WO2006083038A1 - Fuel cell - Google Patents

Abstract

There is provided a fuel cell capable of supplying a sufficient amount of reaction gas, improving the use efficiency of a reaction component in the supplied reaction gas, and suppressing drying of an electrolyte film. The fuel cell includes a hollow-shaped electrolyte film and a cell module having a pair of electrodes arranged on an inner surface and an outer surface of the electrolyte film. At least one of the two electrodes has a catalyst layer and a gas diffusion layer in this order from the electrolyte film side. The porous degree of the catalyst layer is distributed such that it becomes smaller from the gas diffusion layer side toward the electrolyte film side.

Description

 Specification

 Fuel cell

Technical field

 The present invention relates to a fuel cell including a cell module having a hollow electrolyte membrane. Background art

 A fuel cell directly converts chemical energy into electrical energy by supplying fuel and an oxidant to two electrically connected electrodes and causing the fuel to oxidize electrochemically. Unlike thermal power generation, it is not subject to the Carnot cycle, so it exhibits high energy conversion efficiency. Among them, the solid polymer electrolyte fuel cell is a fuel cell that uses a solid polymer electrolyte membrane as an electrolyte, and has advantages such as easy miniaturization and operation at a low temperature. It is attracting attention as a power source for mobiles.

 In solid polymer electrolyte fuel cells, when hydrogen is used as the fuel, the reaction of equation (1) proceeds at the node.

H ₂ → 2 H ⁺ + 2 e "(1)

The electrons generated in Eq. (1) reach the force sword after working with an external load via an external circuit. And the proton produced by the formula (1) is hydrated with water. In the solid polymer electrolyte membrane, it moves from the anode side to the force sword side by electroosmosis.

 In addition, when oxygen is used as the oxidizing agent, the reaction of formula (2) proceeds with force sword.

4 H + + 0 ₂ + 4 e— → 2 H ₂ 0 · · · (2)

 The water generated by the force sword is discharged to the outside mainly through the gas diffusion layer. As described above, the fuel cell is a clean power generation device having no emission other than water. Conventionally, as a solid polymer electrolyte fuel cell, a planar membrane / electrode joint obtained by mainly providing a catalyst layer serving as an anode and a force sword on the other surface of a planar solid polymer electrolyte membrane is obtained. A fuel cell stack has been developed that is obtained by stacking a plurality of flat single cells produced by further providing gas diffusion layers on both sides of the body and finally sandwiching them with a planar separator. I came.

 In order to improve the output density of the solid polymer electrolyte fuel cell, a proton conductive polymer membrane having a very thin film thickness is used as the solid polymer electrolyte membrane. This film thickness is typically less than 100 um; even if a thinner electrolyte membrane is used to further increase the power density, the thickness of a single cell can be drastically reduced from the current one. I can not do such a thing. Similarly, the catalyst layer, gas diffusion layer, separator, etc. are also being made thinner, but there is a limit to improving the output density per unit volume even by making all these members thinner. is there.

In addition, a sheet-like carbon material having excellent corrosivity is usually used for the separator. This carbon material itself is also expensive, but it also has a flat membrane / electrode contact. In order to distribute the fuel gas and the oxidant gas almost uniformly over the entire surface of the coalescence, a groove serving as a gas flow path is usually finely processed on the surface of the separator. It became expensive and pushed up the manufacturing cost of fuel cells.

 In addition to the above problems, the flat single cell must be surely sealed at the periphery of a plurality of single cells stacked so that fuel gas and oxidant gas do not leak from the gas flow path. However, there are a number of problems, such as technical difficulties, and power generation efficiency may decrease due to deflection or deformation of the planar membrane-electrode assembly.

 In recent years, solid polymer electrolyte fuel cells have been developed that use a cell module with electrodes on the inner and outer surfaces of a hollow electrolyte membrane as a basic power generation unit.

 (For example, see JP-A-9-223507, JP-A-2002-124273, JP-A-2002-158015 and JP-A-2002-26085).

Usually, in a fuel cell having such a hollow cell module, it is not necessary to use a member corresponding to a separator used in a flat type. Since different types of gas are supplied to the inner surface and the outer surface for power generation, it is not necessary to form a gas flow path. Therefore, the manufacturing cost is expected to be reduced. Furthermore, since the cell module has a three-dimensional shape, the specific surface area relative to the volume can be increased compared to a flat single cell, and the power generation output density per volume can be expected to improve. In a polymer electrolyte fuel cell using a polymer electrolyte membrane that is one of proton conducting membranes as an electrolyte membrane, the electrodes provided on the inner surface side and outer surface side of the hollow electrolyte membrane are usually the catalyst layer in order from the electrolyte membrane side. And a gas diffusion layer. The reaction gas (oxidant gas, fuel gas) supplied to the gas diffusion layer diffuses in the gas diffusion layer, reaches the catalyst surface in the catalyst layer, and causes the above-described electrochemical reaction.

 At this time, since a sufficient amount of reaction gas necessary for power generation is supplied to the catalyst layer, it is desirable that the gas diffusion from the gas diffusion layer to the catalyst layer is high, but on the other hand, the catalyst on the electrolyte membrane side When the gas flow is intense in the layer, the reaction gas tends to remove moisture from the catalyst layer and the electrolyte membrane, and the ratio of reaction components that cause a reaction on the catalyst surface may be reduced.

 The present invention has been accomplished in view of the above circumstances, and a sufficient amount of reaction gas is supplied, the utilization efficiency of reaction components in the supplied reaction gas is improved, and the electrolyte membrane is dried. An object of the present invention is to provide a fuel cell that can be suppressed. Disclosure of the invention

The fuel cell of the present invention is a fuel cell comprising a cell module having a hollow electrolyte membrane and a pair of electrodes provided on the hollow inner surface and outer surface of the electrolyte membrane, wherein at least one of the pair of electrodes is A catalyst layer and a gas diffusion layer in order from the electrolyte membrane side, and the porosity of the catalyst layer decreases from the gas diffusion layer side toward the electrolyte membrane side. It is characterized by having a distribution.

 According to the present invention, the diffusibility of the reaction gas in the thickness direction of the catalyst layer can be adjusted. That is, on the gas diffusion layer side, the porosity of the catalyst layer is large, a sufficient amount of reaction gas for power generation can be taken from the gas diffusion layer, and the taken reaction gas is sufficiently diffused into the catalyst layer. Can do. On the other hand, on the electrolyte membrane side, the porosity of the catalyst layer is small, and more reaction components come into contact with the catalyst, so the amount of reaction components contributing to the electrochemical reaction increases. As a result, the utilization efficiency of the reaction gas can be improved, and furthermore, cross-reaction in which the reaction components in the reaction gas permeate the electrolyte membrane in a molecular state can be prevented. In addition, since the diffusion of gas in the catalyst layer on the electrolyte membrane side is limited, the amount of water removed by the reaction gas flowing from the catalyst layer and electrolyte membrane on the electrolyte membrane side is reduced. In addition, drying of the catalyst layer can be prevented.

 From the viewpoint of more reliably preventing cross leak, the catalyst layer preferably further has a distribution in which the amount of catalyst component per unit volume increases from the gas diffusion layer side toward the electrolyte membrane side.

Cross leak is a force that easily occurs on the anode side when hydrogen is used as a fuel. Among the pair of electrodes, at least the anode has a catalyst layer and a gas diffusion layer in order from the electrolyte membrane side. By adopting a structure having a distribution in which the porosity decreases from the gas diffusion layer side toward the electrolyte membrane side, hydrogen cross-leakage can be prevented. At this time, the catalyst layer of the anode further has a unit volume. It is preferable that the catalyst component amount has a distribution that increases from the gas diffusion layer side toward the electrolyte membrane side.

 As a specific configuration of the fuel cell according to the present invention, the porosity of the catalyst layer is 80 to 90% from the gas diffusion layer side to the one-third thickness of the catalyst layer, and from the gas diffusion layer side. The catalyst layer thickness is 70 to 80% from 1/3 to 2/3, and 60 to 70% from the gas diffusion layer side to the catalyst layer thickness from 2/3 to the electrolyte membrane side. Some are listed. The invention's effect

 The fuel cell of the present invention can supply a sufficient amount of reaction gas necessary for power generation to the catalyst layer, and can increase the amount of reaction components contributing to the electrochemical reaction in the reaction gas. It is possible to improve the power generation performance and reaction gas utilization efficiency of the fuel cell. In addition, by improving the utilization efficiency of the reaction gas, it is possible to prevent a cross leak in which hydrogen and oxygen permeate through the electrolyte membrane in a molecular state, thereby extending the life of the fuel cell. Furthermore, by preventing the electrolyte membrane and the catalyst layer from drying, the power generation performance of the fuel cell can be improved.

Therefore, according to the present invention, while ensuring the supply amount of the reaction gas, it is possible to prevent the electrolyte membrane and the catalyst layer from being dried, and to increase the amount of reaction components that contribute to the electrochemical reaction. It is possible to improve the power generation performance and extend the life of the fuel cell. Brief Description of Drawings

 FIG. 1 is a schematic view showing one embodiment of a cell module provided in the fuel cell of the present invention.

 FIG. 2 is a partially enlarged sectional view of the cell module.

 In the accompanying drawings, 1 0 1 is a cell module, 1 is a hollow electrolyte membrane (perfluorocarbon sulfonic acid resin membrane), 2 is a force sword, 3 is an anode, 4 is a cathode catalyst layer, 5 is a force sword gas diffusion layer , 6 is an anode catalyst layer, 7 is a cathode gas diffusion layer, 8 is a hollow portion, and 9 and 10 are current collectors. BEST MODE FOR CARRYING OUT THE INVENTION

 The fuel cell of the present invention is a fuel cell comprising a cell module having a hollow electrolyte membrane and a pair of electrodes provided on the hollow inner surface and outer surface of the electrolyte membrane, wherein at least one of the pair of electrodes is A catalyst layer and a gas diffusion layer are provided in order from the electrolyte membrane side, and the porosity of the catalyst layer has a distribution that decreases from the gas diffusion layer side toward the electrolyte membrane side.

 Hereinafter, the fuel cell of the present invention will be described by taking as an example the case where a solid polymer electrolyte membrane which is a kind of proton conductive membrane is used as the electrolyte membrane. Here, a perfluorocarbon sulfonic acid resin membrane is used as the solid polymer electrolyte membrane.

First, an embodiment of a fuel cell to which the present invention is applied will be described with reference to FIG. 1 and FIG. FIG. 1 is a diagram showing an example of a cell module used in the present invention. is there.

 In FIG. 1, the cell module 10 1 has a tubular electrolyte membrane (perfluorocarbon sulfonic acid resin membrane) 1, the force sword 2 is on the hollow outer surface side of the electrolyte membrane 1, and the anode 3 is the electrolyte membrane. 1 is formed on the hollow inner surface side. A hollow portion (usually a flow path for a fuel gas such as hydrogen gas) 8 through which a reaction gas supplied to the anode 3 flows is formed inside the anode 3. Current collectors 9 and 10 are connected to the force sword 2 and the anode 3, respectively, and one end of the current collectors 9 and 10 functions as an output terminal. Here, a force sword is provided on the outer surface side of the tubular electrolyte membrane, and an anode is provided on the inner surface side. However, the arrangement of each electrode is not particularly limited, and a force sword is provided on the inner surface side and an anode is provided on the outer surface side. It may be provided. Further, the flow direction of the reaction gas (oxidant gas, fuel gas) is not particularly limited.

FIG. 2 is a partially enlarged sectional view of the cell module shown in FIG. In FIG. 2, force sword 2 and anode 3 each have a structure in which catalyst layers 4 and 6 and gas diffusion layers 5 and 7 are laminated in order from the electrolyte membrane side. The catalyst layer 4 of force sword 2 consists of three regions 4 a, 4 b, and 4 c with different porosity, and the catalyst layer 4 as a whole has a distribution in which the porosity decreases from the gas diffusion layer 5 side toward the electrolyte membrane 1 side. The porosity of each region is 4 a> 4 b> 4 c. The catalyst layer 6 of the anode 3 is also composed of three regions 6 a, 6 b, and 6 c having different porosities. The porosity of each region is such that the entire catalyst layer 6 has a porosity from the gas diffusion layer 7 side to the electrolyte membrane 1 side. 6 a> 6 b> 6 c so that the distribution becomes smaller toward the bottom. In FIG. 2, both the catalyst layer 4 of the force sword 2 and the catalyst layer 6 of the anode 3 have the above-described porosity distribution, but in the present invention, at least of the force sword and the canode It is sufficient that one of them has a porosity distribution in the catalyst layer. Here, the porosity is a ratio of the volume occupied by voids in a unit volume expressed as 100 fraction (%).

 The fuel cell of the present invention has a distribution in which the porosity of the catalyst layer decreases from the gas diffusion layer side toward the electrolyte membrane side as described above. By having such a distribution of porosity, the diffusibility of the reaction gas can be adjusted by the position in the catalyst layer. That is, on the gas diffusion layer side, since the porosity of the catalyst layer is large and the gas diffusibility is high, a sufficient amount of reaction gas for power generation can be taken from the gas diffusion layer, and the taken reaction gas is taken into the catalyst layer. It is possible to diffuse sufficiently.

On the other hand, on the electrolyte membrane side, since the porosity of the catalyst layer is small and gas diffusion is limited, the reaction components (oxygen, hydrogen) in the reaction gas stay for a long time. Since the catalyst comes into contact, the amount of reaction components contributing to the electrochemical reaction increases. Increasing the amount of reaction components that contribute to the electrochemical reaction improves the power generation performance and reaction gas utilization efficiency of the fuel cell. In addition, since the amount of hydrogen and oxygen present in the molecular state in the vicinity of the electrolyte membrane is reduced by improving the utilization efficiency of the reaction gas, cross leakage in which hydrogen and oxygen permeate the electrolyte membrane in the molecular state is prevented. can do. A cross leak causes a hydrogen combustion reaction, which causes deterioration of the electrolyte membrane and catalyst due to the heat generated during the combustion reaction. This prevents the fuel cell from extending its life.

 Furthermore, since the diffusion of gas in the catalyst layer on the electrolyte membrane side is restricted, the amount of water carried away by the reaction gas flowing from the catalyst layer and electrolyte membrane on the electrolyte membrane side is reduced. Drying of the electrolyte membrane and the catalyst layer can be prevented. By preventing the electrolyte membrane and the catalyst layer from drying, the power generation performance of the fuel cell is enhanced.

 As described above, according to the present invention, it is possible to prevent the electrolyte membrane and the catalyst layer from being dried while ensuring the supply amount of the reaction gas, and to increase the amount of reaction components that contribute to the electrochemical reaction. It is possible to improve the power generation performance and extend the life of the fuel cell.

 Hydrogen is more prone to cross-leakage than oxygen, and there is no generation of water due to electrochemical reaction on the anode side, and the proton moves along with water to the force sword side. Easier to dry than the side. Therefore, at least in the anode, it is preferable that the porosity of the catalyst layer has a distribution that decreases from the gas diffusion layer side toward the electrolyte membrane side.

In the force sword, water is generated by the electrochemical reaction, and further, water accompanies the movement of the proton from the anode side, so that excess water stays in the catalyst layer, and the diffusibility of the oxidizing gas May fall. However, in the fuel cell of the present invention, when the force sword catalyst layer has a structure having the above-described porosity distribution, the porosity of the catalyst layer is low on the electrolyte membrane side where drying is desired to be prevented. It shows high water retention, while gas expansion is caused by excess water being pushed out from the electrolyte membrane side. On the dispersion side, the catalyst layer has a high porosity and exhibits high drainage. That is, according to the present invention, it is possible to obtain a fuel cell equipped with a power sword excellent in moisture management ability.

 In the present invention, the porosity distribution state of the catalyst layer may change stepwise as shown in Fig. 1 if the porosity is smaller on the electrolyte membrane side than on the gas diffusion layer side. It may be good or change with a continuous slope. From the viewpoint of ease of production, the catalyst layer is divided into two or five regions equally or non-equally from the gas diffusion layer side to the electrolyte membrane side, and the porosity of each region is determined by gas. It is preferable to set the electrolyte membrane side to be smaller than the diffusion layer side. The distribution state of the porosity may be different between the force sword side and the anode side, or may be the same.

The porosity of the catalyst layer is preferably about 80 to 90% in the region in contact with the gas diffusion layer from the viewpoint of gas diffusibility from the gas diffusion layer, while the viewpoint of preventing the electrolyte membrane from drying out Therefore, in the region in contact with the electrolyte membrane, the content is preferably about 60 to 70%. Furthermore, it is usually preferable to adjust the porosity in each region so that the porosity of the entire catalyst layer is about 60 to 90%. For example, in the catalyst layer having a three-stage distribution as shown in Fig. 1, the porosity of 4a and 6a is about 80 to 90%, and the porosity of 4b and 6b is 70 to 80%. The porosity of 4c and 6c is preferably about 60 to 70%. In addition, when the catalyst layer is divided into three as shown in Fig. 1, the range of the gas diffusion layer side regions 4a and 6a is from the gas diffusion layer side to 1/3 of the catalyst layer region, and the region 4b 6b range from gas diffusion layer side to catalyst layer thickness 3 It is preferable that the region 4c and 6c on the most electrolyte membrane side from 1/3 to 2/3 is from the gas diffusion layer side to the catalyst layer thickness 2/3 to the electrolyte membrane.

 The catalyst layer can be formed using an electrode material such as that used in a polymer electrolyte fuel cell, and is usually formed of a catalyst component, a conductive material, and a proton conductive material. The catalyst component is not particularly limited as long as it has a catalytic action for the hydrogen oxidation reaction at the anode and the oxygen reduction reaction in the power sword. For example, platinum (Pt), ruthenium (Ru), iridium (Ir :), rhodium (Rh), palladium (Pd), osmium (Os), tungsten (W), lead (Pb), iron (Fe), chromium (Cr), cobalt (C o), Nickel (N i), Mangan (Mn), Vanadium (V), Molybdenum (Mo), Gallium (Ga), Aluminum (A1), or other metals, or their alloys it can. Preferable are platinum and an alloy made of platinum and another metal such as ruthenium. Usually, these catalyst components are used by being supported on conductive materials such as carbon materials such as carbonaceous particles and carbonaceous fibers. Since the fuel cell of the present invention has a cell module having a hollow shape, the electrode area per unit volume can be made larger than that of a fuel cell having a flat cell, so that the catalytic action is not as great as that of platinum. Even if a catalyst component is used, a fuel cell having a high power density per unit volume can be obtained.

As the proton conductive substance, an electrolyte that can be used as an electrolyte membrane described later can be used. In addition, the catalyst layer can be further water-repellent if necessary. Other materials such as a conductive polymer and a binder may be used.

 The porosity of the catalyst layer may be adjusted as long as the catalyst function, gas diffusibility, conductivity, and proton conductivity in the catalyst layer are not impaired, and the method is not particularly limited.

 Between the areas where the porosity of the catalyst layer is different, the volume occupied by the entire solid material forming the catalyst layer as described above is different. At this time, between the regions having different porosities, the solid material for adjusting the volume occupied by the entire solid material forming each region may be only one type, or two or more types, or a catalyst. The volume of the solid material may be adjusted by changing the amount of all the solid materials forming the layer. Further, the material forming the catalyst layer may be different between the regions of the catalyst layer having different porosity.

 The catalyst layer having regions with different porosities may be formed by using, for example, catalyst pastes having different volume concentrations of solid components or catalyst pastes having different particle sizes of solid components, or laser ablation. It can be produced by forming catalyst layers having different porosities by sol-gel method, sputtering, oxide plating, etc., and laminating them by a method such as transfer.

From the viewpoint of further preventing the cross leak of the reaction gas, it is preferable that the catalyst component has a distribution in which the amount of the catalyst component per unit volume in the catalyst layer increases from the gas diffusion layer side toward the electrolyte membrane side. When the amount of catalyst component is large in the region of the electrolyte membrane with low porosity, the reaction components in the reaction gas with limited diffusion more reliably come into contact with the catalyst and cause a reaction, so hydrogen or oxygen is in the molecular state of the electrolyte. The probability of passing through the membrane Get smaller.

 The distribution state of the catalyst component in the catalyst layer may be a distribution in which the amount of the catalyst component per unit volume is larger on the electrolyte membrane side than on the gas diffusion layer side, and may change stepwise or continuously. It may change with a certain inclination. Usually, since the formation of the catalyst layer is easy, the density of the catalyst component may be distributed in the same form as the distribution of the porosity of the catalyst layer. For example, if the porosity of the catalyst layer changes stepwise in three stages as shown in Fig. 1, the amount of catalyst component in the cathode side catalyst layer 4 is 4 a <4 b <4 c, In the side catalyst layer 6, the amount of the catalyst component may be 6a <6b <6c.

 The distribution of the catalyst component amount may be different from the distribution of the porosity of the catalyst layer. Further, the distribution state of the catalyst component amount may be different between the force sword side and the anode side, or may be the same.

Although the amount of catalyst component in the catalyst layer depends on the catalyst component used, it is usually preferred to be about 0.1 to 0.2 mgZcm ² per unit area for the entire catalyst layer, so the amount of catalyst component for the entire catalyst layer Is preferably distributed in the thickness direction of the catalyst layer (the direction from the electrolyte membrane side to the gas diffusion layer) so that the above is in the above range. In addition, the amount of the catalyst component in each region in the thickness direction of the catalyst layer is not particularly limited, but in the region in contact with the electrolyte membrane, about 0.3 to 0.4 mgZ cm ³ per unit volume from the viewpoint of preventing cross leakage. It is preferred to be with. For example, in a catalyst layer with a three-level porosity distribution as shown in Fig. 1, if the catalyst component amount is also distributed, 4 a and 6 a catalyst component amount per unit volume is about 0.05 to 0. l mg / cm ³ , 4 b and 6 b platinum amount is 0.1 to 0.2 mg / cm ³ per unit volume It is preferable that the amount of platinum of about 4 c and 6 c be about 0.3 to 0.4 mg / cm ³ per unit volume.

 As described above, since hydrogen gas is prone to cross-leakage, a distribution in which the amount of catalyst components per unit volume increases from the gas diffusion layer side to the electrolyte membrane side, especially in at least the anode catalyst layer. It is preferable to have.

 The catalyst layer can be formed using a catalyst paste in which a catalyst component, a conductive material, a proton conductive material, and other components as necessary are dispersed in a solvent.

 Here, a method for forming a catalyst layer having a distribution of porosity and a distribution of the amount of catalyst components will be described using a method of forming a catalyst layer as shown in FIG. 1 as an example.

For example, first, a catalyst paste C for the regions 4 c and 6 c located closest to the electrolyte membrane in the catalyst layer is prepared. The catalyst paste C can form a catalyst layer having a porosity of 60 to 70% and a catalyst component amount of 0.3 to 0.4 mg / cm ³ per unit volume. This catalyst paste C is divided into three parts, one is used as it is as catalyst paste C for the regions 4 c and 6 c, and the other two have a porosity of 4 a> 4 b> 4 c, 6 a> 6 b> 6 c and the proton conductivity as described above so that the catalyst layers 4 and 6 with the catalyst component amounts of 4 a 4 b <4 c, 6 a 6 b 6 c can be formed. Dilute with the addition of organic substances, conductive materials, or other components (eg, ethanol, etc.) to obtain catalyst paste B for regions 4b and 6b (porosity 70 to 80%, unit of catalyst components) 0.1 to 0.2 mg Z cm ³ catalyst layer per volume), catalyst paste A for regions 4a and 6a (porosity 80 to 90%, catalyst component amount per unit volume) 0. 5 to 0. lmg no cm ³ of catalyst layer) is prepared.

 The method for forming the catalyst layers 4 and 6 on the inner and outer surfaces of the tubular electrolyte membrane 1 using the catalyst paste thus obtained is not particularly limited. For example, a tube-shaped electrolyte membrane is prepared, and catalyst paste C is first applied to the inner and outer surfaces of the electrolyte membrane and dried to form catalyst layers in regions 4c and 6c. Use catalyst paste B to form regions 4 b and 6 b, and catalyst paste A to form regions 4 a and 6 a. Further, a solution containing carbonaceous particles and Z or carbonaceous fibers and a water-repellent resin is applied to the regions 4 a and 6 a and dried to form the gas diffusion layers 5 and 7. And a cathode) are obtained. At this time, the catalyst layer 6 and the gas diffusion layer 7 are formed so that the hollow portion 8 exists on the inner surface of the gas diffusion layer 7 formed on the inner surface side of the electrolyte membrane.

Alternatively, gas diffusion of an electrode (anode 3) containing carbonaceous particles and a carbon material such as Z or carbonaceous fiber and formed in a tube shape (tubular carbonaceous material) on the inner surface of the tubular electrolyte membrane The catalyst paste A is applied to the outer surface of the gas diffusion layer 7 and dried to form the catalyst layer in the region 6a, and then the catalyst base B and the catalyst paste C are used. Similarly, the catalyst layers of the regions 6 b and 6 c are formed. Next, a solution containing an electrolyte is applied to the outer surface (6 c) of the catalyst layer 6 and dried to form an electrolyte membrane layer. Furthermore, using catalyst pastes C, B, A on the outer surface of the electrolyte membrane layer The catalyst layers of the regions 4 c, 4 b, and 4 a are formed in this order, and a solution containing a carbon material is applied to the outer surface of the region 4 a and dried to form the gas diffusion layer 5. A tubular electrolyte membrane having a force sword 3) is obtained.

 Here, the solvent used in forming the electrolyte membrane, the catalyst layer, and the gas diffusion layer may be appropriately selected according to the dispersion and Z or the material to be dissolved, and the coating method for forming each layer Also, it can be appropriately selected from various methods such as spraying and screen printing.

 In FIG. 1, an electrolyte membrane having a tubular hollow shape is used as the hollow electrolyte membrane. However, the hollow electrolyte membrane in the present invention is not limited to the tubular shape, and has a hollow portion, and the hollow portion is in the hollow portion. Any reaction component may be used as long as it can supply the reaction components necessary for the electrochemical reaction to the inner surface side electrode by flowing the reaction gas.

In this embodiment, the perfluorocarbon sulfonic acid resin film, which is one of solid polymer electrolyte membranes, which is a kind of proton conducting membrane, is used as the electrolyte membrane. Has a cell module with a hollow shape and can have a larger electrode area per unit volume than a fuel cell with a flat cell. Even if an electrolyte membrane that does not have high proton conductivity is used, a fuel cell having a high output density per unit volume can be obtained. As the polymer electrolyte membrane, in addition to perfluorocarpone sulfonic acid resin, materials such as those used in electrolyte membranes of polymer electrolyte fuel cells can be used. For example, perfluorocarbon sulfonic acid Tree Fluorine ion exchange resins other than fat, polystyrene-based cation exchange membranes with sulfonic acid groups, and other hydrocarbons such as polyolefins as skeletons, at least sulfonic acid groups, phosphonic acid groups, and phosphoric acid groups Proton exchange groups having one type, such as polybens imidazole, polypyrimidine, polybenzoxazole, etc. disclosed in Japanese Patent Publication No. 11-500 Examples thereof include polymer electrolytes such as solid polymer electrolytes composed of a complex of a basic polymer having a strong acid doped in the molecule and a strong acid.

 Solid polymer electrolyte membranes using such electrolytes can be reinforced with perfluorocarbon polymers in the form of fibrils, fabrics, fabrics, and porous sheets, and inorganic oxides or metals on the membrane surface. It can also be captured by coating. In addition, examples of perfluorocarbon sulfonic acid resin membranes include commercially available products such as Nafion (trade name) manufactured by DuPont, USA and Flemion (trade name) manufactured by Asahi Glass.

 The proton conductive electrolyte membrane is not limited to the solid polymer electrolyte membrane as described above, and a proton conductor made by impregnating a porous electrolyte plate with a phosphoric acid aqueous solution or a porous conductor made of porous glass. Hydrogelated phosphate glass, Organic mono-inorganic hybrid proton conductive membrane with proton conductive functional groups introduced into the surface and pores of nano-porous porous glass, inorganic metal fiber reinforced electrolyte polymer Etc. can be used.

The method for forming the tubular electrolyte membrane is not particularly limited. An electrolyte membrane formed in a tube shape may be used.

 As the gas diffusion layer, a conductive material mainly composed of a carbon material such as carbonaceous particles and / or carbonaceous fibers can be used. The sizes of the carbonaceous particles and the carbonaceous fibers may be appropriately selected in consideration of the dispersibility in the solution when the gas diffusion layer is produced, the drainage of the obtained gas diffusion layer, and the like. The configuration of the electrodes provided on the inner and outer surfaces of the electrolyte membrane, the materials used for the electrodes, etc. may be the same or different. For example, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), perfluoroethylene carbon alkoxy decane, ethylene-tetrafluoroethylene polymer, because the gas diffusion layer enhances the drainage of water such as generated water. It is preferable to perform water-repellent treatment by impregnating with a mixture of these materials or by forming a water-repellent layer using these substances.

 Examples of the tube-like carbonaceous material that includes the carbonaceous particles and / or carbonaceous fibers and is formed into a tube shape include, for example, carbon materials such as carbonaceous particles and epoxy and Z or phenolic materials. It can be obtained by dispersing the resin in a solvent, forming it into a tupe shape, thermosetting, and firing.

The inner and outer diameters, length, etc. of the tubular cell module can be designed as appropriate according to the output required for the fuel cell and the design and operating conditions of the fuel cell, such as the equipment to which the fuel cell is applied. However, the outer diameter of the tubular electrolyte membrane is preferably from 0.1 to 10 mm, more preferably from 0.1 to 1 mm, and from 0.1 to 0.5 mm. Particularly preferred is mm. Outside the tubular electrolyte membrane At present, it is difficult to manufacture a product with a diameter of less than 0.01 mm due to technical problems. On the other hand, a product with an outer diameter of more than 10 mm has a small surface area relative to the occupied volume. This is not preferable because the power generation output per unit volume of the obtained cell module is reduced.

 Perfluorocarbon sulfonic acid resin membranes are preferred to be thin from the viewpoint of improving the proton conductivity. However, if they are too thin, the function of sequestering gas will be reduced and the permeation rate of non-proton hydrogen will increase. End up. However, compared with the conventional fuel cell in which flat cells for a flat fuel cell are stacked, the fuel cell produced by collecting a large number of hollow cell modules can take up a large electrode area, so it is slightly thicker. Even when a membrane is used, sufficient output is shown. From this viewpoint, the thickness of the perfluorocarbon sulfonic acid resin membrane is 10 to 100 m, more preferably 50 to 60 μm, and further preferably 50 to 55 m. It is.

 In addition, from the preferable range of the outer diameter and the film thickness of the above-mentioned perfluorinated carbon sulfonic acid resin film, the preferable range of the inner diameter is from 0.01 to 10 mm, and more preferably from 0.0 :! ˜l mm, and more preferably 0.5:! ˜0.5 mm.

 Further, the thickness of the catalyst layer provided on the inner and outer surfaces of the electrolyte membrane is preferably about 1 to 10 μιη, and the thickness of the gas diffusion layer is preferably about 3 to 10 μπι.

The cell module having a hollow shape used in the fuel cell of the present invention is not limited to the configuration exemplified above, and a layer other than the catalyst layer and the gas diffusion layer may be provided for the purpose of enhancing the function of the cell module. good. The form and material of the current collector (9, 10) are not particularly limited. Examples of the current collector material include a metal wire or foil such as stainless steel. For example, the current collector may be fixed on the electrode with a conductive adhesive such as a strong bonding adhesive or an Ag paste. Les.

In the embodiment shown in FIG. 1, a perfluorocarbon sulfonic acid resin film, which is a proton conducting film, is used as the electrolyte film, but the electrolyte film used in the fuel cell of the present invention is used. Is not particularly limited, and may be proton-conductive or other ion-conductive such as hydroxide ion or oxide ion (O ² —). Examples of other ion-conducting electrolytes such as hydroxide ions and oxide ions (O ² —) include those containing ceramics. When using an oxide ion-conducting electrolyte membrane, the oxide ion generated on the force sword side passes through the electrolyte membrane and reaches the anode side, and reacts with hydrogen to produce water. Release.

The cell modules having the configuration as shown in FIG. 1 usually form a group of cells that are arrayed and supported by a support plate, and the anode terminals and force sword terminals of each cell module are bundled and connected in parallel. This parallel cell group is connected in series with other cell groups to form a cell assembly, which is surrounded by an exterior member and casing. By connecting the internal space of the exterior member to the oxidant gas supply source and the hollow portion of the cell module to the fuel gas supply source, the reaction gas is supplied to the surface of each electrode. Note that the configuration of the fuel cell, such as the cell module and the connection configuration and arrangement configuration of the cell group, is not particularly limited. For example, a cell group in which cell modules are connected in series may be used, or for each cell group. And each internal space thereof may be communicated with a reaction gas supply source. Industrial application fields

 As described above, the fuel cell according to the present invention is useful as a fuel cell that is easy to downsize and operates at a low temperature and further improves the power generation performance and extends the life. Yes, especially suitable for use as a portable or mobile power source.

Claims

The scope of the claims 1. A fuel cell including a cell module having a hollow electrolyte membrane and a pair of electrodes provided on a hollow inner surface and an outer surface of the electrolyte membrane, at least one of the pair of electrodes being an electrolyte membrane A fuel cell comprising a catalyst layer and a gas diffusion layer in order from the side, wherein the porosity of the catalyst layer decreases from the gas diffusion layer side toward the electrolyte membrane side.  2. The fuel cell according to claim 1, wherein the catalyst layer further has a distribution in which the amount of the catalyst component per unit volume increases from the gas diffusion layer side toward the electrolyte membrane side.  3. At least one of the pair of electrodes has a catalyst layer and a gas diffusion layer in order from the electrolyte membrane side, and the porosity of the catalyst layer decreases from the gas diffusion layer side to the electrolyte membrane side. The fuel cell according to claim 1 or 2, wherein the fuel cell has a distribution. ' 4. The fuel cell according to claim 3, wherein the catalyst layer of the anode further has a distribution in which the amount of catalyst component per unit volume increases from the gas diffusion layer side toward the electrolyte membrane side.  5. The porosity of the catalyst layer is 80 to 90% from the gas diffusion layer side to the catalyst layer thickness 1/3, and the catalyst layer thickness from the gas diffusion layer side 1/3 to 3 minutes. 5 to 70 to 80%, and from the gas diffusion layer side to the catalyst layer thickness from two thirds to the electrolyte membrane side is 60 to 70%. A fuel cell according to claim 1.