JP2002289051A - Manufacturing method for proton conductive membrane and proton conductive membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-temperature-activated solid polymer complex electrolyte membrane, a membrane/electrode junction, and a fuel cell, which have superior durability and are low cost. SOLUTION: A hydrated metal oxide represented by hydrated tungstic oxide, tin oxide, etc., is employed as a proton carrier, and a heat resistant polymer membrane obtained by chemically modifying organic polymer, or organic molecule and inorganic molecule, at nano-level is employed as a matrix material for forming a membrane. The hydrated metal oxide is made to complex the heat resistant polymer membrane to form an electrolyte membrane. Thus, as the purpose of this invention, the solid polymer electrolyte with conductivity and durability sufficient for practical use and producible in low cost can be provided, and the complex electrolyte membrane retaining sufficiently high ion conductivity even in a high temperature range of approximately 150 deg. can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a fuel cell, water electrolysis,
The present invention relates to a low-cost, high-durability composite electrolyte membrane of an inorganic substance and an organic polymer having excellent oxidation resistance and the like, which is suitable for a proton-conductive electrolyte membrane used for a humidity sensor, a gas sensor, and the like.

[0002]

2. Description of the Related Art A solid polymer electrolyte is a solid polymer material having an electrolyte group such as a sulfonic acid group in a polymer chain, and is capable of firmly binding to a specific ion or selectively forming a cation or anion. Because it has the property of transmitting, particles,
It is formed into fibers or membranes and is used for various applications such as electrodialysis, diffusion dialysis, battery membranes, and electrolyte membranes for sensors.

A solid polymer electrolyte fuel cell is provided with a pair of electrodes on both sides of a proton conductive solid polymer electrolyte membrane,
Hydrogen gas obtained by reforming low molecular hydrocarbons such as methane and methanol is supplied as fuel gas to one electrode (fuel electrode), and oxygen gas or air is used as an oxidant to the other electrode (air electrode). To obtain power. Water electrolysis is a method for producing hydrogen and oxygen by electrolyzing water using a solid polymer electrolyte membrane.

[0004] In fuel cells and water electrolysis, DuPont, Dow and
Fluoride-based electrolyte membranes represented by perfluorocarbon sulfonic acid membranes proposed by Asahi Kasei and Asahi Glass have excellent chemical stability, and are therefore used as electrolyte membranes used under severe conditions.

[0005] Salt electrolysis is performed by electrolyzing an aqueous sodium chloride solution using a solid polymer electrolyte membrane.
This is a method for producing sodium hydroxide, chlorine and hydrogen. In this case, since the solid polymer electrolyte membrane is exposed to chlorine and a high-temperature, high-concentration aqueous sodium hydroxide solution, it is not possible to use a hydrocarbon-based electrolyte membrane having poor resistance to these. Therefore, the solid polymer electrolyte membrane for salt electrolysis is generally durable against chlorine and high-temperature, high-concentration aqueous sodium hydroxide, and is partially applied to the surface to prevent back diffusion of generated ions. A perfluorosulfonic acid membrane having a carboxylic acid group introduced thereinto is used.

Meanwhile, a fluorine-based electrolyte typified by a perfluorosulfonic acid membrane has a very high chemical stability due to having a C—F bond, and is used for the above-mentioned fuel cell.
In addition to solid polymer electrolyte membranes for water electrolysis or salt electrolysis, they are also used as solid polymer electrolyte membranes for hydrohalic acid electrolysis.Furthermore, utilizing proton conductivity, humidity sensors, gas sensors, oxygen sensors It is widely applied to concentrators and the like.

However, the fluorine-based electrolyte has a drawback that the production process is complicated and very expensive. Further, even if it is said that it has high heat resistance, the heat resistance limit does not exceed 100 ° C. For this reason, fluorine-based electrolyte membranes are used for special applications such as solid-state or military solid-state polymer fuel cells, and are used as low-pollution power sources for automobiles. When reforming low-molecular hydrocarbons into hydrogen gas as a raw fuel for use in portable power sources, etc., it is necessary to cool the reformed gas or remove carbon monoxide in the reformed gas This was a factor that complicated the system. In addition, there are problems such as low proton conductivity due to low operating temperature limit of the electrolyte membrane, large polarization caused by the electrode reaction rate, and complicated water management due to operation in the two-phase region of water. This has hindered the feasibility of this fuel cell.

Therefore, various attempts have hitherto been made to obtain a solid polymer electrolyte membrane having oxidation resistance deterioration characteristics equal to or higher than that of the fluorine-based electrolyte membrane and which can be manufactured at low cost. For example, JP-A-9-102322 discloses a main chain made by copolymerization of a fluorocarbon vinyl monomer and a hydrocarbon vinyl monomer, and a hydrocarbon side chain having a sulfonic acid group. Sulfonic acid type polystyrene-graft-ethylenetetrafluoroethylene copolymer (ETFE) membranes have been proposed. JP-A-9-102322
The sulfonic acid type polystyrene-graft-ETFE membrane disclosed in Japanese Patent Application Publication No. H06-27139 is inexpensive, has sufficient strength as a solid polymer electrolyte membrane for fuel cells, and has a conductivity by increasing the amount of sulfonic acid groups introduced. It is possible to improve. However, the sulfonic acid type polystyrene-graft-ETFE membrane has a high oxidation resistance property of a main chain portion formed by copolymerization of a fluorocarbon vinyl monomer and a hydrocarbon vinyl monomer. The chain portion is a hydrocarbon polymer that is susceptible to oxidative degradation. Therefore, when this is used for a fuel cell, there is a problem that the oxidation deterioration resistance of the whole membrane is insufficient and the durability is poor.

Further, US Pat. No. 4,012,303 and US Pat. No. 4,605,685 disclose that α, β, β-trifluorostyrene is added to a film formed by copolymerizing a fluorocarbon vinyl monomer and a hydrocarbon vinyl monomer. Sulfonic acid type poly (trifluorostyrene) obtained by graft polymerization and introducing a sulfonic acid group into a solid polymer electrolyte membrane
-Graft-ETFE membranes have been proposed. This is based on the premise that the chemical stability of the polystyrene side chain into which the sulfonic acid group is introduced is not sufficient, and instead of styrene, partially fluorinated α, β, β-trifluoro is used. It uses styrene. However, since α, β, β-trifluorostyrene, which is a raw material for the side chain portion, is difficult to synthesize, when considering application as a solid polymer electrolyte membrane for a fuel cell, the aforementioned Nafion There is a problem that the cost is high as in the case of (1).
Further, α, β, β-trifluorostyrene has a low polymerization reactivity, so that a small amount can be introduced as a graft side chain,
There is a problem that the conductivity of the obtained film is low. In addition, the above-mentioned membrane has a relatively low glass transition point, and since the sulfonic acid group is an ion-conducting site, the ionic conductivity of the membrane is greatly reduced when the relative humidity is reduced in an environment having a high water vapor pressure exceeding 100 ° C. There is a problem that the device cannot be used essentially in a device operating in a high temperature region because of its lowering.

[0010]

The problem to be solved by the present invention is the heat resistance limit of the conventional fluorine-based electrolyte membrane.
Provided is a low-cost proton conductive membrane that maintains stable proton conductivity and mechanical strength even at a temperature of 00 ° C. or higher.

[0011]

Means for Solving the Problems In order to achieve the above object, the present inventors have paid attention to an inorganic proton conductive material and have intensively studied an electrolyte membrane in which the material is combined with a heat-resistant organic polymer material. . As a result, a metal oxide hydrate represented by a hydrate of tungsten oxide or tin oxide as a proton carrier and an organic polymer having high heat resistance and acid resistance as a matrix material for forming a film are combined to form an electrolyte. By forming a film, it is equivalent to or more than the fluorine-based electrolyte intended for the present invention, or has practically sufficient deterioration resistance,
In addition, it has been found that a highly durable proton conductive electrolyte membrane that can be manufactured at low cost can be provided. Furthermore, upon producing an electrolyte membrane, a solution of a compound or a plurality of compounds to be a precursor of an inorganic proton conductor, a liquid mixture containing at least an organic monomer or a polymer was formed into a film, and this was cured or crosslinked. Later, they found a method of forming an inorganic solid proton conductor in a membrane by treating the precursor of the inorganic proton conductor with a solution or gas containing a drug for converting the precursor into a proton conductor. By adopting such a method, it is possible to finely and uniformly disperse the matrix material and the inorganic solid proton conductor that form an incompatible film, and it is possible to increase the dispersion concentration.
The inventors have invented that a composite electrolyte membrane of an inorganic proton conductor and an organic polymer having sufficiently high ionic conductivity can be realized even in a high temperature range of about the same level.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail below.

[0013] The proton conductive membrane according to the present invention forms a liquid mixture containing at least a solution of one or more compounds as precursors of an inorganic proton conductor, an organic monomer or a polymer, and cures or hardens the mixture. After the crosslinking, the precursor of the inorganic proton conductor is treated with a solution or gas containing an agent for converting the precursor into a proton conductor, thereby forming an inorganic solid proton conductor in the membrane. . Tungsten oxide hydrate, tin oxide hydrate or tungsten oxide hydrate doped with niobium can be used as the inorganic proton conductor functioning at 100 ° C. or higher in the present invention, A single component of these proton conductors or a mixture of a plurality of components can be used. The material for forming the organic polymer film is not particularly limited as long as it has heat resistance, acid resistance, and flexibility, but a polyimide material, an epoxy material, and a polyether acrylate material are preferable materials. . In preparing the proton conductive membrane, the precursors of the proton conductor include chlorides, sulfates, various alkoxides, and organic acids and amine complexes, and are compatible with the above-described organic polymer membrane precursors. Those with are selected. The proton conductive electrolyte membrane is composed of 1) a solution of an organic polymer material or a precursor solution serving as a matrix, a proton conductor precursor having compatibility with the solution, and, if necessary, an appropriate dispersant. 2) adding a curing agent or a polymerization catalyst to the homogeneous mixed system, 3) casting the uniform mixed system into a film, and forming a film. It is produced through a step of converting a proton conductor precursor into an oxide hydrate. In the step of forming a film, there is no particular limitation as long as the organic polymer film has sufficient strength and flexibility, and reactions such as thermosetting, cross-linking polymerization, and photopolymerization depending on the characteristics of the organic polymer film precursor are performed. Is selected. The conversion to the proton conductor precursor is tungsten oxide hydrate,
The purpose is to obtain an oxide hydrate such as a tin oxide hydrate or a tungsten oxide hydrate doped with niobium in a tungsten oxide hydrate. When the precursor is chloride, sulfate, or each alkoxide, hydrolysis with an acidic aqueous solution or an alkaline aqueous solution is performed. When the precursor is an organic acid complex or a hydrogen peroxide complex, a relatively low temperature of 40 to 100 ° C. It is effective to use a method in which thermal decomposition is performed in a region and then activated by contact with an aqueous solution or steam.

When the proton conductive electrolyte according to the present invention is used for a fuel cell, it is generally used in the form of a membrane, but is not limited to this, and may be used in the form of a cylinder. It is. That is, a method in which a dispersion mixture of the above-described inorganic oxide hydrate serving as a proton carrier and a polymer matrix material is directly cast into a membrane, or the dispersion mixture is cast into a porous core material, a woven fabric or a nonwoven fabric, and the like. And so on. In particular, the method using a core material is advantageous in reducing the effective resistance of the electrolyte membrane since the film obtained by using a high-strength core material can be thinned. Further, when using the proton conductive electrolyte membrane produced according to the present invention, a surface treatment such as dissolving only part of the organic matrix material on the surface with an organic solvent or partially polishing the surface of the membrane is performed. Is an effective method for reducing the contact resistance with the electrode.

The thickness of the proton conductive electrolyte membrane according to the present invention is not particularly limited, but is preferably larger than 10 μm in order to obtain a practically strong membrane, and smaller than 200 μm in order to reduce the membrane resistance. More preferably, it is more preferably 10 to 30 μm in order to reduce the internal resistance of the fuel cell and to increase the sensitivity as a sensor. The film thickness can be controlled by the viscosity of the homogeneous mixed system or the thickness of the cast on the substrate. Further, when producing the proton conductive electrolyte according to the present invention, additives such as a plasticizer, a stabilizer, a release agent, and the like used for a general polymer are used within a range that does not impair the object of the present invention. You can also.

A gas diffusion electrode used in a membrane / electrode assembly used for a fuel cell is formed by applying a conductive material carrying fine particles of a catalyst metal on an electrolyte membrane or bonding an electrode layer formed in a film shape in advance. Is composed of
If necessary, a water repellent or a binder may be contained. Further, a layer formed of a conductive material not carrying a catalyst, a water repellent and a binder may be formed outside the catalyst layer. As the catalytic metal used for this gas diffusion electrode,
Any metal that promotes the oxidation reaction of hydrogen and the reduction reaction of oxygen may be used, for example, platinum, gold, silver,
Palladium, iridium, rhodium, ruthenium, iron,
Cobalt, nickel, chromium, tungsten, manganese, vanadium, or alloys thereof are mentioned.
Among such catalysts, a binary system of platinum and ruthenium is often used, particularly for the cathode and platinum for the anode. The particle size of the metal serving as a catalyst is usually 10 to 300 Å. The supported amount of the catalyst is desirably, for example, 0.01 to 10 mg / cm ² in a state where the electrode is formed.

As the conductive material, any material may be used as long as it is an electron conductive material, and examples thereof include various metals and carbon materials. Examples of the carbon material include carbon black such as furnace black and acetylene black, activated carbon, graphite and the like, and these are used alone or in combination. As the water repellent, for example, a fluorinated carbon or a polytetrafluoroethylene dispersant is used. As the binder for forming the catalyst layer, the proton conductive electrolyte matrix polymer of the present invention is preferably used as it is, but other various resins may be used. In that case, a fluorine-containing resin having water repellency is preferable, and those having excellent heat resistance and oxidation resistance are more preferable. For example, polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, and tetrafluoroethylene -Hexafluoropropylene copolymer.

The method for bonding the electrolyte membrane and the electrode used for the fuel cell is not particularly limited, and a known method can be applied. As a method of manufacturing a membrane / electrode assembly,
For example, a platinum catalyst powder is mixed with a polytetrafluoroethylene suspension, applied to carbon paper, and heat-treated to form a catalyst layer. Next, there is a method in which the same electrolyte solution or precursor solution as the electrolyte membrane is applied to the catalyst layer, impregnated, and integrated with the electrolyte membrane by hot pressing. In addition, a method of applying a solution of an electrolyte membrane or an electrolyte membrane precursor according to the present invention to a platinum catalyst powder in advance coated on a platinum catalyst powder, and a method of coating the electrolyte membrane or an electrolyte membrane precursor solution according to the present invention with a catalyst. A method of forming a paste and applying it to the electrolyte membrane, a method of electrolessly plating an electrode on the electrolyte membrane, a method of adsorbing platinum group metal complex ions on the electrolyte membrane, and then reducing the same can be selected.

The fuel cell includes a fuel distribution plate as a current collector having a groove for forming a fuel flow path and an oxidant flow path outside the joined body of the electrolyte membrane and the gas diffusion electrode formed as described above. A single cell provided with an oxidant distribution plate is shown in FIG. The voltage of a single cell varies depending on the operating temperature under an external load, but is generally 0.5 to 0.8 V. Stacking by stacking multiple units via cooling plates etc. corresponding to the voltage required for a single cell Is configured. Operating the fuel cell at a high temperature is a preferable condition because the electrode catalyst becomes highly active, the electrode overvoltage is reduced, and the electrode is less poisoned by carbon monoxide, but the proton conductive electrolyte membrane is hydrated. If it is not in a state, it will not work well, so it must be operated at a temperature that allows moisture management. The proton conductive electrolyte according to the present invention is superior in characteristics at high temperatures as compared with the conventional electrolyte membrane, and the operating temperature of the fuel cell is 100 ° C.
The feature is that it functions sufficiently even with the above. (Examples) Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto. In addition,
The measurement conditions of each physical property are as follows. (Example 1) As an example of the present invention, a method for producing a tungsten oxide hydrate / epoxy resin composite proton conductive electrolyte membrane will be described below. 30g of metal tungsten powder 10g
% Polyperoxytungstic acid that is dissolved and reacted as a precursor while being reacted with aqueous hydrogen peroxide. A 5N aqueous solution of sodium hydroxide (NaOH) is added to the obtained aqueous solution to completely decompose the polyacid, and then 6N hydrochloric acid is added to obtain a yellow opaque precipitate. The precipitate was filtered and dried in a desiccator. 400 g of pure water was added to 10 g of the dry powder obtained by the above method, stirred for 30 minutes and left for 24 hours. The supernatant of the solution in which the powder settled and became completely separated was discarded, and the same amount of pure water was newly added. The same washing operation was repeated six times to remove impurity ions derived from unreacted raw materials.
500 g of pure water is added to 5 g of tungsten oxide hydrate after washing.
The solution A was added to the solution A, and the solution A was stirred. Five minutes after the stirring was stopped, 50 ml of the solution was collected from the surface of the solution A with a dropper. The collected solution A was rapidly dried in a spray-type high-temperature drying oven at 500 ° C. The spray-type high-temperature drying furnace is a furnace in which the solution is sprayed from above into a mist, and the solvent is evaporated by a heater installed around the solution particles while the solution particles descend. When the obtained tungsten oxide hydrate was observed with an electron microscope, it was found to be fine particles having a maximum particle diameter of 76 nm.
Select Araldite (manufactured by Showa Polymer Co., Ltd.) as the epoxy resin used as the membrane matrix material, add 2 g of tungsten oxide hydrate to 1 g of the main agent and 1 g of the curing agent, mix them evenly, and cure them on the slide glass. Was cast with an applicator so that the thickness of the film became about 70 μm. 2 at room temperature
After curing for 4 hours, the both sides are uniformly polished by about 20 μm with a polishing tape (LT-C2000; manufactured by Fuji Photo Film) to about 3 μm.
Finished to a thickness of 0 μm to obtain a tungsten oxide hydrate / epoxy resin composite proton conductive electrolyte membrane.

Next, a dry weight of the platinum-ruthenium-supported carbon catalyst has an electrolytic mass of 5% by weight corresponding to 60% by weight of the catalyst amount.
Nafion 117 alcohol aqueous solution (water, isopropanol, normal propanol in a weight ratio of 20: 40: 4
No. 0 mixed solvent: manufactured by Fluka Chemika) was added and kneaded into a paste, and the resultant mixture was 30 mm × 60 mm × 60 mm size tungsten oxide hydrate / epoxy resin composite proton conductive electrolyte membrane obtained above. Apply at 30mm size and 60 ℃
For 3 hours to form an anode. The amount of platinum supported on the obtained anode was about 0.5 mg / cm ² , and the amount of supported ruthenium was about 0.5 mg / cm ² . On the opposite side of the formed electrolyte membrane, 5% by weight of Nafion 117 corresponding to 60% by weight of the catalyst amount was added to the platinum-supported carbon powder catalyst by dry weight.
An alcohol aqueous solution is added and kneaded into a paste. The paste is applied so that the thickness when dried becomes 15 μm so as to overlap with the anode, and dried at 60 ° C. for 3 hours to form a cathode to form an electrolyte membrane / electrode assembly. did. The amount of platinum carried on the obtained cathode was about 0.3 mg / cm ² . Embodiment 2 A method for producing a niobium-doped tungsten oxide hydrate / epoxy resin composite proton conductive electrolyte membrane according to another embodiment of the present invention will be described below. 10g of metal tungsten powder and 500mg of niobium metal powder
A polytungstic peroxide solution and a polyniobate peroxide aqueous solution which are dissolved and reacted as a precursor while reacting with a 30% aqueous hydrogen peroxide solution are prepared respectively. The obtained aqueous solution was mixed so that the metal ratio became (Nb / (W + Nb)) = 0.005, and a 5N aqueous solution of caustic soda (NaOH) was added to completely decompose the polyacid, and then 6N hydrochloric acid was added. A yellow opaque precipitate is obtained. The precipitate was filtered and dried in a desiccator. 400 g of pure water was added to 10 g of the dry powder obtained by the above method, stirred for 30 minutes and left for 24 hours. The supernatant of the solution in which the powder settled and became completely separated was discarded, and the same amount of pure water was newly added. The same washing operation was repeated six times to remove impurity ions derived from unreacted raw materials. 500 ml of pure water is newly added to 5 g of the niobium-doped tungsten oxide hydrate after washing to form a solution B.
Was stirred. Five minutes after stopping the stirring, 50 ml of the solution was collected from the surface of the solution B with a dropper. Collected solution B
Was quickly dried in a spray-type high-temperature drying oven at 500 ° C. Observation of the obtained niobium-doped tungsten oxide hydrate with an electron microscope revealed that the particles were fine particles having a maximum particle diameter of 73 nm. Araldite was selected as the epoxy resin to be used as the film matrix material, 1 g of the base resin, 2 g of niobium-doped tungsten oxide hydrate were added to 1 g of the curing agent, and mixed uniformly so that the thickness at the time of curing on the slide glass was reduced. Casting was performed with an applicator so that the thickness became about 70 μm. After curing at room temperature for 24 hours, both surfaces were uniformly polished with a polishing tape to a thickness of about 20 μm and finished to a thickness of about 30 μm to obtain a niobium-doped tungsten oxide hydrate / epoxy resin composite proton conductive electrolyte membrane. Next, an electrode of 30 mm × 30 mm size was formed on the niobium-doped tungsten oxide hydrate / epoxy resin composite proton conductive electrolyte membrane of 60 mm × 60 mm size obtained above. Formation method,
The electrode composition is the same as in Example 1. (Embodiment 3) A method for producing a tin oxide hydrate / epoxy resin composite proton conductive electrolyte membrane according to another embodiment of the present invention will be described below. Stannic chloride (SnCl ₄ · 5H
The ₂ O) 17.5 g was hydrolyzed by heating to dissolve to 60 ° C. in water 50 ml. Aqueous ammonia was added thereto, and the mixture was heated and aged at 100 ° C. for 1 hour. The obtained precipitate was filtered and dried to obtain a proton conductive tin oxide hydrate (SnO ₂ .nH ₂ O). . From the thermogravimetric change measurement, n was about 1.7.

400 g of pure water was added to 10 g of the prepared tin oxide hydrate, stirred for 30 minutes and left for 24 hours. The supernatant liquid of the precipitated and separated tin oxide hydrate was collected and discarded, and the same amount of pure water was newly added. The same washing operation was repeated six times to remove impurity ions derived from unreacted raw materials.
500 ml of pure water was newly added to 5 g of the washed tin oxide hydrate to obtain a solution C, and the solution C was stirred. Five minutes after stopping the stirring, 50 ml of the solution C was collected from the vicinity of the surface of the solution C with a dropper. The collected solution C was rapidly dried in a spray-type high-temperature drying oven at 500 ° C. Observation of the obtained tin oxide hydrate with an electron microscope revealed that the hydrate was fine particles having a maximum particle diameter of 75 nm. Select Araldite as the epoxy resin to be the film matrix material, add 2 g of tin oxide hydrate to 1 g of the main agent and 1 g of the curing agent, mix them uniformly, and set the thickness on a slide glass to about 70 μm when cured. Was cast with an applicator. After curing at room temperature for 24 hours, use a polishing tape to uniformly coat both sides with about 20μ.
polished to about 30μm thickness and tin oxide hydrate /
An epoxy resin composite proton conductive electrolyte membrane was used.

Next, a 30 mm × 30 mm electrode was formed on the 60 mm × 60 mm tin oxide hydrate / epoxy resin composite proton conductive electrolyte membrane obtained above. The forming method and electrode composition are the same as those in the first embodiment. Embodiment 4 A method for producing a tungsten oxide hydrate / epoxy resin composite proton conductive electrolyte membrane according to another embodiment of the present invention will be described below. 1 g of metal tungsten powder is dissolved in a 30% aqueous hydrogen peroxide solution while reacting to produce a polytungstic peroxide as a precursor. A 5N aqueous solution of sodium hydroxide (NaOH) is added to the obtained aqueous solution to completely decompose the polyacid, and then 6N hydrochloric acid is added to obtain a yellow opaque precipitate. The precipitate was filtered and dried in a desiccator. 1.2 g of the dry powder obtained by the above method was added to 1.2 ml of a 5N aqueous sodium hydroxide solution to prepare a precursor solution. Next, araldite was selected as an epoxy resin to be a film matrix material, 0.6 g of the above precursor solution and 0.3 ml of acetone were added to 2 g of the main agent and 2 g of the curing agent, and mixed so as to be uniform, and placed on a slide glass. Approximately 70μ thick when cured
m was cast with an applicator. After the casting, it was allowed to stand at room temperature for 24 hours and peeled off from the slide glass to form a precursor film. This membrane was immersed in a 3N hydrochloric acid aqueous solution for about 24 hours and then repeatedly washed with distilled water to obtain a yellow opaque tungsten oxide hydrate / epoxy resin composite proton conductive electrolyte membrane. The obtained thickness of about 70μ
The proton conductive electrolyte membrane having a thickness of about 30 μm was uniformly polished on both sides with a polishing tape to about 20 μm. When the cross section of the film was confirmed with an electron microscope, the maximum diameter of the particles present in the film was 71 nm.

Next, a 30 mm × 30 mm electrode was formed on the 60 mm × 60 mm tungsten oxide hydrate / epoxy resin composite proton conductive electrolyte membrane obtained above. The forming method and electrode composition are the same as those in the first embodiment. Embodiment 5 A method for producing a niobium-doped tungsten oxide hydrate / epoxy resin composite proton conductive electrolyte membrane according to another embodiment of the present invention will be described below. 30 g of metal tungsten powder 1 g and metal niobium powder 50 mg
% Polytungstic acid and a polyniobate peroxide aqueous solution which are dissolved and reacted as precursors while reacting with a hydrogen peroxide solution. The resulting aqueous solution is adjusted to a metal ratio (N
b / (W + Nb)) = 0.005, and a 5N aqueous solution of caustic soda (NaOH) was added to completely decompose the polyacid. Then, 6N hydrochloric acid was added to obtain a yellow opaque precipitate. The precipitate was filtered and dried in a desiccator. 1.2 g of the dry powder obtained by the above method was added to 1.2 ml of a 5N aqueous sodium hydroxide solution to prepare a precursor solution. Next, araldite was selected as an epoxy-based resin serving as a film matrix material, and 2 g of a main agent and 2 g of a curing agent were added to the precursor solution described above.
Add 6 ml and 0.3 ml of acetone and mix until uniform,
Casting was performed on a slide glass with an applicator so that the thickness at the time of curing was about 70 μm. After the casting, it was allowed to stand at room temperature for 24 hours and peeled off from the slide glass to form a precursor film. This membrane was immersed in a 3N hydrochloric acid aqueous solution for about 24 hours, and then repeatedly washed with distilled water to obtain a yellow opaque niobium-doped tungsten oxide hydrate / epoxy resin composite proton conductive electrolyte membrane. The obtained proton conductive electrolyte membrane having a thickness of about 70 μm was uniformly polished on both sides with a polishing tape to about 20 μm to a thickness of about 30 μm. When the cross section of the film was confirmed with an electron microscope, the maximum diameter of the particles present in the film was 70 nm.

Next, a 30 mm × 30 mm size electrode was formed on the 60 mm × 60 mm niobium-doped tungsten oxide hydrate / epoxy resin proton conductive electrolyte membrane obtained above. The forming method and electrode composition are the same as those in the first embodiment. Embodiment 6 A method for producing a tin oxide hydrate / polyamide composite proton conductive electrolyte membrane according to another embodiment of the present invention will be described below. Stannic chloride as the precursor of the oxide hydrate dimethylacetamide 0.3ml (SnCl ₄ · 5H
₂ O) Add 1.0 g and stir to produce a clear viscous liquid.
This liquid and polyamic acid varnish (polyamic acid 20)
4.0 g of a wt% N-methylpyrrolidone solution (manufactured by Ube Industries) is mixed and stirred to produce a light brown transparent viscous solution. This solution was cast on a glass substrate and heat-treated at 80 ° C. for 1 hour in an air atmosphere. Under the air atmosphere,
The casting film is heat-treated at 130 ° C., 160 ° C., and 200 ° C. for 1 hour each, and further kept at 200 ° C. in a vacuum state for about 10 hours to promote complete solvent removal and dehydration imidization. A proton conductive electrolyte precursor membrane was prepared. The obtained precursor film was uniformly polished on both sides with a polishing tape to about 10 μm, and then immersed in a 25 wt% ammonia aqueous solution for 20 minutes. When the precursor film becomes cloudy, take it out and wash it with distilled water 4 to 5 times to obtain a thickness of about 30 μm.
A hydrated tin oxide / polyamide composite proton conductive electrolyte membrane was obtained. When the cross section of the film was confirmed with an electron microscope,
The largest diameter of the particles present in the film was 74 nm.

Next, an electrode having a size of 30 mm × 30 mm was formed on the 60 mm × 60 mm size tin oxide hydrate / polyamide composite proton conductive electrolyte membrane obtained above. The forming method and electrode composition are the same as those in the first embodiment. Embodiment 7 A method for producing a tin oxide hydrate / epoxy resin composite proton conductive electrolyte membrane according to another embodiment of the present invention will be described below. Araldite (Showa Polymer) was selected as the epoxy resin used as the membrane matrix material, and 370 mg of tri-N-butyltin trimethoxide, a precursor of tin oxide hydrate, was added to 370 mg of the modified polythiol used as a curing agent. Upon stirring, a viscous transparent liquid is produced. This is added to the modified epoxy resin, which is the main component of Araldite, and mixed to form a viscous, uniform liquid.
Cast with an applicator to 70 μm. The curing reaction of this casting film is advanced in air at 60 ° C. for 3 hours. The obtained precursor film was immersed in a 25 wt% ammonia aqueous solution for 1 hour, and then taken out and distilled water for 4 to 5 minutes.
The membrane was washed twice to obtain a tin oxide hydrate / epoxy matrix composite proton conductive electrolyte membrane having a thickness of about 70 μm. This proton conductive electrolyte membrane is uniformly polished on both sides with a polishing tape.
It was polished by about 20 μm and finished to about 30 μm thickness. When the cross section of the film was confirmed with an electron microscope, the maximum diameter of the particles present in the film was 72 nm.

Next, a 30 mm × 30 mm electrode was formed on the 60 mm × 60 mm tin oxide hydrate / epoxy resin composite proton conductive electrolyte membrane obtained above. The forming method and electrode composition are the same as those in the first embodiment. (Embodiment 8) A method for producing a tin oxide hydrate / polyether acrylate resin composite proton conductive electrolyte membrane according to another embodiment of the present invention will be described below. Polyether acrylate is obtained by modifying the terminal of an oligomer obtained by randomly copolymerizing ethylene oxide and propylene oxide at a molar ratio of 4: 1 with acrylic acid. To 1 g of this polyether acrylate, 1 g of tri-N-butyltin trimethoxide, which is a precursor of tin oxide hydrate, is added and stirred to prepare a viscous liquid. Benzoyl peroxide was added to this liquid as a polymerization initiator, mixed, cast on a smooth polytetrafluoroethylene substrate with an applicator, and heat-treated to obtain a precursor film having a thickness of 50 μm. This precursor film was immersed in a 25 wt% aqueous ammonia solution for 20 minutes. When the cloudy precursor film turned yellow, it was taken out and washed 4-5 times with distilled water to obtain a tin oxide hydrate having a thickness of about 50 μm. / Polyether acrylate resin composite proton conductive electrolyte membrane was obtained. When the cross section of the film was confirmed with an electron microscope, the maximum diameter of the particles present in the film was 75 nm.

Next, an electrode having a size of 30 mm × 30 mm was formed on the 60 mm × 60 mm tin oxide hydrate / polyether acrylate resin composite proton conductive electrolyte membrane obtained above. The forming method and electrode composition are the same as those in the first embodiment. (Comparative Example 1) As one comparative example of the present invention, a method for producing a tin oxide hydrate / polyether acrylate resin composite proton conductive electrolyte membrane will be described below. Material as stannic chloride proton conductor (SnCl ₄ · 5H ₂ O) and 17.5 g 50
Dissolve in ml of water and heat to 60 ° C to hydrolyze. Ammonia water is added to this and heated at 100 ° C. for 1 hour to ripen. The obtained precipitate was filtered and dried to obtain a proton conductive tin oxide hydrate (SnO ₂ · nH ₂ O). From the thermogravimetric change measurement, n was about 1.7.

Next, ether acrylate oligomer 10
Then, 5 g of the tin oxide hydrate (SnO ₂ .nH ₂ O) powder obtained above was added to the resulting mixture, and the mixture was mixed for about 2 minutes with a high-speed rotary mixer. Benzoyl peroxide as a polymerization initiator was added thereto, and the mixture was further mixed by a high-speed rotary mixer. Thereafter, about 0.1% by weight of cetyltrimethylammonium bromide was added as a surfactant and cast on a slide glass. The casting film was heat-treated to obtain a tin oxide hydrate / polyether acrylate resin composite proton conductive electrolyte film. When the cross section of the film was confirmed with an electron microscope, the maximum diameter of the particles present in the film was 1.1 μm.

Next, the platinum / ruthenium-supported carbon catalyst was dried at a weight of 5 wt% corresponding to 60 wt% of the catalyst amount.
The Nafion 117 alcohol aqueous solution was added and kneaded into a paste. The 30 mm x 30 mm tin oxide hydrate / polyether acrylate resin composite proton conductive electrolyte membrane obtained above was 30 mm x 30 mm in size. And dried at 60 ° C. for 3 hours to form an anode. The amount of platinum supported on the obtained anode was about 0.5 mg / cm ² , and the amount of supported ruthenium was about 0.5 mg / cm ² . On the opposite surface of the formed electrolyte membrane, Nafion 117 was added to a platinum-supported carbon powder catalyst by dry weight, and a 5% by weight aqueous solution of Nafion 117 alcohol equivalent to 60% by weight of the catalyst amount was added and kneaded into a paste and dried. The coating was applied so as to overlap the anode so that the thickness at the time became 15 μm, and dried at 60 ° C. for 3 hours to form a cathode, thereby producing an electrolyte membrane / electrode assembly. The amount of platinum carried on the obtained cathode was about 0.3 mg / cm ² . (Comparative Example 2) As another comparative example of the present invention, a method for producing a tin oxide hydrate / epoxy resin composite proton conductive electrolyte membrane will be described below. Araldite (manufactured by Showa Polymer Co., Ltd.) was selected as an epoxy resin serving as a membrane matrix material, and proton conductive tin oxide hydrate (SnO ₂ .nH ₂ ) synthesized by the method of Comparative Example 2 was added to 1 g of the main agent and 1 g of the curing agent. ₂ O; n-1.
7) was added thereto and mixed so as to be uniform, and was cast on a slide glass with an applicator so that the thickness at the time of curing was about 70 μm. After curing at room temperature for 24 hours, both sides are polished uniformly with a polishing tape about 20μm about 30μm
Finished to a thickness, a tin oxide hydrate / epoxy resin composite proton conductive electrolyte membrane was obtained. When the cross section of the film was confirmed with an electron microscope, the maximum diameter of the particles existing in the film was 1.0
μm.

Next, an electrode having a size of 30 mm × 30 mm was formed on the obtained 60 mm × 60 mm tin oxide hydrate / epoxy resin composite proton conductive electrolyte membrane. The forming method and electrode composition are the same as in Comparative Example 1.

In each of the examples and comparative examples produced by the above-described method, carbon paper treated with PTFE for water repellency was disposed on the anode and cathode electrode surfaces, and was sandwiched between high-density carbons in which gas flow grooves were machined, and tightened in a predetermined manner. The whole was fixed using bolts in a state where pressure was applied, to produce a test cell. This test cell is set in a constant temperature bath, a gas supply line having a heater function for heating, and a gas outlet line having an outlet pressure regulating valve and a heater for maintaining temperature are connected, respectively.
Water was supplied to the cell by a liquid mass flow controller.
By raising the temperature of the supplied water with a heating heater, and further adjusting the temperature of the heater in the outlet line and the temperature control chamber and the pressure regulating valve, the steam pressure and temperature are maintained at the test set values,
In this state, the conductivity of the cell was evaluated by an AC measurement method. Since the measured values in this case include the conductivity of the carbon separator, carbon paper, electrodes, and the like and the contact resistance of each material, a blank cell was separately prepared and evaluated under the same conditions as a reference.

FIG. 2 shows the temperature dependence of the electrolyte membrane conductivity under a saturated vapor pressure in Examples and Comparative Examples. FIG. 3 shows the dependence of the ionic conductivity at 150 ° C. on the water vapor pressure.

In the measurement temperature range from 50 ° C. to 150 ° C., the ionic conductivity of Comparative Examples 1 and 2 showed the highest value at 150 ° C., but was only about 10 ⁻³ S / cm. Furthermore, the water vapor pressure dependence was large, and the ion conductivity dropped to 10 ^-4 S / cm or less under the condition of the water vapor partial pressure of 0.2.
This indicates that in order to maintain Comparative Examples 1 and 2 in a state of high conductivity, the water vapor partial pressure must be kept high, and as a result, a system that can withstand the high pressure is required.

As shown in FIG. 1, the ionic conductivity at 150 ° C. of Example 1 was 10 ⁻² S / cm, which was an order of magnitude improvement over the comparative example. This is considered to be the effect of reducing the particle size of the ionic conductor in the film and dispersing it highly. On the other hand, Example 2 is 15
It was 2 × 10 ^-2 S / cm at 0 ° C., and ionic conductivity higher than that of Example 1 was confirmed. In the first and second embodiments, the base material of the ion conductor is the same tungsten oxide, but in the second embodiment, niobium doping treatment is performed. It was suggested that the addition of niobium had a favorable effect on the properties of the proton conductive membrane of the tungsten oxide hydrate.

Further, the ionic conductivity at 150 ° C. under the saturated steam pressure of Example 3 was 2 × 10 ⁻² S / cm or more. Also one
Even in a temperature range of less than 50 ° C., Example 3 has a higher conductivity than Examples 1 and 2. On the other hand, from FIG.
Example 3 has a small water vapor pressure dependency of the ionic conductivity, and maintains a conductivity of 3 × 10 ⁻³ S / cm or more even when the water vapor pressure partial pressure is 0.2. This is considered to be due to the fact that the tin oxide hydrate used in Example 3 has a property that protons are easily conducted, and also has a property that hydration water is hardly desorbed, so that the tin oxide hydrate exhibits high conductivity even in an environment where the water vapor partial pressure is low.

In Examples 4 and 5, the proton conductors used in Examples 1 and 2 were the same, and the dispersed particle diameter in the membrane was almost the same at 80 nm or less. From FIG. 2 and FIG. 3, almost the same results are obtained for the ionic conductivity and the water vapor pressure dependence of the conductivity. However, in Example 4, 92.3% of tungsten contained in the starting material used was contained in the finally produced proton conductive membrane, whereas in the production method of Example 1, only 2.04% of tungsten used as a raw material was used. It cannot be used as a proton conductive membrane, and the rest is discarded during production.
Furthermore, Example 1 is different from Example 4 in that a supernatant liquid is separated from a tungsten oxide hydrate solution in the process of forming a tungsten oxide hydrate having a particle size of 80 nm or less, and drying using a spray-type high-temperature drying furnace is performed. Processes such as processing are added. In other words, Example 4 can be said to be a material in which an ion conductive film having the same characteristics as that of Example 1 was produced more efficiently and at a significantly lower cost. The above also applies to Example 5 in which niobium is doped into tungsten as an ion conductor.

As shown in FIGS. 2 and 3, Examples 6, 7, and 8 show almost the same conductivity characteristics as Example 3.
In these examples, tin oxide hydrate was used as the ion conductor, and the particle size in the film was 80 nm or less. However, Example 3
Only 3.45% of the tin used in the raw material can be used for the proton conducting membrane, and the rest is discarded during fabrication. Here, Examples 6, 7, and 8 each show 92% of tin contained in the starting material.
3, 91.5 and 93.2% are contained in the finally obtained proton conducting membrane. Further, in Example 3, the steps of preparing an aqueous tin chloride solution, heating, adding aqueous ammonia, followed by filtration, washing and drying are required in the process of preparing the hydrated tin oxide. In No. and No. 8, although a hydrolysis reaction after forming a film is required, a tin compound as a raw material can be directly dispersed in an organic material in a solution state, and the above-described plurality of steps can be omitted. That is, Examples 6, 7,
8 is a proton conductive membrane having the same characteristics as in Example 3, but the raw material and production cost can be significantly reduced.

From the above, it was found that in this example, the metal oxide hydrate which is a proton conductor and the organic polymer material of the membrane have good heat resistance, so that stable conductivity at 150 ° C. can be secured. Further, by forming a uniform membrane in the form of an oxide hydrate precursor and then producing a metal oxide hydrate by hydrolysis, the dispersion of the proton conductor in the membrane is greatly increased. Therefore, proton conductivity can be improved as compared with the related art. Furthermore, the use of tin hydrated oxide makes it possible to reduce the steam pressure dependence of conductivity. In addition, the production method and the proton conductive membrane using the present material can significantly reduce the production cost as compared with the related art.

[0039]

The composite electrolyte of a metal oxide hydrate having proton conductivity and an organic polymer according to the present invention has a sufficiently high ionic conductivity even at a higher temperature than that of a conventional electrolyte. Further, according to the method of the present invention, it is possible to produce a proton conductor membrane having lower ionic conductivity and a sufficiently high ionic conductivity even at a higher temperature than the conventional method.

[Brief description of the drawings]

FIG. 1 is a diagram showing a unit configuration of a polymer electrolyte fuel cell according to the present invention.

FIG. 2 is an experimental result showing the temperature dependence of the ionic conductivity at the saturated water vapor pressure of the electrolyte membrane according to the present invention.

FIG. 3 is an experimental result showing the dependence of the ionic conductivity at 150 ° C. of the electrolyte membrane of the present invention on the partial pressure of water vapor pressure.

[Explanation of symbols]

1, 2 ... separator, 3 ... cathode side carbon paper, 4 ... anode side carbon paper, 5 ... electrolyte membrane,
6: cathode gas flow path, 7: anode gas flow path.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 8/10 G01N 27/58 Z (72) Inventor Takeshi Yamaga 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture No. 7 Hitachi Research Laboratory, Hitachi Ltd. (72) Inventor Yuichi Kamo 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. 7-22-1 (72) Inventor Masaru Miyayama 7-22-1 Roppongi, Minato-ku, Tokyo (72) Inventor Yumi Tanaka 7-22-1 Roppongi, Minato-ku, Tokyo (72) Inventor Tadashi Honma Ibaraki 1-4 1-4 Umezono, Tsukuba, Japan F-term (reference) 2E004 ZA01 ZA05 5G301 CA18 CA30 CD01 5H026 AA06 BB00 BB10 CC03 CX05 EE11 EE18 HH01

Claims (6)

[Claims] 1. A method for producing a proton conductive membrane, comprising:
A solution of at least one compound serving as a precursor of the inorganic proton conductor, a liquid mixture containing an organic monomer or a polymer is formed into a film, and after curing or crosslinking, a precursor of the inorganic proton conductor is formed. A method for producing a proton-conductive membrane, comprising: treating a body with a solution or gas containing an agent for converting a substance into a proton conductor to form an inorganic solid proton conductor in the membrane. 2. The method for producing a proton conductive membrane according to claim 1, wherein the inorganic proton conductor is tungsten oxide hydrate or tungsten oxide hydrate doped with niobium. 3. The method according to claim 1, wherein the inorganic proton conductor is tin oxide hydrate. 4. A proton conductive membrane containing at least an inorganic proton conductor and an organic polymer, wherein the maximum particle diameter of the inorganic proton conductor dispersed in the membrane is 80 nm or less. Conductive membrane. 5. The proton conductive membrane according to claim 4, wherein the inorganic proton conductor is tungsten oxide hydrate or tungsten oxide hydrate doped with niobium. 6. The proton conductive membrane according to claim 4, wherein the inorganic proton conductor is tin oxide hydrate.