JP5294474B2 - High power power generation cell with laminated solid electrolyte - Google Patents

Description

  The present invention relates to a high-output power generation cell including a laminated solid electrolyte, in which a solid electrolyte of a power generation cell is formed by laminating a support film and an electrolyte film made of a lanthanum gallate oxide.

  In general, solid oxide fuel cells generate electricity using pure hydrogen gas as fuel, but since pure hydrogen gas is relatively expensive, in recent years, city gas, natural gas, methanol, coal gas, etc. have been reformed. It has become mainstream to use hydrogen gas obtained in this way as fuel. This solid oxide fuel cell generally has a structure in which an air electrode is laminated on one side of a solid electrolyte made of oxide and a fuel electrode is laminated on the other side of the solid electrolyte. An air electrode current collector is laminated outside the air electrode of the power generation cell, and a fuel electrode current collector is laminated outside the fuel electrode of the power generation cell. It has a structure in which a plurality of laminated structures each having a separator laminated on the outside of the electric body are laminated.

And it is known that a lanthanum gallate-based oxide ion conductor is used as a solid electrolyte constituting the power generation cell, and this lanthanum gallate-based oxide ion conductor has a general formula: La _1-X Sr _X Ga _1-Y-Z in Mg _Y a Z _{O 3} (wherein, a = Co, Fe, Ni , 1 or more kinds of Cu, X = 0.05~0.3, Y = 0~0.29, Z = 0.01-0.3, Y + Z = 0.025-0.3) (Patent Document 1).

  Incidentally, in order to realize a small and high output solid oxide fuel cell, it is indispensable to increase the output per power generation cell. For this purpose, in the case of an electrolyte support membrane cell, it is indispensable to increase the area of the electrolyte and reduce the thickness of the electrolyte. However, when generating power with an actual machine, the cell ( Electrolyte) is easily damaged and cracked. For this reason, power generation cells using an anode and a cathode as a supporting film have been developed (Patent Document 2). Since the supporting film is a porous body, there is a problem that the strength is not improved enough to meet expectations.

Japanese Patent Laid-Open No. 11-335164 JP-A-2001-238776

  In order to improve the performance of solid oxide fuel cells, there is an increasing demand for smaller and higher output fuel cells. To achieve this, even when the cell area is increased and the thickness is reduced. Therefore, a solid electrolyte for a high-strength power generation cell that does not break or crack is desired.

Accordingly, the inventors of the present invention have developed a power cell using a lanthanum galade (LaGaO ₃ ) -based oxide as a solid electrolyte to prevent damage and cracking by increasing the strength of the cell and to prevent the output from being lowered. As a result of earnest research on electrolytes, the following findings were obtained.

As a solid electrolyte of a solid oxide fuel cell, it is known to use a lanthanum galade (LaGaO ₃ ) -based oxide ion conductor because of its large oxygen ion conductivity. LSGMF (general formula: La _1-X Sr _X Ga _1-YZ Mg _Y Fe _Z O ₃ (wherein X, X, Sr _X added to La site and Mg and Fe added to Ga site)) Y and Z each represent an atomic ratio).)) Is known to not show a large output density because it has high oxygen ion conductivity but also has electron conduction, and thus electron leakage occurs inside the electrolyte. Yes. Further, when the solid oxide fuel cell using the above LSGMF as a solid electrolyte is operated for a certain period, a decrease in power generation efficiency is observed.

  The cause of the decrease in the power generation efficiency is that the solid electrolyte made of LSGMF is easily reduced. Therefore, when the solid oxide fuel cell is operated for a certain period of time, the solid electrolyte fuel gas made of LSGMF Reduction occurs on the contact side, and as a result, the internal resistance of the cell increases, which is a major factor in the decrease in power generation efficiency.

In order to prevent the solid electrolyte composed of LSGMF from being reduced by the fuel gas, the present inventors used LSGM (general formula: La _1-X Sr _X Ga _{1 -Y} Mg _Y O ₃ (wherein , X, and Y represent atomic ratios))) and LSGMF, respectively, and the presence or absence of reduction by the fuel gas by interposing the LSGM between the fuel electrode and the LSGMF. As a result of the study, by configuring the solid electrolyte as the above laminated structure, it succeeded in preventing the reduction reaction between the solid electrolyte and the fuel gas and at the same time preventing the generation cell from being broken and cracked.

  That is, the present inventors have a dense structure and a relatively high strength LSGMF as a solid electrolyte of a power generation cell used for a solid oxide fuel cell or the like, and a dense structure as well. By using a laminated solid electrolyte composed of a thin LSGM layer structure having a relatively thin film, and interposing an electrolyte membrane made of LSGM in contact with the fuel electrode between the fuel electrode and the LSGMF, a real machine for a certain period of time. It has been found that a high-power and high-power density power generation cell that does not cause breakage or cracking can be provided without lowering the power generation efficiency of the cell even if it is operated at.

This invention has been made based on the above findings,
“(1) A laminated solid comprising a laminated structure of an electrolyte A having a thickness of 200 μm to 1 mm and an electrolyte B having a thickness of 5 to 200 μm, which has electronic conductivity but oxygen ion conductivity is 5 times or more that of the electrolyte B A power generation cell comprising an electrolyte,
The electrolyte A is
General _formula: La in _{1-X Sr X Ga 1-} Y-Z Mg Y Fe Z O 3 ( wherein, X, Y, Z represents respectively atomic ratio, X = 0.05 to 0.3, Y = 0-0.2, Z = 0.05-0.5, Y + Z = 0.05-0.7)
In addition, the electrolyte B is
General _{formula: La 1-α Sr α Ga} 1-β Mg β O 3 ( where, alpha, beta denotes the respective atomic ratio, α = 0.05~0.3, β = 0~0.3 ) A lanthanum galade oxide ion conductor having a dense structure represented by:
A power generation cell comprising a laminated solid electrolyte characterized by comprising:
(2) In the power generation cell including the laminated solid electrolyte according to (1), the fuel electrode is a cermet made of Ni and Ce _M Gd _1-M O ₂ or a cermet made of Ni and Ce _N Sm _1-N O _2. And the air electrode is Sm _U Sr _1-U CoO ₃ or Ba _V La _1-V CoO ₃ , and the electrolyte B having a thickness of 5 to 200 μm is present in contact with the fuel electrode. A power generation cell comprising the laminated solid electrolyte according to (1) above. "
It has the characteristics.

  The present invention is described in detail below.

LSGMF constituting the multilayer electrolyte of the present invention is:
General _formula: La in _{1-X Sr X Ga 1-} Y-Z Mg Y Fe Z O 3 ( wherein, X, Y, Z represents respectively atomic ratio, X = 0.05 to 0.3, Y = 0-0.2, Z = 0.05-0.5, Y + Z = 0.05-0.7), and since it has a dense structure, it has high strength and electron conductivity, but high oxygen ion conductivity It is known as a lanthanum galade oxide oxide conductor having
However, since it is easy to be reduced when the actual machine operation is performed for a certain period, reduction is prevented by forming a laminated structure with an electrolyte made of LSGM, which will be described later, and this laminated structure does not cause a decrease in output of the power generation cell, By increasing the strength of the power generation cell, the occurrence of breakage, cracking, etc. is prevented.
When the film thickness of LSGMF is less than 200 μm, the strength of the laminated electrolyte cannot be maintained. On the other hand, when the film thickness exceeds 1 mm, the solid electrolyte becomes too thick and it becomes impossible to increase the output density of the power generation cell. Therefore, the film thickness of LSGMF was determined to be 200 μm or more and 1 mm or less.
Further, since the LSGMF needs to have high oxygen ion permeability even though it is thick as described above, the oxygen ion conductivity of LSGMF is determined to be 5 times or more that of the electrolyte membrane made of LSGM.
To this end, the general _{formula: La 1-X Sr X Ga} 1-Y-Z Mg Y Fe Z O 3 ( In the formula, X, Y, Z is independently an atomic ratio) in,
X = 0.05-0.3, Y = 0-0.2, Z = 0.05-0.5, Y + Z = 0.05-0.7,
When the values of X, Y, and Z are out of the numerical ranges, high oxygen ion conductivity cannot be obtained. Therefore, X = 0.05 to 0.3, Y = 0 to 0.2. Z = 0.05-0.5, Y + Z = 0.05-0.7,
It was determined.

In the laminated solid electrolyte of the present invention, the LSGM constituting the laminated structure with the above LSGMF is:
General _{formula: La 1-α Sr α Ga} 1-β Mg β O 3 ( where, alpha, beta denotes the respective atomic ratio, α = 0.05~0.3, β = 0~0.3 ) It is known as a lanthanum galade oxide oxide conductor represented by the following formula. Like a LSGMF electrolyte, it has a dense structure and has a high strength, and is suitable as a solid electrolyte for an electrolyte support membrane cell.
However, if the thickness of the LSGM electrolyte is less than 5 μm, electron leakage occurs in the electrolyte, so that a large output density cannot be obtained. On the other hand, if the film thickness exceeds 200 μm, the solid electrolyte becomes too thick, and again a high output density is obtained. Therefore, the thickness of the electrolyte was determined to be 5 to 200 μm.
Moreover, since the LSGM is an electrolyte and needs to have predetermined oxygen ion conductivity, it constitutes an electrolyte of a laminated solid electrolyte, and the composition ratio of the LSGM constituting the laminated structure with the LSGMF is ,
In the general formula: La _1-α Sr _α Ga _1-β Mg _β O ₃ (wherein α and β each represent an atomic ratio), α = 0.05 to 0.3, β = 0 to 0. 3 is required. If the values of α and β are out of the numerical range, oxygen ion conductivity is lowered. Therefore, α is set to 0.05 to 0.3 and β is set to 0 to 0.3.

As the fuel electrode of the power generation cell, a known normal fuel electrode, for example, a cermet made of Ni and Ce _M Gd _{1 -M} O ₂ (GDC), or Ni and Ce _N Sm _{1 -N} O ₂ ( Cermet made of SDC) can be used. In the Ni-GDC, the value of M (atomic ratio) is usually 0.1 to 0.3, and in the Ni-SDC, the value of N (atomic ratio) is usually 0.1 to 0.3. 3.
By using the laminated solid electrolyte of the present invention, peeling between the fuel electrode and the solid electrolyte and occurrence of breakage can be prevented, and the strength of the power generation cell can be increased.

The air electrode of the power generation cell, ordinary air electrode already known, for _{example, Sm U Sr 1-U CoO} 3 (SSC), or _can be used _{Ba V La 1-V CoO 3} (BLC) . In the SSC, the value of U (atomic ratio) is usually 0.4 to 0.6, and in the BLC, the value of V (atomic ratio) is usually 0.4 to 0.6.

Next, an example of the manufacturing method of the laminated solid electrolyte and power generation cell of the present invention will be described below.
(A) First, powders of the respective oxides are mixed so as to have a predetermined blending ratio to prepare an LSGM slurry, followed by molding to obtain a LSGM compact.
At this time, it is important that the amount of the binder used is about 1.6 times that when the LSGMF slurry is produced, thereby preventing firing cracks due to the difference in thermal expansion from LSGMF during firing. Can do.
(B) Next, as in the case of LSGM, each oxide powder is mixed so as to have a predetermined blending ratio to prepare a slurry of LSGMF, and on the surface of the dried LSGM compact, The slurry is drawn to a predetermined thickness.
(C) After drying this, it cuts out by predetermined diameter (for example, diameter 200mm), for example, performs main baking and rebaking for 6 hours at 1400 degreeC, respectively, and produces a laminated solid electrolyte with a diameter of about 144 mm.
(D) A fuel electrode of the present invention can be produced by printing and applying a fuel electrode on the surface of LSGM of the laminated solid electrolyte and an air electrode on the surface of LSGMF and baking at 1000 to 1300 ° C. it can.

  The power generation cell of the present invention having a laminated solid electrolyte composed of a layered structure of LSGMF and LSGM does not cause breakage or cracking of the power generation cell with high strength, and at the same time, it is possible to achieve a high power density, while reducing output High output can be maintained for a long time without incurring.

  Hereinafter, the present invention will be specifically described by way of examples.

(A) First, powders of lanthanum oxide, strontium carbonate, gallium oxide, and magnesium oxide were prepared, and the composition represented by (La _0.8 Sr _0.2 ) (Ga _0.8 Mg _0.2 ) O ₃ After being mixed and ball milled, the mixture was heated and held at 1200 ° C. for 3 hours in the air. The resulting massive sintered body was coarsely pulverized with a hammer mill and then finely pulverized with a ball mill. An 8 μm lanthanum gallate-based electrolyte raw material powder was produced.
The raw material powder for lanthanum gallate electrolyte is mixed with an organic binder solution in which an organic binder is dissolved in a toluene-ethanol mixed solvent (1.57 times the amount of LSGMF used) to form a slurry, and the blade interval is determined by a doctor blade method. It was molded into a thin plate with a thickness of 0.24 mm and dried to prepare an LSGM molded body.
(B) Next, powders of lanthanum oxide, strontium carbonate, gallium oxide, magnesium oxide, and iron oxide were prepared, and (La _0.8 Sr _0.2 ) (Ga _0.8 Mg _0.15 Fe _0.05 ) Weighed to a composition represented by O ₃ , mixed with a ball mill, heated and held at 1200 ° C. for 3 hours in air, and coarsely pulverized the resulting sintered body with a hammer mill and then finely pulverized with a ball mill. Thus, a raw material powder for lanthanum gallate electrolyte having an average particle size of 1.8 μm was produced. The lanthanum gallate electrolyte raw material powder is mixed with an organic binder solution in which an organic binder is dissolved in a toluene-ethanol mixed solvent to form a slurry, and this slurry is formed by the doctor blade method with a blade interval of 0.94 mm and the LSGM molded body. In addition, the laminated solid electrolyte green sheet having a circular plate shape of 200 mm in diameter and formed of a laminated structure of an LSGM molded body and an LSGMF molded body is drawn up to a predetermined thickness, dried and cut out to have a diameter of 200 mm. Was made.
(C) The laminated solid electrolyte green sheet was subjected to main firing and refiring at 1400 ° C. for 6 hours to produce a laminated solid electrolyte having a laminated structure of a 50 μm thick LSGM electrolyte and a 300 μm thick LSGMF electrolyte.
(D) Next, a slurry of cermet made of Ni and Ce _M Gd _1-M O ₂ (GDC) is printed on the surface of the laminated solid electrolyte made of LSGM on the electrolyte membrane side, and baked at 1200 ° C. in the atmosphere. By attaching, the fuel electrode was formed so that it might contact | connect the surface which consists of LSGM.
(E) On the other hand, a slurry of Sm _U Sr _1-U CoO ₃ (SSC) is printed on the surface made of LSGMF of the above-mentioned laminated solid electrolyte, and baked at 1100 ° C. in the atmosphere to make the surface of LSGMF An air electrode was formed.
According to the above (a) to (e), three types of the present power generation cells 1 to 3 having a diameter of 170 to 240 mm and a cell size of the laminated solid electrolyte of the present invention were produced.

For comparison, in the same manner as in (a) above, an LSGM molded body having the same composition as in (a) above (however, the amount of the organic binder solution used is 1.57 times the amount of LSGMF used), Thereafter, main firing and re-firing are performed at 1400 ° C. for 6 hours to produce a solid electrolyte made of LSGM with a film thickness of 150 μm, and then Ni and Ce _M Gd _1-M O ₂ (GDC) are formed on one surface of the solid electrolyte. The cermet slurry is printed and applied, and baked at 1200 ° C. in the air to form a fuel electrode. On the other side of the solid electrolyte, Sm _U Sr _1-U CoO ₃ (SSC) The slurry is printed and applied to form an air electrode by baking at 1100 ° C. in the atmosphere, and a plurality of comparative power generation cells 1 having a solid electrolyte made of LSGM and a cell having a diameter of 200 mm are produced. It was.

For further comparison, an LSGMF molded body having the same composition as (b) above (composition represented by (La _0.8 Sr _0.2 ) (Ga _0.8 Mg _0.15 Fe _0.05 ) O ₃ ) is used. After that, firing and re-baking are performed at 1400 ° C. for 6 hours to produce a solid electrolyte made of LSGMF with a film thickness of 150 μm. Then, in the same manner as in the comparative example power generation cell 1, one surface of the solid electrolyte is formed. By forming a fuel electrode and an air electrode on the other surface, a plurality of comparative power generation cells 2 having a solid electrolyte made of LSGMF and a cell having a diameter of 200 mm were produced.

About the above-described power generation cells 1 to 3 of the present invention and comparative power generation cells 1 and 2 produced in a plurality,
Temperature: 750 ° C.
Fuel gas: hydrogen,
Fuel gas flow rate: 3 cc · cm ² / min,
Oxidant gas: air,
Oxidant gas flow rate: 15 cc · cm ² / min,
A cell test was conducted for 1 hour under the power generation conditions, the cell output obtained at that time was measured, and the results are shown in Table 1.
In addition, the present power generation cells 1 to 3 and the comparative power generation cells 1 to 2 are actually operated (supplying city gas 13A and water vapor at S / C = 3 in a module in which two stacks are assembled with 50 sheets as one stack), The state of cell cracking was observed.
The observation results are also shown in Table 1.

  From the results shown in Table 1, the power generation cells 1 to 3 of the present invention are thin and have a dense structure and a relatively strong LSGMF and a dense structure as a solid electrolyte of the solid oxide fuel cell. The cell output can be increased by using a laminated solid electrolyte having a relatively strong LSGM laminated structure and interposing an electrolyte made of LSGM in contact with the fuel electrode between the fuel electrode and the LSGMF electrolyte. While it is possible to produce a high-strength power generation cell that does not cause breakage or cracking without being reduced, the comparative power generation cell 1 in which the solid electrolyte is composed of a single LSGM layer is cracked (5/100). Only a power generation cell with a low output (157 W / sheet) could be obtained. Moreover, the comparative example power generation cell 2 in which the solid electrolyte is composed of a single layer of LSGMF has a low output (74 W / sheet), a very large number of cell cracks (21/100), and a high-strength power generation cell can be obtained. I understand that I can't.

    According to the present invention, even when the solid electrolyte has a large area and is thinned, it does not cause breakage or cracking with high strength, and a high-output power generation cell can be obtained. It can be said that the application to solid oxide fuel cells that are required to be improved is greatly expected.

Claims (2)

A power generation including a laminated solid electrolyte having a laminated structure of an electrolyte A having a thickness of 200 μm to 1 mm and an electrolyte B having a thickness of 5 to 200 μm, which has electron conductivity but oxygen ion conductivity is 5 times or more that of the electrolyte B A cell,
The electrolyte A is
General _formula: La in _{1-X Sr X Ga 1-} Y-Z Mg Y Fe Z O 3 ( wherein, X, Y, Z represents respectively atomic ratio, X = 0.05 to 0.3, Y = 0 to 0.2, Z = 0.05 to 0.5, and Y + Z = 0.05 to 0.7).
In addition, the electrolyte B is
General _{formula: La 1-α Sr α Ga} 1-β Mg β O 3 ( where, alpha, beta denotes the respective atomic ratio, α = 0.05~0.3, β = 0~0.3 ) A lanthanum galade oxide oxide conductor represented by:
A power generation cell comprising a laminated solid electrolyte characterized by comprising: In the power generation cells with stacked solid electrolyte according to claim 1, the fuel electrode is a cermet of Ni and _Ce M _{Gd 1-M} consist of _{O 2} cermet or Ni and _Ce N _{Sm 1-N O 2,} also The air electrode is Sm _U Sr _1-U CoO ₃ or Ba _V La _1-V CoO ₃ , and the electrolyte B having a thickness of 5 to 200 μm is present in contact with the fuel electrode. A power generation cell comprising the laminated solid electrolyte according to claim 1.