JPH10144337A - Fuel electrode of solid electrolytic fuel cell and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel electrode having an electrode structure in which a large quantity of three-phase interface is present and a metal is hardly sintered and high electrode catalytic activity can be obtained even in the case a small amount of the metal is used, and provide a method to produce such a fuel electrode. SOLUTION: In a fuel electrode of a solid electrolytic fuel cell constituted of an oxide 3 having oxygen ion conductivity and a metal 4 having an electrode activity, the metal 4 is made to be adsorbed on the surface of the oxide 3. Consequently, the three-phase interface where the metal 4, the oxide 3, and a fuel gas are brought into contact is extremely increased and an electrode with low voltage decrease following an electrode reaction and having excellent output performance can be obtained. Moreover, since fine particles of the metals are strongly restricted by the oxide powder, sintering of the fine particles of the metal hardly occurs and as a result, an electrode having stability for a long time and scarcely deteriorated with the lapse of time can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel electrode for a solid oxide fuel cell and a method for producing the same, and more particularly, to a solid oxide fuel cell (Solid Oxide Fuel, Ce).
11 (hereinafter abbreviated as SOFC) and a method for producing the same.

[0002]

2. Description of the Related Art SOFC is a general term for a fuel cell which generates electricity by supplying two kinds of gases, an oxidant and a fuel, to an oxidant electrode and a fuel electrode, and uses a solid substance for all constituent materials. In the SOFC, the following ceramics are frequently used, and the SOFC is usually operated at a temperature around 1000 ° C.

Electrolyte: Yttria stabilized zirconia (YSZ) Fuel electrode: Nickel zirconia cermet (Ni-Y)
SZ) Oxidizing agent electrode: Lanthanum manganite (LSM)

Here, Ni is frequently used as the metal of the fuel electrode because Ni is excellent in stability against YSZ and is excellent in sulfur resistance when coal gas is used as fuel. . As a technique for producing a fuel electrode at low cost, a technique of mixing YSZ powder or NiO powder, which is a raw material, with a ball mill or the like, applying the paste to an electrolyte as a paste, and sintering is used.

[0005] The fuel electrode has a role as a catalyst for reacting the fuel gas and the oxidizing agent, and the electrode reaction field is a three-phase interface where Ni, YSZ and the fuel gas are in contact. . Therefore, increasing the three-phase interface leads to improvement in the output characteristics of the SOFC. further,
Increasing the conductivity of the electrode itself leads to an improvement in the output characteristics of the SOFC. Therefore, NiO powder and YSZ
Consider increasing the three-phase interface by adjusting the particle size and particle size ratio of the powder to highly disperse the Ni and YSZ particles, or increasing the conductivity by adjusting the mixing ratio of the NiO powder and the YSZ powder. Has been performed conventionally.

[0006]

However, an SOFC is composed of the fuel electrode manufactured as described above,
When the fuel electrode is operated at a temperature around 0 ° C., as the operating time of the fuel electrode elapses, the agglomeration of the electrode proceeds due to sintering of Ni particles, which causes a decrease in the three-phase interface and an increase in the electrode resistance. There is a problem that it decreases.

As a method for solving this problem, the use of another metal which has the same catalytic activity as Ni and does not easily undergo sintering at a temperature near 1000 ° C. has been studied. For example,
In ruthenium zirconia cermet (Ru-YSZ) using Ru as an electrode metal, an electrode having no deterioration over time due to sintering is obtained. However, the catalytic ability is excellent,
In addition, metals that are unlikely to be sintered even at a temperature around 1000 ° C. are limited to expensive noble metals. Therefore, if the powder is adjusted by a conventional method of mixing the powder, there is a problem that the cost is increased due to an increase in the amount of the noble metal used, and the practicability is poor.

The present invention provides a structure and a method for producing a fuel electrode which has an electrode structure having a large number of three-phase interfaces and in which metal is difficult to be sintered, and which can obtain an electrocatalytic activity even when a small amount of the metal is used. To overcome the disadvantages of the fuel electrode.

[0009]

(First Means) The present invention relates to an electrode structure for a solid oxide fuel cell, which comprises a yttria-stabilized zirconia (YS)
Z), partially stabilized zirconia (PSZ), samarium-doped ceria (SDC), etc. on the oxide surface, Ni, Ru, C
It is characterized by carrying a metal such as o and making it a sintered body.

(Second Means) According to the present invention, there is provided an electrode structure of a solid oxide fuel cell, wherein yttria-stabilized zirconia (YSZ) supporting a metal such as Ni, Ru, Co, etc., partially stabilized zirconia (PSZ), An oxide powder such as Samaria dove ceria (SDC) and a metal powder such as Mo, W and Pt which do not sinter even at the operating temperature of the fuel cell are dispersed in the sintered body.

(Third Means) The present invention is characterized in that the oxide powder supporting a metal described in the first and second means of the solid oxide fuel cell is a sintered body. In the method for producing an electrode, yttria-stabilized zirconia (YSZ) and partially stabilized zirconia (PS
Z), an oxide powder such as Samaria-doped ceria (SDC) is immersed in an aqueous solution containing metal ions such as Ni, Ru, Co, etc., and dried to form Ni (NO) on the surface of the oxide powder.
_{3) 2,} RuCl _2, is supported in a state of CoSO metal compound such as _4, further Ni by heat treatment, Ru, it is supported in a metal state such as Co, characterized in that the electrode as a raw material.

(Fourth Means) According to the present invention, there is provided a solid oxide fuel cell wherein the oxide powder supporting a metal described in the second means is a sintered body, and the operating temperature of the fuel cell is However, in a method for producing an electrode, wherein a metal powder that is not sintered is dispersed in a sintered body, an oxide powder having a metal supported on a surface is produced by the process shown in the third means, Next, a metal powder such as Mo, W, or Pt that does not sinter even at the operating temperature of the fuel cell is mixed with the oxide powder, and this mixture is used as a raw material to form an electrode.

(Fifth Means) According to the present invention, there is provided a solid oxide fuel cell wherein the oxide powder supporting a metal described in the second means is a sintered body, and the operating temperature of the fuel cell is A method for producing an electrode, characterized in that non-sintered metal powder is dispersed in a sintered body, wherein the yttria-stabilized zirconia (YSZ), the partially stabilized zirconia (PSZ), and the samarium-doped ceria (SDC) And a metal that does not sinter even at the operating temperature of the fuel cell, such as Mo, W, and Pt, is immersed in an aqueous solution containing metal ions such as Ni, Ru, and Co, and dried to dry the oxide. A metal compound such as Ni (NO ₃ ) ₂ , RuCl ₂ , CoSO ₄ is supported on the surface of the powder, and Ni, R
It is characterized by being supported in the state of a metal such as u, Co, etc., and using such a powder as a raw material to form an electrode.

[0014]

The electrode structure of the solid oxide fuel cell according to the present invention has the following functions.

FIG. 1 schematically shows an embodiment of an electrode structure of a solid oxide fuel cell according to the present invention. Since the fuel electrode 1 has a structure in which metal particles 4 such as Ni, Ru, and Co are supported on a surface of an oxide powder 3 such as YSZ, PSZ, or SDC on a substrate 2, a metal, an oxide, and a fuel The three-phase interface with which the gas comes into contact becomes very large, and a voltage drop due to the electrode reaction is small, resulting in an electrode having excellent output characteristics.

In addition, since the metal is adsorbed on the oxide powder and strongly bound, the metal is less likely to be sintered, resulting in an electrode having little deterioration over time and excellent long-term stability.

Furthermore, since only a small amount of metal is required to be supported on the oxide powder, even if an expensive noble metal such as Ru or Pt is used, the cost does not increase, and there is practicality.

Depending on the type of metal, the electrode may not show sufficient electron conductivity because the adsorbing power to the surface of the oxide powder 3 is weak and the amount of adsorbed metal particles 4 is small. However, in this case, as in another embodiment of the present invention (FIG. 2), M
By adding the metal powder 5 that does not easily sinter at the operating temperature of the fuel cell such as o or W, a conductive path is formed, and electron conductivity is secured.

[0019]

Embodiment 1 In this embodiment, a method of manufacturing the fuel electrode shown in FIG. 1 by a method of immersing an oxide powder in an aqueous solution containing metal ions to support a metal in a fuel electrode composed of Ni-YSZ will be described. First, Y having an average particle size of 0.3 μm
10 g of SZ powder was added to a 100 m saturated aqueous solution of Ni (NO ₃ ) ₂
and kept at 90 ° C. for 2 hours with stirring. Subsequently, this was cooled to room temperature, and then filtered using a filter paper, and the YSZ powder remaining on the filter paper was dried. The dried YSZ powder is green and Ni (NO ₃ ) ₂ is Y
It can be confirmed that the surface of the SZ powder is covered. This Y
The SZ powder was placed in an electric furnace and kept at 700 ° C. for 2 hours.
(NO ₃ ) ₂ was pyrolyzed. Ni (NO
₃ ) It was confirmed by X-ray diffraction that all of ₂ were NiO. In addition, as a result of elemental analysis of the surface of the YSZ powder by EPMA, it was confirmed that the Ni element was dispersed at a high density on the surface of the YSZ powder.

Next, as described above, the NiO-supported Y
To a powder of SZ, polyvinyl butyral as a binder and terpineol as a solvent were added, and a slurry was applied to a disc-shaped YSZ substrate having a diameter of 3.5 cm as a solid electrolyte in the form of a 2 cm × 2 cm square, It was sintered at 1250 ° C. for 2 hours to obtain a porous electrode. YS in this process
The amount of Ni metal supported on the surface of the Z powder was about 15% by weight. The thickness of the fuel electrode after sintering was about 0.1 mm. Here, the YSZ substrate is made of a paste of YSZ powder having the same average particle diameter of 0.3 μm as that used as the material of the fuel electrode, and sintered at 1400 ° C. for 2 hours to have a thickness of about 0.3 m.
m is a dense body.

The fuel electrode thus manufactured was
NiO was reduced to Ni metal in a hydrogen gas atmosphere at 00 ° C. and kept for 1000 hours. The fuel electrode was taken out after 1 hour and 1000 hours from under a hydrogen gas atmosphere at 1000 ° C., and the cross section was observed by SEM. As a result, there was hardly any difference between the two, and it was confirmed that there was no change with time. Furthermore, EPMA
As a result of elemental analysis of the electrode cross section at
After 000 hours, a high-density and wide distribution of the Ni element was observed in both samples. From this, it was confirmed that many three-layer interfaces existed in the electrode, and a fuel electrode was obtained in which the aggregation of Ni did not occur and the deterioration with time was extremely small. Here, the loading amount of Ni metal was about 15 wt%, but the loading amount was changed to 30 wt% by changing the immersion time, the type of the aqueous solution of the compound to be used, and the particle size of the YSZ powder.
%.

As described above, in the first embodiment, YSZ and Ni (NO ₃ ) ₂ are used as materials for manufacturing the fuel electrode. Has PSZ, SDC, (Bi ₂ O ₃ )
_x (Y ₂ O ₃ ) _1-x , (Ta ₂ O ₅ ) _x (Sc ₂ O ₃ ) _1-x , (Z
rO ₂ ) _x (CaO) _{1 -x} (0 ≦ x ≦ 1) and the like could also be used. In addition to the aqueous solution of Ni (NO ₃ ) ₂ , N
iCl ₂ , NiBr ₂ , NiSO ₄ , Ni (ClO ₃ ) ₂ ,
An aqueous solution such as Ni (ClO ₄ ) ₂ can also be used, and an organic solvent system may be used as long as Ni exists as an ion. Further, in addition to Ni as the metal to be supported on the oxide powder, the melting point is 1000 ° C., which is the operating temperature of the SOFC.
Higher than near, Sc, Ti, V, Cr, Mn, Fe,
Co, Cu, Y, Zr, Nb, Mo, Tc, Ru, R
h, Pd, Hf, Ta, W, Pt, Au, etc. could also be used.

[0023]

Embodiment 2 In this embodiment, an oxide powder carrying a metal and a metal powder which does not sinter even at the operating temperature of a fuel cell are mixed in a fuel electrode composed of Ni-YSZ and Mo. A method for manufacturing a fuel electrode having a structure will be described. First, an average particle size of 3 μm
100 g of YSZ powder, 20 g of Mo powder having an average particle size of 0.7 μm, 20 zirconia balls having a diameter of 1 cm, and 150 ml of a saturated aqueous solution of Ni (NO ₃ ) ₂ were placed in a high-temperature bath at a temperature of 70 ° C. After rotating for 2 hours, the YSZ powder and the Mo powder were mixed. Subsequently, the YSZ powder and the Mo powder were separated from the aqueous solution of Ni (NO ₃ ) ₂ using a filter paper and dried. The surface of the mixed powder of YSZ and Mo after drying is Ni
It is covered with (NO ₃ ) ₂ and has a green color. This mixed powder was placed in an electric furnace and maintained at 700 ° C. for 2 hours.
(NO ₃ ) ₂ was pyrolyzed. Ni (NO ₃ ) ₂ is all NiO
Was confirmed by X-ray diffraction. In addition, as a result of elemental analysis of the surface of the mixed powder by EPMA, it was confirmed that the Ni element was dispersed at a high density on the surfaces of the YSZ powder and the Mo powder.

Next, a slurry of the mixed powder was prepared in the same manner as in Example 1, and applied to the same electrolyte substrate. The fuel electrode thus manufactured was kept in a hydrogen gas atmosphere at 1000 ° C. for 1000 hours. One hour after in a hydrogen gas atmosphere at 1000 ° C. and 1000 hours
After a lapse of time, the fuel electrode was taken out, and the cross section was observed by SEM. As a result, there is little difference between the two,
It was confirmed that there was no change with time. Further, E
As a result of elemental analysis of the electrode cross section by PMA, a high-density and wide distribution of the Ni element was observed in both the samples after 1 hour and after 1000 hours. From this, it can be confirmed that the electrode has many three-layer interfaces.
Thus, a fuel electrode was obtained in which the aggregation of i did not occur and the deterioration with time was very small. Also, a Pt paste was applied in a circular shape having a diameter of 3 cm on the other surface of the YSZ substrate, which is a solid electrolyte, and a Pt mesh was attached on the fuel electrode.
The AC impedance (absolute value) at 1 kHz was measured. The AC impedance value is about 0.1Ω, and the electrode of the present structure has an AC impedance of about 1/5 that of the electrode of the structure of FIG. Was improved.

As described above, in Example 2, YSZ and Ni (NO ₃ ) ₂ were used as materials for manufacturing the fuel electrode, but other materials shown in Example 1 could be used. In addition, as material powder for forming the conductive path in the fuel electrode, in addition to Mo, W, Ti, V, Cr, Zr, Nb, M
Metals such as o, Tc, Ru, Rh, Hf, Ta, and W, and alloys could also be used. Further, oxides of these metals may be used as long as they are reduced at the operating temperature of the fuel cell.

[0026]

The electrode structure of the present invention has the following effects.

(1) The three-phase interface where the metal, oxide, and fuel gas come into contact with each other becomes very large, and an electrode having a small voltage drop due to the electrode reaction and having excellent output characteristics can be obtained.

(2) Since the metal fine particles are strongly bound by the oxide powder, sintering between the metal fine particles hardly occurs.
An electrode with excellent long-term stability and little deterioration over time can be obtained.

(3) Since only a small amount of metal is required to be supported on the oxide powder, a practical electrode can be obtained which does not increase the cost even if an expensive noble metal is used.

(4) For an electrode which does not exhibit sufficient electron conductivity only by supporting a metal on an oxide powder and sintering, a conductive path is formed by adding a metal powder which is hardly sinterable at the operating temperature of the fuel cell. The new construction improves the electron conductivity of the electrodes.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a fuel electrode obtained by the present invention.

FIG. 2 is a sectional view showing a second embodiment of the fuel electrode obtained by the present invention.

[Description of Signs] 1 Fuel electrode 2 YSZ substrate 3 Oxide powder 4 Metal particle 5 Metal powder

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masayasu Arakawa 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Corporation (72) Inventor Daisuke Ikeda 3-192-1, Nishishinjuku, Shinjuku-ku, Tokyo No. Japan Telegraph and Telephone Corporation

Claims (6)

[Claims] 1. A fuel electrode for a solid oxide fuel cell comprising an oxide having oxygen ion conductivity and a metal having electrode activity, wherein the metal is adsorbed on the surface of the oxide. Fuel electrode for solid oxide fuel cells. 2. The fuel electrode for a solid oxide fuel cell according to claim 1, wherein a metal that does not aggregate even at the operating temperature of the fuel cell is added. 3. The oxide is at least one selected from yttria-stabilized zirconia, partially stabilized zirconia, and samarium-doped ceria, and the metal having electrode activity is one selected from nickel, ruthenium, and cobalt. 3. The fuel electrode according to claim 1, wherein the metal that does not aggregate even at the operating temperature of the fuel cell is at least one selected from molybdenum, tungsten, and platinum. 4. An oxide powder having oxygen ion conductivity is immersed in a solution containing ions of a metal having electrode activity, and then dried to allow the metal compound to be supported on the surface of the oxide. A method for producing a fuel electrode for a solid oxide fuel cell, comprising: performing a heat treatment so that the metal is supported on the oxide surface; and then molding and sintering the metal. 5. The method according to claim 4, wherein, after the step of supporting the metal on the oxide surface, a metal powder that does not aggregate even at the operating temperature of the fuel cell is mixed, and then molded and sintered. A method for manufacturing a fuel electrode of a solid oxide fuel cell. 6. An oxide powder having oxygen ion conductivity and a metal powder which does not agglomerate even at the operating temperature of a fuel cell are immersed in a solution containing ions of a metal having an electrode activity, and then dried and dried. 5. The method according to claim 4, wherein the metal compound having electrode activity is supported on the surface of the oxide, and then heat treatment is performed to support the metal having electrode activity on the oxide surface, followed by molding and sintering. A method for producing a fuel electrode for a solid oxide fuel cell as described above.