Frame-shaped sub-gasket arrangement and electrochemical cell

Abstract

The invention relates to a frame-shaped sub-gasket arrangement (1), comprising two plastic films (1a) firmly connected to one another and having a first side (A) and a second side (C), wherein the plastic films (1a) have a rectangular circumference (U) and a central rectangular opening (2) for receiving a rectangular membrane electrode unit (10), wherein the plastic films (1a) further have a plurality of fluid passage openings (3), and wherein an edge region (R) of the plastic films (1a) is folded over by 180° onto the first side (A) and / or onto the second side (C), at least in partial regions of their circumference (U). The invention further relates to an electrochemical cell (20), in particular a polymer electrolyte fuel cell, comprising at least one such frame-shaped sub-gasket arrangement (1) and a membrane electrode unit (10) connected to the frame-shaped sub-gasket arrangement (1).

Description

The invention relates to a frame-shaped sub-sealing arrangement comprising two plastic films firmly connected to one another with a first side and a second side, wherein the plastic films have a rectangular circumference and a rectangular opening in the middle for receiving a rectangular membrane electrode unit between the two plastic films, wherein the plastic films furthermore have a plurality of fluid passage openings. The invention further relates to an electrochemical cell having at least one such frame-shaped sub-seal arrangement.Such plastic foil sub-sealing arrangements for holding membrane electrode units in electrochemical cells are known and are frequently also described under the English-language term "sub-rocket". A membrane electrode assembly typically comprises a thin polymer electrolyte membrane having on one side a first electrode layer functioning as an anode and on the opposite side a second electrode layer functioning as a cathode. The electrode layers are generally each covered with a catalyst material. Such a membrane electrode unit is fixed between two thin plastic films, wherein the two thin plastic films are firmly connected to one another and form the frame-shaped lower seal arrangement for the membrane electrode unit.DE 10 2013 217 759 A1 or also DE 10 2012 214 268 A1 describe frame-shaped lower sealing arrangements for use in fuel cell stacks.It is an object of the invention to improve the mechanical stability of such a frame-shaped underseal arrangement. It is a further object of the invention to provide an electrochemical cell having a frame-shaped underseal arrangement improved in this way.The object is achieved for the frame-shaped lower seal arrangement comprising two plastic films firmly connected to one another and having a first side and a second side, wherein the plastic films have a rectangular circumference and a rectangular opening in the middle for receiving a rectangular membrane electrode unit between the two plastic films, wherein the plastic films furthermore have a plurality of fluid passage openings, characterized in that an edge region of the plastic films is folded over by 180° onto the first side and / or onto the second side at least in partial regions of their circumference.The frame-shaped lower sealing arrangement is mechanically reinforced due to the folding in the edge region of the two plastic films firmly connected to one another and is thus easier to handle. The thus reinforced and thicker edge of the frame-shaped sub-sealing arrangement can thereby be positioned more accurately and offers a stable stop during such a positioning, for example during the construction of a stack arrangement with the formation of a plurality of electrochemical cells. In this case, improved electrical insulation is present between the electrode plates or bipolar plates in an electrochemical cell adjoining the frame-shaped sub-sealing arrangement on the first side and the second side thereof, since the fold is arranged between the electrode plates or bipolar plates. In addition, there is sufficient installation space for the folding.It has proven to be effective if the edge region of the plastic films is folded over onto the first side by 180° on their complete circumference. As a result, the frame-shaped lower seal arrangement acquires good mechanical stability and handling on all sides.In a preferred embodiment of the frame-shaped lower seal arrangement, the edge region of the plastic films is folded over onto the first side in at least a first partial region of their circumference and onto the second side in at least a second partial region of their circumference.The edge region of the plastic films can be folded over once or at least folded over twice. Multiple folding further increases the stability of the frame-shaped sub-seal arrangement.It has proven to be effective if less than 3% of the length of the frame-shaped lower seal arrangement is folded over on both sides. Furthermore, it has proven to be effective if less than 5% of the width of the frame-shaped lower seal arrangement is folded over on both sides. However, if an excessively short region of the plastic films is folded over, there is the risk that the fold is not sufficiently dimensionally stable and the folded-over region is re-erected.The plastic films are preferably formed from a plastic of the polypropylene (PP) or polyethylene terephthalate (PET) or polyethylene naphthalate (PEN) type.The two plastic films firmly connected to one another have in particular a thickness in the range from 50 to 250 μm. Thus, a single plastic film has a thickness in the range of 25 to 125 μm. Such thin plastic films are not very dimensionally stable and are expensive to handle mechanically, so that here the mechanical stabilization of the two plastic films firmly connected to one another by the folded-over edge region has a particularly positive effect.The fold formed in the edge region of the plastic films is produced in a preferred embodiment merely by bending the plastic films. In an alternative embodiment, however, the folding can also be fixed by a subsequent local thermal treatment of the plastic films, in which overlapping regions of the plastic films are fused together locally or over a large area. It is also possible here for the fold to be fixed by means of an adhesive, it being possible for the adhesive to be applied in the edge region before or after the formation of the fold. This may be a photoreactive adhesive.The object is furthermore achieved for the electrochemical cell, in particular polymer electrolyte fuel cell, by comprising at least one frame-shaped sub-sealing arrangement according to the invention and a membrane electrode unit connected to the frame-shaped sub-sealing arrangement.In this case, the membrane electrode unit is fastened between the two plastic films, in particular covering the rectangular opening in the plastic films. In particular, the membrane electrode unit is welded or bonded to the plastic films in a fluid-tight manner in the edge region around the rectangular opening in the plastic films.In an electrochemical cell, the frame-shaped sub-seal assembly with the membrane-electrode assembly is disposed between two electrode plates or bipolar plates. In a preferred configuration of the electrochemical cell, at least one fluid diffusion layer is arranged between each electrode plate or bipolar plate and a membrane electrode unit.FIGS. 1 to 7 are intended to illustrate the invention by way of example. Thus: FIG. 1 shows a single plastic film in plan view, FIG. 2 shows a first frame-shaped lower seal arrangement, FIG. 3 is a section III--III' through the frame-shaped underseal arrangement according to FIG. 2, FIG. 4 shows an alternative sectional illustration through a frame-shaped lower sealing arrangement with a double fold in the edge region, FIG. 5 shows a further alternative sectional illustration through a frame-shaped sub-sealing arrangement with an edge region which is partially folded onto the first side and partially folded onto the second side, FIG. 6 shows the frame-shaped sub-sealing arrangement according to FIG. 2 with the membrane electrode unit applied, and FIG. 7 shows a stack arrangement of electrochemical cells.FIG. 1 shows an individual plastic film 1 ain a plan view of the plane spanned by the plastic film 1 a. The plastic film 1 acomprises a rectangular circumference U and, in the middle, a rectangular opening 2 for receiving a rectangular membrane electrode unit 10 (compare FIG. 6 ). The plastic film 1a further has a plurality of fluid passage openings 3. The corners E of the plastic film 1 acan optionally be cut off at a 45° angle. In the edge region R of the plastic film 1 a, a folding line 4 is indicated, along which folding is to be folded over later. To form a frame-shaped lower seal arrangement 1 (compare FIG. 6 ), two such plastic films 1 ahaving the same construction are firmly connected to one another, wherein a rectangular membrane electrode unit 10 is fixed between the two plastic films 1 a.FIG. 2 shows a first frame-shaped sub-sealing arrangement 1 without a membrane electrode unit ( 10) for improved clarity. The first frame-shaped lower sealing arrangement 1 has a length L and a width B, as is present after the introduction of the fold 5 at the fold lines 4 of the two plastic films 1 afixedly connected to one another according to FIG. 1. The same reference numerals as in FIG. 1 identify the same elements. The edge region R of the plastic films 1 ais simply folded over on all sides at the circumference U by 180° onto the first side A of the frame-shaped lower seal arrangement 1.FIG. 3 shows the section III-III' through the frame-shaped lower seal arrangement 1 according to FIG. 2, wherein here the two separate, but firmly connected plastic films 1a are shown separated from one another by the dashed line. The fold 5 of the edge region R of the plastic films 1 ais laid on all sides on the first side A of the frame-shaped sub-sealing arrangement 1, while the second side C of the frame-shaped sub-sealing arrangement 1 is present without overlapping film regions.FIG. 4 shows an alternative sectional illustration through a frame-shaped sub-sealing arrangement 1' with a double fold 5' in the edge region R of the plastic films 1a. In FIG. 4, a representation of the two separate, but firmly connected plastic films 1a has been omitted for the sake of better clarity.Here too, the double fold 5' is placed on the first side A of the frame-shaped lower sealing arrangement 1.FIG. 5 shows a further alternative sectional illustration through a frame-shaped sub-sealing arrangement 1" with an edge region R partially folded onto the first side A and partially onto the second side C of the frame-shaped sub-sealing arrangement 1". In FIG. 5, an illustration of the two separate, but firmly connected plastic films 1a has been omitted for the sake of better clarity. Thus, in the region of the longitudinal sides of the plastic films 1a, a folding 5 onto the first side A has taken place, while in the region of the short sides of the rectangular plastic films 1a, a folding 5" onto the second side C has taken place.FIG. 6 shows the frame-shaped sub-sealing arrangement 1 according to FIG. 2 with a membrane electrode unit 10 fixed between the two plastic films 1 a, which covers the openings 2 in the plastic films 1 ain this case and is connected to the plastic films 1 ain a fluid-tight manner. The position of the membrane electrode unit 10 between the two plastic films 1 ais indicated by dashed lines.FIG. 7 shows a stack arrangement 21 of a plurality of electrochemical cells 20, here a fuel cell stack. Each electrochemical cell 20 comprises a frame-shaped sub-sealing arrangement 1 with a membrane electrode unit 10 between two bipolar plates 6, which likewise have fluid passage openings 3' which are congruent with the fluid passage openings 3 of the frame-shaped sub-sealing arrangement 1. The bipolar plates 6 have active fields 7 on both sides, which are arranged adjacent to the membrane electrode unit 10. The membrane electrode assembly 10 includes a thin polymer electrolyte membrane, not separately shown, having a first electrode layer functioning as an anode on one side and a second electrode layer functioning as a cathode on the opposite side. The electrode layers are generally each covered with a catalyst material and are likewise not shown separately.List of reference characters1, 1', 1" frame-shaped sub-sealing arrangement 1 aplastic film 2 rectangular opening 3 fluid passage opening in plastic film 1 a 3' fluid passage opening in bipolar plate 6 4 fold line 5, 5', 5" fold 6 bipolar plate 7 active field 10 membrane electrode unit 20 electrochemical cell 21 stack arrangement A first side C second side U periphery R edge region E corner region L length of plastic film B width of the plastic film

Claims

Frame-shaped sub-sealing arrangement (1) comprising two plastic films (1a) firmly connected to one another and having a first side (A) and a second side (C), wherein the plastic films (1a) have a rectangular circumference (U) and, in the middle, a rectangular opening (2) for receiving a rectangular membrane electrode unit (10) between the two plastic films (1a), wherein the plastic films (1a) furthermore have a plurality of fluid passage openings (3), characterized in that an edge region (R) of the plastic films (1a) is folded over by 180° onto the first side (A) and / or onto the second side (C) at least in partial regions of their circumference (U).Frame-shaped lower sealing arrangement (1) according to Claim 1, characterized in that the edge region (R) of the plastic films (1a) is folded over by 180° onto the first side (A) on its complete circumference (U).Frame-shaped lower sealing arrangement (1) according to Claim 1, characterized in that the edge region (R) of the plastic films (1a) is folded over onto the first side (A) in at least a first partial region of its circumference (U) and onto the second side (C) in at least a second partial region of its circumference (U).Frame-shaped lower sealing arrangement (1) according to one of Claims 1 to 3, characterized in that the edge region (R) of the plastic films (1a) is folded over once or is folded over at least twice.Frame-shaped sub-sealing arrangement (1) according to one of Claims 1 to 4, characterized in that less than 3% of the length (L) of the frame-shaped sub-sealing arrangement (1) is folded over on both sides.Frame-shaped sub-sealing arrangement (1) according to one of Claims 1 to 4, characterized in that less than 5% of the width (B) of the frame-shaped sub-sealing arrangement (1) is folded over on both sides.Frame-shaped lower sealing arrangement (1) according to one of Claims 1 to 6, characterized in that the fold (5, 5', 5") is fixed by local thermal treatment of the plastic films (1a) or an adhesive.Frame-shaped lower seal arrangement (1) according to one of Claims 1 to 7, characterized in that the two plastic films (1a) which are firmly connected to one another together have a thickness in the range from 50 to 250 μm.Electrochemical cell (20), in particular polymer electrolyte fuel cell, comprising at least one frame-shaped sub-sealing arrangement (1) according to one of Claims 1 to 8 and a membrane electrode unit (10) connected to the frame-shaped sub-sealing arrangement (1).Electrochemical cell (20) according to claim 9, characterised in that the membrane electrode unit (10) is fastened between the two plastic films (1a) covering the rectangular opening (2) in the plastic films (1a).

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