Fuel cell stack, bipolar plate and gasket assembly, and method for providing sealing around a bipolar plate - Patents.com

Abstract

The fuel cell stack assembly is composed of bipolar plates (2) BPP, in combination with a gasket (3) abutting and covering the edge region (5) of each BPP for protecting the edge (5) of the corresponding BPP (2) and for electrically and thermally insulating the BPP (2). Advantageously, the gasket (3) is made of an elastically stretchable material and is preloaded by stretching to fit snugly around the edge (5) of the BPP (2) and is held in place by elastically contracting the gasket (3) around its periphery.

Description

[Technical field]

[0001] The present invention relates to a gasket for a bipolar plate for a fuel cell, in particular to a fuel cell stack, a bipolar plate and gasket assembly and a method for providing a seal around a bipolar plate according to the preambles of the independent claims. [Background technology]

[0002] Polymer gaskets are commonly used for sealing between anode and cathode plates, especially bipolar plates (BPPs). Not only is precise positioning required during manufacturing, but it is also necessary to ensure that the gasket remains in place for long-term sealing. The latter is a challenge because repeated thermal cycling of the fuel cell tends to cause the gasket to expand and contract relative to the bipolar plates, which can end up causing significant movement and deformation of the gasket to the point that it leads to leakage.

[0003] Various examples of electrode plate and gasket combinations in which protrusions or grooves are used to hold the gasket in place are disclosed in International Patent Application WO 2009 / 010066, US 2007 / 298310, US 2012 / 164560 and US 2014 / 0120452, DE 102014104015 A1, DE 102005046461 A1, DE 102006054849 A1 and DE Utility Model No. 202017103257 A1.

[0004] U.S. Patent Application Publication No. 7,081,316 to Rock discloses a fuel cell in which a bipolar plate is sandwiched between two gaskets that sit on the bipolar plate in grooves near the edges of the bipolar plate. The gaskets provide openings near opposing edges for channels required to transport fuel gas and air along the stack. The bipolar plate assembly is made from metal plates joined together with canals between the plates for cooling.

[0005] US Patent Application Publication No. 2005 / 079400 to Sugiura and US Patent Application Publication No. 2002 / 0122970 to Inoue disclose molding gaskets onto bipolar assemblies. However, while this can provide good long-term sealing, it is a complicated and expensive solution. US Patent No. 8,865,362 to Korsgaard, assigned to Serenergia A / S, discloses grooves in which a gasket is placed to secure the gasket. Korean International Patent Application WO 2013 / 069888 discloses a fuel cell assembly in which a gasket is provided with protrusions along edge regions that fit into respective grooves.

[0006] Providing long term stability for the gasket also poses challenges in manufacturing since the gasket must be molded or precisely positioned onto the plate. It would be desirable to provide further improvements in the long term stability of gaskets on bipolar plates and ease of assembly during manufacturing. Summary of the Invention

[0007] The object of the present invention is to provide improvements in the art, in particular to provide an improved gasket for a bipolar plate BPP and an improved manufacturing method. This object is achieved by the assembly of a fuel cell stack, a BPP and a gasket, as well as a method for providing a sealing around a bipolar plate, as described in the independent claims and below.

[0008] The assembly includes a BPP and a gasket for the BPP. Typically, multiple such assemblies are stacked to form part of a fuel cell stack with ion exchange membranes between adjacent BPPs, particularly proton conducting membranes.

[0009] For example, the BPP comprises an anode side and a cathode side that are integrally provided as part of a bipolar plate for a fuel cell stack. Alternatively, the anode and cathode plates are combined with the bipolar plate by attaching them back-to-back to each other, for example by gluing or welding, with an enclosed coolant flow field therebetween. An example of such a coolant flow field is a channel, for example a meander-shaped channel.

[0010] For BPP, various materials and manufacturing methods are possible. For example, metal plates, such as steel plates, are pressed into the correct shape with projections by corresponding presses. Alternatively, the plates used are produced by milling or molding. Examples of materials in the latter case are graphite, graphite-containing polymers, ceramics, metals and metal alloys.

[0011] For each BPP, a sealing non-conductive polymer gasket is provided, such that one gasket is located between two adjacent BPPs to gasket the volume between the membrane and its adjacent BPP.

[0012] Each BPP has an edge region along the outer periphery of the BPP. The gasket abuts and covers this edge region and extends circumferentially along the periphery of the BPP to protect the edge of the corresponding BPP and to thermally and electrically insulate the BPP. In some practical embodiments, the gasket extends along the outer periphery of only one of the BPPs such that an equal number of gaskets are provided as BPPs to cover the edges of all the BPPs.

[0013] In some embodiments, the fuel cell is of a type that operates at high temperatures. The term "high temperature" is a term commonly used and understood in the fuel cell art, and refers to an operating temperature above 120°C, as opposed to low temperature fuel cells that operate at lower temperatures, e.g., 70°C. Optionally, the fuel cell operates in a temperature range of 120-200°C. The gasket is correspondingly manufactured from a polymeric material that is resistant to such temperatures.

[0014] The gasket is made from a deformable, preferably elastic, polymer so that pressure during assembly of the stack causes the polymer to deform and provide a reliable seal between the BPPs.

[0015] For example, the gasket is made of a fluoropolymer. Examples are fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE), or perfluoroalkoxy polymer (PFA). Fluoropolymers offer a high degree of long-term stability even when made very thin.

[0016] Advantageously, the gasket is formed from an elastically extensible material, such as an elastomeric polymer. Fluorinated elastomers, such as fluorinated carbon-based synthetic rubbers, including fluoroelastomers FKM and perfluoroelastomers FFKM, or fluorinated silicones are particularly useful.

[0017] For example, to provide a tight connection to the BPP, the gasket is provided with an inner perimeter that is smaller than the outer perimeter of the BPP, such that the gasket must be preloaded by stretching before mating to the edge of the BPP. The gasket is held in place on the edge of the BPP by elastically contracting the gasket around the perimeter. For example, the inner perimeter of the gasket is 1-5% shorter than the outer perimeter of the BPP.

[0018] Typically, the stack comprises a canal extending from one end of the stack to the opposite end for the flow of gas or coolant through the canal. In practice, a number of such canals are provided for the coolant and the gases used in the reaction. In the stack, such canals are formed by stacked canal segments, each canal segment being provided as an opening extending through the corresponding BPP. Such openings have rims that define the interior volume of the canal segment.

[0019] In some embodiments, to fix two adjacent BPPs relative to each other, a gasket extends around the periphery of one BPP, for example around the periphery of only one of the BPPs, inside the canal section of the adjacent BPP, where the gasket abuts at least a portion of the rim of the corresponding canal section of the adjacent BPP. As the gasket abuts the outer periphery of one BPP and the inner periphery of the canal of the adjacent BPP, the two adjacent BPPs are locked together at the sides, ensuring their proper position in the stack. As a result, this locking of each of the two subsequent BPPs to each other locks the BPPs of the entire stack in a fixed position defined by the gaskets.

[0020] In a practical embodiment, the gaskets of adjacent BPPs of a stack abut closely against one another to form an outer seal along the stack.

[0021] Due to the fact that the gaskets surround the BPPs of the stack, the stack is electrically insulated from the surroundings. Optionally, each gasket includes a probe opening for receiving an electrical probe to measure the potential of the various BPPs for diagnostic purposes. The probe opening extends from the outside of the gasket through the gasket to the BPPs, and the voltage of the PBBs is measured by the probe. For example, the probe opening of the gasket extends along its outer periphery to a BPP adjacent to the BPP surrounded by the gasket.

[0022] The gasket provides a seal between the probe opening and the gas flow field to prevent leakage through the probe opening. Optionally, the gasket includes ribs that closely abut the BPP between the probe opening and the flow field and / or the BPP includes protrusions that sealingly abut the gasket.

[0023] In some generally advantageous embodiments, the gasket comprises one or more ribs against a first side of the BPP, and the BPP comprises a protrusion or protrusions on the first side, the ribs and protrusions being arranged side by side and parallel to the periphery, the ribs being spaced farther from the periphery than the protrusions so as to prevent the protrusions from passing through the rim from the protrusions towards the periphery and to prevent the gasket from sliding outwardly away from the periphery.

[0024] Such projections are advantageously provided prior to assembly of the anode and cathode plates into a BPP, for example by pressing into the material with a tool acting on one side of such plates, resulting in the formation of projections on the opposite side. In this way, both the cathode and anode plates can be provided with projections prior to assembly into the BPP, so that the BPP ultimately has projections on both sides.

[0025] Optionally, the gasket has a first part that fits around the outer periphery of the only BPP and a second part that extends between two adjacent BPPs. Advantageously, the second part is provided with a rib on the opposite side so that it is prevented from escaping by the projection from both of the two adjacent BPPs. For example, the two parts form a first leg and a second leg of an L-shaped gasket when viewed in a cross section provided as a cut through the gasket material perpendicular to the edge. For sealing purposes, the gasket advantageously extends between two adjacent BPPPs and surrounds the canal section to seal it.

[0026] As mentioned above, typically the BPP includes flow patterns on both sides of the BPP for hydrogen flow on one side and oxygen flow on the other side. Advantageously, each gasket extends sealingly around one of the flow patterns of the BPP to prevent gas escape along the periphery. A membrane can seal the flow patterns of the adjacent BPP. Optionally, a membrane is provided between the gasket and the BPP, with each gasket directly abutting a surface of the BPP on one side and contacting the membrane on the other side.

[0027] Prior to being attached to the stack, the bipolar plates are optionally provided as a single assembly of bipolar plate and gasket, where the gasket is placed on the BPP, for example by stretching as described above, so that it abuts and covers the edges and extends around the periphery of the BPP to protect the edges. Each such single assembly can then be safely transported to a location where a selected number of such BPP / gasket assemblies are combined into a fuel cell stack having a desired number of BPP / gasket combinations.

[0028] For example, the fuel cell of the fuel cell system may be a high temperature polymer electrolyte membrane fuel cell (HT-PEM), which operates at temperatures above 120°C, as opposed to low temperature PEM fuel cells which operate at temperatures below 100°C, e.g., 70°C. The normal operating temperature of an HT-PEM fuel cell is in the range of 120°C to 200°C, e.g., 160°C to 170°C. The polymer electrolyte membrane PEM in an HT-PEM fuel cell is mineral acid based, typically a polymer membrane, e.g., polybenzimidazole doped with phosphoric acid. HT-PEM fuel cells can advantageously tolerate relatively high CO concentrations, and therefore do not require a PrOx reactor between the reformer and the fuel cell stack, allowing the use of a simple, lightweight and inexpensive reformer, thereby minimizing the size and weight of the overall system, with the aim of providing a compact fuel cell system, e.g., for the automotive industry.

[0029] The invention will now be described with reference to the drawings. [Brief description of the drawings]

[0030] [Figure 1A] The assembly of the BPP and gasket is shown. [Figure 1B] 2 shows an enlarged corner region of FIG. [Figure 2A] 13 shows the extension of the gasket into the canal. [Figure 2B] The canal of FIG. 2A is shown from the opposite side. [Diagram 3] FIG. 2 is an enlarged cross-sectional view of the gasket. [Figure 4] 1 shows the probe passage in the gasket. [Diagram 5] FIG. 13 is a view of the probe passage when open. [Figure 6] Shows the gasket ribs and BPP protrusions. [Figure 7] Details of the BPP are shown below. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] FIG. 1A shows an assembly 1 of a bipolar plate 2, a BPP and a gasket 3, which for illustrative reasons is only half shown. In reality, the gasket 3 extends around the entire circumference of the BPP 2 along its edge 5. The gasket 3 has several functions, including: - Shock resistance, - protection of the edges of the BPP during assembly, - electrical insulation, - Thermal insulation, -Easy relative positioning of BPPs during stacking, - Maintaining the position of the BPPs relative to each other, - prevention of delamination or gradual movement of the gasket which may cause leakage; - Access to the BPP by electrical probe, despite its airtightness.

[0032] Advantageously, the gasket 3 is manufactured slightly shorter than the perimeter around the BPP so that it has to be stretched to fit snugly around the edge 5. This makes assembly easier and the gasket 3 holds itself in place on the BPP 2.

[0033] For example, the perimeter of the BPP is 1-5% longer than the length along the circumference of the gasket. Typically, the BPP is rectangular, as are gaskets having two first gasket portions and two second gasket portions that combine to form a rectangle, where the first portions are longer than the second portions. Optionally, the long edge 5A of the BPP is 1.5% longer than the corresponding long portion 3A of the gasket 3, so that the mounting gasket 3 is first mounted around the short edge 5B of the rectangular BPP, and then extends parallel to the long edge 5A of the BPP 2 to fit snugly around the opposing short edge 5B of the BPP 2.

[0034] To provide good stretching capabilities, the gasket is advantageously made from an elastomeric material, with fluorinated elastomers, such as fluorinated carbon-based synthetic rubbers, including fluoroelastomers FKM and perfluoroelastomers FFKM, or fluorinated silicones being particularly useful.

[0035] The BPPs 2 have a flow channel pattern 4 on either side for air flow to supply oxygen to one side of the membrane and hydrogen fuel to the other side of the membrane. A membrane is provided between each pair of stacked BPPs. Air and hydrogen fuel as well as refrigerant are transported through the stack through corresponding canals 6.

[0036] To more easily appreciate the extension of the gasket, a corner 2A of the assembly 1 of FIG. 1a is shown in an enlarged grayscale image in FIG. 1B, where the gasket 3 has a darker shade than the BPP. It can be seen that the gasket 3 not only extends around the edge 5 of the BPP 2, but also includes a raised collar 7 that grips the canal portion 6A of adjacent BPPs 2 in the stack of BPPs 2 to fix the position of the two adjacent BPPs 2 relative to each other. The latter is shown for a stack of two BPPs in FIG. 2A. By using such a gasket 3, each BPP 2 is provided with a raised collar 7 to fix the position of the BPPs in the entire stack. In FIG. 2B, the corner 2A is shown from the opposite side.

[0037] FIG. 3 shows the abutment of the gasket 3 against the BPP 2 in more detail. The cross section of the long part 3A of the gasket 3 is generally L-shaped with the short leg 9A and the long leg 9B at a right angle. The short leg 9A abuts against the periphery 5 of the BPP 2, while the long leg 9B forms a spacer between two adjacent BPPs. Inside the right angle formed by the two legs 9A, 9B, a set of first longitudinal ribs 8A extends from the long leg 9B. Correspondingly, a set of second longitudinal ribs 8B extends from the opposite side of the long leg 9B. The first rib 8A is illustrated as being rounded, but this is typically also true for the second rib 8B, unless it is pressed against the abutting BPP, which is why the second rib is illustrated as having a flat surface against the BPP 2.

[0038] Also shown in Figure 3 is a fuel cell membrane 14 for transporting hydrogen ions between the electrodes of the BPP 2. In Figure 6, the fuel cell membrane 14 is shown in darker shading. As illustrated, the gasket abuts directly against a surface of one BPP on a first gasket side and directly against a membrane on an opposing gasket side.

[0039] As the gasket 3 is elastic and surrounds the edge 5 of the BPP 2 along its periphery, the BPP 2 is protected from damage to the edge 5, which is a major advantage. However, access to the BPP should not be hindered, for example to potentially measure the voltage of the BPP for diagnostic purposes. To allow an electrical probe 3 to be inserted between the gasket 3 to contact the BPP, the gasket 3 comprises a probe passage 10 that extends from the outside of the gasket 3 to the BPP 2 behind the gasket 3. As best shown in FIG. 5, the probe passage 10 extends beyond one of the outer second ribs 8B to provide a suitable contact with the BPP 2.

[0040] As shown in Figure 6, the longitudinal rib 8A of the gasket 3 cooperating with the longitudinal projection 11 of the BPP prevents the gasket 3 from sliding outwardly away from the BPP 2. This is important during repeated heating and cooling of the fuel cell. The longitudinal projection 11 of the BPP 2 is located between the edge 5 of the BPP 2 and the location of the longitudinal rib 8A of the gasket 3 when the gasket 3 abuts against the edge 5 of the BPP 2. Optionally, a projection is adjacent the longitudinal rib 8A to hold the gasket 3 in place. A similar projection arrangement is provided on the opposite longitudinal rib 8B of the gasket 3.

[0041] If the BPP has protrusions 11 on the side on which the membrane 14 is provided, the membrane 14 is correspondingly deformed by the protrusions 11, so that the protrusions can still fulfill the purpose of preventing parts of the gasket 3 from escaping from their dedicated position.

[0042] For example, the BPP 2 is provided as a pair of anode and cathode plates that are bonded together to form the BPP. An example is shown in Figure 7. Apart from the flow patterns for hydrogen and oxygen gas, typically air, for the fuel cell, a coolant flow pattern is also provided between the anode plate 16 and the cathode plate 17, which is provided to efficiently cool the BPP.

[0043] FIG. 7 illustrates the passages 13 entering the BPP2 from the canals 6. As shown in FIG. 1A, there are three canals 6 near either narrow edge 5B of the BPP2. A passage 13 as shown in FIG. 7 is connected to each canal 6. One of the six canals 6 supplies the coolant to the channel flow pattern provided between the anode plate 16 and the cathode plate 17. Another of the six canals 6 is used for exhaust of the coolant from the BPP2. Hydrogen gas from one of the other canals 6 flows into a corresponding set of passages 13 between the anode plate 16 and the cathode plate 17 of the BPP, flows through the openings in the anode plate, and reaches the flow pattern 4 on the outer anode side of the BPP. Similarly, oxygen gas such as air flows from the corresponding canal 6 into the corresponding passages 13 between the anode plate 16 and the cathode plate 17 of the BPP2, and reaches the flow pattern 4 on the outer cathode side of the BPP, through the openings in the cathode plate. Such an opening 15 in flow communication with a set of passages 13 is shown in Figure 4. Correspondingly, there is one canal 6 for water-laden, oxygen-depleted air from the cathode side of the BPP after reaction in the fuel cell, and another canal 6 for the anode exhaust gas.

[0044] Additionally, Figure 7 shows a projection for cooperating with the second longitudinal rib 8B of the gasket shown in Figure 3. Similar projections and cooperating ribs are provided at various other locations on the BPP 2 and gasket 3.

[0045] The protrusions 11 are advantageously provided by pressing a tool against one side of the anode plate 16 and / or cathode plate 17, deforming said plate to accommodate a recess on one side and a corresponding protrusion on the other side. This can be done for metal plates, but also during the shaping of plates made from conductive polymers, in particular carbon-containing polymers.

Claims

1. 1. A fuel cell stack comprising a stack of bipolar plates (BPPs) (2) with an ion exchange membrane (14) between adjacent BPPs (2), each of the plurality of BPPs (2) having an edge region (5) along an outer periphery of the BPP, and a plurality of sealing non-conductive polymer gaskets (3) being provided between each two adjacent BPPs (2), one gasket (3) being provided between the two adjacent BPPs (2) for sealing a volume between the membrane (14) and its adjacent BPP (2) by the gasket (3); the gasket abuts and covers the edge region (5) and extends along and around the periphery of the BPP (2) to protect the edge (5) of the corresponding BPP (2) and to electrically and thermally insulate the BPP (2), the gasket (3) being made from a deformable, elastic polymer configured to deform under pressure during assembly of the stack to provide a reliable seal between the BPPs (2).

2. 2. The stack of claim 1, wherein the gasket (3) is formed from an elastically stretchable material having an inner perimeter smaller than an outer perimeter of the BPP, the gasket (3) being preloaded by stretching to fit around an edge (5) of the BPP (2) and held in place by elastic contraction of the gasket (3) around said perimeter.

3. The stack of claim 2, wherein the inner circumference of the gasket (3) is 1-5% shorter than the outer circumference of the BPP (2).

4. 4. The stack according to claim 1, wherein the stack comprises a canal (6) extending from one end to an opposite end of the stack for flow of gas or refrigerant therethrough, the canal (6) being formed by stacked canal segments (6A), each canal segment (6A) being an opening extending through a corresponding BPP (2), the opening having a rim defining an interior volume of the canal segment (6A), and the gasket (3) extends around a circumference of only one of the plurality of BPPs (2) and extends with a portion (7) into the canal section (6A) of an adjacent BPP (2) and abuts against a portion of the rim of the corresponding canal section (6A) to fix two adjacent BPPs (2) relative to each other.

5. 4. The stack according to any one of claims 1 to 3, wherein the gaskets (3) of adjacent BPPs (2) in the stack abut against each other to form an outer seal along the stack.

6. 4. The stack of claim 1, wherein each gasket (3) comprises a probe opening (10) for receiving an electric probe, the probe opening (10) extending from the outside of the gasket (3) through the gasket (3) to a BPP (2) for measuring the voltage of the PBB (2) by the probe.

7. 7. The stack of claim 6, wherein the probe opening (10) extends to a BPP (2) adjacent the BPP, and the gasket (3) covers the periphery.

8. 4. The stack of any one of claims 1 to 3, wherein the gasket (3) comprises a rib (8A) against a first side of the BPP (2), the rib (8A) also made from the deformable, elastic polymer, the BPP comprising a protrusion (11) on the first side, the rib (8A) and the protrusion (11) being arranged side by side parallel to the perimeter, the rib (8A) being located further away from the perimeter than the protrusion (11), the protrusion (11) preventing the rim (8A) from passing from the protrusion (11) towards the perimeter and preventing the gasket (3) from sliding outwards in a direction away from the perimeter.

9. 9. The stack of claim 8, wherein the circumferential gasket (3) has a first portion (3A) that fits around only one BPP (2) and a second portion (3B) that extends between two adjacent BPPs (2), the second portion (3B) including ribs (8A, 8B) on opposite sides such that it is prevented from escaping by protrusions (11) from both of the two adjacent BPPs (2).

10. 10. The stack according to claim 9, wherein the two parts (3A, 3B) form a first leg (9A) and a second leg (9B) of an L-shaped gasket (3) when viewed in cross section in a plane perpendicular to the edge (5).

11. The stack according to any one of claims 1 to 3, wherein the gasket (3) extends between two adjacent BPPs (2) and surrounds the canal section (6A) to seal the canal section (6A).

12. 4. A stack according to any one of claims 1 to 3, wherein the BPP (2) on either side is provided with a flow pattern (4) for hydrogen flow on one side and oxygen flow on the other side, the gasket (3) extending sealingly around one of the flow patterns to prevent escape beyond an edge (5) of the BPP (2).

13. An assembly of a bipolar plate (BPP) (2) and a gasket (3) for a stack according to any one of claims 1 to 12, wherein the BPP has an edge region (5) along a periphery around the BPP (2), 1. An assembly comprising: a gasket (3) that abuts and covers said edge (5) and extends along the periphery of said BPP (2) for protection and sealing of said edge (5); said gasket (3) is made from an elastically stretchable material having an inner periphery smaller than the outer periphery of said BPP (2); said gasket (3) is preloaded by stretching to fit around the periphery of the edge (5) of said BPP (2) and is held in place by elastic contraction of said gasket (3) around said periphery; and said inner periphery of said gasket (3) is 1-5% shorter than the outer periphery of said BPP (2).

14. Assembly according to claim 13, in which the gasket (3) along the periphery (5) of the BPP (2) has a first part (3A) that fits around the periphery of only one BPP (2) and a second part (3B) that extends between two adjacent BPPs (2), said two parts (3A, 3B) being made from an elastically extensible polymer and, when viewed in a cross section perpendicular to the edge (5), forming a first leg (9A) and a second leg (9B) of an L-shaped gasket (3), said second leg (9B) including a rib (8A) also made from said elastically extensible polymer.

15. 1. A method of providing sealing around bipolar plates (BPPs) (2) for a fuel cell stack comprising a plurality of stacked bipolar plates (2) with an ion exchange membrane (14) between adjacent BPPs (2), each of the plurality of BPPs (2) having an edge (5) area along an outer periphery of the BPP (2), the method comprising providing a plurality of sealing non-conductive polymer gaskets (3) and disposing one gasket (3) between each two adjacent BPPs (2) to seal a volume between the membrane (14) and its adjacent BPP (2) with the gasket (3), 13. The method of claim 12, further comprising: providing a gasket (3) of elastically stretchable polymeric material having an inner perimeter smaller than the outer perimeter of the BPP (2); and preloading the gasket (3) by stretching when placing the gasket (3) on the BPP (2) so that the gasket (3) fits around an edge (5) of the BPP (2) and is held in place by elastic contraction of the gasket (3) around said perimeter, the gasket (3) abutting and covering the edge (5) area of ​​the BPP (2) and extending along and around the perimeter of the BPP (2) to protect the corresponding edge (5) of the BPP (2) and to electrically insulate the BPP (2), the inner perimeter of the gasket (3) being 1-5% shorter than the outer perimeter of the BPP (2).

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