JP3095342B2 - Solid oxide fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a solid oxide fuel cell, and more particularly to a solid oxide fuel cell using a separator plate made of a heat-resistant alloy containing a chromium component.

[0002]

2. Description of the Related Art A solid oxide fuel cell alternates between a cell having an anode disposed on one side of a solid electrolyte plate and a cathode disposed on the other side, and a separator plate having ribs and gas flow passages formed therein. It has a structure in which a plurality of sheets are stacked.
It is operated at a high temperature of 0 ° to 1000 ° C. and generates power by an electrochemical reaction between a fuel gas (hydrogen-rich gas) and an oxidizing gas (air) inside.

[0003] The fuel cell having the above structure is generally called a flat plate type, and has an advantage that the power generation efficiency per unit volume of the fuel cell is high. To prevent the mixing of gas and oxidizing gas, and to collect electricity from each cell. Therefore, even in a high-temperature oxidizing atmosphere during fuel cell operation, high airtightness, conductivity, heat resistance, and oxidation resistance It is required to have many properties such as

Therefore, conductive ceramics, various alloys, and the like have been proposed as materials for the separator plate so far. As a material having excellent workability, a heat-resistant alloy made of a Ni-Cr-Fe-based material is exemplified. Here, in the separator plate made of a Ni—Cr—Fe heat-resistant alloy, a dense Cr ₂ O ₃ layer is formed on the surface thereof in a high-temperature oxidizing atmosphere, so that the progress of oxidation into the inside of the separator plate is suppressed. And the oxidation resistance during fuel cell operation.

[0005]

However, on the other hand, since a chromium component evaporates from the surface of the Cr ₂ O ₃ layer, a separator plate made of a Ni—Cr—Fe heat-resistant alloy was used for a fuel cell. In this case, the chromium component diffuses from the surface of the separator plate and mixes into the adjacent cathode. Therefore, there has been a problem that the power generation performance of the cell is reduced and the operating life of the fuel cell is shortened.

In order to solve such a problem, for example, in Japanese Patent Application No. Hei 5-190636, a surface of a separator plate facing a cathode is coated with a perovskite oxide having high electron conductivity and oxidation of Sr, La or the like. The diffusion of the chromium component from the surface of the separator plate to the cathode has been achieved by disposing an oxide layer composed of a mixture with a material.

According to this method, the chromium component diffused from the separator plate reacts with an oxide such as Sr, La or the like, whereby the diffusion of the chromium component to the cathode can be suppressed. Can be lengthened. By the way, the demand for the power generation life of the solid oxide fuel cell is increasing year by year, and it is necessary to extend the life of at least 40,000 hours in order to obtain a fuel cell having high practical value. In order to respond to such a demand, in the above-mentioned method, in order to enhance the effect of suppressing chromium component diffusion in the oxide layer, Sr, L
Increasing the content of the oxide such as a and increasing the thickness can be considered.

[0008] However, if the thickness of the oxide layer is too large, the layer is separated and the effect of suppressing the diffusion of the chromium component tends to be lost, so that the practical limit is about 250 µm. Further, if the content of oxides such as Sr and La is too high, the electronic conductivity of the entire oxide layer is reduced.
Because of the problem that the current collection efficiency from the cathode is reduced, it has been difficult to achieve a longer service life of 40000 hours or more.

In view of the above problems, the present invention suppresses the diffusion of the chromium component from the separator plate to the cathode for a long period of time and prevents a decrease in the power generation performance of the cell, thereby extending the life of the cell by more than 40000 hours. It is an object of the present invention to provide a solid oxide fuel cell capable of realizing the above.

[0010]

In order to solve the above-mentioned problems, the invention according to claim 1 comprises a cell in which an anode and a cathode are arranged via a solid electrolyte plate, and a heat-resistant alloy containing a chromium component. In a solid oxide fuel cell, a plurality of separator plates are alternately stacked, and an oxide layer for suppressing diffusion of a chromium component is disposed on a surface of the separator plate facing the cathode. The layer is composed of a mixture of conductive ceramics and La ₂ O _3, and has a La ₂ O ₃ content C of the oxide layer.
(Vol%) and the thickness T (μm) are set so as to satisfy Equation 1 and Equation 2 (where σ ₀ is the conductivity of the conductive ceramic). .

In the invention described in claim 2, the conductive ceramic is represented by a general formula: ABO ₃ (where A
Represents at least one element of Ca, Sr, Ba, Y, La, and Ce, and B represents Mg, Al, Ti, V, Cr,
At least one element among Mn, Fe, Co, Ni, and Cu is shown. ), Which is a perovskite oxide having high electron conductivity.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have argued that, among oxide layers made of a mixture of a conductive ceramic such as a conductive perovskite oxide and an oxide such as Sr and La, particularly the conductive ceramic and La The mixture with ₂ O ₃ has a good effect of suppressing the diffusion of the chromium component.
In order to obtain the effect of suppressing the diffusion of the chromium component enough to obtain a battery life of 0000 hours or more, the La ₂ O ₃ content C and the thickness T of the oxide layer only have to satisfy the relationship of the above mathematical formula 1. And that the La ₂ O ₃ content C and the thickness T of the oxide layer satisfy the relationship of the above formula 2 in order to secure the necessary conductivity of the oxide layer in view of the practicality of the battery; And found the present invention.

That is, the La ₂ O ₃ content C (vol%) and the thickness T expressed by the inequality described in claim 1
By disposing the (μm) oxide layer on the surface of the separator plate facing the cathode, the diffusion of the chromium component from the surface of the separator plate can be effectively suppressed.
A longer service life of 00 hours or more can be realized. According to the second aspect of the present invention, since the conductive ceramic has a thermally stable perovskite structure, even at a high operating temperature of the solid oxide fuel cell,
No impurities are mixed into the cathode or anode due to the thermal decomposition of the conductive ceramic, which is more advantageous for extending the battery life.

An embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a perspective view of a solid oxide fuel cell according to the present invention. The solid oxide fuel cell is an internal manifold type flat plate stacked type, and is a solid electrolyte plate 1 made of 3 mol% yttria-added partially stabilized zirconia (hereinafter referred to as 3-YSZ).
A cell 3 having an anode 2 prepared from NiO and 3-YSZ on one side and a cathode prepared from La _0.9 Sr _0.1 MnO ₃ and 3-YSZ on the other side
And a separator plate 4 having ribs 5 and gas flow passages 6 formed on both sides of a heat-resistant alloy having a composition of Ni; 70, Cr; 22, Fe; 8 (wt%) by cutting and polishing. Are stacked.
Further, openings 10 and 11 serving as internal manifolds for the anode gas and the cathode gas are formed on both sides of the cell 3 and the separator plate 4. 1, only a pair of cells 3 and a separator plate 4 are shown for convenience of illustration.

Further, the surface 7 of the separator plate 4 facing the cathode (the entire surface of the rib 5 and the surface of the gas flow passage 6; the same applies hereinafter) is used to prevent the diffusion of the chromium component from the separator plate 4 to the cathode. To suppress, La _0.9 S
An oxide layer (not shown) made of a mixture of r _0.1 CoO ₃ and La ₂ O ₃ is provided. Also, the separator plate 4
The surface in contact with the anode 2 is made of Ni felt (not shown) in order to improve the current collection efficiency of the separator plate 4.
Is arranged.

Here, the above-mentioned cell 3 was formed as follows. As a raw material of the anode 2, an average particle size of 0.1.
5 μm of 8 mol% yttria-added partially stabilized zirconia (hereinafter referred to as 8-YSZ) powder and an average particle diameter of 1 μm
m of NiO powder was used. Then, at the time of NiO reduction, these were mixed in a weight ratio of 5: 5, and a slurry was formed using a terpineol solvent and PVB to obtain an anode slurry.

As a raw material for the cathode, the average particle diameter is 1 μm.
La _0.9 Sr _0.1 MnO ₃ powder and 8-YSZ powder having an average particle size of 1 μm were used. These are mixed so that the weight ratio becomes 8: 2, and the terpineol solvent and PV are mixed.
The mixture was slurried using B to obtain a cathode slurry. The anode slurry is applied to one surface of the solid electrolyte plate 1 at a thickness of 50 μm, dried, and then dried in air.
It was baked at 0 ° C. for 2 hours. Subsequently, the cathode slurry was applied to the other surface at a thickness of 50 μm, dried, and then fired in air at 1100 ° C. for 4 hours to obtain a target cell 3.

The oxide layer was formed as follows. As raw materials for the oxide layer, La _0.9 Sr _0.1 CoO ₃ powder having an average particle diameter of 1 μm and L _0.9 Sr _0.1 CoO ₃ powder having an average particle diameter of 1 μm were used.
a ₂ O ₃ powder was used. And these are 9:
1 and slurried using a terpineol solvent and PVB. This was applied to a surface of the separator plate facing the cathode so as to have a thickness of 200 μm and dried to obtain a target oxide layer.

In the solid oxide fuel cell having the above-described structure, the La ₂ O ₃ content C and the thickness T of the oxide layer are determined in order to determine conditions for setting the battery life to 40000 hours or more.
Experiment 1 described below was prepared by changing
And Experiment 2 were performed. (Experiment 1) First, in Experiment 1, La _{2 of the} oxide layer was used.
Product C × T of O ₃ content C (vol%) and thickness T (μm)
And the relationship between the fuel cell life and the fuel cell life (hr). In the experiments, solid electrolyte fuel cells having various La ₂ O ₃ contents C and thicknesses T were subjected to a temperature of 900 ° C. and a current density of 0.5.
The cell was operated at 1 A / cm ² and the cell voltage was 0 V from the start of the experiment.
The time until the current density reached 0.3 A / cm ² was measured and defined as the battery life.

FIG. 2 is a graph showing the results of Experiment 1 described above, and each plot is obtained by averaging a plurality of measurement data having the same product C × T. According to FIG.
It can be seen that the life of the fuel cell is proportional to the change in the product C × T. Here, considering the practical use of the solid oxide fuel cell, the life of the fuel cell needs to be at least 40000 hours. Therefore, when the graph of FIG. 2 is extrapolated to the upper right, the value of the product C × T needs to be larger than 1000 in order to obtain the effect of suppressing the diffusion of the chromium component such that the fuel cell life exceeds 40,000 hours. You can see that. Therefore, Equation 1 is derived.

The product C × T is used as a factor in the graph for the following reason. That is, as described above, since the chromium component diffused from the surface 7 of the separator plate 4 facing the cathode reacts with La ₂ O ₃ in the oxide layer, the La ₂ O ₃ content C It is considered that the larger the value, the more the diffusion to the cathode is suppressed, and the longer the battery life. Similarly, as the thickness T of the oxide layer increases, the diffusion of the chromium component is suppressed, and in this case, the battery life is considered to be prolonged.

(Experiment 2) In Experiment 2, the relationship between the La ₂ O ₃ content C (vol%) of the oxide layer and the conductivity σ (Ω ⁻¹ · cm ⁻¹ ) of the oxide layer was examined. Examined. FIG.
Is a graph showing the results of Experiment 2 above. According to FIG. 3, it can be seen that the conductivity σ decreases as the La ₂ O ₃ content C of the oxide layer increases.

It has been derived that each of the measurement points substantially overlaps a curve represented by the following equation (3).

[0024]

(Equation 3) On the other hand, the electrical resistance R (Ω · cm ² ) of the oxide layer is calculated using the following equation (a) using the thickness T (μm) of the oxide layer and the conductivity σ (Ω ⁻¹ · cm ⁻¹ ). It is represented as R = T / σ × 10 ⁻⁵ (a) Here, the electric resistance R of the oxide layer is the internal resistance of the solid oxide fuel cell. The value of the resistance R needs to be smaller than 0.01 Ω · cm ² , and the following equation (b) is obtained from the above equation (a).

T / σ <10 ³ (b) Therefore, as a condition for suppressing the internal resistance of the fuel cell to a practical level, from the above equations (3) and (b),
Equation 2 above is derived. Experiment 1 and Experiment 2 described above
Specifically, the ranges of the La ₂ O ₃ content C and the thickness T of the oxide layer satisfying both Expressions 1 and 2 derived from are shown in FIG. Part (the part with a horizontal line). It should be noted that the curves 20 and 21 are curves represented by equations obtained by replacing the inequalities in the above equations 1 and 2, respectively, with the equal signs.

Here, there is no particular upper limit on the thickness T of the oxide layer. However, considering the oxide layer forming process and the separation from the separator plate 4 due to thermal stress, etc.
It is desirable that the thickness be 250 μm or less (the hatched portion in FIG. 4). Therefore, the ranges of the La ₂ O ₃ content C and the thickness T of the oxide layer where practically excellent effects are recognized with respect to the diffusion suppression of the chromium component, the electronic conductivity, the peeling durability, and the like are shown in FIG. It is indicated by a common part with both horizontal and diagonal lines.

The oxide layer manufactured in this embodiment mode
Is La_TwoO_ThreeThe content C is 10 vol% and the thickness T
Is 200 μm, the horizontal and oblique lines in FIG.
This fuel cell is included in the common part where both were applied.
Achieved more than 40,000 hours of fuel cell power generation life
can do. In the present embodiment, in the oxide layer
La as a conductive ceramic_0.9Sr _0.1CoO_Three
(Σ₀= 150Ω^-1・ Cm^-1), But this
It is not limited, and the electronic conductivity slightly decreases
For example, La_0.9Sr_0.1MnO_Three(Σ₀= 20Ω^-1
・ Cm^-1) Can also be used.

Reference Example As in the above-described embodiment,
When an oxide layer made of a mixture of conductive ceramics and La ₂ O ₃ is formed on the separator plate 4, if the thickness T of the oxide layer is set too large, the oxide layer may have a different thermal expansion coefficient. Although the layer is easily peeled off from the separator plate 4, the following method can be used to avoid this.

In the present embodiment, the overall structure of the solid oxide fuel cell is the same as that of the above embodiment, but no oxide layer is provided on the surface 7 of the separator plate 4 facing the cathode. Instead, a solution prepared by dissolving 0.5 g of lanthanum nitrate in 20 ml of ethanol was applied to the surface 7 to a thickness of 50 μm. According to this method,
Operating temperature of the solid oxide fuel cell (about 800 to 100
At 0 ° C.), the lanthanum film reacts with the chromium component of the separator plate 4 to form a perovskite LaCrO ₃ film. This perovskite-type oxide LaCrO ₃ film has perfect electronic conductivity, and has a higher Ni, Fe, and Fe content than the Cr ₂ O ₃ layer.
Since the ionic conductivity of Cr, O and the like is low, the effect of suppressing the progress of oxidation of the separator plate 4 is obtained without increasing the electric resistance through the surface coating.

Further, since a film is formed by a reaction with a chromium component diffused from the inside of the separator plate 4 to the surface by heat treatment or the like, a thin and uniform dense film having good adhesion on the surface of the separator plate 4 can be formed. is there. Therefore, the surface protective film does not cause peeling, which has been a problem in protecting the surface of the separator plate 4, and can efficiently suppress the diffusion of the chromium component.

[0031]

As described above, according to the first aspect of the present invention, in a solid oxide fuel cell provided with an oxide layer for suppressing diffusion of a chromium component, in order to obtain a battery life of 40,000 hours or more, oxidation is performed. La ₂ O ₃ content C of the material layer
(Vol%) and the range of values to be taken for the thickness T (μm) are shown. Therefore, by disposing an oxide layer having C and T within this range on the surface of the separator plate facing the cathode, it is possible to effectively suppress the diffusion of the chromium component without significantly lowering the electronic conductivity. Thus, a fuel cell having a long power generation life (about 40,000 hours or more) can be obtained, and thus has a great practical utility value.

In the invention according to the second aspect, the conductive ceramic in the oxide layer is a perovskite oxide. Therefore, even at a high operating temperature of the solid oxide fuel cell, the conductive ceramics do not undergo thermal decomposition and the like, there is no impurity in the cathode or the anode, and a decrease in power generation performance can be prevented, so that the battery life is extended. It is even more advantageous for

[Brief description of the drawings]

FIG. 1 is a perspective view of a solid oxide fuel cell according to an embodiment.

FIG. 2 is a diagram showing a relationship between a product C × T (μm · vol%) of a La ₂ O ₃ content C (vol%) of an oxide layer and a thickness T (μm), and a battery life (hr). It is.

FIG. 3 is a graph showing the relationship between the La ₂ O ₃ content C (vol%) of the oxide layer and the conductivity σ (Ω ⁻¹ · cm ⁻¹ ) of the oxide layer.

FIG. 4 shows an appropriate La ₂ O ₃ content C (vol.
%) And a range of thickness T (μm) (a common portion indicated by both horizontal and oblique lines).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid electrolyte plate 2 Anode 3 Cell 4 Separator plate 5 Rib 6 Gas flow path 7 Surface facing cathode

Continuation of the front page (72) Inventor Kotoku Akiyama 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Yasuo Miyake 2-5-5-1 Keihanhondori, Moriguchi-shi, Osaka Sanyo JP-A-1-100866 (JP, A) JP-A-4-138670 (JP, A) JP-A-7-45291 (JP, A) JP-A-7-153469 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 8/00-8/24

Claims (2)

(57) [Claims] 1. A cell in which an anode and a cathode are arranged via a solid electrolyte plate, and a plurality of separator plates made of a heat-resistant alloy containing a chromium component are alternately laminated, and the separator plate faces the cathode of the separator plate. A solid oxide fuel cell in which an oxide layer for suppressing diffusion of a chromium component is disposed on the surface of the solid oxide fuel cell, wherein the oxide layer comprises a mixture of conductive ceramics and La ₂ O ₃ ; The La ₂ O ₃ content C (vol%) and the thickness T (μm) of the material layer are as follows: And, (Where σ ₀ is set to satisfy the conductivity of the conductive ceramics). 2. The conductive ceramic is represented by the general formula: ABO ₃ (where A is Ca, Sr, Ba, Y,
At least one element of La and Ce, B is M
g, Al, Ti, V, Cr, Mn, Fe, Co, Ni,
At least one or more elements of Cu are shown. 2. The solid oxide fuel cell according to claim 1, which is a perovskite oxide having high electron conductivity represented by the following formulas.