EP1856751A2 - Fabrication d'un materiau catalyseur de chelate sans platine servant de produit intermediaire et traitement ulterieur de ce materiau en revetement electrocatalytique en tant que produit fini - Google Patents

Fabrication d'un materiau catalyseur de chelate sans platine servant de produit intermediaire et traitement ulterieur de ce materiau en revetement electrocatalytique en tant que produit fini

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Publication number
EP1856751A2
EP1856751A2 EP06722515A EP06722515A EP1856751A2 EP 1856751 A2 EP1856751 A2 EP 1856751A2 EP 06722515 A EP06722515 A EP 06722515A EP 06722515 A EP06722515 A EP 06722515A EP 1856751 A2 EP1856751 A2 EP 1856751A2
Authority
EP
European Patent Office
Prior art keywords
plasma
transition metal
chelate
treatment
metal chelate
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.)
Withdrawn
Application number
EP06722515A
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German (de)
English (en)
Inventor
Peter Bogdanoff.
Sebastian Fiechter
Iris Herrmann
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.)
Helmholtz-Zentrum Berlin für Materialien und Energie
Original Assignee
Hahn Meitner Institut Berlin GmbH
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Publication date
Application filed by Hahn Meitner Institut Berlin GmbH filed Critical Hahn Meitner Institut Berlin GmbH
Publication of EP1856751A2 publication Critical patent/EP1856751A2/fr
Withdrawn legal-status Critical Current

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    • 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
    • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
    • B01J37/349—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of flames, plasmas or lasers
    • 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
    • B01J31/00—Catalysts comprising hydrides, coordination complexes or organic compounds
    • B01J31/16—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes
    • B01J31/18—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes containing nitrogen, phosphorus, arsenic or antimony as complexing atoms, e.g. in pyridine ligands, or in resonance therewith, e.g. in isocyanide ligands C=N-R or as complexed central atoms
    • B01J31/1805—Catalysts comprising hydrides, coordination complexes or organic compounds containing coordination complexes containing nitrogen, phosphorus, arsenic or antimony as complexing atoms, e.g. in pyridine ligands, or in resonance therewith, e.g. in isocyanide ligands C=N-R or as complexed central atoms the ligands containing nitrogen
    • 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
    • B01J37/08—Heat treatment
    • B01J37/082—Decomposition and pyrolysis
    • B01J37/086—Decomposition of an organometallic compound, a metal complex or a metal salt of a carboxylic acid
    • 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
    • H01M4/9008—Organic or organo-metallic compounds
    • 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
    • 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
    • B01J2531/00—Additional information regarding catalytic systems classified in B01J31/00
    • B01J2531/80—Complexes comprising metals of Group VIII as the central metal
    • B01J2531/84—Metals of the iron group
    • B01J2531/845—Cobalt
    • 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
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive 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
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1009—Fuel cells with solid electrolytes with one of the reactants being liquid, solid or liquid-charged
    • H01M8/1011—Direct alcohol fuel cells [DAFC], e.g. direct methanol fuel cells [DMFC]
    • 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
    • Y02E60/10—Energy storage using batteries
    • 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 invention relates to a process for the preparation of a pJatinbuild chelate catalyst material as an intermediate for the selective, electro-catalytic oxygen reduction with a porous, conductive carbon matrix with embedded electrochemically active centers of a transition metal chelate and a method for further processing of the intermediate into a elektrokataiytician coating as a final product on a substrate and on an application of the final product.
  • Platinum-free chelate catalyst material for the electrocatalytic reduction of oxygen can be used in electrochemical cells, so-called fuel cells, as cathode material (alkaline and acidic fuel cell, polymer electrolyte membrane fuel cell with hydrogen or methanol operation).
  • fuel cells alkaline and acidic fuel cell, polymer electrolyte membrane fuel cell with hydrogen or methanol operation.
  • cathode material alkaline and acidic fuel cell, polymer electrolyte membrane fuel cell with hydrogen or methanol operation.
  • platinum-free chelated catalyst material behaves selectively and is tolerant to methanol.
  • the catalyst material of this kind can be used for detecting oxygen in gases as a gas sensor.
  • transition metal chelate molecules e.g., phthalocyanines, porphyrins, tetraazaannulenes.
  • a transition metal chelate molecule is a complex compound in which a central metal ion of a transition metal is under
  • the disclosed there chelate catalyst material having a porous, conductive carbon matrix with embedded electrochemically active centers of a transition metal chelate has in addition to a first transition metal, a nitrogen-containing organometallic transition complex with a different transition metal to the second transition metal and a chalcogen component.
  • the advantages of various transition metals and chalcogens as electrically conductive compounds can thus be combined.
  • the ertse transition metal in the form of a salt serves as a filler during the carbon matrix formation, so that it is formed by a foaming action in the thermal decomposition of the salt ultrahochporös.
  • the chelate catalyst differs from a commercial catalyst such as the platinum catalyst in that it consists not of fine metal particles but of molecule-integrated catalyst sites in a carbon matrix.
  • a conductive carbon matrix forms from the organic ring structure of the chelate molecule during the high-temperature reaction in which the described catalyst centers are embedded.
  • the conductivity of the carbon matrix ensures fast electron transport from the back contact of the electrode to the catalytic converter centers.
  • the delocalized ⁇ -electron carbon matrix forms a fast electron donor for electron transfer at the catalyst center. This stabilizes the catalyst sites and gives them a high reactivity because four electrons can be transferred to the center with sufficient speed. This better coupling of catalyst sites to electron transport favors efficient oxygen reduction, resulting in higher current densities.
  • a further example can be found in DE 199 53 110 A1, in which organometallic complexes (and / or at least one alkoxide containing such metal) are likewise added to a plasma reactor.
  • organometallic complexes and / or at least one alkoxide containing such metal
  • These complexes react to their metal oxide particles or with addition of sulfur to their metal sulfides.
  • These semiconductors are photocatalytically active.
  • toxic pollutants are added to the reactor, which are converted by the ongoing plasma treatment in intermediates.
  • the resulting photocatalyst accelerates the degradation of these intermediates, so that a complete decomposition of the pollutants into harmful substances can take place.
  • a method is known from DE 41 07 595 C2, in which the preparation of a platinum, palladium or their alloys containing catalyst by means of plasma and / or flame spraying is described.
  • EP 0 830 464 B1 describes the production of an electrode layer via high-speed oxygen combustion, plasma spraying, wire or powder flame spraying, arc spraying and explosion spraying.
  • a cathode-active material inorganic oxides and salts, for example silver vanadium oxide, CuS
  • a high heat input (1650 0 C to 2480 0 C) in the molten and / or plasticized state, so that the material is separated.
  • the separated particles are deposited on a substrate.
  • the resulting layer has a roughness in the ⁇ m range and a porosity of about 2 to 17 vol .-%.
  • reactive acetylene gas produced from an H 2 plasma treatment
  • the reactive molecules are deposited on a steel substrate layer grow under the given synthesis conditions (600 0 C to 800 0 C, 1 - 10 Torr acetylene gas) to carbon nanotubes zoom.
  • the production of the active material from the precursor during electrode preparation can only take place via a heat input.
  • the substrate may be, for example, a carbon nanotube electrode fabricated by chemical vacuum deposition which is switched as a cathode in an electrochemical cell.
  • the electrolyte used is an acid platinum solution.
  • the platinum ions of the electrolyte are reduced to metallic platinum particles at about -0.25 V (SCE) at the carbon nanotube surface.
  • SCE -0.25 V
  • a newer method for producing coatings is the sputtering process, which enables the production of nanoscale particles.
  • high-energy ions are generated from a low-energy plasma.
  • By bombarding a sputtering target with high kinetic energy with these high-energy ions individual atoms or molecules can be released from the sputtering target and then re-deposited as a thin layer on a substrate.
  • Sputtering technology is also used in catalyst production. By means of the sputtering process, an in-situ catalyst preparation and fine distributed deposition of the resulting few nm-sized catalyst particles can be achieved.
  • the methods described above are all based on the process steps of singulating the particles and then depositing them on a substrate. In this way, a fine distribution up to the nanometer range can be achieved. However, a simultaneous chemical reaction and formation of a new substance that has nanoscale particles is not described.
  • Sputter deposition is also used to make thin ytterium stabilized zirconia electrodes for the solid oxide fuel cell.
  • a target made of an ytterium-zirconium composite and a reactive oxygen-containing plasma are used, which incorporates oxygen atoms into the deposited ytterium-zirconium layer.
  • reactive sputtering only a radical formation takes place on the deposited layer, so that foreign atoms can be embedded in the layer and connected.
  • the object of the present invention is therefore - starting from the closest prior art to the invention - to further develop the generic manufacturing method of the type described above to improve the catalytic ability so that co-sintering of the particles is prevented during the reaction. Rather, a product should be made available that consists of nm-sized particles a high, catalytically active surface. Furthermore, from this product as an intermediate in a simple, efficient and cost-effective manner, an end product in the form of an electrocatalytic coating, which is particularly suitable for use for gas diffusion electrodes, can be produced.
  • the process of the invention for producing a platinum-free chelate catalyst material for selective, electrocatalytic, oxygen reduction having a porous, conductive carbon matrix with embedded transition metal chelate electrochemically active sites is characterized by low temperature plasma treatment of the powdered transition metal chelate in a plasma reactor space with an inert Plasma gas with such a choice of plasma power, plasma gas pressure, plasma initialization and treatment time that the molecules of the transition metal chelate are fragmented in the plasma and cross-linked in a subsequent chemical reaction, on the one hand forms the carbon matrix, but on the other hand get the chelate structure in the vicinity of the transition metal remains.
  • a chelate catalyst material which has a higher activity for the electrocatalytic reaction of oxygen reduction by a low sintering and thus generating nanoscale particles with a large, catalytically active surface than the conventional thermal treatment.
  • the process of the invention produces a chelate catalyst material consisting of an electrically conductive carbon matrix with embedded electrochemically active centers.
  • the plasma treatment controls the fragmentation of the chelate molecules as starting material, the cross-linking of these fragments as a chemical reaction in the plasma, leaving the inert plasma gas completely unaffected in the reaction, and the final formation of a carbon matrix.
  • the chelate basic structure is retained in the environment of the metal ion.
  • the method according to the invention differs already in that non-metal particles or their - oxides or sulfides in the plasma treatment involving a chemically reactive plasma gas should be formed. Rather, in the invention, the organometallic complex (chelate molecule) is converted in the plasma so that a carbon matrix with embedded electrochemically active centers (metal ion coordinated by nitrogen atoms) is formed. As already mentioned, the electrochemical activity of the catalyst is reduced when metal particles or their oxides are formed from the organometallic complex.
  • the method of the invention solves the challenge of maintaining the internal chelate structure and preventing reduction to metal particles, but nevertheless decomposing the molecule to form a carbon matrix.
  • the chelate molecule is converted to a conductive, carbon-based, electrochemically active material.
  • an efficient low temperature plasma with a high power to create a high penetration depth Formed fragments of the chelate molecule, which are linked in a subsequent chemical reaction to a conductive carbon matrix.
  • the method according to the invention fundamentally differs in the parameterization.
  • the basic building blocks of the polymer films (thus after the UV / VIS analysis according to publication III) are retained.
  • the plasma treatment with a high plasma power by splitting the molecular bonds leads to a carbon matrix (graphite), which has a significantly higher conductivity than the untreated starting material.
  • the plasma-treated product according to the invention is electrochemically active for the oxygen reduction. Thereby, the expensive high-temperature process used in the prior art, which is required to treat the chelate molecules on a rus carrier, and which - as shown in publication I - leads to a sintering of the molecules, can be substituted.
  • the process of the invention involves plasma treatment with high plasma power and low plasma temperature to produce a platinum-free chelate catalyst material of high catalytic activity. Due to the length of the treatment time, the high plasma power and the associated high penetration depth of the plasma into the starting material to be treated, the desired fragmentation of the chelate molecules and their restructuring into the desired graphite matrix with catalytically active centers is achieved.
  • the person skilled in the art will be aware of the range for the parameterization of the method according to the invention. In particular, it has been shown by own experiments that it is particularly advantageous to use a plasma gas pressure in the plasma reactor.
  • the transition metal may preferably be a Group VIII transition metal, in particular cobalt or iron.
  • the nitrogen-containing organometallic transition metal complex may advantageously be a metalloporphyrin. In this case, this cobalt or iron and in particular as cobalt tetramethoxyphenylporphyrin (CoTMPP) or Eisentetramethoxyphenylporphyrinchlorid (FeTMPP-CI) may be formed.
  • CoTMPP cobalt tetramethoxyphenylporphyrin
  • FeTMPP-CI Eisentetramethoxyphenylporphyrinchlorid
  • Metal porphyrins show excellent starting material properties because they have the structure of a catalytic center consisting of an active transition metal ion coordinated by four nitrogen bonds.
  • the substituents of the porphyrin molecule contribute to a conductive carbon matrix in the crosslinking reaction, so that a good surface accessibility and catalytic effect is achieved.
  • the metal porphyrin combines the nitrogen and the carbon donors with each other.
  • the process according to the invention described above leads to the production of a platinum-free chelate catalyst material of high catalytic activity, which can be provided as an intermediate for the production of catalytically active coatings as a final product on a substrate.
  • a new preparation method for producing a catalytically active coating which is then used for example in a gas diffusion electrode application.
  • Such an electrode with a platelet-free chelate catalyst material for selective, electrocatalytic oxygen reduction with a porous, conductive carbon matrix with embedded electrochemically active centers of a transition metal chelate on a substrate can advantageously be obtained by a plasma treatment of the type described above - also in all Variations in execution - to be made in combination with a sputtering treatment.
  • the production of a coating is then characterized by
  • an end product in the form of a coating is produced from the intermediate product in the form of a pulverulent (crystalline) carbonated, platinum-free chelate catalyst material.
  • the structure of the intermediate product (special combination of materials with a spongy, highly porous surface) is retained in the end product, so that the advantageous catalytic activity is retained in the coating due to the large surface area of the catalytically active material.
  • the combined process can take place in alternating or in two successive process stages.
  • a low-temperature plasma is alternately parameterized alternately (for example with a frequency in the kHz to MHz range), so that alternately two different plasma powers (low plasma power preferably below 150 W for the sputtering process and high plasma power of preferably over 250 W for the plasma process ) can be achieved.
  • low plasma power preferably below 150 W for the sputtering process and high plasma power of preferably over 250 W for the plasma process
  • cover the sputtering target so that it is not destroyed.
  • the parallel treatment in two different reactor areas results in a modified reactor design.
  • the particles sputtered in the first low-temperature plasma treatment are then passed within the reactor into a second low-temperature plasma (two-zone plasma) whose parameters are independent can be adjusted from the first plasma.
  • a second low-temperature plasma two-zone plasma
  • high plasma power then converts the previously sputtered molecules into the pulverized (crystallized) carbonated chelate catalyst material.
  • the carbonation process can be specifically controlled independently of the sputtering process.
  • the process stage concludes with the substrate positioned outside the plasma, on which the produced nanoscale catalyst particles produced in the second plasma are deposited as a nanoporous coating.
  • a modification of the above-described manufacturing method provides that the substrate is disposed within the plasma for the second low-temperature plasma treatment.
  • the CoTMPP molecules formed in the plasma are deposited directly as a thin layer on the substrate.
  • the loading and the process parameters of the process can be used to set the thickness and structure of the catalytically active coating to be produced as the end product.
  • a polymer electrolyte membrane, for example Nafion, on which the produced platinum-free chelate catalyst material is deposited can also be used as the substrate.
  • the catalytic layers produced in this way can be used by known and established methods for the production of membrane electrode assemblies (MEA) for the PEM fuel cell technology.
  • MEA membrane electrode assemblies
  • the first plasma is for providing the high-energy gas ions and the second plasma is for producing the chelate catalyst material as well as depositing it on the electrode surface.
  • the singling of the starting material takes place in the sputtering target via a sputtering process without heat input.
  • the described combination of the two methods according to the invention makes it possible to produce in a simple and cost-effective manner a coating which has a novel highly porous structure and thus catalytically highly active.
  • an integration of all required for the production of the coating process steps in one automated inline process so that corresponding electro-catalytic electrodes can be produced in large quantities quickly, with high quality, and yet still inexpensively, without great personnel expenditure.
  • the electrodes are formed as gas diffusion electrodes, which are increasingly used in the selective reduction of oxygen.
  • FIG. 1 shows a Raman spectrum of a CoTMPP / KBr sample at a plasma power of 80 W
  • Figure 2 is a Raman spectrum of a CoTMPP / KBr sample at a
  • Plasma power of 150 W is a Raman spectrum of a CoTMPP / KBr sample at a
  • Plasma power of 250 W is a Raman spectrum of a CoTMPP / KBr sample at a
  • FIG. 5 Plasma power of 400 W
  • FIG. 5 a comparison of a plasma-treated and a pyrolyzed CoTMPP / KBr sample
  • FIG. 6 a diagram of the current density behavior
  • FIG. 7 a diagram of the particle size distribution
  • Figure 8 is a comparison of the Raman spectra of the original Precursors (CoTMPP) and a sample from the combined
  • Figure 9 shows two SEM images of a substrate before and after the
  • FIG. 10 shows an SEM image of a substrate according to FIG.
  • the starting material is prepared as follows: 0.264 g of cobalt tetra-methoxyphenylporphyrin (hereinafter CoTMPP, from ACROS) are dissolved in 200 ml of tetrahydrofuran (hereinafter THF).
  • CoTMPP cobalt tetra-methoxyphenylporphyrin
  • THF tetrahydrofuran
  • the plasma treatment is carried out in a plasma shaker reactor.
  • 0.5 g to 0.8 g of the starting material are placed on a sample plate in the reactor space.
  • the plasma is initialized with excitation in the radio frequency range (13, 56 MHz).
  • the reactor room contains 10 Pa argon as an inert plasma gas.
  • the samples are thoroughly mixed by vibrating the sample plate in the reactor chamber so that each particle is exposed to the plasma.
  • a high plasma power greater than 250W
  • a treatment time of 5 minutes to 40 minutes an effective implementation of the CoTMPP to carbon-based chelate catalyst achieved.
  • the starting material was treated at 400W for 20 minutes.
  • the starting material in a flow-through oven (110 ml / min argon) for 2 h at 45O 0 C and then for 1 h at 75O 0 C heated. After cooling, the material can be used.
  • an intense broad band at 1250 cm -1 which is assigned to sp 2 -hybridized carbon in low-molecular weight compounds, is found in addition to fragments of the porphyrin disintegrated by the low-temperature plasma, which are not yet graphene-free.
  • increasing plasma power 250 W, 400 W, Raman spectra according to Figures 3 and 4
  • the proportion of these species in the sample decreases significantly, since these fragments are now largely consumed in the formation of Graphene levels
  • at 150 W 2 observed a dominant band at 1510 cm -1 indicating superposition of Raman active intermediates of unknown structure, supported by the fact that the proportion of this signal together with the signal at 1250 cm -1 decreases significantly with increasing plasma power.
  • Plasma treatment of CoTMPP is formed as in the thermal treatment. From 250 W results in a perfect fürkarbonmaschine the material used. At a high plasma power (400 W), however, the reaction comes to an end more quickly.
  • the diffusion-corrected current densities as a function of the potential at the working electrode are shown in the diagram according to FIG. 6 in comparison between plasma-treated starting material (plasma-treated sample (circles, curve a), 400 W, 20 min, argon) and thermally treated starting material (reference sample (triangles, curve b), thermal treatment).
  • plasma-treated starting material plasma-treated sample (circles, curve a), 400 W, 20 min, argon)
  • thermally treated starting material reference sample (triangles, curve b), thermal treatment
  • the behavior of the untreated starting material rhombs, curve c
  • the particularly good behavior of the plasma-treated chelate catalyst material according to the invention over the other two samples is clearly recognizable.
  • the untreated starting material shows a very low current density.
  • the treated samples show higher current densities than the starting material.
  • the plasma-treated material shows significantly higher current densities.
  • the following table compares the difference between the achieved current densities for different potentials:
  • gas sorption measurements are performed to determine the specific surface area according to the BET model.
  • the reference sample has a specific surface area of 1047 m 2 / g.
  • a specific surface area of 693 m 2 / g was determined.
  • the plasma-treated sample has a lower specific surface area, it exhibits higher kinetic current densities than the reference sample. It becomes clear that the chelate catalyst produced in the plasma treatment has a higher specific activity than the chelate catalyst prepared in the conventional method.
  • the particle size distribution of the catalyst particles is determined.
  • the measured particle size distributions of the reference sample and the plasma-treated chelate catalyst material are shown in the diagram according to FIG. 7 (particle number PA in% over the particle size PG in ⁇ m).
  • the largest proportion of the particles of the reference sample (solid lines, b) has a particle size of about 0.87 microns.
  • particles of only about 0.06 ⁇ m are formed in the plasma treatment (dashed lines, a).
  • the heat input during the thermal treatment known from the prior art (compare Tuinstra, F. and Koenig, JL, "Raman Spectrum of Graphite", The Journal of Chemical Physics, 33, 1126 (1970)) melts the CoTMPP at approx.
  • the formation of the liquid CoTMPP film of the particles leads to sintering during the melt caused thereby aggregates the size of which adversely affect the preparation of, for example gas diffusion electrodes.
  • the sintering is prevented in the plasma treatment according to the invention.
  • the plasma treatment predominantly electronic energy and only lower heat are introduced, so that melting of the CoTMPP and sintering of the particles is largely prevented, resulting in small particles which are prerequisite for the preparation of efficient electrodes (eg porous gas diffusion electrodes) ,
  • a sputtering target is made of CoTMPP.
  • CoTMPP CoTMPP
  • about 15 g of CoTMPP are pressed into a 94.5 cm round copper target with the aid of a stamping press (3 t, 3 x 10 min).
  • stamping press 3 t, 3 x 10 min.
  • Smaller material saving targets can also be used if the sputtering system has a magnetron.
  • the manufactured target is mounted in the sputtering system so that it can be used as an electrode.
  • the target is a substrate for the production of the gas diffusion electrode (substrate: carbon paper) opposite.
  • the sputtering system is purged with argon and finally set an operating pressure of about 10 Pa argon.
  • the plasma is initialized by applying a voltage and ignited by means of excitation in the radio frequency range.
  • the following operating parameters for sputtering have proven particularly advantageous: low-temperature plasma, inert plasma gas, argon, pressure 10 Pa, Plasma power for the first low-temperature plasma treatment less than 100 W (for the sputtering process), plasma power for the second low-temperature plasma treatment greater than 250 W (for the plasma process), between the two plasma treatments, a two-zone plasma is used or it is alternately switched (the switching frequency can in kHz - in the plasma process, the sputtering target is protected from charring (total process time up to 60 min).
  • the thickness of the catalyst layer can be determined.
  • the coated carbon paper can then be processed into a membrane electrode assembly (MEA for short). Furthermore, as a substrate for coating with the platinum-free chelate catalyst material according to the invention, a polymer electrolyte membrane, for example Nafion, can be used.
  • a polymer electrolyte membrane for example Nafion
  • a carbon-free, Raman inactive substrate (TLC plate silica gel) was used.
  • a combined sputter plasma process was performed.
  • FIG. 8 shows the Raman spectra of the original precursor (CoTMPP) and the sample from the combined sputter plasma process.
  • the precursor has the typical Raman bands of CoTMPP as described in Publication VIII. In contrast, these bands can not be redetected in the Raman spectrum in the sample obtained from the combined sputtering plasma process.
  • the sample has two bands found by peak unfolding at about 1365 cm -1 and 1575 cm -1 , which are known from the prior art and are typical for black carbons.
  • the peak at about 1575 cm -1 (so-called G peak) is sp 2 -hybridized C-V vibrations are assigned to the graphene planes, while the peak at 1365 cm -1 (D-peak) is caused by the marginal carbon atoms.
  • particles sizes are on the order of commercial platinum catalysts as used in fuel cells, materials produced by this process can also be used via established techniques to make gas diffusion electrodes for PEM fuel cells.

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Abstract

Un matériau catalyseur de chélate sans platine est employé pour la réduction d'oxygène sélective dans des cellules électrochimiques à l'hydrogène et au méthanol, par exemple dans l'industrie automobile. La porosité et l'activité catalytique obtenues ne sont pas suffisantes du fait de l'effet de frittage apparaissant lors d'un traitement haute température intervenant dans la fabrication de produits commerciaux. Le procédé selon l'invention est caractérisé par un traitement plasma basse température du chélate de métal de transition pulvérulent dans une chambre de réacteur plasma avec un gaz plasma inerte, la puissance, la pression de gaz et l'initialisation de plasma comme le temps de traitement pouvant être choisis de telle manière que les molécules du chélate de métal de transition sont fragmentés dans le plasma, et réticulés dans une réaction chimique consécutive de façon que la matrice de carbone se forme d'une part, et que d'autre part la structure de base de chélate soit conservée au niveau du métal de transition. Les particules de catalyseur de chélate produites sont très poreuses et ont une taille de 0,06 ?m. Le produit intermédiaire ainsi fabriqué peut être traité ultérieurement par traitement plasma/pulvérisation combiné avec deux plasmas basse température différents, de puissances différentes, employés en parallèle ou de façon alternée, de manière à former un revêtement électrocatalytique en tant que produit fini, notamment utilisé sur une électrode de diffusion gazeuse.
EP06722515A 2005-02-20 2006-02-20 Fabrication d'un materiau catalyseur de chelate sans platine servant de produit intermediaire et traitement ulterieur de ce materiau en revetement electrocatalytique en tant que produit fini Withdrawn EP1856751A2 (fr)

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