JP5383232B2 - Power generation membrane of solid oxide fuel cell and solid oxide fuel cell having the same - Google Patents

Description

  The present invention relates to a power generation membrane for a solid oxide fuel cell and a solid oxide fuel cell including the same.

  As a general configuration of a solid oxide fuel cell (SOFC), the one shown in FIG. 1 is known. The power generation membrane 10 includes a solid electrolyte 1, a fuel side electrode 2 and an air side electrode 3 formed on both surfaces thereof. A conductive bonding material 4 and an interconnector 6 are formed on the fuel side electrode 2 side, and a conductive bonding material 5 and an interconnector 7 are formed on the air side electrode 3 side.

As the solid electrolyte 1, it has been proposed to use yttria stabilized zirconia (YSZ). As the air side electrode 3, since excellent power density and high durability can be obtained, lanthanum strontium manganese oxide (LSM) represented by the composition formula (La _(1-y) Sr _y ) _z MnO ₃ and A composite with YSZ is used. The fuel side electrode 2 is required to have excellent electron conductivity, electrode reactivity, and stability in a hydrogen atmosphere. As a material for the fuel side electrode 2, a mixture of nickel oxide (NiO) and YSZ (NiO / YSZ cermet) is generally used.

  The operating temperature of a solid oxide fuel cell is generally about 1000 ° C., but a solid oxide fuel cell that operates at a lower temperature (for example, about 800 ° C. or less) is desired. However, in the conventional solid oxide fuel cell, when the operating temperature of the solid oxide fuel cell is decreased from 1000 ° C. to 800 ° C. or less, the polarization of the fuel side electrode increases, the reaction resistance increases, and the power generation performance decreases. There was a problem. Therefore, in order to operate at a relatively low temperature of about 800 ° C., a fuel side electrode having a low reaction resistance even at 800 ° C. has been required.

  In order to obtain a solid electrolyte fuel cell having high power generation performance by reducing electrical resistance at the interface, for example, Patent Document 1 discloses a ceria layer doped with an element such as samaria between an electrolyte membrane and an air electrode. Is disclosed.

JP 2001-283877 A

  When samaria-doped ceria is applied to the fuel side electrode, the reaction activity in a reducing atmosphere at 800 ° C. can be improved as compared with YSZ. However, samaria-doped ceria exhibits ionic conductivity and electronic conductivity in a reducing atmosphere, and thus the conductivity is improved compared to YSZ that exhibits only ionic conductivity, but the conductivity is insufficient for application to electrode materials. There was a problem.

  The present invention has been made in view of such circumstances, and a power generation membrane of a solid oxide fuel cell in which the occurrence of polarization of a fuel-side electrode is suppressed even at a low operating temperature, and a solid oxide fuel cell including the same provide.

A power generation membrane of a solid oxide fuel cell according to the present invention includes a solid electrolyte, an air side electrode provided on one side of the solid electrolyte, and a fuel side electrode provided on the other side. The fuel-side electrode comprises, in order from the solid electrolyte side, NiO and Ce _1-x Ln _x O ₂ (Ln: Gd or Tm, 0.03 ≦ x ≦ 0.5). A first layer including a mixture, a second layer including NiO, and a second layer including a mixture of a highly conductive oxide having higher conductivity than Ce _1-x Ln _x O ₂ in a reducing atmosphere.

The inventors have found that Ce _1-x Gd _x O ₂ and Ce _1-x Tm _x O ₂ have higher electrical conductivity than samaria doped ceria. Furthermore, it has been found that by using the above composition range, the conductivity is remarkably high in both the oxidizing atmosphere and the reducing atmosphere.
In the fuel-side electrode of the present invention, the first layer on the solid electrolyte side is a mixture of NiO and Ce _1-x Gd _x O ₂ or Ce _1-x Tm _x O ₂ (0.03 ≦ x ≦ 0.5). It is made into the layer containing. Thereby, polarization resistance is reduced. In addition, a second layer containing a mixture of oxide and NiO having higher conductivity (electron conductivity) in a reducing atmosphere than Ce _1-x Gd _x O ₂ or Ce _1-x Tm _x O ₂ on the first layer. A layer is formed. Thereby, the electroconductivity of the whole fuel side electrode can be improved. According to the fuel-side electrode having the two-layer structure described above, the reaction activity can be improved.

In the above invention, the mixing ratio of the NiO and the _Ce 1-x _Ln x _{O 2} is preferably in the range of 20:80 to 60:40 by mass ratio. Thereby, the polarization resistance at 800 ° C. can be greatly reduced.

  In the above invention, the highly conductive oxide is preferably at least one of lanthanum-doped strontium titanate and strontium doped lanthanum chromite.

Lanthanum-doped strontium titanate (Sr _1-m La _m TiO ₃ ) and strontium doped lanthanum chromite (La _1-n Sr _n CrO ₃ ) are oxides that exhibit high electronic conductivity in a reducing atmosphere. By using the second layer containing a mixture of NiO and these oxides, the conductivity of the fuel side electrode can be improved.

  In the said invention, it is preferable that the mixing ratio of the said NiO and the said highly conductive oxide exists in the range of 40:60 to 80:20 by mass ratio. If it is the said mixing ratio, it is possible to ensure sufficient electroconductivity also at 800 degreeC.

The present invention also provides a solid oxide fuel cell comprising the above power generation membrane.
The power generation film of the present invention exhibits high conductivity while reducing polarization resistance and obtaining high reaction activity. Therefore, in the solid oxide fuel cell including the above-described power generation membrane, power generation characteristics are greatly improved.

  By using the two-layer fuel side electrode as described above, the polarization resistance at the fuel side electrode at 800 ° C. can be reduced, and the conductivity of the fuel side electrode can be improved. Thereby, it can be set as the electric power generation film | membrane with high reaction activity in a fuel side electrode. Therefore, the solid oxide fuel cell including the power generation membrane of the present invention can improve power generation characteristics.

It is the schematic which shows an example of a solid oxide fuel cell. It is the schematic of the electric power generation film | membrane of the solid oxide fuel cell which concerns on this invention. And Ce _{1-x Gd} x _{O Gd} content in ₂ is a graph showing the relationship between the conductivity of the oxygen atmosphere or a reducing atmosphere at 800 ° C..

Hereinafter, embodiments of the present invention will be described.
FIG. 2 is a cross-sectional view of the power generation membrane of the solid oxide fuel cell according to this embodiment. In the power generation film 10 of FIG. 2, lanthanum strontium manganese oxide (La _(1-y) Sr _y ) _z MnO ₃ (LSM) is formed on one surface of a flat solid electrolyte 1 made of yttria-stabilized zirconia (YSZ). An air side electrode 3 made of a composite of YSZ and YSZ is formed. On the other surface of the solid electrolyte 1, a fuel side electrode 2 in which a first layer 2 a and a second layer 2 b are laminated in order from the solid electrolyte 1 side is formed.

The first layer 2 a includes a mixture of NiO and a doped ceria compound represented by Ce _1-x Ln _x O ₂ (Ln: Gd or Tm, 0.03 ≦ x ≦ 0.5).

Table 1 shows the conductivity in hydrogen gas at 800 ° C. for Ce _0.8 Ln _0.2 O _{2 in} which the dopant (Ln) is changed. A sample for conductivity measurement was obtained by synthesizing a powder having a composition represented by Ce _0.8 Ln _0.2 O ₂ by a powder mixing method and sintering it at 1500 ° C. for 4 hours. The conductivity was measured by a direct current four-terminal method. The conductivity of YSZ in 800 ° C. hydrogen gas is 0.05 S / cm.
Even if any element was used as a dopant, the conductivity was improved from that of YSZ. Particularly high electrical conductivity was obtained when Gd or Tm was used as a dopant.

FIG. 3 shows the amount of Gd (x value) in a compound represented by Ce _1-x Gd _x O ₂ and the conductivity in an oxidizing atmosphere (in air) or reducing atmosphere (in hydrogen gas) at 800 ° C. The graph showing the correlation of is shown. In the figure, the horizontal axis represents the amount of Gd, and the vertical axis represents the conductivity in the oxidizing atmosphere (main axis) and the conductivity in the reducing atmosphere (second axis). The conductivity measurement sample was prepared by synthesizing a powder having a composition represented by Ce _1-x Gd _x O ₂ (0 ≦ x ≦ 0.5) by a powder mixing method (width 4 mm, length 20 mm, height 3 mm). And then sintered under the condition of 1500 ° C. for 4 hours. The conductivity was measured by a direct current four-terminal method.
The conductivity in the oxidizing atmosphere (air) is mainly oxygen ion conduction, and the conductivity in the reducing atmosphere (hydrogen gas) is mainly electron conduction. From the viewpoint of electrode characteristics, the higher the conductivity of both the oxidizing atmosphere and the reducing atmosphere, the higher the reaction activity. As shown in FIG. 3, the conductivity in the oxidizing atmosphere increased rapidly after increasing rapidly from the Gd amount x = 0.03. At x = 0.3 or more, it was almost constant. The conductivity in the reducing atmosphere increased with increasing Gd amount up to x = 0.05, and gradually decreased when exceeding x = 0.05. From the result of FIG. 3, in order to obtain high conductivity in both the oxidizing atmosphere and the reducing atmosphere, the Gd amount in the compound represented by Ce _1-x Gd _x O ₂ is 0.03 ≦ x ≦ 0.5. Preferably, 0.03 ≦ x ≦ 0.1.

Thus, since the compound represented by Ce _1-x Gd _x O ₂ or Ce _1-x Tm _x O ₂ having the above composition has high conductivity in an oxidizing atmosphere and a reducing atmosphere, polarization at the fuel side electrode Resistance can be reduced and high activity is achieved.

However, Ce _1-x Gd _x O ₂ or Ce _1-x Tm _x O ₂ has lower electronic conductivity than Ni (NiO is reduced in hydrogen gas). For this reason, if the ratio of the doped ceria compound in the first layer is large, the polarization resistance increases, and the power generation performance when a solid oxide fuel cell is obtained is lowered. Therefore, the mixing ratio of NiO and the doped ceria compound is in the range of 20:80 to 60:40, preferably 40:60 to 50:50 by mass ratio.

The second layer 2b has higher conductivity in a reducing atmosphere than NiO and a doped ceria compound represented by Ce _1-x Ln _x O ₂ (Ln: Gd or Tm, 0.03 ≦ x ≦ 0.5). Includes a mixture with an oxide (high conductivity oxide).
As shown in Table 1, the electrical conductivity of Ce _0.8 Gd _0.2 O ₂ and Ce _0.8 Tm _0.2 O ₂ is 1.6 S / cm and 1.1 S / cm, respectively. Since conductivity suitable as an electrode material is required to be 100 S / cm or more, the conductivity is insufficient only with the above-described doped ceria compound. Therefore, the conductivity of the entire fuel-side electrode is improved by forming a second layer containing a mixture of a highly conductive oxide having high electron conductivity in a reducing atmosphere and NiO.

The highly conductive oxide is, for example, lanthanum-doped strontium titanate (Sr _1-m La _m TiO ₃ ) or strontium doped lanthanum chromite (La _1-n Sr _n CrO ₃ ).
The highly conductive oxide is inferior in electronic conductivity as compared with Ni. Therefore, if the ratio of the highly conductive oxide in the second layer is large, the polarization resistance increases, and the power generation performance when a solid oxide fuel cell is obtained decreases. Therefore, the mixing ratio of NiO and highly conductive oxide is 40:60 to 80:20, preferably 60:40 to 70:30 in terms of mass ratio.

Example 1
A 10 mol% Sc ₂ O ₃ −1 mol% CeO ₂ stabilized zirconia flat plate (diameter 30 mm, thickness 200 μm) was prepared as a solid electrolyte. On one side of the solid electrolyte, mixed powder of LSM (La _0.8 Sr _0.2 MnO ₃ ) / YSZ (8 mol% Y ₂ O ₃ stabilized zirconia) = 80: 20 (mass ratio) and solvent (ethanol) The mixed solution was applied with a diameter of 10 mm. Then, it baked on 1300 degreeC and the conditions for 4 hours, and produced the half cell which formed the air side electrode.

As a fuel-side electrode material, Ce _0.95 Gd _0.05 O ₂ (Gd-doped ceria, hereinafter referred to as GDC) powder having a particle size of 0.1 μm was synthesized by a powder mixing method. A mixed liquid of NiO: GDC = 50: 50 (mass ratio) mixed powder and solvent (ethanol) is applied to the surface of the solid electrolyte opposite to the air side electrode in a size of 10 mm in diameter, and the fuel side electrode The first layer of was formed. The coating amount was adjusted so that the thickness of the first layer after drying was 10 μm.
After drying the first layer, a mixed solution of NiO: SLT (lanthanum-doped strontium titanate, Sr _0.7 La _0.3 TiO ₃ ) = 70: 30 (mass ratio) and a solvent (ethanol) has a diameter of 10 mm. The second layer of the fuel side electrode was formed on the first layer. The coating amount was adjusted so that the thickness of the second layer after drying was 50 μm.
After drying the second layer, the solid electrolyte was baked at 1250 ° C. for 4 hours to obtain a power generation film of Example 1.

(Example 2)
Under the same conditions as in Example 1, an air-side electrode and a fuel-side electrode first layer were formed on the solid electrolyte.
After drying the first layer, a mixed solution of NiO: LSC (strontium dope lanthanum chromite, La _0.7 Sr _0.3 CrO ₃ ) = 70: 30 (mass ratio) and solvent (ethanol) has a diameter of 10 mm. The second layer of the fuel side electrode was formed on the first layer. The coating amount was adjusted so that the thickness of the second layer after drying was 50 μm.
After drying the second layer, the solid electrolyte was fired at 1250 ° C. for 4 hours to obtain a power generation film of Example 2.

(Comparative example)
A half cell was manufactured under the same conditions as in Example 1.
A mixed liquid of mixed powder of NiO: YSZ = 70: 30 (mass ratio) and solvent (ethanol) is applied to the surface of the solid electrolyte opposite to the air side electrode in a size of 10 mm in diameter, and the fuel side electrode Formed. The coating amount was adjusted so that the film thickness of the fuel side electrode after drying was 80 μm.
After drying the fuel side electrode, the solid electrolyte was fired at 1300 ° C. for 4 hours to obtain a comparative power generation film.

表２に示すように、２層構造とした実施例１及び実施例２では、８００℃での分極抵抗が比較例の１／３〜１／２程度に低減した。 A platinum electrode for a power generation test was attached to the power generation films of Example 1, Example 2, and Comparative Example 1, and the IR resistance and polarization resistance of the fuel side electrode at 800 ° C. were measured. Table 2 shows the IR resistance and polarization resistance at 0.7V.

As shown in Table 2, in Example 1 and Example 2 having a two-layer structure, the polarization resistance at 800 ° C. was reduced to about 1/3 to 1/2 of the comparative example.

(Example 3)
A half cell was manufactured under the same conditions as in Example 1.
As a fuel-side electrode material, a particle size of _{0.1μm Ce 1-x Gd x O} 2 (x = 0~0.5) powders were synthesized by a powder mixing method. About GDC of each composition, NiO: GDC = 50: 50 (mass ratio) mixed powder was prepared. A mixed liquid of each mixed powder and a solvent (ethanol) was applied to the surface of the solid electrolyte opposite to the air side electrode in a size of 10 mm in diameter to form the first layer of the fuel side electrode. The coating amount was adjusted so that the thickness of the first layer after drying was 10 μm.
After drying the first layer, a second layer was formed in the same manner as in Example 1. Then, the solid electrolyte was baked on the same conditions as Example 1, and each power generation film was obtained.

表３に示すように、Ｇｄドープ量が０．０３原子％から０．５原子％の範囲で、比較例１の分極抵抗に比べて、低い分極抵抗が得られた。特に、Ｇｄドープ量０．０３原子％から０．１原子％の範囲で、分極抵抗が大幅に低下した。 A platinum electrode for power generation test was attached to each power generation membrane, and the polarization resistance of the fuel side electrode at 800 ° C. was measured. Table 3 shows the polarization resistance at 0.7V.

As shown in Table 3, when the Gd doping amount was in the range of 0.03 atomic% to 0.5 atomic%, a low polarization resistance was obtained as compared with the polarization resistance of Comparative Example 1. In particular, the polarization resistance was significantly reduced when the Gd doping amount was in the range of 0.03 atomic% to 0.1 atomic%.

Example 4
Each power generation membrane was obtained in the same manner as Example 3 except that the fuel-side electrode material of the first layer was Ce _1-x Tm _x O ₂ (x = 0 to 0.5).

表４に示すように、Ｔｍドープ量が０．０５原子％から０．５原子％の範囲で、比較例１の分極抵抗に比べて、低い分極抵抗が得られた。特に、Ｇｄドープ量０．０５原子％から０．１原子％の範囲で、分極抵抗が大幅に低下した。なお、Ｔｍドープ量０．０３原子％においても、実施例３と同様に、低い分極抵抗が得られることは容易に推測できる。 A platinum electrode for power generation test was attached to each power generation membrane, and the polarization resistance of the fuel side electrode at 800 ° C. was measured. Table 4 shows the polarization resistance at 0.7V.

As shown in Table 4, when the Tm doping amount was in the range of 0.05 atomic% to 0.5 atomic%, a lower polarization resistance was obtained compared to the polarization resistance of Comparative Example 1. In particular, the polarization resistance was significantly reduced when the Gd doping amount was in the range of 0.05 atomic% to 0.1 atomic%. It can be easily estimated that a low polarization resistance can be obtained even at a Tm doping amount of 0.03 atomic%, as in Example 3.

(Example 5)
A half cell was produced in the same manner as in Example 1.
As a fuel-side electrode material, Ce _0.95 Gd _0.05 O ₂ powder having a particle size of 0.1 μm was synthesized by a powder mixing method. A mixed powder in which NiO and GDC powder having the above composition were mixed at a mass ratio of 10:90 to 80:20 was prepared. On the surface of the solid electrolyte opposite to the air-side electrode, a mixed liquid of mixed powder and solvent (ethanol) with each mixing ratio was applied in a size of 10 mm in diameter to form the first layer of the fuel-side electrode. The coating amount was adjusted so that the thickness of the first layer after drying was 10 μm.
After drying the first layer, a second layer was formed in the same manner as in Example 1. Then, the solid electrolyte was baked on the same conditions as Example 1, and each power generation film was obtained.

以上の結果から、ＮｉＯ：ＧＤＣを２０：８０〜６０：４０（質量比）とすることにより、８００℃での分極抵抗を低下させることができた。特に、ＮｉＯ：ＧＤＣ＝４０：６０から５０：５０の範囲内で、分極抵抗を大幅に低減することができた。 A platinum electrode for power generation test was attached to each power generation membrane, and the polarization resistance of the fuel side electrode at 800 ° C. was measured. Table 5 shows the polarization resistance at 0.7V.

From the above results, the polarization resistance at 800 ° C. could be reduced by setting NiO: GDC to 20:80 to 60:40 (mass ratio). In particular, the polarization resistance could be greatly reduced within the range of NiO: GDC = 40: 60 to 50:50.

(Example 6)
A mixed powder in which NiO and SLT (Sr _0.7 La _0.3 TiO ₃ ) were mixed at a mass ratio of 20:80 to 80:20 was prepared. A mixed powder of each mixing ratio was formed into a rectangular parallelepiped having a width of 4 mm, a length of 20 mm, and a height of 3 mm, and sintered at 1500 ° C. for 4 hours to obtain a sample for measuring conductivity.

(Comparative Example 2)
A mixed powder in which NiO and YSZ were mixed at a mass ratio of 16.2: 83.8 to 63.5: 36.5 was prepared. A mixed powder of each mixing ratio was formed into a rectangular parallelepiped having a width of 4 mm, a length of 20 mm, and a height of 3 mm, and sintered at 1500 ° C. for 4 hours to obtain a sample for measuring conductivity.

For the sample of Example 6, the conductivity in hydrogen gas at 800 ° C., 900 ° C. and 1000 ° C. was measured. Further, the conductivity of the sample of Comparative Example 2 in hydrogen gas at 800 ° C. was measured. The conductivity was measured by a direct current four-terminal method. The results of Example 6 are shown in Table 6, and the results of Comparative Example 2 are shown in Table 7.

  As shown in Table 6, in Example 6 (NiO / SLT), the conductivity was almost the same even when the temperature was changed. In Comparative Example 2 (NiO / YSZ), the electrical conductivity significantly decreased as the NiO ratio decreased. In particular, the conductivity was very low when NiO was 40% by mass or less. On the other hand, Example 6 showed high conductivity even when NiO was 40% by mass or less.

  Thus, since NiO / SLT shows higher conductivity than NiO / YSZ, the power generation characteristics of the solid oxide fuel cell are greatly improved by applying NiO / SLT to the second layer of the fuel side electrode. Can be made.

DESCRIPTION OF SYMBOLS 1 Solid electrolyte 2 Fuel side electrode 2a 1st layer 2b 2nd layer 3 Air side electrode 4,5 Conductive joining material 6,7 Interconnector 10 Power generation film

Claims (4)

A power generation membrane of a solid oxide fuel cell having a solid electrolyte, an air-side electrode provided on one side of the solid electrolyte, and a fuel-side electrode provided on the other side,
The fuel side electrode, in order from the solid electrolyte side,
A first layer comprising a mixture of NiO and Ce _1-x Ln _x O ₂ (Ln: Gd or Tm, 0.03 ≦ x ≦ 0.5);
A second layer comprising a mixture of NiO and a highly conductive oxide having a conductivity higher than that of Ce _1-x Ln _x O ₂ in a reducing atmosphere ;
The power generation film of a solid oxide fuel cell, wherein the highly conductive oxide is at least one of lanthanum-doped strontium titanate and strontium doped planan chromite . _2. The power generation membrane of a solid oxide fuel cell according to claim 1, wherein a mixing ratio of the NiO and the Ce _1-x Ln _x O ₂ is in a range of 20:80 to 60:40 by mass ratio. 2. The power generation membrane of a solid oxide fuel cell according to claim 1 , wherein a mixing ratio of the NiO and the highly conductive oxide is within a range of 40:60 to 80:20 by mass ratio. A solid oxide fuel cell comprising the power generation film according to any one of claims 1 to 3 .

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