JP2011150949A - Membrane electrode assembly, its manufacturing method, and fuel battery cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane electrode assembly which is chemically and mechanically stable under a use condition as a fuel cell and a hydrogen generation device and is applicable suitably for a medium temperature type fuel cell, and its manufacturing method, and a fuel battery cell using the same. <P>SOLUTION: The membrane electrode assembly (11) used in the fuel battery cell (10) has a hydrogen permeable metal foil (12) with a thickness of 1 μm or more and having self-supporting performance and an amorphous inorganic solid electrolyte membrane (13) having hydrogen ion conductivity, and is manufactured by a method which has, for example, a process to prepare a reaction liquid containing a precursor of a solid electrolyte membrane and a process in which the reaction liquid is coated on the surface of the hydrogen permeable metal foil, and the precursor is reacted while heat treating at 100-600°C and the inorganic solid electrolyte membrane (13) is formed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a membrane electrode assembly, a method for producing the same, and a fuel cell using the same.

Fuel cells that obtain power continuously by reacting hydrogen (fuel) and oxygen (oxidant) using the reverse reaction of water electrolysis are clean power generation technologies, as well as kinetic energy and Since chemical energy is directly converted into electrical energy without passing through thermal energy, it has the advantages of excellent power generation efficiency and low noise and vibration.

So far, fuel cells using various electrolytes such as solid polymer type (PEFC), phosphoric acid type (PAFC), molten carbonate type (MCFC), solid oxide type (SOFC) have been proposed. When fuel cells are classified from the viewpoint of operating temperature, they are roughly classified into a low temperature type (for example, ˜200 ° C.), a medium temperature type (for example, 200 to 500 ° C.), and a high temperature type (for example, 500 ° C.). Each of these has advantages and disadvantages, but from the viewpoint of application to the power source of automobiles, (1) the amount of expensive platinum catalyst used can be reduced compared to the low temperature type, and (2) startup compared to the high temperature type The medium temperature fuel cell is attracting attention as a promising option because it can shorten the time, (3) does not require a high heat resistant material, and (4) can use a fuel other than hydrogen. As a promising candidate for an electrolyte material that can be suitably applied to a medium temperature fuel cell, ion conductive ceramics can be cited.

As a fuel cell using ceramics as a solid electrolyte, for example, an anode (fuel electrode) hydrogen permeable metal foil 12 made of a hydrogen permeable alloy and a fuel cell made of a proton conductive perovskite ceramic electrolyte thin film have been proposed (for example, (See Patent Documents 1 to 4 and Non-Patent Documents 1 and 2). These fuel cells are composed of Pd-based hydrogen permeable alloy foils and proton-conductive perovskites such as perovskite BaCe _0.9 Y _0.1 O ₃ and BaZr _0.9 In _0.1 O _3. A polycrystalline thin film of type ceramics is formed by vapor deposition by the PLD method, and further, a cathode (air electrode) made of Pt or La _0.9 Sr _0.1 CoO ₃ is formed thereon by screen printing. ing.

In Patent Documents 5 and 6, the present inventor has proposed an amorphous ion conductive film having hydrogen ion conductivity and oxide ion conductivity.

JP 2008-4372 A JP 2008-16457 A JP 2008-34111 A Japanese Patent Publication No. 2008-212820 International Publication No. 2009/041479 Pamphlet International Publication No. 2007/105422 Pamphlet

J. Power Sour., 152 (2005) 200−203. J. Power Sour., 185 (2008) 922-926.

However, if the fuel cell using the BaCeO ₃ type proton conductive ceramic is exposed to water vapor, the proton conductive ceramic will be decomposed by corrosion. Since water is always generated under the fuel cell operating environment, a fuel cell made of such a material cannot withstand operation for a long time (several hundred hours).

Further, when a thin film of BaZrO ₃ based material is formed on a hydrogen permeable metal foil, columnar crystals oriented in the vertical direction of the hydrogen permeable metal foil grow (for example, J. Power Sour., 185 (2008) 922- 926.). In such a material, voids and pinholes are easily formed between the crystals, so that gas leakage in the film thickness direction and diffusion of the electrode material are likely to occur. Gas leaks in the electrolyte membrane cause an explosion due to direct mixing of fuel and air, and diffusion of electrode materials causes electrical shorts, both of which are serious problems in fuel cell applications and proton conductivity. It is difficult to reduce the thickness of the electrolyte membrane, which is necessary for improving the temperature and lowering the operating temperature.

Furthermore, when a hydrogen permeable alloy is used as an anode hydrogen permeable metal foil electrode, a large stress is applied to the ceramic electrolyte thin film due to the difference in the thermal expansion coefficient between the alloy and the ceramic electrolyte membrane and the expansion caused by hydrogenation of the alloy. There is a risk of film breakage.

In order to reduce the operating temperature of the fuel cell and to reduce the size of the fuel cell stack, it is necessary to make the solid electrolyte membrane as thin as possible. Necessary. However, it is difficult to prevent the occurrence of defects with the techniques described in Patent Documents 1 to 4 and Non-Patent Documents 1 and 2. Patent Documents 5 and 6 do not describe the thinning of the entire membrane electrode assembly and the expression of self-supporting properties.

The present invention has been made in view of such circumstances, and is a membrane electrode assembly that is chemically and mechanically stable under the conditions of use as a fuel cell or a hydrogen generator, and can be suitably applied to a medium temperature fuel cell. An object of the present invention is to provide a manufacturing method thereof and a fuel cell using the same.

The 1st aspect of this invention in alignment with the said objective solves the said subject by providing the membrane electrode assembly in any one of following (1)-(7).
(1) A membrane / electrode assembly having a hydrogen-permeable metal foil having a thickness of 1 μm or more and having a self-supporting property and an amorphous inorganic solid electrolyte membrane having hydrogen ion conductivity.
(2) The membrane electrode assembly according to (1), further comprising an intermediate layer made of a metal that is less deformed when storing hydrogen than the hydrogen permeable metal between the hydrogen permeable metal foil and the solid electrolyte membrane.

(3) The inorganic solid electrolyte membrane has five or more coordinations in one or more metal oxides selected from the group consisting of SiO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ and CeO _2. Any one of (1) and (2), which is an amorphous material doped with a cation that can take a number (excluding a metal ion of the same kind as that of the metal oxide) and bonded via an oxygen atom 2. The membrane electrode assembly according to item 1.
(4) The inorganic solid electrolyte membrane is an amorphous aluminosilicate having a molar ratio of silicon (Si) to aluminum (Al) of 50:50 to 99.9: 0.1 (1) and (2) The membrane electrode assembly according to any one of the above.

(5) the solid electrolyte membrane includes one or more metals selected from the group consisting of hafnium (Hf), titanium (Ti), indium (In), zirconium (Zr), and tin (Sn), boric acid, Any one of (1) and (2), which is an amorphous material in which a residue derived from one or more oxygen acids selected from the group consisting of phosphoric acid, sulfuric acid, carbonic acid and nitric acid is bonded via an oxygen atom The membrane electrode assembly according to claim 1.
(6) The solid electrolyte membrane is one or more selected from the group consisting of yttrium (Y), aluminum (Al), iridium (Ir), scandium (Sc), and a lanthanoid group (including lanthanum (La)). The membrane / electrode assembly according to (5), further comprising a trivalent metal.
(7) The metal according to any one of (5) and (6), wherein the metal is one or more of zirconium (Zr), titanium (Ti), and hafnium (Hf), and the oxygen acid is phosphoric acid. Membrane electrode assembly.

The second aspect of the present invention solves the above problem by providing a method for producing a membrane / electrode assembly according to any one of (8) to (16) below.
(8) a step of preparing a reaction solution containing a precursor of the inorganic solid electrolyte membrane;
An amorphous inorganic solid electrolyte membrane having hydrogen ion conductivity is formed by applying the reaction solution to the surface of a hydrogen-permeable metal foil having a thickness of 1 μm or more and having self-supporting properties, and reacting the precursor. The manufacturing method of the membrane electrode assembly which has a process to form.
(9) The method for producing a membrane / electrode assembly according to (8), wherein the inorganic solid electrolyte membrane is formed by a sol-gel method.
(10) The film according to any one of (8) and (9), further comprising a step of surface-treating the surface of the hydrogen-permeable metal foil to a predetermined surface roughness before applying the reaction solution. Manufacturing method of electrode assembly.
(11) before applying the reaction solution, further comprising the step of forming on the surface of the hydrogen permeable metal foil an intermediate layer made of a metal that is less deformed when storing hydrogen than the hydrogen permeable metal, The method for producing a membrane / electrode assembly according to any one of (8) to (10), wherein the reaction solution is applied to the surface of the intermediate layer.

(12) The reaction solution is an alkoxide of one or more metals selected from the group consisting of silicon (Si), titanium (Ti), zirconium (Zr), aluminum (Al), and cerium (Ce), and at least 5 Any one of (8) to (11), which contains, as the precursor, an alkoxide of a metal ion that can have a coordination number equal to or higher than coordination (excluding the same metal ion as that of the metal oxide). The manufacturing method of the membrane electrode assembly of description.
(13) The reaction solution contains tetraalkoxysilane and aluminum trialkoxide as a precursor, and the molar ratio (Si: Al) of the tetraalkoxysilane to aluminum trialkoxide is 50:50 to 99.9: 0. The method for producing a membrane / electrode assembly according to (12), which is 1.

(14) The precursor is an alkoxide of one or more metals selected from the group consisting of hafnium (Hf), titanium (Ti), indium (In), zirconium (Zr), and tin (Sn), and boric acid The method for producing a membrane / electrode assembly according to any one of (8) to (11), which is one or more oxygen acids selected from the group consisting of phosphoric acid, sulfuric acid, carbonic acid and nitric acid, or a precursor thereof.
(15) The reaction solution is one or more selected from the group consisting of yttrium (Y), aluminum (Al), iridium (Ir), scandium (Sc), and a lanthanoid group (including lanthanum (La)). (14) The manufacturing method of the membrane electrode assembly as described in (14) which further contains a valent metal alkoxide.
(16) The method for producing a membrane / electrode assembly according to (15), wherein the reaction solution contains one or more of zirconium tetraalkoxide, titanium tetraalkoxide, and hafnium tetraalkoxide and phosphoric acid as the precursor.

The third aspect of the present invention is:
(17) The above-described problem is solved by providing a fuel cell including the membrane electrode assembly according to the first aspect of the present invention.

ADVANTAGE OF THE INVENTION According to this invention, the membrane electrode assembly which is chemically and mechanically stable on the use conditions as a fuel cell or a hydrogen generator, and can be applied suitably to an intermediate temperature type fuel cell is provided. The basic structure is a metal-oxygen cross-linking network, and it uses a solid electrolyte membrane made of an amorphous material that forms a particle-free dense thin film and a hydrogen-permeable metal foil with self-supporting properties. Easy-to-form airtight electrolyte thin film that does not contain grain boundaries can be formed, gas leakage, diffusion of electrode material and combustion reaction at the bonding interface can be suppressed. It can be carried out.
In addition, according to the present invention, there is provided a fuel cell that has the above-described characteristics, can be operated in an intermediate temperature range, and can be suitably used for a power source of an automobile.
Furthermore, according to this invention, the manufacturing method of the membrane electrode assembly which can manufacture the membrane electrode assembly which has the above characteristics at low cost is provided. Since the wet method is used for forming the solid electrolyte membrane, an expensive vacuum apparatus is not required and the area can be easily increased.

(A) is a schematic diagram showing the schematic structure of the fuel cell using the membrane electrode assembly which concerns on one embodiment of this invention, (b) is permeation | transmission of the cross section of the fuel cell produced in Example 1 It is a type | mold microscope picture. It is a figure which shows the manufacturing method of the membrane electrode assembly which concerns on one embodiment of this invention. 2 is an impedance cole-cole plot at various temperatures of the fuel battery cell produced in Example 1. FIG. 4 is an impedance cole-cole plot at 400 ° C. of the fuel battery cell produced in Example 2. 4 is an impedance cole-cole plot at 400 ° C. of a fuel battery cell produced in Example 3. 6 is a current-voltage curve and a current-output curve of a fuel cell produced in Example 4. FIG. FIG. 6 is an impedance cole-cole plot of the fuel battery cell produced in Example 4 under an open circuit condition.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
A membrane electrode assembly 11 used in a fuel cell 10 according to an embodiment of the present invention functions as a hydrogen permeable metal foil (a fuel electrode in the fuel cell 10) as shown in FIG. .) 12 and an amorphous inorganic solid electrolyte membrane 13 having hydrogen ion conductivity. In the fuel cell 10, an air electrode 14 is formed on the surface of the inorganic solid electrolyte membrane 13 opposite to the hydrogen permeable metal foil 12. In the fuel cell 10, an intermediate layer 15 made of a metal having a smaller expansion during hydrogen storage than the hydrogen permeable metal foil 12 is formed between the hydrogen permeable metal foil 12 and the inorganic solid electrolyte membrane 13. ing.

The fuel cell 10 includes a step of preparing a reaction solution containing a precursor of the solid electrolyte membrane 13, a step of forming the intermediate layer 15 on the surface of the hydrogen permeable metal foil 12, and a reaction solution on the surface of the intermediate layer 15. And a step of forming a solid electrolyte membrane 13 by reacting a precursor while applying heat treatment at 100 to 600 ° C.

As the hydrogen permeable metal foil 12, a metal foil made of Pd alloy such as palladium (Pd), palladium-silver (Pd-Ag), palladium-platinum (Pd-Pt), palladium-copper (Pd-Cu) or the like is used. Can be mentioned. Alternatively, a film in which a film containing Pd as described above is formed on both surfaces of a metal film containing any one selected from vanadium (V), niobium (Nb), and tantalum (Ta) can also be used. The thickness of the hydrogen permeable metal foil 12 is preferably 20 μm or more. If the thickness is less than 20 μm, defects such as pinholes and wrinkles may occur when the inorganic solid electrolyte membrane 13 is formed, and the mechanical strength of the resulting membrane electrode assembly 11 may be insufficient. There is. The upper limit of the thickness of the hydrogen permeable metal foil 12 is not particularly limited, but is appropriately adjusted so that sufficient hydrogen is supplied to the inorganic solid electrolyte membrane 13.

The surface of the hydrogen permeable metal foil 12 on the side where the inorganic solid electrolyte membrane 13 is formed may be subjected to a surface treatment so as to have a predetermined surface roughness. The surface roughness is appropriately adjusted so as to obtain a sufficient bonding strength between the inorganic solid electrolyte membrane 13 and is, for example, 2 to 5 μm. As the surface treatment, an arbitrary method capable of achieving a predetermined surface roughness can be appropriately selected according to the material and thickness of the hydrogen permeable metal foil 12, but oxygen plasma treatment, dry etching such as RIE, buffing, Examples thereof include mechanical polishing with an abrasive. Examples of the abrasive include “Pical (registered trademark)” manufactured by Nippon Polishing Co., Ltd.

In the membrane electrode assembly 11, when an intermediate layer 15 made of a metal that is less deformed when storing hydrogen than the hydrogen permeable metal foil 12 is formed between the hydrogen permeable metal foil 12 and the inorganic solid electrolyte membrane 13, Due to the expansion and contraction of the hydrogen permeable metal foil 12 that accompanies occlusion-release, the stress applied to the joint surface between the two can be relaxed and the life of the membrane electrode assembly 11 can be improved. Further, by selecting the intermediate layer 15 having a thermal expansion coefficient intermediate between the hydrogen permeable metal foil 12 and the inorganic solid electrolyte membrane 13, the hydrogen permeable metal foil 12 and the inorganic solid electrolyte membrane 13 caused by heat shock The intermediate layer 15 can function as a buffer layer against stress concentration on the bonding surface, and the stability of the membrane electrode assembly 11 against heat can also be improved.

The metal that can be used for the intermediate layer 15 advantageously has hydrogen permeability in order to supply hydrogen to the inorganic solid electrolyte membrane 13. Specific examples of such metals include nickel (Ni), platinum (Pt), niobium (Nb), zirconium (Zr), vanadium (V), and alloys thereof.

The thickness of the intermediate layer 15 is preferably 0.5 to 500 nm. The intermediate layer 15 can be formed by using an arbitrary method such as a high-frequency sputter deposition method.

By using a film made of an amorphous material as the inorganic solid electrolyte film 13, gas leakage and bonded interface combustion reaction can be suppressed in the membrane electrode assembly 11 and the fuel battery cell 10 using the same. Further, even if the film thickness is reduced, gas leakage and electrode material diffusion can be suppressed, so that ionic conductivity can be improved. Therefore, the operating temperature can be lowered as compared with the conventional solid oxide fuel cell, and it can be suitably used as an electrolyte membrane for an intermediate temperature fuel cell.

In the present invention, the “amorphous material” includes, in addition to those that do not contain anything other than an amorphous material, other than an amorphous material, as long as they do not depart from the spirit of the present invention. The thing containing the component of is included. Examples of components other than the amorphous material include impurities mixed in the manufacturing process. Further, the inorganic solid electrolyte membrane 13 may include a crystal structure within a range not departing from the gist of the present invention. The crystal structure in this case is, for example, 20% or less, more preferably 10% or less of the entire volume of the amorphous material.

The inorganic solid electrolyte membrane 13 has hydrogen ion conductivity. In the present invention, “hydrogen ion conductivity (proton conductivity)” means that only proton (H ⁺ ) is conducted by an external electric field or chemical potential, and does not cause electron or other ion conductivity and permeation of hydrogen molecules. Solid material.

As a material used for the inorganic solid electrolyte membrane 13,
(1) a metal ion capable of taking a coordination number of at least five or more in one or more metal oxides selected from the group consisting of SiO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ and CeO ₂ ( However, an amorphous material doped with an oxygen atom or a molar ratio of silicon (Si) to aluminum (Al) is 50:50. To 99.9: 0.1 amorphous aluminosilicate (hereinafter referred to as “metal oxide material”), and (2) hafnium (Hf), titanium (Ti), indium (In), zirconium ( Derived from one or more metals selected from the group consisting of Zr) and tin (Sn) and one or more oxygen acids selected from the group consisting of boric acid, phosphoric acid, sulfuric acid, carbonic acid and nitric acid And an amorphous material in which a residue is bonded through an oxygen atom (hereinafter referred to as “metal oxide-oxygen acid material”).

(1) Metal oxide material As an example of the metal oxide material, one or more selected from the group consisting of SiO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ and CeO ₂ and Al ₂ O ₃ And a metal oxide doped with a cation capable of taking a coordination number of 5 or more (excluding the same metal ion as the metal oxide), SiO ₂ and Al ₂ More preferably, the aluminosilicate composed of O ₃ is doped with a cation capable of taking a coordination number of five or more. The cation is not the same kind of metal ion as the metal contained in the metal oxide.

By adopting a metal oxide such as silica as a main component and doping with a specific cation capable of taking a coordination number of 5 or more, hydrogen ion conductivity can be expressed. Here, “dope” means that metal cation atoms having a coordination number of five or more coordinations are dispersed and in a metal oxide such as SiO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ , or CeO _2. Means that it exists. In addition, only one type of metal oxide may be sufficient, and arbitrary two or more types may be sufficient.

In the inorganic solid electrolyte membrane 13, oxygen may be contained in an ion state or the like in excess of the composition of SiO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ or CeO ₂ . It is not excluded that such oxide ions and the like are included within a range not departing from the spirit.

The cation capable of taking a coordination number of 5 or more is preferably a cation capable of taking a coordination number of 6 or more, and more preferably a cation capable of taking a coordination number of 6 to 12. More specifically, the cation used in the present invention is preferably a metal ion, such as a rare earth metal ion, an aluminum (Al) ion, a zirconium (Zr) ion, a niobium (Nb) ion, a hafnium (Hf) ion, or tantalum. (Ta) ion or first transition metal ion is more preferable, and cerium (Ce) ion, aluminum (Al) ion, titanium (Ti) ion, zirconium (Zr) ion, niobium (Nb) ion, yttrium (Y ) Ions, lanthanum (La) ions, hafnium (Hf) ions, or tantalum (Ta) ions, more preferably hafnium (Hf) ions, aluminum (Al) ions, and zirconium (Zr) ions. .
Further, only one kind of cation may be contained, or two or more kinds of cations may be contained.

The metal (for example, silicon): cation ratio (molar ratio) in the metal oxide-based material is preferably 99.9: 0.1 to 70:30, and 99: 1 to It is more preferably 50:50, further preferably 95 to 75: 5 to 25, and particularly preferably 90:10 to 80:20.

In order to improve proton conductivity, it is preferable to use an aluminosilicate material made of SiO ₂ and Al ₂ O ₃ , which is another example of a metal oxide material. Aluminosilicates exhibit strong Pronsted acidity because they contain many protons due to the negative charge on the —O—Si ⁴⁺ —O—Al ³⁺ —O— bond. Therefore, it is known that zeolite which is a crystalline aluminosilicate compound exhibits proton conductivity. However, zeolite is easy to permeate H ₂ and O ₂ gas due to its channel structure. Also, since zeolite is a hardly sinterable material, it is very difficult to produce a uniform thin film. However, by adopting an amorphous material having an aluminosilicate skeleton, both gas barrier properties and excellent proton conductivity can be achieved. The molar ratio of silicon and aluminum in the aluminosilicate material is, for example, 50:50 to 99.9: 0.1, preferably 90:10 to 99.9: 0.1, and the membrane electrode assembly 11 and the fuel It adjusts suitably according to the use of the battery cell 10, etc.

The inorganic solid electrolyte membrane 13 made of a metal oxide material reacts on the surface of the hydrogen permeable metal foil 12 or the intermediate layer 15 formed thereon after preparing a reaction solution containing the precursor of the inorganic solid electrolyte membrane 13. It is formed by applying a liquid and reacting the precursor while heat-treating at 100 to 600 ° C. Hereinafter, a case where a film-like ion conductive material (conductive film) using an amorphous material in which a cation is doped in silica is manufactured will be described as an example, but the same process is performed when another metal oxide is used. be able to. Thus, by forming the inorganic solid electrolyte membrane 13 by a solution process instead of the conventional vacuum process, the fuel cell 10 having a large area surface can be manufactured at low cost.

For example, as shown in FIG. 2, the inorganic solid electrolyte membrane 13 is prepared by preparing a reaction solution containing a compound containing a silica precursor and a cation, which is an example of a metal oxide, and the obtained reaction solution is a hydrogen-permeable metal foil. 12 is applied to the surface of 12 (the surface of the intermediate layer 15 when an intermediate layer is formed; the same applies to the description of the present embodiment hereinafter), and the precursor contained in the coating film is hydrolyzed. It is preferably formed by reacting and baking by a sol-gel method. If necessary, the fired inorganic solid electrolyte membrane 13 may be annealed. The application and baking and the annealing treatment may be repeated a plurality of times as necessary.

As a coating method on the hydrogen permeable metal foil 12, a known method such as a spin coating method can be employed. Employing the spin coating method is preferable because the number of coatings can be controlled and the film thickness can be adjusted. Furthermore, in this invention, it is preferable that it is a laminated body which laminated | stacked the thin layer. By setting it as such a structure, a film | membrane is produced more uniformly and the thin film excellent in conductivity is obtained.
At this time, it is preferable that the density | concentration of the compound containing the cation in a reaction liquid is 2 mM-100 mM. The ratio of silicon: cation is determined by conversion from the ratio of the finally produced ion conductive material.

Hydrolysis is not particularly defined as long as the silica precursor is silica and the cation is doped in the silica. For example, it is preferable to heat-treat the solid on which the reaction liquid has been adsorbed in steam treatment, water treatment or wet air. In this case, it is preferable to use ion-exchanged water in order to prevent contamination of impurities and the like and to form a thin layer made of a highly pure reaction solution.

After hydrolysis, if necessary, the surface may be dried with a drying gas such as nitrogen gas. Furthermore, by using a catalyst such as an acid or a base, the time required for these steps can be significantly shortened.

Firing is preferably performed at 100 to 500 ° C. for 10 seconds to 24 hours.
In addition, since all processes can be performed at 500 degrees C or less, it is preferable also from the point that the performance degradation by reaction with another battery constituent material can be suppressed.

Here, a silica precursor means what becomes silica after hydrolysis. Specifically, alkoxysilane, halogenated silane, water glass and silane isocyanate are preferable as the silica precursor, and alkoxysilane is more preferable when the sol-gel method is adopted.

As the alkoxysilane, tetraalkoxysilane is preferable, and tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane, tributoxysilanol, and methyltriethoxysilane are more preferable.
Further, when TiO ₂ , ZrO ₂ , Al ₂ O ₃ or CeO ₂ is used, it is preferable to employ a halide or an alkoxy compound each containing a corresponding metal.

Examples of the compound containing a cation include all reagents capable of forming a metal oxide by hydrolysis, such as metal alkoxide, isocyanate metal compound, halide, chelate complex, and organometallic complex.
As a metal alkoxide, what is represented by M (OR) _n is preferable, for example. Here, M is a rare earth metal atom, aluminum (Al), zirconium (Zr), niobium (Nb), hafnium (Hf), tantalum (Ta) or a first transition metal atom, cerium (Ce), aluminum (Al ), Titanium (Ti), zirconium (Zr), niobium (Nb), yttrium (Y), lanthanum (La), hafnium (Hf), or tantalum (Ta). Here, R is a group containing an alkyl group, preferably an alkyl group having 1 to 7 carbon atoms, an alkylcarbonyl group, an alkyl ketone group, or an alkyl diketone group. In addition, it is preferable that n is an integer of 1-6.

Specific examples of M (OR) _n include Ce (OC ₂ H ₄ OCH ₃ ) ₃ , Hf (OC ₄ H ₉ ) ₄ , Ta (OC ₂ H ₅ ) ₅ , Zr (OC ₄ H ₉ ) ₄ , Al ( OCH (CH ₃ ) ₂ ) ₃ , La (OC ₂ H ₄ OCH ₃ ) ₃ , Nb (OC ₂ H ₅ ) ₅ , Ti (OC ₄ H ₉ ) _{4 and the} like can be mentioned. Specific examples of the metal halide compound include CeCl ₃ , ZrCl ₄ , TiCl ₄ , LaCl ₃ , AlCl ₃ , TaCl _{5 and the} like. Moreover, it is preferable to prepare so that the molar ratio of M (OR) _n : silica precursor may be 1-50: 99-50.

(2) Metal oxide-oxygen-based material The metal oxide-oxygen-based material is selected from the group consisting of hafnium (Hf), titanium (Ti), indium (In), zirconium (Zr), and tin (Sn). Amorphous in which one or more selected metals are bonded to a residue derived from one or more oxygen acids selected from the group consisting of boric acid, phosphoric acid, sulfuric acid, carbonic acid and nitric acid via an oxygen atom Quality materials. The metal oxide-oxygen acid-based material is usually produced by subjecting a metal oxide precursor and oxyacid or a precursor thereof to a sol-gel reaction, and then heating and baking.

(Metal oxide precursor)
Examples of the metal oxide precursor in the present invention include all compounds capable of generating a metal oxide by a sol-gel reaction. Specific examples include metal alkoxides, isocyanate metal compounds, halides, chelate complexes, and organometallic complexes, and metal alkoxides are preferred.

(Oxygen acid or its precursor)
The oxygen acid in the present invention is not particularly defined, but boric acid, sulfuric acid, phosphoric acid, carbonic acid and nitric acid are preferable, and phosphoric acid is most preferable. Only one type of oxygen acid and its precursor may be used, or two or more types may be used. In addition, the oxygen acid precursor means a substance that has substantially the same function as oxygen acid in the sol-gel reaction, and examples thereof include P ₂ O ₅ , polyphosphoric acid, and SO ₃ .

The main component of the metal component of the metal oxide precursor is at least one selected from hafnium (Hf) ions, titanium (Ti) ions, indium (In) ions, zirconium (Zr) ions, and tin (Sn) ions. It is more preferable that it contains zirconium (Zr) ions, titanium (Ti) ions, or hafnium (Hf) ions. Here, the main component means a component having the largest content (mol%) among metal components.

Further, the metal oxide precursor preferably contains a trivalent metal ion in addition to the above metal ions. The trivalent metal ions are at least one selected from yttrium (Y) ions, aluminum (Al) ions, indium (In) ions, scandium (Sc) ions, and lanthanoid ion groups (including lanthanum (La) ions). A seed is preferred, and yttrium is more preferred. Such trivalent metal ions are preferably contained in a proportion of 0.03 to 0.20 mol per 1 mol of the metal ions, and 0.03 to 0.10 per mol of metal ions. More preferably, it is contained in a molar ratio. Thus, by including a trivalent metal ion in the metal oxide precursor, proton conductivity may be further improved, which is preferable.

When a metal alkoxide is used as the metal oxide precursor, a metal alkoxide represented by M (OR) _n is more preferable. Here, M is a rare earth metal atom, aluminum (Al), zirconium (Zr), niobium (Nb), hafnium (Hf), tantalum (Ta) or a first transition metal atom, cerium (Ce), aluminum (Al ), Titanium (Ti), zirconium (Zr), niobium (Nb), yttrium (Y), lanthanum (La), hafnium (Hf), or tantalum (Ta). Here, R is a group containing an alkyl group, preferably an alkyl group having 1 to 7 carbon atoms, an alkylcarbonyl group, an alkyl ketone group, or an alkyl diketone group. Moreover, it is preferable that n is an integer of 1-6.

Specific examples of M (OR) _n include Ce (OC ₂ H ₄ OCH ₃ ) ₃ , Hf (OC ₄ H ₉ ) ₄ , Ta (OC ₂ H ₅ ) ₅ , Zr (OC ₄ H ₉ ) ₄ , Al ( OCH (CH ₃ ) ₂ ) ₃ , La (OC ₂ H ₄ OCH ₃ ) ₃ , Y (OC ₂ H ₄ OCH ₃ ) ₃ , Nb (OC ₂ H ₅ ) ₅ , Ti (OC ₄ H ₉ ) _4, etc. Can be mentioned. Only one type of metal oxide precursor may be used, or two or more types may be used.

In the metal oxide-oxygen-based material, the molar ratio of the group derived from oxyacid to the metal oxide is preferably 10: 1 to 1:10, and preferably 3: 1 to 1: 5. More preferred.

Since the manufacturing method of the inorganic solid electrolyte membrane 13 made of the metal oxide-oxygen-based material is the same as that of the inorganic solid electrolyte membrane 13 made of the above-described metal oxide-based material, detailed description thereof is omitted.

The thickness of the inorganic solid electrolyte membrane 13 can be, for example, 0.005 μm to 1.0 μm, further, a thickness of 100 nm or less, particularly 10 nm or less. A conventional electrolyte membrane made of crystalline ceramic is usually made of crystal particles of several tens of nanometers or more, and thus cannot have a thickness of 5 μm or less. Is extremely significant in that this point can be avoided.

The hydrogen ion conductivity of the inorganic solid electrolyte membrane 13 is, for example, preferably 1 × 10 ⁻⁶ S · cm ⁻¹ or more at an operating temperature of 0 to 500 ° C., preferably 100 to 400 ° C., and 5 ×. More preferably, it is 10 ⁻⁵ S · cm ⁻¹ or more.

Furthermore the area resistance value of the inorganic solid electrolyte film 13 can be a 10 .OMEGA.cm ² or less, further may be a 1 .OMEGA.cm ² or less, in particular can be a 0.5Omucm ² or less, preferably, 0.2Omucm What is ² or less can be made. Among these, at the operating temperature of 0 to 500 ° C., preferably at the operating temperature of 100 to 400 ° C., the sheet resistance value is more preferably the above value. When the area resistance ratio is so small, there is an advantage that the ion transport efficiency is increased and, for example, the performance as a fuel cell is improved. Thus, the highly practical inorganic solid electrolyte membrane 13 has not been obtained conventionally.

As described above, the inorganic solid electrolyte membrane 13 can be in the form of a film (hereinafter sometimes referred to as “conductive membrane”), and the inorganic solid electrolyte membrane 13 is used as an electrolyte membrane of a solid fuel cell. Can do.

The fuel cell 10 has a current collector closely attached to both sides of a joined body of an inorganic solid electrolyte membrane 13 and a pair of electrodes (a hydrogen permeable metal foil 12 that is a fuel electrode and an air electrode 14), and an electrode chamber is formed from both sides. Conductive separators (bipolar plates) that serve as separation and gas supply passages to the electrodes are arranged. The fuel cell 10 is a single cell, and a plurality of single cells are stacked to constitute a fuel cell stack.
Here, the structure of the air electrode 14, the material, the bonding method to the membrane electrode assembly 11, and the like can be arbitrarily selected. For example, “Solid Oxide Fuel Cell: Development of SOFC” (Publisher: CMC Publishing Co., Ltd.), Chapter 7 of “Fuel Cell Technology and its Applications” (Publisher: Techno System Co., Ltd.), “ Those described in various documents such as “Commentary / Fuel cell system” (publisher: Ohm) can be adopted as appropriate.

It is desirable to operate the fuel cell at a high temperature because the catalytic activity of the electrode is increased and the electrode overvoltage is reduced. However, there is a problem of deterioration due to the chemical reaction of the electrode, the inorganic solid electrolyte membrane 13, the current collector, and the separator. There is. The operating temperature of the fuel cell using the fuel cell 10 is not particularly limited as long as it does not depart from the gist of the present invention. For example, even at a high temperature of 500 ° C. or less, 100 ° C. to 500 ° C., more preferably less than 500 ° C. This is extremely significant in that it can be sufficiently operated even at a temperature of 400 ° C. or lower.

Furthermore, for example, a fuel cell that operates in an intermediate temperature range of 200 to 400 ° C. can be obtained. This is advantageous from the viewpoint of expanding the choice of fuel and catalyst to be used and constructing a highly versatile battery system.

In the present embodiment, the case where the membrane electrode assembly 11 is used in the fuel battery cell 10 has been described. However, the membrane electrode assembly obtained in this way can also be used in a hydrogen gas generator or the like. .

Next, examples carried out for confirming the effects of the present invention will be described.
Example _{1~3: Pt / Al-SiO x} // Pd manufacturing of the fuel cell (1) Preparation Al-Si mixed precursor solution of the reaction mixture (Al-Si precursor solution) was prepared by the following procedure. First, 10 mL of chloroform was added to aluminum tri-sec-butoxide (0.3 g), and the mixture was shaken lightly, followed by ultrasonic irradiation for 1 minute to prepare a solution. This is an aluminum solution.
Separately, 15 mL of tetraethoxylane (0.49 g) was added to 1-propanol. Furthermore, 85.5 μL of hydrochloric acid (1N) was added thereto and stirred at room temperature for 1 hour to prepare a solution. This is a silane solution.

1 mL of an aluminum solution was added to the silane solution prepared by the above operation while irradiating ultrasonic waves, and the mixture was heated and stirred at 50 ° C. for 1 hour. Then, this mixed solution was filtered through a cellulose acetate filter (filter pore size: 0.2 μm), 1-propanol was added to the filtrate, and the mixture was diluted to 50 mL as a whole. An Al—Si mixed precursor solution having a total metal concentration (Al + Si) of 50 mM and an Al / Si molar ratio of 5/95 was prepared.

(2) Film Formation Operation of Solid Electrolyte Membrane 200 μL of the Al—Si mixed precursor solution obtained as described above was dropped on palladium (Pd) foil set on a spin coater, and was spun at 3000 rpm for 40 seconds. Subsequently, while rotating the Pd foil at 3000 rpm, the Pd foil was heated by hot air irradiation from a heat gun for 45 seconds, and then allowed to cool for 120 seconds while blowing nitrogen gas. The operation process from dropping of the precursor solution to blowing of nitrogen gas was performed once, and this operation was repeated a predetermined number of times to produce an electrolyte membrane on the palladium foil (see FIG. 2).

Example 1
A self-supporting palladium (Pd) foil (thickness: 0.05 mm) whose surface was not polished was heated from room temperature to 450 ° C. over 3 hours, and the temperature was maintained for 1 hour. Then, it naturally left to cool. Next, the temperature was raised again from room temperature to 450 ° C. in 20 minutes, the temperature was maintained for 1 hour, and then allowed to cool naturally. Next, this surface was subjected to oxygen plasma treatment (10 W, 10 cm ³ / min, 30 seconds). The electrolyte membrane was formed 45 times. After film formation, the temperature was raised to 450 ° C. over 3 hours, and the temperature was maintained for 1 hour. Then, it naturally left to cool. Next, a circular platinum electrode having a diameter of 1 mm was formed on the surface of the electrolyte membrane, and the impedance of the electrolyte membrane was measured at room temperature, 200 degrees, 300 degrees, and 400 degrees. FIG. 3 shows an impedance cole-cole plot of the cell at each temperature. Only capacitive semicircular curves were observed at room temperature, but as the temperature increased, diffusion spikes (straight-up straight line portions) were observed, and the Pt / Al-SiO _x / Pd cells joined as fuel cells. It was confirmed that

Example 2
A self-supporting palladium (Pd) foil (thickness: 0.05 mm) having a mirror-polished surface was heated from room temperature to 450 ° C. over 3 hours, and the temperature was maintained for 1 hour. Then, it naturally left to cool. Next, the temperature was raised again from room temperature to 450 ° C. in 20 minutes, the temperature was maintained for 1 hour, and then allowed to cool naturally. Next, platinum was sputtered on the surface for 150 seconds, and then oxygen plasma treatment (10 W, 10 cm ³ / min, 10 seconds) was performed. The electrolyte membrane formation operation was performed 60 times. After film formation, the temperature was raised to 450 ° C. over 3 hours, and the temperature was maintained for 1 hour. Then, it naturally left to cool. Further, a circular platinum electrode having a diameter of 1 mm was formed on the surface of the electrolyte membrane, and a Pt / Al—SiO _x / Pd cell composed of an electrode (platinum circular electrode) -electrolyte membrane-electrode (Pd foil) was produced. Using this Pt / Al—SiO _x // Pd cell, impedance measurement was performed at 400 ° C. FIG. 4 shows a cell impedance cole-cole plot. In the low-frequency region, spikes (upward straight lines) were observed, and it was confirmed that Pt / Al—SiO _x / Pd cells were joined as fuel cells.

Subsequently, a Pt / Al—SiO _x // Pd cell was attached to a dedicated holder and heated to 400 ° C., then a nitrogen / oxygen mixed gas humidified on the cathode side (Pt electrode) (the flow rates of nitrogen and oxygen were respectively 80 cm ³ / min and 20 cm ³ / min) was supplied, and each flow rate of the anode (Pd pole) in a hydrogen / nitrogen mixed gas (nitrogen and hydrogen were respectively supplied to 50 cm ³ / min and 50 cm ³ / min). When the open circuit voltage at that time was measured, it was 0.26V.

Example 3
Self-supporting palladium (Pd) foil (thickness: 0.05 mm) having an unpolished surface was used to polish the surface using an abrasive (trade name: Picard (registered trademark)). Then, it was immersed in Pd foil in hexane, and ultrasonically cleaned for 5 minutes with a bath-type sonicator. After drying, the temperature was raised from room temperature to 450 ° C. over 3 hours, and the temperature was maintained for 1 hour. Then, it naturally left to cool. Next, the temperature was raised again from room temperature to 450 ° C. in 20 minutes, the temperature was maintained for 1 hour, and then allowed to cool naturally. Next, platinum was sputtered on the surface for 150 seconds, and then oxygen plasma treatment (10 W, 10 cm ³ / min, 10 seconds) was performed. The electrolyte membrane formation operation was performed 60 times. After film formation, the temperature was raised to 450 ° C. over 3 hours, and the temperature was maintained for 1 hour. Next, a circular platinum electrode having a diameter of 1 mm was formed on the surface of the electrolyte membrane, and a Pt / Al-SiO _x / Pd cell composed of an electrode (platinum circular electrode) -electrolyte membrane-electrode (intermediate layer) -Pd foil was produced. Using this Pt / Al—SiO _x // Pd cell, impedance measurement was performed at 400 ° C. FIG. 5 shows a cell impedance cole-cole plot. In the low-frequency region, spikes (upward straight lines) were observed, and it was confirmed that Pt / Al—SiO _x / Pd cells were joined as fuel cells.

Subsequently, a Pt / Al—SiO _x // Pd cell was attached to a dedicated holder and heated to 400 ° C., then a nitrogen / oxygen mixed gas humidified on the cathode side (Pt electrode) (the flow rates of nitrogen and oxygen were respectively 80 cm ³ / min and 20 cm ³ / min) was supplied, and each flow rate of the anode (Pd pole) in a hydrogen / nitrogen mixed gas (nitrogen and hydrogen were respectively supplied to 50 cm ³ / min and 50 cm ³ / min). When the open circuit voltage at that time was measured, it was 0.29V.

Example 4: Production of Pt / ZrP ₃ O _x / Ni / Pd fuel cell As a proton conductive solid electrolyte membrane, amorphous zirconium phosphate, ZrP _2.4 O _8.6 H _x (hereinafter referred to as ZrP ₃ O _x) ) Were used as hydrogen permeable alloy anodes and Pd alloy foils (thickness 0.05 mm) having self-supporting properties, respectively, to produce heterojunction Pt / ZrP ₃ O _x / Ni / Pd fuel cells. As a pretreatment, the surface of the Pd foil was polished with a metal abrasive (Pical (registered trademark)) for about 10 minutes, ultrasonically cleaned in water for 5 minutes, and finally ultrasonically cleaned in acetone for 5 minutes.
An Ni metal ultrathin film (thickness 0.5 to 50 nm) was formed as a hydrogen-permeable metal intermediate layer on the surface-polished alloy foil by a high-frequency sputter deposition method. After vapor deposition, the sample was heated in a tubular electric furnace in a 1% -H ₂ / Ar atmosphere at a heating rate of 1.5 ° C./min and then heat-treated at 400 ° C. for 1 hour.

Preparation of the reaction liquid (Zr-P mixed precursor solution) containing the precursor of the solid electrolyte membrane was performed as follows. Zirconium tetrabutoxide and diphosphorus pentoxide were weighed in predetermined amounts, each dissolved in 2-methoxyethanol and stored at room temperature for 1 hour. The Zr and P solutions thus obtained were mixed in 5 mL portions, diluted by adding 20 mL of ethanol, and a Zr-P mixed precursor solution having a total metal concentration (Zr + P) of 50 mM and a Zr / P molar ratio of 1/3 was prepared. Prepared.

A ZrP ₃ O _x electrolyte film was produced on a Ni / Pd foil by a multilayer spin casting method (see FIG. 2) using a Zr—P mixed precursor solution. A Zr—P mixed precursor solution (about 100 μL) was dropped onto a hydrogen permeable metal foil fixed to a spin coater, and spin coated at a rotational speed of 3000 rpm for 20 seconds to precipitate a Zr—P gel ultrathin film. Subsequently, the gel layer was hydrolyzed by blowing hot air on the hydrogen permeable metal foil 12 for 1 minute with a heat gun to form a Zr-P oxide layer. Finally, air was blown to cool the hydrogen permeable metal foil. The above spin casting / hydrolysis / cooling process was repeated a predetermined number of times to deposit an oxide thin film, and then fired in a muffle furnace at 450 ° C. for 1 hour. Furthermore, the process of precipitation and baking was repeated twice or more to form a ZrP ₃ O _x electrolyte film having a thickness of about 100 nm. A Pt porous electrode layer (thickness: 50 nm) was sputter-deposited as an air electrode on the surface of the ZrP ₃ O _x thin film to form a Pt / ZrP ₃ O _x / Ni / Pd fuel cell. A schematic diagram of the fuel cell thus obtained is shown in FIG. 1 (a), and a scanning electron micrograph of the cross section is shown in FIG. 1 (b).

The Pt / ZrP ₃ O _x / Ni / Pd cell obtained as described above was attached to a dedicated holder and heated to 400 ° C., and then humidified air (P (H ₂ O) = the 0.02 atm) was supplied at 100 cm ³ / min, also a 50% _-H 2 / Ar mixed gas to the anode side (Pd pole) power generation test was performed by supplying at 100 cm ³ / min. The current-voltage curve and current-output curve at that time are shown in FIG. The time shown in FIG. 6 represents the elapsed time from the start of gas supply to the Pt / ZrP ₃ O _x / Ni / Pd cell.

It can be seen that the open circuit voltage and the maximum output of the cell improve as time passes from the start of gas supply. In particular, after 56 minutes, the open circuit voltage reaches 1.05 V, which is approximately equal to the theoretical fuel cell open circuit voltage of 1.1 V. From the above, it has been shown that the amorphous ZrP ₃ O _x electrolyte thin film maintains airtightness even at a film thickness of about 100 nm, and gas leakage through pinholes or cracks can be ignored. The maximum output of the cell is about 1.0 mW / cm ² after 56 minutes.

FIG. 7 shows an impedance cole-cole plot of a cell under an open circuit voltage condition in a Pt / ZrP ₃ O _x / Ni / Pd cell. The impedance plot shows two large semicircles on the high frequency side and the low frequency side. The semicircle on the high frequency side indicates the charge transfer resistance at the Ni / ZrP ₃ O _x interface, and the low frequency side indicates the cathode polarization resistance component on the air electrode side. This indicates that the cathode and anode reactions are proceeding in the fuel cell power generation environment, and that the cell of FIG. 1b is operating as a fuel cell.

10: Fuel cell 11: Membrane electrode assembly 12: Hydrogen permeable metal foil 13: Solid electrolyte membrane 14: Air electrode 15: Intermediate layer

Claims (17)

A hydrogen permeable metal foil having a thickness of 1 μm or more and having a self-supporting property;
A membrane electrode assembly comprising an amorphous inorganic solid electrolyte membrane having hydrogen ion conductivity. 2. The membrane electrode assembly according to claim 1, further comprising an intermediate layer made of a metal that is less deformed when storing hydrogen than the hydrogen permeable metal between the hydrogen permeable metal foil and the solid electrolyte membrane. . The inorganic solid electrolyte membrane takes a coordination number of 5 or more in one or more metal oxides selected from the group consisting of SiO ₂ , TiO ₂ , ZrO ₂ , Al ₂ O ₃ and CeO _2. 3. An amorphous material doped with an obtained cation (except a metal ion of the same kind as that of the metal oxide) and bonded via an oxygen atom. 2. The membrane electrode assembly according to item 1. The inorganic solid electrolyte membrane is an amorphous aluminosilicate having a molar ratio of silicon (Si) to aluminum (Al) of 50:50 to 99.9: 0.1. The membrane electrode assembly according to any one of the above. The solid electrolyte membrane includes one or more metals selected from the group consisting of hafnium (Hf), titanium (Ti), indium (In), zirconium (Zr), and tin (Sn), boric acid, phosphoric acid, 3. An amorphous material in which a residue derived from one or more oxygen acids selected from the group consisting of sulfuric acid, carbonic acid and nitric acid is bonded via an oxygen atom. The membrane electrode assembly according to claim 1. The solid electrolyte membrane is one or more trivalent selected from the group consisting of yttrium (Y), aluminum (Al), iridium (Ir), scandium (Sc), and a lanthanoid group (including lanthanum (La)). The membrane electrode assembly according to claim 5, further comprising a metal. The metal is any one or more of zirconium (Zr), titanium (Ti) and hafnium (Hf), and the oxygen acid is phosphoric acid. Membrane electrode assembly. Preparing a reaction solution containing a precursor of an inorganic solid electrolyte membrane;
An amorphous inorganic solid electrolyte membrane having hydrogen ion conductivity is formed by applying the reaction solution to the surface of a hydrogen-permeable metal foil having a thickness of 1 μm or more and having self-supporting properties, and reacting the precursor. And a process for forming the membrane electrode assembly. 9. The method for producing a membrane / electrode assembly according to claim 8, wherein the solid electrolyte membrane is formed by a sol-gel method. 10. The membrane electrode bonding according to claim 8, further comprising a step of surface-treating the hydrogen-permeable metal foil to a predetermined surface roughness before applying the reaction solution. 11. Body manufacturing method. Before applying the reaction solution, the method further comprises a step of forming an intermediate layer made of a metal that is less deformed when storing hydrogen than the hydrogen permeable metal on the surface of the hydrogen permeable metal foil, The method for producing a membrane / electrode assembly according to claim 8, wherein the method is applied to a surface of the intermediate layer. The reaction solution is an alkoxide of one or more metals selected from the group consisting of silicon (Si), titanium (Ti), zirconium (Zr), aluminum (Al), and cerium (Ce), and at least 5-coordination or more. 12. The alkoxide of a metal ion capable of taking the coordination number of (except for a metal ion of the same kind as that of the metal oxide) is included as the precursor. 12. The manufacturing method of the membrane electrode assembly of description. The reaction solution contains tetraalkoxysilane and aluminum trialkoxide as a precursor, and a molar ratio of the tetraalkoxysilane to aluminum trialkoxide is 50:50 to 99.9: 0.1. The manufacturing method of the membrane electrode assembly of Claim 12. The precursor is an alkoxide of one or more metals selected from the group consisting of hafnium (Hf), titanium (Ti), indium (In), zirconium (Zr) and tin (Sn), boric acid, phosphoric acid The method for producing a membrane electrode assembly according to any one of claims 8 to 11, which is one or a plurality of oxygen acids selected from the group consisting of sulfuric acid, carbonic acid, and nitric acid, or a precursor thereof. The reaction solution is one or more trivalent metals selected from the group consisting of yttrium (Y), aluminum (Al), iridium (Ir), scandium (Sc), and a lanthanoid group (including lanthanum (La)). The method for producing a membrane / electrode assembly according to claim 14, further comprising: The method for producing a membrane / electrode assembly according to claim 15, wherein the reaction solution contains one or more of zirconium tetraalkoxide, titanium tetraalkoxide, and hafnium tetraalkoxide and phosphoric acid as the precursor. A fuel cell comprising the membrane electrode assembly according to any one of claims 1 to 7.