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
  • H01M4/88—Processes of manufacture
  • H01M4/8878—Treatment steps after deposition of the catalytic active composition or after shaping of the electrode being free-standing body
  • H01M4/8892—Impregnation or coating of the catalyst layer, e.g. by an ionomer
• • 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
  • H01M4/88—Processes of manufacture
  • H01M4/8803—Supports for the deposition of the catalytic active composition
  • H01M4/8807—Gas diffusion layers
• • 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
  • H01M4/88—Processes of manufacture
  • H01M4/8817—Treatment of supports before application of the catalytic active composition
• • 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
  • H01M4/88—Processes of manufacture
  • H01M4/8825—Methods for deposition of the catalytic active composition
  • H01M4/8828—Coating with slurry or ink
  • H01M4/8835—Screen printing
• • 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
  • H01M4/88—Processes of manufacture
  • H01M4/8878—Treatment steps after deposition of the catalytic active composition or after shaping of the electrode being free-standing body
  • H01M4/8882—Heat treatment, e.g. drying, baking
• • 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
  • H01M4/90—Selection of catalytic material
  • H01M4/92—Metals of platinum group
  • H01M4/925—Metals of platinum group supported on carriers, e.g. powder carriers
  • H01M4/926—Metals of platinum group supported on carriers, e.g. powder carriers on carbon or graphite
• • 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
  • H01M4/90—Selection of catalytic material
  • H01M4/92—Metals of platinum group
  • H01M4/928—Unsupported catalytic particles; loose particulate catalytic materials, e.g. in fluidised state
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1004—Fuel cells with solid electrolytes characterised by membrane-electrode assemblies [MEA]
• • 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
  • H01M4/88—Processes of manufacture
  • H01M4/8817—Treatment of supports before application of the catalytic active composition
  • H01M4/8821—Wet proofing
• • 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
• • 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
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• the invention relates to a gas diffusion electrode for use in PEM fuel cells and to a method for its production.
• the production method is intended, in particular, to make possible hydrophobicization of the gas diffusion electrode.
• the core of a PEM fuel cell is a membrane electrode unit that is built up from a membrane with an electrode that is coated on both sides and includes an electrocatalyst layer.
• the electrode normally has a solid, gas-permeable and electrically conductive carrier (e.g., carbon fabric or carbon paper), which is preferably hydrophobicized with a polymer suspension (in the following text, the polymer will be called polymer A, which here concerns polymers such as PTFE, i.e., polytetrafluoroethylene, TEFLON®).
• a polymer A which here concerns polymers such as PTFE, i.e., polytetrafluoroethylene, TEFLON®.
• Applied to the carrier is an electrocatalyst layer that, in turn, is again hydrophobicized. Therefore, the polymer A can be contained both in the carrier and in the electrocatalyst layer.
• the electrode can contain a further polymer as binder, which, in the present connection, is designated poly
• polymer A for hydrophobicizing the electrocatalyst layer has generally been 20-60% by weight.
• the polymer A for hydrophobicizing the electrocatalyst layer can also be referred to as a “catalyst inhibitor”.
• the wetting agent is used to compensate for the poor processing properties that arise from the high content of polymer A in the screen-printing paste.
• the mixture is then pulverized.
• the method is very complicated, and a uniform thickness of the electrocatalyst layer in low layer thicknesses may be produced technically only with great difficulty and in low numbers.
• disadvantages with the method include:
• a wetting agent for the purpose of processing, a wetting agent must be added, which has to be removed specifically and leaves behind interfering residues.
• the prior art discloses gas diffusion electrodes for use in electrochemical cells. See, for example, U.S. Pat. No. 4,568,442 to Goldsmith, and U.S. Pat. No. 4,615,954 to Solomon et al. In such a case, the surface of a gas diffusion electrode is to be hydrophobic, with a polymer proportion of 30% being viewed as suitable. See, in particular, the example in U.S. Pat. No. 4,615,954 to Solomon et al.
• the proportion of TEFLON® used for hydrophobicization in the screen-printing paste, and, therefore, that which is present in the resulting electrocatalyst layer is about 25% by weight.
• the paste is printed onto a solid carrier, for example, carbon paper, which again contains 60% by weight of TEFLON®.
• the result is a total content of TEFLON® of about 85%.
• the drawback with the electrode produced by such a method in addition to the extremely high content of polymer A for hydrophobicizing the electrocatalyst layer (here: TEFLON®), is also the wetting agent added to more than 50% by weight (of the catalyst paste).
• a gas diffusion electrode for a PEM fuel cell including a metallic catalyst, and an electrocatalyst layer having a polymer A for hydrophobicizing the electrocatalyst layer, a content of the polymer A being less than 10% by weight based on a content of the metallic catalyst, and a uniform thickness of between 3 to 40 ⁇ m.
• a method of producing a gas diffusion electrode for a PEM fuel cell including the steps of screen printing a screen-printing paste onto a carrier, the screen-printing paste including at least one metallic catalyst with a content of polymer A up to at most 10% by weight, and a screen-printing medium, and removing the screen-printing medium by heating.
• the subject of the invention is a gas diffusion electrode for a PEM fuel cell having an electrocatalyst layer having a content of hydrophobicizing polymer A of less than 10% by weight and a uniform thickness of the electrocatalyst layer of less than or equal to 20 ⁇ m. Also, the invention relates to a gas diffusion electrode that is produced by a screen-printing process with a screen-printing paste that includes a polymer A content for hydrophobicizing the electrocatalyst layer of at most 10% (based on the content of metallic catalyst), at least one metallic catalyst, and a high-boiling solvent.
• the invention further relates to a method for producing a gas diffusion electrode in which, in the screen-printing process, a catalyst paste that includes at least one metallic catalyst and a screen-printing medium is printed onto an electrode and/or a membrane, and the screen-printing medium is removed by heating in a following, second operation.
• the invention relates to a method for hydrophobicizing a gas diffusion electrode in which a ready-coated electrode is dipped into a solution of the polymer A for hydrophobicization.
• the invention also relates to using a gas diffusion electrode according to the invention in a fuel cell.
• the electrocatalyst conveyor and/or the screen-printing paste (based on their content of metallic catalyst) contain only 0.01 to 1% by weight, preferably, 0.05 to 0.5% by weight, particularly, 0.075 to 0.2% by weight, and, in particular, 0.1% by weight of polymer A for hydrophobicizing the electrocatalyst layer.
• the polymer A for hydrophobicizing the electrocatalyst layer is TEFLON®, in particular, an amorphous modification of TEFLON® that can be brought into solution.
• the metallic catalyst used is platinum black or platinum on carbon.
• the high-boiling solvent used in the screen-printing and/or catalyst paste is an ester and/or a ketone and/or an alcohol, in particular, glycolic acid butyl ester, cyclohexanone, and/or terpineol.
• the catalyst paste apart from the metallic catalyst and the high-boiling solvent, also has added to it as binder a polymer B, preferably, a polymer that can be baked out to 400° C.
• the content of the polymer A in the electrocatalyst layer for hydrophobicizing the electrocatalyst layer approaches zero, with zero being ruled out.
• the polymer A can be omitted completely from the screen-printing paste, the hydrophobicization of the finished electrocatalyst layer is carried out after the screen-printing coating by dipping the complete electrode into a solution of the hydrophobicizing polymer A.
• the solution contains the polymer A preferably at 0.01 to 1% by weight, particularly preferably, 0.05 to 0.5% by weight, and, quite particularly, preferably 0.075 to 0.2% by weight, in particular, 0.1% by weight.
• the solvent is a perfluorinated solvent like a completely fluorinated organic compound that, for example, can be produced by the electrochemical fluorination of alkanes.
• the electrode is dried in a further operation, preferably at temperatures between 20° C. and 120° C.
• a carbon paste including electrically conductive carbon black and screen-printing medium is first printed onto the carrier.
• the printing produces the very first screen-printed coating of the carrier with carbon. Only following the drying of the first screen-printed coating is the screen printing with the—considerably more expensive—catalyst paste carried out.
• the carrier is precoated with a carbon paste of electrically conductive carbon black prior to the screen-printing step.
• both the carbon paste of the first screen-printing operation and the carrier, or both can additionally contain polymer A.
• the total content of polymer A in the gas diffusion electrode is conceptually separated from the critical content of “polymer A for hydrophobicizing the electrocatalyst layer” because the designation listed is understood to mean only the quantity of polymer A that is applied to the electrocatalyst layer by the dip bath and/or through the screen-printing paste.
• the total content of polymer A in the gas diffusion electrode (that is to say, the content of polymer A in the carrier, in the first screen-printed layer, and in the electrocatalyst layer together) advantageously adds up to up to 20% by weight, preferably, to less than 15% by weight, particularly preferably, to less than 10% by weight, quite particularly preferably, to less than 5% by weight and, in particular, to less than 3.5% by weight.
• the polymer A preferably used is TEFLON®, in particular, a modification that is present in amorphous and/or transparent form and may be dissolved completely in fluorinated solvents.
• TEFLON® a modification that is present in amorphous and/or transparent form and may be dissolved completely in fluorinated solvents.
• a different polymer such as ethylene propylene copolymer or a different fluorine-containing polymer, e.g., polyvinylidene fluoride (PVDF) can also be used.
• PVDF polyvinylidene fluoride
• the electrocatalyst layer referred to here is the layer that is preferably applied to a solid, gas-permeable and electrically conductive carrier of the electrode, and on whose catalytic surface the anodic oxidation of the fuel to protons or the cathodic reduction of the oxygen takes place.
• the electrocatalyst layer includes at least the metallic catalyst, which preferably contains platinum and can be used in pure form as platinum black or in diluted form as platinum on carbon in the catalyst paste.
• the electrocatalyst layer preferably contains no further constituents because, according to the preferred embodiment of the invention, the screen-printing medium that is added to the catalyst paste for processing has been removed by drying and heating the finished, that is to say, coated, electrode.
• the “uniform electrocatalyst layer thickness” referred to here is a layer 3-40 ⁇ m thick, which has been applied by a conventional screen-printing process and whose thickness fluctuation is generally below that which can be achieved with a different coating technique for fuel-cell electrodes.
• the screen-printing paste (also called carbon or catalyst paste, depending on the operation) has added to it at least a high-boiling solvent as a screen-printing medium, such as an ester, ketone, and/or an alcohol, in particular, glycolic acid butyl ester, cyclohexanone, and/or terpineol.
• a high-boiling solvent such as an ester, ketone, and/or an alcohol, in particular, glycolic acid butyl ester, cyclohexanone, and/or terpineol.
• a screen-printing medium it is not only a high-boiling solvent that is added but also, as a binder, a polymer B, such as polyvinyl alcohol and/or polyethylene oxide.
• a polymer B such as polyvinyl alcohol and/or polyethylene oxide.
• the polymer B can be baked out, in particular, at temperatures up to 400° C., or leaves behind only residues that do not interfere with the operation of the fuel cell.
• the electrode is a gas-permeable, electrically conductive layer on the membrane, which preferably includes a carrier with an electrocatalyst layer.
• the carrier or substrate used is, preferably, a carbon fabric or a carbon paper or another porous and electrically conductive substrate.
• the carbon or catalyst powder is added to a screen-printing medium, made of polyethylene oxide dissolved in terpineol, for example, while stirring.
• the content of binder is 0 to 20% by weight, preferably, 5 to 15% by weight.
• the catalyst used is platinum black or platinum on carbon.
• Screen printing is carried out with a commercially available screen-printing machine. Stainless-steel screens with a size of up to 760*700 mm 2 are used, with a mesh width of 100 to 300 meshes per inch (about 39 to 118 meshes per cm). Using the latter, wet layer thicknesses from 6 to 60 ⁇ m per printing operation can be achieved. Virtually any desired areas are coated per printing operation, limited by the size of the printable area of the screen-printing machine. Following the printing operation, the electrodes are dried at 120° C. and baked out at 360° C. in order to remove the binder.
• the platinum covering determined by weighing is 2-3 mg/cm 2 if pure platinum black is used as the catalyst and 0.15 to 0.4 mg/cm 2 if platinum on carbon is used as the catalyst, depending on the platinum covering of the carbon.
• the ready-coated gas diffusion electrode is dipped into a solution of a polymer A for hydrophobicizing the electrocatalyst layer and is then dried. Any desired gas diffusion electrode can be hydrophobicized retrospectively in this way.
• the present screen printing method makes it possible to reduce the costs for electrode production considerably. Using the screen-printing process, a uniform layer thickness is achieved over the entire electrode, even in the case of large electrodes (e.g., 36*36 cm 2 ), as well as good reproducibility during mass production. Because the hydrophobicization is carried out only at the conclusion of the method, if at all, by dipping the complete electrode into a solution of the polymer A, the processing properties (and the bake-out behavior) of the screen-printing pastes are not impaired by the polymer suspension and additional wetting and dispersion agents, which tend to coagulate and/or foam.
• the electrocatalyst layer advantageously contains only 0.01 to 0.5% by weight, preferably, 0.05 to 0.3% by weight, particularly preferably, 0.075 to 0.2% by weight, and, in particular, 0.1% by weight of polymer A for hydrophobicizing the electrocatalyst layer, instead of 20 to 60% by weight as hitherto.
• 0.1% by weight of polymer A for hydrophobicizing the electrocatalyst layer instead of 20 to 60% by weight as hitherto.
• the invention replaces the previous hydrophobicization technique in gas diffusion electrodes of fuel cells.
• the ready-coated electrode is dipped into a hydrophobicization bath.
• the particular advantage of such a gas diffusion electrode is, in addition to having a low polymer A content, also an improved homogeneity of the layer thickness because the electrocatalyst paste can be processed better in the screen-printing process without the addition of polymer A.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Sustainable Development (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Energy (AREA)
• Composite Materials (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Inert Electrodes (AREA)
• Printing Methods (AREA)
• Fuel Cell (AREA)
• Superconductors And Manufacturing Methods Therefor (AREA)
• Inks, Pencil-Leads, Or Crayons (AREA)

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• 1999
  • 1999-08-20 WO PCT/DE1999/002620 patent/WO2000013242A2/de active IP Right Grant
  • 1999-08-20 CN CNB99812561XA patent/CN1195336C/zh not_active Expired - Fee Related
  • 1999-08-20 ES ES99953554T patent/ES2214895T3/es not_active Expired - Lifetime
  • 1999-08-20 DE DE59908263T patent/DE59908263D1/de not_active Expired - Lifetime
  • 1999-08-20 EP EP99953554A patent/EP1118130B1/de not_active Expired - Lifetime
  • 1999-08-20 CA CA2341494A patent/CA2341494C/en not_active Expired - Lifetime
  • 1999-08-20 JP JP2000571099A patent/JP4707834B2/ja not_active Expired - Fee Related
  • 1999-08-20 AT AT99953554T patent/ATE257621T1/de not_active IP Right Cessation
  • 1999-08-20 CN CNB998125601A patent/CN1173426C/zh not_active Expired - Fee Related
  • 1999-08-20 AT AT99953556T patent/ATE415713T1/de not_active IP Right Cessation
  • 1999-08-20 JP JP2000571098A patent/JP4792160B2/ja not_active Expired - Fee Related
  • 1999-08-20 WO PCT/DE1999/002622 patent/WO2000013243A2/de active Application Filing
  • 1999-08-20 CA CA2341495A patent/CA2341495C/en not_active Expired - Lifetime
  • 1999-08-20 DE DE59914914T patent/DE59914914D1/de not_active Expired - Lifetime
  • 1999-08-20 ES ES99953556T patent/ES2315020T3/es not_active Expired - Lifetime
  • 1999-08-20 EP EP99953556A patent/EP1118129B1/de not_active Expired - Lifetime
• 2001
  • 2001-02-26 US US09/793,329 patent/US6645660B2/en not_active Expired - Lifetime
  • 2001-02-26 US US09/793,411 patent/US20010018145A1/en not_active Abandoned

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