WO2008110651A1 - Ternary catalyst of pt-ru-meox (me = mo, w, v) on carbon with high co tolerance in fuel cell anodes and preparation method thereof - Google Patents

Ternary catalyst of pt-ru-meox (me = mo, w, v) on carbon with high co tolerance in fuel cell anodes and preparation method thereof Download PDF

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WO2008110651A1
WO2008110651A1 PCT/ES2008/070037 ES2008070037W WO2008110651A1 WO 2008110651 A1 WO2008110651 A1 WO 2008110651A1 ES 2008070037 W ES2008070037 W ES 2008070037W WO 2008110651 A1 WO2008110651 A1 WO 2008110651A1
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ternary catalyst
carbon
catalyst
support
ternary
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PCT/ES2008/070037
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Spanish (es)
French (fr)
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Nikolaos Tsiouvaras
José Luis Garcia Fierro
Miguel Antonio PEÑA JIMENEZ
María Victoria MARTINEZ HUERTA
Elena Pastor Tejera
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Consejo Superior De Investigaciones Científicas
Universidad De La Laguna
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    • 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
    • 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
    • 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
    • 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
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M2008/1095—Fuel cells with polymeric electrolytes
    • 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
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Definitions

  • the present invention relates to the preparation of new catalysts for use as anodes in fuel cells. Therefore, this invention is related to the manufacture of new materials and its application is part of the use of clean energy.
  • a membrane-electrode assembly consisting of a layer of a solid membrane that acts as an electrolyte exchanging protons between two layers that are located on both sides of said membrane, and which are the two electrodes of the battery, the anode and the cathode, where the fuel is activated electrochemically (hydrogen in the case of PEMFCs, and methanol in the case of DMFCs) and the oxidizer (usually oxygen present in the air), respectively.
  • the fuel is activated electrochemically (hydrogen in the case of PEMFCs, and methanol in the case of DMFCs) and the oxidizer (usually oxygen present in the air), respectively.
  • the fuel is activated electrochemically (hydrogen in the case of PEMFCs, and methanol in the case of DMFCs) and the oxidizer (usually oxygen present in the air), respectively.
  • the fuel is activated electrochemically (hydrogen in the case of PEMFCs, and methanol in the case of DMFCs) and the
  • This active metal phase must be deposited on a support that has a high specific surface area and high electronic conductivity. Therefore, the most widely used supports are carbon blacks, materials produced by high-temperature pyrolytic cracking of hydrocarbon-rich fuels (HP Boehm, Some aspects of the surface chemistry of carbon blacks and other carbons. Carbon 32, 759 -769, 1994). In fact, the use of carbon black as a catalytic support for precious metals is increasing considerably due to the rapid progress in the development of fuel cells. Its use has a special interest because it allows a fine dispersion and stabilization of small metal particles, provides a high specific area and a high electrical conductivity necessary for an efficient electrooxidation of hydrogen from reforming and methanol.
  • coals with controlled mesoporosity are also beginning to be used. These coals have numerous advantages, such as a greater specific area with respect to carbon black, relatively uniform pore size, orderly pore structure, flexibility of surface properties and better thermal and mechanical stability (J. Lee, J. Kim and T. Hyeon, Recent progress in the synthesis of porous carbon materials, Advanced Materials, 18, 2073-2094, 2006).
  • the commercial anode electrocatalyst most widely used in this type of batteries, and which serves as a reference material for possible improvements of the electrocatalytic activity are those of the HiSPEC series marketed by Johnson Matthey, which have a weight content of Pt- Ru in the range 30-60% with an atomic ratio of Pt: Ru of 1: 1, and using carbon black as support.
  • PtRuMe ternary catalysts have shown to be somewhat more tolerant to CO, and efficient in the oxidation of methanol, than PtRu binary catalysts, although not enough to solve the problem of Ia PEMFC implementation.
  • Different methods have been used for the preparation of PtRuMe ternary catalysts supported on carbon.
  • Another object of the invention is the process for preparing the ternary catalyst Pt-Ru-MeO x / C of the invention, which is carried out by incorporating the Me, in one step, and the Pt and Ru, at a different stage, on the carbon support, using two different methods:
  • Another object of the invention is the use of the ternary catalyst Pt-Ru-MeO x / C of the invention as anode in fuel cells of proton exchange membrane or polymer electrolyte, both fed with hydrogen from the reformed and direct methanol.
  • FIGURES Figure 1 DESCRIPTION OF THE FIGURES Figure 1.- Representation of the faradaic current (I / A) against the potential (EA /) for the samples of (A) Pt-Ru-MoO x / C, with atomic ratio Pt: Ru: Mo of 1: 1: 0.6 and metal content of 25% by weight, synthesized in example 1; (B) Pt-Ru-Mo ⁇ / C, with atomic ratio Pt: Ru: Mo of 1: 1: 0.8 and metal content of 20% by weight, synthesized in example 2; (C) Pt-Ru-MoO x / C, with atomic ratio Pt: Ru: Mo of 1: 0.9: 1, 2 and metal content of 20% by weight, synthesized in example 3; (D) Johnson Matthey HiSPEC 5000 commercial catalyst from Pt-Ru / C with 1: 1 atomic ratio and metal content of 30% by weight.
  • the electrooxidation of CO to CO2 previously absorbed on the electrocatalyst is a technique that provides information about the ease that the material has towards the oxidation of CO in the fuel cell and, therefore, of its tolerance to CO.
  • anodic catalysts for fuel cells with a high tolerance towards CO have been obtained for the first time, capable of oxidizing CO to CO2 to potentials from 0.1 V referred to the normal hydrogen potential (NHE).
  • a particular object of the invention constitutes the ternary catalyst Pt-Ru-MeO ⁇ / C of the invention in which the atomic ratio of Pt / Ru is in the range 0.5-1.5, and preferably around one.
  • a particular object of the invention constitutes the ternary catalyst
  • a ternary catalyst Pt-Ru-MeO x compared to another binary Pt-Ru is that the incorporation of a transition metal such as molybdenum allows to reduce the weight content of Pt and Ru in the catalyst, reducing the cost of the system.
  • this decrease in the cost of the catalyst is accompanied by an increase in the tolerance towards the CO of the catalyst, constituting a highly novel system.
  • Another particular object of the invention is the ternary catalyst Pt-Ru-
  • MeO x / C of the invention in which the carbon support is carbon black.
  • Another particular object of the invention is the ternary catalyst Pt-Ru-MeO x / C of the invention in which the support is a carbon with controlled mesoporosity.
  • Another object of the invention constitutes the process for preparing the ternary catalyst Pt-Ru-MeO x / C of the invention, which is carried out by incorporating the Me, in one stage, and the Pt and the Ru, in another different stage, on the carbon support, using two different methods: i) Impregnation method using a Me precursor in the presence of an aqueous solution of H 2 O 2 for the incorporation of the Me to the support.
  • the process of preparing the ternary catalyst Pt-Ru-MeO x / C of the invention can be carried out by first incorporating the Me, to subsequently incorporate the Pt and the Ru, or vice versa.
  • another particular object of the invention is the process of preparing the ternary catalyst Pt-Ru-MeO x / C of the invention in which in a first stage the Me (method (i)) is incorporated, to subsequently incorporate the Pt and Ru (method (ii)), (examples 1 and 2)
  • Another particular object of the invention is the process of preparing the ternary catalyst Pt-Ru-MeO x / C of the invention in which the Pt and Ru (method (ii)) are incorporated in a first stage, to subsequently incorporate the Me (method (i)), (example 3).
  • the invention is preferably within the range 1 to 15 M, and more preferably within the range 7 to 12 M.
  • Another particular object of the invention is the process for preparing the ternary catalyst Pt-Ru-MeO x / C of the invention in which the incorporation of the transition metal is carried out by means of the impregnation method in the absence of H2O2.
  • Another object of the invention is the use of the ternary catalyst Pt-Ru-MeO x / C of the invention as anode in fuel cells.
  • Another particular object of the invention is the use of the ternary catalyst Pt-Ru-MeO ⁇ / C of the invention as anode in proton-exchange membrane fuel cells or polymer electrolyte fed with hydrogen from reforming.
  • Another particular object of the invention is the use of the ternary catalyst Pt-Ru-MeO ⁇ / C of the invention as an anode in direct methanol fuel cells.
  • EXAMPLE 1 Preparation of the ternary catalyst of Pt-Ru-MoOx / C with atomic ratio Pt: Ru: Mo of 1: 1: 0.6 and metallic content of 25% by weight.
  • This catalyst was obtained by the following steps:
  • the electrocatalyst obtained contains 25% by weight of platinum-ruthenium-molybdenum on black of one in an atomic ratio of 1: 1: 0.6.
  • a conventional three electrode electrochemical cell is used.
  • the working electrode is prepared by depositing the electrocatalyst on a polished surface of vitreous carbon. Platinum is used as a counter electrode and HgZHg 2 SO 4 as the reference electrode.
  • the electrolyte used is a 0.5 M aqueous solution of H 2 SO 4 . The measurement is made at 25 0 C.
  • the electrocatalyst is characterized by cyclic voltammetry once the CO has been previously adsorbed. This characterization is done by bubbling CO over the electrolyte for 12 min at a potential of 0.07 V versus the normal hydrogen potential (NHE).
  • Figure 1 shows the electrooxidation of CO to CO 2 during the anodic scanning of the first cycle for the ternary catalyst of Pt / Ru / MoO ⁇ with a weight content of 25% and an atomic ratio Pt: Ru: Mo of 1: 1: 0.6 of this invention and for the Johnson Matthey HiSPEC 5000 commercial catalyst, which has a Pt-Ru weight content of 30% with a Pt / Ru atomic ratio of 1, and that uses carbon black as support. It is observed how the catalyst begins to oxidize CO to CO2 at 0.13 V, while the commercial one does it from 0.3 V.
  • the electrocatalyst obtained contains 20% by weight of platinum-ruthenium-molybdenum in an atomic ratio of 1: 1: 0.8, and its tolerance to CO is shown in Figure 1, together with the catalyst of example 1 and the commercial sample Johnson Matthey HiSPEC 5000. It is observed in the figure that this catalyst begins to oxidize CO to CO 2 at 0.12 V, while the commercial one does from 0.3 V.
  • EXAMPLE 3 Preparation of the ternary catalyst of Pt-Ru-MoO ⁇ / C with atomic ratio Pt: Ru: Mo of 1: 0.9: 1.2 and metallic content of 20% by weight, by the procedure by which first incorporate the Pt / Ru on the carbon black, and then incorporate the Mo.
  • the electrocatalyst obtained contains 20% by weight of platinum-ruthenium-molybdenum in an atomic ratio of 1: 0.9: 1, 2, and its tolerance to CO is shown in Figure 1 (C). It is observed how the catalyst begins to oxidize the CO to CO 2 at 0.14 V, while the commercial one starts from 0.3 V.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Catalysts (AREA)
  • Inert Electrodes (AREA)

Abstract

The invention tackles the problem associated with deactivating the anode catalysts of fuel cells. The invention relates to a ternary catalyst of Pt-Ru-MeOX (wherein Me = Mo, W or V) on a carbon support, capable of oxidising CO to CO2 at potentials above 0.1 V in respect of the normal potential of hydrogen (NHE). The invention also relates to the method for preparing said catalysts, as well as the use thereof as anodes in polymer electrolyte or proton exchange membrane fuel cells supplied with hydrogen obtained from reforming (PEMFC) or direct methanol (DMFC).

Description

CATALIZADOR TERNARIO DE Pt-Ru-MeOx (Me = MO, W, V) SOBRE CARBÓN CON ALTA TOLERANCIA AL CO EN ÁNODOS DE PILAS DE COMBUSTIBLE Y SU MÉTODO DE PREPARACIÓNPt-Ru-MeO TERNARY CATALYST x (Me = MO, W, V) ON CARBON WITH HIGH TOLERANCE TO CO IN FUEL BATTERY ANODES AND ITS PREPARATION METHOD
SECTOR DE LA TÉCNICASECTOR OF THE TECHNIQUE
La presente invención se refiere a Ia preparación de nuevos catalizadores para su utilización como ánodos en pilas de combustible. Por tanto, esta invención esta relacionada con Ia fabricación de nuevos materiales y su aplicación se enmarca dentro de Ia utilización de energías limpias.The present invention relates to the preparation of new catalysts for use as anodes in fuel cells. Therefore, this invention is related to the manufacture of new materials and its application is part of the use of clean energy.
ESTADO DE LA TÉCNICASTATE OF THE TECHNIQUE
La actual situación energética hace necesaria una apuesta clara por Ia implantación de las Pilas de Combustible como uno de los medios más seguros, limpios y eficaces de convertir Ia energía contenida en diversos combustibles en electricidad (M. S. Dreseselhaus and I. L. Thomas, Alternative energy technologies. Nature, 414, 332- 337, 2001 ). Entre los diferentes tipos de pilas de combustible destacan las pilas de combustible de membrana intercambiadora de protones o de electrolito polimérico (PEMFC, del inglés "Protón Exchange Membrana Fuel CeIIs") las cuales muestran una alta eficiencia cuando el combustible es hidrógeno puro. Sin embargo, Ia producción, almacenaje y transporte del hidrógeno puro plantea graves problemas técnicos y serios inconvenientes económicos. Este hecho hace que el hidrógeno obtenido a partir del reformado de hidrocarburos o de Ia oxidación parcial de alcoholes se presente como una alternativa interesante para las PEMFC (M.Z. Jacobson, W.G. CoIeIIa and D. M. Golden, Cleaning the air and improving health with hydrogen fuel-cell vehicles. Science 308, 1901-1905, 2005) Otra posibilidad es Ia utilización de metanol como combustible en las pilas de combustible de metanol directo (DMFC, del inglés "Direct Methanol Fuel CeIIs") en las cuales se elimina el paso inicial del reformado. Además, Ia utilización de metanol como combustible presenta Ia ventaja, frente al hidrógeno, de ser más fácil de almacenar y transportar (R. Dillon, S. Srinivasan, A. S. Arico and V. Antonucci, International activities in DMFC R&D: status of technologies and potential applications. Journal of Power Sources, 127, 112- 126 2004).The current energy situation requires a clear commitment to the implementation of the Fuel Cells as one of the safest, cleanest and most efficient means of converting the energy contained in various fuels into electricity (MS Dreseselhaus and IL Thomas, Alternative energy technologies. Nature , 414, 332- 337, 2001). Among the different types of fuel cells, proton exchanger membrane or polymer electrolyte (PEMFC) fuel cells ("Proton Exchange Membrane Fuel CeIIs") stand out, which show high efficiency when the fuel is pure hydrogen. However, the production, storage and transport of pure hydrogen poses serious technical problems and serious economic inconveniences. This fact makes the hydrogen obtained from the reforming of hydrocarbons or the partial oxidation of alcohols present as an interesting alternative for PEMFCs (MZ Jacobson, WG CoIeIIa and DM Golden, Cleaning the air and improving health with hydrogen fuel-cell vehicles Science 308, 1901-1905, 2005) Another possibility is the use of methanol as fuel in direct methanol fuel cells (DMFC) in which the initial step of the reforming is eliminated . In addition, the use of methanol as fuel has the advantage, compared to hydrogen, of being easier to store and transport (R. Dillon, S. Srinivasan, AS Arico and V. Antonucci, International activities in DMFC R&D: status of technologies and potential applications. Journal of Power Sources, 127, 112-126 2004).
En este tipo de pilas se emplea un ensamblaje membrana-electrodo (MEA) consistente en una capa de una membrana sólida que actúa como electrolito intercambiando protones entre dos capas que se sitúan a ambos lados de dicha membrana, y que son los dos electrodos de Ia pila, el ánodo y el cátodo, donde se activan electroquímicamente el combustible (hidrógeno en el caso de las PEMFC, y metanol en el caso de las DMFC) y el comburente (habitualmente el oxígeno presente en el aire), respectivamente. Para Ia activación tanto del hidrógeno procedente del reformado como del metanol es necesaria, con Ia actual tecnología, Ia presencia de Pt en el electrodo anódico. En el caso de las DMFC Ia cantidad de Pt utilizado es 10 veces superior al necesario en las PEMFC (H. Liu, C. Song, L. Zhang, J. Zhang, H. Wang, D. P. Wilkinson, A review of anode catalysis in the direct methanol fuel cell, Journal of Power Sources, 155, 95-110, 2006). En ambos casos, el monóxido de carbón (CO) que acompaña al H2 procedente del reformado, o se forma como intermedio en Ia oxidación del metanol, se absorbe fuertemente sobre los centros activos existentes en Ia superficie del Pt, bloqueando drásticamente Ia reacción de oxidación de hidrógeno o metanol. Por tanto, Ia presencia de CO en el combustible contamina el catalizador anódico produciendo una pérdida irreversible del potencial de Ia pila o sobrepotencial con respecto a su potencial ideal, Io que da lugar a un descenso de Ia eficiencia en Ia pila de combustible. Esto constituye uno de los principales problemas para Ia posible aplicación de esta tecnología. Es esencial, de esta forma, el desarrollo de electrocatalizadores mucho más tolerantes al CO. La forma usual de obtener electrocatalizadores más tolerantes al CO es Ia incorporación de rutenio al catalizador, obteniéndose de esta forma electrocatalizadores bimetálicos Pt-Ru. La disminución del contenido de Pt en los catalizadores anódicos, reduciendo los costes de este tipo de sistemas, es también un punto fundamental para Ia posible implantación de esta tecnología. Para la obtención de electrocatalizadores eficientes es necesario Ia utilización de nanopartículas de Pt-Ru, con tamaños de partícula inferiores a 8 nm, posibilitando valores más altos del área metálica por peso de metal incorporado. Los métodos coloidales permiten obtener nanopartículas con un buen control del tamaño y de Ia dispersión (M. Watanabe, M. Uchida, S. Motoo, Preparation of highly dispersed Pt + Ru clusters and the activity for the electrooxidation of methanol. J. Electroanal. Chem., 229, 395-406, 1987; TJ. Schmidt, M. Noeske, H.A. Gasteiger, RJ. Behm, W. Brijoux, HJ. Bonnemann, Electrocatalytic activity of PtRu alloy colloids for CO and COZH2 electrooxidation: stripping voltammetry and rotating disk measurements. Langmuir, 13, 2591-2595, 1997). Esta fase metálica activa se debe depositar en un soporte que tenga una alta superficie específica y elevada conductividad electrónica. Por ello, los soportes más ampliamente usados actualmente son los negros de humo, materiales producidos por el craqueo pirolítico a alta temperatura de combustibles ricos en hidrocarburos (H. P. Boehm, Some aspects of the surface chemistry of carbón blacks and other carbons. Carbón 32, 759-769, 1994). De hecho, el uso de negro de humo como soporte catalítico de metales preciosos se está incrementando considerablemente debido al rápido avance en el desarrollo de las pilas de combustible. Su utilización presenta un interés especial debido a que permite una fina dispersión y estabilización de pequeñas partículas metálicas, aporta una elevada área específica y una alta conductividad eléctrica necesaria para una electrooxidación eficaz del hidrógeno procedente del reformado y del metanol. En Ia actualidad están comenzando a emplearse también carbones con mesoporosidad controlada (tamaño medio de poro 2-50 nm). Estos carbones presentan numerosas ventajas, tales como una mayor área específica con respecto al negro de humo, tamaño de poro relativamente uniforme, estructura de poros ordenada, flexibilidad de las propiedades superficiales y una mejor estabilidad térmica y mecánica (J. Lee, J. Kim and T. Hyeon, Recent progress in the synthesis of porous carbón materials. Advanced Materials, 18, 2073- 2094, 2006). Actualmente, el electrocatalizador anódico comercial más extensamente utilizado en este tipo de pilas, y que sirve como material de referencia para posibles mejoras de Ia actividad electrocatalítica, son los de Ia serie HiSPEC comercializados por Johnson Matthey, que presentan un contenido en peso de Pt-Ru en el rango 30-60% con una relación atómica de Pt: Ru de 1 :1 , y que usan negro de humo como soporte.In this type of batteries a membrane-electrode assembly (MEA) is used consisting of a layer of a solid membrane that acts as an electrolyte exchanging protons between two layers that are located on both sides of said membrane, and which are the two electrodes of the battery, the anode and the cathode, where the fuel is activated electrochemically (hydrogen in the case of PEMFCs, and methanol in the case of DMFCs) and the oxidizer (usually oxygen present in the air), respectively. For the activation of both hydrogen from reforming and methanol it is necessary, with current technology, the presence of Pt in the anode electrode. In the case of DMFCs, the amount of Pt used is 10 times higher than necessary in PEMFCs (H. Liu, C. Song, L. Zhang, J. Zhang, H. Wang, DP Wilkinson, A review of anode catalysis in the direct methanol fuel cell, Journal of Power Sources, 155, 95-110, 2006). In both cases, the carbon monoxide (CO) that accompanies the H 2 from the reforming, or is formed as an intermediate in the oxidation of methanol, is strongly absorbed on the active centers existing on the surface of the Pt, drastically blocking the reaction of oxidation of hydrogen or methanol. Therefore, the presence of CO in the fuel contaminates the anode catalyst producing an irreversible loss of the potential of the cell or overpotential with respect to its ideal potential, which results in a decrease in the efficiency in the fuel cell. This constitutes one of the main problems for the possible application of this technology. It is essential, in this way, the development of electrocatalysts much more tolerant to CO. The usual way to obtain electrocatalysts that are more tolerant to CO is the incorporation of ruthenium into the catalyst, thus obtaining Pt-Ru bimetallic electrocatalysts. The decrease of the content of Pt in the anodic catalysts, reducing the costs of this type of systems, is also a fundamental point for the possible implementation of this technology. In order to obtain efficient electrocatalysts, it is necessary to use Pt-Ru nanoparticles, with particle sizes smaller than 8 nm, allowing higher values of the metal area by weight of incorporated metal. Colloidal methods allow obtaining nanoparticles with good control of size and dispersion (M. Watanabe, M. Uchida, S. Motoo, Preparation of highly dispersed Pt + Ru clusters and the activity for the electrooxidation of methanol. J. Electroanal. Chem., 229, 395-406, 1987; TJ. Schmidt, M. Noeske, HA Gasteiger, RJ. Behm, W. Brijoux, HJ. Bonnemann, Electrocatalytic activity of PtRu alloy colloids for CO and COZH 2 electrooxidation: stripping voltammetry and rotating disk measurements Langmuir, 13, 2591-2595, 1997). This active metal phase must be deposited on a support that has a high specific surface area and high electronic conductivity. Therefore, the most widely used supports are carbon blacks, materials produced by high-temperature pyrolytic cracking of hydrocarbon-rich fuels (HP Boehm, Some aspects of the surface chemistry of carbon blacks and other carbons. Carbon 32, 759 -769, 1994). In fact, the use of carbon black as a catalytic support for precious metals is increasing considerably due to the rapid progress in the development of fuel cells. Its use has a special interest because it allows a fine dispersion and stabilization of small metal particles, provides a high specific area and a high electrical conductivity necessary for an efficient electrooxidation of hydrogen from reforming and methanol. At present, carbons with controlled mesoporosity (average pore size 2-50 nm) are also beginning to be used. These coals have numerous advantages, such as a greater specific area with respect to carbon black, relatively uniform pore size, orderly pore structure, flexibility of surface properties and better thermal and mechanical stability (J. Lee, J. Kim and T. Hyeon, Recent progress in the synthesis of porous carbon materials, Advanced Materials, 18, 2073-2094, 2006). Currently, the commercial anode electrocatalyst most widely used in this type of batteries, and which serves as a reference material for possible improvements of the electrocatalytic activity, are those of the HiSPEC series marketed by Johnson Matthey, which have a weight content of Pt- Ru in the range 30-60% with an atomic ratio of Pt: Ru of 1: 1, and using carbon black as support.
Una forma de mejorar estos catalizadores es Ia adición de un metal de transición que sea capaz de aumentar Ia tolerancia al CO y mejorar así Ia eficiencia de Ia pila de combustible, con Ia ventaja de que Ia sustitución de parte de los metales nobles Pt y Ru por un metal mucho más económico abarataría considerablemente los costes de esta tecnología. En los últimos años, los catalizadores ternarios PtRuMe (Me: metal de transición) han mostrado ser algo más tolerantes al CO, y eficientes en Ia oxidación de metanol, que los catalizadores binarios PtRu, aunque no Io suficiente como para solucionar el problema de Ia implantación de las PEMFC. Se han utilizado diferentes métodos para Ia preparación de catalizadores ternarios PtRuMe soportados sobre carbón. Gotz y colaboradores sintetizaron catalizadores de PtRuMe (relación atómica 1 :1 :1 )/C (Me = W, Mo y Sn) utilizando un método de preparación coloidal (M. Gotz and H. Wendt, Bynary and ternary anode catalyst formulations including the elements W, Sn and Mo for PEMFCs operated on methanol or refórmate gas. Electrochimica Acta, 43, 3637-3650, 1998). Estos materiales mostraron una mayor eficiencia en Ia oxidación de hidrógeno procedente del reformado y metanol que los preparados por el método de impregnación convencional. Más recientemente (Z. Hou, B. Yi, H. Yu, Z. Lin and H. Zhang, CO tolerante electrocatalyst of PtRu- HxMeOyC (Me = W, Mo) made by composite support method. Journal of Power Sources 123, 116-125, 2003) se han preparado catalizadores PtRu-HxMeO3/C (Me = Mo, W) mediante dos etapas fundamentales. En un primer paso se forma un coloide del tipo HxMeθ3 (20 % en peso) soportado sobre el carbón, seguido a continuación de Ia adición de Pt y Ru (30 % en peso, relación atómica 1 :1 ) mediante un método de impregnación. Estos catalizadores muestran una buena tolerancia al CO en comparación con el catalizador bimetálico PtRu/C (30 % en peso, relación atómica 1 :1 ), aunque Ia cantidad de metales nobles PtRu utilizada tanto en los catalizadores binarios como en los ternarios es Ia misma.One way to improve these catalysts is the addition of a transition metal that is capable of increasing the tolerance to CO and thus improving the efficiency of the fuel cell, with the advantage that the replacement of part of the noble metals Pt and Ru for a much cheaper metal, it would significantly reduce the costs of this technology. In recent years, PtRuMe ternary catalysts (Me: transition metal) have shown to be somewhat more tolerant to CO, and efficient in the oxidation of methanol, than PtRu binary catalysts, although not enough to solve the problem of Ia PEMFC implementation. Different methods have been used for the preparation of PtRuMe ternary catalysts supported on carbon. Gotz and collaborators synthesized PtRuMe catalysts (1: 1: 1 atomic ratio) / C (Me = W, Mo and Sn) using a colloidal preparation method (M. Gotz and H. Wendt, Bynary and ternary anode catalyst formulations including the elements W, Sn and Mo for PEMFCs operated on methanol or refuel gas Electrochimica Acta, 43, 3637-3650, 1998). These materials showed a greater efficiency in the oxidation of hydrogen from reforming and methanol than those prepared by the conventional impregnation method. More recently (Z. Hou, B. Yi, H. Yu, Z. Lin and H. Zhang, CO electrocatalyst tolerant of PtRu- H x MeOyC (Me = W, Mo) made by composite support method. Journal of Power Sources 123 , 116-125, 2003) PtRu-H x MeO 3 / C catalysts (Me = Mo, W) have been prepared by two fundamental steps. In a first step a colloid of the type H x Meθ3 (20% by weight) supported on the carbon is formed, followed by the addition of Pt and Ru (30% by weight, 1: 1 atomic ratio) by a method of impregnation. These catalysts they show a good tolerance to CO compared to the bimetallic catalyst PtRu / C (30% by weight, 1: 1 atomic ratio), although the amount of noble PtRu metals used in both binary and ternary catalysts is the same.
DESCRIPCIÓN BREVEBRIEF DESCRIPTION
Un objeto de Ia presente invención Io constituye un catalizador ternario de Pt-Ru-MeOx (siendo Me = Mo, W o V) sobre un soporte de carbón, en adelante catalizador ternario Pt-Ru-MeOx/C de Ia invención, de forma que el Pt y el Ru se encuentran en forma de nanopartículas metálicas, y el Me se encuentra en forma de óxidos con diferentes estados de oxidación, caracterizado por:An object of the present invention constitutes a ternary catalyst of Pt-Ru-MeOx (being Me = Mo, W or V) on a carbon support, hereinafter ternary catalyst Pt-Ru-MeO x / C of the invention, of so that Pt and Ru are in the form of metal nanoparticles, and Me is in the form of oxides with different oxidation states, characterized by:
(a) tener una relación atómica de Pt/Ru dentro del rango 0,1- 2,(a) have an atomic ratio of Pt / Ru within the range 0.1-2,
(b) tener una relación atómica de Pt/Mo dentro del rango 0,1- 10, (c) ser capaz de oxidar el CO a CO2 a potenciales a partir de 0,1(b) have an atomic ratio of Pt / Mo within the range 0.1-10, (c) be able to oxidize CO to CO2 at potentials from 0.1
V referido al potencial normal de hidrógeno (NHE) Otro objeto de Ia invención Io constituye el procedimiento de preparación del catalizador ternario Pt-Ru-MeOx/C de Ia invención, el cual se realiza incorporando el Me, en una etapa, y el Pt y el Ru, en otra etapa diferente, sobre el soporte de carbón, utilizando dos métodos diferentes:V referred to the normal hydrogen potential (NHE) Another object of the invention is the process for preparing the ternary catalyst Pt-Ru-MeO x / C of the invention, which is carried out by incorporating the Me, in one step, and the Pt and Ru, at a different stage, on the carbon support, using two different methods:
(i) Método de impregnación utilizando un precursor de Me en presencia de una disolución acuosa de H2O2 para Ia incorporación del Me al soporte.(i) Impregnation method using a Me precursor in the presence of an aqueous solution of H 2 O 2 for the incorporation of Me into the support.
(ii) Método coloidal para Ia incorporación de Pt y Ru sobre el soporte.(ii) Colloidal method for the incorporation of Pt and Ru on the support.
Otro objeto de Ia invención es el uso del catalizador ternario Pt-Ru- MeOx/C de Ia invención como ánodo en pilas de combustibles de membrana intercambiadora de protones o de electrolito polimérico, tanto alimentadas con hidrógeno procedente del reformado como de metanol directo.Another object of the invention is the use of the ternary catalyst Pt-Ru-MeO x / C of the invention as anode in fuel cells of proton exchange membrane or polymer electrolyte, both fed with hydrogen from the reformed and direct methanol.
DESCRIPCIÓN DE LAS FIGURAS Figura 1.- Representación de Ia corriente faradaica (I/ A) frente al potencial (EA/) para las muestras de (A) Pt-Ru-MoOx/C, con relación atómica Pt:Ru:Mo de 1 :1 :0,6 y contenido metálico del 25% en peso, sintetizado en el ejemplo 1 ; (B) Pt-Ru-Moθχ/C, con relación atómica Pt:Ru:Mo de 1 :1 :0,8 y contenido metálico del 20% en peso, sintetizado en el ejemplo 2; (C) Pt-Ru-MoOx/C, con relación atómica Pt:Ru:Mo de 1 :0,9:1 ,2 y contenido metálico del 20% en peso, sintetizado en el ejemplo 3; (D) catalizador comercial Johnson Matthey HiSPEC 5000 de Pt-Ru/C con relación atómica 1 :1 y contenido metálico del 30% en peso.DESCRIPTION OF THE FIGURES Figure 1.- Representation of the faradaic current (I / A) against the potential (EA /) for the samples of (A) Pt-Ru-MoO x / C, with atomic ratio Pt: Ru: Mo of 1: 1: 0.6 and metal content of 25% by weight, synthesized in example 1; (B) Pt-Ru-Moθχ / C, with atomic ratio Pt: Ru: Mo of 1: 1: 0.8 and metal content of 20% by weight, synthesized in example 2; (C) Pt-Ru-MoO x / C, with atomic ratio Pt: Ru: Mo of 1: 0.9: 1, 2 and metal content of 20% by weight, synthesized in example 3; (D) Johnson Matthey HiSPEC 5000 commercial catalyst from Pt-Ru / C with 1: 1 atomic ratio and metal content of 30% by weight.
DESCRIPCIÓN DETALLADADETAILED DESCRIPTION
La utilización de hidrógeno procedente del proceso de reformado como reactivo en las pilas de combustible de membrana intercambiadora de protones o de electrolito polimérico (PEMFC, del inglés "Protón Exchange Membrane Fuel CeIIs"), así como el uso de metanol como combustible en las pilas combustible de metanol directo (DMFC, del inglés "Direct metanol Fuel CeIIs") implica Ia inevitable presencia de CO produciendo Ia desactivación del catalizador anódico. Esta desactivación produce una pérdida irreversible del potencial de Ia pila o sobrepotencial con respecto a su potencial ideal, Io que da lugar a un descenso de Ia eficiencia en Ia pila de combustible. Esto constituye uno de los principales problemas para Ia posible aplicación de esta tecnología. La presente invención se enfrenta al problema de Ia desactivación de los catalizadores anódicos de las pilas de combustible.The use of hydrogen from the reforming process as a reagent in proton exchanger or polymer electrolyte (PEMFC) fuel cells, as well as the use of methanol as fuel in batteries Direct methanol fuel (DMFC) of the English "Direct methanol Fuel CeIIs") implies the inevitable presence of CO causing the deactivation of the anodic catalyst. This deactivation produces an irreversible loss of the potential of the battery or overpotential with respect to its ideal potential, which results in a decrease in the efficiency in the fuel cell. This constitutes one of the main problems for the possible application of this technology. The present invention faces the problem of deactivation of the anode catalysts of the fuel cells.
La electrooxidación de CO a CO2 previamente absorbido sobre el electrocatalizador es una técnica que proporciona información acerca de Ia facilidad que tiene el material hacia Ia oxidación del CO en Ia pila de combustible y, por tanto, de su tolerancia al CO. Cuanto más bajo sea el potencial sobre el cual comienza a oxidarse el CO a CO2, más tolerante al CO será el electrocatalizador. En Ia presente invención se han obtenido, por primera vez, catalizadores anódicos para pilas de combustible con una alta tolerancia hacia el CO, capaces de oxidar el CO a CO2 a potenciales a partir de 0,1 V referido al potencial normal de hidrógeno (NHE). Estos resultados son muy significativos teniendo en cuenta los potenciales de entre 0,2 - 0,4V conseguidos hasta el momento. De acuerdo con estos resultados el material preparado en Ia presente invención posibilita un descenso considerable en el sobrepotencial de Ia pila de combustible, mejorando su eficiencia.The electrooxidation of CO to CO2 previously absorbed on the electrocatalyst is a technique that provides information about the ease that the material has towards the oxidation of CO in the fuel cell and, therefore, of its tolerance to CO. The lower the potential over which CO begins to oxidize to CO2, the more tolerant to CO the electrocatalyst will be. In the present invention, anodic catalysts for fuel cells with a high tolerance towards CO have been obtained for the first time, capable of oxidizing CO to CO2 to potentials from 0.1 V referred to the normal hydrogen potential (NHE). These results are very significant considering the potentials between 0.2 - 0.4V achieved so far. According to these results, the material prepared in the present invention allows a considerable decrease in the overpotential of the fuel cell, improving its efficiency.
Por Io tanto, un objeto de Ia presente invención Io constituye un catalizador ternario de Pt-Ru-MeOx (siendo Me = Mo, W o V) sobre un soporte de carbón, en adelante catalizador ternario Pt-Ru-MeOx/C de Ia invención, de forma que el Pt y el Ru se encuentran en forma de nanopartículas metálicas, y el Me se encuentra en forma de óxidos con diferentes estados de oxidación, caracterizado por:Therefore, an object of the present invention constitutes a ternary catalyst of Pt-Ru-MeOx (being Me = Mo, W or V) on a carbon support, hereinafter ternary catalyst Pt-Ru-MeO x / C of The invention, so that Pt and Ru are in the form of metal nanoparticles, and Me is in the form of oxides with different oxidation states, characterized by:
(a) tener una relación atómica de Pt/Ru dentro del rango 0,1- 2,(a) have an atomic ratio of Pt / Ru within the range 0.1-2,
(b) tener una relación atómica de Pt/Mo dentro del rango 0,1- 10, (c) ser capaz de oxidar el CO a CO2 a potenciales a partir de 0,1 V referido al potencial normal de hidrógeno (NHE)(b) have an atomic ratio of Pt / Mo within the range 0.1-10, (c) be able to oxidize CO to CO2 at potentials from 0.1 V based on the normal hydrogen potential (NHE)
Un objeto particular de Ia invención Io constituye el catalizador ternario Pt-Ru-MeOχ/C de Ia invención en el que Ia relación atómica de Pt/Ru está comprendida dentro del rango 0,5 - 1 ,5, y preferentemente entorno a uno. Un objeto particular de Ia invención Io constituye el catalizador ternarioA particular object of the invention constitutes the ternary catalyst Pt-Ru-MeOχ / C of the invention in which the atomic ratio of Pt / Ru is in the range 0.5-1.5, and preferably around one. A particular object of the invention constitutes the ternary catalyst
Pt-Ru-MeOχ/C de Ia invención en el que el metal de transición (Me) es Molibdeno.Pt-Ru-MeOχ / C of the invention in which the transition metal (Me) is Molybdenum.
La ventaja que presenta Ia utilización de un catalizador ternario tipo Pt- Ru-MeOx frente a otro binario de Pt-Ru consiste en que Ia incorporación de un metal de transición como el molibdeno permite disminuir el contenido en peso de Pt y Ru en el catalizador, reduciendo el coste del sistema. En el catalizador ternario Pt-Ru-MeOx/C de Ia invención, este descenso en el coste del catalizador viene acompañado de un aumento de Ia tolerancia hacia el CO del catalizador, constituyendo un sistema altamente novedoso. Otro objeto particular de Ia invención es el catalizador ternario Pt-Ru-The advantage presented by the use of a ternary catalyst Pt-Ru-MeO x compared to another binary Pt-Ru is that the incorporation of a transition metal such as molybdenum allows to reduce the weight content of Pt and Ru in the catalyst, reducing the cost of the system. In the ternary catalyst Pt-Ru-MeO x / C of the invention, this decrease in the cost of the catalyst is accompanied by an increase in the tolerance towards the CO of the catalyst, constituting a highly novel system. Another particular object of the invention is the ternary catalyst Pt-Ru-
MeOx/C de Ia invención en el que el soporte de carbón es negro de humo. Otro objeto particular de Ia invención es el catalizador ternario Pt-Ru- MeOx/C de Ia invención en el que el soporte es un carbón con mesoporosidad controlada.MeO x / C of the invention in which the carbon support is carbon black. Another particular object of the invention is the ternary catalyst Pt-Ru-MeO x / C of the invention in which the support is a carbon with controlled mesoporosity.
Otro objeto de Ia invención Io constituye el procedimiento de preparación del catalizador ternario Pt-Ru-MeOx/C de Ia invención, el cual se realiza incorporando el Me, en una etapa, y el Pt y el Ru, en otra etapa diferente, sobre el soporte de carbón, utilizando dos métodos diferentes: i) Método de impregnación utilizando un precursor de Me en presencia de una disolución acuosa de H2O2 para Ia incorporación del Me al soporte.Another object of the invention constitutes the process for preparing the ternary catalyst Pt-Ru-MeO x / C of the invention, which is carried out by incorporating the Me, in one stage, and the Pt and the Ru, in another different stage, on the carbon support, using two different methods: i) Impregnation method using a Me precursor in the presence of an aqueous solution of H 2 O 2 for the incorporation of the Me to the support.
(ii) Método coloidal para Ia incorporación de Pt y Ru sobre el soporte.(ii) Colloidal method for the incorporation of Pt and Ru on the support.
El método de impregnación y el método coloidal no son novedosos, y han sido ampliamente utilizados para Ia preparación de catalizadores. Sin embargo, su combinación para preparar, en dos etapas diferentes, un catalizador ternario de Pt-Ru-MeOx (siendo Me = Mo, W o V) es totalmente novedosa, y posibilita que el catalizador obtenido tenga unas propiedad especiales de alta tolerancia al CO, nunca antes conseguidas.The impregnation method and the colloidal method are not novel, and have been widely used for the preparation of catalysts. However, its combination to prepare, in two different stages, a ternary catalyst of Pt-Ru-MeOx (being Me = Mo, W or V) is completely new, and allows the catalyst obtained to have special properties of high tolerance to CO, never before achieved.
El procedimiento de preparación del catalizador ternario Pt-Ru-MeOx/C de Ia invención se puede realizar incorporando primero el Me, para posteriormente incorporar el Pt y el Ru, o viceversa.The process of preparing the ternary catalyst Pt-Ru-MeO x / C of the invention can be carried out by first incorporating the Me, to subsequently incorporate the Pt and the Ru, or vice versa.
Por tanto, otro objeto particular de Ia invención es el procedimiento de preparación del catalizador ternario Pt-Ru-MeOx/C de Ia invención en el que en una primera etapa se incorpora el Me (método (i)), para posteriormente incorporar el Pt y Ru (método (ii)), (ejemplos 1 y 2)Therefore, another particular object of the invention is the process of preparing the ternary catalyst Pt-Ru-MeO x / C of the invention in which in a first stage the Me (method (i)) is incorporated, to subsequently incorporate the Pt and Ru (method (ii)), (examples 1 and 2)
Otro objeto particular de Ia invención es el procedimiento de preparación del catalizador ternario Pt-Ru-MeOx/C de Ia invención en el que en una primera etapa se incorpora el Pt y Ru (método (ii)), para posteriormente incorporar el Me (método (i)), (ejemplo 3). La disolución acuosa de H2O2 utilizada en el método (i) del procedimiento de preparación del catalizador ternario Pt-Ru-MeOx/C de Ia invención se encuentra preferentemente dentro del rango 1 a 15 M, y más preferentemente dentro del rango 7 a 12 M.Another particular object of the invention is the process of preparing the ternary catalyst Pt-Ru-MeO x / C of the invention in which the Pt and Ru (method (ii)) are incorporated in a first stage, to subsequently incorporate the Me (method (i)), (example 3). The aqueous H2O2 solution used in the method (i) of the preparation process of the ternary catalyst Pt-Ru-MeO x / C of Ia The invention is preferably within the range 1 to 15 M, and more preferably within the range 7 to 12 M.
Otro objeto particular de Ia invención es el procedimiento de preparación del catalizador ternario Pt-Ru-MeOx/C de Ia invención en el que Ia incorporación del metal de transición se realiza mediante el método de impregnación en ausencia de H2O2.Another particular object of the invention is the process for preparing the ternary catalyst Pt-Ru-MeO x / C of the invention in which the incorporation of the transition metal is carried out by means of the impregnation method in the absence of H2O2.
Otro objeto de Ia invención es el uso del catalizador ternario Pt-Ru- MeOx/C de Ia invención como ánodo en pilas de combustibles.Another object of the invention is the use of the ternary catalyst Pt-Ru-MeO x / C of the invention as anode in fuel cells.
Otro objeto particular de Ia invención es el uso del catalizador ternario Pt-Ru-MeOχ/C de Ia invención como ánodo en pilas de combustible de membrana intercambiadora de protones o de electrolito polimérico alimentadas con hidrógeno procedente del reformado.Another particular object of the invention is the use of the ternary catalyst Pt-Ru-MeOχ / C of the invention as anode in proton-exchange membrane fuel cells or polymer electrolyte fed with hydrogen from reforming.
Otro objeto particular de Ia invención es el uso del catalizador ternario Pt-Ru-MeOχ/C de Ia invención como ánodo en pilas de combustible de metanol directo.Another particular object of the invention is the use of the ternary catalyst Pt-Ru-MeOχ / C of the invention as an anode in direct methanol fuel cells.
EJEMPLOS DE REALIZACIÓN DE LA INVENCIÓNEXAMPLES OF EMBODIMENT OF THE INVENTION
EJEMPLO 1. - Preparación del catalizador ternario de Pt-Ru-MoOx/C con relación atómica Pt: Ru: Mo de 1 :1 :0,6 y contenido metálico del 25% en peso.EXAMPLE 1. - Preparation of the ternary catalyst of Pt-Ru-MoOx / C with atomic ratio Pt: Ru: Mo of 1: 1: 0.6 and metallic content of 25% by weight.
Este catalizador se obtuvo mediante las siguientes etapas:This catalyst was obtained by the following steps:
1 ) Incorporación de Mo sobre negro de humo1) Incorporation of Mo over carbon black
A una suspensión de 2 g de negro de humo Vulcan XC-72R (Cabot Co.) en 21 mi de una disolución acuosa de H2O2 [9 M] se Ie añaden 0,92 g de (NH4)eMθ7θ24.4H2θ. La mezcla se deja agitando durante 48 horas a 250C. Después de este tiempo Ia muestra obtenida se seca a 1200C en aire durante 24 horas. A continuación el catalizador se trata en N2 a 13O0C durante una hora y a 4000C durante 2 horas. Muestra etiquetada como 1 Mo/C.To a suspension of 2 g of Vulcan XC-72R carbon black (Cabot Co.) in 21 ml of an aqueous solution of H2O2 [9 M] is added 0.92 g of (NH4) eMθ7.424.4H2θ. The mixture is allowed to stir for 48 hours at 25 0 C. After this time the sample obtained is dried at 120 0 C in air for 24 hours. The catalyst is then treated in N2 at 13O 0 C for one hour and at 400 0 C for 2 hours. Sample labeled 1 Mo / C.
2) Incorporación del Pt y Ru sobre 1 Mo/C Se mezclan 84 mi de una disolución acuosa 0,007 M de hbPtClβ con una disolución de 253 mg de Na2S2θs en 3 mi de H2O a 250C y bajo agitación constante. A Ia mezcla se Ie añade Ia cantidad adecuada de una disolución acuosa 0,6 M de Na2CÜ3 hasta obtener un pH de 5, y 30 mi de H2O2 al 33% en peso. El pH de Ia disolución se ajusta a un valor de 5 añadiendo Ia cantidad adecuada de una disolución 1 ,0 M de NaOH. A continuación, se añaden 30,5 mi de una disolución acuosa 0,02 M de RuCU para formar el coloide platino- rutenio. A Ia disolución resultante se Ie añaden 750 mg de Ia muestra 1 Mo/C, y se deja agitando durante 10 min. Se borbotea hidrógeno en Ia dispersión obtenida durante 2 horas. Después de filtrar y lavar el filtrado con agua destilada, el sólido resultante se seca en Ia estufa a 1100C durante 12 horas. El electrocatalizador obtenido contiene 25% en peso de platino-rutenio-molibdeno sobre negro de uno en una relación atómica de 1 :1 :0,6.2) Incorporation of Pt and Ru over 1 Mo / C 84 ml of a 0.007 M aqueous solution of hbPtClβ are mixed with a solution of 253 mg of Na 2 S 2 ens in 3 ml of H 2 O at 25 0 C and under stirring constant. To the mixture is added the appropriate amount of a 0.6 M aqueous solution of Na2CÜ3 until a pH of 5 is obtained, and 30 ml of H2O2 at 33% by weight. The pH of the solution is adjusted to a value of 5 by adding the appropriate amount of a 1.0 M NaOH solution. Next, 30.5 ml of a 0.02 M aqueous solution of RuCU are added to form the platinum-ruthenium colloid. To the resulting solution 750 mg of the 1 Mo / C sample is added, and it is left stirring for 10 min. Hydrogen is bubbled in the dispersion obtained for 2 hours. After filtering and washing the filter with distilled water, the resulting solid is dried in the heater 110 0 C for 12 hours. The electrocatalyst obtained contains 25% by weight of platinum-ruthenium-molybdenum on black of one in an atomic ratio of 1: 1: 0.6.
Para Ia caracterización de los catalizadores se usa una celda electroquímica convencional de tres electrodos. El electrodo de trabajo se prepara depositando el electrocatalizador sobre una superficie pulida de carbón vitreo. Como contraelectrodo se usa platino y como electrodo de referencia HgZHg2SO4. El electrolito utilizado es una disolución acuosa 0,5 M de H2SO4. La medida se efectúa a 250C. El electrocatalizador se caracteriza mediante voltamperometría cíclica una vez adsorbido previamente el CO. Esta caracterización se realiza borboteando CO sobre el electrolito durante 12 min a un potencial de 0,07 V frente al potencial normal de hidrógeno (NHE). A continuación se borbotea Ar durante 20 min para asegurarse que todo el CO de Ia disolución se ha eliminado dejando sólo el CO absorbido sobre Ia superficie del catalizador. Después se realizan dos ciclos de voltamperometría cíclica a una velocidad de 5 mV/s desde 0,05 V hasta 0,8 V. Es en el primer ciclo donde tiene lugar Ia oxidación del CO a CO2. En el segundo ciclo se observa el comportamiento del catalizador sin presencia de CO y se utiliza como blanco para comparar. En Ia figura 1 se muestra Ia electrooxidación de CO a CO2 durante el barrido anódico del primer ciclo para el catalizador ternario de Pt/Ru/MoOχ con un contenido en peso del 25 % y una relación atómica Pt:Ru:Mo de 1 :1 :0,6 de esta invención y para el catalizador comercial Johnson Matthey HiSPEC 5000, que presenta un contenido en peso de Pt-Ru del 30% con una relación atómica Pt/Ru de 1 , y que usa negro de humo como soporte. Se observa como el catalizador comienza a oxidar el CO a CO2 a 0,13 V, mientras que el comercial Io hace a partir de 0,3 V.For the characterization of the catalysts, a conventional three electrode electrochemical cell is used. The working electrode is prepared by depositing the electrocatalyst on a polished surface of vitreous carbon. Platinum is used as a counter electrode and HgZHg 2 SO 4 as the reference electrode. The electrolyte used is a 0.5 M aqueous solution of H 2 SO 4 . The measurement is made at 25 0 C. The electrocatalyst is characterized by cyclic voltammetry once the CO has been previously adsorbed. This characterization is done by bubbling CO over the electrolyte for 12 min at a potential of 0.07 V versus the normal hydrogen potential (NHE). Then Ar is bubbled for 20 min to ensure that all the CO of the solution has been removed leaving only the CO absorbed on the catalyst surface. Then two cycles of cyclic voltammetry are performed at a speed of 5 mV / s from 0.05 V to 0.8 V. It is in the first cycle where the oxidation of CO to CO 2 takes place . In the second cycle the behavior of the catalyst is observed without the presence of CO and is used as a blank for comparison. Figure 1 shows the electrooxidation of CO to CO 2 during the anodic scanning of the first cycle for the ternary catalyst of Pt / Ru / MoOχ with a weight content of 25% and an atomic ratio Pt: Ru: Mo of 1: 1: 0.6 of this invention and for the Johnson Matthey HiSPEC 5000 commercial catalyst, which has a Pt-Ru weight content of 30% with a Pt / Ru atomic ratio of 1, and that uses carbon black as support. It is observed how the catalyst begins to oxidize CO to CO2 at 0.13 V, while the commercial one does it from 0.3 V.
EJEMPLO 2. Preparación del catalizador ternario de Pt-Ru-MoOx/C con relación atómica Pt: Ru: Mo de 1 :1 :0,8 y contenido metálico del 20% en peso.EXAMPLE 2. Preparation of the ternary catalyst of Pt-Ru-MoOx / C with atomic ratio Pt: Ru: Mo of 1: 1: 0.8 and metallic content of 20% by weight.
Para preparar este catalizador se llevaron a cabo las siguientes etapas: 1 ) Incorporación de Mo sobre negro de humo A una suspensión de 2,5 g de negro de humo Vulcan XC-72R (CabotThe following steps were carried out to prepare this catalyst: 1) Incorporation of Mo over carbon black To a suspension of 2.5 g of Vulcan XC-72R carbon black (Cabot
Co.) en 30 mi de una disolución acuosa de H2O2 [10 M] se Ie añaden 461.4 mg de (NH4)6Mθ7θ24.4H2O. La mezcla se deja agitando durante 48 horas a 250C. Después de este tiempo el catalizador Mo/C obtenido se seca a 1200C en aire durante 24 horas. Muestra etiquetada como 2Mo/C. 2) Incorporación del Pt y Ru sobre 2Mo/CCo.) in 30 ml of an aqueous solution of H2O2 [10 M] is added 461.4 mg of Ie (NH 4) 2 6Mθ7θ24.4H O. The mixture was left stirring for 48 hours at 25 0 C. After this time the Mo catalyst / C obtained was dried at 120 0 C in air for 24 hours. Sample labeled 2Mo / C. 2) Incorporation of Pt and Ru over 2Mo / C
Se mezclan 201.6 mi de una disolución acuosa 0,007 M de H2PtCIe con una disolución de 576 mg de Na2S2O5 en 5 mi de H2O a 250C y bajo agitación constante. A Ia mezcla se Ie añade Ia cantidad adecuada de una disolución acuosa 0,6 M de Na2Cθ3 hasta obtener un pH de 5, y 69 mi de H2O2 al 33% en peso. El pH de Ia disolución se ajusta a un valor de 5 añadiendo Ia cantidad adecuada de una disolución 1 ,0 M de NaOH. A continuación, se añaden 73 mi de una disolución acuosa 0,02 M de RuCI3 para formar el coloide platino- rutenio. A Ia disolución se Ie añaden 2 gramos de Ia muestra 2Mo/C, y se deja agitando durante 10 min. Se borbotea hidrógeno en Ia dispersión obtenida durante 2 horas. Después de filtrar y lavar el filtrado con agua destilada, el sólido resultante se seca en Ia estufa a 1100C durante 12 horas.201.6 ml of a 0.007 M H 2 PtCIe aqueous solution with a solution of 576 mg of Na 2 S 2 O 5 in 5 ml of H 2 O at 25 0 C and under constant stirring are mixed. To the mixture is added the appropriate amount of a 0.6 M aqueous solution of Na 2 C 3 until obtaining a pH of 5, and 69 ml of H 2 O 2 at 33% by weight. The pH of the solution is adjusted to a value of 5 by adding the appropriate amount of a 1.0 M NaOH solution. Next, 73 ml of a 0.02 M aqueous solution of RuCI 3 are added to form the platinum-ruthenium colloid. To the solution 2 grams of the 2Mo / C sample are added, and it is left stirring for 10 min. Hydrogen is bubbled in the dispersion obtained for 2 hours. After filtering and washing the filter with distilled water, the resulting solid is dried in the heater 110 0 C for 12 hours.
El electrocatalizador obtenido contiene 20% en peso de platino-rutenio- molibdeno en una relación atómica de 1 :1 :0.8, y su tolerancia al CO se muestra en Ia figura 1 , junto con el catalizador del ejemplo 1 y Ia muestra comercial Johnson Matthey HiSPEC 5000. Se observa en Ia figura que este catalizador empieza a oxidar el CO a CO2 a 0,12 V, mientras que el comercial Io hace a partir de 0,3 V.The electrocatalyst obtained contains 20% by weight of platinum-ruthenium-molybdenum in an atomic ratio of 1: 1: 0.8, and its tolerance to CO is shown in Figure 1, together with the catalyst of example 1 and the commercial sample Johnson Matthey HiSPEC 5000. It is observed in the figure that this catalyst begins to oxidize CO to CO 2 at 0.12 V, while the commercial one does from 0.3 V.
EJEMPLO 3. Preparación del catalizador ternario de Pt-Ru-MoOχ/C con relación atómica Pt: Ru: Mo de 1 :0,9:1,2 y contenido metálico del 20% en peso, mediante el procedimiento por el que se incorpora primero el Pt/Ru sobre el negro de carbón, para posteriormente incorporar el Mo.EXAMPLE 3. Preparation of the ternary catalyst of Pt-Ru-MoO χ / C with atomic ratio Pt: Ru: Mo of 1: 0.9: 1.2 and metallic content of 20% by weight, by the procedure by which first incorporate the Pt / Ru on the carbon black, and then incorporate the Mo.
Para preparar este catalizador se llevaron a cabo las siguientes etapas:To prepare this catalyst the following steps were carried out:
1 ) Incorporación del PtRu sobre negro de humo1) Incorporation of PtRu on carbon black
Se mezclan 127 mi de una disolución acuosa 0,007 M de H2PtCIe con una disolución de 380 mg de Na2S2θ5 en 4 mi de H2O a 250C y bajo agitación constante. A Ia mezcla se Ie añade Ia cantidad adecuada de una disolución acuosa 0,6 M de Na2COs hasta obtener un pH de 5, y 40 mi de H2O2 al 33% en peso. El pH de Ia disolución se ajusta a un valor de 5 añadiendo Ia cantidad adecuada de una disolución 1 ,0 M de NaOH. A continuación, se añaden 45 mi de una disolución acuosa 0,02 M de RuCb para formar el coloide platino- rutenio. A Ia disolución se Ie añaden 1 ,1 gramos de negro de humo Vulcan XCMix 127 ml of a 0.007 M H 2 PtCIe aqueous solution with a solution of 380 mg of Na2S2θ 5 in 4 ml of H 2 O at 25 0 C and under constant stirring. To the mixture is added the appropriate amount of a 0.6 M aqueous solution of Na 2 COs until a pH of 5 is obtained, and 40 ml of H 2 O 2 at 33% by weight. The pH of the solution is adjusted to a value of 5 by adding the appropriate amount of a 1.0 M NaOH solution. Next, 45 ml of a 0.02 M aqueous solution of RuCb are added to form the platinum-ruthenium colloid. To the solution, 1.1 grams of Vulcan XC carbon black are added
72R y se deja agitando durante 10 min. Se borbotea hidrógeno en Ia dispersión obtenida durante 2 horas. Después de filtrar y lavar el filtrado con agua destilada, el sólido resultante se seca en Ia estufa a 1100C durante 12 horas. Muestra etiquetada como PtRu/C.72R and let stir for 10 min. Hydrogen is bubbled in the dispersion obtained for 2 hours. After filtering and washing the filter with distilled water, the resulting solid is dried in the heater 110 0 C for 12 hours. Sample labeled as PtRu / C.
2) Incorporación del Mo sobre PtRu/C2) Incorporation of Mo over PtRu / C
A una suspensión de 600 mg de PtRu/C en 37 mi de metanol se Ie añade gota a gota 1 mi de una disolución acuosa 0.1 M de (NH4)BMo7O24.4H2O. La mezcla se deja agitando durante 1 hora a 250C. Después de este tiempo el catalizador obtenido se filtra y se seca a 1100C en aire durante 24 horas.To a suspension of 600 mg PtRu / C in 37 ml of methanol was added dropwise Ie 1 ml of a 0.1 M (NH 4) 7 O 24 · 4H BMo 2 O. The aqueous mixture is stirred for 1 hour at 25 0 C. After this time the catalyst is filtered and dried at 110 0 C in air for 24 hours.
El electrocatalizador obtenido contiene 20% en peso de platino-rutenio- molibdeno en una relación atómica de 1 :0,9:1 ,2, y su tolerancia al CO se muestra en Ia figura 1 (C). Se observa como el catalizador comienza a oxidar el CO a CO2 a 0,14 V, mientras que el comercial Io hace a partir de 0,3 V. The electrocatalyst obtained contains 20% by weight of platinum-ruthenium-molybdenum in an atomic ratio of 1: 0.9: 1, 2, and its tolerance to CO is shown in Figure 1 (C). It is observed how the catalyst begins to oxidize the CO to CO 2 at 0.14 V, while the commercial one starts from 0.3 V.

Claims

REIVINDICACIONES
1.- Catalizador ternario de Pt-Ru-MeOx (siendo Me = Mo, W o V) sobre un soporte de carbón, de forma que el Pt y el Ru se encuentran en forma de nanopartículas metálicas, y el Me se encuentra en forma de óxidos con diferentes estados de oxidación, caracterizado por: a) tener una relación atómica de Pt/Ru dentro del rango 0,1- 2, b) tener una relación atómica de Pt/Mo dentro del rango 0,1- 10, c) ser capaz de oxidar el CO a CO2 a potenciales a partir de 0,1 V referido al potencial normal de hidrógeno (NHE)1.- Pt-Ru-MeOx ternary catalyst (Me = Mo, W or V) on a carbon support, so that Pt and Ru are in the form of metal nanoparticles, and Me is in shape of oxides with different oxidation states, characterized by: a) having an atomic ratio of Pt / Ru within the range 0.1-2, b) having an atomic ratio of Pt / Mo within the range 0.1-10, c ) be able to oxidize CO to CO 2 to potentials from 0.1 V based on the normal hydrogen potential (NHE)
2.- Catalizador ternario según reivindicación 1 caracterizado porque Ia relación atómica de Pt/Ru está comprendida dentro del rango 0,5 - 1 ,5, y preferentemente entorno a uno.2. Ternary catalyst according to claim 1 characterized in that the atomic ratio of Pt / Ru is within the range 0.5-1.5, and preferably around one.
3.- Catalizador ternario según reivindicación 1 caracterizado porque el metal de transición (Me) es Molibdeno. 3. Ternary catalyst according to claim 1 characterized in that the transition metal (Me) is Molybdenum.
4.- Catalizador ternario según reivindicación 1 caracterizado porque el soporte de carbón es negro de humo.4. Ternary catalyst according to claim 1 characterized in that the carbon support is carbon black.
5.- Catalizador ternario según reivindicación 1 caracterizado porque el soporte es un carbón con mesoporosidad controlada.5. Ternary catalyst according to claim 1 characterized in that the support is a carbon with controlled mesoporosity.
6.- Procedimiento de preparación del catalizador descrito en las reivindicaciones 1-5, caracterizado porque se incorpora el Me, en una etapa, y el Pt y el Ru, en otra etapa diferente, sobre el soporte de carbón, utilizando dos métodos diferentes:6. Process for preparing the catalyst described in claims 1-5, characterized in that the Me is incorporated, in one stage, and the Pt and Ru, in a different stage, on the carbon support, using two different methods:
(i) Método de impregnación utilizando un precursor de Me en presencia de una disolución acuosa de H2O2 para Ia incorporación del Me al soporte.(i) Method of impregnation using a Me precursor in the presence of an aqueous solution of H2O2 for the incorporation of Me into the support.
(ii) Método coloidal para Ia incorporación de Pt y Ru sobre el soporte.(ii) Colloidal method for the incorporation of Pt and Ru on the support.
7.- Procedimiento según reivindicación 6 caracterizado porque en una primera etapa se incorpora el Me (método (i)), para posteriormente incorporar el Pt y Ru7. Method according to claim 6 characterized in that in a first stage the Me (method (i)) is incorporated, to subsequently incorporate the Pt and Ru
(método (ii)) 8.- Procedimiento según reivindicación 6 caracterizado porque en una primera etapa se incorpora el Pt y el Ru (método (ii)), para posteriormente incorporar el Me (método (i)).(method (ii)) 8.- Method according to claim 6 characterized in that in a first stage the Pt and the Ru (method (ii)) are incorporated, to subsequently incorporate the Me (method (i)).
9.- Procedimiento según reivindicación 6 caracterizado porque Ia disolución acuosa de H2O2 utilizada en el método (i) se encuentra preferentemente dentro del rango 1 a 15 M, y más preferentemente dentro del rango 7 a 12 M. 9. Method according to claim 6 characterized in that the aqueous H2O2 solution used in the method (i) is preferably within the range 1 to 15 M, and more preferably within the range 7 to 12 M.
10.- Procedimiento según reivindicación 6 caracterizado porque Ia incorporación de Me se realiza mediante el método de impregnación (i) en ausencia de H2O2.10. Method according to claim 6 characterized in that the incorporation of Me is carried out by the impregnation method (i) in the absence of H2O2.
11.- Uso del catalizador ternario según reivindicaciones 1-5 como ánodo en pilas de combustibles. 11. Use of the ternary catalyst according to claims 1-5 as anode in fuel cells.
12.- Uso del catalizador ternario según reivindicación 11 en pilas de combustible de membrana intercambiadora de protones o de electrolito polimérico alimentadas con hidrógeno procedente del reformado.12. Use of the ternary catalyst according to claim 11 in proton-exchange membrane fuel cells or polymer electrolyte fed with hydrogen from reforming.
13.- Uso del catalizador ternario según reivindicación 11 en pilas de combustible de metanol directo. 13. Use of the ternary catalyst according to claim 11 in direct methanol fuel cells.
PCT/ES2008/070037 2007-03-15 2008-02-29 Ternary catalyst of pt-ru-meox (me = mo, w, v) on carbon with high co tolerance in fuel cell anodes and preparation method thereof WO2008110651A1 (en)

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GB2473550A (en) * 2009-09-11 2011-03-16 Univ Washington Fuel cell catalyst materials and methods for reforming hydrocarbon fuels
GB2473550B (en) * 2009-09-11 2012-03-28 Univ Washington State Res Fdn Catalyst materials and methods for reforming hydrocarbon fuels
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