WO2006090207A2 - Anode pour pile a combustible liquide - Google Patents

Anode pour pile a combustible liquide Download PDF

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Publication number
WO2006090207A2
WO2006090207A2 PCT/IB2005/002464 IB2005002464W WO2006090207A2 WO 2006090207 A2 WO2006090207 A2 WO 2006090207A2 IB 2005002464 W IB2005002464 W IB 2005002464W WO 2006090207 A2 WO2006090207 A2 WO 2006090207A2
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WO
WIPO (PCT)
Prior art keywords
anode
fuel cell
cobalt
carrier
oxidation catalyst
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Ceased
Application number
PCT/IB2005/002464
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English (en)
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WO2006090207A3 (fr
Inventor
Vladimir Meiklyar
Gennadi Finkelshtain
Yuri Katsman
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More Energy Ltd
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More Energy Ltd
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Publication date
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Priority to PCT/IB2005/002464 priority Critical patent/WO2006090207A2/fr
Publication of WO2006090207A2 publication Critical patent/WO2006090207A2/fr
Anticipated expiration legal-status Critical
Publication of WO2006090207A3 publication Critical patent/WO2006090207A3/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
    • H01M4/88—Processes of manufacture
    • H01M4/8825—Methods for deposition of the catalytic active composition
    • H01M4/8828—Coating with slurry or ink
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/74—Iron group metals
    • B01J23/75—Cobalt
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/16—Reducing
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/9075—Catalytic material supported on carriers, e.g. powder carriers
    • H01M4/9083—Catalytic material supported on carriers, e.g. powder carriers on carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/08—Fuel cells with aqueous electrolytes
    • H01M8/083—Alkaline fuel cells
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/18—Carbon
    • 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 a cobalt containing anode for a liquid fuel cell and a fuel cell comprising same.
  • the invention also relates to an oxidation catalyst suitable for use in such an anode and to a process for the preparation thereof.
  • An electrochemical liquid fuel cell is a device that converts the energy of a chemical reaction into electricity.
  • a fuel cell produces electricity by bringing a fuel into contact with a catalytic anode while bringing an oxidant into contact with a catalytic cathode.
  • the fuel is oxidized at catalytic centers to produce electrons.
  • the electrons travel from the anode to the cathode through an electrical circuit connecting the electrodes.
  • the oxidant is catalytically reduced at the cathode, consuming the electrons generated at the anode.
  • Mass balance and charge balance are preserved by the corresponding production of ions at either the cathode or the anode and the diffusion of these ions to the other electrode through an electrolyte with which the electrodes are in contact.
  • One of the drawbacks of conventional fuel cells in general is their cost of manufacture and, in particular, the high price of the raw materials for the oxidation/reduction catalysts used in the anode/cathode thereof. These catalysts usually are based on expensive metals such as platinum and gold. It would, therefore, be beneficial to have available a relatively inexpensive catalyst for an electrode of a liquid fuel cell with which satisfactory discharge characteristics and electrical output can be achieved without having to rely on the presence of noble metals.
  • the present invention provides an anode suitable for use in a liquid fuel cell, which anode comprises metallic cobalt supported on a finely divided electrically conductive carrier.
  • the anode is substantially free of noble metals.
  • the anode further comprises up to a maximum of about 40 % by weight of at least one additional metal, based on the combined weight of all metals present. This at least one other metal may comprise a transition metal and/or a rare earth metal.
  • the electrically conductive carrier comprises carbon.
  • the carrier has a specific surface area of at least about 20 m 2 /g and/or a particle size of not higher than about 30 ⁇ m, in particular, not higher than about 20 ⁇ m.
  • the metallic cobalt has been deposited on the carrier by reducing a cobalt salt in the presence of the carrier.
  • the concentration of cobalt is from about 0.5 to about 40 weight percent, based on the combined weight of cobalt plus carrier.
  • the metallic cobalt comprises a cobalt containing alloy.
  • the cobalt containing alloy may comprise one or more other metals selected from transition metals, rare earth metals, Al and Mg.
  • the cobalt containing alloy may comprise at least about 1 mol-% of cobalt.
  • the anode is capable of providing, in an alkaline fuel cell, a current density of at least about 100 mA/cm 2 , e.g., at least about 200 mA/cm 2 , and/or a power of at least about 50 mW/cm 2 , e.g., at least about 70 mW/cm 2 , at a cathode/anode potential difference of 0.55 V and within a temperature range from about 1O 0 C to about 65 0 C.
  • the anode has a surface area of about 0.5 cm 2 to about 200 cm 2 .
  • the present invention also provides a process for making an oxidation catalyst suitable for use in an anode as set forth above.
  • This process comprises the addition of an at least about 3-fold stoichiometric excess of a reducing agent to an aqueous solution of a cobalt(II) compound in the presence of an electrically conductive carrier having a specific surface area of at least about 50 m 2 /g.
  • the addition rate of the reducing agent is such that it provides an average particle size of the resultant metallic cobalt of not higher than about 30 nm.
  • the cobalt(II) compound comprises a Co(II) salt such as, e.g., Co(II) nitrate (including hydrates thereof) and/or the reducing agent comprises a borohydride salt.
  • the borohydride salt may comprise an alkali metal borohydride such as, e.g., sodium borohydride.
  • the reducing agent may be in the form of an aqueous solution and the pH of this solution may be from about 9 to about 12 and/or such that the pH of the reaction mixture following the complete addition of the reducing agent is about 1 to about 12.
  • the solution may comprise an alkali metal hydroxide.
  • concentration of the reducing agent in the aqueous solution may be about 0.1 to about 1 molar.
  • the stoichiometric excess of the reducing agent is at least about 10-fold.
  • the electrically conductive carrier comprises carbon.
  • the carbon has a specific surface area of at least about 100 m 2 /g.
  • the cobalt compound is present in the aqueous solution prior to adding the reducing agent at a concentration of from about 0.01 mol/1 to about 0.5 mol/1 and/or the electrically conductive carrier is present in an amount which results in a concentration of the cobalt of about 0.5 to about 40 weight percent, based on the combined weight of cobalt plus carrier.
  • the process is carried out within a temperature range of form about
  • the process is carried out in the substantial absence of noble metals. Furthermore, the process may be carried out in the additional presence of a compound of at least one metal different from cobalt, and the weight ratio of cobalt and the at least one metal different form cobalt is not lower than about 0.005 : 1.
  • the process further comprises filtering the catalyst, rinsing it with water and drying it.
  • the catalyst may be dried at a temperature of about
  • the present invention furthermore provides an oxidation catalyst which is obtainable by the process set forth above, including the various aspects of this process.
  • the present invention additionally provides an oxidation catalyst suitable for use in an anode of a liquid fuel cell.
  • This catalyst comprises metallic cobalt supported on an electrically conductive carrier having a specific surface area of at least about 20 m ⁇ /g in a concentration of the metallic cobalt of about 0.5 to about 40 weight percent, based on the combined weight of cobalt plus carrier.
  • the catalyst is substantially free of noble metals.
  • the catalyst further comprises up to a maximum of about 40 % by weight of at least one additional metal, based on the combined weight of all metals present.
  • the at least one other metal may comprise a transition metal and/or a rare earth metal.
  • the carrier comprises carbon and/or the carrier has an average particle size of not higher than about 30 ⁇ m.
  • the present invention further provides a process for making an anode suitable for use in a liquid fuel cell.
  • This process comprises mixing the oxidation catalyst set forth above, including the various aspects thereof, with water, a lower alcohol and a binder to form a paste.
  • the lower alcohol may comprise isopropanol and/or the binder may comprise polytetrafluoroethylene.
  • the process further comprises applying the paste on carbon paper.
  • the carbon paper with the paste thereon may be combined under pressure with a current collector, for example, a current collector which comprises a metal grid, e.g., a nickel grid.
  • a current collector for example, a current collector which comprises a metal grid, e.g., a nickel grid.
  • the present invention also provides a fuel cell comprising a cathode and an anode.
  • the anode comprises the anode set forth above, including the various aspects thereof.
  • the cathode comprises an air-breathing cathode.
  • the fuel cell further comprises a liquid fuel and/or a liquid electrolyte.
  • the liquid fuel may comprise a borohydride salt.
  • it may comprise an alkali metal borohydride such as, e.g., sodium borohydride.
  • the liquid fuel may comprise a solvent and an oxidizable material, e.g., wherein the oxidizable material is both dissolved and dispersed in the solvent.
  • the solvent comprises water and/or the oxidizable material comprises LiAlH 4 , NaBH 4 , KBH 4 , LiBH 4 , (CH 3 ) 3 NHBH 3 , NaAlH 4 , NaCNBH 3 , CaH 2 , LiH, NaH, KH, Na 2 S 2 O 3 , Na 2 HPO 3 , Na 2 HPO 2 , K 2 S 2 O 3 , K 2 HPO 3 , K 2 HPO 2 , NaCOOH, KCOOH or any combination of two or more thereof.
  • the oxidizable material may comprise NaBH 4 .
  • the liquid fuel further comprises a monohydric or polyhydric alcohol such as, for example, methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, ethylene glycol, propylene glycol, glycerol or any combination of two or more thereof, e.g., methanol and/or glycerol.
  • a monohydric or polyhydric alcohol such as, for example, methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, ethylene glycol, propylene glycol, glycerol or any combination of two or more thereof, e.g., methanol and/or glycerol.
  • the liquid electrolyte of the fuel cell has a pH of higher than about 7.
  • it may comprise water and a basic compound.
  • the basic compound may comprise a hydroxide, e.g., an alkali metal hydroxide.
  • Non-limiting examples of the alkali metal comprise Na and K.
  • the basic compound is present in the liquid electrolyte at a concentration of about 0.1 to about 5 mol/1.
  • the present invention furthermore provides an electrical device, e.g., a portable device, which is in electrical contact with the fuel cell set forth above, including the various aspects thereof, as well as a method of powering an electrical device.
  • the method comprises establishing electrical contact between the device and the fuel cell set forth above, including the various aspects thereof.
  • the anode according to the present invention comprises cobalt in metallic form which is supported (e.g., deposited) on a finely divided, electrically conductive carrier.
  • a finely divided, electrically conductive carrier e.g., a finely divided, electrically conductive carrier.
  • noble metals Pt, Pd, Ru, Rh, Au, Ag
  • the anode of the present invention is preferably substantially free of noble metals.
  • the anode may contain trace amounts of noble metals, e.g., less than about 1 % by weight, or even less than about 0.1 % by weight (e.g., less than about 0.01 % by weight), based on the total weight of all metals present in the anode.
  • the anode may comprise one or more other non-noble metals. These metals may be present in an amount of up to about 40 % by weight, e.g., up to about 25 % by weight, up to about 10 % by weight, up to about 5 % by weight, or up to about 2 % by weight, based on the total weight of all metals present.
  • transition metals in particular, one or more of Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ni, Cu, Zn and Cd
  • rare earth metals in particular, one or more of La, Ce, Pr, N
  • a corresponding alloy will usually contain at least about 1 mol-%, e.g., at least about 2 mol-%, at least about 5 mol-%, at least about 10 mol-%, at least about 20 mol- %, at least about 50 mol-%, at least about 75 mol-%, or at least about 90 mol-%, of cobalt.
  • Preferred elements for use in such an alloy with cobalt are nickel, molybdenum, ytterbium and combinations thereof.
  • alloys having the general formula Co x Mi -x Yby wherein M represents Ni and/or Mo, x is in the range from greater than 0 to about 0.5 and y is in the range from 0 to about 0.05 may be used in the present invention.
  • the electrically conductive carrier for supporting the metallic cobalt (as such and/or in the form of an alloy) and any other metal that may optionally be present will usually have a specific surface area (as determined by the BET method using nitrogen gas) of at least about 20 m 2 /g, e.g., at least about 50 m 2 /g, at least about 100 m 2 /g, at least about 200 m 2 /g or even at least about 250 m 2 /g.
  • a specific surface area as determined by the BET method using nitrogen gas
  • the specific surface area of the carrier will usually not be higher than about 400 m 2 /g .
  • the electrically conductive carrier will usually have a particle size (as determined by, e.g., sieving) of not higher than about 30 ⁇ m, e.g., not higher than about 25 ⁇ m, not higher than about 20 ⁇ m, or not higher than about 10 ⁇ m.
  • a preferred electrically conductive carrier for the purposes of the present invention is carbon, although it will be apparent to those skilled in the art that other electrically conductive carriers can be used as well.
  • the relative proportions of carrier and metallic cobalt can vary over a wide range, although it is preferred that the amount of carrier is equal to at least that amount that is necessary for supporting all of the metallic cobalt (as well as any additional metals that may be present).
  • the cobalt will usually be present at a concentration of at least about 0.5 % by weight, e.g., at least about 1 % by weight, at least about 2 % by weight, at least about 3 % by weight, at least about 5 % by weight, but usually not more than about 40 % by weight, e.g., not more than about 30 % by weight, not more than about 25 % by weight, not more than about 20 % by weight, not more than about 15 % by weight, or not more than about 10 % by weight. If cobalt is present in combination with other metals (e.g., in the form of an alloy), the above percentages apply to the total amount of all metals present. In other words, based on the combined weight of all metals plus carrier, the combined metals usually will account for at least about 0.5 % by weight, but for not more than about 40 % by weight.
  • a suitable process for making a cobalt containing oxidation catalyst for use in the anode of the present invention comprises the addition of an at least about 3 -fold stoichiometric excess of a reducing agent to an aqueous solution of a cobalt(II) compound in the presence of an electrically conductive carrier as set forth above.
  • the stoichiometric excess of reducing agent will more often be at least about 10-fold, e.g., at least about 20-fold, at least about 30-fold, at least about 50-fold, or even at least about 60-fold, although it will usually not be higher than about 200-fold, e.g., not higher than about 100-fold.
  • the cobalt(II) compound can, for example, be a Co(II) complex, but will more often be a Co(II) salt of an inorganic acid or an organic acid (e.g., acetic acid), preferably an inorganic acid such as, e.g., hydrochloric acid, hydrobromic acid, sulfuric acid, nitric acid, and phosphoric acid.
  • Co(II) nitrate is a particularly suitable compound for the purposes of the present invention. Of course, mixtures of different Co(II) salts (compounds) may also be used.
  • concentration of the Co(II) compound in the aqueous solution prior to the addition of the reducing agent can be within a wide range.
  • the Co(II) compound is present in a concentration of at least about 0.01 molar, e.g., at least about 0.05 molar, but not higher than about 0.5 molar, e.g., not higher than about 0.1 molar.
  • the reducing agent can be any compound that is capable of reducing a Co(II) compound to metallic cobalt.
  • Non-limiting examples thereof include hydrides such as NaBH 4 , KBH 4 , LiBH 4 , (CHa) 3 NHBH 3 , LiAlH 4 , NaAlH 4 , NaCNBH 3 , CaH 2 , LiH, NaH, KH, hydrazine, alkali and alkaline earth metal thiosulfates, sulfites, phosphites and hypophosphites and mixtures thereof.
  • Currently preferred reducing agents comprise borohydride salts, in particular, alkali metal borohydrides such as, e.g., NaBH 4 .
  • the reducing agent will usually be added as a solution in an aqueous solvent, preferably water.
  • the pH of the solution will usually be at least about 9 and not higher than about 12. This pH depends to some extent on the pH of the aqueous solution of the Co(II) compound, and will usually be such that following the complete addition of the reducing agent, the pH of the resulting mixture is not lower than about 1, e.g., not lower than about 2, but usually not higher than about 12, e.g., not higher than about 11.
  • the solution will usually contain a base, for example, an inorganic base such as NaOH, KOH or ammonia.
  • a base for example, an inorganic base such as NaOH, KOH or ammonia.
  • concentration of the reducing agent in the solution will usually be at least about 0.1 molar, e.g., at least about 0.2 molar, but usually not higher than about 1 molar, e.g., not higher than about 0.5 molar.
  • the reducing agent is added to the Co(II) containing solution preferably in a continuous fashion and at a rate which provides the desired small particle size.
  • the rate of addition should also be sufficient to reduce already formed cobalt particles which have been oxidized on their surface by the oxygen present in the solution. This rate depends on, inter alia, the concentrations and the pH values of the solutions of the Co(II) compound and the reducing agent, the types of reducing agent and Co(II) compound employed, and the temperature at which the process is carried out.
  • a suitable rate of addition can be determined by routine experimentation.
  • the particle size of the formed cobalt particles (cobalt clusters) preferably is not higher than about 30 nm, e.g., not higher than about 20 nm, not higher than about 10 nm, not higher than about 5 nm, or not higher than about 2 nm.
  • the process of the present invention can be carried out over a wide temperature range. Best results are usually obtained with a temperature of at least about 10 0 C, e.g., at least about 2O 0 C, but usually not higher than about 7O 0 C, e.g., not higher than about 6O 0 C.
  • the electrically conductive carrier e.g., carbon
  • the metallic cobalt deposited thereon will usually be filtered, rinsed with water and dried.
  • the drying operation is carried out preferably at a temperature of at least about 6O 0 C, e.g., at least about 8O 0 C, but not higher than about 12O 0 C, e.g., not higher than about 100 0 C. Drying times will usually range from about 0.5 hours to about 24 hours, mainly depending on the drying temperatures employed.
  • An anode for a fuel cell can be made from the cobalt containing oxidation catalyst of the present invention in a conventional manner well known to those skilled in the art.
  • a material comprising the cobalt oxidation catalyst of the present invention may, for example, be formed into a paste.
  • the paste may be applied onto a suitable two-dimensional substrate (e.g., a sheet of paper or metal), and the substrate with the catalyst thereon may be brought into the desired shape and dimensions of the anode, optionally before or after reinforcement with, e.g., a metal grid or the like.
  • the catalyst may be mixed with a liquid, e.g., water or a mixture thereof with a lower alcohol (such as, e.g., methanol, ethanol, propanol, isopropanol and butanol) and a suitable binder (such as, e.g., polytetrafluoroethylene).
  • a liquid e.g., water or a mixture thereof with a lower alcohol (such as, e.g., methanol, ethanol, propanol, isopropanol and butanol) and a suitable binder (such as, e.g., polytetrafluoroethylene).
  • the substrate may, for example, be carbon paper.
  • the substrate with the catalyst paste thereon may be reinforced with a reinforcing element, e.g., a metal grid such as a nickel grid. A reinforcing element may be applied on one side or on both sides of the substrate. Also, two or more of the reinforced substrates may be combined,
  • the material comprising the Co oxidation catalyst of the present invention may be employed as the anode of a liquid fuel cell.
  • the cathode of the fuel cell may be any cathode that can be used in combination with a liquid fuel cell. Examples thereof are well known to those skilled in the art.
  • the cathode is an air-breathing cathode.
  • Non-limiting examples thereof are a cathode comprising Pt on a electrically conductive carrier such as carbon and a cathode on the basis of a Co porphyrine catalyst (see Examples below).
  • the structure of a typical fuel cell according to the present invention comprises an anode which in its operative state is in contact with a liquid fuel on one side, and is in contact with a liquid electrolyte on its other side, and a cathode which also is in contact with the liquid electrolyte on one side thereof.
  • the other side of the cathode is in contact with an oxidant, preferably oxygen, air or any other oxygen containing gas.
  • a liquid fuel for use in a fuel cell of the present invention may be any fuel that is suitable for liquid fuel cells.
  • the liquid fuel may comprise a (monohydric or polyhydric) lower alcohol (usually a saturated aliphatic alcohol), optionally in combination with a solid fuel such as, e.g., LiAlH 4 , KBH 4, NaBH 4 , LiBH 4 , (CH 3 ) 3 NHBH 3 , NaAlH 45 NaCNBH 3 , CaH 2 , LiH, NaH, KH, Na 2 S 2 O 3 , Na 2 HPO 3 , Na 2 HPO 2 , K 2 S 2 O 3 , K 2 HPO 3 , K 2 HPO 2 , NaCOOH, KCOOH or any combination of two or more thereof.
  • the lower alcohol may, for example, be an alcohol having 1 to 6, e.g., 1 to 4 carbon atoms, and, 1 or more, e.g., 1 to 4, OH groups.
  • Non-limiting examples thereof are methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, pentanol, hexanol, ethylene glycol, propylene glycol, glycerol, pentaerythritol and any combination of two or more thereof.
  • the liquid fuel may also comprise a basic compound, e.g., for the purpose of stabilizing the solid fuel.
  • the basic compound may be any suitable organic or inorganic base, for example, an inorganic hydroxide, non-limiting examples whereof are ammonium and (alkali and alkaline earth) metal hydroxides, such as, e.g., NaOH, KOH and LiOH, and NH 4 OH.
  • a liquid electrolyte that is suitable for use in the a liquid fuel cell may comprise a base, for example an aqueous inorganic hydroxide.
  • Non-limiting examples of the inorganic hydroxide are alkali metal hydroxides, such as, e.g., NaOH, KOH and LiOH.
  • liquid fuels and liquid electrolytes suitable for use in the fuel cell of the present invention are disclosed in U.S.
  • the surface area of the anode (and of the cathode) of a fuel cell of the present invention is not particularly limited. Usually, however, the surface area is at least about 0.5 cm 2 , e.g., at least about 2 cm 2 , at least about 5 cm 2 , at least about 10 cm 2 , at least about 20 cm 2 , or at least about 30 cm 2 . On the other hand, the surface area usually is not larger than about 500 cm 2 , e.g., not larger than about 300 cm 2 , not larger than about 200 cm 2 , not larger than about 100 cm 2 , not larger than about 75 cm 2 , or not larger than about 50 cm 2 .
  • the liquid fuel cell of the present invention can be used to supply electrical energy to a virtually unlimited number of electric and electronic devices.
  • Non-limiting examples thereof are (cellular) phones, (portable) computers, PDAs, consumer electronics, (portable) medical devices and components and peripherals thereof.
  • Fig. 1 shows an ambient temperature CV(current-voltage)-curve of an anode (surface area 4 cm 2 ) comprising a catalyst with 10 % by weight of Co on carbon.
  • Fig. 2 shows an ambient temperature CV-curve of an anode (surface area 4 cm 2 ) based on a 20 % Co on carbon catalyst.
  • Fig. 3 shows an ambient temperature CV-curve of an anode (surface area 10 cm 2 ) based on a 10 % Co on carbon catalyst.
  • Fig. 4 shows ambient temperature dicharge (current and capacity) curves at a constant potential of 0.55 V for an alkaline fuel cell (surface area of anode 4 cm 2 ) having Co based anode and cathode.
  • Fig. 5 shows ambient temperature dicharge (voltage and capacity) curves at a constant current of 0.5 A for an alkaline fuel cell (surface area of anode 4 cm 2 ) having Co based anode and cathode.
  • Fig. 6 shows ambient temperature dicharge (current and capacity) curves at a constant power of 320 mW for an alkaline fuel cell (surface area of anode 4 cm 2 ) having Co based anode and cathode.
  • Granulated carbon Vulcan XC-72 (Cabot Corp., 4.5 grams, specific surface area according to BET 254 m 2 /g) was placed in a beaker and intimately mixed with 100 ml of distilled water. The resultant dispersion was heated under reflux for 30 min. with vigorous stirring. Thereafter, it was cooled to 6O 0 C, and a solution of Co(NO 3 )2 x 6H 2 O (2.47 g in 25 ml of distilled water) was added thereto. The obtained mixture was stirred for 30 min at 6O 0 C and under vigorous stirring. Thereafter, a reducing agent for reducing the cobalt(II) ions to metallic cobalt was added at 6O 0 C. The reducing agent was composed OfNaBH 4 (5.23 g) and
  • the catalyst so obtained was filtered and rinsed with distilled water. Then the catalyst was dried for 12 hours in a vacuum furnace at 9O 0 C. The catalyst weight after the completion of the above-described procedure was 5.0 g (10% Co + 90% carbon).
  • the catalyst from step (a) above (0.42 g) was wetted with 1.5 ml of water in order to reduce its pyrophoric properties.
  • the wetted catalyst was homogenized by means of ultrasound for 6 min.
  • an aqueous polytetrafluoroethylene (PTFE) dispersion (0.14 ml, 60 % by weight of PTFE) was added thereto, and ultrasound homogenization was carried out for 6 min.
  • About 1.5 ml of isopropyl alcohol was added to the resultant paste in order to increase the plasticity thereof.
  • PTFE polytetrafluoroethylene
  • the paste so obtained was applied at a layer thickness of about 0.20 mm onto carbon paper ( B-2 Toray Carbon Paper TGPH-060, thickness 0.17 mm, surface area 42 cm 2 ; E-TEK, Somerset, NJ, USA) which had been hydrophilized with polyvinyl alcohol.
  • the thus coated paper was dried in ambient air for 30 min. and then for an additional 1.5 hours in a vacuum furnace at 9O 0 C. Thereafter, two semifinished products of the required dimensions (surface area 4 cm ) were cut out of the coated and dried carbon paper.
  • a nickel grid of corresponding dimensions (NP-2, "Elecrocabel”, Kolchugino, Russia; wire diameter about 0.12 mm, average linear dimension of grid units about 0.2 mm) was placed between these two semi-finished products.
  • NP-2 "Elecrocabel", Kolchugino, Russia; wire diameter about 0.12 mm, average linear dimension of grid units about 0.2 mm
  • two additional nickel grids of corresponding dimensions were placed on both sides of this sandwich structure, and the resultant assembly was subjected to a pressure of 575 kg/cm 2 at a temperature of 7O 0 C to form an anode material.
  • This anode material was glued onto a polyvinyl mandrel, and then it was placed in a fuel semi-cell. Thereafter, its electrochemical activity on the basis of the voltage-current and discharge characteristics in various modes was investigated.
  • Voltage-current characteristics of the anode were obtained on a semi-cell having a fuel chamber volume of 20 ml, with a nickel plate being used as the counter-electrode (cathode). Electrolyte (6.6 M KOH, 5 ml) was placed between the anode and the counter-electrode. The semi-cell was connected to a MACCOR® measuring system (Maccor, Inc., Tulsa, OK, USA).
  • Figure 1 shows typical voltage-current characteristics at ambient temperature of the anode so formed (surface area 4 cm 2 ).
  • Example 1 The procedure of Example 1 was repeated, except that the catalyst contained 20 weight-% of cobalt and 80 weight-% of carbon (Vulkan XC-72). In this case, 4.0 gram of carbon were dispersed in 100 ml of water. After boiling and cooling to 6O 0 C, 4.94 gram of Co(NOs) 2 x 6H 2 O, dissolved in 50 ml of distilled water (6O 0 C), was added to the dispersion. The addition rate of the reducing agent was 40 ml/min.; compositions and concentrations corresponded to those given in Example 1. Anode fabrication was performed as described in Example 1.
  • Fig. 2 shows the voltage-current characteristics at ambient temperature of the corresponding anode.
  • Example 1 was repeated, but the surface area of the anode was 10 cm 2 instead of 4 cm 2 as in Example 1.
  • Fig. 3 shows the voltage-current characteristics at ambient temperature of the corresponding anode.
  • the discharge characteristics of fuel cells comprising an anode according to the present invention were studied.
  • the fuel elements used for these studies comprised a fuel tank (volume 17 cm 3 ), two electrodes (anode and cathode, 4 cm 2 each) and an electrolyte chamber (6.6 M KOH, 5 ml) between them.
  • the anodes were anodes fabricated according to Example 1. An air-breathing cathode was used as counter-electrode.
  • the cathode was based on a Co porphyrine catalyst.
  • This cathode may be prepared as follows: A mixture of 5-15 weight-% of Co-porphyrine (Aldrich) and 85-95 weight-% of carbon (Vulcan XC-72) is milled and thereafter subjected to pyro lysis in a nitrogen atmosphere for about 2 hours at 700-800 0 C. The resultant product is mixed with about 20-30 weight-% of aqueous PTFE dispersion (60 weight-% PTFE) and placed on a Ni grid as current collector. Thereafter a gas diffusion layer (SB carbon mixed with 20-40 weight-% of PTFE dispersion) is pressed on one side (the air-breathing side) of the resultant structure.
  • SB carbon gas diffusion layer
  • Figure 4 is a graph showing the observed discharge characteristics of the fuel cell.
  • the surface areas of the tested electrodes were 4 cm 2 each.
  • Maximal discharge currents exceeded 900 mA (at a constant potential of -0.55 V), and the average output during 5 hours of operation was of the order of 100 mW.
  • the discharge capacity over 6 hours of operation was at least 4,000 mAh.
  • Figures 5 and 6 are graphs showing the galvanostatic discharge characteristics of the same fuel cell as above (at a constant current of 0.5 A), as well as the discharge characteristics at a constant output of 320 mW. These discharge characteristics were obtained after the cell had been discharged 12 times at a constant potential of -0.55 V.

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Abstract

L'invention concerne une anode pouvant être utilisée dans une pile à combustible liquide, comprenant du cobalt métallique sur support électroconducteur finement divisé. L'invention concerne également un catalyseur d'oxydation destiné à être utilisé dans cette anode, ainsi qu'un procédé destiné à la fabrication de ce catalyseur d'oxydation et une pile à combustible comprenant cette anode. L'objectif du présent abrégé n'est aucunement de définir l'invention décrite dans le présent mémoire descriptif ou de limiter le champ d'application de l'invention.
PCT/IB2005/002464 2005-02-23 2005-02-23 Anode pour pile a combustible liquide Ceased WO2006090207A2 (fr)

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CA1306284C (fr) * 1987-08-24 1992-08-11 Karl V. Kordesch Electrodes metalliques et electrodes catalysees au moyen d'un oxyde de metalpour les cellules electrochimiques et methode de fabrication de ces electrodes
DE4426973C1 (de) * 1994-07-29 1996-03-28 Degussa Verfahren zur Herstellung eines als Brennstoffzellenelektrode einsetzbaren Plattinlegierungskatalysators
US5804329A (en) * 1995-12-28 1998-09-08 National Patent Development Corporation Electroconversion cell
US6554877B2 (en) * 2001-01-03 2003-04-29 More Energy Ltd. Liquid fuel compositions for electrochemical fuel cells

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