JP2007280860A - Membrane-electrode junction and fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell which can reduce the number of flooding phenomena and maintaining stable output. <P>SOLUTION: This fuel cell comprises a polymer polyelectrolyte membrane, a pair of conductive, diffusible diffusion layers having the polyelectrolyte membrane between two catalysis layers and a pair of conductive power collectors positioned in a way that it corresponds to the pair of conductive, diffusible diffusion layers. In addition, this fuel cell comprises a channel connected to the catalysis layers so that oxidation agent and fuel can be supplied via the channel. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell that supplies an oxidant to a cathode electrode layer by natural convection.

  At present, secondary batteries represented by lithium secondary battery lead-acid batteries are the mainstream as distributed power sources. When the secondary battery and the fuel cell are compared, the fuel cell does not require charging time, and in principle, there is an advantage that power can be generated semi-permanently only by replenishing the fuel cell.

  The fuel supplied to the fuel cell is mainly a gas or liquid containing hydrogen. For example, when methanol is used as fuel and oxygen is used as oxidant, the chemical energy possessed by methanol is directly converted into electrical energy by the following electrochemical reaction. On the anode side, the supplied aqueous methanol solution reacts according to the equation (1) to dissociate into carbon dioxide, hydrogen ions, and electrons.

CH ₃ OH + H ₂ O → CO ₂ + 6H ⁺ + 6e ⁻ (1)
The generated hydrogen ions move in the electrolyte membrane from the anode to the cathode side, and react with oxygen gas diffused from the air on the cathode electrode and electrons on the electrode according to the formula (2) to generate water.

6H ⁺ + 3 / 2O ₂ + 6e ⁻ → 3H ₂ O (2)
Accordingly, in the entire chemical reaction accompanying power generation, methanol is oxidized by oxygen as shown in the formula (3) to generate carbon dioxide gas and water.

CH ₃ OH + 3 / 2O ₂ → CO ₂ + 3H ₂ O (3)
In addition to these electrode reactions, a crossover phenomenon occurs in which fuel on the anode side directly permeates the electrolyte membrane. The fuel that has reached the cathode side due to the crossover phenomenon burns without contributing to the electrochemical reaction due to the reaction expressed by the equation (3), and generates heat.

  Fuel cells are classified into an active type and a passive type depending on the fuel supply system. The active type supplies fuel or oxidant to the fuel cell by forced convection using auxiliary equipment such as a blower, a fan, and a pump. On the other hand, the passive type does not use these auxiliary machines and supplies fuel or oxidant to the fuel cell by natural diffusion or natural convection. Therefore, in the case of a passive fuel cell, power generation is possible by adopting a structure in which the cathode is in contact with the outside air. Patent Document 1 discloses a passive fuel cell.

JP 2000-268836 A

  When the oxidant is supplied to the cathode by natural diffusion or natural convection, the water produced by the reaction expressed by the reaction (2) in the cathode becomes condensed water in the cathode or on the surface, which prevents the supply of oxygen ( Flooding phenomenon).

  The generated water exists as water vapor immediately after the reaction of the formula (2), and is considered to be discharged to the outside by diffusion. However, when the fuel cell continues to generate electricity, the diffusion of water vapor does not match the generation of water vapor, and the flooding phenomenon Occurs.

  When the flooding phenomenon occurs, it is difficult for the oxidant to reach the cathode, the electrode reaction of the formula (2) is hindered, and the output of the fuel cell is reduced.

  An object of the present invention is to provide a fuel cell capable of reducing flooding and maintaining stable output.

  By separating the passage through which the oxidant reaches the cathode and the passage through which generated water is discharged, the fuel cell can smoothly supply the oxidant to the cathode and smoothly discharge the generated water vapor.

  ADVANTAGE OF THE INVENTION According to this invention, the flooding phenomenon can be reduced and the fuel cell which can maintain the stable output can be provided.

  The active method requires a device for forced circulation, and cannot cope with downsizing of the fuel cell. On the other hand, in the passive method based on the diffusion mechanism, the reaction product is discharged and the fuel and oxidant necessary for the electrochemical reaction are supplied through the diffusion layer. As a result, the flow of discharge and supply is offset. The reaction product is not sufficiently discharged. In addition, a method of discharging a reaction product water by arranging a thermoplastic resin porous membrane layer or water absorbent sheet close to the catalyst reaction layer or diffusion layer is a thermoplastic resin porous membrane layer or water absorbent sheet. The reaction product water is accumulated in the water and the humidity in the vicinity of the catalyst reaction layer increases from the time when the water absorption is saturated. As a result, the obstacle due to condensation of the reaction product water is not essentially solved.

  According to the present embodiment, in the fuel cell, it is possible to efficiently discharge unnecessary substances generated during the reaction, provide a means for accurately supplying the fuel and the oxidant, and obtain a stable output. Can be.

  In this embodiment, a hydrogen ion conductive polymer electrolyte membrane and a pair of diffusion layers having both conductivity and diffusivity arranged opposite to each other with a catalytic reaction layer sandwiched between both surfaces of the polymer electrolyte thin film And a pair of conductive current collectors disposed opposite to each other, and supplying an oxidant and fuel connected to the catalytic reaction layer in the fuel cell The fuel cell is characterized in that a flow path is provided.

  By providing the flow path for supplying the oxidant and the fuel, it becomes easy for the flow of only the discharge to occur in the diffusion layer, and as a result, the influence of the supply and discharge flow canceling each other in the diffusion layer can be reduced. Further, from the chemical reaction formula (3) shown above, reaction heat is generated in the catalytic reaction layer. The flow path for supplying the oxidant and the fuel generates a natural convection based on the heat of reaction, and the natural convection improves the discharge of the reactive organism and the efficiency of the supply of the oxidant or the fuel. In addition, in order to more effectively discharge reactive organisms by natural convection and supply oxidant or fuel, the catalytic reaction layer is composed of a thick part and a thin part, and the temperature difference due to reaction heat is reduced. A flow path for supplying the oxidant and fuel is connected to a thin portion of the catalyst reaction layer or a portion of the catalyst reaction layer where no catalyst is present. By doing so, the reaction product flows out through the diffusion layer from the place where the reaction heat is high, and the oxidant and the fuel easily flow through the flow path from the place where the reaction heat is low. Here, in order to increase the flow of exhaust from the diffusion layer, it is more effective if an exhaust duct is provided. In addition, when air is taken in as an oxidant, if a dehumidifying agent is placed at the entrance of the flow path, dry air can be supplied and adverse effects caused by the reaction product water can be reduced.

  Meanwhile, the catalytic reaction layer has a high relative temperature and a high atmospheric pressure due to reaction heat. As a result, there is a risk that the reactive organisms generated in the catalytic reaction layer are discharged not only from the diffusion layer but also from the flow path provided for supplying the oxidant and fuel. In this case, the reactive organism may block the flow path, and the oxidant and fuel may not be supplied. In order to prevent this, a water repellent or a hydrophilic agent is added at a portion where the flow path and the catalytic reaction layer are connected. If what is supplied is a gas that is discharged as water vapor, adding a water repellent to the connection part makes it difficult for water vapor to flow through the water repellent part and flow into the flow path. Is not affected. On the other hand, when what is supplied is a gas such as carbon dioxide that is discharged as an aqueous methanol solution, adding a hydrophilic agent to the connecting portion allows the aqueous methanol solution to pass easily, but makes it difficult for the gas to pass therethrough.

  FIG. 14 is a conceptual model diagram illustrating the flow of supply and discharge on the cathode side (air electrode). In the conventional conceptual model 141 illustrating the flow of supply and discharge, oxygen is supplied and water is discharged through the surface of the diffusion layer. As a result, supply and discharge flows are offset and there is a problem with efficiency. In the conceptual model diagram 142 and the conceptual model diagram 144 for explaining the flow when the flow path is provided, the supply and the discharge are different routes, and the flow is generated. Also in the conceptual model diagram 143 for explaining the flow when a water repellent or hydrophilic agent is applied to the diffusion layer to provide a water repellent region or a hydrophilic region and these regions are used as flow paths, supply and discharge are different routes. And a flow occurs.

  One embodiment of a membrane electrode assembly 80 according to the present invention is shown in FIG. The electrolyte membrane 1 is a membrane having a proton conductive electrolyte. In order to maintain mechanical strength, a core material such as a porous body may be impregnated with a proton conductive electrolyte. The membrane electrode assembly 80 according to the present embodiment is formed by forming a cathode electrode layer 81 and an anode electrode layer 82 with a substantially thick center and a thin edge on both surfaces of the electrolyte membrane 1. In FIG. 1, a cathode diffusion layer 83 and an anode diffusion layer 84 are disposed so as to cover the cathode electrode layer 81 and the anode electrode layer 82, respectively. The diffusion layer is a member for supplying the fuel or the oxidant to each electrode as uniformly as possible. In the left diagram of FIG. 1, concentric circles drawn on the electrodes mean the contour lines of the electrode layer, which means that the thickness of the electrodes gradually increases from the edge of the electrode toward the substantial center.

  In this embodiment, the electrode layer uses a material in which catalyst particles are supported on carbon particles and kneaded with a binder. As the catalyst particles, platinum particles are used for the cathode electrode layer 81, and an alloy of platinum and ruthenium is used for the anode electrode layer 82.

  As in this embodiment, by making the thickness in the vicinity of the center of the membrane electrode assembly thicker than the thickness of the edge, the electrode reaction in the vicinity of the center is activated, and the edge makes the electrochemical reaction inactive compared to the vicinity of the center. be able to. However, this phenomenon occurs when catalyst particles that cause an electrochemical reaction are present almost uniformly in the electrode layer. The present invention is not limited to this embodiment, and is to bias the activity of the electrochemical reaction performed in the electrode layer. That is, the activity of the electrode reaction can be biased by controlling the distribution of the catalyst particles and biasing the abundance of the catalyst particles.

  On the other hand, in the conventional membrane electrode assembly, the thickness of the electrode and the distribution of the catalyst particles are substantially uniform, and the electrode reaction is also performed substantially uniformly on the front surface of the electrode. Since the passages to be discharged are the same, it is considered that the flow in the opposite directions collides with each other and smooth supply / discharge is not performed.

  In the membrane electrode assembly according to the present embodiment, the region where the electrode reaction occurs is biased. Therefore, in the region where the electrode reaction on the cathode side is active, the electrochemical reaction of formula (2) is actively performed, And the fuel that has reached the cathode due to the crossover phenomenon is burned to generate heat. As a result, in the vicinity of the region where the electrode reaction on the cathode side is active, an ascending air current is generated and water vapor is easily discharged. On the other hand, the region where the electrode reaction is inactive serves as a flow path for supplying the oxidizing agent to the active region.

  At this time, when the oxidizing agent is a gas such as oxygen, it is preferable that a part or all of the region where the electrode reaction is inactive is subjected to water repellent treatment. This is because the region where the electrode reaction is inactive is a passage for oxygen, so that it is necessary to prevent the generated water from entering as much as possible. In the case of this embodiment, the water repellent treatment part 87 is provided along the edge of the cathode electrode layer.

  The embodiment shown in FIG. 2 may be used as a method for dividing the supply path for the oxidant and the discharge path for the generated water vapor.

  That is, the cathode electrode layer 91 and the anode electrode layer 92 are formed on both surfaces of the solid polymer electrolyte membrane 1, and the cathode diffusion layer 93 and the anode diffusion layer 94 are formed so as to cover the respective electrodes. A plurality of through holes are formed in the diffusion layer. Water repellent treatment is applied to the wall surface of the through hole and the electrode surface in contact with the through hole. The water vapor thus generated is less likely to be discharged from the through hole provided in the diffusion layer, and is discharged to the outside through the diffusion layer other than the through hole. On the other hand, the oxidizing agent is supplied to the cathode electrode layer 91 through the water-repellent treated portion without being hindered by the generated water.

  The holes formed in the diffusion layer may be filled with a water repellent material.

  An embodiment of the present invention will be described below with reference to the drawings.

  The fuel cell of this embodiment supplies power by causing a fuel such as hydrogen or methanol to react electrochemically with oxygen. The central part is what is called the electrode electrolyte membrane assembly (MEA 15) shown in FIG. The MEA 15 is composed of a polymer electrolyte membrane 1 made of a fluororesin containing a sulfone group and a cathode side electrode 6 and an anode side electrode 7 sandwiching the polymer electrolyte membrane 1 and integrated. The cathode side electrode 6 and the anode side electrode 7 are the catalytic reaction layers 2 and 3 mainly composed of carbon powder supporting a platinum-based metal catalyst, the cathode side diffusion layer 4 and the anode having both gas permeability and conductivity. The side diffusion layer 5 is used. FIG. 2 shows a direct methanol fuel cell 20 produced using this MEA 15. FIG. 3 is a diagram for explaining the configuration and assembly method of the direct methanol fuel cell 20. As shown in FIG. 3, the fuel cell 20 includes the solid polymer electrolyte membrane 1 of the MEA 15 and the cathode of the MEA 15. It is sandwiched between two gas sealing materials 10 and 11 having windows opened so that the side electrode 6 and the anode side electrode 7 are not covered, and the outside of the gas sealing materials 10 and 11 is further connected to the cathode side current collector plate 8 and the anode side current collector. A gas seal material 12 is disposed between the current collector plate 9 and the anode side current collector plate 9 so that fuel does not leak. The MEA 15, the gas seal materials 10 and 11, the current collector plates 8 and 9, and the gas seal material 12. A hole is made in the four corners, and fixed by tightening with four bolts 13 and nuts 14. The gas seal material 12 is provided with a manifold 12a for supplying fuel and a manifold 12b for discharging spent fuel. The cathode-side current collector plate 8 and the anode-side current collector plate 9 are provided with slits 8a and 9a. The cathode-side current collector plate 9 and the anode-side current collector plate 9 supply an oxidant and fuel such as hydrogen or methanol aqueous solution to the cathode-side and anode-side electrodes. The reaction product produced by the electrochemical reaction is discharged.

  Next, the mechanism of the direct methanol fuel cell 20 will be described with reference to FIG. FIG. 2 is a conceptual diagram illustrating a direct methanol fuel cell 20 according to the present embodiment, which is a plan view with the cathode side as an upper surface, and the fuel cell is cut along a straight line A and viewed from the direction of the arrow. A cross-sectional view of the case is shown below. In FIG. 2, the fuel is supplied from a manifold 12 a provided in the gas seal material 12, passes through the slide 9 a of the anode side current collector plate 9, and reaches the anode side catalytic reaction layer 3 in the anode side electrode 7.

  Examples of the present invention will be described below.

Example 1
FIG. 4 is a conceptual diagram of the direct methanol fuel cell 30 showing the first embodiment relating to the present invention, and FIG. 5 is a sketch showing the configuration and assembly method of the direct methanol fuel cell 30. The direct methanol fuel cell 30 uses an aqueous methanol solution as fuel and air as an oxidant, and carbon dioxide is discharged from the anode electrode and water is discharged from the cathode electrode as reaction products. The direct methanol fuel cell 30 uses an MEA 80 shown in FIG. 8 as an electrode electrolyte membrane assembly (MEA) as a central part. First, a method for manufacturing the MEA 80 will be described with reference to FIGS.

  In FIG. 8, the MEA 80 is configured such that a cathode side electrode 85 and an anode side electrode 86 are sandwiched between both sides of the solid polymer electrolyte membrane 1. As the solid polymer electrolyte membrane 1, an ion exchange membrane having proton conductivity, for example, a fluorine-based ion exchange membrane using perfluorosulfonic acid / PTFE copolymer 117 (175 μm, manufactured by Du Pont) or the like is used. Those having good suppression of methanol crossover, for example, composite membranes made of zeolite and styrene-butadiene rubber, hydrocarbon graft membranes and the like can also be used. Here, perfluorosulfonic acid / PTFE copolymer 117 was used.

On the other hand, the cathode side electrode 85 and the anode side electrode 86 are respectively composed of the catalyst reaction layer 81,
82 and diffusion layers 83 and 84. The cathode side diffusion layer 83 and the anode side diffusion layer 84 must have both the diffusibility of the fuel or oxygen-containing gas, the discharge function of carbon dioxide and reaction product water generated by power generation, and the electronic conductivity. It is possible to apply a conductive porous material such as carbon cloth which has been subjected to water repellent treatment. Here, a carbon nonwoven fabric (TGP-H060 manufactured by Toray Industries, Inc.) having a thickness of 250 μm was used as the conductive porous material. The carbon nonwoven fabric was cut into 3 cm square, immersed in a fluorine-based water repellent emulsion (Daikin D1) for water repellent treatment, dried and then heat treated at 350 ° C. for 10 minutes to form diffusion layers 83 and 84.

  The catalytic reaction layers 81 and 82 are thin films having a thickness of about 30 to 80 μm mainly composed of conductive carbon particles supporting a catalytic metal and a polymer electrolyte. In the anode side catalyst reaction layer 82, anode catalyst-supported particles in which 25% by weight of platinum and ruthenium are supported on Ketjen Black (manufactured by AKZO Chemie), which is conductive carbon particles having an average primary particle diameter of 30 nm, are provided. used. The cathode-side catalyst reaction layer 81 was made of cathode catalyst-supporting particles in which 50% by weight of platinum was supported on ketjen black. The cathode side catalyst reaction layer 81 and the anode side catalyst reaction layer 82 are obtained by dispersing each catalyst-supporting particle in an isopropanol aqueous solution and a polymer electrolyte, for example, perfluorosulfonic acid / PTFE copolymer 117, in ethanol. The catalyst solution and the polymer electrolyte were mixed so that the weight ratio of the catalyst-supporting particles and the polymer electrolyte was 1: 1, and then the slurry for the cathode and the anode was prepared by high dispersion using a bead mill. The diffusion layers 83 and 84 were applied using a spray quarter and formed by drying in the atmosphere at room temperature for 6 hours. Thus, the cathode side electrode 85 and the anode side electrode 86 were formed by forming the cathode side catalyst reaction layer 81 and the anode side catalyst reaction layer 82 on the diffusion layers 83 and 84.

  At this time, in order to effectively supply the fuel or oxygen-containing gas (air), as shown in FIG. 8, the cathode-side catalyst reaction layer 81 and the anode-side catalyst reaction layer 82 have thick and thin portions. The temperature difference due to reaction heat is generated, and natural convection is easily caused. For example, in the cathode side catalyst reaction layer 81, a catalyst reaction layer having a thickness of 80 μm is formed on a circular region 81 a having a diameter of 1 cm at the center of the diffusion layer cut into a 3 cm square, and the diameter from the center is 1 cm. A catalytic reaction layer having a thickness of 50 μm was formed in a 2-cm donut-shaped region 81b, and a catalytic reaction layer having a thickness of 30 μm was formed in a donut-shaped region 81c having a diameter of 2 to 3 cm from the center. The anode-side catalytic reaction layer 82 was also formed with a thick portion and a thin portion by the same method.

Here, the catalyst reaction layers 81 and 82 have a higher relative temperature and higher atmospheric pressure than other portions due to reaction heat. As a result, the reaction product generated in the catalyst reaction layers 81 and 82 may be discharged not only from the diffusion layers 83 and 84 but also from a flow path provided for supplying an oxidant and fuel. Therefore, in order to prevent this, water repellent treatment or hydrophilic treatment is performed at the portion where the flow path and the catalytic reaction layer are connected. For the water repellent treatment, when the cathode side diffusion layer 83 of 3 cm square is formed, the water repellent treatment portion 87 from the outer side to 3 mm is again immersed in the emulsion liquid (D1 made by Daikin) of the fluorinated water repellent and dried. Heat treatment at 350 ° C. for 10 minutes. By doing so, the water repellent treatment part 87 of the cathode side diffusion layer 83 can obtain a strong water repellent effect. In the hydrophilic treatment, when the anode side diffusion layer 84 of 3 cm square is formed, a region 88 from the outer side to 3 mm is formed into a solution in which a polymer electrolyte, for example, perfluorosulfonic acid / PTFE copolymer 117 is dispersed in ethanol. Immerse and dry at ambient temperature in the atmosphere for 6 hours. By doing so, the hydrophilic treatment portion 88 of the anode side diffusion layer 84 can obtain a hydrophilic effect.

Finally, the electrode 85 prepared for the cathode and the electrode 86 prepared for the anode were prepared, respectively, and the polymer electrolyte membrane 1 (perfluorosulfonic acid / PTFE copolymer 117 manufactured by DuPont, 175 μm), the centers were aligned and integrated by hot pressing (125 ° C., 4 MPa, 10 minutes) to produce MEA80.

  Next, a method for producing the direct methanol fuel cell 30 showing the first embodiment of the present invention using the MEA 80 will be described.

As shown in FIG. 5, the solid polymer electrolyte membrane part of MEA 80 has an outer dimension of 5 cm × 5 cm,
It is sandwiched between two gas seal materials 31 and 32 having a thickness of 250 μm with a 3 cm square window so as not to cover the cathode side electrode and the anode side electrode of the MEA 80, and the outside of the gas seal materials 31 and 32 is further Similarly, it is sandwiched between two current collector plates 34 and 35 with an outer dimension of 5 cm x 5 cm and a thickness of 4 mm, and the fuel of 4 mm thickness with an outer dimension of 5 cm x 5 cm does not leak outside the current collector plate 35 on the anode side. The gas seal material 36 is placed, holes are made in four corners of the MEA 80, the gas seal materials 31 and 32, the current collector plates 34 and 35, and the gas seal material 36, and are fastened with four bolts 13 and nuts 14 and fixed. The fastening pressure at this time was 10 kgf / cm ² per area of the current collector plate. The current collecting plates 34 and 35 are formed with slits 34s and 35s having a width of 1 mm and a length of 30.0 mm, and supply of fuel and air or discharge of reaction products is performed through the slits 34s and 35s. The current collector plates 34 and 35 are made of stainless steel plates subjected to gold plating.

  The gas seal material 36 is provided with manifolds 36a and 36b for supplying fuel, and a groove 36d having a width of 1 mm and a depth of 1 mm so as to make a round parallel to the outer side at a position 10 mm from the outer side. A manifold 36c for discharging spent fuel is provided.

  The current collector plates 34 and 35 and the gas seal materials 31 and 32 are provided with slits having a width of 1 mm and a length of 30.0 mm at positions 10 mm from the outer side in equilibrium with the four sides. Or the flow path for supplying oxygen-containing gas was formed.

Next, this flow path will be described with reference to FIG. FIG. 4 is a conceptual diagram illustrating a direct methanol fuel cell 30 using the MEA 80 according to the first embodiment of the present invention. A plan view with the cathode side as the upper surface and a sectional view when the methanol fuel cell 30 is cut directly along the straight line A and viewed from the direction of the arrow are shown below. A flow path 38a, a flow path 38b, a flow path 38c, and a flow path 38d are provided along the outer side. For example, the flow path 38a has a width of 1 mm and a length of 30.0 mm provided on the current collector plate 34. The slit 34a and the slit 31a provided in the gas sealing material 31 have a width of 1 mm and a length of 30.0 mm. As can be seen from the sectional view, the slit 31 a is cut to a depth of 125 μm (near the center), and then a slit having a width of 100 μm is provided along the surface and reaches the cathode side electrode of the MEA 80.

  On the other hand, FIG. 11 is a schematic diagram illustrating another form of the flow path on the cathode side. As shown in this figure, in addition to the flow path 802 of FIG. 11a described above, as shown in FIGS. 11b and 11c, a slit 814 is provided in the gasket, and a shape like the flow path 811 and the flow path 812 is formed. It may be configured.

  Similarly, a flow path along the outer side is also provided on the anode side. For example, the flow path 39a is provided in the groove 36d having a width of 1 mm provided in the gas seal material 36 and the current collecting plate 35. A slit 35a having a width of 1 mm and a length of 30.0 mm and a slit 32a having a width of 1 mm and a length of 30.0 mm provided in the gas sealing material 32 are configured. As can be seen from the cross-sectional view, the slit 32 a is cut to a depth of 125 μm (near the center), and then a slit having a width of 100 μm is provided along the surface and reaches the anode side electrode of the MEA 80. Each channel is connected to the outside of the catalyst reaction layer, that is, in a place where the catalyst reaction layer having a thickness of 30 μm or less is thin, and is devised so as to easily obtain the effect of natural convection utilizing reaction heat. By providing such a flow path, the fuel flows in from the manifolds 36a and 36b, fills the groove 36d, reaches the anode side electrode of the MEA 80 via the anode side flow path, for example, the flow path 39a, and the catalytic reaction layer. Consumed at. The reaction product (carbon dioxide) generated in the catalytic reaction layer is discharged from the manifold 36c through the slit 35s. On the other hand, on the cathode side, air reaches the cathode side electrode of the MEA 80 via the cathode side flow path, for example, the flow paths 38a, 38b, 38c, 38d, and is consumed in the catalytic reaction layer. The reaction product (water) generated in the catalytic reaction layer is discharged to the outside through the slit 34s.

Here, on the cathode side, when the catalyst reaction layer of MEA 80, the diffusion layer, and the slit 34s of the current collector plate are considered as one discharge pipe, for example, the duct 120 shown in FIG. If it is installed, the flow of exhaust from the catalytic reaction layer is improved. Further, as shown in FIG. 13, a dehumidifying agent, for example, silica gel powder in a package having good air permeability at the entrances of the flow path 38a, the flow path 38b, the flow path 38c, and the flow path 38d for taking in air 130a, If 130b, 130c, and 130d are placed, dry air can be supplied and adverse effects caused by the reaction product water can be reduced.

  The fuel cell obtained by the above method was designated as cell A (without a duct and a dehumidifying agent).

(Example 2)
FIG. 6 is a conceptual diagram of a direct methanol fuel cell 40 showing a second embodiment relating to the present invention, in which the methanol fuel cell 40 is cut directly by a plan view with the cathode side as the upper surface and a straight line A, A cross-sectional view as seen from the direction of the arrow is shown below. FIG. 7 is a sketch showing the configuration and assembly method of the direct methanol fuel cell 40.

  The direct methanol fuel cell 40 shown in FIG. 6 has a natural convection effect when the direct methanol fuel cell 30 shown in Example 1 is always used with the cathode electrode on the upper side and the anode electrode on the lower side. It has been improved so that it can be obtained. That is, in the direct methanol fuel battery cell 30, on the anode side, the flow of fuel is flow path → catalyst reaction layer → diffusion layer → discharge manifold, whereas supply manifold → diffusion layer → catalyst reaction layer → Flow path → Discharge manifold. Accordingly, the fuel flows from the bottom to the top, and the reaction product heated by the reaction heat in the catalytic reaction layer is easily discharged, so that the effect of natural convection on the anode electrode side can be obtained.

The production method of the direct methanol fuel battery cell 40 is the same as the production method of the direct methanol fuel battery cell 30 shown in Example 1, but the MEA used, the gas seal material, the current collector plate, and the gas seal material are used. The configured flow path is different. The MEA used in the direct methanol fuel cell 40 was subjected to the same water repellent treatment as the cathode side electrode 85 in the MEA 80 on the region 88 where the anode side electrode 86 was subjected to hydrophilic treatment. By doing so, it is possible to prevent the fuel from entering the discharge channel described later. The MEA thus created is referred to as MEA 80-1.

  Next, the flow path will be described with reference to FIGS. In FIG. 7, a gas seal material 41, a current collector plate 9, and a gas seal material 42 are used instead of the gas seal material 32, the current collector plate 35, and the gas seal material 36 used in the first embodiment. As shown in FIG. 6, the gas seal material 41 is provided with discharge manifolds 41e, 41f, 41g, and 41h on each side, and four slits parallel to the sides. This slit is a slit having a width of 1 mm and a length of 30.0 mm as shown in 41i. As can be seen from the sectional view, the slit is cut to a depth of 125 μm (near the center), and then a slit having a width of 100 μm extends along the surface. And reaches the cathode side electrode of the MEA 80-1. The current collector plate 9 is used for the direct methanol fuel battery cell 20 described in the prior art, and uses a stainless steel plate subjected to gold plating with an outer dimension of 5 cm × 5 cm and a thickness of 4 mm.

  Similarly, the gas seal material 42 has an outer dimension of 5 cm × 5 cm and a thickness of 4 mm, and a fuel supply manifold 42z is provided at the center.

  The fuel cell obtained by the method as described above was designated as battery B.

  In Example 1 and Example 2, the current collector plate and the gasket were provided with slits to form the flow path. However, in Examples 3 and 4 shown below, a small hole was formed in the MEA. Natural convection is generated using a hole as a flow path, an oxidizing agent and fuel are supplied to the catalytic reaction layer, and the reaction product is discharged from the catalytic reaction layer.

(Example 3)
FIG. 9 is a conceptual diagram of the MEA 90 showing a third embodiment relating to the present invention.

1 is a solid polymer electrolyte membrane, on both sides of which a catalytic reaction layer 91, 92 and a diffusion layer 93,
Electrodes 95 and 96 made of 94 are formed.

  Diffusion layers 93 and 94 are made of a conductive porous material, a carbon non-woven fabric having a thickness of 250 μm (TGP-H060 manufactured by Toray Industries, Inc.), cut into 3 cm squares, and subjected to a water repellent treatment. After dipping in D1) and drying, heat treatment was performed at 350 ° C. for 10 minutes.

  As shown in FIG. 9, holes with a diameter of 2 mm and a depth of 220 μm are opened from the upper surfaces of the diffusion layers 93 and 94 at intervals of 5 mm to form flow paths 93 a and 94 b for supplying fuel or oxygen-containing gas.

Here, the catalytic reaction layer has a high relative temperature and a high atmospheric pressure due to the reaction heat, and as a result, the reactive organisms generated in the catalytic reaction layer supply not only the diffusion layer but also the oxidant and fuel. There is also a risk of discharge from the flow paths 93a, 94b provided in. Therefore, in order to prevent this, water repellent treatment or hydrophilic treatment is applied to the periphery 93b, 94b of the hole having a diameter of 2 mm and a depth of 220 μm. Here, the water repellent treatment is applied to the cathode side electrode 95 and the hydrophilic treatment is applied to the anode side electrode 96. However, when the MEA shape or the anode side is used upward, it is properly used. In the water-repellent treatment of the cathode side electrode 95, after making a hole, the periphery 93b of the hole is again coated with an emulsion solution of a fluorinated water repellent (D1 made by Daikin) so that the fluorinated water repellent is densely applied. . Then, it is dried and heat-treated at 350 ° C. for 10 minutes. By doing so, a strong water repellent effect can be obtained around the hole 93b. In the hydrophilic treatment of the anode side electrode 96, after forming a hole, the periphery 94b of the hole is wetted with a polymer electrolyte, for example, a solution in which perfluorosulfonic acid / PTFE copolymer 117 is dispersed in ethanol. Let dry for hours. By doing so, a hydrophilic effect is obtained around the hole 94b.

The catalyst reaction layers 91 and 92 have catalyst supports in which platinum and ruthenium are supported by 25% by weight on Ketjen Black (manufactured by AKZOChemie), which is conductive carbon particles having an average primary particle diameter of 30 nm, for the anode side. For the cathode side, catalyst-carrying particles in which 50% by weight of platinum is supported on ketjen black are used, and slurry for cathode and anode is prepared in the same manner as MEA80 of Example 1. did.

  Next, the cathode slurry and the anode slurry prepared previously are applied to the diffusion layers 93 and 94 using a spray quarter, and the catalyst reaction layers 91 and 92 are formed by drying the slurry for 6 hours at room temperature in the atmosphere. Thus, a cathode electrode 95 and an anode electrode 96 were prepared.

  At this time, the catalyst reaction layers 91 and 92 were uniformly formed so as to have a thickness of 50 μm.

  Next, a cathode diffusion electrode 95 and an anode diffusion electrode 96 were prepared, and both surfaces of a polymer electrolyte membrane 1 (manufactured by DuPont, perfluorosulfonic acid / PTFE copolymer 117, 175 μm) cut to 5 cm square were prepared. The MEA 90 was made by aligning the centers and integrating them by hot pressing (125 ° C., 4 MPa, 10 minutes).

Next, a methanol fuel cell is directly produced using MEA90. The production method is the same as that of the direct methanol fuel battery cell 20 described in the prior art. The solid polymer electrolyte membrane 1 is sandwiched around the MEA 90, the outer dimension is 5 cm × 5 cm, and the electrodes 95 and 96 of the MEA 90 are used. Two gas seals 10 with a thickness of 250 μm, with a 3 cm square window opened so as not to cover
11 and two current collector plates 8 and 9 each having an outer dimension of 5 cm × 5 cm and a thickness of 4 mm, and fixed with bolts 13 and nuts 14. The fastening pressure at this time is 10 kgf / per area of the current collector plate.
It was cm ^2. The current collecting plates 8 and 9 are formed with slits having a width of 1.5 mm and a length of 30.0 mm, and the current collecting plates 8 and 9 are made of a stainless steel plate subjected to gold plating. On the fuel side, a gas seal material 12 for preventing fuel from leaking is installed outside the current collector plate 9. The gas seal material 12 is provided with an inlet 12a into which an aqueous methanol solution serving as fuel enters and an outlet 12b through which fuel consumed by the MEA 90 is discharged.

  The fuel cell obtained by the method as described above was designated as cell C.

Example 4
FIG. 10 is a conceptual diagram of the MEA 100 showing a third embodiment relating to the present invention.

  Reference numeral 1 denotes a solid polymer electrolyte membrane on which electrodes 105 and 106 composed of catalytic reaction layers 101 and 102 and diffusion layers 103 and 104 are formed.

  The method for creating the diffusion layers 103 and 104 and the catalyst reaction layers 101 and 102 is the same as that in the third embodiment, and a description thereof will be omitted. Next, a method for forming the flow paths 107 and 108 will be described.

  As shown in FIG. 10, holes having a diameter of 2 mm and a depth of 220 μm are formed from the upper surfaces of the diffusion layers 103 and 104 at intervals of 5 mm, and the holes are formed in a cylindrical shape having a diameter of 2 mm and a length of 220 μm, and are subjected to water repellent treatment or hydrophilic treatment. The applied carbon nonwoven fabric (TGP-H060 manufactured by Toray Industries, Inc.) is embedded.

  Here, a carbon non-woven fabric having a water repellent treatment applied to the cathode-side electrode 105 and a hydrophilic treatment applied to the anode-side electrode 106 is embedded. However, the MEA shape or the case where the anode side is used upward is properly used. The method of water repellent treatment or hydrophilic treatment is the same as in Example 3.

  By doing so, the reaction-generated water generated in the cathode electrode layer 91 does not easily pass through the water repellent flow path 107 of the cathode side electrode 105, and air from the outside easily flows in instead. In addition, the channel 108 subjected to the hydrophilic treatment of the anode electrode 108 is difficult to pass through the carbon dioxide layer generated in the cathode electrode layer 91, and instead, the methanol aqueous solution, which is the fuel, easily flows in.

The schematic diagram which showed MEA of the prior art. The schematic diagram which showed the direct methanol fuel cell using MEA of a prior art. The schematic diagram which showed the direct methanol fuel cell of the prior art. The schematic diagram which showed the direct methanol fuel cell of one embodiment of this invention. The schematic diagram which showed the direct methanol fuel cell of one embodiment of this invention. The schematic diagram which showed the direct methanol fuel cell of one embodiment of this invention. The schematic diagram which showed the direct methanol fuel cell of one embodiment of this invention. The schematic diagram which showed MEA of one embodiment of this invention. The schematic diagram which showed MEA of one embodiment of this invention. The schematic diagram which showed MEA of one embodiment of this invention. The schematic diagram which showed the flow path of one embodiment of this invention. The schematic diagram which showed the exhaust apparatus of one embodiment of this invention. The schematic diagram which showed the example which supplies the dried air of one embodiment of this invention. The conceptual model figure explaining the flow of supply and discharge | emission.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Solid polymer electrolyte membrane, 2,101 ... Cathode side catalyst reaction layer, 3,102 ... Anode side catalyst reaction layer, 4 ... Cathode side diffusion layer, 5 ... Anode side diffusion layer, 6,105 ... Cathode side electrode, 7, 106 ... anode side electrode, 8, 9 ... current collector plate, 10, 11, 12, 31, 32, 36, 41, 42 ... gas seal material, 13 ... bolt, 14 ... nut, 15 ... MEA, 20, 30, 40 ... Direct methanol fuel cell, 34, 35 ... Current collector plate with flow path, 80 ... Membrane electrode assembly, 80-1 ... MEA described in Example 2, 81, 91 ... Cathode electrode layer, 82,
92 ... Anode electrode layer, 83, 93 ... Cathode diffusion layer, 84,94 ... Anode diffusion layer,
85... Cathode side electrode using a catalyst reaction layer having a thick central part, 86... Anode side electrode using a catalyst reaction layer having a thick central part, 87... Water-repellent treatment part, 88. MEA explained in Example 3, 95 ... diffusion electrode for cathode, 96 ... diffusion electrode for anode, 100 ... carbon in which a number of small-diameter holes were made on the surface of the diffusion layer in Example 4 and water repellent or hydrophilic treatment was made in the holes MEA fitted with paper, 103 ... Cathode side diffusion layer with many small-diameter holes and water repellent treated carbon paper, 104 ... Anode side diffusion layer with many small-diameter holes and fitted with carbon paper treated with hydrophilic treatment 120 ... exhaust duct, 141 ... conceptual model diagram explaining the flow of conventional supply and discharge, 142 ... conceptual model diagram explaining the flow when a flow path is provided, 143 ... flow path through the region Conceptual model diagram for explaining a flow in the case of the concept model diagram for explaining a flow in a case in which a 144 ... flow path.

Claims (18)

  A polymer electrolyte membrane, a pair of diffusion layers having both conductivity and diffusivity arranged opposite to each other with a catalyst reaction layer sandwiched between both sides of the polymer electrolyte membrane, and a pair arranged opposite to each other A fuel cell comprising a conductive current collector provided with a flow path connected to the catalytic reaction layer for supplying an oxidant and fuel.   In the fuel cell, a fuel cell is provided which is connected to the catalyst reaction layer and has a flow path for discharging a reaction product generated in the catalyst reaction layer.   The catalyst reaction layer is composed of a thick portion of the catalyst and a thin portion or a portion where no catalyst exists, and the flow path is connected to the thin portion of the catalyst or a portion where no catalyst exists. Fuel cell.   A fuel cell, wherein a water repellent or a hydrophilic agent is added to a portion where the flow path and the catalytic reaction layer are connected.   A fuel cell, wherein an exhaust duct is provided in a flow path for discharging the reaction product.   A fuel cell, wherein a dehumidifying agent is installed in the flow path for supplying the oxidizing agent.   In the MEA, comprising: a polymer electrolyte membrane; and a pair of diffusion layers having both conductivity and diffusivity arranged opposite to each other with a catalyst reaction layer sandwiched between both surfaces of the polymer electrolyte membrane, the diffusion layer A MEA comprising a plurality of holes formed in a hole, water-repellent treatment or hydrophilic treatment around the holes, and the holes serving as flow paths connected to the catalyst reaction layer.   In the MEA, the MEA is characterized in that a water repellent treatment region or a hydrophilic treatment region is provided in the diffusion layer, and the water repellent treatment region or the hydrophilic treatment region is used as a flow path connecting to the catalyst reaction layer. The electrolyte membrane,
A cathode electrode layer having a first region in which an electrode reaction is active and a second region in which an electrode reaction is more inactive than the first region; an anode electrode layer;
A membrane electrode assembly comprising an electrolyte membrane having an electrolyte having proton conductivity formed between the cathode electrode layer and the anode electrode layer.   The membrane electrode assembly according to claim 9, wherein the first region is thicker than the second region.   The membrane electrode assembly according to claim 9, wherein the first region has a higher density of catalyst particles than the second region.   The membrane electrode assembly according to claim 9, wherein the second region has higher water repellency than the first region. The electrolyte membrane,
A cathode electrode layer having a first region in which an electrode reaction is active and a second region in which an electrode reaction is more inactive than the first region; an anode electrode layer;
A fuel cell comprising: an electrolyte membrane having an electrolyte having proton conductivity formed between the cathode electrode layer and the anode electrode layer. The casing of the fuel cell has a cathode end plate with a hole and a fuel container for holding fuel,
The fuel cell according to claim 13, wherein the cathode electrode layer is disposed to face the cathode end plate.   The fuel cell according to claim 13, wherein a housing of the fuel cell has a flow path leading to the second region.   The fuel cell according to claim 13, wherein the flow path includes a dehumidifying agent.   The fuel cell according to claim 5, wherein the cathode electrode layer is covered with a porous diffusion layer, and the diffusion layer has a through hole communicating with the thirteenth region. 14. The fuel cell according to claim 13, wherein the wall surface of the through hole is subjected to water repellent treatment.

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