JPH04248272A - Manufacture of interconnector of lateral-striped cylindrical solid electrolyte fuel cell - Google Patents

Abstract

PURPOSE:To manufacture a connector of a lateral-striped cylindrical solid electrolyte fuel cell with lanthanum chromite, and to manufacture it at a low cost, in a short time, and in a simple way. CONSTITUTION:A powder of a specific mixing ratio of lanthanum calcium chromite La1-xCaxCr1-yO3 in which 0<x<=0.40<=0.05, and y<=x is made into a slurry, and coated on an air electrode 2 and baked, so as to form an interconnector 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertically striped cylindrical solid electrolyte fuel cell. More specifically, the present invention provides a vertically striped cylindrical solid electrolyte fuel in which an air electrode, a solid electrolyte, and a fuel electrode are formed concentrically in a C-shape on a porous base tube, and an interconnector is formed in the part where the ring is split. It is related to batteries.

0002

[Prior art] Lanthanum chromite (LaCrO3)
has excellent chemical stability in oxidizing and reducing atmospheres at high temperatures. However, due to its low conductivity,
Alkaline earth metals (Mg,
By replacing lanthanum or chromium with Ca, Sr), conductivity is enhanced. On the other hand, in a vertically striped cylindrical solid electrolyte fuel cell, as shown in Fig. 1, cell constituent materials are laminated in the order of an air electrode 2, an electrolyte 3, an interconnector 4, and a fuel electrode 5 on a porous base tube 1. It constitutes a unit cell 6 or an assembly thereof, and generates electricity by flowing fuel gas and oxidizing gas into and out of the support tube. This vertically striped cylindrical solid electrolyte fuel cell has relatively high mechanical strength, so it is the most advanced in development, and a 25 kW class type is already about to be tested.

By the way, when a sintered body of lanthanum chromite substituted with an alkali metal is used as an interconnector, it not only has excellent chemical stability and electronic conductivity in an oxidizing/reducing atmosphere as described above, but also High airtightness is required to prevent cross-leakage of fuel gas and oxidizer (mixing of fuel gas and oxidizer through the interconnector material).

However, in the conventional sintering method used to mold lanthanum chromite, which is an interconnect, into parts, ie, the method of firing in air, chromium oxide (Cr2) evaporated into the lanthanum chromite powder.
O3 ) and compounds containing hexavalent chromium that easily evaporate (
(La2 CrO6, etc.), mass transfer occurs through evaporation and recondensation, and compaction due to intraparticle diffusion is inhibited, making it impossible to obtain an airtight sintered body. The fact that a dense interconnector sintered body cannot be obtained means that hydrogen or oxygen permeates through the membrane and burns directly, creating localized high temperature areas that can lead to battery destruction and
There is a significant problem of battery voltage drop.

[0005] Conventionally, methods for solving this sinterability problem have been 1) high-temperature sintering in a reducing atmosphere (for example, around 1700°C), 2) aluminum (Al), copper (Cu) ), zinc (Zn), etc. in the perovskite crystal structure of lanthanum chromite.
3) a method of adding an alkaline earth metal to the A site or B site and sintering it;
4) Various measures have been considered, such as adding sintering aids such as fluoride.

However, with these methods, 1) a dense sintered body that does not allow gas to pass through cannot be obtained; 2) Even if an airtight sintered body is obtained, it is not easy to manufacture interconnectors because a high firing temperature and reducing atmosphere are required. 3) The conditions for dense sintering are lanthanum manga, which is an air electrode material. Conditions that reduce the catalytic properties of night,
4) There are problems such as the evaporation of the sintering aid causing deterioration of the characteristics of other battery constituent materials.

Under these circumstances, in order to solve these problems, an electrochemical vapor deposition method (electrochemical vapor deposition method) capable of densely sintering lanthanum magnesium chromite (La(Cr,Mg)O3) at a low temperature of 1400°C or less has been developed. Electrochemical vapor deposition (hereinafter referred to as EVD method) is the mainstream method for manufacturing interconnectors. The interconnector is manufactured by this EVD method by attaching lanthanum chromite powder to the 3 parts of the electrolyte on the base tube 1 for masking, and then growing an interconnector film of lanthanum chromite in a reducing atmosphere at 1300°C. It is done.

[0008]

[Problem to be solved by the invention] However, EVD
The fabrication of interconnectors by this method has the following problems: 1) The masking and demasking steps become complicated. 2) Due to the difference in reaction energy between oxides and chlorides, only Mg, which cannot be expected to have high conductivity, can be used as a substituent atom. For this reason, implementation cannot be expected for Ca, Sr-doped lanthanum chromite, which is excellent in improving the conductivity of lanthanum chromite. 3) Due to the slow diffusion rate in lanthanum chromite, strong reducing atmosphere conditions are required for a long time to grow the interconnector film. For this reason, the lanthanum manganite that is the air electrode deteriorates. It has the following disadvantages. These drawbacks increase the manufacturing cost and reduce the performance of cylindrical solid electrolyte fuel cells.

The present invention provides a vertically striped cylindrical solid electrolyte fuel cell in which a lanthanum chromite interconnector is formed.
It is an object of the present invention to provide a low-cost manufacturing method that can be manufactured in air in a short time without being limited to substituted alkali metal substances.

0010

[Means for Solving the Problems] In order to achieve the above object, the method for manufacturing an interconnector for a vertically striped cylindrical solid electrolyte fuel cell according to the present invention provides a method for manufacturing an interconnector for a vertically striped cylindrical solid electrolyte fuel cell. The molar ratio of La:Ca:Cr=(1-
x):x:(1-y), and the values of x and y are (1), (
2), (3) 0<x≦0.4…(1) 0<y≦0.
05...(2) y≦x
...An interconnector is formed by slurrying lanthanum calcium chromite (La1-x Cax Cr1-y O3) powder that satisfies (3), coating the slurry and lanthanum calcium chromite on an air electrode, and firing it. ing.

[0011]

[Operation] The values of x and y of lanthanum chromite represented by La1-x Cax Cr1-y O3 are 0<x≦0.
4. When 0<y≦0.05, y≦x, this x, y
A single phase of perovskite with a composition of Lanthanum oxide and calcium oxide inhibit electrical conduction, and chromium oxide significantly impairs sinterability. On the other hand, lanthanum chromite having a composition that satisfies the above conditions can be fired at a relatively low temperature to yield a dense sintered body. Therefore, if it is made into a slurry and applied onto the fuel electrode and fired, an interconnector film with a uniform thickness without unevenness can be obtained without causing diffusion on the fuel electrode.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the structure of the present invention will be explained in detail based on embodiments shown in the drawings.

First, the production of lanthanum calcium chromite and its powder suitable for use in interconnectors of vertically striped cylindrical solid electrolyte fuel cells will be described. Here, the lanthanum calcium chromite powder used is La,
It is a ceramic whose main components are Ca and Cr. The main components of the mixture before synthesizing this powder are such that the molar ratio of each element is La:Ca:Cr=(1-x):x:(1-y),
And the values of x and y are 0<x≦0.4, 0<y≦0.05
, y≦x. The method for producing the mixture having the above-mentioned composition range is not particularly limited, and may be produced by any method such as a powder method, a coprecipitation method, a sol-gel method, or the like. Since the lanthanum chromite raw material powder with this composition lacks chromium, sinterability can be improved by reducing the amount of evaporation of chromium. Therefore, it is possible to realize an interconnector with excellent airtightness. Furthermore, it is possible to obtain the chemical stability in a redox atmosphere and the like required for an interconnector, as well as high electronic conductivity. For example, a method for synthesizing lanthanum chromite powder using a coprecipitation method is shown below. First, add 4 lanthanum nitrate (La(NO3)3 ・6H2 O)
01g, calcium nitrate (Ca(NO3)2 ・4H
2O), 100g of chromium nitrate (Cr(NO3)3)
・9H2O) was dissolved in 529g of distilled water and mixed.
It was added dropwise to an ethanol solution in which excess oxalic acid ((COOH) 2 .2H 2 O) was dissolved. After that, the mixed solution was dried with cold air from a dryer, degreased at 360°C or less for about 5 hours, mixed in a ball mill, baked at 1000°C for about 10 hours, mixed again in a ball mill, and mixed again for about 1 hour.
It was fired for 0 hours to obtain lanthanum calcium chromite powder for slurry. The lanthanum calcium chromite powder thus obtained is easily sintered at low temperatures.

Next, this powder is mixed with, for example, 300-400 ml of a mixed solution of toluene and isopropanol as a solvent, 48-53 g of polyvinyl butyral as a binder, 50-55 ml of di-n-butyl phthalate as a plasticizer, and 13-40 ml of a nonionic dispersant as a binder.
After mixing 18 ml and 13-18 ml of antifoaming agent mono-p-isooctylphenyl ether, the viscosity was adjusted by defoaming to obtain a slurry for slurry coating. According to the slurry having this composition, the organic solvent evaporates slowly during the heating process during firing to prevent the generation of pores, and other slurry conditioners also burn stably. Then, as described below, by holding it in a temperature range of 1100 to 1300 degrees Celsius for 4 hours or more, or by firing it at a temperature of 1400 degrees Celsius, a molten material is created and an interconnector with a uniform thickness without irregularities and excellent airtightness is created. can form a film of

[0015] Therefore, for example, a vertically striped cylindrical solid electrolyte fuel cell is fabricated using this slurry lanthanum chromite according to the following procedure. 1) First, lanthanum manganite, which is the air electrode 2, is attached to the porous substrate tube 1 by a slurry coating method. Then, it is heated and fired in air at 1300° C. for 5 hours. 2) Next, the interconnector film 4 is formed using the above-mentioned slurry calcium lanthanum chromite. That is, the slurry is applied to the air electrode 2 in a predetermined width in the axial direction and fired in air at 1300° C. for 5 hours or at 1400° C. with no holding time. Under such relatively low-temperature firing conditions, a dense lanthanum chromite sintered body can be obtained without causing diffusion of the air electrode material. Here, relatively low temperature means a temperature range lower than the 1700° C. firing temperature of conventional lanthanum chromite. 3) Furthermore, after masking the interconnector 4 by attaching lanthanum chromite powder, a film of the zirconia electrolyte 3 is grown on the air electrode around the interconnector 4 by the EVD method at 1200° C. or higher in a reducing atmosphere. 4) Thereafter, nickel zirconia cermet, which is the fuel electrode 5, is produced by a slurry coating method and an EVD method. That is, a slurry of nickel metal powder dispersed in a solvent is deposited on a cylindrical electrolyte 3, and zirconia is further deposited thereon by the EVD method to form a fuel electrode 5 made of nickel-zirconia cermet.
form. Several layers of nickel metal and zirconia are formed as necessary.

[0016]

[Effects of the Invention] As is clear from the above explanation, the method for manufacturing the vertically striped cylindrical solid electrolyte fuel cell interconnector of the present invention involves slurrying lanthanum chromite powder at a predetermined mixing ratio and coating it on the air electrode. Since the interconnector part is formed by firing the
Interconnectors can be fabricated under relatively low temperature firing conditions in air without masking the zirconia electrolyte. Furthermore, the steps in which the air electrode is exposed to a reducing atmosphere and the masking/demasking steps are reduced, and a vertically striped cylindrical solid electrolyte fuel cell with high power generation performance can be produced in a short time and at low cost.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a vertically striped cylindrical solid electrolyte fuel cell of a type in which one unit cell is arranged on a porous substrate tube.

[Explanation of symbols]

1 Porous base tube 2 Air electrode 4 Interconnector

Claims (1)

[Claims] [Claim 1] The molar ratio of each element of the main components of the mixture before synthesizing the powder is La:Ca:Cr=(1-x):
x: (1-y), and the values of x and y are (1), (2),
(3) 0<x≦0.4…(1) 0<y≦0.
05...(2) y≦x
...The interconnector is formed by slurrying lanthanum calcium chromite (La1-x Cax Cr1-y O3) powder that satisfies (3), coating the slurry lanthanum calcium chromite on the air electrode, and firing it. A method for manufacturing a vertically striped cylindrical solid electrolyte fuel cell interconnector.