JP2003142124A - Electrolyte film and solid high polymer type fuel cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte film for a solid high polymer type fuel cell having excellent durability, wherein deterioration of the material is hardly caused even under 100 deg.C or higher. SOLUTION: This electrolyte film having high ion conductivity is formed by compounding a metal oxide hydrate represented by hydrates of tungsten oxide and tin oxide as a proton carrier and an ion conductive organic high polymer as a film base material.

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 proton conductive electrolyte membrane used in humidity sensors, gas sensors, etc. and a polymer electrolyte fuel cell using the same.

[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, which is capable of firmly binding to a specific ion or selectively cation or anion. Since it has the property of transmitting particles,
It is formed into fibers or membranes and is used in various applications such as electrodialysis, diffusion dialysis, battery diaphragms, and electrolyte membranes for sensors.

A solid polymer electrolyte fuel cell is a hydrogen gas obtained by reforming low molecular hydrocarbons such as methane and methanol by providing a pair of electrodes on both sides of a proton conductive solid polymer electrolyte membrane. Is supplied to one electrode (fuel electrode) as a fuel gas, and oxygen gas or air is supplied to the other electrode (air electrode) as an oxidant to obtain electric power.

The water electrolysis is a method for producing hydrogen and oxygen by electrolyzing water using a solid polymer electrolyte membrane.

In a fuel cell or water electrolysis, a perfluorocarbon sulfonic acid (for example, Nafion 1 manufactured by DuPont) proposed by DuPont, Dow, Asahi Kasei, Asahi Glass Co., Ltd. as a proton conductive solid polymer membrane is proposed.
17) A fluorinated electrolyte membrane represented by a membrane is used as an electrolyte membrane used under severe conditions because of its excellent chemical stability.

The salt electrolysis is a method of producing sodium hydroxide, chlorine and hydrogen by electrolyzing an aqueous sodium chloride solution using a solid polymer electrolyte membrane. 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 electrolyte membrane having poor resistance to these. Therefore, solid polymer electrolyte membranes for salt electrolysis are generally resistant to chlorine and high-temperature, high-concentration sodium hydroxide aqueous solution, and in addition, partially carbonized on the surface to prevent back diffusion of generated ions. A perfluorosulfonic acid membrane having an acid group introduced is used.

By the way, the fluorine-based electrolyte typified by the perfluorosulfonic acid membrane has a very high chemical stability because it has a C--F bond, so that the above-mentioned fuel cell-use electrolyte for
For water electrolysis, or other than the solid polymer electrolyte membrane for salt electrolysis, also used as a solid polymer electrolyte membrane for hydrohalic acid electrolysis, further utilizing the proton conductivity,
It is also widely applied to humidity sensors, gas sensors, oxygen concentrators, etc.

However, the fluorine-based electrolyte has a drawback that the manufacturing process is complicated and that it is very expensive. Moreover, even if it says high heat resistance, the heat resistance limit does not exceed 100 ° C. Therefore, the fluorine-based electrolyte membrane is limited to special applications such as space-use or military-use solid polymer fuel cells, and solid polymer fuel cells as a low-pollution power source for automobiles, small distributed power sources for consumer use, For applications such as portable power sources, it is necessary to cool the reformed gas or remove carbon monoxide in the reformed gas when using low molecular hydrocarbons as raw fuel for hydrogen gas reforming. It was a factor that complicates the system.

In addition, since the electrolyte membrane has a low operating temperature limit, the proton conductivity is low, the polarization due to the electrode reaction rate is large, and the proton conduction resistance of the membrane increases unless it is sufficiently moistened with water, and the battery performance is improved. There is a problem related to water management, which is said to significantly decrease, and this has hindered the feasibility of fuel cells.

Regarding moisture management, for example, Japanese Patent Laid-Open No. 7-
Japanese Patent No. 90111 proposes an electrolyte membrane in which a metal having catalytic activity, a metal oxide such as silica, titania, or the like is contained in the electrolyte membrane.

The metal having a catalytic activity is added so that hydrogen that permeates the electrolyte membrane produces water by an oxidation reaction and the water is used for wetting the electrolyte membrane. Similarly, the metal oxide is added for the purpose of efficiently retaining water in the film. However, as described in the text of the above publication, the problem that the specific resistance of the electrolyte membrane is not improved when an excessive amount of metal oxide is contained, so that the content of the metal oxide is 50% by weight. It is suppressed by%. This is because the added metal oxide is an obstacle to proton conduction.

Various attempts have been made in the past in order to obtain oxidation deterioration resistance characteristics equivalent to or better than those of fluorine-based electrolyte membranes. For example, in Japanese Patent Laid-Open No. 9-102322,
Sulfonic acid type polystyrene-graft-ethylene tetrafluoroethylene copolymerization composed of a main chain formed by copolymerization of a fluorocarbon vinyl monomer and a hydrocarbon vinyl monomer, and a hydrocarbon side chain having a sulfonic acid group A combined (ETFE) membrane has been proposed.

The above-mentioned sulfonic acid type polystyrene-graft-ETFE membrane is inexpensive, has sufficient strength as a solid polymer electrolyte membrane for a fuel cell, and increases conductivity by increasing the introduction amount of sulfonic acid group. It is possible to improve.

However, the sulfonic acid type polystyrene-graft-ETFE membrane has a high oxidative deterioration resistance of the main chain portion due to the copolymerization of the fluorocarbon vinyl monomer and the hydrocarbon vinyl monomer, but the side to which the sulfonic acid group is introduced is high. The chain portion is a hydrocarbon-based polymer that is susceptible to oxidative deterioration.
Therefore, when this is used in a fuel cell, there is a problem that the oxidation resistance of the entire membrane is insufficient and the durability is poor.

Further, in US Pat. Nos. 4,012,303 and 4,605,685, a film made by copolymerization of a fluorocarbon vinyl monomer and a hydrocarbon vinyl monomer is described as α, β, A sulfonic acid type poly (trifluorostyrene) -graft-ETFE membrane has been proposed in which β-trifluorostyrene is graft-polymerized and a sulfonic acid group is introduced into the graft polymer to form a solid polymer electrolyte membrane.

This is based on the assumption that the chemical stability of the polystyrene side chain portion introduced with the sulfonic acid group is not sufficient, instead of styrene, partially fluorinated α, β, β -Using trifluorostyrene. However, since it is difficult to synthesize α, β, β-trifluorostyrene, which is a raw material of the side chain portion, when considering application as a solid polymer electrolyte membrane for a fuel cell, Nafion 117 manufactured by DuPont is used. As in the case, there is a problem that the cost becomes high.

Further, since α, β, β-trifluorostyrene has low polymerization reactivity, there is a problem that the amount thereof which can be introduced as a graft side chain is small and the conductivity of the obtained membrane is low.

Further, since the above-mentioned membrane has a relatively low glass transition point, in an environment with a high water vapor pressure exceeding 100 ° C., the ionic conductivity of the membrane is significantly lowered with a decrease in relative humidity. As a result, there is a problem that it cannot be essentially used for a device that operates in a high temperature region.

[0019]

An object of the present invention is to provide a proton conductive membrane which maintains stable proton conductivity and mechanical strength even at a temperature of 100 ° C. or higher, which is the heat resistance limit of conventional fluorine-based electrolyte membranes. A certain electrolyte membrane and a polymer electrolyte fuel cell using the same are provided.

[0020]

In order to achieve the above-mentioned object, the inventors have focused on an inorganic proton-conducting metal oxide hydrate material having proton conductivity, and this and an ion-conducting organic polymer. The research of the electrolyte membrane which compounded the material was done earnestly.

As a result, a metal oxide hydrate as a proton carrier and an ion conductive organic polymer having high heat resistance and acid resistance are combined to form an electrolyte membrane.
Equal to or more than the fluorine-based electrolyte targeted by the present invention, and
We have found a highly heat-resistant proton conductive electrolyte membrane that has practically sufficient deterioration resistance.

The metal oxide hydrate used herein preferably has a proton conductivity of at least 10 ^-4 S / cm, more preferably 5 × 10 ^-3 S / cm or more.

Further, the composition of the above electrolyte membrane has an ion exchange capacity per dry weight of 0.91 to 1.67 m · eq.
/ G of ion conductive organic polymer is used, and the weight concentration of the proton conductive metal oxide hydrate to be added is 10 to 80 w.
It is said that the heat resistance and conductivity at t% are the best.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as the proton conductor electrolyte membrane that functions at 100 ° C. or higher, a tungsten oxide hydrate, a tungsten oxide hydrate obtained by doping niobium into a tungsten oxide hydrate, a tin oxide. A hydrate, a silicon oxide hydrate, a phosphorus oxide hydrate, a silicon oxide hydrate doped with a zirconia oxide hydrate, or the like can be used, and a single component or a plurality of components of these proton conductors can be used. Can be mixed and used.

The material for forming the ion-conductive organic polymer is not particularly limited as long as it is a material having heat resistance, acid resistance, and flexibility, and perfluorocarbon sulfonic acid represented by Nafion 117, and further Chemically modified polystyrene, polyetherketone, polyetheretherketone, polysulfone, polyethersulfone or other engineering plastic materials such as sulfonic acid, phosphoric acid or other proton carrier doped or chemically bonded and immobilized are preferable. .

Further, in the above material, if the material has a crosslinked structure or is partially fluorinated to improve the material stability, more preferable physical properties can be obtained.

When the proton conductive electrolyte according to the present invention is used in a fuel cell, it is generally used in the form of a membrane, but it is not limited to this and it is also possible to use it in a tubular shape. . That is, a method of directly casting a dispersion mixture of the above-mentioned metal oxide hydrate serving as a proton carrier and an ion-conducting organic polymer into a film, or a porous core material, woven cloth or non-woven cloth of the dispersion mixture. It is possible to adopt a method such as impregnating and casting.

In particular, the method of using the core material is advantageous in reducing the effective resistance of the electrolyte membrane because the obtained membrane can be thinned by using the core material of high strength.

In using the proton conductive electrolyte membrane produced according to the present invention, only the surface of the partially removed membrane is polished by dissolving only the organic matrix material on the surface with an organic solvent. The surface treatment is effective in 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 it is preferably thicker than 10 μm in order to obtain a membrane which can be practically used, and more than 200 μm in order to reduce the membrane resistance. The thinner one is preferable. Particularly, in order to reduce the internal resistance of the fuel cell and increase the sensitivity as a sensor, 10 to 30 μm is more preferable.
The film thickness can be controlled by the viscosity of the homogeneous mixture system or the thickness of the cast film on the substrate.

Further, when the proton conductive electrolyte according to the present invention is produced, additives such as a plasticizer, a stabilizer and a release agent which are used for usual polymers are used within a range not impairing the object of the present invention. It can also be used.

In the gas diffusion electrode used in the membrane / electrode assembly used for a fuel cell, a conductive material carrying fine particles of a catalytic metal is applied on an electrolyte membrane or an electrode layer formed in advance in a membrane shape is laminated. It is composed of
A water repellent or a binder may be contained if necessary.

Further, a layer composed of a conductive material not supporting a catalyst, a water repellent and a binder may be formed outside the catalyst layer.

The catalyst metal used in this gas diffusion electrode may be any metal that promotes the oxidation reaction of hydrogen and the reduction reaction of oxygen, such as platinum, gold,
Silver, palladium, iridium, rhodium, ruthenium,
Examples include iron, cobalt, nickel, chromium, tungsten, manganese, vanadium, and alloys thereof. Of these catalysts, platinum, especially at the cathode,
A binary system of platinum and ruthenium is often used in the anode.

The particle size of the catalyst metal is usually 10 to 3
It is 00 angstrom. The supported amount of the catalyst is, for example, 0.01 to 10 mg / cm ² when the electrode is molded.
Is desirable.

The conductive material may be any 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 can be used alone or in combination.

As the water repellent, for example, fluorinated carbon or polytetrafluoroethylene dispersant is used. As the binder 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 a resin having excellent heat resistance and oxidation resistance is particularly preferable. Examples thereof include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer and tetrafluoroethylene-hexafluoropropylene copolymer.

There is no particular limitation on the method of joining the electrolyte membrane and the electrode used for the fuel cell, and a known method can be applied. As a method for producing the membrane / electrode assembly, for example, platinum catalyst powder is mixed with a polytetrafluoroethylene suspension, coated on carbon paper, and heat-treated to form a catalyst layer. Then, there is a method in which the same electrolyte solution or precursor solution as the electrolyte membrane is applied to and impregnated in the catalyst layer, and the catalyst layer is integrated with the electrolyte membrane by hot pressing.

In addition, a method of applying a solution of the electrolyte membrane or the electrolyte membrane precursor according to the present invention coated on platinum catalyst powder in advance to the electrolyte membrane, the electrolyte membrane or the electrolyte membrane precursor according to the present invention. It is possible to select a method of forming a paste with a solution and a catalyst and applying it to an electrolyte membrane, a method of electrolessly plating an electrode on the electrolyte membrane, a method of adsorbing a platinum group metal complex ion on the electrolyte membrane, and then reducing it. it can.

In the fuel cell, the fuel distribution plate as a current collector with a groove for forming a fuel flow path and an oxidant flow path is provided outside the assembly of the electrolyte membrane and the gas diffusion electrode formed as described above. And the oxidant distribution plate is a single cell.

The voltage of the single cell is generally 0.5 to 0.8 V, though it varies depending on the operating temperature under the condition that an external load is applied. A stack is formed by stacking via the.

In the fuel cell, it is preferable to operate the fuel cell at a high temperature because the electrode catalyst becomes more active, the electrode overvoltage is reduced, and the carbon monoxide poisoning of the electrode is small, but the proton conductive electrolyte membrane is preferable. It does not work well unless it is in a hydrated state, so it must be operated at a temperature that allows water control.

The proton-conducting electrolyte according to the present invention is superior in characteristics at high temperature as compared with the conventional electrolyte membrane, and is characterized in that it functions sufficiently even when the operating temperature of the fuel cell is 100 ° C. or higher. is there. The present invention will be specifically described below with reference to examples.

Example 1 To 450 ml of 3N hydrochloric acid aqueous solution cooled to 5 ° C., 1.0 mol of Na ₂ WO ₃ aqueous solution 50 was added.
ml was gradually added dropwise with stirring with a magnetic stirrer to obtain a yellow precipitate. After removing the supernatant, 300 ml of a 0.1N hydrochloric acid aqueous solution was added, and the mixture was stirred for 10 minutes and allowed to stand for sedimentation, and then the supernatant was removed. Next, add 300 ml of pure water to the precipitate, stir for 10 minutes,
Filtered and dried at room temperature for 24 hours.

The precipitate prepared as described above was measured by X-ray diffraction,
It was confirmed by thermogravimetric / differential thermal analysis that it was H ₂ WO ₄ .H ₂ O.

H ₂ WO ₄ .H ₂ O synthesized and washed as described above
To 10.0 g of an alcohol solution of 5 wt% perfluorocarbon sulfonic acid (a mixed solvent of water: isopropanol: normal propanol in a weight ratio of 20:40:40,
35.3 g of ion-exchange capacity 0.83 meq / g) was added and stirred at room temperature for 30 minutes to prepare a varnish. A casting sheet was prepared from the varnish by the doctor blade method and dried at 60 ° C. for 10 hours, and H ₂ WO ₄ .H ₂ O
An electrolyte membrane containing 5 wt% was obtained. The blade gap was adjusted so that the thickness of the electrolyte membrane was 30 μm after drying.

After the above electrolyte membrane / electrode assembly was sufficiently absorbed with water, a platinum plate having platinum black formed on its surface was pressed against the front and back surfaces of the electrode assembly, and a platinum plate having a humidifier was installed in a pressure-resistant thermostatic chamber for 10 minutes.
The temperature was raised to 0 to 150 ° C. An impedance measuring device was attached to the terminal wire which made contact with the platinum plate, and the resistance of the electrolyte membrane at each temperature under saturated steam pressure was measured.

Example 2 H produced in the same manner as in Example 1
₂ WO ₄ · H ₂ O 10.0g, the ion exchange capacity is 1.1
35.3 g of an alcohol solution of perfluorocarbon sulfonic acid of 7 meq / g was added, and stirred at room temperature for 30 minutes to prepare a varnish. A casting sheet was prepared from the varnish by the doctor blade method and dried at 60 ° C. for 10 hours to obtain an electrolyte membrane containing 85 wt% of H ₂ WO ₄ .H ₂ O. The blade gap was adjusted so that the thickness of the electrolyte membrane was 30 μm after drying.

After the electrolyte membrane / electrode assembly obtained above was sufficiently absorbed with water, platinum plates having platinum black formed on the front surfaces were pressed from the front and back surfaces, and were placed in a pressure-resistant constant temperature bath incorporating a humidifying device.
The temperature was raised to 00 to 150 ° C. An impedance measuring device was attached to the terminal wire which made contact with the platinum plate, and the resistance of the electrolyte membrane was measured at each temperature under saturated steam pressure.

Separately from the above, a test cell was assembled by disposing carbon paper on the front and back surfaces of the electrolyte membrane, sandwiching it with a carbon separator having gas channel grooves processed, and fixing it with bolts.

Supplying hydrogen and nitrogen to the test cell,
The nitrogen outlet gas was collected while applying a differential pressure depending on the conditions, and the amount of hydrogen gas that permeated the electrolyte membrane was quantified by gas chromatography. The quantified hydrogen was regarded as a proton that migrated during power generation, and the hydrogen permeation current was determined from the charge amount.

Example 3 H produced in the same manner as in Example 1
₂ WO ₄ · H ₂ O 10.0g has an ion exchange capacity of 1.17
200 g of an alcohol solution of perfluorocarbon sulfonic acid having a meq / g was added and stirred at room temperature for 30 minutes to prepare a varnish. A casting sheet was prepared from the varnish by the doctor blade method and dried at 60 ° C. for 10 hours to obtain an electrolyte membrane containing 50% of H ₂ WO ₄ .H ₂ O. The blade gap was adjusted so that the thickness of the electrolyte membrane was 30 μm after drying.

A carbon paper was placed on the front and back surfaces of the above-mentioned electrolyte membrane, further sandwiched by a carbon separator having a gas channel groove processed, and fixed with bolts to assemble a test cell.

Hydrogen and nitrogen were supplied to the test cell, the nitrogen outlet gas was collected while applying a differential pressure depending on the conditions, and the amount of hydrogen gas passing through the electrolyte membrane was quantified by gas chromatography. The quantified hydrogen was regarded as a proton that moved during power generation, and the hydrogen permeation current was calculated from the charge amount.

Example 4 0.5 g of dried polyether sulfone was added to NMP (N-methylpyrrolidone) and stirred at 25 ° C. for 2 hours to prepare a 5 wt% solution. 45 ml of sulfuric acid was added to the solution, and the mixture was heated and stirred at 45 ° C. for 3 hours under an inert gas atmosphere. Put the whole reaction vessel in a 15 ° C water bath and add 20 ml of fuming sulfuric acid to 1 m
It was added at a rate of 1 / min, and after the addition was completed, the mixture was continuously stirred for 1.5 hours to allow the sulfonation reaction to proceed. The sulfonated polyether sulfone was precipitated by dropping in 2 liters of pure water with respect to 5 ml of the obtained solution. The obtained precipitate was filtered, washed with pure water and then dried to obtain a sulfonated polyether sulfone.

The ion exchange capacity of the obtained sulfonated polyether sulfone was 1.42 meq / g.

The above sulfonated polyether sulfone
A 20 wt% solution was prepared by dissolving it in an NMP solution. this
For 50 g of the solution, H produced in the same manner as in Example 1₂WO_Four
・ H ₂Add 10 g of O and stir for 30 minutes at room temperature
Prepared. The varnish was removed using the doctor blade method.
Make a sting sheet and dry at 60 ℃ for 10 hours.
Let's H₂WO_Four・ H₂Electrolyte membrane containing 50 wt% O
Got The thickness of the electrolyte membrane should be 30 μm after drying.
Adjusted the blade gap.

A test paper cell was assembled by disposing carbon paper on the front and back surfaces of the electrolyte membrane, sandwiching it with a carbon separator having gas channel grooves processed, and fixing it with bolts. Hydrogen and nitrogen were supplied to the test cell, the nitrogen outlet gas was collected while applying a differential pressure depending on the conditions, and the amount of hydrogen gas that permeated the electrolyte membrane was quantified by gas chromatography. The quantified hydrogen was regarded as a proton that moved during power generation, and the hydrogen permeation current was calculated from the charge amount.

The electrolyte membrane produced here was incorporated into a single cell for a power generation test in the same procedure as in Example 5 described below, and a power generation test was conducted.

Example 5 H produced in the same manner as in Example 1
₂ WO ₄ · H ₂ O 10.0g, the ion exchange capacity is 1.1
200 g of an alcohol solution of 7 meq / g of perfluorocarbon sulfonic acid was added, and stirred at room temperature for 30 minutes to prepare a varnish. A casting sheet was prepared from the varnish by the doctor blade method and dried at 60 ° C. for 10 hours to obtain an electrolyte membrane containing 50 wt% of H ₂ WO ₄ .H ₂ O. The blade gap was adjusted so that the thickness of the electrolyte membrane was 30 μm after drying.

Next, for the platinum / ruthenium-supported carbon catalyst,
The dry mass corresponds to an electrolytic mass of 60 wt% of the catalyst amount. 5
An alcohol solution of wt% perfluorocarbon sulfonic acid was added, and the mixture was kneaded into a paste to obtain 6 above.
A 30 mm × 30 mm size was applied onto a 0 mm × 60 mm size proton conductive electrolyte membrane 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 ruthenium supported was about 0.5 mg / cm ² .

On the opposite surface of the formed electrolyte membrane, an alcohol solution of 5 wt% perfluorocarbon sulfonic acid corresponding to 60 wt% of Nafion 117 in a dry weight was added to a platinum-supported carbon powder catalyst and kneaded in a paste form. The dried product was applied so as to overlap the anode so that the thickness when dried was 15 μm, and dried at 60 ° C. for 3 hours to prepare an electrolyte membrane / electrode assembly having a cathode formed thereon. The amount of platinum supported on the obtained cathode was about 0.3 mg / cm ² .

On the electrolyte membrane / electrode assembly in which the electrolyte membrane 1 and the electrode 2 are joined, the carbon paper 3 treated with PTFE for water repellency is arranged on the anode and cathode electrode surfaces, and the gas flow channel groove is processed. It was sandwiched between the separators 4 made of high-density carbon that had been applied, and the whole was fixed using bolts, to produce a test cell. FIG. 4 shows a schematic sectional view of the test cell.

The test cell was set in a constant temperature bath, and an anode / cathode gas supply line having a heater function for heating, an outlet pressure adjusting valve, and a gas outlet line having a temperature keeping heater were connected to each other.

A liquid mass flow controller was used to humidify the supply gas. An electronic load was connected to this test cell, and the cell voltage was measured when a current of 0.5 A per square centimeter was taken out.

[Comparative Example 1] Nafion 117 membrane manufactured by DuPont (Ion exchange capacity 0.91 me)
q / g), a platinum plate having platinum black formed on the surface was pressed from the front and back surfaces, and the temperature was raised in a humid atmosphere. An impedance measuring device was attached to the terminal wire which was contacted with the platinum plate, and the resistance of the film was measured.

Separately from the above, a test cell was assembled by disposing carbon paper on the front and back surfaces of the electrolyte membrane, sandwiching it with a carbon separator having a gas channel groove processed, and fixing it with bolts.

Hydrogen and nitrogen were supplied to the test cell, the nitrogen outlet gas was collected while applying a differential pressure depending on the conditions, and the amount of hydrogen gas passing through the electrolyte membrane was quantified by gas chromatography. The quantified hydrogen was regarded as a proton that moved during power generation, and the hydrogen permeation current was calculated from the charge amount.

[Comparative Example 2] A platinum-ruthenium-supported carbon catalyst was kneaded into a paste by adding an alcohol solution of 5 wt% perfluorocarbon sulfonic acid whose dry mass corresponds to 60 wt% of the catalytic amount in dry weight. , Nafion 117 membrane (ion exchange capacity 0.91 meq / g)
A 30 mm x 30 mm size was applied onto the top 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 ruthenium supported was about 0.5 mg / cm ² .

On the opposite surface of the formed electrolyte membrane, 5 wt% perfluorocarbon sulfonic acid alcohol solution of Nafion 117, which corresponds to a catalyst amount of 60 wt% in dry weight, was added to a platinum-supported carbon powder catalyst and kneaded in a paste form. did. This is dried to a thickness of 15 μm, and
It was coated so as to overlap with the anode and dried at 60 ° C. for 3 hours to form a cathode, to prepare an electrolyte membrane / electrode assembly.
The amount of platinum supported on the obtained cathode was about 0.3 mg / cm ² .

In this electrolyte membrane / electrode assembly, carbon paper water-repellent treated with PTFE was placed on the anode and cathode electrode surfaces, sandwiched between high-density carbon separators having gas channel grooves, and bolts were used. Then, the whole was fixed and a test cell was prepared. The test cell was set in a constant temperature bath, and an anode / cathode gas supply line having a heater function for heating, an outlet pressure adjusting valve, and a gas outlet line having a temperature keeping heater were connected to each other. A liquid mass flow controller was used to humidify the supply gas.

An electronic load is connected to this test cell, and 1
The cell voltage was measured while drawing a current of 0.5 A per square centimeter.

FIG. 1 shows Examples 1 and 2 and Comparative Example 1-1.
It is a graph which shows the ionic conductivity in 00-150 degreeC. The measurement was performed after 300 hours had elapsed after reaching each temperature.

Comparative Example 1 shows a good ionic conductivity at about 100 ° C., but when it exceeds 100 ° C., the decrease is remarkable, and it deteriorates to about 10 ⁻³ S / cm at 130 ° C.

Example 1 maintains stable conductivity even at a temperature over 100 ° C., and Comparative Example 1 at 110 ° C. or higher.
Above the conductivity of. This is because the use of tungsten oxide hydrate as the membrane material improves the heat resistance of the electrolyte membrane and also improves the water holding power of interlayer water, adsorbed water, etc. in Comparative Example 1.
It is thought that this is because it is higher than the above.

Further, the fact that the tungsten oxide hydrate used as the membrane material itself has proton conductivity means that good proton conductivity is obtained even if the content rate in the electrolyte membrane is as high as 85 wt%. It was understood that this is a factor that can be secured.

In Example 2, the ionic conductivity of the electrolyte membrane is further improved as compared with Example 1. This gives an ion exchange capacity of 0.83 for the ion-conducting organic polymer in the electrolyte membrane.
This is the effect of increasing from meq / g to 1.2 meq / g. According to a detailed experiment in which the ion exchange capacity of the ion conductive polymer was changed, the ion exchange capacity of the ion conductive polymer used as the electrolyte membrane was 0.9.
It has been found that 1 to 1.67 meq / g is preferable.

FIG. 2 is a graph showing hydrogen gas permeability of the electrolyte membranes of Examples 2-4 and Comparative Example 1. The vertical axis in the figure is the equivalent current when the detected hydrogen is regarded as a charge carrier.

It can be seen from FIG. 2 that Example 2 has a smaller hydrogen permeation amount than Comparative Example 1. It is considered that in Comparative Example 1, the composition of the electrolyte membrane was deteriorated by the high temperature condition of 130 ° C., and hydrogen was easily permeated.

On the other hand, in Examples 3 and 4, the hydrogen permeation equivalent current was 1 mA, showing that the gas barrier property was extremely high. This is because the heat resistance of the electrolyte membrane is improved by the addition of the hydrated tungsten oxide, and the gas barrier effect of the polymer is improved by changing the hydrated tungsten oxide to the ion conductive polymer to 50 wt%. This is because they could be expressed.

Further detailed tests showed that the weight ratio of metal oxide hydrate to ion-conductive polymer was 10%.
It was found that the hydrogen barrier property and the ion conductivity as the electrolyte membrane were suitable as the material of the fuel cell when the content was ˜80 wt%.

FIG. 3 shows 13 of Examples 4 and 5 and Comparative Example 2.
It is a graph which shows the measurement result of the cell voltage on 0.5 A / cm < ² > constant load conditions at 0 degreeC. In Comparative Example 2, the cell voltage decreased to about 200 mV as a result of the internal resistance of the battery rising due to the deterioration of the material of the electrolyte membrane due to the high temperature environment, but in Examples 4 and 5, almost no effect on the performance due to the high temperature was observed. It was found that the voltage was maintained at about 600 mV.

As described above, the electrolyte membrane of the present invention typified by the examples contains the ion-conductive organic polymer and the proton-conductive metal oxide hydrate, so that the high ionic conductivity can be obtained even at a high temperature of 100 ° C. or higher. It was shown to have sex.

The ion exchange capacity of the ion conductive organic polymer is 0.91-1.67 meq / g, and the weight ratio of the proton conductive metal oxide hydrate to the ion conductive organic polymer is 10 to 80 wt. %, It was found that the gas barrier property as an electrolyte membrane and the ionic conductivity are conditions having sufficient properties for a fuel cell.

When this electrolyte membrane is applied to a fuel cell, the cell can operate at high temperature, the system energy efficiency is improved by effectively utilizing the exhaust heat of the cell, and the poisoning of the electrode catalyst by a trace amount of carbon monoxide in the fuel gas is caused. And reduction in overvoltage of the electrode reaction due to high temperature can be realized.

[0086]

EFFECTS OF THE INVENTION The composite electrolyte of a proton conductive metal oxide hydrate and an organic polymer according to the present invention has a sufficiently high ionic conductivity even at a higher temperature than conventional ones.

Further, the cost is lower than that of the conventional one, and
It is possible to obtain a proton conductor membrane having sufficiently high ionic conductivity even at high temperature.

[Brief description of drawings]

FIG. 1 is a graph showing the ionic conductivity of an electrolyte membrane at 100 to 150 ° C.

FIG. 2 is a graph showing hydrogen gas permeability of an electrolyte membrane.

FIG. 3 is a graph showing the cell voltage of an electrolyte membrane at 130 ° C. and 0.5 A / cm ² .

FIG. 4 is a schematic cross-sectional view of a test cell incorporating the electrolyte membrane of the present invention.

[Explanation of symbols]

1 ... Electrolyte membrane, 2 ... Electrode, 3 ... Carbon paper, 4 ... Separator.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01M 8/00 H01M 8/00 Z 8/10 8/10 (72) Inventor Shin Morishima Omika Hitachi, Ibaraki Prefecture 7-1-1, Machi, Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor, Yuichi Kamo 7-1, 1-1, Omika-cho, Hitachi-shi, Ibaraki Hitachi, Ltd. (72) Inventor, Kazutoshi Higashiyama 7-1-1, Omika-cho, Hitachi-shi, Ibaraki F-term inside Hitachi Research Laboratory, Hitachi, Ltd. (reference) 4F071 AA01 AA22 AA26 AA51 AA64 AA78 AB18 AB25 AB26 AE15 AH19 FB07 FC01 FC07 4J002 AA001 BC021 BC101 BD121 CH091 CN031 DE01696 FD116 GQ00 GT00 5H026 AA06 CX05 EE12 EE19 HH05 HH06

Claims (5)

[Claims] 1. An electrolyte membrane comprising a metal oxide hydrate having proton conductivity and an ion conductive organic polymer. 2. The electrolyte membrane according to claim 1, wherein the metal oxide hydrate has a proton conductivity of at least 10 ⁻⁴ S / cm. 3. The ion exchange capacity per dry weight of the ion-conductive organic polymer is 0.91-1.67 m · eq /
The electrolyte membrane according to claim 1, which is g. 4. The metal oxide hydrate having proton conductivity is 10 to 80 wt% with respect to the ion conductive organic polymer.
The electrolyte membrane according to claim 1 or 2, which is contained. 5. An electrode containing carbon particles carrying a noble metal, a diffusion layer for gas diffusion and current collection to the electrode, and a separator having electronic conductivity and a gas flow groove.
A polymer electrolyte fuel cell comprising the electrolyte membrane according to any one of claims 1 to 4.