JPH07326364A - Fuel electrode for fuel cell using solid electrolyte - Google Patents

Abstract

PURPOSE:To provide a high power generation function and restrain a drop in function over long-time operation by reforming the particle surface of a fuel electrode material made of a metal and a ceramic using oxygen ion and electron mixed conductive oxide, and thereby preparing a fuel electrode. CONSTITUTION:A fuel electrode for a solid electrolytic fuel cell is mainly formed out of metal 3 and surface reformed ceramic with an oxygen ion and electron mixed conductor 2 having both functions of oxygen ion conductivity and electron conductivity attached to the surface of a ceramic particle 1. The oxygen ion and electron mixed conductor 2 is cerium oxide, and composed of one substance selected from groups of (CeO2)0.8 (Sm2O3)0.2 (CeO2)0.8 (Y2O3)0.2 and (CeO2)0.8 (La2O3)0.2, or a mixture of two or more substances selected from the groups.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel electrode of a solid oxide fuel cell, and more particularly to improvement of such a fuel electrode.

[0002]

2. Description of the Related Art A fuel cell is expected to have high power generation efficiency because it directly converts chemical energy of supplied gas into electric energy. Among them, the high temperature type solid electrolyte fuel cell is a cell that operates at a high temperature of about 1000 ° C. Therefore, by effectively utilizing the waste heat, the power generation efficiency can be improved by the phosphoric acid type fuel cell and the molten carbonate type fuel cell. It has the advantage that it can be further improved as compared with the above, and has recently attracted attention as a third generation fuel cell.

In this type of solid electrolyte fuel cell, oxygen ions are passed from the oxidant electrode side through the electrolyte and moved to the fuel electrode side, where they are reacted with fuel gas to generate water and electrons (e ⁻ ). The battery is based on the principle that electric current is taken out to the outside through the battery reaction. Therefore, it is desired that the electrode base material forming the fuel electrode is excellent in thermal stability and has electronic conductivity, gas permeability, and oxygen ion conductivity. Conventionally, as an electrode base material having such characteristics,
Ni-YSZ (yttria-stabilized zirconia) cermet is used, and such a cermet material is useful as an electrode base material capable of suitably conducting an electrode reaction.

By the way, as shown in FIG. 4, the anode reaction actually takes place in the fuel electrode composed of such an electrode base material as shown in FIG. It is considered to be a three-phase interface where the conductors YSZ (1) and the anode gas meet together.

[0005]

However, in the conventional fuel electrode using the above electrode base material, the three-phase interface is limited, so that a sufficient power generation capacity has not been obtained. Also,
Since the solid electrolyte fuel electrode is operated at a high operating temperature of 1000 ° C., in the conventional fuel electrode, nickel in the Ni-YSZ cermet, which is the electrode base material, becomes a semi-molten state with the lapse of cell operation time, and gradually agglomerates. Coarse particles. Therefore, the contact area between Ni and YSZ is reduced, and the three-phase interface is reduced. Therefore, there is a problem that the electrode performance is deteriorated as the battery operation is extended.

The present invention solves the above problems and provides an excellent fuel electrode which has a high power generation capacity and can suppress the deterioration of the electrode performance due to the decrease of the electrode reaction area even during long-term operation. With the goal.

[0007]

In order to achieve the above object, the invention according to claim 1 provides an oxygen ion / electron mixed conductor having both oxygen ion conductivity and electron conductivity properties on the surface of ceramic particles. It is a fuel electrode for a solid electrolyte fuel cell, which is mainly composed of a surface-modified ceramics adhered to and a metal.

According to a second aspect of the present invention, in the fuel electrode for a solid oxide fuel cell according to the first aspect, the oxygen ion / electron mixed conductor is a Ce-based oxide.
According to a third aspect of the present invention, in the fuel electrode for a solid electrolyte fuel cell according to the _{second aspect} , the Ce-based oxide is (CeO ₂ ).
_{0.8 (Sm 2 O 3) 0.2} , (CeO 2) 0.8 (Y 2 O 3) 0. 2,
It is characterized in that it is a substance selected from the group consisting of (CeO ₂ ) _0.8 (La ₂ O ₃ ) _0.2 or a mixture of two or more substances selected from the group.

According to a fourth aspect of the present invention, in the fuel electrode for a solid electrolyte fuel cell according to the first aspect, the mixed oxygen ion / electron conductor is praseodymium oxide. According to a fifth aspect of the present invention, in the fuel electrode for a solid electrolyte fuel cell according to the fourth aspect, the praseodymium oxide is PrO _x (0 <x ≦ 3).

[0010]

According to the present invention having the above-described structure, the main constituents are the surface-modified ceramics having the oxygen ion / electron mixed conductive oxide having the properties of both oxygen ion conductivity and electron conductivity attached to the surface, and a metal. A fuel electrode was constructed using an electrode base material as a material. When the electrode substrate having such a structure is used, N
The electrode reaction (anode reaction) proceeds also in the oxygen ion / electron mixed conductive oxide existing around the so-called three-phase interface where i, YSZ and the anode gas associate. That is,
In the fuel electrode according to the present invention, the electrode reaction, which was conventionally performed only at the three-phase interface, can be expanded to the oxygen ion / electron mixed conductive oxide region attached to the ceramic surface, so that the power generation performance is remarkably increased. improves.

Further, even if Ni agglomerates and coarsens due to thermal effects and the three-phase interface decreases due to it, the reaction site of the anode reaction expands to the oxygen ion / electron mixed conductive oxide region. Therefore, the reaction sites do not decrease. Therefore, excellent power generation capacity can be maintained for a long period of time. According to the present invention, due to the action of the oxygen ion / electron mixed conductive oxide as described above, it is possible to form a fuel electrode having a high power generation capacity and a small decrease in electrode performance.

Here, oxygen ion / electron mixed conductive oxidation
The material is oxygen ion conductive and electronic conductive in a reducing atmosphere.
Any substance that has
Examples include Ce-based oxides and praseodymium oxides.
You can Specific examples of the Ce-based oxide include (CeO
₂)_0.8(Sm₂O₃)_0.2, (CeO₂)_0.8(Y₂O₃)_0.2,
(CeO₂)_0.8(La₂O₃)_0.2Etc.
Out of this (CeO₂) _0.8(Sm₂O₃)_0.2But the cost
In terms of Also preferred praseodymium oxide
As PrO_x(0 <x ≦ 3).

The above various kinds of oxygen ion / electron mixed conductive oxides may be used alone or in combination of two or more kinds. Further, the compounding ratio of the ceramics and the oxygen ion / electron mixed conductive oxide is not particularly limited. However, since the Ce-based oxide is more expensive than the YSZ, the YSZ is costly.
It is not suitable for practical use to substitute all Ce and the like for Z and the like. Therefore, considering the cost and the surface modification effect, it is preferable to appropriately set the amount within the range in which the purpose of surface modification of ceramics can be sufficiently exerted. For example, according to the methods described in the following examples, the function and effect can be sufficiently exerted with an impregnated amount of 10% or less.

[0014]

EXAMPLES A fuel electrode base material for a solid electrolyte fuel cell according to the present invention can be manufactured by the following method. [Fabrication of Fuel Electrode Base Material] Cerium oxalate and samarium oxalate were mixed so that the molar ratio of Ce and Sm was 8: 2,
Zirconia (hereinafter referred to as YSZ) powder stabilized with 3% yttria is put into this mixed solution, mixed, and then dried. This dry powder was placed in a furnace at 1300 to 1500 ° C. and fired for several hours. In this way, a surface-modified ceramic was prepared in which about 10 wt% of (CeO ₂ ) _0.8 (Sm ₂ O ₃ ) _0.2 (oxygen ion / electron mixed conductor) was attached to the surface of the YSZ particles.

Next, 200 parts by weight of the surface-modified ceramic, 150 parts by weight of nickel oxide (NiO) powder, and 5 parts by weight of binder (polyvinyl butyral resin).
And 100 parts by weight of a solvent (terpineol) were mixed to prepare a slurry for a fuel electrode. 8 this slurry
% Solid electrolyte composed of dense yttria-stabilized zirconia sintered body (outer dimensions 150 mm x 150 mm, thickness 0.2)
mm) was applied to one surface and baked to prepare a fuel electrode on the surface of the solid electrolyte.

Hereinafter, the fuel electrode constituted by using the surface-modified ceramics as the fuel electrode base material in this manner is referred to as the fuel electrode A of the present invention, and the fuel electrode A of the present invention and the solid electrolyte are integrated. Will be referred to as an invention example fuel electrode / electrolyte assembly for convenience. [Comparative Example] YS without surface modification as the fuel electrode base material
A fuel electrode / solid electrolyte assembly was prepared in the same manner as in the above-mentioned example except that Z was used. The fuel electrode thus formed on one surface of the solid electrolyte is referred to as a comparative fuel electrode X, and the one in which the comparative fuel electrode X and the solid electrolyte are integrated is referred to as a comparative fuel electrode / electrolyte assembly for convenience. I will decide.

[Experiment] For the fuel electrode / electrolyte assembly of the present invention and the comparative fuel electrode / electrolyte assembly of the present invention produced in the above-mentioned examples, an oxidant electrode was produced on the other surface of each fuel electrode by the following production method. At the same time, other known cell constituent members were incorporated to form a solid electrolyte fuel cell as shown in FIG. Then, the characteristics of these batteries were examined to evaluate the performance of the fuel electrode A of the present invention.

(Preparation of oxidizer electrode) 400 parts by weight of La
_0.9 Sr _0. MnO ₃ powder, 100 parts by weight YSZ powder, and 5 parts by weight binder (polyvinyl butyral resin)
And 70 parts by weight of a solvent (terpineol) were mixed, and the oxidant electrode slurry was applied to the other surface of each of the fuel electrode / electrolyte bonded bodies and baked. The firing may be the same as the firing of the fuel electrode.

(Battery Structure) An outline of the battery structure used in the experiment will be described based on the schematic sectional view shown in FIG. A fuel electrode 12 and an oxidizer electrode 13 are arranged on each surface of the solid electrolyte 10 (outer dimensions 150 mm × 150 mm, thickness 0.2 mm) to form a cell 14
Are formed. Then, a fuel electrode side current collector 17 and an oxidant electrode side current collector 18 are arranged on the electrode forming surface of the solid electrolyte 10, respectively, and a sealing material 19 is arranged on the electrode non-coated surface of the solid electrolyte 10, It has a structure in which a pair of separators 15 and 16 are arranged so as to sandwich them. In addition, Ni felt was used for the fuel electrode side current collector 17, and fibrous Inconel alloy was used for the oxidizer electrode side current collector 18.

Hereinafter, a battery using the fuel electrode A of the present invention is referred to as a battery A _{cell of the} present invention, and a battery using the fuel electrode X of the comparative example is referred to as a comparative battery X _cell . (Experimental conditions) Battery operating temperature 1000 ° C, discharge current density 3
The battery voltage was measured over time by continuous operation at 00 mA / cm ² for 1000 hours. In addition, at this battery operating temperature,
The nickel oxide used in the preparation of the fuel electrode base material is present in a state reduced to nickel which is a metal under a high temperature hydrogen atmosphere.

The measurement results are shown in FIG. As is clear from FIG. 2, the battery A _cell according to the present invention has a 1
No decrease in battery voltage was observed until after 000 hours. Comparative Example battery X _cell contrast is the initial battery voltage operation with less than the present invention applies the battery A _{ce ll,} the battery voltage with the lapse of operation time tended to decrease.

Here, the battery A to which the present invention is applied_cellAnd ratio
Comparative battery X_cellIs A_cellIs surface-modified ceramics
A fuel electrode formed by using (YSZ) as an electrode material.
X _cellDoes not perform surface modification (YS
The only difference is that it is a fuel electrode using Z). So above
The experimental result is a difference depending on the presence or absence of surface modification,
Such a fuel electrode has a higher electrode property than the conventional fuel electrode (comparative example).
You can conclude that it is excellent in Noh. The reason for this is
It will be described using a schematic diagram showing the mechanism of the gas-chemical reaction.

FIG. 4 is a diagram schematically showing an anode reaction in a conventional fuel electrode. The anodic reaction does not occur in the entire fuel electrode, but as shown in FIG. 4, the so-called three-point structure in which the fuel gas is associated with the electronic conductor (3) such as Ni and the oxygen ion conductor (1) such as YSZ. It occurs at the phase interface. However, the conventional fuel electrode does not necessarily have many three-phase interfaces, and Ni and YSZ have poor wettability with each other. Therefore, when the battery is operated for a long time, Ni becomes a semi-molten state due to a high temperature of about 1000 ° C. and gradually aggregates. -Coarse particles are formed to reduce the contact area with YSZ and reduce the three-phase interface.

That is, in the comparative cell X _cell , since the number of three-phase interfaces of the fuel electrode is small, the cell voltage is low even at the beginning of operation, and the three-phase interfaces are contracted with the progress of the cell operation.
It is probable that there was a tendency for the battery voltage to drop. On the other hand, in the fuel electrode A of the present invention, which uses the surface-modified ceramics having the oxygen ion / electron mixed conductor attached to the surface,
Since the oxygen ion / electron mixed conductor attached to the surface of the YSZ (1) can conduct oxygen ions and electrons, it is considered that the electrode reaction occurs in this region as well as the three-phase interface. That is, in the conventional fuel electrode, the anode reaction area, which was limited to the three-phase interface, is expanded to the shaded area (reaction part 4) in FIG. 1, and the power generation capacity is improved accordingly. Also Ni
Even if the three-phase interface is reduced due to the aggregation and coarsening of oxygen, the oxygen ion / electron mixed conductor maintains the reaction site.
High power generation capacity is maintained.

In this way, the oxygen ion / electron mixed conductor attached to the ceramic surface exerts two functions of expanding the anode reaction area and preventing electrode deterioration. The electrode performance is higher than that of the fuel electrode X of the comparative example, and the performance can be maintained for a long time. Therefore, it is considered that the battery A _{cell according to the} present invention obtained a high battery voltage from the beginning of the battery operation and did not have a decrease in the battery voltage even after a long time operation.

[Other Matters] In the above embodiments, the surface-modified ceramic fuel electrode base material is a material for forming a fuel electrode for a solid fuel cell, and is made of a constituent material other than the surface-modified ceramics. It may include one. The method for producing the surface-modified ceramic is not limited to the above method. In short, on the surface of ceramic particles (CeO ₂ )
_0.8 (Sm ₂ O ₃₎ as long as it is a method capable impregnated oxygen ion and electronic mixing conductors such as _0.2 may, for example, complexes of elements and organic substances which constitute the oxygen ion and electronic mixing conductive material such as Ce and Sm Surface-modified ceramics can also be prepared by preparing a compound or a compound in which the above element is added to the carbonyl end of an organic substance, and adding an appropriate amount of these compounds to a NiO (nickel oxide) -YSZ slurry and sintering. Can be produced.

Further, in the above embodiment, the surface modifying substance (C
eO₂)_0.8(Sm₂O₃)_0.2However, the surface modifier is
At the operating temperature of the solid electrolyte fuel cell, oxygen ions
Any substance having an electronic mixed conductor may be used.
As the substance, for example, (CeO ₂)_0.8(Sm₂O₃)_0.2,
(CeO₂)_0.8(Y₂O₃)_0.2 , (CeO₂)_0.8(La₂
O₃)_0.2, PrO_x(However, 0 <x ≦ 3)
One selected from the above, or two selected from the above group
A mixture of the above substances may be mentioned.

[0028]

As described above, according to the present invention, in the solid electrolyte fuel cell comprising the electrolyte and the pair of electrodes, the surface of the particles of the fuel electrode material composed of the metal and the ceramic is made of the oxygen ion / electron mixed conductive oxide. By reforming and using it as a fuel electrode, a reaction occurs between the reformed oxide phase and the gas phase in addition to the conventional reaction part, so that the reaction area and reactivity are increased and the cell characteristics are improved. Further, by suppressing the reduction of the reaction area due to the sintering of Ni particles during long-term operation, the battery life is improved.

[Brief description of drawings]

FIG. 1 is an enlarged schematic view of a main part of a fuel electrode for a solid oxide fuel cell according to the present invention.

FIG. 2 Fuel electrode A for solid electrolyte fuel cell according to the present invention
3 is a graph showing the cell characteristics of a fuel cell A _cell using the above and a comparative cell X _cell configured using the comparative fuel electrode X.

FIG. 3 is a schematic cross-sectional view of an experimental fuel cell assembled to examine the fuel electrode performance.

FIG. 4 is an enlarged schematic view of a main part of a fuel electrode of a comparative example (conventional example).

[Explanation of symbols]

1 Yttria-stabilized zirconia (ceramic particles) 2 (CeO ₂ ) _0.8 (Sm ₂ O ₃ ) _0.2 (oxygen ion / electron mixed conductor) 3 nickel (metal) 4 electrode reaction part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunsuke Taniguchi 2-5-5 Keihanhondori, Moriguchi-shi Sanyo Electric Co., Ltd. (72) Inventor Koji Yasou 2-5-5 Keihanhondori, Moriguchi-shi Sanyo Denki Co., Ltd. (72) Inventor Kotoku Akiyama 2-5-5 Keihan Hondori, Moriguchi Sanyo Denki Co., Ltd. (72) Inventor Yasio Miyake 2-5-5 Keihan Hondori, Moriguchi Sanyo Denki Co., Ltd. (72) Inventor Toshihiko Saito 2-5-5 Keihan Hondori, Moriguchi City Sanyo Electric Co., Ltd.

Claims (5)

[Claims] 1. A main constituent material comprising a surface-modified ceramic in which an oxygen ion / electron mixed conductor having both oxygen ion conductivity and electron conductivity is attached to the surface of ceramic particles, and a metal. Fuel electrode for solid electrolyte fuel cell. 2. The oxygen-ion / electron mixed conductor is C
The fuel electrode for a solid electrolyte fuel cell according to claim 1, which is an e-based oxide. 3. The Ce-based oxide is (CeO ₂ ) _0.8 (S
m ₂ O ₃ ) _0.2 , (CeO ₂ ) _0.8 (Y ₂ O ₃ ) _0.2 , (CeO
_2. The solid electrolyte fuel cell according to claim 2, wherein the solid electrolyte fuel cell is a substance selected from the group consisting of ₂ ) _0.8 (La ₂ O ₃ ) _0.2 , or a mixture of two or more substances selected from the group. Fuel electrode. 4. The fuel electrode for a solid oxide fuel cell according to claim 1, wherein the oxygen ion / electron mixed conductor is praseodymium oxide. 5. The praseodymium oxide is PrO _x.
The fuel electrode for a solid electrolyte fuel cell according to claim 4, wherein (0 <x ≦ 3).