JP5280151B2 - Solid oxide fuel cell thin plate and solid oxide fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an extremely thin plate element for a single cell of a solid-oxide fuel cell (SOFC), the thin plate element suppressing an increase in reaction loss of an air electrode layer with an increase in operation time of the SOFC. <P>SOLUTION: The thin plate element 11 is formed by laminating and burning a fuel electrode layer 11b and the air electrode layer 11c on upper and lower surfaces of an electrolyte layer 11a so as to interpose the electrolyte layer 11a between them. The air electrode layer 11c is a porous burned element constituted of many particles of a mixed-conductive substance (LSCF: lanthanum strontium cobalt ferrite) through which oxygen ions and electrons pass. The specific surface area of the air electrode layer 11c is 1.5-9.0 m<SP>2</SP>/g and the pore diameter of the air electrode layer 11c is 30-100 nm. The thicknesses of the electrolyte layer 11a, the fuel electrode layer 11b and the air electrode layer 11c are at least 0.5 &mu;m and not more than 10 &mu;m, at least 5 &mu;m and not more than 500 &mu;m and at least 5 &mu;m and not more than 200 &mu;m, respectively. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a solid oxide fuel cell (SOFC), and more particularly, to a thin plate (also referred to as “single cell”) used in SOFC.

Conventionally, a solid electrolyte layer, a fuel electrode layer formed on the upper surface of the solid electrolyte layer and supplied with fuel gas (for example, hydrogen) from the upper surface, and formed on the lower surface of the solid electrolyte layer and oxygen from the lower surface thereof A thin plate body for a single cell of SOFC obtained by laminating and firing an air electrode layer supplied with a gas containing gas (for example, air or the like) is known (see, for example, Patent Document 1).
JP 2006-139966 A

  In such a thin plate body, a porous fired body composed of a large number of particles of a mixed conductive material (for example, LSCF (lanthanum strontium cobalt ferrite)) that allows oxygen ions and electrons to pass through is adopted as the air electrode layer. Is preferred. This is because the electrical conductivity is low due to the high electrical conductivity, the specific surface area of the air electrode layer is increased and a high output is obtained, and the film corresponding to the air electrode layer at low temperature (room temperature) (by firing) This is based on the possibility of forming a film that later becomes an air electrode layer.

  When a porous fired body made of such fine particles and having a large specific surface area is employed as the air electrode layer, the reaction resistance of the air electrode layer (reaction loss, details will be described later) as the SOFC operating time increases. Through experiments and the like, it has become clear that the output of SOFC is likely to increase greatly, and therefore the output of SOFC is likely to decrease greatly.

  This phenomenon is caused by the fact that the operating temperature of the SOFC is as high as at least 600 ° C., and as the operating time of the SOFC increases, the growth of the particles of the substance constituting the air electrode layer (sintering, air It is considered that this is based on the fact that the specific surface area of the air electrode layer decreases and the specific surface area of the air electrode layer decreases.

  The present inventor suppresses an increase in reaction loss of the air electrode layer accompanying an increase in the operating time of the SOFC when a porous fired body made of such mixed conductive material particles is employed as the air electrode layer. Therefore, the conditions required for the air electrode layer which is a porous fired body were found.

The thin plate of the solid oxide fuel cell according to the present invention is formed by laminating and firing the same solid electrolyte layer, fuel electrode layer, and air electrode layer as described above. The thin plate member of the body oxide fuel cell according to the present invention is characterized in that the air electrode layer is a porous fired body made of a large number of particles of a mixed conductive material that allows oxygen ions and electrons to pass through, and the air A specific surface area of the electrode layer is 1.5 to 9.0 m ² / g, and the air electrode layer has a pore diameter of 30 to 100 nm.

  The substance having mixed conductivity is, for example, lanthanum strontium cobalt ferrite (LSCF) or the like. Moreover, it is preferable that the average particle diameter of the particle | grains of the substance which has the said mixed conductivity is 0.1-5 micrometers.

  According to the study, in the air electrode layer, which is a porous fired body composed of a large number of particles having a mixed conductivity, when the specific surface area and the pore size distribution are combined as described above, the operating time of the SOFC is increased. It has been found that the accompanying increase in reaction loss in the air electrode layer can be suppressed. This means that when the specific surface area and the pore size distribution are combined as described above, the growth (sintering) of particles of the substance constituting the air electrode layer is suppressed and the specific surface area of the air electrode layer is difficult to decrease. Means.

  As a measure for suppressing the microstructural change during holding at a high temperature, a so-called “pinning effect” in which a different material is added to stabilize the structure can be considered. In the case of SOFC, it is known that stabilization of an electrode structure having a fine porosity can be achieved by adding zirconia particles. However, when zirconia particles are added, the electronic conductivity decreases. Therefore, in the SOFC thin plate body that requires high output, the addition of zirconia particles is not a preferable measure from the viewpoint of securing high output.

  Further, when the specific surface area and the pore size distribution in the air electrode layer are combined as described above, even if the thickness of the solid electrolyte layer is as thin as 0.5 to 10 μm, It was proved that the effect of suppressing the increase in reaction loss was ensured. The following are additional points regarding this.

  When the thickness of the solid electrolyte layer is as thin as 0.5 to 10 μm, the IR resistance (details will be described later) of the solid electrolyte layer is extremely small, and the oxygen ion conductivity in the solid electrolyte layer is sufficiently large. As a result, the “catalytic reaction that ionizes oxygen” in the air electrode layer is promoted, and the reaction loss of the air electrode layer is also reduced at the same time, resulting in a very large output compared to the case where the thickness of the solid electrolyte layer is large. Is obtained. Under such a situation where a very large output is generated, a very large current flows in the air electrode layer. As a result, it is considered that “growth of particles (sintering) of the substance constituting the air electrode layer” generated during the high temperature holding as described above becomes more remarkable due to this large current. That is, it is considered that due to this large current, the specific surface area of the air electrode layer is further reduced and the reaction loss of the air electrode layer is more likely to increase. Even in such a situation, when the specific surface area and pore size distribution in the air electrode layer are in the above combination, the above-described “inhibition effect of increasing the reaction loss of the air electrode layer” can be sufficiently ensured. found.

  As described above, the solid oxide fuel cell using the thin plate member according to the present invention includes one or more thin plate members having the above-described configuration, and a plurality of support members that support the one or more thin plate members. The thin plate members and the support members are alternately stacked one by one, and for each thin plate member, fuel gas is passed between the thin plate member and the support member adjacent above the thin plate member. A fuel flow path that is a flow path is partitioned and formed, and an air flow path that is a flow path of oxygen-containing gas is defined and formed between the thin plate body and the support member adjacent to the lower side of the thin plate body. Configured.

  Hereinafter, a solid oxide fuel cell according to an embodiment of the present invention will be described with reference to the drawings.

(Overall structure of fuel cell)
FIG. 1 is a cutaway perspective view of a solid oxide fuel cell (hereinafter simply referred to as “fuel cell”) 10 which is a device according to an embodiment of the present invention. FIG. 2 is a partially exploded perspective view of the fuel cell 10. The fuel cell 10 is formed by alternately laminating thin plate members 11 and separators 12 (support members). That is, the fuel cell 10 has a flat stack structure.

  In the flat plate stack structure, the upper lid member 21 is disposed and fixed on the upper side of the thin plate body 11 positioned at the uppermost position, and the lower lid member 22 is disposed and fixed on the lower side of the thin plate body 11 positioned at the lowermost position. ing. The thin plate member 11 is also referred to as a “single cell” of the fuel cell 10.

  As shown in an enlarged circle A in FIG. 2, the thin plate member 11 includes an electrolyte layer (solid electrolyte layer) 11a, a fuel electrode layer 11b formed on the upper surface of the electrolyte layer 11a, and a lower surface of the electrolyte layer 11a. A fired body having an air electrode layer 11c. The planar shape of the thin plate member 11 is a square (length of one side = A ′) having sides along the x-axis and y-axis directions orthogonal to each other, and the thin plate member 11 is orthogonal to the x-axis and y-axis. A plate body (thickness = t1) having a thickness direction in the z-axis direction.

  In this example, the electrolyte layer 11a is a fired body of YSZ (yttria stabilized zirconia). The fuel electrode layer 11b is a fired body made of NiO and YSZ, and is a porous electrode layer. The fuel electrode layer 11b becomes Ni-YSZ cermet after the reduction process and functions as a fuel electrode. The air electrode layer 11c is a fired body made of LSCF (La0.6Sr0.4Co0.2Fe0.8O3: lanthanum strontium cobalt ferrite) and is a porous electrode layer.

  The thin plate member 11 includes a pair of cell through holes 11d and 11d. Each cell through hole 11d passes through the electrolyte layer 11a, the fuel electrode layer 11b, and the air electrode layer 11c. The pair of cell through holes 11d and 11d are formed in the vicinity of one side of the thin plate member 11 and in the vicinity of both ends of the side. Details of the shape and the like of the thin plate member 11 will be described later.

  FIG. 3 is a cross-sectional view of the separator 12 that includes the 1-1 line parallel to the x axis in FIG. 2 and is cut along the plane parallel to the xz plane. As shown in FIGS. 2 and 3, the separator 12 includes a flat portion 12 a, an upper frame portion 12 b, and a lower frame portion 12 c. Here, the upper and lower frame parts 12b and 12c constitute “a frame part of the separator”. The planar shape of the separator 12 is a square (side length = A, A is slightly larger than A ′) having sides along the x-axis and y-axis directions orthogonal to each other. The thickness of the flat surface portion 12a is tz, and the thickness of the “frame body portion” is t2 (> tz).

  The length A of one side of the separator 12 is 5 mm or more and 200 mm or less in this example. The length L of one side of the planar shape (= square) of the planar portion 12a of the separator 12 is 4 mm or more and 190 mm or less in this example. The thickness “t2” of the “frame portion” of the separator 12 is 200 μm or more and 1000 μm or less. The thickness tz of the planar portion 12a of the separator 12 is 50 μm or more and 100 μm or less.

  The separator 12 is made of a Ni-based heat-resistant alloy (for example, ferrite-based SUS, Inconel 600, Hastelloy, etc.). For example, in the case of SUS430, which is a ferrite SUS, the average thermal expansion coefficient of the separator 12 from room temperature to 1000 ° C. is approximately 12.5 ppm / K. Therefore, the thermal expansion coefficient of the separator 12 is larger than the average thermal expansion coefficient of the thin plate member 11. Therefore, when the temperature of the fuel cell 10 changes, a difference in expansion and contraction occurs between the thin plate member 11 and the separator 12.

  The flat surface portion 12a is a thin flat plate having a thickness direction in the z-axis direction. The planar shape of the flat surface portion 12a is a square (length of one side = L (<A)) having sides along the x-axis and y-axis directions.

  The upper frame body portion 12b is a frame body erected upward in the periphery of the flat surface portion 12a (a region near four sides, that is, a region near the outer periphery). The upper frame body portion 12b includes an outer peripheral frame portion 12b1 and a step forming portion 12b2.

  The outer peripheral frame portion 12 b 1 is located on the outermost peripheral side of the separator 12. The shape of the longitudinal section of the outer peripheral frame portion 12b1 (for example, a cross section obtained by cutting the outer peripheral frame portion 12b1 having a longitudinal direction in the y-axis direction along a plane parallel to the xz plane) is a rectangle (or a square).

  The step forming portion 12b2 is a portion that extends from the inner peripheral surface of the outer peripheral frame portion 12b1 toward the center of the separator 12 at one of the four corners of the flat surface portion 12a. The lower surface of the step forming portion 12b2 is connected to the flat portion 12a. The shape of the step forming portion 12b2 in plan view (top view) is substantially square. The upper surface (plane) of the step forming portion 12b2 is continuous with the upper surface (plane) of the outer peripheral frame portion 12b1. A through hole TH is formed in the step forming portion 12b2. The through hole TH also penetrates the flat surface portion 12a located below the step forming portion 12b2.

  The lower frame body portion 12c is a frame body erected downward around the flat surface portion 12a (a region near the four sides, that is, a region near the outer periphery). The lower frame part 12c has a symmetrical shape with the upper frame part 12b with respect to the center line CL in the thickness direction of the plane part 12a. Accordingly, the lower frame body portion 12c includes an outer peripheral frame portion 12c1 and a step forming portion 12c2 that have the same shape as the outer peripheral frame portion 12b1 and the step forming portion 12b2, respectively. However, the step forming portion 12c2 is arranged and formed at one corner portion of two corner portions adjacent to the corner portion where the step forming portion 12b2 is formed among the four corner portions of the flat surface portion 12a. .

  4 shows the thin plate body 11 and the pair of separators 12 in a state of supporting (holding) the thin plate body 11, including a 2-2 line parallel to the y axis in FIG. 2 and along a plane parallel to the yz plane. It is the longitudinal cross-sectional view cut | disconnected by. As described above, the fuel cell 10 is formed by alternately laminating the thin plate members 11 and the separators 12.

  Here, of the pair of separators 12, those adjacent to the lower and upper sides of the thin plate member 11 are referred to as a lower separator 121 and an upper separator 122 for convenience. As shown in FIG. 4, the lower separator 121 and the upper separator 122 are coaxially arranged on the upper frame portion 12 b of the lower separator 121 so that the lower frame portion 12 c of the upper separator 122 faces each other. .

  The entire periphery of the thin plate member 11 is sandwiched between the upper surface of the upper frame portion 12b (peripheral portion) of the lower separator 121 and the lower surface of the lower frame portion 12c (peripheral portion) of the upper separator 122. . At this time, the thin plate member 11 is disposed so that the air electrode layer 11 c faces the upper surface of the flat portion 12 a of the lower separator 121, and the fuel electrode layer 11 b faces the lower surface of the flat portion 12 a of the upper separator 122. Is done.

  The entire periphery of the thin plate 11, the upper frame 12 b of the lower separator 121, and the lower frame 12 c of the upper separator 122 are joined (sealed) to each other by the sealing material 13.

  The sealing material 13 includes a space (boundary portion) between the upper surface of the peripheral portion of the thin plate member 11 and the lower surface of the lower frame portion 12 c of the upper separator 122, and the lower surface of the peripheral portion of the thin plate member 11 and the lower separator 121. It has the 1st seal | sticker part 13a which each joins (seal | stickers) the space (boundary part, 1st junction part) between the upper surfaces of the upper frame part 12b. Further, the sealing material 13 is a space (gap between the lower end (lower end of the side surface) of the lower frame portion 12 c of the upper separator 122 and the upper end (upper end of the side surface) of the upper frame portion 12 b of the lower separator 121. The second seal portion 13b is separated from the first seal portion 13a. The second seal portion 13b is continuous over the entire side surface of the fuel cell 10 having a stack structure.

  The entire first seal portion 13a is made of amorphous glass having a first softening point lower than the operating temperature of the fuel cell 10 (for example, 600 ° C. to 800 ° C.). The 1st seal | sticker part 13a exhibits the function which seals the said 1st junction part. In addition, when the temperature of the fuel cell 10 (specifically, the temperature of the first seal portion 13a) is lower than the first softening point, the first seal portion 13a disables relative movement of the first joint portion. . On the other hand, when the temperature of the fuel cell 10 (specifically, the temperature of the first seal portion 13a) is equal to or higher than the first softening point, the first seal portion 13a is caused by the softening of the first seal portion 13a. The relative movement of the first joint is made possible. Thereby, the internal stress (thermal stress) resulting from the expansion-contraction difference between the thin plate body 11 and the separator 12 described above can be canceled.

  On the other hand, the second seal portion 13b is made of ceramics (specifically, a material containing a crystal such as crystallized glass or glass ceramic, or amorphous and crystalline may be mixed). The second seal portion 13b exhibits a function of sealing the second joint portion. In addition, the second seal portion 13b always disables relative movement of the second joint portion. Thereby, the shape (shape which has a stack structure) of the fuel cell 10 whole can be maintained.

  In addition, as described above, materials having the same composition can be used for the material selection of the first seal portion 13a having a thermal stress buffering function and the second seal portion 13b having a gas seal function. By using the materials having the same composition, it is possible to suppress the deterioration of the joint that may occur due to the thermal history during the SOFC operation when materials having different compositions are used.

  Specifically, while making the composition the same, by providing a difference in the particle size of the glass, the progress of crystallization is made different so that the functions of both the seal portions 13a and 13b are made different. For example, a glass material having a large particle size (for example, about 1 μm) is used as the material for the first seal portion 13a, and a glass material having a small particle size (for example, 0.3 μm or less) is used as the material for the second seal portion 13b. Thereby, it is possible to make a difference in the progress of crystallization at the heat treatment temperature (for example, 850 ° C.) for glass bonding during stack assembly. That is, in the first seal portion 13a having a large particle size, crystallization does not proceed completely and a semi-crystalline state in which a part of the amorphous layer remains is maintained, and in the second seal portion 13b having a small particle size, crystallization is performed. Can be completed. Accordingly, the first seal portion 13a in the semi-crystalline state can have a thermal stress buffer function, and the second seal portion 13b that has been crystallized can have a gas seal function.

  As described above, as shown in FIG. 4, the upper surface of the flat portion 12a of the lower separator 121, the inner wall surface of the upper frame portion 12b (the outer peripheral frame portion 12b1 and the step forming portion 12b2) of the lower separator 121, and the thin plate body 11 The air flow path 21 to which a gas (air) containing oxygen is supplied is formed by the lower surface of the air electrode layer 11c. The gas containing oxygen flows into the air flow path 21 through the through hole TH of the upper separator 122 and the cell through hole 11d of the thin plate member 11 as shown by the dashed arrows in FIG.

  Also, the lower surface of the flat portion 12a of the upper separator 122, the inner wall surface of the lower frame portion 12c (the outer peripheral frame portion 12c1 and the step forming portion 12c2) of the upper separator 122, the upper surface of the fuel electrode layer 11b of the thin plate member 11, Thus, a fuel flow path 22 to which a fuel containing hydrogen is supplied is formed. The fuel flows into the fuel flow path 22 through the through hole TH of the lower separator 121 and the cell through hole 11d of the thin plate member 11 as indicated by the solid arrow in FIG.

  As shown in FIG. 4, a current collecting metal mesh (for example, a metal mesh having an embossed structure) is internally provided in the air flow path 21 and the fuel flow path 22. Thereby, the electrical connection between the lower separator 121 and the thin plate member 11 and the electrical connection between the upper separator 122 and the thin plate member 11 are ensured. In addition, the gas distribution path is regulated by the interior of the metal mesh. As a result, in the air flow path 21 and the fuel flow path 22, the area (flow area) in which the power generation reaction can substantially occur due to the gas flow in a plan view can be expanded. The reaction can occur effectively.

In the fuel cell 10 configured as described above, for example, as shown in FIG. 5, a fuel flow path 22 formed between the fuel electrode layer 11 b of the thin plate member 11 and the lower surface of the flat portion 12 a of the separator 12. In addition, the following chemical reaction is caused by supplying fuel to the air flow path 21 formed between the air electrode layer 11c of the thin plate member 11 and the upper surface of the flat portion 12a of the separator 12. Power generation based on equations (1) and (2) is performed.
(1/2) · O ₂ +2 ^e− → O ²⁻ (at: air electrode layer 11c) (1)
H ₂ + O ²⁻ → H ₂ O + 2 ^e− (in the fuel electrode layer 11b) (2)

  Since the fuel cell (SOFC) 10 generates power using the oxygen conductivity of the solid electrolyte layer 11a, the operating temperature of the fuel cell 10 is generally at least 600 ° C. or higher. For this reason, the fuel cell 10 has an external heating mechanism (for example, a resistance heater type heating mechanism or a heating mechanism that uses heat obtained by burning fuel gas) from normal temperature to an operating temperature (for example, 800 ° C.). ) Is used in a heated state.

(Details of thin plate)
Hereinafter, the details of the thin plate member 11 will be described. As shown in FIG. 6, which is a partial side view of the thin plate member 11, the electrolyte layer 11a is a dense layer made of fine particles of YSZ. In this example, the particle diameter of the YSZ particles contained in the electrolyte layer 11a is 0.3 to 3 μm. The fuel electrode layer 11b is a porous layer made of fine particles of Ni and YSZ. In this example, the particle diameters of the Ni and YSZ particles contained in the fuel electrode layer 11b are 0.3 to 1.5 μm and 0.5 to 2 μm, respectively.

The air electrode layer 11c is a porous layer made of fine particles of LSCF having mixed conductivity through which oxygen ions O ²⁻ and electrons e ⁻ pass. About the particle diameter of the particle | grains of LSCF contained in the air electrode layer 11c, an average particle diameter is 0.1-5 micrometers in this example. In particular, the specific surface area of the porous air electrode layer 11c is 1.5 to 9.0 m ² / g, and the pore diameter of the porous air electrode layer 11c is 30 to 100 nm.

  The thickness t1 of the thin plate member 11 is uniform throughout, and is 20 μm or more and 500 μm or less in this example. The thicknesses ta, tb, and tc of the electrolyte layer 11a, the fuel electrode layer 11b, and the air electrode layer 11c are, for example, 0.5 μm to 10 μm, 5 μm to 500 μm, and 5 μm to 200 μm, respectively. It is.

  Thus, in this example, the fuel electrode layer 11b is the thickest in the thin plate member 11, and thus the fuel electrode layer 11b supports the entire thin plate member 11. Since the fuel electrode layer 11b contains metal (Ni), the fuel electrode layer 11b (after the reduction treatment) is richer in flexibility (toughness) than the electrolyte layer 11a and the air electrode layer 11c. Therefore, by making the fuel electrode layer 11 thickest in the thin plate member 11, the thin plate member 11 can be made a flexible structure.

  In this example, the average thermal expansion coefficients of the electrolyte layer 11a, the fuel electrode layer 11b, and the air electrode layer 11c from room temperature to 1000 ° C. are 10 to 11.5 ppm / K, 11.5 to 13.0 ppm / K, 10-14 ppm / K.

(Example of manufacturing method)
Hereinafter, an example of a method for manufacturing the fuel cell 10 will be briefly described. First, a method for manufacturing the thin plate member 11 will be described. First, a ceramic sheet (a YSZ tape, a layer to be an electrolyte layer 11a) manufactured by a green sheet method is laminated on a lower surface of a sheet (YSZ + NiO tape, a layer to be a fuel electrode layer 11b). The ceramic sheet may be formed on the lower surface of the sheet (the layer that becomes the fuel electrode layer 11b) by a printing method.

  Next, this laminate (a laminate of the layer to be the electrolyte layer 11a and the layer to be the fuel electrode layer 11b) is fired at 1400 ° C. for 1 hour. And the material (layer used as the air electrode layer 11c) by which the predetermined calcination process was performed previously is formed by the printing method on the lower surface of the baking body, and the material is baked at 850 degreeC and 1 hour. Here, the calcination treatment refers to preliminary heat treatment of the ceramic powder (raw material powder), and in this example, as described later, for adjusting the specific surface area and pore state of the material of the air electrode layer 11c. Refers to heat treatment. As described above, the thin plate member 11 including the electrolyte layer 11a, the fuel electrode layer 11b, and the air electrode layer 11c is manufactured.

  The separator 12 can be formed by etching, cutting, or the like.

  Next, a glass material (boron) constituting the first seal portion 13a at the portion (in other words, the lower surface of the lower frame portion 12c and the upper surface of the upper frame portion 12b) sandwiching the thin plate member 11 in the outer peripheral portion of each separator 12 is used. Silicate glass) is applied by a printing method. Next, the separators 12 and the thin plate members 11 are alternately stacked, and heat treatment (830 ° C./1 hr) is performed to integrate the stack structure. Thereafter, the material constituting the second seal portion 13b (silicic acid borate crystallized glass or the like) is applied to the outer peripheral portion of the stack, and heat treatment (for example, 850 ° C./1 hr) is applied to reinforce the stack structure. Thereby, the fuel cell 10 is completed.

(Action / Effect)
Hereinafter, as described above, in the air electrode layer 11c that is porous, the air electrode layer is obtained by setting the “specific surface area to 1.5 to 9.0 m ² / g” and the “pore diameter to 30 to 100 nm”. The effect of suppressing increase in reaction loss (described later) of 11c will be described.

First, as this preparation, the electrical resistance in the thickness direction of the thin plate member will be described. Inside the thin plate member described above, the electric resistance when passing current (specifically, electrons e−, oxygen ions O ²⁻ ) in the thickness direction, and the fuel electrode layer and the air electrode resulting from the power generation reaction. Each reaction resistance in the layer inevitably exists. As a result, as shown in FIG. 7, the output voltage V of the thin plate decreases from the theoretical electromotive force V0 as the current I flowing through the thin plate increases. Here, the voltage drop due to the electric resistance of the thin plate member is referred to as “IR loss”, and the voltage drop due to the reaction resistance of the thin plate member is referred to as “reaction loss”.

  The output of the thin plate can be represented by the area of the hatched area in FIG. 7. For example, when the current I = I1, the output of the thin plate is “I1 · V1”. Therefore, by reducing the IR loss and the reaction loss, it is possible to increase the output of the thin plate (and hence the output of SOFC). The present invention pays particular attention to the reaction loss of the air electrode layer among these reaction losses, and suppresses the increase of the reaction loss of the air electrode layer accompanying the increase in the operating time of the SOFC, thereby reducing the output of the thin plate (therefore, , To suppress a decrease in the output of the fuel cell.

  When a porous fired body made of particles of a material having mixed conductivity is employed as the air electrode layer 11c as in this embodiment, generally, as the operating time of the SOFC increases, the air electrode layer 11c Reaction loss tends to increase greatly. This tendency is attributed to the fact that the operating temperature of the SOFC is at a high temperature of 600 ° C. or more, and as the operating time of the SOFC increases, the particle growth (sintering) of the material constituting the air electrode layer 11c increases. This is considered to be based on the fact that the specific surface area of the air electrode layer 11c decreases and becomes remarkable.

On the other hand, as described above, the present inventor makes the “specific surface area 1.5 to 9.0 m ² / g” and the “pore diameter 30 to 100 nm” in the air electrode layer 11c. It has been found that “an increase in reaction loss of the air electrode layer 11c” accompanying an increase in the operating time of the SOFC can be suppressed.

  Hereinafter, an experiment for confirming this will be described. In this experiment, a plurality of types of thin plate bodies (with the same thickness of each layer) having different combinations of the specific surface area and pore diameter distribution of the air electrode layer corresponding to the embodiment shown in FIG. Each was prepared and prepared using it. Specifically, in each of the produced thin plate members, the thickness of the fuel electrode layer (Ni-8YSZ) is 120 μm, the thickness of the electrolyte layer (8YSZ) is 3 μm, and the thickness of the air electrode layer (LSCF) is 20 μm. Yes, the planar shape is a square with a side of 30 mm. Adjustment of the combination of the specific surface area and the pore size distribution of the air electrode layer was performed by adjusting the above-described calcination conditions, the above-described firing temperature, etc. of the material (LSCF) constituting the air electrode layer itself. .

  A durability test relating to the stability of the output voltage of the stack was carried out using a single-stage stack including the single thin plate thus produced in a high temperature atmosphere of 700 ° C. while maintaining a constant current. The reduction rate (deterioration rate) of the output voltage at the time when 1000 hr passed was calculated, and the evaluation result was that the deterioration rate was “within −1%” as “pass (◯)”. The evaluation results are shown in Table 1.

As is apparent from Table 1, in the air electrode layer 11c, when the “specific surface area is 1.5 to 9.0 m ² / g” and the “pore diameter is 30 to 100 nm”, the operation time of the SOFC is increased. The increase in the reaction loss of the air electrode layer 11c due to is suppressed. This is because, when the specific surface area and the pore size distribution are in the above combination, the growth (sintering) of particles of the substance constituting the air electrode layer 1s1c is suppressed, and the specific surface area of the air electrode layer 11c is difficult to decrease. Means that.

  As described above, before the material corresponding to the air electrode layer 11c (the layer that will later become the air electrode layer 11c) is printed in the manufacturing process of the thin plate member, the above-described calcination treatment is applied to the material in advance. By applying, it has been found that the combination of the specific surface area and pore diameter distribution of the air electrode layer 11c after firing can be easily adjusted to the above combination.

In Table 1 above, the evaluation result is shown only when the thickness of the electrolyte layer (8YSZ) is 3 μm, but the thickness of the electrolyte layer (8YSZ) is in the range of 0.5 to 10 μm. A similar experiment was conducted. As a result, the electrolyte layer (8YSZ) has a thickness of 0.5 to 10 μm, and the air electrode layer 11c has a “specific surface area of 1.5 to 9.0 m ² / g” and a “pore diameter of 30”. It has been confirmed that the "increased reaction loss of the air electrode layer 11c" can be suppressed by setting it to "~ 100 nm". The following is a supplementary explanation.

  When the thickness of the solid electrolyte layer is as extremely thin as 0.5 to 10 μm, the IR resistance of the solid electrolyte layer becomes extremely small. Accordingly, the oxygen ion conductivity in the solid electrolyte layer is sufficiently increased. As a result, the “catalytic reaction for ionizing oxygen” in the air electrode layer is promoted, and the reaction loss in the air electrode layer is simultaneously reduced. That is, a very large output can be obtained as compared with the case where the thickness of the solid electrolyte layer is large.

Here, that a very large output is generated means that a very large current flows in the air electrode layer. As a result, due to this large current, “growth (sintering) of particles of the material constituting the air electrode layer” will become more prominent, that is, the specific surface area of the air electrode layer is further reduced. It is thought that the reaction loss of the air electrode layer is likely to increase. Even in such a situation, in the air electrode layer 11c, the “specific surface area is 1.5 to 9.0 m ² / g” and the “pore diameter is 30 to 100 nm”, the above-mentioned “reaction of the air electrode layer”. Sufficient loss suppression effect is ensured.

As described above, in the thin plate member 11 of the solid oxide fuel cell (SOFC) 10 having the flat stack structure according to the embodiment of the present invention, the air electrode layer 11c has mixed conductivity through which oxygen ions and electrons pass. The porous fired body is composed of a large number of particles of a substance (LSCF) having a specific surface area of the air electrode layer 11c of 1.5 to 9.0 m ² / g and the air electrode layer 11c has a pore diameter of 30. ~ 100 nm. The thicknesses of the electrolyte layer 11a, the fuel electrode layer 11b, and the air electrode layer 11c constituting the thin plate member 11 are 0.5 μm to 10 μm, 5 μm to 500 μm, and 5 μm to 200 μm, respectively. is there. As a result, a very thin SOFC single-cell thin plate body in which the “increase in reaction loss of the air electrode layer 11c” accompanying the increase in the SOFC operating time is suppressed can be provided.

  In addition, this invention is not limited to the said embodiment, A various modification can be employ | adopted within the scope of the present invention. For example, in the above embodiment, the fuel electrode layer 11b can be composed of platinum, platinum-zirconia cermet, platinum-cerium oxide cermet, ruthenium, ruthenium-zirconia cermet, or the like.

  The air electrode layer 11c can be made of, for example, a perovskite complex oxide containing lanthanum (for example, lanthanum cobaltite, lanthanum ferrite in addition to the lanthanum strontium cobalt ferrite described above). These may be doped with strontium, calcium, chromium, cobalt, iron, nickel, aluminum or the like.

  In addition, in the above embodiment, the planar shape of the thin plate member 11 and the separator 12 is a square, but may be a rectangle, a circle, an ellipse, or the like.

1 is a cutaway perspective view of a solid oxide fuel cell according to an embodiment of the present invention. FIG. 2 is a partially exploded perspective view of the fuel cell shown in FIG. 1. It is sectional drawing of the separator which cut | disconnected the separator along the plane parallel to an xz plane while including the 1-1 line | wire shown in FIG. It is the longitudinal cross-sectional view which cut | disconnected the separator in the state which supported the thin plate body shown in FIG. 1 and the thin plate body along the plane parallel to a yz plane while including the 2-2 line shown in FIG. It is a figure explaining the distribution | circulation of the fuel and air in the fuel cell shown in FIG. FIG. 3 is a partial side view of the thin plate member illustrated in FIG. 2. It is a figure for demonstrating IR loss and reaction loss.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Fuel cell, 11 ... Thin plate body, 11a ... Zirconia solid electrolyte layer, 11b ... Fuel electrode layer, 11c ... Air electrode layer, 12 ... Separator, 12a ... Planar part, 12b ... Upper frame part, 12c ... Lower frame body Part, 21 ... air flow path, 22 ... fuel flow path

Claims (5)

A solid electrolyte layer; a fuel electrode layer formed on an upper surface of the solid electrolyte layer and supplied with fuel gas from the upper surface; and an air electrode formed on a lower surface of the solid electrolyte layer and supplied with a gas containing oxygen from the lower surface. A thin plate body of a solid oxide fuel cell obtained by laminating and firing layers,
The air electrode layer is a perovskite complex oxide containing lanthanum, and is a porous fired body made of a large number of particles of a substance having a mixed conductivity that allows oxygen ions and electrons to pass through. A thin plate body of a solid oxide fuel cell having a specific surface area of 1.5 to 9.0 m ² / g and the air electrode layer having a pore diameter of 30 to 100 nm. In the thin plate of the solid oxide fuel cell according to claim 1,
The mixed conductive material is a thin plate body of a solid oxide fuel cell, which is lanthanum strontium cobalt ferrite. The thin plate member of the solid oxide fuel cell according to claim 1 or 2,
A solid oxide fuel cell thin plate having a thickness of the solid electrolyte layer of 0.5 to 10 μm. The thin plate member of the solid oxide fuel cell according to claim 1 or 2,
A thin plate body of a solid oxide fuel cell, wherein the average particle diameter of the particles of the substance having mixed conductivity is 0.1 to 5 μm. One or a plurality of thin plate members according to any one of claims 1 to 4,
A plurality of support members that support the one or more thin plate members;
The thin plate member and the support member are alternately stacked one by one,
For each of the thin plate bodies, a fuel flow path as a fuel gas flow path is defined and formed between the thin plate body and the support member adjacent above the thin plate body, and the thin plate body and the thin plate body A solid oxide fuel cell in which an air flow path, which is a flow path of oxygen-containing gas, is partitioned and formed between the support member adjacent to the lower side.

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