JP2006134603A - Catalyst structure and film-electrode junction for solid, polymer type fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst structure made to carry a catalyst material on a carrier by reactive sputtering method, and to provide a film-electrode junction for a solid, polymer type fuel cell that uses the catalyst structure. <P>SOLUTION: The catalyst structure is formed by coating a catalyst material on the surface of the carrier by reactive sputtering method. The film-electrode junction for solid, polymer type fuel cell is composed of a solid, polymer type electrolyte film, a catalyst layer arranged on both sides of the solid, polymer type electrolyte film, and a diffusion layer arranged on both sides of the catalyst layer. The film-electrode junction for solid, polymer type fuel cell uses this catalyst structure as the catalyst layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a catalyst structure and a membrane electrode assembly for a polymer electrolyte fuel cell using the catalyst structure, and more particularly to a catalyst structure suitable for a catalyst layer of a membrane electrode assembly of a polymer electrolyte fuel cell. Is.

  In recent years, fuel cells have attracted attention as a battery with high power generation efficiency and a low environmental load, and extensive research and development has been conducted. Among fuel cells, polymer electrolyte fuel cells with high output density and low operating temperature are easier to reduce in size and cost than other types of fuel cells. It is expected to spread widely as a household cogeneration system.

  In general, in a polymer electrolyte fuel cell, a pair of electrodes are arranged with a polymer electrolyte membrane sandwiched between them, a fuel gas such as hydrogen is brought into contact with the surface of one electrode, and oxygen is applied to the surface of the other electrode. The oxygen-containing gas contained is brought into contact, and electric energy is taken out between the electrodes by using an electrochemical reaction that occurs at this time (see Non-Patent Documents 1 and 2). A catalyst layer is disposed on the electrode in contact with the polymer electrolyte membrane, and an electrochemical reaction occurs at the three-phase interface between the polymer electrolyte membrane, the catalyst layer, and the gas. Therefore, in order to improve the power generation efficiency of the polymer electrolyte fuel cell, it is necessary to expand the reaction field of the electrochemical reaction.

  In order to form a catalyst layer capable of expanding the reaction field of the electrochemical reaction, generally, a paste or slurry containing catalyst powder in which a noble metal catalyst such as platinum is supported on granular carbon such as carbon black, The method of apply | coating on electroconductive porous supports, such as carbon paper, is taken. However, even a polymer electrolyte fuel cell including a catalyst layer formed by this method still has room for improvement in terms of power generation efficiency, and the reaction field for the electrochemical reaction can be further expanded. Development of a catalyst layer is required.

The Chemical Society of Japan, “Chemical Review No. 49, Material Chemistry of New Batteries”, Academic Publishing Center, 2001, p. 180-182 “Polymer fuel cell <2001 edition>”, Technical Information Association, 2001, p. 14-15

  Under such circumstances, an object of the present invention is to provide a catalyst structure in which a catalyst material is supported on a support by a novel method that has not been attempted in the past, and a polymer electrolyte fuel cell using the catalyst structure. The object is to provide a membrane electrode assembly.

  As a result of trying various catalyst loading methods, the present inventors obtained a catalyst structure having high catalytic activity by coating a catalyst on a support by a reactive sputtering method, in which a solid polymer fuel is obtained. The inventors have found that there is a material that functions sufficiently as a catalyst layer of a membrane electrode assembly for a battery, and completed the present invention.

  That is, the catalyst structure of the present invention is characterized in that the catalyst surface is coated with a catalyst material by a reactive sputtering method.

  The catalyst structure of the present invention is preferably one in which one or a plurality of metals or metal compounds are simultaneously sputtered and the catalyst surface is coated with the catalyst material. Here, as the catalyst structure of the present invention, when the plurality of metals or metal compounds are sputtered, a plurality of cathodes are simultaneously discharged to coat the support surface with a catalyst material, and When sputtering a metal or metal compound, it is more preferable that a plurality of targets are attached to one cathode, and a plurality of metals are simultaneously sputtered at the cathode during discharge to coat the support surface with a catalyst material. When sputtering the plurality of metals or metal compounds, a plurality of targets are attached to one cathode, and a plurality of metals are simultaneously sputtered at the cathode during discharge to coat the catalyst material on the surface of the support. It is also preferable to remove at least one kind of metal or metal compound in the prepared catalyst material with an acid and / or an alkali. Further, when attaching the plurality of targets to one cathode, when there are two targets, the targets are arranged to face each other, and when there are three or more targets, the targets are arranged in a polyhedral shape. Is preferred.

  As the catalyst structure of the present invention, in the reactive sputtering, the amount of luminescence at the time of discharge is monitored, and a reactive gas is supplied in the vicinity of the cathode or the carrier according to the amount of luminescence, or the power supply unit at the time of discharge It is also preferable to monitor the impedance and supply a reactive gas in the vicinity of the cathode or the carrier in accordance with the impedance value. Here, it is more preferable that the catalyst structure is obtained by performing the reactive sputtering in a transition region in which current, voltage, and power change greatly according to the amount of reactive gas.

  As the catalyst structure of the present invention, in the reactive sputtering, a hidden anode is provided near the cathode and an AC voltage is applied between the cathode and the anode, or a plurality of cathodes are provided and an AC voltage is applied to the cathode. Is also preferable. Here, it is preferable that the waveform of the AC voltage is a sine wave or a rectangular wave. Further, it is more preferable that the rectangular wave has a pulse shape, and the application pattern, more specifically, the application pattern defined by positive / negative application voltage, positive / negative application time and application ratio is arbitrarily controlled.

  In a preferred embodiment of the catalyst structure of the present invention, the metal is Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, Mo, Ru, Rh, Ag, Cd, In, Sn, Sb, Cs, Ba, La, Hf, Ta, W, Re, Os, Ir, Tl, Pb, It is at least one selected from the group consisting of Bi, Ce, Pr, Nd, Sm and Eu.

  In another preferred embodiment of the catalyst structure of the present invention, the metal is a noble metal. Here, it is preferable that the noble metal is at least one selected from the group consisting of Ag, Pt and Au.

In another preferred embodiment of the catalyst structure of the present invention, the metal compound is a metal oxide. Here, the metal oxide is AlO _x , SiO _x , TiO _x , FeO _x , CoO _x , NiO _x , CuO _x , ZnO _x , NbO _x , MoO _x , LaO _x , TaO _x , WO _x and PbO _x. It is preferable that the value of x is controlled by the oxygen flow rate during sputtering.

In another preferred embodiment of the catalyst structure of the present invention, the metal compound is a metal nitride. Here, the metal nitride is AlN _x , SiN _x , TiN _x , FeN _x , CoN _x , NiN _x , CuN _x , ZnN _x , NbN _x , MoN _x , LaN _x , TaN _x , WN _x and PbN _x. It is preferable that the value of x is controlled by a nitrogen flow rate during sputtering.

In another preferred embodiment of the catalyst structure of the present invention, the metal compound is a metal carbide. Here, the metal carbide is composed of AlC _x , SiC _x , TiC _x , FeC _x , CoC _x , NiC _x , CuC _x , ZnC _x , NbC _x , MoC _x , LaC _x , TaC _x , WC _x and PbC _x. It is preferable that the value of x is controlled by the hydrocarbon flow rate during sputtering.

In another preferred embodiment of the catalyst structure of the present invention, the metal compound is a metal oxynitride. Here, the metal oxynitride is AlO _x N _y , SiO _x N _y , TiO _x N _y , FeO _x N _y , CoO _x N _y , NiO _x N _y , CuO _x N _y , ZnO _x N _y , NbO _x N _y , MoO _x N _y , LaO _x N _y , TaO _x N _y , WO _x N _y, and PbO _x N _y , and at least one of the values of x and y are sputtered. It is preferable to control by the oxygen flow rate and the nitrogen flow rate.

  In the catalyst structure of the present invention, the use efficiency of the target material used in the reactive sputtering is preferably 80% or more.

  In another preferred embodiment of the catalyst structure of the present invention, the carrier is a carbon fiber aggregate. Here, as the carbon fiber aggregate, carbon paper, a fibrillar carbon fiber aggregate having a diameter of 1 nm to 1 μm, and the fibrillar carbon fiber aggregate having a diameter of 1 nm to 1 μm are disposed on the carbon paper. A composite carbon aggregate is preferred.

  As the carrier of the catalyst structure of the present invention, a three-dimensional continuous product obtained by oxidative polymerization of a compound having an aromatic ring to obtain a fibril-like polymer, and firing the fibril-like polymer, preferably in a non-oxidizing atmosphere. A carbon fiber is particularly preferred. Here, the compound having an aromatic ring is preferably a compound having a benzene ring or an aromatic heterocyclic ring, and is at least one compound selected from the group consisting of aniline, pyrrole, thiophene and derivatives thereof. Further preferred.

  Further, a membrane electrode assembly for a polymer electrolyte fuel cell of the present invention comprises a solid polymer electrolyte membrane, a catalyst layer disposed on both sides of the solid polymer electrolyte membrane, and a diffusion layer disposed on both sides of the catalyst layer In the membrane electrode assembly for a polymer electrolyte fuel cell comprising the above, the catalyst structure is used for the catalyst layer.

  ADVANTAGE OF THE INVENTION According to this invention, the novel catalyst structure which coated the catalyst material on the support | carrier by the reactive sputtering method, and the membrane electrode assembly for polymer electrolyte fuel cells using this catalyst structure can be provided.

The present invention is described in detail below. The catalyst structure of the present invention is obtained by coating the support surface with a catalyst material by a reactive sputtering method. By coating the catalyst surface on the surface of the support by reactive sputtering, the film can be formed at a film formation rate of 2 to 20 times in the case of a metal oxide thin film, compared with a normal sputtering method (planar type magnetron sputtering). it can. As a high-speed film formation method, a vacuum deposition method is popular, but the adhesion with the base material is poor. On the other hand, a film firmly bonded to the base material can be produced by using the sputtering method. Therefore, in order to obtain a certain film thickness for exerting the catalytic performance, the sputtering method can form a film in a short time, so that it can be formed at a low temperature and has excellent adhesion to the carrier. A catalyst support material can be formed. On the other hand, the control of reactive gas flow to flow during film formation, as described in the present application, e.g., MeO _x (Me represents a metal, hereinafter the same) x values such, MeO _x N _y or the like of the x, y The value can be controlled, and this control is not possible with vacuum deposition. The catalyst structure of the present invention is effective as a catalyst for various chemical reactions, but is particularly suitable as a catalyst layer of a polymer electrolyte fuel cell.

  In the present invention, the reactive sputtering method used to coat the catalyst surface on the support surface is a method in which a reactive gas is mixed in a sputtering gas and the composition and properties of the thin film of the catalyst material formed by sputtering are controlled. is there. The reactive sputtering method is preferably performed by a dual cathode type magnetron sputtering method, more preferably by a bipolar type dual cathode type magnetron sputtering method or a unipolar type dual cathode type magnetron sputtering method. FIG. 1 is a schematic diagram of a bipolar type dual cathode type magnetron sputtering apparatus suitable for implementing the present invention, and FIG. 2 is a schematic diagram of a unipolar type dual cathode type magnetron sputtering apparatus suitable for implementing the present invention.

  In the bipolar dual cathode magnetron sputtering apparatus shown in FIG. 1, targets 2A and 2B are disposed on the cathodes 1A and 1B, and magnets 3A and 3B are disposed on the back surfaces of the cathodes 1A and 1B. The cathodes 1A and 1B are connected to AC power supplies 5A and 5B via the switching unit 4. Further, gas inlets 6A and 6B are arranged in the vicinity of the targets 2A and 2B, and the reactivity controlled by the piezo valves 7A and 7B capable of instantaneous gas supply from the inlets 6A and 6B. Gas is supplied. Here, instead of the piezo valve, other control devices such as a high-speed responsive mass flow controller may be used for the reactive gas supply control. Further, sensors 8A and 8B for monitoring the light emission amount at the time of discharge are arranged in the vicinity of the gas inlets 6A and 6B. The sensors 8A and 8B send signals to the controllers 9A and 9B. 9A and 9B control the opening and closing of the piezo valves 7A and 7B according to the signal. It is also possible to monitor the impedance of the AC power supplies 5A and 5B and control the supply of the reactive gas according to the impedance value. In the sputtering apparatus shown in FIG. 1, electric power is alternately supplied to the cathode 1 </ b> A and the cathode 1 </ b> B by the switching unit 4. Therefore, the coating of the catalyst material can be formed at high speed and stably, and the polarity is changed by switching by the switching unit 4, and the charge accumulated in the targets 2A and 2B is eliminated, so that stable sputtering is performed. In addition, the composition in the thin film made of the catalyst material can be made uniform.

  On the other hand, in the unipolar type dual cathode magnetron sputtering apparatus shown in FIG. 2, targets 2A and 2B are disposed on the cathodes 1A and 1B, and magnets 3A and 3B are disposed on the back surfaces of the cathodes 1A and 1B. Yes. The cathodes 1A and 1B are connected to AC power supplies 5A and 5B via switching units 4A and 4B, respectively. Further, gas inlets 6A and 6B are arranged in the vicinity of the targets 2A and 2B, and the reactivity controlled by the piezo valves 7A and 7B capable of instantaneous gas supply from the inlets 6A and 6B. Gas is supplied. Further, sensors 8A and 8B for monitoring the light emission amount at the time of discharge are arranged in the vicinity of the gas inlets 6A and 6B. The sensors 8A and 8B send signals to the controllers 9A and 9B. 9A and 9B control the opening and closing of the piezo valves 7A and 7B according to the signal. Furthermore, hidden anodes 10A and 10B are disposed in the vicinity of the cathodes 1A and 1B, and an alternating voltage can be applied between the cathode and the anode. In the sputtering apparatus shown in FIG. 2, it is possible to apply a voltage independently to the cathodes 1A and 1B by the switching units 4A and 4B.

  1 and 2, the carrier 11 is supported by a holder 12, and a coating of a catalyst material having a desired composition can be formed on the surface of the carrier 11 from sputtered particles and a reactive gas.

  The catalyst material is usually composed of a metal and / or a metal compound. In the present invention, at least one of the metal and the metal compound is sputtered to form a film of the catalyst material on the surface of the support. Here, the metal and metal compound to be sputtered may be a single kind or a mixture of two or more kinds. When a plurality of metals or metal compounds are sputtered to form a catalyst material layer on the support surface, it is preferable to simultaneously sputter the plurality of metals or metal compounds.

  When sputtering the plurality of metals or metal compounds, it is preferable to discharge simultaneously using the plurality of cathodes 1A and 1B and coat the catalyst material on the surface of the carrier. Here, by disposing the targets 2A and 2B made of different metals on the respective cathodes 1A and 1B, it becomes possible to form a catalyst material film by simultaneously sputtering a plurality of metals or metal compounds.

  When sputtering the plurality of metals or metal compounds, it is also preferable to attach a plurality of targets to one cathode, and simultaneously coat the catalyst material on the support surface by sputtering a plurality of metals at the cathode during discharge. Here, after a plurality of metals are simultaneously sputtered on the cathode to coat the catalyst material on the surface of the support, at least one of the metals or metal compounds in the coated catalyst material may be removed with an acid and / or alkali. Good. Here, the acid and alkali used for removing the metal or metal compound are appropriately selected according to the type of the metal or metal compound to be removed and the metal or metal compound to be left. For example, the acid is hydrochloric acid. , Sulfuric acid, nitric acid, phosphoric acid, acetic acid, hydrofluoric acid, chromic acid, hydrogen peroxide, perchloric acid, chloric acid, chlorous acid, hypochlorous acid, citric acid, oxalic acid, hydrogen bromide, etc. These can be used as an aqueous solution alone or with a mixed acid obtained by mixing them. Further, depending on the metal to be dissolved, a mixed aqueous solution of a mixed acid, a metal chloride such as ferric chloride, and a metal sulfide can be used. On the other hand, as the alkaline aqueous solution, an aqueous solution such as sodium hydroxide or potassium hydroxide, aqueous ammonia, or the like can be used. In addition, the density | concentration and composition of acid aqueous solution and alkali aqueous solution can be suitably selected according to the kind of metal to melt | dissolve.

  Further, when attaching the plurality of targets to one cathode, when there are two targets, the targets are preferably arranged facing each other, and when there are three or more targets, the targets are preferably arranged in a polyhedral shape. For example, when there are three targets, it is preferable that the targets are arranged in a triangular shape, and when there are four targets, the targets are arranged in a quadrangular shape.

  In the reactive sputtering, it is preferable to monitor the amount of light emitted during discharge and supply a reactive gas to the cathode or the vicinity of the carrier according to the amount of light emitted. In the reactive sputtering, it is also preferable to monitor the impedance of the power supply units 5A and 5B during discharge and supply a reactive gas to the cathode or the vicinity of the carrier according to the impedance value. A catalyst that is supported by supplying a reactive gas to the cathodes 1A, 1B or the vicinity of the carrier 11 according to the amount of luminescence, or by supplying a reactive gas to the cathodes 1A, 1B or the vicinity of the carrier 11 according to the impedance value. The composition of the material can be controlled uniformly. Here, it is preferable to perform the reactive sputtering in a transition region where the current, voltage, and power change greatly according to the amount of reactive gas.

  In the reactive sputtering, it is preferable to provide hidden anodes 10A and 10B in the vicinity of the cathodes 1A and 1B and apply an AC voltage between the cathode and the anode. It is also preferable to provide a plurality of cathodes 1A and 1B and apply an AC voltage to the cathodes 1A and 1B. Here, as the waveform of the AC voltage, a sine wave and a rectangular wave are preferable. Further, when the waveform of the AC voltage is a rectangular wave, the rectangular wave is in a pulse shape, and it is preferable to arbitrarily control the application pattern. Here, the application pattern is defined by positive / negative applied voltage, positive / negative application time, application ratio, and the like.

  The metals to be sputtered are Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr. , Nb, Mo, Ru, Rh, Ag, Cd, In, Sn, Sb, Cs, Ba, La, Hf, Ta, W, Re, Os, Ir, Tl, Pb, Bi, Ce, Pr, Nd, Sm And Eu are preferably selected, and the catalyst structure of the present invention may use these metals alone or in combination of two or more of these metals.

  Further, depending on the purpose of use of the catalyst structure, the metal is preferably a noble metal, and examples of the noble metal include Ag, Pt, and Au. One or more of these noble metals can be used in the catalyst structure of the present invention. In addition, when using a catalyst structure for the catalyst layer of the membrane electrode assembly for polymer electrolyte fuel cells, Pt is particularly preferable among noble metals. By using Pt as the noble metal, hydrogen can be oxidized with high efficiency even at a low temperature of 100 ° C. or lower. Further, by using Pt as an alloy with other metals such as Ru, it is possible to prevent poisoning of Pt by CO and prevent a decrease in the activity of the catalyst.

  Examples of the metal compound sputtered in the present invention include metal oxides, metal nitrides, metal carbides, and metal oxynitrides. The catalyst structure is used as a catalyst layer of a membrane electrode assembly for a polymer electrolyte fuel cell. When used, it is preferable to sputter metal oxynitride. When these metal compounds are coded on the surface of the carrier, it is preferable to perform reactive sputtering by using the above metals for the targets 2A and 2B and introducing a reactive gas from the inlets 6A and 6B.

The metal _{oxide, AlO x, SiO x, TiO} x, FeO x, CoO x, NiO x, CuO x, ZnO x, NbO x, MoO x, LaO x, TaO x, etc. WO _x and PbO _x is In the catalyst structure of the present invention, these metal oxides may be used alone, or two or more of these metal oxides may be used. Here, according to the reactive sputtering, the value of x in each chemical formula can be controlled to a desired value by adjusting the flow rate of oxygen introduced from the inlets 6A and 6B during sputtering. Become.

Further, as the metal _{nitride, AlN x, SiN x, TiN} x, FeN x, CoN x, NiN x, CuN x, ZnN x, NbN x, MoN x, LaN x, TaN x, WN x and PbN _x In the catalyst structure of the present invention, these metal nitrides may be used alone, or two or more of these metal nitrides may be used. Here, according to the reactive sputtering, the value of x in each chemical formula can be controlled to a desired value by adjusting the flow rate of nitrogen introduced from the inlets 6A and 6B during sputtering. Become.

The metal _{carbide, AlC x, SiC x, TiC} x, FeC x, CoC x, NiC x, CuC x, ZnC x, NbC x, MoC x, LaC x, TaC x, WC x and PBC _x or the like can be mentioned In the catalyst structure of the present invention, these metal carbides may be used alone, or two or more of these metal carbides may be used. Here, according to the reactive sputtering, the value of x in each chemical formula can be controlled to a desired value by adjusting the flow rate of hydrocarbons introduced from the inlets 6A and 6B during sputtering. It becomes. In addition, there is no restriction | limiting in particular as hydrocarbon used in reactive sputtering, Methane, ethane, ethylene, acetylene etc. are mentioned.

Examples of the metal oxynitride include AlO _x N _y , SiO _x N _y , TiO _x N _y , FeO _x N _y , CoO _x N _y , NiO _x N _y , CuO _x N _y , ZnO _x N _y , NbO _x N _y , MoO _x N _y , LaO _x N _y , TaO _x N _y , WO _x N _y, PbO _x N _{y and the} like can be mentioned. The catalyst structure of the present invention includes one of these metal oxynitrides. You may use independently and 2 or more types of these metal oxynitrides may be used. Here, according to the reactive sputtering, the values of x and y in the chemical formulas are controlled to desired values by adjusting the flow rates of oxygen and nitrogen introduced from the inlets 6A and 6B during sputtering. It becomes possible. In addition, when using a catalyst structure for the catalyst layer of the membrane electrode assembly for polymer electrolyte fuel cells, it is more preferable to use TiO _x N _y among these metal oxynitrides.

  In a preferred embodiment of the present invention, the use efficiency of the target material used in the reactive sputtering is 80% or more. In this case, an expensive target material can be used effectively.

The supported amount of the catalyst material in the catalyst structure of the present invention varies greatly depending on the catalyst performance of the material, but is preferably in the range of 0.001 mg / cm ^{2 to} 10 g / cm ² . When the supported amount is less than 0.001 mg / cm ² , the function as a catalyst is insufficient. On the other hand, when it exceeds 10 g / cm ² , the effective area as a catalyst cannot be obtained and the catalyst performance is saturated.

  The carrier constituting the catalyst structure of the present invention is preferably a carbon fiber aggregate. Here, as the carbon fiber aggregate, carbon paper and a fibrillar carbon fiber aggregate having a diameter of 1 nm to 1 μm are more preferable. Further, as the carrier, a composite carbon aggregate obtained by disposing fibrillar carbon fiber aggregates having a diameter of 1 nm to 1 μm on carbon paper is particularly preferable.

  The fibrillar carbon fiber aggregate used as the carrier is obtained by oxidatively polymerizing a compound having an aromatic ring to obtain a fibrillar polymer, and firing the fibrillated polymer, preferably in a non-oxidizing atmosphere. Particularly preferred is a three-dimensional continuous carbon fiber. In addition, examples of the compound having an aromatic ring include a compound having a benzene ring and a compound having an aromatic heterocyclic ring. As the compound having a benzene ring, aniline and aniline derivatives are preferable, and the aromatic heterocyclic ring. As the compound having pyrrole, pyrrole, thiophene and derivatives thereof are preferable. These compounds having an aromatic ring may be used alone or as a mixture of two or more.

  The fibrillar polymer obtained by oxidative polymerization of the compound having an aromatic ring has a diameter of 30 to several hundred nm, preferably 40 to 500 nm, and a length of 0.5 to 100,000 μm, preferably 1 to 10,000 μm. .

As the oxidative polymerization method, an electrolytic oxidative polymerization method is preferable. Moreover, in oxidative polymerization, it is preferable to mix an acid with the compound which has a raw material aromatic ring. In this case, the negative ion of the acid is taken into the fibril polymer synthesized as a dopant to obtain a fibril polymer excellent in conductivity, and the conductivity of the carbon fiber finally obtained by using this fibril polymer is obtained. Can be improved. The acid mixed in the polymerization is not particularly limited, and examples thereof include HBF ₄ , H ₂ SO ₄ , HCl, HClO ₄ , and the concentration of the acid is 0.1 to 3 mol / The range of L is preferable, and the range of 0.5 to 2.5 mol / L is more preferable.

When a fibrillated polymer is obtained by the electrolytic oxidation polymerization, the working electrode and the counter electrode are immersed in a solution containing the compound having an aromatic ring, and a voltage higher than the oxidation potential of the compound having the aromatic ring is applied between both electrodes. Or a current having such a condition that a voltage sufficient to polymerize the compound having an aromatic ring may be passed, whereby a fibril-like polymer is formed on the working electrode. Here, as the working electrode and the counter electrode, a plate made of a highly conductive material such as stainless steel, platinum, or carbon, a porous material, or the like can be used. Also, the current density in the electrolytic oxidation polymerization is preferably in the range of 0.1~1000mA / cm ^2, more preferably in the range of 0.2~100mA / cm ^2, the concentration of the electrolytic solution of the compound having an aromatic ring, 0.05 to 3 mol / The range of L is preferable, and the range of 0.25 to 1.5 mol / L is more preferable. In addition to the above components, a soluble salt or the like may be appropriately added to the electrolytic solution in order to adjust the pH.

  The fibrillated polymer obtained on the working electrode as described above is washed with a solvent such as water or an organic solvent, dried, then fired, preferably fired in a non-oxidizing atmosphere and carbonized. A fibril-like three-dimensional continuous carbon fiber is obtained. Here, the drying method is not particularly limited, and examples thereof include a method using a fluidized bed drying device, an air dryer, a spray dryer, etc., in addition to air drying and vacuum drying. In addition, the firing conditions are not particularly limited, and may be set as appropriate so as to obtain the optimum conductivity. Particularly, when high conductivity is required, the temperature is 500 to 3000 ° C., preferably 600 to Baking is preferably performed at 2800 ° C. for 0.5 to 6 hours. Further, examples of the non-oxidizing atmosphere include a nitrogen atmosphere, an argon atmosphere, and a helium atmosphere, and in some cases, a hydrogen atmosphere can also be used. The non-oxidizing atmosphere may contain a small amount of oxygen as long as the fibrillated polymer is not completely oxidized.

The three-dimensional continuous carbon fiber has a diameter of 30 to several hundred nm, preferably 40 to 500 nm, a length of 0.5 to 100,000 μm, preferably 1 to 10,000 μm, and a surface resistance of 10 ⁶ to 10 ⁻² Ω. It is preferably 10 ⁴ to 10 ⁻² Ω. The carbon fiber has a residual carbon ratio of 95 to 30%, preferably 90 to 40%. Since the carbon fiber has a structure in which the entire carbon is three-dimensionally continuous, the carbon fiber has higher conductivity than the granular carbon.

Further, a membrane electrode assembly for a polymer electrolyte fuel cell of the present invention comprises a solid polymer electrolyte membrane, a catalyst layer disposed on both sides of the solid polymer electrolyte membrane, and a diffusion layer disposed on both sides of the catalyst layer The catalyst structure of the present invention described above is used for the catalyst layer. Here, the combination of the catalyst layer and the gas diffusion layer located on each side of the solid polymer electrolyte membrane constitutes a fuel electrode and an air electrode, respectively, and the reaction expressed by 2H ₂ → 4H ⁺ + 4e ⁻ at the fuel electrode. The generated H ⁺ reaches the air electrode through the solid polymer electrolyte membrane, and the generated e ⁻ is taken out to become an electric current. In the air electrode, a reaction represented by O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O occurs, and water is generated. Here, the carrier of the catalyst structure is a composite carbon aggregate comprising carbon paper and a fibrillar carbon fiber aggregate disposed on the carbon paper, and the fibrillar carbon fiber aggregate of the aggregate When the catalyst material is coated on the surface of the substrate by the reactive sputtering method, the fibrillar carbon fiber aggregate coated with the catalyst material corresponds to the catalyst layer, and the carbon paper functions as a diffusion layer. As the solid polymer electrolyte membrane, an ion conductive polymer can be used, and the ion conductive polymer has an ion exchange group such as sulfonic acid, carboxylic acid, phosphonic acid, and phosphonous acid. Mention may be made of polymers, which may or may not contain fluorine. Examples of the ion conductive polymer include perfluorocarbon sulfonic acid polymers such as Nafion (registered trademark).

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

Example 1
[Production of carrier]
In an acidic aqueous solution containing 0.5 mol / L of aniline monomer and 1.0 mol / L of HBF ₄ , carbon paper [manufactured by Toray] was installed as a working electrode, a platinum plate was used as a counter electrode, and 10 mA / cm ² at room temperature. Electropolymerization was performed at a constant current for 10 minutes, and polyaniline was electrodeposited on the working electrode. The obtained polyaniline was washed with ion-exchanged water, vacuum-dried for 24 hours, and then observed with SEM. As a result, fibrillar polyaniline having a diameter of 50 to 100 nm was formed on the side of the carbon paper facing the platinum plate. It was confirmed.

  Next, the polyaniline was heated to 950 ° C. at a rate of 3 ° C./min in an Ar atmosphere together with the carbon paper, and then calcined by holding at 950 ° C. for 1 hour. When the obtained fired product was observed by SEM, it was confirmed that fibril-like and three-dimensional continuous carbon fibers having a diameter of 40 to 100 nm were formed on the carbon paper. The obtained carbon fiber had a residual carbon ratio of 45% and a surface resistance of 1.0Ω (measured by Mitsubishi Yuka, Loresta IP or Hiresta IP).

[Supporting catalyst]
Using the sputtering apparatus shown in FIG. 2, a TiO _x N _y thin film was formed under the following conditions to produce a catalyst structure. In addition, the titanium compound film is formed by first causing a discharge only with argon gas, and measuring the emission intensity of titanium at that time, setting the value as a reference value (9.5), and zero when no light is emitted, between 0 and 9.5 The set value (set point) was determined by (1), and the supply of the reactive gas was controlled by a high-speed responsive mass flow controller so that the set value could be maintained.
<Pulse reactive sputtering conditions>
・ Target dimensions: 75mmφ × 5mmt
-Board position and distance between boards: Parallel plate (target on one side, board 80mm away)
・ Sputtering pressure: 0.5Pa
・ Sputtering power: 300W
・ Ar gas flow rate: 50sccm
・ O ₂ gas flow rate: 0 ~ 25sccm
・ N ₂ gas flow rate: 0 ~ 10sccm
・ Gas control set point: 1 ~ 5
・ Substrate temperature: Room temperature (no substrate heating)
Substrate fixing and sputtering time: 1 minute to 100 minutes, TiO _x N _y catalyst loading: 0.4 mg / cm ²

[Production and evaluation of fuel cells]
A 5 mass% Nafion (registered trademark) solution was applied to the catalyst structure formed on the carbon paper, and then dried to form a catalyst layer on the carbon paper. Next, carbon paper with a catalyst layer is arranged so that the catalyst layer is in contact with both surfaces of a solid polymer electrolyte membrane (film thickness: 175 μm) made of Nafion (registered trademark), and the membrane electrode assembly ( MEA) was prepared. In the obtained membrane / electrode assembly, the thickness of the catalyst layer was 10 μm, and the catalyst structure / Nafion = 4/1 (mass ratio). The membrane electrode assembly was incorporated into a test cell (EFC25-01SP) manufactured by Electrochemical Co., to produce a fuel cell. The voltage-current characteristics of the fuel cell were measured under the conditions of an H ₂ flow rate of 300 cm ³ / min, an O ₂ flow rate of 300 cm ³ / min, a cell temperature of 80 ° C., and a humidification temperature of 80 ° C. The results are shown in Table 1.

(Comparative Examples 1-2)
For comparison, an example in which no reactive gas was introduced (Comparative Example 1) and an example in which only oxygen was introduced as a reactive gas (Comparative Example 2) were performed. These results are shown in 1.

As is apparent from Table 1, the catalyst structure in which TiO _x N _y is coated on the three-dimensional continuous carbon fiber by the reactive sputtering method acts as a catalyst layer of the membrane electrode assembly for a polymer electrolyte fuel cell. The voltage was generated by the current sweep, but no voltage was generated in the case where a film made of only titanium or titanium oxide was provided.

The schematic of an example of the bipolar type dual cathode system magnetron sputtering apparatus suitable for manufacture of the catalyst structure of this invention is shown. The schematic of an example of the unipolar type | mold dual cathode system magnetron sputtering apparatus suitable for manufacture of the catalyst structure of this invention is shown.

Explanation of symbols

1A, 1B Cathode 2A, 2B Target 3A, 3B Magnet 4, 4A, 4B Switching unit 5A, 5B AC power supply 6A, 6B Gas inlet 7A, 7B Piezo valve 8A, 8B Sensor 9A, 9B Controller 10A, 10B Hidden anode 11 Carrier 12 holder

Claims (36)

  A catalyst structure obtained by coating a support material with a catalyst material by a reactive sputtering method.   The catalyst structure according to claim 1, wherein one or a plurality of metals or metal compounds are simultaneously sputtered to coat a catalyst material on the surface of the carrier.   3. The catalyst structure according to claim 2, wherein when the plurality of metals or metal compounds are sputtered, a plurality of cathodes are simultaneously discharged to coat the support surface with a catalyst material.   When sputtering the plurality of metals or metal compounds, a plurality of targets are attached to one cathode, and a plurality of metals are simultaneously sputtered on the cathode during discharge to coat a catalyst material on the support surface. Item 3. The catalyst structure according to Item 2.   When sputtering the plurality of metals or metal compounds, a plurality of targets are attached to one cathode, and a plurality of metals are simultaneously sputtered at the cathode during discharge to coat a catalyst material on the surface of the support, and then the coated The catalyst structure according to claim 4, wherein at least one of a metal or a metal compound in the catalyst material is removed with an acid and / or an alkali.   2. The catalyst structure according to claim 1, wherein in the reactive sputtering, a light emission amount at the time of discharge is monitored, and a reactive gas is supplied in the vicinity of the cathode or the carrier in accordance with the light emission amount.   2. The catalyst structure according to claim 1, wherein, in the reactive sputtering, an impedance of a power supply unit during discharge is monitored, and a reactive gas is supplied in the vicinity of the cathode or the carrier in accordance with the impedance value.   The catalyst structure according to claim 6 or 7, wherein the reactive sputtering is performed in a transition region in which current, voltage, and power vary greatly according to the amount of reactive gas.   2. The catalyst structure according to claim 1, wherein in the reactive sputtering, a hidden anode is provided in the vicinity of the cathode, and an AC voltage is applied between the cathode and the anode.   2. The catalyst structure according to claim 1, wherein a plurality of cathodes are provided in the reactive sputtering, and an AC voltage is applied to the cathodes.   The catalyst structure according to claim 9 or 10, wherein the waveform of the AC voltage is a sine wave.   The catalyst structure according to claim 9 or 10, wherein the waveform of the AC voltage is a rectangular wave.   The catalyst structure according to claim 12, wherein the rectangular wave has a pulse shape and an application pattern is arbitrarily controlled.   The catalyst structure according to claim 13, wherein the application pattern is defined by a positive / negative applied voltage, a positive / negative application time, and an application ratio.   The metal is Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Rb, Sr, Y, Zr, Nb, From Mo, Ru, Rh, Ag, Cd, In, Sn, Sb, Cs, Ba, La, Hf, Ta, W, Re, Os, Ir, Tl, Pb, Bi, Ce, Pr, Nd, Sm and Eu The catalyst structure according to claim 2, wherein the catalyst structure is at least one selected from the group consisting of:   The catalyst structure according to claim 2, wherein the metal is a noble metal.   The catalyst structure according to claim 16, wherein the noble metal is at least one selected from the group consisting of Ag, Pt and Au.   The catalyst structure according to claim 2, wherein the metal compound is a metal oxide. The metal oxide is composed of AlO _x , SiO _x , TiO _x , FeO _x , CoO _x , NiO _x , CuO _x , ZnO _x , NbO _x , MoO _x , LaO _x , TaO _x , WO _x and PbO _x. The catalyst structure according to claim 18, wherein the value of x is controlled by an oxygen flow rate during sputtering.   The catalyst structure according to claim 2, wherein the metal compound is a metal nitride. Wherein the metal _nitride, the group consisting of _{AlN x, SiN x, TiN x} , FeN x, CoN x, NiN x, CuN x, ZnN x, NbN x, MoN x, LaN x, TaN x, WN x and PbN _x 21. The catalyst structure according to claim 20, wherein the value of x is controlled by a nitrogen flow rate during sputtering.   The catalyst structure according to claim 2, wherein the metal compound is a metal carbide. The metal _{carbide, AlC x, SiC x, TiC} x, FeC x, CoC x, NiC x, CuC x, ZnC x, NbC x, MoC x, LaC x, TaC x, from the group consisting of WC _x and PBC _x The catalyst structure according to claim 22, wherein the catalyst structure is at least one selected, and the value of x is controlled by a hydrocarbon flow rate during sputtering.   The catalyst structure according to claim 2, wherein the metal compound is a metal oxynitride. The metal oxynitride is AlO _x N _y , SiO _x N _y , TiO _x N _y , FeO _x N _y , CoO _x N _y , NiO _x N _y , CuO _x N _y , ZnO _x N _y , NbO _x N _y , MoO _x N _y , LaO _x N _y , TaO _x N _y , WO _x N _y, and PbO _x N _y , and the values of x and y are oxygen values during sputtering. The catalyst structure according to claim 24, which is controlled by a flow rate and a nitrogen flow rate.   The catalyst structure according to claim 1, wherein the use efficiency of the target material used in the reactive sputtering is 80% or more.   When attaching the plurality of targets to one cathode, when there are two targets, the targets are arranged facing each other, and when there are three or more targets, the targets are arranged in a polyhedral shape. The catalyst structure according to claim 4 or 5.   The catalyst structure according to any one of claims 1 to 27, wherein the carrier is a carbon fiber aggregate.   The catalyst structure according to claim 28, wherein the carbon fiber aggregate is carbon paper.   The catalyst structure according to claim 28, wherein the carbon fiber aggregate is a fibrillar carbon fiber aggregate having a diameter of 1 nm to 1 µm.   29. The catalyst structure according to claim 28, wherein the carrier is a composite carbon aggregate in which the fibrillar carbon fiber aggregate having a diameter of 1 nm to 1 [mu] m is disposed on the carbon paper.   The said support | carrier is a three-dimensional continuous carbon fiber obtained by oxidatively polymerizing the compound which has an aromatic ring, obtaining a fibril polymer, and baking this fibril polymer. Catalyst structure.   The catalyst structure according to claim 32, wherein the calcination is performed in a non-oxidizing atmosphere.   The catalyst structure according to claim 32, wherein the compound having an aromatic ring is a compound having a benzene ring or an aromatic heterocyclic ring.   The catalyst structure according to claim 34, wherein the compound having an aromatic ring is at least one compound selected from the group consisting of aniline, pyrrole, thiophene, and derivatives thereof.   In the membrane electrode assembly for a polymer electrolyte fuel cell, comprising: a solid polymer electrolyte membrane; a catalyst layer disposed on both sides of the solid polymer electrolyte membrane; and a diffusion layer disposed on both sides of the catalyst layer. A membrane electrode assembly for a polymer electrolyte fuel cell, wherein the catalyst structure according to any one of claims 1 to 35 is used for a layer.

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