figures 20 to 26 provides a particularly wide, open cross-section of the flow channel 12, while at the same time there are flat, material-friendly contacts of the expanded metal 3 against the first plate-shaped arrangement 5.

[0048] List of reference symbols

[0049] 1 Electrochemical cell, fuel cell

[0050] 2 plate arrangement

[0051] 3 Expanded metal, mesh

[0052] 4 second plate, bipolar plate

[0053] 5 first plate-shaped arrangement, MEA

[0054] 6 knots

[0055] 7 first node section

[0056] 8 second node section, inclined

[0057] 9 Opening

[0058] 10 jetty

[0059] 11 jetty

[0060] 12 Flow channel a Angle d Distance

[0061] KB node width

[0062] KR1, KR2 knot rows

[0063] LI length

[0064] L2 length

[0065] L3 length

[0066] LR longitudinal direction

[0067] LWD width in transverse direction

[0068] SH expanded metal height

[0069] SWD width in longitudinal direction

[0070] WS wall thickness

Claims

Claims: Plate arrangement (2) for an electrochemical cell (1), comprising a grid designed as expanded metal (3) for sandwich-like arrangement between a first plate (5) lying in a base plane and a second plate (4) parallel thereto, which has a plurality of nodes (6) and webs (10, 11) connecting the nodes (6), wherein in a top view of the grid (3) parallel rows of nodes (KR1, KR2) are formed which define a longitudinal direction (LR), wherein all nodes (6) have a planar, bent shape with a bend line oriented transversely to the longitudinal direction (LR), which separates two node sections (7, 8) from each other, characterized in that at least in a subset of the nodes (6) one of the node sections (7) is arranged at least approximately parallel to the aforementioned plates (4, 5).A plate arrangement (2) according to claim 1, characterized in that, at least in some of the nodes (6) belonging to the aforementioned subset, the first node segment (7) forms an angle of less than 15 degrees with the base plane, and in particular lies flat on the base plane. A plate arrangement (2) according to claim 2, characterized in that there are additional nodes (6) which also belong to the aforementioned subset, but each have a node segment (7) spaced apart from the base plane. A plate arrangement (2) according to any one of claims 1 to 3, characterized in that there are nodes (6) whose node segments (7, 8) have the same length (LI, L2). A plate arrangement (2) according to any one of claims 1 to 4, characterized in that the length (LI, L3) of the first node segment (7) differs from the length (L3, LI) of the second node segment (8) at least in some nodes (6).Plate arrangement (2) according to claims 4 and 5, characterized in that in one of the node rows (KR2) exclusively nodes (6) with two node sections (7, 8) of equal length are arranged, wherein nodes (6) with two long. Node sections (7, 8) alternate with nodes (6) which are formed from two short node sections (7, 8), and in another node array (KR1) exclusively nodes (6) with node sections (7, 8) of unequal length are arranged, wherein in this case a node (6) with a long section (7) at least approximately parallel to the plates (4, 5) and a short, more strongly inclined section (8) and a node (6) with a short section (7) at least approximately parallel to the plates (4, 5) and a long, comparatively strongly inclined section (8) are arranged one after the other.Plate arrangement (2) according to claim 6, characterized in that the row of nodes (KR2) formed from nodes (6) with node segments (7, 8) of equal length is tangent to the base plane with its node segments (7) which are at least approximately parallel to the plates (4, 5), whereas the other row of nodes (KR1) with its node segments (7) which are at least approximately parallel to the base plane is raised from the base plane by a distance (d) which corresponds to at least 30% and at most 60% of the distance (SH) between the two plates (4, 5), i.e., the thickness of the grid (3). Plate arrangement (2) according to any one of claims 1 to 7, characterized in that an angle (a) of at least 90° and at most 150° is enclosed between the two node segments (7, 8) of a node (6). Use of a plate arrangement (2) according to claim 1 in a fuel cell (1).Stack of electrochemical cells (1) comprising a plurality of plate arrangements (2) according to claim 1, each comprising a grid designed as expanded metal (3) and two plates (4, 5) contacting the grid (3), namely a membrane electrode arrangement (5) as the first plate and a bipolar plate (4) as the second plate.

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