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
• • 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
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/56—Platinum group metals
  • B01J23/64—Platinum group metals with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
  • B01J23/648—Vanadium, niobium or tantalum or polonium
  • B01J23/6486—Tantalum
• • 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
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/56—Platinum group metals
  • B01J23/64—Platinum group metals with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
  • B01J23/652—Chromium, molybdenum or tungsten
  • B01J23/6525—Molybdenum
• • 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
  • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
  • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
  • B01J23/56—Platinum group metals
  • B01J23/64—Platinum group metals with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
  • B01J23/652—Chromium, molybdenum or tungsten
  • B01J23/6527—Tungsten
• • 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
• • 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
  • B01J37/341—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 electric or magnetic fields, wave energy or particle radiation
  • B01J37/344—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 electric or magnetic fields, wave energy or particle radiation of electromagnetic wave energy
  • B01J37/346—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 electric or magnetic fields, wave energy or particle radiation of electromagnetic wave energy of microwave energy
• • 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
  • H01M4/9016—Oxides, hydroxides or oxygenated metallic salts
• • 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
• • 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

• This invention relates to fuel cell electrode catalysts comprising alternating platinum-containing layers and layers containing suboxides of a second metal that display an early onset of CO oxidation.
• the early onset is manifest as a pre- peak, in addition to the normal Pt CO oxidation peak, in CO oxidation cyclic voltametry.
• Methods of manufacturing the subject catalysts are also provided.
• the fuel cell catalysts of the present invention show improved reformate tolerance, and in particular improved CO tolerance.
• the fuel stream feeding a hydrogen fuel cell may be supplied by reformation of hydrocarbons.
• the reformate stream will typically contain constituents including CO, CO 2 , N 2 and CH 3 in addition to hydrogen.
• Typical fuel cell catalysts are susceptible to carbon monoxide poisoning, which causes significant loss of power and durability.
• U.S. Pat No. 4,910,099 discloses one method of improving CO tolerance in fuel cells. In this method, O 2 or air is "bled" to the anode side of the cell, where it reacts with any CO present in the fuel gas stream to form CO 2 . However, this method reduces cell efficiency.
• U.S. Pat. No. 5,183,713 concerns a fuel cell catalyst with improved CO tolerance comprised of platinum alloyed with 2-10% tantalum. The metals are not alternately layered and suboxides are not taught.
• U.S. Pat. No. 5,523,177 concerns a direct-methanol fuel cell including a partially reduced metal oxide anode porous electrode having an oxide content of between 5 wt % and 20 wt %.
• the exemplary catalyst is composed of an alloy of platinum and ruthenium.
• This reference does not teach an alternately layered catalyst. The reference indicates that "partial reduction” proceeds by reduction of PtO x , without significant reduction of RuO x . (US 5,523,177 at col. 4, In. 62 - col. 5, In. 4). In addition, the reference teaches that reduction of RuO x is not desirable. (Id.) The reference does not teach that the catalyst disclosed therein has any favorable CO tolerance characteristics in a hydrogen/air or reformate/air fuel cell.
• U.S. Pat. No. 6,040,077 concerns an alternately layered catalyst of Pt and Ru, including Pt and Ru oxides and suboxides.
• the present invention provides fuel cell electrode catalysts comprising alternating platinum-containing layers and layers containing suboxides of a second metal, where the catalyst demonstrates an early onset of CO oxidation. Preferably the early onset appears as a shoulder in CO oxidation cyclic voltametry and more preferably as a pre-peak.
• the present invention provides fuel cell electrode catalysts comprising alternating platinum-containing layers and layers containing suboxides of a second metal selected from the group consisting of Group Illb metals, Group IVb metals, Group Vb metals, Group Vlb metals and Group Vllb metals.
• the second metal is selected from the group consisting of Ti, Ta, W and Mo.
• the present invention provides methods of making such catalysts. In particular, the present invention provides methods of making such catalysts by alternate deposition of platinum and second metals in the presence of substoichiometric amounts of gaseous oxygen.
• suboxide means a ccmposition MO x of a metal M having one or more chemical oxidation states MO, where n is one or more positive rational numbers (typically a ratio of small positive integers), wherein x is not equal to any n and wherein x is less than the greatest n; and
• substituted means substituted by conventional substituents which do not interfere with the desired product, e.g., substituents can be alkyl, alkoxy, aryl, phenyl, halo (F, Cl, Br, I), cyano, nitro, etc.
• peak means a local maximum value
• pre-peak means, in regard to CO oxidation cyclic voltametry, a peak in addition to and appearing at a lower potential than a Pt CO oxidation peak
• shoulder means a local maximum in the first derivative of a value
• “early onset of CO oxidation” means CO oxidation occurring at a potential lower than that of the Pt CO oxidation peak.
• the Pt CO oxidation peak typically occurs at around 400 mV, referenced to a saturated calomel electrode, but may be shifted as low as 200 mV by the presence of other metals, e.g. Ru.
• Early onset of CO oxidation may be demonstrated by CO oxidation cyclic voltametry, where it is indicated by a rise in current reflecting the oxidation of CO.
• Preferable conditions for performing cyclic voltametry are 80°C temperature, ambient pressure and 25 mV/sec scan rate.
• early onset may be demonstrated by comparison of the subject CO oxidation cyclic voltametry curve to a curve obtained for a Pt catalyst.
• the y-axis of the subject curve (representing electrical current) is normalized to the Pt curve by multiplying the values of the subject curve by a scaling factor such that the two curves have the same value at the Pt oxide reduction peak (label (1) in Fig. 3).
• the curves are not normalized in the x-axis (representing electrical potential).
• “Early onset” is defined with regard to the region of the subject curve between the point of H2 evolution and a point 140 millivolts more positive than the reference electrode (saturated calomel electrode (SCE)), preferably in the region between H2 evolution and 110 millivolts above SCE, more preferably in the region between H2 evolution and 80 millivolts above SCE, and most preferably in the region between H2 evolution and 50 millivolts above SCE.
• “Early onset” is seen where a point in that region of the subject curve has a positive slope or, more preferably, demonstrates at least 10% greater capacitive (double layer) current than the Pt curve.
• Figure 1 is a schematic depiction of an apparatus for practice of the method of the present invention.
• Figure 2 is a graph demonstrating CO oxidation cyclic voltametric scans of two comparative catalysts, Pt and PtRuO x , and one catalyst according to the present invention, PtMoO x .
• the PtRuO x and PtMoO x scans are normalized to the Pt scan for comparison.
• Figure 3 is a graph demonstrating CO oxidation cyclic voltammetric scans of a comparative catalyst, PtTa2 ⁇ 5, and a catalyst according to the present invention
• PtTaO x The PtTaO x and PtTa2U5 scans were normalized to the same Pt oxide reduction peak (1).
• the present invention provides fuel cell catalysts, preferably anode catalysts, comprising alternating platinum-containing layers and layers containing suboxides of a second metal. It has been discovered that such catalysts provide improved CO tolerance in fuel cell use by their improved ability to oxidize CO at lower potentials.
• the platinum-containing layers of the present invention contain 1-100 atom% platinum, but preferably 50-100 atom%.
• the platinum may also be present as an suboxide. This layer may also contain 0-30 atom% oxygen, but preferably 2-10 atom%.
• the suboxide-containing layers contain oxygen and at least one second metal M.
• Preferred metals include selected from the group consisting of Group Illb metals, Group IVb metals, Group Vb metals, Group Vlb metals and Group Vllb metals. More preferred metals include Ti, Ta, W and Mo.
• the atomic ratio x of oxygen to M is not equal to that in any stoichiometric oxidation state n of M.
• x varies from any n by 2% or more, more preferably by 5% or more, and more preferably by 10% or more.
• x is less than the highest ratio of O to M in a chemical oxidation state of M.
• x is between 0.1 and 5.0.
• a catalyst can be made that combines a variety of layers.
• PtMO x and PtRu catalysts are combined by alternate deposition.
• the layers of the second catalyst material, MO x , and Ru-containing layers are not adjacent but are interleaved with layers of Pt-containing catalyst material, e.g. where the repeating unit of layers is Pt:MO x :Pt:Ru.
• Pt-containing catalyst material e.g. where the repeating unit of layers is Pt:MO x :Pt:Ru.
• Such a catalyst may take advantage of both the early onset of CO oxidation according to the present invention and the shift of the Pt CO oxidation peak observed in the PtRuO x catalyst, as can be seen in Fig. 2.
• the catalysts of the present invention comprising at least one platinum- containing layer and one suboxide-containing layer, but preferably contain at least 30 of each layer and more preferably more than 60 alternating layers of each kind. It is understood that in some cases interstitial layers may be generated between the Pt and suboxide layers, which may contain alloys of materials found in the two principal layer types.
• the total loading of catalyst material is preferably at least .01 mg/cm 2 , and more preferably at least .1 mg/cm 2 .
• the total loading of catalyst material is preferably not more than 1 mg/cm 2 . CO tolerance and onset potential of CO oxidation tend to increase with loading.
• the catalysts of the present invention can be made by any appropriate method.
• the catalyst is made by alternating layer deposition of at least two different types of materials.
• Deposition techniques include sputter deposition, vapor deposition, cathodic arc deposition, laser ablation, wet chemical methods including electrochemical methods, chemical vapor deposition, combustion vapor deposition and JVDTM.
• One preferred method is sputter deposition.
• Deposition of the suboxide layers is accomplished by deposition of the selected metal in the presence of substoichiometric amounts of oxygen used as a sputtering gas, preferably in mixture with argon.
• the manufacture of catalyst is preferably preceded by determination of what Ar/O ratio determines what oxide form of the material that is to be deposited with Pt.
• a material's target potential is a function of the oxide state of the target's surface when operated in a constant power mode.
• a metal oxide target might by used in argon without oxygen gas by using an RF power supply.
• the catalysts of the present invention can be used to manufacture membrane electrode assemblies (MEA's) incorporated in electrochemical cells such as are described in U.S. Patents Nos. 5,879,827 and 5,879,828, the teachings of which are incorporated herein by reference.
• the catalysts of the present invention are used in hydrogen fuel cells.
• the catalysts of the present invention may be used as anode or cathode electrodes but preferably anode electrodes.
• the catalysts of the present invention may be used in fuel cells which operate on any electrooxidizable fuels such as hydrogen, alcohols, including methanol and ethanol, ketones, aldehydes, ethers, ammonia, hydrazine, and the like.
• Prefened fuel cells operate on hydrogen or methanol fuel and most preferably hydrogen.
• This invention is useful in fuel cells, particularly where CO tolerance is advantageous or required.
• Nanostructured perylene red (PR 149, American Hoechst Corp., Somerset, NJ) films on polyimide substrates were made using the techniques described in U.S. Patent Nos. 4,812,352 and 5,039,561 by thermal evaporation and vacuum annealing of the organic pigment C.I. Pigment Red 149, i.e., N,N'-di(3,5-xylyl)perylene-3,4:9,10-bis(dicarboximide).
• microstructures are nonconductive and separate readily from the polyimide substrate when pressed into ion conducting membrane material such as NafionTM (DuPont Chemicals, Wilmington, DE, available from ElectroChem, Inc., Woburn, MA, and Aldrich Chemical Co., Inc., Milwaukee, WI).
• ion conducting membrane material such as NafionTM (DuPont Chemicals, Wilmington, DE, available from ElectroChem, Inc., Woburn, MA, and Aldrich Chemical Co., Inc., Milwaukee, WI).
• catalyst metal coatings were applied either to the PR 149 support described above, to an optically flat polyimide witness slide, and/or to a glassy carbon substrate with the PR 149 support on it, by sputter deposition, using a vacuum system schematically depicted in Fig. 1.
• the apparatus consisted of a three- source magnetron sputtering system arranged around the outer circumference of a cylindrical chamber containing a 38 cm (15 inch) diameter rotating drum. The substrates were mounted on the drum and rotated sequentially past positions in front of the sputtering sources at rates of between 1 and 8 ⁇ m. The sources were shielded such that the sample could not be coated from any two fluxes at the same time.
• the vacuum pump used was a Varian AV8 cryopump (Varian Associates, Inc., Lexington, MA) equipped with an Alactel 2012A rotary vane roughing pump (Alactel Vacuum Products, Hingham, MA).
• the cryopump was partially isolated from the chamber by a butterfly valve. During deposition, pressure was maintained at .28 Pa (2.1 milliton) as the sputtering gas flow rate was controlled by MKS flow controllers (MKS Instruments, Inc., Andover, MA).
• the sputtering gases used were either argon or an argon/oxygen mix. Control of oxygen stoichiometry was achieved by varying the argon/oxygen flow ratio.
• Target potential is a function of the argon/oxygen flow ratio.
• Three inch targets (Target Materials, Inc., Columbus, OH) were used, consisting of 0.76 cm (0.3 inches) of target material bonded with indium to a copper backing.
• An Advanced Energy MDX 500 power supply (Advanced Energy Industries, Inc., Fort Collins, CO) was used in the constant power mode for each deposition. For the last two rotations, only the Pt target was active, so as to provide a Pt-rich surface. Measurement of catalyst loading was done by a simple gravimetric method after deposition.
• Nanostructures for use in the anode were made as indicated in each example, below.
• Nanostructures for use in the cathode were made by deposition of Pt on PR 149 nanostructures using argon sputtering gas. The catalyst loading was 0.21 mg/cm 2 .
• Some PR 149 supported catalysts were fabricated into membrane electrode assemblies (MEA's) for testing in a fuel cell as described below.
• the MEA's were made from the supported catalyst, an ion conducting membrane (ICM) and electrode backing material as follows.
• the ion conducting membranes used were perfluorinated sulfonic acid materials, specifically, NafionTM 1 17 membranes (DuPont Chemicals, Wilmington, DE, available from ElectroChem, Inc., Woburn, MA, and Aldrich Chemical Co., Inc., Milwaukee, WI).
• the Nafion membrane was pretreated by sequentially immersing into a) boiling water for one hour, b) boiling 3% H 2 O? for one hour, c) boiling ultra pure H 2 O for 1 hour, d) boiling 0.5 M H 2 SO for one hour, e) boiling ultra pure DI H 2 O for one hour.
• the Nafion was then stored in ultrapure DI water until use.
• Prior to forming an MEA the Nafion was dried by laying it between several layers of clean linen cloth at 30° C for 10-20 minutes.
• Each MEA was made using a static pressing procedure which consisted of transfer of the catalyst-coated nanostructured elements into the Nafion 117 membrane by pressing under vacuum at 130° C and a pressure of 160 MPa (11.6 tons per square inch).
• a static pressing procedure which consisted of transfer of the catalyst-coated nanostructured elements into the Nafion 117 membrane by pressing under vacuum at 130° C and a pressure of 160 MPa (11.6 tons per square inch).
• two 5 cm square pieces of the nanostructured elements on a polyimide substrate - one for the anode, one for the cathode - were placed on either side of the center of a 7.6 cm x 7.6 cm Nafion 117 membrane.
• a 50 micrometer thick, 7.6 cm x 7.6 cm sheet of polyimide was placed on each side of the catalyst coated substrate/Nafion/catalyst coated substrate sandwich.
• This assembly was then placed between two steel shim plates and pressed under a low grade vacuum at 130° C and a pressure of 160 MPa (11.6 tons per square inch) using a Carver lab press (Carver Inc., Wabash, IN). A low grade vacuum (less than about 2 Torr) was applied to partially remove air from the stack just prior to applying the maximum pressure. The original 5 cm 2 polyimide substrates were then peeled away leaving the catalyst attached to the surface of the Nafion membrane.
• Both catalyst electrodes of the MEA were covered with 0.4 cm (0.015") thick ELATTM electrode backing material (E-tek, Inc., Natick, MA), and centered in a 5 cm 2 square hole, cut to match the catalyst area, of a 250 micrometers thick TeflonTM coated fiberglass gasket (The Furon Co., CHR Division, New Haven, CT).
• the Elat electrode backing material is designated as carbon only, i.e., it contains no catalyst.
• XPS X-ray Photoelectron Spectroscopy
• the test station includes a variable electronic load with separate anode and cathode gas handling systems to control gas flow, pressure and humidity.
• the electronic load and gas flow are computer controlled.
• Fuel cell polarization curves were obtained the under the following test parameters: electrode area, 5 cm"; cell temperature, 75° C, anode gas pressure (gauge), 62.0 kPa (9 psig); anode gas flow rate, 40-150 standard cc/min; anode humidification temperature, 105° C; cathode gas pressure (gauge), 414 kPa (60 psig); cathode flow rate, 600 standard cc/min; cathode humidification temperature, 65° C.
• Humidification of the gas streams was provided by passing the gas through sparge bottles maintained at the stated temperatures. Each fuel cell was brought to operating conditions at 75° C under hydrogen and oxygen flows.
• Test protocols were initiated after 24 hours of operation and the following variables were measured: anode pressure, anode flow, cathode pressure, cathode flow, cell temperature and CO concentration.
• the H2 and CO gas mixture came in commercially available premixed tanks (Oxygen Services, St. Paul, MN). The tanks came with a certificate of analysis.
• the change in cmrent as measured in a potentiodynamic scan at 700mV between operation from H 2 and operation under a CO challenge is taken as the metric for determination of CO tolerance.
• the reason for 700mV as the metric is that lies somewhat between the kinetic and the mass transport regions of the polarization curve. As such it is less susceptible, to other artifacts in the MEA that might more adversely effect other regions of the curve.
• the glassy carbon electrodes were tested in 1.0 M H 2 SO solutio 1, which was chosen as the electrolyte solution in order to more closely mimic the environment of the perfluorosulfonic acid based proton exchange membranes. Tests were conducted at 80°C temperature and atmospheric pressure.
• the potentiostat used for these experiments was a Solartron 1280B (Solartron Ltd., UK).
• the setup consisted of the standard 3-electrode cell configuration using a working electrode with an area of 0.95cm 2 .
• the reference electrode for measurement of potentials was a saturated calomel electrode (SCE).
• SCE saturated calomel electrode
• the cell was first purged with N 2 for 15 minutes to remove any oxygen. CO gas was then applied for 15 minutes to poison the catalyst surface. The CO gas was then replaced with nitrogen and the potentistat was used to apply a potential sweep and measure the cmrent.
• the voltage sweep rate was 25mV/sec.
• Fig. 2 demonstrates CO oxidation cyclic voltametry curves observed for Pt, PtRuO x , and PtMoO x catalysts.
• the PtRuO x and PtMoO x curves were normalized to the Pt curve by multiplying the values of the subject curve by a scaling factor such that the curves have the same value at the Pt oxide reduction peak (not appearing in this
• Fig. 3 demonstrates CO oxidation cyclic voltametry curves observed for PtTaO x and PtTa2 ⁇ 5 catalysts.
• the PtTaO x and PtTa2 ⁇ 5 scans were normalized, as described above.
• the PtMoO x catalyst according to the present invention demonstrates early onset of CO oxidation, appearing as a distinct pre-peak in the CV curve.
• the CV curves for the comparative Pt and PtRuO x catalysts are flat, having a slope of zero, in the same range, and continuing until the begining of the Pt CO oxidation peak.
• the Pt CO oxidation peak of the comparative PtRuO x catalyst is shifted by about 150mV from the Pt CO oxidation peak of the Pt catalyst, whereas the Pt CO oxidation peak of the PtMoO x catalyst was only slightly shifted.
• the PtMoO x catalyst according to the present invention provides improved CO oxidation by a distinctly different mechanism than the PtRuO x catalyst, i.e. an early onset of CO oxidation rather than a shift of the Pt CO oxidation peak.
• the PtTaO x catalyst according to the present invention also demonstrates early onset of CO oxidation, appearing as a distinct shoulder in the CV curve.
• the CV curves for the comparative PtTa2 ⁇ 5 catalyst shows a later onset of CO oxidation associated with the Pt CO oxidation peak.
• Test catalysts for this Example consisted of Pt and Mo in a 3: 1 ratio as determined by the deposition rates and confirmed by ED AX. During deposition of the catalyst metals, the Mo target power was held at 100 Watts and the target voltage was 390 volts for the PtMo catalyst, 575 volts for Pt(MoO ) catalyst, and 675 volts for
• Pt(MoO 3 ) catalyst For each sample the as deposited finishing surface had an atomic ratio of approximately Pt:Mo of 6:1 as determined by XPS.
• Test catalysts for this Example consisted of Pt and Ti in a 3: 1 ratio as determined by deposition rates.
• the Ti target power was held at 100 Watts and the target voltage was 414 volts for PtTi, 434 volts for Pt(TiO ), and 474 volts for Pt(TiO 2 ).
• the as deposited finishing surface had an atomic ratio of approximately Pt:Ti of 6:1 as determined by XPS.
• the atomic ratio of Pt to Ta was 2:1 as determined by deposition rates.
• the Ta target power was held at 100 Watts and the target voltage was 390 volts for PtTa, 435 volts for Pt(TaO x ), and 510 volts for PtTa2 ⁇ 5_
• the as deposited finishing surface had an atomic ratio of approximately Pt:Ta of 6: 1 as determined by XPS.

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• 2000
  • 2000-12-22 US US09/745,501 patent/US6482763B2/en not_active Expired - Lifetime
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