JP5662612B1 - Fuel cell - Google Patents

Abstract

To provide a fuel cell including a solid electrolyte membrane, a fuel electrode, and an air electrode, in which separation is unlikely to occur at the edge of the air electrode. The solid oxide fuel cell includes a fuel electrode, a solid electrolyte membrane, and an air electrode. The air electrode 30 includes a thin plate-shaped air electrode active layer 31 formed on the upper surface of the solid electrolyte membrane 20 and a thin plate-shaped air electrode current collecting layer 32 formed on the upper surface of the air electrode active layer 31. The Concavities and convexities are formed along the circumferential direction of the side surface of a part or the entire periphery of the side surface of the air electrode current collecting layer 32. The top part of each convex part and the bottom part of each concave part each have an arc shape. The ratio of the “arc radius at the top of the projection” to the “arc radius at the bottom of the recess” is 0.4 to 2.5, and the difference in height between the top of the projection and the bottom of the recess is 0. It is 05-1 mm. [Selection] Figure 1

Description

  The present invention relates to a fuel cell.

  Conventionally, “solid electrolyte membrane”, “a fuel electrode related to the reaction of fuel gas provided on one surface side of the solid electrolyte membrane”, and “provided on the other surface side of the solid electrolyte membrane” In addition, a solid oxide fuel cell (hereinafter referred to as “SOFC”) including an “air electrode relating to a reaction of air” is known (see, for example, Patent Document 1). In such an SOFC, the fuel electrode and the air electrode are usually formed in a film shape.

Japanese Patent No. 4824135

  By the way, the SOFC described above has a problem that peeling easily occurs at the edge of the air electrode membrane. This is considered to be based on the fact that the stress due to the difference in thermal expansion coefficient between the air electrode membrane and the solid electrolyte membrane tends to remain at the edge of the air electrode membrane.

  An object of the present invention is to provide a fuel cell including a solid electrolyte membrane, a fuel electrode, and an air electrode, which is unlikely to peel off at the edge of the air electrode.

  The fuel cell according to the present invention includes a solid electrolyte membrane, a fuel electrode, and an air electrode as described above. The air electrode has a film shape. It is preferable that the fuel electrode also has a film shape.

  A feature of the fuel cell according to the present invention resides in that unevenness in which a concave portion and a convex portion are alternately repeated is formed along a circumferential direction of the side surface in a part or the entire periphery of the side surface of the air electrode. . Here, the air electrode is in contact with the air electrode active layer on the side opposite to the solid electrolyte membrane with respect to the air electrode active layer and from the air electrode active layer. Air cathode current collector layer made of a material having a high electrical conductivity '', and a part or the entire circumference of the side surface of the air electrode current collector layer, along the circumferential direction of the side surface, It is preferable that unevenness is formed.

  According to this, the unevenness is formed on the side surface of the air electrode along the circumferential direction, whereby the above-mentioned “stress remaining on the edge of the air electrode” is dispersed, and the stress concentration is easily suppressed. Become. As a result, peeling hardly occurs at the edge of the air electrode.

  In the fuel cell according to the present invention, when the top part of each convex part and the bottom part of each concave part have an arc shape, the top part of the convex part with respect to the arc radius (R2) of the bottom part of the concave part. The ratio (R1 / R2) of the arc radius (R1) is preferably 0.4 to 2.5. Moreover, it is suitable that the height difference (H) between the topmost part of the said convex part and the bottommost part of the said recessed part is 0.05-1 mm. These points will be described later.

It is the schematic diagram which showed SOFC which concerns on embodiment of this invention. It is the enlarged view which showed in detail the shape of a part of side surface of the air electrode shown in FIG. It is a figure corresponding to FIG. 1 of SOFC which concerns on the modification of embodiment of this invention. It is a figure corresponding to FIG. 1 of SOFC which concerns on the other modification of embodiment of this invention. It is a figure corresponding to FIG. 1 of SOFC which concerns on the other modification of embodiment of this invention. It is a figure corresponding to FIG. 1 of SOFC which concerns on the other modification of embodiment of this invention. It is a figure corresponding to FIG. 1 of SOFC which concerns on the other modification of embodiment of this invention.

(Constitution)
FIG. 1 shows an example of a solid oxide fuel cell (SOFC) according to an embodiment of the present invention. The SOFC shown in FIG. 1 includes a membrane fuel electrode 10, a solid electrolyte membrane 20 formed (laminated) on the upper surface of the fuel electrode 10, and a membrane air formed (laminated) on the upper surface of the solid electrolyte membrane 20. A laminated fired body including the electrode 30.

  The shape of the SOFC viewed from above is, for example, a square having a side of 1 to 10 cm, or a rectangle having a long side of 5 to 30 cm and a short side of 3 to 15 cm. In the present specification, unless otherwise specified, the value of the dimension such as the shape is a value at room temperature after the “reduction treatment” described later is performed.

  The fuel electrode 10 (anode electrode) is, for example, a porous plate-like fired body composed of nickel oxide NiO and yttria-stabilized zirconia YSZ. The porosity of the fuel electrode 10 is 25 to 50%. The thickness of the fuel electrode 10 is 0.1 to 3 mm. The thickness of the fuel electrode 10 is the largest among the thicknesses of the constituent members of the SOFC, and the fuel electrode 10 functions as a support substrate for the SOFC. The anode 10 is sandwiched between the anode current collecting layer and the anode current collecting layer and the solid electrolyte membrane, and the volume ratio of the substance having oxygen ion conductivity is larger than that of the anode current collecting layer. The fuel electrode active layer ”may be used. The “substance having oxygen ion conductivity” is, for example, yttria-stabilized zirconia YSZ.

  The solid electrolyte membrane 20 is a dense thin plate-like fired body made of, for example, YSZ. The porosity of the electrolyte membrane 20 is 0 to 10%. The thickness of the electrolyte membrane 20 is 0.5 to 30 μm.

  The air electrode 30 (cathode electrode) includes a film-shaped air electrode active layer 31 formed (laminated) on the upper surface of the solid electrolyte membrane 20 and a film-shaped air formed (laminated) on the upper surface of the air electrode active layer 31. And an electrode current collecting layer 32. Both the air electrode active layer 31 and the air electrode current collecting layer 32 are porous thin plate-like fired bodies. The air electrode active layer 31 mainly exhibits a function of promoting a reaction related to air, and the air electrode current collecting layer 32 mainly exhibits a function of collecting electrons supplied from the outside.

The air electrode active layer 31 can be made of, for example, LSCF = (La, Sr) (Co, Fe) O ₃ (lanthanum strontium cobalt ferrite). Alternatively, LSF = (La, Sr) FeO ₃ (lanthanum strontium ferrite), LNF = La (Ni, Fe) O ₃ (lanthanum nickel ferrite), LSC = (La, Sr) CoO ₃ (lanthanum strontium cobaltite), etc. It may be configured. The thickness of the air electrode active layer 31 is 20 to 30 μm. The porosity of the air electrode active layer 31 is 35 to 45%.

The air electrode current collecting layer 32 can be made of, for example, LSCF = (La, Sr) (Co, Fe) O ₃ (lanthanum strontium cobalt ferrite). Alternatively, LSC = (La, Sr) CoO ₃ (lanthanum strontium cobaltite) may be used. Or you may comprise from Ag (silver) and Ag-Pd (silver palladium alloy). Alternatively, it may be composed of La (Ni, Fe, Cu) O ₃ (lanthanum nickel ferrite to which copper is added). The thickness of the air electrode current collecting layer 32 is 80 to 120 μm. The porosity of the air electrode current collecting layer 32 is 35 to 45%.

  The electrical conductivity of the material constituting the air electrode current collecting layer 32 is larger than the electrical conductivity of the material constituting the air electrode active layer 31. The thickness of the air electrode current collecting layer 32 is larger than the thickness of the air electrode active layer 31. Details of the shape of the side surface of the air electrode current collecting layer 32 will be described later.

A reaction preventing film may be interposed between the solid electrolyte membrane 20 and the air electrode 30 (more specifically, the air electrode active layer 31). This reaction preventing film is a dense thin plate-like fired body made of, for example, GDC = (Ce, Gd) O ₂ (gadolinium-doped ceria). The thickness of the reaction preventing film is 3 to 50 μm.

  The reaction preventing film 50 is interposed because the YSZ in the solid electrolyte film reacts with the Sr in the air electrode in the SOFC during or during the production of the SOFC and the interface between the solid electrolyte film and the air electrode. This is to suppress the occurrence of a phenomenon in which a reaction layer having a large electric resistance is formed.

(Production method)
Next, an example of the above-described SOFC manufacturing method will be described.

  First, a molded body of a plate-like fuel electrode is formed. The molded body of the fuel electrode is embedded and formed using a slurry obtained by adding a binder or the like to powder of the fuel electrode material (for example, Ni and YSZ), for example, using a printing method or the like.

  Next, a solid electrolyte membrane molded body is formed on the upper surface of the fuel electrode molded body. The molded body of the solid electrolyte membrane is formed, for example, using a slurry obtained by adding a binder or the like to a powder of the material of the solid electrolyte membrane (for example, YSZ), using a printing method, a dipping method, or the like.

  Subsequently, this laminated molded body (fuel electrode molded body + solid electrolyte membrane molded body) is fired in air at 1500 ° C. for 3 hours. As a result, the SOFC shown in FIG. 1 in which the air electrode 30 (the air electrode active layer 31 and the air electrode current collecting layer 32) is not formed is obtained.

  Next, a molded body of the air electrode active layer is formed on the upper surface of the solid electrolyte membrane 20 (fired body). The molded body of the air electrode active layer is formed using a slurry obtained by adding a binder or the like to the powder of the material of the air electrode active layer (for example, LSCF), using a printing method or the like.

Subsequently, the air electrode current collecting layer formed body is formed on the upper surface of the air electrode active layer formed body. The molded article of the air electrode current collecting layer is printed using, for example, a slurry obtained by adding a binder or the like to the powder of the material of the air electrode current collecting layer (for example, La (Ni, Fe, Cu) O ₃ ). It is formed using the law.

  And this laminated molded object (The molded object of an air electrode active layer + the molded object of an air electrode current collection layer) is baked at 1050 degreeC in the air for 3 hours. Thereby, the SOFC (sintered body) shown in FIG. 1 is obtained. In the above, an example of the manufacturing method of SOFC shown in FIG. 1 was demonstrated.

  At this time, the Ni component in the fuel electrode 10 is NiO by firing in an oxygen-containing atmosphere. Therefore, in order to acquire the conductivity of the fuel electrode 10, thereafter, a reducing fuel gas is caused to flow through the fuel electrode 10 and NiO is reduced at 800 to 1000 ° C. for 1 to 10 hours. This reduction process may be performed during power generation.

(Roughness on the side of the air current collector layer)
Next, the characteristics of the side surface of the SOFC air electrode current collecting layer 32 according to the above embodiment will be described. As shown in FIG. 1 and “FIG. 2 showing an enlarged part of the side surface of the air electrode current collecting layer 32 shown in FIG. 1”, the side surface Concavities and convexities in which concave and convex portions are alternately repeated are formed along the circumferential direction. The irregularities are already formed using a printing method or the like at the stage of forming the air electrode current collecting layer formed body (before firing).

  The top of each projection and the bottom of each recess each have an arc shape. Arc radius R1 at the top of each projection, arc radius R2 at the bottom of each recess, pitch P between adjacent projections (or recesses), and uneven height difference (circumferential direction of the side surface of the air electrode current collecting layer 32) The distance H between the topmost portion of the convex portion and the bottommost portion of the concave portion in a direction perpendicular to the direction along the direction will be described later.

(Action / Effect)
In the above embodiment, unevenness is formed along the circumferential direction of the side surface of the entire circumference of the side surface of the air electrode current collecting layer 32. Thereby, the unevenness is formed along the circumferential direction on the side surface of the air electrode current collecting layer 32, whereby the "stress remaining on the edge of the air electrode" described in the background art section is dispersed, Stress concentration is easily suppressed. As a result, peeling hardly occurs at the edge of the air electrode current collecting layer 32. In the above embodiment, unevenness is formed on the side surface of the air electrode current collecting layer 32, while no unevenness is formed on the side surface of the air electrode active layer 31. Since it is thicker than the active layer 31, peeling of the air electrode current collecting layer 32 is particularly likely to be a problem.

(Ratio of arc radius of concave and convex parts)
In the SOFC shown in FIG. 1 after the above-described reduction treatment, cracks do not occur on the side surface (surface on which irregularities are formed) of the air electrode current collecting layer 32 when operated in a normal environment. However, when the SOFC is operated in a severe environment due to thermal stress, cracks may occur on the side surfaces. The present inventor has found that the occurrence of such cracks is the ratio (R1 / R2) of the “arc radius R1 at the top of the convex portion to the arc radius R2 at the bottom of the recess” (hereinafter referred to as “arc radius ratio R1 / R2”). And found a strong correlation. Hereinafter, test A in which this has been confirmed will be described.

(Test A)
In the test A, for the SOFC shown in FIG. 1, the material of the air electrode current collecting layer, the pitch P of the unevenness formed on the side surface of the air electrode current collecting layer, the height difference H, and the arc radius R1 of the top of the convex part A plurality of samples having different combinations of the arc radius R2 and the arc radius ratio R1 / R2 at the bottom of the recess were produced. Specifically, as shown in Table 1, 10 types (combinations) were prepared. Ten samples (N = 10) were made for each level. Each value described in Table 1 is a value after the reduction treatment described above (an average value of N = 10).

  In each sample (SOFC shown in FIG. 1), after the above-described reduction treatment, the thickness of the air electrode active layer 31 was set to 20 to 30 μm, and the thickness of the air electrode current collecting layer 32 was set to 80 to 120 μm. . The unevenness pitch P was set to 0.2 to 2 mm, and the height difference H was set to 0.05 to 1 mm. The porosity of the air electrode active layer 31 was 35 to 45%, and the porosity of the air electrode current collecting layer 32 was 35 to 45%. The porosity of each layer was adjusted by adjusting the particle size of the powder in the slurry, the added amount of the pore former, and the like. The co-firing temperature of the air electrode 30 (two layers of the active layer 31 and the current collecting layer 32) was adjusted within a range of 900 to 1100 ° C. The co-firing time was adjusted within a range of 1 to 10 hours. The reduction treatment temperature was adjusted within the range of 800 to 1000 ° C. The reduction treatment time was adjusted within a range of 1 to 10 hours.

  For each sample after the reduction treatment, “a pattern in which the ambient temperature is raised from room temperature to 750 ° C. in 2 hours and then lowered from 750 ° C. to room temperature in 4 hours while reducing fuel gas is circulated through the fuel electrode 10. The heat cycle test was repeated 10 times. And about each sample, the presence or absence of the generation | occurrence | production of the crack in the side surface (surface in which the unevenness | corrugation was formed) of the air electrode current collection layer 32 was confirmed. This confirmation was made by visual observation as well as observation using a microscope. The results are as shown in Table 1.

  As can be understood from Table 1, after the thermal cycle test that is severe in terms of thermal stress, if the arc radius ratio R1 / R2 is less than 0.4 or greater than 2.5, the reason is unknown. However, cracks are likely to occur on the side surface (surface on which irregularities are formed) of the air electrode current collecting layer 32. On the other hand, when the arc radius ratio R1 / R2 is within the range of 0.4 to 2.5, it can be said that the crack is hardly generated.

  In addition, the present inventor, when the above-described embodiment is used under normal conditions and environment (for example, a pattern in which the temperature is raised from room temperature to 750 ° C. in 4 hours and then lowered from 750 ° C. to room temperature in 12 hours) Even if the radius ratio R1 / R2 is outside the range of 0.4 to 2.5, it has been separately confirmed that no cracks are generated on the side surface (surface on which the unevenness is formed) of the air electrode current collecting layer 32.

(Difference in unevenness)
The inventor of the present invention has a strong correlation between the occurrence of the cracks generated when the SOFC shown in FIG. 1 is operated under a severe environment in terms of thermal stress and “difference level difference H” (see FIG. 2). Found that there is. Hereinafter, test B in which this has been confirmed will be described.

(Test B)
In the test B, for the SOFC shown in FIG. 1, the material of the air electrode current collecting layer, the pitch P of the unevenness formed on the side surface of the air electrode current collecting layer, the arc radius R1 at the top of the convex part, the bottom of the concave part A plurality of samples having different combinations of the arc radius R2 and the height difference H were prepared. Specifically, as shown in Table 2, ten kinds of levels (combinations) were prepared. Ten samples (N = 10) were made for each level. Each value described in Table 2 is a value after the reduction treatment described above (an average value of N = 10).

  In each sample (SOFC shown in FIG. 1), after the above-described reduction treatment, the thickness of the air electrode active layer 31 was set to 20 to 30 μm, and the thickness of the air electrode current collecting layer 32 was set to 80 to 120 μm. . The unevenness pitch P was set to 0.2 to 2 mm, and the arc radius ratio R1 / R2 was set to 0.4 to 2.5. The porosity of the air electrode active layer 31 was 35 to 45%, and the porosity of the air electrode current collecting layer 32 was 35 to 45%. The co-firing temperature, co-firing time, reduction treatment temperature, and reduction treatment time of the air electrode 30 (two layers of the active layer 31 and the current collecting layer 32) were the same as those in Test A above.

  And, for each sample after the reduction treatment, as in the case of the test A, “750 ° C. after raising the ambient temperature from room temperature to 750 ° C. in 2 hours while circulating the reducing fuel gas to the fuel electrode 10. The thermal cycle test was repeated 20 times for the “pattern from 4 to room temperature in 4 hours”. And about each sample, the presence or absence of the generation | occurrence | production of the crack in the side surface (surface in which the unevenness | corrugation was formed) of the air electrode current collection layer 32 was confirmed. This confirmation was made by visual observation as well as observation using a microscope. The results are as shown in Table 2.

  As can be understood from Table 2, after the thermal cycle test, which is severe in terms of thermal stress, if the height difference H of the unevenness is less than 0.05 mm or greater than 1 mm, the reason is unknown. Cracks are likely to occur on the side surface (surface on which irregularities are formed) of the pole current collecting layer 32. On the other hand, when the height difference H is in the range of 0.05 to 1 mm, it can be said that the crack is hardly generated.

  In addition, when the above-described embodiment is used under normal conditions and environment (for example, a pattern in which the temperature is raised from room temperature to 750 ° C. in 4 hours and then lowered from 750 ° C. to room temperature in 12 hours), the inventor Even if the height difference H is outside the range of 0.05 to 1 mm, it has been separately confirmed that no cracks are generated on the side surface (surface on which irregularities are formed) of the air electrode current collecting layer 32.

  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, as shown in FIG. 1, irregularities are formed on the entire circumference of the side surface of the air electrode current collecting layer 32, but as shown in FIG. Concavities and convexities may be formed only in part. In the example shown in FIGS. 1 and 3, the side surface of the air electrode active layer 31 is not formed with unevenness having the same or similar shape as the unevenness formed on the side surface of the air electrode current collecting layer 32. It may be formed.

  Moreover, in the said embodiment, as shown in FIG. 1, the air electrode 30 consists of two layers, the air electrode active layer 31 and the air electrode current collection layer 32, and an unevenness | corrugation is formed in the perimeter of the side surface of the air electrode current collection layer 32. Although formed, as shown in FIG. 4, the air electrode 30 may be composed of only one layer, and irregularities may be formed on the entire circumference of the side surface of the air electrode 30 (= 1 layer) itself. Similarly, as shown in FIG. 5, unevenness may be formed only on a part of the side surface of the air electrode 30 (= 1 layer) itself.

  In the above embodiment, as shown in FIG. 1, the entire air electrode current collecting layer 32 is placed on the upper surface of the air electrode active layer 31 (that is, the air electrode current collecting layer 32 is the air electrode active layer 31. The side surface of the air electrode current collecting layer 32 is uneven, and irregularities are formed on the entire circumference of the side surface of the air electrode current collecting layer 32. As shown in FIG. The entire surface (all of the upper surface and the side surface) may be covered, and unevenness may be formed on the entire circumference of the side surface of the air electrode current collecting layer 32. The entire periphery of the peripheral edge of the air electrode current collecting layer 32 is in contact with the upper surface of the solid electrolyte membrane 20. Also in this case, as shown in FIG. 7, irregularities may be formed only on a part of the side surface of the air electrode current collecting layer 32. In the example shown in FIGS. 6 and 7, the side surface of the air electrode active layer 31 is not formed with unevenness having the same or similar shape as the unevenness formed on the side surface of the air electrode current collecting layer 32. It may be formed.

  In addition, when tests A and B described above are performed for each of the modes shown in FIGS. 3 to 7 described above, it is separately confirmed that the same results as those shown in Tables 1 and 2 are obtained. ing.

  DESCRIPTION OF SYMBOLS 10 ... Fuel electrode, 20 ... Solid electrolyte membrane, 30 ... Air electrode, 31 ... Air electrode active layer, 32 ... Air electrode current collection layer

Claims (4)

A solid electrolyte membrane;
A fuel electrode that is provided on one surface of the solid electrolyte membrane and is associated with a reaction of fuel gas;
An air electrode provided on the other surface side of the solid electrolyte membrane and relating to a reaction of a gas containing oxygen;
A fuel cell comprising:
The air electrode has a film shape,
In a part or the entire circumference of the side surface of the air electrode, along the circumferential direction of the side surface, concave and convex portions that are alternately repeated with concave portions and convex portions are formed ,
The top of each convex portion and the bottom of each concave portion each have an arc shape,
The ratio (R1 / R2) of the arc radius (R1) of the top of the convex portion to the arc radius (R2) of the bottom of the concave portion is 0.4 to 2.5 . A solid electrolyte membrane;
A fuel electrode that is provided on one surface of the solid electrolyte membrane and is associated with a reaction of fuel gas;
An air electrode provided on the other surface side of the solid electrolyte membrane and relating to a reaction of a gas containing oxygen;
A fuel cell comprising:
The air electrode has a film shape,
In a part or the entire circumference of the side surface of the air electrode, along the circumferential direction of the side surface, concave and convex portions that are alternately repeated with concave portions and convex portions are formed,
The air electrode is
An air cathode active layer;
An air electrode current collecting layer made of a material having electrical conductivity larger than that of the air electrode active layer, in contact with the air electrode active layer on the side opposite to the solid electrolyte membrane with respect to the air electrode active layer,
Including
The fuel cell , wherein the unevenness is formed along a circumferential direction of the side surface in a part or the entire periphery of the side surface of the air electrode current collecting layer . The fuel cell according to claim 2 , wherein
The top of each convex portion and the bottom of each concave portion each have an arc shape,
The ratio (R1 / R2) of the arc radius (R1) of the top of the convex portion to the arc radius (R2) of the bottom of the concave portion is 0.4 to 2.5. The fuel cell according to any one of claims 1 to 3 , wherein
The height difference (H) between the topmost part of the convex part and the bottommost part of the concave part is 0.05 to 1 mm.

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