JP4977945B2 - Membrane electrode assembly, method for producing the same, and fuel cell - Google Patents

Description

  Membrane / electrode assembly suitable for the construction of a power generation cell of a fuel cell, such as a polymer electrolyte fuel cell (PEFC) and a direct methanol fuel cell (DMFC), and a method for producing the same, and the membrane electrode assembly, The present invention relates to a fuel cell suitable for a configuration such as DMFC.

  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. A catalyst layer responsible for an electrochemical reaction and a diffusion layer functioning as a current collector are provided.

  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 source 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. 9, the design of this 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. Furthermore, 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 the separator / diffusion layer / Although it has a laminated structure of catalyst layer / electrolyte membrane, it is necessary to prevent deterioration of the contact resistance between the separator / diffusion layer and the diffusion layer / catalyst layer in particular, so that the power generation efficiency is deteriorated. Tightening is indispensable and has a problem of adversely affecting the durability of the membrane. In particular, it has been a major problem in terms of reducing electrical contact resistance between separator / diffusion layers, that is, ensuring electrical conductivity (see, for example, Patent Document 1).

In addition, there is a technique disclosed regarding an electrode catalyst using fibrous carbon as a carrier (see, for example, Patent Document 2). However, simply using a configuration using fibrous carbon does not necessarily provide good power generation efficiency, and is similar to the above in that it adversely affects the durability of the membrane.
JP 2002-246034 A JP-A-8-17440 Development and application of polymer electrolyte fuel cells (p.6, NTS Corporation)

  As described above, the noble metal catalyst supported in the vicinity of the three-phase interface away from the fuel supply side can be effectively used for the electrode reaction, and it is good without giving a high surface pressure due to tightening that adversely affects the membrane. The present condition is that the technique which produces the membrane electrode assembly from which power generation efficiency is obtained is not yet established.

  The present invention has been made in view of the above, enables effective use of the supported expensive noble metal catalyst for electrode reaction, does not cause deterioration in film durability due to application of high surface pressure by tightening, and is high. It is an object of the present invention to provide a membrane electrode assembly capable of exhibiting good power generation performance without applying surface pressure, a method for producing the same, and a fuel cell including the membrane electrode assembly, and to achieve the object And

The present invention is to orient the substantially vertically mosquitoes over carbon nanotubes to the polymer electrolyte membrane, as a carrier for carrying the electrode catalyst metal oriented carbon nanotubes, which separator (or diffusion layer) / the polymer electrolyte membrane between Obtaining the knowledge that it is useful to secure conductivity (lowering the contact resistance) without giving a high surface pressure has been 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 comprises a polymer electrolyte membrane, a polymer electrolyte membrane, oriented substantially perpendicular to the surface of the polymer electrolyte membrane, and having a proton conductive material on the surface, Rutotomoni that having a more water-repellent material on the said proton conductive material, which is constituted by carbon nanotubes carrying the electrode catalyst metal. That is, the carbon nanotube carrying the electrocatalytic metal functions as an electrode of a fuel cell (for example, PEFC or DMFC). For example, in the case of a polymer electrolyte fuel cell (PEFC), a carbon nanotube carrying an electrocatalyst metal is disposed between a polymer electrolyte membrane and a separator that forms a flow path for supplying and discharging a source gas.

In the membrane electrode assembly according to the first aspect of the present invention, it is possible to ensure that the area of the supported surface is widened and to carry the electrode catalyst metal at a high density by using carbon nanotubes as a carrier for supporting the electrode catalyst metal. , directly on the front surface of the polymer electrolyte membrane, the electrode catalyst metal was to constitute the electrode oriented substantially perpendicularly carbon nanotubes carried on the surface, (the side for example, the separator (flow path)) supplied Fuel (raw material gas, etc.) reaches the vicinity of the three-phase interface and is uniformly diffused, that is, the gas supply is performed well, and the supported electrocatalyst metal is effectively used for the electrode reaction. Can do. Carbon nanotubes are also advantageous in that they have lower electrical resistance than carbon black or the like.

  In addition, since carbon nanotubes are bonded to a polymer electrolyte membrane in this way, a diffusion layer is not necessarily required, and a high surface pressure due to tightening with bolts or the like, which has been indispensable for securing power generation performance in the past. The application is not necessary, and the deterioration of the durability of the film due to tightening can be eliminated, and high power generation performance (power generation operation at a high current density) can be ensured with high durability. In addition, high electrode loading improves electrode reactivity and contributes to a reduction in catalyst loading.

  The carbon nanotube may have a single-layer or multi-layer structure, and the tube diameter is preferably 10 to 100 nm in terms of the outer diameter from the viewpoint of high density support.

  The carbon nanotube according to the first aspect of the present invention is a carbon nanotube in the case where a separator that forms a flow path for supplying and discharging fuel (source gas, etc.) without providing a diffusion layer in a fuel cell such as PEFC or DMFC is provided. The separator provided opposite to the nanotube can be provided in a region of the polymer electrolyte membrane facing the front end surface of the convex portion protruding to the carbon nanotube side. As described above, the carbon nanotube is oriented at one end to the polymer electrolyte membrane (for example, the surface), and the other end has a convex shape other than the concave portion forming the separator fuel flow path. Therefore, it is sufficient that the carbon nanotubes are selectively provided only in the region of the polymer electrolyte membrane facing the surface of the tip of the convex portion to be joined, It can be configured such that unnecessary carbon nanotubes are not provided in the region of the polymer electrolyte membrane facing the recess (fuel flow path) where the separator is not joined.

As described above, when the carbon nanotube is provided between the polymer electrolyte membrane and the separator (preferably, its convex portion), the length of the carbon nanotube is generally not provided when the diffusion layer is not provided between the separator / electrode (catalyst). Is preferably 200 μm or more. By setting the length to 200 μm or more , supply of the supplied raw material gas, diffusibility, and sufficient discharge of water generated by the electrode reaction (product water) can be ensured, and power generation performance can be stably maintained and improved. be able to.

  Further, the carbon nanotube is more preferably at least on the membrane surface of the polymer electrolyte membrane (particularly the membrane surface facing the separator when the separator is provided) on the membrane surface and the convex surface of the separator. On the other hand, it is effective to be oriented substantially vertically. When the carbon nanotubes are oriented substantially vertically, the supply property of the supplied fuel (raw material gas, etc.) and the discharge property of the generated water are improved, so that stable power generation performance can be maintained. .

  The carbon nanotubes can be supported by appropriately selecting a known metal that causes an electrode reaction. In particular, it is preferable to support platinum (Pt) or an alloy composed of platinum and another metal as an electrode catalyst metal. is there. 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.

  It is effective that the electrocatalyst metal (preferably an alloy composed of Pt or Pt and another metal) supported on the carbon nanotube has a particle diameter equal to or smaller than the outer diameter of the carbon nanotube 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 high density. Preferably it is 1-3 nm.

The carbon nanotube is configured by providing a proton conductive material (preferably a 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. Further, it is effective to provide the proton conductive material so that the thickness is 1 to 70 nm .

Further, (preferably fluorine resin) further water-repellent material on the provided proton conductive material is formed by providing a. 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.

  The membrane electrode assembly of the present invention can be constituted by further providing an oxygen-enriching heat insulating member for covering at least a part of the carbon nanotubes. Since the heat insulating member is configured to be oxygen-enriched, particularly on the cathode electrode side of the membrane electrode assembly, the electrode catalyst metal is supported and oxygen can be supplied to the carbon nanotubes constituting the electrode, and the electrode catalyst metal is supported. In the carbon nanotubes constituting the electrode, the electrochemical reaction (battery reaction) proceeds and locally generates heat. Therefore, it is possible to retain heat by providing a heat insulating member and covering at least the heat generating portion of the carbon nanotube from the outside. . By using the retained thermal energy, it is possible to improve startability (low temperature startability) in a low temperature environment (for example, 0 ° C. or less), without applying other energy such as applying a differential pressure, The oxygen enrichment characteristic of the heat insulating member can be improved more effectively. As the oxygen-enriching heat insulating member, an oxygen-enriched ceramic material is suitable.

  In addition, the heat insulating member preferably has a cylindrical shape, and can be configured by providing at least one (one) of carbon nanotubes oriented in the polymer electrolyte membrane inside the cylinder. The carbon nanotubes can be configured either in a form in which each carbon nanotube is covered with a heat insulating member or in a form in which each carbon nanotube is covered in a desired unit.

  The fuel cell according to the second invention is constructed using the membrane electrode assembly according to the first invention described above. Since the membrane electrode assembly of the first invention configured as described above is provided, the supported electrocatalyst metal is effectively utilized for the electrode reaction, and a power generation operation at a high current density is possible. It has durability. Moreover, it is excellent in low temperature startability.

  In particular, in the case of a configuration having no diffusion layer, a polymer electrolyte membrane, a separator having a recess on the polymer electrolyte membrane side and forming a fuel flow path, and protruding toward the polymer electrolyte membrane side of the separator The carbon nanotube is provided in the region of the polymer electrolyte membrane facing the front end surface of the convex portion, and can be composed of a carbon nanotube carrying an electrode catalyst metal.

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

According to a third aspect of the present invention, there is provided a method of manufacturing a membrane electrode assembly comprising an electrode catalyst supporting step of supporting an electrode catalyst metal on a carbon nanotube produced on a catalyst support, and a proton conductivity of the carbon nanotube supporting the electrode catalyst metal. Adding a substance and further providing a water repellent material on the proton conductive material; and an electrode catalyst metal supported on the carbon nanotube to which the proton conductive material and the water repellent material are provided A transfer step of transferring to a molecular electrolyte membrane, joining one end of the carbon nanotube to the polymer electrolyte membrane, and orienting the carbon nanotube substantially perpendicularly to the membrane surface of the polymer electrolyte membrane.

In the third invention, carbon nanotubes are generated using a catalyst support on which a catalyst metal for generating carbon nanotubes is supported, and after the electrode catalyst metal is supported on the generated carbon nanotubes (for example, the tube surface), the electrode The carbon nanotube carrying the catalyst metal is transferred to the polymer electrolyte membrane by a transfer method. At this time, the other end of the carbon nanotube connected to the catalyst carrier at one end is joined to the polymer electrolyte membrane and oriented substantially perpendicular to the membrane surface .

  When aligning carbon nanotubes directly on the polymer electrolyte membrane as described above, it is generally difficult to expose the polymer electrolyte membrane to the high temperature at the time of carbon nanotube formation and it is difficult to produce tubes on the electrolyte membrane. By adopting it, it becomes possible to provide carbon nanotubes directly on the polymer electrolyte membrane. Then, it can be oriented on the electrolyte membrane in the orientation state at the time of production. For example, when it is produced substantially perpendicular to the support surface of the catalyst carrier, carbon that is oriented substantially perpendicular to the membrane surface of the polymer electrolyte membrane Nanotubes can be easily provided. According to the third invention, the membrane electrode assembly of the first invention described above can be produced.

  In the third invention, after the transfer step, a separator that forms a fuel flow path is provided on the side of the polymer electrolyte membrane on which the carbon nanotubes are oriented, and the carbon nanotube that is bonded to the polymer electrolyte membrane at one end is provided. An adhesion step of adhering the other end and the front end surface of the convex portion of the separator using a conductive adhesive can be further provided.

  The other end of the carbon nanotube, which is transcribed and joined to the polymer electrolyte membrane at one end, is selectively conductive with the tip surface of the separator (the surface facing the polymer electrolyte membrane at the tip of the protrusion other than the recess forming the flow path). Therefore, the electrical conductivity in the laminated structure of the separator / electrode / polymer electrolyte membrane is ensured, and good power generation performance can be obtained without applying a high surface pressure by conventional tightening.

  The conductive adhesive is an adhesive that provides conductivity after drying, and can be appropriately selected from known ones. Among conductive adhesives, carbon-based conductive adhesives are particularly effective, and examples thereof include phenolic and polyester adhesives.

  The carbon nanotube according to the third invention can be generated by setting the flow rate of the supplied source gas on the surface of the catalyst carrier to 2 mm / sec or more in the process of producing the carbon nanotube on the catalyst carrier. By adjusting the generation conditions to the flow rate in the above range, it is useful for efficiently generating carbon nanotubes having a long length in the direction perpendicular to the outer diameter, particularly 200 μm or more.

  The electrode catalyst metal, particularly platinum, is preferably supported on the carbon nanotubes by a wet method or a dry method. Details of the wet method and the dry method will be described later.

Furthermore between the electrode catalyst loading step and the transfer step, applying step is Ru provided electrocatalyst metal further imparts proton conductive material into carbon nanotubes supported. In this case, a proton conductive material is provided in advance on the surface of the carbon nanotube after supporting the catalyst before the transfer step, and the carbon nanotube provided with the proton conductive material is transferred in the subsequent transfer step. Further, in the application step to grant water repellent material on the further proton conductive material after providing a proton conductive material. In this case, before the transfer step, a proton conductive material and a water repellent material are provided in advance from the surface side on the surface of the carbon nanotube after supporting the catalyst, and in the subsequent transfer step, the proton conductive material and the water repellent material are provided. The carbon nanotube in a state where the chemical material is provided is transferred.

  In addition, in the application step, a proton conductive material precursor is applied to the carbon nanotubes, and after application, in a state of being applied to the carbon nanotubes (on-site), for example, before applying a water repellent material, radiation or the like is applied in advance. It can also be used for polymerization (on-site polymerization) to give a proton conductive substance. As the proton conductive material precursor, for example, a styrene sulfonic acid monomer or the like can be used, and an initiator that accelerates the polymerization reaction by emitting radicals or acids together with the proton conductive material precursor may be used in combination. .

  In the membrane / electrode assembly according to the third invention as well, the perfluorosulfonic acid compound is suitable for the proton conductive material, and the fluororesin is used for the water repellent material, as in the first invention. (More preferably, polytetrafluoroethylene and / or polyvinylidene fluoride) is suitable, and both of these proton conductive materials and water repellent materials can be provided by an impregnation method. The impregnation method is carried out by impregnating carbon nanotubes, which are to be imparted, in a liquid proton conductive material or water repellent material and drying it.

  In the third invention, it is further possible to provide a covering step of covering at least a part of the carbon nanotubes that are aligned and bonded to the polymer electrolyte membrane in the transfer step with an oxygen-rich heat insulating member in a low temperature environment. This is useful in that the startability can be improved and the oxygen enrichment when the heat insulating member is provided can be more effectively improved.

  According to the present invention, it is possible to effectively use a supported expensive noble metal catalyst for an electrode reaction, there is no decrease in film durability due to application of high surface pressure by tightening, and good without applying high surface pressure A membrane electrode assembly capable of exhibiting excellent power generation performance, a manufacturing method thereof, and a fuel cell including the membrane electrode assembly can be provided. It is also possible to configure without using a diffusion layer.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of a membrane electrode assembly and a fuel cell of the present invention will be described in detail with reference to the drawings, and embodiments of a method for producing a 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) using hydrogen gas and air (oxygen) as fuel used for power generation operation. However, the present invention is not limited to the following embodiment.

(First embodiment)
A membrane electrode assembly and a fuel cell according to a first embodiment of the present invention will be described with reference to FIGS. In the present embodiment, platinum (Pt; electrocatalyst metal) is supported on the outer wall of a tube of linear carbon nanotubes (hereinafter also referred to as CNT) that is bonded and oriented to a fluorine ion exchange resin (polymer electrolyte) membrane. A carbon-based conductive bond is formed on the non-bonding side of the CNT end, and the front end surface of the convex portion protruding in a convex shape other than the gas flow path of the separator having a concave gas flow path for supplying and discharging the source gas (hydrogen gas, air). It is composed by bonding with an agent.

  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. Pass through, that is, supply and discharge hydrogen gas flow path 23 and a pair of separators 21 forming air flow path 24 through which air (air) passes, that is, supply and discharge, to the oxidant electrode (cathode electrode) 13 side. , 22. 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 reactions on the anode side and cathode side, respectively, and equation (3) represents the total reaction in 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 film 11 and an anode electrode 12 and a cathode electrode 13 that sandwich the fluorine-based ion exchange resin membrane 11 (these may be collectively referred to as “CNT electrodes”). It has a laminated structure. Hereinafter, a description will be given 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 joined and oriented at one end substantially perpendicular to the film surface of the fluorine-based ion exchange resin film 11. The other end of the separator is joined to the front end surface of the convex portion of the separator 22. The carbon nanotubes 31 are oriented only in the region of the fluorine-based ion exchange resin film 11 that faces the convex portions of the separator 22, and the separator 22, the fluorine-based ion exchange resin film 11, and the carbon nanotubes 31 are joined by the convex portions. The electrical conductivity is ensured. The same applies to the anode side.

  Each of the carbon nanotubes 31 carries platinum (Pt) 32 having a particle diameter of 3 nm as an electrocatalyst 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. Further, Pt 32 has a structure that is supported from one end of the carbon nanotube 31, that is, the end of the bonding side with the film surface of the fluorine-based ion exchange resin film 11. The contact resistance from Pt32, which is a power generation site, to the separator 22 can be effectively suppressed without applying surface pressure by tightening using the like.

  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. 1, it is desirable that the carbon nanotube 31 has a length of 200 μm or more when no diffusion layer is provided between the separator 21 and the anode electrode 12 and between the separator 22 and the cathode electrode 13. . This is the length of the carbon nanotube in the longitudinal direction, that is, the length of the cylinder, and if the length is less than 200 μm, the supply and diffusion of the fuel gas component may be reduced to lower the power generation efficiency.

The carbon nanotube 31 uses an arc discharge method, a laser vapor deposition method, a catalyst metal for generating a carbon nanotube (hereinafter referred to as a “CNT generation catalyst metal”), and a hydrocarbon gas or a hydrogen gas is supplied thereto. CVD method to synthesize, HiPco method to synthesize carbon monoxide by 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 (for example, 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 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 are 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.

  In addition, Pt (electrocatalyst metal) can be supported on the surface of the carbon nanotube 31 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 of which will be described later.

  As shown in FIG. 2, a Nafion solution (Aldrich Chemical Co .; proton conductive material) is further applied to the outer wall surface of the carbon nanotube 31 on which Pt 32 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) other than the Nafion solution can be used. In addition, the thickness of the Nafion layer (proton conductive material) 33 is effectively within a range satisfying 10 to 70 nm other than the above thickness, and more preferably 10 to 30 nm.

  In addition, a PTFE layer 34 made of polytetrafluoroethylene (water repellent material; PTFE) is further provided on the Nafion layer 33 on the carbon nanotubes 31 to discharge generated water generated by the battery reaction. Can be secured. 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.

  The CNT electrodes (anode electrode 12 and cathode electrode 13) composed of the carbon nanotubes 31 are bonded to the separators 21 and 22 by the carbon-based conductive adhesive 35 at the front end surfaces of the respective convex portions, and after drying, Conductivity is ensured between the separator and the membrane electrode assembly, and sufficient conductivity can be obtained without applying surface pressure to the membrane electrode assembly by tightening with bolts or the like as in the prior art. ing.

  The concave portions other than the convex portions of the separators 21 and 22 form flow paths 23 and 24 between the separators 21 and 22 and the fluorine-based ion exchange resin film 11. 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, recesses (ribs) are formed on both sides of one separator, the hydrogen gas flow path 23 in the anode electrode is formed on one side, and the air flow in the cathode electrode of the adjacent membrane electrode assembly is formed on the other side. A path is formed.

Next, a manufacturing method of the membrane electrode assembly 20 shown in FIGS.
The membrane electrode assembly 20 includes an electrode catalyst supporting step of supporting Pt (electrode catalyst metal) on a carbon nanotube 31 generated on a catalyst supporting body on which a CNT generating catalyst is supported on a substrate, and a carbon nanotube 31 supporting Pt. Is transferred to the fluorine-based ion exchange resin membrane 11 (polymer electrolyte membrane), and a transfer step is performed in which one end of the carbon nanotube 31 is joined to the fluorine-based ion exchange resin membrane 11 and oriented.

  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 surface of the carbon nanotube 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 surface of 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, the electrode catalyst supporting step can be appropriately provided with other steps such as the above-described carbon nanotube producing step, a catalyst supporting step, a substrate cleaning step, and a post-treatment step. 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.

  The catalyst carrier is peeled off and transferred, so that the alignment state at the time of generation is substantially maintained, and the carbon nanotubes 31 are aligned on the fluorine-based ion exchange resin film 11. 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.

  After the transfer process is performed as described above, an adhesion process is provided, and the other end of the carbon nanotube 31 joined to the fluorine-based ion exchange resin film 11 at one end is connected to the separator 21 facing the fluorine-based ion exchange resin film 11, The protruding front end surface of the protruding portion 22 is bonded and bonded using a carbon-based conductive adhesive 35.

  The carbon-based conductive adhesive 35 can be provided by preparing a coating solution and then applying it using a known coating method such as a doctor blade method or a bar coating method.

  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.

  In addition, when the application step is provided, the Nafion layer 33 is formed as described above, and a polytetrafluoroethylene (PTFE; water repellent material) solution is applied onto the Nafion layer 33 thus formed to form the PTFE layer 34. 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.

(Second Embodiment)
A membrane electrode assembly and a fuel cell according to a second embodiment of the present invention will be described with reference to FIGS. In this embodiment, a diffusion layer is further provided between the fluorine-based ion exchange resin film 11 and the separator in the membrane electrode assembly of the first embodiment, and the CNT electrode (anode electrode and cathode electrode) is connected to the CNT catalyst layer and the diffusion layer. It is made up of and. In addition, the fuel used in 1st Embodiment can be used for the fuel for electric power generation, and the same referential mark is attached | subjected to the component similar to 1st Embodiment, and the detailed description is abbreviate | omitted.

  In the present embodiment, as shown in FIG. 3, the fuel cell (single cell) 40 includes the membrane electrode assembly 50 and the membrane electrode assembly 50 sandwiched from both sides, and the hydrogen gas passage 23 and the air passage 24. Are formed of a pair of separators 21 and 22. Further, the single cell shown in FIG. 3 can also be made into a stack structure by stacking a plurality of layers with a separator interposed therebetween.

  The membrane electrode assembly 50 has a laminated structure including a fluorine ion exchange resin film 11 and an anode diffusion electrode 46 and a cathode diffusion electrode 47 provided so as to narrow the fluorine ion exchange resin film 11. Each of the anode diffusion electrode 46 and the cathode diffusion electrode 47 is composed of CNT catalyst layers 42 and 43 responsible for battery reaction (electrochemical reaction) and diffusion layers 44 and 45 functioning as current collectors.

  As described in detail in the first embodiment, the CNT catalyst layers 42 and 43 are formed by similarly transferring and aligning the carbon nanotubes 31 on the fluorine-based ion exchange resin film 11 using the transfer method. It is a thing. Hereinafter, a description will be given with reference to FIG. FIG. 4 is an enlarged schematic view showing the cathode electrode side of the membrane electrode assembly 50.

  As shown in FIG. 4, linear carbon nanotubes 31 are joined and oriented at one end substantially perpendicular to the film surface of the fluorine-based ion exchange resin film 11 to form a CNT catalyst layer 43. The end is bonded to one surface of the diffusion layer 45. The same applies to the anode side.

  In this embodiment, since the diffusion layer is provided between the CNT catalyst layer and the separator, current can be collected regardless of the presence or absence of the separator flow path (recess), and the configuration is easy and simple. be able to.

  Furthermore, the other surfaces of the diffusion layers 44 and 45 are joined to the front end surfaces of the convex portions of the separators 22 and 23, and the carbon nanotubes 31 are connected to the separators of the fluorine-based ion exchange resin film 11 as shown in FIGS. Oriented over the entire opposing surface. Both diffusion layers 44 and 45 are formed of carbon cloth woven with yarns made of carbon fibers. In addition to the carbon cloth, the diffusion layer is preferably formed of carbon paper or carbon felt made of carbon fiber.

(Third embodiment)
A membrane electrode assembly and a fuel cell according to a third embodiment of the present invention will be described with reference to FIGS. In this embodiment, Pt32 is supported on the inner wall of the tube on the bonding side of the linear carbon nanotubes 31 to the fluorine-based ion exchange resin film 11 in the membrane electrode assembly of the first embodiment, and each of the carbon nanotubes (CNTs) is supported. the oxygen-enriched while internally provided in CeO ₂ tube, which is constituted by adhering a CNT terminal of the non-bonding with the convex front edge surface and the carbon-based conductive adhesive that protrudes in a convex shape of the separator. In addition, the fuel used in 1st Embodiment can be used for the fuel for electric power generation, and the same referential mark is attached | subjected to the component similar to 1st Embodiment, and the detailed description is abbreviate | omitted.

  In the present embodiment, as shown in FIG. 5, linear carbon nanotubes 31 (length 500 μm, outer diameter 10 nm) are joined and oriented at one end substantially perpendicular to the film surface of the fluorine-based ion exchange resin film 11. The other end of the carbon nanotube 31 is joined to the front end surface of the convex portion of the separator 22. The carbon nanotubes 31 are oriented only in the region of the fluorine-based ion exchange resin film 11 that faces the convex portions of the separator 22, and the separator 22 and the fluorine-based ion exchange resin film 11 are interposed via the carbon nanotubes 31 joined at the convex portions. Conductivity is ensured. The same applies to the anode side.

  As shown in FIGS. 5 and 6, platinum (Pt) 32 having a particle diameter of 3 nm is supported on each inner wall surface of each carbon nanotube 31 as an electrode catalyst metal responsible for a battery reaction. By using a plurality of oriented carbon nanotubes as a carrier, it is possible to secure a large surface area and carry it at a high density, and there is no decrease in water discharge even in an environment where water is excessively generated during power generation. The gas supply to the three-phase interface and the diffusibility are maintained, and the supported Pt 32 can effectively contribute to the cell reaction, and the power generation efficiency corresponding to the supported amount can be obtained.

  The Pt 32 has a structure that is supported on one end of the carbon nanotube 31 (that is, an end portion on the bonding side with the membrane surface of the fluorine-based ion exchange resin film 11; hereinafter also referred to as a tip portion). Therefore, it is possible to effectively suppress the contact resistance from Pt32, which is the power generation site, to the separator 22 without applying surface pressure by tightening the membrane electrode assembly using bolts or the like as in the prior art. Yes.

  Also in this embodiment, the particle diameter of Pt32 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. Even when Pt is supported on the inner wall surface of the carbon nanotube 31 as in the present embodiment, it can be performed by either a wet method or a dry method, as in the first embodiment. Details are as described above.

  The Pt 32 is covered with a Nafion film 54 provided by applying a Nafion solution (Aldrich Chemical Co.), which is a proton conductive material, and is further provided over the tip of the carbon nanotube 31 and fluorine through the Nafion film 54. It is joined to the membrane surface of the system ion exchange resin membrane 11. Thereby, the proton conductivity in the battery reaction and the bonding strength with the fluorine-based ion exchange resin film 11 are ensured.

  Each tube wall of the carbon nanotube 31 is provided with a plurality of holes 51 for oxygen in the supplied air to pass therethrough (see FIG. 6) in the vicinity of the Pt 32 support. The formation ratio of the holes 51 per each carbon nanotube is desirably 50% or less. In order to form pores in the carbon nanotube, a method such as adapting with a firing temperature, a catalyst or the like is suitable. In the present embodiment in which no diffusion layer is provided, the length of the carbon nanotube 31 is desirably 200 μm or more.

As shown in FIG. 5 and FIG. 6, the carbon nanotubes 31 carrying Pt are installed inside an oxygen-enriched CeO ₂ tube 52 that is hollow inside, has a circular cross section of 500 μm, and has an inner diameter of 15 mm. The entire outer wall surface of each carbon nanotube is covered with an oxygen-enriched CeO ₂ tube 52. The oxygen-enriched CeO ₂ pipe can pass oxygen out of air components faster than nitrogen, and the air supplied to the air flow path 24 is in a state of high oxygen partial pressure (oxygen partial pressure of 20% or more). Then, air having a high oxygen concentration is supplied to the CNT electrode to obtain power generation efficiency.

In addition to oxygen-enriched CeO ₂ tubes, ceramic materials such as ZrO ₂ , CeO ₂ / ZrO ₂ , Ce _0.8 Zr _0.2 O ₂ , V ₂ O ₅ , composite materials thereof, and other J. Oxygen-enriched ceramics made by appropriately selecting ceramic materials having oxygen-enrichment properties such as ceramic materials described in power sources 115 (2003) 40-43, ceramic materials described in JP-A-2003-320607, etc. Tubes can be used. Oxygen enrichment is a characteristic that increases oxygen partial pressure by allowing oxygen to pass faster than nitrogen from one side of the air atmosphere to the other side through the ceramic material.

The inner diameter of the oxygen-enriched ceramic tube is not limited as long as the carbon nanotube can be internally provided, but the outer diameter of the carbon nanotube to be provided is +0.1 to 0.01 μm, specifically, the outer diameter is +15 to The range of 10 nm is desirable, and the length may be selected as desired. Moreover, the shape of the oxygen-enriched CeO ₂ tube can be configured to have an arbitrary shape such as a rectangle, a rectangle, or an ellipse in addition to the above-described circular shape. The oxygen-enriched CeO ₂ tube can be produced by a method such as extrusion molding or sol-gel, for example.

The carbon nanotubes do not necessarily have to be coated on the entire outer wall surface, and the oxygen-enriched CeO ₂ tube 52 can be provided so as to cover at least the supporting part of Pt32 that is a power generation site. Since the battery reaction proceeds in the carbon nanotubes constituting the electrode, particularly the Pt support portion forming the power generation site and locally generates heat, an oxygen-enriched CeO ₂ tube is provided to cover at least the heat generation site of the carbon nanotube from the outside. The heat is retained, and this thermal energy can be used to further improve the low temperature startability and the oxygen enrichment of the oxygen enriched CeO ₂ tube.

  Although not shown in the present embodiment, in the same manner as in the first embodiment, polytetraethylene is further formed on the Nafion film 54 of the carbon nanotube 31 from the viewpoint of ensuring the discharge of produced water generated by the battery reaction. A PTFE film made of fluoroethylene (water repellent material; PTFE) can also be provided.

  The CNT electrodes (anode electrode 12 and cathode electrode 13) composed of the carbon nanotubes 31 are bonded to the separators 21 and 22 by the carbon-based conductive adhesive 35 at the front end surfaces of the respective convex portions, and after drying, Conductivity is ensured between the separator and the membrane electrode assembly, and sufficient conductivity can be obtained without applying surface pressure to the membrane electrode assembly by tightening with bolts or the like as in the prior art. ing.

The membrane electrode assembly of the present embodiment includes an electrode catalyst supporting step and a transfer step similar to those of the first embodiment, and a covering step in which the carbon nanotubes 31 after the transfer are installed inside the oxygen-enriched CeO ₂ tube 52 and covered. Can be produced. The details of the electrode catalyst supporting step and the transfer step are as described above.

In the covering step, the carbon nanotubes 31 oriented on the fluorinated ion exchange resin film 11 by transfer are provided and covered through a separately prepared oxygen-enriched CeO ₂ tube 52. After the coating process is performed, an adhesion process is provided, and the other end of the carbon nanotube 31 bonded to the fluorine-based ion exchange resin film 11 at one end and the oxygen-enriched CeO ₂ tube 52 in which the carbon nanotube 31 is provided are replaced with a fluorine-based one. The protruding tip end surfaces of the separators 21 and 22 facing the ion exchange resin film 11 are bonded and fixed using a carbon-based conductive adhesive 35.

  Between the electrode catalyst supporting step and the transferring step, there is provided an applying step for forming a Nafion film 54 by applying a Nafion solution (proton conductive substance) to the carbon nanotubes 31 on which Pt 32 is supported. In this case, the carbon nanotube 31 is transferred in a state where the Pt 32 and the Nafion film 54 are provided in the subsequent transfer process. Further, when the application step is provided, the Nafion film 54 can be formed, and a polytetrafluoroethylene (PTFE; water repellent material) solution can be further applied onto the Nafion film 54 to further provide a PTFE film. In this case, the carbon nanotubes 31 are transferred in a state where the Pt 32, the Nafion film 54 and the PTFE film are provided in the subsequent transfer process.

Next, another example of the membrane electrode assembly of the present invention will be described. The membrane electrode assembly of FIG. 7 is formed by bundling a plurality of carbon nanotubes 31 bundled in a desired unit by using a single oxygen-enriched CeO ₂ tube 55 having an inner hollow shape of a circular section of 500 μm and an inner diameter of 15 nm. It is installed inside and covered. The separator 22 has a structure in which a group of carbon nanotubes bonded on the front end surface of the convex portion protruding toward the fluorine-based ion exchange resin film 11 is coated as a unit. This example can also be applied to each of the above embodiments.

  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.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

Example 1
A membrane electrode assembly and a fuel cell were prepared according to the following steps.
-Electrode catalyst loading process-
(1) Formation of carbon nanotubes Two 50 mm × 50 mm silicon substrates were placed in an electric furnace, heated to 800 ° C. at 10 ° C./min in an atmosphere with a degree of vacuum of 1.0 × 10 ⁻³ Pa, and 5 Washed by heat treatment for hours. After washing and cooling, an Fe thin film (CNT-forming catalytic metal) having a thickness of 5 nm was formed on the surface of the silicon substrate by an electron beam vapor deposition method to obtain an Fe-supporting silicon substrate.

  A quartz board having a slit structure (slit width 3 mm) is installed in a quartz reaction tube having an inner diameter of 50 mm to increase the flow rate of the source gas flowing on the surface of the substrate when the substrate is installed. The Fe-supported silicon substrate obtained above was placed on the board. By using this quartz board, the cross-sectional area becomes about 1/10 as compared with a quartz board that is usually used, so that the flow rate of the source gas can be increased about 10 times.

  Helium gas was supplied at 200 ml / min to the quartz reaction tube in which the quartz boat was installed, and the temperature was raised to 730 ° C. After the temperature in the tube reached 730 ° C., acetylene gas was further introduced into the helium gas at 30 ml / min for 10 minutes. Thereafter, the introduction of acetylene gas was stopped and the system was cooled to room temperature. In this way, linear carbon nanotubes (about 250 μm in length) that were substantially parallel to the surface normal direction (substantially perpendicular to the surface) were formed on the surface of the Fe thin film of the Fe-supporting silicon substrate.

(2) Loading of electrocatalytic metal Next, chloroplatinic acid was dissolved in ethanol so as to have a ratio of 50 mg / ml to prepare an ethanol solution of chloroplatinic acid (Pt / EtOH solution). Subsequently, two Fe-supported silicon substrates are placed so that the surface on which the carbon nanotubes are generated faces upward (antigravity direction), and the above Pt / EtOH solution is pipetted from above the carbon nanotubes with a pipette. The solution was evenly dropped so as to be 7 μl / cm ² . After dripping, it was placed in an argon gas at 300 ° C. and heat-treated for 2 hours. In this way, two electrode precursors having platinum supported on the surface of the carbon nanotubes were obtained.

-Granting process-
Each of the electrode precursors obtained as described above was impregnated in Nafion solution (EW1100 (0.1% ethanol solution), Aldrich Chemical Co .; proton conductive material), taken out, and vacuum dried at 140 ° C. . Subsequently, each of the dried electrode precursors was further immersed in a 0.1% N-methyl-2-pyrrolidone solution (water repellent material) of polyvinylidene fluoride (PVDF) and taken out at 100 ° C. Dry and water repellent treatment.

-Transfer process-
Next, a 100 mm × 100 mm Nafion membrane (thickness 25 μm; polymer electrolyte membrane) is prepared, and this Nafion membrane is sandwiched between the two Fe-supported silicon substrates so that the carbon nanotube production surface is in contact with the Nafion membrane. A sandwich structure was obtained. This sandwich structure was placed on a hot plate, heated to 120 ° C. while being pressurized at 1 MPa, held in that state for 1 minute, then cooled to room temperature and released from the pressure.

  Next, the silicon substrate is mechanically peeled from the sandwich structure, so that the Nafion-treated and water-repellent treated Pt-supported carbon nanotubes (platinum CNT electrode; length of about 250 μm) are formed on both surfaces of the Nafion film. Was transcribed. The carbon nanotubes had a linear shape, and were bonded to the Nafion film by being oriented substantially parallel to the surface normal direction (substantially perpendicular to the surface). As described above, a membrane electrode assembly (MEA) having a structure of platinum CNT electrode / Nafion membrane / platinum CNT electrode was obtained.

-Adhesion process-(Fabrication of fuel cell)
Two separators having a channel formed in a concave shape each having a groove width and a groove depth of 1 mm are prepared, and a JEF120 ( Nippon Acheson Co., Ltd. (carbon conductive adhesive) was applied to a thickness of 10 μm. Then, the MEA obtained as described above is combined before drying the conductive adhesive so that the surface of the platinum CNT electrode and the tip of the convex portion coated with the conductive adhesive are in contact with each other. To produce a fuel cell having a separator / MEA / separator.

(Example 2)
A membrane electrode assembly (MEA) was obtained in the same manner as in Example 1 except that the water-repellent treatment was not performed after impregnation in the Nafion solution in the “-application step” of Example 1, and a fuel cell A cell was produced.

Example 3
In Example 1, the operation of “-adhesion step” was changed as follows, and a fuel cell was prepared in the same manner as in Example 1 except that a diffusion layer was provided between the platinum CNT electrode and the separator. Produced.
-Adhesion process-
Two sheets of carbon paper for providing a diffusion layer were prepared, and carbon paper was sandwiched and provided on both surfaces of the platinum CNT electrode of MEA obtained as described above. Subsequently, two separators having a channel formed in a concave shape each having a groove width and a groove depth of 1 mm are prepared, and the surface of the convex part protruding in a convex shape other than each channel is formed by a doctor blade method. JEF120 (Nippon Acheson Co., Ltd .; carbon-based conductive adhesive) was applied to a thickness of 10 μm. Then, the carbon paper surface and the convex surface coated with the conductive adhesive are bonded in combination before drying so that the conductive adhesive is dried, and separator / diffusion layer / MEA / diffusion layer / A fuel battery cell configured as a separator was produced.

Example 4
In Example 2, the operation of “-adhesion step” was changed as follows, and a fuel cell was prepared in the same manner as in Example 1 except that a diffusion layer was provided between the platinum CNT electrode and the separator. Produced.
-Adhesion process-
Two sheets of carbon paper for providing a diffusion layer were prepared, and carbon paper was sandwiched and provided on both surfaces of the platinum CNT electrode of MEA obtained as described above. Subsequently, two separators having a channel formed in a concave shape each having a groove width and a groove depth of 1 mm are prepared, and the surface of the convex part protruding in a convex shape other than each channel is formed by a doctor blade method. JEF120 (Nippon Acheson Co., Ltd .; carbon-based conductive adhesive) was applied to a thickness of 10 μm. Then, the carbon paper surface and the convex surface coated with the conductive adhesive are bonded in combination before drying so that the conductive adhesive is dried, and separator / diffusion layer / MEA / diffusion layer / A fuel battery cell configured as a separator was produced.

(Example 5)
Implementation was performed except that the quartz board having the slit structure used in “(1) Production of carbon nanotubes” was replaced with a quartz board having no slit structure in “-Electrode catalyst supporting step” of Example 1. In the same manner as in Example 1, a membrane electrode assembly (MEA) was obtained, and a fuel cell was produced.

(Example 6)
In the “-electrode catalyst supporting step” of Example 2, the quartz board having the slit structure used in “(1) Production of carbon nanotube” was replaced with a quartz board having no slit structure. In the same manner as in Example 1, a membrane electrode assembly (MEA) was obtained, and a fuel cell was produced.

(Example 7)
In the “-applying step” of Example 1, before the water-repellent treatment, the solution of the styrene sulfonic acid monomer (proton conductive material precursor) is impregnated and taken out, and then the ultraviolet rays are used until the polymerization reaction is completed. A membrane electrode assembly (MEA) is obtained in the same manner as in Example 1 except that polystyrene sulfonic acid (proton conductive material) is provided by irradiation and on-site polymerization, followed by water repellency treatment. A fuel cell was produced.

(Evaluation 1)
Using the fuel cells produced in Examples 1 to 7, the cell set temperature was 80 ° C., the hydrogen gas supply amount was 300 ml / mim, and the air supply amount was 1000 ml / min, and the current density during power generation operation was 2 A / cm ^2. The cell voltage at the time of output and the voltage in the output standby state (OCV) where output is possible were measured by changing the tightening pressure. The measurement results are shown in Table 1 below.

  As shown in Table 1 above, in any fuel cell, good power generation performance could be obtained without applying surface pressure due to excessive tightening. In particular, the fuel cells of Examples 1 and 2 in which no diffusion layer was provided had excellent power generation performance that did not depend on the tightening pressure. In addition, in the fuel cells of Examples 3 to 4 in which the diffusion layer is provided as compared with Examples 1 and 2, it was found that the power generation performance gradually decreases at a low tightening pressure. Moreover, in Examples 5-6 with the short carbon nanotube length, although the fluctuation | variation of the power generation performance by clamping pressure was not recognized, as a result of being inferior to gas diffusivity, the power generation performance also fell a little. Furthermore, better power generation performance was obtained in Example 7 in which carbon nanotubes were subjected to on-site polymerization.

(Example 8)
In Example 1, the following coating process was provided between the transfer process and the bonding process, and the covered platinum CNT electrode / Nafion was coated with the entire platinum CNT electrode in an oxygen-enriched CeO ₂ tube. A fuel cell constituted of a separator / MEA / separator was produced in the same manner as in Example 1 except that a membrane / electrode assembly (MEA) having a membrane / coated platinum CNT electrode structure was obtained.

-Coating process-
First, CeO ₂ powder and epoxy, phenol or the like were mixed to form a paste, which was extruded and fired at 1200 ° C. to produce an oxygen-enriched CeO ₂ tube having a length of about 250 μm and an inner diameter of about 50 nm. If a sintering aid such as yttria or silica is added, the pores are filled, so no sintering aid is added. Then, the transferred Pt-supported carbon nanotube (platinum CNT electrode; length of about 250 μm) is coated through the inside of the obtained oxygen-enriched CeO ₂ tube, and the structure of coated platinum CNT electrode / Nafion film / coated platinum CNT electrode A membrane electrode assembly (MEA) was obtained. After that, it shifted to the bonding process.

(Evaluation 2)
Using the fuel cell produced in Example 8 (with oxygen-enriched CeO ₂ tube) and the fuel cell produced in Example 1 (without oxygen-enriched CeO ₂ tube), the cell set temperature was 80 ° C., hydrogen The operation was performed with a gas supply amount of 300 ml / mim and an air supply amount of 1000 ml / min, and a voltage (V) -current density (A) curve during power generation operation was created. FIG. 8 shows a VA curve.

As shown in FIG. 8, the fuel cell of Example 8 was constructed by coating a carbon nanotube forming the electrode with oxygen-enriched CeO ₂ tubes, fuel of Example 1 were not coated with oxygen-enriched CeO ₂ tube Compared to battery cells, it showed better power generation characteristics in a wide current density region.

It is a schematic sectional drawing which shows the fuel battery cell which concerns on 1st Embodiment of this invention. It is a schematic sectional drawing which expands and shows the membrane electrode assembly which concerns on 1st Embodiment of this invention. It is a schematic sectional drawing which shows the fuel cell concerning 2nd Embodiment of this invention. It is a schematic sectional drawing which expands and shows the membrane electrode assembly which concerns on 2nd Embodiment of this invention. It is a schematic sectional drawing which expands and shows the membrane electrode assembly which concerns on 3rd Embodiment of this invention. It is a perspective view which expands and shows a part of cathode electrode of the membrane electrode assembly which concerns on 3rd Embodiment of this invention. It is a schematic sectional drawing which expands and shows the other example of the membrane electrode assembly of this invention. It is a voltage-current density curve which shows the effect of the presence or absence of an oxygen-enriched CeO ₂ tube. It is a schematic sectional drawing for demonstrating the structure of the conventional fuel cell.

Explanation of symbols

10, 40 ... Fuel cell (single cell)
11 ... Fluorine ion exchange resin membrane (polymer electrolyte membrane)
20, 50 ... Membrane electrode assembly 21, 22 ... Separator 31 ... Carbon nanotube 32 ... Platinum (electrode catalyst metal)
33 ... Nafion layer (proton conductive material)
34 ... PTFE layer (water repellent material)
35 ... carbon conductive adhesive 42, 43 ... CNT catalyst layers 44 and 45 ... diffusion layer 52, 55 ... oxygen enrichment CeO ₂ tube (heat insulating member)

Claims (25)

A polymer electrolyte membrane;
Oriented substantially perpendicular to at least the film surface of the polymer electrolyte membrane has a proton conductive material on the surface, Rutotomoni to have a more water-repellent material on the said proton conductive material, an electrode catalyst metal supported Carbon nanotubes ,
A membrane electrode assembly comprising:   The carbon nanotube is provided in a region of the polymer electrolyte membrane facing a convex end surface projecting toward the carbon nanotube side of the separator when a separator forming a fuel flow path is provided to face the carbon nanotube. Item 2. The membrane electrode assembly according to Item 1.   The membrane electrode assembly according to claim 1 or 2, wherein the carbon nanotube has a length of 200 µm or more.   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 less than an outer diameter of the carbon nanotube. The proton conducting membrane electrode assembly according to any one of claims 1 to 5 material is a perfluorosulfonic acid-based compounds. The membrane electrode assembly according to any one of claims 1 to 6 the thickness of the proton conductive material is 1 to 70 nm. Membrane electrode assembly according to any one of claims 1 to claim 7 wherein the water repellent material is a fluorine-based resin. The membrane electrode assembly according to claim 8 , wherein the fluororesin contains at least one of polytetrafluoroethylene and polyvinylidene fluoride. The membrane electrode assembly according to any one of claims 1 to 9 , further comprising an oxygen-enriching heat insulating member that covers at least a part of the carbon nanotubes. The membrane electrode assembly according to claim 10 , wherein the heat insulating member is made of an oxygen-enriched ceramic material. The membrane electrode assembly according to claim 10 or 11 , wherein the heat insulating member has a cylindrical shape, and at least one of the carbon nanotubes is provided inside the cylinder. A fuel cell comprising the membrane electrode assembly according to any one of claims 1 to 12 . A region of the polymer electrolyte membrane facing the polymer electrolyte membrane, a separator having a recess on the polymer electrolyte membrane side to form a fuel flow path, and a convex tip end surface protruding to the polymer electrolyte membrane side of the separator The fuel cell according to claim 13 , further comprising a carbon nanotube which is provided on the electrode and carries an electrode catalyst metal. An electrode catalyst supporting step of supporting an electrocatalyst metal on the carbon nanotubes produced on the catalyst support;
An imparting step of imparting a proton conductive material to the carbon nanotubes on which the electrode catalyst metal is supported, and further imparting a water repellent material on the proton conductive material;
The carbon nanotubes supported with an electrode catalyst metal and provided with a proton conductive material and a water repellent material are transferred to a polymer electrolyte membrane, and one end of the carbon nanotube is bonded to the polymer electrolyte membrane, A transfer step of orienting substantially perpendicularly to the membrane surface of the polymer electrolyte membrane;
The manufacturing method of the membrane electrode assembly which has this. After the transfer step, a separator that forms a fuel flow path is provided on the side of the polymer electrolyte membrane on which the carbon nanotubes are oriented, and the other end of the carbon nanotube that is joined to the polymer electrolyte membrane at one end and the separator The method for producing a membrane / electrode assembly according to claim 15 , further comprising an adhesion step of adhering the leading end surface of the convex portion with a conductive adhesive. The method for producing a membrane / electrode assembly according to claim 16 , wherein the conductive adhesive is a carbon-based conductive adhesive. The method for producing a membrane electrode assembly according to any one of claims 15 to 17 , wherein the carbon nanotubes are generated at a flow rate of the source gas on the surface of the catalyst carrier of 2 mm / sec or more. The method for producing a membrane electrode assembly according to any one of claims 15 to 18 , wherein the electrode catalyst metal is supported on carbon nanotubes by either a wet method or a dry method. The method for producing a membrane electrode assembly according to any one of claims 15 to 19, wherein the proton conductive substance is a perfluorosulfonic acid compound. The method for producing a membrane / electrode assembly according to any one of claims 15 to 20, wherein the water repellent material is a fluororesin. The method for producing a membrane / electrode assembly according to claim 21 , wherein the fluororesin contains at least one of polytetrafluoroethylene and polyvinylidene fluoride. The method for producing a membrane / electrode assembly according to any one of claims 15 to 22 , wherein the applying step is performed by an impregnation method. The applying step, a proton conductive material precursor imparted to the carbon nanotubes, granted after the proton conductive material according to claim precursor is polymerized by proton conductive material is to be applied 15 to claim 23 The manufacturing method of the membrane electrode assembly of any one of these. The coating process according to any one of claims 15 to 24 , further comprising a covering step of covering at least a part of the carbon nanotubes aligned and bonded to the polymer electrolyte membrane in the transfer step with an oxygen-rich heat insulating member. The manufacturing method of the membrane electrode assembly.

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