JP2007305402A - Solid polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid polymer electrolyte fuel cell which can be operated safely. <P>SOLUTION: This solid polymer electrolyte fuel cell is formed by mutually laminating a membrane-electrode assembly 10 and porous separators 30, 40. The membrane-electrode assembly 10 has a polymer electrolyte membrane 11, a fuel electrode 60 including a fuel electrode catalyst layer 12 and a fuel electrode gas diffusing layer 13, disposed on one side of the polymer electrolyte membrane 11, and an oxidizer electrode 61, including an oxidizer electrode catalyst layer 12 and an oxidizer electrode gas diffusing layer 13, disposed on the other side of the polymer electrolyte membrane 11. The porous separators include the porous fuel electrode separator 30, having a fuel gas passage groove 62 on the outside of the fuel electrode 60, and the porous oxidizer electrode 40, having an oxidizer gas passage groove 64 on the outside of the oxidizer electrode 61. A water passage 22 for circulating water is formed at the back of the fuel electrode separator 30 and the oxidizer electrode separator 40, and the bubble pressure of the fuel electrode separator 30 is higher than the bubble pressure of the oxidizer electrode separator 40. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a solid polymer electrolyte fuel cell formed by laminating a plurality of membrane / electrode assemblies, a porous separator, and the like.

  In general, in a solid polymer electrolyte fuel cell, a fuel gas containing hydrogen is supplied to a fuel electrode, an oxidant gas containing oxygen is supplied to an oxidant electrode, and electricity and heat are generated by an electrochemical reaction. The reaction occurring at the fuel electrode is expressed by the following equation (1), and the reaction occurring at the oxidant electrode is expressed by the following equation (2). As a result of these reactions, water is generated at the oxidizer electrode.

H ₂ → 2H ⁺ + e− (1)
4H ⁺ + O ₂ + e − → 2H ₂ O (2)
The above reaction occurs in the catalyst applied to each electrode. Usually, a catalyst in which platinum or an alloy of platinum and other elements is dispersed on a carbon support is used.

  In a solid polymer electrolyte fuel cell, a proton conductive polymer electrolyte membrane is disposed between a fuel electrode and an oxidant electrode (see, for example, Patent Document 1). This polymer membrane has a role as a proton conductor, and at the same time has a role of separating gases from both electrodes. The fuel electrode and the oxidant electrode are formed by applying the catalyst layer made of the above-described catalyst and electrolyte on the gas diffusion layer. These fuel electrode and oxidant electrode are arranged on both surfaces of the polymer film, respectively, and are thermocompression-bonded and integrated at a temperature of 120 ° C. or higher and 150 ° C. or lower.

  A membrane / electrode assembly (MEA) in which the electrolyte membrane and electrodes formed in this way are integrated. Alternatively, a membrane / electrode assembly can be formed by applying a catalyst layer on a polymer membrane and sandwiching the polymer membrane with the catalyst layer between gas diffusion layers.

  In order for the aforementioned polymer electrolyte membrane to function as a proton conductor, it is necessary to contain moisture. Therefore, in the solid polymer electrolyte fuel cell, it is necessary to keep the moisture of the polymer electrolyte membrane by humidifying from the outside. When protons move from the fuel electrode to the oxidant electrode, they are accompanied by water molecules, so the fuel electrode tends to lose water. On the other hand, when water generated in the oxidizer electrode accumulates in the pores of the electrode, gas diffusion may be hindered and battery performance may be reduced. Therefore, for stable operation of the fuel cell, water must be supplied to the fuel electrode and water must be removed from the oxidant electrode. As a water supply method, there are an external humidification method in which water is supplied as vapor into the gas, and an internal humidification method in which water is supplied to the fuel cell stack and evaporated inside the fuel cell.

  Separators having gas flow paths are disposed on both surfaces of the membrane / electrode assembly. In general, a separator having grooves formed on a plate of a porous material is applied. In this case, it corresponds to the aforementioned internal humidification, and water required for power generation is supplied to the fuel cell through the pores of the separator. In the fuel electrode, water is supplied from the separator to the electrode, and in the oxidizer electrode, water is removed through the separator. Both the fuel electrode separator and the oxidant electrode separator are porous separators, and water flowing through the cooling water groove on the back surface thereof is supplied to the membrane / electrode assembly through the pores of the separator.

  Examples of methods for producing these porous separators are disclosed in Patent Document 2, Patent Document 3, and the like. In any case, after carbon powder and resin are mixed and molded, heat treatment is performed at 800 ° C. or 1200 to 1500 ° C. The resin is carbonized by heat treatment at 800 ° C. and graphitized by heat treatment at 1200 to 1500 ° C. That is, the material has excellent corrosion resistance necessary for the fuel cell.

  During operation of the fuel cell, the pores of the porous separator are maintained in a state of being impregnated with water. At this time, the separator not only has a humidifying function, but also functions to prevent the permeation of gas from the gas flow path to the water flow path by sealing the water in the pores. If the amount of moisture in the separator is insufficient, the sealing function is weak and the amount of gas permeating into the water channel increases.

  The bubble pressure is a pressure limit value that can maintain the gas sealing function when a differential pressure is applied to both sides of the separator. For the bubble pressure measurement, water is applied to one side of a separator that is sufficiently impregnated with water in the pores, the pressure on the other side is gradually increased from atmospheric pressure, and the pressure at which gas begins to leak to the water side Use bubble pressure. A separator with a high bubble pressure has a strong water holding power and is difficult for gas to permeate.

The bubble pressure is determined by the porosity and pore diameter of the porous body and the thickness of the porous body. In order for water to permeate, the porosity is increased, that is, the number of pores is increased to increase the number of water passages. Or thin the porous body. On the other hand, in order to prevent the permeation of gas, it is necessary to appropriately control the pore diameter and retain water in the pores. In manufacturing a porous separator, it is necessary to have an appropriate porosity and pore diameter.
JP 2002-373680 A Japanese Patent Laid-Open No. 2005-197022 JP 2005-26135 A

  In the above-described solid polymer electrolyte fuel cell, when a differential pressure exceeding the bubble pressure is applied between the cooling water and the reaction gas, the reaction gas leaks into the cooling water. In particular, the fuel gas permeates through the separator on the fuel electrode side, and a combustible gas containing hydrogen is mixed into the aqueous system. That is, if the combustible gas is discharged out of the fuel cell stack through the water system, it may hinder safe operation.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a solid polymer electrolyte fuel cell that can be operated safely even when an inexpensive material is applied.

  In order to achieve the above object, the present invention provides a polymer electrolyte fuel cell in which a plurality of membrane-electrode assemblies and a plurality of porous separators are laminated with each other. A fuel electrode including a polymer electrolyte membrane, a fuel electrode catalyst layer disposed adjacent to the first surface of the polymer electrolyte membrane, and a fuel electrode gas diffusion layer disposed adjacent to the fuel electrode catalyst layer; An oxidant electrode including an oxidant electrode catalyst layer disposed adjacent to the second surface of the polymer electrolyte membrane and an oxidant electrode gas diffusion layer disposed adjacent to the oxidant electrode catalyst layer; Each of the porous separators has a fuel gas channel groove adjacent to the outside of the fuel electrode, and a porous fuel electrode separator having a water channel through which water flows on the back surface thereof, and the oxidizing agent Having an oxidant gas channel groove adjacent to the outside of the pole A porous oxidant electrode separator having a water flow path through which water flows, and the bubble pressure of the fuel electrode separator is configured to be higher than the bubble pressure of the oxidant electrode separator, It is characterized by.

  According to the present invention, it is possible to provide a solid polymer electrolyte fuel cell that can be operated safely even when an inexpensive material is applied.

  Hereinafter, embodiments of a solid polymer electrolyte fuel cell according to the present invention will be described with reference to the drawings. Here, the same or similar parts are denoted by common reference numerals, and redundant description is omitted.

  First, a first embodiment of a solid polymer electrolyte fuel cell according to the present invention will be described with reference to FIG. FIG. 1 is a cross-sectional view of the unit cell of the first embodiment. A plurality of unit cells are stacked in the left-right direction in FIG. 1 to form a solid polymer electrolyte fuel cell as a stacked body.

  As shown in FIG. 1, the polymer electrolyte membrane 11 is disposed between the fuel electrode 60 and the oxidant electrode 61. The polymer electrolyte membrane 11 has a function as a proton conductor and a function of separating the gas from the fuel electrode 60 and the oxidant electrode 61. The fuel electrode 60, the oxidant electrode 61 and the polymer electrolyte membrane 11 are integrally formed and are called a membrane / electrode assembly (MEA) 10. Each of the fuel electrode 60 and the oxidant electrode 61 includes a catalyst layer 12 adjacent to the polymer electrolyte membrane 11, an electrode base material (gas diffusion layer) 13 outside the catalyst layer 12, and a catalyst layer 12 and an electrode base material (gas). The intermediate layer 14 formed between the diffusion layers 13 is formed by applying a catalyst layer made of a catalyst and an electrolyte on the gas diffusion layer 13.

  A fuel electrode separator 30 made of a porous material is disposed adjacent to the outside of the fuel electrode 60. A fuel gas passage groove 62 is formed in the fuel electrode separator 30, and the fuel gas passage groove 62 is disposed adjacent to the electrode base material 13 of the fuel electrode 60.

  Similarly, an oxidant electrode separator 40 made of a porous material is disposed adjacent to the outside of the oxidant electrode 61. The oxidant electrode separator 40 is formed with an oxidant gas channel groove 64, and the oxidant gas channel groove 64 is disposed adjacent to the electrode substrate 13 of the oxidant electrode 61.

  A water separator 50 is disposed outside the fuel electrode separator 30 and the oxidant electrode separator 40. A water channel groove 22 is formed in the water separator 50, and the water channel grooves 22 are disposed adjacent to the fuel electrode separator 30 and the oxidant electrode separator 40, respectively.

  In this embodiment, the shapes and dimensions of the fuel electrode 60 and the fuel electrode separator 30 are the same as the shapes and dimensions of the oxidant electrode 61 and the oxidant electrode separator 40, respectively, and the central surface of the polymer electrolyte membrane 11 is a plane of symmetry. As shown in FIG. However, in this embodiment, the bubble pressure of the fuel electrode separator 30 is higher than the bubble pressure of the oxidizer electrode separator 40. For example, the bubble pressure can be increased by reducing the porosity of the fuel separator 30, that is, by increasing the bulk density. Alternatively, even if the porosity is the same, the same effect can be obtained by reducing the average pore diameter.

  The pore diameter and porosity are generally measured by mercury porosimetry. This measurement method measures the volume of mercury that is injected when mercury is injected into the pores of the porous body. Assuming a cylindrical pore, the pore diameter can be calculated from the pressure. The volume of mercury at a certain pressure is just the volume of the pore diameter corresponding to that pressure. Thus, the pore diameter and pore volume of the porous body can be determined. From the total pore volume, the ratio of the pore volume to the volume of the porous body, that is, the porosity is obtained.

  In the solid polymer electrolyte fuel cell, water moves from the fuel electrode 60 to the oxidant electrode 61 as the proton moves from the fuel electrode 60 to the oxidant electrode 61. When a porous separator is applied, water is supplied to the fuel electrode 60 through the fuel electrode separator 30. At this time, if the water content of the fuel electrode separator 30 decreases, the bubble pressure becomes weak, and the fuel gas is likely to permeate into the water system.

  On the other hand, at the oxidizer electrode 61, water is generated by the battery reaction, and excess water flows into the porous separator. Therefore, since the oxidizer electrode separator 40 can maintain a high water content, it is not necessary to apply a separator having a high bubble pressure. Rather, by applying a separator with low bubble pressure and high water permeability to the oxidant electrode separator 40, the generated water is efficiently removed, and the diffusion of the oxidant gas to the catalyst layer is kept good. The performance of the fuel cell can be increased. That is, by applying this embodiment, it is possible to prevent gas diffusion inhibition on the oxidant electrode 61 side and to prevent permeation of fuel gas into the water flow path.

  In a general-purpose product, the bubble pressure of about 30 kPa can be improved to 50 kPa by optimizing the porosity and pore diameter of the material. By applying a proper separator to the fuel electrode and applying a general-purpose product to the oxidizer electrode, the cost can be reduced.

  Next, a second embodiment of the solid polymer electrolyte fuel cell according to the present invention will be described with reference to FIG. FIG. 2 is a cross-sectional view of the unit cell of the second embodiment. This embodiment is a modification of the first embodiment, and unlike the first embodiment, there is no water separator, and a water channel groove 22 through which cooling water flows is formed on the back surface of the oxidant electrode separator 40. Yes. The cooling water is supplied to the membrane / electrode assembly 10 through the water flow channel 22 of the oxidant electrode separator 40.

  The fuel cell stack is formed by stacking a plurality of unit cells shown in FIG. At this time, the fuel electrode separator 30 of the next unit cell is disposed next to the oxidant electrode separator 40 (right adjacent in FIG. 2). Therefore, the cooling water flowing through the water channel groove 22 is also supplied to the next membrane / electrode assembly through the fuel electrode separator 30.

  It is the first embodiment that the bubble pressure of the fuel electrode separator 30 is made higher than the bubble pressure of the oxidant electrode separator 40 by making the porosity of the fuel electrode separator 30 lower than the porosity of the oxidant electrode separator 40. It is the same.

  According to the second embodiment, as in the first embodiment, it is possible to prevent a fuel gas containing hydrogen as a combustible gas from entering the water flow path while applying an inexpensive material. Can be driven more safely.

  Next, a third embodiment of the solid polymer electrolyte fuel cell according to the present invention will be described with reference to FIG. FIG. 3 is a cross-sectional view of the unit cell of the third embodiment. This embodiment is a modification of the second embodiment, and instead of forming the water channel groove 22 on the back surface of the oxidant electrode separator 40, the water channel groove 22 is formed on the back surface of the fuel electrode separator 30. . At this time, the oxidant electrode separator 40 of the next unit cell is disposed next to the fuel electrode separator 30 (next to the left in FIG. 3). Therefore, the cooling water flowing through the water channel groove 22 is also supplied to the next membrane / electrode assembly through the oxidant electrode separator 40.

  The relationship between the bubble pressures of the fuel electrode separator 30 and the oxidant electrode separator 40 is the same as in the second embodiment.

  According to the third embodiment, similarly to the second embodiment, it is possible to prevent a fuel gas containing hydrogen as a combustible gas from entering the water flow path while applying an inexpensive material. Can be driven more safely.

  Next, a fourth embodiment of the solid polymer electrolyte fuel cell according to the present invention will be described with reference to FIG. FIG. 4 is a cross-sectional view of the unit cell of the fourth embodiment. This embodiment is a modification of the first embodiment.

  In the fourth embodiment, as in the first embodiment, the water separator 50 is disposed outside the fuel electrode separator 30 and the oxidant electrode separator 40, and the water channel groove 22 is formed in the water separator 50. The water channel grooves 22 are disposed adjacent to the fuel electrode separator 30 and the oxidant electrode separator 40, respectively.

  In the first embodiment, the shape and size of the fuel electrode 60 and the fuel electrode separator 30 are the same as the shape and size of the oxidant electrode 61 and the oxidant electrode separator 40, respectively. It has a symmetrical shape as the symmetry plane. The bubble pressure of the fuel electrode separator 30 is higher than the bubble pressure of the oxidant electrode separator 40 by making the bulk density of the fuel electrode separator 30 higher than the bulk density of the oxidant electrode separator 40. .

  On the other hand, in the fourth embodiment, the dimensions of the fuel electrode separator 30 and the oxidant electrode separator 40 are different and are asymmetrical. That is, the fuel electrode separator bottom thickness L3f is larger than the oxidant electrode separator bottom thickness L3o. Here, when the thickness of the fuel electrode separator 30 is L1f and the depth of the fuel gas passage groove 62 is L2f, L3f = L1f−L2f. Similarly, when the thickness of the oxidant electrode separator 40 is L1o and the depth of the oxidant gas channel groove 64 is L2o, L3o = L1o−L2o.

  When the thickness of the fuel electrode separator 30 or the oxidant electrode separator 40 is increased, the sealing distance of the separator is increased, the sealing performance is improved, and the effect of increasing the bubble pressure is obtained. The separators 30 and 40 have gas flow channel grooves 62 and 64. Since the seal distance is short at the bottom of the gas flow channel grooves 62 and 64, the sealing performance is affected. Therefore, it is necessary to pay attention to the remaining separator bottom thicknesses L3f and L3o obtained by subtracting the gas flow channel groove depths L2f and L2o from the separator thicknesses L1f and L1o.

  In this embodiment, even if the bulk density and the average porosity of the fuel electrode separator 30 and the oxidant electrode separator 40 are the same, the bubble pressure of the fuel electrode separator 30 is higher than the bubble pressure of the oxidant electrode separator 40. can do. However, the bulk density of the fuel electrode separator 30 is made higher than the bulk density of the oxidant electrode separator 40, or the porosity of the fuel electrode separator 30 is made lower than the porosity of the oxidant electrode separator 40. It goes without saying.

  Next, a fifth embodiment of a solid polymer electrolyte fuel cell according to the present invention will be described with reference to FIG. FIG. 5 is a cross-sectional view of the unit cell of the fifth embodiment. This embodiment is a modification of the second embodiment and a modification of the fourth embodiment. That is, in the fifth embodiment, as in the second embodiment, there is no water separator, and the water flow channel 22 through which the cooling water flows is formed on the back surface of the oxidant electrode separator 40.

  The cooling water is supplied to the membrane / electrode assembly 10 through the water flow channel 22 of the oxidant electrode separator 40. However, as in the fourth embodiment, the fuel electrode separator bottom thickness L3f is larger than the oxidizer electrode separator bottom thickness L3o. However, in the fifth embodiment, the oxidant electrode separator bottom thickness L3o is the thickness of the thinnest part of the oxidant electrode separator 40 between the bottom of the oxidant gas channel groove 64 and the bottom of the water channel groove 22. Is defined as

  Next, a sixth embodiment of the solid polymer electrolyte fuel cell according to the present invention will be described with reference to FIG. FIG. 6 is a cross-sectional view of the unit cell of the sixth embodiment. This embodiment is a modification of the third embodiment and also a modification of the fifth embodiment. That is, in the sixth embodiment, as in the third embodiment, there is no water separator, and the water flow channel groove 22 is formed on the back surface of the fuel electrode separator 30.

  The cooling water is supplied to the membrane / electrode assembly 10 through the water flow channel 22 of the fuel electrode separator 30. However, as in the fifth embodiment, the fuel electrode separator bottom thickness L3f is larger than the oxidizer electrode separator bottom thickness L3o. However, in the sixth embodiment, the fuel electrode separator bottom portion thickness L3f is defined as the thickness of the thinnest portion of the fuel electrode separator 30 between the bottom portion of the fuel gas passage groove 62 and the bottom portion of the water passage groove 22. Is done.

  FIG. 7 shows the effects of the above embodiments. The figure compares the amount of gas mixed into the water system due to the difference in bubble pressure applied to the fuel electrode separator. As shown in the figure, the amount of mixed gas can be reduced by increasing the bubble pressure of the fuel electrode separator.

  Although various embodiments have been described above, these are merely examples, and the present invention is not limited to these embodiments. Moreover, it is also possible to combine the characteristic part of each embodiment. For example, it is good also as a structure which satisfies both the relationship of the bulk density and porosity in 1st-3rd embodiment, and the relationship of the separator bottom part thickness in 4th-6th embodiment.

1 is a cross-sectional view of a unit cell of a first embodiment of a solid polymer electrolyte fuel cell according to the present invention. Sectional drawing of the unit cell of 2nd Embodiment of the solid polymer electrolyte fuel cell which concerns on this invention. Sectional drawing of the unit cell of 3rd Embodiment of the solid polymer electrolyte fuel cell which concerns on this invention. Sectional drawing of the unit cell of 4th Embodiment of the solid polymer electrolyte fuel cell which concerns on this invention. Sectional drawing of the unit cell of 5th Embodiment of the solid polymer electrolyte fuel cell which concerns on this invention. Sectional drawing of the unit cell of 6th Embodiment of the solid polymer electrolyte fuel cell which concerns on this invention. The graph which shows the relationship between the bubble pressure of the fuel electrode separator in the polymer electrolyte fuel cell according to the present invention, and the amount of gas mixed into the water system.

Explanation of symbols

10. Membrane / electrode assembly (MEA)
11 ... polymer electrolyte membrane 12 ... catalyst layer 13 ... electrode substrate (gas diffusion layer)
14 ... Intermediate layer 22 ... Water channel groove (water channel)
30 ... Fuel electrode separator 40 ... Oxidant electrode separator 50 ... Water separator 60 ... Fuel electrode 61 ... Oxidant electrode 62 ... Fuel gas channel groove 64 ... Oxidant gas channel groove

Claims (8)

In a solid polymer electrolyte fuel cell in which a plurality of membrane / electrode assemblies and a plurality of porous separators are laminated with each other,
Each of the membrane / electrode assemblies includes a polymer electrolyte membrane, a fuel electrode catalyst layer disposed adjacent to the first surface of the polymer electrolyte membrane, and a fuel disposed adjacent to the fuel electrode catalyst layer. A fuel electrode including an electrode gas diffusion layer, an oxidant electrode catalyst layer disposed adjacent to the second surface of the polymer electrolyte membrane, and an oxidant electrode gas disposed adjacent to the oxidant electrode catalyst layer An oxidizer electrode including a diffusion layer,
Each of the porous separators has a fuel gas channel groove adjacent to the outside of the fuel electrode, a porous fuel electrode separator having a water channel for circulating water on the back surface, and an outer side of the oxidant electrode. A porous oxidant electrode separator having an adjacent oxidant gas flow channel groove and a water flow channel through which water flows on the back surface thereof;
The bubble pressure of the fuel electrode separator is configured to be higher than the bubble pressure of the oxidant electrode separator,
A solid polymer electrolyte fuel cell.   2. The solid polymer electrolyte fuel cell according to claim 1, wherein the bulk density of the fuel electrode separator is higher than the bulk density of the oxidant electrode separator.   3. The solid polymer electrolyte fuel cell according to claim 1, wherein an average pore diameter of the fuel electrode separator is smaller than an average pore diameter of the oxidant electrode separator.   4. The water separator is disposed adjacent to the outside of each of the fuel electrode separator and the oxidant electrode separator, and the water flow path is formed in the water separator. 5. 2. A solid polymer electrolyte fuel cell according to 1.   The fuel electrode separator bottom thickness obtained by subtracting the depth of the fuel gas flow channel from the thickness of the fuel electrode separator is obtained by subtracting the depth of the oxidant gas flow channel from the thickness of the oxidant electrode separator. The solid polymer electrolyte fuel cell according to claim 4, wherein the thickness is thicker than the bottom thickness of the oxidant electrode separator.   5. The solid according to claim 1, wherein the water flow path is formed by a water flow path groove formed in at least one of the fuel electrode separator and the oxidant electrode separator. Polymer electrolyte fuel cell. The water channel groove is formed in the oxidant electrode separator;
The bottom thickness of the fuel electrode separator obtained by subtracting the depth of the fuel gas channel groove from the thickness of the fuel electrode separator is determined from the thickness of the oxidant electrode separator and the depth of the oxidant gas channel groove and the water flow. It is thicker than the thickness of the bottom of the oxidizer electrode separator minus the depth of the groove.
The solid polymer electrolyte fuel cell according to claim 6. The water channel groove is formed in the fuel electrode separator;
The fuel electrode separator bottom thickness obtained by subtracting the depth of the fuel gas channel groove and the depth of the water channel groove from the thickness of the fuel electrode separator is determined based on the thickness of the oxidant electrode separator. It is thicker than the thickness of the bottom of the oxidizer electrode separator minus the depth of the groove.
The solid polymer electrolyte fuel cell according to claim 6.

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