JP3162881B2 - Solid oxide fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Since a fuel cell directly converts chemical energy of supplied gas into electric energy, high power generation efficiency can be expected. In particular, solid oxide fuel cells (SO
Since the FC operates at a high temperature of about 1000 ° C., the power generation efficiency including the use of waste heat is reduced by the phosphoric acid type fuel cell (PA).
FC) and a molten carbonate fuel cell (MCFC). Therefore, P
It is attracting attention as a third-generation fuel cell after AFC and MCFC, and is being studied in various fields.

In general, a solid oxide fuel cell has a structure in which a cell in which a fuel electrode and an oxidant electrode face each other via a solid electrolyte having oxygen ion conductivity and a separator for separating gas are laminated. The conductivity between the electrode and the separator is maintained by a current collector interposed between the electrode and the separator. Conventionally, as a fuel electrode side current collector,
As shown in 106063, Ni felt is used. On the other hand, as the oxidant-electrode-side current collector, a platinum net that has sufficient conductivity and is less deteriorated in an oxidizing atmosphere at 1000 ° C. is used.

[0004]

However, since the operating temperature of the solid oxide fuel cell is as high as about 1000 ° C., Ni felt, which is a fuel electrode current collector, sinters during long-term operation. Therefore, there is a problem that the gap between the fibers of the Ni felt becomes small and the gas diffusivity deteriorates, so that the permeability of the fuel gas decreases. Further, there is a problem that the thickness of the current collector is reduced (increased in bulk density) by sintering the Ni felt, and a gap is generated between the current collector and the separator, so that the contact resistance is increased. As a result, there is a problem that battery performance is reduced.

[0005] In order to solve the above problems, an object of the present invention is to provide a solid oxide fuel cell having improved cell performance by suppressing sintering of Ni felt, which is a fuel electrode side current collector.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, a first aspect of the present invention provides a fuel cell system in which a fuel electrode and an oxidant electrode face each other via an electrolyte, and a separator for separating gas are laminated. In a solid oxide fuel cell having a structure in which a current collector is interposed between each electrode and a separator, the fuel electrode side current collector interposed between the fuel electrode and the separator has a surface of fibrous nickel. And a nickel felt to which an electrolyte material adheres.

The invention according to claim 2 is characterized in that the fuel electrode side current collector and the fuel electrode are integrated by cermet formation.

[0008]

According to the present invention, if the electrolyte material is attached to the surface of the fibrous Ni, the electrolyte material concentrates particularly at a portion where the fiber intersects with each other.
Felt sintering is suppressed, and a sufficient gap between fibers can be secured. Therefore, a decrease in the permeability of the fuel gas and an increase in the contact resistance can be suppressed, so that the cell performance is improved.

Further, if an electrolyte material is present on the surface of the fibrous Ni, the three-phase interface (Ni.gas.
The number of electrolytes) increases, and the reaction at the three-phase interface, which occurs mainly in the electrode portion, also occurs in the current collecting portion, so that the battery performance is improved. In addition, when the fuel electrode side current collector and the fuel electrode are integrated by cermet formation as in claim 2, the contact resistance between the fuel electrode side current collector and the fuel electrode is reduced, so that the battery performance is improved. Is further improved.

[0010]

Embodiment 1 FIG. 1 is a cross-sectional view of a solid oxide fuel cell according to one embodiment of the present invention, which is a solid made of a dense sintered body of zirconia (8YSZ) stabilized with 8% yttria. A fuel electrode 2 made of Ni-YSZ cermet is connected through an electrolyte 1 (external size 150 mm × 150 mm, thickness 0.2 mm) to L
a cell 4 in which an oxidizer electrode 3 made of a perovskite oxide such as aMnO ₃ is opposed to each other, is sandwiched between a pair of separators 5 and 9, and a fuel electrode-side current collector is provided between the fuel electrode 2 and the separator 5. 6 has a structure in which an oxidant electrode-side current collector 7 is interposed between the oxidant electrode 3 and the separator 9. Further, the surface of the solid electrolyte 1 where the electrodes are not coated and the separator 5
A seal material 8 was interposed between the seal material 9 and the seal material 9. As the fuel electrode-side current collector 6, Ni felt formed by carrying YSZ on the surface of fibrous Ni was used, and as the oxidant electrode-side current collector 7, a platinum net was used.

The loading of YSZ on the surface of the fibrous Ni was carried out by adjusting the viscosity of the octylate of Zr and Y at a quantitative ratio with glycerin and impregnating Ni felt almost uniformly. Hereinafter, the fabrication of the battery will be specifically described. First, 200 parts by weight of NiO powder, 150 parts by weight of Y ₂ O ₃ stabilized ZrO _2, 10 parts by weight of a binder (polyvinyl butyral resin), and 1 part of a solvent (terpineol)
And 100 parts by weight thereof were sufficiently mixed by a ball mill, and minute bubbles contained in the slurry were removed by stirring under reduced pressure to obtain a slurry for a fuel electrode.

On the other hand, La_0.9Sr_0.1MnO_ThreePowder 40
0 parts by weight and Y_TwoO_ThreeStabilized ZrO _Two150 parts by weight,
10 parts by weight of a binder (polyvinyl butyral resin),
100 parts by weight of a solvent (terpineol)
And thoroughly mix the small air bubbles contained in the slurry.
The mixture was stirred and removed under reduced pressure to obtain an oxidant electrode slurry. So
After that, the fuel electrode slurry is applied to one surface of the solid electrolyte.
Is applied to a thickness of 50 μm and dried,
This was fired in air at 1250 ° C. for 2 hours. Next,
On the other side of the solid electrolyte, apply the same oxidizer electrode slurry
After coating to a thickness of 50 μm and drying,
This was fired in air at 1100 ° C. for 4 hours.

Finally, after assembling the battery,
Humidified hydrogen as fuel and air as oxidant. Next, after purging with nitrogen, air is introduced to oxidize, then purging with nitrogen and reducing by introducing hydrogen, the cermet of the fuel electrode side current collector is converted to fibrous N.
The adhesion between i and YSZ was increased, and the anodic collector and the anode were made cermet.

The battery thus prepared is hereinafter referred to as battery (A). Comparative Example 1 A battery was produced in the same manner as in Example 1 except that Ni felt not carrying YSZ on the surface was used as the fuel electrode side current collector. [Experiment 1] Continuous discharge was performed using the battery (A) of the present invention and the battery (X) of the comparative example (both were single cells having an outer size of 150 mm × 150 mm). Shown in
In the experiment, the temperature was raised to 1000 ° C. under predetermined conditions, and then continuous discharge was performed at 300 mA / cm ² using hydrogen as a fuel and air as an oxidant. FIGS. 3 and 9 are schematic diagrams showing the main parts of the battery (A) of the present invention and the battery (X) of the comparative example after continuous discharge. Shows a three-phase interface.

As is apparent from FIG. 2, (A) of the present invention
It was confirmed that both the initial performance and the battery life of the battery were improved as compared with the battery (X) of the comparative example. It is clear from FIG. 3 and FIG. 7 that the improvement of not only the battery life but also the initial characteristics of the battery is achieved by the present invention.
In the battery, the number of three-phase interfaces at the current collector is increased as compared with the battery of the comparative example (X), and the reaction at the three-phase interface that occurs around the electrode also occurs at the current collector, and It is considered that this is due to the fact that the contact resistance between the Ni felt and the fuel electrode is reduced because the Ni felt was oxidized and reduced to form a cermet after the battery configuration. Embodiment 2 FIG. 4 is a schematic view of a small solid oxide fuel cell according to an embodiment of the present invention, and is a disk-shaped solid electrolyte made of a dense sintered body of zirconia (YSZ) stabilized at 3%. 11 (diameter 25 mm, thickness 0.2 mm), Ni
-Fuel electrode 12 made of YSZ cermet (external size 6 mm x 1
2.5 mm) and an oxidizer electrode 13 (external size 6 mm × 12.5 mm) made of a perovskite-type oxide such as LaMnO _{3. The} solid electrolyte 11 and the alumina pipe 1
4, a glass ring 15 is interposed as a sealing material. In addition, a reference electrode 16 (external size: 3 mm × 4 mm) was arranged next to the oxidizer electrode 13 for comparison, and an alumina plate 19 for inhibiting air permeability of the fuel electrode 12 was arranged. The reference electrode 16 and the alumina plate 19 are members to be used in the following experiments, and have no direct relation to the configuration of the present invention.

FIG. 5 is an enlarged view of a main part showing the electrode of FIG. 4, wherein a fuel electrode side current collector 17 is provided on the surface of the fuel electrode 12, and an oxidant electrode side current collector is provided on the surface of the oxidant electrode 13. 18 are arranged respectively. The fuel electrode side current collector 17 has a fibrous N
The Ni-Felt made of i was impregnated with a thinned fuel electrode slurry, and the oxidant electrode-side current collector 18 was a platinum net.

Here, the battery was manufactured as follows. First, a fuel electrode slurry and an oxidant electrode slurry were prepared in the same manner as in Example 1. Next, a fuel electrode and a current collector for the fuel electrode are sequentially superimposed on one surface of the solid electrolyte, and a thinner of the slurry for the fuel electrode is applied from above the current collector for the fuel electrode, and the like. Both the anode current collector and the anode were impregnated with the anode slurry. On the other hand, the oxidant electrode slurry was applied to the other surface of the solid electrolyte in the same manner as in Example 1 above.

Thereafter, a battery was manufactured in the same manner as in Example 1. The battery thus created is hereinafter referred to as (B) battery. Comparative Example 2 A battery was prepared in the same manner as in Example 2 except that Ni felt not impregnated with the anode slurry was used as the anode-side current collector.

The battery prepared in this manner is hereinafter referred to as (Y) battery. [Experiment 2] The reaction resistance of the fuel electrode was measured using the battery (B) of the present invention and the battery (Y) of the comparative example. The results are shown in FIG. The experiment used humidified hydrogen as fuel,
In order to use air as the oxidant and to observe the reactivity under high steam pressure (high fuel utilization state), the humidification temperature of the fuel gas was changed to change the partial pressure of steam in the fuel. The condition is that the reaction resistance is determined by the current interrupter method.

As is apparent from FIG. 6, (B) of the present invention
It was confirmed that the reaction resistance of the battery was substantially constant at each water vapor partial pressure, and that the overall reaction resistance was lower than that of the battery (Y) of the comparative example. In addition, when the fuel electrode side resistance before oxidation / reduction and after oxidation / reduction of the battery of the present invention (B) was measured, the fuel electrode side resistance before oxidation / reduction was 42.3Ω, but after oxidation / reduction. It was also confirmed that the resistance was significantly reduced to 0.8Ω. Therefore, it is understood that the cermet of the anode current collector and the anode reduces the anode resistance. [Experiment 3] Using the battery (B) of the present invention and the battery (Y) of the comparative example, a time-dependent change in cell voltage was measured by an accelerated deterioration test. The results are shown in FIG. In the accelerated deterioration test, the both ends of the anode current collector were pressed with an alumina plate, a load of ² kgf / cm ² was applied, and the anode current collector was held and fixed in a hydrogen atmosphere at 1000 ° C. for 30 hours. , The humidification temperature of hydrogen was raised to 95 ° C (83% H
₂ O) to create a state of high fuel utilization and a current density of 30
The condition is that the measurement is performed at a constant value of 0 mA / cm ² .

As is apparent from FIG. 7, (B) of the present invention
It was confirmed that both the initial performance and the battery life of the battery were improved as compared with the battery (Y) of the comparative example. Also,
The deterioration rate per hour is about 1.5 mV for the battery (B) of the present invention.
/ Hr, and the battery of the comparative example (Y) was about 3.6 mV / hr.
Therefore, it was also confirmed that in the battery (B) of the present invention, the deterioration rate per unit time was improved by half or less. [Experiment 4] The pore size distribution was measured by a mercury intrusion method to confirm whether the anode slurry was impregnated in the Ni-Felt as the anode current collector in the battery (B) of the present invention. The results are shown in FIG.
As comparative materials, Ni felt not impregnated with the slurry for the anode in the battery (Y) of the comparative example and the slurry for the anode in the battery (B) were used.

As is apparent from FIG. 8, the pore size of Ni felt not impregnated with the slurry for the anode has a pore size of 1 to 10 μm.
m, and that of the anode slurry is 0.0
While the pore size distribution in the current collector of the present invention is large in the range of 04 to 0.1 μm, both the Ni felt and the slurry for the fuel electrode exist in the pore size distribution. As a result, it was confirmed that the Ni electrode, which is the current collector of the present invention, was impregnated with the anode slurry. [Other Matters] As the electrolyte material to be supported on the surface of the fibrous Ni that is the fuel electrode side current collector, any material may be used as long as it can be used as an electrolyte material, and in particular, the following (a) to
The materials listed in (c) are preferred.

(A) 3 mol% to 12 mol% YSZ (b) Gd ₂ Zr ₂ O ₇ system or Ln (Zr _0.8 Ti _0.2 )
₂ O ₇ [where Ln is Sm, Eu, Gd, Ho, Er,
Lanthanide-based (rare-earth-based) oxide represented by Yb, Lu) or the like. (C) Proton conductor such as BaCeO ₃ -based ceramics.
Of course, it is also possible to use _X , (CeO ₂ ) _0.8 (S _m O _1.5 ) _0.2 , _Pr O _x or the like. Examples of a method for supporting the electrolyte material include a method in which the YSZ powder is slurried using the solvent used for the electrode, and is impregnated substantially uniformly.

[0024]

According to the present invention described above, since the electrolyte material is concentrated particularly at the portions where the fibers intersect, the sintering of Ni felt during long-term operation at high temperature is suppressed, and Gap can be sufficiently secured. Therefore, a decrease in the permeability of the fuel gas and an increase in the contact resistance can be suppressed, so that the cell performance is improved.

If the electrolyte material is present on the surface of the fibrous Ni, the three-phase interface (Ni.gas.
The number of electrolytes) increases, and the reaction at the three-phase interface, which occurs mainly in the electrode portion, also occurs in the current collecting portion, so that the battery performance is improved. In addition, if the fuel electrode side current collector and the fuel electrode are integrated by cermet, the contact resistance between the fuel electrode side current collector and the fuel electrode is reduced, so that the cell performance is further improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of a solid oxide fuel cell according to one embodiment of the present invention.

FIG. 2 is a graph showing a change over time in cell voltage when continuous discharge is performed using the battery (A) of the present invention and the battery (X) of the comparative example.

FIG. 3 is a schematic view showing a main part of the battery (A) of the present invention.

FIG. 4 is a schematic diagram of a small solid oxide fuel cell according to one embodiment of the present invention.

FIG. 5 is an enlarged view of a main part showing the electrode of FIG. 4;

FIG. 6 is a graph showing the relationship between the partial pressure of water vapor and the reaction resistance of the fuel electrode when the battery (B) of the present invention and the battery (Y) of the comparative example are used.

FIG. 7 is a graph showing a change over time of a cell voltage when an accelerated deterioration test is performed using the battery (B) of the present invention and the battery (Y) of the comparative example.

FIG. 8 shows (B) the Ni-Felt impregnated with the anode slurry in the battery of the present invention, (Y) the Ni-Felt not impregnated with the anode slurry in the (Y) battery of the comparative example, and the (B) battery. 4 is a graph showing a pore size distribution by a mercury intrusion method when the fuel electrode slurry is used.

FIG. 9 is a schematic diagram showing a main part of a battery (X) of a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrolyte 2 Fuel electrode 3 Oxidant electrode 4 Cell 5.9 Separator 6 Current collector for fuel electrode 7 Current collector for oxidant electrode

Continuing on the front page (72) Inventor Koji Yasuo 2--18 Keihanhondori, Moriguchi-shi Sanyo Electric Co., Ltd. (72) Inventor Yukinori Akiyama 2-18 Keihanhondori, Moriguchi-shi Sanyo Electric Co., Ltd. (72) Inventor Toshihiko Saito 2-18 Keihanhondori, Moriguchi-shi Sanyo Electric Co., Ltd. (56) References JP-A-6-243873 (JP, A) JP-A-6-36783 (JP, A) JP-A 5- 101836 (JP, A) JP-A-5-343080 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 8/02 H01M 8/12

Claims (2)

(57) [Claims] 1. A cell in which a fuel electrode and an oxidizer electrode face each other with an electrolyte interposed therebetween and a separator for separating gas, and a current collector is interposed between each electrode and the separator. In the solid oxide fuel cell having the above structure, the fuel electrode side current collector interposed between the fuel electrode and the separator is formed of nickel felt in which an electrolyte material is attached to a surface of fibrous nickel. Solid electrolyte fuel cell. 2. The solid oxide fuel cell according to claim 1, wherein the fuel electrode side current collector and the fuel electrode are integrated by cermet formation.