JP4625658B2 - Fuel cell electrode, membrane electrode composite, and fuel cell - Google Patents

Description

  The present invention relates to a proton conductor preferably used for an electrode for a fuel cell 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 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 a solid superacidity (for example, Patent Document 1) is known. Specifically, zirconium, titanium, iron, tin, silicon, aluminum, molybdenum, Sulfuric acid is supported on the oxide surface containing one or more elements selected from tungsten, and the sulfuric acid is immobilized on the oxide surface by heat treatment. Sulfuric acid-supported metal oxides exhibit proton conductivity due to immobilized sulfate radicals, but the sulfate radicals deviate from hydrolysis, and the proton conductivity decreases, so fuel that generates water during the power generation process. The proton conductive solid electrolyte of a battery, particularly a fuel cell using a liquid fuel, is unstable and presumed to be an inappropriate material for long-term stable power supply.

Patent Document 2 describes that a metal oxide hydrate having proton conductivity is used as the proton conductive substance. In this metal oxide hydrate, the structure shrinks when the hydrated water is removed by drying by power generation at a high temperature and the like. There is a problem that power generation performance cannot be obtained.
JP 2002-216537 A JP 2003-142124 A

  In conventional fuel cells, a large amount of entrained water is required for proton conduction in the proton-conducting solid electrolyte, and sufficient water must be supplied to the electrolyte, which is complicated for stable power supply. Management of water that requires a system has become essential. In addition, 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.

  Another object of the present invention is to provide an electrode for a fuel cell, a membrane electrode assembly, and a fuel cell capable of supplying a stable output.

A fuel cell electrode according to the present invention is a fuel cell electrode provided with a catalyst layer containing a redox catalyst and a proton conductive inorganic oxide,
The proton conductive inorganic oxide is supported on the surface of an oxide carrier containing at least one element Y selected from the group consisting of Ti, Zr, Si and Al, and the surface of the oxide carrier, W, And oxide particles containing at least one element X selected from the group consisting of Mo, Cr and V.

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 and the oxidizer electrode, Ti, Zr, and oxide carrier containing the element Y consisting of at least one selected from the group consisting of Si and Al, the oxide support Proton-conducting inorganic oxide which is supported on the surface and contains oxide particles containing at least one element X selected from the group consisting of W, Mo, Cr and V It is.

A fuel cell according to the present invention includes a membrane electrode assembly including 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 and the oxidizer electrode, Ti, Zr, and oxide carrier containing the element Y consisting of at least one selected from the group consisting of Si and Al, the oxide support Proton-conducting inorganic oxide which is supported on the surface and contains oxide particles containing at least one element X selected from the group consisting of W, Mo, Cr and V It is.

It is possible to provide a fuel cell electrode, a membrane electrode assembly and a fuel cell capable of supplying an output to stable.

  First, the proton conductive inorganic oxide used in the present invention will be described.

  This proton conductive inorganic oxide is supported on the surface of an oxide carrier containing at least one element Y selected from the group consisting of Ti, Zr, Si and Al, and the surface of the oxide carrier, W, And oxide particles containing at least one element X selected from the group consisting of Mo, Cr and V.

  Although the exact proton conduction mechanism in the proton conductive inorganic oxide used in the present invention has not yet been elucidated, the element X is contained on the surface of an oxide carrier containing the element Y (hereinafter referred to as oxide carrier A). By supporting oxide particles (hereinafter referred to as oxide particles B), Lewis acid points are generated in the structure of oxide particles B, and the Lewis acid points are hydrated to bring them to Bronsted acid points. Thus, it is considered that a proton conduction field is formed. 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. It is possible to obtain a large amount of power generation without performing strict water management during power generation. Therefore, by including this proton conductive inorganic oxide in at least one of the fuel electrode, the oxidant electrode and the electrolyte membrane, the cell resistance can be lowered and the maximum power generation amount of the fuel cell can be increased. it can.

  Moreover, according to the proton conductive solid electrolyte containing this proton conductive inorganic oxide, it is possible to suppress permeation of a liquid fuel such as methanol. In particular, when a polymer material is added for binding the proton conductive inorganic oxide, the density of the proton conductive solid electrolyte is further increased, and thus the permeation of the liquid fuel can be further suppressed.

  By the way, the oxide particle B has water solubility although its solubility varies depending on the element and pH environment. Since the oxide particles B are supported on the oxide carrier A having low water solubility, the dissolution of the oxide particles B in water can be suppressed, and the stability of the proton conductive inorganic oxide to water and liquid fuel can be suppressed. Can be high. Further, contamination of other fuel cell materials and devices due to ions of the eluted oxide particles B can be avoided. Therefore, according to the present invention, 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. Considering 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, it is desirable that both the oxide particles B and the oxide carrier A are amorphous. Further, it is more desirable that the oxide particles B are amorphous and the oxide carrier 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 desirably exhibits a solid superacid. 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 proton conductive solid electrolyte used in the membrane electrode assembly and fuel cell according to one embodiment preferably contains a proton conductive inorganic oxide and a polymer material. In such a proton conductive solid electrolyte, it is more desirable that the proton conductive inorganic oxide is contained in the polymer material or that the proton conductive inorganic oxide is bound by the polymer material. The polymer material is not particularly limited, and specific examples include polystyrene, polyether ketone, polyether ether ketone, polysulfone, polyether sulfone, and other engineering plastic materials. Further, the polymer material may be a material in which sulfonic acid, phosphoric acid or other proton carriers are doped, chemically bonded or immobilized, or a polymer material exhibiting proton conductivity such as perfluorosulfonic acid. Among these, polyacrylonitrile (PAN) is preferable because of its high polarity.

  In the proton conductive solid electrolyte, it is desirable that the mixing ratio of the proton conductive inorganic oxide and the polymer material satisfies the condition for preventing the permeation of 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 0.5, 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 0.5 to 0.999.

  When a proton conductive solid electrolyte is used as a solid electrolyte of a fuel cell, it is generally used in the form of a membrane, but is not limited to this and can be used in a cylindrical shape. That is, a method in which a dispersion mixture of a proton conductive inorganic oxide and the above organic polymer is directly cast into a film, or a method in which the dispersion mixture is impregnated into a porous core material, a woven fabric, a nonwoven fabric, or the like. 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 organic polymer is directly cast into a film, the cast proton conductive inorganic oxide and the organic It can be changed by the amount of polymer dispersion mixture or the cast area, and after film formation, the film can be heated and pressurized with a hot press machine to reduce the film thickness, but is not particularly limited. .

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

  The electrode according to the present invention contains a proton conductive inorganic oxide 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 one embodiment of the electrode according to the present invention, an electrode provided with a catalyst layer including a redox catalyst, a proton conductive inorganic oxide, and a polymer material serving as a binder is provided.

  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.

  In order to immobilize the metal catalyst or metal catalyst-carrying carbon and the proton conductive inorganic oxide in the catalyst layer, a polymer material serving as a binder is used. The polymer material is not particularly limited, and specific examples include polystyrene, polyether ketone, polyether ether ketone, polysulfone, polyether sulfone, and other engineering plastic materials. Further, it may be a material obtained by doping or chemically binding and fixing sulfonic acid, phosphoric acid or other proton carriers to the above polymer material, or a polymer material exhibiting proton conductivity such as perfluorosulfonic acid. . Since it is desirable to form a catalyst layer structure that maintains porosity while maintaining high proton conductivity and conductivity, the compounding ratio of the metal catalyst or carbon supported on the metal catalyst and the proton conductive inorganic oxide to the polymer material is When the weight ratio (P / C) of the polymer material (P) to the total weight (C) of the catalyst layer is larger than 0.5, the continuity of the proton conductive inorganic oxide or metal catalyst is lowered and protons Therefore, 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 polymer material are mixed and dispersed in an organic solvent such as water or alcohol to form a slurry, and this slurry is used as a support. The catalyst layer is formed by coating, drying and firing on the top. 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 a composite membrane electrode assembly may be formed with the electrolyte membrane.

  According to one embodiment of the present invention, in the membrane electrode assembly comprising a fuel electrode, an oxidizer electrode, and an electrolyte membrane disposed between the fuel electrode and the oxidizer electrode, the electrolyte membrane is as described above. A proton conductive solid electrolyte is included, or the electrode includes the catalyst layer described above, or the electrolyte membrane and the electrode include the proton conductive solid electrolyte and the catalyst layer described above. A membrane electrode assembly including both 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 polymeric material 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 5, the fuel permeation unit 7, and the fuel vaporization unit 6 also serve as a current collector plate that conducts 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), so that the fuel cell can be further reduced in size. 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 a fuel cell, a cell reaction occurs even from room temperature. However, it is preferable to operate at a high temperature of 50 ° C. to 150 ° C. in order to improve the catalytic activity of the electrode and reduce 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. A preferable range of the operating temperature of the fuel cell is room temperature to 150 ° C.

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

[ Reference 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 maintained at 700 ° C. for 4 hours, thereby vanadium oxide vanadium element ( 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 shown in Table 1 below 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 N, N-dimethylacetamide (DMAc) solution of 5% polyacrylonitrile (PAN) and stirred at room temperature for 10 minutes to prepare a slurry. This slurry was put into a petri dish made of a tetrafluoroethylene perfluoroalkoxy vinyl ether copolymer (PFA) resin, and the solvent was dried at 60 ° 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.

[ Reference 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) between X) and silicon element (Y) of silicon oxide of 0.1 was obtained.

  1 g of this proton conductive inorganic material powder was added to 2 g of DMAc solution of 5% PAN, 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. 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.

[ Reference 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 ( A molybdenum oxide-supported silicon oxide having an element ratio X / Y of 0.1) between X) and silicon element (Y) of silicon oxide of 0.1 was obtained. 1 g of this proton conductive inorganic material powder was added to 2 g of DMAc solution of 5% PAN, 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. 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 152 μm.

[ Reference 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. Furthermore, by holding at 700 ° C. for 4 hours, tungsten oxide-supporting silicon oxide having an element ratio X / Y of tungsten element (X) of tungsten oxide to silicon element (Y) of silicon oxide of 0.1 was obtained. .

  1 g of this proton conductive inorganic material powder was added to 2 g of DMAc solution of 5% PAN, 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. 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 152 μm.

[ Reference Example 5]
The same operation as in Reference Example 1 was carried out 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. As a result, vanadium oxide-supported titanium oxide having a ratio of 0.1 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-PAN composite membrane of 0.9 and a film thickness of 152 μm was obtained.

[ Reference Example 6]
The same operation as in Reference Example 2 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 chromium element (X) of chromium oxide and titanium element (Y) of titanium oxide was changed. As a result, a chromium oxide-supported titanium oxide having a 0.1 was 0.1. 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-PAN composite membrane of 0.9 and a film thickness of 153 μm was obtained.

[ Reference Example 7]
The same operation as in Reference Example 3 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 molybdenum element (X) of molybdenum oxide to titanium element (Y) of titanium oxide was changed. 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-PAN composite membrane of 0.9 and a film thickness of 151 μm was obtained.

[ Reference Example 8]
The same operation as in Reference Example 4 was carried out 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 to titanium element (Y) of titanium oxide was changed. As a result, a tungsten oxide-supported titanium oxide having a ratio of 0.1 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-PAN composite membrane of 0.9 and a film thickness of 150 μm was obtained.

[ Reference Example 9]
The same operation as in Reference Example 1 was carried out 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 Thus, a vanadium oxide-supported zirconium oxide having a ratio of 0.1 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-PAN composite membrane of 0.9 and a film thickness of 148 μm was obtained.

[ Reference Example 10]
The same operation as in Reference 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 of chromium element (X) of chromium oxide and zirconium element (Y) of zirconium oxide was As a result, a chromium oxide-supported zirconium oxide having a ratio of 0.1 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-PAN composite membrane of 0.9 and a film thickness of 150 μm was obtained.

[ Reference Example 11]
The same operation as in Reference 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 As a result, molybdenum oxide-supported zirconium oxide having a ratio of 0.1 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-PAN composite membrane of 0.9 and a film thickness of 152 μm was obtained.

[ Reference Example 12]
The same operation as in Reference Example 4 was carried out except that 5 g of silicon oxide was changed to 11 g of zirconium oxide (ZrO ₂ ), and the element ratio X / Y between tungsten element (X) of tungsten oxide and zirconium element (Y) of zirconium oxide was changed. Thus, zirconium oxide-supported zirconium oxide having a ratio of 0.1 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-PAN composite membrane of 0.9 and a film thickness of 155 μm was obtained.

[ Reference Example 13]
Except for changing 5 g of silicon oxide to 16 g of zirconia-silica composite oxide (ZrSiO ₄ ), the same operation as in Reference Example 1 was performed, and vanadium element (X) of vanadium oxide and zirconium and silicon element of zirconia-silica composite oxide. A vanadium oxide-supported zirconia-silica composite oxide having an element ratio X / Y with (Y) of 0.1 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-PAN composite membrane of 0.9 and a film thickness of 153 μm was obtained.

[ Reference Example 14]
The same operation as in Reference Example 2 was performed except that 5 g of silicon oxide was changed to 16 g of zirconia-silica composite oxide (ZrSiO ₄ ), and chromium element (X) of chromium oxide and zirconium and silicon element of zirconia-silica composite oxide A chromium oxide-supported zirconia-silica composite oxide having an element ratio X / Y with (Y) of 0.1 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-PAN composite membrane of 0.9 and a film thickness of 155 μm was obtained.

[ Reference Example 15]
The same operation as in Reference Example 3 was performed except that 5 g of silicon oxide was changed to 16 g of zirconia-silica composite oxide (ZrSiO ₄ ), and molybdenum element (X) of molybdenum oxide and zirconium and silicon element of zirconia-silica composite oxide A molybdenum oxide-supported zirconia-silica composite oxide having an element ratio X / Y with (Y) of 0.1 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-PAN composite membrane of 0.9 and a film thickness of 153 μm was obtained.

[ Reference Example 16]
The same operation as in Reference Example 4 was performed except that 5 g of silicon oxide was changed to 16 g of zirconia-silica composite oxide (ZrSiO ₄ ), and tungsten element (X) of tungsten oxide and zirconium and silicon elements of zirconia-silica composite oxide A tungsten oxide-supported zirconia-silica composite oxide having an element ratio X / Y with (Y) of 0.1 was obtained.

[ Reference Example 17]
The same operation as in Reference Example 1 was performed except that the DMAc solution of 5% PAN was changed to the DMAc solution of 5% polybenzimidazole (PBI), and vanadium element (X) of vanadium oxide and titanium element (Y) of titanium oxide. The vanadium oxide-supported titanium oxide-PBI composite membrane having an element ratio X / Y of 0.1 is 0.1, and the ratio S / T of the proton conductive inorganic material (S) to the total membrane weight (T) is 0.9. Thus, an electrolyte membrane having a thickness of 150 μm was obtained.

[ Reference Example 18]
The same operation as in Reference Example 1 was performed except that the DMAc solution of 5% PAN was changed to a chloroform solution of 5% polystyrene (PS), and the vanadium element (X) of vanadium oxide and the titanium element (Y) of titanium oxide were combined. A vanadium oxide-supported titanium oxide-PS composite film having an element ratio X / Y of 0.1 was prepared, and the ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the film was 0.9. An electrolyte membrane having a thickness of 155 μm was obtained.

[ Reference Example 19]
The same operation as in Reference Example 1 was carried out except that 5 g of silicon oxide was changed to 17 g of tetraethoxysilane (Si (OH ₅ C ₂ ) ₄ ), and vanadium element (X) of vanadium oxide and Si element (Y) of silicon oxide. Thus, a vanadium oxide-supported titanium oxide having an element ratio X / Y of 0.1 was obtained. When X-ray diffraction measurement was performed on this vanadium oxide-supported silicon oxide, no diffraction peak was observed, and it was confirmed that both vanadium oxide and silicon oxide had an amorphous structure. 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-PAN composite membrane of 0.9 and a film thickness of 153 μm was obtained.

[Comparative Example 1]
A sulfuric acid-supported metal oxide described in Patent Document 1 was prepared. Distilled water was added to 6 g of concentrated sulfuric acid (96%) to prepare a sulfuric acid aqueous solution having a total weight of 100 g. 20 g of zirconium oxide (ZrO ₂ ) was added to this sulfuric acid aqueous solution and stirred for 3 hours to prepare a slurry. This slurry was heated from room temperature to 100 ° C. at a temperature rising rate of 5 ° C./min, and kept at 100 ° C. for 3 hours to remove water. Thereafter, the white powder was obtained by further heating to 200 ° C. at a temperature rising rate of 1 ° C./min and holding at 200 ° C. for 3 hours. The white powder is further heated to 500 ° C. at a rate of temperature increase of 1 ° C./min and held at 500 ° C. for 3 hours, whereby sulfur (S) of sulfuric acid and hydroxide and / or oxide as a carrier A white powder of sulfuric acid-supported zirconia SO ₄ / ZrO ₂ having an element ratio S / M with the metal element (M) constituting 0.03 was obtained. Further, by the same operation as in Reference Example 1, the ratio S / T of the proton conductive inorganic material (S) to the total weight (T) of the proton conductive inorganic material-PAN composite membrane is 0.9, and the electrolyte membrane has a film thickness of 155 μm. Got.

[Comparative Example 2]
A Nafion 117 membrane manufactured by Dupont was prepared as an electrolyte membrane.

The obtained proton conductive membranes of Reference Examples 1 to 19 and Comparative Example 1 were slightly 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 larger amount of moisture than that of the reference example before swelling.

Moreover, the liquid fuel cell was assembled by the method demonstrated below using the electrolyte membrane of Reference Examples 1-19 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.

Into the liquid fuel cell thus obtained, a 20% aqueous methanol solution was introduced as a liquid fuel from the side surface of the fuel permeation section 7 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 case of the Nafion 117 membrane of Comparative Example 2 was 1.

For methanol permeability, a proton conductive membrane is inserted into a cell with an area of 10 cm ² , 10% methanol aqueous solution is placed in one cell, and pure water is placed in the other cell, and after a certain period of time at room temperature. 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 to be ready for use as an electrolyte membrane, and then the water was drained and the methanol permeability was measured.

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

As is clear from Table 1, the proton conductive membranes of Reference Examples 1 to 19 have a significantly lower methanol permeability than the Nafion 117 membrane of Comparative Example 2, and the membrane resistance is within a range of several times. I understand that. In addition, as shown in Reference Example 1, Reference Example 17, and Reference Example 18, by changing the polymer material used for the film, the wettability and dispersibility of the inorganic material and the organic material are changed, and the microstructure of the film is changed. It was found that proton conductivity and methanol permeability were changed by the influence. Further, as shown in Reference Example 1 and Reference Example 19, it was found that the proton conductivity was changed by changing the crystallinity of the proton conductive inorganic material. Specifically, reference example 19 in which oxide particles B and oxide carrier A are both amorphous is more than the amount of Lewis acid points than in reference example 1 in which oxide particle B is amorphous and oxide carrier A is crystalline. It can be assumed that the acidity is high and the proton conductivity is high.

As shown in Comparative Example 2 of Table 1, in a fuel cell provided with a Nafion membrane 117 as an electrolyte membrane, a 20% methanol solution has too much crossover, so that only a maximum power generation amount of ² mW / cm ² is obtained. I couldn't. On the other hand, in the fuel cell provided with the proton conductive membranes of Reference Examples 1 to 19 as the electrolyte membrane, a good power generation amount was obtained because the crossover was suppressed. Among them, the power generation amount of the fuel cells of Reference Examples 9 to 12 using ZrO ₂ as the oxide carrier was large, and the reference example 12 on which tungsten oxide particles were supported was the most excellent.

About the unit cell which used the proton conductive membrane of the reference examples 1-19 as the electrolyte membrane 1, 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 time 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 2) as an electrolyte membrane, a 20% methanol aqueous 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., the humidification could not be strictly controlled. Therefore, the electrolyte membrane was dried and an output could not be obtained.

[ Reference Example 20]
The same procedure as in Reference Example 1 was carried out except that 1 g of proton conductive inorganic material powder was changed to 0.7 g and 2 g of 5% PAN DMAc solution was changed to 1.3 g, and vanadium element (X) of vanadium oxide and silicon oxide were used. Of vanadium oxide-supported silicon oxide-PAN composite film having an element ratio X / Y of 0.1 with respect to Si element (Y), and the ratio S of the proton conductive inorganic material (S) to the total weight (T) of the film An electrolyte membrane having a / T of 0.9 and a film thickness of 100 μm was obtained.

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

[ Reference Example 21]
The same procedure as in Reference Example 1 was carried out except that 1 g of proton conductive inorganic material powder was changed to 0.3 g and 2 g of DMAc solution of 5% PAN was changed to 0.7 g, and vanadium oxide (X) and silicon oxide of vanadium oxide were used. Of vanadium oxide-supported silicon oxide-PAN composite film having an element ratio X / Y of 0.1 with respect to Si element (Y), and the ratio S of the proton conductive inorganic material (S) to the total weight (T) of the film An electrolyte membrane having a / T of 0.9 and a film thickness of 50 μm was obtained.

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

For the obtained Reference Examples 20 and 21, 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 Reference Example 1 described above.

  As is apparent from Table 2, the thinner the electrolyte membrane, the shorter the diffusion distance of methanol, so that the permeability increases, and the effective membrane resistance also decreases with respect to proton conduction. These conditions have been combined, and as a result, the membrane characteristics have been determined, and the thinner the electrolyte membrane, the greater the methanol permeability. On the other hand, the membrane resistance is greatly affected, so the output seems to have increased. It is.

[ Reference Example 22]
Big silicon oxide having a specific surface area than Example 1 (SiO ₂₎ was changed to 3.5g following the procedure of Reference Example 1, vanadium element of vanadium oxide (X) and silicon oxide of Si element (Y) Vanadium oxide-supporting silicon oxide having an element ratio (X / Y) of 0.2 was obtained. The specific surface area of this proton conductive inorganic material was 150 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-PAN composite membrane of 0.9 and a film thickness of 150 μm was obtained.

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

[ Reference Example 23]
The same operation as in Reference Example 1 was carried out except that silicon oxide (SiO ₂ ) having a specific surface area larger than that of Reference Example 1 and Reference Example 22 was changed to 2.5 g, and vanadium oxide (X) of vanadium oxide and Si of silicon oxide. A vanadium oxide-supported silicon oxide having an element ratio (X / Y) with the element (Y) of 0.3 was obtained. The specific surface area of this proton conductive inorganic material was 300 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-PAN 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 Reference Example 1 described above.

As apparent from Table 3, it is speculated that the higher the amount of vanadium oxide supported on SiO ₂ having a larger specific surface area, the larger the specific surface area of the resulting proton-conductive inorganic material and the more the amount of Lewis acid points. can do. As a result, the proton conduction field increased, the membrane resistance decreased, and the output increased.

Example 24
A slurry was prepared by mixing the proton conductive inorganic material obtained in Reference Example 1 with a platinum / ruthenium supported catalyst, PAN, and DMAc at 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 Reference Example 1, the platinum-supported catalyst, PAN, and DMAc 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.

  Further, a Nafion 117 membrane similar to that used in Comparative Example 2 was prepared as an electrolyte membrane.

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

Example 25
A fuel cell was fabricated in the same manner as described in Reference Example 1 except that the fuel electrode and oxidant electrode obtained in Example 24 and the proton conductive membrane obtained in Reference Example 1 were used. did.

For the obtained Examples 24 and 25, 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 shows the results of Reference Example 1 and Comparative Example 2 described above.

As is clear from Table 4, the resistance of the proton conductor used for the electrode and the electrolyte membrane is small, so the cell resistance is low, and as shown in Table 1, the methanol permeability of the electrolyte membrane obtained in Reference Example 1 is low. Thus, the membrane electrode composites obtained in Reference Example 1, Example 24, and Example 25 exhibited higher output characteristics than the membrane electrode composite obtained in Comparative Example 2.

In Table 5 below, the proton conductive membrane obtained in Reference Example 1 and Comparative Example 1 was boiled in boiling water for 1 hour, and the conductivity (membrane resistance) and methanol permeability were measured in the same manner as above. Examined.

In Table 5, it is considered that the conductivity of the membrane of Comparative Example 1 was greatly reduced after the boiling water treatment, and the sulfate radicals supported on the zirconia surface were detached by hydrolysis. On the other hand, it was found that the membrane of Reference Example 1 had no influence on the conductivity by boiling water treatment and had high durability against heat and hydrolysis.

From this, it was found that the proton conductive solid electrolyte used in the fuel cell of the embodiment can more effectively prevent methanol permeability while maintaining proton conductivity.

  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 constituent elements 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. Sectional drawing which showed typically the structure of the liquid fuel cell of the reference example 1. FIG.

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 (6)

An electrode for a fuel cell comprising a catalyst layer containing a redox catalyst and a proton conductive inorganic oxide,
The proton conductive inorganic oxide includes an oxide carrier containing at least one element Y selected from the group consisting of Ti, Zr, Si and Al, and is supported on the surface of the oxide carrier, W, Mo, fuel cell electrode, wherein the benzalkonium to containing the oxide particles containing an element X formed of at least one kind selected from the group consisting of Cr and V. The proton conductive inorganic oxide has a specific surface area of 10 m ² / g or more and 2000 m ² / g or less, and an element ratio (X / Y) between the element X and the element Y is 0.0001 or more. 2. The electrode for a fuel cell according to claim 1 , wherein the electrode is in a range of 20 or less. 3. The fuel cell electrode according to claim 1, wherein the proton conductive inorganic oxide is a solid superacid having a Hammett acidity function H ₀ of H ₀ <−11.93. The proton conductive inorganic oxide is selected from the group consisting of W, Mo, Cr and V in an oxide carrier containing at least one element Y selected from the group consisting of Ti, Zr, Si and Al. The oxide precursor containing at least one kind of element X to be obtained is retained and then heat-treated at 200 ° C. or higher and 1000 ° C. or lower, to obtain the oxide precursor. The electrode for fuel cells as described. 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,
The membrane electrode assembly using the fuel cell electrode according to any one of claims 1 to 4 for at least one of the fuel electrode and the oxidant electrode. A fuel cell comprising the membrane electrode assembly according to claim 5.

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