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• • H—ELECTRICITY
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  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
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  • 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
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  • B01J35/40—Catalysts, in general, characterised by their form or physical properties characterised by dimensions, e.g. grain size
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
  • B01J21/18—Carbon
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  • B01J35/40—Catalysts, in general, characterised by their form or physical properties characterised by dimensions, e.g. grain size
  • B01J35/45—Nanoparticles
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  • B01J37/08—Heat treatment
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  • B01J37/084—Decomposition of carbon-containing compounds into carbon
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  • C04B35/52—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite
  • C04B35/524—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite obtained from polymer precursors, e.g. glass-like carbon material
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
  • C07C5/22—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by isomerisation
  • C07C5/2206—Catalytic processes not covered by C07C5/23 - C07C5/31
  • C07C5/226—Catalytic processes not covered by C07C5/23 - C07C5/31 with metals
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  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B11/00—Electrodes; Manufacture thereof not otherwise provided for
  • C25B11/04—Electrodes; Manufacture thereof not otherwise provided for characterised by the material
  • C25B11/051—Electrodes formed of electrocatalysts on a substrate or carrier
  • C25B11/073—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material
  • C25B11/091—Electrodes formed of electrocatalysts on a substrate or carrier characterised by the electrocatalyst material consisting of at least one catalytic element and at least one catalytic compound; consisting of two or more catalytic elements or catalytic compounds
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/28—Electrolytic cell components
  • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
  • G01N27/308—Electrodes, e.g. test electrodes; Half-cells at least partially made of carbon
• • 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
  • H01M4/96—Carbon-based electrodes
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2521/00—Catalysts comprising the elements, oxides or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium or hafnium
  • C07C2521/18—Carbon
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C2523/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group C07C2521/00
• • 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 invention relates to glassy carbon.
• Glassy carbon has a unique combination of properties, including chemical and thermal inertness, hardness, impermeability to gases and liquids, and electrical conductivity. Because of these properties, glassy carbon commonly is used in carbon electrodes. It is known to use oligomers containing acetylene groups as starting materials for making glassy carbon.
• the invention features, in one aspect, glassy carbon containing a dispersion of metal particles having an average size of less than 1 micron.
• the invention features, in another aspect, an electrochemical cell in which one of the electrodes includes glassy carbon containing a dispersion of metal particles having an average particle size of less than 1 micron.
• the invention features, in another aspect, an electrochemical cell in which one or both of the electrodes includes glassy carbon containing a dispersion of metal particles having a relatively uniform size distribution.
• relatively uniform size distribution it is meant that the diameter of 70% of the metal particles are less than 5 times (more preferably 3 times) the number average diameter of the particles.
• the invention features, in another aspect, a method of producing glassy carbon containing metal particles.
• the method involves heating a metal complexed to a molecule (preferably including acetylene groups) for a sufficient period of time for the molecule to cross ⁇ link to provide glassy carbon.
• a metal complexed to a molecule preferably including acetylene groups
• cross-linking is performed at temperatures of less than 1000°C, more preferably less than 750°C most preferably less than 600°C.
• the glassy carbon can be incorporated into an electrode for an electrochemical cell.
• the invention features, in another aspect, a method of producing a cross-linked carbon matrix that includes metal particles.
• the method includes providing a metal complexed to a molecule capable of cross-linking to form an sp 2 -hybridized carbon matrix, and cross- linking (preferably by heating) the molecules sufficiently to form an sp -hybridized carbon matrix having microcrystalline graphite domains having average lattice dimensions of between 1 and 20 nanometers (more preferably between 2.5 and 7.5 nanometers).
• the invention features, in another aspect, a method of producing a cross-linked, conductive carbon matrix.
• the method includes providing a metal complexed to a molecule capable of cross-linking to form a conductive sp 2 -hybridized matrix, and cross-linking (preferably by heating) the molecules sufficiently to form an sp 2 -hybridized carbon matrix having a conductivity of at least 0.01 s/cm (more preferably at least 0.1 s/cm) .
• glassy carbon containing a dispersion of small metal particles to catalyze a chemical reaction (e.g., reforming, hydrogenations, dehydrogenations, isomerizations of hydrocarbons, oxidations, reductions, and pollutant removal) , or to catalyze an electrochemical reaction in an electrochemical cell (e.g., a fuel cell, a cell for electrochemical synthesis, or a sensor) .
• a chemical reaction e.g., reforming, hydrogenations, dehydrogenations, isomerizations of hydrocarbons, oxidations, reductions, and pollutant removal
• an electrochemical cell e.g., a fuel cell, a cell for electrochemical synthesis, or a sensor
• the preferred metals are transition metals that have desirable catalytic or electrocatal tic properties, for example, platinum, palladium, iron, cobalt, and silver.
• the preferred molecules are oligomers that include diacetylene and aromatic groups.
• the particles Preferably have an average size of less than 100 nanometers, more preferably less than 15 nanometers, most preferably less than 5 nanometers.
• the preferred glassy carbon has a carbon content of at least 80%. Glassy carbon is a form of sp -hybridized carbon composed of branched and entangled graphite ribbons.
• glassy carbon The structure and properties of glassy carbon are well known in the art, and are described, for example, in conventional texts such as Kinoshita, Carbon: Electrochemical and Physiochemical Properties (Wiley: New York, 1988) As is recognized by these skilled in the art, although glassy carbon is a well-known material, its properties vary somewhat based on the specific mode of preparation. For example, glassy carbons in general have good conductivity, but some forms have better conductivity than others.
• the size of the metal particles is readily regulated by controlling the initial loading of the metal in the complex; the lower the atom percent of metal in the starting complex (preferably less than 10%, more preferably less than 5%) , the smaller the resultant particle size.
• the small particle size makes a large surface area of metal available for participation in, for example, electrochemical or catalytic reactions. The invention thus provides a highly efficient mode of delivery for catalytic metals, most of which are very expensive.
• acetylenic chemical precursors of glassy carbons are soluble in organic solvents, which makes them easy to handle and form into desired shapes, such as thin films or coatings on the outside of conventional carbon electrodes.
• the amount of metal in the coating can be controlled by the dilution of the complex in the solution; the more dilute the complex, the thinner the coating formed.
• the cross-linking of the acetylene precursors occur at relatively low temperatures.
• the invention provides a convenient way to introduce more than one type of metal into glassy carbon, for example, by mixing acetyleni ⁇ molecules complexed to different metals together prior to cross-linking.
• the preferred glassy carbon are prepared from aromatic acetylene molecules, typically oligomers or even larger polymers, complexed to a transition metal. Heteroatoms such as nitrogen or boron can be included in the glassy carbon as part of the aromatic ring. Other heteroatoms such as halides or silicon can be substituted for a hydrogen atom in the aromatic ring.
• the acetylene groups cross link at a low temperature (e.g., less than 400°C) to form a highly cross-linked carbon network. Further heating at temperatures typically less than 600°C causes the microcrystalline lattice to increase in size.
• the transition metals can complex to either the acetylene groups, or aromatic rings, or other complexing groups included in the molecule, and are released from the complex during the cross-linking process. The metal remains trapped in the glassy carbon network as small particles of a relatively uniform size.
• the transition metal selected will depend on the catalytic, or electrocatalytic, properties desired, but can be, for example, platinum, palladium, titanium, ruthenium, zirconium, hafnium, iron, nickel, and silver, or combinations of these metals, if desired.
• acetylenic oligomers that are suitable for complexing with transition metals to provide precursors for glassy carbon are legion, and are well- known to those skilled in the art.
• suitable complexed oligomeric precursors include those having formula 1-10, below.
• the oligomers may be end-capped with mono-functional acetylenes (not shown) .
• the illustrated repeat unit of the oligomers is shown complexed to the metal; usually in the full oligomer, only a portion of the repeat units are complexed to metal atoms, depending on the metal loading into the reaction mixture that generated 1-10.
• Oligomers 1-10 can be prepared by standard chemical procedures. For example, the synthesis of 1 can be accomplished by reaction of 11 with butyllithiu followed by reaction with chlorodiphenylphosphine to give 12. Reaction of 12 with (PPh 3 ) 3 RhCl or Ag(PPh 3 ) 4 BF4 gives 1.
• the synthesis of 2 can be accomplished by treatment of 13 with magnesium in diethyl ether, followed by reaction with cyclopentenone, followed by dehydration to give a general cyclopentadiene ligand which can be used for complexation with various metals.
• Platinum complex 3 which serves as a precursor to metal doped glassy carbon containing a bypyridyl ligand complexed with platinum, can be prepared by reaction of 15 with 16 using bis(triphenylphosphine)palladium(II) chloride as a catalyst in toluene to give 17. Reaction of 17 with (cyclooctadiene)diphenylplatinum(II) gives 3.
• the complex containing iron 4 can be prepared by reaction of l,l'-bromoacetylferrocene (18) with copper to give 19. Treatment of 19 with P0C1 3 in dimethylformamide followed by reaction with sodium hydroxide gives 20. Reaction of 20 in the presence of copper chloride and oxygen gives 4.
• Cud Glassy carbon precursor 5 which contains nickel, can be prepared by reaction of 21 with ethylene bis(triphenylphosphine)nickel(0) .
• the starting complex can also include more than one metal.
• the molecular weight of the oligomers and polymers can be controlled by suitable use of end-capping groups such as phenyl acetylene, pentafluoroacetylene and the like when the molecules are prepared.
• the level of metal incorporated in these molecules also can be controlled by the amount of metal complex added to the acetylene molecule.
• glassy carbon containing a dispersion of two or more types of metal particles also can be prepared by simply mixing different metal containing oligomeric complexes prior to cross-linking and annealling.
• the most preferred glassy carbons include a dispersion of platinum particles. Platinum is a catalyst for many important chemical reactions, including oxygen and hydrogen reduction. Glassy carbon including the dispersion of platinum particles can be used, for example, in oxygen/hydrogen or methanol/oxygen fuel cells. It is highly suitable for these uses because the platinum is provided efficiently in a stable matrix.
• the preferred glassy carbons containing platinum particles were prepared according to the following procedures.
• Ethylene bis(triphenylphosphine) latinum(0) was prepared by a three-step process.
• Triphenylphosphine (1.46 g, 5.6 mmol) was dissolved in 20 mL of absolute ethanol at 65°C. When the solution was clear, 0.14 g (0.0025 mol) of potassium hydroxide in 1 mL of water and 4 mL of ethanol was added. To this was then added 0.5 g (1.2 mmol) of potassium tetrachloroplatinate(II) dissolved in 5 mL of water while stirring at 65°C. A pale yellow solid precipated within a few minutes of the first addition. After cooling, the compound was recovered by filtration, washed with 50 L of warm ethanol, 20 mL of water and 12 mL of cold ethanol to give 1.17 g (78 %) of product.
• An alternative starting complex, tetrakis[bis[l- (3-phenylbutadiyny1)phenyl]phenylphosphine]platinum(0) which has the below formula, was prepared in two steps.
• the reaction was quenched with a saturated solution of ammonium chloride, the solids removed by decantation, and the organic layer was washed with ammonium chloride solutions and dried with anhydrous magnesium sulfate. After filtration of the solid, the solvent was removed in vacuo, and the yellow residue was purified by column chro atography on silica gel (20% CH 2 C1 2 in hexanes) to give 0.7 g (20 %) of light white crystals.
• the bis[l-(3- phenylbutadiyne)phenylJphenylphosphine (0.47 g, 0.09 mmol) was dissolved in the minimum amount of benzene (4 mL) and then diluted in 10 mL of ethanol. The solution was heated to 65°C and when the solution turned clear, 0.5 mL of a solution of 0.21 g (0.004 mol) of potassium hydroxide in 1 mL of water and 4 mL of ethanol was added. To this, was then added dropwise, 0.0832 g (0.2 mmol) of potassium tetrachloroplatinate(II) dissolved in 5 mL of water, while stirring at 65°C.
• the acetylenic complexes described above can be converted to glassy carbon at relatively low temperatures.
• the initial heating causes the acetylene groups to cross-link, forming a highly cross-linked carbon matrix.
• the cross-linking can be carried out at temperatures below 500°C (e.g., 350°C).
• the cross-linked matrix anneals, to provide glassy carbon.
• Annealization typically requires heating at a higher temperature (e.g., 550°C - 700°C) than the initial cross-linking. Both steps can be carried out simultaneously by simply heating at the higher temperature.
• the glassy carbons should have a conductivity greater than 0.01 s/cm, more preferably greater than 0.1 s/cm, and most preferably greater than 0.7 s/cm.
• the microcrystalline graphite dimensions as determined by conventional Raman spectroscopy and X-ray powder diffraction techniques, are between 1 and 20 nanometers, more preferably greater than 2 nanometers, most preferably between 2.5 and 7.5 nanometers.
• the glassy carbon electrode should function as a practical electrode.
• the oxidation-reduction separation should be ⁇ Ep ⁇ 200 V, more preferably ⁇ 150mV, and most preferably ⁇ 100mV.
• Glassy carbon pellets were made in two steps. Approximately 150 mg of a precursor were submitted to a pressure of 3500 psi at a temperature of 350°C for 2 hours in a 1 cm diameter steel die. A Carver laboratory press model C was used. The sample was allowed to cool slowly. At the end of this period, a 1 cm diameter black disc of cross-linked carbon solid was obtained. The pellets were then sealed in vacuo in a quartz tube and heated to 600°C at a rate of l°C/min for a total period of 15 hours in a Thermolyne type 6000 furnace, and then allowed to cool at a rate of l°C/min to room temperature. b) Glassy carbon films
• a toluene solution of a precursor was spin-coated (Headway Research, PWM101 model) on an Atomergic V25 glassy carbon disc. The solvent was evaporated and the disc was sealed in vacuo and thermally treated to 600°C under the same conditions as that for the pellets.
• a similar procedure can be used to coat a variety of materials, including carbon felt, carbon filters, other metals, silica, and alumina. Importantly, this provides the uses with the ability to take a variety of backings and turn them into, e.g., a platinum electrode, by simple coating procedures.
• Raman analysis confirms the glassy carbon microcrystalline structure of these carbon solids exhibiting bands at approximately 1580 cm -1 and 1360 cm "1 , consistent with the formation of an sp 2 -hybridized carbon lattice.
• X-ray photoelectron spectroscopic analyses and icroprobe analysis confirmed the incorporation of approximately 0.5 to 1 atom % of platinum(0) in glassy carbon.
• the size of platinum particles can be determined by standard transmission microscopic analysis. For example, a thin film of the glassy carbon containing dispersed platinum particles was prepared by evaporation of a glassy carbon precursor onto a sodium chloride disc to give a 2-3 micron thick coating. The disc was then heated to 600°C to provide a film of glassy carbon. The film was then lifted from the disc, and a transmission electron micrograph of the edge of the film is taken, and the diameters of the particles (or clusters) are recorded, and a mean obtained. The average platinum particle size in the glassy carbons obtained from the previously described precursors in the range of 1.4 to 2.1 nanometers.
• glassy carbons of the invention are useful in a wide variety of catalytic and electrochemical applications.
• glassy carbon containing dispersed platinum particles when used in place of platinum in a platinum disc electrode and studied for its effect on the reduction of H + to H 2 , exhibited a performance close to that of a pure platinum disc.
• An electrode was also prepared by applying 5 drops of a saturated solution of a 1:2 platinum:diyne ratio of poly[ (phenylenediacetylene) bis(tri ⁇ phenylphosphine) platinu (0) ] in toluene to each side of a carbon felt electrode, which consisted of a matrix of carbon fibers.
• the electrode was heated under vacuum to 600°C (l°C/min) , and cured at 600°C for 6 hours to provide the glassy carbon.
• the resulting electrode was used in place of a standard platinum disc electrode. Voltrametry was taken in a 1M H 2 S0 solution at different scan rates in the range of 0.2V to -0.6V versus a conventional Ag/AgCl reference electrode.
• the activity of the platinum dispersed in glassy carbon was compared to a polycrystalline platinum electrode and a conventional glassy carbon electrode for oxygen reduction.
• a 1 atom % platinum in glassy carbon thin film on conventional glassy carbon was exposed to oxygen in 1M HC10 4 buffer and scanned at 50 mV/sec from 1.0 to -0.5 V vs SSCE.
• the current density and potential for 0 2 reduction with the platinum in glassy carbon electrode exhibited a performance close to that of a pure platinum disc.
• the carbon felt electrode including a thin coating of glassy carbon containing platinum particles the porosity, stability, and catalytic efficiency of the electrode should be very useful for electrochemical applications.
• glassy carbons containing heteroatoms such as N can be prepared, for example, by cross-linking and annealling a complex having formulae 3.
• Glassy carbons containing dispersions of metal particles can be prepared from acetylenic oligomers lacking aromatic groups, for example, some of the acetylenic oligomers described in Hay, U.S. 3,332,916, which is hereby incorporated by reference.
• the glassy carbons can be prepared from other, non- acetylenic precursors, such as phenolic formaldehyde oligomers, that are complexed to a metal.
• the activity of the platinum dispersed in glassy carbon was compared to a polycrystalline platinum electrode and a conventional glassy carbon electrode for oxygen reduction.
• a 1 atom % platinum in glassy carbon thin film on conventional glassy carbon was exposed to oxygen in 1M HC10 4 buffer and scanned at 50 mV/sec from 1.0 to -0.5 V vs SSCE.
• the current density and potential for 0 2 reduction with the platinum in glassy carbon electrode exhibited a performance close to that of a pure platinum disc.
• the carbon felt electrode including a thin coating of glassy carbon containing platinum particles the porosity, stability, and catalytic efficiency of the electrode should be very useful for electrochemical applications.
• glassy carbons containing heteroatoms such as N can be prepared, for example, by cross-linking and annealling a complex having formulae 3.
• Glassy carbons containing dispersions of metal particles can be prepared from acetylenic oligomers lacking aromatic groups, for example, some of the acetylenic oligomers described in Hay, U.S. 3,332,916, which is hereby incorporated by reference.
• the glassy carbons can be prepared from other, non- acetylenic precursors, such as phenolic formaldehyde oligomers, that are complexed to a metal.

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