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
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/1041—Polymer electrolyte composites, mixtures or blends
  • H01M8/1046—Mixtures of at least one polymer and at least one additive
  • H01M8/1051—Non-ion-conducting additives, e.g. stabilisers, SiO2 or ZrO2
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/20—Manufacture of shaped structures of ion-exchange resins
  • C08J5/22—Films, membranes or diaphragms
  • C08J5/2206—Films, membranes or diaphragms based on organic and/or inorganic macromolecular compounds
  • C08J5/2218—Synthetic macromolecular compounds
  • C08J5/2231—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds
  • C08J5/2237—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds containing fluorine
• • 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
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/102—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer
  • H01M8/1023—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer having only carbon, e.g. polyarylenes, polystyrenes or polybutadiene-styrenes
• • 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
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/102—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer
  • H01M8/1027—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer having carbon, oxygen and other atoms, e.g. sulfonated polyethersulfones [S-PES]
• • 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
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/102—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer
  • H01M8/1032—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer having sulfur, e.g. sulfonated-polyethersulfones [S-PES]
• • 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
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/1039—Polymeric electrolyte materials halogenated, e.g. sulfonated polyvinylidene fluorides
• • 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
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/1058—Polymeric electrolyte materials characterised by a porous support having no ion-conducting properties
• • 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
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/1069—Polymeric electrolyte materials characterised by the manufacturing processes
  • H01M8/1072—Polymeric electrolyte materials characterised by the manufacturing processes by chemical reactions, e.g. in situ polymerisation or in situ crosslinking
• • 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
  • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
  • H01M8/1018—Polymeric electrolyte materials
  • H01M8/1069—Polymeric electrolyte materials characterised by the manufacturing processes
  • H01M8/1081—Polymeric electrolyte materials characterised by the manufacturing processes starting from solutions, dispersions or slurries exclusively of polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
  • C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
  • C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
  • C08J2327/18—Homopolymers or copolymers of tetrafluoroethylene
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M2300/00—Electrolytes
  • H01M2300/0088—Composites
  • H01M2300/0091—Composites in the form of mixtures
• • 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]
• • 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

• This invention relates to fuel cell membrane electrode assemblies and fuel cell polymer electrolyte membranes comprising bound anionic functional groups and polyvalent cerium cations which demonstrate increased durability, and methods of making same.
• TFE tetrafluoroethylene
• a polymer electrolyte membrane having a thickness of 90 microns or less and comprising a polymer, said polymer comprising a highly fluorinated backbone and recurring pendant groups according to the formula: YOSO2-CF2-CF 2 -CF2-CF2-O-[polymer backbone] where Y is H + or a monovalent cation such as an alkali metal cation.
• the membrane is a cast membrane.
• the polymer has a hydration product of greater than 22,000.
• the polymer has an equivalent weight of 800-1200.
• the present invention provides a fuel cell membrane electrode assembly comprising a polymer electrolyte membrane which comprises a polymer that comprises bound anionic functional groups, wherein the polymer electrolyte membrane additionally comprises cerium cations.
• tie amount of cerium cations present is between 0.001 and 0.5 charge equivalents based on the molar amount of anionic functional groups present in the polymer electrolyte, more typically between 0.005 and 0.2, more typically between 0.01 and 0.1, and more typically between 0.02 and 0.05.
• the distribution of cerium cations across the thickness of the polymer electrolyte membrane is uniform.
• the cations are Ce ⁇ + cations or Ce ⁇ + cations.
• the polymer may have an equivalent weight of 1200 or less, more typically 1000 or less, and is in some embodiments 900 or less or 800 or less.
• the polymer may be highly fluorinated or perfluorinated, and may comprise pendent groups according to the formula: -0-CF 2 -CF 2 -CF 2 -CF 2 -SO 3 H or the formula: -O-CF2-CF(CF 3 )-O-CF 2 - CF 2 -SO 3 H.
• the present invention provides a fuel cell membrane electrode assembly comprising a polymer electrolyte membrane which comprises a polymer that comprises bound anionic functional groups, wherein at least a portion of the anionic functional groups are in acid form and at least a portion of the anionic functional groups are neutralized by cerium cations.
• the amount of cerium cations present is between 0.001 and 0.5 charge equivalents based on the molar amount of anionic functional groups present in the polymer electrolyte, more typically between 0.005 and 0.2, more typically between 0.01 and 0.1, and more typically between 0.02 and 0.05.
• the distribution of cerium cations across the thickness of the polymer electrolyte membrane is uniform.
• the cations are Ce ⁇ + cations or Ce ⁇ + cations.
• the polymer may have an equivalent weight of 1200 or less, more typically 1000 or less, and is in some embodiments 900 or less or 800 or less.
• the polymer may be highly fluorinated or perfiuorinated, and may comprise pendent groups according to the formula: -O-CF2-CF2-CF2-CF2-SO3H or the formula: -O-CF 2 -CF(CF 3 )-O-CF 2 - CF 2 -SO 3 H.
• the present invention provides a polymer electrolyte membrane which comprises a polymer that comprises bound anionic functional groups, wherein the polymer electrolyte membrane additionally comprises cerium cations, and wherein the amount of cerium cations present is between 0.001 and 0.5 charge equivalents based on the molar amount of acid functional groups present in the polymer electrolyte, more typically between 0.005 and 0.2, more typically between 0.01 and 0.1, and more typically between 0.02 and 0.05.
• the distribution of cerium cations across the thickness of the polymer electrolyte membrane is uniform.
• the cations are Ce ⁇ + cations or Ce ⁇ + cations.
• the polymer may have an equivalent weight of 1200 or less, more typically 1000 or less, and is in some embodiments 900 or less or 800 or less.
• the polymer may be highly fluorinated or perfiuorinated, and may comprise pendent groups according to the formula: -0-CF 2 -CF 2 -CF 2 -CF 2 -SO 3 H or the formula: -O-CF 2 -CF(CF 3 )-O-CF 2 -CF 2 -SO 3 H.
• the present invention provides a polymer electrolyte membrane which comprises a polymer that comprises bound anionic functional groups, wherein at least a portion of the anionic functional groups are in acid form and at least a portion of the anionic functional groups are neutralized by cerium cations, and wherein the amount of cerium cations present is between 0.001 and 0.5 charge equivalents based on the molar amount of acid functional groups present in the polymer electrolyte, more typically between 0.005 and 0.2, more typically between 0.01 and 0.1, and more typically between 0.02 and 0.05.
• the distribution of cerium cations across the thickness of the polymer electrolyte membrane is uniform.
• the cations are
• the polymer may have an equivalent weight of 1200 or less, more typically 1000 or less, and is in some embodiments 900 or less or 800 or less.
• the polymer may be highly fluorinated or perfluorinated, and may comprise pendent groups according to the formula: -O-CF2-CF2-CF2-CF2-SO3H or the formula: -O-
• the present invention provides a method of making a polymer electrolyte membrane comprising the steps of: a) providing a polymer electrolyte comprising bound anionic functional groups; b) adding 0.001 to 0.5 charge equivalents of one or more cerium salts, based on the molar amount of the acidic functional groups; and c) forming a membrane comprising the polymer electrolyte. More typically between 0.005 and 0.2 charge equivalents are added, more typically between 0.01 and
• the polymer may have an equivalent weight of 1200 or less, more typically 1000 or less, more typically 900 or less, and more typically 800 or less.
• the polymer may be highly fluorinated or perfluorinated, and may comprise pendent groups according to the formula: -0-CF 2 -CF 2 -CF 2 -CF 2 -SOSH or the formula: -0-CF 2 -
• the polymer electrolyte membrane thus formed may be incorporated into a membrane electrode assembly.
• "uniform" distribution of an additive in a polymer membrane means that the amount of additive present does not vary more than +/- 90%, more typically not more than +/- 50% and more typically not more than +/- 20%;
• "equivalent weight” (EW) of a polymer means the weight of polymer which will neutralize one equivalent of base;
• polyvalent cation means a cation having a charge of 2+ or greater
• highly fluorinated means containing fluorine in an amount of 40 wt% or more, typically 50 wt% or more and more typically 60 wt% or more;
• acid form means, with regard to an anionic functional group, that it is neutralized by a proton.
• Figure 1 is a graph reporting results from a Fuel Cell Lifetime Test for three membrane electrode assemblies (MEA' s), including cell potential for the Example 9C comparative MEA (Trace Al, left-hand scale), cell potential for the Example 10 MEA of the invention (Trace Cl, left-hand scale), cell potential for a comparative MEA comprising Mn salt additive (Trace Bl, left-hand scale), fluoride ion release rate for the Example 9C comparative MEA (Trace A2, right-hand scale), fluoride ion release rate for the Example 10 MEA of the invention (Trace C2, right-hand scale), and fluoride ion release rate for a comparative MEA comprising Mn salt additive (Trace B2, right-hand scale).
• the present invention provides a polymer electrolyte membrane (PEM) which comprises a polymer that comprises bound anionic functional groups and cerium cations, or a fuel cell membrane electrode assembly (MEA) comprising such a PEM.
• PEM polymer electrolyte membrane
• MEA fuel cell membrane electrode assembly
• At least a portion of the anionic functional groups are in acid form and at least a portion of the anionic functional groups are neutralized by the Ce cations.
• the amount of cerium cations present is between 0.001 and 0.5 charge equivalents based on the molar amount of acid functional groups present in the polymer electrolyte.
• the distribution of the cerium cations across the thickness of the PEM is uniform.
• a membrane electrode assembly (MEA) or polymer electrolyte membrane (PEM) according to the present invention may be useful in electrochemical cell such as a fuel cell.
• An MEA is the central element of a proton exchange membrane fuel cell, such as a hydrogen fuel cell.
• Fuel cells are electrochemical cells which produce usable electricity by the catalyzed combination of a fuel such as hydrogen and an oxidant such as oxygen.
• Typical MEA's comprise a polymer electrolyte membrane (PEM) (also known as an ion conductive membrane (ICM)), which functions as a solid electrolyte.
• PEM polymer electrolyte membrane
• ICM ion conductive membrane
• protons are formed at the anode via hydrogen oxidation and transported across the PEM to the cathode to react with oxygen, causing electrical current to flow in an external circuit connecting the electrodes.
• Each electrode layer includes electrochemical catalysts, typically including platinum metal.
• the PEM forms a durable, non-porous, electrically non-conductive mechanical barrier between the reactant gases, yet it also passes H + ions readily.
• Gas diffusion layers facilitate gas transport to and from the anode and cathode electrode materials and conduct electrical current.
• the GDL is both porous and electrically conductive, and is typically composed of carbon fibers.
• the GDL may also be called a fluid transport layer (FTL) or a diffuser/current collector (DCC).
• the anode and cathode electrode layers are applied to GDL's and the resulting catalyst-coated GDL's sandwiched with a PEM to form a five-layer MEA.
• the five layers of a five-layer MEA are, in order: anode GDL, anode electrode layer, PEM, cathode electrode layer, and cathode GDL.
• the anode and cathode electrode layers are applied to either side of the PEM, and the resulting catalyst-coated membrane (CCM) is sandwiched between two GDL's to form a five- layer MEA.
• the PEM according to the present invention may comprise any suitable polymer electrolyte.
• the polymer electrolytes useful in the present invention typically bear anionic functional groups bound to a common backbone, which are typically sulfonic acid groups but may also include carboxylic acid groups, imide groups, amide groups, or other acidic functional groups.
• the polymer electrolytes useful in the present invention are typically highly fluorinated and most typically perfluorinated, but may also be partially fluorinated or non-fluorinated.
• the polymer electrolytes useful in the present invention are typically copolymers of tetrafluoroethylene and one or more fluorinated, acid-functional comonomers. Typical polymer electrolytes include
• the polymer typically has an equivalent weight (EW) of 1200 or less and more typically 1100 or less.
• EW equivalent weight
• polymers of unusually low EW can be used, typically 1000 or less, more typically 900 or less, and more typically 800 or less, often with improved performance in comparison to the use of higher EW polymer.
• polyvalent cerium ions may strengthen the polymer by forming crosslinks between bound anionic groups.
• the polymer can be formed into a membrane by any suitable method.
• the polymer is typically cast from a suspension. Any suitable casting method may be used, including bar coating, spray coating, slit coating, brush coating, and the like.
• the membrane may be formed from neat polymer in a melt process such as extrusion. After forming, the membrane may be annealed, typically at a temperature of 120 0 C or higher, more typically 130 0 C or higher, most typically 150 0 C or higher.
• the PEM typically has a thickness of less than 50 microns, more typically less than 40 microns, more typically less than 30 microns, and most typically about 25 microns.
• a salt of cerium is added to the acid form polymer electrolyte prior to membrane formation.
• the salt is mixed well with or dissolved within the polymer electrolyte to achieve substantially uniform distribution.
• cerium salt means a compound including cerium cations wherein the positive charge of ionized cerium is balanced by an equal negative charge of an anion, excluding compounds comprising O 2" oxygen anions as the primary counterions to the cerium cations; i.e., excluding cerium oxides.
• the salt may comprise any suitable anion, including chloride, bromide, hydroxide, nitrate, carbonate, sulfonate, phosphate, and acetate and the like. More than one anion may be present.
• Suitable cerium salts may also contain additional non-cerium organic or inorganic cations, including other metal cations or other ammonium cations, including organic ammonium cations.
• additional non-cerium organic or inorganic cations including other metal cations or other ammonium cations, including organic ammonium cations.
• Cerium cations may be in any suitable oxidation state, including Ce ⁇ + and Ce ⁇ + .
• cerium cations persist in the polymer electrolyte because they are exchanged with H + ions from the anion groups of the polymer electrolyte and become associated with those anion groups.
• polyvalent cerium cations may form crosslinks between anion groups of the polymer electrolyte, further adding to the stability of the polymer.
• cerium salts may be present in solid or precipitate form.
• cerium cations may be present in a combination of two or more forms including solvated cation, cation associated with bound anion groups of the PEM, and cation bound in a cerium salt precipitate.
• the amount of salt added is typically an amount which provides between 0.001 and 0.5 charge equivalents of cerium ion based on the molar amount of acid functional groups present in the polymer electrolyte, more typically between 0.005 and 0.2, more typically between 0.01 and 0.1, and more typically between 0.02 and 0.05.
• the polymer electrolyte is formed into a PEM or PEM precursor, such as a roll good or a shot of material for molding, prior to treatment.
• a solution or suspension of one or more cerium salts, such as are described above, is applied to the PEM or PEM precursor, e.g., by coating the PEM or PEM precursor with the solution or suspension or immersing the PEM or PEM precursor in the solution or suspension.
• the solution or suspension may be in any suitable carrier, such as a solvent or solvent system, which typically includes water, alcohols, and the like.
• Immersion time and temperature may be any suitable for addition to the PEM or PEM precursor of between 0.001 and 0.5 charge equivalents of cerium ion based on the molar amount of acid functional groups present in the polymer electrolyte, more typically between 0,005 and 0.2, more typically between 0.01 and 0.1, and more typically between 0.02 and 0.05.
• the PEM precursor may be formed into a PEM by any suitable means, including cutting, especially of roll goods, and molding, especially of a shot of material for molding, and the like or combinations thereof.
• catalyst may be applied to the PEM by any suitable means, including both hand and machine methods, including hand brushing, notch bar coating, fluid bearing die coating, wire-wound rod coating, fluid bearing coating, slot- fed knife coating, three-roll coating, or decal transfer. Coating may be achieved in one application or in multiple applications.
• any suitable catalyst may be used in the practice of the present invention.
• carbon-supported catalyst particles are used. Typical carbon-supported catalyst particles are 50-90% carbon and 10-50% catalyst metal by weight, the catalyst metal typically comprising Pt for the cathode and Pt and Ru in a weight ratio of 2: 1 for the anode.
• the catalyst is applied to the PEM or to the FTL in the form of a catalyst ink. Alternately, the catalyst ink may be applied to a transfer substrate, dried, and thereafter applied to the PEM or to the FTL as a decal.
• the catalyst ink typically comprises polymer electrolyte material, which may or may not be the same polymer electrolyte material which comprises the PEM.
• the catalyst ink typically comprises a dispersion of catalyst particles in a dispersion of the polymer electrolyte.
• the ink typically contains 5-30% solids (i.e. polymer and catalyst) and more typically 10-20% solids.
• the electrolyte dispersion is typically an aqueous dispersion, which may additionally contain alcohols and polyalcohols such a glycerin and ethylene glycol. The water, alcohol, and polyalcohol content may be adjusted to alter rheological properties of the ink.
• the ink typically contains 0-50% alcohol and 0-20% polyalcohol. In addition, the ink may contain 0-2% of a suitable dispersant.
• the ink is typically made by stirring with heat followed by dilution to a coatable consistency.
• the electrode or the catalyst ink comprises a polymer that comprises bound anionic functional groups and cerium cations, as provided herein for polymers comprising a PEM according to the present invention.
• the anionic functional groups are in acid form and at least a portion of the anionic functional groups are neutralized by the Ce cations, as provided herein for polymers comprising a PEM according to the present invention.
• a PEM according to the present invention may additionally comprise a porous support, such as a layer of expanded PTFE or the like, where the pores of the porous support contain the polymer electrolyte.
• a PEM according to the present invention may comprise no porous support.
• a PEM according to the present invention may comprise a crosslinked polymer.
• GDL 's may be applied to either side of a CCM by any suitable means.
• Any suitable GDL may be used in the practice of the present invention.
• the GDL is comprised of sheet material comprising carbon fibers.
• the GDL is a carbon fiber construction selected from woven and non- woven carbon fiber constructions.
• Carbon fiber constructions which may be useful in the practice of the present invention may include: TorayTM Carbon Paper, SpectraCarbTM Carbon Paper, AFNTM non-woven carbon cloth, ZoltekTM Carbon Cloth, and the like.
• the GDL may be coated or impregnated with various materials, including carbon particle coatings, hydrophilizing treatments, and hydrophobizing treatments such as coating with polytetrafluoroethylene (PTFE).
• PTFE polytetrafluoroethylene
• the MEA according to the present typically sandwiched between two rigid plates, known as distribution plates, also known as bipolar plates (BPP 's) or monopolar plates.
• the distribution plate must be electrically conductive.
• the distribution plate is typically made of a carbon composite, metal, or plated metal material.
• the distribution plate distributes reactant or product fluids to and from the MEA electrode surfaces, typically through one or more fluid-conducting channels engraved, milled, molded or stamped in the surface(s) facing the MEA(s). These channels are sometimes designated a flow field.
• the distribution plate may distribute fluids to and from two consecutive MEA' s in a stack, with one face directing fuel to the anode of the first MEA while the other face directs oxidant to the cathode of the next MEA (and removes product water), hence the term "bipolar plate.”
• the distribution plate may have channels on one side only, to distribute fluids to or from an MEA on only that side, which may be termed a "monopolar plate.”
• the term bipolar plate typically encompasses monopolar plates as well.
• a typical fuel cell stack comprises a number of MEA' s stacked alternately with bipolar plates.
• This invention is useful in the manufacture and operation of fuel cells.
• Comonomer A was made according to the procedures disclosed in U.S. patent applications 10/322,254 and 10/322,226, incorporated herein by reference. Polymerization was performed by aqueous emulsion polymerization as described in U.S. patent application 10/325,278. The equivalent weight (EW) was 1000 (ion exchange capacity of 0.001 mol per gram). The ionomer was provided in a casting solution containing 22.3% solids in 70:30 n propanol/water.
• the casting solution contained iron at a level of less than lppm.
• Membranes were made by casting the dispersions on window glass by hand-spread technique using the 0.020 inch (0.0508 cm) gap of a 4-inch multiple clearance applicator (Cat. No. PAR-5357, BYK-Gardner, Columbia, Maryland). The membrane films were dried in ambient air for 15 minutes, followed by drying in an 80 0 C air oven for 10 minutes, followed by heating in a 200 0 C air oven for 15 minutes.
• Peroxide Soak Test Oxidative stability of the perfluorinated ionomer membranes made in several of the examples was tested as follows. A sample of membrane weighing between .03 g and .06 g was carefully weighed and then immersed in 50 g of hydrogen peroxide solution (IM starting concentration) in a glass jar. The jar was sealed and placed in an oven at 90-95 °C for 5 days. After a 5-day soak period, the sample was removed from solution, rinsed with DI water, dried at room temperature for at least three hours, and weighed. A raw weight loss figure was calculated.
• IM starting concentration hydrogen peroxide solution
• Titrations were performed to determine the acid content of ionomer membranes prepared with addition of ionic cerium. For each titration, a carefully weighed sample of ionomer film, approximately 0.05g, was added to 100ml of 0.1 M NaCl solution.
• 0.05M NaOH solution was slowly added to the sample solution using a burette and the end point was determined using a pH meter. The amount of NaOH necessary to neutralize the acid was taken as the acid content of the membrane.
• Fuel cell membrane electrode assemblies having 50 cm ⁇ of active area were prepared as follows. Catalyst dispersions were prepared according to the method described in WO 2002/061,871, incorporated herein by reference. To prepare catalyst- coated membranes, anode and cathode layers were applied to membranes according to the decal transfer method described in the same reference, WO 2002/061,871. PTFE- treated carbon paper gas diffusion layers and polytetrafluoroethylene/glass composite gaskets were applied to the CCM by pressing in a Carver Press (Fred Carver Co., Wabash, IN) with 13.4 kN of force at 132 0 C for 10 minutes. MEA Lifetime Test
• the MEA's were tested in a test station with independent controls of gas flow, pressure, relative humidity, and current or voltage (Fuel Cell Technologies, Albuquerque, New Mexico).
• the test fixture included graphite current collector plates with quad-serpentine flow fields.
• MEA's were operated with H ⁇ /air under subsaturated conditions at 9O 0 C with anode overpressure.
• the MEA's were subjected to an accelerated load cycle lifetime test by imposition of a variety of current density values. After each load cycle, the open circuit voltage (OCV) of the cell was measured and recorded.
• OCV open circuit voltage
• the point at which the decay rate increases can be taken as the lifetime of the MEA.
• a lower threshold voltage value can be selected to indicate the end of life for an MEA.
• the evolution rate of fluoride ions in the effluent water of the operating fuel cell was also measured by ion chromatography. A higher fluoride evolution rate indicates more rapid degradation for fluoropolymer membranes.
• a control membrane was prepared according to details presented above, except that the casting dispersion included additional iron (500ppm on a polymer weight basis), added as iron nitrate. 0.08 Ig of ferric nitrate (Fe(N ⁇ 3)3-9H2 ⁇ , (Product
• Example 2 An aliquot of casting dispersion prepared according to Example 1C was further combined with ammonium cerium nitrate (ACN; (NH4)2Ce(NO3)g (Product Number 33254, Alfa Aesar, Ward Hill, Massachusetts) at a cerium content of 0.02 mmols cerium per gram of polymer. 0.036g of ammonium cerium nitrate (0.066mmols) was combined with 14.64g of ionomer solution (22.7wt%) and stirred for 24 hours. The salt initially dissolved to give regions of clear yellow solution. After several hours, the mixture grew slightly turbid and colorless. A membrane was cast according to the procedure given above. Table I reports the results of the Peroxide Soak Test and Acid Content Measurement for the membrane. The addition of ammonium cerium nitrate reduced the weight loss of the perfluorinated ionomer, indicating a higher level of oxidative stability.
• ACN ammonium cerium nitrate
• a control membrane was prepared according to the method described in Comparative Example 1 C.
• Table II reports the results of the Peroxide Soak Test for the membrane. Two samples were made and the reported results are the average of both samples.
• Example 4 An aliquot of polymer casting dispersion prepared according to Example 3 C
• Example 5 An aliquot of polymer casting dispersion prepared according to Example 3 C
• a control membrane was prepared according to the method described in the Example of U.S. Pat. 6,649,295, incorporated herein by reference.
• a polymer casting dispersion was prepared as given in Example 9C above, and further combined with ammonium cerium nitrate (NH4)2Ce(NO3)g (Product Number 33254, Alfa Aesar, Ward Hill, Massachusetts) at a cerium content of 0.02 mmols cerium per gram of polymer.
• 1.0Og of ammonium cerium nitrate (1.82mmols) was combined with 40Og of ionomer solution (22.7wt%) and stirred for 24 hours.
• the salt initially dissolved to give regions of clear yellow solution. After several hours, the mixture grew slightly turbid and colorless.
• the membrane was cast according to the method described in the Example of U.S. Pat. 6,649,295, incorporated herein by reference.
• Fig. 1 reports results from the Fuel Cell Lifetime Test for these MEA' s, including cell potential for the Example 9C comparative MEA (Trace Al, left-hand scale), cell potential for the Example 10 MEA of the invention (Trace Cl , left-hand scale), fluoride ion release rate for the Example 9C comparative MEA (Trace A2, right- hand scale), and fluoride ion release rate for the Example 10 MEA of the invention (Trace C2, right-hand scale).
• Fig. 1 additionally reports cell potential and fluoride ion release rate for a comparative MEA made with a Mn salt additive (Traces Bl and B2).
• the Example 10 MEA of the invention demonstrated dramatically extended lifetime and reduced fluoride ion evolution.

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