Electrode materials

Abstract

The present invention relates to a method for producing an electrode material for a gas diffusion layer, the electrode material produced thereby, and its use.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an electrode material for a gas diffusion layer, an electrode material manufactured thereby, and its use. [Background technology]

[0002] A gas diffusion layer (GDL) is a highly porous conductive material based on carbon or metal, primarily used in polymer electrolyte fuel cells (PEMFCs), metal-air batteries, electrochemical reactors, and electrolytic cells. GDLs containing electrocatalytic active components are called gas diffusion electrodes (GDEs).

[0003] The main roles of a gaseous or liquid fuel (hydrogen, methanol) and an oxidizer (oxygen) are to supply gaseous or liquid fuel (hydrogen, methanol) and an oxidizer (oxygen) to the electrochemically active layer, to dissipate electric current and heat, and to remove reaction products. Carbon-based GDLs generally consist of a macroporous electrode material containing carbon fibers. This electrode material is hydrophobized with a fluoropolymer, and one side has a microporous layer (MPL) of carbon particles and fluoropolymer (generally polytetrafluoroethylene, PTFE). The MPL partially penetrates the macroporous electrode material.

[0004] Macroporous electrode materials are manufactured by weaving carbon fibers or by nonwoven fabric processes (dry or wet lamination nonwoven fabric technology). Currently, GDLs are almost entirely based on carbon fiber nonwoven fabrics, with woven fabrics playing only a secondary role.

[0005] To manufacture GDL electrode materials, a primary nonwoven fabric is produced from carbon fibers and a binder, or from a carbon fiber precursor, and then this nonwoven fabric is carbonized. In industrial practice, substantially two different methods are used to manufacture the primary nonwoven fabric. A) Dry laminated nonwoven fabric from precursor fibers Here, nonwoven fabrics are manufactured using water-flow entanglement (spunlace technique) from crimped staple fibers made of polyacrylonitrile (PAN) or oxidized polyacrylonitrile, typically with finenesses of 0.8 dtex to 4 dtex and fiber lengths of 30 mm to 70 mm. These nonwoven fabrics are then further carbonized to give carbon fiber nonwoven fabrics, where prior thermal stabilization occurs if PAN is used as a precursor fiber. Carbonization causes a shrinkage of approximately 10% to 15% of the nonwoven fabric. B) Wet-laid nonwoven fabric technology using carbon short fibers (paper manufacturing) Here, carbon short fibers made of polyacrylonitrile (PAN), with typical fiber lengths of 3 mm to 15 mm, are dispersed and processed by an inclined wire paper machine with the help of an aqueous dispersion of binder fibers or binder polymer to form a nonwoven fabric. Afterward, optionally, a carburable resin is impregnated, and the resin matrix is ​​cured by subsequent carbonization.

[0006] Patent Document 1 describes a process based on Method A, which uses crimped pre-oxidized polyacrylonitrile staple fibers having a length of 40 mm to 80 mm to which polyvinyl alcohol-based binder fibers are added. The polyvinyl alcohol-based binder fibers flow due to the influence of temperature and moisture (water flow entanglement). The primary nonwoven fabric is compressed by a calender and subsequently carbonized.

[0007] The pathway according to Method B is based on carbon short fibers having a length of 6 mm to 12 mm, which are treated with a thermoplastic binder to form paper. The primary nonwoven fabric ("paper") generally has a low weight (<30 g / m²). 2 ), they have low mechanical stability. These can be impregnated with a carburable resin, such as a phenolic resin, and then re-carbonized to improve electrical and thermal conductivity and increase strength. (Patent Document 2).

[0008] Patent Document 3 describes a method based on Method B (paper process) using carbon short fibers and fibrillated or pulverized polyacrylonitrile fibers as a binder. The polyacrylonitrile fibers are added by metering to a suspension of fibrous raw materials. After the formation of the nonwoven fabric, the web is compressed under the influence of heat by a double belt press.

[0009] The manufacturing method described in Patent Document 4 uses a dry or wet lamination process in which the binder is introduced, in particular, in the form of uncured phenolic resin fibers (e.g., Noboroid® (uncured phenolic resin fibers)). The electrode material is obtained by thermal crosslinking under pressure and then carbonization.

[0010] Fuel cells for automotive applications require increasingly thin gas diffusion layers (<200 μm) due to their high current density, which involves limited structural space and demanding tolerances and homogeneity for thickness. This is because the fuel cell stack consists of up to 400 individual cells, and therefore, if the variation in GDL thickness is relatively large (compared to the remaining components), problems with uniform compression and stack dimensions can arise.

[0011] The drawback of Method B is that, especially in the case of carbon fiber paper, an impregnation process is required after the paper manufacturing process, which involves additional process steps and cost factors. This is particularly related to the costs of dispersion and drying, as well as longer process cycles. In addition, if the impregnation of the filler or binder resin is not carried out uniformly, the impregnation process can sometimes lead to non-uniformity. Furthermore, in the classical manufacturing method, where the impregnated material is not compressed, the volume fraction of fibers is too low, making it impossible to produce thin substrates with sufficient mechanical stability. During the operation of a fuel cell, water may preferentially accumulate in the binder matrix, which is detrimental as it degrades the performance of the battery; therefore, a high fiber content or a low binder content is desirable. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] European Patent No. 1328947 [Patent Document 2] U.S. Patent No. 7144476 [Patent Document 3] European Patent Application Publication No. 1502992 [Patent Document 4] European Patent No. 2089925 [Overview of the project] [Problems that the invention aims to solve]

[0013] Therefore, an object of the present invention is to provide an alternative method for manufacturing electrode material for a gas diffusion layer with reduced thickness, which avoids additional process steps and thus cost disadvantages. [Means for solving the problem]

[0014] According to the present invention, this objective is achieved by providing a method for manufacturing an electrode material for a gas diffusion layer, comprising the following steps: a) A step of providing at least one layer of fiber structure, b) A step of providing at least one layer of thermoplastic material, c) stacking at least one fibrous structure from step a) with at least one thermoplastic material from step b), d) The step of joining the stacked layers from step c) by applying a pressure of 2 bar to 80 bar and a temperature of 70°C to 280°C to the composite material, and e) A step of carbonizing the composite material from step d) in a protective gas atmosphere at a temperature of 1400°C to 2500°C.

[0015] The advantage of the method according to the invention is that an impregnation step of the fibrous structure is not required in the further production of the electrode material, and as a result, a simpler and more cost-effective method is provided. This is because a composite made of at least one layer of fibrous structure and at least one layer of thermoplastic material is formed by joining the layers under the influence of temperature and pressure to form a composite material, so that the thermoplastic material penetrates the fibrous structure and thus impregnation is not required. Further, the thermoplastic material is provided with a carbonizable resin and / or a carbon-based filler, whereby the porosity of the carbonized material can be adjusted. Further, the electrode material is more stable and has a higher fiber volume content. The method according to the invention can be carried out either in a continuous process or in a batch process. In a continuous process (roll-to-roll process), a sheet of fibrous structure and a thermoplastic material are used. In contrast, sheet products are used in a batch process. The continuous process is preferred as the process time is thus shortened. The stacking of the layers described in step c) can be carried out in any order without any limitation on the number of layers. However, two and three layers are preferred. The composite is obtained by the influence of heat and pressure in step d) using a double punch press, a laminating system, a double belt press or calendering. As the protective gas used in step e), any protective gas such as argon or nitrogen can be used.

[0016] Within the scope of the present invention, the fibrous structure is understood to mean a non-woven fabric of short fibers or staple fibers, and fiber fabrics also fall within the fibrous structures. The short fibers have a length of 1 mm to 20 mm, and the staple fibers have a length of 30 mm to 80 mm. The fabric is a woven cloth (textile fabric), and the latter has at least two yarn systems that do not run parallel and thus cross each other. The non-woven fabric is understood to mean a structure made of short fibers or staple fibers produced by wet lamination or dry lamination.

[0017] In an advantageous embodiment, at least one layer of the fibrous structure from step a) is a carbon fiber non-woven fabric or a carbon fiber woven fabric. The carbon fiber non-woven fabric can be obtained by various methods such as the melt-blown method, the spunlace method, or the wet lamination method.

[0018] In an advantageous embodiment, at least one layer of the fibrous structure has a thickness of 50 μm to 400 μm, preferably 100 μm to 250 μm. When the thickness is less than 50 μm, the fibrous structure is too unstable and more difficult to handle, and when the fibrous structure is thicker than 400 μm, compression becomes more difficult. Here, since the ratio of stability to compression performance is particularly preferable, a thickness range of 100 μm to 200 μm is preferred.

[0019] According to the present invention, at least one layer of the thermoplastic material from step b) is selected from the group consisting of polyethylene (low-density polyethylene (LDPE), high-density polyethylene (HDPE)), polypropylene (PP), ethylene-vinyl acetate copolymer (EVA), polyvinyl butyral (PVB), cellulose acetate (CA), polyvinyl alcohol (PVA), vinyl pyrrolidone-vinyl acetate copolymer, styrene-maleic anhydride copolymer (styrene-maleic anhydride (SMA)), thermoplastic elastomer (thermoplastic polyolefin (TPO), styrene block copolymer (TPS)), preferably polyvinyl butyral, cellulose acetate, or polyvinyl alcohol. Polymers having a hydroxyl group or an anhydride group are preferred. This is because they can undergo a condensation reaction with the resin or can crosslink by themselves.

[0020] The thermoplastic material is advantageously formed as a film or a woven structure. Since the material is a sheet-like material, the method can be implemented as a continuous process, so films and woven structures are preferred.

[0021] Advantageously, the thermoplastic material has a thickness of 10 μm to 300 μm, preferably 20 μm to 75 μm. Thermoplastic materials with a thickness of less than 10 μm are not commercially available, and thermoplastic materials thicker than 300 μm reduce the stability of the substrate and impair compression. A range of 50 μm to 250 μm is preferred because it results in a favorable ratio of fibrous structure to thermoplastic material. In a more advantageous embodiment, at least one layer of thermoplastic material is coated with a carburable resin and / or carbon material. Since the carburable resin is converted to carbon during carbonization, the coating results in an increased carbon yield. The resin and carbon material may be in the form of powder, suspension, dispersion, or solution. Suspensions, dispersions, or solutions can be applied by dip coating, spray, screen printing, squeegee, curtain coating, roller coating, prepreg technology, or inkjet printing. Powdered materials can be applied by spraying. The mechanical properties of the electrode material can be controlled by coating, and the coating also contributes to eliminating the need for an impregnation process in the further manufacture of the electrode material.

[0022] Advantageously, the resin is selected from the group consisting of phenolic resins, melamine resins, resorcinol resins, cyanate ester resins, and vinyl ester resins. The resin has a particularly high carbon yield. The carbon material is advantageously selected from the group consisting of molasses, bitumen, graphite, carbon black, activated carbon, crushed carbon fibers, coal tar pitch, or coke particles.

[0023] In a more advantageous embodiment, the coating includes a crosslinking additive (1% to 5% based on the proportion of thermoplastic material). The crosslinking additive increases the carbon yield of the thermoplastic component, thereby resulting in an electrode material with improved stability and conductivity.

[0024] Advantageously, the crosslinking additive is selected from the group consisting of organic peroxides, dialdehydes, diamines, or UV-curable polymers. The crosslinking additive has a particularly high carbon yield.

[0025] In a more advantageous embodiment, the composite in step d) is further irradiated with ionizing radiation or UV radiation (ultraviolet radiation).

[0026] As a result, carbon yield can be increased, leading to higher conductivity in the electrode material.

[0027] A further subject of the present invention is electrode materials manufactured by the method according to the present invention.

[0028] An advantage of electrode materials is that they reduce contact resistance within the battery, particularly due to their smooth surfaces. Furthermore, a high fiber volume in electrode materials means that water accumulation is significantly reduced, resulting in higher battery output, while simultaneously increasing thermal and electrical conductivity, which also contributes to higher battery conductivity. A higher fiber volume content also results in higher material stiffness, or a higher shear modulus. This reduces the penetration of electrode material into the bipolar plate channels within the battery. This has the advantage of reducing contact resistance and minimizing the concentration of liquid water within the bipolar plate channels.

[0029] In a preferred embodiment, the electrode material has a thickness of 50 μm to 500 μm, preferably 70 μm to 200 μm. In yet another preferred embodiment, the electrode material has a thickness of 0.1 g / cm³. 3 ~0.6g / cm 3 Preferably 0.15 g / cm³ 3 ~0.40g / cm 3 It has a density of [value]. The selected thickness of the electrode material provides desirable stability, and the selected density of the electrode material ensures the pore space that is important for GDL.

[0030] Yet another subject of the present invention is the use of electrode materials in polymer electrolyte fuel cells, phosphate fuel cells, microbial fuel cells, electrochemical reactors, oxygen depolarized cathodes (ODCs), metal-air batteries, PEM electrolytic cells, or batteries.

[0031] The present invention will be described below simply as an example, with reference to advantageous embodiments and the accompanying drawings. [Brief explanation of the drawing]

[0032] [Figure 1] The method according to the present invention is shown. [Figure 2] The method according to the present invention is shown. [Figure 3] This shows a thermoplastic material having a coating. [Figure 4] This shows a substrate having two layers. [Figure 5] This shows a substrate having three layers. [Figure 6] This shows a substrate having three layers. [Modes for carrying out the invention]

[0033] Figure 1 shows the method according to the present invention. First, a thermoplastic film (1) is coated with a dispersion (2) to obtain a film web (4) having the coating. Using multiple heated calenders or belt presses (7, 8), two film webs (4) having the coating are combined with a carbon fiber nonwoven fabric (6) to form a composite (9). In the next step, the composite (9) is then carbonized in a protective gas atmosphere in a continuous furnace (10) to form an electrode material (11).

[0034] Figure 2 further shows crosslinking of thermoplastic polymers by ionizing radiation or UV radiation (12).

[0035] Figure 3 shows a coated thermoplastic material (4) according to the present invention, in which the coating (5) is applied to the thermoplastic material (1).

[0036] Figure 4 shows a two-layer electrode material according to the present invention, in which a coating (5) of thermoplastic material (1) is adjacent to a layer of carbon fiber nonwoven fabric (6).

[0037] Figure 5 shows a three-layer electrode material according to the present invention, where the layer order is a thermoplastic material (1) with a coating (5), a carbon fiber nonwoven fabric (6), and another thermoplastic material (1) with a coating (5), and in each case, the coating (5) is adjacent to the carbon fiber nonwoven fabric (6).

[0038] Figure 6 shows a three-layer electrode material according to the present invention, with the layers in the order of carbon fiber nonwoven fabric (6), thermoplastic material having a coating (5), and carbon fiber nonwoven fabric (6).

[0039] The present invention will be described below with reference to exemplary embodiments, but these exemplary embodiments do not define any limitations of the present invention.

[0040] The manufacturing of prosthesis components can be carried out as described below.

[0041] [Exemplary Embodiment 1] Dissolve or suspend 1.5 parts novolac phenol resin (Bakelit, Hexion) and 1 part synthetic graphite (d50=4μm) in 1.5 parts ethanol. Coat a polyvinyl butyral film (Trosifol®, Kuraray, 50μm) (wet film thickness 40μm) using the squeegee method with this viscous dispersion. Subsequently, coat the coated polyvinyl butyral film and carbon fiber nonwoven fabric (23g / m²) with a squeegee. 2 A two-layer composite is manufactured by hot pressing (160°C, 5 bar) (layer order: film | carbon fiber nonwoven fabric | film). Subsequently, this composite is carbonized at a temperature of 1400°C in a protective gas atmosphere.

[0042] [Exemplary Embodiment 2] Dissolve or suspend 150 g of novolak phenol resin (Bakelit PF0227 SP, Hexion), 100 g of crushed carbon fiber (Sigrafil® CM80, SGL Carbon) and 100 g of phenol-modified indenemaleic resin (Novar CA80, Rutgers) in 150 g of acetone. Coat the viscous dispersion onto a polyvinyl butyral film (Trosifol®, Kuraray, 50 μm) (wet film thickness 50 μm) using the squeegee method. Subsequently, a two-layer composite of the coated polyvinyl butyral film and carbon fiber non-woven fabric (23 g / m 2 ) is produced by hot pressing (layer order: film | carbon fiber non-woven fabric | film). Thereafter, the composite is carbonized at a temperature of 1400 °C in a protective gas atmosphere.

[0043] [Exemplary Embodiment 3] Coat a polyethylene film (HDPE, 50 μm, Folienwerk Lahr) with a dispersion of phenol resin (10 parts) and acetylene black (5 parts) in isopropanol (18.5 parts) on a desk coater and dry at 80 °C. The coating amount was 10 g / m 2 . Produce a composite consisting of a layer of carbon fiber structure (23 g / m 2 ) between two layers of the coated film using a high-temperature calendar machine (180 °C, 10 bar). Here, the coating is directed towards the carbon fiber structure in each case. Subsequently, carbonize at 1700 °C in a protective gas atmosphere.

[0044] [Exemplary Embodiment 4] By continuous pressing (140 °C, 5 bar), a layer of carbon fiber non-woven fabric (18 g / m 2 ) is laminated and has films based on ethylene-vinyl acetate copolymer (TecWeb®, 20) on both sides in each case. Subsequently, electron irradiation (dose 150 Gy) is performed to crosslink the polymer. Thereafter, the composite is carbonized at a temperature of 1750 °C in a protective gas atmosphere.

[0045] The following table outlines exemplary embodiments.

[0046] [Table 1]

[0047] The following table shows the physical properties of exemplary embodiments compared to commercially available reference materials (Sigracet® GDL 29 AA and Sigracet® GDL 28 AA) based on established techniques. The electrode material according to the present invention is found to have properties comparable to those of the reference material at thinner thicknesses. Surface resistivity was measured according to DIN 51911-1997, and longitudinal and transverse bending strengths were measured according to ISO 5628-2019.

[0048] [Table 2] [Explanation of symbols]

[0049] 1 Thermoplastic film 2 Dispersion 3 rollers 4. Thermoplastic materials with coatings 5 Coating 6. Carbon fiber nonwoven fabric 7. High-temperature calender or belt press 8. High-temperature calender or belt press 9 Complex 10 furnace 11 Electrode materials 12 Ionizing radiation or UV radiation

Claims

1. A method for manufacturing electrode material for gas diffusion layer, a) The step of providing at least one layer of fiber structure, b) A step of providing at least one layer of thermoplastic material, wherein the at least one layer of thermoplastic material is formed as a film, c) Laminating the at least one fiber structure from step a) with the at least one thermoplastic material from step b) to obtain a laminated layer, d) A step of obtaining a composite material by joining the laminated layers in step c) by applying a pressure of 2 bar to 80 bar and a temperature of 70°C to 280°C, wherein the thermoplastic material penetrates the at least one layer of fibrous structure. e) The step of carbonizing the composite material from step d) in a protective gas atmosphere at a temperature of 1400°C to 2500°C, The at least one fibrous structure from step a) is a carbon fiber nonwoven fabric or a carbon fiber fabric, A method comprising coating the at least one layer of thermoplastic material with a carburable resin and / or carbon material.

2. The method according to claim 1, wherein the at least one fibrous structure from step a) has a thickness of 50 μm to 400 μm.

3. The method according to claim 1, wherein the at least one layer of thermoplastic material from step b) is selected from the group consisting of polyethylene, polypropylene, ethylene-vinyl acetate copolymer, polyvinyl butyral, cellulose acetate, polyvinyl alcohol, vinylpyrrolidone-vinyl acetate copolymer, styrene-maleic anhydride copolymer, and thermoplastic elastomers.

4. The method according to claim 1, wherein the at least one layer of thermoplastic material from step b) is selected from the group consisting of polyethylene, polyvinyl butyral, and cellulose acetate.

5. The method according to claim 1, wherein the at least one layer of thermoplastic material has a thickness of 10 μm to 300 μm.

6. The method according to claim 1, wherein the carbonizable resin is selected from the group consisting of phenolic resin, melamine resin, resorcinol-formaldehyde resin, phenol-modified hydrocarbon resin, benzoxazine resin, cyanate ester resin, vinyl ester resin, furan resin, polyimide, polyoxadiazole, and polyacrylonitrile.

7. The method according to claim 1, wherein the carbon material is selected from the group consisting of molasses, bitumen, coal tar pitch, graphite, carbon black, activated carbon, crushed or cut carbon fibers, and coke particles.

8. The method according to claim 1, wherein the at least one layer of thermoplastic material is further coated with a crosslinking additive.

9. The method according to claim 8, wherein the crosslinking additive is selected from the group consisting of organic peroxides, dialdehydes, diamines, and ultraviolet crosslinking polymers.

10. The method according to claim 1, wherein in step d), the composite material is further irradiated with ionizing radiation or ultraviolet radiation.

11. The method according to any one of claims 1 to 10, wherein the electrode material for the gas diffusion layer is used in a polymer electrolyte fuel cell, a phosphoric acid fuel cell, a microbial fuel cell, an electrochemical reactor, an oxygen reduction cathode, a metal-air battery, a PEM electrolytic cell, or a battery.

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