JP4963561B2 - Catalyst and method for producing the same - Google Patents

Description

  The present invention relates to a novel catalyst using platinum or a platinum-based alloy and a method for producing the same.

Fuel cells have been attracting attention in recent years because of their high power generation efficiency and the ability to reduce emissions of harmful substances such as NO _x , SO _x , and PM, which are burdens on the environment. Fuel cells include solid oxide fuel cells (SOFCs), molten carbonate fuel cells (MCFCs), phosphoric acid fuel cells (PAFCs), solid high fuel cells. It can be broadly divided into molecular fuel cells (PEFC). In particular, solid polymer fuel cells are actively researched because they can efficiently generate power at a lower temperature than solid oxide fuel cells and phosphoric acid fuel cells.

  The PEFC has a basic structure in which an ion exchange membrane such as a perfluorosulfonic acid membrane is used as an electrolyte, and anode and cathode electrodes are joined to both surfaces of the ion exchange membrane. In power generation of the fuel cell, hydrogen is supplied to the anode and oxygen is supplied to the cathode, and the following electrochemical reaction is performed at each electrode, whereby chemical energy can be taken out as electric energy without going through a combustion process.

Anode: H ₂ → 2H ⁺ + 2e ⁻
Cathode: 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O
Total reaction: H ₂ + 1 / 2O ₂ → H ₂ O
However, if hydrogen is used directly as a fuel, there is a problem in terms of the storage method of hydrogen and the volume density of energy being small, so practically, methane, methanol, etc. are used as fuel and converted to hydrogen. Used. However, in this case, the fuel contains carbon monoxide (CO) and carbon dioxide (CO ₂ ) as impurities. In fuel cells, noble metal catalysts such as platinum, palladium, and ruthenium are usually used as anode electrode catalysts. However, this catalyst is poisoned by carbon monoxide, and its characteristics deteriorate over time. There was a problem.

  In recent years, direct methanol fuel cells (DMFC) that use methanol as a fuel and react directly on an electrode without converting the methanol into hydrogen have attracted particular attention in recent years. In the direct methanol fuel cell, there is no need to use a reformer for reforming methanol into hydrogen, and there is an advantage that a fuel cell reduced in size and weight can be realized. The reaction at the electrode in DMFC is performed as follows.

Methanol fuel electrode (anode electrode): CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻
Air electrode (cathode electrode): 3 / 2O ₂ + 6H ⁺ + 6e ⁻ → 3H ₂ O
Total reaction: CH ₃ OH + 3 / 2O ₂ → CO ₂ + 2H ₂ O
However, even in the direct methanol fuel cell, carbon monoxide is generated as an intermediate product, so that there is still a problem of poisoning of the anode electrode catalyst.

Conventionally, platinum and other metals such as ruthenium (Ru), rhodium (Rh), molybdenum (Mo), osmium (Os), iridium (Ir), tin, and the like have been used to eliminate the problem of poisoning of these anode electrode catalysts. It has been proposed to use various catalysts using an alloy (platinum alloy) with one or more selected from (Sn) or the like (for example, see Patent Documents 1 to 6). Among them, the platinum-ruthenium alloy catalyst is relatively high by using ruthenium having hydrophilicity, and oxidizing and removing carbon monoxide adsorbed on platinum by the hydroxyl group (OH ⁻ ) bonded to the ruthenium. Poisoning resistance can be obtained.
Japanese Patent Laid-Open No. 9-035723 JP 2000-003712 A JP 2000-012043 A JP 2001-015121 A Japanese Patent Laid-Open No. 2003-187851 JP-A-2005-123169 Andrew et al., "Increasing Proton Exchange Membrane Fuel Cell Catalyst Effectiveness Through Sputter Deposition". Journal of The Electrochemical Society 149 (3). P.280-287, 2002. Katayama., "Electrooxidation of Methanol on a Platinum-Tin Oxide Catalyst". The Journal of Physical Chemistry 84, p.376-381, 1980. Rajesh et al., "Electronically conducting hybrid material as high performance catalyst support for electrocatalytic application". Journal of Power Sources 141, p.35-38, 2005. Iwasita., "Electrocatalysis of Methanol Oxidation". Electrochimica Acta 47, p.3663-3674, 2002.

  However, these conventionally proposed alloy-based catalysts are all expensive, and it is difficult to say that high poisoning resistance sufficient for practical use is obtained, and more useful catalysts. Development is required.

  The present invention has been made to solve the above-mentioned problems, and the object of the present invention is to produce a catalyst that can suppress the deterioration of the activity over time due to carbon monoxide poisoning at a lower cost than conventional ones. It is providing the manufacturing method of the catalyst which can be performed, and the catalyst obtained by the said method.

  The catalyst of the present invention is a composite catalyst of platinum or a platinum-based alloy and carbon, and the peak of the 4f orbit of platinum or the platinum-based alloy of the composite catalyst measured using an X-ray photoelectron spectrometer is used. It is characterized by shifting to the high energy side within a range of 0.01 to 0.40 eV.

  The catalyst of the present invention preferably has a carbon molar ratio in the atomic composition of 0.1 to 85%.

The catalyst of the present invention can be particularly suitably used as a catalyst for fuel cell electrodes.
The present invention also provides a catalyst characterized in that a film is formed in a state where carbon is combined with platinum or a platinum-based alloy by performing a PVD method or a CVD method while introducing a carbon source into platinum or the platinum-based alloy. A manufacturing method is provided.

  In the method for producing a catalyst of the present invention, it is preferable to use an aliphatic hydrocarbon or aromatic hydrocarbon having 1 to 7 carbon atoms as a carbon source.

  In the catalyst production method of the present invention, it is preferable to perform a hydrogen-based plasma treatment after the film formation.

  ADVANTAGE OF THE INVENTION According to this invention, the usage-amount of the noble metal material used for a catalyst can be reduced conventionally, and the poisoning tolerance with respect to carbon monoxide is improved rather than before, improving the utilization efficiency of a noble metal material. Can be provided. Moreover, since the manufacturing method of the catalyst of this invention can process a large area, it can anticipate industrialization.

  The present invention provides a composite catalyst of platinum or a platinum-based alloy and carbon. In the present invention, the “composite catalyst” refers to a catalyst in which platinum or a platinum-based alloy and carbon are integrated and combined at an atomic level, and 4f of platinum measured by an X-ray photoelectron spectrometer described later. Whether or not the catalyst is a composite catalyst using platinum or a platinum-based alloy can be determined based on whether or not the peak of the orbit is shifted to the high energy side.

  In the composite catalyst of the present invention, platinum or a platinum-based alloy is used as the noble metal material composited with carbon. Examples of platinum alloys include platinum, ruthenium (Ru), nickel (Ni), cobalt (Co), iron (Fe), tin (Sn), tungsten (W), molybdenum (Mo), and tantalum (Ta). An alloy with one or more metals selected from niobium (Nb), rhodium (Rh), osmium (Os), iridium (Ir), chromium (Cr), titanium (Ti), and the like can be used, and is particularly limited. Although not, platinum-ruthenium is considered to have a remarkable effect of supplying a hydroxyl group (—OH) that oxidizes carbon monoxide, or weakening the adsorption power with carbon monoxide to secure a reactive site. An alloy based on platinum, a nickel-nickel alloy, a platinum-cobalt alloy or a platinum-iron alloy can be preferably used.

FIG. 1 is a graph showing the results obtained by measuring the composite catalyst of the present invention and conventional platinum using an X-ray photoelectron spectroscopy (ESCA). In the graph of FIG. 1, the vertical axis represents strength (Arb. Units), and the horizontal axis represents binding energy (eV). In the composite catalyst of the present invention, the peak of 4f orbit of platinum or platinum-based alloy in the composite catalyst measured using an X-ray photoelectron spectrometer is 0.01 to 0.40 eV (preferably 0.05 to It is characterized by a shift (chemical shift) to the high energy side within the range of 0.15 eV). The X-ray photoelectron spectroscopic analyzer emits photoelectrons having specific energy for each element from the sample surface by irradiating the sample surface with X-rays, and the type, amount, and amount of the element from the energy position and intensity of the photoelectron. An apparatus for analyzing a chemical bonding state, for example, PHI 5700 ESCA (manufactured by Physical Electronics) can be suitably used. In FIG. 1, as an example of the composite catalyst of the present invention, the peak shift of 4f orbit of platinum in the composite catalyst measured using an X-ray photoelectron spectrometer is 0.16 eV on the high energy side, carbon When a platinum-carbon composite catalyst having a molar ratio of 80% (platinum: carbon = 20: 80) is used ( Reference Example 1 described later; curve B in FIG. 1), and X-ray photoelectron spectroscopy The platinum 4f orbit peak shift in the composite catalyst measured using an analyzer is 0.09 eV on the high energy side and the molar ratio of carbon is 53% (platinum: carbon = 47: 53). The case where a composite catalyst with carbon is used (Example 1 described later; curve C in FIG. 1) is shown. FIG. 1 also shows an example of a conventional platinum catalyst in which the peak shift of the 4f orbit of platinum measured using an X-ray photoelectron spectrometer is 0 eV (platinum molar ratio: 100%). (Curve A in FIG. 1).

  When platinum is measured with an X-ray photoelectron spectrometer, a peak of platinum 4f orbit appears at 71.8 eV and 75.1 eV (see curve A in FIG. 1). For example, platinum- When a ruthenium-based alloy is measured with a photoelectron spectroscopic analyzer, a peak of 4f orbit of platinum contained in the platinum-ruthenium-based alloy appears at 71.1 eV and 74.4 eV. In the composite catalyst of the present invention, the peak appearing when platinum or a platinum-based alloy before composite is measured with an X-ray photoelectron spectrometer is shifted to the high energy side within the above-mentioned range. The shift value can be calculated from the difference between the maximum values of the peaks.

FIG. 2 is a graph showing the poisoning resistance to carbon monoxide of the composite catalyst of the present invention, in which the vertical axis indicates the standardized current density and the horizontal axis indicates time (minutes). The composite catalyst of the present invention has a significantly improved resistance to poisoning against carbon monoxide as compared with conventionally used platinum catalysts and platinum-based alloy catalysts. In FIG. 2, as an example of the composite catalyst of the present invention, the peak shift of platinum 4f orbit in the composite catalyst measured using an X-ray photoelectron spectrometer is 0.16 eV on the high energy side, carbon When a composite catalyst of platinum and carbon having a molar ratio of 80% (platinum: carbon = 20: 80) is used ( Reference Example 1 described later; curve B in FIG. 2), and X-ray photoelectron spectroscopy The platinum 4f orbit peak shift in the composite catalyst measured using an analyzer is 0.09 eV on the high energy side and the molar ratio of carbon is 53% (platinum: carbon = 47: 53). The case where a composite catalyst with carbon is used (Example 1 described later; curve C in FIG. 2) is shown. FIG. 2 also shows an example of a conventional platinum catalyst in which the peak shift of the 4f orbit of platinum measured using an X-ray photoelectron spectrometer is 0 eV (platinum molar ratio: 100%). (Curve A in FIG. 2).

Note that the graph shown in FIG. 2 shows the decay rate of current density over time for carbon monoxide generated by methanol oxidation by tripolar electrochemical measurement using the equipment schematically shown in FIG. The experimental result which measured was shown. Tripolar electrochemical measurement refers to a method in which changes in chemical substances are regarded as electrochemical reactions, and the chemical reactions are examined using potential, current, and the like as measurement scales. For example, the measurement is performed using equipment as shown in FIG. be able to. That is, the working electrode 3, the counter electrode 4 and the reference electrode 5 are immersed in the electrolyte accommodated in the water tank 2. Here, as the working electrode 3, for example, a cylindrical glassy carbon end face with a catalyst film is used, the counter electrode 4 is a platinum wire, and the reference electrode 5 is Ag / AgCl (sat. KCl). Is used. The working electrode 3, the counter electrode 4, and the reference electrode 5 are electrically connected via a potentiostat, measure the potential between the working electrode 3 and the reference electrode 5, and measure the current between the working electrode 3 and the counter electrode 4. When measuring the poisoning resistance against carbon monoxide, a mixed liquid (20 ° C.) of 0.5 MH ₂ SO ₄ and 1M CH ₃ OH is accommodated in the water tank 2, for example. Note that nitrogen (N ₂ ) is supplied to the mixed liquid in the water tank 2 through the gas introduction pipe 6. Using such equipment, the potential between the working electrode 3 and the reference electrode 5 is set to a constant potential of 570 mV, and the current is measured between the working electrode 3 and the counter electrode 4 by an electrochemical measurement system HZ-5700 (manufactured by Hokuto Denko). Use to measure. In the experiment whose result is shown in FIG. 2, the current density at 30 seconds after the start of measurement is set to 1 (normalized) using the equipment shown in FIG. 3, and the decay rate of current density after 120 minutes (%) ) Was measured.

  As shown in FIG. 2, the composite catalyst of the present invention (curves B and C in FIG. 1 and FIG. 2) starts measurement compared to the conventional platinum catalyst (curve A in FIG. 1 and FIG. 2). It can be seen that the decay rate (%) of the current density after 120 minutes is remarkably low. As shown in FIG. 3, the mixed solution accommodated in the water tank 2 contains methanol, and as the measurement proceeds, the methanol in the mixed solution is oxidized, and carbon monoxide is generated as one of the intermediate products. The Therefore, the current density decay rate indicates the poisoning resistance of the catalyst against carbon monoxide, and the composite catalyst of the present invention, which has a much lower current density decay rate than the conventional platinum catalyst. It can be seen that it has extremely excellent poisoning resistance to carbon monoxide.

  In the composite catalyst of the present invention, a noble metal material conventionally used for imparting poisoning resistance to carbon monoxide (for example, in the case of a platinum-ruthenium alloy catalyst, poisoning resistance to carbon monoxide is imparted. Even if the amount of the ruthenium component used) is lower than that of the prior art, it is possible to realize a catalyst having better poisoning resistance to carbon monoxide than in the past. According to such a composite catalyst of the present invention, the amount of the noble metal material used for the catalyst can be reduced as compared with the conventional one, and the utilization efficiency of the noble metal material can be improved while the carbon monoxide is covered more than before. A catalyst with improved poison resistance can be provided.

  In the composite catalyst of the present invention, the 4f orbital peak of platinum or platinum-based alloy in the composite catalyst measured using an X-ray photoelectron spectrometer is shifted to the high energy side within the above-mentioned range. If so, the molar ratio of carbon in the composite catalyst is not particularly limited, but is preferably in the range of 0.1 to 85%. When the molar ratio of carbon is less than 0.1%, there is a possibility that platinum and carbon are not complexed. When the molar ratio of carbon exceeds 85%, the reaction activity of platinum This is because it is considered that there is a possibility of obstructing the point. The molar ratio of carbon in the composite catalyst of the present invention can be calculated from the peak area for each element using the above-described X-ray photoelectron spectrometer (for example, PHI 5700 ESCA (manufactured by Physical Electronics)). .

  In FIG. 2, the peak shift of the platinum 4f orbit in the composite catalyst measured using an X-ray photoelectron spectrometer was 0.16 eV, and the molar ratio of carbon was 80% (platinum: carbon = 20: 80). Shift of the peak of the platinum 4f orbit in the composite catalyst measured using an X-ray photoelectron spectrometer compared to the case of using a composite catalyst of platinum and carbon (curve B in FIG. 2) Is 0.09 eV, and when a platinum-carbon composite catalyst having a carbon molar ratio of 47% (platinum: carbon = 47: 53) is used (curve C in FIG. 2), the measurement starts 120 minutes. The later decay rate (%) has been greatly improved. Thus, the molar ratio of carbon in the composite catalyst of the present invention is preferably in the range of 10 to 70% among the above, because particularly excellent poisoning resistance to carbon monoxide is exhibited. Thus, the reason why the poisoning resistance to carbon monoxide particularly excellent when the molar ratio of carbon in the composite catalyst of the present invention is in the range of 10 to 70% is unknown, This is thought to be due to the change in the electronic structure of platinum due to the formation of fine particles of platinum or the interaction between platinum and carbon.

The composite catalyst of the present invention has a larger actual area than conventional platinum catalysts and platinum alloy catalysts. Specifically, for example, the actual area of the conventional platinum catalyst was about 0.20 to 0.45 cm ² , whereas the composite catalyst of the present invention has an actual area of about 0.45 to 2.9 cm ^2. Have As described above, the actual area of the composite catalyst of the present invention is larger than that of the conventional platinum catalyst and platinum-based alloy catalyst. It is thought to be due to the increase and the fine particles.

Here, the actual area refers to the area of platinum in consideration of surface irregularities in the composite catalyst, and can be calculated from the cyclic voltammetry measured by the above-described tripolar electrochemical measurement. Here, FIG. 4 is a graph showing an example of cyclic voltammetry (electrolyte: 0.5 MH ₂ SO ₄ ) of the composite catalyst of the present invention and a conventional platinum catalyst, and the vertical axis represents current (mA), horizontal The axis is the potential (V vs Ag / AgCl). FIG. 5 is a graph showing an example of cyclic voltammetry (electrolyte: 0.5 MH ₂ SO ₄ + 1M CH ₃ OH) of the composite catalyst of the present invention and a conventional platinum catalyst, and the vertical axis represents current density (mA). / Cm ² ), the horizontal axis is the potential (V vs Ag / AgCl). Cyclic voltammetry as shown in FIG. 4 and FIG. 5 can be created from values measured by tripolar electrochemical measurements using equipment as described above with reference to FIG. 3, for example. The cyclic voltammetry shown in FIG. 4 and FIG. 5 is a graph showing the results of measuring nitrogen (N ₂ ) into the electrolyte through the gas introduction tube 6 and measuring the scan speed at 100 mV / sec. Is.

In the cyclic voltammetry shown in FIGS. 4 and 5, the results for the composite catalyst of the present invention are indicated by a solid line, and the results for a conventional platinum catalyst are indicated by a broken line. 4 and 5, as an example of the composite catalyst of the present invention, the shift of the peak of the 4f orbit of platinum in the composite catalyst measured using the X-ray photoelectron spectrometer described above is on the high energy side. The results are shown for a case where a composite catalyst of platinum and carbon having a molar ratio of 0.09 eV and a carbon molar ratio of 53% (platinum: carbon = 47: 53) was used (Example 1 described later). In cyclic voltammetry when the current (mA) is taken on the vertical axis shown in FIG. 4, (1) shows the adsorption behavior of hydrogen ions, (2) shows the desorption behavior of hydrogen ions, (3 ) Shows the behavior of the oxide film formation, and (4) shows the behavior of the oxide film.

  The actual platinum area in the catalyst described above can be calculated from the cyclic voltammetry based on the value of the amount of electricity (C) for desorption of hydrogen atoms by the following equation.

Actual area of platinum (cm ² )
= Electricity of desorption of hydrogen atoms (C) / 210 × 10 ⁻⁶ (C / cm ² )
Here, 210 × 10 ⁻⁶ (C / cm ² ) of the denominator is a value according to the literature (Electrochemical Measurement Manual Practice Edition, Electrochemical Society, Maruzen Co., Ltd. p.116-117), and the actual area of platinum in the catalyst It is a value normally used in the calculation of.

  As described above, the composite catalyst of the present invention is excellent in poisoning resistance against carbon monoxide, and is a catalyst for a fuel cell electrode such as a solid polymer fuel cell including a direct methanol fuel cell ( It can be suitably applied as a catalyst for an anode electrode). In addition to use as a fuel cell electrode, use as a catalyst for removing carbon monoxide in hydrogen gas, a catalyst for treating and purifying exhaust gas, and the like is also expected.

  The composite catalyst of the present invention has a 4f orbital peak of platinum or a platinum-based alloy in the composite catalyst measured using an X-ray photoelectron spectroscopic analyzer within the range of 0.01 to 0.40 eV. The catalyst may be a composite catalyst of platinum or a platinum-based alloy and carbon that has shifted to the above, and the production method is not particularly limited, but PVD (Physical) is introduced while introducing a carbon source into platinum or the platinum-based alloy. It is preferably manufactured by a method of forming a film in a state where carbon is combined with platinum or a platinum-based alloy by performing a vapor deposition (CVD) method or a chemical vapor deposition (CVD) method. The present invention thus also provides a method for producing the composite catalyst of the present invention.

  As the PVD method and the CVD method used in the method for producing the catalyst of the present invention, various conventionally known PVD methods and CVD methods can be applied without particular limitation. Note that the PVD method includes a sputtering method, a vacuum deposition method, and the like. In the production method of the present invention, the PVD method or the CVD method is performed while introducing a carbon source into platinum or a platinum-based alloy, so that carbon is compounded into the platinum or platinum-based alloy, and the X-ray photoelectron spectroscopic analysis as described above is performed. A composite catalyst having a shift within a specific range of the peak of the 4f orbit of platinum or a platinum-based alloy measured using the apparatus is produced. According to such a production method of the present invention, the above-described composite catalyst of the present invention can be suitably produced, and a large area can be processed, so industrialization can be expected.

  FIG. 6 is a view schematically showing an example of an apparatus preferably used in the method for producing a catalyst of the present invention. In the manufacturing method of the present invention, sputtering at a relatively high vacuum is possible, and the target voltage can be controlled independently of the plasma generation mechanism. Therefore, using a quadrupole plasma sputtering apparatus such as the example shown in FIG. It is preferable to perform film formation while introducing a carbon source into the platinum-based alloy. As such a quadrupole plasma sputtering apparatus, for example, a VSD-61 quadrupole sputtering apparatus (manufactured by NEC) can be suitably used.

  In the quadrupole plasma sputtering apparatus of the example shown in FIG. 6, an anode 13 and a cathode 14 are provided facing each other in the reaction chamber 12 (in FIG. 6, the anode 13 is on the upper side and the cathode 14 is on the lower side with respect to the paper surface. Installation) A substrate 15 and a target 16 are provided to face each other between the anode 13 and the cathode 14 (in FIG. 6, the substrate 15 is installed on the left side and the target 16 is installed on the right side with respect to the paper surface). A stabilizing electrode 17 is provided in the vicinity of the cathode 14. The reaction chamber 12 is provided with an inlet 18 through which the raw material gas flows, and is configured so that the air in the reaction chamber 12 can be degassed by a vacuum pump 19. Further, an electromagnetic coil 20 is provided outside the reaction chamber 12.

  In the manufacturing method of the present invention, platinum or a platinum-based alloy is used as the target 16, and a mixed gas of a gas serving as a carbon source and a carrier gas is used as a raw material gas that flows into the reaction chamber 12 from the inlet 18. When a voltage is applied to the anode 13, the cathode 14, and the stabilization electrode 17 using such a four-pole plasma sputtering apparatus, and a voltage is applied to the target 16, thermoelectrons are emitted from the cathode 14, and these thermoelectrons Is drawn out to the center of the reaction chamber 12 by the stabilizing electrode 17 and discharge occurs between the anode 13 and the anode 13. Note that the voltage applied to the electrode for plasma generation and the voltage applied to the target 16 are controlled independently. The plasma generated by this discharge converges in the center of the reaction chamber 12 by the electromagnetic coil 20. Due to this plasma, atomic platinum or a platinum-based alloy is ejected from the target 16 and deposited on the substrate 15. At this time, platinum or a platinum-based alloy in an atomic state is deposited on the substrate 15 in a state where it is combined with carbon by a carbon source supplied into the reaction chamber 12. The composite catalyst of the present invention in which is combined is deposited on the substrate 15 to form a film.

  The carbon source used in the method for producing the catalyst of the present invention is not particularly limited, and for example, a compound containing carbon such as aliphatic hydrocarbon and aromatic hydrocarbon can be used. From the viewpoint that the complexing of carbon and carbon can be carried out smoothly and reliably, an aliphatic hydrocarbon or aromatic hydrocarbon having 1 to 7 carbon atoms as a carbon source, that is, methane, ethane, propane, butane, n-hexane, acetylene It is preferable to use ethylene, benzene or the like. This is because when the number of carbon atoms in the aliphatic hydrocarbon or aromatic hydrocarbon exceeds 7, the boiling point is high, and thus a carbon source heating device is required. Among these, methane or acetylene, which is inexpensive and gaseous at normal temperature, is used as a particularly preferable carbon source.

  As the carrier gas introduced into the reaction chamber 12 together with the carbon source, an inert gas usually used in this field such as argon, neon, helium, xenon and the like can be used without particular limitation. Among them, it is preferable to use argon, which is inexpensive and has a high sputtering rate, as the carrier gas.

The amount of the carbon source introduced in the method for producing a catalyst of the present invention is not particularly limited, but the pressure (partial pressure) of the gas serving as the carbon source with respect to the pressure of the entire raw material gas including the carrier gas is 2.5. It is preferable to be in the range of × 10 ^{−2 to} 1.0 × 10 ⁻¹ Pa. When the partial pressure of the gas serving as the carbon source is less than 2.5 × 10 ⁻² Pa, there is a possibility that the composite of platinum and carbon may not be observed, and the partial pressure of the gas serving as the carbon source is This is because when it exceeds 1.0 × 10 ⁻¹ Pa, it is considered that the reaction active point of platinum is hindered.

  In addition, each condition at the time of film formation in the method for producing a catalyst of the present invention is not particularly limited, and may be appropriately selected from film formation conditions usually performed in this field according to a desired catalyst composition. Can be applied. Specifically, when the quadrupole plasma sputtering apparatus of the example shown in FIG. 6 is used, the voltage applied for plasma generation is 60V, and the voltage applied to the target 16 is in the range of 100 to 1000V. The target 16 has a current of 15 to 35 mA and a film formation time of 20 to 30 minutes, which are exemplified as suitable conditions. However, the conditions are not limited to these.

  In the catalyst production method of the present invention, a conventionally known appropriate substrate can be applied as the substrate 15 used in the film formation according to the use of the composite catalyst produced by the present invention. For example, when the composite catalyst produced by the present invention is applied to the use of a catalyst for a fuel cell electrode as described above, a gas permeable electrode (carbon paper) or an electrolyte sheet used for the fuel cell electrode is used as a substrate. On top of that, the composite catalyst of the present invention can be deposited.

  In the method for producing a catalyst of the present invention, it is preferable to further perform a hydrogen plasma treatment after the above-described film formation. By performing the hydrogen-based plasma treatment after the film formation, as described above, the carbon molar ratio in the composite catalyst is in the range of 50 to 60%, and the composite exhibits particularly excellent poisoning resistance to carbon monoxide. It becomes possible to manufacture the catalyst. The reason why it is possible to produce a composite catalyst having a molar ratio of platinum within the above-mentioned particularly preferred range by performing hydrogenated plasma treatment is not clear in detail, but platinum or platinum finely divided by composite with carbon This is considered to be because carbon atoms are removed from the surface of the alloy and increase the catalytic active point.

In the case where film formation is performed using the four-pole plasma sputtering apparatus as shown in FIG. 6 described above, after the film formation, the same apparatus is used, and plasma treatment is performed while introducing a mixed gas of hydrogen and a carrier gas. You just have to do it. The amount of hydrogen introduced during the hydrogen-based plasma treatment is not particularly limited, but the pressure (partial pressure) in the mixed gas is 5.0 × from the trade-off between maintaining the plasma state and the treatment effect. It is preferably within the range of 10 ^{−2 to} 1.2 × 10 ⁻¹ Pa.

When hydrogen-based plasma treatment is performed after film formation, the conditions are not particularly limited. Specifically, the discharge voltage is 60 V, the discharge current is 8 A, and the hydrogen gas partial pressure is 1.0 × 10 ^{−. A} hydrogen-based plasma treatment performed under conditions such as ¹ Pa can be suitably employed.

  EXAMPLES Hereinafter, although an Example, a comparative example, and a reference comparative example are given and this invention is demonstrated in detail, this invention is not limited to these.

< Reference Example 1>
A quadrupole plasma sputtering apparatus (VDS-61 quadrupole sputtering apparatus (manufactured by NEC)) shown in FIG. 6 was used, platinum (purity: 99.9%) as a target, and cylindrical glassy carbon (triode described later) Was used as a working electrode in the electrochemical measurement of the formula, and film formation was performed while introducing methane gas (partial pressure: 7.5 × 10 ⁻² Pa) and argon gas as a carbon source from the inlet (total) (Gas pressure: 1.8 × 10 ⁻¹ Pa) The film forming conditions were an applied voltage for plasma discharge of 60 V, an applied voltage to the target of 750 V, and a time of 20 minutes.

  About the obtained composite catalyst, the value of the shift to the high energy side of the peak of the 4f orbit of platinum calculated by measurement using an X-ray photoelectron spectrometer (PHI 5700 ESCA (manufactured by Physical Electronics)) is It was 0.16 eV (curve B in FIG. 1). Moreover, when the molar ratio of platinum in the obtained composite catalyst was calculated using an X-ray photoelectron spectrometer (PHI 5700 ESCA (manufactured by Physical Electronics)), it was 80% (platinum: carbon = 20: 80). there were.

Further, cyclic voltammetry was prepared for the obtained composite catalyst by tripolar electrochemical measurement using the equipment shown in FIG. As described above, a composite catalyst formed on the end face of the cylindrical glassy carbon as the working electrode 3, a platinum wire as the counter electrode 4, and Ag / AgCl (sat. KCl) as the reference electrode 5 were used. 0.5 MH ₂ SO ₄ was used as the electrolyte accommodated in the water tank 2, and nitrogen (N ₂ ) was supplied to the electrolyte through the gas introduction pipe 6. Using such equipment, the potential between the working electrode 3 and the counter electrode 4 and between the reference electrode 5 and the working electrode 3 is measured using an electrochemical measurement system (made by Hokuto Denko), and cyclic voltammetry is performed. Created. Further, the value of the actual area of platinum calculated by dividing the atomic amount (C) of desorption of hydrogen obtained by cyclic voltammetry by the literature value of 210 × 10 ⁻⁶ (C / cm ² ) is 1.2 cm ² Met.

About the composite catalyst obtained in Reference Example 1, a mixed solution of 0.5 MH ₂ SO ₄ and 1 M CH ₃ OH (20 ° C.) as an electrolyte to be stored in the water tank 2 using the equipment shown in FIG. ), While supplying nitrogen (N ₂ ) into the electrolyte through the gas introduction tube 6, the decay rate (%) of the current density 120 minutes after the start of measurement was measured. The value of current density was specified (standardized) with the current density 30 seconds after the start of measurement as 1. The result is as shown by the curve B in FIG. 2 described above, and the current density decay rate was calculated to be 88.7%.

<Example 1 >
A composite catalyst was prepared in the same manner as in Reference Example 1 except that hydrogen plasma treatment was performed after film formation. The hydrogen-based plasma treatment was performed under the conditions that the hydrogen gas partial pressure was 1.0 × 10 ⁻¹ Pa, the total gas pressure was 1.8 × 10 ⁻¹ Pa, and the time was 10 minutes. With respect to the obtained composite catalyst, the value of the shift to the high energy side of the peak of the platinum 4f orbit calculated in the same manner as in Reference Example 1 is 0.09 eV (curve C in FIG. 1). The molar ratio of carbon in the composite catalyst was calculated to be 53% (platinum: carbon = 47: 53). The actual area value of platinum was 2.9 cm ² . For composite catalyst obtained in this Example 1 were measured the attenuation factor of similarly current density as in Reference Example 1 (%). The result is as shown by the curve C in FIG. 2 described above, and the current density decay rate was calculated to be 67.8%.

<Comparative Example 1>
Film formation was performed in the same manner as in Reference Example 1 except that only methane gas was introduced without introducing methane gas as the source gas (the total gas pressure was the same as in Reference Example 1). With respect to the obtained catalyst, the value of the peak shift of the 4f orbit of platinum calculated in the same manner as in Reference Example 1 was 0 eV (curve A in FIG. 1), and the molar ratio of platinum in the catalyst was calculated. However, it was 100% (platinum: carbon = 100: 0). The actual area value of platinum in the obtained catalyst was 0.43 cm ² . For the catalyst obtained in Comparative Example 1, the current density decay rate (%) was measured in the same manner as in Reference Example 1. The result is as shown by the curve A in FIG. 2 described above, and the current density decay rate was calculated to be 97.0%.

< Reference Example 2 >
A film was formed in the same manner as in Reference Example 1 except that the partial pressure of methane gas in the source gas was 5.0 × 10 ⁻² Pa (the total gas pressure was the same as in Reference Example 1). With respect to the obtained catalyst, the value of shift of the peak of 4f orbit of platinum to the high energy side calculated in the same manner as in Reference Example 1 was 0.19 eV, and the molar ratio of carbon in the catalyst was calculated. It was 90% (platinum: carbon = 90: 10). Further, the value of the actual area of platinum in the obtained catalyst was 0.84 cm ² . When the decay rate (%) of the current density was measured in the same manner as in Reference Example 1 for the catalyst obtained in Reference Example 2 , it was calculated to be 86.5%.

<Comparative example 2>
Film formation was performed in the same manner as in Reference Example 1 except that the partial pressure of methane gas in the source gas was 1.2 × 10 ⁻² Pa (total gas pressure was the same as in Reference Example 1). With respect to the obtained catalyst, the peak shift value of platinum 4f orbit calculated in the same manner as in Reference Example 1 was 0 eV, and the platinum molar ratio in the catalyst was calculated to be 100% (platinum: carbon = 100: 0). Further, the value of the actual area of platinum in the obtained catalyst was 0.39 cm ² . When the decay rate (%) of the current density was measured for the catalyst obtained in Comparative Example 2 in the same manner as in Reference Example 1, it was calculated to be 98.5%.

<Example 2 >
Film formation was performed in the same manner as in Example 1 except that the partial pressure of methane gas in the raw material gas was 5.0 × 10 ⁻² Pa (total gas pressure was the same as in Reference Example 1). About the obtained catalyst, the value of the shift to the high energy side of the peak of the platinum 4f orbit calculated in the same manner as in Reference Example 1 was 0.06 eV, and the molar ratio of carbon in the catalyst was calculated. It was 4% (platinum: carbon = 96: 4). Further, the value of the actual platinum area in the obtained catalyst was 0.66 cm ² . When the decay rate (%) of the current density was measured for the catalyst obtained in Example 2 in the same manner as in Reference Example 1, it was calculated to be 86.2%.

< Reference Example 3 >
Film formation was performed in the same manner as in Example 1 except that the partial pressure of methane gas in the raw material gas was 1.0 × 10 ⁻¹ Pa (total gas pressure was the same as in Reference Example 1). About the obtained catalyst, the value of shift to the high energy side of the peak of the platinum 4f orbit calculated in the same manner as in Reference Example 1 was 0.05 eV, and the molar ratio of carbon in the catalyst was calculated. It was 57% (platinum: carbon = 43: 57). Further, the value of the actual area of platinum in the obtained catalyst was 0.71 cm ² . When the decay rate (%) of the current density was measured in the same manner as in Reference Example 1 for the catalyst obtained in Reference Example 3 , it was calculated to be 69.5%.

<Reference Comparative Example>
In Non-Patent Documents 2 and 3, regarding the poisoning resistance to carbon monoxide in the methanol decomposition reaction in the platinum fine particle catalyst-supporting carbon electrode which is the prior art, the current density decay rate after 120 minutes is 75 to 78%. Are listed. Non-Patent Document 4 describes that the decay rate of current density after 10 minutes is 100% regarding the poisoning resistance against carbon monoxide in the methanol decomposition reaction in the platinum-based catalyst-supporting carbon electrode which is the prior art. ing.

  It should be understood that the embodiments, examples and comparative examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

FIG. 5 is a graph showing the results of measurement using an X-ray photoelectron spectroscopy analyzer (ESCA: Electron Spectroscopy for Chemical Analysis) for the composite catalyst of the present invention and conventional platinum, where the vertical axis represents intensity (Arb. Units), and horizontal The axis is the binding energy (eV). It is a graph which shows the poisoning tolerance with respect to the carbon monoxide of the composite catalyst of this invention, a vertical axis | shaft is the standardized current density and a horizontal axis is time (minutes). It is a figure which shows typically the installation used for a tripolar electrochemical measurement. It is a graph which shows an example of the cyclic voltammetry of the composite catalyst of this invention, and the conventional platinum catalyst, A vertical axis | shaft is an electric current (mA), and a horizontal axis is an electric potential (V vs Ag / AgCl) (electrolyte: 0.5M). H ₂ SO _4). 2 is a graph showing an example of cyclic voltammetry of the composite catalyst of the present invention and a conventional platinum catalyst, where the vertical axis represents current density (mA / cm ² ) and the horizontal axis represents potential (V vs Ag / AgCl) (electrolyte). : 0.5 MH ₂ SO ₄ +1 M CH ₃ OH). It is a figure which shows typically an example of the apparatus preferably used for the manufacturing method of the catalyst of this invention.

Explanation of symbols

  2 Water tank, 3 working electrode, 4 counter electrode, 5 reference electrode, 12 reaction chamber, 13 anode, 14 cathode, 15 substrate, 16 target, 17 stabilizing electrode, 18 inlet, 19 vacuum pump, 20 electromagnetic coil.

Claims (3)

  By performing a PVD method or a CVD method while introducing a carbon source into platinum or a platinum-based alloy, a film is formed in a state where carbon is combined with platinum or a platinum-based alloy, and then a hydrogen-based plasma treatment is performed. A method for producing a catalyst for a fuel cell electrode.   The method according to claim 1, wherein an aliphatic hydrocarbon or an aromatic hydrocarbon having 1 to 7 carbon atoms is used as a carbon source. A catalyst for a fuel cell electrode produced by the method according to claim 1 or 2,
A platinum or platinum-based alloy and carbon composite catalyst, wherein the 4f orbital peak of platinum or platinum-based alloy of the composite catalyst measured using an X-ray photoelectron spectrometer is 0.01-0. A catalyst for a fuel cell electrode, wherein the catalyst is shifted to a high energy side within a range of 40 ev.

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