JP2604437B2 - High-temperature fuel cell interelectrode assembly and high-temperature fuel cell cathode current collector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a joined body of a cathode and an anode of a high-temperature fuel cell and a cathode current collector.

[Problems to be solved by conventional technology and invention]

For high-temperature fuel cells, the molten salt type used at 650 ° C and 800-
There is a solid electrolyte type used at 1000 ° C. As shown in FIG. 8, the basic structure of a solid oxide fuel cell is such that a cathode (for example, perovskite type LaSrMnO ₃ ) 2 and an anode (for example, NiO / ZrO ₂ ) 3 are sandwiched between a solid electrolyte (for example, partially stabilized zirconia) 1. It is formed in a film shape, and oxygen or air is supplied to the cathode 2 side, and fuel, for example, hydrogen is supplied to the anode 3 side. Zirconia (ZrO ₂ ) is 0.5Ω at 1000 ° C
^Exhibit an electrical conductivity of ^-1 cm ^-1 which is ionic conduction or O ^2-
Although zirconia is very brittle, it is stabilized by calcium and yttrium. The reaction of a battery like this example is represented by cathode: 4e ⁻ + O ₂ → 2O ²⁻ anode: O ²⁻ + H ₂ → H ₂ O + 2e ⁻ , and O ²⁻ is transported through zirconia.

Although this is a unit cell structure, in order to integrate unit cells and connect a plurality of unit cells in parallel (or in series), the electrodes of adjacent unit cells are connected by a joint (interconnector). Connecting. The actual structure of the fuel cell is determined by the manner in which the unit cells are integrated, and some integrated structures have been proposed so far, and development for practical use is in progress.

By the way, it is considered that such a fixed electrolyte fuel cell assembly preferably satisfies the following conditions.

1) Stable under high temperature oxidation and reduction atmosphere.

2) Good conductors in oxidizing and reducing atmospheres at high temperatures.

3) It has a thermal expansion coefficient close to that of an oxide ion conductive solid such as stabilized zirconia.

4) It has a thermal expansion coefficient close to that of the electrode material.

The following conditions are required for the cathode current collector.

1) Stable under reinforced atmosphere at high temperature.

2) Good conductor under high temperature oxidizing atmosphere.

3) It has a thermal expansion coefficient close to that of an oxide ion conductive solid such as stabilized zirconia.

4) It has a thermal expansion coefficient close to that of the oxygen electrode material.

Conventionally, metal or conductive ceramics has been used as a joined body or a current collector. However, when metal is used at a temperature of 600 ° C. or higher, a surface oxide layer is formed, contact resistance is significantly increased, power resistance loss is increased, and fuel cell characteristics are deteriorated. Further, as the conductive ceramics, metal composite oxides such as La _1-x M ¹ _x M ² O ₃ (M ¹ is Sr, Ca or Ba, M ²
Has been proposed as a perovskite-type oxide represented by O ≦ x ≦ 1), particularly La _1-x Sr _x CrO _3, which is Co, Fe, Mn, Ni or Cr, satisfying the above requirements. However,
Although such ceramics are conductive, their resistance cannot be ignored.For example, in a thin-film cylindrical fuel cell using a perovskite-type oxide as a cathode material proposed by Westinghouse of the United States, the resistance of the cathode is low. It accounts for about 65% of the total cell resistance and is an obstacle to improving the energy efficiency of fuel cells.

On the other hand, in recent years, a battery having a new structure has been proposed for the purpose of developing a higher performance fuel cell. Examples are shown in FIG. 6 and FIG. FIG. 6 shows that a honeycomb structure 5 is made of a solid electrolyte such as partially stabilized zirconia, and fuel 6 and air (oxygen) 7 are supplied countercurrently to every other pore (cell) of the honeycomb structure. The anode is formed on the wall surface in the pore supplying air, and the cathode is formed on the wall surface in the pore supplying air (oxygen) 7. FIG. 7 shows a plurality of solid electrolyte partitions
Fuel 1 in every other stratified space 12, 13 formed by 11
4 and air (oxygen) 15 are supplied at right angles to the fuel
An anode 16 is formed on the 4 side, and a cathode 17 is formed on the air (oxygen) side. These types of batteries can be expected to have an extremely high energy density per unit volume, and are suitable for mass production because conventional ceramics technology can be applied. However, the biggest problem is the current collector in the structure of FIG. 6 and the joined body in the structure of FIG.

The present invention has been made particularly for the purpose of providing such a current collector or a joined body.

[Means for solving the problem]

The present invention solves the above problems, chromium, cobalt, nickel,
(I) lanthanum, (ii) lanthanum oxide, (iii) a combination of lanthanum and (strontium or calcium), (iv) lanthanum oxide and (strontium or calcium) on the surface of iron or manganese or an alloy containing these metals. (V) a combination of lanthanum and (strontium oxide or calcium oxide), and (vi) a lanthanum oxide and (strontium oxide or calcium oxide)
And a combination of a cathode of a unit cell for a high-temperature fuel cell and an anode of an adjacent unit cell, and a similar high-temperature fuel cell characterized by being coated with any one of the group consisting of: By providing a cathode conductor of

This coating reacts with chromium, cobalt, nickel, iron or manganese in the substrate in a high-temperature oxygen atmosphere to produce La _1-x M ¹ _x
M ² O ₃ (M ¹ is an alkaline earth metal composed of strontium or calcium, M ² is chromium, cobalt, nickel, iron or manganese, and 0 ≦ x ≦ 1) forms a perovskite-type composite oxide. In particular, this perovskite-type composite oxide is stable at high temperatures and has excellent electrical conductivity.
It has a value of 10 to 1000 Ω ^-1 cm ^-1 . For this reason, while the alloy or pure metal alone forms an oxide film at a high temperature and insulates the surface, the material according to the present invention has excellent surface electrical conductivity due to the formation of a composite oxide film, and a bonded body, Ideal for aggregates. In addition, since the main body is a heat-resistant alloy or a pure metal, it is excellent in all of its rigidity, workability, and electric conductivity, thereby enhancing its practicality.

The base metal may be an alloy containing chromium, cobalt, nickel, iron or manganese or a pure metal of chromium or cobalt, but the alloy is preferably a so-called heat-resistant alloy containing 9 wt% or more of chromium, cobalt, nickel, iron or manganese. . For example, it is useful to use Ni10.0, Cr20.0, W15.0, Fe1.5, Co residue, or a composition having a composition as shown in Examples described later.

Composition ratio x / of alkaline earth oxide consisting of lanthanum oxide and strontium oxide or calcium oxide in the coating
While (1-x) is not particularly limited, M ₁ / L _a ratio (M _1: an alkaline earth metal) in a molar ratio of 0 to 0.7, particularly 0
0.5 is preferred. This is because the electric conductivity and the oxidation resistance are excellent in this range.

The method of forming a film on an alloy or a pure metal is not particularly limited, and as a coating method, a coating method, a thermal spraying method,
Sputter method, evaporation method, plasma CVD method, MBE method, MOCVD
Any of the film forming techniques such as a CVD method, a CVD method, an ion plating method, and a plasma spraying method can be used, but a thermal spraying method, a sputtering method, and an ion plating method, which are excellent in denseness and adhesion, are particularly preferable.

The thickness of the coating is preferably in the range of 0.1 μm to 1 μm. If the thickness is smaller than 0.1 μm, the effect of protecting the surface is not sufficient, while if it is larger than 1 μm, the conductivity is reduced.

The coating of the present invention is a perovskite-type composite oxide La _1-x M ¹ _x
The conditions for M ² O ₃ are as follows: the composition ratio of La and M ¹ and the composition of the base material (especially
M ² ), depends on the film thickness, atmosphere, etc., but in general,
Changes to a composite oxide by heat treatment at 1000 ° C for about 1 hour. Such a heat treatment may be performed specially in order to convert the coating into a desired composite oxide before putting the present invention into practical use, or when the present invention is put into practical use, depending on the practically used high-temperature conditions. May be.

La _1-x M ¹ _x M ² obtained by heat-treating the coating of the present invention.
The O ₃ perovskite-type composite oxide exhibits high conductivity (100 to 1000 S cm ⁻¹ ) at a high temperature as described above, and its thermal expansion coefficient (9 × 10 ⁻⁶ / ° C.) 16-19 × 1
(Approximately 0 ⁻⁶ / ° C.), and has a feature and an advantage that it reacts with chromium, cobalt, nickel, iron or manganese contained in the base material during heat treatment to form an extremely dense film. Further, the thermal expansion coefficient of this composite oxide is relatively close to that of the solid electrolyte (10 × 10 ⁻⁶ / ° C.), which makes the application of the present invention to a solid electrolyte fuel cell more suitable.

〔Example〕

Example 1 Cobalt-based alloy plate (10 mm × 10 mm × 1 mm, composition: W14.57
%, Co 52.51%, Cr 19.69%, Ni 9.39%, C 0.10%, Si 0.4
8%, Mn1.51%) La ₂ O ₃ -SrO (Mole ratio of SrO / La ₂ O ₂ is 2: 1) mixture by Rf sputtering method on the both sides to a thickness of about 1 mm Attached. The Rf sputtering method was performed for 1 hour at a Margon gas ratio of 2 to 5 mTorr and a power of 100 to 200 W. This sample was heated in air at 1000 ° C. for 24 hours.

After heating, the reaction product was gradually cooled to room temperature, and the reaction product in the area was identified by an X-ray diffractometer. As a result, La _1-x Sr _x CrO ₃ (X = 0.1 to 0.
5). Weight to (M ² is, Cr is established, and Co is not confirmed, the reactivity of Cr is thought to be because higher than Co) time when the sample was heated at 1000 ° C. in air in Figure 1 Change and surface resistance change. The surface resistance was measured by a four-probe method according to a conventional method. For comparison, the weight change of the same alloy without the La ₂ O ₃ -SrO thin film on the surface is also shown.

In the case of the alloy alone, the increase in weight became maximum after heating for about 100 hours, and then decreased. This weight loss is due to the exfoliation of oxides formed on the alloy surface, mainly chromium oxide and cobalt oxide. The surface resistance of the sample containing only the alloy showed a value close to that of an insulator when heated at 1000 ° C. for 24 hours, because chromium oxide and cobalt oxide were formed on the surface. Under a reducing atmosphere at 1000 ° C. (hydrogen 10%, argon 90%), no change in the surface and an increase in the resistance of this cobalt-based alloy were observed.

Examples 2 to 5 In the same manner as in Example 2, La ₂ O ₃ -SrCO ₃ (La ₂ ) was deposited on each alloy plate having the composition (% by weight) shown in Table 1 by Rf sputtering.
The O ₃ / SrCO ₃ molar ratio 3: 1) mixture was deposited on both sides to a thickness of about 1 μm and heated in air at 1000 ° C. for 24 hours.

As a result of X-ray diffraction analysis of the reaction product on the alloy surface, it was confirmed that the products shown in Table 2 were formed.

FIG. 2 shows the weight change when the sample after La ₂ O ₃ —SrCO ₃ deposition was heated at 1000 ° C. in air. La on the surface for comparison
FIG. 3 shows a change in weight of the alloy not coated with ₂ O ₃ -SrCO _{3 due} to similar heating.

Table 2 shows the electric resistance of the surface of the coated alloy and the bare alloy after the heating.

Example 6 In the same manner as in Example 1, a cobalt pure metal plate (10 mm × 10
(mm × 1 mm), metallic lanthanum was sputtered to a thickness of 2 to 3 μm on both surfaces by Rf sputtering. Then 1000 in the air
Heat treated at 5 ° C. for 5 hours.

After heating, the mixture was gradually cooled to room temperature, and the reaction product on the surface was analyzed by an X-ray diffraction method. As a result, it was confirmed to be LaCoO ₃ .

When this sample was heated in air at 1000 ° C for 5 hours, 36S
It showed an electrical conductivity of cm ^-1 and showed very good results.
No change over time was observed after 168 hours, and no peeling of the film was observed even after the temperature was lowered.

FIG. 4 shows the air conductivity of the coatings examined in this way with respect to the measured temperature.

FIG. 5 is a developed view showing a stacked structure of a solid oxide fuel cell to which the present invention is applied. In the figure, 21 is a sheet of a solid electrolyte (eg, Ca stabilized zirconia), an anode (eg, La _0.9 Sr _0.1 MnO ₃ ) 22 on the upper surface, and a cathode (eg, NiO /
ZrO ₂ cermet) 23 is formed. 24 is a joined body, and the material of the present invention (eg, La ₂ O
_3- SrO coating). 25 is a heat-resistant component like 24, but is used as an external output terminal. As can be seen in FIG. 5, the joint 24 has air
A separator that constitutes a flow path for the fuel cell 26 and the fuel (eg, hydrogen) 27 and separates the air 26 and the fuel 27, and also has a role of electrically connecting the cathode 23 and the anode 22 of the adjacent unit cell. Things. The external output terminal 25 is also a member that forms a flow path for the air 26 and the fuel 29 at both ends of the integrated unit cell and also performs an electrical connection with the cathode 23 or the anode 22, which is also a heat-resistant component of the present invention. Configure. FIG. 5 shows a fuel cell in which two unit cells are integrated, but it is also possible to integrate three or more unit cells. In this case, a joined body 24 is inserted between each unit cell.

When such a fuel cell is used by supplying air and fuel (hydrogen) at a high temperature of 1000 ° C., the coating (La ₂ O ₃ —SrO) of the heat-resistant parts of the joined body 24 and the external output terminal 25 is immediately formed after use. It becomes a composite oxide (La _1-x Sr _x CrO ₃ ), the resistance is reduced, and power is generated stably for a long time thereafter.

Further, the material of the present invention is extremely useful as a current collector and a joined body of the fuel cell shown in FIGS. 6 and 7.

〔The invention's effect〕

According to the present invention, there is provided a current collector and a joined body for a solid oxide fuel cell made of a heat-resistant and good-conductive metal provided with a good conductive coating that withstands an oxidizing and reducing atmosphere at a high temperature. These can be made of, for example, a good conductor substrate having a protective coating that withstands an oxidation-reduction atmosphere at a high temperature of 1000 ° C. or higher and has an electric conductivity of 10 to 1000 S cm ⁻¹ .

By using a current collector and a joint for a solid oxide fuel cell composed of this oxidation-resistant and reducing metal conductor, an integrated structure that can be expected to have much better performance than a conventional high-temperature solid electrolyte fuel cell A high-temperature solid electrolyte fuel cell can be produced.

[Brief description of the drawings]

FIG. 1 is a graph showing the weight change and the resistance change of the coated material of the example in air at 1000 ° C., and FIGS. 2 and 3 are the weights of the coated material and the uncoated alloy of the example in air at 1000 ° C. FIG. 4 is a graph showing a change in the electric conductivity of the coating of the embodiment, and FIG. 5 is a diagram showing a structure of a high-temperature solid electrolyte fuel cell using the joined body of the high-temperature fuel cell of the present invention. 6 and 7 are schematic views of a high-temperature solid electrolyte fuel cell, and FIG. 8 is a schematic view showing a basic structure of the solid electrolyte fuel cell. 1 ... solid electrolyte, 2 ... cathode, 3 ... anode, 6 ... fuel, 7 ... air, 11 ... solid electrolyte, 14 ... fuel, 15 ... air, 16 ... anode, 17 ... Cathode, 21: Solid electrolyte, 22: Anode, 23: Cathode, 24: Joint, 25: External output terminal, 26: Air, 27: Fuel.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location H01M 8/02 H01M 8/02 Y 8/12 8/12 (72) Inventor Atsushi Tsunoda Iruma, Saitama 1-3-1, Nishi-Tsurugaoka, Oi-machi, Gunma Within Toa Fuel Industry Co., Ltd. (72) Inventor Hiroyuki Iwasaki 1-3-1, Nishi-Tsurugaoka, Oi-machi, Irima County, Saitama Prefecture Toa Fuel Industry Co., Ltd. (72) Inventor Tsukasa Shima 1-3-1, Nishitsurugaoka, Oi-machi, Iruma-gun, Saitama Prefecture Inside the Toa Fuel Industry Co., Ltd. (72) Isao Mukaizawa 1-3-3 Nishi-Tsurugaoka, Oi-machi, Iruma-gun, Saitama No. 1 Toa Fuel Industry Co., Ltd. (72) Inventor Satoshi Sakurada 1-3-1 Nishitsurugaoka, Oi-machi, Iruma-gun, Saitama Prefecture No. 1 Toa Fuel Industry Co., Ltd. (56 References JP-A-64-27116 (JP, A) JP-A-63-245829 (JP, A) JP-A-63-270450 (JP, A) JP-A-58-161777 (JP, A) 61-259462 (JP, A) JP-A-1-258364 (JP, A)

Claims (2)

(57) [Claims] 1. The surface of chromium, cobalt, nickel, iron or manganese or an alloy containing these metals, (i)
Lanthanum, (ii) lanthanum oxide, (iii) a combination of lanthanum and strontium or calcium, (iv) a combination of lanthanum oxide and strontium or calcium,
A high-temperature fuel cell coated with any one of the group consisting of (v) a combination of lanthanum and strontium oxide or calcium oxide; and (vi) a combination of lanthanum oxide and strontium oxide or calcium oxide. Of a cathode of a unit cell for use with an anode of another adjacent unit cell. 2. The method according to claim 1, wherein the surface of chromium, cobalt, nickel, iron or manganese or an alloy containing these metals comprises (i)
Lanthanum, (ii) lanthanum oxide, (iii) a combination of lanthanum and strontium or calcium, (iv) a combination of lanthanum oxide and strontium or calcium,
A high-temperature fuel cell coated with any one of the group consisting of (v) a combination of lanthanum and strontium oxide or calcium oxide; and (vi) a combination of lanthanum oxide and strontium oxide or calcium oxide. Cathode current collector.