Abstract
An electrochemical, media-guiding system, a contact element for electrically and mechanically contacting such a plate, and a transmission device containing such a contact element. The present disclosure further relates to the production of such a plate or such a contact element. A plate having at least one contact point forming a voltage take-off point, a current supply point, and/or a current take-off point. The at least one contact point having a laser-surface-treated region.
Claims
1. An electrochemical, media-guiding system, comprising: a plate, wherein the plate is a separator plate, a media distribution plate, a current supply plate or a current collector plate, and at least one contact point forming a voltage take-off point, a current supply point, and/or a current take-off point, wherein the at least one contact point has a laser-surface-treated region and is arranged in a non-media-guiding region of the plate.
2. The system according to claim 1, wherein the plate is a separator plate comprising: a media-guiding inner region, a non-media-guiding outer region, and at least one sealing element which seals off the media-guiding inner region with respect to the non-media-guiding outer region, wherein the contact point is provided in the outer region.
3. The system according to claim 1, wherein the contact point is electrically and mechanically, connected to a transmission device and the connection is force-fit and/or form-fit.
4. The system according to claim 3, wherein the contact point forms a socket for a plug-in element of the transmission device or forms a plug-in element for a socket of the contact element of the transmission device.
5. The system according to claim 1, wherein the contact point is a flat, substantially planar, region that extends at least in part along a flat side of the plate.
6. The system according to claim 1, further comprising a contact element for electrical and mechanical, force-fitting and/or form-fitting, connection to a contact point of the plate, wherein the contact element has a laser-surface-treated region.
7. The system according to claim 6, wherein the contact element is a plug-in element for a socket of the contact point of the plate or as a socket for a plug-in element of the plate.
8. The system according to claim 6, further comprising a transmission device for use in measuring an electrical voltage and/or in transmitting an electrical current onwards from at least one sub-region of an electrochemical system.
9. The system according to claim 1, wherein the laser-surface-treated region has periodic surface structures with a mean spatial period of less than 10 μm.
10. The system according to claim 9, wherein the surface structures comprise depressions, which extend substantially parallel to one another.
11. The system according to claim 10, wherein the depressions have a depth of at least 8 nm, and/or at most 0.5 μm, a width of at least 0.1 μm and/or at most 2 μm, and/or a period in one spatial direction of at least 0.3 μm and/or at most 3 μm.
12. The system according to claim 9, wherein the surface structures are at least in part arranged periodically in relation to one another at least in one spatial direction.
13. The system according to claim 9, wherein an electrical conductivity is greater in the laser-surface-treated region than outside of the laser-surface-treated region.
14. The electrochemical system according to claim 1, comprising a plurality of stacked separator plates, which are arranged between a first current collector plate and a second current collector plate.
15. The electrochemical system according to claim 14, comprising a transmission device.
16. The electrochemical system according to the claim 1, comprising a plurality of stacked media distribution plates, which are arranged between a first current supply plate and a second current supply plate.
17. A method for producing a plate for an electrochemical, media-guiding system, comprising the steps: providing a plate that has at least one contact point forming a voltage take-off point, a current supply point, and/or a current take-off point, and the at least one contact point arranged in a non-media-guiding region of the plate, irradiating the contact point using a pulsed laser with a pulse duration of less than 1 ns, creating periodic surface structures on the contact point using the laser radiation.
18. A method for producing a contact element for mechanical and electrical connection to a contact point of a plate of an electrochemical system, the method comprising the steps: irradiating the contact element using a pulsed laser with a pulse duration of less than 1 ns, creating periodic surface structures on the contact element using the laser radiation.
Description
BRIEF DESCRIPTION OF THE FIGURES
[0062] FIG. 1 schematically shows a perspective view of an electrochemical system comprising a plurality of bipolar plates and two unipolar plates.
[0063] FIG. 2 schematically shows, in a perspective view, two bipolar plates for an electrochemical system of the type shown in FIG. 1 and a membrane electrode assembly arranged between the bipolar plates.
[0064] FIGS. 3A and 3B show a sectional view through a contact point of a separator plate and a contact element of a transmission device.
[0065] FIGS. 4A and 4B show a sectional view through a contact point of a separator plate and a contact element of a transmission device.
[0066] FIG. 4C shows a sectional view of a contact element.
[0067] FIG. 5 shows a sectional view through a contact point of a separator plate and a contact element of a transmission device.
[0068] FIG. 6 shows a sectional view through a contact point of a separator plate and a contact element of a transmission device.
[0069] FIG. 7A shows a plan view of a transmission device with multiple contact elements.
[0070] FIG. 7B shows a sectional view of the transmission device of FIG. 7A with plug-in elements of the contact points of separator plates received therein.
[0071] FIG. 7C schematically shows a plan view of a plug-in element of a contact point from FIG. 7B.
[0072] FIG. 8A shows a sectional view of part of an electrochemical system.
[0073] FIG. 8B shows a sectional view of part of an electrochemical system.
[0074] FIG. 9A shows a microscopic image of periodic surface structures in plan view.
[0075] FIG. 9B shows a detail from FIG. 9A.
[0076] FIG. 10 shows a microscopic image of periodic surface structures in plan view.
[0077] FIG. 11A schematically shows part of a separator plate in a perspective view.
[0078] FIG. 11B schematically shows part of a separator plate in a perspective view.
[0079] FIG. 12A shows a detail of part of an article.
[0080] FIG. 12B shows a detail of part of an article.
[0081] FIG. 12C shows a detail of a plan view of an article.
[0082] FIG. 12D shows a detail of a cross-section of an article.
[0083] FIG. 12E shows a detail of a plan view of an article.
[0084] FIG. 13 schematically shows, in a perspective view, a laser system for creating periodic surface structures.
[0085] FIG. 14A schematically shows a cross-section of the laser system of FIG. 13.
[0086] FIG. 14B shows a detail of the laser system of FIGS. 13 and 14A.
[0087] FIG. 15 shows resistance measurements at the transition point between two (optionally treated) stainless steel sheets.
[0088] FIG. 16 shows resistance measurements at the transition point between two (optionally treated) stainless steel sheets with a carbon fleece positioned therebetween.
[0089] FIGS. 1-14A are shown approximately to scale. Here and below, features that recur in different figures are denoted by the same or similar reference signs in each case.
DETAILED DESCRIPTION
[0090] FIG. 1 shows an electrochemical system 1 of the type proposed here, comprising a plurality of structurally identical metal bipolar plates 2 which are arranged in a stack 6 and are stacked along a z-direction 7. The bipolar plates 2 of the stack are clamped between two end plates 3, 4. A unipolar plate 200, 201 is arranged between each of the end plates 3, 4 and the bipolar plate stack 6. The current collector plate arranged between an end plate 3, 4 and the adjacent unipolar plate 200, 201 is not visible in FIG. 1, but the projections 310, 311 of a current collector plate that protrude through the end plate 4 are visible. The z-direction 7 will also be referred to as the stacking direction. The bipolar plates 2 usually comprise in each case two metal separator plates 2a, 2b which are connected to one another (see, for example, FIG. 2). In the present example, the system 1 is a fuel cell stack. Each two adjacent bipolar plates 2 of the stack therefore enclose between them an electrochemical cell, which serves for example to convert chemical energy into electrical energy. The electrochemical cells usually each comprise a membrane electrode assembly (MEA) 10 (see, for example, FIG. 2). Each MEA typically contains at least one membrane, for example an electrolyte membrane. Furthermore, a gas diffusion layer (GDL) may be arranged on one or both surfaces of the MEA.
[0091] The z-axis 7, together with an x-axis 8 and a y-axis 9, spans a right-handed Cartesian coordinate system. The bipolar plates 2 and separator plates 2a, 2b each define a plate plane, wherein the plate planes of the separator plates 2a, 2b are each oriented parallel to the x-y plane and thus perpendicular to the stacking direction or to the z-axis 7. The end plate 4 has a plurality of media ports 5, via which media can be supplied to the system 1 and via which media can be discharged from the system 1. These media that can be supplied to the system 1 and discharged from the system 1 may comprise for example fuels such as molecular hydrogen or methanol, reaction gases such as air or oxygen, reaction products such as water vapour or depleted fuels, or coolants such as water and/or glycol.
[0092] FIG. 2 shows, in a perspective view, two conventional bipolar plates 2, as can be used for example in electrochemical systems of the type shown in FIG. 1. FIG. 2 also shows a membrane electrode assembly (MEA) 10 arranged between these adjacent bipolar plates 2, the MEA 10 in FIG. 2 being largely obscured by the bipolar plate 2 facing towards the viewer. The bipolar plate 2 is formed of two separator plates 2a, 2b which are joined together in a materially bonded manner, of which in each case the first separator plate facing towards the viewer is visible in FIG. 2, said first separator plate obscuring the second separator plate. The separator plates may each be formed of a shaped metal sheet, for example of an embossed or deep-drawn stainless steel sheet. This metal sheet may for example have a thickness of at most 150 μm, for example at most 100 μm, for example at most 90 μm, for example at most 80 μm. The separator plates may be welded to one another, for example by laser welds.
[0093] The separator plates have through-openings which are aligned with one another, which form through-openings 11a-c and 11′ a-c of the bipolar plate 2. When a plurality of bipolar plates 2 are stacked, the through-openings 11a-c, 11′ a-c form media channels which extend through the stack of the system 1 in the stacking direction 7 (see FIG. 1). Typically, each of the media channels formed by the through-openings 11a-c, 11′a-c is fluidically connected to one of the ports 5 in the end plate 4 of the system 1. For example, coolant can be introduced into the stack via the media channels formed by the through-openings 11a and can be discharged from the stack via the through-openings 11′a. In contrast, the lines formed by the through-openings 11b, 11c may be designed to supply fuel and reaction gas to the electrochemical cells of the fuel cell stack of the system 1, while the lines formed by the through-openings 11′b, 11′c may be designed to discharge the reaction products from the stack.
[0094] The first separator plates have, on the front side thereof facing towards the viewer of FIG. 2, a flow field 17 with structures for guiding a reaction medium along the front side of the separator plate. The electrochemically active region 18 forms part of this flow field 17. In FIG. 2, these structures of the electrochemically active region 18 are defined by a plurality of webs 15 and by channels 16 extending between the webs 15 and delimited by the webs 15. On the rear sides of the channels, for example on the opposite surface of the separator plate, rear-side webs are formed, in the region of which the separator plates 2a, 2b bear against one another. On the front side of the bipolar plates 2, facing towards the viewer of FIG. 2, the first separator plates 2a additionally each have a distribution and collection region 20 for reaction medium, with a distribution and collection region for coolant (not visible) being located opposite this on the rear side of the separator plate 2a, for example on the inner side of the bipolar plate 2. The distribution region 20 comprises structures which are designed to distribute over the active region 18 a medium that is introduced into the distribution region 20 from a first 11b of the through-openings 11a, 11b, 11c, while the collection region 20 comprises structures which are designed to collect or to pool a medium flowing towards a first 11′b of the through-openings 11′a, 11′b, 11′c from the active region 18. To this end, the distribution and collection regions 20 have guide structures, which in FIG. 2 are defined by webs 14 and by channels 19 formed between the webs 14. The channels 16 may each be fluidically connected to one of the through-openings 11b, 11′b via the channels 19. The electrochemically active region 18 is thus fluidically connected to the through-openings 11b, 11′b via the distribution and collection regions 20.
[0095] The structures of the active region 18 and the guide structures of the distribution region 20 and of the collection region 20 are in each case formed in one piece with the separator plates 2a, 2b and are integrally formed in the separator plates 2a, 2b, for example in an embossing, hydroforming or deep-drawing process. The same usually applies to the corresponding guide structures on the second separator plates 2b.
[0096] Each of the through-openings 11a, 11′a has a sealing element 12a, 12′a that surrounds it. The region of the through-openings 11b, 11c, 11′b, 11′c and of the active region 18 and of the distribution and collection regions 20 are jointly surrounded by a sealing element 12d. The through-openings 11a, 11′a, 11b, 11′b, 11c, 11′c, the active region 18 and the distribution and collection region 20 together form the media-guiding inner region 21. Together, the sealing elements 12a, 12′a and 12d seal off the fluid-guiding region with respect to the non-media-guiding outer region 22.
[0097] By way of example, three elements 30, 31, 32 for individual cell voltage measurement (CVM) are formed in the outer region 22, these elements forming contact points 37, 38, 39. The two elements 30, 31 are integrally formed in the separator plates 2a, 2b as a socket 30, 31 of the contact points 37, 38. In contrast, the element 32 is designed as a plug-in element 32 of the contact point 39, which protrudes beyond the adjacent outer edge 24.
[0098] FIGS. 3 to 6 show different CVM measurement points comprising contact points and contact elements, as can be formed both in separator plates for bipolar plates and also in unipolar plates.
[0099] FIG. 3A shows a sectional view of a contact point 37 in the outer region 22 of a bipolar plate 2, which is comparable to the contact point 37 of FIG. 2. The two separator plates 2a, 2b of the bipolar plate 2 are in turn shaped in their outer region in a bead-like manner away from one another and thus define a socket 30. A plug-in element 54 of a contact element 52 of a transmission device 50, illustrated here in the form of a cable, is received in this socket 30. FIG. 3B shows a section perpendicular to the section of FIG. 3A; here, as in FIG. 2, a second socket 31 is present in addition to the socket 30. In the exemplary embodiment of FIGS. 3A and 3B, the plug-in element 52 is designed with a substantially rectangular cross-section.
[0100] FIGS. 4A and 4B show comparable sectional views of a contact point 37 with a plug-in element 54 received therein, as in FIGS. 3A-3B. Here, the plug-in element 54 is designed with an oval cross-section, as can also be seen from FIG. 4C.
[0101] FIG. 5 shows a sectional view through a contact point 37 of a bipolar plate 2 and a contact element 52 of a transmission device 50. This exemplary embodiment differs from that of FIGS. 3A and 3B in that a web-shaped embossment 34 is formed in the upper separator plate 2a in the region of the socket 30, said embossment engaging in a groove 55 on the upper side of the rectangular plug-in element 54 of the contact element 52 and thus may already bring about an improvement in the mechanical connection between the contact element 52 and the contact point 37.
[0102] FIG. 6 likewise shows a sectional view through a contact point 37 of a bipolar plate 2 and a contact element 52 of a transmission device 50. Compared to the exemplary embodiment of FIG. 5, now no embossment is provided in the separator plate 2, but instead a locking tab 33 is provided, which engages in a groove 56 that extends circumferentially around the surface of the round contact element 52. Compared to the exemplary embodiment of FIGS. 4A and 4B, this configuration might provide an improvement in the mechanical connection between the contact element 52 and the contact point 37.
[0103] FIG. 7A shows a plan view of a transmission device 50 with six contact elements 51a-51f. The contact elements 51a-51f are each designed as sockets 53a-53f. The transmission device may have a frame 59 made of an electrically insulating polymer material, in which the actual sockets 53a-53f are held. FIG. 7B shows a sectional view of the transmission device of FIG. 7A with three plug-in elements 32a-32c of the contact points 39a-39c of separator plates received therein. The plan view of one such plug-in element 32 is shown in FIG. 7C, which also shows how the plug-in element 32 extends from the outer edge 24 of a separator plate 2a of a bipolar plate. FIG. 7B shows, in a manner not true to scale, that a plug-in element 32a, 32b may be formed in just one single plate 2b, 2a or, like the plug-in element 32c, may be formed of projections from both plates 2a, 2b of a bipolar plate.
[0104] FIG. 8A shows a sectional view of part of an electrochemical system similar to the one shown in FIG. 1. Unlike in FIG. 1, the current collector plate 300 between the end plate 3 and the unipolar plate 200 is also visible here, as well as the recess 320 in the end plate 3, in which the current collector plate 300 can be accommodated. A contact layer 250, which may for example comprise a metal or graphite-fibre material comparable to a gas diffusion layer, may be accommodated between the unipolar plate 200, which is shown here in a simplified and unstructured form but nevertheless may have embossments in the same way as a separator plate of a bipolar plate, and the current collector plate 300. From a first perspective, the surface of the unipolar plate 200 acts as a contact point 38 and the surface of the current collector plate 300 acts as a contact element 57; from a second perspective, the surface of the current collector plate 300 acts as a contact point 38 and the surface of the unipolar plate 200 acts as a contact element 57.
[0105] According to the present disclosure, the separator plates 2a, 2b of a bipolar plate 2 and/or the unipolar plate 200, 201 as a further separator plate and/or the current collector plate 300 and/or the contact element 51, 52, 57 and/or the transmission device 50, collectively an “article” 60, have at least in part a laser-surface-treated region 41, in which periodic surface structures 40 are formed with a mean spatial period of less than 10 The surface structures 40 are thus arranged at least in part at periodic intervals. The periodic surface structures 40 are created on the surface of the separator plate 2a, 2b by irradiation using an ultrashort-pulse laser. For instance, one contiguous region or multiple contiguous regions of the separator plate 2a, 2b may have the periodic surface structures 40. The periodic surface structures 40 will be further explained below with reference to FIGS. 9A to 10 and 12A to 12E.
[0106] FIG. 8B shows a sectional view of part of another electrochemical system, namely an electrolytic system. It shows an end plate 3 designed as a current supply plate 300′ as well as the first media distribution plate 200′ of an electrolyzer stack in a section distanced to the media conducts, thus in a non-media guiding region. In a simplifying manner, the media distribution plate 200′ in the section shown is depicted as a flat plate. However, it usually comprises channels on its surface facing away from the end plate, at one end of the stack for the distribution of water and the collection of oxygen and at the other end of the stack for the collection for hydrogen. In the same way as the unipolar plate 200 in FIG. 8A, the media distribution plate 200′ may also comprise structures, however, it at least in sections rests on the current supply plate 300′. FIG. 8B additionally shows a screw 81 taken up in the current supply plate 300′, which is connected to a current source via a cable 80. The current supply plate 300′ may be made from stainless steel. The media distribution plates may for instance be made from a titanium alloy or from a stainless steel, which may be coated at least in the media-guiding areas of its surface.
[0107] FIGS. 9A, 9B and 10 show greatly enlarged images of periodic surface structures 40, which are formed on the surface of a metal sheet, such as a stainless steel sheet, by a laser surface treatment and form at least one laser-surface-treated region 41 thereon. The enlarged parts may be parts of surfaces of a separator plate 2a, 2b, 200, 201, of a current collector plate 300, of a contact element 52, of a transmission device 50, or of a metal sheet for such an article 60. The stainless-steel sheet may be shaped by embossing, hydroforming or deep-drawing, and optionally punching, in order to form the article 60. Alternatively, the article 60 is first formed by embossing, hydroforming or deep-drawing, and optionally punching, and then is provided with the periodic surface structures 40. It is also possible for the surface structuring to be applied to the surface, or formed thereon, between two mechanical machining steps by means of irradiation with laser radiation.
[0108] While for a contact element 52 comprising a rectangular or substantially rectangular plug-in element 54, the periodic surface structures 40 may be present at least on two sides, such as on an upper side and a lower side, it is in contrast sufficient in some embodiments for the plates 2a, 2b, 200, 201, 300 if the periodic surface structures 40 are present only on one surface. In principle, the articles 60 may be provided with the periodic surface structures 40 at least in part on one and/or both sides. In the case of a plug-in element 54 having a round or oval cross-section, it is also possible to provide said plug-in element with the periodic surface structures 40 around the circumference.
[0109] As can be seen from FIGS. 9A to 10 and 12A to 12E, the periodic surface structures 40 (hereinafter also surface structures 40) may comprise a plurality of depressions 42 and elevations 44. The depressions 42 extend between the elevations 44 and are delimited and/or formed by the latter. The surface structures 40 are arranged periodically with respect to one another in at least one spatial direction x, y. For instance, the surface structures 40 may be aligned with one another along their longitudinal direction. For example, the surface structures 40, that is to say the depressions 42 and the elevations 44, extend substantially parallel to one another. The surface structures 40 may be arranged in parallel one next to the other and/or one behind the other. For example, it can be seen in FIGS. 12B, 12C that the surface structures 40 are arranged in parallel one next to the other, for example perpendicular to the longitudinal direction of the surface structures. Furthermore, FIG. 10 shows that surface structures 40 can be arranged both in parallel one behind the other (one after the other in the longitudinal direction) and in parallel one next to the other. Such surface structures 40 can likewise be seen in FIGS. 12A and 12E.
[0110] The surface structures 40 may extend, for example, in a wavy or linear manner along their longitudinal direction. One example of the surface structures 40 extending in a wavy manner is shown in FIGS. 12B and 12C.
[0111] FIG. 12D shows a depth t, a width b and a period Px of the surface structures, for example of the depressions 42. The surface structures 40 may have a depth t of at least 8 nm, for example at least 50 nm, and/or at most 3 μm, for example at most 1 μm, for example at most 500 nm and/or at most 300 nm and/or at most 250 nm. In the present example, the depth is, for example, t=0.4 μm or t=100 nm. In one exemplary embodiment, the surface structures 40 have a width b, measured halfway up, of at least 0.1 μm and/or at most 2 μm. In the present example, the width is b=0.45 μm. In addition, the surface structures 40 may have a period Px in one spatial direction x of at least 0.3 μm and/or at most 3 μm. In the present example, the period is 1 μm. In FIG. 12D, the period Px denotes the lateral spacing between two adjacent elevations 44.
[0112] In FIG. 12E, the surface structures 40 have a length 1 of 5 μm in one spatial direction y. The surface structures are arranged in parallel one behind the other, with a period Py of 5 μm.
[0113] Owing to the surface structures 40, the surface of the article 60 has chemical and/or electrical properties that differ from regions of the article 60 without surface structures 40. For example, as a result of the surface structures 40, an oxygen content of the surface material of the article 60 may be greater in the region of the periodic surface structures 40 than outside of the periodic surface structures 40.
[0114] FIGS. 11A and 11B show, based on the example of two sockets 30, how the surfaces of separator plates can be provided with the periodic surface structures 40 in the region of a contact point 37. Said surface structures may for example be provided, as in the example of FIG. 11A, only on the base surface 30a of the socket 30, which extends substantially parallel to the plate plane E. However, they may for example also additionally be provided, as in the example of FIG. 11B, on the side walls 30b, 30c of the socket, which extend obliquely to the plate plane E.
[0115] In FIGS. 3A and 3B comparable surface structures 40′ and 40″ are provided on the base surfaces 30a of the sockets 30 and 31, as in the example of FIG. 11A. The surface structures may improve the conductivity.
[0116] In contrast, in FIGS. 4A to 4C, the surface structures 40 are formed around the circumference of a plug-in element 54 of a contact element 52, while the sockets 30, 31 are manufactured without a corresponding laser surface structure.
[0117] In the exemplary embodiment of FIG. 5, a surface structure 40 is formed only on the base surface 30a of the socket 30 of the separator plate 2b. By pressing the contact element 52 onto this base surface 30a by means of the locking embossment 34, good voltage transmission from the separator plate 2 to the transmission device 50 is thus achieved.
[0118] In contrast, FIG. 6 has the surface structure 40 on the entire inner side of the socket 30 of the separator plate 2b, but not on that of the separator plate 2a. Here, the surface structure 40 may result in an improvement in the voltage transmission compared to an analogous arrangement without such a laser treatment.
[0119] FIGS. 7A to 7C show, on the basis of a transmission device 50, different embodiments of CVM measurement points comprising plug-in elements 32 of the contact points 39 and sockets 53 of the contact element 51. Usually, a transmission device 50 has only identical sockets; here, the different embodiments are combined in one transmission device for illustration purposes. The sockets 53a, 53c and 53f are provided with a surface structure 40 across their entire surface, while the plug-in elements 32a and 32c received in the sockets 53a and 53c are designed with no surface structure. In contrast, the socket 53b, like the socket 53d as well, is free of any surface structure but receives a plug-in element 32b that is provided with a surface structure 40 on the upper side and lower side. The embodiment of socket 53e has a surface structure 40 only on its side faces 53′. The plan view of FIG. 7C shows a plug-in element 32 comparable to the plug-in element 32b. On this plug-in element 32, it is clear that an article 60 may have a plurality of laser-surface-treated regions 41, 41*, for example arranged at a distance from one another, and the respective surface structures 40, 40* may for example be phase-shifted relative to one another.
[0120] FIG. 8A shows a current collector plate 300, a unipolar plate 200, and an optional contact layer 250 arranged therebetween. In the exemplary embodiment shown, the unipolar plate 200 is designed as a smooth plate, but it may also have embossments and channels formed by the embossments; in this case, the webs between the channels bear directly or indirectly against the current collector plate 300, whereas in the exemplary embodiment shown there is a full-surface bearing across the entire extent of the current collector plate 300. Here, on their mutually facing surfaces, both the unipolar plate 200 and the current collector plate 300 are provided with a surface structure 40′ or 40″, respectively, across the extent of the area of the current collection plate 300. However, it would also be possible that just one surface, either that of the current collector plate 300 or that of the unipolar plate 200, is provided with such a surface structure 40′ or 40″.
[0121] In FIG. 8B, the surface of the endplate 3 pointing towards the media distribution plate 200′ is provided with a surface structure 40′ and this way shows a laser-surface-treated region 41′, which forms a contact point 38 to the media distribution area 200′, with the media distribution plate 200′ often being made from a titanium alloy. If the media distribution plate is however made from a stainless-steel sheet, which in most cases is coated in the media-guiding areas, then the media distribution plate 200′ might be provided with a surface structure 40′, while the surface of the endplate might or might not be surface structured.
[0122] The current supply plate 300′ on its surface pointing away from the media distribution plate 200′ may be provided—at least in sections—with a surface structure 40″, which forms a contact point 36 to the screw 81. This screw 81 enables the current provided via the cable 80 to enter into the system. As an alternative or in addition, it is possible that the screw 81 on its surface facing the endplate 3, such as its planar surface, is provided with a surface structure 40″ and this way forms a laser-surface-treated region 41″. The screw 81 here thus serves as contact element 58 and the contact area of the current distribution plate 300′ as contact point 36.
[0123] A method for producing an article 60 for an electrochemical system 1 will be disclosed below. The method may be suitable for producing one of the above-described plates 2a, 2b, 200, 200′, 201, 300 and 300′ and a contact element 51, 52, 57, 58.
[0124] The method is characterized by a laser treatment using a laser 100 shown in FIGS. 13 and 14A. FIG. 14B shows some components of the laser 100, namely a laser head 101, a first mirror 102, a second mirror 103, a λ/2 plate 104, a polarizer, such as a linear polarizer, 105, a beam splitter 106, a shutter 107, and a lens 108. Of course, a different setup of the laser 100 is also possible.
[0125] For the method, a pulsed laser 100 may be used, wherein each pulse has a pulse duration of less than 1 ns, for example less than 100 ps. The laser 100 may therefore be a picosecond laser (pulse duration shorter than 1 ns and greater than or equal to 1 ps) or a femtosecond laser (pulses shorter than 1 ps, for example shorter than 500 fs and/or greater than or equal to 30 fs). The laser 100 may generate linearly polarized laser radiation. A beam diameter or a smallest lateral dimension of the laser parallel to the surface of the plate 2a, 2b, 200, 200′, 201, 300 and 300′ may be, for example, at least 20 μm and/or at most 2 mm, in the example shown approximately 60 μm. The wavelength λ, generated by the laser 100 lies, for example, between 200 nm and 2000 nm, for example between 400 nm and 1500 nm. Customary wavelengths are, for example, 700 to 1000 nm in accordance with a Ti:sapphire laser system; 1064 nm (fundamental wavelength) or 532 nm, 355 nm or 266 nm (frequency multiplication) in accordance with an Nd:YAG laser system. A fluence of the laser often depends on the material of the plate 2a, 2b, 200, 200′, 201, 300 and 300′ and may be, for example, at least 0.001, at least 0.01 or at least 0.1 and/or at most 10.0 J/cm.sup.2, at most 5.0 J/cm.sup.2, at most 2.0 J/cm.sup.2. The repetition rate of the laser may be, for example, at least 10 Hz, for example at least 1 kHz, and/or at most 1000 kHz, for example at most 20 kHz.
[0126] Höhm 2014 includes a detailed description of the interaction of laser radiation with material to create periodic surface structures 40, with advantageous combinations of laser parameters also being published in Hohm 2014. For this reason, there is no need for any further description here.
[0127] In a first variant, the method comprises at least the following steps:
[0128] a method for producing a plate 2a, 2b, 200, 200′, 201, 300 and 300′ for an electrochemical, media-guiding system 1, comprising the steps: [0129] providing a plate 2a, 2b, 200, 200′, 201, 300 and 300′ [0130] that has at least one contact point 36, 37, 38, 39 designed as a voltage take-off point or, as a current supply point, and/or one contact point 36, 37, 38, 39 designed as a current take-off point, which contact point is arranged in a non-media-guiding region 22 of the plate, [0131] irradiating the contact point 36, 37, 38, 39 by means of a pulsed laser, a pulse duration of the laser pulses being less than 1 ns, for example less than 100 ps, for example less than 50 ps, [0132] creating periodic surface structures 40 on the contact point 36, 37, 38, 39 by means of the laser radiation.
[0133] In a second variant, the method comprises at least the following steps:
[0134] a method for producing a contact element 51, 52, 57, 58 for mechanical and electrical connection to a contact point 36, 37, 38, 39 of a plate 2a, 2b, 200, 201, 300 and 300′ of an electrochemical system 1, the method comprising the steps: [0135] irradiating the contact element 51, 52, 57, 58 by means of a pulsed laser, a pulse duration of the laser pulses being less than 1 ns, for example less than 100 ps, for example less than 50 ps, [0136] creating periodic surface structures 40 on the contact element 51, 52, 57, 58 by means of the laser radiation.
[0137] In this second variant, when using a rotationally symmetrical plug-in element 54 of the contact element 52, during the irradiation, the laser beam may be moved and/or the rotationally symmetrical plug-in element 54 may be moved, for instance may be rotated about its axis of rotation.
[0138] The creation of this plurality of periodic surface structures 40 is already completed before the next laser pulse hits the surface of the plate 2a, 2b, 200, 201, 300 or 300′ or contact element 51, 52, 57, 58. For example, at least 10 or at least 20 surface structures, for instance trench structures, may be created per laser pulse. Typically, the surface structures 40 are oriented perpendicular to the linear polarization direction of the incident laser radiation. The laser 100 may therefore be directed onto a surface of the plate 2a, 2b, 200, 200′, 201, 300 or 300′ or of the contact element 51, 52, 57, 58 in such a way that surface structures 40 are created with a desired orientation. This may apply to the core regions of the irradiated region. When the laser pulse hits the surface of the plate 2a, 2b, 200, 200′, 201, 300 or 300′ or of the contact element 51, 52, 57, 58, the incident laser radiation interferes with an electromagnetic surface wave generated by the laser pulse in the surface material of the plate 2a, 2b, 200, 200′, 201, 300 or 300′ or of the contact element 51, 52, 57, 58. The periodic surface structures 40 are formed as a result of this interaction.
[0139] A mean spatial period Px of the surface structures 40 usually depends on the wavelength λ of the laser 100. For metals (metal sheet, stainless steel sheet), the period P is approximately in the order of magnitude of the wavelength λ. By way of example, the mean spatial period P of the surface structures 40 is at least 2%, for example at least 5%, for instance at least 20%, and/or at most 200%, for example at most 120% of the laser wavelength used.
[0140] In principle, a single laser beam is sufficient to create the surface structures 40. This laser beam can then scan the surface of the plate 2a, 2b, 200, 201, 300 or 300′ or of the contact element 51, 52, 57, 58 that is to be treated. In this case, the aforementioned plurality of periodic surface structures is created by each individual laser pulse within a spatial projection of the laser radiation onto the plate 2a, 2b, 200, 201, 300 or 300′ or the contact element 51, 52, 57, 58. The process can be accelerated if an interference pattern or diffraction pattern is formed by at least two laser beams, and the surface is scanned using the interference pattern in order to create the surface structures 40. To this end, a linearly polarized laser beam of the laser 100 may be split by way of the beam splitter 106. The two linearly polarized partial beams thereby produced are then used to form the interference pattern. The interference pattern of the laser beams that is used serves to enlarge the scanned surface area and has no direct influence on the periodicity of adjacent surface structures 40. The spatial period of the surface structures 40 thus differs from the spatial period of the interference pattern or diffraction pattern and is usually significantly smaller, for example 10 times smaller. However, comparative measurements have shown that, by means of this surface structuring applied in an accelerated way, the volume resistance cannot be reduced to the same extent as when using just one single laser beam. As an alternative or in addition, a line laser (also called a linear laser) may also be used, the laser line thereof may have a width of at least 20 μm.
[0141] FIG. 15 shows the results of resistance measurements at the transition point between two stainless steel sheets, for example between a contact point 32 and a contact element 52, comparable to the situation at a CVM measurement point. The stainless-steel sheets have no surface structuring (“blank”) or different surface structuring or coatings. It is obvious that the two combinations involving a blank stainless-steel sheet have the highest contact resistance. The contact resistances between laser-surface-treated stainless steel sheets, or between laser-surface-treated stainless-steel sheets and gold-coated stainless-steel sheets, are approximately equal, such as at higher contact pressures, while the laser-surface-treated stainless-steel sheets have significantly lower manufacturing costs.
[0142] FIG. 16 shows the results of resistance measurements at the transition point between two stainless steel sheets with a carbon fleece 250 arranged therebetween, for example between a contact point 38 and a contact element 57, comparable to the situation between a unipolar plate 200 and a current collector plate 300. The stainless-steel sheets have no surface structures (“blank”) or different surface structures introduced by laser treatment. The pairing of two blank stainless-steel sheets leads to a very high contact resistance, whereas already significantly lower contact resistances are measured when a blank stainless-steel sheet is combined with a laser-surface-treated stainless-steel sheet. The lowest contact resistances are achieved when two laser-surface-treated stainless steel sheets are combined.
[0143] The resistance measurement results shown in FIGS. 15 and 16 indicate that, both for a voltage measurement point and for a current take-off point, a reduced contact resistance and an improved conductivity at the contact area are achieved when the contact point 36, 37, 38, 39 and/or the contact element 51, 52, 57, 58 is laser-surface-treated, compared to when using untreated sheet surfaces.
[0144] FIGS. 1-14A show example configurations with relative positioning of the various components. If shown directly contacting each other, or directly coupled, then such elements may be referred to as directly contacting or directly coupled, respectively, at least in one example. Similarly, elements shown contiguous or adjacent to one another may be contiguous or adjacent to each other, respectively, at least in one example. As an example, components laying in face-sharing contact with each other may be referred to as in face-sharing contact. As another example, elements positioned apart from each other with only a space there-between and no other components may be referred to as such, in at least one example. As yet another example, elements shown above/below one another, at opposite sides to one another, or to the left/right of one another may be referred to as such, relative to one another. Further, as shown in the figures, a topmost element or point of element may be referred to as a “top” of the component and a bottommost element or point of the element may be referred to as a “bottom” of the component, in at least one example. As used herein, top/bottom, upper/lower, above/below, may be relative to a vertical axis of the figures and used to describe positioning of elements of the figures relative to one another. As such, elements shown above other elements are positioned vertically above the other elements, in one example. As yet another example, shapes of the elements depicted within the figures may be referred to as having those shapes (e.g., such as being circular, straight, planar, curved, rounded, chamfered, angled, or the like). Further, elements shown intersecting one another may be referred to as intersecting elements or intersecting one another, in at least one example. Further still, an element shown within another element or shown outside of another element may be referred as such, in one example.
[0145] It will be appreciated that the configurations and routines disclosed herein are exemplary in nature, and that these specific embodiments are not to be considered in a limiting sense, because numerous variations are possible. Moreover, unless explicitly stated to the contrary, the terms “first,” “second,” “third,” and the like are not intended to denote any order, position, quantity, or importance, but rather are used merely as labels to distinguish one element from another. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations, and other features, functions, and/or properties disclosed herein.
[0146] As used herein, the term “approximately” or “substantially” is construed to mean plus or minus five percent of the range unless otherwise specified.
[0147] The following claims particularly point out certain combinations and sub-combinations regarded as novel and non-obvious. These claims may refer to “an” element or “a first” element or the equivalent thereof. Such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and sub-combinations of the disclosed features, functions, elements, and/or properties may be claimed through amendment of the present claims or through presentation of new claims in this or a related application. Such claims, whether broader, narrower, equal, or different in scope to the original claims, also are regarded as included within the subject matter of the present disclosure.
