JP2006252967A - Solid polymer electrolyte membrane for fuel cell, and fuel cell using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid polymer electrolyte membrane with mechanical strength improved without loss of proton conductivity. <P>SOLUTION: The above-mentioned problem is solved by providing a solid polymer electrolyte membrane 100 for a fuel cell wherein a reinforcing material 101 containing conductive nanofiber is provided on at least one of the surfaces of the solid polymer electrolyte membrane 100. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a solid polymer electrolyte membrane for a fuel cell, and more particularly to a solid polymer electrolyte membrane for a fuel cell having excellent mechanical strength.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. Fuel cells include polymer electrolyte fuel cells (PEFC), phosphoric acid fuel cells (PAFC), alkaline fuel cells (AFC), solid oxide fuel cells (SOFC), and molten carbonate fuel cells (MCFC). )and so on. Among them, the polymer electrolyte fuel cell is expected as a power source for electric vehicles because it operates at a relatively low temperature and obtains a high output density.

  The polymer electrolyte fuel cell generally has a structure in which a membrane-electrode assembly (hereinafter also simply referred to as “MEA”) is sandwiched between separators. The MEA is formed by sandwiching a solid polymer electrolyte membrane between a pair of electrode catalyst layers and a gas diffusion layer.

  The electrode catalyst layer is a porous layer formed by a mixture of a solid polymer electrolyte and an electrode catalyst in which catalyst particles are supported on a conductive carrier. In addition, a gas diffusion layer is used in which a carbon water repellent layer composed of carbon particles, a water repellent and the like is formed on the surface of a gas diffusion base material such as carbon cloth.

  In the polymer electrolyte fuel cell, the following electrochemical reaction proceeds. First, hydrogen contained in the fuel gas supplied to the fuel electrode (anode) side electrode catalyst layer is oxidized by the electrode catalyst into protons and electrons. Next, the generated protons pass through the solid polymer electrolyte contained in the fuel electrode side electrode catalyst layer and the solid polymer electrolyte membrane in contact with the fuel electrode side electrode catalyst layer, and then the air electrode (cathode) side electrode catalyst. Reach the layer. Further, the electrons generated in the fuel electrode side electrode catalyst layer are in contact with the conductive carrier constituting the fuel electrode side electrode catalyst layer, and further on the side different from the solid polymer electrolyte membrane of the fuel electrode side electrode catalyst layer. The air electrode side electrode catalyst layer is reached through the gas diffusion layer, the separator and the external circuit. The protons and electrons that have reached the air electrode side electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the cathode side by the electrode catalyst to generate water. In the fuel cell, electricity can be taken out through the above-described electrochemical reaction.

  A solid polymer electrolyte membrane used for a polymer electrolyte fuel cell is required to have high proton conductivity and a function as a separator sandwiched between electrodes. In addition, conventional solid polymer electrolyte membranes have been attempted from the viewpoint of reducing the internal resistance of the battery and increasing the output, thereby reducing the thickness and increasing the sulfonic acid group concentration.

  However, a significant increase in the sulfonic acid group concentration causes problems such as lowering the durability of the solid polymer electrolyte membrane. On the other hand, the reduction in thickness lowers the mechanical strength of the solid polymer electrolyte membrane itself, which causes a problem that pinholes or the like are likely to occur during the production of the solid polymer electrolyte membrane or during long-term operation. The generation of pinholes causes not only a decrease in proton conductivity but also a gas leak to the counter electrode of fuel gas and oxidant gas, leading to a decrease in battery output.

Therefore, Patent Document 1 includes a laminate of two or more cation exchange layers made of a perfluorocarbon polymer having a sulfonic acid group, and one or more layers of the cation exchange layer are made of a fibrillar fluorocarbon polymer. There is disclosed a solid polymer electrolyte membrane that is reinforced with a reinforcing material and in which one or more of the cation exchange layers are not substantially reinforced with a reinforcing material. According to Patent Document 1, it is possible to improve the mechanical strength of the solid polymer electrolyte membrane by using a porous body or fibril made of PTFE or the like as a reinforcing material.
JP 2002-25583 A

  However, although the solid polymer electrolyte membrane described in Patent Document 1 has improved mechanical strength, there is a fear that sufficient proton conductivity cannot be obtained. This is an insulator, such as PEFE that does not have proton conductivity, as a reinforcing material for the solid polymer electrolyte membrane, and such a reinforcing material is disposed in the solid polymer electrolyte membrane. This is considered to be the cause.

  In the practical use of solid polymer fuel cells, it is desired to maintain high power generation performance over a long period of time. Therefore, the solid polymer electrolyte membrane needs to be excellent not only in mechanical strength but also in proton conductivity.

  Therefore, an object of the present invention is to provide a solid polymer electrolyte membrane having improved mechanical strength while ensuring proton conductivity.

  As a result of various studies on the durability of the solid polymer electrolyte membrane, the present inventor used conductive nanofibers as a reinforcing material and arranged the conductive nanofibers outside the solid polymer electrolyte membrane. I found that the problem could be solved.

  That is, the present invention provides a solid polymer electrolyte membrane for a fuel cell, wherein the solid polymer electrolyte membrane for a fuel cell is provided with a reinforcing material containing conductive nanofibers on at least one surface of the solid polymer electrolyte membrane for a fuel cell. It is a molecular electrolyte membrane.

  In the present invention, conductive nanofibers are used as a reinforcing material, and the reinforcing material is disposed outside the solid polymer electrolyte membrane to reinforce the solid polymer electrolyte membrane without reducing proton conductivity. And mechanical strength can be improved.

  A first aspect of the present invention is a solid polymer electrolyte membrane for a fuel cell, wherein a solid material for a fuel cell in which a reinforcing material containing conductive nanofibers is disposed on at least one surface of the solid polymer electrolyte membrane for a fuel cell. It is a polymer electrolyte membrane (hereinafter also simply referred to as “solid polymer electrolyte membrane”).

  First, the cross-sectional schematic diagram of the solid polymer electrolyte membrane of this invention is shown in FIG. As shown in FIG. 1, the solid polymer electrolyte membrane 100 of the present invention has a reinforcing material 101 containing conductive nanofibers on at least one surface of the solid polymer electrolyte membrane 100, not in the solid polymer electrolyte membrane 100. Be placed. As described above, the reinforcing material including the conductive nanofibers is disposed outside the solid polymer electrolyte membrane, so that the mechanical strength can be improved while ensuring the proton conductivity of the solid polymer electrolyte membrane. It becomes.

  In the present invention, as the conductive nanofiber used for the reinforcing material, a fiber having a diameter of 1000 nm or less and a nanometer-sized diameter is used. Thus, when MEA etc. are assembled because electroconductive nanofiber has a nanometer size diameter, the contact property of a solid polymer electrolyte membrane and an electrode catalyst layer is high, and a proton conduction path | route can be ensured. The diameter of the conductive nanofiber may be appropriately determined so that the desired strength of the solid polymer electrolyte membrane can be obtained, and more preferably 500 nm or less.

  Moreover, in order to reduce electric resistance and improve power generation performance when an MEA or the like is assembled using the solid polymer electrolyte membrane, the conductive nanofibers preferably have conductivity. Specifically, an electrical resistance of the conductive nanofiber is preferably 10 mΩ · cm or less, more preferably 2 mΩ · cm or less.

  Specifically, the conductive nanofibers are preferably carbon nanofibers because high conductivity is obtained. Preferred examples of the carbon nanofiber include carbon nanofiber, carbon nanotube, carbon nanohorn, carbon nanocoil, and carbon silk.

  The carbon nanofiber is made of a fibrous carbon material having a predetermined diameter as described above. The carbon nanotube is made of a tubular carbon material having the above-mentioned predetermined diameter and having a cavity at the center of the fiber. Although the carbon nanotube is not particularly limited, it has a structure in which graphite is rolled into a cylindrical shape, and the cylinder is a single-walled carbon nanotube (SWNTs) having a single layer, and the multi-walled carbon nanotube in which the cylinder is multi-layered concentrically. (MWNT). The carbon nanohorn is made of single-layer graphite, and is made of an aggregate of conical structures having the predetermined diameter described above.

  Among the carbon nanofibers listed above, carbon nanotubes, carbon nanohorns, carbon nanocoils, carbon silk, and the like are preferably used because they are made of a carbon material having a high degree of graphitization and are excellent in corrosion resistance.

  Further, among the carbon nanofibers listed above, it is particularly preferable to use tube-like ones such as carbon nanotubes and carbon nanohorns. These tubular carbon nanofibers can occlude hydrogen. Since hydrogen has reducibility, platinum ions and the like can be reduced and deposited. Further, during operation of the fuel cell, hydrogen gas is supplied as the fuel gas. Therefore, if tube-like carbon nanofibers are used as a reinforcing material for the solid polymer electrolyte membrane, the supplied hydrogen gas can be occluded in the carbon nanofibers, and thus platinum ions eluted from the electrode catalyst layer and the like. The catalyst particle component can be captured and reduced and deposited as fine particle catalyst particles on the surface of the carbon nanofiber. Furthermore, by disposing the tubular carbon nanofibers on the air electrode side surface of the solid polymer electrolyte membrane, before the hydrogen gas crossed over from the fuel electrode side electrode catalyst layer enters the air electrode side electrode catalyst layer. In addition to the function of reducing and precipitating catalyst particle components such as platinum ions, it is possible to occlude the carbon nanofibers, and the solid polymer electrolyte membrane has a function of suppressing deterioration of the solid polymer due to crossover gas. It becomes possible to do.

  When a tube-shaped material such as carbon nanotube is used as the conductive nanofiber, it is preferable to use a conductive nanofiber having an inner diameter of 500 nm or less, particularly 100 to 300 nm.

  If the length of the conductive nanofibers is too short, the solid polymer electrolyte membrane may be damaged by piercing the solid polymer electrolyte membrane or the like. Therefore, the length of the conductive nanofibers is 10 μm or more, preferably 50 μm. More preferably, the thickness is 100 μm or more.

  The said reinforcing material used for the solid polymer electrolyte membrane of this invention contains the electroconductive nanofiber mentioned above. The length of the reinforcing material may be appropriately determined in consideration of the size and mechanical strength of the solid polymer electrolyte membrane to be used, but is desirably 100 μm or more, preferably 1 cm or more.

  If the desired length is obtained, the reinforcing material may be composed of a single conductive nanofiber, or may be composed of an aggregate of a plurality of conductive nanofibers. For example, an aggregate formed by intertwining conductive nanofibers can be used as the reinforcing material. By using conductive nanofibers as an aggregate, even conductive nanofibers having a short length can be adjusted to have a desired length as a whole by entanglement or the like and used as a reinforcing material. Moreover, it can also be set as the reinforcing material which has various characteristics by making the electroconductive nanofiber which has a different characteristic into an aggregate.

  The reinforcing material may be disposed on at least one side of the solid polymer electrolyte membrane of the present invention. Specifically, it is desirable that the reinforcing material is disposed on a surface of the solid polymer electrolyte membrane that can come into contact with the electrode catalyst layer when the MEA or the like is assembled. In addition, when the reinforcing material is provided with a Pt capturing function, an effect of suppressing Pt elution into the solid polymer electrolyte membrane can be obtained. Therefore, the surface of the solid polymer electrolyte membrane that can be in contact with the air electrode side electrode catalyst layer Preferably, the reinforcing material is disposed on both sides of the solid polymer electrolyte membrane that can come into contact with the electrode catalyst layer in order to obtain higher mechanical strength.

  Furthermore, it is desirable that the reinforcing material is regularly arranged on at least one surface of the solid polymer electrolyte membrane. “Regularly arranged” means that the reinforcing material is arranged at regular intervals over the entire surface of the solid polymer electrolyte membrane on which the reinforcing material is arranged with a certain regularity. As a result, the amount of the reinforcing material containing conductive nanofibers can be reduced, and the mechanical strength of the solid polymer electrolyte membrane can be efficiently improved.

  Specifically, the reinforcing members 101 are arranged at equal intervals and in parallel as shown in FIG. 2, the reinforcing members 101 are arranged in a lattice shape as shown in FIG. 3, or the reinforcing members 101 as shown in FIG. It is desirable that the reinforcing material is regularly arranged on at least one surface of the solid polymer electrolyte membrane 100 by, for example, arranging them vertically in a grid arrangement.

  Moreover, when arrange | positioning a reinforcing material on both surfaces of a solid polymer electrolyte membrane, the reinforcement | strengthening material may be arrange | positioned in a different pattern in each surface, and the improvement of the opportunity strength of a solid polymer electrolyte membrane may be aimed at more efficiently. For example, as shown in FIG. 5, the reinforcing material 101a is arranged in parallel on one surface of the solid polymer electrolyte membrane 100 (FIG. 5 (a)), and the reinforcing material 101b is arranged on the other surface in the opposite direction. Are preferably arranged in parallel (FIG. 5B). By arranging the reinforcing material in this way, the reinforcing materials 101a and 101b can be arranged in a lattice shape as a whole (FIG. 5C), and the solid polymer electrolyte membrane can be used even with a small amount of the reinforcing material used. High mechanical strength can be obtained. In addition to this, the reinforcing material is arranged in a lattice shape as a whole by arranging the reinforcing material in a lattice shape on one surface of the solid polymer electrolyte membrane and vertically arranging the reinforcing material on the other surface. The pattern may be arranged perpendicular to the object.

The amount of the conductive nanofibers disposed as the reinforcing material can be increased to increase the strength of the solid polymer electrolyte membrane. However, if the amount is too large, when the MEA is assembled, the solid polymer electrolyte membrane, the electrode catalyst layer, There is a risk that the power generation performance will be deteriorated and sufficient power generation performance may not be obtained. Therefore, the conductive nanofiber is preferably 0.1 to 1.0 mg / mm ² , more preferably 0.1 to 0.5 mg / mm ² with respect to the area of the solid polymer electrolyte membrane. . This is a value obtained by dividing the amount (mg) of the conductive nanofibers arranged in the solid polymer electrolyte membrane by the area (mm ² ) of the surface of the solid polymer electrolyte membrane where the conductive nanofibers are arranged. .

  The reinforcing material disposed on at least one surface of the solid polymer electrolyte membrane is preferably coated with the solid polymer electrolyte. As a result, when the MEA is assembled, not only can the proton conductivity between the solid polymer electrolyte membrane and the electrode catalyst layer be maintained high, and an MEA having sufficient power generation performance can be obtained, but the solid polymer electrolyte It can serve as a binder and can bind the conductive nanofibers to improve the stability of the reinforcing material.

  The solid polymer electrolyte membrane in which the reinforcing material is disposed on at least one side may be used as it is for a fuel cell MEA or the like without the reinforcing material being coated with the solid polymer electrolyte. When an MEA is formed using such a solid polymer electrolyte membrane, the solid polymer electrolyte membrane is sandwiched between two electrode catalyst layers and two gas diffusion layers, and then hot pressed or the like to obtain a solid polymer. A part of the solid polymer electrolyte contained in the electrolyte membrane and / or the electrode catalyst layer can cover the reinforcing material. However, in order to further improve the proton conductivity, the binding property between the conductive nanofibers, etc., it is desirable that the reinforcing material is previously coated with a solid polymer electrolyte. At this time, it is sufficient that at least a part of the reinforcing material is covered with the solid polymer electrolyte, but it is more preferable that the reinforcing material is completely covered with the solid polymer electrolyte.

  Further, the solid polymer electrolyte covering the reinforcing material can be appropriately selected and used in consideration of the proton conductivity of the solid polymer electrolyte membrane, and the same polymer electrolyte membrane may be used, Different ones may be used. Specific examples of the solid polymer electrolyte covering the reinforcing material include those listed as solid polymer electrolytes used for the solid polymer electrolyte membrane described later.

  The reinforcing material may carry catalyst particles that promote the electrode reaction used in the electrode catalyst layer. In conventional MEAs, fuel gas or oxidant gas that has not been used for power generation permeates (crosses over) the solid polymer electrolyte membrane and generates radicals by a chemical reaction in the electrode catalyst layer of the counter electrode, thereby producing a solid polymer. There was a risk of deterioration. However, by supporting the catalyst particles on the reinforcing material, the catalyst particles can be arranged at the interface between the solid polymer electrolyte membrane and the electrode catalyst layer, and the gas crossing over the solid polymer electrolyte membrane is used as a counter electrode. Deterioration of the solid polymer can be prevented by reacting with the catalyst particles to form water before entering the electrode catalyst layer.

  The catalyst particles are not particularly limited as long as they are catalyst particles that promote the oxidation reaction of hydrogen and / or the reduction reaction of oxygen. In addition to platinum, ruthenium, iridium, rhodium, palladium, iron, chromium Preferred is an alloy of platinum and at least one metal selected from the group consisting of cobalt, nickel, manganese, and vanadium. The catalyst particles may be used alone, but may be used as an alloy containing platinum as a main component in order to increase the stability and activity of the catalyst particles.

  The average particle diameter of the catalyst particles carried on the reinforcing material is 1 to 20 nm, preferably 1 to 10 nm. In order to obtain the desired effect of suppressing deterioration due to crossover, the above range is desirable. The “average particle diameter of catalyst particles” can be measured by the crystallite diameter determined from the half-value width of the diffraction peak of the catalyst particles in X-ray diffraction or the average value of the catalyst particle diameters examined from a transmission electron microscope image. it can.

  The supported amount of the catalyst particles is 5 to 50% by mass, preferably 10 to 30% by mass, based on the total amount of conductive nanofibers used for the reinforcing material. If the loading amount is too small, the desired effect of suppressing deterioration due to crossover may not be obtained, and if the loading amount is too large, the production cost may increase.

  The reinforcing material desirably has a function of reducing and precipitating platinum ions. Thereby, platinum ions eluted from the electrode catalyst layer during the operation of the fuel cell can be deposited and reused as a catalyst for promoting the electrode reaction, and the platinum ions are precipitated in the solid polymer electrolyte membrane. It is possible to prevent the performance degradation of the solid polymer electrolyte membrane.

  Moreover, the object to be reduced / deposited is not particularly limited to platinum ions, and may be any ion that can be eluted from the catalyst particles used in the electrode catalyst layer to promote the electrode reaction. Examples of the catalyst particles that promote the hydrogen oxidation reaction or the oxygen reduction reaction include the ions listed above.

  Specific examples of the reinforcing material having a function of reducing and precipitating platinum ions include a reinforcing material having a reducing surface functional group. With the reducing surface functional group, catalyst particle components such as platinum ions eluted from the electrode catalyst can be reduced and deposited on the surface of the reinforcing material.

The surface functional group is not particularly limited as long as it has reducibility and is capable of reducing and depositing the eluted catalyst particle component. Examples thereof include a carboxyl group (—COOH), a phenol group (—OH), and a ketone group (> C═O). Since such a surface functional group has a high capturing ability and reducing ability of the catalyst particle component, the reduced and precipitated catalyst particles can be fixed to the reinforcing material surface in a fine particle state. Among these, a carboxyl group is preferably used because a hydrogen ion (H ⁺ ) that easily dissociates exists at the terminal and the reduction performance of the catalyst particle component is high.

  The amount of the surface functional group that the reinforcing material has may be appropriately determined so that the obtained solid polymer electrolyte membrane exhibits desired characteristics, but is about 100 to 2000 μmol / g, 300 to 1000 μmol / g. Is preferred. The effect as expected when the amount of the surface functional group is less than 100 μmol / g may not be obtained, and if it exceeds 2000 μmol / g, the affinity between the reinforcing material and water may be greatly changed. In the present invention, a temperature-programmed desorption spectrometer (TPD) or acid / base titration is used for quantitative analysis of the surface functional groups of the reinforcing material.

  As the reinforcing material having a function of reducing and precipitating platinum ions, a reinforcing material in which a trap material having a function of reducing and precipitating platinum ions is supported in addition to those described above. Also by this, the eluted platinum ions can be reduced to deposit platinum particles on the surface of the trap material, and the function of reducing and precipitating platinum ions can be imparted to the reinforcing material.

  Preferred examples of the trap material include reducing compounds and / or hydrogen storage materials.

  The reducing compound is not particularly limited as long as it has reducibility and is capable of reducing and depositing eluted platinum ions and the like. For example, sodium hypophosphite, sodium sulfite, sodium thiosulfate, An acid etc. are mentioned. These may be used individually by 1 type, and may mix and use 2 or more types. Since the reductive compound easily causes reductive precipitation of platinum ions, the collection efficiency of the catalyst particle component is high, and the reductively precipitated catalyst particles can be fixed on the support surface in a fine particle state.

  Next, the function of precipitating platinum ions on the reinforcing material can also be imparted by the hydrogen storage material. Thus, if the material having hydrogen storage properties is supported on the reinforcing material, the same effect as that obtained when the tube-shaped conductive nanofiber is used can be obtained. That is, hydrogen gas supplied from the outside can be stored in the hydrogen storage material, and not only reducing and depositing platinum ions eluted from the electrode catalyst layer on the surface of the conductive nanofibers, but also solid polymer by crossover gas. It is also possible to suppress the deterioration of the. Moreover, when the said hydrogen storage material is carry | supported by the tube-shaped electroconductive nanofiber, the said effect can be heightened further.

Specific examples of the hydrogen storage material include Ti-Ni alloys, AB ₅ type alloys such as La or Mm (Misch metal: a mixture of rare earth elements) represented by LaNi ₅ and Ni alloys, Ti-Mn alloys, Examples include hydrogen storage alloys such as Ti-Cr-based and Zr-Mn-based AB type ₂ alloys. Such a material is preferably used because it has not only hydrogen storage properties but also electron conductivity.

  The shape of the trap material may have any shape such as a particle shape, an elliptical shape, a cubic shape, etc., but considering the ease of carrying on the reinforcing material and the ease of handling, the shape of the trap material is It is preferable to have it. In this case, the trap material is not particularly limited, but those having an average particle diameter of preferably 100 nm or less, more preferably about 5 to 50 nm may be used.

  The amount of the trap material supported may be determined as appropriate so that the solid polymer electrolyte membrane exhibits the desired characteristics, but it is 5 to 30% by mass, preferably 10 to 10%, based on the total amount of the conductive nanofibers. It is preferably about 20% by mass. If the amount of the reducing compound is less than 5% by mass, the effect as expected can be not obtained, and if it exceeds 30% by mass, the electrode reaction may be inhibited. In order to quantitatively analyze the reducing compound introduced on the surface of the conductive nanofiber, inductively coupled plasma emission spectroscopy (ICP) can be used.

  Next, the material of the solid polymer electrolyte membrane used in the present invention is not particularly limited, and any conventionally known material can be used without particular limitation. Specifically, the polymer skeleton is a fluorinated polymer in which all or a part of the polymer skeleton is fluorinated and has an ion exchange group, or a polymer polymer skeleton that does not contain fluorine. And solid polymer electrolytes having ion exchange groups.

Examples of the ion-exchange group is not particularly _{limited, -SO 3 H, -COOH, -PO} (OH) 2, -POH (OH), - SO 2 NHSO 2 -, - Ph (OH) (Ph represents a phenyl group A cation exchange group such as —NH ₂ , —NHR, —NRR ′, —NRR′R ″ ⁺ , —NH ₃ ^{+ and the} like (R, R ′, R ″ represent an alkyl group, cycloalkyl Anion exchange groups such as a group, an aryl group, and the like.

  Specific examples of solid polymer electrolytes that are fluorine-based polymers and have ion exchange groups include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Corporation), and Flemion (registered trademark). Perfluorocarbon sulfonic acid polymers such as Asahi Glass Co., Ltd., polytrifluorostyrene sulfonic acid polymers, perfluorocarbon phosphonic acid polymers, trifluorostyrene sulfonic acid polymers, ethylenetetrafluoroethylene-g-styrene sulfonic acid polymers Suitable examples include polymers, ethylene-tetrafluoroethylene copolymers, polytetrafluoroethylene-g-polystyrene sulfonic acid polymers, and polyvinylidene fluoride-g-polystyrene sulfonic acid polymers.

  Specific examples of the solid polymer electrolyte having the ion exchange group as the hydrocarbon polymer include polysulfone sulfonic acid polymer, polyether ether ketone sulfonic acid polymer, polybenzimidazole alkyl sulfonic acid polymer, Preferred examples include benzimidazole alkylphosphonic acid polymers, cross-linked polystyrene sulfonic acid polymers, polyethersulfone sulfonic acid polymers, and the like.

  The material of the solid polymer electrolyte membrane has a high ion exchange ability, and is excellent in chemical durability and mechanical durability. Therefore, the solid polymer electrolyte having the ion exchange group is the above-mentioned fluorine-based polymer. Among them, Nafion (registered trademark, manufactured by DuPont) and Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.) are more preferable.

  The thickness of the solid polymer electrolyte membrane may be appropriately determined in consideration of proton conductivity, mechanical strength, etc. of the obtained solid polymer electrolyte membrane, preferably 5 to 300 μm, more preferably 10 to 200 μm, Especially preferably, it is good to set it as 15-150 micrometers. From the viewpoint of strength and durability during film formation, the thickness is preferably 5 μm or more, and from the viewpoint of proton conductivity, it is preferably 300 μm or less.

  Below, the method to arrange | position the reinforcing material containing electroconductive nanofiber on the single side | surface of the solid polymer electrolyte membrane of this invention is demonstrated. In addition, the following method shows one preferable embodiment of the present invention, and the method of disposing a reinforcing material on one side of the solid polymer electrolyte membrane is not limited to the following method.

  In order to arrange the reinforcing material on one surface of the solid polymer electrolyte membrane, a screen printing method, a doctor blade method, a die coater method, a spray method, or the like can also be used. Among these, the screen printing method and the spray method are preferably used because they can be arranged in a desired pattern by a simple method.

  Screen printing is a printing method in which a screen on which a pattern is formed with or without openings is placed on the substrate to be printed, and paste is attached to the openings using a squeegee only. Say the method.

  In the present invention, a paste containing at least conductive nanofibers is used as the paste. The solvent used in the paste is not particularly limited as long as it is a common solvent such as water, lower alcohol, glycols and the like. What is necessary is just to make content of the electroconductive nanofiber in the said paste into about 5-50 mass% with respect to the total mass of a paste.

  As shown in FIGS. 2 to 4 and the like, the screen used when applying the paste has an opening by a known method so that the conductive nanofibers are disposed at a desired position of the solid polymer electrolyte membrane. What is formed may be used. The material used for the screen is not particularly limited, but polyethylene or the like may be used.

  The substrate on which the paste is applied is not particularly limited, but a PET film, a PTFE film, or the like may be used. In addition, the base material may be pre-coated with a perfluoro polymer, a hydrocarbon polymer, or the like, which is a solid polymer electrolyte used for a solid polymer electrolyte membrane or an electrode catalyst layer, as an adhesive. Good. Thereby, applicability | paintability improves.

  The drying of the applied slurry is not particularly limited, and may be performed at 20 to 80 ° C. for about 1 to 10 hours in an air atmosphere or an inert atmosphere. Thereby, it becomes possible to arrange the reinforcing material made of conductive nanofibers in a predetermined pattern on the substrate.

  Next, after the base material on which the reinforcing material is disposed is laminated on the solid polymer electrolyte membrane, the reinforcing material is transferred onto the solid polymer electrolyte membrane by hot pressing or the like, and only the base material is peeled off. Thereby, a solid polymer electrolyte membrane in which a reinforcing material containing conductive nanofibers is arranged on one side is obtained. The hot pressing is not particularly limited, but is preferably performed at 110 to 170 ° C. and a pressing pressure of 1 to 5 MPa for 3 to 10 minutes.

  Further, the surface of the reinforcing material can be coated with the solid polymer electrolyte by applying and drying the solid polymer electrolyte solution on the surface where the reinforcing material of the solid polymer electrolyte membrane is disposed as described above. . The solid polymer electrolyte solution can be prepared by dispersing the solid polymer electrolyte in a solvent such as water, ethanol, methanol, or isopropyl alcohol. As a method for applying the solid polymer electrolyte solution, a flow coating method, a spray method, a screen printing method, a doctor blade method, or the like may be used. The method for drying the applied solid polymer electrolyte solution is not particularly limited, and may be performed using a known method.

  In addition, the conductive nanofibers coated with the solid polymer electrolyte on the base material can be obtained by mixing the solid polymer electrolyte in addition to the conductive nanofibers and the solvent into the paste used for screen printing. It becomes possible to arrange in a pattern. At this time, the method of applying and drying the paste is the same as described above. The content of the solid polymer electrolyte in the paste may be about 5 to 30% by mass with respect to the total weight of the paste.

  Further, the paste can be directly applied to the solid polymer electrolyte membrane by a screen printing method. Thereby, a transfer process etc. can be omitted.

  In order to dispose the reinforcing material on one side of the solid polymer electrolyte membrane, in addition to the above method, a method in which conductive nanofibers are formed in a sheet shape in advance is disposed on one side of the solid polymer electrolyte membrane. Thereafter, the solid polymer electrolyte solution is applied to the surface of the solid polymer electrolyte membrane on which the reinforcing material composed of the conductive nanofibers is disposed and dried, thereby covering the reinforcing material with the solid polymer electrolyte. can do.

  In the present invention, the reinforcing material preferably has a reducing surface functional group. Therefore, it is preferable to use conductive nanofibers having a reducing surface functional group in advance as a reinforcing material. A method for producing the conductive nanofiber having the reducing surface functional group is not particularly limited, and various known techniques for oxidizing the surface of the conductive nanofiber may be used. For example, the oxidation treatment is a liquid phase method using a strong oxidizing aqueous solution containing potassium permanganate, nitric acid, chlorate, persulfate, perborate, percarbonate, hydrogen peroxide, etc .; ozone, nitrogen oxide, Examples include a gas phase method using air, oxygen, etc .; a method using low temperature plasma. Among these, it is preferable to use an oxidation treatment by a liquid phase method because the surface of the conductive nanofibers can be uniformly oxidized and many carboxyl groups that are suitably used as surface functional groups can be introduced.

  Specifically, the oxidation treatment by the liquid phase method is performed by putting conductive nanofibers such as carbon nanotubes in the strong oxidizing aqueous solution and stirring and mixing them. After adding the conductive nanofibers to the strong oxidizing aqueous solution, the conductive nanofibers may be sufficiently dispersed in the solution by an appropriate dispersing means such as a homogenizer or an ultrasonic dispersing device. May be combined as appropriate.

  Next, the conductive nanofibers, the surface of which is oxidized with the strong oxidizing aqueous solution, are collected by filtration using a known means such as a separating means such as suction filtration, and dried, thereby reducing the reducing property. Conductive nanofibers having surface functional groups can be obtained. The drying method is not particularly limited as long as a known method such as vacuum drying, natural drying, rotary evaporator, and drying by a blower dryer is used. What is necessary is just to determine drying time etc. suitably according to the method to be used.

  In the present invention, it is desirable that the reinforcing material carry catalyst particles for promoting the oxidation reaction of hydrogen or the reduction reaction of oxygen, or a trap material such as a reducing compound or a hydrogen storage material. Therefore, it is preferable to use conductive nanofibers on which the catalyst particles or the trap material is previously supported as a reinforcing material.

  First, the method for supporting the catalyst particles on conductive nanofibers is not particularly limited, but a method of adding a reducing agent or the like after immersing the conductive nanofibers in a catalyst compound solution can be mentioned. According to such a method, catalyst particles can be highly dispersed and supported on the conductive nanofibers, and aggregation of the catalyst particles can be suppressed.

  The catalyst compound solution is a solution containing a compound containing elements constituting the catalyst particles (also simply referred to as “catalyst compound”). Specifically, when Pt is used as the catalyst particles, for example, a solution containing a catalyst compound such as chloroplatinic acid, chloroplatinum chloride, or dinitrodiammineplatinum can be used. In order to obtain a platinum alloy, other than platinum, a desired catalyst particle compound such as nitrate, chloride or sulfate may be dispersed in the solution. As the solvent to which the catalyst compound is added, water and / or alcohols such as ethanol and methanol can be used. Moreover, what is necessary is just to determine suitably the catalyst particle density | concentration in a catalyst compound solution, etc. so that the desired catalyst particle load may be obtained.

  The reducing agent is not particularly limited as long as it can reduce the catalyst compound. Sodium thiosulfate, citric acid, sodium citrate, L-ascorbic acid, sodium borohydride, hydrazine, formaldehyde, methanol, ethanol, hydrogen, Ethylene, carbon monoxide and the like can be used. By adding the reducing agent, the catalyst compound can be supported as catalyst particles on the conductive fiber. After immersing the conductive fiber in the catalyst compound solution described above, an appropriate amount of the reducing agent is added, heated to 60 to 100 ° C. using a reflux reactor or the like, and then allowed to cool to room temperature to reduce the catalyst particles. Carrying on.

  As described above, when alloying the catalyst particles supported on the conductive nanofibers, it is preferable to perform further firing. Moreover, you may dry as needed before baking.

  The method for drying the conductive nanofibers after the catalyst particles are reduced and supported is not particularly limited as long as a publicly known method such as vacuum drying, natural drying, rotary evaporator, and drying with a blow dryer is used. What is necessary is just to determine drying time etc. suitably according to the method to be used.

  Further, as a firing method in the case of alloying, the firing temperature is 300 to 1000 ° C., preferably 300 to 700 ° C. in an inert atmosphere such as nitrogen, helium, or argon, or in a reducing atmosphere such as hydrogen. Then, it may be performed for about 1 to 6 hours.

  In addition to the above-described method using a reducing agent, methods such as an impregnation method, a coprecipitation method, a competitive adsorption method, and a microemulsion (reverse micelle method) can be applied as a method for supporting catalyst particles on conductive nanofibers. . From the viewpoint that the catalyst particles can be highly dispersed and firmly supported on the conductive nanofibers, a method using a reducing agent, a microemulsion (reverse micelle method) and the like are preferably used. Moreover, you may carry | support catalyst particles using PVD methods, such as sputtering and vapor deposition.

  Next, a method for supporting the trap material on the surface of the conductive nanofiber is not particularly limited. For example, the conductive nanofiber is added to the solution containing the trap material and mixed by stirring. Examples include a method of impregnating the surface with the solution.

  Specific examples of the solution containing the trap material include a solution obtained by dissolving or dispersing the trap material in water, alcohol, or a mixture thereof.

  After adding the conductive nanofibers to the solution containing the trapping material, the conductive nanofibers may be sufficiently dispersed in the solution by a suitable dispersing means such as a homogenizer or an ultrasonic dispersing device. May be combined as appropriate. Thereafter, the conductive nanofibers impregnated with the solution are collected by filtration using a known means such as a separating means such as suction filtration, and dried to dry the conductive nanofibers carrying the trap material. Fiber can be obtained. The drying method is not particularly limited as long as a known method such as vacuum drying, natural drying, rotary evaporator, and drying by a blower dryer is used. What is necessary is just to determine drying time etc. suitably according to the method to be used.

  A second aspect of the present invention is a fuel cell MEA (hereinafter also simply referred to as “MEA”) using the above-described first solid polymer electrolyte membrane of the present invention.

  The first solid polymer electrolyte membrane of the present invention has excellent mechanical strength while ensuring proton conductivity by arranging a reinforcing material containing conductive nanofibers on at least one side. Furthermore, it is possible to prevent deterioration such as radical attack on the solid polymer in the electrode catalyst layer and elution of the catalyst metal, preferably by supporting the conductive nanofibers with catalyst particles, trapping material and the like. . Therefore, according to the solid polymer electrolyte membrane, high power generation performance can be exhibited over a long period of time, and an MEA excellent in durability and power generation performance can be provided.

  The structure of the MEA includes a fuel electrode side gas diffusion electrode having a fuel electrode side electrode catalyst layer and a fuel electrode side gas diffusion layer on both sides of the solid polymer electrolyte membrane, and an air electrode side electrode catalyst layer and an air electrode side gas diffusion. If it is a conventionally well-known thing, such as the structure by which the air electrode side gas diffusion electrode which has a layer is respectively arrange | positioned facing, it will not restrict | limit.

  The MEA of the present invention is characterized in that the first solid polymer electrolyte membrane of the present invention is used as the solid polymer electrolyte membrane. Therefore, the MEA is not particularly limited except that the first solid polymer electrolyte membrane of the present invention is used, and various known techniques may be referred to as appropriate. The electrode catalyst layers in the fuel electrode and the air electrode and A detailed description of the gas diffusion layer is omitted here.

  A third aspect of the present invention is a fuel cell using the above-described second MEA of the present invention. According to the above-described MEA of the present invention, it is possible to provide a fuel cell that can exhibit excellent power generation performance over a long period of time. Thereby, a highly reliable fuel cell can be obtained as a power source for moving bodies and a stationary power source. Among these, since the solid polymer electrolyte membrane is excellent in mechanical strength, the fuel cell according to the present invention is preferably used as a power source for moving bodies such as vehicles such as automobiles.

  The structure of the fuel cell is not particularly limited, and examples thereof include a structure in which MEA is sandwiched between separators.

  The separator has a function of separating air and fuel gas, and any conventional separator can be used without particular limitation. As the separator, conventionally known separators such as those made of carbon such as dense carbon graphite and a carbon plate and those made of metal such as stainless steel can be used without particular limitation. Moreover, in order to ensure the flow path of air and fuel gas, a gas distribution groove | channel may be formed and a conventionally well-known technique can be utilized suitably. The shape of the separator is not particularly limited, and may be appropriately determined in consideration of the output characteristics of the obtained fuel cell.

  Furthermore, a stack in which a plurality of MEAs are stacked via a separator and connected in series may be formed so that the fuel cell can obtain a desired voltage or the like. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  Hereinafter, the present invention will be specifically described based on examples. In addition, this invention is not limited only to these Examples.

Example 1
(1) Arrangement of carbon nanofibers Carbon nanofibers (manufactured by Showa Denko, VGCF, diameter 100 nm, length 10 μm) were added to purified water to obtain a mixed liquid containing 10% by mass of the carbon nanofibers. The mixed solution is opened in a predetermined pattern on a substrate made of a PET film (thickness 0.1 mm) spray-coated with Nafion (registered trademark) / n-propyl alcohol solution (manufactured by DuPont, containing 5 wt% of Nafion). It was applied by screen printing using a screen with a part formed and dried at 30 ° C. for 2 hours. Thereby, as shown in FIG. 2, the said carbon nanofiber was affixed on the said base material in parallel with the space | interval of 50 micrometers.

Next, after using two sheets of the base material on which the reinforcing material is pasted, disposed on both sides of a solid polymer electrolyte membrane (Nafion (registered trademark) 111, size 80 mm × 80 mm, thickness 25 μm), 2 After hot pressing at 130 ° C. for 5 minutes at a pressure of 0.0 MPa, only the substrate was peeled off to obtain a solid polymer electrolyte membrane in which the reinforcing material was disposed on both sides. At this time, as shown in FIG. 5C, the direction of the pattern of the reinforcing material including the carbon nanofibers is reversed on both surfaces of the solid polymer electrolyte membrane, and the carbon nanofibers on one surface of the solid polymer electrolyte membrane are formed. The amount was 0.2 mg / mm ² .

(2) Preparation of electrode catalyst layer Platinum-supported carbon (TEC10E50E, Tanaka Kikinzoku Kogyo Co., Ltd., platinum content 46.5 wt%), Nafion (registered trademark) / n-propyl alcohol solution (DuPont, Nafion 5 wt% contained) Pure water and isopropyl alcohol were mixed at a mass ratio of 1: 0.5: 2.5: 1 and mixed and dispersed in a glass container in a water bath set at 25 ° C. for 3 hours using a homogenizer. Thus, a catalyst ink was prepared. Next, the catalyst layer ink was applied on a Teflon sheet using a screen printer and dried in the atmosphere at 30 ° C. for 2 hours, whereby an electrode catalyst layer (platinum weight 0 per 1 cm ^{2 of} area 0 cm ² was formed on the Teflon sheet. 40 mg).

(3) Production of Gas Diffusion Layer A substrate was prepared by punching carbon paper (Carbon Paper TGP-H-060, thickness 190 μm, manufactured by Toray Industries, Inc.) into a 50 mm square. After immersing this base material in a PTFE fluorine-based aqueous dispersion solution (polyflon D-1E manufactured by Daikin Industries, Ltd., containing PTFE 60 wt%) to a predetermined concentration with pure water, the substrate was immersed in an oven. The PTFE was dispersed in the substrate by drying at 60 ° C. for 30 minutes. At this time, the PTFE content was 25 wt%. As a result, a water repellent treated substrate was obtained.

  Subsequently, 5.4 g of carbon black (VULCAN (registered trademark) XC-72R manufactured by CABOT Co., Ltd.), 1.0 g of the same fluorine-based aqueous dispersion solution of PTFE as used above, and 29.6 g of water, A slurry was prepared by mixing and dispersing for 3 hours in a homogenizer. This slurry was uniformly applied to one surface of the water-repellent treated substrate prepared previously by a bar coater, dried in an oven at 60 ° C. for 1 hour, and further in a muffle furnace at 350 ° C. for 1 hour. Heat treatment was performed. As a result, a gas diffusion layer in which a carbon particle layer was formed on the water repellent treated substrate was obtained.

(4) Production of MEA and Evaluation Single Cell Two electrode catalyst layers produced in (2) above were placed on both sides of the solid polymer electrolyte membrane produced in (1) above, and then 130 ° C. by hot pressing. After hot pressing at 2.0 MPa for 10 minutes, the Teflon sheet was peeled off to obtain a joined body. An MEA was produced by sandwiching the joined body using the two gas diffusion layers produced earlier with the carbon particle layer inside. This was sandwiched between a carbon separator and a current collector plate to obtain an evaluation cell.

(Example 2)
In the same manner as in Example 1 (1), reinforcing materials containing carbon nanofibers were disposed on both sides of the solid polymer electrolyte membrane. Next, a Nafion (registered trademark) / isopropyl alcohol solution (manufactured by DuPont, containing 5 wt% Nafion) was applied to one side of the solid polymer electrolyte membrane so that the amount of Nafion was 0.2 mg / cm ^2. The reinforcement was coated with Nafion® by drying at 0 ° C. for 1 hour. In the same manner, the reinforcing material on the other surface of the solid polymer electrolyte membrane was coated with Nafion (registered trademark).

  A single cell for evaluation was assembled in the same manner as in Example 1 except that a solid polymer electrolyte membrane in which conductive nanofibers coated with Nafion (registered trademark) were arranged on both sides was used as described above.

(Example 3)
10 g of carbon nanofibers (manufactured by Showa Denko, VGCF, diameter 100 nm, length 10 μm) are added to 500 ml of an aqueous potassium permanganate solution having a concentration of 1 mol / l, and stirred and mixed at 60 ° C. for 3 hours. The oxidation treatment was performed. Thereafter, the carbon nanofibers were separated by filtration, sufficiently washed with distilled water, and dried at 80 ° C. for 3 hours in a vacuum dryer to obtain oxidized carbon nanofibers. Carboxyl groups were mainly introduced into the surface of the oxidized carbon nanofibers at 800 μmol / g.

  A single cell for evaluation was assembled in the same manner as in Example 1 except that the oxidized carbon nanofiber was used.

(Comparative Example 1)
A single cell for evaluation was assembled in the same manner as in Example 1 except that the carbon nanofibers were not arranged on both sides of the solid polymer electrolyte membrane.

(Evaluation)
Using each evaluation single cell produced in Examples 1 to 3 and Comparative Example 1, durability was evaluated according to the following procedure.

Hydrogen was supplied as a fuel to the anode side of each evaluation single cell, and air was supplied to the cathode side. Supply pressure for both gases is atmospheric pressure, hydrogen is 60 ° C, air is saturated and humidified at 55 ° C, the temperature of the fuel cell body is set to 70 ° C, hydrogen utilization is 70%, and air utilization is 40%. The operation was continued at a current density of 1 A / cm ² for 10 minutes. When power generation was stopped, the current density to be taken out was reduced to zero, and then the anode was purged with air to discharge hydrogen, and the outlet side was opened to the atmosphere, and the cathode was similarly opened to the atmosphere. At this time, temperature control of the fuel cell main body was not performed, and the stop time was 10 minutes. When power generation was stopped, the experimental environment was a room temperature of 20-25 ° C. and a humidity of 40-60% RH. When the operation was resumed after the stop, gas was again introduced into the cell under the above conditions to generate power. By repeating this operation-stop cycle, the durability of each evaluation single cell was evaluated by measuring the number of cycles until a generated voltage of 0.4 V or more was obtained. The results are shown in Table 1.

  According to the solid polymer electrolyte membrane of the present invention, it is possible to provide a fuel cell excellent in power generation performance and durability.

The cross-sectional schematic diagram of the solid polymer electrolyte membrane of this invention by which the reinforcing material containing electroconductive nanofiber is arrange | positioned on the single side | surface is shown. The arrangement pattern of the reinforcing material in the solid polymer electrolyte membrane of the present invention is schematically shown. The arrangement pattern of the reinforcing material in the solid polymer electrolyte membrane of the present invention is schematically shown. The arrangement pattern of the reinforcing material in the solid polymer electrolyte membrane of the present invention is schematically shown. FIG. 5 (a) schematically shows a reinforcing material arrangement pattern on one side of the solid polymer electrolyte membrane of the present invention, and FIG. 5 (b) shows a reinforcing material arrangement pattern on the other side of the solid polymer electrolyte membrane. FIG. 5 (c) schematically shows an arrangement pattern of the reinforcing material that combines both surfaces of the solid polymer electrolyte membrane.

Explanation of symbols

100: solid polymer electrolyte membrane,
101, 101a, 101b ... conductive nanofibers.

Claims (11)

A solid polymer electrolyte membrane for a fuel cell,
A solid polymer electrolyte membrane for a fuel cell, wherein a reinforcing material containing conductive nanofibers is disposed on at least one surface of the solid polymer electrolyte membrane for a fuel cell.   The solid polymer electrolyte membrane for a fuel cell according to claim 1, wherein the conductive nanofiber is a carbon nanofiber.   The solid polymer electrolyte membrane for a fuel cell according to claim 1 or 2, wherein the reinforcing material is regularly arranged on at least one surface of the solid polymer electrolyte membrane for a fuel cell.   The solid polymer electrolyte membrane for a fuel cell according to any one of claims 1 to 3, wherein the reinforcing material is coated with a solid polymer electrolyte.   5. The solid polymer electrolyte membrane for a fuel cell according to claim 1, wherein the reinforcing material carries catalyst particles that promote an oxidation reaction of hydrogen and / or a reduction reaction of oxygen.   The solid polymer electrolyte membrane for a fuel cell according to any one of claims 1 to 5, wherein the reinforcing material has a function of reducing and precipitating platinum ions.   The fuel cell electrode according to claim 1, wherein the reinforcing material has a reducing surface functional group.   The solid polymer electrolyte membrane for a fuel cell according to any one of claims 1 to 7, wherein the reinforcing material carries a trap material having a function of reducing and precipitating platinum ions.   The solid polymer electrolyte membrane for a fuel cell according to claim 8, wherein the trap material is a reducing compound and / or a hydrogen storage material.   A fuel cell MEA using the solid polymer electrolyte membrane for a fuel cell according to any one of claims 1 to 9.   A fuel cell using the fuel cell MEA according to claim 10.

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