JP4539145B2 - Membrane electrode assembly and fuel cell - Google Patents

Description

  The present invention relates to a membrane electrode assembly suitable for the configuration of a power generation cell of a fuel cell using a polymer electrolyte membrane, and a fuel cell including the membrane electrode assembly.

  In recent years, fuel cells that generate electricity by electrochemical reaction between hydrogen and oxygen have attracted attention as an energy supply source. In general, a fuel cell using an ion exchange resin membrane is configured such that an ion exchange resin membrane, which is a polymer electrolyte, is sandwiched between both an anode electrode and a cathode electrode. It is usual to provide a catalyst layer responsible for a chemical reaction and a diffusion layer that functions as a current collector.

  Generally, the catalyst layer is made by dispersing carbon (C) powder supporting a catalyst metal for electrode reaction such as platinum (Pt) noble metal in an appropriate organic solvent, adding an appropriate amount of an electrolyte solution to the paste, It is formed on an ion exchange resin film which is a conductive substance. Therefore, the conventional fuel cell electrode has a gas diffusion structure in which carbon black is mainly used as a base, and a catalytic metal, a proton conductive material, and the like responsible for the electrode reaction are solidified (for example, Non-Patent Document 1). reference).

  The electrode reaction occurs when the raw material gas is supplied to the portion where the electrode and the proton conductive material are in contact, that is, the three-phase interface. As shown in FIG. 4, the design of the three-phase interface is very difficult. Due to the technology, there has been a problem that the supply of the raw material gas does not sufficiently reach the vicinity of the three-phase interface, and the expensive noble metal catalyst supported near the three-phase interface cannot be effectively used. Therefore, even if it tries to reduce the usage-amount of a noble metal catalyst, it leads to the fall of electric current supply, and it is also difficult to aim at reduction of a usage-amount, without inhibiting electric power generation efficiency.

  In general, a diffusion layer is provided as described above. In this case, a diffusion layer is provided between a separator and a catalyst layer for forming a flow path for fuel supply / discharge, and a separator / diffusion layer / Although it has a laminated structure of catalyst layer / polymer electrolyte membrane, it is necessary to prevent the deterioration of the contact resistance between the diffusion layer / catalyst layer and the separator / diffusion layer in particular, so that the power generation efficiency is not deteriorated. It is indispensable to apply a surface pressure by tightening, etc., and there is a problem of adversely affecting the durability of the film. In particular, reduction of electrical contact resistance between the diffusion layer / catalyst layer and improvement of diffusibility of fuel or the like, that is, ensuring of electrical conductivity have been major issues (see, for example, Patent Document 1).

  There has been disclosed a technique for reducing contact resistance between a catalyst layer and a gas diffusion layer (see, for example, Patent Document 2). However, it has a structure in which a layer of carbon particles only is provided as a diffusion layer on the catalyst electrode, and although the internal resistance is slightly reduced, gas diffusion is not improved and is insufficient in terms of the effect of improving power generation efficiency. is there.

In addition, there is also disclosed a technique related to an electrode catalyst using fibrous carbon as a carrier (see, for example, Patent Document 3). However, it is the same as the above in that the power generation efficiency is insufficient only by constituting with carbon fiber, and the adverse effect on the durability of the membrane is not avoided.
JP 2002-246034 A JP 2001-6699 A JP-A-8-17440 Development and application of polymer electrolyte fuel cells (p.6, NTS Corporation)

  As described above, in order to increase the power generation efficiency of the fuel cell, it is effective to reduce the contact resistance inside the cell. However, if a diffusion layer using carbon paper or the like is simply provided as in the conventional case, the contact resistance is reduced. Improvement effect is poor. In addition, a technology that can effectively use a noble metal catalyst supported near the three-phase interface remote from the fuel or oxidant gas supply side for the electrode reaction has not yet been established. That is, the present situation is that a membrane / electrode assembly capable of expressing good power generation efficiency without giving a high surface pressure due to tightening that adversely affects the membrane has not yet been provided.

  The present invention has been made in view of the above, and efficiently uses a supported expensive noble metal catalyst for an electrode reaction and does not give a high surface pressure by tightening, and is highly durable and generates electricity at a high current density. It is an object of the present invention to provide a membrane electrode assembly that can be used, and a fuel cell that includes the membrane electrode assembly and exhibits high durability and good power generation performance (power generation operation at a high current density). The goal is to achieve this.

  The present invention provides a membrane electrode assembly composed of a polymer electrolyte membrane and an electrode having a diffusion layer, and orients the first conductive fibers in the polymer electrolyte membrane (preferably substantially perpendicular to the membrane surface). The second conductive fiber is oriented in the diffusion layer (preferably substantially perpendicular to the layer surface), and the oriented first conductive fiber and / or the second conductive fiber is supported on the electrode catalyst metal. And having a configuration in which the first conductive fiber and the second conductive fiber are in contact with each other is useful in securing conductivity (lowering contact resistance) without giving a high surface pressure. This knowledge has been obtained and achieved based on this knowledge. Specific means for achieving the above object are as follows.

In order to achieve the above object, a membrane electrode assembly according to the first invention includes a polymer electrolyte membrane in which the first conductive fibers are aligned, the second conductive fibers are aligned, and the second conductive fibers are aligned. a sexual fibers first conductive fibers and the contacted with arranged diffused layer, an electrode catalyst metal supported on at least one of the first conductive fibers and a second conductive fibers, said first and The second conductive fiber has a proton conductive material on at least one surface thereof .

  In other words, the conductive fiber carrying the electrocatalyst metal constitutes the electrode of the membrane electrode assembly and functions as a catalyst reaction part (catalyst layer) that takes charge of the cell reaction when fuel or oxidant gas is supplied. is there. For example, when configured in a polymer electrolyte fuel cell (PEFC), the conductive fiber carrying the electrocatalyst metal is located between the polymer electrolyte membrane and the diffusion layer, and the separator / diffusion layer / conductive fiber. (Catalyst layer) / Polymer electrolyte membrane laminated structure.

  In the membrane electrode assembly of the first invention, the fibers of the first conductive fiber oriented to the polymer electrolyte membrane side and the second conductive fiber oriented to the diffusion layer side are brought into contact with each other, for example, The first conductive fiber on the polymer electrolyte membrane side and the second conductive fiber on the diffusion layer side are brought into contact with each other by interposing one conductive fiber between the other conductive fibers, etc. Conductive fibers that are strongly connected to each other by the entanglement of the fibers formed a laminated structure of diffusion layer / catalyst layer / polymer electrolyte membrane constituting the catalyst layer, so that lamination between the diffusion layer / catalyst layer / polymer electrolyte membrane is performed. The electrical contact resistance in the direction (layer thickness direction) is drastically reduced, and the conductivity can be effectively improved. Therefore, it is not necessary to apply high surface pressure by tightening with bolts, etc., which has been indispensable for securing the power generation performance (conductivity) in the past. Good power generation performance (power generation operation at a high current density) can be ensured.

In addition, by using conductive fibers as a carrier for supporting an electrocatalyst metal, it is possible to ensure a large area of the supported surface and to support the electrocatalyst metal at a high density, and a polymer electrolyte membrane (for example, a membrane surface) ) And the diffusion layer (for example, the surface of the layer), the conductive fiber carrying the electrocatalyst metal is oriented to constitute the electrode, so that the supplied fuel (for example, from the separator (flow path) side) ( H ₂ gas, etc.) and oxidant gas (air, etc.) reach the vicinity of the three-phase interface, so that the supply of fuel, etc. will be performed uniformly, and the supported electrocatalyst metal should be used effectively for the electrode reaction. Can do. As a result, the electrode reactivity is improved, contributing to a reduction in the amount of catalyst supported.

  In the first invention, the first conductive fiber is oriented substantially perpendicularly to the membrane surface of the polymer electrolyte membrane, and the second conductive fiber is oriented substantially perpendicularly to the surface of the diffusion layer. Is effective. In the conductive fiber group provided on each of the membrane surface and the layer surface, there is a gap between the individual fibers, so that the conductive fiber on the polymer electrolyte membrane side is the gap between the conductive fibers on the diffusion layer side. In addition, since the conductive fiber on the diffusion layer side is inserted toward the gap between the conductive fibers on the polymer electrolyte membrane side, the electrical contact resistance between the diffusion layer / catalyst layer / polymer electrolyte membrane is This is effective for reducing the diffusivity and improving the diffusibility of the fuel, that is, improving the conductivity.

  The conductive fiber is preferably a conductor having a hollow internal structure, and specifically, is preferably a carbon nanotube. Carbon nanotubes are advantageous in terms of lower electrical resistance and drainage than carbon black and the like. In addition to carbon nanotubes, conductive fibers include carbon nanohorns and carbon fibers.

  In the conductive fiber, a known metal that causes an electrode reaction can be appropriately selected and supported, but it is particularly preferable to support platinum (Pt) or an alloy composed of platinum and another metal as an electrode catalyst metal. It is. Generally, platinum-based catalytic metals belong to noble metals and are expensive. However, as described above, electrode catalyst metals are effectively used for electrode reactions, so the amount of catalyst used can be reduced. It is advantageous.

  The electrocatalyst metal (preferably an alloy composed of Pt or Pt and another metal) supported on the conductive fiber is effective when the particle diameter is equal to or smaller than the outer diameter of the conductive fiber as a carrier. Since the particle diameter is equal to or smaller than the outer diameter, it is possible to ensure a large supporting area and to support the electrocatalyst metal at a high density. Preferably it is 1-3 nm.

The conductive fiber is configured by providing a proton conductive material (preferably perfluorosulfonic acid compound) on the surface thereof, and can enhance proton conductivity when placed in a wet state. Proton conductivity is particularly improved when it is composed of a perfluorosulfonic acid compound. Furthermore, it is effective to provide the proton conductive material so as to have a thickness of 1 to 70 μm. Moreover, it is preferable that the length of the first conductive fiber is 10 μm or less and the length of the second conductive fiber is 200 μm or more.

  Further, it is desirable that a water repellent material (preferably a fluorine resin) be further provided on the provided proton conductive material. Since a water-repellent substance is provided between the carbon nanotubes forming the electrode, the generated water generated by the electrode reaction does not adhere to and stay on the carbon nanotubes, ensuring sufficient supply of the source gas, and generating power that does not cause a decrease in output Performance can be ensured. When composed of a fluorine-based resin, the supply efficiency of the raw material gas can be improved, and polytetrafluoroethylene and / or polyvinylidene fluoride are more effective.

  A fuel cell according to a second aspect of the present invention includes a membrane electrode assembly according to the first aspect of the present invention, a groove formed in a recess, and a non-oriented region of the second conductive fiber of the diffusion layer (for example, the first of the diffusion layer). 2 and a separator that forms a flow path between the side on which the conductive fibers are oriented and the opposite layer surface). Since the membrane electrode assembly of the first invention configured as described above is provided, it is highly durable and can generate power at a high current density.

  Examples of the fuel cell include a polymer electrolyte fuel cell (PEFC) and a direct methanol fuel cell (DMFC).

  According to the present invention, a membrane electrode joint that makes it possible to efficiently use a supported expensive noble metal catalyst for an electrode reaction and to perform a power generation operation with high durability and high current density without applying a high surface pressure by tightening. It is possible to provide a fuel cell that includes the body and the membrane electrode assembly and exhibits high durability and good power generation performance (power generation operation at a high current density).

  Hereinafter, embodiments of the fuel cell of the present invention will be described in detail with reference to the drawings, and embodiments of the membrane electrode assembly of the present invention will be described in detail through the description. In the following embodiment, a description will be given focusing on a polymer electrolyte fuel cell (PEFC) that uses hydrogen gas and air (oxygen) as fuel for power generation operation. However, the present invention is not limited to the following embodiment.

  Embodiments of a membrane electrode assembly and a fuel cell according to the present invention will be described with reference to FIGS. In the present embodiment, single-walled carbon nanotubes (hereinafter, the single-walled carbon nanotubes may be abbreviated as “CNT”) are used as the conductive fibers, and the tube is disposed on the fluorine-based ion exchange resin (polymer electrolyte) membrane side. Linear Pt-supported CNTs with platinum (Pt; electrocatalyst metal) supported on the outer wall are provided so as to be oriented substantially perpendicular to the film surface, and linear non-supported CNTs that do not support Pt on the diffusion layer side. The Pt-supported CNT and the non-supported CNT are inserted between the other CNTs so as to be in contact with each other.

  As shown in FIG. 1, a fuel cell (single cell) 10 of this embodiment holds a membrane electrode assembly 20 and a membrane electrode assembly 20 from both sides, and hydrogen gas on the fuel electrode (anode electrode) side. A pair of separators 21 forming a hydrogen gas flow path 23 through which air is passed, that is, an air flow path 24 through which air (air) passes, that is, is fed and discharged to the oxidant electrode (cathode electrode) side, 22 is comprised. The single cell configured as shown in FIG. 1 can be made into a stack structure by stacking a plurality of cells with a separator interposed therebetween.

In the fuel cell 10, hydrogen gas having a high hydrogen (H ₂ ) density is supplied to the hydrogen gas passage 23, and air containing oxygen (O ₂ ) is supplied to the air passage 24. Electric power can be supplied to the outside by an electrochemical reaction (battery reaction) represented by 3). Equations (1) and (2) represent the reactions on the anode side and the cathode side, respectively, and Equation (3) represents the total reaction of the fuel cell.

H ₂ → 2H ⁺ + 2e ⁻ (1)
(1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
H ₂ + (1/2) O ₂ → H ₂ O (3)

  The membrane electrode assembly 20 includes a fluorine-based ion exchange resin membrane 11 and an anode electrode 12 and a cathode electrode 13 provided so as to sandwich the fluorine-based ion exchange resin membrane 11 (these may be collectively referred to as “CNT electrodes”). The anode electrode 12 and the cathode electrode 13 are each composed of CNT catalyst layers 14 and 15 that are responsible for battery reaction and diffusion layers 16 and 17 that function as current collectors. Hereinafter, the cathode electrode side will be described in more detail with reference to FIG. FIG. 2 is an enlarged schematic cross-sectional view showing the cathode electrode side of the membrane electrode assembly 20.

  As shown in FIG. 2, a linear carbon nanotube 31 having a length of 500 μm and an outer diameter of 10 nm is bonded to one end of the fluorine-based ion exchange resin film 11 on the side facing the diffusion layer 17 substantially perpendicular to the film surface. The carbon nanotubes 31 are formed on the entire surface of the fluorine-based ion exchange resin film 11 on the side facing the diffusion layer 17.

  Each of the carbon nanotubes 31 provided on the fluorine-based ion exchange resin film 11 carries platinum (Pt) 32 having a particle diameter of 3 nm as an electrode catalyst metal responsible for a battery reaction on the outer wall surface. By using linear carbon nanotubes as a support, the surface area is expanded and high density is supported, and water discharge is not reduced even in an environment where water is excessively generated during power generation. Supply to the three-phase interface, diffusivity is maintained, and the supported Pt32 effectively contributes to the cell reaction to obtain power generation efficiency according to the supported amount, so that a large voltage drop (concentration overvoltage) does not occur. It has become. The electrode catalyst metal can be provided not only on the outer wall surface of the carbon nanotube, but also on the inner wall surface, and may be supported on both the outer wall surface and the inner wall surface.

  Further, the particle diameter of Pt (electrode catalyst metal) 32 is selected to be equal to or smaller than the outer diameter of the carbon nanotube 31, and it is effective to set the particle diameter within a range of about 1 to 3 nm except for the above particle diameter. As the electrode catalyst metal, an alloy made of Pt and another metal other than Pt can be used.

  As shown in FIG. 3, a Nafion solution (Aldrich Chemical Co .; proton conductive material) is further applied to the outer wall surface of the carbon nanotube 31 on which Pt32 is supported to provide a Nafion layer 33 having a layer thickness of 10 to 100 nm. Thus, the proton conductivity in the battery reaction and the bonding strength with the fluorine-based ion exchange resin film 11 are ensured.

  As the proton conductive substance, a perfluorosulfonic acid compound (perfluorosulfonic acid polymer or the like) can be used in addition to the Nafion solution. In addition, the thickness of the proton conductive material (here, Nafion layer 33) is effectively within a range satisfying 10 to 70 nm in addition to the above thickness, and more preferably 10 to 30 nm. .

  Further, a PTFE layer 34 made of polytetrafluoroethylene (water repellent material; PTFE) is further provided on the Nafion layer 33 on the carbon nanotube 31 as shown in FIG. It is possible to secure the discharge of generated water. As the water repellent material, it is preferable to select and use at least one fluorine-based resin as appropriate. Polyvinylidene fluoride (PVDF) can also be mentioned as an effective compound in addition to the above polytetrafluoroethylene. Moreover, you may use multiple types together.

  As shown in FIG. 2, a linear carbon nanotube 35 having a length of 10 μm and an outer diameter of 10 nm is bonded to one end of the diffusion layer 17 on the side facing the fluorine-based ion exchange resin film 11 as shown in FIG. The carbon nanotubes 35 are formed on the entire surface of the diffusion layer 17 on the side facing the fluorine-based ion exchange resin film 11.

  The carbon nanotubes 35 provided in the diffusion layer 17 have a configuration in which an electrode catalyst metal (for example, Pt) that bears a battery reaction is supported on the outer wall surface and / or the inner wall surface in the same manner as the carbon nanotube 31 described above. Is also suitable. In this case, the battery reaction is more activated and a power generation operation with a higher current density is possible. In addition, a proton conductive material such as a Nafion solution can be applied to the outer wall surface of the carbon nanotube 35 with or without supporting an electrode catalyst metal. A hydrated material can also be provided.

  The fluorine-based ion exchange resin film 11 and the diffusion layer 17 are arranged so that the carbon nanotubes 31 and 35 oriented to each other face each other, and the carbon nanotubes 31 are placed in the gaps between the tube groups of the carbon nanotubes 35. Are inserted in the gaps between the tube groups of the carbon nanotubes 31, and the carbon nanotubes are in contact with each other via the Pt 32, the Nafion layer 33 and the PTFE layer 34, thereby forming the CNT catalyst layer 15.

  As described above, one of the carbon nanotubes constituting the CNT catalyst layer is bonded and oriented to the fluorine ion exchange resin film 11 and the other to the diffusion layer 17 to maintain conductivity, and the carbon nanotubes 31 and 35 are As a result, the conductivity of the diffusion layer 17 / CNT catalyst layer 15 / ion exchange resin film 11 is ensured by forming a structure in which one of the CNTs is entangled with the other CNT to ensure the conductivity. ing. Accordingly, sufficient electrical conductivity can be obtained without applying surface pressure to the membrane electrode assembly by tightening with a bolt or the like as in the prior art.

  In the above description, the description is focused on the cathode side, but the same applies to the anode side.

  The length of the carbon nanotube 31 is 10 μm or less, preferably 1 to 3 μm, and the carbon nanotube 35 is preferably 200 μm or more, more preferably 200 to 500 μm. This is the length of the carbon nanotube, that is, the length of the tube (cylinder), and if the length is less than 200 μm, the supply and diffusion of hydrogen gas (fuel) and air (oxidant gas) will decrease. As a result, power generation efficiency may decrease.

Each of the carbon nanotube 31 and the carbon nanotube 35 uses an arc discharge method, a laser vapor deposition method, or a catalytic metal for generating carbon nanotubes (hereinafter referred to as “CNT-forming catalytic metal”), and a hydrocarbon gas or a hydrogen-based one. CVD method for synthesizing by supplying gas, etc., HiPco method for synthesizing carbon monoxide disproportionation reaction (CO + CO → C + CO ₂ ) under high temperature and high pressure conditions (P. Nikolaev, MJ Bronikowski) RK Bradley, F. Rohmund, DT Colbert, KA Smith, RE Smalley, Chem. Phys. Lett. 313 (1999) 91-97, etc.) and the like.

  Hereinafter, an example of a method for producing carbon nanotubes will be described, taking as an example the case of synthesizing single-walled carbon nanotubes using a catalyst carrier.

  Generated by supplying a raw material gas (carbon nanotube production process) to a catalyst carrier that supports Fe, which is a CNT-forming catalyst metal, in a desired thickness (for example, 4 nm) and heated to a predetermined temperature or higher in a vacuum. Can do. In addition to the carbon nanotube production step, other steps such as a catalyst supporting step, a substrate cleaning step, and a post-treatment step can be appropriately provided.

  In the carbon nanotube production step, the catalyst carrier is placed in a vacuum chamber and heated to a predetermined temperature suitable for the production of carbon nanotubes, and a raw material gas (hydrocarbon gas, alcohol gas, And hydrogen gas). Adjusting the flow rate of raw material gas, reaction temperature, and staying temperature for supply, changing the size (particle diameter) of the CNT-forming catalytic metal, or heating the generated carbon nanotubes in the temperature range of 1500-1850 ° C, etc. By doing so, the tube diameter can be controlled. It is also useful to control the source gas according to the shape and orientation of the layer structure, diameter, length, etc. of the carbon nanotubes, such as ionizing the source gas using an ion gun, for example. is there.

  The flow rate of the raw material gas on the surface of the catalyst carrier when the raw material gas is supplied is desirably 2 mm / sec or more. When the flow rate is not less than the above range, carbon nanotubes of 200 μm or more can be efficiently generated.

The predetermined temperature of the catalyst carrier when supplying the raw material gas is preferably 400 ° C. or higher. When the predetermined temperature is within the above range, the production rate can be secured, and carbon nanotubes having a uniform diameter, length, and orientation can be stably produced. Particularly preferably, the temperature is 500 ° C. to 1000 ° C. When the temperature is within this range, homogeneous carbon nanotubes can be generated more efficiently. In addition, the vacuum state in this step is generally preferably about 10 ⁻³ to 10 Pa.

  The raw material gas includes a hydrocarbon gas, an alcohol gas (CH gas), and a hydrogen gas (H gas). Specifically, at least one selected from a hydrocarbon-based gas and an alcohol-based gas, or both at least one selected from a hydrocarbon-based gas and an alcohol-based gas and at least one selected from a hydrogen-based gas ( (In some cases, it can be gasified). Preferred examples of the hydrocarbon component of the hydrocarbon-based gas include hydrocarbons having 1 to 6 carbon atoms (eg, methane, ethane, acetylene, benzene, etc.), and examples of the alcohol-based gas include methanol, ethanol, and the like. Preferably mentioned. Moreover, as said hydrogen type gas, hydrogen gas, ammonia gas, etc. are mentioned suitably, for example. When the CH-based or H-based raw material is in a liquid phase or a solid phase, it can be supplied in a gas phase in advance. In the case of a mixed system of CH-based gas and H-based gas, the mixing ratio (CH-based: H-based) is preferably 1: 1 to 1:20 (partial pressure ratio or flow rate ratio).

  The catalyst carrier is configured by carrying a CNT-forming catalyst metal on the surface of the substrate. Examples of the CNT-forming catalytic metal include Pd, Co, Ni, W, Mo, Mn, and alloys thereof in addition to Fe. Examples of the substrate include Al, Ni, stainless steel, Si, SiC, zeolite, activated carbon (C), and the like, and can be configured in an arbitrary shape, but is preferably configured in a plate shape.

  In the production of carbon nanotubes, a substrate washing step, a catalyst supporting step, and the like can be further provided in a pre-step of the carbon nanotube production step, and a post-treatment step and the like can be further provided in a post-step of the carbon nanotube production step.

  In the substrate cleaning step, the surface of the substrate (substrate or the like) to be used is cleaned. For example, cleaning can be performed by heat-treating a substrate as a base in an electric furnace in a vacuum. In the catalyst supporting step, a catalyst supporting body used for generating carbon nanotubes is prepared by supporting a CNT-forming catalytic metal on a substrate. The specific method is not particularly limited. For example, a catalyst carrier can be obtained by uniformly atomizing and supporting a desired CNT-forming catalyst metal such as Fe on a desired substrate by vapor deposition or the like.

  In the post-treatment step, the carbon nanotubes produced in the carbon nanotube production step and the catalyst carrier on which the carbon nanotubes are produced can be post-treated. Specifically, the following steps can be performed. For example, the produced carbon nanotube can be further heated at 1500 to 1850 ° C. to control and adjust the tube diameter. In addition, the carbon nanotubes can be heated again in the air to about 500 to 600 ° C. (air oxidation treatment), or can be subjected to acid treatment using hydrochloric acid, aqua regia, etc., and reheated as in the former case. Sometimes the tube end can be opened (cap open). Even with the latter acid treatment, the tube end is cut to open the cap, the carbon nanotube is generated and the catalyst metal removal treatment is removed, and the adhering amorphous carbon is removed. It is possible to perform a removal process or the like.

  Note that Pt (electrocatalyst metal) can be supported on the surface of the carbon nanotube 31 (and possibly the carbon nanotube 35) by using a solvent diluent such as an alcohol of a platinum chemical solution such as chloroplatinic acid or platinum nitric acid solution. The details will be described later.

  Both of the diffusion layers 16 and 17 are formed of carbon cloth woven with yarns made of carbon fibers. In addition to carbon cloth, the diffusion layer is preferably formed of carbon paper or carbon felt made of carbon fiber.

  A plurality of grooves (ribs) are provided in the separators 21 and 22, and a hydrogen gas flow is provided between the side of the diffusion layer 17 where the carbon nanotubes 35 are oriented and the surface on the opposite side, on the anode electrode side. An air passage 24 is formed on the cathode side of the passage 23 (see FIG. 1). The separator can be composed of a gas-impermeable conductive member, for example, dense carbon that has been compressed by gas to be gas-impermeable.

  When the separators 21 and 22 are single cells, the flow path is formed only on one side of each cell. However, when a plurality of single cells are stacked to form a stack structure, one separator is between two membrane electrode assemblies. And a flow path is formed on both sides of each separator. That is, concave ribs are formed on both sides of one separator, a hydrogen gas channel 23 in the anode electrode is formed on one side, and an air channel in the cathode electrode of the adjacent membrane electrode assembly on the other side. Is formed.

Next, an example of a method for producing the membrane electrode assembly 20 will be described.
The membrane / electrode assembly 20 includes an electrode catalyst supporting step of supporting Pt (electrode catalyst metal) 32 on a carbon nanotube 31 generated on a catalyst supporting member supporting a CNT generating catalyst on a substrate, and a carbon nanotube 31 supporting Pt 32. Is transferred to the fluorine-based ion exchange resin membrane 11 (polymer electrolyte membrane), one end of the carbon nanotube 31 is joined to the fluorine-based ion exchange resin membrane 11 and oriented substantially perpendicular to the film surface, and fluorine-based ions By placing the exchange resin film 11 and the diffusion layer 17 in such a manner that the carbon nanotubes 31 and the carbon nanotubes 35 oriented substantially perpendicularly to the surface of the diffusion layer 17 are brought into contact with each other (preferably so as to be intertwined). Can be made. In the present embodiment, an application step of forming the Nafion layer 33 and the PTFE layer 34 on the carbon nanotube 31 on which Pt 32 is supported is further provided between the electrode catalyst support step and the transfer step.

  In the electrode catalyst supporting step, Pt (electrode catalyst metal) is supported on the carbon nanotubes 31 generated on the catalyst support. Pt can be supported on the carbon nanotubes 31 by either a wet method or a dry method. In the case of the wet method, it is desirable to apply a solution in which an appropriate amount of a platinum chemical solution such as chloroplatinic acid or a platinum nitric acid solution is dissolved in an alcohol such as ethanol and then heat-treat in a hydrogen atmosphere at 150 ° C. or higher. The application can be suitably performed, for example, by immersing the carbon nanotubes 31 in a solution or by dropping or spraying the carbon nanotubes 31 on the carbon nanotubes 31. In the case of a dry method, an electron beam evaporation method, a sputtering method, an electrostatic coating method, or the like is desirable.

  In addition, before the electrode catalyst supporting step, other steps such as the above-described carbon nanotube generating step, a catalyst supporting step, a substrate cleaning step, and a post-treatment step can be appropriately provided. These are as described above.

  In the transfer step, the carbon nanotubes 31 carrying Pt are transferred to the fluorine-based ion exchange resin film 11. In the transfer, the carbon nanotubes 31 are generated on the catalyst carrier, and the end on the side not in contact with the catalyst carrier is placed in contact with the fluorine-based ion exchange resin film 11, and heated and pressurized. It can be carried out by forming a joined body and peeling and removing the catalyst carrier from the joined body.

  The heating and pressure treatment in this step can be performed using a pair of hot plates that can be pressurized, such as a hot press method. The heating temperature here is preferably about 110 to 130 ° C., and the pressure is preferably about 1 to 2 MPa from the viewpoint of bondability with the fluorine-based ion exchange resin film 11.

  When the catalyst carrier is peeled off and transferred, the carbon nanotubes 31 are oriented on the fluorine-based ion exchange resin film 11 while maintaining the orientation state at the time of generation. Therefore, when the carbon nanotubes generated in the carbon nanotube generation step are generated in a straight line substantially perpendicular to the support surface of the catalyst support, the film surface of the fluorine-based ion exchange resin film 11 is transferred by transferring the carbon nanotubes. It is possible to provide linear carbon nanotubes substantially perpendicular to the above. As a technique for aligning substantially vertically as described above, the method described in Japanese Patent Application No. 2002-51391 and the “method of aligning carbon nanotubes synthesized on a substrate by transferring to a thermoplastic material approximately vertically” are applied. be able to.

  In the arranging step, the fluorinated ion exchange resin film 11 and the diffusion layer 17 are interleaved between the carbon nanotubes 31 and the carbon nanotubes 35 oriented substantially perpendicular to the surface of the diffusion layer 17 between the CNTs on the other side, Preferably, the membrane electrode assembly is manufactured by entwining the membrane electrode assembly. The carbon nanotubes 35 oriented in the diffusion layer can be formed directly on the diffusion layer using the synthesis method described above.

  Between the above-described electrode catalyst supporting step and transfer step, a Nafion solution (proton conductive material) is applied to the carbon nanotubes 31 supporting Pt (electrode catalyst metal) 32 to form a Nafion layer 33 having a layer thickness of 10 nm. An application step for forming is provided. In this case, the carbon nanotube 31 is transferred in a state where the Pt 32 and the Nafion layer 33 are provided in the subsequent transfer process.

  When the application step is provided as in the present embodiment, the Nafion layer 33 is formed, and a polytetrafluoroethylene (PTFE; water repellent material) solution is further applied on the formed Nafion layer 33 to provide a PTFE layer. 34 is further provided. In this case, the carbon nanotubes 31 are transferred in a state where the Pt 32, the Nafion layer 33, and the PTFE layer 34 are provided in the subsequent transfer process.

  The formation of the Nafion layer 33 and the PTFE layer 34 in the applying step is performed by a known method such as a coating method or a dipping method using a Nafion solution (proton conductive material solution) or a PTFE solution (water repellent material solution). In particular, the dipping method is desirable in that it can be uniformly applied to the surface of each fine carbon nanotube.

  In the above, the case where the carbon nanotubes 31 and 35 are configured in a straight line and each carbon nanotube is oriented substantially perpendicular to the film surface or the layer surface has been described. An aspect in which the carbon nanotubes 31 and 35 are configured so as to be intertwined with each other is also preferable. Further, the carbon nanotube is not limited to a single wall, and the same applies to the case of a multi-wall carbon nanotube having a two-layer structure or more.

  In the above-described embodiment, the description has focused on the polymer electrolyte fuel cell (PEFC) using hydrogen gas and air as the fuel, but the same applies to the case of a direct methanol fuel cell (DMFC) using a methanol solution. is there.

  The membrane electrode assembly and the fuel cell of the present invention can be applied as a power supply source for vehicles such as electric vehicles, ships, airplanes, and the like.

It is a schematic sectional drawing which shows the fuel cell which concerns on embodiment of this invention. It is a schematic sectional drawing which expands and shows the cathode pole side of the membrane electrode assembly which concerns on embodiment of this invention. It is a schematic sectional drawing which expands and shows a CNT catalyst layer. It is a schematic sectional drawing for demonstrating the structure of the conventional fuel cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel cell 11 ... Fluorine ion exchange resin membrane 16, 17 ... Diffusion layer 20 ... Membrane electrode assembly 21,22 ... Separator 31 ... Carbon nanotube (1st electroconductive fiber)
32 ... Pt (Electrocatalyst metal)
33 ... Nafion layer 34 ... PTFE layer 35 ... Carbon nanotube (second conductive fiber)

Claims (9)

A polymer electrolyte membrane in which the first conductive fibers are oriented, a diffusion layer in which the second conductive fibers are oriented, and the second conductive fibers are disposed in contact with the first conductive fibers; A membrane electrode assembly comprising an electrode catalyst metal supported on at least one of the first and second conductive fibers, and having a proton conductive material on at least one surface of the first and second conductive fibers .   The first conductive fiber is oriented substantially perpendicular to the membrane surface of the polymer electrolyte membrane, and the second conductive fiber is oriented substantially perpendicular to the layer surface of the diffusion layer. The membrane electrode assembly as described.   The membrane electrode assembly according to claim 1, wherein the conductive fiber is a carbon nanotube.   The membrane electrode assembly according to any one of claims 1 to 3, wherein the electrode catalyst metal is platinum or an alloy composed of platinum and another metal.   The membrane electrode assembly according to any one of claims 1 to 4, wherein a particle diameter of the electrode catalyst metal is equal to or smaller than an outer diameter of the conductive fiber. The membrane electrode assembly according to any one of claims 1 to 5, further comprising a water repellent material on the proton conductive material. The membrane electrode assembly according to claim 1, wherein the proton conductive material is a perfluorosulfonic acid compound. The membrane electrode assembly according to any one of claims 1 to 7, wherein a length of the first conductive fiber is 10 µm or less and a length of the second conductive fiber is 200 µm or more. The separator which forms a flow path between the membrane electrode assembly of any one of Claims 1-8 , and a groove | channel and the groove | channel is recessed and the non-orientation area | region of the 2nd conductive fiber of a diffusion layer is formed. Fuel cell provided.

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