JP2008034293A - Fuel cell reducing short circuit between electrodes - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell reducing possibility of occurrence of a short circuit between electrodes. <P>SOLUTION: At least either of two electrode layers 11 of a membrane-electrode assembly 100a used for this fuel cell is composed of a plurality of members different in melting points or electron conductivity. The plurality of members are arranged such that the melting point Ma of the electrode layer on an interfacial surface between the electrode layer and an electrolyte membrane is set higher than the average melting point Mavg in the thickness direction of the electrode layer. Alternatively, the plurality of members are arranged such that the electron conductivity Ea of the electrode layer on the interfacial surface between the electrode layer and the electrolyte membrane is set lower than the average electron conductivity Eavg in the thickness direction of the electrode layer. For instance, a cathode electrode layer 11 is formed into a two-layer structure, a first layer 11a in contact with the electrolyte layer 10 may be formed with a ceramics-based member, and a second layer 11b without contacting the electrolyte membrane 10 may be formed with a metallic member. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell.

  Various electrode layers and electrolyte configurations have been proposed in order to improve the output performance and durability of the fuel cell (Patent Document 1, etc.).

JP-A-2005-158355 JP 2005-322547 A US2002 / 0003085

  In a fuel cell, reducing the thickness of the electrolyte membrane is preferable as a means for reducing membrane resistance, improving ion conductivity, and improving the output of the fuel cell. On the other hand, reducing the thickness of the electrolyte membrane is accompanied by technical difficulties. For example, when the electrolyte membrane is formed, there is a tendency to increase the possibility of generating micropores such as microcracks and pinholes.

  When a fuel cell is configured using an electrolyte membrane having such fine holes, a part of the constituent members of the electrode layer, which is a conductive member, may enter the fine holes, causing a short circuit between the electrodes. However, until now, there has not been enough ingenuity for such problems.

  An object of this invention is to provide the technique which reduces possibility that a short circuit will generate | occur | produce between electrode layers in a fuel cell.

  In order to achieve the above object, the present invention is a fuel cell, comprising an electrolyte membrane, and first and second electrode layers sandwiching the electrolyte membrane, wherein at least a first of the electrode layers is provided. The electrode layer includes a plurality of members having different melting points, and the melting point is higher than the average melting point of the entire first electrode layer present in the fuel cell at the interface between the first electrode layer and the electrolyte membrane. It has a high melting point portion.

  According to this configuration, even if a minute hole exists in the electrolyte membrane, the possibility that a part of the constituent members of the electrode layer moves to the minute hole can be reduced. Therefore, the possibility of occurrence of a short circuit between the electrode layers is reduced.

  At least the first electrode layer of the electrode layers may have a melting point distribution in the thickness direction of the first electrode layer that changes continuously or stepwise.

  According to this configuration, portions having different melting points can be provided in the thickness direction of the electrode layer, and a melting point higher than the average melting point can be provided at the interface. Therefore, the possibility of occurrence of a short circuit between the electrode layers is reduced.

  At least the first electrode layer of the electrode layers may have a multilayer structure in which the plurality of members are stacked.

  According to this structure, it can comprise by the multilayer structure which laminated | stacked the electrode layer for every structural member, and can provide the layer of a member with a high melting | fusing point in an interface. Therefore, the possibility of occurrence of a short circuit between the electrode layers is reduced.

  At least the first electrode layer of the electrode layers may have a lowest melting point portion having a lowest melting point between the interface and the outer surface of the first electrode layer that is not in contact with the electrolyte membrane.

  According to this configuration, the possibility of occurrence of a short circuit between the electrode layers can be reduced without using a configuration having the highest melting point at the interface.

  A fuel cell comprising an electrolyte membrane and first and second electrode layers sandwiching the electrolyte membrane, wherein at least the first electrode layer of the electrode layers is a plurality of members having different electronic conductivity A low-electron-conductivity site where the electronic conductivity is lower than the average electronic conductivity of the entire first electrode layer present in the fuel cell at the interface between the first electrode layer and the electrolyte membrane. It is characterized by having.

  According to this configuration, even if a part of the member constituting the low electron conductivity portion of the electrode layer moves and enters the minute hole of the electrolyte membrane and a short circuit occurs, the influence can be reduced. .

  At least the first electrode layer of the electrode layers may have an electronic conductivity distribution in the thickness direction of the first electrode layer that changes continuously or stepwise.

  According to this structure, the site | part from which an electronic conductivity differs in the thickness direction of an electrode layer can be provided, and an electronic conductivity higher than an average electronic conductivity can be given in an interface. Therefore, even if a short circuit occurs between the electrode layers, the influence can be reduced.

  At least the first electrode layer of the electrode layers may have a multilayer structure in which a plurality of members having different electronic conductivities are stacked.

  According to this structure, it can comprise by the multilayered structure which laminated | stacked the electrode layer for every structural member, and can provide the layer of a member with low electronic conductivity in an interface. Therefore, even if a short circuit occurs between the electrode layers, the influence can be reduced.

  At least the first electrode layer of the electrode layers has a highest electron conductivity portion having the highest electron conductivity between the electrode film interface and an outer surface of the first electrode layer that is not in contact with the electrolyte film. It may be included.

  According to this configuration, the possibility of occurrence of a short circuit between the electrode layers can be reduced without using a configuration having the lowest electronic conductivity at the interface.

  At least the first electrode layer of the electrode layers may include ceramics and a noble metal, and the component ratio of the noble metal may increase as the distance from the interface increases.

  According to this configuration, the melting point of the electrode layer can be changed for each part depending on the component ratio of the ceramic and the noble metal.

  At least the first electrode layer of the electrode layers may include only ceramics at the interface.

  According to this configuration, the interface between the electrolyte membrane and the electrode layer can be made of ceramics, the possibility of occurrence of a short circuit can be reduced, and even if a short circuit occurs, the influence thereof can be reduced.

  At least the first electrode layer of the electrode layers has the high melting point portion at a portion where the temperature becomes highest among the entire first electrode layer when the operation state of the fuel cell is continued. Also good.

  According to this configuration, the high melting point portion can be provided at the highest temperature portion in the first electrode layer under a predetermined condition, and the possibility of occurrence of a short circuit can be reduced.

  When a plurality of unit cells including the electrolyte membrane and the first and second electrode layers are provided, and the operation state of the fuel cell is continued, an average operating temperature for each unit cell among the unit cells is It is good also as what has the said high melting-point part in the said 1st electrode layer in the single cell higher than the average operating temperature of the said whole fuel cell.

  According to this configuration, in the fuel cell stack, the electrode layer included in the single cell that is higher than the average operating temperature under a predetermined condition can be configured with a member having a melting point higher than the average operating temperature. The possibility of occurrence of a short circuit can be reduced.

  At least one of the electrode layers may include ceramics and a noble metal, and when the operation state of the fuel cell is continued, the higher the temperature, the lower the component ratio of the noble metal.

  According to this configuration, the melting point of the electrode layer can be changed by the component ratio of the noble metal and the ceramic, and the noble metal component decreases as the operating temperature is higher under a predetermined condition. Becomes higher. Therefore, the possibility that a short circuit occurs between the electrodes is reduced. On the contrary, the part having a lower operating temperature has more noble metal components and the electrode reaction becomes more active than the part having a lower operating temperature.

  The electrolyte membrane may be a solid oxide.

  According to this configuration, the possibility of a short circuit occurring between the electrodes of the solid oxide fuel cell (SOFC) can be reduced.

  The electrolyte membrane may have proton conductivity.

  According to this structure, possibility that a short circuit will generate | occur | produce between the electrodes of the fuel cell which employ | adopts a proton conductive solid oxide for an electrolyte membrane can be reduced.

  The present invention can be realized in various forms, for example, in the form of a fuel cell, a fuel cell system using the fuel cell, a vehicle including the fuel cell, and the like.

Next, embodiments of the present invention will be described in the following order based on examples.
A. Comparative example:
B. First embodiment:
C. Second embodiment:
D. Third embodiment:
E. Fourth embodiment:
F. Example 5:
G. Example 6:
H. Example 7:
I. Variation:

A. Comparative example:
FIG. 1 is an explanatory diagram showing a configuration of a membrane electrode assembly 100 used in a fuel cell as a comparative example of the present invention. The membrane electrode assembly 100 has a configuration in which the electrolyte membrane 10 is sandwiched between two electrode layers 11 and 12.

  The electrolyte membrane 10 is a thin film (thickness of about submicron to several μm) made of a proton conductive solid oxide showing good proton conductivity. As the electrolyte membrane 10, for example, a perovskite proton conductor (BaCe0.8In0.2O3, SrCe0.8In0.2O3, BaZr0.8In0.2O3, SrZr0.8In0.2O3, etc.) can be used.

  The two electrode layers 11 and 12 include a cathode electrode layer 11 to which oxygen is supplied and an anode electrode layer 12 to which hydrogen is supplied. When fuel gas is supplied to each of the two electrode layers 11 and 12, protons are conducted through the electrolyte membrane 10 to generate electricity by electrochemical reaction with oxygen.

  The two electrode layers 11 and 12 carry a catalyst (for example, platinum) for promoting an electrochemical reaction. In addition, a porous body made of carbon is provided on the outer surfaces (hereinafter simply referred to as “outer surfaces”) of the two electrode layers 11 and 12 that do not contact the electrolyte membrane 10, and two gases are diffused by diffusing gas in the thickness direction. Fuel gas may be supplied to the entire surface of the electrode layers 11 and 12.

  The two electrode layers 11 and 12 can be composed of, for example, a metal member or a ceramic member. Specifically, La0.6Sr0.4CoO3, La0.5Sr0.5MnO3, Ba0.5Pr0.5CoO3, or the like can be used as the ceramic component. Moreover, as a metal-type structural member, platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), these alloys, etc. are employable, for example. Further, carbon carrying these metals and alloys, alumina (Al2O3), and silicon dioxide (SiO2) may be used.

  In general, a metal-based member has a lower melting point than a ceramic-based member, but can be said to have a high electronic conductivity. The “electronic conductivity” is a value that can be obtained as the reciprocal of the volume resistivity, and is a value that does not take into account the conductivity due to ion content.

  Here, consider a case where the two electrode layers 11 and 12 are made of only metal members. For example, when the fuel cell is operating in a low temperature range (400 ° C. or lower), the metal-based member has higher electrode reaction activity than the ceramic-based member, so the two electrode layers 11 and 12 are made of metal. It can be said that it is preferable to be comprised of the members of the system. However, there are the following disadvantages.

  In general, the electrolyte membrane 10 which is a thin film tends to generate micro through holes (micro holes) called micro cracks or pin holes in the formation process. In the electrolyte membrane 10 having such minute holes, some of the constituent members of the two electrode layers 11 and 12 may enter the minute holes and cause a short circuit.

  In particular, when the two electrode layers 11 and 12 are composed of metal members, the metal members generally have a lower melting point than the ceramic members, and therefore it can be said that there is a high possibility of the occurrence of the short circuit described above. In addition, since the metal-based member has a higher electronic conductivity than the ceramic-based member, when a short circuit occurs, the influence is greater than when a ceramic-based member is employed.

  Based on the above problems, embodiments of the present invention will be described below.

B. First embodiment:
FIG. 2A is a schematic diagram showing the configuration of the membrane electrode assembly 100a as the first embodiment. FIG. 2A shows that only the cathode electrode layer 11 of the two electrode layers 11 and 12 is shown, the anode electrode layer 12 is not shown, and the configuration of the cathode electrode layer 11 is different. Is substantially the same as FIG. The anode electrode layer 12 (not shown) may have the same configuration as the cathode electrode layer 11 described below (hereinafter the same applies to the second to fifth embodiments).

  The cathode electrode layer 11 shown in FIG. 2A has a multilayer structure composed of a first layer 11 a in contact with the electrolyte membrane 10 and a second layer 11 b not in contact with the electrolyte membrane 10. The two layers 11a and 11b are composed of different members, and the first layer 11a is composed of a member having a melting point higher than that of the second layer 11b. For example, the first layer 11a may be composed of a ceramic member, and the second layer 11b may be composed of a metal member.

  FIG. 2B is a graph showing the relationship between the distance x from the interface of the cathode electrode layer 11 and the melting point of the constituent members of the cathode electrode layer 11. Here, “distance x from the interface” refers to the distance in the thickness direction of the cathode electrode layer 11 when the interface B1 between the cathode electrode layer 11 and the electrolyte membrane 10 is set to “0”. Note that the distance from the interface B1 to the interface B2 between the first layer 11a and the second layer 11b is indicated by x1 (FIG. 2A).

  In FIG. 2B, the melting point of the cathode electrode layer 11 at the interface B1 is indicated by “Ma”, the melting point on the outer surface of the cathode electrode layer 11 is indicated by “Mb”, and the average of the melting points in the thickness direction of the cathode electrode layer 11 is The average melting point taken is indicated by “Mavg”. In the present embodiment, the melting point Ma is the melting point of the constituent member of the first layer 11a, and the melting point Mb is the melting point of the constituent member of the second layer 11b. Therefore, as shown in FIG. The shape of the graph is a shape having steps. Naturally, the melting point Ma is higher than the average melting point Mavg.

  With such a configuration, the first layer 11a reduces the possibility that a part of the metal-based member constituting the second layer 11b reaches the electrolyte membrane 10. Therefore, the possibility of occurrence of a short circuit in the minute hole of the electrolyte membrane 10 can be reduced as compared with the case where the cathode electrode layer 11 is composed of only a metal-based member. Even when the operating temperature of the fuel cell is in a low temperature range (400 ° C. or lower), since the second layer 11b is a metal-based component, the electrode is more than the case where the cathode electrode layer 11 is composed of only a ceramic-based member. The reaction becomes highly active.

  The first layer 11a may employ a member having an electronic conductivity lower than that of the second layer 11b. That is, similar to the above-described configuration, such a relationship is generally established when the first layer 11a is formed of a ceramic member and the second layer 11b is formed of a metal member.

  FIG. 2C is a graph showing the relationship between the distance from the interface and the electronic conductivity of the constituent members of the cathode electrode layer 11. In FIG. 2C, the electronic conductivity of the cathode electrode layer 11 at the interface B1 is indicated by “Ea”, the electronic conductivity of the cathode electrode layer 11 on the outer surface of the cathode electrode layer 11 is indicated by “Eb”, and the cathode electrode layer The average electronic conductivity obtained by averaging the electronic conductivity in the thickness direction of 11 is indicated by “Eavg”.

  In this example, the electronic conductivity Ea is the electronic conductivity of the first layer 11a, and the electronic conductivity Eb is the electronic conductivity of the constituent members of the second layer 11b. It becomes the shape which has. Naturally, the electronic conductivity Ea is lower than the average electronic conductivity Eavg.

  By adopting such a configuration, even if a part of the constituent members of the first layer 11a enters the minute holes of the electrolyte membrane 10 and a short circuit occurs, the electronic conductivity Ea of the constituent members of the first layer 11a. The effect of a short circuit is reduced because of the low.

  FIG. 2D shows the melting points and volume resistivity values of the metals Pd, Pt, Rh, and Ag. As can be understood from the values in the table, even when Pd is adopted as the constituent member of the first layer 11a and Ag is adopted as the constituent member of the second layer 11b, the distance from the interface, the melting point, and the electronic conductivity. This relationship shows the same tendency as the above two graphs. That is, the two layers 11a and 11b may be composed of only metal members. Even with such a configuration, the same effect as that obtained when a ceramic member is used for the first layer 11a can be obtained.

  Note that the constituent members of the cathode electrode layer 11 may have the melting point tendency shown in FIG. 2B, and may not have the electronic conductivity tendency shown in FIG. On the contrary, as long as it has the tendency of the electronic conductivity shown in FIG.2 (C), it does not need to have the tendency of the melting | fusing point shown in FIG.2 (B). However, the configuration having both tendencies is most preferable.

  Further, if the same configuration as that described above is applied to the anode electrode layer 12, the same effect can be obtained, and the most effective when both the two electrode layers 11 and 12 are configured similarly. Is expensive. The same applies to the second to fifth embodiments described below.

C. Second embodiment:
FIG. 3A is a schematic diagram showing the configuration of a membrane electrode assembly 100b as an embodiment of the present invention. FIG. 3A is substantially the same as FIG. 2A except that the configuration of the cathode electrode layer 11 is different.

  In the second embodiment, the cathode electrode layer 11 has a single layer structure in which a plurality of constituent members having different melting points are mixed. In the following, for example, a case where two kinds of constituent members composed of a ceramic constituent member and a metal constituent member are mixed will be considered. If it is set as such a structure, it can suppress that structural members peel by the difference in the expansion coefficient of structural members.

  FIG. 3B is a graph showing the ratio (metal concentration) of the metal component in the cathode electrode layer 11 at a distance x from the interface. As can be understood from the graph of FIG. 3B, the cathode electrode layer 11 has a higher metal concentration in a portion away from the interface B1. That is, the cathode electrode layer 11 has a lower metal concentration in a portion closer to the interface B1, and a larger proportion of ceramic-based constituent members.

  FIG. 3C is a graph showing the relationship between the distance x from the interface and the melting points of the constituent members of the cathode electrode layer 11, and corresponds to the graph of FIG. FIG. 3D is a graph showing the relationship between the distance x from the interface and the electronic conductivity of the constituent members of the cathode electrode layer 11, and corresponds to the graph of FIG.

  Here, the “melting point of the constituent member” means “an average value of the melting points of the plural constituent members included in the cathode electrode layer 11”, and the “electron conductivity of the constituent member” means “the cathode electrode layer 11 It means “average value of electronic conductivity of a plurality of constituent members included”.

  As described above, the closer the cathode electrode layer 11 is to the interface B1, the lower the metal concentration. Therefore, as shown in FIG. 3C, the melting point of the cathode electrode layer 11 is closer to the melting point of the ceramic member as it is closer to the interface B1. Getting closer and higher. Therefore, the possibility that a part of the constituent members of the cathode electrode layer 11 enters the minute hole of the electrolyte membrane 10 is reduced, and the possibility that a short circuit occurs between the two electrodes 11 and 12 can be reduced.

  As shown in FIG. 3D, the cathode electrode layer 11 has a lower electronic conductivity as it is closer to the interface B1. Therefore, even if a short circuit occurs between the two electrodes 11 and 12, the influence is reduced.

  The constituent member of the cathode electrode layer 11 is not limited to a combination of a ceramic member and a metal member, and may be a mixture of metal constituent members having different melting points or electronic conductivity. . In this case, it is preferable that the difference in melting point or electronic conductivity between the constituent members is large.

  Note that the constituent members of the cathode electrode layer 11 need only have the melting point tendency shown in FIG. 3C and may not have the electronic conductivity tendency shown in FIG. On the contrary, as long as it has the tendency of the electronic conductivity shown in FIG.3 (D), it does not need to have the tendency of the melting | fusing point shown in FIG.3 (C). However, the configuration having both tendencies is most preferable.

D. Third embodiment:
FIG. 4A is a schematic diagram showing the configuration of a membrane electrode assembly 100c as one embodiment of the present invention, which is substantially the same as FIG. 4B to 4D are graphs showing the properties of the constituent members of the cathode electrode layer 11 of the membrane electrode assembly 100c. Except for the differences in the shape of the graphs, FIGS. ).

  Also in the present embodiment, as in the second embodiment, as the constituent member of the cathode electrode layer 11, a mixture of a ceramic constituent member and a metal constituent member is used. However, in the present embodiment, the site where the metal concentration is highest is between the interface B1 and the outer surface (the site where the distance from the interface B1 is x2) (FIG. 4B). Therefore, the melting point is the lowest at that portion (FIG. 4C; melting point Mc), and the electronic conductivity is the highest (FIG. 4D; electronic conductivity Ec).

  Even in such a configuration, as shown in FIG. 4C, if the melting point Ma of the cathode electrode layer 11 at the interface B1 is higher than the average value Mavg of the melting points of the cathode electrode layer 11 in the thickness direction, The same effect as the second embodiment can be obtained. On the other hand, unlike the tendency of the melting point shown in FIG. 4C, for example, even if there is a portion where the melting point is highest in the portion other than the interface B1, the melting point Ma should be higher than the average melting point Mavg.

  Further, even when the portion x2 where the electron conductivity is highest is present, the electron conductivity Ea of the cathode electrode layer 11 at the interface B1 is lower than the average value Eavg of the electron conductivity in the thickness direction of the cathode electrode layer 11. Therefore, the same effects as those of the first and second embodiments can be obtained. Conversely, even if there is a portion having an electronic conductivity lower than the electronic conductivity Ea, it is sufficient that the electronic conductivity Ea is lower than the average electronic conductivity Eavg.

  Furthermore, in the case where a constituent member having a melting point Ma higher than the average melting point Mavg is employed, the electronic conductivity Ea does not have to be lower than the average electronic conductivity Eavg. On the other hand, when a constituent member is employed in which the electronic conductivity Ea is lower than the average electronic conductivity Eavg, the melting point Ma does not have to be higher than the average melting point Mavg. However, it is most preferable that the melting point Ma is higher than the average melting point Mavg and the electronic conductivity Ea is lower than the average electronic conductivity Eavg.

E. Fourth embodiment:
5A and 5B are schematic views showing a membrane electrode assembly 100d as an embodiment of the present invention. 5A is an overall schematic view of the membrane electrode assembly 100d as viewed from the cathode electrode layer 11 side, and FIG. 5B is a schematic cross-sectional view taken along 4B-4B shown in FIG. 4A. It is. FIG. 5B is almost the same as FIG. 2A except that the configuration of the cathode electrode layer 11 is different.

  In FIG. 5A, when the fuel cell is used under a predetermined condition, a portion where the temperature is highest in the cathode electrode layer 11 is indicated by “T high”, and a portion where the temperature is lowest is indicated by “T”. Low. In the present embodiment, a fuel cell is assumed that exhibits a temperature distribution in which the temperature gradually decreases from the center of the cathode electrode layer 11 toward the outer peripheral edge of the cathode electrode layer 11 (in the direction of the arrow in the drawing).

  The temperature distribution varies depending on the “predetermined condition”. In the present specification, the “predetermined condition” is defined as a state in which the fuel cell is continuously operated at room temperature (about 20 ° C.) and the average temperature of the entire fuel cell (operating temperature of the fuel cell) is the highest. it can. However, this condition is only a condition in the examples in the present specification, and does not limit the use condition of the fuel cell.

  The cathode electrode layer 11 is divided into a part where the temperature is high (high temperature part 11c) and a part where the temperature is low (low temperature part 11d), and each is composed of members having different melting points. The division between the high temperature part 11c and the low temperature part 11d may be based on, for example, the average temperature of the cathode electrode layer 11 as a whole. The member constituting the first layer 11a in the first embodiment is used for the high temperature portion 11c, and the member constituting the second layer 11b in the first embodiment is used for the low temperature portion 11d.

  With such a configuration, the melting point of the high-temperature part 11c that is highly likely to cause a short circuit becomes higher than that of the low-temperature part 11d. Further, since the electronic conductivity in the high temperature portion 11c is lower than that in the low temperature portion 11d, the influence can be suppressed even when a short circuit occurs. Since the low temperature part 11d is comprised with a metal-type member, an electrode reaction becomes highly active.

  6A and 6B are substantially the same as FIGS. 5A and 5B except that the temperature distribution of the cathode electrode layer 11 is different and the configuration of the cathode electrode layer 11 is different.

  As shown in FIG. 5A, the membrane electrode assembly 100e is supplied from the direction in which oxygen and hydrogen are opposed to each other. In such a configuration, it is generally known that the temperature distribution of the cathode electrode layer 11 under a predetermined condition is such that the temperature decreases from the oxygen supply side toward the hydrogen supply side. . The cathode electrode layer 11 of the membrane electrode assembly 100e can be classified as a high temperature portion 11c on the side supplied with oxygen and a low temperature portion 11d on the side supplied with hydrogen.

  As described above, when the temperature distribution of the cathode electrode layer 11 under a predetermined condition is known in advance, the arrangement of the constituent members can be changed according to an arbitrary standard according to the temperature distribution of the cathode electrode layer 11.

  In addition to the configuration of the present embodiment, for example, in the configurations shown in the first to third embodiments described above, the melting point distribution and electronic conductivity of the electrode layer according to the temperature distribution in the thickness direction of the electrode layer. The distribution can also be changed.

F. Example 5:
7A and 7B are schematic views showing membrane electrode assemblies 100f and 100g as one embodiment of the present invention. Membrane electrode assemblies 100f and 100g are membrane electrode assemblies used in a fuel cell called a tube type, and are formed in a cylindrical shape so that one of the two electrode layers 11 and 12 is inside and the other is outside. Has been.

  In the membrane / electrode assembly 100f in FIG. 7A, the cathode electrode layer 11 is provided on the outer side of the cylinder, and the anode electrode layer 12 is provided on the inner side of the cylinder. Accordingly, oxygen is supplied to the outside of the cylinder, and hydrogen is supplied to the inside of the cylinder from one opening of the cylinder toward the other opening. In such a configuration, as shown in FIG. 7A, it is generally known that the temperature decreases in the hydrogen supply direction.

  Accordingly, the hydrogen supply side of the cathode electrode layer 11 is classified as a high temperature region 11c, and the hydrogen discharge side is classified as a low temperature region 11d, and components are used in the respective regions as in the fourth embodiment. it can.

  In the membrane electrode assembly 100g of FIG. 7B, the cathode electrode layer 11 is provided on the inner side of the cylinder, and the anode electrode layer 12 is provided on the outer side of the cylinder. Accordingly, hydrogen is supplied to the outside of the cylinder, and oxygen is supplied to the inside of the cylinder from one opening of the cylinder toward the other opening. In such a configuration, as shown in FIG. 7B, it is generally known that the temperature decreases in the oxygen supply direction.

  Therefore, the oxygen supply side of the cathode electrode layer 11 is classified as a high temperature region 11c, and the oxygen discharge side is classified as a low temperature region 11d, and components are used in the respective regions as in the fourth embodiment. it can.

G. Example 6:
FIGS. 8A to 8C are schematic views showing the configuration of a fuel cell stack as one embodiment of the present invention.

  FIG. 8A shows a single cell 80a in which a membrane electrode assembly 100h is sandwiched between separators SP. The membrane / electrode assembly 100h is configured by forming the two electrode layers 11 and 12 of the membrane / electrode assembly 100 shown in FIG. 1 with ceramic members. The outer peripheral edge may be formed with a seal gasket. The separator SP is a three-layer separator composed of three thin metal plates, and realizes a current collecting function, a fuel gas supply function, and a cooling function. The separator SP may have a configuration other than the three-layer type.

  FIG. 8B shows a single cell 80b in which a membrane electrode assembly 100i is sandwiched between separators SP, and the two electrode layers 11 and 12 of the membrane electrode assembly 100i are made of a metal-based member. Except for this point, it is almost the same as FIG.

  The two electrode layers 11 and 12 of the single cell 80a are configured by the constituent members of the first layer 11a in the first embodiment, and the two electrode layers 11 and 12 of the single cell 80b are the second in the first embodiment. It is good also as what is comprised by the structural member of the layer 11b of

  FIG. 8C shows a fuel cell stack 80c in which single cells 80a and 80b are stacked, and shows the temperature distribution of the fuel cell under predetermined conditions in the same notation as in FIG. 5A. The “predetermined condition” may be the same as the definition in the fourth embodiment.

  In general, in the fuel cell stack, as shown in FIG. 8C, the temperature of the single cell located at the center of the stack (average temperature of the entire single cell) is the highest, and the temperature of the single cell closer to the upper and lower ends of the stack is higher. It is known to tend to be lower.

  Therefore, in this embodiment, the single cell group of 1/4 from the top and the single cell group of 1/4 from the bottom are set as the low temperature single cell group 80cb (the hatching in FIG. 8C is added). Single cell group) and the remaining half of the single cell group is divided as a high temperature single cell group 80ca. As a reference for dividing the low temperature part 80cb and the high temperature part 80ca, for example, the average temperature of the entire fuel cell stack 80c may be used as a reference.

  The fuel cell stack 80c uses a single cell 80a as a single cell of the high-temperature single cell group 80ca, and uses a single cell 80b as a single cell of the low-temperature single cell group 80cb. Even with such a configuration, in the high-temperature single cell group 80ca, the possibility of occurrence of a short circuit between the electrodes can be reduced, and in the low-temperature single cell group 80cb, the two electrodes 11 and 12 are in a state of high reaction activity. Accordingly, the fuel cell stack 80c is effective as a whole.

H. Example 7:
FIG. 9 is a schematic view showing the configuration of a fuel cell (hydrogen separation membrane cell) using a hydrogen permeable membrane as one embodiment of the present invention.

  The hydrogen separation membrane battery 90 is configured by a membrane electrode assembly 100j in which a hydrogen separation membrane 91 that selectively transmits hydrogen is disposed in the anode electrode layer 12 of the membrane electrode assembly 100a of the first embodiment. The hydrogen separation membrane 91 is provided with a plate-like support member 92 provided with a plurality of through holes 92h for allowing hydrogen to pass through the outer surface not in contact with the electrolyte membrane 10.

  The membrane electrode assembly 100j is sandwiched between separators SP1 and SP2 from both sides. Separator SP1 is arrange | positioned at the cathode electrode layer 11 side, and the cathode gas flow path 93c for supplying oxygen is provided. The separator SP2 is disposed on the hydrogen separation membrane 91 side so as to be in contact with the support member 92, and is provided with an anode gas flow path 93a for supplying hydrogen.

  As the hydrogen separation membrane 91, Pd or a Pd alloy (for example, Pd / Ag alloy, Pd / Ag / Au alloy, Pd / Gd alloy, Pd / Cu alloy, etc.) can be employed. The hydrogen separation membrane 91 may be formed as a support membrane provided with the above-described support member 92, or may be formed as a self-supporting membrane without the support member 92.

  As the hydrogen separation membrane 91, any one of vanadium (V), tantalum (Ta), and niobium (Nb) and nickel (Ni), cobalt (Co), titanium (Ti), and copper (Cu) are used. It is also possible to form a thin film formed of an alloy with any of the above as a sandwich film sandwiched from both sides with the above-mentioned Pd alloy.

  As the configuration of the cathode electrode layer 11 of the hydrogen separation membrane battery 90, the configuration shown in any of the second to fifth embodiments can be adopted in addition to the configuration of the first embodiment. Further, the fuel cell stack 80c can be realized as a hydrogen separation membrane battery stack by replacing the anode electrode layers 12 of the single cells 80a and 80b in the sixth embodiment with the hydrogen separation membrane 91.

I. Variation:
The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

I1. Modification 1:
In the above embodiment, the proton conductive solid oxide is used as the electrolyte membrane. However, the present invention can be applied to fuel cells using other types of electrolyte membranes. For example, it is possible to use an electrolyte membrane that is not proton-conductive but oxide-conductive. It is also possible to use a fluororesin ion exchange membrane electrolyte membrane instead of a solid oxide. However, since a fuel cell using a solid oxide electrolyte membrane is generally operated at a high temperature (for example, about 1000 ° C.), a short circuit caused by a part of the constituent members of the electrode layer entering the microhole of the electrolyte membrane. It is likely to occur. Therefore, if the present invention is applied, there is an advantage that the possibility of occurrence of a short circuit is further reduced and a highly conductive member can be employed for the electrode layer.

I2. Modification 2:
In the first embodiment, the cathode electrode layer 11 is composed of two layers of the first layer 11a and the second layer 11b. However, it may have a multilayer structure using a plurality of constituent members. Even in such a configuration, it is sufficient that the melting point Ma is higher than the average melting point Mavg, or the electronic conductivity Ea is lower than the average electronic conductivity Eavg.

I3. Modification 3:
In the second embodiment, two types of constituent members are mixed. However, various types of constituent members may be mixed. Even in such a configuration, it is sufficient that the melting point Ma is higher than the average melting point Mavg, or the electronic conductivity Ea is lower than the average electronic conductivity Eavg.

I4. Modification 4:
In the fourth to sixth embodiments, the cathode electrode layer 11 is divided into two parts, a high temperature part 11c and a low temperature part 11d, but it is further divided into a plurality of parts according to the temperature. Different constituent members may be used accordingly.

I5. Modification 5:
In the fourth to sixth embodiments, different constituent members are used depending on the temperature distribution of the cathode electrode layer 11, but a plurality of constituent members are mixed as in the second and third embodiments. The concentration distribution of the constituent members may be changed according to the temperature distribution. In other words, the higher the temperature, the higher the concentration of the constituent member having a higher melting point.

Schematic which shows the structure of the membrane electrode assembly in a comparative example. Explanatory drawing which shows the structure of the cathode electrode layer in 1st Example. Explanatory drawing which shows the structure of the cathode electrode layer in 2nd Example. Explanatory drawing which shows the structure of the cathode electrode layer in 3rd Example. Explanatory drawing which shows the structure of the cathode electrode layer in 4th Example. Explanatory drawing which shows the structure of the cathode electrode layer in 4th Example. Schematic which shows the structure of the tube type membrane electrode assembly in 5th Example. Schematic which shows the structure of the fuel cell stack in 6th Example. Schematic which shows the structure of the hydrogen separation membrane battery in 7th Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electrolyte membrane 11 ... Cathode electrode layer 11a ... 1st layer 11b ... 2nd layer 11c ... High temperature part 11d ... Low temperature part 12 ... Anode electrode layer 80a, 80b ... Single cell 80c ... Fuel cell stack 80ca ... High temperature single cell Group 80cb ... Low-temperature single cell group 90 ... Hydrogen separation membrane battery 91 ... Hydrogen separation membrane 92 ... Support member 92h ... Through hole 93a ... Anode gas passage 93c ... Cathode gas passage 100 ... Membrane electrode assembly 100a-j ... Membrane electrode Bonded body B1 ... interface between electrode layer and electrolyte membrane B2 ... interface between first layer and second layer Ea ... electronic conductivity at interface Eav ... average electron conductivity Eb ... electron conductivity at outer surface Ec ... highest Electronic conductivity Ma ... Melting point at interface Mavg ... Average melting point Mb ... Melting point at outer surface Mc ... Highest melting point SP, SP1, SP2 ... Separator

Claims (16)

A fuel cell,
An electrolyte membrane;
First and second electrode layers sandwiching the electrolyte membrane;
With
At least a first electrode layer of the electrode layers includes a plurality of members having different melting points, and the first electrode present in the fuel cell at an interface between the first electrode layer and the electrolyte membrane. A fuel cell having a high melting point portion having a melting point higher than the average melting point of the entire layer. The fuel cell according to claim 1,
At least the first electrode layer of the electrode layers has a melting point distribution in the thickness direction of the first electrode layer that changes continuously or stepwise. The fuel cell according to claim 1 or 2, wherein
At least a first electrode layer of the electrode layers has a multilayer structure in which the plurality of members are stacked. A fuel cell according to any one of claims 1 to 3,
At least the first electrode layer of the electrode layers has a lowest melting point portion having a lowest melting point between the interface and an outer surface of the first electrode layer that is not in contact with the electrolyte membrane. Fuel cell. A fuel cell,
An electrolyte membrane;
First and second electrode layers sandwiching the electrolyte membrane;
With
At least the first electrode layer of the electrode layers includes a plurality of members having different electronic conductivities, and the first electrode layer present in the fuel cell at an interface between the first electrode layer and the electrolyte membrane. A fuel cell comprising a low electron conductivity portion where the electron conductivity is lower than the average electron conductivity of the entire electrode layer. The fuel cell according to claim 5, wherein
At least a first electrode layer of the electrode layers is characterized in that the electronic conductivity distribution in the thickness direction of the first electrode layer changes continuously or stepwise. The fuel cell according to claim 5 or 6, wherein
At least a first electrode layer of the electrode layers has a multilayer structure in which a plurality of members having different electronic conductivities are stacked. A fuel cell according to any one of claims 5 to 7,
At least the first electrode layer of the electrode layers has a highest electron conductivity portion having the highest electron conductivity between the electrode film interface and an outer surface of the first electrode layer that is not in contact with the electrolyte film. A fuel cell comprising: A fuel cell according to any one of claims 1 to 8,
At least a first electrode layer of the electrode layers contains ceramics and a noble metal, and the component ratio of the noble metal increases as the distance from the interface increases. A fuel cell according to any one of claims 1 to 9,
At least a first electrode layer of the electrode layers contains only ceramics at the interface. The fuel cell according to claim 1,
At least the first electrode layer of the electrode layers has the high melting point portion at a portion where the temperature is highest among all the first electrode layers when the operation state of the fuel cell is continued. A fuel cell. The fuel cell according to claim 11, wherein
A plurality of unit cells including the electrolyte membrane and the first and second electrode layers;
When the operating state of the fuel cell is continued, among the single cells, the average operating temperature for each single cell is higher than the average operating temperature of the entire fuel cell. A fuel cell having a high melting point portion. The fuel cell according to claim 11 or 12,
At least one of the electrode layers contains ceramics and a noble metal, and when the operating state of the fuel cell is continued, the higher the temperature, the lower the component ratio of the noble metal. The fuel cell according to any one of claims 1 to 13,
A fuel cell comprising a hydrogen separation membrane that allows hydrogen to pass through any one of the electrode layers. The fuel cell according to any one of claims 1 to 14,
The fuel cell, wherein the electrolyte membrane is a solid oxide. The fuel cell according to claim 15, wherein
The fuel cell according to claim 1, wherein the electrolyte membrane has proton conductivity.

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