WO2002031903A1 - Corps de carbone poreux pour cellule electrochimique et procede de fabrication - Google Patents

Corps de carbone poreux pour cellule electrochimique et procede de fabrication Download PDF

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Publication number
WO2002031903A1
WO2002031903A1 PCT/US2001/030357 US0130357W WO0231903A1 WO 2002031903 A1 WO2002031903 A1 WO 2002031903A1 US 0130357 W US0130357 W US 0130357W WO 0231903 A1 WO0231903 A1 WO 0231903A1
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WIPO (PCT)
Prior art keywords
porous carbon
compound
carbon body
pores
amount
Prior art date
Application number
PCT/US2001/030357
Other languages
English (en)
Inventor
Wayde R. Schmidt
Albert T. Pucino
Bardia Guilani
Myron Krasij
Ned E. Cipollini
Brian F. Dufner
Original Assignee
International Fuel Cells, Llc
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.)
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Application filed by International Fuel Cells, Llc filed Critical International Fuel Cells, Llc
Priority to AU2001293157A priority Critical patent/AU2001293157A1/en
Publication of WO2002031903A1 publication Critical patent/WO2002031903A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8605—Porous electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/02—Details
    • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
    • H01M8/0204—Non-porous and characterised by the material
    • H01M8/0213—Gas-impermeable carbon-containing materials
    • 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
    • H01M8/1007—Fuel cells with solid electrolytes with both reactants being gaseous or vaporised
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to fuel cells that are suited for usage in 5 transportation vehicles, portable power plants, or as stationary power plants, and the invention especially relates to a porous carbon body that may be used within a fuel cell for transporting reactant, product and coolant fluids to, through and from the fuel cell, for conducting electricity from one cell to an adjacent cell, for providing a fluid barrier to gaseous reactants, for defining gaseous reactant distribution channels, o and/or for providing mechanical integrity to the fuel cell.
  • Fuel cells are well-known and are commonly used to produce electrical energy from reducing and oxidizing reactant fluids to power electrical apparatus such as apparatus on-board space vehicles, or on-site generators for buildings.
  • a plurality of 5 planar fuel cells are typically arranged in a stack surrounded by an electrically insulating frame structure that defines manifolds for directing flow of reducing, oxidant, coolant and product fluids as part of a fuel cell power plant.
  • Each individual fuel cell generally includes an anode electrode and a cathode electrode separated by an electrolyte.
  • a reducing fluid such as hydrogen is supplied to the anode electrode, 0 and an oxidant such as oxygen or air is supplied to the cathode electrode.
  • the electrons are conducted to an external load circuit and then returned to the cathode electrode, while the hydrogen ions transfer through 5 the electrolyte to the cathode electrode, where they react with the oxidant and electrons to produce water and release thermal energy.
  • PEM proton exchange membrane
  • the anode and cathode electrodes of such fuel cells are separated by different types of electrolytes depending on operating requirements and limitations of the working environment of the fuel cell.
  • One such electrolyte is the aforesaid proton o exchange membrane ("PEM”) electrolyte, which consists of a solid polymer well- known in the art.
  • PEM proton o exchange membrane
  • Other common electrolytes used in fuel cells include phosphoric acid or potassium hydroxide held within a porous, non-conductive matrix between the anode and cathode electrodes.
  • PEM cells have substantial advantages over cells with liquid acid or alkaline electrolytes in satisfying specific operating parameters because the membrane of the PEM provides a barrier between the reducing fluid and oxidant that is more tolerant to pressure differentials than a liquid electrolyte held by capillary forces within a porous matrix. Additionally, the 5 PEM electrolyte is fixed, and cannot be leached from the cell, and the membrane has a relatively stable capacity for water retention.
  • An operational limit on performance of a fuel cell is defined by an ability of the cell to maintain the water balance as electrical current drawn from the cell into the external load circuit varies and as an operating environment of the cell varies.
  • Such a component is typically formed of a porous carbon body and is commonly o referred to under various names including "cooler plate”, “water transport plate”,
  • a porous carbon body that makes up such a water transport plate must be porous, wettable to water, have a high rate of water permeability, have a high bubble pressure, be a good electrical and thermal conductor, have good compressive and flexural strength, and the porous carbon body must be chemically stable in the s environment of an operating PEM fuel cell.
  • Some of these qualities require characteristics that are inconsistent with characteristics appropriate for other such qualities. For example, to increase bubble pressure to thereby enhance a gaseous seal between gaseous oxidant and fuel reactants on opposed sides of the porous carbon body, it is appropriate to have a small mean pore size of the pores within the body.
  • porous carbon body includes a resin
  • Austrian Patent 389,020 issued on February 15, 1989 to Schutz also discloses a porous carbon structure that may be utilized in a variety of roles within a fuel cell, 5 including usage as a transport medium for water, and usage as an end plate secured between a cathode of a first cell and an anode of a second, adjacent cell.
  • the porous carbon body is prepared by mixing with finely ground graphite or carbon black a pore formation agent such as baking powder or sugar, and or 0 - 50% microporous fillers such as kaolin or asbestos. The mixture is then mixed with 0 - 10% sodium o carboxymethycellulose and suspended in a polysulfone solution.
  • That mixture is then applied to a carrier substance, then dried and sintered, and the pore formation agents are removed by boiling and/or washing.
  • the resultant porous carbon body is described as having a majority of pores having a size of 0.001 - 1 microns. While the Schutz porous carbon structure describes some valuable characteristics for application 5 in a fuel cell, the experience of the present inventors is that such porous carbon bodies operate satisfactorily for a limited duration, but eventually the bodies becomes non- wetting, or hydrophobic, and hence unable to prevent cross-over through the body of gaseous reactant fluids resulting in a dangerous mixing of the reactant fluids.
  • the hydrophilic or wetting agent is mixed together with the electronically conductive material and resin to produce a "uniform dispersion" of the wetting agent, and the mixture is then molded into a plate at 500 - 4,000 p.s.i. (3447 Kpa - 27,580 Kpa) and 250 - 800°F (121°C - 427°C) so that the wetting agent "promotes the formation of 5 pores in the molded product by preventing the resin and other components from forming one continuous phase" (Col. 6, lines 34 - 38). Koncar et al.
  • porous carbon body for a fuel cell that may be efficiently manufactured, and that provides appropriate porosity and mean pore size to support effective water transport, thermal and electrical conduction, and o mechanical strength necessary for operation of a PEM fuel cell.
  • the invention is a porous carbon body and method of manufacture of the body for usage in a fuel cell.
  • the porous carbon body comprises an electrically conductive graphite powder in an amount of between 40% - 60% by weight of the body; a carbon 5 fiber in an amount of between 20% - 40% by weight of the body; a hydrophobic binder in an amount of between 10% - 30% by weight of the body; wherein the body has a mean pore size of greater than 2.0 microns, and an open porosity of greater than 25%; and, wherein the pores in the body are rendered partially hydrophilic by incorporation of a hydrophilic rendering compound onto an interior surface of the o pores, the compound being a metal oxide, hydroxide, oxyhydroxide, oxyhydroxide hydrate, or oxide hydrate compound, and the compound having a solubility in water of less than about 10 "6 moles per liter.
  • the body has a bubble pressure of greater than 5 pounds per square inch (“p.s.i.") 34.47 Kpa, liquid water permeability of greater than 10 x 10 "16 square meters and a loading of the hydrophilic rendering compound of greater than 15 mg. per gram of the porous carbon body.
  • the porous carbon body as described achieves long term chemical stability for 5 operation in a PEM fuel cell operating up to 1,000 - 2,000 amps per square foot
  • the porous carbon body may be efficiently made by first mixing together an electrically conductive graphite powder in an amount between 40% - 60% by weight of the mixture, a carbon fiber in an amount of between 20% - 40% by weight of the mixture, and a hydrophobic binder in an amount of between 10% - 30% by weight of 5 the mixture; then simultaneously compressing and heating the mixture in a mold at a pressure of between 100 - 2,500 p.s.i.
  • the step of heating the porous carbon body includes heating the body to a temperature high enough and heating for a period of time long enough to hydrolyze the metal salt to a metal hydroxide, and to a temperature less than a heat deflection temperature of the hydrophobic binder to enhance conductivity of the body.
  • the porous carbon body of the present invention may be efficiently manufactured without the known costly and time consuming high temperature heating 5 undertaken to graphitize many known porous carbon bodies used in fuel cells.
  • the resulting porous carbon body also exhibits appropriate bubble pressure, water permeability, electrical resistivity, thermal conductivity, compressive and flexural strength to efficiently serve as a water transport plate, separator plate or related component of a PEM fuel cell operating at 1,000 - 2,000 ASF (1.1 to 2.15 amps per 5 square cm) for a very long time period.
  • Figure 1 is a cross-sectional, schematic representation of a fuel cell employing a porous carbon body constructed in accordance with the present invention.
  • Figure 2 is a graph showing degradation of conductivity of a porous carbon body as a function of a drying temperature employed in rendering pores of the body o hydrophilic.
  • Figure 3 is a graph showing per cent fill of a void volume of a porous carbon body as a function of loading of a hydrophilic rendering compound.
  • FIG. 1 shows a schematic, cross-sectional representation of a fuel cell means for generating electrical energy from process oxidant and reducing fluid reactant streams that is generally designated by the reference numeral 10.
  • the fuel cell 10 has a porous carbon body constructed in accordance with the present invention in the form of a first or anode water transport plate 12 and a second or cathode water transport plate 14.
  • the anode and cathode water transport plates 12, 14 are at opposed sides of the fuel cell 10, which includes a membrane electrode assembly (“M.E.A.") 16 that consists of an electrolyte such as a proton exchange membrane (“PEM”) 18, an anode catalyst 20 and a cathode catalyst 22 secured on opposed sides of the electrolyte 18.
  • M.E.A. membrane electrode assembly
  • the fuel cell 10 may also include an anode support means that is secured between and in fluid communication with the anode catalyst 20 and the anode water transport plate 12 for passing a reducing fluid or fuel stream adjacent the anode catalyst 20.
  • the anode support means may include one or more porous layers, any one or all of which may be wetproofed, as is well known in the art, such as a porous anode substrate 24 and a porous anode diffusion layer 26.
  • the fuel cell may also include a cathode support means that is secured between and in fluid communication with the cathode catalyst 22 and the cathode water transport plate 14 for passing a process oxidant stream adjacent the cathode catalyst 22.
  • the cathode support means may include one or more porous layers, any one or all of which may be wetproofed, as is well known in the art, such as a porous cathode substrate 28, and a porous cathode diffusion layer 30.
  • the anode and cathode support means may be one or more layers of carbon-carbon fibrous composites that may be wetproofed with a hydrophobic substance such as "Teflon", in a manner well-known in the art.
  • the anode water transport plate 12 defines a plurality of fuel flow channels 32 that are in fluid communication with each other and with a fuel inlet 34 that receives the reducing fluid so that the fuel inlet 34 and flow channels 32 cooperate to pass the reducing fluid fuel through the fuel cell 10 in fluid communication with the anode catalyst 20.
  • the cathode water transport plate 14 defines a plurality of oxidant flow channels 36 that are in fluid communication with each other and with an oxidant inlet 38 that receives the process oxidant so that the oxidant inlet 38 and oxidant flow channels 36 cooperate to pass the process oxidant through the fuel cell 12 in fluid communication with the cathode catalyst 22.
  • the plurality of fuel flow channels 32 are often characterized as an "anode flow field" secured adjacent the anode catalyst, and the anode flow field may include the pore volume of the anode diffusion layer 26 and anode substrate 24.
  • the plurality of oxidant flow channels 36 may be characterized as a "cathode flow field", 5 and may also include the pore volume of the cathode diffusion layer 30 and cathode substrate 28.
  • the anode and cathode flow fields may be formed instead by cavities, differing channels or grooves well known in the art and defined within fuel cell components to direct the fuel and oxidant reactant streams to 0 pass adjacent the anode and cathode catalysts 20, 22.
  • the anode water transport plate 12 also includes a plurality of anode coolant channels 40A, 40B, 40C that deliver and remove a coolant stream to and from the plate 12, and similarly, the cathode water transport plate 14 includes a plurality of cathode coolant channels 42 A, 42B, 42C that deliver and remove a coolant stream to and from the plate 14. As shown in FIG.
  • the anode and cathode water transport plates 12, 14 may be structured to cooperate with adjacent water transport plates (not shown) of adjacent fuel cells in a fuel cell stack assembly (not shown), so that the anode coolant channels 40A, 40B, 40C may cooperate in mirror-image association with coolant channels in water transport plates of an adjacent fuel cell (not shown) to form a network of coolant channels for o delivering a coolant stream to the anode and cathode water transport plates 12, 14.
  • the plates 12, 14 become impermeable to gaseous movement and 5 thus form a gas barrier or seal so that the reducing fluid and process oxidant streams do not mix.
  • the fuel flow channels direct the stream of hydrogen rich reducing fluid to pass through pores of the anode diffusion layer 26 and anode substrate 24 to thereby contact the anode catalyst 20 so that the hydrogen o electrochemically reacts at the anode catalyst 20 to form protons which pass through the PEM 18 to electrochemically react with oxygen at the cathode catalyst 22 to form product water.
  • the product water must be removed from the cathode substrate diffusion layers 28, 30 and oxidant flow channels 36 at a sufficient rate to avoid flooding of the cathode catalyst 22 and thereby permit adequate oxidant to continue 5 flowing into contact with the cathode catalyst 22.
  • the cathode water transport plate 14 must have appropriate pore volume, pore size and wettability to permit the aforesaid movement of the product liquid water from the cathode support means through the plate 14 into the cathode coolant channels 42A, 42B, 42C, and to simultaneously support movement of the cooling fluid from the cathode coolant 5 channels 42 A, 42B, 42C through the plate 14 and into the oxidant flow channels 36 to humidify the oxidant stream.
  • the cathode water transport plate 14 must also be chemically stable in the acidic environment of the operating PEM fuel cell 10 for a long term (exceeding for example 2,000 hours of operation for an automotive application, and as much as 40,000 hours for a stationary application); the plate 14 0 must be capable of withstanding mechanical compressive loads necessary for sealing an ordinary cell stack assembly, such as (345 Kpa to 1379 Kpa) 50 - 200 p.s.i.; and, the plate must have adequate flexural strength to be capable of withstanding varying handling requirement for manufacture and cell stack assembly of the fuel cell 10, such as approximately 1,000 p.s.i. (6895 Kpa).
  • the cathode water transport plate 14 and the anode water transport plate 12 are therefore porous carbon bodies constructed in accordance with the present invention.
  • Such an improved porous carbon body formed into the cathode or anode water transport plate 14, 12 that satisfies the aforesaid and other important requirements includes an electrically conductive o graphite powder in an amount of between 40% - 60% by weight of the body; a carbon fiber in an amount of between 20% - 40% by weight of the body; a hydrophobic binder in an amount of between 10% - 30% by weight of the body; wherein the body has a mean pore size of greater than 2.0 microns, and an open porosity of greater than 25% of the body; and, wherein the pores in the body are rendered partially 5 hydrophilic by incorporation of a hydrophilic rendering compound onto an interior surface of the pores, the compound being a metal oxide, hydroxide, oxyhydroxide, oxyhydroxide hydrate, or oxide hydrate compound, and the compound having a
  • the porous carbon body also has a bubble pressure of greater than 5 pounds per square inch (“p.s.i.") 34.5 (Kpa), liquid water permeability of greater than 10 x 10 "16 square meters, and a loading of the hydrophilic rendering compound of greater than 15 mg.
  • the phrase “open porosity” it is meant that the pores are open to flow of fluids through a plane defined by a longest axis of the body within the pores, as opposed to sealed pores that cannot permit through flow.
  • a "through plane” flow of product water through the cathode water transport plate 14 in FIG. 1 means flow in a direction from the cathode substrate layer 28 to the cathode coolant channels 42A, i o 42B, 42C, and a through-plane flow of coolant water is in a direction from the cathode coolant channels 42A, 42B, 42C to the cathode substrate layer 28.
  • mean pore size it is meant that the measurement of "greater than 2.0 microns" is measuring mean widest diameters across the pores.
  • ammonium hydroxide was added to the solution to bring the pH up to about 1.0.
  • the salt to a metal hydroxide.
  • the body was heated to about 195°F (90.56) Kpa) for a period of about 30 minutes to hydrolyze the tin salt as well as to increase a size of the salt crystals. Sufficient humidity was maintained during the heating step to prevent drying of the solution.
  • the impregnated body was then dried at 300°F for about two hours. The dried porous carbon body was then washed in 5 water to remove ammonium chloride from its surfaces.
  • the resulting porous carbon body contained tin oxyhydrate at a loading of between about fifteen to about forty mg. per gram of the porous carbon body; had a bulk density of 1.3 - 1.4 grams per cubic centimeter; had an open porosity of 30%; had a mean pore size of 2.0 - 2.4 microns; had gas bubble pressure 7 p.s.i. (48.26 o Kpa); had a liquid water permeability of 35 x 10 "16 square meters; had a through-plane electrical resistivity of 0.2 ohm-cm; had a through plane thermal conductivity of 2.0 Btu Hr (2.11 Ki per hour) per square foot (929 square cm); and a flexural strength of 2,000 p.s.i.
  • the prior art water transport plates contained epoxy, phenolic, and vinyl ester resins as the binders and were provided by known suppliers. The specific grades of the resins are proprietary to the suppliers.
  • the prior art plates were aged for 2,000 hours 5 as described above. It was found that plates made with the epoxy resin as a binder lost 0.43% by weight; those made with the vinyl ester resin lost 0.43% by weight; and, those made with phenolic binder lost 3.4% by weight. These data show a stability benefit for the water transport plate of the present invention made with the polyvinylidene fluoride hydrophobic binder that lost only 0.05% by weight under the o same test conditions.
  • Exemplary hydrophobic polymers that are believed to be 5 acceptable and their respective surface energies are: polyvinylidene fluoride (PNDF) with a surface energy of 25 dyne/cm; co-polymer of ethylene and tetrafluoroethylene (ETFE) with a surface energy of 27 dyne/cm; polyvinyl fluoride (PNF) with a surface energy of 28 dyne/cm; polypropylene with a surface energy of 29 dyne/cm; polychlorotrifluoroethylene (PCTFE) with a surface energy of 31 dyne/cm; 5 polyethylene, with a surface energy of 32 dyne/cm; and any thermoset or thermoplastic polymer that has long term stability in the operating environment of a PEM fuel cell.
  • PNDF polyvinylidene fluoride
  • ETFE ethylene and tetrafluoroethylene
  • PCTFE polychlorotrifluoroethylene
  • the heating step and subsequent drying steps include heating the body to a temperature that is below a heat deflection temperature of the hydrophobic binder.
  • the "heat deflection temperature of the binder” is meant to describe a temperature at which a binder material transitions from a solid phase to a plastic phase, which is a temperature below the melting temperature for the binder.
  • the deflection temperature is about 240°F (115°C) at a mechanical loading of about 260 p.s.i. (1793 Kpa).
  • FIG. 2 presents a graph plotting the impact on volume conductivity of a porous carbon body with a polyvinylidene fluoride binder subject to varying "drying temperatures" listed on the horizontal axis of the graph.
  • a porous graphite body after the mixing and simultaneous compressing and heating steps and before the rendering partially hydrophilic steps is
  • the temperatures on the horizontal axis refer to maximum temperatures of the heating step to hydrolyze the metal salt, and of the subsequent drying step.
  • the temperatures on the horizontal axis refer to maximum temperatures of the heating step to hydrolyze the metal salt, and of the subsequent drying step.
  • 3 o significant aspect of the present invention is the step of heating the hydrophilic compound impregnated porous carbon body to a temperature that is adequate to hydrolyze the metal salt to a metal hydroxide but that is less than a heat deflection temperature of the hydrophobic binder in the body.
  • FIG. 3 is a graph showing a volume per cent fill of the void volume of the porous carbon body made in accordance with the present invention as a function of tin oxide loading.
  • a zero loading at 44A provides for zero fill of the void volume; a 28 milligram per gram loading of tin results in about 18 per cent fill of void volume; and, about 50 milligrams per gram loading results in about 28 per cent fill of void volume.
  • the above described treatment results in only about 18 to about 28 per cent of the void volume being filled with water.
  • the treated carbon bodies or plates had acceptable bubble pressure and water permeability characteristics as described above, which was unexpected with the 18 per cent to 28 per cent of the void volume being filled with water.
  • the fact that the per cent fill of the void volume of the treated plates with water is in the range of 18 to 28 per cent establishes that the body is only partially hydrophilic. A perfectly hydrophilic body would have nearly 100 per cent of its pore volume hydrophilic.
  • Koncar et al. disperses wettability enhancing materials with graphite powder, carbon fiber and a resin prior to molding the separator plate. (See Koncar et al., at Col. 5, lines 1 - 67.)
  • a graphite powder grade A-99 from the aforesaid Asbury Carbons, Inc. was pre-treated with tin oxide to a loading of 25 - 40 mg/gm by way of the tin oxide deposition technique previously described to enhance its wettability.
  • the following three components were dry blended for five minutes: 45 per cent by weight of A-99 graphite powder treated with the tin oxide; 45 per cent by weight AGM-99 carbon fiber; and 10 per cent by weight polyvinylidene fluoride.
  • the hydrophilic rendering compound may be oxides, hydroxides, oxyhydroxides, oxyhydroxide hydrates, or oxide hydrates of tin, titanium, 0 aluminum, zirconium, gallium, indium, niobium, tantalum, ruthenium, zinc, and/or hafnium.
  • the general formula for the appropriate compounds is M x O y (OH) w »(H 2 0), wherein the H 2 0 component is optional, i.e. is only included in the hydrate compounds which may be used in performance of this invention, and wherein the x, y, z, are generally small integers between zero and five, and preferably two or three, and s M is the metal.
  • Preferred hydrophilic rendering compounds have been determined to be tin oxyhydroxide and tin hydroxide.
  • a preferred loading range for the compound is about 25 to about 50 milligrams per gram of the porous carbon body.
  • a preferred embodiment of this invention includes a porous carbon body having a conductive graphite powder between 40% - 60% by o weight of the body; a carbon fiber in an amount of between 20% - 40% by weight of the body; a hydrophobic binder in an amount of between 10% - 30% by weight of the body; wherein the body has a mean pore size of greater than 2.0 microns, and an open porosity of greater than 25% of the body; and, wherein the pores in the body are rendered partially hydrophilic by incorporation onto the interior surface of the pores 5 of a metal oxide, hydroxide, oxyhydroxide, oxyhydroxide hydrate, or oxide hydrate compound, said compound having a solubility in water of less than about 10 "6 moles per liter.
  • the favorable porosity and mean pore size may be produced by the simultaneous compression and heating of the graphite powder, carbon fiber and hydrophobic resin.
  • conductive graphite particles may be mixed with the hydrophobic binder, and with a foaming agent or a leachable solid known in the art. The mixture is then compression molded and heated to form a desired shape for the body and so that the foaming agent produces the pores. The leachable solid is subsequently leached out so 5 that the resulting porosity is an "open porosity" permitting flow through the body, as defined above.
  • Such a formed carbon body having a mean pore size of greater than 2.0 microns and an open porosity of greater than 25% could then be rendered partially hydrophilic by incorporation onto the interior surface of the pores of the body of the aforesaid hydrophilic rendering compound, being a metal oxide, hydroxide, oxyhydroxide, oxyhydroxide hydrate, or oxide hydrate compound, said compound having a solubility in water of less than about 10 "6 moles per liter.
  • increased electrical conductivity of a porous carbon body made in accordance with the present invention has been achieved by including a high conductivity carbon black with the graphite powder, carbon fiber, and hydrophobic binder.
  • exemplary high conductivity carbon blacks include "VULCAN XC-72", and "BLACK PEARL 2000”, manufactured by Cabot Corporation of Boston, Massachusetts, U.S.A., or "KETJEN BLACK”, made by the Ketjen Black International Company of Tokyo, Japan. Experiments were performed to identify preferred ranges of a high conductivity carbon black mixed with the graphite powder, carbon fiber and hydrophobic binder, the results of which are included in TABLE 1 herein below.
  • the porous carbon body as described achieves long term chemical stability for operation in a PEM fuel cell operating up to 1,000 - 2,000 amps per square foot (“ASF") (1.1 to 2.15 amps per o square cm), without any need for time consuming and costly high temperature treatments to graphitize the body.
  • ASF amps per square foot
  • the hydrophilic compound By incorporation of the hydrophilic compound to an adequate loading onto the interior surface of the pores defined by the combined graphite, carbon fibers and resin, the body remains wettable during long term operation of the fuel cell.
  • the porous carbon body resulting from the described s efficient manufacturing process also exhibits appropriate bubble pressure, water permeability, electrical conductivity, thermal conductivity, compressive and flexural strength to efficiently serve as a water transport plate, separator plate or related component of a PEM fuel cell operating at 1,000 - 2,000 ASF (1.1 to 2.15 amps per square cm) for a very long duration.
  • FIG. 1 shows schematically a single fuel cell including two porous carbon bodies of the present invention in the form of the anode and cathode water transport plate 12, 14 components
  • the invention includes application of the porous carbon body as differing fuel cell components such as o separator plates, support plates, end plates, etc., and the invention also contemplates usage of the porous carbon body in a plurality of fuel cells cooperatively secured in a well known fuel cell stack. Accordingly, reference should be made primarily to the following claims rather than the foregoing description to determine the scope of the invention.

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Abstract

L'invention concerne un corps (12, 14) de carbone poreux et un procédé de fabrication du corps destiné être utilisé dans une cellule électrochimique. Le corps (12, 14) de carbone poreux comprend une poudre de graphite électroconductrice représentant entre 40 % et 60 % en poids du corps, une fibre de carbone représentant entre 20 % et 40 % en poids du corps, et un liant hydrophobe représentant entre 10 % et 30 % en poids du corps. Le corps présente une dimension de pores moyenne supérieure à 2,0 microns, et une porosité ouverte supérieure à 25 %. Les pores du corps sont partiellement hydrophilisés par incorporation d'un composé hydrophilisant dans la surface interne des pores. Le composé est un oxyde, un hydroxyde, un oxyhydroxyde, un hydrate d'oxyhydroxyde, ou un hydrate d'oxyde métallique. Le corps (12, 14) de carbone poreux présente une stabilité chimique de longue durée pouvant être exploitée dans une cellule électrochimique à membrane d'échange de protons (MEP).
PCT/US2001/030357 2000-10-06 2001-09-26 Corps de carbone poreux pour cellule electrochimique et procede de fabrication WO2002031903A1 (fr)

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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US7029781B2 (en) 2003-01-21 2006-04-18 Stmicroelectronics, Inc. Microfuel cell having anodic and cathodic microfluidic channels and related methods
WO2015009233A1 (fr) * 2013-07-17 2015-01-22 Temasek Polytechnic Milieu de diffusion s'utilisant dans une pile à combustible, pile à combustible et procédé de fabrication du milieu de diffusion
US11239475B2 (en) * 2018-05-11 2022-02-01 Toyota Jidosha Kabushiki Kaisha Catalyst layer for fuel cell and production method therefor

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US3634569A (en) * 1969-01-08 1972-01-11 United Aircraft Corp Method of manufacture of dense graphite structures
US5942347A (en) * 1997-05-20 1999-08-24 Institute Of Gas Technology Proton exchange membrane fuel cell separator plate
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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2387476A (en) * 2002-06-24 2003-10-15 Morgan Crucible Co Flow field plate geometries
GB2387476B (en) * 2002-06-24 2004-03-17 Morgan Crucible Co Flow field plate geometries
US7029781B2 (en) 2003-01-21 2006-04-18 Stmicroelectronics, Inc. Microfuel cell having anodic and cathodic microfluidic channels and related methods
WO2015009233A1 (fr) * 2013-07-17 2015-01-22 Temasek Polytechnic Milieu de diffusion s'utilisant dans une pile à combustible, pile à combustible et procédé de fabrication du milieu de diffusion
US11239475B2 (en) * 2018-05-11 2022-02-01 Toyota Jidosha Kabushiki Kaisha Catalyst layer for fuel cell and production method therefor

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