JP4920945B2 - Catalyst layer, membrane electrode assembly, production method thereof, and fuel cell - Google Patents

Description

The present invention relates to a catalyst layer, a membrane electrode assembly, a production method thereof, and a fuel cell using the membrane electrode assembly.

  A fuel cell is a device that obtains electrical energy using oxygen or air for a cathode and hydrogen, methanol, hydrocarbon, or the like for an anode, and can obtain clean and high power generation efficiency. Depending on the type of electrolyte, it can be classified into alkaline aqueous solution type, phosphoric acid aqueous solution type, molten carbonate type, etc. In recent years, solid polymer fuel cells have attracted attention. The polymer electrolyte fuel cell is easy to handle due to low-temperature operation, the battery structure is simple and easy to maintain, the membrane can withstand differential pressure, the pressure control of the battery is easy, and the high output density can be obtained to reduce the size and weight. Has the advantage of being possible.

This polymer electrolyte fuel cell generally uses a fluorine resin ion exchange membrane as a proton conductor solid electrolyte, and uses platinum fine particles with low activation overvoltage as a catalyst for promoting hydrogen oxidation reaction and oxygen reduction reaction. It is done. The electrode reaction occurs at the so-called three-phase interface (electrolyte-catalyst electrode-fuel), but in a polymer electrolyte fuel cell, the electrolyte is a solid film, so the reaction site is limited to the contact interface between the catalyst electrode and the electrolyte film. , The utilization rate of platinum tends to decrease. As an example of improving this, Patent Document 1 is cited.
JP-A-6-176765

  However, conventional polymer electrolyte fuel cells have used small spherical particles having a diameter of several to several tens of nanometers as a catalyst in order to increase the surface area. For this reason, the utilization rate of the catalyst is very low because the space between the fine particles or the catalyst-supporting carbon is very narrow, the electrolyte does not permeate between the catalyst electrodes, and the reaction gas cannot enter the inside of the catalyst electrode. And development of the new membrane electrode assembly for fuel cells which hold | maintained the advantage of the conventional polymer electrolyte fuel cell was strongly calculated | required.

  The present invention has been made in view of the background art as described above, and can increase the three-phase interface, expand the gas permeability, and secure the electron transfer path, thereby improving the power generation efficiency. Provided are a membrane electrode assembly for a fuel cell, a method for producing the same, and a fuel cell.

That is, the catalyst layer that solves the above-described problem is characterized by comprising at least a wire-like catalyst and a conductive film that is present on the surface of the catalyst and has a film thickness of 5 nm to 50 nm .
The conductive film is preferably made of gold, silver, copper, titanium, or platinum.
A membrane / electrode assembly that solves the above problem is a membrane / electrode assembly comprising two catalyst layers and a polymer electrolyte membrane that is sandwiched between the two catalyst layers. The catalyst layer is the catalyst layer described above.

In addition, a method for producing a catalyst layer that solves the above-described problems includes a step of forming a conductive film having a thickness of 5 nm to 50 nm on a substrate by a vapor phase growth method or a liquid phase growth method; And a step of applying a wire-like catalyst to the surface of the membrane.
The step of forming a wire-like catalyst on the surface of the conductive film comprises the steps of forming a template having holes on the surface of the conductive film, applying a wire-like catalyst to the holes, and And removing.

In addition, a method of manufacturing a membrane electrode assembly that solves the above problems includes a step of forming a conductive film having a film thickness of 5 nm or more and 50 nm or less on a substrate by vapor phase growth or liquid phase growth, The method includes a step of applying a wire-shaped catalyst to the surface of the conductive film, a step of bonding the wire-shaped catalyst and the solid polymer electrolyte membrane, and a step of removing the substrate.
The step of applying a wire-like catalyst to the surface of the conductive film includes the steps of forming a template having holes on the surface of the conductive film, the step of applying a wire-like catalyst to the holes, and the template. And removing.

  The vapor phase growth method or liquid phase growth method is preferably a sputtering method, resistance heating vapor deposition, electron beam vapor deposition (EB vapor deposition), ion plating method, electrolytic plating or electroless plating.

The template is preferably a template having alumina nanoholes, silicon nanoholes, or silica nanoholes.
Moreover, the fuel cell which solves said subject is a fuel cell using said membrane electrode assembly for fuel cells, It is characterized by the above-mentioned.

  According to the present invention, it is possible to increase the three-phase interface, expand the gas permeability, secure the electron transfer path, and improve the power generation efficiency. Membrane electrode assembly for fuel cells, its manufacturing method, and the membrane A fuel cell using the electrode assembly can be provided.

  Furthermore, the fuel cell of the present invention is easy to handle due to low-temperature operation, simple battery structure and easy maintenance, easy to control the pressure of the battery because the membrane can withstand differential pressure, and small in size and weight because high output density can be obtained Has any advantage possible.

Hereinafter, the present invention will be described in more detail.
The membrane electrode assembly for fuel cells of the present invention comprises a solid polymer electrolyte and a catalyst layer, and the catalyst layer contains a catalyst made of a wire-like substance provided with at least a thin film. .

  Here, the definition and configuration of a wire-like substance provided with a thin film, an example of a method for producing a wire-like substance provided with a thin film in a liquid phase and a gas phase, a solid polymer electrolyte membrane, a carrier, a supplied fuel, and a fuel cell The structure and manufacturing method will be described in detail.

(About wire-like materials with thin films)
FIG. 1 is a schematic diagram showing the configuration of the membrane electrode assembly of the present invention.
The wire-like substance provided with the thin film contained in the catalyst layer of the polymer electrolyte fuel cell according to the present invention is placed on the upper part of the wire-like substance 12 present in the membrane electrode assembly 11 of FIG. This is indicated by the thin film 17. Reference numeral 13 denotes a solid polymer electrolyte, and 16 denotes a catalyst layer. The catalyst layer 16 includes a thin film 17 and a wire-like substance 12 as a catalyst.

  The thin film in the present invention is a layer provided on the upper part of the wire-like substance, and refers to a layer in which at least one adjacent wire-like substance is electrically joined. Here, the upper part of the wire-like substance refers to the end part of the wire-like substance on the fuel diffusion layer side shown in FIG. At this time, as shown in FIG. 6B, the fuel such as hydrogen and oxygen and the generated water enter and exit the catalyst layer rather than the state where the wire is completely covered as shown in FIG. It is preferable to form a thin film having vent holes 18. The porosity is not particularly limited, but is preferably 5% or more and 95% or less, and more preferably 30% or less and 95% or less.

  As a thin film material, all conductors and semiconductors to which electrons can move are applied, but it is ideal that this bonding layer itself does not become a resistor, so that metals such as gold, silver, copper, titanium, platinum, etc. The film thickness is preferably 5 nm to 50 nm, preferably 10 nm to 30 nm.

  Here, the wire-like substance is a one-dimensional structure formed in a thin line shape, and is a structure in which the length direction of the structure is longer than the maximum length passing through the center of gravity of the transverse cut surface of the structure. Further, as shown in FIGS. 2 (a), (b), (c), (d) and (e), the wire-like material has a tetrapod shape, and more wire-like materials have grown than one point. 2 (FIG. 2A), a dendritic shape (FIG. 2B), a polygonal line shape (FIG. 2C), or a mesh shape (FIG. 2). (D)), those grown in a beaded shape (FIG. 2 (e)), etc., and those in which each wire-like substance is hollow (tubular) or plate-like.

  As the catalyst layer included in the membrane electrode assembly, a catalyst layer standing in a direction perpendicular to the side surface of the solid polymer electrolyte membrane as shown in FIG. Also, a catalyst comprising a state in which the wire-like substance 12 is dispersed without directivity as shown in FIG. 1 (b), and a mixture of the wire-like substance 12 and fine particles 14 as shown in FIG. 1 (c). May be formed. Of course, as shown in FIG. 1 (d), a carrier 15 may be included.

  In addition, wire-like substances are all cylinders and cones, cones with a flat tip or a large tip, cylinders with a sharp tip, a flat tip, or a large tip. Including. Further, a triangular pyramid, a quadrangular pyramid, a hexagonal pyramid, other polygonal pyramids, and those having a flat tip or a large tip are included. In addition, triangular prisms, quadrangular columns, hexagonal columns, other polygonal column shapes, or triangular, quadrangular, hexagonal columns, other polygonal column shapes with sharpened tips or large tips, and other flat or tip shapes This includes things that are getting bigger. Furthermore, these broken line structures are also included.

  Further, the aspect ratio of the wire-like substance used in the membrane electrode assembly of the present invention is preferably 5 or more, particularly preferably 10 or more, and the maximum length passing through the center of gravity of the transverse cross section of the wire-like substance is preferably 50 nm or less, and further 20 nm or less. Is preferred. Here, the aspect ratio means the ratio of the length 32 to the diameter when the transverse cut surface 33 of the wire-like substance 31 is circular or nearly circular as shown in FIG. When the transverse cut surface 33 of the wire-like substance 31 is a hexagonal shape or a distorted figure as shown in FIG. 3B, the ratio of the length to the maximum length 35 passing through the center of gravity 34 of the transverse cut surface 33 is meant. 3C, when the transverse cut surface 33 of the wire-like substance 31 is ring-shaped, it is assumed that the structure is formed by the outermost ring 36 of the transverse cut surface 33, and the maximum length passing through the center of gravity 34 thereof. Let us say the ratio of length 32 to 35.

  Here, the wire-like substance may be any substance that can be a catalyst electrode of a fuel cell, and it is particularly preferable to use platinum, an alloy containing platinum, or a mixture containing platinum. Materials that are included with platinum as an alloy of platinum or a mixture containing platinum are gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt, nickel, chromium, tungsten, manganese, vanadium, rhenium, cobalt, lithium, lanthanum Strontium, yttrium, osmium and the like. The catalyst used for the catalyst electrode is not limited to these as long as it is a material that promotes the oxidation reaction of the anode side fuel such as hydrogen and the reduction reaction of the cathode side fuel such as oxygen.

(About manufacturing method of wire-like substance coated with thin film)
The basic configuration of the membrane electrode assembly is shown in FIG. A configuration comprising a catalyst 41, a carrier 42, and a solid polymer electrolyte 43 is common.

  When this membrane electrode assembly is used and, for example, hydrogen is used on the anode side and oxygen is used on the cathode side as the fuel, the following reaction proceeds.

  As can be seen from this reaction formula, the supplied fuel generates electrons and cations on the anode side, and only the generated cations move to the cathode side to react with oxygen and consume electrons to generate electricity. It has become. That is, it is important that the cathode and the anode are completely separated by the solid polymer electrolyte while being installed in the same membrane electrode assembly. Furthermore, since the above reaction is carried out at the interface between the three kinds of substances, that is, the catalyst electrode, the solid polymer electrolyte, and the fuel, it is important that the solid polymer electrolyte is more widely installed on the catalyst electrode. It is important that is efficiently supplied to the deep part of the membrane electrode assembly. Therefore, the mixing ratio of the catalyst electrode material and the solid polymer electrolyte can also be an important parameter for improving the performance of the fuel cell.

Here, the manufacturing method of the wire-like substance with which the thin film of this invention was coat | covered is demonstrated using FIG.
a. <Process of placing a material that can become a thin film on the substrate>
7A and 7B are process diagrams showing a method for producing a membrane electrode assembly of the present invention.

  First, as shown in FIG. 7A, there is a step of placing a material that can become the thin film 17 on the substrate 19, but the substrate used here is not particularly limited as long as it is a material on which the thin film can be placed. Here, an example in which a thin film of Cu is installed using a silicon wafer as a substrate will be described.

  On the prepared silicon wafer, 20 nm of copper was placed by sputtering. As film formation conditions, an RF power source was used under the conditions of Ar flow rate: 50 sccm and input power: 300 W. The film forming method is not limited to the sputtering method, but includes vapor deposition methods such as resistance heating vapor deposition, electron beam vapor deposition (EB vapor deposition), ion plating method, electrolytic plating and electroless plating, or liquid phase growth methods. The production method is not limited to these as long as it can satisfy the conditions of the present invention. Further, although at least one material layer is required as a thin film, two or more thin films may be formed.

b. <Process for forming a wire-like substance on a thin film>
Next, the step of forming a wire-like substance on the thin film will be described with reference to FIG. As a method of installing the wire-like substance, there are a method of installing the prepared wire-like substance after mixing with the solid polymer electrolyte, and a method of installing the wire-like substance after installing the mold on the thin film, The latter will be described in detail.

  First, a mold for preparing a wire-like substance is prepared. Here, as an example of the template of the wire-like substance, an alumina nanohole produced by anodizing aluminum is taken as an example. Further, silicon nanoholes produced by simultaneously sputtering aluminum and silicon, and silica nanoholes produced by using a silica raw material and a surfactant are also used. Further, any template can be used as long as it can form a wire-like substance such as a polymer template such as polymethyl methacrylate formed by molecular self-assembly.

  7 (b) -1 was prepared as a working electrode by depositing aluminum as a mold precursor 20 on the thin film by sputtering, and the aluminum electrode serving as the working electrode and the counter electrode was heated to 3 ° C. in a constant temperature water bath. Place in a retained 0.3 M aqueous sulfuric acid solution. Here, the anodic oxidation voltage was DC 25 V, and the current value was displayed on the monitor, and it was confirmed that the current penetrated into the base layer when the current value became small.

After the anodizing treatment, cleaning with pure water and isopropyl alcohol was performed.
Thereafter, by performing a pore wide treatment immersed in a 5 wt% phosphoric acid solution for 20 minutes, a mold 22 having holes 21 is formed as shown in FIG. 7B-2. It was confirmed that the produced alumina nanohole was a mold penetrating to a thin film having an average pore diameter of 20 nm. As a method for producing this alumina nanohole, for example, a method described in JP 2000-31462 A can be used.

  Next, an electrolytic solution containing at least platinum ions is prepared. By immersing the alumina nanohole substrate in this solution and applying a potential, the platinum wire-like substance 17 can be produced as shown in FIG. 7B-3. Here, as a compound which can be used as a salt containing platinum, for example, chloroplatinic (IV) acid, dinitrodiammineplatinum (II), tetraamminedichloroplatinum (II), potassium hexahydroxoplatinum (IV) and the like can be mentioned. Moreover, when producing a platinum alloy by an electrodeposition method, it can produce by mixing the salt containing a desired metal in the electrolyte solution containing the said platinum ion.

Further, when the wire-like substance is produced and then placed on the thin film, it can be placed without directivity as shown in FIG. 7 (b) -4.
Here, the manufacturing method of a wire-like substance is explained in full detail.

  Examples of the method for producing the wire-like substance include a liquid phase growth method in which a potential is applied to the solution in the presence of a metal ion that is a raw material for the wire-like substance or reduction is performed to grow the wire-like substance. Moreover, the vapor phase growth method etc. which produce a wire-like substance in a gaseous phase by giving external energy to the raw material of a wire-like substance are mentioned, However It is not limited to these.

  Here, as a vapor phase growth method, a metal raw material is evaporated or sublimated and condensed at a site lower than the temperature to produce a wire-like material, or a metal halide is vacuumed or an inert gas. A pyrolysis method is preferably used in which a wire-like substance is produced by pyrolysis in the medium. Alternatively, a VLS method in which a wire-like substance grows by using a catalyst that can be a growth starting point and reacting a desired metal vapor with the catalyst is preferably used.

  In addition, as a liquid phase growth method, a plating method in which a mold on which a wire-like material is formed is used to grow desired metal ions by electrolysis, or an electroless plating method in which a wire-like material is grown using a catalyst or a light source. Are preferably used. Alternatively, a reduction method in which a reducing agent and a surfactant for forming a wire-like substance are mixed and grown in a solution is preferably used.

c. <Step of joining on solid polymer electrolyte membrane>
The wire-like substance is fixed on the thin film in the step b. The step of joining this sample to the solid polymer electrolyte membrane will be described in detail here.

  First, in order to join a wire-like substance to a solid polymer electrolyte membrane, it is preferable to provide a solid polymer electrolyte in the wire-like substance. At this time, the solid polymer electrolyte can be provided up to the deep part of the wire-like substance by using a solution dissolved in a solvent such as isopropyl alcohol. As described in the process of FIG. 7b, when the wire-like substance is provided on the thin film in the previously isolated state, it is mixed with the solid polymer electrolyte and provided as shown in FIG. 7 (c) -4. Are preferably used. When a mold is used, a method of providing a solid polymer electrolyte as shown in FIG. 7 (c) -3 by dissolving a part or all of the mold after placing a wire-like substance in the mold is preferably used. .

  Here, an example will be described in which a part of a wire-like material template prepared using alumina nanoholes as a template is dissolved, a solid polymer electrolyte is set, and transferred onto the solid polymer electrolyte membrane by a hot press method.

  By immersing the alumina nanoholes placed on the thin film in a 5 wt% phosphoric acid aqueous solution for 20 minutes, a 10 nm gap 23 is formed between the wire-like substance and the alumina nanoholes as shown in FIG. It was. Next, as shown in FIG. 7 (c) -2, a 5 wt% Nafion solution, which is a solid polymer electrolyte 13, was poured into the gap and dried appropriately. A commercially available Nafion membrane was used as the solid polymer electrolyte membrane. As a pretreatment, an aqueous hydrogen peroxide solution was heated to 80 ° C., and a Nafion film cut to a desired size was immersed for 60 minutes. After the hydrogen peroxide treatment and washing with water, the Nafion film was immersed in an aqueous sulfuric acid solution heated to 80 ° C. for 60 minutes. Then, after washing with water, a dried product was used. Next, a hot-pressed mixture of the wire-like substance and the solid polymer electrolyte using the previously prepared alumina nanohole as a template on the Nafion membrane after the treatment, as shown in FIG. 7 (c) -3, A membrane electrode assembly of Nafion-containing platinum nanowire-like material was prepared.

d. <Process to remove the substrate>
Up to the above steps, the substrate remains installed on the membrane electrode assembly. Therefore, it is necessary to remove the substrate.

  As a removing method, there are a case where separation is possible by peeling off the substrate as it is after hot pressing, a case where it is immersed in a solution of acid or base, and the film is peeled off while slightly dissolving the thin film, but is not limited thereto.

  Further, when a template is used, it is necessary to dissolve the template. As a melting method, there is a method in which the substrate is melted after being peeled, or the template is melted and the substrate is peeled off, or processing is performed simultaneously.

  Here, an example will be described in which a solid polymer electrolyte is coated on a wire-like substance produced in alumina nanoholes, hot-pressed, and then immersed in a sulfuric acid solution, and the dissolution of the template and the separation of the substrate are performed simultaneously.

  By immersing the produced substrate-containing membrane / electrode assembly in a 0.1 M sulfuric acid aqueous solution for 12 hours, as shown in FIG. It was able to dissolve. At this time, the substrate may be peeled off before being immersed in the solution, and then immersed in the acid solution. In addition, when mixed in a solution in which wire-like fine particles and a solid polymer electrolyte are dissolved, a membrane-electrode assembly having no directionality to the wire-like substance as shown in FIG. 7 (d) -2 can be obtained. .

(About solid polymer electrolyte)
The solid polymer electrolyte, which is a constituent of the membrane electrode assembly of the present invention, is required to have a high ion conductivity role in order to quickly move cations generated on the anode side to the cathode side. As the solid polymer electrolyte, a material excellent in hydrogen ion conductivity and organic liquid fuel permeability such as methanol is preferably used in order to satisfy these requirements.

  Specifically, as the organic group capable of hydrogen ion dissociation, an organic polymer having a sulfonic acid group, a sulfinic acid group, a carboxylic acid group, a phosphonic acid group, a phosphinic acid group, a phosphoric acid group, a hydroxyl group, or the like is preferably used. It is done. Such organic polymers include perfluorocarbon sulfonic acid resin, polystyrene sulfonic acid resin, sulfonated polyamideimide resin, sulfonated polysulfonic acid resin, sulfonated polyetherimide semipermeable membrane, perfluorophosphonic acid resin, perfluorosulfonic acid resin, etc. Can be illustrated. Although the solid polymer electrolyte illustrated above is used suitably, it is not limited to these.

(About fine particles)
The membrane / electrode assembly may contain fine particles as a catalyst, as shown in FIG. As the fine particles, any material and shape can be used as long as they function as a fuel cell catalyst or a co-catalyst for improving catalytic performance. In particular, when considering increasing the reaction field of the wire-like substance of the present invention, those smaller than the diameter of the wire-like substance are preferably used. Specifically, the particle diameter is 20 nm or less, preferably 10 nm or less. Fine particles can be used. In addition, it is particularly preferable to use platinum, an alloy containing platinum, or a mixture containing platinum as the catalyst material. Materials that are included with platinum as an alloy of platinum or a mixture containing platinum are gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt, nickel, chromium, tungsten, manganese, vanadium, rhenium, cobalt, lithium, lanthanum Strontium, yttrium, osmium and the like.

(About carrier)
Since the membrane electrode assembly basically has a solid polymer membrane that can transport cations to the anode side and a catalyst electrode that can take out electrons generated at the anode and cathode, power generation is possible. It is not necessarily a necessary material. However, for the purpose of mainly reducing the amount of platinum used, a material capable of transferring electrons is supported in the membrane electrode assembly.

  As the carrier, carbon can be mainly used. However, the carrier is not limited thereto as long as it is an electron transfer material. Examples of the carbon carrier include carbon black such as furnace black, channel black, and acetylene black, activated carbon, graphite, fullerene, carbon nanotube, carbon fiber, and the like, and these are used alone or in combination. At this time, a wire-like substance may be formed on the carrier, and the carrier and the wire-like substance may be dispersed in the membrane electrode assembly.

(About fuel supply)
The fuel of the solid polymer electrolyte-catalyst composite type fuel cell may be any fuel that generates electrons and cations by the action of a catalyst electrode such as hydrogen, reformed hydrogen, methanol, dimethyl ether, etc. and the solid polymer electrolyte on the anode side. Also, any fuel can be used as long as it accepts cations such as air and oxygen on the cathode side and takes in electrons. However, hydrogen or methanol is suitable for the anode side and air is suitable for the cathode side in terms of reaction efficiency and practical use.

(Configuration of fuel cell and manufacturing method)
A schematic diagram of the configuration of the fuel cell is shown in FIG. Solid polymer electrolyte 51, anode catalyst layer 52, cathode catalyst layer 53, anode side current collector plate 54, cathode side current collector plate 55, external output terminal 56, fuel introduction line 57, fuel discharge line 58, anode side fuel diffusion layer 59, the cathode-side fuel diffusion layer 60, and electric power is generated by a chemical reaction occurring at the three-phase interface on the surface of the catalyst layer. Here, as the configuration of the cell, for example, by forming a plurality of layers as shown in FIG. 5, the generated voltage value and the current value can be increased. In this case, it is possible to reduce the size and increase the output of the fuel cell system by manufacturing the cell by applying a semiconductor process.

  For example, when hydrogen is used as the fuel on the anode side and air is used on the cathode side, it is important to pack the fuel so that the fuel supplied to the anode side does not leak, and fuel is injected into the cathode side. It is important to be open to the air so that it can be easily done. The diffusion layer is a conductive member having a high porosity that is installed in order to easily carry fuel into the cell and form a three-phase interface, and preferably uses a carbon fiber fabric, carbon paper, or the like. I can do it.

  Here, not only when using a solid polymer electrolyte that performs cation exchange, but also using a wire-like substance for the catalyst electrode of a bipolar electrolyte fuel cell or the like using a cation exchange membrane on the anode side and an anion exchange membrane on the cathode side Of course, the fuel cell membrane electrode assembly of the present invention is also applied.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these Examples.
Example 1
In this example, gold was formed as a thin film on a silicon substrate, and a platinum electrode was plated using an aluminum-silicon mixed film placed thereon as a mold to produce a wire-like material, and then a membrane electrode assembly was produced. To state.

  First, 20 nm of gold was placed on a 4 inch (101.6 mm) silicon wafer by RF magnetron sputtering, and then a 200 nm aluminum-silicon mixed film was formed on a Si wafer on which gold was formed. At this time, a thin film in which air holes were naturally formed was installed by setting the thickness of gold to 20 nm.

  The target used for producing the mold was obtained by placing six 15 mm square silicon chips on a 4 inch (101.6 mm) aluminum target on a backing plate. Sputtering was performed using an RF power source under the conditions of Ar flow rate: 50 sccm, discharge pressure: 0.7 Pa, and input power: 90 W. The substrate temperature was room temperature. This aluminum-silicon structure thin film was immersed in a 5 wt% phosphoric acid aqueous solution for 10 hours, and only aluminum columnar structure portions were selectively etched to form pores. As a result of observing the etched film with FE-SEM, it was confirmed that the film was a porous film having an average pore diameter of about 5 nm.

Next, a columnar structure of platinum was produced by electrodeposition (electroplating) in the pores of the porous film produced as described above. An acidic bath (70 ° C.) in which a porous thin film of silicon oxide prepared in the above process is placed in a commercially available electroplating solution (manufactured by High Purity Chemical Laboratory, electroplating solution for gold, product code PT-100E) In the case of pH = 0.1), electrodeposition was performed at a current density of 1.5 A / dm ² .

  Next, the substrate was taken out of the solution and immersed in a 0.2 M aqueous sodium hydroxide solution for 30 minutes to dissolve the template, thereby producing a platinum wire-like material grown from the thin film. As a result of observing the etched film with FE-SEM, it was confirmed that a gold thin film of 20 nm was placed on the substrate side of a wire-like substance having a length of 200 nm and an average diameter of about 5 nm reflecting the mold.

Next, a 5 wt% Nafion solution was immersed in this film and dried in the air for 30 minutes.
Here, a process for preparing a solid polymer electrolyte membrane will be described. Here, a commercially available Nafion (DuPont, registered trademark) membrane was used. The aqueous hydrogen peroxide solution was warmed to 80 ° C., and a Nafion film cut to a desired size was immersed for 60 minutes. After the hydrogen peroxide treatment and washing with water, the Nafion film was immersed in an aqueous sulfuric acid solution heated to 80 ° C. for 60 minutes. Then, after washing with water, a dried product was used.

  On the Nafion film after the treatment, a film obtained by applying the Nafion solution in the wire-like substance prepared earlier was transferred by a hot press method. After the transfer, the silicon wafer was peeled off from the membrane electrode assembly portion to separate the gold and the substrate.

  FIG. 5 shows a schematic diagram of a configuration in which this membrane electrode assembly is incorporated in a cell. Solid polymer electrolyte 51, anode catalyst layer 52, cathode catalyst layer 53, anode side current collector plate 54, cathode side current collector plate 55, external output terminal 56, fuel introduction line 57, fuel discharge line 58, anode side fuel diffusion layer 59, a cathode side fuel diffusion layer 60.

  As a comparative example, platinum fine particles having an average particle diameter of 5 nm were used. 1 g of platinum fine particles was put in a crucible, and 0.4 cc of pure water was dropped with a micropipette. Thereafter, 1.5 cc of 5% Nafion solution was added to the crucible using a micropipette, followed by 0.2 cc of isopropyl alcohol. Then, the crucible was subjected to ultrasonic cleaning for 5 minutes. Furthermore, the stirring bar was put in the crucible, and it stirred at 200 rpm with the magnetic stirrer. The thus prepared platinum nanowire-like substance dispersion solution was applied onto a PTFE sheet on which 20 nm of copper was placed by the doctor blade method. The prepared catalyst sheet was moved separately and dried in the air. Then, on the treated Nafion film, the film in which the Nafion solution was applied in the previously prepared wire-like substance was transferred by a hot press method to produce a membrane electrode assembly, and a cell was produced using it.

  When this was used to evaluate the current-potential characteristics of a single fuel cell, the output of Example 1 was improved by about 10% compared to the particulate film of the comparative example. This is considered that the incorporation of the platinum wire-like substance of the present invention into a membrane electrode assembly makes it possible to increase the three-phase interface and expand the gas permeability, thereby improving the power generation efficiency.

Evaluation Method of Current-Potential Characteristics Hydrogen humidified with 80 ° C. saturated steam was used on the anode side, and air humidified in the same manner was used on the cathode side. The produced single cells were operated by supplying the flow rates at 200 mL / min and 600 mL / min, respectively. The cell operating temperature was set to 80 ° C., power generation evaluation and AC impedance measurement were performed, and the measurement method measured voltage change and IR change when the current flowing through the load was changed.

Example 2
In this example, a platinum wire-like substance prepared by using a condensation method from a gas phase is mixed with a solid polymer electrolyte, and the slurry is placed on a substrate on which copper is formed as a thin film. The example which produced the electrode assembly is described.

  First, platinum was vacuum sealed in a reaction tube and allowed to stand in a reaction furnace. A platinum wire-like substance could be obtained by applying a temperature of 1650 ° C. to the raw material site to evaporate platinum and setting the upper part in the reaction tube to 750-950 ° C. The produced platinum wire-like substance was scraped off from the reaction tube. The wire-like substance had a length of 1000 nm and a diameter of 50 nm.

  A membrane electrode assembly was prepared from the platinum nanowire-like material by the same method as the above-described method of manufacturing a membrane electrode assembly, and a cell was assembled by injecting hydrogen on the anode side and air on the cathode side. In this method, 1 g of the produced platinum nanowire-like substance was put in a crucible, and 0.4 cc of pure water was dropped with a micropipette. Thereafter, 1.5 cc of 5% Nafion solution was added to the crucible using a micropipette, followed by 0.2 cc of isopropyl alcohol. Then, the crucible was subjected to ultrasonic cleaning for 5 minutes. Furthermore, the stirring bar was put in the crucible, and it stirred at 200 rpm with the magnetic stirrer. The thus prepared platinum nanowire-like substance dispersion solution was applied onto a PTFE sheet on which 20 nm of copper was placed by the doctor blade method. At this time, a thin film in which air holes were naturally formed was installed by setting the copper thickness to 20 nm. The prepared catalyst sheet was moved separately and dried in the air.

Using this catalyst sheet, a membrane electrode assembly was produced in the same manner as in Example 1, and a cell was further produced.
As a comparative example, a membrane electrode assembly was prepared in the same manner as in Example 1 using platinum fine particles having an average particle diameter of 5 nm, and a cell was prepared using the membrane electrode assembly.

  When this was used to evaluate the current-potential characteristics of a single cell of a fuel cell, the output was improved by about 10% compared to the particulate film of the comparative example. This is considered that the incorporation of the platinum wire-like substance of the present invention into a membrane electrode assembly makes it possible to increase the three-phase interface and expand the gas permeability, thereby improving the power generation efficiency.

Example 3
In this example, copper is formed on a silicon substrate, followed by platinum, silica nanoholes are formed on the film, a platinum tungsten alloy wire-like material is formed by a plating method, and a solid polymer film is formed on the template. An example will be described in which a membrane electrode assembly was fabricated by dissolving the template after fixing the substrate and further providing a solid polymer film on the dendritic wire-like substance.

  Nitrogen 0.7 mol, water 12 mol, ethanol 15 mol, n-hexadecyltrimethylammonium chloride 0.2 with respect to 1 mol of tetraethylorthosilicate (TEOS) as a raw material for preparing a reaction liquid for producing silica nanoholes Mole. This solution was added onto a silicon wafer on which copper 10 nm was formed by sputtering and then platinum 30 nm was formed by plating, and spin-coated under conditions of 3000 rpm. At this time, a thin film in which air holes were naturally formed was installed by setting the copper thickness to 10 nm. As the conditions for the plating method used here, an electrolytic solution having 0.03 mol / L platinum chloride using a 30 g / L boric acid aqueous solution was used. Silver / silver chloride was used as the working electrode, and platinum mesh was used as the counter electrode. As an applied potential, −0.7 V was applied for 1 second, and then 0 V was applied for 0.5 second. By repeating this application condition 5 times while stirring at a rotation speed of the stirrer of 300 rpm, platinum could be formed on the copper thin film. Then, the silica nanohole was produced by performing heat processing at 400 degreeC in air | atmosphere.

Next, 1.5 g of chloroplatinic acid in a platinum concentration and 10 g of sodium tungstate in a tungsten concentration were dissolved in 800 ml of water, and then 1.0 g of disodium hydrogen phosphate and 1.0 g of sodium dihydrogen phosphate were added. Further, a Pt—W alloy plating bath was prepared so as to have a predetermined pH value with sodium hydroxide and sulfuric acid. Using this bath, plating was carried out under electrolysis conditions of a current density of 5 mA / cm ² , a time of 150 seconds, and a temperature of 65 ° C.

Next, the template was dissolved by immersing the prepared membrane in an aqueous sodium hydroxide solution, and a dendritic wire-like substance having an average diameter of about 5 nm was prepared reflecting the template.
Next, a 5% Nafion solution was applied by a spin coating method, a Nafion film was sandwiched between the spin coated surfaces, and hot pressing was performed as it was.

After hot pressing, the substrate and the thin film were separated by being immersed in a sulfuric acid solution, and the membrane electrode assembly of the present invention was produced.
As a comparative example, a membrane / electrode assembly was prepared using platinum-tungsten alloy fine particles having an average particle diameter of 5 nm, and a cell was formed using the assembly.

  When this was used to evaluate the current-potential characteristics of a single cell of the fuel cell, the output was improved by about 12% compared to the fine particle film of the comparative example. This is considered that the incorporation of the wire-like substance of the present invention into the membrane electrode assembly makes it possible to increase the three-phase interface and expand the gas permeability, thereby improving the power generation efficiency.

  The membrane electrode assembly of the present invention can increase the three-phase interface, expand the gas permeability, and improve the power generation efficiency. Therefore, it can be used for various energy generation units from small mobile fuel cells such as mobile phones, notebook computers, digital video cameras, and digital cameras to large fuel cells for home use and automobiles. In fields other than fuel cells, it can also be used as an electrode for water electrolysis.

It is a schematic diagram which shows the structure of the membrane electrode assembly of this invention. It is a schematic diagram which shows the shape of the wire-like substance in the membrane electrode assembly of this invention. It is a schematic diagram explaining the definition of the wire-like substance in the membrane electrode assembly of the present invention. It is a schematic diagram of a membrane electrode assembly. It is a schematic diagram of a fuel cell. It is a schematic diagram which shows the structure of the thin film of this invention. It is process drawing which shows the manufacturing method of the membrane electrode assembly of this invention. It is process drawing which shows the manufacturing method of the membrane electrode assembly of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Membrane electrode assembly 12 Wire-like substance 13 Solid polymer electrolyte 14 Fine particle 15 Carrier 16 Catalyst layer 17 Thin film 18 Vent 19 Substrate 20 Template precursor 21 Hole 22 Template 23 Crevice 31 Wire-like substance 32 Length 33 Horizontal cut surface 34 Center of gravity 35 Maximum length 36 Outer ring 41 Catalyst 42 Carrier 43 Solid polymer electrolyte 51 Solid polymer electrolyte 52 Anode catalyst layer 53 Cathode catalyst layer 54 Anode-side current collector 55 Cathode-side current collector 56 External output terminal 57 Fuel introduction Line 58 Fuel discharge line 59 Anode side fuel diffusion layer 60 Cathode side fuel diffusion layer

Claims (10)

A catalyst layer comprising at least a wire-like catalyst and a conductive film present on the surface of the catalyst and having a thickness of 5 nm to 50 nm .   The catalyst layer according to claim 1, wherein the conductive film is made of gold, silver, copper, titanium, or platinum. A membrane electrode assembly comprising two catalyst layers and a polymer electrolyte membrane present between the two catalyst layers, wherein the two catalyst layers are catalyst layers according to claim 1 or 2. There is a membrane electrode assembly characterized in that there is. A fuel cell comprising the membrane electrode assembly according to claim 3 . Forming a conductive film having a film thickness of 5 nm or more and 50 nm or less on a substrate by a vapor phase growth method or a liquid phase growth method; and a step of applying a wire-like catalyst to the surface of the conductive film. A method for producing a catalyst layer, comprising: The step of forming a wire-like catalyst on the surface of the conductive film comprises the steps of forming a template having holes on the surface of the conductive film, applying a wire-like catalyst to the holes, and The method for producing a catalyst layer according to claim 5 , comprising a step of removing the catalyst layer. The method for producing a catalyst layer according to claim 6 , wherein the template is made of alumina nanoholes, silicon nanoholes, or silica nanoholes. Forming a conductive film having a film thickness of 5 nm or more and 50 nm or less on a substrate by a vapor phase growth method or a liquid phase growth method, a step of applying a wire-like catalyst to the surface of the conductive film, A method for producing a membrane electrode assembly, comprising: a step of bonding a wire-shaped catalyst and a solid polymer electrolyte membrane; and a step of removing the substrate. The step of applying a wire-like catalyst to the surface of the conductive film includes the steps of forming a template having holes on the surface of the conductive film, the step of applying a wire-like catalyst to the holes, and the template. The method for producing a membrane electrode assembly according to claim 8 , comprising the step of removing. The method for producing a membrane electrode assembly according to claim 9 , wherein the template is made of alumina nanoholes, silicon nanoholes, or silica nanoholes.

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