JPH0450155A - Lanthanum manganite ceramic and cylindrical solid electrolyte fuel cell and plane solid electrolyte fuel cell using the same - Google Patents

Abstract

PURPOSE:To obtain a ceramic material having low electric resistance and keeping the porosity even after sintering by using a lanthanum manganite consisting of a solid solution containing La, Ca, Mn, Cr and O and having a specific composition. CONSTITUTION:The objective ceramic material is a lanthanum manganite composed mainly of the solid solution expressed by formula wherein x, y and alphasatisfy the formulas 0<x<=0.4, 0<y<=0.2 and 0<=alpha<=0.1. The development of molten phase is suppressed in the above ceramic material by doping the material with chromium to an extent to keep the lowering of electrical conductivity below a practically permissible level and, accordingly, it has high gas- permeability and an electrical conductivity sufficiently high as a constitution material of a solid electrolyte fuel cell. The material keeps the porosity even after the use for a long period at a high temperature or during the baking process in the manufacture of cell.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to lanthanum mankanite ceramics suitable for use in solid electrolyte fuel cells, and cylindrical and flat plate solid electrolyte fuel cells using the same. More specifically, the present invention relates to improvements in supports for cylindrical solid oxide fuel cells, cassette diffusers or current collectors in planar solid oxide fuel cells, and support portions thereof.

(Prior art) Research has been conducted on two types of solid electrolyte fuel cells: cylindrical and flat plate structures. Among them, the cylindrical structure has a low output density per unit volume or has strong mechanical strength. Research and development is ahead.

The reason why the output density per unit volume of this cylindrical solid electrolyte fuel cell is low is because the generated electricity is collected via the air electrode and fuel electrode around the cylinder, so the current collection path is long. This is because the contribution of the electrode resistance to the internal resistance of the battery increases, causing a decrease in energy conversion efficiency.

Among them, the resistance of the air electrode is about 10% compared to that of the fuel electrode.
Because it is more than twice as large, voltage drop due to the resistance of the air electrode, heat generation due to Joule heat, etc. have become major problems that hinder the development of high-performance cylindrical solid electrolyte fuel cells. Therefore, attempts have been made to reduce the electrical resistance of the air electrode as much as possible and reduce the contribution of internal resistance by increasing the thickness of the air electrode.

As one example, a zirconia support that plays a sufficient role in mechanical strength but does not contribute at all to current collection is replaced with lanthanum manganite [(La, Sr
)MnO3]. In this way, the specific resistance of the air electrode that collects current becomes smaller, and its contribution to internal resistance, which causes considerable energy loss, becomes smaller.

Also, self-supporting types and non-self-supporting types are being considered for the flat plate type, and recently, like the cylindrical type, gas diffusers are being considered! There is a tendency to consider using materials of the same quality as the electrode materials for the electric body and the support.

(Problem to be solved by the invention) However, lanthanum manganite [(La 1-ml S rz ) +-e MnOs, which is currently being reinstated as an air electrode material,
] has high sinterability, so high temperature treatment or 1000℃
If the device is operated for a long period of time at an operating temperature of 2, the appearance of molten material may clog the ventilation holes, forming a dense M-weave, which may impede air diffusion and make it impossible to generate electricity. That is, in forming a film or a cylindrical body of alkaline earth metal-doped lanthanum manganite, no matter which forming method is used, the temperature during sintering should be 1400°C or higher, preferably 1400°C or higher, considering mechanical strength.
However, when lanthanum mankanite is treated at a high temperature of 1400°C or higher, when observed with an SEM (electron microscope) photograph, it is found that
As shown in figure (A), the powder itself melts and a melt appears,
Spreads like candy. Therefore, it has been found that when a cylindrical support or the like is produced by extrusion molding or the like using such a material and subjected to high temperature treatment, a factor that inhibits air diffusion occurs. This also applies to flat plate solid electrolyte fuel cells.

However, if it is possible to find a material with high conductivity that does not cause such melting even when subjected to high-temperature treatment at temperatures above 1400°C, it is possible to find a material that has high conductivity, such as a cylindrical support, a flat plate, or a gas diode. It can be used as a fuser, a current collector, and a support, and can greatly contribute to the development of cylindrical and flat plate solid electrolyte fuel cells.

The present invention has been made in response to the above-mentioned needs, and it not only reduces the chance of sintering and loss of porosity even when used at high temperatures for long periods of time or during the firing process during battery manufacturing, but The object of the present invention is to provide a lanthanum manganite ceramic with low electrical resistance, and a cylindrical solid electrolyte fuel cell and a flat solid electrolyte fuel cell using the same.

(Means for Solving the Problems) In order to achieve the above object, the lanthanum manganite ceramics of the present invention has the following properties: (La++- + ca, ) +-(1-y+ Cr
, ) Lanthanum mankanite whose main component is an Os-based solid solution, and the values of x, y, and α are such that they satisfy the following relationships: 0<x≦0.4 o<y≦0.2 0≦α≦0.1 I have to.

Further, the cylindrical solid electrolyte fuel cell of the present invention has a cylindrical body formed of the above-mentioned lanthanum manganite ceramic,
This is used as a support for supporting the unit cell.

Further, in the flat plate type solid electrolyte fuel cell of the present invention, the above-mentioned lanthanum manganite ceramic is used as a flat plate diffuser or current collector, or a flat plate support for supporting these.

Here, although the addition of Ca improves the electrical conductivity, the sintering rate also increases and the material is densely sintered, which deteriorates the gas permeability. Therefore, the amount X of Ca added to lanthanum manganite is O< x≦0°4, preferably 0.04≦
The range is X≦0.20.

In addition, the addition of Cr suppresses the appearance of molten material and prevents the pores for ventilation from collapsing, suppressing the adverse effects of adding Ca, but if too much is added, the electrical resistance increases and the conductivity becomes worse and reduces the output of the fuel cell. Therefore, the amount y of Cr added to lanthanum manganite within a range that does not impair its practicality as a fuel cell is in the range of O<y≦0.4, preferably 0<y<0.2.

(Function) In the above solid solution, it is considered that calcium substitutes for lanthanum at the A site and chromium substitutes for manganese at the B site due to the ionic radius. If Cr is partially substituted with Mn, the high valence of Cr is more stable than that of Mn, so lattice defects occur at the A site, which impedes cation movement and leads to sintering. I think it will become difficult. In addition, due to the presence of Mn and Cr in the B site, the crystal structure changes from herovskite orthorhombic to rhombohedral, which is thought to increase the distortion of the crystal structure and cause cation movement. . Moreover, in addition to this, La and alkaline earth metals coexist at the A site, and Mn and Cr coexist at the B site, and it is thought that the valences of these elements increase, resulting in good electrical conductivity.

(Example) Hereinafter, the structure of the present invention will be explained in detail based on an example shown in the drawings.

The lanthanum mankanite ceramics of the present invention is (L
a++-+c+ CaK) +-,, (1-y+ Cr
, ) Lanthanum manganite whose main component is an Os-based solid solution, and the values of x, y, and α are O<x≦0.
4.0<y≦0.2.0≦α≦0.1 Preferably O×X
It is adjusted to satisfy the following ranges: ≦0.2 and O<y≦0.2.0≦α≦0.08.

This lanthanum manganite ceramic powder is suspended in a highly viscous slurry containing a predetermined amount of functional additives such as a solvent, a plasticizer, a binder, and an antifoaming agent.
It can be obtained by preparing a green sludge (sludge) and forming it into a green sheet of uniform thickness by the doctor blade method or extrusion molding, or by forming it into a cylindrical body.

The lanthanum manganite film and cylindrical body thus obtained have gas permeability, good electrical conductivity, and a certain degree of strength, as described below, and can be used in various fields. For example, it can be suitably applied as a gas diffuser, current collector, or support for a flat plate type fixed electrolyte fuel cell, and as a support for supporting a single cell of a cylindrical solid electrolyte fuel cell.

FIG. 1 shows an example of a cylindrical solid electrolyte fuel cell.
In this cylindrical electrolyte fuel cell, an air electrode 21, a solid electrolyte 22, and a fuel electrode 23 are formed concentrically around a cylindrical support 20, and the air electrode is separated from the solid electrolyte 22 and the fuel electrode 23. The current on the air electrode 21 side is taken out by an interconnector 24 formed on the air electrode 21. A gap 25 is provided between the interconnector 24 and the fuel electrode 23 for electrical insulation.

In this cylindrical solid electrolyte fuel cell, air flows inside the support 20 and is supplied to the air electrode 21 through the porous support 20 . Since the support 20 also has electrical conductivity, the air f! 21 becomes part of the air f
! The thickness of the air electrode 2 is increased to the thickness of the support 20.
1 and prevents a decrease in energy conversion efficiency.

In addition, an example of a flat plate solid electrolyte fuel cell is shown in Figure 2 (A
). This flat plate solid electrolyte fuel cell consists of a single cell
A stack 5 is constructed by laminating gas diffusers 2.3 and separators 4 which sandwich the unit cell 1 from both sides. At the center of this stack 5 is a fuel waste supply F! which is connected to a gas differential user 2.3 that sandwiches the single cell 1! A pipe 9 having @7 and an air supply path 8 passes through it. The waste supply F#r7 communicates with the gas diffuser 2 of the ten fuel electrodes of the unit cell 1, and the air supply path 8 communicates with the gas diffuser 3 of the air electrode 11 pJ. The unit cell 1 is formed by forming an air electrode 10 and a fuel electrode 11 on the front and back sides of a solid electrolyte 9. As shown in FIG. 2(B), the gas diffuser 2.3 is a disk made of lanthanum manganite ceramics with a zigzag groove 6 that communicates in the radial direction. It is configured to supply gas or air to the fuel electrode 10 and the air electrode 11 through it.

In the case of this embodiment, the gas diffuser 2.3 has both a current collector and a support for reinforcement, but each may be formed separately from lanthanum manganite ceramics and incorporated. , code 12.13 is 1 profit and lower cover.

Chestnut vomit 1 Lanthanum oxide (La 20 s) as starting material 14
．． 9607g, calcium carbonate (CaCOt) 1.
0110g, manganese carbonate (M n COs ) 11
．． 4950 g, chromium oxide (Cr20-) 0
．． 6722g was mixed using the powder mixing method and heated at 1000℃ for 1
Firing was repeated twice for 0 hours. As a result, L ao, oc ao, +oM no, eoc r O
, +(+03 solid solution was obtained.

Using this lanthanum manganite powder, 1208 Pa
Pressure molding was performed to obtain a pellet having a size of 20 Inlφ and a thickness of 1 round, which was further sintered at 1500° C. for 2 hours.

Dog's own milk Lanthanum oxide (La203 > 7.480) as starting material
3g, calcium carbonate (CaCOs) 0.505
5 g, manganese carbonate (M n COs ) 3.83
17g, Mized ROM (Cr, O,) 1.535
3 g was mixed by a powder mixing method and baked twice at 1000° C. for 10 hours.

As a result, L ao, ac ao, +oM no, boc r
o, <oos solid solution.

Using this lanthanum manganite powder, 120 HP
Pressure molding was performed in step A to obtain a pellet having a diameter of 20 rmφ and a thickness of 1 round, which was further sintered at 1500° C. for 2 hours.

Example 3 Lanthanum oxide (La, O, > 4.986
9g, calcium carbonate (Caco, ) 2.0220
g, manganese carbonate (MncOs) 5.7475g
, 0.3836 g of chromium oxide (Cr2ON') were mixed by a powder mixing method and fired twice at 1000° C. for 110 hours.

As a result, La@, 6oCao4oMno, eoc r o, +o
An os solid solution was obtained.

Using this lanthanum manganite powder, 120 HP
Pressure molding was performed in Step a to obtain pellets with a size of 20 meshes and a thickness of 1 round, which were further sintered at 1500°C for 2 hours.

Lanthanum oxide (La 20 s) as starting material 4.
986'9g, calcium carbonate (CaCOs) 2
．． 0220 g, mankan carbonate (MnCOs) 3.8
317g, @Nari ROM (Cr 20s) 1.535
3 g was mixed by a powder mixing method and baked twice at 1000° C. for 10 hours.

As a result, L ao, eoc ao, 4oM no, s, Cr O
, 4 (obtain a +03 solid solution.

Using this lanthanum manganite powder, 120 HP
Pressure molding was performed in Step a to obtain a pellet having a size of 20 mm and a thickness of III, which was further sintered at 1500"C for 12 hours.

The starting material is lanthanum oxide (L a2 oj ) 9.9
738g, calcium carbonate (CaCOi) 6.2
821 g, manganese carbonate (M n COs ) 12
．． 7722 g, D ROM (Cr 20 s)
Mix 0.7676g using the powder mixing method, and heat at 1000℃.
Firing was repeated twice for 10 hours. As a result, (L ao, aoCao4o) o, e+M no, e
An oc r o, roos solid solution was obtained.

Using this lanthanum manganite powder, 120 HP
Pressure molding was performed in step A to obtain a pellet with a diameter of 20 mm and a thickness of 1 mm, which was further sintered at 1500° C. for 2 hours.

Lanthanum oxide (L a 20 s ) as the starting material 9.
9738g, calcium carbonate (CacOs) 6.2
821g, manganese carbonate (M n COs ) 3.8
317g, 11! Chromium chloride (Cr203) 1.
5353g was mixed by powder mixing method and heated at 1000℃ for 10
The firing was repeated twice for an hour.

This gives (Lao6oCao, to)o, t+Mno6oCro
, obtain a noOs-based solid solution.

Using this lanthanum mancanite powder, 120 HP
Pressure molding was performed in step A to obtain a pellet having a diameter of 20 mm and a thickness of one layer, which was further sintered at 1500° C. for 2 hours.

1 sip of dog milk - Lanthanum oxide (L a 20 s ) as starting material 7.
4803g, calcium carbonate (CacOx) 0.5
005g, manganese carbonate (M n COs ) 6.3
861g, M ROM (CR2O, > 0.3
836 g was mixed by a powder mixing method and baked twice at 1000° C. for 10 hours.

This results in (L ao,)oCao, to)o,elM no
, boc ro, and robs solid solutions were obtained.

Using this lanthanum manganite powder, 120 HP
Pressure molding was performed in step A to obtain a pellet with a size of 20 m + φ and 1 mm thick, which was further sintered at 1500° C. for 2 hours.

Lanthanum oxide (La, Os) as starting material 5.8
180g, calcium carbonate (CaCOs) 1.5
165g, manganese carbonate (M n COs ) 6.3
861g, chromium oxide (Cr 20.) 0.38
36 g was mixed by a powder mixing method and baked twice at 1000° C. for 10 hours.

As a result, (L ao 7oc aO, 3°) o, elM n
o, boc r o, and aoos solid solutions were obtained.

Using this lanthanum manganite powder, 120 HP
Pressure molding was performed in Step a to obtain a pellet with a size of 20 m+φ and 1 m+ thick, which was further sintered at 1500° C. for 2 hours.

Le! 102 Lanthanum oxide (L a20s ) as starting material 14.9
607g, calcium carbonate (CacOs) 1.01
10 g, manganese carbonate (M n COs > 12.7
722 g was mixed using the powder mixing method and heated at 1000°C for 10
The firing was repeated twice for an hour. As a result, a L ao, sac ao, +oM n Os solid solution was obtained.

Using this lanthanum manganite powder, 120 HP
Pressure molding was performed in step A to obtain a pellet with a size of 20 m + φ and 1 mm thick, which was further sintered at 1500° C. for 2 hours.

] Lu Lanthanum oxide (L a 20 s ) as starting material 9.
9738g, calcium carbonate (CaCOs) 4
, 0440 g, manganese carbonate (MnCOs) 12
．． 7722 g was mixed using the powder mixing method and heated to 1000°C.
Firing was repeated twice for 10 hours. As a result, a L a o, hoca O, 4OM n Os based solid solution was obtained.

Using this lanthanum manganite powder, 120 HP
Pressure molding was performed in Step a to obtain a pellet with a diameter of 201Wlφ and a thickness of 11III, which was further sintered at 1500°C for 2 hours.

The lanthanum manganite ceramics obtained in each of the above examples did not exhibit any melt even after high-temperature heat treatment, and had good gas permeability.

Figure 3 shows the relationship between the amount of calcium added and the shrinkage rate of chromium-doped lanthanum manganite, determined from some of the above examples and comparative examples. The shrinkage rate, and the horizontal axis is the amount of chromium substitution. The higher you go up on the vertical axis, the lower the sinterability, that is, the better the gas permeability, and the more you go right on the horizontal axis, the more Ca added.

Here, the shrinkage rate is [100(1,-1,)/lo]
Indicated by However, lo is the initial length, and 11 is the length of the sample after firing. This shrinkage rate was used as an index of sinterability.

This graph clearly shows that the progress of sintering caused by the addition of Ca is suppressed by the addition of chromium, and that the sinterability is reduced, that is, the gas permeability is improved. That is, as the amount of Ca added increases, the chromium-doped lanthanum manganite tends to shrink, become more densely sintered, and have a lower gas permeability. However, C
It can be seen that this is improved by the addition of r, and that the improvement becomes more effective as the amount of Ca added increases.

Incidentally, the electrical conductivity improves as more Ca is added, but there is a problem that the sinterability is high and the gas permeability is poor.

4! Earth X Emperor, La0.8 Ca6.2 Mn03-(a), L
ao s Cao, z Mno, t CrO,
l Os −” (b), Lao, s
Cao,t Mno,s Cro 20s-(c
) were obtained, and the temperature dependence of their electrical conductivity was determined. By keeping the amount of Ca added constant and changing the amount of Cr added, an experiment was conducted to examine the effect of Cr addition on conductivity. According to this, the electrical conductivity of the one with Cr added is worse than that of the one with no Cr added (a), and the decrease is lower than that of the lanthanum mancanite (a) which is not doped with chromium and the one with chromium doped. There is almost no difference between the lanthanum manganites (b) and (c) in the vicinity of the operating temperature of the solid electrolyte fuel cell, so it can be seen that the decrease in conductivity due to the addition of Cr does not pose a practical problem.

(Effects of the Invention) As is clear from the above explanation, the lanthanum manganite ceramics of the present invention can be doped with chromium to the extent that the decrease in conductivity is not a practical problem, thereby suppressing the appearance of molten material. This material has excellent gas permeability and sufficient electrical conductivity as a constituent material of solid electrolyte fuel cells, and even when used at high temperatures for long periods of time, and during the firing process during battery manufacturing, it sinters and becomes porous. This shows that the SE of the chromium-doped lanthanum manganite of the present invention and the chromium-doped lanthanum manganite after heat treatment at 1400°C for 4 hours
This is clear by comparing the M photos. Lanthanum manganite not doped with chromium [Figure 5 (B)
] shows the development of melt, but it is clear that the chromium-doped lanthanum manganite [Fig. 5(A)] does not show any melt. This suggests that by doping with chromium, the development of melt and the densification process are suppressed, and high gas permeability is maintained.

Therefore, when this ceramic is used as a support for a cylindrical solid electrolyte fuel cell, the thickness of the air electrode can be increased to reduce electrical resistance and improve the output of the cylindrical solid oxide fuel cell. Furthermore, when used as a gas diffuser, current collector, or support for a flat plate solid oxide fuel cell, it greatly contributes to the realization of a high temperature operating body for the flat plate solid oxide fuel cell.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a cylindrical solid electrolyte fuel cell. FIG. 2(A) is a sectional view of a main part showing an embodiment of a flat plate solid electrolyte fuel cell. FIG. 2(B) is a plan view of a gas diffuser that serves as both a current collector and a support for the same battery. FIG. 3 is a graph showing the shrinkage rate for each increase in calcium in chromium-doped lanthanum manganite. FIG. 4 is a graph showing the temperature dependence of the electrical conductivity of chromium-doped lanthanum manganite. FIG. 5(A) is an electron micrograph of a chromium-doped lanthanum manganite according to the present invention, and FIG. 5(B) is an electron micrograph of a chromium-doped lanthanum manganite after heat treatment at 1400° C. for 14 hours. 2.3... Gas diffuser for flat solid electrolyte fuel cell (combines the functions of current collector and support) 20... Support for cylindrical solid electrolyte fuel cell.

Claims (5)

[Claims] (1) (La_(_1_-_x_)Ca_x)_1_-
_α(Mn_(_1_-_y_)Cr_y)O_3-based solid solution is the main component of lanthanum manganite, and the values of x, y and α are 0<x≦0.4 0<y≦0.2 0≦α A lanthanum manganite ceramic that satisfies ≦0.1. (2) forming a cylindrical body from the ceramic according to claim 1;
A cylindrical solid electrolyte fuel cell characterized by using this as a support for supporting a single cell. (3) A flat plate type solid electrolyte fuel cell characterized in that a flat plate is formed from the ceramic according to claim 1 and used as a support. (4) A flat solid electrolyte fuel cell characterized in that a gas diffuser is formed of the ceramic according to claim 1. (5) A flat solid electrolyte fuel cell characterized in that a current collector is formed of the ceramic according to claim 1.