Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/8605—Porous electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
  • H01B1/04—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors mainly consisting of carbon-silicon compounds, carbon or silicon
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B13/00—Apparatus or processes specially adapted for manufacturing conductors or cables
  • H01B13/0016—Apparatus or processes specially adapted for manufacturing conductors or cables for heat treatment
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• the present invention relates to a method for producing an electrode material for gas diffusion layers, the electrode material produced using this method and its use.
• GDLs Gas diffusion layers
• PEMFCs polymer electrolyte fuel cells
• metal-air batteries metal-air batteries
• electrochemical reactors electrolyzers
• GDLs which additionally contain electrocatalytically active components, are referred to as gas diffusion electrodes (GDEs).
• the core task of the GDL is the supply of the electrochemically active layers with gaseous or liquid fuels (hydrogen, methanol) and with oxidants (oxygen) as well as the dissipation of electricity and heat or the removal of reaction products.
• Gaseous or liquid fuels hydrogen, methanol
• oxidants oxygen
• Carbon-based GDLs usually have a macroporous electrode material comprising carbon fibers, which is made hydrophobic with fluoropolymers and has a micro-porous layer (MPL) made of carbon particles and fluoropolymers (usually polytetrafluoroethylene, PTFE) on one side .
• MPL micro-porous layer
• the macroporous electrode materials are manufactured either by weaving carbon fibers or by non-woven processes (dry or wet non-woven technology).
• Today's GDLs are based almost exclusively on nonwovens made from carbon fibers, while woven fabrics only play a subordinate role.
• a primary fleece is made from carbon fibers and binders, or a primary fleece is made from carbon fiber precursors and this fleece is then carbonized.
• a primary fleece is made from carbon fiber precursors and this fleece is then carbonized.
• A) Dry laying of nonwovens made of precursor fibers Here, webs are produced from crimped staple fibers made from polyacrylonitrile (PAN) or oxidized polyacrylonitrile with a typical fiber titre of 0.8 to 4 dtex and a fiber length of 30 to 70 mm using water jet bonding (spunlace technology). These fleeces are then further carbonized into carbon fiber fleeces, with prior thermal stabilization taking place when PAN is used as a precursor fiber. The carbonization causes the fleece to shrink by around 10 to 15%.
• PAN polyacrylonitrile
• oxidized polyacrylonitrile with a typical fiber titre of 0.8 to 4 dtex and a fiber length of 30 to 70 mm using water jet bonding (spunlace technology).
• These fleeces are then further carbonized into carbon fiber fleeces, with prior thermal stabilization taking place when PAN is used as a precursor fiber. The carbonization causes the fleece to shrink by around 10 to 15%.
• short-cut carbon fibers made of polyacrylonitrile (PAN) with a typical fiber length of 3 to 15 mm are dispersed and applied using an inclined wire paper machine with the aid of binder fibers or aqueous dispersions of binder polymers fleece processed. This is followed by optional impregnation with carbonizable resins and hardening of the resin matrix with subsequent carbonization.
• PAN polyacrylonitrile
• EP1328947B1 describes a process based on method A with crimped, preoxidized polyacrylonitrile staple fibers having a length of 40 to 80 mm with the addition of binding fibers based on polyvinyl alcohol. The latter flow as a result of the effects of temperature and moisture (hydroentanglement). These primary fleeces are compacted using calenders and then carbonized.
• Routes according to Method B are based on short-cut carbon fibers with a length of 6 to 12 mm, which are processed into paper using thermoplastic binders.
• These primary fleeces usually have a low grammage ( ⁇ 30 g/m 2 ) and are mechanically less stable.
• carbonizable resins eg phenolic resins and carbonized again (US7144476B2).
• EP1502992A1 describes a method based on method B (paper process) with short-cut carbon fibers and using fibrillated or ground lenen polyacrylonitrile fibers as a binding substance. The latter are added to the pulp suspension. After the formation of the non-woven fabric, the web is compressed under the influence of heat using double-belt presses.
• Production methods according to EP 2089925B1 use dry or wet laying processes in which the binder is introduced in the form of uncured phenolic resin fibers (for example Novoloid® (uncured phenolic resin fibers)).
• An electrode material is obtained by thermal crosslinking under the action of pressure with subsequent carbonization.
• fuel cells for automotive use increasingly require thinner gas diffusion layers ( ⁇ 200 ⁇ m) with high requirements in terms of thickness tolerances and homogeneity. This has to do with the fact that these fuel cell stacks consist of up to 400 individual cells, and problems with regard to uniform compression and stack dimensioning can therefore arise with relatively large fluctuations in thickness of the GDL (compared to the other components).
• the disadvantage of method B is that, especially in the case of carbon fiber papers, impregnation processes are required after the paper production process, which require additional process steps and cost factors. This relates in particular to the effort involved in dispersing and drying and the longer process cycles.
• the impregnation processes can sometimes lead to inhomogeneities if the impregnation with fillers or binder resins is uneven.
• classic manufacturing processes without compression of the impregnated material do not allow the production of thin substrates with sufficient mechanical stability, since the fiber volume fraction is too low.
• a high proportion of fibers or a low proportion of binder is desirable, since during fuel cell operation water accumulation can occur preferentially on the binder matrix, which is disadvantageous since this reduces the performance of the cell.
• the object of the present invention is therefore to provide an alternative method for producing an electrode material for gas diffusion layers with a small thickness provide, which prevents the disadvantages of additional process steps and thus costs.
• this object was achieved by providing a method for producing an electrode material for gas diffusion layers, which comprises the following steps: a) providing at least one layer of fiber structures, b) providing at least one layer of thermoplastic material, c) stacking the at least one layer Fibrous structure from step a) with at least one layer of thermoplastic material from step b) d) connecting the stacked layers from step c) by applying a pressure of 2 to 80 bar and a temperature of 70 to 280 °C to form a composite material, and e) carbonization of the composite material from step d) at temperatures of 1400 to 2500° C. under a protective gas atmosphere.
• the advantage of the method according to the invention is that no impregnation steps of the fiber structure are necessary in the further production of the electrode material, so that a simpler and more cost-effective method is made available.
• the reason for this is that by forming a composite of at least one layer of fiber structure and at least one layer of thermoplastic material, by connecting the layers under the influence of temperature and pressure to form a composite material, the thermoplastic material penetrates into the fiber structure, making impregnation superfluous will.
• the thermoplastic material is equipped with carbonizable resins and/or carbon-based fillers, as a result of which the porosity of the carbonized material can be adjusted.
• the electrode material described is more stable and has a higher fiber volume content.
• the method according to the invention can be carried out either as a continuous or batch process.
• continuous process roll-to-roll process
• sheet material is used in the batch process.
• the continuous process is preferred because it reduces process times.
• Stacking of the tiers can be in any order, with no limit to the number of tiers. However, two and three layers are preferred.
• the composite is obtained by the action of heat and pressure in step d), which is done by means of double stamp presses, laminating systems, double belt presses or calendering.
• Any protective gas, such as argon or nitrogen, can be used for the protective gas used in step e).
• fiber structures are understood to mean nonwovens made from short fibers or staple fibers, with fiber fabrics also counting among the fiber structures.
• Short fibers have a length of 1 mm - 20 mm and staple fibers have a length of 30-80 mm.
• Woven fabrics are textile fabrics that have at least two thread systems that do not run parallel and thus intersect.
• a non-woven fabric is a structure made of short fibers or staple fibers that are produced by wet laying or dry laying.
• the at least one layer of fiber structure from step a) is a carbon fiber fleece or a carbon fiber fabric.
• the carbon fiber nonwovens can be obtained using various processes such as meltblown, spunlace or wet-laid processes.
• the at least one layer of the fiber structure has a thickness of 50 ⁇ m to 400 ⁇ m, preferably 100 ⁇ m to 250 ⁇ m. With a thickness of less than 50 ⁇ m, the fibrous structure is too unstable, so that handling is made more difficult, and with a thickness of the fibrous structure greater than 400 ⁇ m, compaction is difficult.
• the thickness range from 100 ⁇ m to 200 ⁇ m is preferred, since the relationship between stability and the possibility of compression is particularly favorable here.
• the at least one layer of 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 copolymers (EVA), polyvinyl butyral (PVB), cellulose acetate (CA), polyvinyl alcohol (PVA), vinylpyrrolidone-vinyl acetate copolymers, styrene-maleic anhydride copolymers (styrene-maleic anhydride (SMA)) or thermoplastic elastomers (thermoplastic polyolefins (TPO ), Styrene block copolymers (TPS)), preferably selected polyvinyl butyral, cellulose acetate or polyvinyl alcohol.
• Polymers with hydroxyl or anhydride groups are preferred, since these enter into condensation reactions with resins or are themselves capable of crosslinking reactions.
• thermoplastic material is advantageously in the form of a film or textile structure.
• Foil and textile structures are preferred because the material is in the form of a web, so that the process can be carried out as a continuous process.
• the thermoplastic material has a thickness of 10 ⁇ m to 300 ⁇ m, preferably 20 ⁇ m to 75 ⁇ m.
• Thermoplastic material with a thickness smaller than 10 ⁇ m is not commercially available and thicker than 300 ⁇ m reduces the stability of the substrate and densification is deteriorated.
• the range from 50 ⁇ m to 250 ⁇ m is preferred, since this results in a preferred ratio of fiber structure to thermoplastic material.
• the at least one layer of thermoplastic material is coated with carbonizable resins and/or carbon materials. The coating increases the carbon yield, because the carbonizable resins convert to carbon during carbonization.
• the resins and carbon materials can be in the form of powders, suspensions, dispersions or solutions.
• Suspensions, dispersions or solutions can be applied by dip coating, spraying, screen printing, knife coating, curtain coating, roller application, prepreg technology or inkjet printing. Powdery substances can be applied by sprinkling.
• the mechanical properties of the electrode material can be controlled by the coating and the coating also contributes to the fact that an impregnation step is not necessary in the further production of the electrode material.
• the resins are advantageously selected from the group consisting of phenolic resins, melamine resins, resorcinol resins, cyanoester resins, and vinylester resins
• the carbon materials are advantageously selected from the group consisting of molasses, bitumen, graphite, soot, activated carbon, ground carbon fibers, coal tar pitch or coke particles.
• the coating comprises crosslinking additives (1-5% based on the proportion of thermoplastic material).
• the carbon yield of the thermoplastic components is increased by the crosslinking additives and an electrode material with improved stability and conductivity is thereby obtained.
• the crosslinking additives are advantageously selected from the group consisting of organic peroxides, dialdehydes, diamines and UV-curable polymers.
• crosslinking additives have a particularly high carbon yield.
• the assembly is additionally irradiated with ionizing radiation or UV radiation in step d).
• the carbon yield can be increased, which creates a higher conductivity of the electrode material.
• a further object of the present invention is an electrode material which has been produced using the method according to the invention.
• the advantage of the electrode material is that it has a particularly smooth surface, so that contact resistances within the cell are reduced.
• the high fiber volume content of the electrode material significantly reduces the accumulation of water, so that the cell has a higher output and, on the other hand, increases the thermal and electrical conductivity, which also leads to a higher conductivity of the cell.
• the higher fiber volume content also causes a higher rigidity or a higher shear modulus of the material. This results in less intrusion of the electrode material into the flow channels of the bipolar plate in the cell. This has the advantage that in turn contact resistances are reduced and there is less accumulation of liquid water in the flow channels of the bipolar plates.
• the electrode material has a thickness of 50 ⁇ m to 500 ⁇ m, preferably 70 ⁇ m to 200 ⁇ m. According to an even more preferred embodiment, the electrode material has a density of 0.1 g/cm 3 to 0.6 g/cm 3 , preferably 0.15 g/cm 3 to 0.40 g/cm 3 .
• the selected thicknesses of the electrode material determine the desired stability and the selected densities of the electrode material ensure a pore space that is important for the GDL.
• Yet another object of the present invention is the use of the electrode material in polymer electrolyte fuel cells, in phosphoric acid fuel cells, microbial fuel cells, electrochemical reactors, oxygen-consuming cathodes, metal-air batteries, PEM electrolyzers or batteries.
• FIG. 1 shows the method according to the invention
• FIG. 2 shows the method according to the invention
• Figure 3 shows a thermoplastic material with a coating
• FIG. 4 shows a substrate with two layers
• FIG. 5 shows a substrate with three layers
• FIG. 6 shows a substrate with three layers
• FIG. 1 shows the method according to the invention.
• a thermoplastic film (1) is coated with a dispersion (2), thereby obtaining a film web with a coating (4).
• Two webs of film with a coating (4) are combined with a carbon fiber fleece (6) to form a composite (9) using a number of hot calenders or belt presses (7, 8).
• the composite (9) then carbonized in a continuous furnace (10) under a protective gas atmosphere to form an electrode material (11).
• FIG. 2 additionally shows the crosslinking of the thermoplastic polymer by ionizing or UV radiation (12).
• FIG. 3 shows a thermoplastic material (4) coated according to the invention, the coating (5) being applied to the thermoplastic material (1).
• FIG. 4 shows a two-layer electrode material according to the invention, the coating (5) of the thermoplastic material (1) adjoining the layer of carbon fiber fleece (6).
• Figure 5 shows a 3-layer electrode material according to the invention, the layer sequence being thermoplastic material (1) with a coating (5), carbon fiber fleece (6), thermoplastic material (1) with a coating (5) and the coating (5th ) in each case adjoins the carbon fiber fleece (6).
• FIG. 6 shows a 3-layer electrode material according to the invention, the sequence of layers being carbon fiber fleece (6), thermoplastic material with coating (5), carbon fiber fleece (6).
• a prosthesis component can be produced as described below.
• novolak phenolic resin (Bakelit PF0227 SP, Hexion), 100 g ground carbon fibers (Sigrafil® CM80, SGL Carbon) and 100 g phenol-modified indene coumarone resin (Novares CA80, Rütgers) are dissolved or suspended in 150 g acetone. died This viscous dispersion is coated onto a polyvinyl butyral film (Trosifol®, Kuraray, 50 ⁇ m) using a doctor blade method (wet film thickness 50 ⁇ m).
• a composite of 2 layers of the coated polyvinyl butyral film and a carbon fiber structure (23 g/m 2 ) is then produced using a hot press (layer sequence film I carbon fiber structure I film). This composite is then carbonized in a protective gas atmosphere at a temperature of 1400°C.
• a polyethylene film (HDPE, 50 ⁇ m, Folienwerk Lahr) is coated with a dispersion of phenolic resin (10 parts), acetylene black (5 parts) in isopropanol (18.5 parts) in a desk coater and dried at 80.degree. The amount applied was 10 g/m 2 .
• a hot calender 180° C., 10 bar
• a composite is produced from one layer of carbon fiber structure (23 g/m 2 ) between 2 layers of the coated film, with the coating being oriented towards the carbon fiber structure in each case. This is followed by carbonization at 1700 °C in a protective gas atmosphere.
• a layer of carbon fiber fleece (18 g/m 2 ) is laminated on both sides with a film based on ethylene-vinyl acetate copolymer (TecWeb®, 20). This is followed by electron irradiation (dose 150 Gy) to crosslink the polymer. The composite is then carbonized in a protective gas atmosphere at a temperature of 1750 °C.
• Electrode materials according to the invention have properties comparable to those of the reference materials with a smaller thickness.
• the area-specific resistance was measured according to DIN 51911-1997 and the longitudinal and transverse bending stiffness according to ISO 5628-2019

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• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Electrochemistry (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Thermal Sciences (AREA)
• Inert Electrodes (AREA)
• Electrodes For Compound Or Non-Metal Manufacture (AREA)
• Hybrid Cells (AREA)
• Fuel Cell (AREA)
• Manufacture Of Metal Powder And Suspensions Thereof (AREA)
• Powder Metallurgy (AREA)

Applications Claiming Priority (2)

Publications (1)

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• 2020
  • 2020-10-26 DE DE102020213461.8A patent/DE102020213461A1/de active Pending
• 2021
  • 2021-10-26 WO PCT/EP2021/079620 patent/WO2022090196A1/de active Application Filing
  • 2021-10-26 CN CN202180073248.9A patent/CN116670865A/zh active Pending
  • 2021-10-26 EP EP21805397.3A patent/EP4233108A1/de active Pending
  • 2021-10-26 JP JP2023525088A patent/JP2023549666A/ja active Pending
  • 2021-10-26 US US18/250,634 patent/US20230395279A1/en active Pending
  • 2021-10-26 CA CA3199942A patent/CA3199942A1/en active Pending
  • 2021-10-26 KR KR1020237017453A patent/KR20230096020A/ko unknown

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