JP2007059140A - Catalyst for fuel cell and its manufacturing method as well as electrode for fuel cell and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide catalyst for a fuel cell of low cost exerting an excellent catalytic action well worth substituting precious metal catalyst such as that of platinum, as well as an electrode for a fuel cell and a fuel cell using the catalyst. <P>SOLUTION: An active component containing one or more elements selected from a group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), and iridium (Ir), and an element of phosphorus (P) are clad on a carbonaceous base body to make up the catalyst for the fuel cell. The electrode for the fuel cell contains the catalyst for the fuel cell, and the fuel cell uses the electrode for the fuel cell. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention includes at least one additive element selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), and iridium (Ir) and a phosphorus (P) element. The present invention relates to a fuel cell catalyst, an active component deposited on a substrate, a method for producing the same, a fuel cell electrode and a fuel cell using the fuel cell 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. ing. 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 based on a noble metal such as platinum, which is expensive and has a problem in terms of resources, has been used for both the cathode and the anode. The amount of platinum used for the exhaust gas purification catalyst of gasoline cars is considerably larger than that of platinum.

  Therefore, in order to commercialize fuel cells, development of fuel cell catalysts that can be put into practical use at low cost, replacing catalysts based on precious metals such as platinum, which are problematic in terms of price and resources. Is one of the essential issues.

Patent Document 1 discloses that PtP ₂ made of platinum element and phosphorus element is used for a fuel cell catalyst in claim 1. However, in this document, the group VIII element is limited to Pt, and there is no disclosure about ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), or iridium (Ir).

Patent Document 2 discloses a phosphide of ruthenium (Ru), rhodium (Rh), palladium (Pd), platinum (Pt), and iridium (Ir) as an electrode catalyst for a fuel cell. The catalyst is contained in a binder made of an organic polymer material such as polytetrafluoroethylene (PTFE), which binds a sheet-like woven fabric formed of carbon fiber and graphite fluoride fiber and a current collector. ing. Therefore, there is no disclosure of a fuel cell catalyst in which the catalyst component is contained in the substrate for electrical conduction.
USP 3,449,169 JP 61-49378 A

  As described in Patent Document 1, it is known that a phosphide of platinum can be used as a catalyst for a fuel cell. However, in this catalyst for a fuel cell, it is necessary to use platinum which is expensive and has problems in terms of resources. However, the problem of developing a catalyst for a fuel cell that can be used practically at low cost instead of a catalyst mainly composed of noble metals such as platinum cannot be solved.

  The present invention provides a fuel cell catalyst that exhibits an excellent catalytic action that is inexpensive and can be substituted for a noble metal catalyst such as platinum, and a fuel cell electrode and a fuel cell using the fuel cell catalyst. Objective.

As a result of intensive studies in view of the above circumstances, the present inventors have high catalytic activity by using a phosphide of a Group VIII element such as ruthenium, and have a utility that can be substituted for a noble metal catalyst such as platinum. It has been found that a catalyst can be obtained. Further, it has been found that by attaching this to a substrate, a fuel cell catalyst can be obtained that is inexpensive, has a higher catalytic activity, and has a practical utility that can replace a noble metal catalyst such as platinum.
The present invention has been completed based on such knowledge, and the gist thereof is as follows.

[1] One or more elements selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), and iridium (Ir) and a phosphorus (P) element A catalyst for a fuel cell, comprising an active component that is deposited on a substrate.

[2] The fuel cell catalyst according to [1], wherein the substrate is a carbon-based substrate.

[3] In [2], the carbon-based substrate is one or more selected from the group consisting of carbon black, carbon nanotube, carbon nanohorn, carbon nanocluster, fullerene, pyrolytic carbon, and activated carbon. A fuel cell catalyst.

[4] A fuel cell catalyst according to [1] to [3], wherein the active component is in the form of particles having an average particle size of 1000 nm or less.

[5] A fuel cell catalyst according to any one of [1] to [4], wherein a transition metal is further deposited on the substrate.

[6] A fuel cell electrode comprising the fuel cell catalyst according to any one of [1] to [5].

[7] A fuel cell using the fuel cell electrode according to [6].

[8] A method for producing a fuel cell catalyst according to [1] to [5], comprising the step of activating the precursor after supporting or mixing the precursor of the active component on the substrate. A method for producing a fuel cell catalyst.

[9] The method for producing a fuel cell catalyst according to [8], further comprising the step of depositing a transition metal on the substrate.

[10] Including one or more elements selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), and iridium (Ir), and a phosphorus (P) element A catalyst for a fuel cell for PEFC, comprising an active component.

  According to the present invention, a practical catalyst for a fuel cell that can be synthesized at low cost, exhibiting a good catalytic action, which can be replaced with a noble metal catalyst such as platinum, which is expensive and problematic in terms of resources, Provided are a fuel cell electrode and a fuel cell using the fuel cell catalyst.

  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 of the present invention is selected from the group consisting of phosphorus (P) element, ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), and iridium (Ir) as active components. And the active ingredient is deposited on a substrate.

In the following, one or more elements selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), and iridium (Ir) are referred to as “Group VIII metal”, It may be represented by “M”.
A fuel cell catalyst in which an active component is deposited on a substrate may be referred to as a “substrate-coated catalyst”.

<Active ingredient>
In the fuel cell catalyst of the present invention, the abundance ratio of the phosphorus (P) element and the group VIII metal element (M) in the active component is described as M ₁ P _{X in} the ratio of the number of elements constituting the active component The lower limit is X> 0.01, preferably X> 0.05, more preferably X> 0.1, particularly preferably X> 0.2, and the upper limit is X <10, preferably X <5. More preferably, X <4. If the abundance ratio of the phosphorus element and the Group VIII metal element is below this lower limit, the activity tends to be low, and even if the upper limit is exceeded, the activity is difficult to be produced.

  The content of phosphorus in the active ingredient is usually 1% or more by weight, preferably 5% or more, more preferably 10% or more, usually 96% or less, preferably 95% or less, more preferably with respect to the whole active ingredient. Is 93% or less. If the phosphorus content in the active ingredient is below this lower limit, the activity tends to be low, and even if the upper limit is exceeded, the activity is difficult to be produced.

  Further, the total content of Group VIII metals in the active ingredient, that is, ruthenium, rhodium, palladium, osnium, and iridium is usually 1% or more, preferably 5% or more, more preferably, based on the whole active ingredient. It is 10% or more, usually 95% or less, preferably 90% or less, more preferably 85% or less. If the content of the Group VIII metal in the active component is below this lower limit, the activity tends to be low, and even if the upper limit is exceeded, the activity is difficult to be produced.

In the present invention, the active ingredient may contain one kind of Group VIII metal alone or two or more kinds, but it is particularly preferred that ruthenium is contained as the Group VIII metal.
In addition, in the active ingredient which concerns on this invention, it is also possible to contain components other than a phosphorus element and a Group VIII metal in the range which does not impair the effect of this invention.

In the active ingredient according to the present invention, phosphorus is an inorganic compound such as P element, oxide such as P ₂ O ₅ , oxo acid such as H ₃ PO ₄ , chloride such as PCl ₃ and PBr ₃ , and PMe. _{3 It} may take the form of an organic compound bonded to a carbon atom such as (Me = methyl group). On the other hand, Group VIII metals can also take the form of metal elements, oxides, chlorides and other inorganic compounds and organic compounds. For example, in the case of ruthenium, in addition to Ru elements, oxides such as RuO and RuO ₂ , It may take the form of an inorganic compound such as a chloride such as RuCl ₃ .xH ₂ O and an organic compound such as Ru ₃ (CO) ₁₂ . Further, _RUP, it may be present as phosphides such RuP 2, RuP _4.

These phosphorus component and group VIII metal component constituting the active component may be present without having a bond, or may be present with a bond like the above-described phosphide. Specific examples of those having a bond include the aforementioned RuP, RuP ₂ , RuP _{4 and the} like. Moreover, the form which phosphorus and two or more elements of the group VIII metals couple | bonded may be sufficient.

  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, RuP ₂ has 2θ (± 0.3 °) peaks of X-ray diffraction as 23.002 °, 30.317 °, 34.731 °, 35.044 °, 35.122 °, It gives characteristic peaks such as 35.836 °, 47.003 °, 47.627 °, 49.685 °, 50.168 °, 56.088 ° and 56.747 °.

<Substrate>
The substrate used in the present invention is not particularly limited except for a binder that binds a sheet-like woven fabric formed of carbon fiber and graphite fluoride fiber and a current collector, and a carbon-based substrate is used. This is preferable in that high catalytic activity can be 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. Further, a nanotube or a vapor grown carbon fiber (Vapor Growth Carbon Fiber: hereinafter sometimes abbreviated as “VGCF”) by vapor phase method is also preferable, and in particular, VGCF which has been heat-treated to increase electrical conductivity has an appropriate elasticity. It is suitable.

Among these carbon-based substrates, carbon black is industrially advantageous in terms of conductivity, availability, and price. Specifically, as carbon black, specifically, channel black, furnace black, thermal Black, acetylene black, oil furnace black, gas furnace black, etc. are mentioned.
These carbon-based substrates can be used singly 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 component is applied to the substrate refers to a state in which the active component and the substrate are in contact with each other so as to obtain electrical conductivity. Accordingly, the active ingredient can be applied to the substrate simply by mixing the active ingredient and the substrate. However, after the active ingredient precursor is supported on or mixed with the substrate, the support or mixture is then subjected to reducing conditions. A method in which the precursor of the active ingredient is activated by baking with the above is preferable. In the following, an adjustment method in which a precursor of an active component is supported or mixed on a substrate, dried as necessary, and then fired to deposit the active component on the substrate 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 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 1.0 nm or more, more Preferably it is 2.0 nm or more. If the particle size of the active ingredient is below this lower limit, it becomes unstable and tends to be deactivated, and if 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 an active ingredient having such a small average particle diameter on a substrate, the production method may be devised as will be described later. In particular, the firing temperature in the supporting firing is lowered and the firing time is shortened. Thus, it is possible to control the state of crystal growth.

  The ratio of the active ingredient to the substrate is not particularly limited, but the weight ratio of active ingredient / (active ingredient + substrate) is usually 0.001 or more, preferably 0.01 or more as a lower limit. Above all, it is 0.05 or more, and the upper limit is usually 0.95 or less, preferably 0.6 or less, and more preferably 0.5 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 further applied to the substrate as long as the effects of the present invention are not impaired.

This transition metal (hereinafter sometimes referred to as “other catalyst component”) is an element belonging to the fourth to sixth periods of groups IIIA to VIIA, VIII, and IB of the periodic table, and titanium ( Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), yttrium (Y), zirconium (Zr), niobium ( Nb), molybdenum (Mo), lanthanum (La), europium (Eu), gold (Au), cerium (Ce), tantalum (Ta), tungsten (W), rhenium (Re), praseodymium (Pr), neodymium ( Nd) is exemplified, and it is preferable that the value of the standard electrode potential E ° (25 ° C.) in an aqueous solution, which is represented by the following electrochemical equilibrium formula oxidant + ne ⁻ = reduced substance, 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 and silver.

  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) The catalyst component is mixed with the active component together with the active component.
(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 ratio of the other catalyst component to the active component is below this lower limit, the desired activity cannot be obtained, and if it exceeds the upper limit, the effect of improving the activity is difficult to appear.

  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.

  In the fuel cell catalyst of the present invention, even if a metal component other than the transition metal element is contained in an amount of several weight percent or less based on the weight of the active component, it is acceptable for the purpose and effect of the present invention. it can.

  By using such other catalyst components in combination, it is particularly preferable to use the other catalyst components by carrying them on a 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.

<Manufacture of substrate-coated catalyst>
The fuel cell catalyst of the present invention is produced by depositing an active component on a substrate. Here, the active component may be deposited on the substrate by, for example, a method in which the active component or a precursor of the active component (element supply compound of the active component) is supported on or mixed with the substrate and then fired. Can be carried out by a known method such as a mixing method in which these are simply mixed, other impregnation methods, precipitation methods, adsorption methods and the like.

  For example, the element supply compound of the active ingredient is dissolved or dispersed in a desired molar ratio in water, an organic solvent or the like, impregnated or immersed in the substrate, and then filtered or evaporated to remove the active component on the substrate. After supporting the element supply compound as a component, it is prepared by performing a step of activating the precursor (for example, reduction treatment) if necessary.

Each element supply compound is not particularly limited as long as it can be thermally decomposed. If it is a phosphorus supply compound, in addition to P element, an oxide such as P ₂ O ₅ , an oxo acid such as H ₃ PO ₄ , PCl ₃ , chlorides such as PBr ₃ and salt compounds such as (NH ₄ ) ₂ HPO ₄ and NH ₄ H ₂ PO ₄ .

Further, as the supply compounds of ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), iridium (Ir), these halides, oxides, inorganic acid salts, organic acid salts, etc. Can be mentioned.
Specifically, RuCl ₃ · _xH 2 O, halides such as _{RuBr 3, Ru (SO 4)} 2, K 2 RuO 4 · H 2 Inorganic salts O _{etc., Ru 2 (OCH 3 CO)} 4 and organic acids Salts, halides such as RhCl ₃ .xH ₂ O, RhBr ₃ , inorganic salts such as KRh (SO ₄ ) ₂ .12H ₂ O, Rh (NO ₃ ) ₃ .2H ₂ O, Rh (OCH ₃ CO) _{3 and the} like Organic acid salts, halides such as PdCl ₂ , PdCl ₂ .2H ₂ O, PdF ₂ , PdCl ₄ , K ₂ PdCl ₄ , K ₂ PdCl ₆ , inorganic salts such as Pd (NO ₃ ) ₂ , Pd (OCH ₃ CO) _{2 and} other organic acid salts, OsCl ₃ , K ₂ OsCl _{6 and} other halides, OsO _{2 and} other oxides, IrCl ₃ and IrBr _{3 and} other halides, IrO _{2 and} other oxides, Ir (SO ₄ ) Inorganic such as ₂ Examples include salts.

These feed compounds may be used alone or in a combination of two or more. Further, a metal complex obtained by complexing an organic phosphorus compound in advance may be used as a precursor of the active component. These include, for example, _{RuCl 2 (PPh 3) 3,} H 2 Ru (PPh 3) 4 and the like.

As a general synthesis method of a substrate-coated catalyst having an active component supported on a substrate, a production method of a catalyst containing Ru and P as active components is exemplified. For example, RuCl ₃ and (NH ₄ ) ₂ HPO ₄ are desired. It is dissolved in a soluble solvent such as water at a mixing ratio according to the molar ratio to be mixed, and a predetermined amount of a substrate such as carbon black is mixed therein, 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, if necessary, the mixture is heated or refluxed at a predetermined temperature, and then a precipitate is obtained by filtration or an evaporator. Next, firing is performed at a predetermined temperature (usually 200 ° C. or higher, preferably 300 ° C. or higher, usually 1000 ° C. or lower, preferably 800 ° C. or lower) under conditions of flowing an oxygen atmosphere gas such as air. Next, an inert gas such as nitrogen or Ar may be mixed under an air stream containing hydrogen at a predetermined temperature (usually 200 ° C or higher, preferably 300 ° C or higher, 1000 ° C or lower, preferably 800 ° C or lower). The concentration of hydrogen in the active gas is not particularly limited, but is heated to 1% or more, preferably 10% or more) to obtain a catalyst in which an active component containing Ru and P is supported on a substrate.

  Thereafter, a passivation treatment is performed in which a passive film is formed by treatment in an inert gas atmosphere at a low oxygen concentration (for example, an oxygen concentration of about 5 wt% or less, especially about 2 wt% or less) for a predetermined time. Can also be done.

  Alternatively, the active ingredient can be applied to the base by preparing the active ingredient in advance, mixing it with the base, and kneading it in a mortar or the like. This mixing may be dry or wet, but is preferably wet mixed using a medium such as water and then dried at about 100 to 200 ° C.

In this case, as a method for preliminarily adjusting the active ingredient, for example, RuCl ₃ and (NH ₄ ) ₂ HPO ₄ are dissolved in water at a blending ratio corresponding to a desired molar ratio, and then, if necessary, predetermined The mixture is heated or refluxed at a temperature of 5 ° C., and then a precipitate is obtained by filtration or an evaporator. Next, firing is performed at a predetermined temperature (usually 200 ° C. or higher, preferably 300 ° C. or higher, usually 1000 ° C. or lower, preferably 800 ° C. or lower) under conditions of flowing an oxygen atmosphere gas such as air. Next, an inert gas such as nitrogen or Ar may be mixed under an air stream containing hydrogen at a predetermined temperature (usually 200 ° C or higher, preferably 300 ° C or higher, 1000 ° C or lower, preferably 800 ° C or lower). The hydrogen concentration in the active gas is not particularly limited, but is heated to 1% or more, preferably 10% or more) to obtain an active component containing Ru and P.

  Thereafter, in an inert gas atmosphere having a low oxygen concentration (for example, an oxygen concentration of about 5 wt% or less, especially about 2 wt% or less), a predetermined time (usually several tens of minutes, preferably 30 minutes or more, usually Passivation treatment may be performed to form a passive film by treatment at a predetermined temperature (usually around room temperature) for 10 hours or less, particularly 5 hours or less.

  In the present invention, among the above-described methods for producing a catalyst, a supported calcining method in which a carbon-based substrate and an active ingredient and an element supply compound of the active ingredient are mixed and then calcined is preferable. The activity of the resulting catalyst can be improved. The reason why the activity can be improved by firing in this way is not necessarily clear, but since the active component is deposited on the carbon-based substrate, the sintering of the active component is suppressed during firing. It is estimated that the activity is improved.

  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. , A carbonyl compound, an amine compound, an olefin coordination compound, a phosphine coordination compound or a phosphite coordination compound. These may be used alone or in combination of two or more.

  As a specific method of depositing other catalyst components together with the active component on the substrate, for example, a catalyst in which the active component containing Ru and P synthesized by the above-described method is supported on the substrate, chloride, etc. A solution in which the transition metal compound is dissolved 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 by an evaporator. In this case, ultrasonic treatment may be performed. Next, under an air stream containing hydrogen (inert gas such as nitrogen or Ar may be mixed, the hydrogen concentration in the inert gas is not particularly limited, but is 1% or more, preferably 10% or more, 100 % Or less, or 80% or less) at a predetermined temperature (usually 100 ° C. or higher, preferably 150 ° C. or higher, usually 800 ° C. or lower, preferably 500 ° C. or lower) for a predetermined time (usually 10 minutes or longer, preferably 30 minutes or longer). (Normally, 50 hours or less, preferably 30 hours or less) By heating, a substrate-adhered catalyst in which an active component containing Ru and P and another catalyst component are both supported on a substrate is obtained.

  Thereafter, in an inert gas atmosphere having a low oxygen concentration (for example, an oxygen concentration of about 5 wt% or less, especially about 2 wt% 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 by mixing it with the substrate on which the active component is deposited (preferably supported firing), or the other catalyst component is deposited (preferably supported firing). You may mix and use an active ingredient for the base | substrate which was made.

[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 (registered trademark manufactured by DuPont), Flemion (registered trademark manufactured by Asahi Glass Co., Ltd.), and Aciplex (registered trademark manufactured by Asahi Kasei Co., Ltd.).

  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. However, an electrolyte having a thickness of 30 to 50 μm has begun to be developed, 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, an active ingredient or a catalyst for a fuel cell of the present invention obtained by adhering an active ingredient to a substrate is placed in a suitable container, and a Nafion solution (concentration of 5% by weight) in which NaPotion (registered trademark) of DuPont is dissolved. , Manufactured by Aldrich) and dispersed in a medium such as alcohol or water to prepare a catalyst slurry. 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 weight 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 so as to have 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) Dry the catalyst slurry by spraying it onto the ion exchange membrane to be used.
(2) Spray the catalyst slurry on a gas diffusion electrode material such as carbon paper and dry.
(3) The catalyst slurry is sprayed onto a transfer film material such as a tetrafluoroethylene-hexafluoropropylene copolymer (FEP) film (development treatment) and dried, and the surface opposite to the transfer film surface is made of 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 the both catalyst layers. Then, an electrolyte membrane / electrode assembly is produced by press-heating using a press machine.

  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 Scan speed: 5 mV / sec Scan range: 100 to 700 mV
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, 4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O between the working electrode and the Pt counter electrode
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 Ru.P / carbon black (CB) catalyst>
Ruthenium chloride (water-containing product, ruthenium content 42 wt%, manufactured by NE Chemcat) 0.364 g and (NH ₄ ) ₂ HPO ₄ (Kishida Chemical) 0.198 g were dissolved in 50 ml of water. Carbon black (VULCAN XC-72R, manufactured by Cabot (specific surface area (BET) 254 m ^{2 /} g)) 0.8 g was placed therein and sonicated for 1 hour at room temperature. Thereafter, the solvent was distilled off with an evaporator, and the obtained residue was calcined at 500 ° C. for 3 hours in an air stream.
Then, after cooling to room temperature, the air was switched from hydrogen gas to hydrogen reduction treatment. That is, the temperature was increased from room temperature to 300 ° C. for 20 minutes and from 300 ° C. to 500 ° C. over 4 hours at a flow rate of 3 L / hr in a hydrogen stream. After holding at 500 ° C. for 1 hour, it was cooled to room temperature. Finally, it was passivated by leaving it in a nitrogen gas stream containing 1% oxygen for 2 hours.

<Creation of cathode electrode>
The active component containing Ru and P elements supported and fired on the obtained carbon black and a separately prepared carbon black (VULCAN XC-72R (manufactured by Cabot, specific surface area (BET) 254 m ² / g)) are mixed in a mortar. The active ingredient was diluted to 0.1% by weight. 28.27 mg of the mixture was mixed with 5 mL of ethanol and sufficiently stirred with an ultrasonic cleaner, and then dropped with a microsyringe onto a glassy carbon electrode as a working electrode so that the amount of active ingredient adhered was 0.4 μg / cm ^2. 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]
The hydrogen reduction treatment conditions employed in Example 1 were increased from 300 ° C. to 500 ° C. over 4 hours and maintained at 500 ° C. for 1 hour, and the temperature was increased from 300 ° C. to 650 ° C. over 4 hours. A catalyst was prepared in the same manner as in Example 1 except that the conditions were changed to those maintained at 1 ° C. for 1 hour.
A cathode electrode was prepared by using the active component containing Ru and P elements supported and fired on the obtained carbon black in the same manner as in Example 1 so that the active component adhesion amount was 0.4 μg / cm ^2. The results are shown in Table 2.

[Example 3]
The hydrogen reduction treatment conditions employed in Example 1 were increased from 300 ° C. to 500 ° C. over 4 hours and maintained at 500 ° C. for 1 hour, and the temperature was increased from 300 ° C. to 800 ° C. over 4 hours. A catalyst was prepared in the same manner as in Example 1 except that the conditions were changed to those maintained at 1 ° C. for 1 hour.
A cathode electrode was prepared by using the active component containing Ru and P elements supported and fired on the obtained carbon black in the same manner as in Example 1 so that the active component adhesion amount was 0.4 μg / cm ^2. The results are shown in Table 2.

[Example 4]
Ruthenium chloride (water-containing product, ruthenium content 42 wt%, manufactured by NE Chemcat) 2.24 g and (NH ₄ ) ₂ HPO ₄ (Kishida Chemical) 1.225 g were dissolved in 50 ml of distilled water, allowed to stand at room temperature for 1 hour, and then an evaporator. The solvent was distilled off to obtain a solid. This solid was put into a firing tube and fired at 500 ° C. for 6 hours at a flow rate of 3 L / hr under an air stream. Then, after cooling to room temperature, the air was switched from hydrogen gas to hydrogen gas, and the temperature was raised from room temperature to 300 ° C. in 20 minutes at a flow rate of 3 L / hr, and then raised to 600 ° C. over 4 hours. Thereafter, the mixture was kept at 600 ° C. for 1 hour and then cooled to room temperature. Finally, it was passivated by treatment under a nitrogen gas stream containing 1% oxygen.
The obtained active ingredient containing Ru and P elements was mixed with carbon black (VULCAN XC-72R (manufactured by Cabot, specific surface area (BET) 254 m ² / g)), and the weight of the active ingredient was 1% by weight. The results are shown in Table 2 and evaluated in the same manner as in Example 1, except that the cathode electrode was prepared so that the amount of the active ingredient adhered was 4 μg / cm ² .

[Example 5]
A catalyst was prepared in the same manner as in Example 4, except that in Example 4, ruthenium chloride was changed to 6.7 g and (NH ₄ ) ₂ HPO ₄ was changed to 1.22 g.
A cathode electrode was prepared for the obtained active component containing Ru and P elements by the same method as in Example 4 so that the active component adhesion amount was 4 μg / cm ^2. It was shown in 2.

[Example 6]
A catalyst was prepared in the same manner as in Example 4 except that in Example 4, ruthenium chloride was changed to 2.24 g and (NH ₄ ) ₂ HPO ₄ was changed to 3.68 g.
A cathode electrode was prepared for the obtained active component containing Ru and P elements by the same method as in Example 4 so that the active component adhesion amount was 4 μg / cm ^2. It was shown in 2.

  As shown in Table 2, the fuel cell catalyst according to the present invention obtained by depositing Ru and P on CB exhibits excellent cathode activity. In particular, it is clear that the catalytic activity is remarkably improved by carrying out the supported firing.

  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 (10)

  An active component containing one or more elements selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), osnium (Os), and iridium (Ir) and a phosphorus (P) element A fuel cell catalyst characterized in that is deposited on a substrate.   2. The fuel cell catalyst according to claim 1, wherein the substrate is a carbon-based substrate.   3. The carbon base according to claim 2, wherein the carbon-based substrate is one or more selected from the group consisting of carbon black, carbon nanotube, carbon nanohorn, carbon nanocluster, fullerene, pyrolytic carbon, and activated carbon. A fuel cell catalyst.   The fuel cell catalyst according to any one of claims 1 to 3, wherein the active component is in the form of particles having an average particle size of 1000 nm or less.   5. The fuel cell catalyst according to claim 1, wherein a transition metal is further deposited on the substrate.   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 fuel cell catalyst according to any one of claims 1 to 5, comprising a step of activating the precursor after the precursor of the active component is supported or mixed on the substrate. A method for producing a catalyst for a fuel cell.   9. The method for producing a fuel cell catalyst according to claim 8, further comprising a step of depositing a transition metal on the substrate.   An active ingredient containing one or more elements selected from the group consisting of ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), and iridium (Ir) and a phosphorus (P) element A fuel cell catalyst for PEFC, comprising: