+

WO2003069713A1 - Ensembles electrodes a membrane pour cellules electrochimiques - Google Patents

Ensembles electrodes a membrane pour cellules electrochimiques Download PDF

Info

Publication number
WO2003069713A1
WO2003069713A1 PCT/US2002/001988 US0201988W WO03069713A1 WO 2003069713 A1 WO2003069713 A1 WO 2003069713A1 US 0201988 W US0201988 W US 0201988W WO 03069713 A1 WO03069713 A1 WO 03069713A1
Authority
WO
WIPO (PCT)
Prior art keywords
membrane
asymmetric
catalyst
alcohol
film
Prior art date
Application number
PCT/US2002/001988
Other languages
English (en)
Inventor
Ramanathan Gopal
Original Assignee
The Electrosynthesis Company, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by The Electrosynthesis Company, Inc. filed Critical The Electrosynthesis Company, Inc.
Priority to AU2002240045A priority Critical patent/AU2002240045A1/en
Priority to PCT/US2002/001988 priority patent/WO2003069713A1/fr
Publication of WO2003069713A1 publication Critical patent/WO2003069713A1/fr

Links

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
    • H01M8/0289—Means for holding the electrolyte
    • 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
    • H01M8/1034—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer having phosphorus, e.g. sulfonated polyphosphazenes [S-PPh]
    • 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
    • H01M2300/00—Electrolytes
    • H01M2300/0088—Composites
    • 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
    • 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
    • H01M8/1025—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer having only carbon and oxygen, e.g. polyethers, sulfonated polyetheretherketones [S-PEEK], sulfonated polysaccharides, sulfonated celluloses or sulfonated polyesters
    • 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]
    • 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

  • This invention relates generally to electrochemical cells, and more specifically, to membrane electrode assemblies particularly useful in energy producing fuel cells and energy consuming electrosynthesis cells and methods of manufacture.
  • Electrochemical cells for converting chemical energy directly to electrical energy rely on chemical reactions between an electrolyte and a fuel.
  • One well known fuel cell namely the hydrogen/oxygen type fuel cell, relies on anodic and cathodic reactions which lead to the generation and flow of electrons and electrical energy as a useful power source for many applications.
  • the anodic and cathodic reactions in a hydrogen/oxygen fuel cell may be represented as follows:
  • Platinum catalysts are used to bring about both of the foregoing anodic and cathodic reactions. These catalysts typically in combination with activated carbon, organic binder and fluorocarbon polymers, such as Teflon® are bonded to either side of a proton conducting ion-exchange membrane to fabricate a membrane electrode assembly (MEA) . In the case of hydrogen/oxygen fuel cells, some improvements in catalyst application methods have been directed towards reducing the amount of costly platinum catalyst in formulations .
  • compositions for example, was achieved by combining solubilized perfluorosulfonate ionomer (Nafion®) , support catalyst (Pt on carbon) , glycerol and water. This led to the use of low platinum loading electrodes.
  • the following publications teach some of these methods for hydrogen/oxygen fuel cells: U.S. Pat. 5,234,777 to Wilson; M.S. Wilson, et al, J. App. Electrochem. , 22 (1992) 1-7; C. Zawodzinski, et al, Electrochem. Soc. Proc , Vol. 95-23 (1995) 57-65; A.K. Shukla, et al, J. App. Electrochem. , 19(1989) 383-386; U.S. Pat. 5,702,755 to Messell; U.S. Pat. 5,859,416 to Mussell; U.S. Pat. 5,501,915 to Hards, et al.
  • Fuel cells utilizing hydrogen as fuel are not viewed as entirely suitable for portable applications, such as motorized vehicles, due mainly to problems associated with hydrogen storage.
  • a more suitable alternative fuel would be a liquid fuel, such as a simple alcohol, like methanol, which can be used in a low cost dilute aqueous solution.
  • MEAs specifically for methanol fed fuel cells. The reactions at the electrodes are as follows:
  • MEA membrane electrode assemblies
  • anodes preferably include a deposited catalyst for converting the alcoholic fuel to needed protons, plus water and carbon dioxide.
  • the asymmetric membrane is a composite structure comprising a non-porous, water and proton permeable, thin polymeric film, and a thicker porous support layer (stratum) or backing in juxtaposition therewith, wherein the alcohol oxidation catalyst is dispersed.
  • the outer polymeric film layer and the porous support layer are preferably part of the same structure and exist as an integral film, wherein the outer film layer is a continuous film which retains the cation exchange properties, including proton transport characteristics and non-porous properties of the original unmodified polymer.
  • the porous support layer backing is physically modified into a high surface area porous stratum having tortuous paths with most of the alcohol oxidation catalyst embedded therein for greater surface exposure to unreacted liquid fuel.
  • Deposition of the alcohol oxidation catalyst mainly in the porous support region provides important benefits, namely more effective proton transport due to continuous presence of cationic proton conducting polymer throughout the catalyst region; the presence of catalyst at the interface between the thin film separating membrane and the adjacent thicker porous support layer allowing for more complete oxidation of any unreacted alcohol; in the case of ion-exchange polymers possessing very low or near zero methanol diffusion coefficients, all or virtually all unreacted methanol is prevented from reaching the cathode, since the polymer is present throughout the catalyst region. The efficiency of the direct fed methanol fuel cell is thereby greatly enhanced.
  • the asymmetric composites are formed from cation-exchange polymers, preferably perfluorosulfonic acid types, such as DuPont's Nafion brand of permselective cation-exchange membrane, or other similar performing water and proton transporting cationic type exchange materials.
  • the asymmetric composites of the invention comprise the aforementioned non-porous, but water and proton transportable films preferably as a continuous, very thin outer layer allowing for the transport of protons formed at the anode, plus water to selectively crossover to the cathode where the protons react with oxygen. Similarly, this continuous film layer also serves to restrict the transport of residual amounts of remaining unreacted alcoholic fuel from crossing over to the cathode.
  • the permselective properties of the continuous, non-porous thin film portion of the asymmetric composite serve as a fail-safe in restricting the transport of still any unreacted fugitive alcoholic fuel, preventing it from crossing over and reacting at the cathode, and causing a reduction cell voltage.
  • the non-porous film layer of the asymmetric composite is very thin relative to the porous support layer. Thicknesses of the non-porous film layer can vary generally from about 2 to about lO ⁇ m.
  • the thicker porous support layer backing for the thin film also performs as a high surface area substrate or bed for the oxidation catalyst for greater surface contact with unreacted alcoholic fuel and for more efficient decomposition of all, or virtually all remaining unreacted alcohol in the alcohol-water fuel mixture.
  • the thicker porous support layer with oxidation catalyst deposited therein facilitates the conversion of unreacted fuel to carbon dioxide, water and protons.
  • asymmetric catalytic membrane composites of the present invention provide for more efficient operating solid polymer electrolytes for use in the operation of direct fed methanol fuel cells, and other types of electrolytic cells.
  • the asymmetric membrane composites of the present invention may also be used in-combination with supplemental ion-exchange membranes.
  • supplemental ion-exchange membranes For example, in the event of surface imperfections in the thin, non-porous polymeric film surface of the asymmetric composite. Such surface imperfections may allow transport of small, but performance impeding amounts of unreacted fuel from the anode to the cathode side of the MEA. This can be remedied by means of the supplemental cation exchange membrane layer applied to the thin outer film layer.
  • the supplemental membrane restricts the transport of residual amounts of unreacted fuels to the cathode while still allowing the passage protons.
  • the supplemental membrane may also be employed as a spacer device in electrochemical cells, when necessary. While useful, this supplemental membrane structure may result in somewhat higher internal resistances (IR) causing some voltage penalty.
  • One embodiment is a type of phase inversion process performed by the steps which comprise:
  • step (ii) forming a catalyst-cationic polymer dispersion by mixing an appropriate catalyst with the solution of cationic polymer of step (i) ;
  • the second solvent should be a non-solvent, e.g., water or alcohol, for the film. That is, the polymeric film should be insoluble in the second solvent, while the first solvent used in the solubilization of the polymer must be completely miscible with the non-solvent, and
  • the two solvent system also forms the substantially thicker, porous support layer backing.
  • the backing of the film is converted to a high surface area support layer having many tortuous paths.
  • the porous support layer also performs as a high surface area substrate or bed for most of the oxidation catalyst introduced into the solution according to step (ii) for facilitating the conversion of unreacted alcohol to protons and water.
  • Pores in the thicker support layer are formed during slow evaporation of the solvent from the film at temperatures ranging from about 10 to about 50 °C causing the polymer to solidify, i.e., undergo gelation.
  • the catalyst-containing asymmetric membrane composites of this invention may also be prepared using salt solutions of precious metals, like platinum and ruthenium and converting the salts in-si tu to their corresponding reactive metals. This alternative embodiment includes the steps of:
  • step (iii) contacting the film with a second solvent which is miscible in the first solvent.
  • the second solvent should also be a non-solvent, e.g., water or alcohol, for the film, i.e., the film should be insoluble in the second solvent;
  • step (iii) converting the film of step (iii) to an asymmetric membrane composite structure by solvent evaporation during gelation of the polymer.
  • the film is converted to an asymmetric membrane composite comprising the non-porous, preferably continuous, water and proton permeable very thin polymeric film and an adjacent thicker porous support layer therefor, free of catalyst;
  • metal salts for exchange by the membrane are any of those known to be suitable for catalyzing the oxidation of unreacted alcohol at least to protons, for example, and
  • the improved MEAs of this invention not only find uses in direct fed methanol fuel cells and in hydrogen/air fuel cells, but are also suitable for use in other electrochemical cells and processes. For instance, in catalytic membrane reactors for
  • L5 conducting reactions They can be used in hydrogenation processes, where one reactant is a gas which preferentially diffuses across the asymmetric membrane in the reactor. Examples of such reactions include the catalytic combining of hydrogen and oxygen to form hydrogen peroxide.
  • the invention can also be used in separating highly explosive mixtures of hydrogen and oxygen.
  • 25 oxidation/reduction can be used when measured against a reference electrode. This provides a suitable means for measuring alcohol concentratio .
  • novel MEAs of this invention may also be employed in electrochemical syntheses reactions in electrolytic cells. They
  • FIG. 1 is an enlarged sectional view of an asymmetric membrane composite
  • FIG. 2 is an enlarged sectional view of the asymmetric membrane composite of Fig. 1 with supplemental membrane;
  • FIG. 3 is exploded view of a membrane electrode assembly with asymmetric membrane
  • FIG. 4 is an exploded view of a membrane electrode assembly with supplemental membrane
  • FIG. 5 is a diagrammatic view of a direct fed methanol type fuel cell with membrane electrode assembly of the invention.
  • FIG. 6 is a diagrammatic view of an energy consuming electrochemical cell for the synthesis of hydrogen peroxide employing a membrane electrode assembly of the invention.
  • Figs. 1 and 2 we find illustrated enlarged views of two embodiments of asymmetric membrane composite structures 10 and 12.
  • the composite structures are readily prepared from known, commercially available cationic polymers, such as E. I. DuPonfs Nafion® brand perfluorosulfonic acid membranes, like Nafion 112, 115 and 117.
  • Other representative polymeric membranes include, Flemion® and Aciplex® brand perfluorosulfonic acid polymeric membranes from Asahi Glass, and Neosepta® brand perfluorinated membranes from Tokuyama Soda.
  • Other representative examples of useful polymeric membrane materials include those having hydrocarbon backbones prepared using non-fluorinated polymers.
  • Sulfonic acid groups are introduced onto their backbones for proton transport conductivity.
  • a few representative examples include poly(styrene sulfonic acid), sulfonated poly (etherether-ketone) or PEEK, sulfonated poly (phenylene sulfide) , sulfonated polyphosphazene, sulfonated poly (ethersulfone) , polybenzimidazole (PBI) , and the like.
  • sulfonic acid based membranes provide the most favorable properties for fuel cell applications, Carboxylic acid type membranes, while satisfactory for some applications, exhibit lower conductivities, and consequently, are less preferred in fuel cell applications.
  • Membranes with the lowest methanol diffusion coefficients are most preferred. This would include such representative examples as Nafion 117 grade material having a diffusion coefficient of 6.5x 10 " cm /sec @ 30°C and polyphosphazene based membranes having even lower methanol diffusion coefficients in the range of 8.5x10 cm /sec. It will be noted that methanol diffusion coefficient data are not always readily available for ion-exchange membranes, however, diffusion coefficients are often based on comparisons against a standard, such as Nafion 117 membrane, and quoted on a basis of percent improvement. See, for example, U.S. Pat. 5,672,439.
  • the foregoing polymeric membranous materials may be generally characterized as being non-porous, but permselective, i.e. , allowing transport of mainly positively charged ions, water and gases, including the transport of protons, so they readily diffuse through and crossover from one side of the membrane to the opposite side.
  • such polymers usually have inherent inefficiencies allowing the diffusion of unwanted molecules and ionized substances to pass from one side of the membrane to the other. This would include alcoholic fuel mixtures, like unreacted methanol in direct feed methanol fuel cells. Unreacted methanol allowed to pass from the anode to the cathode side of a fuel cell becomes oxidized by oxygen and catalyst to form carbon dioxide and water. Consequently, there is both loss of fuel and a voltage penalty.
  • the asymmetric membranes of the invention retain a very thin outer film or skin layer 14 of the continuous, non-porous, proton conducting polymeric membrane.
  • the thin skin layer 14 may have a thickness ranging generally from about 1 to about 10 microns.
  • the thin outer continuous film layers 14 of the asymmetric composites 10 and 12 retain the important native properties of the original polymer, including the selective transport of mainly water, gases, protons, and other positively charged ions. Similarly, properties of the outer layer 14 restrict crossover of anions and non-polar solvents like alcohol fuels .
  • backside stratum or support layer 16 of the same asymmetric membrane composite is substantially different in its physical properties.
  • Backside support layer 16, which is an extension of thin film layer 14, is several fold thicker than the outer membrane layer 14.
  • thicker support layer 16 is comprised of a matrix of tortuous paths 18 providing a high surface area for maximizing contact with unreacted fuel or other electrolyte-containing liquids.
  • high surface area internal matrices 18 provide a useful substrate or bed for the deposition of catalytic material 20, and as reaction site for efficient mass transport of even minor amounts of unreacted methanol remaining in fuel cell fuel .
  • the thicker, higher surface area backing layer 16 with catalyst 20 deposited mainly in the high surface area interstices of tortuous paths 18 assures very prompt reaction kinetics, whereby unreacted methanol, for instance, is taken to its highest oxidation state, i.e., protons, water and carbon dioxide. Thus, little if any unreacted fuel is available for transport to the cathode side of the membrane for unwanted diminution of voltage.
  • the potential for unwanted crossover occurring will be reduced further as a result of the continuous, non-porous and permselective properties of layer 14.
  • the thin outer film layer 14 with its non-porous, permselective properties will perform much as a fail-safe, limiting transport of any unoxidized methanol to the cathode side while readily allowing transport of protons and water after contact with the porous support layer.
  • Fig. 2 provides a still further option of employing a supplemental cationic membrane film layer 22 which can be engaged with thin film layer 14 of the asymmetric membrane.
  • supplemental membrane 22 is also a permselective, cationic type membrane it may be optionally employed in the event of any imperfections, for example, which may occur in the thin outer film layer 14.
  • Supplemental film layer 22 may also be used in the event a spacer is needed in filing a gap in any electrolytic cell employing the asymmetric membranes of this invention.
  • the starting ion-exchange polymeric material will determine the initial steps employed in preparing the asymmetric membranes of the invention. If the starting ion-exchange polymer is a perfluorosulfonic acid type, like Nafion, solutions can be prepared by means of a mixed solvent system. In this regard, a mixture of 1-propanol, 2-propanol, butanol and methanol can be used as the solvent system. Nafion brand polymer commercially available in the form of beads or powder is mixed with the above solvent mixture using high shear at temperatures ranging up to about 90°C and under pressure. A solution containing >10% polymer can be prepared by this method.
  • preformed solutions of Nafion ion-exchange polymer are available from DuPont.
  • the solution consists of at least 10% perfluorosulfonic acid polymer dissolved in a solvent containing 1-propanol (up to 30%) , 2- propanol (up to 30%), butanol (up to 10%), and methanol (from 5 to 10%) .
  • the solution as received from the manufacturer can be used as is to prepare the asymmetric membranes of the invention.
  • perfluorosulfonic acid polymer solutions can be prepared from the thermoplastic form containing sulfonyl fluoride groups (S0 2 F) in place of sulfonic acid groups ⁇ SO H) .
  • the sulfonyl fluoride polymer is usually the starting material for preparation of ion exchange membrane, like Nafion brand, etc.
  • the sulfonyl fluoride polymer can also be used to prepare the asymmetric membranes by conversion of the sulfonyl fluoride groups to sulfonic acid (salt form such as sodium) by hydrolysis of the polymer.
  • the sulfonyl fluoride is immersed in at least 25 weight-percent sodium hydroxide for about 16 hours at a temperature of about 90 °C. Sulfonyl fluoride is thus converted to sodium sulfonate (S0Na) .
  • the sulfonic acid form of the membrane is prepared by equilibrating the membrane in acid solution, such as sulfuric acid, followed by rinsing in deionized water.
  • Sulfonated polyphos-phazene, poly(styrene sulfonic acid)-, sulfonated poly (etherether-ketone) (PEEK), sulfonated poly (phenylene sulfide) poly (ether-sulfone) , and so on, are soluble in organic solvents like N-methyl pyrrolidone, dimethyl formamide (DMF) , dimethyl acetamide, dimethyl acetate, etc.
  • Solutions of the above membranes are prepared in concentrations generally ranging from about 10 to about 30 percent by-weight.
  • a film of the polymer is cast on a glass plate heated to 50 to 70°C using a doctor blade to control the desired thickness.
  • the film is then immersed in a second solvent, usually water, alcohol or a mixture of solvents which prompts the formation of a non-porous thin skin layer typically in the range of 1 to 10 microns depending on the rate of evaporation of the solvent.
  • This process also provides the thicker, highly porous support layer backing for the thin film layer.
  • the thickness of the membrane should be sufficient to withstand the pressures generated by transport without rupturing the membrane.
  • the asymmetric membrane will have a thickness ranging from about 0.1 to about 1.0 mm.
  • Platinum and ruthenium metal alloys are preferred for oxidation of methanol to carbon dioxide, however, other known solid catalytic materials may be employed in order to meet the end-use applications of the asymmetric membrane composites disclosed herein.
  • the catalyst for example, can be deposited on high surface area carbons, such as Vulcan® XC-72 available from Cabot Carbon. Similar type catalysts are also commercially available from E-TEK, Division of DeNora N.A., Inc. (Somerset, NJ) , and Johnson-Matthey Company, UK.
  • Platinum-ruthenium alloy catalyst may be used at a loading in the range from about 25 to about 75 percent-by-weight. Most preferred platinum and ruthenium catalyst compositions comprise equal quantities of both platinum and ruthenium metals or metal alloys.
  • the catalyst-containing membrane can also be fabricated by first making the asymmetric membrane. Salt solutions of platinum and ruthenium, such as metal chlorides can be exchanged into the asymmetric membrane. The metal salts imbibed by the membrane are then reduced in-si tu to the corresponding metal by contacting with reducing agents, such as sodium borohydride, stannous chloride, hydrazine, formic acids, to name but a few.
  • reducing agents such as sodium borohydride, stannous chloride, hydrazine, formic acids, to name but a few.
  • the asymmetric membrane and the supplemental ion-exchange membrane can be bonded together by methods generally known among ordinary skilled artisans in the field. This would include such methods as solvent gluing where a uniform layer of solvent is first painted onto the thin film layer 14 of the asymmetric membrane. The supplemental membrane is then compressed onto the asymmetric membrane. The assembly is then dried to evaporate the solvent.
  • Figs. 3 and 4 are exploded views of MEAs of the invention.
  • Fig. 3 is illustrative of MEA 24 with the asymmetric membrane composite of the type shown by Fig. 1
  • Fig. 4 is illustrative of MEA 26 having incorporated the asymmetric membrane of Fig. 2 with supplemental membrane 22.
  • MEAs 24 and 26 comprise asymmetric membranes 10 and 12, respectively, each utilizing high surface area porous cathode electrodes 28 and a cathode catalytic layer 30 bonded to inside surface of the cathode 28 and the asymmetric membrane composite.
  • the porous cathodes 28 are preferably high surface area carbon cloths or papers.
  • Catalytic layer 30 is needed in a fuel cell to facilitate the reduction of air or oxygen with protons to form water at the cathode 28.
  • Catalyst layer 30 preferably comprises platinum metal or other precious metal deposited onto a high surface area carbon substrate, such as Vulcan XC-72 carbon from Cabot Carbon. Such catalysts are also commercially available through ordinary channels of commerce. Platinum loading can range from about 1 to about 5 mg/cm While catalytic layer 30 and high surface area cathode 28 are illustrated in exploded view, in practice they are in intimate contact with one another. Cathode electrode 28 and catalytic layer 30 are bonded with adhesive, and with the application of heat and pressure formed into a unit structure (not shown) using methods familiar to persons skilled in the art. This cathode-catalyst structure can also be affixed to the thin non-porous film layer 14 (Fig 3) or the supplemental membrane 22 (Fig.4) of the asymmetric membrane composites using the same technique.
  • porous, high surface area anode electrode structures 32 are prepared using carbons, e.g., cloths, papers, etc., like those used in the cathode electrode structures.
  • anode catalyst layers 34 are employed in combination with the anode structures to facilitate the oxidation of alcohol/water fuel mixtures to form protons, water and carbon dioxide.
  • the normal catalyst loading for an anode in a methanol fuel cell is in the range of about 1 to about 10 mg/cm , and more preferably at about 2 to about 5 mg/cm .
  • the required amount of catalyst e.g. 20% platinum-ruthenium on carbon
  • Teflon® from about 5 to about 30 percent, available as a dispersion from E. I.
  • the composite structure of porous carbon cloth or paper with the catalyst layer thus forms the anode structure for the methanol fuel cell.
  • the MEAs of the invention are useful in both energy producing and energy consuming electrochemical cells.
  • a preferred embodiment of an energy producing fuel cell is illustrated by Fig. 5 which incorporates the MEA of Fig. 4.
  • Direct feed methanol fuel cell 36 comprises asymmetric membrane composite 12 with a centrally positioned non-porous, permselective, thin, continuous proton exchange membrane 14, thicker porous support layer backing 16 with methanol oxidation ' catalyst and supplemental non-porous proton exchange membrane 22 adjacent to membrane 14.
  • Fuel cell 36 also includes an anode electrode assembly comprising high surface area anode electrode 32 and anode catalytic layer 34 for converting incoming methanol fuel mixture to protons, carbon dioxide and water.
  • the fuel cell is equipped with a cathode assembly comprising cathode electrode 28 and cathode catalytic coating 30 for reducing air or oxygen at the cathode assembly in the presence of protons from the anode side to water.
  • a cathode assembly comprising cathode electrode 28 and cathode catalytic coating 30 for reducing air or oxygen at the cathode assembly in the presence of protons from the anode side to water.
  • Each side of the fuel cell employs graphite blocks 38 and 42 with horizontal channels 40 and 44. Graphite is used in the fuel cell as a current collector and provides the channels 40 and 44 for reactant and product flow.
  • a flat sheet of graphite of appropriate thickness, usually in the range of Va to H inch can be used to produce the channels
  • the fuel cell also employs copper current collectors 46 and 48 in engagement with graphite blocks 38 and 42. Current collectors 46 and 48 complete the cell circuit for power transmission to a load 58.
  • the cell employs stainless steel end plates 50 and 52 with an insulative plastic film layers 54 and 56.
  • an aqueous solution of methanol ranging from about 0.5 to about 2 molar in strength (approximately 7 percent solution of methanol and water) is circulated past the anode. Simultaneously, oxygen or air is used as the oxidant and past through the cathode. If air is used (oxygen content of 21%) as the oxidant, the flow requirements are at least 3 times the stoichiometric flow required at the desired current density.
  • the concentration of methanol in the feed solution should be monitored to determine the utilization of methanol fuel for cell operation. Maintenance of a steady voltage (>0.4 volts) at even 80 to 90% utilization of methanol indicates an improved fuel cell operation.
  • Maximum utilization of methanol fuel refers to the fact that the fuel cell maintains a steady voltage even when 90% of the methanol in the feed has been depleted. If any of the methanol fuel is lost to the cathode due to diffusion across the membrane, the utilization factor could be as low as 50%, or even less .
  • Fig. 6 illustrates a representative electrochemical cell employing the MEAs of the invention for the synthesis of hydrogen peroxide.
  • the production of hydrogen peroxide may be illustrated by the following reactions:
  • cell 59 includes an asymmetric membrane composite structure with a thin, non-porous permselective film layer 14 and a porous support layer 16 with a catalyst, either a high surface area carbon or a metal oxide catalyst.
  • Electrolytic cell 59 includes a porous carbon cloth 62 with catalytic layer 60. Oxides of platinum, iridium, nickel and ruthenium are used as the catalyst. These catalysts are deposited onto high surface area carbons to form the catalytic layer 60.
  • the catalyst layer 60 is bonded to thin film layer 14 of the asymmetric membrane.
  • a very narrow channel 64 is provided for the flow of reactants and products (water and oxygen) at the anode.
  • any suitable catalyst for oxygen evolution including metal oxides, such as ruthenium, iridium, nickel and platinum can be employed.
  • Catalyst layer 68 may comprise high surface area carbons, like Vulcan XC- 72, quinones, e.g., hydroquinone and anthraquinone, and various substituted anthraquinones, such as alizarine, quinizarine, etc., adjacent to a porous carbon cloth 70 is used to effect the reduction of oxygen to hydrogen peroxide.
  • a graphite block cathode 74 flow channels 76 for reactant oxygen and hydrogen peroxide (product) is in direct contact with porous carbon cloth 70.
  • a stainless steel 72 acts as a current collector, as well as a distributor from the DC. power supply.
  • Each side of the cell includes stainless steel end plates 78 and 80 and insulative polyethylene sheet 82 and 84 positioned between the electrodes and end plates .
  • An asymmetric membrane composite portion of a membrane electrode assembly is first prepared.
  • a solution of sulfonated polyphosphazene, poly (bis3-methylphenoxy phosphazene) , in dimethylacetamide solvent is prepared to a concentration of at least 20 percent-by-weight.
  • the solution (100 to 200 ml) is stirred in a round-bottomed flask fitted with a heating mantle.
  • the mixture is stirred vigorously at a temperature of 60 to 70°C to obtain a homogeneous solution.
  • 0.1 to 0.3 grams of Pt/Ru on carbon is added to the polymer solution as a methanol oxidation catalyst.
  • the particles are homogeneously dispersed in the solution (100 to 200 ml) .
  • a clean dry glass plate @ 50 to 70°C is prepared for casting the solution to form the asymmetric membrane.
  • the polymer/ oxidation catalyst solution is. spread over 100 to 150 cm of the glass plate. The thickness of the membrane is then adjusted by means of a doctor blade.
  • the glass plate with the cast film is then immediately immersed in a cold water bath to form an asymmetric membrane.
  • the plate is removed from the bath after 5 to 15 minutes and the film is peeled off the glass plate.
  • the resulting membrane contains a very thin (1 to 10 ⁇ m) continuous polymer film on top with a porous under layer (0.1 to 1 mm) . Since the film is cast with the catalyst particles distributed homogeneously in solution, the film contains catalyst deposited in the. orous layer of the membrane, also with some of the catalyst in the continuous top layer.
  • the presence of methanol oxidation catalyst distributed through the high surface area of the porous layer promotes the oxidation of any residual methanol reaching the membrane separator.
  • EXAMPLE 2 A second asymmetric membrane is prepared following the protocol of Example 1, except a solution of the ion-exchange polymer is prepared without the addition of catalyst. In this case, a similar film is cast from a solution of sulfonated polyphosphazene in dimethyl acetate (at least 20%) without the addition of catalyst. The membrane is equilibrated in a solution containing platinum and ruthenium salts, i.e., a 1:1 ratio of potassium chloroplatinate and ruthenium chloride. Platinum and ruthenium are exchanged into the ion exchange polymer. The membrane is then washed thoroughly in water. The membrane is equilibrated in a solution of sodium borohydride or hydrazine for reduction of the metal ion exchanged in the membrane. An asymmetric membrane with metal catalyst distributed throughout the membrane results. EXAMPLE 3
  • the formation of a thin continuous layer of proton exchange polymer is important for use in fuel cells or any other type of electrochemical device.
  • the film provides a barrier for complete mixing of reactants and products from the anode and cathode. Thicker films provide better barriers than thinner films. However, the resistance across the membrane also increases with the thickness of the film formed. With the methods described above, it is possible to control the thickness of the continuous film by controlling the temperature and the solvent mixture used as the non-solvent (water) . The thickness of the film can be measured by cross-sectional SEM.
  • the thickness of the film is found to be too small ( ⁇ 5 ⁇ ) to withstand the pressure applied during cell operation, it is necessary to bond a supplemental membrane layer of the same compositional makeup as the separator between the two asymmetric membrane layers used in the anode and cathode side. They can be bonded together using a solvent or by the application of pressure and temperature (500 to 1500 psi at 50 to 90°C) .
  • the asymmetric membranes can be formed directly on catalyzed porous carbon electrodes (anode) .
  • the porous carbon electrode with a layer of anode catalyst is placed on a clean glass plate. The edges are taped to the glass with masking tape.
  • a concentrated solution of a proton-transporting membrane in a first organic solvent, with or without methanol oxidation catalyst added to the solution according to Examples 1 or 2 , respectively is cast directly onto the porous carbon electrode.
  • the coated electrode is then immersed in a cold water bath to form the asymmetric membrane composite structure with a thin non-porous outer film layer and a thicker porous inner layer with methanol oxidation catalyst distributed mainly in within the porous layer of the ion-exchange polymer securely affixed to the anode electrode structure .
  • the membrane-anode composite is then fabricated into an MEA by bonding the cathode component.
  • a high surface area carbon cloth having a platinum metal coating is applied to the opposite side, i.e., the thin film layer of the asymmetric coating and at temperatures in the range from about 30 to about 110°C @ pressures from about 1500 to about 2500 psi bonding the structure together into a one-piece MEA.
  • the methods disclosed herein are also well suited for asymmetric membranes prepared from proton exchange polymers having hydrocarbon polymer backbones, unlike Nafion brand perfluorosulfonic acid membranes. While Nafion brand membranes are preferred, the invention contemplates membranes prepared from proton exchange polymers having sulfonic acid reactive groups with non-fluorinated polymer backbones, such as poly(styrene sulfonic acid) membranes.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Sustainable Development (AREA)
  • Sustainable Energy (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Fuel Cell (AREA)

Abstract

L'invention porte sur des ensembles électrodes à membrane comprenant un composite à membrane asymétrique, une cathode et une anode en contact électrique avec le composite de façon à former des électrolytes polymères solides. Les composites à membrane asymétrique comprennent une couche de film polymère mince, continue, non poreuse, mais perméable à l'eau et aux protons, une strate ou couche adjacente plus épaisse constituée d'un renfort à support poreux et un catalyseur imprégné principalement dans la région à support poreux. Le catalyseur peut être, par exemple, approprié à l'oxydation d'un alcool inaltéré. Les ensembles électrodes à membrane peuvent être utilisés à la fois dans des cellules électrochimiques produisant de l'énergie telles que des piles à combustible, et des cellules électrochimiques consommant de l'énergie utilisées dans la synthèse des produits chimiques. Les ensembles électrodes à membrane peuvent être adaptés pour des piles à combustible à alimentation directe au méthane et sont notamment utiles pour éliminer la liaison du méthanol à la cathode et la réduction de tension non désirée.
PCT/US2002/001988 2002-01-24 2002-01-24 Ensembles electrodes a membrane pour cellules electrochimiques WO2003069713A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AU2002240045A AU2002240045A1 (en) 2002-01-24 2002-01-24 Membrane electrode assemblies for electrochemical cells
PCT/US2002/001988 WO2003069713A1 (fr) 2002-01-24 2002-01-24 Ensembles electrodes a membrane pour cellules electrochimiques

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US2002/001988 WO2003069713A1 (fr) 2002-01-24 2002-01-24 Ensembles electrodes a membrane pour cellules electrochimiques

Publications (1)

Publication Number Publication Date
WO2003069713A1 true WO2003069713A1 (fr) 2003-08-21

Family

ID=27732060

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US2002/001988 WO2003069713A1 (fr) 2002-01-24 2002-01-24 Ensembles electrodes a membrane pour cellules electrochimiques

Country Status (2)

Country Link
AU (1) AU2002240045A1 (fr)
WO (1) WO2003069713A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1905797A4 (fr) * 2005-07-19 2009-04-22 Toyota Motor Co Ltd Membrane poreuse, procédé de production de la membrane poreuse, membrane à électrolyte polymère solide, et pile à combustible

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0631337A2 (fr) * 1993-06-18 1994-12-28 Tanaka Kikinzoku Kogyo K.K. Composition d'électrolyte solide à base de polymères
JPH07201344A (ja) * 1993-12-28 1995-08-04 Toto Ltd 低温作動固体電解質型燃料電池
JPH10270057A (ja) * 1997-03-21 1998-10-09 Toshiba Corp 固体高分子型燃料電池

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0631337A2 (fr) * 1993-06-18 1994-12-28 Tanaka Kikinzoku Kogyo K.K. Composition d'électrolyte solide à base de polymères
JPH07201344A (ja) * 1993-12-28 1995-08-04 Toto Ltd 低温作動固体電解質型燃料電池
JPH10270057A (ja) * 1997-03-21 1998-10-09 Toshiba Corp 固体高分子型燃料電池

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1905797A4 (fr) * 2005-07-19 2009-04-22 Toyota Motor Co Ltd Membrane poreuse, procédé de production de la membrane poreuse, membrane à électrolyte polymère solide, et pile à combustible

Also Published As

Publication number Publication date
AU2002240045A1 (en) 2003-09-04

Similar Documents

Publication Publication Date Title
US6602630B1 (en) Membrane electrode assemblies for electrochemical cells
US6946211B1 (en) Polymer electrolyte membrane fuel cells
JP3607862B2 (ja) 燃料電池
US6562446B1 (en) Multi-layer polymer electrolyte-membrane, electrochemical apparatus and process for the preparation of multi-layer polymer electrolyte membrane
JP3970390B2 (ja) 固体高分子燃料電池用膜−電極接合体
EP2168187B1 (fr) Couche de catalyseur
JP2003515894A (ja) 循環電解質を有する直接メタノール電池
JP2005537618A (ja) 燃料電池電極
WO2009109780A1 (fr) Structures de membrane conductrice d'ions
CN100521317C (zh) 用于直接甲醇燃料电池的膜电极单元及其制造方法
JP2004512652A (ja) 固体ポリマー燃料電池用カソード層構造物及びこのような構造物を含有する燃料電池
KR101201816B1 (ko) 막-전극 어셈블리, 그 제조방법, 및 이를 포함하는 연료전지 시스템
US20090042091A1 (en) Supported catalyst layers for direct oxidation fuel cells
JP5058429B2 (ja) 複合薄膜
KR100524819B1 (ko) 고온용 양성자 전도성 고분자막과 이의 제조방법 및 이를이용한 막-전극 어셈블리와 이를 포함하는 연료전지
JP3931027B2 (ja) 固体高分子電解質、それを用いた固体高分子電解質膜、電極触媒被覆用溶液、膜／電極接合体及び燃料電池
Lobato et al. Application of Sterion® membrane as a polymer electrolyte for DMFCs
US20040209965A1 (en) Process for preparing a solid polymer electrolyte membrane
JP2003142124A (ja) 電解質膜およびそれを用いた固体高分子型燃料電池
WO2006064542A1 (fr) Membrane electrolytique pour pile a combustible, procede de production de ladite membrane, assemblage electrode/membrane et pile a combustible
EP1284518A1 (fr) Membrane polymère conductrice ionique composite renforcée et cellule à combustible l'utilisant
WO2003069713A1 (fr) Ensembles electrodes a membrane pour cellules electrochimiques
JP5609475B2 (ja) 電極触媒層、電極触媒層の製造方法、この電極触媒層を用いた固体高分子形燃料電池
JP2009238754A (ja) 固体高分子電解質とその膜及びそれを用いた膜／電極接合体並びに燃料電池
KR100708489B1 (ko) 수소이온 전도성 고분자 전해질막의 제조방법 및 이를이용한 연료전지

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): AE AG AL AM AT AU AZ BA BB BG BR BY BZ CA CH CN CO CR CU CZ DE DK DM DZ EC EE ES FI GB GD GE GH GM HR HU ID IL IN IS JP KE KG KP KR KZ LC LK LR LS LT LU LV MA MD MG MK MN MW MX MZ NO NZ OM PH PL PT RO RU SD SE SG SI SK SL TJ TM TN TR TT TZ UA UG UZ VN YU ZA ZM ZW

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): GH GM KE LS MW MZ SD SL SZ TZ UG ZM ZW AM AZ BY KG KZ MD RU TJ TM AT BE CH CY DE DK ES FI FR GB GR IE IT LU MC NL PT SE TR BF BJ CF CG CI CM GA GN GQ GW ML MR NE SN TD TG

121 Ep: the epo has been informed by wipo that ep was designated in this application
DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
122 Ep: pct application non-entry in european phase
NENP Non-entry into the national phase

Ref country code: JP

WWW Wipo information: withdrawn in national office

Country of ref document: JP

点击 这是indexloc提供的php浏览器服务，不要输入任何密码和下载