JP2007042519A - Catalyst for fuel cell, its manufacturing method, and electrode for fuel cell and fuel cell using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for fuel cell inexpensive, safely synthesized, and substitutable for a noble metal catalyst such as platinum, and capable of exerting excellent catalyst action; and to provide an electrode for fuel cell and a fuel cell using the catalyst for fuel cell. <P>SOLUTION: The catalyst for fuel cell wherein a compound including sulfur (S) and ruthenium (Ru) element is adhered on a substrate as an active ingredient is characterized in that hydrogen sulfide is not used in a synthesis process of the compound, and a precursor of the compound is carried on the substrate which is not processed by hydrogen sulfide and then fired. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to a fuel cell catalyst produced without using hydrogen sulfide and having a compound containing sulfur (S) and ruthenium (Ru) elements as active components deposited on a substrate, a method for producing the same, and a method for producing this fuel cell. The present invention relates to a fuel cell electrode and a fuel cell using a catalyst.

  In recent years, in order to further improve energy efficiency and solve environmental problems, attempts have been made to clean exhaust gas by using a fuel cell as a power source for automobiles. It has been. In particular, development of a polymer electrolyte fuel cell (PEFC) as a fuel cell for a fuel vehicle (FCHV) has been rapidly progressing.

  A fuel cell is a power generator that supplies fuel to the anode and oxidant to the cathode, takes out the potential difference between the anode and cathode as voltage, and supplies it to the load. Hydrogen is commonly used as the anode fuel, and oxidant is generally used as the oxidant. For this, oxygen in the air is used. A fuel cell is composed of an anode and a cathode and an electrolyte sandwiched between them. In a polymer electrolyte fuel cell, an ion exchange membrane is used as an electrolyte. Specifically, a catalyst layer is formed on both surfaces of an ion exchange membrane as an electrolyte, and an anode gas diffusion layer and a cathode gas / fuel diffusion layer are integrally formed outside the catalyst layer, respectively. A fuel cell is constructed by stacking several tens to several hundreds of cells as unit cells composed of a laminate of a partition plate, an electrolyte membrane / electrode assembly, and a partition plate so as to obtain a desired voltage according to the application. Has been.

  In such a fuel cell, when hydrogen reaches the anode catalyst layer, protons and electrons are generated by an electrochemical reaction process. Protons generated here move sequentially in the electrolyte and reach the cathode. On the other hand, electrons are sent to the cathode via an external load. In the cathode catalyst layer, electrons sent via an external load, oxygen in the air as an oxidant, and protons that have moved through the electrolyte combine to form water through an electrochemical reaction process. .

  Conventionally, as a catalyst for such a fuel cell, a catalyst mainly composed of a noble metal such as platinum, which is expensive and has a problem in terms of a supply compound, has been used for both the cathode and the anode. It is considerably larger than the amount of platinum used for the exhaust gas purification catalyst of gasoline cars that generate NO.

  Therefore, in order to commercialize a fuel cell, a fuel cell catalyst that can be used practically at low cost instead of a catalyst mainly composed of noble metals such as platinum, which is problematic in terms of cost and supply compounds. Development is one of the essential issues.

Non-Patent Document _{1, Ru 5 W 2 S 5} , Ru 5 Mo 2 Ru 3 which is a precursor compound of the _{S 5 (CO) 12, W} (CO) 6 and Mo _{(CO) 6} and sulfur and carbon black ( Vulcan XC-72R) is refluxed in xylene under nitrogen atmosphere for 20 hours, then filtered, heat-treated at 350 ° C. for 2 hours, and used as a cathode catalyst for DMFC (Direct Methanol Fuel Cell). However, in this document, carbon black (Vulcan XC-72R) is functionalized using highly toxic hydrogen sulfide gas, which is not preferable because of high risk in catalyst synthesis.

On the other hand, Patent Document _{1, Ru x M y S (} M = Ni, Re, Cr, Mo, Ir) salts, for example, after the chloride was mixed with the carbon-based substrate, hydrogen sulfide after the solvent was distilled off The ruthenium sulfide compound supported on the carbon-based substrate is obtained by storing in a gas and then calcining at 100 ° C. or higher, preferably 300 ° C. to 500 ° C. in a hydrogen sulfide gas atmosphere. However, even in this method, since highly toxic hydrogen sulfide gas is essential, there is a high risk in catalyst synthesis, which is not preferable.

As described above, it is conventionally known that an active component compound can be used as a catalyst for a fuel cell. However, in any case, a process using highly toxic hydrogen sulfide is included. The technology for making a fuel cell catalyst that can be substituted for a noble metal catalyst such as platinum by safely synthesizing the fuel cell catalyst deposited on the catalyst and further exhibiting sufficient activity as a fuel cell catalyst. The current situation is not established.
J. Electrochem. Soc., 145, 3463, (1998) WO2004 / 106591

  The present invention is inexpensive, can be safely synthesized, can be replaced with a noble metal catalyst such as platinum, and exhibits a superior catalytic action, and a fuel cell electrode using the fuel cell catalyst It is another object of the present invention to provide a fuel cell.

  As a result of intensive studies in view of the above circumstances, the present inventors have mixed a ruthenium zero-valent precursor compound with a substrate, and then calcined it in an inert gas atmosphere such as argon without using hydrogen sulfide gas. It has been found that a fuel cell catalyst can be obtained that is inexpensive, safe, has high catalytic activity, and has practical utility that can be substituted for a noble metal catalyst such as platinum. The present invention has been completed based on such knowledge.

  That is, the present invention relates to a fuel cell catalyst characterized in that a compound containing sulfur (S) and ruthenium (Ru) elements as active components is deposited on a substrate. The present invention provides a catalyst for a fuel cell containing the compound, characterized in that the precursor of the compound is supported on a substrate that does not use hydrogen and is not treated with hydrogen sulfide and then calcined.

  The present invention also provides a fuel cell electrode comprising the fuel cell catalyst described above.

  The present invention also provides a fuel cell using the fuel cell electrode described above.

  The present invention also relates to a method for producing a fuel cell catalyst, characterized in that a compound containing sulfur (S) and ruthenium (Ru) elements as active components is deposited on a substrate. For a fuel cell containing an active ingredient compound, characterized in that hydrogen sulfide is not used in the compound synthesis process and the precursor of the compound is supported on a carbon-based substrate that is not treated with hydrogen sulfide and then fired. A method for producing a catalyst is provided.

  According to the present invention, a practical catalyst for a fuel cell that can be replaced with a noble metal catalyst such as platinum, which is expensive and has a problem in terms of a supply compound, shows a good catalytic action and can be synthesized safely at low cost. A fuel cell electrode and a fuel cell using the fuel cell catalyst can be provided.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present invention.

[Fuel cell catalyst]
The fuel cell catalyst in the present invention is a fuel cell catalyst in which a compound containing sulfur (S) and ruthenium (Ru) elements as active components is deposited on a substrate, and is manufactured without using hydrogen sulfide. It is characterized by.

<Active ingredient>
In addition to sulfur and Ru, the active component may further contain one or more elements of tungsten (W), molybdenum (Mo), and rhenium (Re). Sulfur in the active ingredient is usually 0.3% or more by weight, preferably 1% or more, more preferably 5% or more, usually 76% or less, preferably 72% or less, more preferably, based on the whole active ingredient. 65% or less. If the lower limit is not reached, the activity tends to be low, and even if the upper limit is exceeded, the activity is difficult to occur.

  The total amount of tungsten, molybdenum and rhenium in the active ingredient is usually 24% or more, preferably 28% or more, more preferably 35% or more, usually 99.7% or less, preferably 99% with respect to the whole active ingredient. Below, more preferably 95% or less. If the lower limit is not reached, the activity tends to be low, and even if the upper limit is exceeded, the activity is difficult to occur.

In the active ingredient of the present invention, sulfur, in addition to S _elements, S ₂ ^{O 3} oxide ^{_{2-like, HS 2 O 3 -, H}} 2 S 2 O 3 and the like inorganic compounds such as thiosulfate ions and thiosulfate , And organic compounds such as thiophene. On the other hand, Ru, W, Mo and Re can also take the form of inorganic compounds and organic compounds such as metal elements, sulfides and oxides. For example, in the case of ruthenium, in addition to Ru elements, RuS, RuS ₂ etc. Or an inorganic compound such as an oxide such as RuO or RuO ₂ , and an organic compound such as Ru ₃ (CO) ₁₂ . In addition, in the active ingredient which concerns on this invention, it is also possible to contain components other than a sulfur element and Ru, W, Mo, and Re in the range which does not impair the effect of this invention.

  The sulfur component and the metal components of Ru, W, Mo, and Re constituting the active component may be present without a bond or may be present with a bond. When the metal elements are directly bonded to each other, the active component includes a so-called alloy form.

Specific examples of the active component having an alloy form include Ru ₅ W ₂ S ₅ and Ru ₅ Mo ₂ S ₅ .

  The presence form of the active component in the fuel cell catalyst of the present invention can be confirmed by X-ray diffraction (XRD). That is, for example, it can be confirmed by irradiating an active ingredient deposited on a substrate described later with X-rays (Cu-Kα rays) and observing the diffraction spectrum thereof.

  Examples of the measurement apparatus and measurement conditions include the following, but the XRD analysis method for the fuel cell catalyst of the present invention is not limited to the following measurement apparatus and measurement conditions.

(Powder XRD analysis)
Measuring device X-ray powder analysis device / PANallytical PW1700
Measurement conditions X-ray output (Cu-Kα): 40 kV, 30 mA
Scanning axis: θ / 2θ
Measurement range (2θ): 3.0 ° to 70.0 °
Measurement mode: Continuous
Reading width: 0.05 °
Scanning speed: 3.0 ° / min
DS, SS, RS: 1 °, 1 °, 0.20mm

Specifically, RuS ₂ is a 2θ (± 0.3 °) peak of X-ray diffraction,
27.513 °, 31.874 °, 35.756 °, 39.302 °, 45.699 °, 54.174 °, 56.795 °, 59.340 °, 61.820 °, 73.516 °, Characteristic peaks such as 75.756 ° and 84.533 ° are given.

<Substrate>
The substrate used in the present invention is not particularly limited except that the hydrogen sulfide treatment is not performed, and the use of a carbon-based substrate is preferable in that high catalytic activity is obtained.

  Various carbon-based substrates can be used and are not particularly limited. Examples thereof include carbon black, carbon nanotube, carbon nanohorn, carbon nanocluster, fullerene, pyrolytic carbon, and activated carbon.

  Among these, carbon black is industrially advantageous in terms of conductivity, availability, price, etc. Specifically, as carbon black, channel black, furnace black, thermal black, acetylene black Oil furnace black, gas furnace black and the like.

  Also preferred are nanotubes or vapor grown carbon fiber (hereinafter, sometimes abbreviated as “VGCF”) by vapor phase method, and especially VGCF which has been heat-treated to increase electrical conductivity is suitable. It has elasticity and is suitable. These can be used alone or in combination of two or more.

Although there is no particular limitation on the specific surface area of the substrate, it is preferable ^{5 m} 2 / g or more 2000m ² / g or less. The form of the substrate is not particularly limited, but the most commonly used is a powder form.

<Adhesion of active ingredient to substrate>
In the present invention, the state in which the active ingredient is deposited on the substrate refers to a state in which both are in contact with each other so as to obtain electrical conductivity between the active component and the substrate. Accordingly, the active ingredient can be deposited on the substrate by simply mixing the active component and the substrate, but it is preferable to calcine the mixture after the active component precursor is supported on the substrate. In the following, the preparation method in which the substrate is supported on a substrate, dried as necessary, and then fired and deposited is referred to as “supported firing”.

  The shape of the active ingredient applied to the substrate is not particularly limited, but the most common is a particulate form. The upper limit of the average particle diameter of the particulate deposited active ingredient is usually 100 μm or less, preferably 1000 nm or less, more preferably 500 nm or less, especially 300 nm or less, and the lower limit is usually 0.5 nm or more, preferably 1 nm or more. Preferably it is 2 nm or more. When the particle size of the active ingredient is less than this lower limit, it becomes unstable and easily deactivated, and when it exceeds the upper limit, it becomes difficult to obtain high activity.

  The average particle size of the active ingredient deposited on the substrate is determined by unifying the direction in which the particle length is measured with a scanning electron microscope (SEM) or transmission electron microscope (TEM). The particle length is measured and indicated as an average value.

  In order to deposit such a smaller average particle size or the above-mentioned specific crystal active component on the substrate, the manufacturing method may be devised as described later. In particular, the substrate and the active component are mixed. A preferable method is to control the crystal growth state by lowering the firing temperature after the annealing and shortening the firing time.

  The ratio of the active ingredient to the substrate is not limited, but the weight ratio of active ingredient / (active ingredient + substrate) is usually 0.001 or more, preferably 0.01 or more, especially as the lower limit. It is 0.05 or more, and the upper limit is usually 0.95 or less, preferably 0.4 or less, and particularly preferably 0.3 or less. If the deposition ratio of the active ingredient is below this lower limit, the desired activity cannot be obtained, and if it exceeds the upper limit, the activity improvement effect due to deposition is less likely to occur.

<Other catalyst components>
In the present invention, a transition metal can be used in combination as long as the effects of the present invention are not impaired (hereinafter abbreviated as “other catalyst component”).

  Other catalyst components include elements belonging to the 4th to 6th groups of groups 3A to 7A, 8 and 1B of the periodic table. For example, titanium (Ti), vanadium (V), chromium ( Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), yttrium (Y), zirconium (Zr), niobium (Nb), rhodium (Rh), palladium ( Pd), silver (Ag), lanthanum (La), europium (Eu), platinum (Pt), gold (Au), cerium (Ce), tantalum (Ta), praseodymium (Pr), iridium (Ir), neodymium ( Nd) and the like are exemplified.

Preferably, the following electrochemical equilibrium formula
Oxidizer + ne ⁻ = Reductant
It is desirable that the standard electrode potential E ° (25 ° C.) in the aqueous solution is positive. This is because elution due to oxidation is unlikely to occur as a natural property of metals, and there is little deterioration of the catalyst due to it. Specific examples of such materials include gold, iridium, palladium, silver, rhodium, and the like.

  However, in order to make the catalyst more industrially advantageous, it is better to reduce the number of expensive catalyst components as much as possible. Of course, platinum (Pt) can be used in combination as a transition metal. However, since platinum is expensive, it is inexpensive and practical to add a small amount while considering the desired catalytic activity. It is desirable to provide a fuel cell catalyst.

  In addition, the following shows the electrochemical equilibrium formula of main transition metals and the standard electrode potential E ° (25 ° C.).

  These other catalyst components may be used individually by 1 type, and may use 2 or more types together.

When other catalyst components are used in combination as a cocatalyst, examples of the combined form of the other catalyst components include the following.
(1) Other catalyst components are mixed with the active component together with the substrate.
(2) The active component and other catalyst components are supported and fired on the substrate.
(3) The active component supported and fired on the substrate is mixed with other catalyst components.
(4) The active component supported and fired on the substrate is further supported and fired with other catalyst components.
(5) The other catalyst component supported and calcined on another substrate is mixed with the active component.
(6) The other catalyst component supported and fired on another substrate is mixed with the active component supported and fired on the substrate.

  When other catalyst components are used, the other catalyst components are generally 0.001 or more, preferably 0.01 or more as a lower limit in terms of the total weight of the other catalyst components / weight ratio of the active components with respect to the active components. It is preferably 0.05 or more and used so that the upper limit is usually 0.5 or less, preferably 0.4 or less, especially 0.3 or less. If the lower limit is not reached, the desired activity cannot be obtained, and if the upper limit is exceeded, the activity improving effect is hardly obtained.

  The other catalyst component is preferably in the form of powder, and the average particle size in this case is usually 1000 nm or less as an upper limit, preferably 500 nm or less, especially 300 nm or less, and the lower limit is usually 0.5 nm or more. preferable. Below this lower limit, it becomes unstable and easily deactivated, and when it exceeds the upper limit, it becomes difficult to obtain high activity.

  Use of such other catalyst components in combination is particularly preferable because the catalyst activity can be enhanced by using the other catalyst components supported and fired on the substrate together with the active components. Although the details of the action mechanism of the effect of improving the catalytic activity by using other catalyst components in combination, in particular, by supporting and firing the other catalyst components on the substrate together with the active component are not necessarily clear, the transition metals of other catalyst components are active. It is estimated that the activity is improved because it functions as a co-catalyst for the component.

  In the fuel cell catalyst of the present invention, a metal component other than the transition metal element, that is, a substance other than the other catalyst component may be contained in an amount of several mass% or less based on the weight of the active component. In the object and effect of the present invention, it is acceptable.

<Manufacture of a deposited catalyst>
The fuel cell catalyst of the present invention is produced by adhering an active component to a substrate. In the present invention, the active component compound is synthesized and the substrate is not treated with hydrogen sulfide gas. . Here, the active component may be applied to the substrate by, for example, a method in which the active component or a precursor of the active component is supported on the substrate and then firing, a mixing method in which the active component and the substrate are simply mixed, and other impregnation methods. Further, it can be carried out by a known method such as a precipitation method or an adsorption method. Hereinafter, when the active component before firing, that is, the “precursor” is referred to when focusing on the element of the active component, it is referred to as an element supply compound or simply an element supply compound.

  For example, in a catalyst in which an active component is supported and calcined on a substrate, an element supply compound of the active component is dissolved or dispersed in an organic solvent or the like at a desired molar ratio, impregnated or immersed in a carbonaceous support, and then filtered or solvent. The compound supported on the substrate is obtained by distilling off and then heated by heating at a predetermined temperature in an inert gas atmosphere such as nitrogen.

  As described above, the method for synthesizing the active ingredient used in the present invention is characterized in that hydrogen sulfide is not used, but there is no particular limitation except that point, and it can be carried out by any known method.

The feed compounds of the respective elements is not particularly limited as long as it can be thermally decomposed, if sulfur-donating compound, other sulfur powder (S), tetrathiafulvalene _{(tetrathiafulvalene, C 6 H 4 S} 4) and the like Is mentioned.

The active component ruthenium element supply compound is not particularly limited as long as it provides a desired active component compound without using hydrogen sulfide, but a Ru zero-valent compound is preferable. Specifically, carbon atom coordinated ruthenium complexes such as carbonyl ligands, cyclopentadienyl ligands, olefinic ligands, nitrogen atom coordinated ruthenium complexes such as pyridine ligands, acetonitrile ligands, phosphines And a phosphorus atom-coordinated ruthenium complex such as a ligand or a phosphite ligand. Further, it may be a complex having a plurality of these ligands or a complex having a plurality of types of ligands. Hydrocarbon ligands and carbonyl ligands that do not leave a nitrogen atom or phosphorus atom in the final product are preferred. Specifically, Ru ₃ (CO) ₁₂ , (COD) Ru (CO) ₃ (“COD” represents “1,5-cyclooctadiene”, the same shall apply hereinafter), Ru ₂ (CO) _{9 and the} like. Is mentioned.

The present invention is also characterized in that hydrogen sulfide is not used when introducing Mo, W, or Re atoms into the active component. The Mo, W, and Re element supply compounds are not limited as long as they provide the desired active component without using hydrogen sulfide, but those with zero valence are preferable for each precursor. It is mentioned as a thing. Specifically, carbon atom coordinated ruthenium complexes such as carbonyl ligands, cyclopentadienyl ligands, olefinic ligands, nitrogen atom coordinated ruthenium complexes such as pyridine ligands, acetonitrile ligands, phosphines And a phosphorus atom-coordinated ruthenium complex such as a ligand or a phosphite ligand. Further, it may be a complex having a plurality of these ligands or a complex having a plurality of types of ligands. Hydrocarbon ligands and carbonyl ligands that do not leave a nitrogen atom or phosphorus atom in the final product are preferred. Specific examples include (COD) Mo (CO) ₄ , Mo (CO) ₆ , W (CO) ₆ , (COD) W (CO) ₄ , (CO) ₁₀ Re _{2, and the} like. These feed compounds may be used alone or in a combination of two or more.

Specifically, as a synthesis method for carrying and firing an active ingredient on a substrate, for example, Ru ₃ (CO) _{12 and the} like, W (CO) ₆ and sulfur are mixed in an organic medium (eg, In a hydrocarbon such as xylene and toluene, alcohols such as ethanol, carbonyls such as acetone, ethers such as tetrahydrofuran, and the like, a predetermined amount of a substrate such as carbon black is mixed, and a predetermined time (usually 10). Minutes or more, preferably 30 minutes or more, usually 50 hours or less, preferably 30 hours or less). In this case, ultrasonic treatment may be performed.

  Next, in an inert gas atmosphere such as nitrogen, argon, etc., at a predetermined temperature (usually 60 ° C. or higher, preferably 100 ° C. or higher, usually 300 ° C. or lower, preferably 200 ° C. or lower) for a predetermined time (normally 10 minutes or longer, Is 30 minutes or more, usually 50 hours or less, preferably 30 hours or less). Heating or refluxing, and then removing the solvent by filtration or evaporator to obtain a precipitate. After drying, in an inert gas atmosphere such as nitrogen, argon, etc., for a predetermined time (usually 10 minutes or more, preferably 30 minutes or more, usually 50 hours or less, preferably 30 hours or less), a predetermined temperature (usually 100 ° C. or more, Preferably, the active component can be generated and supported and fired on the substrate by heating at 200 ° C. or higher and 1000 ° C. or lower, preferably 800 ° C. or lower.

  Thereafter, in an inert gas atmosphere having a low oxygen concentration (for example, an oxygen concentration of about 5% by mass or less, especially about 2% by mass or less) for a predetermined time (usually several tens of minutes, preferably 30 minutes or more, usually 10%). It is also possible to perform a passivation treatment for forming a passive film by treatment at a predetermined temperature (usually around room temperature) for a time or less, particularly 5 hours or less.

  Moreover, an active ingredient can also be made to adhere by preparing an active ingredient beforehand, mixing this with a base | substrate and kneading | mixing with a mortar etc. This mixing may be dry or wet, but preferably it is wet-mixed using a medium such as alcohol or ether and then dried at about 100 to 200 ° C.

  As a method of preparing the active ingredient in advance, the present invention is characterized in that hydrogen sulfide gas is not treated in the process of synthesizing the active ingredient compound. For example, it is prepared by dissolving or dispersing the element supply compound of the active ingredient in an organic solvent or the like at a desired molar ratio, filtering or distilling off the solvent, and then heating at a predetermined temperature in an inert gas atmosphere such as nitrogen. The

Specifically, for example, Ru ₃ (CO) _{12 and the} like, W (CO) ₆ and sulfur are blended in accordance with a desired molar ratio in an organic medium (for example, hydrocarbons such as xylene and toluene, ethanol, etc. Alcohol, carbonyls such as acetone, ethers such as tetrahydrofuran) and left for a predetermined time (usually 10 minutes or more, preferably 30 minutes or more, usually 50 hours or less, preferably 30 hours or less). If necessary, next, under an inert gas atmosphere such as nitrogen or argon, at a predetermined temperature (usually 60 ° C or higher, preferably 100 ° C or higher, usually 300 ° C or lower, preferably 200 ° C or lower) for a predetermined time (usually 10 ° C). Min. Or more, preferably 30 min. Or more, usually 50 hours or less, preferably 30 hours or less) Heating or refluxing, and then removing the solvent by filtration or evaporator to obtain a precipitate.

  After drying, in an inert gas atmosphere such as nitrogen, argon, etc., for a predetermined time (usually 10 minutes or more, preferably 30 minutes or more, usually 50 hours or less, preferably 30 hours or less), a predetermined temperature (usually 100 ° C. or more, Preferably, the active component can be generated and supported and fired on the substrate by heating at 200 ° C. or higher and 1000 ° C. or lower, preferably 800 ° C. or lower.

  Thereafter, in an inert gas atmosphere having a low oxygen concentration (for example, an oxygen concentration of about 5% by mass or less, especially about 2% by mass or less) for a predetermined time (usually several tens of minutes, preferably 30 minutes or more, usually 10%). It is also possible to perform a passivation treatment for forming a passive film by treatment at a predetermined temperature (usually around room temperature) for a time or less, particularly 5 hours or less.

  In the present invention, among the above-described catalyst production methods, a method in which an active component or an element supply compound of an active component ((compound) precursor) is supported on a carbon-based substrate and then calcined is preferable. Can be improved. The reason why the activity can be improved by carrying the support firing in this way is not necessarily clear, but since the active ingredient is deposited on the carbon-based substrate, the sintering of the active ingredient is suppressed during firing. Furthermore, it is estimated that the activity is improved. Particularly preferred is a method in which an active ingredient element supply compound ((compound) precursor) is supported on a carbon-based substrate and then fired.

  When the above-mentioned other catalyst component is applied to the substrate together with the active component, the other catalyst component may be applied at the same time in the active component application step, and the other component may be applied before or after the active component application step. A catalyst component may be deposited. Here, the “active component deposition step” includes the treatment process for depositing the active component, that is, the entire process from the addition of the active component supply compound to the provision of the active component.

  Transition metal supply compounds for depositing other catalyst components on the substrate include oxides, inorganic acid salts such as nitrates, sulfates and carbonates, organic acid salts such as acetates, halides and hydrides. , Carbonyl compounds, amine compounds, olefin coordination compounds, phosphine coordination compounds, or phosphite coordination compounds, etc., preferably halogen-free oxides, carbonates, organic acid salts, carbonyl compounds, olefin coordinations. Is a coordination compound. These may be used alone or in combination of two or more.

  Specifically, in order to deposit another catalyst component together with the active component on the substrate, for example, a transition metal compound such as a carbonyl compound is dissolved in the catalyst obtained by supporting and firing the active component synthesized by the method described above. The solution is added and allowed to stand for a predetermined time (usually 10 minutes or more, preferably 30 minutes or more, usually 50 hours or less, preferably 30 hours or less), and then the solvent is distilled off with an evaporator or the like. In this case, ultrasonic treatment may be performed. Next, after drying, a predetermined time (usually 10 minutes or more, preferably 30 minutes or more, usually 50 hours or less, preferably 30 hours or less) and a predetermined temperature (usually 100 hours or less) in an inert gas atmosphere such as nitrogen or argon. The fuel cell catalyst in which the active component compound and the other catalyst component are both supported and calcined on the substrate is obtained by heating at a temperature of not lower than ° C., preferably not lower than 200 ° C., not higher than 1000 ° C., preferably not higher than 800 ° C.

  Thereafter, in an inert gas atmosphere having a low oxygen concentration (for example, an oxygen concentration of about 5% by mass or less, especially about 2% by mass or less) for a predetermined time (usually several tens of minutes, preferably 30 minutes or more, usually 10%). It is also possible to perform a passivation treatment for forming a passive film by treatment at a predetermined temperature (usually around room temperature) for a time or less, particularly 5 hours or less.

  As described above, the other catalyst component may be used as it is mixed with the substrate on which the active component is supported and calcined, or the active component is mixed with the substrate on which other catalyst component is supported and calcined. Also good.

[Fuel cell electrode and fuel cell]
The fuel cell electrode of the present invention is characterized by containing the above-described fuel cell catalyst of the present invention. The fuel cell of the present invention is characterized by using such a fuel cell electrode of the present invention.

  The fuel cell according to the present invention is a power generator that supplies fuel to the anode and oxidant to the cathode, takes out the potential difference between the anode and cathode as a voltage, and supplies it to the load as described above. In a polymer electrolyte fuel cell, an ion exchange membrane is used as an electrolyte. That is, an electrolyte membrane / electrode assembly in which a catalyst layer is formed on both surfaces of an ion exchange membrane as an electrolyte, and an anode gas diffusion layer and a cathode gas / fuel diffusion layer are integrally formed on the outside of the catalyst layer, respectively. ing. The electrolyte membrane / electrode assembly has a partition plate disposed on the diffusion layer side, and several tens of cells until the unit cell of the partition plate, electrolyte membrane / electrode assembly, and partition plate has a desired voltage according to the application. Several hundred cells are stacked to form a fuel cell.

  In the present invention, the aforementioned fuel cell catalyst of the present invention is used as a catalyst for forming the catalyst layer of the electrolyte membrane / electrode assembly.

  An ion exchange membrane as an electrolyte is only required to have a cation exchange capacity, but it is practically desired to withstand an oxidation-reduction atmosphere at a temperature of about 80 to 100 ° C., which is a use temperature of a fuel cell. Alkyl sulfonic acid resins are exclusively used. Specific examples include perfluoroalkylsulfonic acid resin membranes such as Nafion (manufactured by DuPont, registered trademark), Flemion (manufactured by Asahi Glass, registered trademark), and Aciplex (registered trademark, manufactured by Asahi Kasei).

  As the thickness of the ion exchange membrane, a thickness of about 10 μm or more and about several 100 μm or less is used, but it is desirable to make the thickness thinner in order to lower the electric resistance. Taking Nafion as an example, Nafion 115 having a thickness of about 120 μm is often used, but an electrolyte of 30 μm to 50 μm has begun to be developed with a reinforcing material, and these can be used in the same manner.

  As the constituent material of the diffusion layer, hydrogen is supplied to the anode and air is supplied to the cathode, and also has a function as a current collector for taking out the generated voltage. A material that allows both gases of air to flow and withstands the use atmosphere is selected. As a material constituting the anode fuel diffusion layer and the cathode gas / fuel diffusion layer, a carbon porous body such as carbon paper or carbon cloth having a thickness of usually about 100 to 500 μm, preferably about 100 to 200 μm is used.

  When an electrolyte membrane / electrode assembly is used in a fuel cell, a partition plate made of a material such as carbon, and in some cases, stainless steel, titanium, etc. is usually disposed behind the membrane to prevent hydrogen and air from mixing. In general, the partition plate is formed with grooves for the purpose of uniform and stable supply of hydrogen and air.

  Although there is no restriction | limiting in particular as a method of producing the electrolyte membrane / electrode assembly of a fuel cell by forming a catalyst layer using the catalyst for fuel cells of this invention, For example, the following methods are mentioned.

  Although there is no restriction | limiting in particular about the method of producing a cathode side catalyst layer and an anode side catalyst layer, For example, it can produce as follows. First, the fuel cell catalyst of the present invention obtained by adhering an active ingredient to a substrate is placed in a suitable container, and a Nafion solution (concentration 5 mass%, manufactured by Aldrich) in which NaPotion (registered trademark) of DuPont is dissolved. Then, a catalyst slurry is prepared by dispersing in a medium such as alcohol or water. At this time, it is more preferable to apply ultrasonic vibration in order to promote the dispersion well. In order to obtain a desired dispersibility, the catalyst concentration for a fuel cell of the present invention in the catalyst slurry is preferably about 1 to 50 g / L. Of course, a binder such as polytetrafluoroethylene (PTFE) can be added to the slurry in the range of about 3 to 30% by mass for the purpose of providing water repellency or preventing the catalyst layer from peeling off. is there. In addition, when the contents are to be agglomerated and made into a paste, the alcohol has 2 to 5 carbon atoms such as ethanol or isopropyl alcohol, preferably a lower alcohol having about 2 to 4 carbon atoms, or 2 to 5 carbon atoms such as ethylene glycol, preferably A polyhydric alcohol having about 2 to 4 carbon atoms can be added and aggregated in a ratio of 0.25 to 1.0 with respect to water.

  The catalyst slurry thus obtained may be dried to form the cathode side catalyst layer and the anode side catalyst layer of the electrolyte membrane / electrode assembly. For example, the catalyst layer may be placed on the ion exchange membrane. A method of laminating the gas / fuel diffusion layer material after the formation and a method of laminating the ion exchange membrane after forming the catalyst layer on the gas / fuel diffusion layer material are exemplified.

Specifically, the cathode side catalyst layer and the anode side catalyst layer are respectively formed on the ion exchange membrane or the gas diffusion electrode material by the following methods.
(1) Spray on the ion exchange membrane to be used and dry.
(2) Spray the catalyst slurry on a gas diffusion electrode material such as carbon paper and dry.
(3) The catalyst slurry is sprayed onto the transfer film material such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP) film (development treatment) and dried, and the surface opposite to the transfer film surface is Nafion, etc. The catalyst layer is transferred onto the desired ion exchange membrane by appropriately pressing.
(4) As in (3), after the catalyst slurry is spread on the FEP film, the slurry is covered with a gas diffusion electrode material such as carbon paper and dried.

Both the cathode side catalyst layer and the anode side catalyst layer are generally 0.01 mg / cm ² or more, preferably 0.5 mg / cm ² or more, preferably several g / cm ² or less, preferably as an active ingredient adhesion amount (weight per unit area). It is preferably formed so as to have an amount of about 1 g / cm ² or less. If the amount of the active component attached is less than the lower limit, sufficient catalytic activity cannot be obtained, and if it exceeds the upper limit, it is difficult to form an electrolyte membrane / electrode assembly.

  After each forming step of the cathode side catalyst layer and the anode side catalyst layer, preliminary pressure molding is appropriately performed, and then the final electrolyte membrane / electrode assembly, that is, the surface on one side of the ion exchange membrane is described above. A cathode-side catalyst layer is formed, and an anode-side catalyst layer is laminated on the opposite surface of the ion-exchange membrane, and a gas / fuel diffusion layer constituting the anode and the cathode is laminated outside both catalyst layers. As described above, pressure membrane is formed by press using a press machine to produce an electrolyte membrane / electrode assembly.

  In addition, as conditions for preliminary pressure molding, it is preferable to set the temperature and pressure lower and the time shorter than the conditions of the main molding performed later within a range in which the catalyst layer can be prevented from collapsing. This is because the catalyst particles and gas / fuel diffusion layer porous body do not cause compressive fracture.

  EXAMPLES Next, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited by a following example, unless the summary is exceeded.

  In the following examples and comparative examples, the performance (catalytic activity) of the produced cathode electrode was measured by the following cyclic voltammetry (CV) measurement.

[CV measurement]
Cyclic voltammetry (CV) measurement was performed under the condition that oxygen was not rate-controlled while bubbling nitrogen or air into the electrolytic solution using a stopper capable of keeping hermeticity in the electrolytic cell. The measurement conditions are as follows.
Electrolyte: 1.0 MH ₂ SO ₄ aqueous solution
Scanning speed: 5mV / sec
Scanning range: 100-700mV
Counter electrode: Pt
Reference electrode: Standard hydrogen electrode (SHE)

When the potential of the electrode is scanned in the direction of about 700 mV to 100 mV with respect to the standard hydrogen electrode, between the working electrode and the Pt counter electrode,
4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O
It can be seen that the oxygen reduction current due to. Measures the current value flowing at 400 mV (SHE standard) when scanned in the base direction, and converts the measured current value into a current value per unit weight (1 g) of the active component contained in the catalyst. Evaluated.

[Example 1]
<Synthesis of Active Component (1a) Supported on VGCF>
As the VGCF (carbon nanofiber) used in this example, the one obtained by the method of Example 4 of JP-A-2003-166130 was used. 20 g of VGCF was refluxed for 3 hours in 100 mL of 50 mass% nitric acid aqueous solution, and used as a carbon material carrier. 0.25 g of dodecacarbonyltriruthenium (Ru ₃ (CO) ₁₂ ), 0.16 g of tungsten carbonyl, 0.038 g of sulfur powder, 0.8 g of VGCF and 20 mL of xylene were added and refluxed for 20 hours. After the reaction, it was filtered and air-dried, and then fired at 350 ° C. for 2 hours in an argon atmosphere. The active component containing Ru, W, and S elements supported by 20% by mass of ruthenium and tungsten metal on VGCF (active component (1a)) And).

<Creation of cathode electrode>
The active ingredient (1a) supported and fired on the obtained VGCF and carbon black (VULCAN XC-72R (manufactured by Cabot, specific surface area (BET) 254 m ² / g)) are mixed in a mortar, and the weight of the active ingredient (1a) Was diluted to 0.1 mass%. 28.27 mg of the mixture was mixed with 5 mL of ethanol and sufficiently stirred with an ultrasonic cleaner. Then, the active ingredient (1a) was added to a glassy carbon electrode as a working electrode so that the active ingredient (1a) would be 0.4 μg / cm ² with a microsyringe. It was dripped and dried by standing. Next, a commercially available Nafion solution in which a Nafion membrane manufactured by DuPont was dissolved in a solvent was dropped, dried by standing, and then further dried under vacuum to obtain a cathode electrode. CV measurement was performed on this cathode electrode, and the evaluation results of catalyst activity are shown in Table 2.

[Example 2]
<Synthesis of Active Component (2a) Supported on VGCF>
The active ingredient (1a) supported and fired on the VGCF obtained in Example 1 was further fired at 500 ° C. for 3 hours in an argon atmosphere, and Ru, W, and S loaded with 20% by mass of ruthenium and tungsten metal on the VGCF. An active component containing element (referred to as active component (2a)) was obtained.

<Creation of cathode electrode>
A cathode electrode was prepared by the same method as in Example 1 so that the active component (2a) was 0.4 μg / cm ² except that the active component (2a) supported and fired on the obtained VGCF was used. The results are shown in Table 2.

[Example 3]
<Synthesis of active ingredient (3a) supported on VGCF>
The active ingredient (1a) supported and fired on VGCF obtained in Example 1 was further fired at 650 ° C. for 3 hours in an argon atmosphere, and Ru, W, and S elements supported on ruthenium and tungsten metal at 20% by mass on VGCF An active ingredient (referred to as active ingredient (3a)) was obtained.

<Creation of cathode electrode>
A cathode electrode was prepared by the same method as in Example 1 so that the active component (3a) was 0.4 μg / cm ² except that the active component (3a) supported and fired on the obtained VGCF was used. The results are shown in Table 2.

[Example 4]
<Synthesis of active ingredient (1a) supported on CB>
Except for using Vulcan XC-72-R carbon black (CB) as a carbon material support in place of VGCF used in Example 1, Vulcan XC-72R was made of ruthenium and tungsten metal in exactly the same manner as in Example 1. The active ingredient (1a) supported by 20% by mass was obtained.

<Creation of cathode electrode>
A cathode electrode was prepared by the same method as in Example 1 except that the active component (1a) supported and fired on the obtained carbon black (CB) was used so that the active component (1a) was 0.4 μg / cm ^2. It was created. CV measurement was performed on this cathode electrode, and the evaluation results of catalyst activity are shown in Table 2.

[Comparative Example 1]
<Synthesis of active ingredient (1b)>
Dodecacarbonyl triruthenium (Ru ₃ (CO) ₁₂ ) 1.36 g, tungsten carbonyl 0.89 g, sulfur powder 0.20 g and 20 mL of xylene were placed in a 100 mL Kolbe and refluxed for 20 hours. After the reaction, the black precipitate was filtered, air-dried at room temperature, and then fired at 350 ° C. for 2 hours in an argon atmosphere to obtain an active component (referred to as active component (1b)) containing Ru, W, and S elements.

After combining the active ingredient (1b), it carbon black (VULCAN XC-72R (Cabot Corporation, specific surface area ^{(BET) 254m 2 / g)} ) was added, and mixed in a mortar, the active ingredient (1b) 0.1 It diluted so that it might become mass%.

<Creation of cathode electrode>
Except for using the active ingredient (1b) supported on the carbon black (CB) obtained, after diluting the active ingredient (1b) to 0.1% by the same method as in Example 1, A cathode electrode was prepared so that the active ingredient (1b) was 1.0 μg / cm ² , evaluation was performed in the same manner as in Example 1, and the results are shown in Table 2.

  From the comparison between the comparative example and the example shown in Table 2, it was revealed that the activity was improved by 10 times or more by carrying and firing. Also, when supported and fired on the same VGCF, the activity is higher at 500 ° C. (Example 2) and at 650 ° C. (Example 3) than at the firing temperature of 350 ° C. (Example 1). I understood. In addition, from comparison between Example 1 and Example 4, the activity was higher when supported and fired on VGCF than CB even at the same firing temperature.

According to the present invention, since a fuel cell using an inexpensive fuel cell catalyst is provided, the expansion and practical use of fuel cells such as fuel vehicles are promoted.

Claims (8)

  A fuel cell catalyst characterized in that a compound containing sulfur (S) and ruthenium (Ru) elements as an active component is deposited on a substrate, wherein hydrogen sulfide is not used in the synthesis process of the compound, and A catalyst for a fuel cell containing the compound, wherein the compound precursor is supported on a substrate not subjected to treatment with hydrogen sulfide and then calcined.   The fuel cell catalyst according to claim 1, further comprising one or more elements selected from W, Mo, and Re.   3. The fuel cell catalyst according to claim 1, wherein the firing temperature is higher than 350 ° C. and 1000 ° C. or lower. 4.   The fuel cell catalyst according to any one of claims 1 to 3, wherein the substrate is a carbon-based substrate.   5. The substrate according to claim 1, wherein the substrate is selected from the group consisting of carbon black, carbon nanotube, carbon nanohorn, carbon nanocluster, fullerene, pyrolytic carbon, and activated carbon. A fuel cell catalyst characterized by being combined.   A fuel cell electrode comprising the fuel cell catalyst according to any one of claims 1 to 5.   A fuel cell using the fuel cell electrode according to claim 6. A method for producing a catalyst for a fuel cell, comprising a compound containing sulfur (S) and ruthenium (Ru) elements as active components, which is deposited on a substrate. A method for producing a catalyst for a fuel cell containing an active component compound, characterized in that a precursor of the compound is supported on a carbon-based substrate that does not use hydrogen and is not treated with hydrogen sulfide and then calcined.