Separator plate

Abstract

The present invention relates to a separator plate, a method for manufacturing a separator plate, and uses of the separator plate.

Description

Technical Field

[0001] The present invention relates to a separator plate, a method for manufacturing a separator plate, and the use of a separator plate.

Background Art

[0002] Separator plates or bipolar plates in proton exchange membrane (PEM) fuel cells, phosphoric acid fuel cells, or redox flow cells are either metal-based or carbon-based. Metal plates are very stable and can be made very thin (<0.2 mm), but it is necessary to protect the metal from corrosion and thus extend the service life of the entire system. Metal plates are often coated with noble metals or carbon / graphite to protect them from corrosion. This approach has the disadvantage of being very costly. Carbon-based plates do not have corrosion problems, but are mechanically unstable and thus have a large wall thickness, generally exceeding 0.6 mm. A large wall thickness adversely affects the structural volume and weight of the entire system, thereby increasing costs due to high production costs of materials and high material usage. In addition, it is advantageous if the separator plate can be manufactured from an infinite material, as a large number of end products are installed, thereby reducing production costs.

[0003] For example, as described in Patent Document 1, carbon fiber paper is known as a primary product for gas diffusion layers in fuel cells or redox flow cells. The method described therein can be implemented in a continuous process. The carbon fiber paper is impregnated with a phenolic resin slurry and then carbonized or graphitized (see Embodiment 1 of Patent Document 1). The carbon fiber paper and the first intermediate product after slurry impregnation and carbonization / graphitization are very porous, i.e., very permeable and have low mechanical stability.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Therefore, an object of the present invention is to provide a separator plate that eliminates the drawbacks of the above-mentioned prior art, as well as its manufacture and use.

Means for Solving the Problems

[0006] The problem is solved by providing a separator plate comprising a single layer of carbon fiber reinforced carbon impregnated with resin, having a continuous conductive carbon network, having a thickness of less than 0.5 mm, preferably 0.1 - 0.3 mm, a tensile strength greater than 30 MPa, preferably exceeding 35 MPa, and particularly preferably exceeding 45 MPa. Thermosetting

[0007] In the context of the present invention, a continuous conductive network is understood to refer to a network that is not interrupted.

[0008] Contact The thickness of the separator plate is understood to refer to the wall thickness. When the thickness is less than 0.5 mm, it is mechanically sufficiently stable, has a low weight, and therefore is advantageous because the required amount of structure in the layer structure of the entire fuel cell is small. When the tensile strength exceeds 30 MPa, the separator plate is mechanically sufficiently stable, and therefore can be manufactured and operated with a small thickness. When the thickness is greater than 0.5 mm, Contact the resistance becomes very large and the entire fuel cell becomes inefficient.

[0009] According to the present invention, the separator plate Contact has a resistance of less than 8 mΩcm 2 and preferably less than 5 mΩcm 2 and particularly preferably less than 3 mΩcm 2 and less.Contact The resistance is 8 mΩcm 2 If it is greater than, the resistance loss becomes excessively large, the fuel cell becomes inefficient, and for example, it is overheated. Contact The measurement of the resistance will be described below.

[0010] The separator plate preferably has a density of less than 1.7 g / cm 3 and preferably less than 1.4 g / cm 3 and particularly preferably less than 1.3 g / cm 3 If the density is greater than 1.7 g / cm 3 it has an adverse effect that the weight of the resulting separator plate increases.

[0011] According to the present invention, the carbon fiber reinforced carbon includes a single layer of a carbon fiber fabric having carbon binder crosslinks between carbon fibers. Thereby, a continuous conductive network is formed by the carbon binder crosslinks between the carbon fibers, so that a particularly thin and high-tensile separator plate can be obtained due to the fiber reinforcement still having good conductivity.

[0012] Advantageously, the carbon fiber fabric is obtained from the group of carbon fiber paper, carbon fiber non-woven fabric, carbon fiber fabric, or staple fiber fabric.

[0013] In the production of carbon fiber paper, a slurry of an aqueous short carbon fiber binder mixture is deposited on a screen in a paper-making machine. After the drying step, the short-cut fibers are combined with each other, and the carbon fibers are aligned in the plane of the paper in a planar orientation (two-dimensional structure). On the other hand, the carbon fiber non-woven fabric is a three-dimensional structure produced by wet or dry storage of short fibers, and this three-dimensional structure is produced by a mechanical strengthening process using needles or water jets. The carbon fiber fabric is a fabric fiber having at least two yarn systems that do not extend parallel and thus cross each other. The staple fiber fabric is a woven yarn made from drawn and twisted filaments.

[0014] According to the present invention, ThermosettingThe resin includes a resin obtained from the group consisting of an epoxy resin, a phenolic resin, a furan resin, or a benzoxazine resin.

[0015] Thermosetting The resin closes the pores of the carbon fiber fabric while maintaining conductivity based on the carbon network. Furthermore, this increases the density and mechanical strength.

[0016] Advantageously, Thermosetting The resin includes a dispersed filler.

[0017] The filler is selected from the group consisting of carbon black, expanded graphite, natural or synthetic graphite, ground carbon fiber, or a mixture thereof. The filler can further increase the conductivity because the continuous conductive carbon network is further expanded by the filler. The filler can also have a favorable effect on the density of the separator plate, for example, by preventing the formation of pores due to better wetting of the carbon network to be impregnated or by forming a toothed layer as a gas barrier in the case of platelet-shaped anisotropic morphology.

[0018] According to the present invention, the mass fraction of the filler is 0% by mass to 40% by mass, preferably 5% by mass to 20% by mass, and particularly preferably 8% by mass to 15% by mass. If it is less than 5% by mass, the conductivity is not high enough, and if it is higher than 40% by mass, the viscosity becomes high, causing problems with the completeness of impregnation.

[0019] Advantageously, the cross-section of the separator plate has a concentration gradient of the filler. This means that the filler can mainly remain on the surface according to the size and shape of the particles and form a concentration gradient. This means that there is a higher concentration of filler in the outer region of the separator plate and a lower concentration of filler in the inner region of the separator plate. The concentration gradient depends on the type of filler, especially the particle size. By the filler mainly remaining on the surface, the density of the separator plate becomes higher, the conductivity is improved, and the contact resistance is reduced.

[0020] The separator plate advantageously has a permeability coefficient of less than 5×10 -5 cm 2 / s, preferably less than 1×10 -5 cm 2 / s. When the permeability coefficient is less than 5×10 -5 cm 2 / s, the separator plate is regarded as a technically dense separator plate, that is, this technical density meets the requirements for use as a separator plate for different gas or liquid spaces.

[0021] According to the present invention, Thermosetting the surface of the carbon fiber reinforced carbon impregnated with resin is structured. This structuring enables a controlled supply of the targeted gas / liquid and the removal of any resulting reaction products. Furthermore, this structuring can be used for water cooling of the stack structure.

[0022] Another subject of the present invention is a method for manufacturing a separator plate, which includes the following steps. a) Providing a carbon fiber fabric b) Impregnating the carbon fiber fabric with a carbon donor c) Heat-treating the impregnated carbon fiber fabric in an inert gas atmosphere where the temperature is higher than 1300 °C, preferably higher than 1700 °C, and particularly preferably higher than 2000 °C d) Thermosetting Providing a resin system e) impregnating the carbon fiber reinforced carbon obtained in step c) with the resin system provided in step d); Thermosetting f) curing and pressing the resin-impregnated carbon fiber reinforced carbon from step e) under a pressure of 1 to 50 bar;

[0023] In the context of the present invention, the carbon donor in step b) is understood to refer to a resin having a carbon yield of more than 20% by mass and additionally capable of being filled with carbon, graphite, or carbon black. The inert gas atmosphere is understood to refer to a nitrogen or argon atmosphere. The impregnation steps b) and e) can be carried out on one side or both sides. Thermosetting The impregnation with the resin system and the curing and pressing in steps e) and f) increase the density and mechanical strength of the carbon fiber reinforced carbon, so that the separator plate can have a very thin configuration.

[0024] Subsequent to step f), advantageously, the surface can be activated by grinding, blasting, chemical treatment, or plasma treatment on both sides. This activation can remove the electrically insulating layer (resin layer) that may be present on the separator plate.

[0025] Advantageously, 0% to 40% by mass, preferably 5% to 20% by mass, particularly preferably 8% to 15% by mass of a filler is dispersed in the thermosetting resin system. The filler can further increase or improve the conductivity and density.

[0026] The pressing step is advantageously carried out using a structured tool. The tool is understood to refer to an embossing roller, a forming roller, or a plate. The structured tool realizes the deformation in the pressing step. The pressing step Thermosetting ​Enable the resin system to further penetrate into the interior of the carbon fiber fabric, allowing the filler to mainly stay on the surface according to the particle size, and form a concentration gradient. This means that the separator plate has a concentration gradient that decreases from the outside to the inside on both sides of the separator plate in cross-section. The concentration gradient depends on the type of filler, especially the particle size. Since the filler mainly stays on the surface, the conductivity can be improved, the contact resistance can be reduced, and the density of the separator plate can be further increased.

[0027] According to the present invention, the method can be implemented as a continuous method or a batch method. In particular, a continuous method is advantageous.

[0028] Another subject is the use of the separator plate in a redox flow battery or a fuel cell or as an electrode for an electrostatic air cleaning device.

[0029] Hereinafter, purely by way of example, the present invention will be described with reference to the accompanying drawings according to advantageous embodiments.

Brief Description of the Drawings

[0030]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Best Mode for Carrying Out the Invention

[0031] Figure 1 shows Thermosetting a separator plate (4) comprising a single layer of carbon fiber reinforced carbon (1) impregnated with a resin (2).

[0032] Figure 2 shows Thermosetting a separator plate (4) comprising a single layer of carbon fiber reinforced carbon (1) impregnated with a resin (2) and having a filler (3). Due to the properties of the filler, a concentration gradient is created such that the filler penetrates only slightly into the porous carbon fiber reinforced carbon (1).

[0033] Figure 3 shows Thermosetting a separator plate (4) comprising a single layer of carbon fiber reinforced carbon (1) impregnated with a resin (2) and having a filler (3). Due to the various particle sizes of the filler, smaller particles penetrate further into the carbon fiber reinforced carbon (1) than larger particles.

[0034] Figure 4 shows Thermosetting a SEM image of the porous carbon fiber reinforced carbon (1) before being sealed using a resin system. The carbon binder cross-links between the carbon fibers can be clearly seen. The combination of the fibers and the binder cross-links forms a continuous conductive network.

[0035] Figure 5 shows a micrograph of the separator plate according to the present invention, in which the filler is accumulated in the outer region and the filler concentration is lower towards the inside.

[0036] Diagram 1 shows the Contact resistance based on the surface pressure. (At low surface pressures) initially high Contact resistance not only represents the pure material resistance but also clearly reflects a significant portion of the contact resistance. As the surface pressure increases, the contact resistance decreases and the measured ContactThe resistance is dominated by the contribution of the material resistance. In the range where the surface pressure is 1 to 1.5 MPa, a substantially steady Contact resistance level is reached. A surface pressure level of 1 MPa generally corresponds to the actual application conditions in a fuel cell stack. Diagram 1 shows Embodiment 1 together with the reference measurement values of the external GDL (gas diffusion layer). It can be seen that the additional material layer of the separator plate contributes only a small part to the overall resistance of the sandwich layer structure including two GDL layers.

[0037] Hereinafter, the present invention will be described using embodiments. However, the embodiments do not represent a limitation of the present invention.

[0038] The separator plate can be manufactured as described later.

[0039] Measurement method Contact Resistance Contact To obtain the application-corresponding measurement values for resistance, the obtained cured separator plate is measured in a layer sandwich similar to the configuration in a fuel cell between two gas diffusion layers (GDL 22BB, SIGRACET (registered trademark)). Using the following formula Contact calculate the resistance Rz: Rz = ΔU·A / ΔI

[0040] ΔU is the voltage between the electrodes, A is the surface area of the sample, and ΔI is the current.

[0041] The electrodes are coated with gold to avoid the interfacial resistance that may occur due to the oxidized surface. During the measurement, different contact pressures from 5 psi (US unit) to 1.5 MPa are applied, and at the same time, the layer thickness is determined. In order to determine the influence of the additional material layer made of GDL 22BB, a reference measurement was carried out using only two GDL 22BB layers. Since the material resistances are added in this series connection, the material resistance of the sample can be determined as the difference between the resistance of the GDL 22BB / sample / GDL 22BB layer structure and the reference measurement value of the two GDL 22BB layers.

[0042] Permeability coefficient The permeability coefficient is measured in accordance with DIN 51935:2019-06.

[0043] Strength The strength was determined by a tensile strength test based on DIN EN ISO 13934-1:2013-08. In the standard-compliant test, a beam with a length of 160 mm and a consistent width of 50 mm was used as the test sample shape, and a tapered sample shape was used as a deviation therefrom. The tapered sample shape also had a width of 50 mm and the same free crack length, but the width of the clamping area was 80 mm to avoid fracture within the clamping area.

[0044] Density The geometric density was determined by adding weight to a circular sample with a diameter of 50 mm.

[0045] A single layer of carbon fiber reinforced carbon can be manufactured, for example, as described in Patent Document 1.

[0046] Embodiment 1: One side of a single layer (1) of carbon fiber reinforced carbon with a thickness of 225 μm (commercially available under the name GDL 36 AA, SIGRACET® from SGL Carbon GmbH) measured at a load of 5 psi was coated with an epoxy resin film (2) with a thickness of 180 μm using a film applicator, and 7% by mass of conductive carbon black (Super P commercially available from Imerys Graphite & Carbon) was dispersed in the epoxy resin. Subsequently, the coated single layer was cured in a hot press at a pressure of 32.5 bar and 130 °C for 60 minutes.

[0047] At a pressure of 1 MPa Contact The resistance is 7.8 mΩcm 2 is. The permeability coefficient is 2.2×10 -6 cm 2It is / s. The thickness of the separator plate thus obtained is 210 μm (measured under a load of 5 psi). The geometric density is 1.14 g / cm 3 It is. The tensile strength is 47 MPa.

[0048] Embodiment 2 (Measured under a load of 5 psi) Coat both sides of a single layer of carbon fiber reinforced carbon (1) with a thickness of 225 μm (commercially available under the name GDL 36 AA, SIGRACET® from SGL Carbon GmbH) with an epoxy resin film (2) with a thickness of 130 μm, and disperse 9% by mass of expanded graphite (Sigratherm® GFG5 commercially available from SGL Carbon) in the epoxy resin. Then, cure the coated single layer in a hot press at a pressure of 32.5 bar and 130 °C for 60 minutes.

[0049] At a surface pressure of 1 MPa Contact The resistance is 7.7 mΩcm 2 It is. The permeability coefficient is 1.4×10 -5 cm 2 / s. The thickness of the separator plate thus obtained is 200 μm (measured under a load of 5 psi). The geometric density is 1.18 g / cm 3 It is. The tensile strength is 39 MPa.

[0050] Embodiment 3 (Measured under a load of 5 psi) Coat one side of a single layer of carbon fiber reinforced carbon (1) with a thickness of 225 μm (commercially available under the name GDL 36 AA, SIGRACET® from SGL Carbon GmbH) with an epoxy resin film (2) with a thickness of 180 μm using a film applicator, and disperse 9% by mass of conductive carbon black (Super P commercially available from Imerys Graphite & Carbon) in the epoxy resin. Then, cure the coated single layer in a hot press at a pressure of 32.5 bar and 130 °C for 60 minutes.

[0051] At a pressure of 1 MPa Contact the resistance is 3.8 mΩcm 2 and the permeability coefficient is 5.5×10 -6 cm 2 / s. The thickness of the separator plate thus obtained is 202 μm (measured under a load of 5 psi). The geometric density is 1.04 g / cm 3 .

[0052] Embodiment 4 (Measured under a load of 5 psi) One side of a single layer of carbon fiber reinforced carbon (1) with a thickness of 225 μm (commercially available from SGL Carbon GmbH under the name GDL 36 AA, SIGRACET®) is coated with an epoxy resin film (2) with a thickness of 180 μm, and 10% by mass of a filler is dispersed in the epoxy resin. The 10% by mass is composed of conductive carbon black (Super P commercially available from Imerys) and expanded graphite (Sigratherm® GFG5 commercially available from SGL Carbon) in a ratio of 70 to 30. Then, the coated single layer is cured in a hot press at a pressure of 32.5 bar and 130 °C for 60 minutes.

[0053] At a surface pressure of 1 MPa Contact the resistance is 6.2 mΩcm 2 and the permeability coefficient is 2.2×10 -6 cm 2 / s. The thickness of the separator plate thus obtained is 220 μm (measured under a load of 5 psi). The geometric density is 1.18 g / cm 3 .

[0054] Embodiment 5 One side of a single layer of carbon fiber reinforced carbon (1) with a thickness of 225 μm (measured under a load of 5 psi), commercially available under the name GDL 36 AA, SIGRACET® from SGL Carbon GmbH, is coated with an epoxy resin film (2) with a thickness of 180 μm, and 10% by mass of a filler is dispersed in the epoxy resin. The 10% by mass is composed of conductive carbon black (Super P commercially available from Imerys Graphite & Carbon) and expanded graphite (Sigratherm® GFG5 commercially available from SGL Carbon) in a ratio of 30 to 70. Then, the coated single layer is cured in a hot press at a pressure of 32.5 bar and 130 °C for 60 minutes.

[0055] At a surface pressure of 1 MPa Contact the resistance is 8 mΩcm 2 and is. The permeability coefficient is 3.7×10 -6 cm 2 / s. The thickness of the separator plate thus obtained is 208 μm (measured under a load of 5 psi). The geometric density is 1.04 g / cm 3 and is.

[0056] Embodiment 6: One side of a single layer of carbon fiber reinforced carbon (1) with a thickness of 225 μm (measured under a load of 5 psi), commercially available under the name GDL 36 AA, SIGRACET® from SGL Carbon GmbH, is coated with an epoxy resin film (2) with a thickness of 180 μm using a film applicator, and 7% by mass of conductive carbon black (Super P commercially available from Imerys Graphite & Carbon) is dispersed in the epoxy resin. Then, the coated single layer is cured in a hot press at a pressure of 10 bar and 130 °C for 60 minutes.

[0057] At a pressure of 1 MPa Contact the resistance is 5.4 mΩcm 2 and is. The permeability coefficient is 3.9×10 -6 cm 2 / s. The thickness of the separator plate thus obtained is 205 μm (measured under a load of 5 psi). The geometric density is 1.15 g / cm 3 is.

Explanation of Symbols

[0058] 1 Single layer of carbon fiber reinforced carbon 2 Thermosetting Resin 3 Filler 4 Separator plate

Claims

Separator plate comprising a single layer of carbon fiber reinforced carbon impregnated with a thermosetting resin, having a continuous conductive carbon network, a thickness of less than 0.5 mm, and a tensile strength of more than 30 MPa.

2. 8 mΩ·cm ２ The separator plate according to claim 1, having a contact resistance of less than

3. 1.7 g / cm ３ The separator plate according to claim 1 or 2, having a density of less than

4. The separator plate according to claim 1, wherein the carbon fiber reinforced carbon comprises a single layer of a carbon fiber fabric having a crosslink between carbon and a binder between the carbon fibers.

5. The separator plate according to claim 1 or 2, wherein the thermosetting resin comprises a resin selected from the group consisting of an epoxy resin, a phenolic resin, a furan resin, and a benzoxazine resin.

6. The separator plate according to claim 1 or 2, wherein the thermosetting resin comprises a dispersed filler.

7. The separator plate according to claim 5 or 6, wherein the mass fraction of the filler is more than 0% by mass and 40% by mass or less.

8. 5 × 10 －５ cm ２ The separator plate according to claim 1 or 2, having a transmission coefficient measured in accordance with DIN 51935:2019-06 of less than / s.

9. The separator plate according to claim 1 or 2, wherein the surface of the carbon fiber reinforced carbon impregnated with the thermosetting resin is structured.

10. The separator plate according to claim 6 or 7, wherein the cross section of the separator plate has a concentration gradient of the filler.

11. A method for manufacturing the separator plate according to claim 1, comprising: Step a of providing a carbon fiber fabric; Step b of impregnating the carbon fiber fabric with a carbon donor; Step c of heat-treating the impregnated carbon fiber fabric in an inert gas atmosphere at a temperature higher than 1300 °C; Step d of providing a thermosetting resin; Step e of impregnating the carbon fiber reinforced carbon obtained in step c with the thermosetting resin provided in step d; Step f of curing and pressing the carbon fiber reinforced carbon impregnated with the resin from step e under a pressure of 1 to 50 bar.

12. The method according to claim 11, wherein following step f, the surface is activated by grinding, blasting, chemical treatment, or plasma treatment on both sides.

13. The method according to claim 11 or 12, wherein a filler of more than 0% by mass and 40% by mass or less is dispersed in the thermosetting resin.

14. The method according to claim 11 or 12, wherein the pressing step is carried out using a structuring tool. Use of the separator plate according to any one of claims 1 to 10 in a redox flow battery or a fuel cell or as an electrode for an electrostatic air cleaning device.

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