JPH07201340A - Solid electrolyte fuel cell - Google Patents

Abstract

PURPOSE:To eliminate difficult points which oxidizing a separator is advanced to decrease conductivity and a long time continuous operation can not be performed. CONSTITUTION:A solid electrolyte fuel cell is formed by alternately laminating a single cell 2 formed by providing an anode 21 in one surface and a cathode 23 in the other surface of a flat plate-shaped solid electrolyte body 22 and a separator 1A. A heat resistant alloy, for instance, nickel base chrome added tungsten added alloy of small thermal expansion coefficient is used in a substrate 11, and a ceramics layer 12 comprising a lanthanum perovskite double oxide, for instance, lanthanum mangnite, having a thermal expansion coefficient almost equal to that of the hear resistant alloy, is flame-sprayed to surface mutually opposed to the cathode 23 of this substrate 11, to form the separator 1A.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a flat plate type solid oxide fuel cell separator and its material.

[0002]

2. Description of the Related Art A solid oxide fuel cell is a fuel cell in which zirconia is used as an electrolyte and is operated at a high temperature of around 1000 [° C.]. It has features such as no need for quality, no maintenance of electrolytes, and expectation for combined power generation with gas turbines and steam turbines. It is actively promoted both inside and outside the country.

Structurally, the solid oxide fuel cell is roughly divided into a cylindrical type and a flat plate type. However, in each type, a partition for separating the supplied fuel gas and oxidant gas is required, The mold is provided with a partition called an interconnector, and the flat plate type is provided with a partition called a separator. These partition walls, that is, interconnectors or separators, are chemically stable in both high-temperature reducing atmospheres and oxidizing atmospheres around 1000 [° C], and have excellent gas impermeability. ,
In addition, excellent electronic conductivity is required as a basic functional physical property.

As a material that has been put to practical use or is being studied as these materials, lanthanum chromite LaCrO which is a lanthanum-based perovskite complex oxide in which B site element is chromium is used as a ceramic material.
There are _three , and heat-resistant alloys have been proposed for metallic materials. Lanthanum chromite is used as an interconnector for a cylindrical solid oxide fuel cell manufactured by Westinghouse. In this solid oxide fuel cell, the EV
A dense lanthanum chromite excellent in gas impermeability is formed by the D method (Electro Chemical Vapor Deposition Method), and an interconnector is used to prevent cross leak between the fuel gas and the oxidant gas. Although application of lanthanum chromite to a separator of a flat plate type solid oxide fuel cell is also being considered, it is considered difficult to form it by the EVD method in terms of manufacturing technology. A method of using a separator, a method of spraying lanthanum chromite on a preformed electrode base material to form a separator, and the like have been studied.

On the other hand, the use of heat-resistant alloys as separator materials has been studied by many research and development institutions,
For example, a nickel-based chromium-added iron-added alloy is a typical example. However, when these heat-resistant alloys are used as they are for the separator, there is no particular problem such as corrosion because reducing gas, that is, hydrogen gas, methane gas, etc. is supplied on the fuel electrode side, but there is no problem such as corrosion on the air electrode side. That is, the surface of the alloy is gradually oxidized by air, oxide scales are formed, and electron conductivity becomes extremely poor, and as a result, the function of the separator as a conductive member is stopped. As a method of compensating for this weak point, a ceramic layer is formed by coating the surface of a nickel-based chromium-added iron-added alloy with lanthanum-cobaltite LaCoO ₃ which is a lanthanum-based perovskite complex oxide containing B site element as cobalt. Attempts have been made to suppress the generation of scale.

FIG. 2 is an exploded perspective view showing a structural example of a conventional flat plate type solid oxide fuel cell. A single cell 2 comprising an anode 21, a solid electrolyte body 22 and a cathode 23;
Substrate 13 made of nickel-based chromium-added iron-added alloy 13
And a separator 1 formed by coating a ceramic layer 14 made of lanthanum cobaltite on the plate are alternately laminated to form a flat plate solid oxide fuel cell. Anode 21
Fuel gas is caused to flow in the groove 15 of the separator 1 in contact with
Oxidant gas is flowed through the groove 16 in contact with the cathode 23. Ceramic layer 14 made of lanthanum cobaltite
Is coated on the surface in contact with the cathode 23. The separator 1 of the present construction has sufficient mechanical strength at high temperature because the substrate 13 is made of a heat-resistant nickel-added chromium-added iron-added alloy, and the ceramic layer 14 is coated on the cathode side in a high temperature oxidizing atmosphere. Therefore, it is also excellent in oxidation resistance and has the basic performance of a separator as a partition wall.

[0007]

However, even in the separator of the solid oxide fuel cell having the above-mentioned structure, the nickel-based chromium-added iron, which is a metal material, is used as a metallic material when it is in a high temperature oxidizing atmosphere for a long time during long-term operation. Deformation due to stress caused by the difference in thermal expansion coefficient between the additive alloy and lanthanum cobaltite, which is a ceramic material, causes a problem that oxidation gradually progresses and electron conductivity deteriorates, mainly due to deformation.

The object of the present invention is to eliminate these drawbacks,
Provided is a solid oxide fuel cell provided with a minute separator in which the progress of oxidation is minute even in a high temperature oxidizing atmosphere for a long time and the deterioration of electronic conductivity does not affect the power generation characteristics of the fuel cell. Especially.

[0009]

In order to achieve the above object, in the present invention, (1) a heat-resistant alloy is used for the substrate of the separator, and a cathode-side surface of this substrate is equivalent to the substrate. Has a coefficient of thermal expansion, preferably a difference from the coefficient of thermal expansion of the substrate is 2 × 10 ^-6
[K ^-1 ] A ceramic layer of lanthanum-based perovskite complex oxide having a coefficient of thermal expansion of not more than that is coated to form a separator, thereby forming a solid oxide fuel cell.

(2) Further, in the above (1), the heat-resistant alloy has a low coefficient of thermal expansion, preferably 16x.
A nickel-base heat-resistant alloy of 10 ^-6 [K ^-1 ] or less is used, and a lanthanum-based perovskite double oxide having an equivalent low thermal expansion coefficient is used to coat the ceramic layer to form a separator. (3) Further, in (2) above, a nickel-base chromium-added tungsten-added alloy or a nickel-base chromium-added iron-added alloy is used as the nickel-base heat-resistant alloy forming the substrate, and a lanthanum-based perovskite forming a ceramic layer is used. It is preferable to use lanthanum manganite La (Sr) MnO _{3 in} which strontium is added to the A site element and manganese is used as the B site element as the complex oxide.

(4) In the above (1), an iron-based chromium-added nickel-added alloy is used as the heat-resistant alloy, and a lanthanum-based perovskite complex oxide forming a ceramic layer is used. For example, lanthanum cobaltite La (Sr) CoO _{3 in} which strontium is added to the site element may be used.

[0012]

[Function] The lanthanum-based perovskite complex oxide is 1000
In a high temperature oxidizing atmosphere near [° C.], the phase is stable and has electronic conductivity, but in a reducing atmosphere where the oxygen partial pressure is extremely low, the phase is not chemically stable and electron conductivity is lost. Further, the lanthanum-based perovskite complex oxide is inferior in mechanical strength to metallic materials in a high temperature oxidizing atmosphere. On the other hand, the metal material is superior in mechanical strength to the lanthanum-based perovskite complex oxide, but even in the case of the heat-resistant alloy, the oxidation progresses in the high-temperature oxidizing atmosphere near 1000 [° C], as described above. However, by effectively utilizing the respective advantages of these heat-resistant alloys and lanthanum-based perovskite complex oxides, the substrate is composed of heat-resistant alloys, and the lanthanum-based perovskite complex oxides with excellent oxidation resistance are formed on the cathode side surface in a high temperature oxidizing atmosphere. By using a hybrid structure separator coated with an oxide ceramic layer, a solid oxide fuel cell satisfying the basic requirements can be constructed.

As described above, since the solid oxide fuel cell is used at a high temperature around 1000 [° C.], when the hybrid structure separator is used, the thermal stress caused by the difference in thermal expansion of the constituent materials is relaxed. Is important. That is, when the difference in thermal expansion between separators in which the ceramic layer of lanthanum-based perovskite complex oxide is coated on the substrate of heat-resistant alloy is too large, the applied thermal stress becomes excessive and the ceramic layer with poor mechanical strength is damaged. However, the performance of the separator will deteriorate during long-term use.

The solid oxide fuel cell is constructed by alternately stacking and sandwiching unit cells and separators. The thermal expansion coefficient of the solid electrolyte body and the thermal expansion coefficient of the separators that form the unit cells. If there is a large difference between and, thermal stress will be exerted on each other, resulting in damage and further deterioration of characteristics. Therefore, as in (1) above, a separator is formed with a substrate of a heat-resistant alloy having a thermal expansion coefficient substantially equal at 20 to 1000 [° C] and a ceramic layer of a lanthanum-based perovskite complex oxide, and a solid electrolyte type When used in fuel cells, the separator satisfies the basic requirements such as mechanical strength, heat resistance, oxidation resistance, gas impermeability, electronic conductivity, etc., and has minimal thermal stress caused by the difference in thermal expansion. The deterioration of the characteristics of the solid oxide fuel cell is reduced even if it is used for a long period of time.

Particularly, if the difference in the average thermal expansion coefficient between the heat-resistant alloy used and the lanthanum-based perovskite complex oxide at 20 to 1000 [° C.] is 2 × 10 ⁻⁶ [K ⁻¹ ] or less, 1000 [° C.]
Even if the temperature changes, the strain applied to the constituent materials is 2x10
It is as small as ^-3 or less, that is, 0.2 [%] or less, and deterioration of the characteristics of the solid oxide fuel cell can be suppressed to a small level.

As described in (2) above, a nickel-base heat-resistant alloy having a low thermal expansion coefficient, for example, 16 × 10 ^-6 [K ^-1 ] or less is used as the heat-resistant alloy used for the substrate, and lanthanum having an equivalent low thermal expansion coefficient is used. Assuming that the ceramic layer is formed by using the perovskite mixed oxide, the coefficient of thermal expansion is close to that of a solid electrolyte body made of yttria-stabilized zirconia YSZ, which has a low coefficient of thermal expansion of 10 to 11 × 10 ⁻⁶ [K ⁻¹ ]. A separator is obtained, which has a configuration that matches a single cell.

As described in Solid State Ionics 9 & 10 (1983), the thermal expansion coefficients of typical heat resistant alloys are shown in Table 1.

[0018]

[Table 1] Table 2 shows the composition and coefficient of thermal expansion of the lanthanum-based perovskite mixed oxide material studied.

[0019]

[Table 2] Therefore, as described in (3) above, a nickel-base chromium-added tungsten-added alloy or a nickel-base chromium-added iron-added alloy is used as the substrate material, and strontium is added to the A-site element as the coating material for forming the ceramics layer. When lanthanum manganite La (Sr) MnO ₃ with manganese as the site element is used, the difference in the coefficient of thermal expansion between the substrate and the ceramics layer is extremely small at 0.5 × 10 ^-6 [K ^-1 ] and the thermal expansion is The absolute value of the coefficient is also close to the coefficient of thermal expansion of the solid electrolyte body YSZ, and thermal stress due to thermal expansion can be effectively suppressed.

If an iron-based chromium-added nickel-added alloy is used as the substrate material and lanthanum cobaltite La (Sr) CoO ₃ or La (Ca) CoO ₃ is used as the coating material, the thermal expansion coefficient and solid electrolyte Although there is a slight difference between the coefficient of thermal expansion of the body YSZ and the difference between the substrate and the ceramic layer, the structure of the separator with reduced thermal stress can be obtained.

[0021]

EXAMPLE FIG. 1 is an exploded perspective view showing an example of a flat plate type solid oxide fuel cell of the present invention. Separator 1A
And unit cells 2 are alternately laminated to form a flat plate type solid oxide fuel cell. As in the case of FIG. 2, the unit cell 2 is integrated by forming the anode 21 on one surface and the cathode 23 on the other surface of the plate-shaped solid electrolyte body 22. The separator 1A comprises a substrate 11 made of a nickel-based chromium-added tungsten-added alloy and a ceramic layer 12 made of strontium-added lanthanum manganite La (Sr) MnO _{3 on the} surface facing the cathode 23. is there. A method is employed in which the substrate 11 is sandblasted in advance to roughen the surface, and then La (Sr) MnO ₃ is sprayed and coated. Groove 1 on the surface of the separator 1A facing the anode 21
5, the fuel gas is flowed to the groove 1 facing the cathode 23.
Oxidant gas is flown through 6. Separator 1A of this configuration
Has a sufficient mechanical strength at a high temperature because the substrate 11 is made of a heat-resistant nickel-added nickel-added tungsten-added alloy, and the strontium-added lanthanum manganite ceramic layer 12 is provided on the cathode side in a high-temperature oxidizing atmosphere. Since it is covered, it has excellent oxidation resistance.

FIGS. 3 and 4 show the results of conducting a long-term heating test using a sample having the same structure as the above separator. 25 [mm] x 25 [mm], thickness 5
The surface of the [mm] thin nickel-base chromium-added tungsten-added alloy was roughened by sandblasting, and then coated with strontium-added lanthanum manganite La (Sr) MnO ₃ by about 200 [μm] by a thermal spraying method. Created. This sample was heated in an air atmosphere with an electric furnace at a temperature rising rate of 200 [° C / h] and heated to 1000 [° C] to 1000
A heating test was performed for a period of time, and changes over time in the amount of change in weight associated with oxide formation and the electrical resistance associated with conductivity were measured. The amount of change in weight was determined by taking out the sample from the electric furnace at each measurement time, allowing it to cool naturally, and then subtracting the initial weight before the heating test from the measured sample weight. The maximum cooling rate in natural cooling is about 500 [° C / h]. In addition, when measuring the electrical resistance,
It is sandwiched between 1 platinum sheet with a surface pressure of 1 [kg / cm ² ], put again in an electric furnace and heated at a heating rate of about 500 [° C / h], and 2 sheets at 1000 [° C] The method of measuring the electric resistance by applying a voltage between the platinum sheets was used.

FIG. 3 shows the results of measuring the amount of change in weight, where the vertical axis is the amount of weight change per unit area and the horizontal axis is the elapsed time. Further, FIG. 4 is a measurement result of electric resistance, in which the vertical axis represents electric resistance converted per unit area and the horizontal axis represents elapsed time. In each figure, the measurement result of the sample having the same configuration as that of this example is shown as (1). In FIGS. 3 and 4, those shown as (2) and (3) are two samples made of the same method and having different materials, that is, a nickel-based chromium-added iron-added alloy with La (Sr) CoO. A sample coated with ₃ ,
It is a test result of a sample in which La (Sr) MnO ₃ is coated on an iron-based chromium-added nickel-added alloy. Further, (4) shows the test results of the nickel-base chromium-added iron-added alloy as an example of the characteristics of only the base material without coating.

Looking at the measurement results of the amount of change in weight in FIG.
In the case of only the base metal without the coating of (4), the weight changes rapidly with the passage of time. Peeling and further removal due to oxidation occur, and although the weight change amount is apparently smaller than that of the other samples, the progress of oxidation is extremely fast. On the other hand, in the samples (1), (2), and (3), the change in weight change over time was small, and the progress of oxidation was suppressed by the coated lanthanum-based perovskite complex oxide. I understand. In particular, it can be seen that the sample (1) having the same structure as that of the separator of the present example has a very small change in weight and is further excellent in oxidation resistance during long-term operation.

Looking at the measurement result of the electric resistance in FIG. 4, (3)
In the sample of (4), the electrical resistance increased rapidly with time, and the amount of change in weight was relatively stable (3). Guessed. On the other hand, in the samples of (1) and (2), a slight increase in the electric resistance is observed at the initial stage of heating, but the increase in the electric resistance is slight after 300 hours. In particular, the sample of (1) shows an almost constant electric resistance, which shows that it has excellent characteristics as a separator.

The difference in the coefficient of thermal expansion between the substrate and the coating material in each of the configurations (1), (2) and (3) used as the sample is shown in the following table.

[0027]

[Table 3] That is, good measurement results are shown in FIGS. 3 and 4 (1),
The difference in the coefficient of thermal expansion between the substrate material and the coating material of the sample of (2) is small, and in the sample of (1) which showed particularly excellent characteristics,
The difference is extremely small, 0.5 × 10 ^-6 [K ^-1 ]. On the other hand, a sample with a large difference in thermal expansion coefficient of 5.5 x 10 ^-6 [K ^-1 ]
In (3), the oxide layer is being deposited and the electrical resistance is increasing. These results clearly show that the difference in the coefficient of thermal expansion between the substrate material and the covering material is an important factor in constructing the separator, and it is desirable that the difference be 3.5 × 10 ^-6 [K ^-1 ] or less. It is a thing.

Therefore, if the material of the substrate 11 of the separator of the above embodiment is a nickel-base chromium-added iron-added alloy and the ceramic layer 12 covering this is strontium-added lanthanum manganite as in the above-mentioned embodiment, Since the difference in the coefficient of thermal expansion between the substrate 11 and the ceramic layer 12 is as small as 0.5 × 10 ⁻⁶ [K ⁻¹ ], a separator having excellent characteristics can be constructed.

Further, the substrate 1 of the separator of the above embodiment
The material of 1 is an iron-based chromium-added nickel-added alloy,
If the ceramic layer 12 covering this is strontium-added lanthanum cobaltite or calcium-added lanthanum cobaltite, the difference in the coefficient of thermal expansion between the substrate 11 and the ceramic layer 12 is 0.5 to 1.5 x10 ^-6 [K ^-1 ]. Since it is very small, a separator with good characteristics can be constructed.

In the above-described various structural examples, the element added to the A site element of the lanthanum-based perovskite complex oxide used for the ceramic layer 12 is specified and explained as strontium or calcium. The crystal structures of the perovskite-type mixed oxides are the same, and since magnesium, strontium and calcium are all alkaline earth elements, lanthanum manganite and lanthanum cobaltite containing them have almost the same thermal properties. It can be estimated that it has a coefficient of expansion. Therefore, even if the element added to the A-site element in the above-described various structural examples is an element of alkaline earth other than those described, it is expected that the same effect can be obtained.

[0031]

As described above, according to the present invention, (1) a heat-resistant alloy is used for a substrate, a cathode-side surface of this substrate is coated with a ceramic layer of a lanthanum-based perovskite complex oxide to form a separator, and The flat plate type solid oxide fuel cell is manufactured by forming the substrate and the ceramic layer with materials having substantially the same coefficient of thermal expansion, preferably with a difference in coefficient of thermal expansion of 2 × 10 ⁻⁶ [K ⁻¹ ] or less. Since it has been configured, the separator satisfies the basic requirements such as mechanical strength, heat resistance, oxidation resistance, gas impermeability, electronic conductivity, etc., and the thermal expansion between the substrate and the ceramic layer. The thermal stress due to the difference is very small, and the characteristics hardly deteriorate even after long-term use. Since the characteristics of the separator are improved in this way, a flat plate type solid oxide fuel cell having stable performance during long-term use can be obtained.

(2) Further, in the above (1), the heat-resistant alloy has a low coefficient of thermal expansion, preferably 16x.
Since a nickel-based heat-resistant alloy having a temperature of 10 ^-6 [K ^-1 ] or less is used and a lanthanum-based perovskite complex oxide having an equivalent low thermal expansion coefficient is used, the separator and the solid electrolyte disposed in the vicinity of the separator are The difference in the coefficient of thermal expansion with the body is reduced, the thermal stress on the solid electrolyte body is relieved, and a flat plate solid oxide fuel cell with more stable performance is obtained for long-term use. .

(3) Further, in the above (2), a nickel-base chromium-added tungsten-added alloy or a nickel-base chromium-added iron-added alloy is used as the nickel-base heat-resistant alloy, and a lanthanum-based perovskite complex oxide is used as the A site. Add strontium to the element,
Lanthanum Manganite La with B site element as manganese
If (Sr) MnO ₃ is used, the difference in coefficient of thermal expansion between the substrate and the ceramic layer is only 0.5 × 10 ⁻⁶ [K ⁻¹ ],
Since the difference in the coefficient of thermal expansion between the separator substrate and the solid electrolyte body is suppressed to 5 to 6 x10 ^-6 [K ^-1 ], it is suitable as a flat plate type solid oxide fuel cell having stable performance for a long period of time. Is.

(4) In (1) above, an iron-based chromium-added nickel-added alloy is used as the heat-resistant alloy, and strontium-added cobaltite La (Sr) CoO ₃ or calcium-added cobaltite is used as the lanthanum-based perovskite complex oxide. If La (Ca) CO ₃ is used, the difference in coefficient of thermal expansion between the substrate and the ceramic layer is only 0.
Since it is suppressed to 5 to 1.5 × 10 ⁻⁶ [K ⁻¹ ], it is possible to obtain a flat plate type solid oxide fuel cell having a small thermal stress and having stable performance even after long-term use.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing an embodiment of a flat plate solid oxide fuel cell according to the present invention.

FIG. 2 is an exploded perspective view showing a configuration example of a conventional flat plate solid oxide fuel cell.

FIG. 3 is a weight change characteristic diagram of various separator constituent materials in a long-time heating test.

FIG. 4 is a characteristic diagram of electric resistance change of various separator constituent materials in a long-time heating test.

[Explanation of Codes] 1 Separator 2 Single Cell 11 Substrate 12 Ceramic Layer 15 Groove 16 Groove 21 Anode 22 Solid Electrolyte 23 Cathode

Claims (12)

[Claims] 1. A single cell having an anode on one main surface and a cathode on the other surface of a plate-shaped solid electrolyte body, and a separator for supplying a reaction gas to the unit cell are alternately laminated. In the solid oxide fuel cell, the separator is a substrate made of a heat-resistant alloy, and a ceramic layer formed by coating the surface of the substrate facing the cathode with a lanthanum-based perovskite complex oxide having a thermal expansion coefficient equivalent to that of the heat-resistant alloy. A solid oxide fuel cell comprising: 2. The solid oxide fuel cell according to claim 1, wherein the difference in average thermal expansion coefficient between the heat-resistant alloy and the lanthanum-based perovskite complex oxide at 20 to 1000 [° C.] is 2 × 10 ^−6.
[K ⁻¹ ] or less, a solid oxide fuel cell. 3. The solid oxide fuel cell according to claim 1 or 2, wherein the heat-resistant alloy is a nickel-base heat-resistant alloy. 4. The solid oxide fuel cell according to claim 3, wherein the nickel-base heat-resistant alloy is a nickel-base chromium-added tungsten-added alloy. 5. The solid oxide fuel cell according to claim 3, wherein the nickel-base heat-resistant alloy is a nickel-base chromium-added iron-added alloy. 6. The solid oxide fuel cell according to claim 3, 4 or 5, wherein the lanthanum-based perovskite complex oxide is lanthanum manganite. 7. The solid oxide fuel cell according to claim 6, wherein the lanthanum manganite is an A-site element lanthanum to which an alkaline earth metal element is added. 8. The solid oxide fuel cell according to claim 7, wherein the alkaline earth metal element added to the lanthanum manganite is magnesium, calcium or strontium. 9. The solid oxide fuel cell according to claim 1 or 2, wherein the heat-resistant alloy is an iron-based chromium-added nickel-added alloy. 10. The solid oxide fuel cell according to claim 9, wherein the lanthanum-based perovskite complex oxide is lanthanum cobaltite. 11. The solid oxide fuel cell according to claim 10, wherein the lanthanum cobaltite is an A-site element lanthanum to which an alkaline earth metal element is added. 12. The solid oxide fuel cell according to claim 11, wherein the alkaline earth metal element added to lanthanum cobaltite is magnesium, calcium or strontium.