JP2008140665A - Proton conductive membrane, membrane-electrode assembly, and solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proton conductive membrane which realizes a high impact resistance and a high polar solvent resistance while maintaining a high proton conductivity, a membrane electrode assembly, and a solid polymer fuel cell. <P>SOLUTION: The proton conductive membrane contains particles 1 composed of a silicon-oxygen cross-linked structure. Furthermore, the terminal of non-reacted hydroxide group of the particles 1 is treated by a sililation reagent. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a proton conductive membrane, a membrane-electrode assembly, and a polymer electrolyte fuel cell.

  Since fuel cells have high power generation efficiency and excellent environmental characteristics, in recent years, fuel cells have attracted attention as next-generation power generation devices that can contribute to solving environmental problems and energy problems that have become major social issues.

  Fuel cells are generally classified into several types according to the type of electrolyte. Among them, a polymer electrolyte fuel cell (hereinafter referred to as “PEFC”) is smaller and smaller than any other type. It is a high-output, small-scale on-site power source for the next generation as a power source for mobile objects such as a power source for vehicles and for portable use.

  As described above, PEFC has excellent advantages in principle, and development for practical use is actively performed. In this PEFC, hydrogen is usually used as a fuel. Hydrogen is decomposed into protons (hydrogen ions) and electrons by a catalyst installed on the anode side of the PEFC. Among these, electrons are supplied to the outside, used as electricity, and circulated to the cathode side of the PEFC. On the other hand, protons are supplied to the proton conductive membrane (electrolyte membrane) and move to the cathode side through the proton conductive membrane. On the cathode side, protons, circulating electrons, and oxygen introduced from the outside are supplied by the catalyst to generate water. In other words, when viewed as a single PEFC, PEFC is a very clean energy source that extracts electricity when making water from hydrogen and oxygen.

  In recent years, fuel cells that use fuels other than hydrogen such as alcohols, ethers, hydrocarbons, and the like as fuels for fuel cells and that extract protons and electrons from these fuels using a catalyst have been studied. A typical example of such a fuel cell is a direct methanol fuel cell (hereinafter referred to as “DMFC”) using methanol (usually used as an aqueous solution) as fuel. Since DMFC does not require an external reformer and fuel is easy to handle, it is most expected as a compact and portable power source among various types of fuel cells.

  In fuel cells such as PEFC and DMFC, the proton conductive membrane has a role of conducting protons generated on the anode side to the cathode side. This proton conduction occurs in concert with the flow of electrons. Therefore, in order to obtain a high output, that is, a high current density in the fuel cell, it is necessary to conduct protons through the proton conductive membrane sufficiently and at high speed. Thus, it is no exaggeration to say that the proton conductive membrane is a key material that determines the performance of the fuel cell.

  The proton conductive membrane also serves as an insulating film that electrically insulates the anode side and the cathode side, and a fuel barrier that prevents fuel such as hydrogen supplied to the anode side from leaking to the cathode side. It also has a role as a membrane.

  Currently, the main proton conductive membrane used in DMFC is a fluororesin membrane having perfluoroalkylene as a main skeleton and partially having a sulfonic acid group at the end of a perfluorovinyl ether side chain. Examples of such a sulfonated fluororesin membrane include Nafion (Nafion (registered trademark) membrane (Du Pont: Du Pont, see Patent Document 1)), Dow (Dow Chemical: Dow Chemical, Patent). Reference 2)), Aciplex (Aciplex (registered trademark) membrane (Asahi Kasei Kogyo Co., Ltd., see Patent Document 3)), Flemion (Flemion (registered trademark) membrane (Asahi Glass Co., Ltd.)), etc. Are known.

  The Nafion membrane has polytetra (or tri) fluoroethylene in the main chain skeleton and a sulfonic acid group in the side chain. Polytetra (or tri) fluoroethylene is non-polar and water-repellent, and the side chain sulfonic acid group is polar and hydrophilic, so it spontaneously forms a phase separation structure, resulting in a high concentration of sulfonic acid groups. An integrated structure is formed and functions as a proton conduction path (see Non-Patent Document 1). Thus, in order to realize high proton conductivity, a proton conductive membrane has been proposed in which a very large number of acid groups are contained in the electrolyte.

  In addition to the fluororesin membranes described above, fuel electrolyte membranes, as well as various types of membranes such as hydrocarbons and inorganics, are also being used as fuel cell electrode binders. Various types of electrolytes are used. However, as a reference electrode, currently, a Nafion electrode (Nafion (registered trademark) electrode), which is a typical fluorine-based electrode, is generally used.

On the other hand, since an organosilicon compound is composed of a silicon-oxygen bond having a strong binding energy, it has high chemical stability, heat resistance and oxidation resistance, and can impart many unique properties depending on its composition. It is used in all industrial fields such as electronics, office equipment, architecture, food, medicine, textile, plastic, paper, pulp, and paint rubber. A proton conductive membrane using this organosilicon compound and having a crosslinked structure composed of a silicon-oxygen bond has been disclosed (for example, see Patent Document 4). The cross-linked structure composed of silicon-oxygen bonds is relatively stable even when exposed to high temperature and high humidity under strong acidic (proton presence) conditions like the proton conductive membrane, and the cross-linked structure inside the fuel cell membrane Can be suitably used.
British Patent No. 4,330,654 JP-A-4-366137 JP-A-6-342665 Japanese Patent No. 3679104 Journal of Polymer Science Polymer Physics (J, Polymer Science, Polymer Physics, Vol. 19, p. 1687, 1981)

  As described above, a proton conductive membrane has been proposed that contains a large number of acid groups in order to maintain high proton conductivity. Such a proton conductive membrane contains a large amount of polar solvent when the concentration of the acid contained exceeds a certain value. As a result, the proton conductive membrane swells and a part thereof is eluted as a result of destroying the structure, so that it is difficult to simultaneously realize high fuel barrier properties and high polar solvent resistance.

  Further, when a proton conductive membrane having a crosslinked structure composed of silicon-oxygen bonds is used, there is a problem that impact resistance against external pressure such as humidity change is low. For example, when an organosilicon compound is used as an electrolyte for a fuel cell that requires high proton conductivity at high temperature and low humidity, the performance greatly changes due to temperature fluctuations, and the proton conductivity performance deteriorates.

  Furthermore, since the organosilicon compound is not thermoplastic, it cannot be bonded to a Nafion electrode, which is a thermoplastic resin, by hot pressing (heating pressing). As a result, the adhesiveness with the Nafion electrode is lowered, the contact resistance between the electrodes is increased, and the high proton conductivity is lost.

  Therefore, in view of the above problems, the present invention provides a proton conductive membrane, a membrane-electrode assembly, and a solid polymer type that achieve high impact resistance and high polar solvent resistance while maintaining high proton conductivity. An object is to provide a fuel cell.

  In order to achieve the above object, a first feature of the present invention is a proton conductive membrane including a crosslinkable electrolyte (A) having an acid group and a crosslink structure by a silicon-oxygen bond, wherein the crosslinkable electrolyte (A The unreacted hydroxyl terminal of (2) is a proton conductive membrane treated with the silylating agent (B).

  According to the proton conductive membrane according to the first feature, high impact resistance and high polar solvent resistance can be realized while maintaining high proton conductivity.

  In the proton conductive membrane according to the first feature, the silicon-oxygen bond rate of the crosslinkable electrolyte (A) is preferably 70% or more and 98% or less.

  In the proton conductive membrane according to the first feature, the molecular weight of the silyl group added to the hydroxyl group by being treated with the silylating agent (B) is preferably 150 or more.

  In the proton conductive membrane according to the first feature, the silyl group added to the hydroxyl group by being treated with the silylating agent (B) preferably contains a hetero atom as a constituent atom.

  Moreover, it is preferable that a hetero atom contains any one of a fluorine atom, a nitrogen atom, an oxygen atom, or a sulfur atom.

  In the proton conductive membrane according to the first feature, the crosslinkable electrolyte (A) contains an organic-inorganic composite structure that is covalently bonded to a plurality of silicon-oxygen bridges and contains carbon atoms, and the carbon atoms % By weight is preferably 10% or more and 50% or less.

  The second feature of the present invention is a membrane-electrode assembly in which gas diffusion electrodes are bonded to both surfaces of a proton conductive membrane, and the proton conductive membrane has a cross-linked structure by an acid group and a silicon-oxygen bond. The gist is that the unreacted hydroxyl terminal of the crosslinkable electrolyte (A) contains a crosslinkable electrolyte (A) and is a membrane-electrode assembly treated with the silylating agent (B).

  According to the membrane-electrode assembly according to the second feature, high impact resistance and high polar solvent resistance can be realized while maintaining high proton conductivity.

  A third feature of the present invention is a polymer electrolyte fuel cell including a membrane-electrode assembly in which gas diffusion electrodes are bonded to both surfaces of a proton conductive membrane, wherein the proton conductive membrane includes an acid group and silicon- The polymer electrolyte fuel cell includes a crosslinkable electrolyte (A) having a crosslink structure by oxygen bonding, and an unreacted hydroxyl terminal of the crosslinkable electrolyte (A) is treated with a silylating agent (B). Is the gist.

  According to the polymer electrolyte fuel cell according to the third feature, high impact resistance and high polar solvent resistance can be realized while maintaining high proton conductivity.

  According to the present invention, it is possible to provide a proton conductive membrane, a membrane-electrode assembly, and a polymer electrolyte fuel cell that achieve high impact resistance and high polar solvent resistance while maintaining high proton conductivity.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic and ratios of dimensions and the like are different from actual ones. Accordingly, specific dimensions and the like should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  The fuel cell according to this embodiment includes a positive electrode (air electrode), a negative electrode (fuel electrode), and a proton conductive membrane disposed between these two electrodes, and is characterized by the structure of this proton conductive membrane. It is what you have. This proton conductive membrane is characterized by having particles made of a silicon-oxygen crosslinked structure, acid groups are added to the surface of the particles, and the particles constitute a continuum. Is configured to pass through this membrane.

  The structure of the proton conductive membrane will be described sequentially for each item.

(Silicon-oxygen cross-linked structure)
In the proton conductive membrane of the present invention, the crosslinked structure is an important component and plays a role in mechanical strength, heat resistance, durability, dimensional stability, and the like of the membrane.

  The proton conductive membrane according to the present embodiment can obtain the mechanical strength, heat resistance, durability, and dimensional stability of the membrane by having such a crosslinked structure. That is, when a crosslinked structure having a sufficient density is obtained, a large dimensional change is not observed and a strength change is not caused even in a wet state or a dry state.

  As described above, the proton conductive membrane of the present invention has no significant change in the dimensions of the membrane when dried and wet. Therefore, the assembly of the proton conductive membrane and the gas diffusion electrode (generally “membrane-electrode assembly”). In the following, it is easy to manufacture “MEA”), and the membrane does not always expand and contract in response to a change in temperature and humidity in the fuel cell due to a change in the operating state even during operation of the fuel cell. Therefore, the film is not broken and the MEA is not broken. Furthermore, since the membrane does not weaken due to swelling, it is possible to avoid the risk of not only the above-mentioned dimensional change but also the membrane tearing when a differential pressure is generated in the fuel cell.

  On the other hand, none of the conventional fluorine-based resin films such as a Nafion film or a proton conductive film made of a polymer material having an aromatic molecular structure in the main chain has a crosslinked structure. For this reason, at high temperatures, the structure of the membrane changes greatly due to the creep phenomenon, and as a result, the operation of the fuel cell at high temperatures becomes unstable.

  The cross-linked structure consisting of silicon-oxygen bonds is relatively stable even when exposed to high temperature and high humidity under strong acidic (proton presence) conditions like a fuel cell membrane. Can be preferably used. Furthermore, since a silicon-oxygen bond can be easily formed and is inexpensive, it can be suitably used.

  As described above, the proton conductive membrane according to this embodiment includes the crosslinkable electrolyte (A) having an acid group and a crosslink structure by a silicon-oxygen bond, and the silicon-oxygen bond of the crosslinkable electrolyte (A). The rate is preferably 70% or more and 98% or less.

  On the other hand, in order to form such a crosslinked structure, for example, an organic polymer material such as an epoxy resin, a crosslinkable acrylic resin, a melamine resin, and an unsaturated polyester resin can be used. It is difficult to obtain long-term stability when exposed to high temperature and high humidity under such strong acidic conditions.

(Particles, particle continuum, and particle gaps)
The proton conductive membrane of the present invention can achieve high proton conductivity by satisfying the following requirements.

  1) A high concentration of acid groups.

  2) Formation of a proton conduction path in which an acid continuously exists.

  During fuel cell operation, protons generated at the anode are supplied to the membrane, while protons in the membrane are consumed at the cathode. A certain amount of protons are present in advance in the proton conductive membrane, and the proton concentration is increased by supplying protons at the anode, and the proton concentration is decreased by proton consumption at the cathode. The proton concentration gradient generated in the membrane in this way is the driving force for proton diffusion from the anode to the cathode. If there are not enough protons in the membrane, there will be insufficient protons on the cathode side, and stable fuel cell operation cannot be expected. Therefore, a sufficient proton concentration is required in the membrane.

  Thus, stable fuel cell operation is achieved by increasing the concentration of protons in the membrane so that the acid groups are present at a high concentration.

  Furthermore, if the diffusion transfer due to the proton concentration gradient does not occur at a sufficiently high rate, the proton shortage of the cathode occurs. Therefore, it is necessary to secure a proton transfer path so that efficient diffusion is possible. Proton usually moves as a hydrate, so it has a good affinity with water, and a continuous phase from the anode to the cathode, that is, a proton-conducting membrane in which acid is accumulated at a high concentration where protons can exist stably. It is preferable to have a proton conduction path communicating from the main surface to the opposite surface.

  That is, a proton conductive membrane that operates stably even at high temperatures needs to form a proton conduction path in which acid groups are present in a high concentration and acid groups are continuously arranged. Furthermore, the structure forming the proton conduction path needs to form a chemical structure that does not deform even at high temperatures.

  The proton conductive membrane of the present invention has particles composed of a silicon-oxygen crosslinked structure, the particles have acid groups on the surface, and the particles constitute a continuum.

  Here, the particle continuum refers to a structure in which the particles continuously exist so as to have contact portions with each other. The continuum of particles will be described with reference to FIG.

  FIG. 1 is an enlarged schematic view of a front conductive film of the present invention. In the proton conductive membrane of the present invention, as shown in FIG. 1, a large number of particles (crosslinkable electrolyte) 1 composed of a silicon-oxygen crosslinked structure are present in a dense and continuous state. Yes. When such a structure is adopted, it is difficult to obtain a geometrically completely dense structure, and voids (particle gaps) 2 are generated between the particles. It is preferable that the dense particles form a bond between the particles. The bond between the particles is a silicon-oxygen bond in which unreacted silicon-oxygen cross-linking groups existing on the particle surface react with each other, or a separately added cross-link. An agent (described later) may serve as an adhesive between the particles. Thus, the strength of the film is further improved by having an interparticle bond in which the silicon-oxygen crosslinking groups react with each other.

  Furthermore, since acid groups are introduced on the surface of the particles, a large number of acid groups exist on the wall surfaces of the gaps between the particles (that is, the boundary between the particles and the gaps between the particles). That is, the gap between the particles serves as a proton conduction path in which acid groups are accumulated.

  It is preferable that the gap between the particles communicates with the opposite surface from the main surface of the proton conductive membrane of the present invention. That is, the proton conduction path communicates from the main surface to the opposite surface, so that protons can efficiently diffuse and move from the anode to the cathode. On the other hand, when the gap between the particles does not communicate with the opposite surface from the main surface of the proton conducting membrane, the proton conducting performance is significantly reduced.

(Details of particles)
The proton conductive membrane of the present invention has particles composed of a silicon-oxygen crosslinked structure, and the particles have acid groups on the surface.

  In addition, regarding the form of the particles, the spherical shape has an advantage that the strength is slightly high, but the shape is not necessarily a spherical shape close to a true sphere, and may be a non-spherical shape such as a flat granular shape or a columnar shape. The particles are not particularly limited as long as they have clear structural boundaries.

  The cross-linked structure composed of silicon-oxygen bonds is a so-called glass structure and is suitable as a basic structure of a proton conductive membrane that requires heat resistance because it is stable at high temperatures as described above.

  In the proton conductive membrane of the present invention, the acid group on the surface of the particle is preferably a sulfonic acid group. Sulfonic acid is a very strong acid, and by using sulfonic acid as an acid group, the dissociation property of protons becomes very good. That is, sulfonic acid has very little suppression of proton diffusion and can be preferably used in the present invention. The sulfonic acid has good oxidation durability and is stable up to 180 ° C. in heat resistance, and can be preferably used in the present invention.

  In the proton conductive membrane of the present invention, it is preferable that the average particle diameter of each particle constituting the continuous particle body having a particulate skeleton structure is 3 to 200 nm. If the average particle diameter exceeds 200 nm, the surface area of the particles that play a major role in proton conduction decreases, and high conductivity cannot be obtained. Also, the gap between the particles becomes too large and becomes brittle, and fuel gas leaks (so-called chemicals). Short circuit) is also a concern. On the other hand, when the thickness is 3 nm or less, the layer is close to a uniform layer, and a sufficient proton conduction path cannot be secured, making efficient proton conduction difficult. Therefore, the preferable average particle diameter range of the particles is 3 to 200 nm, more preferably 5 to 100 nm, and still more preferably 10 to 50 nm. By setting the average particle diameter range to the above-described range, it is possible to sufficiently secure the proton conduction path while ensuring sufficient strength.

  The particle size distribution may be a continuum of particles having a uniform particle size or a continuum of particles having a non-uniform particle size. Here, when the particle size distribution of the particles is uniform, although it depends on the particle size, a gap is easily formed geometrically, and there is a possibility that high ion conductivity can be exhibited. On the other hand, when the particle size distribution is wide, dense packing is possible, which contributes to improvement of fuel gas barrier properties and membrane strength. Therefore, it is desirable to select the particle size distribution according to the usage situation. The particle size distribution of the particles is appropriately determined in consideration of ion conductivity, fuel gas barrier properties, and membrane strength. The particle size can be controlled by adjusting the conditions such as the structure / molecular weight of the raw material used, solvent type / concentration, catalyst type / amount, and reaction temperature. A detailed method of controlling the particle size will be described in the method for producing a proton conductive membrane of the present invention described later. The particle size distribution can be obtained from the aforementioned small-angle X-ray scattering or the like.

  As described above, acid groups, preferably sulfonic acid groups are present on the surfaces of the particles contained in the proton conducting membrane of the present invention. The sulfonic acid group may be in a state where a sulfonic acid-containing compound is injected (doped) into the gaps between the particles. In this case, when used as an electrolyte membrane for a fuel cell for a long time, the proton conductive membrane is used. There is a possibility of dissipation (so-called dope out).

  On the other hand, when the sulfonic acid group is immobilized on the particle surface by a covalent bond, stable performance can be exhibited.

  In the proton conductive membrane according to this embodiment, the unreacted hydroxyl terminal of the crosslinkable electrolyte (A) is treated with the silylating agent (B).

  Here, silylation is widely used in organic synthesis as one of the methods for protecting the hydroxyl group. As a general method of silylation, silylation occurs rapidly by reacting a compound having a hydroxyl group with silyl chloride in the presence of a base such as imidazole. As the solvent, dimethylformamide, tetrahydrofuran, pyridine and the like are generally used. When the reactivity is low, silyl triflate is allowed to react in the presence of 2,6-lutidine or N, N-diisopropylethylamine. In this embodiment, as shown in FIG. 2, silylation is carried out by reacting, for example, silyl chloride with the remaining half of silanol (HO—Si) terminal near the surface of the proton conductive membrane.

  Moreover, it is preferable that the molecular weight of the silyl group added to the hydroxyl group by being treated with the silylating agent (B) is 150 or more. Examples of the silylating agent (B) having a silyl group molecular weight of 150 or more include triphenylsilyl chloride and t-butyldiphenylsilyl chloride as shown in FIG.

  Moreover, it is preferable that the silyl group added to the hydroxyl group by being treated with the silylating agent (B) contains a hetero atom as a constituent atom. This heteroatom preferably contains at least any one of a fluorine atom, a nitrogen atom, an oxygen atom and a sulfur atom. Examples of the atomic group in which the silyl group includes a hetero atom as a constituent atom include methyl-3,3,3-trifluoropropyldichlorosilane and 3,3,4,4,5,5, as shown in FIG. Examples include 6,6,6-nonafluorohexylmethyldichlorosilane.

  The crosslinkable electrolyte (A) contains an organic-inorganic composite structure that is covalently bonded to a plurality of silicon-oxygen bridges and contains carbon atoms, and the weight% of the carbon atoms is 20% or less. preferable.

(Gap between particles)
As described above, the proton conductive membrane of the present invention has particles composed of a silicon-oxygen crosslinked structure, the particles have acid groups on the surface, and the particles constitute a continuum. The particle continuum geometrically creates particle gaps as described above. In particular, when the gap between the particles communicates with the opposite surface from the main surface of the proton conductive membrane, the gap between the particles becomes a proton conduction path through which protons efficiently diffuse and move from the anode to the cathode.

  The gap width of the particle gap is not particularly limited, but if it is extremely narrow, proton conduction is inhibited, and if it is too wide, not only the membrane becomes brittle, but also fuel gas leaks (so-called chemical short) and power generation efficiency decreases. To do. The specific average gap width is, for example, preferably 0.5 nm to 500 nm, more preferably 1 nm to 200 nm, and still more preferably 1 to 10 nm.

  Although it is difficult to directly observe the width of the gap between the particles, as an alternative evaluation, it can be estimated from a pore size distribution obtained by measuring a specific surface area by a mercury intrusion method or a BET method.

  By the way, as described above, since acid groups are introduced into the wall surfaces of the particle gap (that is, the particle surface), the particle gap is hydrophilic, and water can be efficiently introduced into the gap. And the gap can be substantially replaced by water. It is essential for the proton conducting membrane that water, which is a proton conducting medium, can be introduced into the gaps between the particles. Normally, during operation of the fuel cell, part or all of the gaps between the particles are filled with humidified water of the fuel gas or water generated by the reaction of the cathode. Protons (hydrogen ions) exist in the form of hydration with these plural water molecules (hydronium ions), and protons are transferred by diffusion movement of the hydronium ions. That is, the gap between the particles is preferably filled with the surrounding atmosphere during drying, but is preferably filled with humidified water of the fuel gas or water generated by the reaction of the cathode during the operation of the fuel cell.

  The volume of the particle gap can also be estimated by the mercury intrusion method or the BET method in the same way, but as a simpler method utilizing the fact that the particle gap can be replaced with water, water content measurement is possible. There is. That is, the wet mass after immersing the proton conductive membrane in water and removing the moisture on the surface and the dry mass obtained by drying the proton conductive membrane (for example, heating at 100 ° C. under reduced pressure) were measured. The water content that can be calculated by the formula of (mass) / (dry mass) is a value that correlates with the volume fraction of the gap. In other words, it corresponds to the porosity.

  In the proton conductive membrane of the present invention, the water content is preferably 3% by mass or more. If the moisture content is less than this, the gap between the particles, that is, the volume of the proton conduction path is insufficient, and high conductivity cannot be obtained. On the other hand, when the water content exceeds 50% by mass, the fuel gas tends to pass through and tends to cause a chemical short circuit, and at the same time, the membrane tends to be brittle and weak. Thus, the water content is preferably 3 to 50% by mass, and more preferably 5 to 30% by mass.

  Further, the volume (volume) of the particle gap is such that the volume difference between the state where the particle gap is filled with water and the state where air is present after drying is 3% by volume or less. Preferably there is. If there is a difference in volume (swelling due to moisture) between drying and moisture content, it is necessary to adjust the moisture content at the time of membrane-electrode joining, which not only complicates the joining process, but also the moisture content of the membrane during fuel cell operation. The rate fluctuation causes a large stress on the membrane-electrode assembly, which causes the membrane to peel off from the electrode or cause contact to drop off.

  This volume difference can be obtained from the difference between the dry capacity measured in the dry state and the moisture content when water is filled, but it can be easily obtained from the swelling rate of the dry and wet membranes. It is. In this case, since the particles have a high-density cross-linked structure and do not swell even when they are hydrated, all the swelling may be caused by volume fluctuations in the gaps between the particles. In the proton conductive membrane of the present invention, the swelling ratio due to water content is usually 3% or less, and there is no large volume change even during operation of the fuel cell, and it can be used very well.

  Furthermore, a hydrophilic material or an electrolyte material may be filled in the gaps between the particles. However, generally, when these materials are filled in the gaps between the particles, proton conductivity decreases. However, it is effective in preventing fuel penetration when preventing chemical short circuit due to fuel gas permeation or when direct liquid fuel such as methanol is introduced into the fuel cell. You may do it.

(Solid polymer fuel cell)
A membrane-electrode assembly can be obtained by bonding the proton conductive membrane and the gas diffusion electrode. In addition, the membrane-electrode assembly is used as a unit cell, and a pair of separators serving as fuel and oxygen passages are installed outside the unit cell, and a plurality of adjacent cells are connected to each other, thereby solid polymer fuel cell Can be obtained.

(Proton conductive membrane production method)
Next, the manufacturing method of the proton conductive membrane of this Embodiment is demonstrated.

  There is no particular limitation on the method for producing a proton conductive membrane having a silicon-oxygen crosslinked structure, in which an acid group is introduced on the surface of the particle, and the particle constitutes a continuum. However, it can be manufactured by the following method, for example.

  That is, the proton conductive membrane of the present invention has a mercapto group-containing compound (D) having a mercapto group and a hydrolyzable silyl group covalently bonded to the mercapto group and / or a silanol group. And a first step of preparing a mixture containing the polarity control agent (E), a second step of forming the film, and hydrolyzing the hydrolyzable silyl group contained in the formed mixture And a third step of forming a film constituting a continuum of particles having a silicon-oxygen crosslinked structure by condensing and / or condensing silanol groups, and further oxidizing the mercapto group in the film to sulfonic acid And a fourth step of introducing a sulfonic acid group to the surface of the particle.

  Hereinafter, each step will be described in detail.

5.1 First Step In the first step, a mercapto group-containing compound having a mercapto group and a hydrolyzable silyl group capable of condensation reaction covalently bonded to the mercapto group and / or a silanol group ( A mixture containing D) and a polarity control agent (E) is prepared.

5.1.1 Mercapto group-containing compound (D)
The mercapto group-containing compound (D) is not particularly limited as long as it has a mercapto group and has a hydrolyzable silyl group and / or silanol group that can be condensed and covalently bonded to the mercapto group.

  Examples of the mercapto group-containing compound (D) are shown below, but the present invention is not limited thereto.

Examples of the mercapto group-containing compound (D) include a mercapto group-containing compound (G) represented by the following formula (1).

(Wherein, R7 represents _{H, CH 3, C 2 H} 5, C 3 H 7, or one of the groups of C ₄ H _9, R1 represents a hydrocarbon group having 20 or less carbon atoms, the R2 CH ₃ represents any group of C ₂ H ₅ , C ₃ H ₇ , or C ₆ H ₅ , and n represents an integer of 1 to _3. When n is 1, R 2 may be a mixture of different substituents. Good.)
Here, R1 is not particularly limited as long as it is a hydrocarbon group having 20 or less carbon atoms, but a methylene chain (a chain of —CH ₂ —) containing no aromatic ring or branch is stable against acid and oxidation. It can be preferably used. In particular, those having 3 carbon atoms (that is, R 1 is —CH ₂ CH ₂ CH ₂ —) are preferably inexpensive and easily available. Even if R1 contains a branched structure or an aromatic ring, there is no particular problem as long as it is stable under the operating conditions of the fuel cell.

Further, when R7 is H, the pot life is shortened, so it must be handled with care. When R7 is an alkyl group, the pot life is long, the reaction control is easy, and it can be suitably used. In particular, R7 is CH _3, a C ₂ H easy is inexpensive and available ones _5, can be suitably used.

Alkylene group (R2) may be used each substituent mentioned in the formula (1), R2 is inexpensive and easily available ones CH _3, can be preferably used.

  The ratio of the cross-linking group (OR7) to the alkyl group (R2) can be more stably immobilized on the particles as the cross-linking group increases. On the other hand, by introducing an alkyl group, the flexibility of the proton conductive membrane can be increased. Can be granted. In view of the balance between physical properties and stability, including combinations with other cross-linking agents, the ratio of the cross-linking group to the alkyl group can be appropriately selected, but preferably the number of cross-linking groups is 2 or 3, Those having 3 groups are more preferred because they can be more stably immobilized.

  As the raw material represented by the formula (1), 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-mercaptopropyltripropoxysilane, 3-mercaptopropyltryptoxysilane, 2-mercaptoethyltrimethoxy Silane, 2-mercaptoethyltriethoxysilane, 2-mercaptoethyltripropoxysilane, 2-mercaptoethyltryptoxysilane, mercaptomethyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropylmethyldiethoxysilane, 3-mercaptopropylmethyldipropoxysilane, 3-mercaptopropylmethyldibutoxysilane, 3-mercaptopropylethyldimethoxysilane, 3-mercaptopropylbutyl Silane, 3-mercaptopropyl phenyl dimethoxy silane, but mercaptomethyl methyldiethoxysilane, and the like, the present invention is not limited thereto.

  Among these, 3-mercaptopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.) can be obtained in large quantities and at low cost, and can be preferably used.

Examples of the mercapto group-containing compound (D) include a mercapto group-containing condensate (H) represented by the following formula (2).

(Wherein, R7 represents _{H, CH 3, C 2 H} 5, C 3 H 6, or one of the groups of C ₄ H _9, R1 represents a hydrocarbon group having 20 or less carbon atoms, the R2 OH , OCH ₃ , OC ₂ H ₆ , OC ₃ H ₆ , OC ₄ H ₉ , CH ₃ , C ₂ H ₆ , C ₃ H ₇ , C ₄ H ₉ , C ₆ H ₅ , Represents an integer of 1 to 100. Also, R7 may be -Si, or R2 may be an O-Si bond or a cyclic structure or a branched structure.
This is a condensate of a mercapto group-containing compound (G), and can be obtained, for example, by condensing a mercapto group-containing compound (G). When such a condensate is used, the continuity of the acid is increased, higher conductivity is obtained, and at the same time, the cross-linking group in one molecule is increased, so that the bond stability with the particles is improved and the durability is increased. Performance can be realized.

  R1, R2, and R7 are based on the mercapto group-containing compound (G), and among them, R7 may be -Si, or R2 may be a cyclic structure or a branched structure in which an O-Si bond is formed.

  On the other hand, if the degree of polymerization (m + 1) is 2 or less, effects such as continuation of acid by condensation and increase in cross-linking group are not observed. If it exceeds 100, gelation occurs and it becomes difficult to use as a raw material.

Furthermore, examples of the mercapto group-containing compound (D) include a mercapto group-containing condensate (I) represented by the following formula (3).

(Wherein, R7 represents _{H, CH 3, C 2 H} 5, C 3 H 6, or one of the groups of C ₄ H _9, R1 represents a hydrocarbon group having 20 or less carbon atoms, R2, R8 , R9 are each independently OH, either _{OCH 3, OC 2 H 6,} OC 3 H 6, OC 4 H 9, CH 3, C 2 H 6, C 3 H 7, C 4 H 9, C 6 H 5 N and m each independently represents an integer of 1 to 100. In addition, R7 is a -Si bond, or R2, R8, R9 is a -O-Si bond, May be)
This is a cocondensate of a mercapto group-containing compound (G) and a crosslinking agent (J) described in detail later. Examples of the cross-linking agent (J) include tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetraptoxysilane and the like. Among these, tetramethoxysilane and tetraethoxysilane are general-purpose products, are inexpensive, and are easily available in large quantities, and therefore can be particularly preferably used. Furthermore, methyltrimethoxysilane, phenyltrimethoxysilane, dimethyldimethoxysilane, phenylmethyldimethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, i-propyltrimethoxysilane, n-butyltrimethoxysilane, n Methoxy compounds such as hexyltrimethoxysilane, n-octyltrimethoxysilane, n-undecyltrimethoxysilane, n-dodecyltrimethoxysilane, n-hexadecyltrimethoxysilane, n-octadecyltrimethoxysilane, and the like Copolymers with ethoxy, isopropoxy, butoxy and the like may also be used. This invention is not limited to this, There will be no limitation if it is a compound represented by Formula (3).

R1, R2 and R7 are in accordance with the mercapto group-containing compound (G), and R8 and R9 are in accordance with the basic structure of the crosslinking agent (J). Of these, R7 is bonded to Si in the molecule to form a cyclic structure, or R2, R8, R9 may contain a cyclic structure or a branched structure in which -O-Si bond is formed. If the degree of polymerization (m + n) is less than 2, acid continuation by condensation, increase of crosslinking groups, etc. No effect is seen, and when it exceeds 200, gelation or the like occurs, making it difficult to use as a raw material. Since the mercapto group-containing condensate (I) has a larger adjustment range of substituents than the mercapto group-containing condensate (H), it can be used as a raw material without gelation to a higher degree of polymerization.

  This mercapto group-containing condensate (I) has a high degree of freedom in structural design, introduces a highly crosslinkable structure, makes it more firmly fixed with particles, exhibits stable proton conductivity, and crosslinks. The degree is rather lowered to give flexibility to the film, and various physical properties can be adjusted.

  These mercapto group-containing condensates (H) and (I) can be synthesized by known methods. For example, these methods are disclosed in JP-A-9-40911, JP-A-8-134219, 2002-30149, Journal of Polymer Science Part A: Polymer of Chemistry (Part A: Polymer Chemistry, Vol. 33, pages 751-754, 1995), Journal of Polymer Science Part A: Journal of Polymer Chemistry (Journal) of Polymer Science: Part A: Polymer Chemistry, Vol. 37, pages 1017-1026, 1999) and the like.

  These mercapto group-containing compounds (D) may be used after being previously oxidized with an oxidizing agent used in the fourth step described later. In this case, the fourth step can be omitted.

Furthermore, in the first step, a crosslinking agent (J) represented by the following formula (4) is added. The crosslinking agent (J) is a crosslinking agent capable of generating more silanol per tetramolecular weight contained in the crosslinkable electrolyte (A).

(Wherein, R3 represents an alkyl group having carbon atoms of 20 or less, R10 represents _{OH, OCH 3, OC 2 H} 5, OC 2 H 5, OC 4 H 9, OCOCH 3, or Cl, n is 2 It is an integer of 4.)
Here, the crosslinking agent (J) is not particularly limited as long as it is a structure that forms a Si—O bond, and any structure can be used as long as it is a structure represented by the formula (4). Examples of the cross-linking agent (J) include imidazole, benzotriazole, pyrazine, (3- (4-pyridinyl) propyl) trimethoxysilane, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetrabutoxysilane and the like. It is done. Among these, tetramethoxysilane and tetraethoxysilane are general-purpose products, are inexpensive, and are easily available in large quantities, and therefore can be particularly preferably used. Still further, methyltrimethoxysilane, phenyltrimethoxysilane, dimethyldimethoxysilane, phenylmethyldimethoxysilane, ethyltrimethoxysilane, n-propyltrimethoxysilane, i-propyltrimethoxysilane, n-butyltrimethoxysilane, n- Methoxy compounds such as hexyltrimethoxysilane, n-octyltrimethoxysilane, n-undecyltrimethoxysilane, n-dodecyltrimethoxysilane, n-hexadecyltrimethoxysilane, n-octadecyltrimethoxysilane, and ethoxys thereof Body, isopropoxy body, butoxy body and the like.

  Moreover, you may use the hydrolyzable compound containing titanium and zirconium as a material which plays the role similar to this. Specific examples include titanium methoxide, titanium ethoxide, titanium n-propoxide, titanium i-propoxide, titanium n-ptoxide, titanium i-ptoxide, titanium t-ptoxide, zirconium ethoxide, zirconium n-propoxide, Zirconium i-propoxide, zirconium n-ptoxide, zirconium i-ptoxide, zirconium t-ptoxide, and acetylacetone, acetoacetate, ethanolamine, diethanolamine, triethanolamine complex, and the like.

  When this crosslinking agent (J) is used, it is possible to adjust the crosslinking density and interparticle bond strength of the particles, and the strength and flexibility can be appropriately controlled.

Furthermore, in the first step, a cross-linking agent (K) represented by the following formula (5) may be added.

(Wherein, R10 is _{OH, OCH 3, OC 2 H} 5, OC 3 H 6, OC 4 H 9, OCOCH 3, or represents Cl, R5 represents a carbon atom-containing molecular chain group having from 1 to 30 carbon atoms , R 4 is any group selected from CH ₃ , C ₂ H ₅ , C ₃ H ₇ , C ₄ H ₉ , or C ₆ H ₅ , and n is an integer of 0, 1 or 2 is there.)
Here, R5 in the formula (5) represents a carbon atom-containing molecular chain group having 1 to 30 carbon atoms, and a linear alkylene group is preferable.

  Specific examples of the crosslinking agent (K) having the structure of the formula (5) include imidazole, benzotriazole, pyrazine, (3- (4-pyridinyl) propyl) trimethoxysilane and the like. In addition, 1,2-bis (triethoxysilyl) ethane, 1,6-bis (trimethoxysilyl) hexane, 1,8-bis (triethoxysilyl) octane, 1,9-bis (triethoxysilyl) nonane Applicable, these are commercially available from Gelest. Organic-inorganic composite crosslinking agents (F) having other chain lengths or other hydrolyzable groups are also used as linear hydrocarbons having unsaturated bonds at both ends, such as 1,3- By carrying out hydrosilylation reaction with various alkoxysilanes using platinum complex catalyst on butadiene, 1,9-decadiene, 1,12-dodecadiene, 1,13-tetradecadiene, 1,21-docosadiene, etc. A compound that is a functional compound can be obtained.

  When this crosslinking agent (K) is used, the crosslinking density of the particulate structure can be adjusted, and the strength and flexibility can be appropriately controlled.

5.1.2 Polarity control agent (E)
The polarity control agent (E) is a structure control agent for forming particles, and can be suitably used in the present invention.

  In the proton conductive membrane of the present invention, it is essential that a substance (hydrogen ion or its hydrate) can diffuse and move. Therefore, it is preferable to form a proton conduction path for transporting ions inside the membrane. As described above, this gap plays a role.

  In the proton conductive membrane of the present invention, the polarity control agent (E) is used for the efficient formation of the particles and the gaps between the particles.

  Usually, if an inorganic material such as tetraethoxysilane is similarly hydrolyzed / condensed and heated sufficiently (for example, at 800 ° C.), a glassy dense cross-linked product can be obtained, and a fine equivalent to an ion channel can be obtained. No holes are formed. Such hydrolysis, condensation, and gelation processes (sol-gel reaction) of alkoxysilanes have been studied in detail. For example, Blinker et al. (SOL-GEL SCIENCE) (Academic Press, Inc. 1990). ), “Chemistry of Sol-Gel Method” (Agune Jofusha, 1988). In the sol-gel reaction, particle growth, particle bonding, and densification occur in this order. Detailed analysis of typical alkoxysilane materials has been made, and reaction conditions have been clarified.

  In the proton conductive membrane of the present invention, the alkoxysilane material having a substituent is used as a raw material, and further, it is necessary to control the particle size of particles, control of bonding between particles, and control of the gap of particles accompanying it. As a result of various investigations, the inventors have found that the addition of the polarity control agent (E) enables the formation of particle continuum and the accompanying particle gap control.

  The polarity control agent (E) is an organic liquid and desirably water-soluble. When the solvent is used in the first step (to be described later), it is possible to adjust the solubility of the mercapto group-containing compound (D) in the solvent. Can be controlled. Furthermore, there is an advantage that the membrane can be easily extracted by washing with water.

  Moreover, it is preferable that the polarity control agent (E) has a boiling point of 100 ° C. or higher and a melting point of 25 ° C. or higher.

  If the boiling point of the polarity control agent (E) is too low, it will volatilize during the condensation reaction (mainly performed under heating conditions) when forming the film, and particle size control and particle gap control will not be possible. Sufficient conductivity cannot be ensured. Accordingly, the boiling point of the polarity control agent (E) is preferably at least the boiling point of the solvent when the solvent is used in the first step, particularly preferably at least 100 ° C., more preferably at 150 ° C. As mentioned above, More preferably, it is 200 degreeC or more.

  In addition, when the intermolecular interaction of the polarity control agent (E) is too large, the polarity control agent (E) may solidify and form a large domain other than the gap between the particles. The fuel gas barrier property of the membrane may be lowered. The magnitude of the intermolecular interaction of the polarity control agent (E) is substantially correlated with the melting point, and the melting point can be used as an index. The melting point of the polarity control agent (E) used in the present invention is preferably 25 ° C. or less. When the melting point is 25 ° C. or lower, an appropriate intermolecular interaction can be expected and preferably used, and more preferably 15 ° C. or lower.

  Examples of such organic substances include those having a polar substituent such as a hydroxyl group, an ether group, an amide group, and an ester group, those having an acid group such as a carboxylic acid group and a sulfonic acid group, or salts thereof. Examples thereof include those having a base group such as amine or a salt thereof. Of these, acids, bases and salts thereof are more preferably nonionic since it is necessary to pay attention to the interaction with these catalysts when using catalysts during hydrolysis and condensation. Can be used.

  Specifically, glycerin and its derivatives, ethylene glycol and its derivatives, ethylene glycol polymers (diethylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycols of various molecular weights, etc.), glucose, fructose, mannitol, sorbit, sucrose, etc. Saccharides, polyhydric hydroxyl compounds such as pentaerythritol, water-soluble resins such as polyoxyalkylene, polyvinyl alcohol, polyvinyl pyrrolidone and acrylic acid, carbonates such as ethylene carbonate and propylene carbonate, alkyl sulfur oxides such as dimethyl sulfoxide, Examples include amides such as dimethylformamide, and polyoxyethylene alkyl ethers such as ethylene glycol monomethyl ether, but the present invention is not limited thereto. Not.

  In addition, ethylene glycol (mono / di) alkyl ethers in which part or all of the terminal OHs of these ethylene glycols are alkyl ethers can also be preferably used. Examples of this include ethylene glycol monomethyl ether, dimethyl ether, monoethyl ether, diethyl ether, monopropyl ether, dipropyl ether, monobutyl ether, diptyl ether, monopentyl ether, dipentyl ether, monodicyclopentenyl ether, monoglycidyl. Examples include ether, diglycidyl ether, monophenyl ether, diphenyl ether, and monovinyl ether divinyl ether. Further, part or all of the terminal OH of ethylene glycol may be an ester. Examples thereof include ethylene glycol monoacetates and diacetates.

  In the case where an acid and a salt thereof may be used, an acid such as acetic acid, propionic acid, dodecyl sulfuric acid, dodecyl sulfonic acid, benzene sulfonic acid, dodecyl benzene sulfonic acid, toluene sulfonic acid, and salts thereof may be used. In addition, when salts thereof may be used, ammonium salts such as trimethylbenzylammonium chloride, amines such as N, N-dimethylbenzylamine, and salts thereof are exemplified. Furthermore, zwitterionic compounds such as amino acids such as sodium glutamate can also be used.

  Although it is possible to use an inorganic salt or the like as the polarity control agent (E), generally, the inorganic salt has a strong cohesive force (high melting point) and is added to the mixture containing the mercapto group-containing compound (D). However, it is difficult to finely disperse at the molecular level, resulting in large crystals or amorphous solids, and there is a high possibility of forming large aggregates that are disadvantageous to film physical properties and gas barrier properties.

  In the present invention, other ionic surfactants can be suitably used, and anionic, cationic, and amphoteric surfactants can also be used in consideration of the interaction with the catalyst.

Among these, polyoxyalkylene which is a liquid water-soluble organic substance and has appropriate compatibility (or appropriate incompatibility) with the mercapto group-containing compound (D) is preferable, and among them, a polymer of ethylene glycol is particularly preferable. It can be preferably used. These polyoxyalkylenes can be represented by the following general formula.

  Such polymers of ethylene glycol are widely available from dimers (diethylene glycol) to polyethylene glycols of various molecular weights, and the compatibility, viscosity, molecular size, etc. can be appropriately selected and can be preferably used. In particular, in the present invention, diethylene glycol having a molecular weight of about 100 to polyethylene glycol having an average molecular weight of 600 can be more preferably used, and tetraethylene glycol or polyethylene glycol having a molecular weight of about 200 can be particularly preferably used.

  The size of the particles and the gap between the particles is such that the compatibility with the mercapto group-containing compound (D), the compatibility balance with the entire film-forming raw material system including the solvent and additives, and the polarity control agent (E) Determined by molecular weight and blending amount. In the case of the present invention, there is a correlation between the average molecular weight of the polarity control agent (E) and the diameter of the gap between particles, and when polyethylene glycol having a molecular weight of more than 600 is used, the diameter becomes large and gas barrier properties and physical properties decrease. On the other hand, if the molecular weight is less than 100, the film has a small diameter and becomes too dense, and there is a tendency that sufficient particle gaps are not formed.

  The amount of the polarity control agent (E) added depends on the type and molecular weight of the polarity control agent (E) to be used and the structure of the film. D) Add 3 to 150 parts by weight per 100 parts by weight. If the amount is less than 3 parts by weight, the effect of controlling the particle diameter and the particle gap is hardly observed. If the amount exceeds 150 parts by weight, the particle gap becomes too large, the film becomes brittle, and gas permeation becomes remarkable. Probability is high.

  As described above, the proton conductive membrane of the present invention can be designed and formed with a custom-made structure of the gap between particles, that is, the proton conduction path, by using the polarity control agent (E). A film having a good balance with various film properties such as permeability and film strength can be formed. This is a point that is different from a conventional sulfonated fluororesin membrane in which the proton conduction path is uniquely determined by the molecular structure.

  In addition, since the proton conduction path controlled in this way does not deform even in a high temperature / high humidity environment, stable operation is possible even when the fuel cell is operated at a high temperature.

5.1.3 Mixing method As described so far, the mercapto group-containing compound (D), the polarity control agent (E), and the optional cross-linking agents (J) and (K) are appropriately adjusted and used. Accordingly, various physical properties such as proton conductivity, heat resistance, durability, and film strength can be adjusted.

  Here, when adding the optional cross-linking agents (J) and (K), the amount of addition varies depending on the composition and process of each material, but it cannot be said unconditionally, but typical values include mercapto groups The total addition amount of (J) and (K) is 900 parts by weight or less with respect to 100 parts by weight of the compound (D).

  If a cross-linking agent in an amount exceeding this is added, the surface acid group concentration of the particles decreases, and proton conductivity may decrease.

  When preparing these mixtures, you may use a solvent. The solvent to be used is not particularly limited as long as the respective materials can be uniformly mixed. In general, alcohol solvents such as methanol, ethanol, 1-propanol, 2-propanol, and t-ptanol, and ether solvents such as tetrahydrofuran and 1,4-dioxane can be preferably used.

  Although there is no restriction | limiting in particular about the ratio of a solvent, Usually, the density | concentration whose solid content concentration is about 90 to 10 weight% can be used preferably.

  Further, as described later, the catalyst (F) may be mixed at the same time in this step.

  Further, water necessary for hydrolysis may be added. Water is usually added in an equimolar amount with respect to the hydrolyzable silyl group, but may be added in a large amount to accelerate the reaction, or may be added in a small amount to suppress the reaction.

  For mixing, a known method such as stirring and vibration may be used, and there is no particular limitation as long as sufficient mixing is possible. Moreover, you may perform a heating, pressurization, defoaming, deaeration, etc. as needed.

  Further, in the first step, a reinforcing material, a softening agent, a dispersing agent, a reaction accelerator, a stabilizer, a colorant, an antioxidant, an inorganic or organic filler, etc., within a range not impairing the object of the present invention. Other optional ingredients can be added.

5.2 Second Step In the method for producing a proton conductive membrane of the present invention, the second step is a step of forming (forming a film) the mixture obtained in the first step into a film.

  In order to form the mixture obtained in the first step into a film, a known method such as casting, coating, or casting can be used. The method for forming the film is not particularly limited as long as a uniform film can be obtained. The thickness of the film is not particularly limited, but can be formed to have an arbitrary thickness between 10 μm and 1 mm. The proton conductive membrane for a fuel cell is appropriately determined from the proton conductivity, fuel barrier properties, and mechanical strength of the membrane, and usually a membrane having a thickness of 20 to 300 μm can be preferably used. The thickness of the proton conductive membrane of the invention is also produced according to this.

  Moreover, when performing this film-forming process, you may add support bodies and reinforcements, such as a fiber, a mat | matte, and a fibril, and you may impregnate these support bodies. These supports and reinforcing materials can be appropriately selected from glass materials, silicone resin materials, fluororesin materials, cyclic polyolefin materials, ultrahigh molecular weight polyolefin materials and the like in consideration of heat resistance and acid resistance. The impregnation method is not limited to a dipping method, a potting method, a roll press method, a vacuum press method, or the like, and a known method may be used, and heating, pressurization, or the like may be performed.

5.3 Third Step In the method for producing a proton conductive membrane of the present invention, the third step includes hydrolyzing and condensing a hydrolyzable silyl group contained in the membrane formed in the second step. And / or a process of forming a film having a continuum of particles composed of a silicon-oxygen crosslinked structure by condensing silanol groups.

  The proton conductive membrane in the present invention is characterized in that a crosslinked structure is formed by hydrolysis and condensation of an alkoxysilyl group or the like, stably exhibits proton conductivity even at high temperatures, and has little shape change. Such generation of Si—O—Si bonds by hydrolysis or condensation of alkoxysilyl groups or the like is well known as a sol-gil reaction.

  In the sol-gel reaction, a catalyst is usually used for accelerating and controlling the reaction. As the catalyst, an acid or a base is usually used.

5.3.1 Catalyst (F)
The catalyst (F) used in the method for producing a proton conductive membrane of the present invention may be an acid or a base.

  When an acid catalyst is used, a Prinsted acid such as hydrochloric acid, sulfuric acid, phosphoric acid or acetic acid is used. The type, concentration, etc. of the acid are not particularly limited as long as it is within the available range. Among these, acetic acid can be suitably used since it has a relatively small amount of acid remaining after the reaction. When hydrochloric acid is used, the concentration and the like are not particularly limited, but those of 0.01 to 12N are usually used.

  In general, it is known that when an acid is used, hydrolysis and condensation compete to form a linear crosslinked structure with few branches.

  On the other hand, when a base is used as a catalyst, it is known that a dendritic structure with many branches is obtained because hydrolysis occurs at once. In the present invention, any method can be used in consideration of film physical properties, but a base catalyst is preferably used in order to highlight the characteristics of the present invention such as formation of particles and continuums thereof. it can.

  As the base catalyst, an aqueous solution of sodium hydroxide, potassium hydroxide, ammonia or the like can be used. Among these, ammonia that does not produce a residual salt can be preferably used. Furthermore, organic amines can also be preferably used in consideration of compatibility with the mercapto group-containing compound (D).

  Organic amines can be used without any particular limitation, but usually those having a boiling point of 50 ° C. or higher are preferably used. Specific examples of organic amines within this range that are readily available include triethylamine, dipropylamine, and isobutyl. Examples thereof include amine, diethylamine, diethylethanolamine, triethanolamine, pyridine, piperazine, and tetramethylammonium hydroxide, and any of them can be suitably used.

  Further, fluorides such as potassium fluoride, ammonium fluoride, tetramethylammonium fluoride, and tetraethylammonium fluoride may be used as the condensation catalyst.

  The addition amount of the catalyst can be arbitrarily set, and is appropriately determined taking into consideration the reaction rate, compatibility with the film material, and the like.

  The step of introducing the catalyst may be any timing from the first step to the third step. The simplest method is the method introduced when preparing the mixture in the first step. In this case, it is necessary to take into consideration the pot line and the set time in the film formation which is the second step.

5.3.1 Condensation reaction Although the condensation reaction can be performed at room temperature, it is better to heat in order to shorten the reaction time and perform more efficient curing. Heating may be performed by a known method, and heating by an oven, pressure heating by an autoclave, far infrared heating, electromagnetic induction heating, microwave heating, or the like can be used. Heating can be performed at any temperature from room temperature to 300 ° C., preferably 100 to 250 ° C. At this time, heating may be performed under an inert gas or the like under reduced pressure, nitrogen, or argon.

  In addition, a method of avoiding a sudden environmental change, such as heating after curing for some time at room temperature and then gradually raising the temperature to a high temperature, may be employed.

  Further, it may be carried out under steam in order to replenish water necessary for hydrolysis, and may be carried out under solvent vapor in order to prevent rapid membrane drying.

The membrane that has undergone the third step may be washed with water to remove unreacted substances and effect catalysts, if necessary, and may further be subjected to ion exchange with sulfuric acid or the like. 5.4 Fourth Step The proton conductive membrane of the present invention In the production method, the fourth step is a step of oxidizing the mercapto group in the film to form a sulfonic acid group and introducing the sulfonic acid group to the surface of the particle.

  As described above, the membrane may be washed with water prior to oxidation. Further, when organic amines are used as a catalyst, the membrane is contacted with an acid such as hydrochloric acid or sulfuric acid prior to oxidation, and the catalyst is May be removed.

  The water used for washing is preferably water containing no metal ions, such as distilled water or ion exchange water. In washing with water, heating may be performed, and washing with water may be made more efficient by applying pressure or vibration. Furthermore, in order to promote the penetration into the membrane, a mixed solvent in which methanol, ethanol, n-propanol, i-propanol, acetone, tetrahydrofuran or the like is added to water may be used.

  The mercapto group oxidation method used in the present invention is not particularly limited, but a general oxidizing agent can be used. Specifically, for example, as described in a new experimental chemistry course (Maruzen, 3rd edition, Vol. 15, 1976), nitric acid, hydrogen peroxide, oxygen, organic peracid (percarboxylic acid), bromine Oxidizing agents such as water, hypochlorite, hypobromite, potassium permanganate, and chromic acid can be used.

  Among these, hydrogen peroxide and organic peracids (peracetic acid and perbenzoic acids) can be suitably used because they are relatively easy to handle and the oxidation yield is good.

  Furthermore, in order to protonate the sulfonic acid group in the membrane obtained by oxidation, it may be contacted with a strong acid such as hydrochloric acid or sulfuric acid. In this case, protonation conditions such as acid concentration, immersion time, and immersion temperature are appropriately determined depending on the sulfonic acid group-containing concentration in the membrane, the porosity of the membrane, the affinity with the acid, and the like. A typical example is a method of immersing the film in 1N sulfuric acid at 50 ° C. for 1 hour.

  The oxidized film is preferably washed with water to remove the oxidizing agent in the film.

  Furthermore, the oxidized film may be subjected to acid treatment with hydrochloric acid, sulfuric acid or the like. It can be expected that impurities and unnecessary metal ions in the film are washed away by the acid treatment. It is preferable to perform water washing after the acid treatment.

  The production method described above is an example. For example, silica or metal oxide particles having a preferable average particle diameter are prepared in advance, and a mercapto group-containing compound (D) is used as a silane coupling agent on these surfaces. A method of oxidizing after surface treatment is also possible. However, it is difficult to obtain stable performance by such a surface treatment method, and it is difficult to perform surface treatment at a high concentration, and it is preferable as a method for producing a proton conductive membrane to use the method described in the present invention. .

(Function and effect)
The proton conductive membrane according to this embodiment includes a crosslinkable electrolyte (A) having an acid group and a crosslink structure by a silicon-oxygen bond, and the unreacted hydroxyl terminal of the crosslinkable electrolyte (A) is a silylating agent ( B). For this reason, the number of silanol groups is intentionally increased, that is, the points to be silylated are increased.

  In this way, the surface of the proton conducting membrane is modified by reacting with a silylating agent on the unreacted silanol (HO-Si) end in the vicinity of the surface of the proton conducting membrane. Can be granted. Specifically, high impact resistance and high polar solvent resistance are improved by imparting a silyl group having large steric hindrance and strong hydrophobicity.

  Conventionally, since an organosilicon compound is not thermoplastic, it cannot be bonded to a Nafion electrode, which is a thermoplastic resin, by hot pressing (heating pressing). As a result, the adhesiveness with the Nafion electrode decreased, the interelectrode contact resistance increased, and the high proton conductivity was lost. In addition, attempts have been made to improve the adhesion by putting an electrolyte between the electrodes, but high proton conductivity could not be maintained.

  In the present invention, by modifying the electrolyte surface by silylation with, for example, fluorine-based silane, sufficient adhesiveness by hot pressing can be realized, and high proton conductivity can be maintained.

  Therefore, according to the proton conductive membrane according to the present embodiment, high proton conductivity, high impact resistance, and high polar solvent resistance can be realized.

  The crosslinkable electrolyte (A) preferably has a silicon-oxygen bond ratio of 70% or more and 98% or less. When the silicon-oxygen bond rate is 70% or more, it has a strong bond energy and can improve chemical stability, heat resistance and oxidation resistance. Further, when the silicon-oxygen bond rate is 98% or less, the effect of the introduced silyl group appears sufficiently remarkably, and flexibility at high temperature can be imparted.

  Moreover, it is preferable that the molecular weight of the silyl group added to the hydroxyl group by being treated with the silylating agent (B) is 150 or more. When the molecular weight of the silyl group added to the hydroxyl group is 150 or more, high proton conductivity, high impact resistance, and high polar solvent resistance due to silylation can be further improved.

  In the proton conductive membrane according to the first feature, the silyl group added to the hydroxyl group by being treated with the silylating agent (B) preferably contains a hetero atom as a constituent atom. Moreover, it is preferable that a hetero atom contains any one of a fluorine atom, a nitrogen atom, an oxygen atom, or a sulfur atom.

  In the proton conductive membrane according to the first feature, the crosslinkable electrolyte (A) contains an organic-inorganic composite structure that is covalently bonded to a plurality of silicon-oxygen bridges and contains carbon atoms, and the carbon atoms % By weight is preferably 10% or more and 50% or less. Since the weight% of carbon atoms is 10% or more, flexibility at high temperature is imparted, and adhesion to the electrode can be more effectively improved by the introduced silyl group. Moreover, since the weight% of carbon atoms is 50% or less, swelling by a polar solvent can be suppressed while maintaining high chemical stability, heat resistance, and oxidation resistance.

  In order to describe the present invention in more detail, examples will be given below, but the present invention is not limited to these examples.

(Example 1)
33.0 g of 3-mercaptopropyltrimethoxysilane, 131.2 g of tetraethoxysilane, and 26.5 g of methanol were weighed in a flask and stirred at 0 ° C. for 10 minutes. A solution obtained by mixing 15.6 g of 0.01N hydrochloric acid and 20.8 g of methanol was added thereto, stirred at 0 ° C. for 1 hour, heated to 40 ° C., and further stirred for 2 hours. Next, a solution obtained by mixing 0.114 g of potassium fluoride and 29.7 g of methanol was added, stirred at 40 ° C. for 1 hour, heated to 80 ° C., and further stirred for 2 hours. The mixed solution was cooled to 0 ° C, and then the alcohol was fractionally distilled at 40 ° C in vacuum. The obtained solution was cooled to 0 ° C., 200 mL of diethyl ether was added, and the mixture was stirred at 0 ° C. for 10 minutes, followed by filtration using a membrane filter (MILLIPORE, Omnipore membrane pore size 0.2 μm). Diethyl ether was fractionally distilled from the obtained filtrate at 40 ° C. under vacuum to obtain an ion-crosslinkable mercapto group-containing silane oligomer as shown in FIG.

  0.11 g of water and 0.05 g of triethylamine were added dropwise to a solution obtained by mixing 5.86 g of the obtained ion-crosslinkable mercapto group-containing silane oligomer and 0.51 g of tetraethoxysilane. After stirring at room temperature for 10 minutes, this solution was impregnated into a polyethylene porous membrane on a fluororesin film. The impregnated film was covered with a fluororesin film, and the film was leveled with an applicator from above. After curing for 80 hours at room temperature with the fluororesin film covered, the film was peeled off and further cured for 24 hours at room temperature. The cured film was sandwiched between two glass plates through a fluororesin film, put in this state with 500 mL of water in a glass container, and heat cured at 80 ° C. for 24 hours using a gear oven.

  The film obtained by baking was immersed in peracetic acid prepared by mixing 125 mL of acetic acid and 100 mL of 30% hydrogen peroxide solution, and heated at 60 ° C. for 1 hour on a hot plate. The obtained film was taken out from the peracetic acid solution and immersed in 80 ° C. water twice for 1 hour each to sufficiently remove the peracetic acid solution to obtain a translucent film.

  Immerse the membrane in a solution containing 5 g of 3,3,4,4,5,5,6,6,6-nonafluorohexylmethyldichlorosilane, 10 g of N, N-diisopropylethylamine and 100 mL of dimethylformamide. And heated on a hot plate at 60 ° C. for 1 hour.

  After washing with 1M sulfuric acid solution at room temperature, it was washed with purified water to obtain a translucent film. This was used as a proton conductive membrane.

(Comparative Example 1)
In Example 1, a mercapto group-containing silane oligomer was synthesized in the same manner from 53.0 g of 3-mercaptopropyltrimethoxysilane and 131.2 g of tetraethoxysilane, and 4.37 g of the oligomer was used, and the subsequent silylation step was not performed. A proton conducting membrane as shown in FIG. 1 was prepared in the same manner except that.

(Comparative Example 2)
A commercially available Nafion 117 (manufactured by DuPont) as shown in FIG. 5 was used as the proton conductive membrane.

(Evaluation)
(1) Evaluation of proton conductivity In a conventional electrochemical cell obtained by the production method of the present invention (for example, the same as that described in FIG. 3 in JP-A-2002-184427) The proton conductive membrane and the platinum plate were brought into close contact with each other. The platinum plate was connected to an electrochemical impedance measuring device (1260 type, manufactured by Solartron), and impedance measurement was performed in a frequency range of 0.1 Hz to 100 kHz to evaluate the proton conductivity of the ion conductive membrane.

  In the above measurement, the sample was supported in an electrically insulated sealed container, and the cell temperature was changed from room temperature to 160 ° C. with a temperature controller in a water vapor atmosphere (95 to 100% RH). The proton conductivity was measured at

(2) Methanol permeability evaluation Methanol permeability coefficient (hereinafter referred to as “MCO”) was measured by the following method.

First, using two circular cells having a circular window with a diameter of 2 cm, sandwiching a proton conductive membrane through a rubber packing at the window part, putting pure methanol into one cell and pure water into the other cell, The mixture was stirred with a stirrer at 25 ° C. for 1 hour. Thereafter, the concentration X (% by weight) of methanol permeated to the pure water side was measured by gas chromatography, and MCO was calculated by the following equation.

(3) Impact resistance evaluation The proton conductive membrane was cut into a square having a side of 10 cm, immersed in pure methanol, and allowed to stand at 25 ° C. for 12 hours. Then, it heated at 60 degreeC for 1 hour, cooled again to 25 degreeC, and left to stand for 12 hours. After removing the proton conductive membrane from pure methanol and removing the liquid on the surface, the dimensions were quickly measured, and the average of four sides of the value obtained by dividing the post-immersion dimension by the pre-immersion dimension and multiplying by 1 and multiplying by 100 The value was expressed as a dimensional swelling rate.

(4) Polar Solvent Resistance Evaluation A proton conductive membrane was cut into a square having a side of 5 cm, immersed in 100 mL of pure methanol filled in a sample bottle, and kept at 60 ° C. After 100 hours, the immersed proton conductive membrane was taken out. After drying, the weight loss by immersion is divided by the weight before immersion to calculate the methanol weight reduction rate. The value obtained by subtracting the methanol weight reduction rate from 1 and multiplying by 100 is defined as the methanol weight retention rate. Expressed as a sex indicator.

(5) Adhesion of Nafion electrode After cutting the proton conductive membrane into a square with 5cm sides, wetting it thoroughly with water and holding it in water, sandwiching the membrane with Nafion electrodes with 2.5cm square on one side, precision press Using a machine, pressing was performed under conditions of 140 ° C. and 1 kN for 3 minutes to obtain a membrane-electrode assembly.

The electrode on one side is fixed with double-sided tape, and the side 75 mm ² of the electrolyte membrane is peeled off at a rate of 1 cm / sec using a 90 ° peel tester, and the adhesion strength between the electrode and membrane is the same as that of the Nafion membrane-Nafion. The ratio divided by the strength obtained with the electrode assembly was used as an index of Nafion electrode adhesion.

(result)
The results are shown in Table 1.

  As shown in Table 1, it was found that the proton conductive membrane obtained in Example 1 maintained high proton conductivity as compared with Comparative Example 1 and Comparative Example 2. The proton conducting membrane obtained in Example 1 showed a very low methanol permeability coefficient, whereas the proton conducting membrane of Comparative Example 2 had a relatively high methanol permeability coefficient.

  In addition, it was found that the proton conductive membrane obtained in Example 1 had higher impact resistance than Comparative Example 1 and Comparative Example 2. Moreover, it was found that the proton conductive membrane obtained in Example 1 was equivalent to Comparative Example 1 and had higher local solvent resistance than Comparative Example 2. Moreover, it was found that the proton conductive membrane obtained in Example 1 was equivalent to Comparative Example 2 and had stronger electrode adhesion than Comparative Example 1. Thus, it was found that the proton conductive membrane according to Example 1 achieves high impact resistance and high polar solvent resistance while maintaining high proton conductivity. Furthermore, it was found that the proton conductive membrane according to Example 1 showed a very low methanol permeability coefficient and had strong electrode adhesion.

It is a schematic diagram which shows the structure of the proton conductive membrane which concerns on this embodiment. It is a figure for demonstrating the proton conductive membrane surface concerning this embodiment. It is an example of the structural formula of the silicifying agent (B) which concerns on this embodiment. It is an example of the structural formula of the silyl group which contains the hetero atom which concerns on this embodiment as a constituent atom. 4 is a structural formula of a proton conductive membrane according to Comparative Example 2.

Explanation of symbols

1 Fine particles composed of silicon-oxygen crosslinked structure 2 Gaps

Claims (8)

A proton conductive membrane comprising a crosslinkable electrolyte (A) having an acid group and a crosslinked structure by a silicon-oxygen bond,
A proton conductive membrane, wherein the unreacted hydroxyl terminal of the crosslinkable electrolyte (A) is treated with a silylating agent (B).   2. The proton conductive membrane according to claim 1, wherein the crosslinkable electrolyte (A) has a silicon-oxygen bond ratio of 70% to 98%.   The proton conductive membrane according to claim 1 or 2, wherein the molecular weight of the silyl group added to the hydroxyl group by being treated with the silylating agent (B) is 150 or more.   The proton conductivity according to any one of claims 1 to 3, wherein the silyl group added to the hydroxyl group by being treated with the silylating agent (B) contains a hetero atom as a constituent atom. film.   5. The proton conductive membrane according to claim 4, wherein the heteroatom contains at least one of a fluorine atom, a nitrogen atom, an oxygen atom, and a sulfur atom.   The crosslinkable electrolyte (A) contains an organic-inorganic composite structure that is covalently bonded to a plurality of silicon-oxygen bridges and contains carbon atoms, and the weight% of the carbon atoms is 10% or more and 50% or less. The proton conductive membrane according to any one of claims 1 to 5, wherein A membrane-electrode assembly in which gas diffusion electrodes are bonded to both sides of a proton conductive membrane,
The proton conductive membrane includes a crosslinkable electrolyte (A) having an acid group and a crosslink structure by a silicon-oxygen bond,
The membrane-electrode assembly, wherein the unreacted hydroxyl terminal of the crosslinkable electrolyte (A) is treated with a silylating agent (B). A polymer electrolyte fuel cell comprising a membrane-electrode assembly in which gas diffusion electrodes are bonded to both sides of a proton conductive membrane,
The proton conductive membrane includes a crosslinkable electrolyte (A) having an acid group and a crosslink structure by a silicon-oxygen bond,
A polymer electrolyte fuel cell, wherein an unreacted hydroxyl terminal of the crosslinkable electrolyte (A) is treated with a silylating agent (B).

Images