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WO2007031795A1 - Electrocatalyseur - Google Patents

Electrocatalyseur Download PDF

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Publication number
WO2007031795A1
WO2007031795A1 PCT/GB2006/050286 GB2006050286W WO2007031795A1 WO 2007031795 A1 WO2007031795 A1 WO 2007031795A1 GB 2006050286 W GB2006050286 W GB 2006050286W WO 2007031795 A1 WO2007031795 A1 WO 2007031795A1
Authority
WO
WIPO (PCT)
Prior art keywords
electrocatalyst
metal particles
carbon
electrocatalyst according
fuel cell
Prior art date
Legal status (The legal status 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 status listed.)
Ceased
Application number
PCT/GB2006/050286
Other languages
English (en)
Inventor
David Thompsett
Shik Chi Tsang
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Johnson Matthey PLC
Original Assignee
Johnson Matthey PLC
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 Johnson Matthey PLC filed Critical Johnson Matthey PLC
Publication of WO2007031795A1 publication Critical patent/WO2007031795A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

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
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • H01M4/925—Metals of platinum group supported on carriers, e.g. powder carriers
    • H01M4/926—Metals of platinum group 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
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8647—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites
    • H01M4/8657—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites layered
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • H01M4/921—Alloys or mixtures with metallic elements
    • 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
    • H01M2004/8678—Inert electrodes with catalytic activity, e.g. for fuel cells characterised by the polarity
    • H01M2004/8684—Negative electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/8605—Porous electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8803—Supports for the deposition of the catalytic active composition
    • H01M4/8807—Gas diffusion layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/88—Processes of manufacture
    • H01M4/8803—Supports for the deposition of the catalytic active composition
    • H01M4/881—Electrolytic membranes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • 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

  • the present invention relates to an electrocatalyst that may be used in a fuel cell, and their use in catalyst inks, catalysed electrodes, catalyst coated membranes and membrane electrode assemblies.
  • a fuel cell is an electrochemical cell comprising two electrodes separated by an electrolyte.
  • a fuel e.g. hydrogen or methanol
  • an oxidant e.g. oxygen or air
  • Electrochemical reactions occur at the electrodes, and the chemical energy of the fuel and the oxidant is converted to electrical energy and heat.
  • Electrocatalysts are used to promote the electrochemical oxidation of the fuel at the anode and the electrochemical reduction of oxygen at the cathode.
  • Electrocatalysts used in fuel cells typically comprise platinum or a platinum alloy.
  • the metal may be unsupported, but is usually supported on a high surface area carbon such as a furnace carbon black or an acetylene black. Supporting the metal increases the available surface area of the metal and reduces the amount of metal required to achieve desired activity.
  • a high surface area carbon such as a furnace carbon black or an acetylene black. Supporting the metal increases the available surface area of the metal and reduces the amount of metal required to achieve desired activity.
  • the present inventors have sought to prepare electrocatalysts that are suitable for use in fuel cells.
  • the inventors have surprisingly found that catalysts wherein a metal particle is encapsulated by carbon are active for the anodic fuel cell reaction. This is very surprising because it is generally understood that the catalytic reactions occur at the surface of the metal.
  • the inventors believe the catalysts may have advantageous properties when compared to known fuel cell catalysts, e.g. they may have better tolerance to poisons such as carbon monoxide and hydrogen sulphide.
  • the present invention provides an electrocatalyst for use in a fuel cell comprising a plurality of metal particles, wherein at least 90% of the surface area of the metal particles is covered by carbon. Preferably at least 95% of the surface area is covered with a layer of carbon, most preferably all of the surface of the metal is covered with a layer of carbon.
  • the carbon may be present as graphitic sheets and the term "a layer of carbon" includes both a single graphitic sheet and multiple graphitic sheets.
  • the one or more metal particles suitably comprise one or more transition metals, which are optionally alloyed with further metals.
  • the metal particles preferably comprise one or more metals from Groups 8 and Ib of the Periodic Table (i.e. the Groups containing platinum group metals and Fe, Co, Ni and Cu), which are optionally alloyed with further metals.
  • the metal particles comprise platinum or palladium, preferably platinum, hi a particularly preferred embodiment, the metal particles consist essentially of platinum or platinum alloyed with one or more metals chosen from precious metals such as ruthenium or gold, or base metals such as molybdenum, tungsten, chromium, tin or titanium.
  • the electrocatalyst consists essentially of a metal particle, wherein the particle is substantially covered with carbon.
  • the particle suitably has an average diameter of from lnm to lOOnm, preferably from lnm to 50nm.
  • the electrocatalyst consists essentially of metal particles dispersed on a carbon support material, wherein the particles are substantially covered with carbon.
  • the particles suitably have an average diameter of from lnm to lOOnm, preferably from lnm to 50nm, most preferably from 1 to lOnm.
  • the carbon support material is suitably a high surface area carbon black, such as a furnace black or an acetylene black.
  • the surface area of the carbon support is suitably at least 5OmVg, preferably at least 200m 2 /g.
  • the amount of metal in the electrocatalyst is from 10 to 80wt% based on the weight of the carbon support material.
  • the covering of carbon on the metal particles is suitably less than 1 Onm in thickness.
  • the inventors believe that thicker carbon layers are likely to reduce the activity of the electrocatalyst.
  • Methods of preparing carbon encapsulated metal particles are disclosed in, for example, WO 03/057626, WO 03/057359 and Lu et al, Chem. Commun., 2005, 98-100. These methods may be adapted for forming the electrocatalysts of the present invention.
  • colloidal particles containing a source of metal are fo ⁇ ned in a liquid medium.
  • the colloidal particles are stabilised by a surfactant.
  • the colloidal particles contain a source of carbon such as cyanide, isocyanide, cyanate or isocyanate ligands.
  • the particles are separated from the liquid medium.
  • the particles are pyrolysed in an inert gas.
  • the particles are dispersed on a carbon support material and are then pyrolysed in an inert gas.
  • a suitable pyrolysis temperature is at least 800 0 C.
  • a metal salt and a carbon source e.g. poly( vinyl alcohol)
  • the solution is sprayed as a fine mist into a closed vessel containing a saturated ammonia solution.
  • a solid precipitates and is collected.
  • the solid is pyrolysed in an inert gas.
  • the precipitate is contacted with a carbon support material, which is then pyrolysed in an inert gas.
  • a suitable pyrolysis temperature is at least 800 0 C.
  • a carbon forming agent e.g. polyvinyl alcohol, furfuryl alcohol or sucrose
  • a pre-formed catalyst material such as platinum particles dispersed on a high surface area carbon support (e.g. HiSpecTM materials available from Johnson Matthey pic).
  • the mixture is dried and then pyrolysed in an inert gas at a temperature of at least 800 0 C to form an electrocatalyst according to the second embodiment of the invention.
  • the present invention provides an electrocatalyst ink comprising a catalyst according to the invention dispersed in a liquid medium.
  • the ink suitably comprises aqueous and/or organic solvents, optional polymeric binders and optional proton-conducting polymers.
  • Methods of making electrocatalyst inks are disclosed in EP 731 520.
  • the present invention provides an electrode comprising a catalyst according to the invention deposited on an electronically conducting substrate.
  • the catalyst can be deposited onto a substrate using well known techniques, such as those disclosed in EP 731 520.
  • the catalyst may be formulated into an ink and the ink may be deposited onto an electronically conducting substrate using techniques such as spraying, printing and doctor blade methods.
  • Suitable substrates include carbon fibre papers and filled carbon fibre non- woven webs, such as those disclosed in EP 791 974.
  • the catalysed electrodes may be used in fuel cells with acid electrolytes such as proton exchange membrane (PEM) fuel cells or phosphoric acid fuel cells, or they may be used in alkaline electrolyte fuel cells.
  • PEM proton exchange membrane
  • the electrolyte is a proton conducting polymer membrane. Electrocatalysts may be deposited onto one or both faces of the membrane to form a catalysed membrane.
  • the present invention provides a catalysed membrane comprising a catalyst according to the invention deposited on an ion-conducting polymer membrane.
  • the catalyst can be deposited onto the membrane using well known techniques.
  • the catalyst may be formulated into an ink and either directly deposited onto the membrane or deposited onto a decal blank for subsequent transfer to a membrane. Suitable membranes are well known to those skilled in the art and include perfluorinated sulphonic acid membranes such as Nafion®, Fleinion® and Aciplex®.
  • the membrane is interposed between two catalyst layers, and each catalyst layer is in contact with an electronically conducting substrate.
  • This five-layer assembly is known as a membrane electrode assembly.
  • the present invention provides a membrane electrode assembly comprising a catalyst according to the invention.
  • the membrane electrode assembly may be prepared by a process wherein an electrode according to the invention is combined with an ion-conducting membrane.
  • the membrane electrode assembly may be prepared by a process wherein a catalysed membrane according to the invention is combined with an electronically conducting substrate.
  • the electrocatalyst according to the invention is present in the anode of the membrane electrode assembly.
  • Fig. 1 is a schematic diagram showing an electrocatalyst according to the first embodiment of the invention.
  • Fig. 2 is a schematic diagram showing an electrocatalyst according to the second embodiment of the invention. The features shown in the schematic diagrams are not to scale.
  • Figure 1 shows a metal particle (1) encapsulated by a layer of carbon (2).
  • the diameter of the metal particle is, e.g. 1-lOOnm and the thickness of the carbon layer is less than lOnm, preferably about 2nm.
  • Figure 2 shows a carbon support material (3), wherein metal particles (4) are dispersed on the support material (3).
  • the metal particles (4) are encapsulated by a layer of carbon (5).
  • the average diameter ofthe metal particles is, e.g. 1-lOnm and the thickness of the carbon layer is less than lOnm, preferably about 2nm.

Landscapes

  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Composite Materials (AREA)
  • Catalysts (AREA)
  • Inert Electrodes (AREA)

Abstract

La présente invention concerne un électrocatalyseur comprenant une ou plusieurs particules métalliques, les particules métalliques étant sensiblement recouvertes de carbone. L’électrocatalyseur peut être intégré à des encres électrocatalytiques, des électrodes catalysées ; des membranes revêtues du catalyseur et des ensembles électrode membrane et il est adapté pour être utilisé dans une pile à combustible.
PCT/GB2006/050286 2005-09-13 2006-09-12 Electrocatalyseur Ceased WO2007031795A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0518635.8 2005-09-13
GBGB0518635.8A GB0518635D0 (en) 2005-09-13 2005-09-13 Catalyst

Publications (1)

Publication Number Publication Date
WO2007031795A1 true WO2007031795A1 (fr) 2007-03-22

Family

ID=35221379

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2006/050286 Ceased WO2007031795A1 (fr) 2005-09-13 2006-09-12 Electrocatalyseur

Country Status (2)

Country Link
GB (1) GB0518635D0 (fr)
WO (1) WO2007031795A1 (fr)

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4137373A (en) * 1977-11-23 1979-01-30 United Technologies Corporation Platinum catalyst and method for making
EP0731520A1 (fr) * 1995-03-09 1996-09-11 Johnson Matthey Public Limited Company Matériaux utilisés dans la fabrication d'électrodes catalytiques
US5593740A (en) * 1995-01-17 1997-01-14 Synmatix Corporation Method and apparatus for making carbon-encapsulated ultrafine metal particles
US6037072A (en) * 1996-09-27 2000-03-14 Regents Of The University Of California Fuel cell with metal screen flow field
US6069107A (en) * 1998-06-17 2000-05-30 Aer Energy Resources, Inc. Recharge catalyst with thin film carbon coating, metal-air electrode including said catalyst and methods for making said catalyst and electrode

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4137373A (en) * 1977-11-23 1979-01-30 United Technologies Corporation Platinum catalyst and method for making
US5593740A (en) * 1995-01-17 1997-01-14 Synmatix Corporation Method and apparatus for making carbon-encapsulated ultrafine metal particles
EP0731520A1 (fr) * 1995-03-09 1996-09-11 Johnson Matthey Public Limited Company Matériaux utilisés dans la fabrication d'électrodes catalytiques
US6037072A (en) * 1996-09-27 2000-03-14 Regents Of The University Of California Fuel cell with metal screen flow field
US6069107A (en) * 1998-06-17 2000-05-30 Aer Energy Resources, Inc. Recharge catalyst with thin film carbon coating, metal-air electrode including said catalyst and methods for making said catalyst and electrode

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
AN-NUI ET AL.: "Highly stable carbon-protected cobalt nanoparticles and graphite shells", CHEM. COMMUN., November 2004 (2004-11-01), pages 98 - 100, XP002411566 *

Also Published As

Publication number Publication date
GB0518635D0 (en) 2005-10-19

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