JP2006278231A - Proton conductive film for fuel cell, film electrode complex and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a proton conductive film, a film electrode complex and a fuel cell capable of obtaining a high-output property. <P>SOLUTION: This proton conductive film 4 for the fuel cell contains proton conductive inorganic oxide showing solid extremely strong acidity and a hydrophilic organic polymer containing at least one kind selected from a group comprising a hydroxyl group, a carboxyl group, an ether linkage and an amide linkage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a proton conductor preferably used for a fuel cell electrode or a solid electrolyte, a membrane electrode composite containing the proton conductor, and a fuel cell provided with the membrane electrode composite.

  Proton-conducting solid electrolytes are being actively researched for applications in electrochromic materials and sensors, particularly recently in high energy density fuel cells operating at low temperatures.

  In the fuel cell, a fuel electrode (anode) is provided on one of the proton conductive solid electrolytes to supply a fuel such as hydrogen or methanol, and an oxidant electrode (cathode) is provided on the other surface of the electrolyte to supply an oxidant. The fuel is oxidized electrochemically at the anode, producing protons and electrons (flowing to the external circuit), protons reach the cathode through the proton-conducting solid electrolyte, and water is generated by the oxidant and electrons coming from the external circuit. The power can be taken out.

  Perfluorosulfonic acid-containing polymers that are organic polymer ion exchange membranes are known as proton-conducting solid electrolytes, specifically based on a copolymer of tetrafluoroethylene and perfluorovinyl ether, Those having a sulfonic acid group as an exchange group (for example, trade name Nafion (registered trademark) manufactured by DuPont) are known. When a perfluorosulfonic acid-containing polymer is used as the electrolyte, the moisture contained in the membrane is reduced by drying and the proton conductivity decreases, so use at around 100 ° C where high output can be obtained requires strict water management. And the system becomes extremely complex. In addition, the perfluorosulfonic acid-containing polymer has a sparse molecular structure because it has a cluster structure, and a crossover in which an organic liquid fuel such as methanol passes through the electrolyte membrane and reaches the cathode side easily occurs. When this phenomenon occurs, the supplied liquid fuel and oxidant react directly, and energy cannot be output as electric power. Therefore, the critical problem that a stable output cannot be obtained arises.

  As an inorganic solid acid-based ion exchange membrane, a sulfuric acid-supported metal oxide having solid superacidity (for example, Patent Document 1) is known. In Patent Document 1, sulfuric acid is supported on an oxide surface containing one or more elements selected from zirconium, titanium, iron, tin, silicon, aluminum, molybdenum, and tungsten, and sulfuric acid is immobilized on the oxide surface by heat treatment. The thing is disclosed.

Patent Documents 2 and 3 describe the use of proton conductive metal oxide hydrates or oxo acid compounds as proton conductive substances. This metal oxide hydrate or oxo acid compound shrinks when hydration water or crystal water is removed by drying by power generation with dry air at high temperature. However, there is a problem that sufficient power generation performance cannot be obtained without returning to the hydrate or oxo acid compound.
JP 2002-216537 A JP 2003-142124 A JP 2004-296243 A

  An object of the present invention is to provide a proton conductive membrane, a membrane electrode assembly, and a fuel cell capable of obtaining high output characteristics.

  The proton conductive membrane for a fuel cell according to the present invention includes a proton conductive inorganic oxide exhibiting solid superacidity and at least one selected from the group consisting of a hydroxyl group, a carboxyl group, an ether bond and an amide bond. It is characterized by containing a hydrophilic organic polymer.

A membrane electrode assembly according to the present invention comprises a fuel electrode, an oxidant electrode, and an electrolyte membrane disposed between the fuel electrode and the oxidant electrode.
At least one of the fuel electrode, the oxidant electrode, and the electrolyte membrane is selected from the group consisting of a proton conductive inorganic oxide that exhibits solid superacidity, a hydroxyl group, a carboxyl group, an ether bond, and an amide bond And a hydrophilic organic polymer containing at least one kind.

A fuel cell according to the present invention comprises a fuel electrode, an oxidant electrode, and an electrolyte membrane disposed between the fuel electrode and the oxidant electrode,
At least one of the fuel electrode, the oxidant electrode, and the electrolyte membrane is selected from the group consisting of a proton conductive inorganic oxide that exhibits solid superacidity, a hydroxyl group, a carboxyl group, an ether bond, and an amide bond And a hydrophilic organic polymer containing at least one kind.

  According to the present invention, it is possible to provide a proton conductive membrane having low membrane resistance and capable of suppressing crossover of liquid fuel such as methanol. In addition, according to the present invention, it is possible to provide a proton conductive membrane, a membrane electrode assembly, and a fuel cell that can improve output characteristics.

  Embodiments of the present invention will be described below.

  The proton conductive membrane comprises a proton conductive inorganic oxide exhibiting solid superacidity and a hydrophilic organic polymer containing at least one selected from the group consisting of hydroxyl group, carboxyl group, ether bond and amide bond. contains.

  Examples of the proton conductive inorganic oxide exhibiting solid superacidity include, for example, a solid acid composed of a sulfuric acid-supported metal oxide as described in Patent Document 1 described above, and a group composed of Ti, Zr, Si, and Al. An oxide carrier containing at least one element Y selected from: and at least one element X selected from the group consisting of W, Mo, Cr and V supported on the surface of the oxide carrier. And proton-containing inorganic oxides (hereinafter referred to as elements X and Y-containing proton conductive inorganic oxides) and the like.

  The sulfate-supporting metal oxide exhibits proton conductivity due to the immobilized sulfate radical, but the sulfate radical tends to deviate by hydrolysis. Since the fuel cell generates water in the process of power generation, the use of a sulfuric acid-supported metal oxide as a proton conductive membrane of a fuel cell that uses liquid fuel may cause a decrease in proton conductivity.

  On the other hand, the exact proton conduction mechanism in the proton conductive inorganic oxide containing elements X and Y has not been elucidated yet, but the element on the surface of the oxide carrier containing element Y (hereinafter referred to as oxide carrier A). By supporting oxide particles containing X (hereinafter referred to as oxide particles B), Lewis acid points are generated in the structure of the oxide particles B, and the Lewis acid points are hydrated so that It is considered that a proton conduction field is formed due to the Stead acid point. In addition, when the proton conductive inorganic oxide has an amorphous structure, it is presumed that this also contributes to the promotion of Lewis acid point generation.

  In addition to the proton generation reaction due to the Lewis acid point, the number of entrained water molecules necessary for proton transfer can be reduced, so high proton conductivity can be achieved with a small amount of water molecules present on the surface of the proton conductive inorganic oxide. This makes it possible to eliminate the need for strict water management during power generation.

  However, the proton conducting membrane containing this proton conducting inorganic oxide is inferior in water absorption, cannot sufficiently supply water necessary for generation of protons to the solid super strong acid, and has high membrane resistance. Further, in the case of a fuel cell using a liquid fuel such as methanol, the methanol crossover could not be sufficiently controlled, and a stable output could not be obtained.

  As a result of intensive studies, the present inventors have made the proton conductive membrane contain a hydrophilic organic polymer containing at least one selected from the group consisting of a hydroxyl group, a carboxyl group, an ether bond and an amide bond. It has been found that phase separation between the proton conductive inorganic oxide and the hydrophilic organic polymer can be suppressed, and the dispersibility of the proton conductive inorganic oxide is improved. Since the obtained proton conductive membrane has high water absorption, a sufficient amount of moisture can be supplied to the proton conductive inorganic oxide, high proton conductivity can be obtained, and membrane resistance can be reduced. . Moreover, since this proton conductive membrane has high density, it is possible to suppress the permeation of liquid fuel and to suppress methanol crossover.

  Therefore, by using this proton conductive membrane as an electrolyte membrane, or by containing a proton conductive inorganic oxide and a hydrophilic organic polymer in the fuel electrode and / or the oxidizer electrode, the maximum power generation amount of the fuel cell is obtained. Can be increased.

  The proton conductive inorganic oxide containing elements X and Y will be further described. Although the solubility of the oxide particles B varies depending on the element and pH environment, the oxide particles B have water solubility. By forming a chemical bond by calcination of the oxide particles B on the oxide carrier A having low water solubility, the dissolution of the oxide particles B in water can be suppressed, and the water of the proton conductive inorganic oxide can be suppressed. In addition, the stability to liquid fuel can be increased. Further, contamination of other fuel cell materials and devices due to ions of the eluted oxide particles B can be avoided. Therefore, high long-term reliability can be obtained in the fuel cell. Furthermore, the manufacturing cost of the battery can be suppressed by using an inexpensive oxide carrier A as a base material.

  Confirmation that the oxide particles B are supported on the oxide carrier A is, for example, X-ray diffraction (XRD), electron probe microanalysis (EPMA), X-ray electron spectroscopy (XPS), energy dispersive X-ray It can be performed by instrumental analysis such as analysis (EDX). In addition, the oxide carriers A are all white, but the oxide particles B are colored (W is yellow, Mo is gray, Cr is green, and V is orange), so that visual confirmation is also possible.

The oxide carrier A contains a gas phase method in which an oxide is produced by decomposing a gas containing the element Y (consisting of at least one selected from the group consisting of Ti, Zr, Si and Al), or the element Y. The metal alkoxide can be synthesized from a sol-gel method or the like as a raw material, but the synthesis method is not limited and may be a complex oxide containing a plurality of elements. _{Specifically, TiO 2, ZrO 2, SiO} 2, Al 2 O 3, Al 2 O 3 -SiO 2, TiO 2 -SiO 2, such as ZrO ₂ -SiO ₂ and the like. In order to sufficiently increase proton conductivity, it is desirable to use ZrO ₂ . Further, in order to obtain high proton conductivity while suppressing the manufacturing cost, it is desirable to use TiO ₂ . By the way, examples of the shape of the oxide carrier A include, but are not limited to, particles, fibers, flat plates, layers, and porous shapes.

  The method of supporting the oxide particles B on the surface of the oxide support A is a solution in which a substance containing the element X (consisting of at least one selected from the group consisting of W, Mo, Cr and V) is dissolved, for example, chloride It is desirable to disperse the oxide carrier A in an aqueous solution of a product, nitrate, hydrogen acid, oxoacid salt, etc. or an alcohol solution of a metal alkoxide, and carry the oxide carrier B by removing the solvent, and then heat treatment to form oxide particles B. The supporting method is not limited to this, and it may be supported in the state of a composite oxide containing a plurality of elements. The oxide particles B may be supported on at least a part of the surface of the oxide carrier A. For example, the oxide particles B are scattered on the surface of the oxide carrier A or cover the surface of the oxide carrier A. The case where it is such a layered material is mentioned. Further, the oxide particles B only have to be supported on the surface of the oxide carrier A, and the crystallinity of the oxide particles B or the oxide carrier A is not limited. The oxide particles B and the oxide support A are preferably amorphous in consideration of the possibility of contributing to the improvement of the degree of production, the reduction of the production cost, and the ease of the production process. More preferably, the amorphous oxide support A is crystalline. However, contrary to the above, it is possible to use both the oxide particles B and the oxide carrier A in a crystal form, or the oxide particles B to be a crystal and the oxide carrier A to be used in an amorphous form. .

As described above, since the surface of the proton conductive inorganic oxide becomes a proton conduction field, it is preferable that the specific surface area of the proton conductive inorganic oxide is as large as possible, but if it exceeds 2000 m ² / g, it is handled and uniform. When the specific surface area is less than 10 m ² / g, there is a possibility that sufficient proton conductivity may not be obtained. Therefore, the specific surface area is preferably in the range of 10 to 2000 m ² / g.

  The oxide particles B supported on the oxide support A have a small amount of support when the element ratio (X / Y) of the element X of the oxide B to the element Y of the oxide A is less than 0.0001. The proton conductivity may be lowered due to the small conduction field. On the other hand, when the element ratio (X / Y) exceeds 20, the supported amount is large, and the oxide particles B containing the element X cover the proton conduction field, which may lower the proton conductivity. Therefore, the element ratio (X / Y) of the element X of the oxide B to the element Y of the oxide A is preferably in the range of 0.0001 to 20, and more preferably in the range of 0.01 to 1. desirable.

  The proton conductive inorganic oxide used in the present invention can be obtained, for example, by supporting the oxide particle B precursor on the oxide carrier A and then performing a heat treatment in an oxidizing atmosphere such as the air. When the treatment temperature is lower than 200 ° C., a sufficient chemical bond is not formed between the oxide support A and the oxide particles B, and the proton conductivity of the obtained oxide may be lowered. On the other hand, when the treatment temperature is higher than 1000 ° C., the particles are fused with each other and the specific surface area is reduced, so that high proton conductivity may not be obtained. The heat treatment temperature is preferably 200 to 1000 ° C., more preferably 400 to 700 ° C. Further, since the temperature is low at 200 ° C., it is difficult to form a bond between the oxide carrier A and the oxide particles B, and a long heat treatment is required. It is synthesized by heat treatment at

The proton conductive inorganic oxide exhibits solid superacidity. The degree of proton dissociation can be expressed as acid strength, the acid strength of solid acid is expressed as Hammett acidity function H ₀ , and in the case of sulfuric acid, H ₀ is −11.93. More preferably, the proton-conductive inorganic oxide exhibits solid superacidity so that H ₀ <-11.93. The solid superacidity of the proton conductive inorganic oxide can be determined indirectly by measuring the solid superacidity of the proton conductive membrane, as will be described later in Examples.

  Next, the hydrophilic organic polymer used in the present invention will be described.

  The hydrophilic organic polymer contains at least one selected from the group consisting of a hydroxyl group, a carboxyl group, an ether bond and an amide bond in the polymer structure.

  In the proton conductive membrane, it is desirable that the proton conductive inorganic oxide is contained in the hydrophilic organic polymer or the proton conductive inorganic oxide is bound by the hydrophilic organic polymer. The solid superacid exhibits a function as a proton conductor when moisture is present on the surface. By selecting a hydrophilic organic polymer as the polymer containing or binding the solid superacid, it becomes possible to supply sufficient water to the solid superacid, and a proton-conducting solid electrolyte having high proton conductivity can be obtained. Can be realized.

  Specific examples of the hydrophilic organic polymer will be given. Examples of the hydrophilic organic polymer having a hydroxyl group include polyvinyl alcohol. Examples of the hydrophilic organic polymer having a carboxyl group include polyacrylic acid. Examples of the organic polymer having an ether bond include polyethylene glycol and cellulose. Examples of the organic polymer having an amide bond include polyamide and polyvinyl pyrrolidone. An organic polymer having an ester bond is also conceivable.

  In particular, with polyvinyl alcohol, the affinity with the proton conductive inorganic oxide is increased, so that the dispersibility of the proton conductive inorganic oxide can be improved, and the proton conductive inorganic oxide and the hydrophilic property can be improved. Phase separation from the organic polymer can also be suppressed. As a result, a proton conductive membrane excellent in water absorption and methanol permeation suppression can be realized.

  The saponification degree of polyvinyl alcohol is desirably 50% or more and 100% or less. This is due to the reason explained below. When the degree of saponification is less than 50%, the resistance of the proton conductive membrane may increase due to a decrease in hygroscopicity of the membrane. On the other hand, when the degree of saponification is 50% to 100%, the permeability of methanol may increase due to an increase in hygroscopicity, but the resistance of the proton conductive membrane can be reduced. The method for measuring the degree of saponification is as described below. Polyvinyl alcohol is completely saponified with an alkaline substance such as sodium hydroxide. Whether it has been completely saponified can be confirmed by infrared absorption analysis. The degree of saponification can be determined from the amount of acetate obtained by saponification.

  The hydrophilic polymer desirably has an equilibrium moisture absorption rate of 5% or higher at 20 ° C. or higher. Since such a hydrophilic polymer has high water absorption, the membrane resistance of the proton conductive membrane can be further reduced. More preferred hydrophilic polymers are those having an equilibrium moisture absorption rate of 5% or more and 95% or less at 20 ° C. or higher and 90 ° C. or lower.

  The equilibrium moisture absorption rate was measured by measuring the weight of the sample film when the sample film was allowed to stand for one week in a constant temperature and humidity controlled at a temperature of 20 ° C. or higher and a relative humidity of 95% or higher. It measured from the difference with the weight after drying at 105 degreeC for 2 hours. Note that the sample film was prepared by dissolving a hydrophilic polymer in water and casting the obtained slurry.

  It is desirable that the mixing ratio of the proton conductive inorganic oxide and the hydrophilic polymer satisfies the condition for preventing the permeation of the liquid fuel while maintaining high proton conductivity. If the weight ratio (S / T) of the proton conductive inorganic oxide (S) to the total membrane weight (T) is less than 0.1, the continuity of the proton conductive inorganic oxide is lowered and the conductivity is low. Therefore, the weight ratio (S / T) is preferably in the range of 0.1 to 0.999.

  The proton conductive membrane is prepared by, for example, preparing a slurry in which a proton conductive inorganic oxide and a hydrophilic organic polymer are dispersed in a polar solvent such as water or alcohol, and casting the slurry on a glass substrate or a resin substrate, followed by drying. After removing the solvent by doing, it is manufactured by heat treatment at a temperature of 200 ° C. or lower. Although details are not clarified, heat treatment at 200 ° C. or lower causes oxidation reaction or dehydration reaction between proton conductive inorganic oxide and hydrophilic organic polymer, interaction consisting of hydrogen bond, hydrophilic organic polymer. It is presumed that crystallization and the like can occur, and swelling and dissolution of the hydrophilic organic polymer can be prevented. At least with respect to polyvinyl alcohol, infrared spectroscopy (IR) shows that a hydrophilic hydroxyl group in polyvinyl alcohol is oxidized by a solid superacid to become a hydrophobic ketone group by heat treatment at a temperature of 200 ° C. or less. ) Result.

  When a proton conductive membrane is produced by performing slurry preparation and heat treatment by the above-described method using polyvinyl alcohol, the polyvinyl alcohol is dissolved in a polar solvent such as water without impairing the affinity for the proton conductive inorganic oxide. Therefore, it is possible to improve the shape retention of the proton conductive membrane during water absorption while improving the dispersion stability of the slurry. Thereby, it is possible to realize a proton conductive membrane that is excellent in water absorption and has suppressed methanol permeation. In addition, by performing the above heat treatment, a film having excellent shape retention can be obtained even if water is used as a solvent used for slurry preparation. Therefore, the hydrophilicity of the film can be further increased by using water in the solvent. is there.

  The heat treatment temperature must be such that the hydrophilic organic polymer is not decomposed or deteriorated, and the heat treatment is preferably performed at a temperature of 200 ° C. or lower. Moreover, in order to make the effect by heat treatment sufficient, the heat treatment temperature is desirably 100 ° C. or higher. A more preferable range of the heat treatment temperature is 130 ° C. or higher and 180 ° C. or lower.

  When the proton conductive membrane is used as a solid electrolyte membrane of a fuel cell, it is generally used as a sheet, but is not limited to this and can be formed into a cylindrical shape. That is, a method of directly casting a dispersion mixture of proton conductive inorganic oxide and the above-mentioned hydrophilic organic polymer into a film, or impregnating the dispersion mixture into a porous core material, woven fabric or nonwoven fabric, etc. This method can be adopted.

  The thickness of the proton conductive solid electrolyte membrane is not particularly limited, but is preferably 10 μm or more in order to obtain a membrane that can withstand practical use such as strength, liquid fuel permeability, and proton conductivity, and also reduces membrane resistance. Therefore, 300 μm or less is preferable. In particular, in order to reduce the internal resistance of the fuel cell, 10 to 100 μm is more preferable.

  In order to control the thickness of the membrane, for example, when the dispersion mixture of the proton conductive inorganic oxide and the hydrophilic organic polymer is directly cast into a membrane, the proton conductive inorganic oxide to be cast and the above In addition to the amount of the hydrophilic organic polymer dispersion mixture or cast area, the film thickness can be reduced by heating and pressurizing the film with a hot press machine after film formation. It is not something.

  Next, the electrode provided by the present invention will be described in more detail.

  The electrode contains a proton conductive inorganic oxide exhibiting solid superacidity and a hydrophilic organic polymer containing at least one selected from the group consisting of hydroxyl group, carboxyl group, ether bond and amide bond And can be used as a fuel electrode of a fuel cell, an oxidant electrode, or both a fuel electrode and an oxidant electrode.

  According to an embodiment of the electrode according to the present invention, there is provided an electrode including a catalyst layer including a redox catalyst, the proton conductive inorganic oxide, and the hydrophilic organic polymer also serving as a binder. .

  Each of the fuel electrode and the oxidant electrode is made of a gas diffusible structure such as a porous body, and fuel gas, liquid fuel, or oxidant gas can flow therethrough. In order to promote a fuel oxidation reaction on the fuel electrode and an oxygen reduction reaction on the oxidant electrode, a metal catalyst is supported on a conductive support material such as carbon. Examples of such metal catalysts include platinum, gold, silver, palladium, iridium, rhodium, ruthenium, iron, cobalt, nickel, chromium, tungsten, molybdenum, manganese, and vanadium. A ternary or ternary alloy may be used. In particular, platinum has a high catalytic activity and is used in many cases. In addition, the support material for supporting the metal catalyst only needs to have conductivity, and a carbon material is often used. Examples thereof include carbon black such as furnace black, channel black, and acetylene black, activated carbon, and graphite.

The method for supporting the metal catalyst on the carbon material is not particularly limited, but a solution in which a substance containing a metal element that serves as a catalyst is dissolved, for example, an aqueous solution of chloride, nitrate, hydrogen acid, oxoacid salt, or an alcohol solution of metal alkoxide. It is possible to support the metal catalyst on the carbon material by dispersing the carbon material in the substrate and removing the solvent and then carrying the heat treatment in a reducing atmosphere. The particle size of the metal serving as the catalyst is usually 1 to 50 nm, and the amount of the catalyst metal is 0.01 to 10 mg / cm ² with the electrode formed.

It is desirable that the proton conductive inorganic oxide in the catalyst layer of the fuel electrode and the oxidant electrode has a sufficient continuity because it is a path for transporting protons to the electrolyte membrane. Alternatively, the carbon material may be supported and used. The proton conductive inorganic oxide is preferably 0.01 to 50 mg / cm ² in a state where an electrode is formed.

  A hydrophilic organic polymer is used as a binder to immobilize the metal catalyst or metal catalyst-supporting carbon and the proton conductive inorganic oxide in the catalyst layer. Examples of the hydrophilic organic polymer include the same ones as described for the proton conductive membrane. Because it is desirable to form a catalyst layer structure that maintains porosity while maintaining high proton conductivity and conductivity, blending metal catalyst or metal catalyst-supported carbon and proton conductive inorganic oxide with hydrophilic organic polymer If the weight ratio (P / C) of the hydrophilic polymer (P) to the total weight (C) of the catalyst layer is greater than 0.5, the continuity of the proton conductive inorganic oxide or metal catalyst is lowered. Since the proton conductivity and conductivity may be lowered, the weight ratio P / C is preferably in the range of 0.001 to 0.5.

  The electrode may be formed as a single catalyst layer, or the catalyst layer may be formed on another support as an electrode. The method for forming the electrode is not particularly limited. For example, the metal catalyst, proton conductive inorganic oxide, and hydrophilic polymer are mixed and dispersed in an organic solvent such as water or alcohol to form a slurry, and this slurry is supported. The catalyst layer is formed by coating, drying and firing on the body. The support is not particularly limited. For example, an electrolyte membrane may be used as a support, and a catalyst layer may be formed on the electrolyte membrane to form a membrane electrode assembly. Alternatively, a catalyst layer may be formed on carbon paper, felt, cloth, etc. having gas permeability and conductivity, and an electrolyte membrane and a laminated membrane electrode composite may be formed.

  According to one embodiment of the present invention, in a membrane electrode assembly including a fuel electrode, an oxidizer electrode, and an electrolyte membrane disposed between the fuel electrode and the oxidizer electrode, the electrolyte membrane is the proton described above. A conductive membrane is used, or the fuel electrode and / or the oxidant electrode includes the above-described catalyst layer, or the fuel electrode and / or the oxidant electrode and the electrolyte membrane are the above-described catalyst. A membrane electrode assembly comprising both the layer and the above-described proton conductive membrane can be provided.

The joining of the electrolyte membrane and the electrode is performed using an apparatus that can be heated and pressurized. Generally, it is performed by a hot press machine. The press temperature in that case should just be more than the glass transition temperature of the hydrophilic polymer used as a binder for an electrode and an electrolyte membrane, and is generally 100-400 degreeC. The press pressure depends on the hardness of the electrode used, but is usually 5 to 200 kg / cm ² .

  Next, a fuel cell including the membrane electrode assembly according to the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically showing a liquid fuel cell according to an embodiment of the fuel cell of the present invention. The liquid fuel cell stack 100 is formed by stacking a plurality of unit cells. A fuel introduction path 1 is disposed on the side surface of the stack 100. Liquid fuel is supplied to the fuel introduction path 1 from a liquid fuel tank (not shown) through an introduction pipe (not shown). Each unit cell includes a membrane electrode assembly (starting electrode) 2, an oxidant electrode (cathode) 3, and an electrolyte membrane 4 arranged between the fuel electrode 2 and the oxidant electrode 3. Electric part) 5. It is desirable that the fuel electrode 2 and the oxidant electrode 3 are made of a conductive porous body so that fuel and oxidant gas can be circulated and electrons can pass therethrough.

  Each unit cell further includes a fuel vaporization unit 6 stacked on the fuel electrode 2, a fuel permeation unit 7 stacked on the fuel vaporization unit 6, and a cathode separator 8 stacked on the oxidant electrode 3. The fuel permeation unit 7 has a function of holding liquid fuel. This liquid fuel is supplied from the fuel introduction path 1. The fuel vaporization unit 6 serves to guide the vaporized component of the liquid fuel held in the fuel permeation unit 7 to the fuel electrode 2. An oxidant gas supply groove 9 for flowing an oxidant gas is provided as a continuous groove on the surface of the cathode separator 8 facing the oxidant electrode 3. The cathode separator 8 also plays a role of connecting the adjacent electromotive parts 5 in series.

  When the stack 100 is configured by stacking single cells as shown in FIG. 1, the separator 8, the fuel permeation unit 7, and the fuel vaporization unit 6 also serve as a current collector plate that conducts the generated electrons. It is desirable to be formed of a conductive material such as a porous body containing carbon.

  As described above, the separator 8 in the unit cell of FIG. 1 also has a function as a channel through which the oxidant gas flows. In this way, the number of components can be reduced by using the component 8 having both functions of a separator and a channel (hereinafter referred to as a channel separator), thereby further reducing the size of the fuel cell. Is possible. Alternatively, a normal channel can be used in place of the separator 8.

  As a method of supplying liquid fuel from a fuel storage tank (not shown) to the liquid fuel introduction path 1, there is a method in which the liquid fuel stored in the fuel storage tank is freely dropped and introduced into the liquid fuel introduction path 1. Can be mentioned. In this method, although there is a structural limitation that the fuel storage tank must be provided at a position higher than the upper surface of the stack 100, the liquid fuel can be reliably introduced into the liquid fuel introduction path 1. As another method, there is a method of drawing the liquid fuel from the fuel storage tank by the capillary force of the liquid fuel introduction unit 1. When this method is employed, the connection point between the fuel storage tank and the liquid fuel introduction path 1, that is, the position of the fuel inlet provided in the liquid fuel introduction path 1 does not need to be higher than the upper surface of the stack 100. Therefore, for example, when combined with the natural fall method, there is an advantage that the installation location of the fuel tank can be freely set.

  However, in order to continuously supply the liquid fuel introduced into the liquid fuel introduction path 1 by the capillary force to the fuel permeation unit 7 smoothly by the capillary force, the liquid fuel introduction path 1 is supplied to the fuel penetration part 7 by the capillary force of the liquid fuel introduction path 1. It is desirable to set the capillary force to be larger. The number of liquid fuel introduction paths 1 is not limited to one along the side surface of the stack 100, and the liquid fuel introduction paths 1 can be formed on the other side surface of the stack.

  The fuel storage tank as described above can be detachable from the battery body. Thus, by replacing the fuel storage tank, the operation of the battery can be continued for a long time. In addition, the liquid fuel is supplied from the fuel storage tank to the liquid fuel introduction path 1 in a configuration in which the liquid fuel is pushed out by the natural fall or the internal pressure in the tank as described above, or the capillary force of the liquid fuel introduction path 1. The fuel can be drawn out by the above.

  The liquid fuel introduced into the liquid fuel introduction path 1 by the method described above is supplied to the fuel permeation unit 7. The form of the fuel permeation unit 7 is not particularly limited as long as it has a function of holding the liquid fuel therein and supplying only the vaporized fuel to the fuel electrode 2 through the fuel vaporization unit 6. For example, a liquid fuel passage may be provided, and a gas-liquid separation membrane may be provided at the interface with the fuel vaporization unit 6. Furthermore, when liquid fuel is supplied to the fuel permeation unit 7 by capillary force without using an auxiliary device, the form of the fuel permeation unit 7 is particularly limited as long as the liquid fuel can be permeated by capillary force. In addition to porous materials made of particles and fillers, non-woven fabrics made by the papermaking method, woven fabrics made of fibers, etc., narrow gaps formed between plates made of glass or plastic are also used. be able to.

  Here, the case where a porous body is used as the fuel permeation portion 7 will be described. As the capillary force for drawing the liquid fuel to the fuel permeation unit 7 side, first, the capillary force of the porous body itself constituting the fuel permeation unit 7 is mentioned. When such capillary force is used, a so-called continuous hole is formed by connecting the holes of the fuel permeation unit 7 which is a porous body, and the diameter of the hole is controlled, and the side surface of the fuel permeation unit 7 on the liquid fuel introduction unit 1 side is controlled. By forming continuous holes from at least one other surface, it is possible to supply liquid fuel smoothly in the lateral direction with capillary force.

  The pore diameter and the like of the porous body used as the fuel permeation section 7 are not particularly limited as long as the liquid fuel in the liquid fuel introduction path 1 can be drawn in. The capillary of the liquid fuel introduction path 1 is not particularly limited. In consideration of the force, it is preferable to be about 0.01 to 150 μm. Moreover, it is preferable that the volume of the hole used as the parameter | index of the continuity of the hole in a porous body shall be about 20 to 90%. When the pore diameter is smaller than 0.01 μm, it is difficult to manufacture the fuel permeation portion 7. On the other hand, when it exceeds 150 μm, the capillary force may be reduced. Further, when the pore volume is less than 20%, the amount of continuous pores is reduced and the number of closed pores is increased, so that it is difficult to obtain sufficient capillary force. On the other hand, if the volume of the pores exceeds 90%, the amount of continuous pores increases, but the strength becomes weak and the manufacture becomes difficult. Practically, the porous body constituting the fuel permeation part 7 preferably has a pore diameter in the range of 0.5 to 100 μm, and the pore volume is preferably in the range of 30 to 75%.

  In such fuel cells, a cell reaction occurs even from room temperature, and it is possible to make the operating temperature range from room temperature to 150 ° C. However, it is more effective to operate at a high temperature of 50 ° C. to 150 ° C. It is desirable for improving the catalytic activity and reducing the electrode overvoltage. Further, in order to sufficiently exhibit the proton conductivity of the electrolyte membrane, it is desirable to operate at a temperature at which moisture management is easy.

[Example]
Hereinafter, the present invention will be described in more detail with reference to specific but non-limiting examples.

[Example 1]
A mixed solution in which 5 g of silicon oxide SiO ₂ was added to 300 ml of distilled water in which 2 g of vanadium chloride VCl ₃ was dissolved was heated to 80 ° C. with constant stirring, and water was removed at an evaporation rate of 100 ml / hour. Thereafter, it was kept in a dryer at 100 ° C. for 12 hours to obtain a powder. After this powder was pulverized in an agate mortar to form a powder, it was heated to 700 ° C. at a rate of temperature increase of 100 ° C./hour in an alumina crucible, and further kept at 700 ° C. for 4 hours, whereby vanadium oxide of vanadium oxide ( A vanadium oxide-supported silicon oxide having an element ratio X / Y of X) of silicon oxide to silicon element (Y) of 0.1 and a specific surface area of 51 m ² / g was obtained. When X-ray diffraction measurement was performed on this vanadium oxide-supported silicon oxide, it was confirmed that all diffraction peaks were attributed to silicon oxide, and that vanadium oxide had an amorphous structure. did it.

  In addition, the element ratio (X / Y) and specific surface area of proton conductive inorganic material powder were measured by the method demonstrated below. The element ratio (X / Y) was measured by energy dispersive X-ray analysis (EDX), X-ray electron spectroscopy (XPS), and atomic absorption analysis. The specific surface area was measured by the BET method.

  1 g of this proton conductive inorganic material powder was added to 2 g of an aqueous solution of 5% polyvinyl alcohol (PVA) and stirred at room temperature for 10 minutes to prepare a slurry. This slurry was put in a petri dish made of a tetrafluoroethylene perfluoroalkoxy vinyl ether copolymer (PFA) resin, and the solvent was dried at 60 ° C. and 150 ° C. in the atmosphere to obtain an electrolyte membrane. The ratio S / T of the proton conductive inorganic material (S) to the total membrane weight (T) was 0.9, and the thickness of the electrolyte membrane was 151 μm.

[Example 2]
A mixed solution of 5 g of silicon oxide SiO ₂ added to 300 ml of distilled water in which 3 g of chromium chloride hexahydrate CrCl ₃ .6H ₂ O was dissolved was heated to 80 ° C. with constant stirring, and water was added at an evaporation rate of 100 ml / hour. Removed. Thereafter, it was kept in a dryer at 100 ° C. for 12 hours to obtain a powder. This powder was pulverized in an agate mortar to form a powder, and then heated to 700 ° C. at a rate of temperature increase of 100 ° C./hour in an alumina crucible, and further maintained at 700 ° C. for 4 hours, whereby chromium element of chromium oxide ( A chromium oxide-supported silicon oxide having an element ratio X / Y of 0.1) of X) to silicon element (Y) of silicon oxide of 0.1 and a specific surface area of 52 m ² / g was obtained. When X-ray diffraction measurement was performed on this chromium oxide-supported silicon oxide, only diffraction peaks attributable to silicon oxide were observed, and it was confirmed that chromium oxide had an amorphous structure. did it.

  1 g of this proton conductive inorganic material powder was added to 2 g of 5% PVA aqueous solution and stirred at room temperature for 10 minutes to prepare a slurry. This slurry was placed in a petri dish made of PFA resin, and the solvent was dried at 60 ° C. and 150 ° C. in the atmosphere to obtain an electrolyte membrane. The ratio S / T of the proton conductive inorganic material (S) to the total membrane weight (T) was 0.9, and the thickness of the electrolyte membrane was 151 μm.

Example 3
A mixed solution in which 5 g of silicon oxide SiO ₂ was added to 300 ml of distilled water in which 2 g of ammonium molybdate (NH ₄ ) ₆ Mo ₇ O ₂₄ · 4H ₂ O was dissolved was heated to 80 ° C. with constant stirring, and evaporated at 100 ml / hour. Water was removed at a rate. Thereafter, it was kept in a dryer at 100 ° C. for 12 hours to obtain a powder. This powder was pulverized in an agate mortar to form a powder, and then heated to 700 ° C. at a rate of temperature increase of 100 ° C./hour in an alumina crucible, and further maintained at 700 ° C. for 4 hours, whereby molybdenum element of molybdenum oxide ( Molybdenum oxide-supporting silicon oxide having an element ratio X / Y of X) of silicon oxide to silicon element (Y) of 0.1 and a specific surface area of 55 m ² / g was obtained. When X-ray diffraction measurement was performed on this molybdenum oxide-supported silicon oxide, it was confirmed that all diffraction peaks were attributed to silicon oxide, and that molybdenum oxide had an amorphous structure. did it.

  1 g of this proton conductive inorganic material powder was added to 2 g of 5% PVA aqueous solution and stirred at room temperature for 10 minutes to prepare a slurry. This slurry was placed in a petri dish made of PFA resin, and the solvent was dried at 60 ° C. and 150 ° C. in the atmosphere to obtain an electrolyte membrane. The ratio S / T of the proton conductive inorganic material (S) to the total membrane weight (T) was 0.9, and the thickness of the electrolyte membrane was 155 μm.

Example 4
A mixed solution obtained by adding 5 g of silicon oxide SiO ₂ and 150 ml of 0.1 N aqueous nitric acid solution to 300 ml of distilled water in which 3 g of sodium tungstate dihydrate NaWO ₄ .2H ₂ O was dissolved was heated to 80 ° C. with constant stirring. The water was removed at an evaporation rate of 100 ml / hour. Thereafter, it was kept in a dryer at 100 ° C. for 12 hours to obtain a powder. This powder was dispersed in 100 ml of a 0.1 N aqueous nitric acid solution, and suction filtration was performed to remove unnecessary sodium ions. The solid content after filtration is kept in a dryer at 100 ° C. for 6 hours to remove moisture, then pulverized in an agate mortar to form a powder, and heated to 700 ° C. in an alumina crucible at a heating rate of 100 ° C./hour. Further, by holding at 700 ° C. for 4 hours, the element ratio X / Y between the tungsten element (X) of tungsten oxide and the silicon element (Y) of silicon oxide is 0.1, and the specific surface area is 50 m ² / g. A tungsten oxide-supported silicon oxide was obtained. When X-ray diffraction measurement was performed on this tungsten oxide-supported silicon oxide, it was confirmed that all diffraction peaks were attributed to silicon oxide, and that tungsten oxide had an amorphous structure. did it.

  1 g of this proton conductive inorganic material powder was added to 2 g of 5% PVA aqueous solution and stirred at room temperature for 10 minutes to prepare a slurry. This slurry was placed in a petri dish made of PFA resin, and the solvent was dried at 60 ° C. and 150 ° C. in the atmosphere to obtain an electrolyte membrane. The ratio S / T of the proton conductive inorganic material (S) to the total membrane weight (T) was 0.9, and the thickness of the electrolyte membrane was 150 μm.

Example 5
The same operation as in Example 1 was conducted except that 5 g of silicon oxide was changed to 7 g of titanium oxide (TiO ₂ ), and the element ratio X / Y between the vanadium element (X) of vanadium oxide and the titanium element (Y) of titanium oxide was changed. Of vanadium oxide having a specific surface area of 54 m ² / g was obtained. Further, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA composite membrane of 0.9 and a film thickness of 155 μm was obtained.

Example 6
The same operation as in Example 2 was conducted except that 5 g of silicon oxide was changed to 7 g of titanium oxide (TiO ₂ ), and the element ratio X / Y of chromium element (X) of chromium oxide and titanium element (Y) of titanium oxide was changed. Was 0.1 and the specific surface area was 49 m ² / g. Further, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA composite membrane of 0.9 and a film thickness of 157 μm was obtained.

Example 7
The same operation as in Example 3 was conducted except that 5 g of silicon oxide was changed to 7 g of titanium oxide (TiO ₂ ), and the element ratio X / Y of molybdenum element (X) of molybdenum oxide to titanium element (Y) of titanium oxide was changed. Of titanium oxide with a specific surface area of 48 m ² / g was obtained. Further, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA composite membrane of 0.9 and a film thickness of 150 μm was obtained.

Example 8
The same operation as in Example 4 was performed except that 5 g of silicon oxide was changed to 7 g of titanium oxide (TiO ₂ ), and the element ratio X / Y of tungsten element (X) of tungsten oxide and titanium element (Y) of titanium oxide was changed. Of tungsten oxide having a specific surface area of 50 m ² / g was obtained. Furthermore, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA composite membrane of 0.9 and a film thickness of 154 μm was obtained.

Example 9
The same operation as in Example 1 was conducted except that 5 g of silicon oxide was changed to 11 g of zirconium oxide (ZrO ₂ ), and the element ratio X / Y between the vanadium element (X) of vanadium oxide and the zirconium element (Y) of zirconium oxide was changed. Of vanadium oxide and zirconium oxide having a specific surface area of 53 m ² / g. Further, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA composite membrane of 0.9 and a film thickness of 149 μm was obtained.

Example 10
The same operation as in Example 2 was performed except that 5 g of silicon oxide was changed to 11 g of zirconium oxide (ZrO ₂ ), and the element ratio X / Y between chromium element (X) of chromium oxide and zirconium element (Y) of zirconium oxide was changed. Was 0.1 and the specific surface area was 50 m ² / g. Further, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA composite membrane of 0.9 and a film thickness of 151 μm was obtained.

Example 11
The same operation as in Example 3 was performed except that 5 g of silicon oxide was changed to 11 g of zirconium oxide (ZrO ₂ ), and the element ratio X / Y of molybdenum element (X) of molybdenum oxide to zirconium element (Y) of zirconium oxide was Was obtained, and molybdenum oxide-supported zirconium oxide having a specific surface area of 51 m ² / g was obtained. Further, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA composite membrane of 0.9 and a film thickness of 151 μm was obtained.

Example 12
The same operation as in Example 4 was performed except that 5 g of silicon oxide was changed to 11 g of zirconium oxide (ZrO ₂ ), and the element ratio X / Y of tungsten element (X) of tungsten oxide and zirconium element (Y) of zirconium oxide was changed. Of tungsten oxide having a specific surface area of 50 m ² / g was obtained. Furthermore, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA composite membrane of 0.9 and a film thickness of 153 μm was obtained.

Example 13
The same operation as in Example 1 was carried out except that 2 g of 5% PVA aqueous solution was changed to 2 g of a mixed solution of 1.5 g of 5% PVA aqueous solution and 0.5 g of 5% polyacrylic acid (PA) aqueous solution. Vanadium oxide-supporting silicon oxide having an element ratio X / Y of 0.1 and a specific surface area of 53 m ² / g between the vanadium element (X) and the silicon element (Y) of silicon oxide was obtained. Further, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA / PA composite membrane of 0.9 and a film thickness of 153 μm was obtained.

Example 14
The same operation as in Example 2 was performed except that 2 g of 5% PVA aqueous solution was changed to 2 g of a mixed solution of 1.5 g of 5% PVA aqueous solution and 0.5 g of 5% PA aqueous solution. ) And silicon element (Y) of silicon oxide, a chromium oxide-supporting silicon oxide having an element ratio X / Y of 0.1 and a specific surface area of 54 m ² / g was obtained. Further, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA / PA composite membrane of 0.9 and a film thickness of 151 μm was obtained.

Example 15
The same operation as in Example 3 was performed except that 2 g of 5% PVA aqueous solution was changed to 2 g of a mixed solution of 1.5 g of 5% PVA aqueous solution and 0.5 g of 5% PA aqueous solution. ) And silicon oxide silicon element (Y) in an element ratio X / Y of 0.1 and a specific surface area of 50 m ² / g were obtained. Further, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA / PA composite membrane of 0.9 and a film thickness of 155 μm was obtained.

Example 16
The same operation as in Example 4 was performed except that 2 g of 5% PVA aqueous solution was changed to 2 g of a mixed solution of 1.5 g of 5% PVA aqueous solution and 0.5 g of 5% PA aqueous solution, and the tungsten element of tungsten oxide (X ) And silicon oxide silicon element (Y) in an element ratio X / Y of 0.1 and a specific surface area of 51 m ² / g were obtained. Further, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA / PA composite membrane of 0.9 and a film thickness of 150 μm was obtained.

Example 17
The same operation as in Example 5 was performed except that 2 g of 5% PVA aqueous solution was changed to 2 g of 5% polyethylene glycol (PEG) aqueous solution, and vanadium element (X) of vanadium oxide and titanium element (Y) of titanium oxide Thus, a vanadium oxide-supported titanium oxide having an element ratio X / Y of 0.1 and a specific surface area of 52 m ² / g was obtained. Furthermore, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PEG composite membrane of 0.9 and a film thickness of 151 μm was obtained.

Example 18
The same operation as in Example 5 was performed except that 2 g of 5% PVA aqueous solution was changed to 2 g of 5% Nylon 6 formic acid solution, and the element ratio of vanadium oxide vanadium element (X) to titanium oxide titanium element (Y). A vanadium oxide-supported titanium oxide having an X / Y of 0.1 and a specific surface area of 51 m ² / g was obtained. Furthermore, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-Nylon 6 composite membrane of 0.9 and a film thickness of 157 μm was obtained.

[Comparative Example 1]
As an electrolyte membrane, a Nafion 117 membrane (registered trademark) manufactured by Dupont was prepared.

[Comparative Example 2]
The same operation as in Example 5 was performed except that 2 g of 5% PVA aqueous solution was changed to 2 g of 5% polystyrene (PS) toluene solution and the drying temperature was changed from 60 degrees and 150 degrees to only 60 degrees, and vanadium oxide vanadium. A vanadium oxide-supported titanium oxide having an element ratio X / Y between the element (X) and titanium element (Y) of titanium oxide of 0.1 and a specific surface area of 54 m ² / g was obtained. Further, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PS composite membrane of 0.9 and a film thickness of 155 μm was obtained.

The obtained proton conductive membranes of Examples 1 to 18 were greatly swollen by applying moisture, and could be easily peeled off from the petri dish made of PFA resin. At this time, the membrane has flexibility, m-nitrotoluene (pKa = -11.99), p-nitrofluorobenzene (pKa = -12.40), p-nitrochlorobenzene (pKa = -12.70), m -An acidic indicator consisting of nitrochlorobenzene (pKa = -13.16), 2,4-dinitrotoluene (pKa = -13.75), 2,4-dinitrofluorobenzene (pKa = -14.52) It was found to show strong acidity. Table 1 below shows the Hammett acidity function H ₀ of each proton conductive membrane.

  On the other hand, the proton conductive membrane of Comparative Example 2 required a large amount of moisture as compared with the example in order to swell.

  Moreover, the liquid fuel cell was assembled by the method demonstrated below using the electrolyte membrane of Examples 1-18 and Comparative Examples 1-2.

An oxidizer electrode 3 was prepared by impregnating an electrode containing a platinum-supported cathode catalyst (catalyst amount: Pt 4 mg / cm ² , manufactured by E-tek) with a 5% Nafion solution. Further, an electrode containing a platinum / ruthenium supported catalyst anode catalyst (amount of catalyst: Pt—Ru 4 mg / cm ² , manufactured by E-tek) impregnated with a 5% Nafion solution was prepared as the fuel electrode 2.

A proton conductive membrane 4 is disposed between the fuel electrode 2 and the oxidant electrode 3, and the membrane electrode assembly 5 is manufactured by hot pressing at 120 ° C. for 5 minutes at a pressure of 100 kg / cm ² , An electromotive part was obtained.

A carbon porous plate having an average pore diameter of 100 μm and a porosity of 70% as the fuel vaporization section 6 was laminated on the fuel electrode 2 of the electromotive section 5 thus obtained. A carbon porous plate having an average pore diameter of 5 μm and a porosity of 40% as a fuel permeation unit 7 was disposed on the fuel vaporization unit 6. These were incorporated into the oxidant electrode holder 10 with the oxidant gas supply groove 9 and the fuel electrode holder 11 to produce a unit cell having the configuration shown in FIG. The reaction area of this unit cell is 10 cm ² . The oxidant gas supply groove 9 of the oxidant electrode holder 10 has a depth of 2 mm and a width of 1 mm.

A 20% aqueous methanol solution was introduced into the liquid fuel cell thus obtained from the side surface of the fuel permeation section 7 by capillary force as shown in FIG. On the other hand, 1 atm of air as oxidant gas was allowed to flow through the gas channel 9 at 100 ml / min for power generation. Carbon dioxide gas (CO ₂ ) generated along with the power generation reaction was released from the fuel vaporization section 6 as shown in FIG. The maximum power generation amount is shown in Table 1 below.

  Table 1 shows the measurement results of methanol permeability and membrane resistance for each proton conductive membrane. Here, the methanol permeability and the membrane resistance were expressed as relative values, assuming that the Nafion 117 membrane of Comparative Example 1 was 1.

For methanol permeability, a proton conductive membrane is inserted into a cell having an area of 10 cm ² , 10% methanol aqueous solution is placed in one cell, and pure water is placed in the other cell. The methanol concentration on the cell side containing pure water was measured by gas chromatography, and the methanol permeability was measured. The membrane was immersed in water for 16 hours, then drained and the methanol permeability was measured.

Moreover, the electrical resistance of the film was measured by a four-terminal DC method. That is, a proton conductive membrane was inserted into a cell having an area of 10 cm ² , a 10% sulfuric acid aqueous solution was put into both cells, a direct current was passed at room temperature, and a voltage drop due to the presence or absence of the proton conductive membrane was measured. Resistance was measured.

  As is clear from Table 1, it can be seen that the proton conductive membranes of Examples 1 to 18 have greatly reduced methanol permeability and membrane resistance as compared to the Nafion 117 membrane of Comparative Example 1. Further, as shown in Example 5, Example 17, Example 18, and Comparative Example 2, by changing the polymer material used for the membrane and changing the equilibrium moisture absorption rate of the polymer, an inorganic material and an organic material are obtained. The wettability, dispersibility, and water absorption of the membrane changed, and the proton conductivity and methanol permeability changed by affecting the microstructure of the membrane. That is, by increasing the equilibrium moisture absorption rate to 0.05%, 10%, 20%, and 25%, the membrane resistance of the proton conductive membrane decreases, and the smaller the equilibrium moisture absorption rate, the smaller the methanol permeability. Become.

As shown in Comparative Example 1 of Table 1, in a fuel cell equipped with a Nafion 117 membrane as an electrolyte membrane, a 20% methanol solution has large crossover and membrane resistance, and power generation of 2.0 mW / cm ² at maximum. Only quantity could be obtained. On the other hand, in the fuel cell provided with the proton conductive membranes of Examples 1 to 18 as the electrolyte membrane, a good power generation amount was obtained because the crossover was suppressed and the membrane resistance was reduced. Among them, the power generation amount of the fuel cells of Examples 9 to 12 using ZrO ₂ as the oxide carrier was large, and the most excellent example was Example 12 on which tungsten oxide particles were supported.

About the unit cell which used the proton-conductive membrane of Examples 1-18 as an electrolyte membrane, while supplying 20% methanol aqueous solution as a fuel, flowing air and heating both surfaces of a cell to 40 degreeC, 10 mA / cm < ² > The current was taken and the temporal stability of the battery performance was observed. As a result, the output was stable even after several hours. Furthermore, as a result of performing the same measurement at 150 ° C., the output was stable even after several hours.

For a fuel cell equipped with a Nafion 117 membrane (Comparative Example 1) as an electrolyte membrane, a 20% aqueous methanol solution was supplied as fuel, air was allowed to flow, and both sides of the cell were heated to 40 ° C. to produce a current of 10 mA / cm ² . Then, the temporal stability of the battery performance was observed. As a result, it became impossible to obtain an output within a few minutes. Furthermore, as a result of performing the same measurement at 150 ° C., humidification could not be strictly controlled, so that the electrolyte membrane was dried and an output could not be obtained.

Example 19
The same operation as in Example 1 was carried out except that 2 g of an aqueous solution of 5% PVA (saponification degree: 100%) was changed to 2 g of an aqueous solution of 5% PVA (saponification degree: 85%), and the vanadium element (X) of vanadium oxide was used. Vanadium oxide-supporting silicon oxide having an element ratio X / Y of silicon oxide to silicon element (Y) of 0.1 and a specific surface area of 53 m ² / g was obtained. Furthermore, the ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA (saponification degree 85%) composite membrane is 0.9, and an electrolyte membrane having a film thickness of 151 μm is obtained. It was.

Example 20
The same operation as in Example 1 was performed except that 2 g of an aqueous solution of 5% PVA (degree of saponification 100%) was changed to 2 g of an aqueous solution of 5% PVA (degree of saponification 70%), and the vanadium element (X) of vanadium oxide was used. Vanadium oxide-supporting silicon oxide having an element ratio X / Y of silicon oxide to silicon element (Y) of 0.1 and a specific surface area of 51 m ² / g was obtained. Furthermore, an electrolyte membrane with a ratio of S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA (degree of saponification 70%) is 0.9 and a film thickness of 150 μm is obtained. It was.

  Using this electrolyte membrane, a liquid fuel cell was produced in the same manner as described in Example 1 above.

For Examples 19 and 20, the methanol permeability and membrane resistance of the proton conductive membrane and the maximum power generation amount of the fuel cell were measured in the same manner as described above, and the results are shown in Table 2 below. Table 2 also shows the results of Example 1 described above.

  As is apparent from Table 2, the equilibrium moisture absorption decreases as the degree of saponification of PVA decreases, so that sufficient water is not supplied to the solid superacid and membrane resistance increases, but methanol permeability Also declined. These conditions were combined, and as a result, the film characteristics were determined, and it was found that the output improved as the degree of saponification of PVA increased.

Example 21
The same operation as in Example 1 was performed except that the drying temperature was changed from 60 ° C. and 150 ° C. to 60 ° C. and 100 ° C., and the element ratio of vanadium oxide (V) of vanadium oxide to silicon element (Y) of silicon oxide A vanadium oxide-supported silicon oxide having X / Y of 0.1 was obtained. The specific surface area of this proton conductive inorganic material was 53 m ² / g. Further, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA composite membrane of 0.9 and a film thickness of 150 μm was obtained.

[Example 22]
The same operation as in Example 1 was carried out except that the drying temperature was changed from 60 ° C. and 150 ° C. to 60 ° C. and 180 ° C., and the element ratio of vanadium element (X) of vanadium oxide to silicon element (Y) of silicon oxide A vanadium oxide-supported silicon oxide having X / Y of 0.1 was obtained. The specific surface area of this proton conductive inorganic material was 55 m ² / g. Further, an electrolyte membrane having a ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PVA composite membrane of 0.9 and a film thickness of 151 μm was obtained.

  Using this electrolyte membrane, a liquid fuel cell was produced in the same manner as described in Example 1 above.

For the obtained Examples 21 and 22, the methanol permeability and membrane resistance of the proton conductive membrane and the maximum power generation amount of the fuel cell were measured in the same manner as described above, and the results are shown in Table 3 below. Table 3 also shows the results of Example 1 described above.

  As apparent from Table 3, it was found that the equilibrium moisture absorption rate decreased as the heat treatment temperature increased. It is presumed that the higher the heat treatment, the more the reaction between PVA and the solid superacid is promoted, the hydrophilic hydroxyl group in PVA is converted to the hydrophobic ketone group, and the equilibrium moisture absorption rate is lowered. That is, the lower the heat treatment temperature, the higher the water absorption of the film, the sufficient water was supplied to the solid super strong acid, and the film resistance was reduced. On the other hand, as for the permeability of methanol, the electrolyte membrane subjected to high temperature heat treatment became denser and smaller. These conditions were synthesized, and as a result, the film characteristics were determined, and the heat treatment at 150 ° C. showed the highest output.

Example 23
A slurry was prepared by mixing the proton conductive inorganic material obtained in Example 1, the platinum / ruthenium supported catalyst, PVA, and water in a weight ratio of 0.45 / 0.45 / 0.1 / 5.0. A fuel electrode having a catalyst amount of Pt—Ru 4 mg / cm ² was prepared by coating on a 32 mm × 32 mm carbon cloth.

In addition, a slurry was prepared by mixing the proton conductive inorganic material obtained in Example 1, the platinum-supported catalyst, PVA, and water at a weight ratio of 0.45 / 0.45 / 0.1 / 5.0. And an oxidant electrode having a catalyst amount of Pt 4 mg / cm ² was prepared by coating on a 32 mm × 32 mm carbon cloth.

  Furthermore, a Nafion 117 membrane similar to that used in Comparative Example 1 was prepared as the electrolyte membrane.

  A fuel cell was produced in the same manner as described in Example 1 except that the fuel electrode, the oxidant electrode, and the electrolyte membrane were used.

Example 24
A fuel cell was fabricated in the same manner as described in Example 1 except that the fuel electrode and the oxidant electrode obtained in Example 23 and the proton conductive membrane obtained in Example 1 were used. did.

For the obtained Examples 23 and 24, the cell resistance and the maximum power generation amount of the fuel cell were measured, and the results are shown in Table 4 below. Table 4 also shows the results of Example 1 and Comparative Example 1 described above.

  As is clear from Table 4, the fuel cells of Examples 1, 23, and 24 exhibited higher output characteristics than the fuel cell of Comparative Example 1. This is because in Example 1, the methanol permeability of the electrolyte membrane is low, and in Example 23, the resistance of the proton conductor used for the electrode is small, and Example 24 obtained the highest output. This is because both the electrolyte membrane of Example 1 and the electrode of Example 23 were used.

  From the above results, when proton conductive materials including proton conductive inorganic oxides and hydrophilic organic polymers are included in at least one of the fuel electrode, the oxidant electrode, and the electrolyte membrane, proton conductivity and methanol permeability are obtained. It was found that both sexes can be satisfied.

  As described above in detail, according to the present invention, it is possible to obtain a fuel cell that is small in size, high in performance, and capable of supplying a stable output, and its industrial value is tremendous.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

1 is a cross-sectional view schematically showing a liquid fuel cell according to an embodiment of the fuel cell of the present invention. FIG. 2 is a cross-sectional view schematically showing the configuration of the liquid fuel cell of Example 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Liquid fuel introduction path, 2 ... Anode, 3 ... Cathode, 4 ... Electrolyte membrane, 5 ... Membrane electrode assembly (electromotive part), 6 ... Fuel vaporization part, 7 ... Fuel penetration part, 8 ... Cathode separator, 9 ... oxidant gas supply groove, 10 ... oxidant electrode side holder, 11 ... fuel electrode side holder, 100 ... stack.

Claims (7)

  A proton conductive inorganic oxide exhibiting solid superacidity and a hydrophilic organic polymer containing at least one selected from the group consisting of hydroxyl group, carboxyl group, ether bond and amide bond Proton conducting membrane for fuel cells.   2. The proton conductivity for a fuel cell according to claim 1, wherein a slurry containing the proton conductive inorganic oxide and the hydrophilic organic polymer is formed and heat-treated at 200 ° C. or lower. film.   The proton conductive membrane for a fuel cell according to claim 1 or 2, wherein the hydrophilic organic polymer has an equilibrium moisture absorption rate of 5% or more at 20 ° C or more. 4. The proton conductive inorganic oxide according to claim 1, wherein the acidity function H _{0 of} Hammett is a proton conductive inorganic oxide satisfying H ₀ <−11.93. 5. Proton conducting membrane for fuel cells.   The proton conductive inorganic oxide is supported on the surface of the oxide support containing an oxide support containing at least one element Y selected from the group consisting of Zr, Ti, Si and Al, and W, 5. The proton conduction for a fuel cell according to claim 1, comprising oxide particles containing at least one element X selected from the group consisting of Mo, Cr and V. 6. Sex membrane. In a membrane electrode assembly comprising a fuel electrode, an oxidant electrode, and an electrolyte membrane disposed between the fuel electrode and the oxidant electrode,
At least one of the fuel electrode, the oxidant electrode, and the electrolyte membrane is selected from the group consisting of a proton conductive inorganic oxide that exhibits solid superacidity, a hydroxyl group, a carboxyl group, an ether bond, and an amide bond And a hydrophilic organic polymer containing at least one kind of the membrane electrode assembly. In a fuel cell comprising a fuel electrode, an oxidant electrode, and an electrolyte membrane disposed between the fuel electrode and the oxidant electrode,
At least one of the fuel electrode, the oxidant electrode, and the electrolyte membrane is selected from the group consisting of a proton conductive inorganic oxide that exhibits solid superacidity, a hydroxyl group, a carboxyl group, an ether bond, and an amide bond A fuel cell comprising a hydrophilic organic polymer containing at least one of the above.

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