Classifications

• • 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
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/023—Porous and characterised by the material
  • H01M8/0241—Composites
  • H01M8/0245—Composites in the form of layered or coated products
• • 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
  • 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
  • H01M4/8803—Supports for the deposition of the catalytic active composition
  • H01M4/881—Electrolytic membranes
• • 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
  • H01M4/8885—Sintering or firing
• • 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
  • H01M4/8885—Sintering or firing
  • H01M4/8889—Cosintering or cofiring of a catalytic active layer with another type of layer
• • 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
  • H01M4/8878—Treatment steps after deposition of the catalytic active composition or after shaping of the electrode being free-standing body
  • H01M4/8896—Pressing, rolling, calendering
• • 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
  • H01M2008/1095—Fuel cells with polymeric electrolytes
• • 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
  • H01M4/8663—Selection of inactive substances as ingredients for catalytic active masses, e.g. binders, fillers
  • H01M4/8668—Binders
• • 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
• • 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

• Provisional Patent Application No. 60/ filed April 21, 2006 (formerly U.S. Application No. 11/408,787, converted to provisional by Petition dated April 16, 2007), which provisional application is incorporated herein by reference in its entirety.
• the present invention relates to methods of making components for electrochemical cells, in particular, catalyst-coated membranes, gas diffusion electrodes, and membrane electrode assemblies.
• Electrochemical fuel cells convert fuel and oxidant into electricity.
• Solid polymer electrochemical fuel cells generally employ a membrane electrode assembly that includes a solid polymer electrolyte membrane disposed between two electrodes.
• the membrane electrode assembly is typically interposed between two electrically conductive flow field plates to form a fuel cell.
• These flow field plates act as current collectors, provide support for the electrodes, and provide passages for the reactants and products.
• Such flow field plates typically include fluid flow channels to direct the flow of the fuel and oxidant reactant fluids to an anode electrode and a cathode electrode of each of the membrane electrode assemblies, respectively, and to remove excess reactant fluids and reaction products.
• the electrodes are electrically coupled for conducting electrons between the electrodes through an external circuit.
• a number of fuel cells are electrically coupled in series to form a fuel cell stack having a desired power output.
• the anode electrode and the cathode electrode each contain a layer of anode catalyst and cathode catalyst, respectively.
• the catalyst may be a metal, an alloy or a supported metal/alloy catalyst, for example, platinum supported on carbon black.
• the catalyst layer typically contains an ion conductive material, such as Nation ® , and, optionally, a binder, such as polytetrafluoroethylene.
• Each electrode further includes an electrically conductive porous substrate, such as carbon fiber paper or carbon cloth, for reactant distribution and/or mechanical support. The thickness of the porous substrate typically ranges from about 50 to about 250 microns.
• the electrodes may include a porous sublayer disposed between the catalyst layer and the substrate.
• the sublayer usually contains electrically conductive particles, such as carbon particles, and, optionally, a water repellent material for modifying its properties, such as gas diffusion and water management.
• One method of making membrane electrode assemblies includes applying a layer of catalyst to a porous substrate in the form of an ink or a slurry typically containing particulates and dissolved solids mixed in a suitable liquid carrier. The liquid is then removed to leave a layer of dispersed particulates, thereby forming an electrode.
• An ion-exchange membrane such as a polymer electrolyte membrane, is then assembled with an anode electrode and a cathode electrode contacting opposite surfaces of the membrane such that the catalyst layers of the electrodes are interposed between the membrane and the respective substrate.
• the assembly is then bonded, typically under heat and pressure, to form a membrane electrode assembly.
• the sublayer may be applied to the porous substrate prior to application of the catalyst.
• the substrate is commonly referred to as a gas diffusion layer or, in the case when a sublayer is employed, the combination of the substrate and sublayer may also be referred to as a gas diffusion layer.
• catalysts Conventional methods of applying catalyst to gas diffusion layers to form gas diffusion electrodes include screen-printing and knife-coating.
• a layer of catalyst can be applied onto both surfaces of the polymer electrolyte membrane to form a catalyst-coated membrane, and then assembled with porous substrates to form a membrane electrode assembly.
• a catalyst slurry may be applied directly onto the membrane by microgravure coating, knife- coating, or spraying.
• sintering temperatures are usually higher than the thermal degradation temperature of the ionomer.
• National® membranes typically start to decompose at about 250 0 C.
• temperatures sufficient to sinter the hydrophobic binder e.g., 330 0 C for PTFE
• the ion-conducting and water uptake properties of the ionomer may be decreased or destroyed.
• the present invention relates to methods of making components for electrochemical fuel cells.
• the method comprises: forming a first transfer assembly, the first transfer assembly comprising a first catalyst layer comprising a first catalytic material and a hydrophobic binder on a surface of a first release sheet; heating the first catalyst layer to a sintering temperature of at least 250 0 C to form a sintered first catalyst layer; transferring the sintered first catalyst layer to a first surface of a polymer electrolyte membrane; and removing the first release sheet from the sintered first catalyst layer after bonding.
• the method comprises: forming a diffusion sublayer on a surface of a release sheet; forming a catalyst layer comprising a first catalytic material on the diffusion sublayer; transferring the catalyst layer to a surface of an ion exchange membrane; and removing the first release sheet from the diffusion sublayer.
• the catalyst layer may comprise a hydrophobic binder or an ionomer.
• the method comprises: forming a first catalyst layer comprising a catalytic material on a surface of a release sheet; forming a first diffusion sublayer on a first surface of the first catalyst layer; forming a second diffusion sublayer on a surface of a gas diffusion substrate; transferring the first diffusion sublayer to the second diffusion sublayer; and removing the first release sheet from the first catalyst layer to form a gas diffusion electrode.
• Figures IA to ID show a sectional view representing a series of steps for forming a catalyst-coated membrane according to a first embodiment of the present invention.
• Figures 2A and 2B show a sectional view representing the steps for forming a catalyst-coated membrane according to a further embodiment of the present invention.
• Figures 3A to 3C show a sectional view representing the steps for forming a catalyst-coated membrane according to yet a further embodiment of the present invention.
• Figures 4A to 4E show a sectional view representing a series of steps for forming a gas diffusion electrode according to another embodiment of the present invention.
• sintering means stabilization of the hydrophobic polymer, typically by heat treatment to temperatures greater than about 250 0 C.
• sintering conditions will be different for different polymers.
• suitable sintering conditions include sintering temperatures that range from about 33O 0 C to about 420 0 C for polytetrafluoroethylene (“PTFE”), about 250 0 C to about 280 0 C for fluorinated ethylene propylene (“FEP”) and about 300° to about 31O 0 C for perfluoroalkoxy (“PFA").
• PTFE polytetrafluoroethylene
• FEP fluorinated ethylene propylene
• PFA perfluoroalkoxy
• loading refers to the amount of material that is formed or applied to a substrate, and is usually expressed as the mass of material per unit surface area of the substrate.
• homogeneous means that the constituents are substantially uniformly dispersed in the mixture.
• the present invention is related to methods of making membrane electrode assembly components by bonding catalyst layers to a polymer electrolyte membrane to form a catalyst-coated membrane ("CCM”) or to a gas diffusion layer (“GDL”) to form a gas diffusion electrode (“GDE”).
• CCM catalyst-coated membrane
• GDL gas diffusion layer
• GDE gas diffusion electrode
• a method of making a CCM is shown in Figures IA to ID.
• the method includes forming a catalyst layer 2 on a release sheet 4 to form a transfer assembly 6 (Figure 1 A); heating catalyst layer 2 to a sintering temperature equal to or greater than about 250 0 C ( Figure IB) to yield a sintered catalyst layer 8; transferring sintered catalyst layer 8 to a membrane 10 ( Figure 1 C) at a suitable transfer temperature and/or pressure ("T/P"); and removing the backing layer ( Figure ID).
• catalyst layer 2 contains a catalytic material, such as a noble metal or compounds thereof, a supported noble metal, a supported noble metal compound, or combinations thereof.
• Catalyst layer 2 also contains a hydrophobic binder, such as PTFE, FEP, PFA, or combinations thereof, and preferably does not contain an ionomeric material.
• the constituents of the catalyst layer may first be dispersed in a suitable liquid carrier such as an alcohol, water, or combinations thereof, homogeneously blended to form a dispersion, and subsequently applied to the release sheet.
• the dispersion may further include a dispersion-stabilizing substance, for example, a surfactant, such as Triton -X or
• Tergitol and/or a pore former, such as methylcellulose.
• a dispersion Any method known in the art for applying a dispersion may be used, such as, but not limited to, knife-coating, screen- printing, slot die coating, microgravure coating, decal transferring, and spraying.
• the liquid carrier may be removed or partially removed prior to sintering by, for example, evaporation. Alternatively, the liquid carrier may be removed during sintering.
• Suitable release sheet materials should be inert, non-adhering, non- porous and heat-resistant to the highest temperature to which it will be subjected so that the release sheet does not deform and may be reused.
• the release sheet is a metal sheet, such as a stainless steel plate with a 2SB finish, a K05 metal coating, or ceramic coating; an aluminum sheet; or a heat-resistant polymeric film, for example, a polyimide film such as Kapton ® .
• the release sheet may be pre-treated with a release agent prior to forming layers thereon to facilitate removal of the release sheet from the catalyst layer or diffusion sublayer after transferring.
• the release agent may be, an alcohol, such as a polyvinyl alcohol.
• sintered catalyst layer 8 is transferred to membrane 10 after sintering by applying heat and/or pressure (TVP).
• suitable transfer temperatures may range from about 9O 0 C to about 200 0 C, and suitable transfer pressures may range from about 5 to about 40 bar.
• the opposing surface of membrane 10 is supported by a support material 12 during transferring.
• Support material 12 should be inert, non-adhering, non-porous and heat-resistant to the highest temperature to which it will be subjected, and does not need to be the same material as release sheet 4 because the transfer temperature is typically lower than the sintering temperature.
• support material 12 may be a PTFE, polyethylene, polypropylene, or polyester film, such as Mylar®.
• Release sheet 4 and support material 12 are removed from the sintered catalyst layer after transferring to form a catalyst-coated membrane 16, as shown in Figure ID.
• Figures 2A and 2B are illustrations of a further embodiment of the present invention, wherein a diffusion sublayer 14 is formed on release sheet 4 ( Figure 2A) and then a catalyst layer 2 is formed on diffusion sublayer 14 ( Figure 2B), prior to sintering and transferring.
• Diffusion sublayer 14 contains an electrically conductive material, which may be fibrous or particulate.
• the conductive material is carbon or graphite, such as, but not limited to, carbon blacks, graphitized carbon blacks, flake graphites, spherical graphites, chopped carbon fibers, milled carbon fibers, carbon whiskers, carbon nanotubes, chopped graphite fibers, milled graphite fibers, graphite whiskers, and graphite nanotubes, or combinations thereof.
• Diffusion sublayer 14 may be formed on release sheet 4 by dispersing the constituents in a suitable liquid carrier and then applied thereon by methods described in the foregoing.
• the diffusion sublayer may help transfer the catalyst layer to the membrane.
• incomplete transfer occurs (Ie., a portion of the catalyst layer may remain on the release sheet after transferring), particularly when the catalyst layer thickness is low, for example, equal to or less than about 5 microns, and typically when the catalyst loading is low, for example, equal to or less than about 0.15 mg Pt/cm 2 . Incomplete transfer of the catalyst layer is undesirable because it results in fuel cell performance loss, durability, and cost issues.
• the catalyst layer can be completely transferred to the membrane.
• a second catalyst layer 18 may be formed on an opposing surface of membrane 10 to form CCM 20, as shown in Figure 3 A.
• Catalyst layer 18 may contain the same composition of materials as in catalyst layer 2 in similar or different amounts, or may contain a different composition of materials, for example, catalyst with an ionomer.
• a catalyst layer with an ionorner, such as a fluorinated- and/or hydrocarbon-based ionomer, may be beneficial for uses where improved ionic conductivity in the catalyst layer is desired.
• One of ordinary skill in the art will readily select a catalyst composition suitable for a given application.
• catalyst layer 18 may be transferred to membrane 10 in a similar manner to that as described in the foregoing (i.e., forming catalyst layer 18 on a release sheet 22), either subsequently ( Figure 3B) or simultaneously ( Figure 3C).
• a diffusion sublayer such as the one described in Figures 2A and 2B, may also be transferred with catalyst layer 18 (not shown). Note that if catalyst layer 18 contains an ionomer, then the diffusion sublayer should be sintered prior to forming catalyst layer 16 thereon.
• catalyst layer 18 can be directly applied to the membrane by any method known in the art, before or after transferring (not shown).
• the CCM of the foregoing embodiments may be assembled with GDLs and/or GDEs to form a membrane electrode assembly ("MEA").
• MEA membrane electrode assembly
• a GDL may be placed adjacent catalyst layer 8 while a GDE may be placed adjacent an opposing second surface of membrane 10.
• a GDL may be placed adjacent sintered catalyst layer 8 while another GDL may be placed adjacent catalyst layer 16.
• the assembled MEA may be subjected to a bonding temperature and/or bonding pressure to substantially bond each of the components together.
• a method of making a GDE is disclosed.
• the method includes forming a catalyst layer 2 on a support material 12 (Figure 4A); forming a diffusion sublayer 14a on catalyst layer 2 to form a transfer assembly 24 (Figure 4B); forming an additional diffusion sublayer 14b on a diffusion substrate 26 to form a partial GDL 28 ( Figure 4C); transferring diffusion sublayer 14a to diffusion sublayer 14b ( Figure 4D); and sintering to form a GDE 30
• Support material 12 may be removed before or after sintering (not shown).
• Catalyst layer 2 preferably contains a hydrophobic binder and a catalytic material, such that described in the foregoing. Furthermore, diffusion sublayers 14a,
• diffusion sublayers 14a, 14b may contain the same constituents as described in previous embodiments.
• diffusion sublayers 14a, 14b may have the same or different compositions, and may have the same or different loadings.
• the liquid carrier of catalyst layer 2 may be removed or partially removed prior to forming first diffusion sublayer 14a thereon.
• any suitable diffusion substrate material may be used, provided that it is electrically conductive and porous.
• exemplary diffusion substrate materials include carbonized or graphitized carbon fiber non-woven mats such as, but not limited to, TGP-H-090 (Toray Industries Inc., Tokyo, Japan); AvCarb ® P50 and EP-40 (Ballard Material Products Inc., Lowell, MA); and GDL 24 and 25 series material (SGL Carbon Corp., Charlotte, NC).
• TGP-H-090 Toray Industries Inc., Tokyo, Japan
• AvCarb ® P50 and EP-40 Allard Material Products Inc., Lowell, MA
• GDL 24 and 25 series material SGL Carbon Corp., Charlotte, NC.
• the porous substrate may be hydrophobized, such as by impregnating the substrate in a solution containing a hydrophobic binder, which is then dried and/or sintered prior to application of diffusion sublayer 14b, or simultaneously sintered with diffusion sublayers 14a, 14b and catalyst layer 2 after transferring. Transferring conditions may be similar to those described in the foregoing embodiments. Furthermore, in some embodiments, the liquid carrier of first and/or second sublayers 14a, 14b is removed during transferring.
• catalyst layer 2 and diffusion sublayers 14a, 14b are sintered after transferring of diffusion sublayers 14a, 14b.
• catalyst layer 2 and diffusion sublayers 14a, 14b may be separately sintered before transferring or simultaneously sintered during transferring (not shown).
• support material 12 may be any of the materials described in the foregoing, so long as it is heat- resistant to the highest temperature to which it will be subjected (e.g., transferring or sintering temperatures, depending on when support material 12 is removed). The inventors have discovered that when transferring a catalyst layer containing a hydrophobic binder to the GDL, incomplete transfer of the catalyst typically occurs, particularly when transferring thin catalyst layers.
• GDE 30 may be assembled with a membrane and another GDE, or may be assembled with a CCM and GDL to form a MEA. For example, with GDE 30 may be assembled with membrane 10 such that the catalyst layer 8 contacts membrane 10 (not shown).
• GDE 30 is then assembled adjacent the opposing surface of membrane 10 to form a MEA.
• GDE 30 may be assembled with a CCM, such as the one shown in Figure ID and a GDL adjacent catalyst layer 8, to form a MEA (not shown). Again, the assembled MEA may be bonded, as described in the foregoing.
• an adhesive layer may be employed between any of the layers prior to transferring, such as that described in U.S. Patent Application No. 2004/0258979.
• the adhesive layer may include an ionomer and, optionally, carbon and/or graphite particles. It is anticipated that the adhesive layer may improve adhesion and may enhance proton conductivity through the catalyst layer.

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• 2007
  • 2007-04-20 WO PCT/US2007/009596 patent/WO2007124011A2/en active Application Filing
  • 2007-04-20 CN CNA200780017958XA patent/CN101479868A/zh active Pending
  • 2007-04-20 JP JP2009506589A patent/JP2009534796A/ja not_active Withdrawn
  • 2007-04-20 CA CA002649903A patent/CA2649903A1/en not_active Abandoned
  • 2007-04-20 EP EP07755747A patent/EP2013930A2/en not_active Withdrawn

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