JP5330849B2 - Conductive bonding material and solid oxide fuel cell having the same - Google Patents

Description

  The present invention relates to a bonding material used when an electrode of a solid oxide fuel cell and another structural member are electrically bonded, and a solid oxide fuel cell having the bonding member.

  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.

Patent Document 1 includes NiO, Fe ₂ O ₃ and TiO ₂ as the conductive bonding material 4 on the fuel side electrode 2 side, and further suppresses thermal shrinkage during sintering and shrinkage due to reduction of NiO A conductive bonding material to which Al ₂ O ₃ is added is disclosed.

  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. Is a problem.

JP 2005-174585 A

Since the conductive bonding material described in Patent Document 1 contains Al ₂ O ₃ that is an insulator, it has been a cause of reducing the conductivity of the bonding material. Along with the lowering of the operating temperature of the solid oxide fuel cell, it has been required to improve the power generation performance by improving the fuel electrode side electrode material and improving the conductivity of the fuel side conductive bonding material. .

  This invention is made | formed in view of such a situation, Comprising: It aims at providing the electroconductive joining material of the fuel side electrode which shows high electroconductivity, and a solid oxide fuel cell provided with the same .

In order to solve the above problems, the conductive bonding material of the present invention is selected from the group consisting of NiO, Fe ₂ O ₃ , TiO ₂ , lanthanum-doped strontium titanate, strontium doped lanthanum chromite, and strontium vanadate. And one or more conductive oxides.

Lanthanum-doped strontium titanate (Sr _1-m La _m TiO ₃ ), strontium doped lanthanum chromite (La _1-n Sr _n CrO ₃ ), and strontium vanadate (SrVO ₃ ) are stable oxides in a reducing atmosphere. In addition, it exhibits high electronic conductivity in a reducing atmosphere at 800 ° C., which is a low temperature operation condition of the solid oxide fuel cell. Specifically, the electron conductivity in a reducing atmosphere at 800 ° C. is about 0 S / cm in the conventional Al ₂ O ₃ , whereas it is 30 to 50 S / cm in the strontium doped planan chromite, for example. Therefore, the conductive bonding material of the present invention containing the conductive oxide has improved conductivity in a reducing atmosphere at, for example, 800 ° C., compared to the conventional conductive bonding material.

In the above invention, the conductive oxide is any one selected within a range of 10% by mass to 20% by mass with respect to the total of the NiO, the Fe ₂ O ₃ and the TiO _2. you a proportion of.

  The conductive bonding material of the present invention contains the conductive oxide in a proportion of 10% by mass or more and 20% by mass or less, thereby preventing volumetric shrinkage due to reduction of NiO and reduction in bonding strength due to decrease in sinterability. Can do.

  In the above invention, the conductive oxide is preferably made from a particulate conductive oxide having an average particle size of 5 μm or more and 15 μm or less.

  When a conductive bonding material is formed from a conductive oxide having an average particle size of less than 5 μm, the shrinkage rate during sintering increases. For this reason, a crack arises in an electroconductive joining material, and joining strength falls. On the other hand, when the conductive bonding material is formed from a conductive oxide having an average particle size exceeding 15 μm, the sinterability is lowered. For this reason, the joint strength between the fuel-side electrode and the interconnector decreases. By setting the average particle size of the particulate conductive oxide used as a raw material to 5 μm or more and 15 μm or less, a conductive bonding material having excellent conductivity and bonding strength can be obtained.

  The solid electrolyte fuel cell of the present invention includes a solid electrolyte, a power generation membrane having an air-side electrode provided on one side of the solid electrolyte, and a fuel-side electrode provided on the other side; An interconnector joined to the fuel side electrode is provided via a conductive joining material.

  The solid oxide fuel cell of the present invention includes a conductive bonding material having excellent conductivity and high bonding strength on the fuel side electrode side. For this reason, since the junction resistance is low even during operation at low temperatures, the power generation characteristics at low temperatures are excellent. Moreover, peeling of the power generation film and the interconnector during operation is prevented, and a solid oxide fuel cell having excellent durability is obtained.

  According to the present invention, since it is a conductive bonding material containing lanthanum-doped strontium, strontium doped lanthanum chromite, and strontium vanadate that is stable in a reducing atmosphere and exhibits high electronic conductivity, it is a solid electrolyte type even at an operation of about 800 ° C. The power generation characteristics can be improved by reducing the junction resistance of the fuel cell.

It is the schematic which shows an example of a solid oxide fuel cell. It is the schematic explaining the method to measure the joint strength of a power generation film and an interconnector.

The conductive bonding material and the solid oxide fuel cell according to this embodiment will be described below.
The solid oxide fuel cell of this embodiment has the configuration shown in FIG. The power generation membrane 10 includes a solid electrolyte membrane 1 made of yttria-stabilized zirconia, and a fuel side electrode 2 and an air side electrode 3 formed on both surfaces thereof. The power generation film 10 has a dimple shape. An interconnector 6 that is electrically connected to the fuel side electrode 2 via the conductive bonding material 4 is provided on the fuel side electrode 2 side of the power generation membrane 10.

In the present embodiment, the conductive bonding material 4 provided on the fuel side electrode 2 side contains NiO, Fe ₂ O ₃ , TiO _2, and a conductive oxide. The conductive oxide is at least one selected from lanthanum-doped strontium titanate (Sr _1-m La _m TiO ₃ ), strontium doped lanthanum chromite (La _1-n Sr _n CrO ₃ ), and strontium vanadate (SrVO ₃ ). It is said. The listed conductive oxides are stable in a reducing atmosphere and exhibit high electronic conductivity. In particular, lanthanum-doped strontium titanate is preferable because it has excellent heat resistance.

The solid oxide fuel cell of FIG. 1 is manufactured by the following steps.
First, as the conductive bonding material raw material, NiO powder, _Fe 2 _{O 3} powder, mixing TiO ₂ powder, and the conductive oxide powder (particle shape). A vehicle is added to the mixed powder and kneaded to prepare a bonding material paste. As the vehicle, butyl carbitol, turpentine oil, butanol or the like can be used.

  The above bonding material paste is uniformly applied to a thickness of 100 μm to 200 μm on one surface of the interconnector 6 provided on the fuel side electrode 2 side by a screen printing method or the like. Then, the dimple-shaped power generation film 10 is arranged on the applied bonding material paste so that the fuel-side electrode 2 is in contact therewith.

  In the solid oxide fuel cell according to the present embodiment, an interconnector 7 electrically connected to the air-side electrode 3 through the conductive bonding material 5 is provided on the air-side electrode 3 side of the power generation membrane 10. An air-side electrode bonding material paste is uniformly applied to a thickness of 100 μm to 200 μm on one surface of the interconnector 7 provided on the air-side electrode 3 side. In this embodiment, strontium dope plantan manganate is used for the air-side electrode bonding material paste. And the interconnector 7 is arrange | positioned so that the bonding material paste for air side electrodes may contact | connect an air side electrode.

  Thereafter, heat treatment is performed in the atmosphere at a temperature of 1200 ° C. to 1300 ° C. By this heat treatment, the raw material powder is sintered, and the power generation film 10 and the interconnectors 6 and 7 are joined by the conductive joining materials 4 and 5, respectively.

Here, in the conductive bonding material of the fuel side electrode of the present embodiment, Fe ₂ O ₃ and TiO ₂ have the effect of improving the strength of the conductive bonding material 4 by firing. In consideration of conductivity and strength, the conductive bonding material of the present embodiment contains NiO: 70 to 90% by mass, Fe ₂ O ₃ : 5 to 15% by mass, TiO ₂ : 5 to 15% by mass. It is preferable.

The conductive bonding material of this embodiment preferably contains the conductive oxide in a proportion of 10% by mass or more and 20% by mass or less with respect to the total of NiO, Fe ₂ O ₃ and TiO ₂ .
NiO shrinks in volume when reduced to Ni in a reducing atmosphere. The conductive oxide has an effect of suppressing volume shrinkage of the conductive bonding material due to reduction of NiO. By containing the above-mentioned conductive oxide at a ratio of 10% by mass or more with respect to the total of NiO, Fe ₂ O ₃ and TiO _2, it is possible to reduce the bonding strength of the conductive bonding material due to the reduction shrinkage of NiO. Can be prevented.
On the other hand, when the content of the conductive oxide exceeds 20% by mass, the sinterability of the bonding material is lowered, so that the bonding strength is lowered. In addition, since the conductive oxide is inferior in electron conductivity in a reducing atmosphere at 800 ° C. compared to Ni, when the ratio of the conductive oxide to NiO is relatively large, the conductivity of the bonding material is lowered.

Moreover, it is preferable that the particulate conductive oxide powder as a raw material has an average particle diameter of 5 μm or more and 15 μm or less.
When the average particle diameter of the conductive oxide raw material powder is smaller than 5 μm, the shrinkage rate during sintering increases. For this reason, a crack arises in an electroconductive joining material, and the adhesiveness (namely, joining strength) of a power generation film and an interconnector falls. In addition, the conductive oxide particles can easily enter between the Ni particles and be filled. Since the conductive oxide has a lower electronic conductivity in the reducing atmosphere than Ni, the conductive oxide that has entered between the Ni particles hinders the conductivity and decreases the conductivity of the sintered joint material after sintering. To do. On the other hand, when the average particle diameter of the conductive oxide raw material powder exceeds 15 μm, the sinterability is lowered, and the bonding strength between the fuel side electrode and the interconnector is lowered.

Example 1
NiO powder (particle size 1 μm), Fe ₂ O ₃ powder (particle size 1 μm), TiO ₂ powder (particle size 1 μm), and SLT powder (Sr _0.7 La _0.3 TiO ₃ , particle size 10 μm) : Fe ₂ O ₃ : TiO ₂ : SLT = 80: 10: 10: 15 (mass ratio). A vehicle (butyl carbitol) was added to the mixed powder and kneaded to prepare a bonding material paste.
The bonding material paste was applied to the surface of the 20 mm square interconnector with a thickness of 150 μm by screen printing. The fuel electrode side of a 20 mm square dimple-shaped power generation film was placed on the bonding material paste. In Example 1, solid electrolyte: yttria stabilized zirconia, fuel side electrode: NiO: YSZ = 70: 30, air side electrode: LSM: YSZ = 80: 20 (where LSM is La _0.8 Sr _{0. 2 A} power generation film composed of 2MnO ₃ ) was used.
It heat-processed in air | atmosphere 1250 degreeC for 1 hour, the joining material paste was sintered, the electric power generation film | membrane and the interconnector were joined by the electroconductive joining material, and it was set as the test piece.

After the heat treatment, terminals were attached to the surface of the power generation film not coated with the conductive bonding material and the surface of the interconnector not coated with the conductive bonding material using a platinum paste and a platinum wire. The terminals were arranged so as to be diagonal to each other. Thereafter, the platinum terminal was baked on the power generation film and the interconnector at 1000 ° C. in an air atmosphere.
A constant current generator and a voltmeter were connected to each terminal. The test piece was heated to 800 ° C. in air in an electric furnace. After the temperature rise, 100% by volume H ₂ was introduced into the electric furnace for reduction treatment, and the bonding resistance of the conductive bonding material was measured by a direct current four-terminal method.

(Example 2)
A test piece was prepared in the same manner as in Example 1 except that LSC powder (La _0.7 Sr _0.3 CrO ₃ , particle size 10 μm) was used instead of STL, and the bonding resistance of the conductive bonding material was determined. It was measured.

(Example 3)
A test piece was prepared in the same manner as in Example 1 except that SrVO ₃ powder (particle size 10 μm) was used instead of STL, and the bonding resistance of the conductive bonding material was measured.

(Comparative example)
A test piece was prepared in the same manner as in Example 1 except that Al ₂ O ₃ powder (particle size: 10 μm) was used instead of STL, and the bonding resistance of the conductive bonding material was measured.

実施例１乃至実施例３の導電性接合材は、比較例の導電性接合材よりも還元雰囲気での接合抵抗を低減させることができた。還元雰囲気での接合抵抗と高温での安定性とを考慮すると、ＳＬＴを含む導電性接合材が最も好適と考えられた。 Table 1 shows the bonding resistance of the conductive bonding materials of Examples 1 to 3 and the comparative example.

The conductive bonding materials of Examples 1 to 3 were able to reduce the bonding resistance in a reducing atmosphere as compared with the conductive bonding material of the comparative example. Considering the bonding resistance in a reducing atmosphere and the stability at high temperature, it was considered that a conductive bonding material containing SLT is most suitable.

Example 4
Using SLT powders (Sr _0.7 La _0.3 TiO ₃ , particle size of 1 to 30 μm) having different particle sizes, test pieces were prepared in the same process as in Example 1. Each test piece was subjected to reduction treatment at 1000 ° C. in a 4% H ₂ —N ₂ balance atmosphere.

With respect to each test piece, the bonding strength between the power generation film and the interconnector after the heat treatment in the air atmosphere and after the reduction treatment was measured by the following method. FIG. 2 is a diagram for explaining a bonding strength measuring method.
The surface of the interconnector 6 where the conductive bonding material 4 and the power generation film 10 are not bonded was bonded to the acrylic plate 8 with an adhesive. As shown in FIG. 2, a container 9 capable of accommodating a weight was attached to a dimple-shaped power generation film 10. The weight (zirconia ball having a diameter of 5 mm) is gradually put into the container 9, and the total weight of the weight when peeled between the interconnector and the conductive bonding material or between the conductive bonding material and the power generation film is calculated. The bonding strength was used.

ＳＬＴ粒径５〜１５μｍの導電性接合材は、還元処理後も高い接合強度を示した。特に、ＳＬＴ粒径１０〜１５μｍである導電性接合材は、還元処理後の接合強度２０００ｇ以上と、十分な強度が得られた。 Table 2 shows the bonding strength of the conductive bonding materials having different SLT particle sizes after firing (heat treatment) in air and after reduction treatment.

The conductive bonding material having an SLT particle size of 5 to 15 μm showed high bonding strength even after the reduction treatment. In particular, the conductive bonding material having an SLT particle size of 10 to 15 μm has a sufficient bonding strength of 2000 g or more after the reduction treatment.

(Example 5)
The same NiO powder, Fe ₂ O ₃ powder, TiO ₂ powder, and SLT powder as in Example 1 were mixed with NiO: Fe ₂ O ₃ : TiO ₂ : SLT = 80: 10: 10: 5 to 30 (mass ratio). Mixed. Using mixed powders having different SLT mixing ratios, each bonding material paste was prepared in the same manner as in Example 1 to obtain test pieces.
About each test piece, the reduction process was implemented by the method similar to Example 4, and the joint strength after a reduction process was measured.

このように、ＳＬＴ比率１０〜２０質量％において、還元処理後の接合強度２０００ｇ以上と、十分な強度が得られた。 Table 3 shows the bonding strength after reduction treatment of conductive bonding materials having different SLT mixing ratios.

Thus, in the SLT ratio of 10 to 20% by mass, a sufficient strength of 2000 g or more after the reduction treatment was obtained.

DESCRIPTION OF SYMBOLS 1 Solid electrolyte 2 Fuel side electrode 3 Air side electrode 4,5 Conductive joining material 6,7 Interconnector 8 Acrylic board 9 Container 10 Power generation film

Claims (3)

Containing one or more conductive oxides selected from the group consisting of NiO, Fe ₂ O ₃ , TiO ₂ , lanthanum-doped strontium titanate, strontium doped lanthanum chromite, and strontium vanadate ,
The conductive oxide is contained in any one ratio selected within a range of 10% by mass or more and 20% by mass or less with respect to the total of the NiO, the Fe ₂ O ₃ and the TiO _2. Conductive bonding material. The conductive bonding material according to claim 1, wherein the conductive oxide is made from a particulate conductive oxide having an average particle diameter of 5 μm or more and 15 μm or less. A power generation membrane 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;
Through the conductive bonding material according to claim 1 or claim 2, the solid electrolyte fuel cell comprising a interconnector and which is bonded to the fuel side electrode.

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