JP3613330B2 - Catalyst for fuel cell, method for producing the same, and electrode for fuel cell - Google Patents

Description

【００６２】
表１に示すように、比較例２で作製した電極の性能に比して、本発明の方法によれば、白金は微細化されて一様に分散しており、熱履歴後もその状態が保持されるため、電極性能は大きく向上し、その寿命も大きく改善されることが明らかとなった。
【００６３】
【発明の効果】
本発明によれば、簡単かつ迅速なる工程により、白金系遷移金属の分散したケイ素系高分子でコートしたカーボン粉体を得ることができ、これは高効率で耐久性に優れる燃料電池用触媒として利用できる触媒電極として使用することができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell catalyst, a method for producing the same, and a fuel cell electrode.
[0002]
[Prior art and problems to be solved by the invention]
Fuel cells have a high energy efficiency of 30 to 40% compared to internal combustion engines and only water is discharged using hydrogen and oxygen as fuel, so the ultimate battery of the 21st century that can revolutionize the world in the area of energy and environment It is considered as one of the candidates. Among them, a solid oxide fuel cell that operates at a low temperature of 70 to 90 ° C. and has a high energy density and a small capacity has attracted much attention as an electric vehicle or household power source.
[0003]
The structure of the fuel cell consists of a cell in which hydrogen and oxygen are supplied from both sides of the outermost separator across the membrane / electrode assembly, and a stack of these cells connected in series It is composed of This membrane / electrode assembly is composed of electrodes having two catalyst layers called a hydrogen electrode and an oxygen electrode on both sides of an ion exchange membrane. At the hydrogen electrode, the hydrogen gas of the fuel is activated by protons (H⁺) Through the ion exchange membrane toward the oxygen electrode. At the oxygen electrode, the oxygen in the air that has been sent reacts with protons by the action of the catalyst to become water. This series of reactions generates electricity. As a catalyst at such a hydrogen electrode or oxygen electrode, a catalyst made of platinum is usually used.
[0004]
The platinum catalyst is generally impregnated with a carbon ion such as activated carbon or carbon black with a platinum ion-containing solvent such as chloroplatinic acid, and this is added to sodium borohydride in the presence of a protective colloid such as polyvinyl alcohol. It is prepared by depositing platinum colloid on carbon alone by acting a reducing agent such as hydrogen or hydrogen.
[0005]
However, this catalyst has the following demands and problems.
(1) Since platinum metal is expensive, we want to reduce the amount used and make it highly active.
(2) When impurities such as carbon monoxide and sulfur enter and cover the catalyst surface, the catalytic activity is reduced (poisoning).
(3) Platinum particles adhere to each other over time, the surface area decreases, and the activity decreases.
[0006]
As a solution to this problem, measures are taken such as (1) using platinum metal as fine particles to increase the surface area and increasing the activity, and (2) adding metal other than platinum such as ruthenium, rhodium and palladium.
[0007]
However, with regard to (3), the mixing ratio of how much protective colloid and reducing agent are used for the main materials platinum and carbon alone, selection of reaction conditions for platinum fine particles, temperature, time, and atmosphere are complicated However, the essential solution was not achieved. In particular, when baked in the final step to form a catalyst electrode, polyvinyl alcohol, polymethyl vinyl ether, polyvinyl pyrrolidone, gelatin, and the like conventionally used as protective colloids are decomposed, and platinum can be stably held. It was not possible to prevent aggregation of platinum when used as an electrode material. For this reason, the high catalytic activity of platinum could not be expressed with a long life of 5000 hours for automobiles and 50000 hours for home use.
[0008]
The present invention has been made in view of the above circumstances, and a carbon powder coated with a silicon-based polymer compound in which platinum fine particles are dispersed and stabilized can be obtained by a simple and rapid process, which is highly efficient and durable. It aims at providing the catalyst for fuel cells which can be utilized as a catalyst which is excellent in the property, its manufacturing method, and also the fuel cell electrode using this catalyst.
[0009]
Means for Solving the Problem and Embodiment of the Invention
As a result of intensive studies, the inventor made platinum fine particles in a simple and rapid process by bringing a reducing silicon polymer thin film formed on carbon powder into contact with a platinum transition metal salt. It was found that a carbon powder coated with a dispersed and stabilized silicon polymer compound can be obtained, and a fuel cell catalyst that can be used as a highly efficient and durable catalyst can be obtained.
[0010]
By the way, silicon-based polymer compounds have high metal resistance compared to carbon, and silicon oxide has high oxidation resistance. Therefore, silicon-based polymer compounds have high heat resistance that cannot be obtained with organic resins. It is a very interesting material that can be used at a wide range of temperatures, exhibiting flexibility at low temperatures and good thin film formation by introducing organic groups. In addition, certain silicon-based polymer compounds, such as polysilane as a precursor of silicon carbide ceramic material and polysiloxane as a precursor of silicon oxide ceramic material, can be a material with extremely high heat resistance by heat treatment or the like. Well known. Furthermore, silicon-based polymer compounds having Si-Si bonds and / or Si-H bonds, particularly polymers having hydrogen atoms directly bonded to polysilane or Si atoms have reducibility and generate metal colloids from metal salts. It is known to do.
[0011]
In the present invention, a highly dispersed platinum colloid is necessary for manifesting the catalytic functionality of the fuel cell. Therefore, the present inventor can use the above-described silicon-based polymer compound to stably form platinum even at a high temperature without using any protective colloid such as polyvinyl alcohol or a reducing agent such as sodium borohydride or hydrogen. It has been found that a carbon carrier coated with a colloid-dispersed polymer can be obtained.
[0012]
In other words, when a platinum-based transition metal salt is brought into contact with a reducible silicon-based polymer compound among metal salts, the silicon-based polymer compound performs two tasks: reduction of the platinum-based transition metal salt and stabilization of its colloid. It was found that the process and control can be simplified because the process can be performed simultaneously. Furthermore, when polysilane is used as the reducing silicon-based polymer compound, when the polysilane reacts with the platinum-based transition metal salt, the platinum salt is reduced to a platinum colloid and at the same time, the polysilane is oxidized to a polysiloxane to form a fine colloidal state. Since it is possible to stably hold platinum even when baked in the final step in order to hold platinum as it is and to make a catalyst electrode, it is found that it can be a long-term durable fuel cell electrode material, The present invention has been achieved.
[0013]
Therefore, the present inventionIt was obtained by bringing platinum transition metal salt into contact with carbon powder whose surface was coated with a reducing silicon-based polymer compound.A fuel cell catalyst comprising carbon powder carrying platinum-based transition metal fine particles, andA carbon powder obtained by treating carbon powder with a solution in which a reducing silicon-based polymer compound is dissolved in an organic solvent, then removing the organic solvent from the surface of the carbon powder and coating the surface with the silicon-based polymer compound. A platinum-based transition metal salt dissolved in or dispersed in a solvent that does not dissolve the silicon-based polymer compound, and the platinum-based transition metal salt is converted into a platinum-based transition metal with the silicon-based polymer compound. A method for producing a catalyst for a fuel cell, characterized in that carbon powder carrying platinum-based transition metal fine particles is obtained by reduction to a colloidAnd a fuel cell electrode containing the fired product of the catalyst.
[0014]
Hereinafter, the present invention will be described in more detail.
As the carbon powder used in the present invention, spherical carbon black, scaly graphite, fibrous carbon fiber, hollow carbon balun and the like can be used. As carbon black, many varieties characterized by particle diameter, specific surface area, DBP oil absorption and the like can be used, and examples thereof include ketjen black, furnace black, acetylene black, vulcan, SRF carbon, activated carbon and the like. In addition, as the carbon fiber, any of isotropic pitch type, liquid crystal pitch type and PAN type can be used, and Kureka (Kureha Chemical), Dona Carbo (Donak), Zyrus (Nittobo), Volca ( Examples include those sold under the name Tonen).
[0015]
In the production method of the present invention, treatment is performed with a silicon polymer compound having reducibility, and a layer of the reducible silicon polymer compound is formed on the outermost surface of the carbon powder.
[0016]
In this case, as the silicon-based polymer compound for treating the powder, those having a reducing action are used. The silicon-based polymer compound having a reducing action can be selected from polysilane, polycarbosilane, polysiloxane, and polysilazane having a Si—Si bond or Si—H bond. A polysiloxane having a hydrogen atom directly bonded to is preferably used.
[0017]
Here, as the silicon-based polymer compound having a Si—Si bond in the molecule, polysilane is preferably used, and polysilane represented by the following general formula (1) is preferable.
(R¹ _mR² _nX_pSi)_q            (1)
(Wherein R¹, R²Is a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group, X is R¹Represents an alkoxy group, a halogen atom, an oxygen atom or a nitrogen atom, m is 0.1 ≦ m ≦ 2, n is 0 ≦ n ≦ 1, p is 0 ≦ p ≦ 0.5, and 1 ≦ m + n + p ≦ It is a number satisfying 2.5. q is an integer satisfying 4 ≦ q ≦ 100,000. )
[0018]
In the polysilane of the above formula (1), R¹, R²Is a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group, R¹And R²May be the same as or different from each other, but as the monovalent hydrocarbon group, an aliphatic, alicyclic or aromatic hydrocarbon group is used. In the case of an aliphatic or alicyclic hydrocarbon, it has 1 to 12, preferably 1 to 6 carbon atoms, such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, cyclopentyl group, cyclohexyl group, etc. Is mentioned. The aromatic hydrocarbon group preferably has 6 to 14 carbon atoms, more preferably 6 to 10 carbon atoms, and examples thereof include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, a benzyl group, and a phenethyl group. . Examples of the substituted hydrocarbon group include those obtained by substituting some or all of the hydrogen atoms of the unsubstituted hydrocarbon groups exemplified above with halogen atoms, alkoxy groups, amino groups, aminoalkyl groups, and the like, such as monofluoromethyl Group, trifluoromethyl group, m-dimethylaminophenyl group and the like. X is R¹Are the same groups, alkoxy groups, halogen atoms, alkoxy groups having 1 to 4 carbon atoms such as methoxy group, ethoxy group, isopropoxy group, etc., halogen atoms are fluorine atom, chlorine atom, bromine atom, etc. Usually, a methoxy group and an ethoxy group are used.
[0019]
m is 0.1 ≦ m ≦ 2, especially 0.5 ≦ m ≦ 1, n is 0 ≦ n ≦ 1, especially 0.5 ≦ n ≦ 1, p is 0 ≦ p ≦ 0.5, especially 0 ≦ p. ≦ 0.2 and 1 ≦ m + n + p ≦ 2.5, particularly 1.5 ≦ m + n + p ≦ 2, and q is 4 ≦ q ≦ 100,000, especially 10 ≦ q ≦ 10,000. An integer in the range.
[0020]
Moreover, as a silicon-type high molecular compound which has the hydrogen atom (Si-H group) directly couple | bonded with the silicon atom, the following general formula (2) which has Si-H group in a side chain and Si-O-Si bond in a principal chain. ) Is preferably used.
(R³ _aR⁴ _bH_cSiO_d)_e          (2)
(Wherein R³, R⁴Represents a hydrogen atom, a substituted or unsubstituted monovalent hydrocarbon group, an alkoxy group or a halogen atom, a is 0.1 ≦ a ≦ 2, b is 0 ≦ b ≦ 1, and c is 0.01 ≦ c ≦ 1. , D is a number satisfying 0.5 ≦ d ≦ 1.95 and satisfying 2 ≦ a + b + c + d ≦ 3.5. e is an integer satisfying 2 ≦ e ≦ 100,000. )
[0021]
In the polysiloxane of the above formula (2), R³, R⁴Is a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group, R³And R⁴May be the same as or different from each other, but as the monovalent hydrocarbon group, an aliphatic, alicyclic or aromatic hydrocarbon group is used. In the case of an aliphatic or alicyclic hydrocarbon, it has 1 to 12, preferably 1 to 6 carbon atoms, such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, cyclopentyl group, cyclohexyl group, etc. Is mentioned. As the aromatic hydrocarbon group, those having 6 to 14 carbon atoms, more preferably 6 to 10 carbon atoms are suitable, and examples thereof include a phenyl group, a tolyl group, a xylyl group, a naphthyl group, a benzyl group, and a phenethyl group. It is done. Examples of the substituted hydrocarbon group include those obtained by substituting some or all of the hydrogen atoms of the unsubstituted hydrocarbon groups exemplified above with halogen atoms, alkoxy groups, amino groups, aminoalkyl groups, and the like, such as monofluoromethyl Group, trifluoromethyl group, m-dimethylaminophenyl group and the like. Examples of the alkoxy group include those having 1 to 4 carbon atoms such as a methoxy group, an ethoxy group, and an isopropoxy group, and examples of the halogen atom include a fluorine atom, a chlorine atom, and a bromine atom.
[0022]
a is 0.1 ≦ a ≦ 2, especially 0.5 ≦ a ≦ 1, b is 0 ≦ b ≦ 1, especially 0.5 ≦ b ≦ 1, c is 0.01 ≦ c ≦ 1, especially 0.1 ≦ c ≦ 1, d is 0.5 ≦ d ≦ 1.95, especially 1 ≦ d ≦ 1.5, and 2 ≦ a + b + c + d ≦ 3.5, preferably 2 ≦ a + b + c + d ≦ 3.2 It is. e is an integer in the range of 2 ≦ e ≦ 100,000, preferably 10 ≦ e ≦ 10,000.
[0023]
In the present invention, the step of treating the powder with a silicon-based polymer compound and forming a layer of the silicon-based polymer compound on the powder surface comprises dissolving the silicon-based polymer compound in an organic solvent, A layer of a silicon-based polymer compound can be formed on the surface of the powder by removing the organic solvent after the powder is added to or mixed with the solution.
[0024]
In this step, examples of the organic solvent for dissolving the silicon polymer compound include aromatic hydrocarbons such as benzene, toluene, and xylene, aliphatic hydrocarbon solvents such as hexane, octane, and cyclohexane, tetrahydrofuran, and dibutyl ether. Preferably used are ether solvents such as ethyl acetate, esters such as ethyl acetate, aprotic polar solvents such as dimethylformamide, dimethyl sulfoxide and hexamethylphosphoric triamide, nitromethane, acetonitrile, and the like.
[0025]
The concentration of the silicon-based polymer compound-containing solution is 0.01 to 50% (% by weight, the same applies hereinafter), preferably 0.1 to 30%, particularly 0.1 to 10%, and the concentration is too low. When the silicon-based polymer compound layer is thin, it is difficult to form a uniform surface on the powder surface, and a large amount of solvent is used, which may increase the cost. On the other hand, if the concentration is too high, the silicon-based polymer compound layer may become thick and tend to cause aggregation of the powder.
[0026]
Next, the solvent is distilled off by raising the temperature or reducing the pressure. Usually, it is effective to stir at a temperature of about 40 to 200 ° C. under a reduced pressure of 1 to 100 mmHg, for example, at a temperature equal to or higher than the boiling point of the solvent. Then, the silicon-based polymer compound-treated powder can be produced by allowing the solvent to be effectively distilled off and dried by standing still in a dry atmosphere or under reduced pressure at a temperature of about 40 to 200 ° C. for a while.
[0027]
The thickness of the silicon-based polymer compound layer is preferably 0.001 to 1.0 μm, and more preferably 0.01 to 0.1 μm. When it is thinner than 0.001 μm, it is difficult to form a silicon-based polymer compound layer uniformly on the powder surface. On the other hand, if the thickness is larger than 1.0 μm, the silicon-based polymer compound layer becomes thick and the powder is likely to be aggregated. Further, the amount of the silicon-based polymer compound increases, resulting in an economical disadvantage. is there.
[0028]
Next, the obtained powder having a silicon-based polymer compound layer formed on the surface of the carbon powder is treated with a solution containing a metal salt composed of a platinum-based transition metal, and the metal colloid is formed on the silicon-based polymer compound layer. The process of depositing is performed. This is a method in which the surface of the silicon polymer compound-treated powder is brought into contact with a solution containing a metal salt. In this treatment, the metal colloid is formed on the surface of the coating film of the silicon polymer compound by the reducing action of the silicon polymer compound. And a metal film is formed.
[0029]
The platinum-based transition metal used in the present invention is preferably one of platinum, Ir, Pd, and Rh or a mixture thereof, and among these, platinum is particularly preferable.
[0030]
Platinum salts include Pt²⁺, Pt³⁺Or Pt⁴⁺PtX₂, PtX₃, PtX₄, [PtA₆] X₂, M^I ₂[PtX₄], M^I ₂[PtX₂Y₂], M^I[PtX₃Y], M^I[PtX₂Y₂], M^I ₂[PtX₆] (X and Y are both F⁻, Cl⁻, Br⁻, I⁻, OH⁻, CN⁻, NO₃ ⁻, N₃ ⁻, CH₃COO⁻, SCN, acetylacetonate, 1 / 2SO₄ ^2-, 1 / 2CO₃ ^2-Anion such as M^IIs a monovalent cation such as K, Na or H, and A is NH₃Or amines. ) And the like. Specifically, PtCl₂, PtBr₂, PtI₂, Pt (CN)₂, Pt (SCN)₂, PtCl₃, PtBr₃, PtI₃, PtF₄, PtCl₄, PtBr₄, PtI₄, K₂[PtCl₂(Acac)₂], H₂PtCl₆Etc. are exemplified.
[0031]
As an iridium salt, Ir⁺, Ir²⁺, Ir³⁺Or Ir⁴⁺IrX, IrX₂, IrX₃, IrX₄, [IrX₆] M^I ₃, M^I[IrX₄] (X is halogen such as Cl and Br, SO₄Anion such as M^IIs a monovalent cation such as K, Na, Rb, Cs or H. ) And the like. Specifically, KIr (SO₄)₂, RbIr (SO₄)₂, CsIr (SO₄)₂Etc. are exemplified.
[0032]
Pd salts include Pd²⁺In general, Pd-Z₂It can be expressed in the form of Z is a salt of halogen such as Cl, Br, and I, acetate, trifluoroacetate, acetylacetonate, carbonate, perchlorate, nitrate, sulfate, oxide, and the like. Specifically, PdCl₂, PdBr₂, PdI₂, Pd (OCOCH₃)₂, Pd (OCOCF₃)₂, PdSO₄, Pd (NO₃)₂, PdO, and the like.
[0033]
Rhodium salts include Rh³⁺RhX₃, Rh₂X₆, [RhA₆] X₃, M^I ₃[RhX₆], M^I[RhX₄] (X is halogen such as F and Cl, CN, SO₄Anion such as M^IIs a monovalent cation such as K, Na or H, and A is NH₃Or amines. ) And the like. Specifically, Rh₂(SO₄)₃, Rh (NO₃)₃, RhCl₃, RhF₃, RhCN₃, KRh (SO₄)₂, NaRh (SO₄)₂, HRh (SO₄)₂Etc. are exemplified.
[0034]
As a method of treating the powder with a platinum-based transition metal salt solution, the platinum-based transition metal salt is dissolved using a solvent that does not dissolve the silicon-based polymer compound and can dissolve or disperse the platinum-based transition metal salt. A solution method is preferred in which a solution is prepared, a powder coated with a silicon-based polymer compound film is added to the solution, and contacted with a platinum-based transition metal salt. By this treatment, the platinum-based transition metal salt is adsorbed on the surface of the silicon-based polymer compound coating surface of the powder coated with the silicon-based polymer compound, and at the same time, the metal-coated powder supported as a reduced colloid. The body is formed.
[0035]
Here, as a solvent that does not dissolve the silicon-based polymer compound and can dissolve or disperse the metal salt, the solubility differs depending on the type of the side chain group. Ketones such as methyl ethyl ketone, esters such as ethyl acetate, alcohols such as methanol and ethanol, aprotic polar solvents such as dimethylformamide, dimethyl sulfoxide and hexamethylphosphoric amide, and others, nitromethane, acetonitrile, etc. Is mentioned. In particular, in the case of phenylmethylpolysilane, hydrophilic organic solvents such as water or alcohol mixed with water or ketone can be suitably used.
[0036]
The concentration of the metal salt varies depending on the solvent in which the salt is dissolved, but from 0.01% to a saturated solution of the salt is used. If it is less than 0.01%, the amount of the metal colloid used as a plating catalyst is not sufficient, and if it exceeds the saturated solution, solid salt is precipitated, which is not preferable. When the solvent is water, 0.01 to 20%, more preferably 0.1 to 5% is often used.
[0037]
The silicon-based polymer compound-treated powder may be immersed in the metal salt solution at a temperature of room temperature to 70 ° C. for 0.1 to 120 minutes, more preferably about 1 to 15 minutes. Thereby, a powder in which a metal colloid is deposited on the surface of the silicon polymer compound on the carbon powder can be produced.
[0038]
The treatment of the solution containing the metal salt is carried out in the presence or absence of a surfactant, and it is particularly desirable to carry out the treatment in the presence of a surfactant. That is, the powder is made hydrophobic by the silicon polymer compound treatment. For this reason, since the affinity with the solution in which the metal salt is dissolved decreases and does not disperse in the solution, the efficiency of the metal colloid generation reaction may decrease. In this case, it is preferable to improve by adding a surfactant, whereby the silicon-based polymer compound-treated powder can be dispersed in a solution containing a metal salt in a short time.
[0039]
Here, as the surfactant, those which do not cause foaming and reduce only the surface tension are desirable, and a nonionic surfactant such as Surfynol 104, 420, 504 (manufactured by Nissin Chemical Industry Co., Ltd.) is suitable. Can be used.
[0040]
In the case of adding a surfactant, the amount of the surfactant added is preferably such that the silicon-based polymer compound-coated powder is uniformly dispersed in the surfactant solution or the metal salt solution containing the surfactant. It is desirable to use in the range of 0.0001 to 10 parts by weight, particularly 0.001 to 1 part by weight, especially 0.01 to 0.5 part by weight, based on 100 parts by weight of the metal salt solution. If the amount of surfactant added is too small, the effect may be poor.
[0041]
As the treatment method, it is preferable that the silicon-based polymer compound-treated powder is first brought into contact with a surfactant or a surfactant diluted with water, stirred and dispersed, and then brought into contact with a solution containing a metal salt, As a result, the reaction of forming the metal colloid on the film surface by the reducing action of the silicon-based polymer compound can be rapidly advanced. Further, if necessary, heat treatment is performed at a temperature of 50 to 60 ° C. to promote the adsorption of the metal salt on the surface of the silicon-based polymer compound film and the formation of the metal colloid from the metal salt.
[0042]
When the surfactant is not used, it is preferable that the silicon-based polymer compound-treated powder is brought into contact with a solvent and sufficiently stirred and dispersed.
[0043]
After such treatment, treatment with the same solvent as above without metal salt is performed, except for the metal salt that is not reduced and merely adsorbed on the powder, and finally the unnecessary solvent is removed from this powder. Thus, a metal colloid-coated powder can be obtained.
[0044]
The silicon-based polymer compound-treated powder may be immersed in the metal salt solution at a temperature of room temperature to 70 ° C. for 0.1 to 120 minutes, more preferably about 1 to 15 minutes. Thereby, a powder in which a metal colloid is deposited on the surface of the silicon-based polymer compound can be produced.
[0045]
After that, by heating as necessary, the formation of metal colloid from the platinum-based transition metal salt on the surface of the silicon-based polymer compound is promoted, and a powder coated with a polymer in which the platinum-based transition metal is well dispersed is obtained. be able to. As heating conditions, it is usually preferable to carry out at room temperature to 150 ° C. for 1 minute to 10 hours at normal pressure or reduced pressure.
[0046]
The amount of platinum-based transition metal supported on the silicon-based polymer compound-treated powder used as a fuel cell catalyst is generally 1 to 50%, and 3 to 25% is desirable from the relationship between electrode price and performance.
[0047]
Thereafter, according to a conventional method, the fuel cell catalyst is mixed with a water repellent such as Teflon dispersion, an admixture such as alcohol, a surfactant, etc., and applied to a conductive porous substrate such as carbon paper. The molded body obtained at the end can be fired to produce a fuel cell electrode.
[0048]
Firing can be performed in an atmosphere of an oxidizing gas, a reducing gas such as argon-hydrogen and ammonia, or an inert gas such as argon, helium, and nitrogen. The heat treatment temperature is desirably 150 ° C. to 350 ° C. in an oxidizing gas atmosphere, and desirably 150 ° C. to 1000 ° C. in a reducing gas or inert gas atmosphere, and is particularly heat treated at a temperature of 200 ° C. or higher. It is preferable. The treatment time is 0.5 to 8 hours, more preferably 1 to 4 hours. As a result, a part or all of the reducing silicon polymer compound between the powder and the metal is converted into a ceramic so that a fuel cell electrode having higher heat resistance, insulation and adhesion can be suitably produced. be able to.
[0049]
【Example】
EXAMPLES Hereinafter, although a synthesis example, an Example, and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.
[0050]
[Synthesis Example 1]
Production method of polysilane
Phenyl hydrogen polysilane (hereinafter abbreviated as PPHS) was produced by the following method.
In a flask purged with argon, a diethyl ether solution of methyllithium was added to a THF solution of bis (cyclopentadienyl) dichlorozirconium and reacted at room temperature for 30 minutes. The catalyst was prepared within. To this was added 10,000 times moles of phenyltrihydrosilane as a catalyst, and the mixture was heated and stirred at 100 to 150 ° C. for 3 hours and then at 200 ° C. for 8 hours. The catalyst was deactivated and removed by dissolving the product in toluene and washing with hydrochloric acid. Magnesium sulfate was added to the toluene solution to remove water, and the solution was filtered. As a result, PPHS having a weight average molecular weight of 1,200 and a glass transition point of 65 ° C. was obtained almost quantitatively.
[0051]
[Example 1]
Polysilane treatment of carbon powder
Commercially available acetylene black was used as the carbon powder. 1 g of PPHS was dissolved in 200 g of toluene, and this solution was added to 100 g of acetylene black and stirred for 1 hour. In a rotary evaporator, toluene was distilled off and dried at a temperature of 60 ° C. and a pressure of 45 mmHg. A 1% polysilane treated powder was obtained.
[0052]
Production of colloidal platinum powder
The polysilane-treated powder is hydrophobized and floats on the water surface when thrown into water. As a surfactant, 10 g of this treated powder was added to 200 g of a 0.5% aqueous solution of Surfynol 504 (surfactant manufactured by Nissin Chemical Industry Co., Ltd.) and dispersed in water by stirring using ultrasonic waves. .
[0053]
The platinum treatment is 2% H with respect to 210 g of the powder-water dispersion.₂PtCl₆50 g of aqueous solution (1 g as chloroplatinic acid, 0.48 g as platinum) was added, stirred for 30 minutes, filtered, and washed with water. By these treatments, a powder having platinum colloid adhered to the powder surface was obtained. This powder was isolated by filtration, washed with water, dried and heated in air at 250 ° C. for 1 hour.
[0054]
Analysis of platinum colloid deposition powder
When this catalyst was observed with an electron microscope, it was confirmed that a platinum colloid of 1 to 5 nm was held on the support in the form of primary particles, and even when heated at 250 ° C. in air for 1 hour, A uniform dispersion was confirmed.
[0055]
[Comparative Example 1]
For comparison, 10 g of acetylene black not subjected to polysilane treatment was added to 200 g of a 0.5% aqueous solution of Surfynol 504, and similarly stirred and dispersed in water.
[0056]
The platinum treatment is 2% H with respect to 210 g of the powder-water dispersion.₂PtCl₆50 g of an aqueous solution was added and treated under the same conditions as in Example 1. In these treatments, no platinum colloid was produced, and a powder having platinum ions attached to the powder surface was obtained. This powder could not carry and carry platinum ions by washing with water.
[0057]
[Comparative Example 2] Conventional general adjustment method
2 g of polyvinyl alcohol was added to 400 g of an aqueous solution of 50% / 50% methanol / water and stirred to dissolve. 5 g of acetylene black not subjected to polysilane treatment was put into 400 g of this aqueous methanol solution, and stirred ultrasonically and dispersed in water.
[0058]
The platinum treatment is 2% H with respect to 405 g of the powder-water dispersion.₂PtCl₆50 g of an aqueous solution was added and stirred vigorously while heating at 70 ° C. under reflux. After 8 hours, it was filtered and washed with water. In these treatments, a powder in which platinum colloid adhered to the powder surface was obtained. When this catalyst was observed with an electron microscope, it was confirmed that the platinum colloid which was agglomerated at 10 to 50 nm and became secondary particles was uniformly dispersed on the carrier. When heated, it was confirmed that it was unevenly distributed on the carrier in a large lump of μm or more.
[0059]
1 g of the catalyst prepared in Example 1 and Comparative Example 2 was weighed, and a 25 V / V% ethanol aqueous solution and a Teflon dispersion liquid were added to the catalyst so that the amount was 25 wt%, and the mixture was kneaded and applied onto carbon paper. did. After air drying at room temperature all day and night, it was dried at 150 ° C. for 2 hours, and further calcined in air at 350 ° C. for 2 hours to form a catalyst electrode.
[0060]
The performance of these electrodes was evaluated in phosphoric acid at 190 ° C. as the monopolar potential of the oxygen electrode with respect to the standard hydrogen electrode. The results are shown in Table 1.
[0061]
[Table 1]

[0062]
As shown in Table 1, compared with the performance of the electrode produced in Comparative Example 2, according to the method of the present invention, platinum is finely dispersed and uniformly dispersed, and the state remains even after the heat history. It was clarified that the electrode performance was greatly improved and the service life was greatly improved because it was maintained.
[0063]
【The invention's effect】
According to the present invention, a carbon powder coated with a silicon-based polymer in which a platinum-based transition metal is dispersed can be obtained by a simple and rapid process, which is a highly efficient and highly durable fuel cell catalyst. It can be used as an available catalyst electrode.

Claims (11)

A fuel cell catalyst comprising a carbon powder carrying platinum-based transition metal fine particles obtained by bringing a platinum-based transition metal salt into contact with a carbon powder whose surface is coated with a silicon polymer compound having a reducing property . The catalyst according to claim 1, wherein the platinum-based transition metal is platinum, Ir, Pd, or Rh. The silicon-based polymer compound having reducibility is selected from polysilane, polycarbosilane, polysiloxane, and polysilazane having a Si-Si bond and / or Si-H bond. catalyst. The catalyst according to claim 3, wherein the polysilane is represented by the following formula (1).
(R ¹ _m R ² _n X _p Si) _q (1)
Wherein R ¹ and R ² are a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group, X is R ¹ , an alkoxy group, a halogen atom, an oxygen atom or a nitrogen atom, and m is 0.1 ≦ m ≦ 2, n is 0 ≦ n ≦ 1, p is 0 ≦ p ≦ 0.5, and 0.1 ≦ m + n + p ≦ 2.5, and q satisfies 4 ≦ q ≦ 100,000 (It is an integer.) The catalyst according to claim 3, wherein the polysiloxane is represented by the following formula (2).
(R ³ _a R ⁴ _b H _c SiO _d ) _e ( 2 )
(Wherein R ³ and R ⁴ represent a hydrogen atom, a substituted or unsubstituted monovalent hydrocarbon group, an alkoxy group or a halogen atom, a is 0.1 ≦ a ≦ 2, b is 0 ≦ b ≦ 1, c is a number satisfying 0.01 ≦ c ≦ 1, d is 0.5 ≦ d ≦ 1.95 and 2 ≦ a + b + c + d ≦ 3.5, and e is an integer satisfying 2 ≦ e ≦ 100,000 .) A carbon powder obtained by treating carbon powder with a solution in which a reducing silicon-based polymer compound is dissolved in an organic solvent, then removing the organic solvent from the surface of the carbon powder and coating the surface with the silicon-based polymer compound. A platinum-based transition metal salt dissolved in or dispersed in a solvent that does not dissolve the silicon-based polymer compound, and the platinum-based transition metal salt is converted into a platinum-based transition metal with the silicon-based polymer compound. A method for producing a catalyst for a fuel cell, characterized in that carbon powder carrying platinum-based transition metal fine particles is obtained by reduction to a colloid. The method according to claim 6, wherein the platinum-based transition metal is platinum, Ir, Pd, or Rh. 8. The silicon-based polymer compound having reducibility is selected from polysilane, polycarbosilane, polysiloxane, and polysilazane having a Si—Si bond and / or a Si—H bond. Method. The method according to claim 8, wherein the polysilane is represented by the following formula (1).
(R ¹ _m R ² _n X _p Si) _q (1)
Wherein R ¹ and R ² are a hydrogen atom or a substituted or unsubstituted monovalent hydrocarbon group, X is R ¹ , an alkoxy group, a halogen atom, an oxygen atom or a nitrogen atom, and m is 0.1 ≦ m ≦ 2, n is 0 ≦ n ≦ 1, p is 0 ≦ p ≦ 0.5, and 0.1 ≦ m + n + p ≦ 2.5, and q satisfies 4 ≦ q ≦ 100,000 (It is an integer.) The method according to claim 8, wherein the polysiloxane is represented by the following formula (2).
(R ³ _a R ⁴ _b H _c SiO _d ) _e ( 2 )
Wherein R ³ and R ⁴ represent a hydrogen atom, a substituted or unsubstituted monovalent hydrocarbon group, an alkoxy group or a halogen atom, a is 0.1 ≦ a ≦ 2, b is 0 ≦ b ≦ 1, c is a number satisfying 0.01 ≦ c ≦ 1, d is 0.5 ≦ d ≦ 1.95, and 2 ≦ a + b + c + d ≦ 3.5, and e is an integer satisfying 2 ≦ e ≦ 100,000 .) An electrode for a fuel cell containing the fired product of the catalyst according to any one of claims 1 to 5.