JP2009009724A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell capable of efficiently humidifying a fuel electrode with water produced in an oxidant electrode by effectively accelerating movement of water from the oxidant electrode to the fuel electrode in the fuel cell in which oxidant gas and fuel gas oppositely flow. <P>SOLUTION: The fuel cell is equipped with a polymer electrolyte membrane; the fuel electrode installed on one surface of the polymer electrolyte membrane; and the oxidant electrode installed on the other surface of the polymer electrolyte membrane, and power is generated by supplying fuel gas to the fuel electrode and oxidant gas to the oxidant electrode. The fuel gas and the oxidant gas is oppositely supplied, the upstream region of the fuel gas flow and the downstream region of the oxidant gas flow, and the downstream region of the fuel gas flow and the upstream region of the oxidant gas flow are faced through the polymer electrolyte membrane, and the thickness of the fuel electrode is relatively decreased from the upstream side of the fuel gas flow toward the downstream side, and the porosity of the fuel electrode is relatively decreased from the upstream side of the fuel gas flow toward the downstream side. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell.

  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 be oxidized electrochemically. Unlike thermal power generation, fuel cells are not subject to the Carnot cycle, and thus exhibit high energy conversion efficiency. A fuel cell is usually formed by laminating a plurality of single cells having a basic structure of a membrane / electrode assembly in which an electrolyte membrane is sandwiched between a pair of electrodes. Among them, a solid polymer electrolyte fuel cell using a solid polymer electrolyte membrane as an electrolyte membrane has advantages such as easy miniaturization and operation at a low temperature. It is attracting attention as a power source for the body.

  FIG. 6 is a cross-sectional view showing an example of a single cell in a general solid polymer electrolyte fuel cell. The unit cell 200 is a membrane in which a fuel electrode (anode) 8 and an oxidant electrode (cathode) 9 are provided on one surface side of a solid polymer electrolyte membrane for a fuel cell (hereinafter sometimes simply referred to as an electrolyte membrane) 7. An electrode assembly 12 is provided. The fuel electrode 8 has a structure in which a fuel electrode side catalyst layer 10a and a fuel electrode side gas diffusion layer 11a are laminated in order from the electrolyte membrane 7 side. Similarly, the oxidant electrode 9 has a configuration in which an oxidant electrode side catalyst layer 10b and an oxidant electrode side gas diffusion layer 11b are sequentially laminated from the electrolyte membrane 7 side.

  Each catalyst layer 10 (10a, 10b) is provided with at least an electrode catalyst having catalytic activity for the electrode reaction in each electrode (8, 9). The electrode catalyst is not particularly limited as long as it has catalytic activity for the oxidation reaction of the fuel at the fuel electrode or the reduction reaction of the oxidant at the oxidant electrode. For example, platinum, ruthenium, iron An alloy of platinum and a metal such as nickel or manganese is used. The electrode catalyst is usually contained in the catalyst layer in a state of being supported on conductive particles made of carbon particles such as carbon black, conductive carbon materials such as carbon fibers, or metal materials such as metal particles and metal fibers.

  The membrane / electrode assembly 12 is sandwiched between two separators 13 a and 13 b to constitute a single cell 200. On one side of each of the separators 13a and 13b, grooves for forming a flow path of the reaction gas (fuel gas, oxidant gas) are provided. The fuel is formed by these grooves and the outer surfaces of the fuel electrode 8 and the oxidant electrode 9. A gas flow path 14a and an oxidant gas flow path 14b are defined. The fuel gas channel 14 a is a channel for supplying fuel gas (a gas containing hydrogen or generating hydrogen) to the fuel electrode 8, and the oxidant gas channel 14 b is oxidant gas to the oxidant electrode 9. It is a flow path for supplying (a gas containing or generating oxygen).

  In FIG. 6, each electrode (fuel electrode, oxidant electrode) has a structure in which a catalyst layer and a gas diffusion layer are laminated. There is also a structure in which a functional layer is provided in addition to the layer and the gas diffusion layer.

In the solid polymer electrolyte fuel cell, the reaction of the following formula (1) proceeds at the fuel electrode (anode).
H ₂ → 2H ⁺ + 2e ⁻ (1)
The electrons generated by the equation (1) reach the oxidant electrode (cathode) after working with an external load via an external circuit. Then, the proton generated in the formula (1) moves in the solid polymer electrolyte membrane from the fuel electrode side to the oxidant electrode side by electroosmosis while being hydrated with water.
On the other hand, the reaction of the following formula (2) proceeds at the oxidant electrode.
4H ⁺ + O ₂ + 4e ⁻ → 2H ₂ O (2)

The water produced at the oxidant electrode by the reaction of the above formula (2) is mainly discharged through the gas diffusion layer and the reaction gas channel on the oxidant electrode side, but a part of the water permeates the electrolyte membrane and passes through the fuel electrode. Move to the side.
Many polymer electrolytes exhibit proton conductivity in a water-containing state. That is, in order to obtain a fuel cell in which protons are efficiently conducted from the fuel electrode to the oxidant electrode and exhibit excellent power generation performance, the water content in the membrane-electrode assembly becomes very important.

  In order to prevent the membrane / electrode assembly from being dried, a reactive gas is also supplied in a humidified state. Examples of the method of humidifying the reaction gas include a method of bringing the reaction gas into contact with moisture through a water permeable membrane before supplying the reaction gas to the single cell, and a method of diffusing the reaction gas in the stored water. . However, these reactive gas humidification methods require space for the humidifier and operating energy, and thus have problems such as an increase in the size of the fuel cell and a decrease in power generation efficiency. There is also a problem of a complicated reaction gas supply system.

The reaction gas (fuel gas, oxidant gas) supplied to each electrode is humidified by the moisture in the electrode while flowing through the membrane / electrode assembly, so the downstream side of the reactive gas is more upstream than the upstream side. Humidity increases. Utilizing this, the oxidant gas and the fuel gas are circulated in a counterflow with the electrolyte membrane interposed therebetween, and the upstream of the oxidant gas and the downstream of the fuel gas, and the downstream of the oxidant gas and the upstream of the fuel gas are opposed to each other. Thus, there is a fuel cell in which the moisture content in the membrane-electrode assembly is improved as compared with the case where the oxidant gas and the fuel gas are circulated in parallel flow (see, for example, Patent Documents 1 to 4).
However, the humidity in the fuel electrode, particularly in the upstream region of the fuel gas, cannot be sufficiently increased by simply circulating the oxidant gas and the fuel gas in a counterflow.

  On the other hand, while the reactive gas supplied to each electrode flows through the membrane / electrode assembly, the active material is consumed by the electrode reaction, and the concentration thereof decreases. Therefore, in the downstream region of the reaction gas, the electrode reaction does not progress as actively as the upstream region. In contrast to such a difference in power generation performance between the upstream region of the reactive gas and the downstream region of the reactive gas, in Patent Document 5, in order to improve the utilization rate of the catalytic component on the downstream side, the thickness of the catalytic layer is changed, Fuel cells with an adjusted amount have been proposed.

JP 2002-280048 A JP 2004-31134 A JP 2001-135326 A JP 2004-273392 A JP 2005-317492 A

  The fuel electrode does not generate water due to the electrode reaction, and further, as described above, the water moves to the oxidant electrode side accompanying the proton movement. In particular, the upstream region of the fuel gas is a region where the flowing reaction gas is in a relatively low humidity state as compared with the downstream region, so that it is easy to dry and proton conductivity is likely to decrease.

The oxidizer electrode is relatively difficult to dry because of the generation of water due to the electrode reaction and the movement of water from the fuel electrode side accompanying proton movement.
In particular, since the oxygen concentration is high in the upstream region of the oxidant gas, the electrode reaction of formula (2) proceeds actively, and as a result, a lot of water is generated. Therefore, there is a lot of liquid water in the upstream region of the oxidant gas, and between the oxidant gas upstream region of the oxidant electrode and the fuel electrode facing the upstream region of the oxidant gas across the electrolyte membrane, A water concentration gradient is formed, and water can be moved to the fuel electrode side by the liquid pressure.
On the other hand, in the downstream area of the oxidant gas, the oxygen concentration is low and the amount of generated water is small because the electrode reaction of formula (2) does not proceed easily, but the humidity state of the oxidant gas is relatively low compared to the upstream area. It is high.

As described above, in the membrane / electrode assembly, a water concentration gradient is formed between the upstream region and the downstream region of the reaction gas, and the water concentration gradient is also formed between the fuel electrode and the oxidant electrode. Is formed. In order to improve the proton conductivity of the membrane / electrode assembly, the moisture content of the membrane / electrode assembly is very important. In particular, it is important to promote the water transfer from the oxidizer electrode rich in water to the fuel electrode.
Among them, as described above, although the oxidant gas has a high humidity state and a large amount of moisture, the driving force for moving the moisture to the fuel electrode is weak, and the oxidant gas downstream region is particularly easy to dry among the fuel electrodes. There is a need for a fuel cell that exhibits excellent power generation performance even when a low-humidified or non-humidified reactive gas is used by promoting water movement to the upstream region of the fuel gas.

  The present invention has been accomplished in view of the above circumstances, and in a fuel cell in which an oxidant gas and a fuel gas are circulated in a counterflow, the water transfer from the oxidant electrode to the fuel electrode is effectively promoted and oxidized. The present invention provides a fuel cell capable of efficiently humidifying a fuel electrode with generated water in the agent electrode.

  The first fuel cell of the present invention includes a polymer electrolyte membrane, a fuel electrode provided on one surface of the polymer electrolyte membrane, and an oxidant electrode provided on the other surface of the polymer electrolyte membrane. A fuel cell that generates power by supplying a fuel gas to the fuel electrode and an oxidant gas to the oxidant electrode, wherein the fuel gas and the oxidant gas are circulated in a counterflow, The upstream region of the gas and the downstream region of the oxidant gas, and the downstream region of the fuel gas and the upstream region of the oxidant gas face each other across the polymer electrolyte membrane, and the thickness of the fuel electrode is upstream of the fuel gas. It is characterized by being relatively thin toward the downstream side.

  As described above, by reducing the thickness of the fuel electrode from the upstream side to the downstream side of the fuel gas, the transpiration of the fuel electrode is relatively increased from the downstream side to the upstream side of the fuel gas. Get higher. In other words, the upstream region of the fuel gas has a greater force for pulling water from the oxidant electrode side than the downstream region. Therefore, according to the first fuel cell of the present invention, the moisture in the downstream region of the oxidant gas can be efficiently moved to the fuel electrode side, so that the fuel electrode and the polymer electrolyte membrane in the upstream region of the fuel gas Drying can be suppressed. Therefore, according to the present invention, it is possible to suppress a decrease in power generation performance due to drying of the upstream region of the fuel gas.

  The second fuel cell of the present invention includes a polymer electrolyte membrane, a fuel electrode provided on one surface of the polymer electrolyte membrane, and an oxidant electrode provided on the other surface of the polymer electrolyte membrane. A fuel cell that generates power by supplying a fuel gas to the fuel electrode and an oxidant gas to the oxidant electrode, wherein the fuel gas and the oxidant gas are circulated in a counterflow, The upstream region of the gas and the downstream region of the oxidant gas, and the downstream region of the fuel gas and the upstream region of the oxidant gas face each other across the polymer electrolyte membrane, and the porosity of the fuel electrode is upstream of the fuel gas. It is characterized by being relatively small from the side toward the downstream side.

  As described above, by making the porosity of the fuel electrode relatively small from the upstream side of the fuel gas toward the downstream side, the transpiration of the fuel electrode is relatively reduced from the downstream side of the fuel gas toward the upstream side. Get higher. That is, the fuel gas upstream region of the fuel electrode has a greater force to pull water from the oxidant electrode side than the downstream region. Therefore, like the first fuel cell, the second fuel cell according to the present invention can efficiently move the moisture in the downstream region of the oxidant gas to the fuel electrode side. It is possible to suppress drying of the electrode and the polymer electrolyte membrane, and it is possible to suppress a decrease in power generation performance due to drying of the fuel gas upstream region.

  As a specific configuration of the second fuel cell, for example, the fuel electrode includes a catalyst layer containing at least an electrode catalyst, and the porosity of the catalyst layer extends from the upstream side to the downstream side of the fuel gas. The fuel electrode has a structure in which a catalyst layer and a gas diffusion layer are laminated in order from the polymer electrolyte membrane side, and the porosity of the gas diffusion layer is the fuel gas. The thing which is relatively small toward the downstream side from the upstream side is mentioned.

  According to the fuel cell of the present invention, the generated water of the oxidant electrode can be efficiently moved to the fuel electrode through the electrolyte membrane. In particular, the moisture in the oxidant gas downstream region of the oxidant electrode can be efficiently transferred to the fuel gas upstream region of the fuel electrode opposite to the oxidant gas downstream region across the electrolyte membrane. That is, the fuel cell of the present invention can effectively use the water produced by the electrode reaction at the oxidant electrode for humidifying the fuel gas, and has excellent power generation efficiency.

  The first fuel cell of the present invention includes a polymer electrolyte membrane, a fuel electrode provided on one surface of the polymer electrolyte membrane, and an oxidant electrode provided on the other surface of the polymer electrolyte membrane. A fuel cell that generates power by supplying a fuel gas to the fuel electrode and an oxidant gas to the oxidant electrode, wherein the fuel gas and the oxidant gas are circulated in a counterflow, The upstream region of the gas and the downstream region of the oxidant gas, and the downstream region of the fuel gas and the upstream region of the oxidant gas are opposed to each other with the polymer electrolyte membrane interposed therebetween, and the thickness of the fuel electrode is upstream of the fuel gas. It is characterized by being relatively thin from the side toward the downstream side.

  The second fuel cell of the present invention includes a polymer electrolyte membrane, a fuel electrode provided on one surface of the polymer electrolyte membrane, and an oxidant provided on the other surface of the polymer electrolyte membrane. A fuel cell that generates power by supplying a fuel gas to the fuel electrode and an oxidant gas to the oxidant electrode, wherein the fuel gas and the oxidant gas circulate in a counterflow The upstream region of the fuel gas and the downstream region of the oxidant gas, and the downstream region of the fuel gas and the upstream region of the oxidant gas face each other with the polymer electrolyte membrane interposed therebetween, and the porosity of the fuel electrode is determined by the fuel gas It is characterized by being relatively small from the upstream side to the downstream side.

  An object of the present invention is to promote water movement from an oxidant gas downstream region of an oxidant electrode to an upstream region of a fuel gas in a fuel cell in which an oxidant gas and a fuel gas are circulated in a counter flow. It is. Then, by adopting means for changing the thickness of the fuel electrode or the porosity of the fuel electrode in the surface direction of the fuel electrode (from the upstream side of the fuel gas toward the downstream side of the fuel gas), the fuel of the fuel electrode The above object is achieved by enhancing the transpiration in the gas upstream region and applying a force for pulling water from the oxidizer electrode to the fuel gas upstream region of the fuel electrode.

Hereinafter, the first and second fuel cells of the present invention will be described.
FIG. 1 shows an embodiment of a membrane / electrode assembly provided in the first fuel cell of the present invention. In FIG. 1, (1B) is a plan view of the surface of the fuel electrode side catalyst layer of the membrane / electrode assembly, and (1A) is a BB cross-sectional view of (1B).
In FIG. 1, a membrane / electrode assembly 6 is provided with a fuel electrode (anode) 2 and an oxidant electrode (cathode) 3 on one surface side of a polymer electrolyte membrane (hereinafter sometimes simply referred to as an electrolyte membrane) 1. ing. Both the fuel electrode 2 and the oxidant electrode 3 have a structure in which a catalyst layer 4 (4a, 4b) and a gas diffusion layer 5 (5a, 5b) are laminated in order from the electrolyte membrane 1 side. In the present embodiment, both the fuel electrode 2 and the oxidant electrode 3 have the above-described laminated structure. However, the fuel electrode 2 and the oxidant electrode 3 may each have a single-layer structure including only a catalyst layer. It may be a multilayer structure having functional layers other than the catalyst layer and the gas diffusion layer.

  The membrane / electrode assembly 6 is sandwiched between two separators to form a single cell (not shown). On one side of each separator, grooves for forming a flow path of the reaction gas (fuel gas, oxidant gas) are provided. The fuel gas flow path is formed by these grooves and the outer surfaces of the fuel electrode 2 and the oxidant electrode 3. An oxidant gas flow path is defined. The fuel gas channel is a channel for supplying fuel gas (a gas containing hydrogen or generating hydrogen) to the fuel electrode 2, and the oxidant gas channel is an oxidant gas (oxygen gas) to the oxidant electrode 3. Or a gas for generating oxygen).

  The polymer electrolyte membrane 1 is not particularly limited, and examples thereof include a fluorine-based polymer electrolyte such as perfluorocarbon sulfonic acid resin represented by Nafion (trade name), polyether ether ketone, polyether ketone, polyethylene sulfide, and the like. And a hydrocarbon polymer electrolyte in which a proton conductive group such as a sulfonic acid group, a boronic acid group, or a hydroxyl group is introduced into the hydrocarbon polymer.

The catalyst layer 4 is usually formed using a catalyst ink containing an electrode catalyst having catalytic activity for an electrode reaction in each electrode and an electrolyte resin.
As the electrode catalyst, one in which a catalyst component is supported on conductive particles is usually used. The catalyst component is not particularly limited as long as it has catalytic activity for the oxidation reaction of the fuel at the fuel electrode or the reduction reaction of the oxidant at the oxidant electrode, and is generally used for solid polymer fuel cells. Can be used. For example, platinum or an alloy of platinum and a metal such as ruthenium, iron, nickel, manganese, cobalt, copper, and the like can be given. As the conductive particles as the catalyst carrier, carbon particles such as carbon black, conductive carbon materials such as carbon fibers, and metal materials such as metal particles and metal fibers can also be used.
As the electrolyte resin, those exemplified as the polymer electrolyte resin constituting the electrolyte membrane can be used.

  The catalyst ink is obtained by dissolving or dispersing the above-described electrode catalyst and electrolyte resin in a solvent. The solvent of the catalyst ink may be appropriately selected. For example, alcohols such as methanol, ethanol and propanol, organic solvents such as N-methyl-2-pyrrolidone (NMP) and dimethyl sulfoxide (DMSO), or organic solvents such as these Mixtures and mixtures of these organic solvents and water can be used. In addition to the electrode catalyst and the electrolyte resin, the catalyst ink may contain other components such as a binder and a water-repellent resin as necessary.

  The method for forming the catalyst layer is not particularly limited. For example, the catalyst layer is formed on the surface of the gas diffusion layer sheet by applying and drying catalyst ink on the surface of the gas diffusion layer sheet forming the gas diffusion layer. Alternatively, the catalyst layer may be formed on the electrolyte membrane surface by applying a catalyst ink to the electrolyte membrane surface and drying. Alternatively, a transfer sheet is prepared by applying a catalyst ink to the transfer substrate surface and drying, and the transfer sheet is joined to the electrolyte membrane or gas diffusion sheet by thermocompression bonding or the like, and the catalyst is formed on the electrolyte membrane surface. A layer may be formed, or a catalyst layer may be formed on the surface of the gas diffusion layer sheet.

The method for applying the catalyst ink, the drying method, and the like can be selected as appropriate. For example, examples of the coating method include a spray method, a screen printing method, a doctor blade method, a gravure printing method, and a die coating method. Examples of the drying method include reduced-pressure drying, heat drying, and reduced-pressure heat drying. There is no restriction | limiting in the specific conditions in reduced pressure drying and heat drying, What is necessary is just to set suitably.
The amount of catalyst ink applied varies depending on the composition of the catalyst ink and the catalyst performance of the catalyst metal used for the electrode catalyst, but the amount of catalyst component per unit area is about 0.1 to 1 mg / cm ^2. do it. The thickness of the catalyst layer may be about 1 to 30 μm.

  The gas diffusion layer has gas diffusibility, conductivity, and strength required as a material constituting the gas diffusion layer, for example, carbon paper, carbon cloth, carbon, which can efficiently supply gas to the catalyst layer. Carbonaceous porous body such as felt, titanium, aluminum, copper, nickel, nickel-chromium alloy, copper and its alloys, silver, aluminum alloy, zinc alloy, lead alloy, titanium, niobium, tantalum, iron, stainless steel, gold Further, it can be formed using a gas diffusion layer sheet made of a conductive porous material such as a metal mesh composed of a metal such as platinum or a metal porous material. The thickness of the conductive porous body is preferably about 50 to 300 μm.

The gas diffusion layer sheet may be composed of a single layer of the conductive porous body as described above, but a water repellent layer may be provided on the side facing the catalyst layer. The water-repellent layer usually has a porous structure containing conductive particles such as carbon particles and carbon fibers, water-repellent resin such as polytetrafluoroethylene (PTFE), and the like. The method for forming the water-repellent layer on the conductive porous body is not particularly limited. For example, conductive particles such as carbon particles, a water-repellent resin, and other components as necessary, ethanol, propanol, A water-repellent layer ink mixed with an organic solvent such as propylene glycol, water or a solvent such as a mixture thereof is applied to at least the side facing the catalyst layer of the conductive porous body, and then dried and / or baked. Good.
By providing the water repellent layer on the surface on the catalyst layer side, the oxidant electrode has an advantage that the water in the catalyst layer is pushed back to the electrolyte membrane side and water movement to the fuel electrode side can be promoted. On the other hand, when there is an excessive amount of moisture in the catalyst layer and the water has moved into the gas diffusion layer, the water repellency prevents water from staying in the gas diffusion layer.

  The electrolyte membrane and the gas diffusion layer sheet in which the catalyst layer is formed by the above-described method are appropriately laminated with a gas diffusion layer sheet or an electrolyte membrane on which the catalyst layer is not formed, and bonded to each other by thermocompression bonding. A membrane / electrode assembly is obtained.

  The produced membrane / electrode assembly 6 is further sandwiched by a separator to form a single cell. The separator has conductivity and gas sealing properties, and can function as a current collector and gas sealing body, for example, a carbon separator containing a high concentration of carbon fiber and made of a composite material with resin, metal A metal separator using a material can be used. Examples of the metal separator include those made of a metal material excellent in corrosion resistance, and those coated with a coating that enhances the corrosion resistance by coating the surface with carbon or a metal material excellent in corrosion resistance. .

In the fuel cell of the present invention, a fuel gas (for example, a gas that generates or contains hydrogen; H ₂ gas, etc.) supplied to the fuel electrode 2 and an oxidant gas (for example, oxygen is supplied) to the oxidant electrode 3. Generated or oxygen-containing gas (air, etc.) is circulated in a counterflow in the membrane / electrode assembly 6 in which the polymer electrolyte membrane 1 is sandwiched between the fuel electrode 2 and the oxidant electrode 3. The upstream region and the downstream region of the oxidant gas, and the downstream region of the fuel gas and the upstream region of the oxidant gas are opposed to each other across the polymer electrolyte membrane 1.

Here, the upstream region and the downstream region of the fuel gas are supplied to the membrane-electrode assembly, circulate in the membrane-electrode assembly, and discharged from the membrane-electrode assembly in the membrane-electrode assembly. It means the upstream side and the downstream side of the flow path, and of the flow path length of the flow path, 1/2 of the gas supply side is the upstream area, and 1/2 of the gas discharge side is the downstream area. .
Similarly, the upstream region and the downstream region of the oxidant gas are supplied to the membrane / electrode assembly, flow through the membrane / electrode assembly, and are discharged from the membrane / electrode assembly. It means the upstream side and the downstream side of the flow path in the body, and of the flow path length of the flow path, 1/2 of the gas supply side is the upstream area and 1/2 of the gas discharge side is the downstream area And

In addition, the fact that the upstream region of the fuel gas and the downstream region of the oxidant gas flow so as to face each other with the polymer electrolyte membrane interposed therebetween means that the fuel electrode 2 provided on one surface of the polymer electrolyte membrane 1 At least part of the upstream region of the supplied fuel gas and at least part of the downstream region of the oxidant gas supplied to the oxidant electrode 3 provided on the other surface of the polymer electrolyte membrane are In this state, the molecular electrolyte membrane 1 is opposed, and the entire upstream region of the fuel gas and the entire downstream region of the oxidant gas may not be opposed.
From the viewpoint of enhancing the effect of the present invention, the region of 1/5 to 1/5 of the gas supply side of the flow length of the fuel gas and the 1/5 of the flow length of the oxidant gas on the gas discharge side. It is preferable that the region of ˜1 / 3 is opposed to the polymer electrolyte membrane. Similarly, the region of 1/3 to 1/5 of the gas discharge side of the flow length of the fuel gas and the region of 1/3 to 1/5 of the flow length of the oxidant gas on the gas supply side Are preferably opposed to each other with the polymer electrolyte membrane interposed therebetween.

  In the oxidant electrode, in the upstream region of the oxidant gas, the oxygen concentration of the flowing oxidant gas is high, so that the electrode reaction (oxygen reduction reaction) proceeds actively (see FIG. 3). That is, since it becomes a high-density current region and a large amount of water is generated, it is between the oxidant gas upstream region of the oxidant electrode and the fuel gas upstream region of the fuel electrode facing the region across the electrolyte membrane. A large water concentration gradient is formed, and a hydraulic pressure is generated from the oxidant electrode side to the fuel electrode side. This hydraulic pressure makes it easy for the water in the oxidizer electrode to move to the fuel electrode through the electrolyte membrane. In particular, moisture generated in the catalyst layer of the oxidant electrode by imparting water repellency to the gas diffusion layer adjacent to the oxidant electrode side catalyst layer or forming a water repellent layer between the gas diffusion layer and the catalyst layer. Is applied to the electrolyte membrane side, and the movement of moisture from the oxidizer electrode to the fuel electrode can be promoted.

  On the other hand, in the oxidant electrode, the downstream region of the oxidant gas has a lower oxygen concentration in the flowing oxidant gas, so that the electrode reaction does not proceed actively and the current density is smaller as the upstream region (see FIG. 3). That is, since the amount of generated water is small, there is no hydraulic pressure that pushes moisture toward the electrolyte membrane unlike the upstream region of the oxidant gas. However, in the downstream region of the oxidant gas, the oxidant gas is humidified with the moisture in the electrode before reaching the downstream region, and is in a high humidity state.

The present inventor provides a fuel that opposes the water vapor in the reaction gas in the oxidant gas downstream region of the oxidant electrode as described above, the water condensed with the water vapor, and the generated water with the electrolyte membrane interposed therebetween. As a result of intensive investigations to efficiently move the fuel gas upstream of the electrode, the force that pulls moisture (water vapor, liquid water) in the oxidant gas downstream region to the fuel electrode upstream of the fuel gas upstream region of the fuel electrode. It has been found that it is effective to give. As a driving force for promoting water movement from the oxidizer electrode to the fuel electrode, attention was paid to the transpiration effect at the fuel electrode.
The transpiration rate (generated water vapor amount) in the electrode having a porous structure is represented by the following formula.

In the above formula, it can be seen that when the surface area (A × Vn) is large, the transpiration rate increases, that is, a large driving force that promotes water movement from the oxidizer electrode to the fuel electrode can be obtained.
The first and second fuel cells of the present invention have been achieved based on the above knowledge. First, on the fuel gas of the fuel electrode facing the downstream region of the oxidant gas of the oxidant electrode with the electrolyte membrane interposed therebetween. By increasing the surface area of the basin, the transpiration of the fuel electrode in the upstream region of the fuel gas is enhanced, and water movement from the oxidizer electrode to the upstream region of the fuel gas is promoted.

As a specific configuration, in the first fuel cell of the present invention, the thickness of the fuel electrode is relatively thin from the upstream side to the downstream side of the fuel gas. In the case of having a similar porous structure (porosity, pore diameter, etc.), if the thickness (volume) is increased, the surface area in the pores of the porous body is increased and the transpiration is increased. On the other hand, when the thickness is reduced, the surface area in the pores of the porous body is reduced, and the transpiration is lowered. That is, in the first fuel cell of the present invention, the force for pulling water from the oxidizer electrode to the fuel electrode is strong in the fuel gas upstream region of the fuel electrode, and the downstream region is weak.
The catalyst layer and gas diffusion layer constituting the electrode of the fuel cell have a porous structure. For example, a general catalyst layer has a porosity [the volume in the pores of the catalyst layer with respect to the volume Vs of the catalyst layer] The ratio of Vps (Vps / Vs × 100%)] is 30% or more.

Therefore, in the first fuel cell of the present invention, in the upstream region of the fuel gas of the fuel electrode, a force pulling moisture acts from the oxidant electrode side, and excess moisture in the oxidant electrode moves to the fuel electrode side. . Therefore, drying of the fuel electrode and the electrolyte membrane can be suppressed by effectively using the excess water of the oxidizer electrode that is relatively rich in water. Further, in the oxidant electrode, in the downstream region of the oxidant gas, the water in which the water vapor in the oxidant gas is condensed and the water generated by the electrode reaction are retained, and the flooding in which the electrode is immersed is likely to occur. Thus, by actively moving moisture to the fuel electrode side, occurrence of flooding in the downstream region of the oxidant gas can be suppressed.
Further, as in the first fuel cell of the present invention, by thinning the fuel electrode from the upstream side of the fuel gas toward the downstream side, the oxidant gas upstream region of the oxidant electrode to the fuel gas downstream region of the fuel electrode. The resistance of water movement due to the above hydraulic pressure is reduced, and water movement from the oxidizer electrode to the fuel electrode is more efficiently performed. That is, the moisture generated in the upstream region of the oxidant gas can be efficiently used for humidifying the downstream region of the fuel gas of the fuel electrode.

As described above, according to the first fuel cell of the present invention, it is possible to effectively use the water generated by the electrode reaction in the oxidizer electrode as humidified water that maintains the wet state of the fuel electrode and the electrolyte membrane. is there. The first fuel cell of the present invention is particularly excellent in the effect of promoting water movement from the oxidant gas downstream region of the oxidant electrode to the fuel gas upstream region of the fuel electrode facing the region.
In addition, according to the first fuel cell of the present invention, the generated water in the oxidizer electrode can be effectively used as humidified water in the fuel electrode, so that the humidifier that humidifies the reaction gas can be omitted or simplified. It is possible to improve the power generation efficiency for the energy required to operate and mount the humidifier, and to reduce the size of the fuel cell by reducing or omitting the humidifier.

Here, the thickness of the fuel electrode is the thickness of the catalyst layer in the case where the fuel electrode has a single layer structure consisting only of the catalyst layer. The fuel electrode has a multilayer structure in which, for example, a catalyst layer and a gas diffusion layer are stacked. In this case, it is the total thickness of all layers constituting the fuel electrode. When the fuel electrode has a multilayer structure in which a plurality of layers are stacked, if the total thickness of all layers constituting the fuel electrode decreases from the upstream side to the downstream side, the thickness of all layers is increased from the upstream side. The thickness may be changed toward the downstream side, or the thickness of a part of the layers constituting the fuel electrode may be changed from the upstream side to the downstream side, and the thicknesses of the remaining layers may be constant.
In order to promote water transfer from the oxidant electrode to the fuel electrode by increasing the transpiration of the fuel electrode, the thickness of at least the layer constituting the fuel electrode that is closest to the oxidant electrode that is the water source. It is effective to change as described above. Typically, it is preferable to control at least the thickness of the catalyst layer as described above. As described above, the catalyst layer can be formed using the catalyst ink, and has an advantage that the thickness can be easily controlled as compared with the gas diffusion layer or the like.

The form of the change in the thickness of the fuel electrode is not particularly limited, and as shown in FIG. 1, the thickness may be changed in a linear shape or a curved shape in addition to a step shape from the upstream side to the downstream side. The specific thickness is not particularly limited, and may be appropriately determined in consideration of the operating conditions and structure of the fuel cell. As a guideline, the thickness of the thinnest part (downstream area) of the fuel electrode Is Tmin and the thickness of the thickest part (upstream region) is Tmax, Tmax / Tmin = 1.5 to 10 is preferable.
The average thickness of the fuel electrode side catalyst layer is preferably in the range of 3 to 30 μm.

  Examples of the method for controlling the thickness of the catalyst layer include control of the coating amount of the catalyst ink. In the method for forming the catalyst layer described above, when applying the catalyst ink to the electrolyte membrane, the gas diffusion layer sheet, and the transfer sheet, the same amount can be used by changing the coating amount for each region using the catalyst ink of the same composition. Thus, catalyst layers having different thicknesses and different thicknesses can be formed.

Alternatively, a method may be used in which the composition of the catalyst ink is changed for each region and applied separately. For example, if the amount of the catalyst carrier is increased while keeping the amount of the catalyst component constant, a bulky and thick catalyst layer can be formed while maintaining the amount of catalyst per unit area of the catalyst layer. At this time, by reducing the amount of catalyst component supported per catalyst carrier and increasing the amount of catalyst carrier loaded with the catalyst component, the amount of catalyst component per catalyst layer unit area is kept constant while the amount of catalyst carrier is kept constant. Or by using a catalyst carrier carrying a catalyst component and a catalyst carrier component not carrying a catalyst component separately, while keeping the amount of the catalyst component per unit area of the catalyst layer constant, The amount of carrier may be increased. Conversely, by increasing the amount of catalyst component supported per catalyst carrier and making the amount of catalyst component per catalyst layer unit area constant, the amount of catalyst carrier used can be reduced and a thin catalyst layer can be formed. .
Thus, by making the amount of catalyst per unit area of the catalyst layer constant, it is possible to change the thickness of the catalyst layer while suppressing the amount of catalyst to the required amount. Compared with the case of changing, there is an advantage that the effective utilization rate of the catalyst is not reduced and the lack of the catalyst does not occur.

  Further, the thickness of the catalyst layer can be changed by changing the ratio of the catalyst carrier particles to the polymer electrolyte resin (catalyst carrier particles / polymer electrolyte resin). Specifically, a thick catalyst layer can be formed by increasing the catalyst carrier particle / polymer electrolyte resin, and a thin catalyst layer can be formed by reducing the catalyst carrier particle / polymer electrolyte resin. Can do.

As a method of changing the thickness of the gas diffusion layer, for example, it can be adjusted by the basis weight of the carbon fibers forming the gas diffusion layer. Specifically, in the case of carbon fibers having the same thickness, a thick catalyst layer can be formed by increasing the basis weight, and conversely, a thin catalyst layer can be formed by reducing the basis weight. Further, the transpiration rate can be increased by increasing the porosity of the gas diffusion layer, and conversely, the transpiration rate can be decreased by decreasing the porosity.
The average thickness of the fuel electrode side gas diffusion layer is preferably in the range of 50 to 300 μm.
The average thickness of the fuel electrode is preferably in the range of 53 to 330 μm.

  Further, the thickness of the water repellent layer may be changed. Examples of the method for controlling the thickness of the water repellent layer include a method for controlling the coating amount of the water repellent layer ink and the amount of conductive particles in the water repellent layer ink as in the catalyst layer.

  In FIG. 1, the membrane / electrode assembly is a rectangular shape having a long side and a short side, and each reactive gas flows in the longitudinal direction, but each reactive gas flows in the short side direction. (See FIG. 2). Further, the specific form of the reaction gas channel is not particularly limited, and may be a serpentine shape or a straight shape.

Hereinafter, the second fuel cell will be described. Descriptions similar to those of the first fuel cell are omitted.
Similar to the first fuel cell described above, the second fuel cell of the present invention enhances the transpiration in the upstream region of the fuel gas at the fuel electrode, thereby allowing the fuel from the oxidant gas downstream region of the oxidant electrode. It promotes water movement to the upstream area of fuel gas upstream. The first fuel cell takes a means of controlling the thickness of the fuel electrode upstream of the fuel gas in order to enhance the transpiration, whereas the second fuel cell of the fuel electrode upstream of the fuel gas Take the measure of porosity control.

Here, the porosity of the fuel electrode is the ratio (Vp / V × 100%) of the pore volume (Vp) to the volume (V) of the fuel electrode.
Specifically, in the second fuel cell of the present invention, the porosity of the fuel electrode is relatively decreased from the upstream side to the downstream side of the fuel gas. In the case of having an equivalent volume, if the porosity is increased, the surface area in the pores of the porous body is increased, and the transpiration is increased. On the other hand, if the porosity decreases, the surface area in the pores of the porous body decreases, and the transpiration property decreases. That is, in the second fuel cell of the present invention, the force for pulling water from the oxidant electrode side is strong in the upstream region of the fuel electrode, and is weak in the downstream region.

Therefore, as in the first fuel cell, in the second fuel cell, in the upstream region of the fuel gas of the fuel electrode, a force for pulling water acts from the oxidant electrode side, and excess water in the oxidant electrode is removed from the fuel electrode side. Move to. Therefore, drying of the fuel electrode and the electrolyte membrane can be suppressed by effectively using the excess water of the oxidizer electrode that is relatively rich in water. Further, in the oxidant electrode, in the downstream region of the oxidant gas, the water in which the water vapor in the oxidant gas is condensed and the water generated by the electrode reaction are retained, and the flooding in which the electrode is immersed is likely to occur. Thus, by actively moving moisture to the fuel electrode side, it is possible to suppress flooding. Further, as in the second fuel cell, the porosity of the fuel electrode is increased from the upstream side of the fuel gas. By decreasing toward the downstream side, the resistance of water movement due to the hydraulic pressure from the oxidant gas upstream region of the oxidant electrode to the fuel gas downstream region of the fuel electrode is reduced, and the resistance from the oxidant electrode to the fuel electrode is reduced. Water transfer is performed more efficiently. That is, the moisture generated in the upstream region of the oxidant gas can be efficiently used for humidifying the downstream region of the fuel gas of the fuel electrode.

As described above, according to the second fuel cell of the present invention, it is possible to effectively use the water generated by the electrode reaction at the oxidizer electrode as humidified water that maintains the wet state of the fuel electrode and the electrolyte membrane. is there. The second fuel cell is particularly excellent in the effect of promoting water movement from the oxidant gas downstream region of the oxidant electrode to the fuel gas upstream region of the fuel electrode facing the region.
Further, according to the second fuel cell of the present invention, the generated water in the oxidizer electrode can be efficiently used effectively as humidified water in the fuel electrode, so that the humidifier that humidifies the reaction gas can be omitted or simplified. It is possible to improve the power generation efficiency for the energy required to operate and mount the humidifier, and to reduce the size of the fuel cell by reducing or omitting the humidifier.

Here, the porosity of the fuel electrode is the porosity of the catalyst layer in the case where the fuel electrode has a single-layer structure consisting of only the catalyst layer, and the fuel electrode has a structure in which, for example, a catalyst layer and a gas diffusion layer are stacked. In the case of a multilayer structure, the average porosity of all layers constituting the fuel electrode. When the fuel electrode has a multilayer structure in which a plurality of layers are stacked, if the average porosity of all layers constituting the fuel electrode decreases from the upstream side to the downstream side, the porosity of all layers constituting the fuel electrode The degree of porosity may be reduced from the upstream side to the downstream side, or only the porosity of some layers constituting the fuel electrode is reduced from the upstream side to the downstream side, and the porosity of the remaining layers May be constant. Typically, the porosity of at least one of the catalyst layer and the gas diffusion layer is changed as described above.
In order to promote water transfer from the oxidizer electrode to the fuel electrode by increasing the transpiration of the fuel electrode, the porosity of at least the layer constituting the fuel electrode that is closest to the oxidizer electrode that is the water source It is effective to change as described above. Typically, it is preferable to control at least the thickness of the catalyst layer as described above. As described above, the catalyst layer can be formed using the catalyst ink, and has an advantage that the porosity can be easily controlled as compared with the gas diffusion layer or the like.
The average porosity means the porosity of the entire fuel electrode in each of the upstream region and the downstream region when the fuel electrode has a multilayer structure composed of a plurality of layers.

  The form of the change in the porosity at the fuel electrode is not particularly limited, and may be changed stepwise from the upstream side to the downstream side, or may be changed in a linear shape or a curved shape. Further, the specific porosity is not particularly limited and may be appropriately determined in consideration of the operating condition and structure of the fuel cell. As a guideline, the portion with the lowest porosity of the fuel electrode (downstream region) When the porosity of Pmin is Pmin and the porosity of the highest portion (upstream region) is Pmax, Pmax / Pmin = 1.5-10.

  Examples of a method for controlling the porosity of the catalyst layer and a method for controlling the porosity of the gas diffusion layer include a method of adding a pore-forming agent to the catalyst ink and changing the amount and size of the pore-forming agent. Can be mentioned. A catalyst layer with high porosity can be formed by increasing the proportion of the pore-forming agent. In addition, a catalyst layer having low porosity can be formed by using a solvent having low volatility as the solvent of the catalyst ink. A catalyst ink using a low-volatility solvent has a low porosity because, when applied, the solid content in the catalyst ink settles and a dense structure is formed, and then the solvent volatilizes and solidifies. A layer can be formed. Alternatively, a highly porous catalyst layer can be formed by using fibrous carbon such as vapor grown carbon fiber (VGCF) or carbon nanotube (CNT) as a catalyst carrier and adding it to the catalyst layer. .

  Further, the porosity of the gas diffusion layer can be adjusted by, for example, the thickness and basis weight of the carbon fibers forming the gas diffusion layer. Specifically, in the case of the same basis weight, a catalyst layer with low porosity can be formed by using thick carbon fibers, and conversely, a catalyst layer with low porosity can be formed by using thin carbon fibers. Can do. When carbon fibers having the same thickness are used, a catalyst layer having a low porosity can be formed by increasing the basis weight, and a catalyst layer having a high porosity can be formed by reducing the basis weight. be able to.

  Further, the porosity of the water repellent layer may be changed. Examples of the method for controlling the porosity of the water repellent layer include the method of adding a pore forming agent and adjusting the amount thereof, the adjustment by the volatility of the solvent of the water repellent layer ink, etc.

  In addition, it can also be set as the structure which has the characteristic of a 1st fuel cell, and the characteristic of a 2nd fuel cell. On the other hand, in the first fuel cell, when the porosity of the fuel electrode is the opposite to that of the second fuel cell, that is, when the fuel gas is relatively increased from the upstream side to the downstream side, the transpiration of the fuel electrode is reduced. Difficult to control. Therefore, in the first fuel cell, the porosity in the upstream region of the fuel electrode is preferably equal to or higher than the porosity in the downstream region. Further, in the second fuel cell, when the thickness of the fuel electrode is opposite to that of the first fuel cell, that is, when the fuel gas becomes relatively thick from the upstream side to the downstream side, the transpiration of the fuel electrode is reduced. Difficult to control. Therefore, in the second fuel cell, the thickness of the upstream region of the fuel electrode is preferably equal to or greater than the thickness of the downstream region.

[Reference Experiment 1]
(Manufacture of single fuel cell)
1 g of carbon black carrying platinum (Pt / C catalyst, Pt carrying ratio: 50 wt%), 0.5 g of perfluorocarbon sulfonic acid resin (trade name Nafion, manufactured by Dupont), ethanol, and water are mixed with stirring to form a catalyst. An ink was prepared.

The catalyst ink was spray-coated on both sides of a perfluorocarbon sulfonic acid resin (film thickness 25 μm, trade name Nafion 111). At this time, the catalyst ink was applied so that the amount of Pt per unit area of the catalyst layer was 0.5 mg / cm ² . The ink was dried to form a catalyst layer (13 cm ² ).

  The membrane / catalyst layer assembly in which the catalyst layer was formed on the polymer electrolyte membrane was sandwiched between carbon papers for gas diffusion layers (thickness: 200 μm) and thermocompression bonded to obtain a membrane / electrode assembly. Furthermore, the membrane / electrode assembly was sandwiched between two separators (made of carbon) to produce a single cell.

The obtained single cell is sandwiched between external electrodes, and under conditions of 80 ° C., air (500 ml / min) is supplied to the electrode serving as the oxidizer electrode and hydrogen gas (1000 ml / min) is supplied to the electrode serving as the fuel electrode in a counter flow. Electric power was generated at a current density of the whole single cell of 0.78 A / cm ² and a resistance of 83.9 mΩ · cm ² . Note that the humidity of air and hydrogen gas was 20% RH, 40 RH%, 60 RH%, 80 RH%, and 100 RH%.
The cell surface was subdivided from the air inlet to the outlet, and the current density, oxygen concentration, air relative humidity (Ca relative humidity), hydrogen gas relative humidity (An relative humidity), and resistance values in each region were measured (map test). ).

Map results of the test using the small cells of the electrode area 13cm ^2, and simulate the plane state in the cells of the electrode area 240 cm ^2. The results are shown in FIG. FIG. 3 shows that the current density is high in the region near the air inlet and the current density is low in the region near the air outlet. Further, it can be confirmed that the oxygen concentration is high on the air inlet side and low on the outlet side, and that the relative humidity of the air increases from the air inlet side toward the outlet side.

[Reference Experiment 2]
In a membrane / electrode assembly in which fuel gas (hydrogen gas) and oxidant gas (air) circulate in opposite flows, the amount of water transferred from the oxidant electrode to the fuel electrode in the upstream region of the fuel gas (downstream region of the oxidant gas) Measured under conditions simulating the upstream region of fuel gas.

(Preparation of membrane / electrode assembly 1)
On both sides of a perfluorocarbon sulfonic acid resin (film thickness 25 μm, trade name Nafion 111), platinum-supported carbon black (Pt support ratio: 50 wt%) and perfluorocarbon sulfonic acid resin (trade name Nafion, manufactured by Dupont) were mixed with ethanol and water. The catalyst ink dispersed in the mixed solvent was applied and dried to form a catalyst layer (platinum amount 0.5 mg / cm ² , thickness about 10 μm, area 13 cm ² ).
The obtained catalyst layer-polymer electrolyte membrane-catalyst layer assembly was sandwiched between two pieces of carbon paper (porosity 70%, thickness 200 μm) to prepare a membrane / electrode assembly 1.

(Preparation of membrane / electrode assembly 2)
In the membrane / electrode assembly 1, the membrane / electrode assembly 1 is the same as the membrane / electrode assembly 1 except that only one of the catalyst layers formed on both sides of the polymer electrolyte membrane has a thickness of about 20 μm. 2 was produced.

(Measurement of water movement)
Oxidant gas (air: RH 100%) and fuel gas (hydrogen gas: RH 20%) are supplied to the membrane / electrode assembly 1 and the membrane / electrode assembly 2 in a counter flow, and power is generated. The amount of water transferred from the agent electrode to the fuel electrode was measured.
The amount of water transferred from the oxidant electrode to the fuel electrode (mol / sec · cm ² ) was calculated by measuring the humidity of the gas at the gas inlet and the gas outlet of each of the fuel electrode and the oxidant electrode (see FIG. 4). ). The results are shown in FIG. In the graph of FIG. 5, the calculated maximum water movement amount is the hydrogen gas supplied to the fuel electrode at a relative humidity of 20% and discharged from the fuel electrode at a relative humidity of 100%. The amount of water transferred to

From FIG. 5, the membrane-electrode assembly 2 in which the thickness of the fuel electrode-side catalyst layer is twice that of the membrane-electrode assembly 1 shows that the oxidant electrode to the fuel electrode in the current density range up to 1.75 A / cm ^2. It can be seen that the amount of water transferred to the membrane is greater than that of the membrane / electrode assembly 1. This result shows that the water mobility from the oxidizer electrode to the fuel electrode is improved by increasing the thickness of the fuel electrode.

It is a figure which shows one example of a membrane electrode assembly in the 1st fuel cell of this invention. It is a figure which shows the other form example of the membrane electrode assembly in the 1st fuel cell of this invention. It is a figure which shows the result of the reference experiment 1. FIG. It is a figure which shows the method of the water movement amount measurement in the reference experiment 2. FIG. It is a figure which shows the result in the reference experiment 2. FIG. It is sectional drawing which shows the example of 1 type of the conventional common single cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Polymer electrolyte membrane 2 ... Fuel electrode 3 ... Oxidant electrode 4 ... Catalyst layer (4a: Fuel electrode side catalyst layer, 4b: Oxidant electrode side catalyst layer)
5. Gas diffusion layer (5a: fuel electrode side gas diffusion layer, 5b: oxidant electrode side gas diffusion layer)
6 ... Membrane / electrode assembly 7 ... Polymer electrolyte membrane 8 ... Fuel electrode 9 ... Oxidant electrode 10 ... Catalyst layer (10a: Fuel electrode side catalyst layer, 10b: Oxidant electrode side catalyst layer)
11 ... Gas diffusion layer (11a: fuel electrode side gas diffusion layer, 12b: oxidant electrode side gas diffusion layer)
13a ... Anode side separator 13b ... Cathode side separator 14a ... Anode side gas flow path 14b ... Cathode side gas flow path 200 ... Single cell

Claims (4)

A polymer electrolyte membrane, a fuel electrode provided on one surface of the polymer electrolyte membrane, and an oxidant electrode provided on the other surface of the polymer electrolyte membrane, and a fuel gas in the fuel electrode And a fuel cell that generates electricity by supplying an oxidant gas to the oxidant electrode,
The fuel gas and the oxidant gas are circulated in opposite directions, and the upstream region of the fuel gas and the downstream region of the oxidant gas, and the downstream region of the fuel gas and the upstream region of the oxidant gas sandwich the polymer electrolyte membrane. At the opposite,
The fuel cell according to claim 1, wherein the thickness of the fuel electrode is relatively reduced from the upstream side to the downstream side of the fuel gas. A polymer electrolyte membrane, a fuel electrode provided on one surface of the polymer electrolyte membrane, and an oxidant electrode provided on the other surface of the polymer electrolyte membrane, and a fuel gas in the fuel electrode And a fuel cell that generates electricity by supplying an oxidant gas to the oxidant electrode,
The fuel gas and the oxidant gas are circulated in opposite directions, and the upstream region of the fuel gas and the downstream region of the oxidant gas, and the downstream region of the fuel gas and the upstream region of the oxidant gas sandwich the polymer electrolyte membrane. At the opposite,
The fuel cell according to claim 1, wherein the porosity of the fuel electrode is relatively reduced from the upstream side to the downstream side of the fuel gas.   3. The fuel electrode according to claim 2, wherein the fuel electrode includes a catalyst layer containing at least an electrode catalyst, and the porosity of the catalyst layer is relatively small from the upstream side to the downstream side of the fuel gas. Fuel cell.   The fuel electrode has a structure in which a catalyst layer and a gas diffusion layer are laminated in order from the polymer electrolyte membrane side, and the porosity of the gas diffusion layer is relative from the upstream side to the downstream side of the fuel gas. The fuel cell according to claim 2, wherein the fuel cell is smaller.

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