JPH08180893A - Solid electrolytic fuel cell - Google Patents

Abstract

PURPOSE: To provide a solid electrolytic fuel cell resistance to heat cycle by forming a cell base into a cermet in which the frame of a heat resisting alloy and the frame of zirconia ceramics are interwoven together. CONSTITUTION: This solid electrolytic fuel cell is formed of a unit cell aggregate 15 consisting of a cell base 11, a solid electrolytic body 12 and a cathode 13; and separators 14, 14. In this solid electrolytic fuel cell, the cell base 11 is formed of a cermet in which the frame of a heat resisting alloy and the frame of zirconia ceramics are interwoven together. As the heat resisting alloy, a Ni-Cr-W alloy based on Xi is effective. For the cermet in which the frame of the heat resisting alloy and the frame of zirconia ceramics, the powder of the heat resisting alloy and the powder of zirconia ceramic are mixed together, molded, and baked in oxidizing atmosphere, whereby the frame of a YSZ sintered body having proper particle size distribution and mixing ratio is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte fuel cell which converts a Gibbs free energy into electric energy by an electrochemical reaction using a solid electrolyte, and more particularly to a cell substrate of a flat plate solid electrolyte fuel cell.

[0002]

2. Description of the Related Art A fuel cell using an oxide solid electrolyte such as zirconia has a high operating temperature of 800 to 1000 ° C., and therefore has high power generation efficiency, requires no catalyst, and simplifies the reforming system. It is expected to be developed, and it has the characteristics that it is easy to handle because the electrolyte is a solid, and further, combined power generation with a gas turbine, etc. is also expected, and its development is expected as a third generation fuel cell. There is.

However, in the solid oxide fuel cell, the cell itself is liable to be thermally damaged because the main battery constituent members including the electrolyte are ceramics, and there is no suitable gas sealing method. It has been difficult to realize a type fuel cell. Therefore, a cylindrical solid oxide fuel cell with a different shape compared to phosphoric acid type fuel cells was devised by Westinghouse,
Development of a 25 kW prototype that structurally solves these problems is in progress. However, in principle, the cylindrical solid oxide fuel cell has a lower output density per unit volume of the cell than the flat plate type fuel cell. For this reason, flat plate type cells, which are expected to have high power density, have been actively developed in recent years.

[0004]

In the flat plate type solid oxide fuel cell, the development subject is to increase the area of the cell in addition to the above-mentioned gas sealing method. For increasing the area of the cell, an electrode on the cell substrate, a supporting membrane method for forming an electrolyte is proposed, which has appropriate mechanical strength, porosity and gas permeability,
Development of a cell substrate composed of nickel oxide NiO and yttria-stabilized zirconia YSZ is under consideration.

FIG. 6 is an exploded perspective view showing a flat plate type supporting membrane type solid oxide fuel cell. The solid electrolyte body 12 and the cathode 13 are placed on the cell substrate 11 to form a single cell assembly 15, and the single cell assembly 15 is sandwiched by the separator 14. A conventional cell substrate is, for example, nickel oxide NiO powder with a particle size of about 100 μm and yttria-stabilized zirconia YSZ calcined powder with 51 vol% Ni / YSZ.
And press molding, then calcination in air, then in hydrogen at a temperature of 1000 ° C nickel oxide NiO
Was produced by reducing.

However, such a conventional cell substrate 11 made of NiO and YSZ has insufficient mechanical strength and ductility, and metallic Ni sinters during battery operation, leading to deterioration in characteristics and a short battery life. There was a problem. The present invention has been made in view of the above points, and an object thereof is to develop a cell substrate having good mechanical strength and ductility without sintering, and provide a flat plate solid oxide fuel cell having excellent characteristics and reliability. To do.

[0007]

According to the present invention, the above object is to provide a solid oxide fuel cell including a unit cell in which a solid electrolyte body is laminated on a cell substrate, in which the cell substrate is a skeleton of a heat-resistant alloy and zirconia ceramics. This is achieved by the fact that the skeleton of is a cermet in which the skeletons are intertwined.

In the above invention, it is effective that the heat resistant alloy is a Ni-based Ni-Cr-W alloy. The cermet in which the skeleton of the heat-resistant alloy and the skeleton of the zirconia ceramics are intertwined, the powder of the heat-resistant alloy and the powder of the zirconia ceramics are mixed, molded, and fired in the temperature range of 1400 to 1550 ° C in an oxidizing atmosphere. As a result, the skeleton of the YSZ sintered body having an appropriate particle size distribution and mixing ratio is formed.

The oxide of a heat-resistant alloy composed of Ni-Cr-W is reduced in a temperature range of 1000 to 1200 ° C. in a hydrogen atmosphere to obtain a Ni-Cr-W heat-resistant alloy having an appropriate particle size distribution and mixing ratio. The skeleton of the union is formed.

[0010]

[Function] The skeleton formation of the YSZ sintered body and the skeleton formation of the Ni-Cr-W heat-resistant alloy sintered body improve the mechanical strength of the cell substrate, and Ni-C
The skeleton formation of the sintered body of the rW base heat-resistant alloy improves the ductility of the cell substrate. Ni-Cr-W heat-resistant alloys are high melting point Cr, W
It is difficult to sinter because it contains, improving the battery life.

Zirconia ceramics makes the coefficient of thermal expansion of cermet approximate the coefficient of thermal expansion of a solid electrolyte body made of zirconia.

[0012]

Embodiments of the present invention will now be described with reference to the drawings. As the raw material powder for the cell substrate, we prepared a heat-resistant alloy powder with a particle size distribution of 1 μm to 50 μm and a composition of Ni-22Cr-14W, and a yttria-stabilized zirconia YSZ powder that had been pre-calcined to have a particle size distribution of 5 μm to 50 μm. To do. A heat-resistant alloy powder of Ni-22Cr-14W composition that was blended to 40 vol% was mixed with a water-soluble binder in an aqueous solution using a ball mill, dried, and then uniaxially press-formed to a diameter of 75 mm and a thickness of 4 mm. Obtain a green molded body.

Next, in air, at a heating rate of 100 ° C./h
A cell substrate is obtained by firing at a temperature of 1550 ° C. and reducing at a temperature of 1200 ° C. in a hydrogen atmosphere. Next, an electron micrograph of a cross section of the obtained cell substrate was obtained. FIG. 1 shows a crystal structure of a cell substrate, (a) is a scanning electron microscope photograph of the cell substrate of the present invention, and (b) is a scanning electron microscope photograph of a conventional cell substrate.

Comparing the two pictures, the conventional substrate is YS
It can be seen that YSZ and the heat-resistant alloy powder are well sintered and the zirconia ceramics and the heat-resistant alloy each form a skeleton, whereas the sintering of Z and Ni powders is insufficient. . Table 1 shows characteristics of the cell substrate according to the embodiment of the present invention and the conventional cell substrate in comparison.

[0015]

[Table 1] The cell substrate of this invention has a gas permeability required for a fuel cell. The bending strength after reduction is about 3 times that of the conventional one, 62 [MPa], and the fracture strain (deflection / (distance between load point and fulcrum) based on the ductility, that is, the amount of deflection up to rupture during bending test. ) × 100) was 2.3 [%], which was about 2.5 times the conventional value.

The above-mentioned ductility (deflection amount / (distance between load point and fulcrum) × 100) was measured by the following method. 2A and 2B show a ductility measuring method. FIG. 2A is a cross-sectional view of a sample 16 in which a load P is applied, and FIG. JISR160
1 stipulates a four-point bending test method for ceramics. The sample size is 3 × 4 × 40 mm, and the crosshead is 0.5 mm / min. Moved at the speed of. a = 1
= 10 mm. Ductility ε is defined by ε = δ / a (%), which is obtained by measuring the delta when cracks occur.

On the cell substrate of the present invention, YSZ as an electrolyte and lanthanum manganite LaMnO ₃ as a cathode were laminated by a plasma spraying method to construct a fuel cell for operation. FIG.
FIG. 4 is a diagram showing the current density dependence (⋄) of the cell voltage of the solid oxide fuel cell according to the example of the present invention in comparison with the conventional cell (∘). The cell substrate has a diameter of 70 mm, the effective electrode area is 38 cm ² , the operating temperature is 1000 ° C, and the fuel gas is humidified 3%.
Uses hydrogen, utilization rate is 60%, oxidant uses air,
The operation rate was 20%. After the measurement was completed, the temperature was returned to room temperature, the temperature was raised to 1000 ° C. again, and the operation was performed to examine the heat cycle characteristics. The rate of temperature increase / decrease is 100 / ° C. It can be seen that the battery using the cell substrate of the present invention has the same battery characteristics as the conventional one and improved heat cycle property. That is, in the conventional battery, cracks were found in the cell substrate after three heat cycles, whereas in the battery using the cell substrate of the present invention, no crack was found after 10 heat cycles.

FIG. 4 is a diagram showing the operating time dependence (⋄) of the cell voltage of the solid oxide fuel cell according to the embodiment of the present invention in comparison with the conventional cell (∘). The test conditions are: electrode effective area 38cm ² , operating temperature 1000 ℃, fuel gas humidified 3% hydrogen, utilization 60%, oxidizer air, utilization 20
%, The load is 0.3 A / cm ² . The deterioration rate of the fuel cell using the conventional Ni-YSZ cell substrate was 30 [μV / h], while that using the cell substrate of the present invention was 5 [μV / h]. Sintering of Ni progresses as the battery operates, but when a heat-resistant alloy is used, sintering is suppressed, deterioration is suppressed, and battery life is extended.

FIG. 5 is a diagram showing the temperature dependence of the linear expansion of the cell substrate for the solid oxide fuel cell according to the embodiment of the present invention. The initial length of the sample is 19.3 mm, and the figure shows that the linear expansion coefficient is 11.2 × 10 ⁻⁶ / ° C.
This is close to the linear expansion coefficient of YSZ of 10.5 × 10 ^-6 / ° C.
Therefore, when the solid electrolyte body is laminated on the cell substrate, thermal damage to the solid electrolyte body due to heat cycle is prevented.

[0020]

According to the present invention, since the cell substrate is a cermet in which the skeleton of the heat-resistant alloy and the skeleton of zirconia ceramics are intertwined with each other, the mechanical strength and ductility of the cell substrate are improved, and the solid electrolyte fuel that is resistant to heat cycle is improved. A battery is obtained. Further, since the heat resistant alloy is a Ni-based Ni-Cr-W alloy, this alloy is difficult to sinter and the life of the battery is improved. Further, the zirconia ceramics of the cell substrate has excellent thermal compatibility with the solid electrolyte body made of zirconia, prevents damage to the solid electrolyte body, and improves the reliability of the solid oxide fuel cell.

[Brief description of drawings]

FIG. 1 shows a crystal structure of a cell substrate, (a) is a scanning electron microscope photograph of the cell substrate of the present invention, and (b) is a scanning electron microscope photograph of a conventional cell substrate.

2A and 2B show a method of measuring ductility, where FIG. 2A is a sectional view of a sample 16 in which a load P is applied, and FIG.
Sectional view of the sample fractured by applying

FIG. 3 is a diagram showing the current density dependence of voltage for a solid oxide fuel cell according to an embodiment of the present invention, in comparison with a conventional cell.

FIG. 4 is a diagram showing the operating time dependency of the voltage of the solid oxide fuel cell according to the embodiment of the present invention in comparison with the conventional cell.

FIG. 5 is a diagram showing the temperature dependence of the linear expansion of the cell substrate for the solid oxide fuel cell according to the embodiment of the present invention.

FIG. 6 is an exploded perspective view showing a flat plate type supporting membrane type solid oxide fuel cell.

[Explanation of symbols]

 11 Cell Substrate 12 Solid Electrolyte Body 13 Cathode 14 Separator 15 Single Cell Assembly 16 Sample

Claims (2)

[Claims] 1. A solid electrolyte fuel cell comprising a unit cell in which a solid electrolyte body is laminated on a cell substrate, wherein the cell substrate is a cermet in which a skeleton of a heat-resistant alloy and a skeleton of zirconia ceramics are intertwined. Solid oxide fuel cell. 2. The solid oxide fuel cell according to claim 1, wherein the heat resistant alloy is a Ni-based Ni—Cr—W alloy.